INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY ENVIRONMENTAL HEALTH CRITERIA 177 1,2-Dibromoethame This report contains the collective views of an international group of experts and does not necessarily represent the decisions or the stated policy of the United Nations Environment Programme, the International Labour Organisation, or the World Health Organization. First draft prepared by Dr J. Sekizawa, National Institute of Health Science, Japan Published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organisation, and the World Health Organization World Health Organization Geneva, 1996 The International Programme on Chemical Safety (IPCS) is a joint venture of the United Nations Environment Programme, the International Labour Organisation, and the World Health Organization. The main objective of the IPCS is to carry out and disseminate evaluations of the effects of chemicals on human health and the quality of the environment. Supporting activities include the development of epidemiological, experimental laboratory, and risk-assessment methods that could produce internationally comparable results, and the development of manpower in the field of toxicology. Other activities carried out by the IPCS include the development of know-how for coping with chemical accidents, coordination of laboratory testing and epidemiological studies, and promotion of research on the mechanisms of the biological action of chemicals. WHO Library Cataloguing in Publication Data 1,2-Dibromoethame. (Environmental health criteria ; 177) 1.Ethylene dibromide - adverse effects 2.Solvents 3.Environmental exposure I.Series ISBN 92 4 157177 2 (NLM Classification: QV 633) ISSN 0250-863X The World Health Organization welcomes requests for permission to reproduce or translate its publications, in part or in full. Applications and enquiries should be addressed to the Office of Publications, World Health Organization, Geneva, Switzerland, which will be glad to provide the latest information on any changes made to the text, plans for new editions, and reprints and translations already available. (c) World Health Organization 1996 Publications of the World Health Organization enjoy copyright protection in accordance with the provisions of Protocol 2 of the Universal Copyright Convention. All rights reserved. The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or of certain manufacturers' products does not imply that they are endorsed or recommended by the World Health Organization in preference to others of a similar nature that are not mentioned. Errors and omissions excepted, the names of proprietary products are distinguished by initial capital letters. CONTENTS ENVIRONMENTAL HEALTH CRITERIA FOR 1,2-DIBROMOETHANE Preamble 1. SUMMARY 1.1. Identity, physical and chemical properties, and analytical methods 1.2. Sources of human and environmental exposure 1.3. Environmental levels and degradation 1.4. Kinetics and metabolism in laboratory animals 1.5. Effects on laboratory mammals and in vitro test systems 1.6. Effects on humans 1.7. Effects on organisms in the environment 2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS 2.1. Identity 2.2. Physical and chemical properties 2.3. Conversion factors 2.4. Analytical methods 2.4.1. Air 2.4.2. Water 2.4.3. Soils and sediment 2.4.4. Food 3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE 3.1. Natural occurrence 3.2. Anthropogenic sources 3.2.1. Production levels and processes 22.214.171.124 World production figures 126.96.36.199 Manufacturing processes 3.2.2. Uses 188.8.131.52 Petrol additive 184.108.40.206 Fumigant 4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION 4.1. Transport and distribution between media 4.1.1. Air 4.1.2. Soil 5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE 5.1. Environmental levels 5.1.1. Air 5.1.2. Water 5.1.3. Food 5.2. Occupational exposure 6. KINETICS AND METABOLISM 6.1. Absorption 6.2. Distribution 6.3. Metabolic transformation 6.4. Elimination and excretion in expired air, faeces and urine 6.5. Retention and turnover 6.6. Reaction with body components 7. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS 7.1. Single exposure 7.1.1. Oral 220.127.116.11 Rat 18.104.22.168 Chicken 7.1.2. Inhalation 22.214.171.124 Rat 126.96.36.199 Guinea-pig 7.1.3. Intraperitoneal injection 188.8.131.52 Mouse 184.108.40.206 Rat 7.2. Short-term exposure 7.2.1. Oral 220.127.116.11 Chicken 7.2.2. Inhalation 18.104.22.168 Mouse 22.214.171.124 Rat 126.96.36.199 Guinea-pig 188.8.131.52 Rabbit 184.108.40.206 Monkey 7.3. Eye and skin irritation 7.3.1. Rabbit 7.4. Long-term exposure 7.4.1. Oral 220.127.116.11 Mouse 18.104.22.168 Rat 7.4.2. Inhalation 22.214.171.124 Mouse 126.96.36.199 Rat 7.5. Developmental toxicity 7.5.1. Reproduction 188.8.131.52 Effects on sperm 184.108.40.206 Effects on ova 7.5.2. Teratogenicity 220.127.116.11 Effects on neonatal behaviour 7.6. Mutagenicity and related end-points 7.6.1. In vitro assays 7.6.2. In vivo assays 7.6.3. Other studies 7.7. Carcinogenicity 7.7.1. Administration by gavage 18.104.22.168 Mouse 22.214.171.124 Rat 7.7.2. Administration in drinking-water 126.96.36.199 Mouse 7.7.3. Inhalation 188.8.131.52 Mouse 184.108.40.206 Rat 7.7.4. Dermal application 220.127.116.11 Mouse 7.7.5. Cell transformation 7.8. Biochemical studies and species specificity 8. EFFECTS ON HUMANS 8.1. Acute toxicity 8.2. Occupational exposure 8.2.1. Cancer incidence 8.2.2. Reproductive effects 9. EFFECTS ON ORGANISMS IN THE ENVIRONMENT 9.1. Aquatic organisms 9.1.1. Invertebrates 9.1.2. Fish 9.2. Terrestrial biota 9.3. Microorganisms 9.4. Plants 10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT 10.1. Evaluation of human health risks 10.2. Evaluation of effects on the environment 11. CONCLUSIONS AND RECOMMENDATIONS 12. FURTHER RESEARCH 13. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES REFERENCES RESUME RESUMEN NOTE TO READERS OF THE CRITERIA MONOGRAPHS Every effort has been made to present information in the criteria monographs as accurately as possible without unduly delaying their publication. In the interest of all users of the Environmental Health Criteria monographs, readers are requested to communicate any errors that may have occurred to the Director of the International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland, in order that they may be included in corrigenda. * * * A detailed data profile and a legal file can be obtained from the International Register of Potentially Toxic Chemicals, Case postale 356, 1219 Châtelaine, Geneva, Switzerland (Telephone No. 9799111). * * * This publication was made possible by grant number 5 U01 ES02617-15 from the National Institute of Environmental Health Sciences, National Institutes of Health, USA, and by financial support from the European Commission. Environmental Health Criteria PREAMBLE Objectives In 1973 the WHO Environmental Health Criteria Programme was initiated with the following objectives: (i) to assess information on the relationship between exposure to environmental pollutants and human health, and to provide guidelines for setting exposure limits; (ii) to identify new or potential pollutants; (iii) to identify gaps in knowledge concerning the health effects of pollutants; (iv) to promote the harmonization of toxicological and epidemiological methods in order to have internationally comparable results. The first Environmental Health Criteria (EHC) monograph, on mercury, was published in 1976 and since that time an ever-increasing number of assessments of chemicals and of physical effects have been produced. In addition, many EHC monographs have been devoted to evaluating toxicological methodology, e.g., for genetic, neurotoxic, teratogenic and nephrotoxic effects. Other publications have been concerned with epidemiological guidelines, evaluation of short-term tests for carcinogens, biomarkers, effects on the elderly and so forth. Since its inauguration the EHC Programme has widened its scope, and the importance of environmental effects, in addition to health effects, has been increasingly emphasized in the total evaluation of chemicals. The original impetus for the Programme came from World Health Assembly resolutions and the recommendations of the 1972 UN Conference on the Human Environment. Subsequently the work became an integral part of the International Programme on Chemical Safety (IPCS), a cooperative programme of UNEP, ILO and WHO. In this manner, with the strong support of the new partners, the importance of occupational health and environmental effects was fully recognized. The EHC monographs have become widely established, used and recognized throughout the world. The recommendations of the 1992 UN Conference on Environment and Development and the subsequent establishment of the Intergovernmental Forum on Chemical Safety with the priorities for action in the six programme areas of Chapter 19, Agenda 21, all lend further weight to the need for EHC assessments of the risks of chemicals. Scope The criteria monographs are intended to provide critical reviews on the effect on human health and the environment of chemicals and of combinations of chemicals and physical and biological agents. As such, they include and review studies that are of direct relevance for the evaluation. However, they do not describe every study carried out. Worldwide data are used and are quoted from original studies, not from abstracts or reviews. Both published and unpublished reports are considered and it is incumbent on the authors to assess all the articles cited in the references. Preference is always given to published data. 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Content The layout of EHC monographs for chemicals is outlined below. * Summary - a review of the salient facts and the risk evaluation of the chemical * Identity - physical and chemical properties, analytical methods * Sources of exposure * Environmental transport, distribution and transformation * Environmental levels and human exposure * Kinetics and metabolism in laboratory animals and humans * Effects on laboratory mammals and in vitro test systems * Effects on humans * Effects on other organisms in the laboratory and field * Evaluation of human health risks and effects on the environment * Conclusions and recommendations for protection of human health and the environment * Further research * Previous evaluations by international bodies, e.g., IARC, JECFA, JMPR Selection of chemicals Since the inception of the EHC Programme, the IPCS has organized meetings of scientists to establish lists of priority chemicals for subsequent evaluation. Such meetings have been held in: Ispra, Italy, 1980; Oxford, United Kingdom, 1984; Berlin, Germany, 1987; and North Carolina, USA, 1995. The selection of chemicals has been based on the following criteria: the existence of scientific evidence that the substance presents a hazard to human health and/or the environment; the possible use, persistence, accumulation or degradation of the substance shows that there may be significant human or environmental exposure; the size and nature of populations at risk (both human and other species) and risks for environment; international concern, i.e. the substance is of major interest to several countries; adequate data on the hazards are available. If an EHC monograph is proposed for a chemical not on the priority list, the IPCS Secretariat consults with the Cooperating Organizations and all the Participating Institutions before embarking on the preparation of the monograph. 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It is accepted that the following criteria should initiate the updating of an EHC monograph: new data are available that would substantially change the evaluation; there is public concern for health or environmental effects of the agent because of greater exposure; an appreciable time period has elapsed since the last evaluation. All Participating Institutions are informed, through the EHC progress report, of the authors and institutions proposed for the drafting of the documents. A comprehensive file of all comments received on drafts of each EHC monograph is maintained and is available on request. The Chairpersons of Task Groups are briefed before each meeting on their role and responsibility in ensuring that these rules are followed. WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR 1,2-DIBROMOETHANE Members Dr T. Bailey, US Environmental Protection Agency, Washington DC, USA Dr A.L. Black, Department of Human Services and Health, Canberra, Australia Mr D.J. Clegg, Carp, Ontario, Canada Dr S. Dobson, Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire, United Kingdom (Vice-Chairman) Dr P.E.T. Douben, Her Majesty's Inspectorate of Pollution, London, United Kingdom (EHC Joint Rapporteur) Dr P. Fenner-Crisp, US Environmental Protection Agency, Washington DC, USA Dr R. Hailey, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, USA Ms K. Hughes, Environmental Health Directorate, Health Canada, Ottawa, Ontario, Canada (EHC Joint Rapporteur) Dr D. Kanungo, Central Insecticides Laboratory, Government of India, Ministry of Agriculture & Cooperation, Directorate of Plant Protection, Quarantine & Storage, Faridabad, Haryana, India Dr L. Landner, MFG, European Environmental Research Group Ltd, Stockholm, Sweden Dr M.H. Litchfield, Melrose Consultancy, Denmans Lane, Fontwell, Arundel, West Sussex, United Kingdom (CAG Joint Rapporteur) Professor M. Lotti, Institute of Occupational Medicine, University of Padua, Padua, Italy (Chairman) Professor D.R. Mattison, University of Pittsburgh, Graduate School of Public Health, Pittsburgh, Pennsylvania, USA Dr J. Sekizawa, National Institute of Health Sciences, Tokyo, Japan Dr P. Sinhaseni, Chulalongkorn University, Bangkok, Thailand Dr S.A. Soliman, King Saud University, Bureidah, Saudi Arabia Dr M. Tasheva, National Centre of Hygiene, Medical Ecology and Nutrition, Sofia, Bulgaria (CAG Joint Rapporteur) Mr J.R. Taylor, Pesticides Safety Directorate, Ministry of Agriculture, Fisheries and Food, York, United Kingdom Dr H.M. Temmink, Wageningen Agricultural University, Wageningen, The Netherlands Dr M.I. Willems, TNO Nutrition and Food Research Institute, Zeist, The Netherlands Secretariat Ms A. Sundén Byléhn, International Register of Potentially Toxic Chemicals, United Nations Environment Programme, Châtelaine, Switzerland Dr P. Chamberlain, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland Dr J. Herrman, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland Dr K. Jager, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland Dr P. Jenkins, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland Dr W. Kreisel, World Health Organization, Geneva, Switzerland Dr M. Mercier, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland Dr M.I. Mikheev, Occupational Health, World Health Organization, Geneva, Switzerland Dr G. Moy, Food Safety, World Health Organization, Geneva, Switzerland Mr I. Obadia, International Labour Organisation, Geneva, Switzerland Dr R. Plestina, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland Dr E. Smith, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland (EHC Secretary) Mr J. Wilbourn, International Agency for Research on Cancer, Lyon, France ENVIRONMENTAL HEALTH CRITERIA FOR 1,2-DIBROMOETHANE The Core Assessment Group (CAG) of the Joint Meeting on Pesticides (JMP) met at the World Health Organization, Geneva from 25 October to 3 November 1994. Dr W. Kreisel, Executive Director, welcomed the participants on behalf of WHO, and Dr M. Mercier, Director, IPCS, on behalf of the IPCS and its cooperating organizations (UNEP/ILO/WHO). The Core Assessment Group reviewed and revised the draft monograph and made an evaluation of the risks for human health and the environment from exposure to 1,2-dibromoethane (ethylene dibromide). The preparation of the first draft of the monograph was coordinated by Dr J. Sekizawa, National Institute of Health Sciences, Japan. The second draft, revised in the light of international comment, was prepared under the coordination of Dr Sekizawa. Dr E. Smith and Dr P.G. Jenkins, both members of the IPCS Central Unit, were responsible for the scientific content and technical editing, respectively. The efforts of all who helped in the preparation and finalization of the monograph are gratefully acknowledged. The authors who contributed to the first draft were: Dr C. Hashida The Jikei University School of Medicine, Japan Dr Y. Hayashi National Institute of Health Sciences, Japan Dr E. Kamata National Institute of Health Sciences, Japan Dr Y. Kurokawa National Institute of Health Sciences, Japan Dr A. Matsuoka National Institute of Health Sciences, Japan Dr T. Matsushima The Japan Industrial Safety and Health Association Dr K. Morimoto National Institute of Health Sciences, Japan Dr M. Nakadate National Institute of Health Sciences, Japan Dr G. Ohmori The Jikei University School of Medicine, Japan Dr Y. Saito National Institute of Health Sciences, Japan Dr J. Sekizawa National Institute of Health Sciences, Japan Dr T. Sohuni National Institute of Health Sciences, Japan Dr M. Takeda National Institute of Health Sciences, Japan Dr M. Takemura Ashiya University, Japan Dr Y. Takenaka National Institute of Health Sciences, Japan Dr S. Tanaka National Institute of Health Sciences, Japan ABBREVIATIONS BCF bioconcentration factor BUN blood urea nitrogen ECD electron capture detector EDB 1,2-dibromoethane (ethylene dibromide) FID flame ionization detector GC gas chromatography GSH glutathione gamma-GT gamma-glutamyltranspeptidase HECD Hall electron capture detector LOEL lowest-observed-effect level MS mass spectrometry NADPH reduced nicotinamide adenine dinucleotide phosphate NOEL no-observed-effect level PIB piperonyl butoxide SGOT serum glutamic-oxalic transaminase SGPT serum glutamic-pyruvic transaminase TEAM total exposure assessment methodology TWA time-weighted average UDS unscheduled DNA synthesis VHH volatile halogenated hydrocarbon VOC volatile organic carbon compound 1. Summary 1.1 Identity, physical and chemical properties, and analytical methods 1,2-Dibromoethane (ethylene dibromide) is a colourless liquid (melting point 9.9°C, boiling point 131.4°C) with a chloroform-like odour. It is quite volatile, with a vapour pressure of 1.47 kPa (11 mmHg) at 25°C and a vapour density compared to air of 6.1. 1,2-Dibromoethane is miscible with most organic solvents. Its solubility in water is 4.3 g/litre at 30°C. 1,2-Dibromoethane in ambient air is analysed by GC after absorption to porous polymers followed by rapid thermal desorption. A purge-trap method is used for water samples. 1,2-Dibromoethane residues in foods and other media can either be extracted by solvents or be subjected to automated headspace analysis under cryogenic conditions followed by analysis by GC and HPLC after derivatization. 1.2 Sources of human and environmental exposure 1,2-Dibromoethane is used as a scavenger of lead antiknock agents in gasoline. It is also used as a soil fumigant and for fumigation of grains and fruits. Reduced use of leaded gasoline in some countries and cancellations of registrations for the use of 1,2-dibromoethane for agricultural applications has reduced human exposure to 1,2-dibromoethane. However, it is still used as a lead scavenger in gasoline in some countries, as a fumigant, for quarantine purposes, as a solvent and as an intermediate for industrial chemicals. 1.3 Environmental levels and degradation Concentrations of 1,2-dibromoethane measured in air range from undetectable to the order of ng/m3 in urban areas. 1,2-Dibromoethane has been found in ground water at up to 0.2 µg/litre and in surface water at up to 50 µg/litre in areas of extensive agricultural use. Although 1,2-dibromoethane leaches through soil, some is retained in the soil matrix and may later contaminate irrigation wells. There is a lack of information on microbial breakdown in soils. The high volatility of 1,2-dibromoethane means that the major environmental sink is the atmosphere. Stratospheric photolysis may lead to the formation of breakdown products with ozone-depleting potential. 1.4 Kinetics and metabolism in laboratory animals 1,2-Dibromoethane is rapidly absorbed orally, dermally and by inhalation. Metabolites are thought to play an important role in 1,2-dibromoethane toxicity for humans. It can be metabolized by an oxidative pathway (cytochrome P-450 system) and a conjugation pathway (glutathione S-transferase system). Two reactive metabolites, bromacetaldehyde formed via the oxidation pathway and thiiranium ion formed via the conjugation pathway, are thought to interact with cellular macromolecules (proteins, DNA) to form covalently bound products. 1.5 Effects on laboratory mammals and in vitro test systems 1,2-Dibromoethane is acutely toxic to animals (oral LD50 for rats of 146-417 mg/kg body weight, inhalation LC50 for rats of 3080 mg/m3 after a 2-h exposure, mortality observed following dermal application of 210 mg/kg to rabbits). Toxic effects of 1,2-dibromoethane were mainly observed in the liver and kidneys. Inhaled 1,2-dibromoethane vapour produced nasal irritation and depression of the central nervous system. In rats exposed to concentrations between 1540 and 77 000 mg/m3 (200-10 000 ppm) for exposure durations between 0.1 and 16.0 h, deaths occurred in all groups and were related to concentration and time. 1,2-Dibromoethane (1.0% solution) caused irritation of shaved abdominal skin and eye irritation in rabbits. After oral subchronic exposure, mortality and decreases in weight gain were observed in rats and mice at 100 mg/kg body weight per day. Decreases in weight gain and nasal pathological effects were noted in rats exposed to 1,2-dibromoethane at 115 mg/m3 (578 ppm) for 6 h/day, 5 days/week, for 13 weeks. The NOEL for histopathological alterations of the nasal cavity was 23 mg/m3 (3 ppm) in this study. In a similar study in mice, the same pathological changes were observed, also with a NOEL of 23 mg/m3 (3 ppm). After mice or rats were administered 1,2-dibromoethane by gavage at 37-107 mg/kg body weight per day (TWA) for 49-90 weeks or mice were administered 103-117 mg/kg body weight per day in drinking-water for 15-17 months, non-carcinogenic changes such as liver degeneration, testicular atrophy, and forestomach acanthosis and hyperkeratosis in addition to mortality were observed. After inhalation exposure (mice or rats exposed to 77-388 mg/m3 for 6-18 months), inflammation of the trachea and nasal cavity, testicular degeneration and hepatic necrosis were observed. 1,2-Dibromoethane was not teratogenic in rats or mice following inhalational exposure. Developmental toxicity (impairment of development of motor coordination) was observed in the offspring of male rats treated intraperitoneally with 1.25 mg/kg body weight per day and in the offspring of female rats treated by inhalation 509 mg/m3, 4 h/day, 3 days/week from day 3 to day 20 of gestation. 1,2-Dibromoethane affected the reproductive performance of rats (in males at the exposure level of 684 mg/m3, 7 h/day, 5 days/week, for 10 weeks, and in females at the exposure level of 614 mg/m3, 7 h/day, 7 days/week, for 3 weeks). The NOEL for this parameter was 300 mg/m3 in both sexes. The NOEL for reproductive performance of male rats in a feeding study was 50 mg/kg per day after a 90-day exposure. Spermatogenesis was affected in bulls following oral dosing with 2 mg/kg per day for less than 21 days and in rabbits following subcutaneous injection of 15 mg/kg for 5 days. Feeding of 1,2-dibromoethane caused diminution of egg size in hens after exposure to 12.5 mg/kg per day for 12 weeks. 1,2-Dibromoethane did not induce dominant lethal mutations in mice or rats, and did not produce chromosomal aberrations or micronuclei in the bone-marrow cells of mice treated in vivo. However, it was mutagenic in bacterial assays and caused single-strand DNA breaks. Metabolites of 1,2-dibromoethane were covalently bound to DNA, in vivo and in vitro. Sister chromatid exchange, mutations and unscheduled DNA synthesis were observed in human cells in vitro. Carcinogenicity studies involving oral administration (mice and rats exposed by gavage to 37-107 mg/kg body weight per day (TWA) for 49-90 weeks; mice given 1,2-dibromoethane in drinking-water at 103-117 mg/kg body weight per day for 15-17 months), inhalational exposure (mice and rats exposed at 10-40 ppm for 6-18 months) or skin administration (25-50 mg/mice, 3 times/week for 400-594 days) showed that 1,2-dibromoethane is carcinogenic to rats and mice, causing tumours in a variety of organs (both at the application site and distant sites, including the nasal cavity, lung, stomach, liver, skin, circulatory system and mammary glands). In many cases it reduced the latency period in developing tumours. 1.6 Effects on humans 1,2-Dibromoethane may produce adverse effects on the respiratory, nervous and renal systems. Acute (single) inhalation exposure to 1,2-dibromoethane at 215 mg/m3 (28 ppm) for 30 min or more has been shown to be fatal for humans. Ingestion of 140 mg/kg body weight was fatal. Long-term exposure to 1,2-dibromoethane (5 y) at a concentration of 0.68 mg/m3 in the breathing zone significantly decreased sperm counts and fertility in occupationally exposed workers. 1.7 Effects on organisms in the environment Few aquatic ecotoxicity studies have been performed with 1,2-dibromoethane. The LC50s for aquatic organisms are greater than 5 mg/litre. No information is available on terrestrial organisms. 2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS 2.1 Identity Chemical name 1,2-dibromoethane (IUPAC): Chemical structure: Br - CH2 - CH2 - Br Molecular formula: C2H4Br2 Relative molecular 187.9 mass: CAS chemical name: ethylene dibromide CAS registry number: 106-93-4 Synonyms: sym-dibromothane, DBE, dibromo, bromure d'ethylene, 1,2-ethylene dibromide, ethylene bromide Major trade names: Nematron, Nemafume, Bromofume, Dowfume W-85, Aadibrom, Iscobrome D Formulations: kerosene (30 and 97%), emulsifiable concentrate (40 and 48%) in combination with other pesticides 2.2 Physical and chemical properties Appearance: colourless liquid with chloroform-like odour Melting point: 9.9°C (Stenger, 1983) Boiling point: 131.4°C (Stenger, 1983) Vapour pressure: 1.47 kPa (11.0 mmHg) (at 25°C) (Verschueren, 1983) Vapour density: 6.1 Specific gravity: 2.172 (Stenger, 1983) (at 25°C) Refractive index (n20): 1.5379 Solubility in water: 4.3 g/litre at 30°C (Verschueren, 1983) soluble in ether, etanol, benzene, acetone (Weast et al., 1988) Saturating concentration 113 g/m3 (at 20°C), 168 g/m3 (at 30°C) in air: Log Pow 1.76 or 1.93 Stability: decomposes gradually when exposed to light 1,2-Dibromoethane is flammable. Chemically, 1,2-dibromoethane is a bifunctional alkylating agent. 2.3 Conversion factors 1 ppm = 7.68 mg/m3 (at 25°C); 1 mg/m3 = 0.13 ppm 2.4 Analytical methods Analytical methods for volatile halogenated hydrocarbons (VHH) are applicable to 1,2-dibromoethane. Determination of 1,2-dibromoethane is usually carried out by gas chromatography with electron capture detection (GC-ECD). High resolution GC capillary columns can be used for multiple analysis in high-resolution gas chromatography (HR-GC) or high-resolution gas chromatography - mass spectrometry (HR-GC-MS). A sensitive photoionization detector (Dumas & Bond, 1982; Collins & Barker, 1983), a Hall electroconductivity detector (Cairns et al., 1984) or mass spectrometry can also be used for determination and confirmation of 1,2-dibromoethane. GC-ECD is the most sensitive method. The preconcentration of trace 1,2-dibromoethane in samples is usually carried out through collection by cryogenic trapping or by absorption on solid absorbents. The former is the preferred preconcentration technique. Ice formation in the trap-tube during sampling can be a problem, especially with ambient water and homogenized food samples. Co-collected water can alter sample or column flow rates in separation techniques that require subfreezing at initial GC oven temperature (Pleil et al., 1987). 2.4.1 Air A convenient analytical method for trace levels of 1,2-dibromoethane in ambient air is a combination of preconcentration by absorption on porous polymers, such as Tenax, Porapack, Florisil, silica-gel or charcoal, followed by rapid thermal desorption and direct application for GC. Tenax GC resin is widely used for 1,2-dibromoethane sampling in ambient air (Barkley et al., 1980; Clark et al., 1982, 1984a,b; Krost et al., 1982; Harkov et al., 1984), although Porapack, Chromosorb, silica gel and charcoal have also been used extensively (Kojima & Seo, 1976; Jagielski et al., 1978; Mann et al., 1980). 1,2-Dibromoethane is absorbed by passing air samples through the columns followed by thermal desorption and direct application to GC. Alternatively, 1,2-dibromoethane in air is collected by cryogenic cooling in capillary trap-tubes and then thermally desorbed for GC analysis using trap-ovens with carrier gases (Barkley et al., 1980; Harkov et al., 1984; McClenny et al., 1984; Ballschmiter et al., 1986). The relatively high concentrations of 1,2-dibromoethane in or near fumigation chambers for foods and in automobile exhaust gases can be directly determined by sampling with a gas-tight syringe followed by GC analysis (Hasanen et al., 1979; Dumas & Bond, 1982; Morris et al., 1982; Collins & Barker, 1983). Analytical methods for measuring 1,2-dibromoethane in ambient air are summarized in Table 1. 2.4.2 Water A purge-trap method using absorbents such as Tenax GC and Amberlite XAD-4 resin is the most effective concentration technique for recovering 1,2-dibromoethane from water samples before GC analysis. The GC test solution is prepared by eluting the absorbent columns with a small volume of hexane (Spingarn et al., 1982; Stottmeister et al., 1986). Another method for 1,2-dibromoethane concentration is direct absorption on organic resins like Amberlite XAD-1, 2, 4, 7 and 8, and XE-340 (Libbey, 1986). Direct absorption of water samples on, for example, Amberlite XAD resins can be used for the concentration of 1,2-dibromoethane in aquatic media (Libbey, 1986; Woodrow et al., 1986). Solvent extraction and headspace collection are simple methods for recovering 1,2-dibromoethane from water samples (Saito et al., 1978; Keough et al., 1984; Koida et al., 1986). Analytical methods for measuring 1,2-dibromoethane in water are summarized in Table 2. 2.4.3 Soils and sediment 1,2-Dibromoethane in sediments can be concentrated by a purge- trap procedure, either after dilution of sediment samples with water or after vacuum extraction from sediment samples into a cryogenically cooled trap (Amin & Narang, 1985). Analytical methods for measuring 1,2-dibromoethane in soils are summarized in Table 3. Table 1. Analytical methods for 1,2-dibromoethane in air Collection from air Preparation for GC GC conditions Minimum detection Detectora Reference limit (amount) Collected on Chromosorb extracted with hexane 1.5% OV-17+1.95% OV-210; 100 pg ECD Mann et al. 101 cartridge (20 ml); extracted with column temp: 75°C; in 70% FSRD (1980) (10 mm i.d. × 10 cm) 1% MeOH in benzene, gas flow: N2 (ambient air) extract kept in a 70 ml/min screw-capped test tube and injected into GC Collected directly with a applied directly with 5.5% DC-200+11% GF-1/Ga 0.1 ng ECD Morris et al. gas-tight syringe gas-tight syringe Chrim Q (0.3 mm o.d. × 150 cm, (1982); Morris stainless steel); column temp: & Rippon (1985) 90°C; gas flow: 40 ml/min Collected directly with a applied directly with 5% Carbowax 20M/Chromosorb 2 µg PID Dumas & gas-tight syringe gas-tight syringe W (3 mm i.d. × 200 cm, stainless FSRD Bond (1982) steel); column temp: 120°C; gas flow: N2 30 ml/min (portable gas chromatograph) Collected with a gas-tight applied by direct CPS-20 M (1/8- × 4 tefron tube); 1 ppb PID Cairns et al. syringe (ambient air) injection column temp: ambient temp; (1984) Collected on Tenax GC applied by rapidly Fused silica SP-2000 FSOT not given ECD Harkov et al. cartridge at a flow rate of raising trap oven GC/MS (1984) approx.300-1000 ml/min for temperature to 140°C 24 h; desorbed from the with purge of high cartridge by heating purity N2 (50 ml/min) rapidly at 250°C and collected in an evacuated stainless steel cylinder under cryogenic conditions using vacuum distillation for 30 min (ambient air) Table 1 (cont'd) Collection from air Preparation for GC GC conditions Minimum detection Detectora Reference limit (amount) Collected on a double applied by rapidly OV-1 fused silica capillary 1 ppb ECD McClenny et loop of 0.32 mm (o.d.) heating the tube (-150 column (0.32 mm i.d. × 50 m); al. (1984) nickel tubing packed with to 100°C in 55 sec) and column temp: -50°C (3 min) 60-80 mesh Pyrex beads cooling quickly (120 8°C/min 150°C (7 min) under cryogenic conditions to -150°C in 225 sec) -50°C (10 min); gas flow: (-150°C) (ambient air) H2 4 ml/min a ECD = electron caputure detector; PID = photoionization detector; GC = gas chromatography; MS = mass spectrometry; FSRD = full-scale recorder deflection Table 2. Analytical methods for 1,2-dibromoethane in water Collection Preparation for GC GC conditions Minimum detection Detectora Reference limit (amount) Headspace method applied on a fused 1.J & W FSOT (0.326 mm i.d. × 30 m); 1.8 pg GC/MS Keough et al. silica line Temp: column 70°C, ion source 299°C; (1984) (0.25 mm i.d. × 100 cm) split ratio: 1:10; gas flow: at 250-275°C with a 1.5 ml/min; ion dwell time: gas-tight syringe 100 msec; 2.OV-1 FSOT (0.32 mm i.d. × 50 m); not given ECD column temp: 60-90°C; split ratio: 1:1; gas flow: He 10 ml/min N2 100 ml/min Extracted with applied directly with a 1.5% OV-17 on Chromosorb W 0.05 mg/litre GC/MS Koida et al. hexane micro-syringe (3 mm i.d. × 150 cm); temp: column (CI-NID) (1986) 200°C; separator 120°C; ion source 200°C; reaction gas: isotutane; gas flow: H2 20 ml/min Collected by purging applied by rapidly 0.2% Carbowax 1500 on Carbopack C 0.3 mg/litre FID Stottmeister et into purge-trap thermal desorption (3 mm i.d. × 200 cm); column temp: al. (1986) tubing (Tenax GC (200°C) 35°C (4 min), (8°C/min) 170°C 155 mg) at flow (20 min); gas flow: N2 4 ml/min rate of 50 ml/min for 30 min Table 2 (cont'd) Collection Preparation for GC GC conditions Minimum detection Detectora Reference limit (amount) Collected by absorption extracted with ether 1.DB-1701 FSOT(0.25 mm i.d. × 30 m); 1 ppt ECD Woodrow et on Amberlite and concentrated in column temp: 230°C; split ratio: al. (1986) XAD-4 cartridge Kudernadanish 1:10; gas flow: H2 19 ml/sec at column ball concentrator with 3 230°C; make-up gas Ar/CH4 20 ml/sec; (4.7 mm o.d. × 12 cm) at Snyder column; applied 2.SE-54 FSOT (0.25 mm i.d. × 30 m); flow rate of 10 ml/min with a microsyringe column temp: 100°C (5°C/min) for 18-24 h 250°C (other conditions described above) a ECD = electron capture detector; GC = gas chromatography; MS = mass spectrometry; FID = flame ionization detector; CI = chemical ionization; NID = negative ion detector Table 3. Analytical methods for 1,2-dibromoethane in soil Collection Preparation for GC GC conditions Minimum detection Detectora Reference limit (amount) Collected by steam fortify 50 ml of the not given ECD Abdel-Kader distillation of an extract to folder paper et al. (1979) aqueous slurry of soil and then measure with into dry-ice-cooled molecular emission cavity solvent (acetone: analyser; 4 mm × 4 mm isooctane = 1:1) deep stainless steel under N2 stream at cavity; gas flow: 60°C and drying H2 2.5 litre/min; over Na2SO4 N2 4.0 litre/min; wave length: 376 nm; split: 1.4 nm Collected on Prapack apply by thermal 4% OV-11 & 6% SP 2100 Supelcopor 7 ppb PID Amin & N by purge of desorption of the (2.0 mm × 2.7 m); column temp: 40°C Narang (1985) an aqueous slurry absorbent spiked with (5 min), (3°C/min) 70°C; gas flow: of soil for 30 min fluorobenzene as an N2 30 ml/min, 15% SF-95 & 6% OV-225 1 ppb ECD internal standard on Chromosorb W (2 mm i.d. × 3.6 m); column temp: 60°C (10 min), (3°C/min) 80°C (10 min) 65°C-75°C (isothermal) DB-5 FSOT(0.25 mm i.d. × 60 m) PID column temp: 50°C (15 min) (4°C/min) ECD 170°C (14 min); gas flow: He 60 cm/sec make-up gas He 8 ml/min a ECD = electron caputure detector; PID = photoionization detector; GC = gas chromatography; FID = flame ionization detector 2.4.4 Food Continuous extraction with hexane in a Dean-Stark apparatus for one hour or soaking in a solvent solution of ethanol or acetone and water (1 : 5) for 2 or 3 days is used for the analysis of 1,2-dibromoethane in agricultural crops and their products. A highly sensitive method for the analysis of 1,2-dibromoethane in flour and biscuits was developed by Rains & Holder (1981). Continuous extraction with hexane is used for fruit, vegetables and grains (Sekita et al., 1981, 1983; Kato et al., 1982; Iwata et al., 1983; Konishi et al., 1985; De Vries et al., 1985; Alleman et al., 1986; Nakamura, 1986). Soaking in aqueous ethanol or acetone and water solution is used for grains and their products (Clower, 1980; Daft, 1983, 1985, 1987; Cairns et al., 1984; Barry & Petzinger, 1985; Sawyer & Walters, 1986; Clower et al., 1986). For fruit (papaya and lemon), hexane, hexane- water and acetonitrile are used. In the case of grain, intermediate products, ready-to-eat products, corn bread mix, baby cereal and bread, 1,2-dibromoethane can be extracted with an acetone-water (5+1) solution, 0.1N HCl or light petroleum. Where necessary, Florisil cleanup is useful for the removal of materials interfering with GC analysis. The purge-trap method on layers of Tenax TA (Heikes, 1985a,b), Tenax resins (GC and TA) or Amberlite XAD-4 (Heikes & Hopper, 1986; Daft, 1988) under a nitrogen gas stream is also used for the collection of 1,2-dibromoethane from grains and their products. The resins are eluted with hexane. Automated headspace analysis is employed for measurement of 1,2-dibromoethane in fumigated crops in combination with GC-ECD and GC-MS (Mestres et al., 1980; Entz & Hollifield, 1982; Gilbert et al., 1985; Pranoto-Soetardhi et al., 1986). Equilibrium partitioning between the samples and the gaseous headspace can be accelerated by warming the vials. For detection, the gas chromatographic method with an electron capture detector is used in all the above-mentioned methods. Gas chromatography-mass spectrometry is also used. The detection limit ranges from 0.1 µg/kg to a few µg/kg according to the method used and the food being tested. 1,2-Dibromoethane can be analysed in animal feed by continuous extraction with hexane in a Dean-Stark apparatus, followed by cleanup on a Florisil column (Ishikuro, 1986). 3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE 3.1 Natural occurrence 1,2-Dibromoethane is not a naturally occurring substance. 3.2 Anthropogenic sources 3.2.1 Production levels and processes 18.104.22.168 World production figures In 1975, 1400 tonnes was produced in Japan. Production in Belgium, France, Italy, the Netherlands, Spain, Switzerland and the United Kingdom, was estimated to be between 3000 and 30 000 tonnes (IARC, 1977). 22.214.171.124 Manufacturing processes 1,2-Dibromoethane is made by direct bromination of ethylene or reacting hydrobromic acid with acetylene (Roskill, 1992). 3.2.2 Uses Major uses of 1,2-dibromoethane are as a lead scavenger in tetraalkyllead petrol and antiknock preparations, as a soil and grain fumigant, as an intermediate in the synthesis of dyes and pharmaceuticals, and as a solvent for resins, gums and waxes (IARC, 1977). Reduction in the use of leaded gasoline from the late-1970s in developed countries and of 1,2-dibromoethane for agricultural applications in the 1980s, owing to its carcinogenicity in animals, reduced human exposure to 1,2-dibromoethane. However, it is still used in large amounts for many industrial purposes in developed countries, and as a petrol additive in developing countries. 126.96.36.199 Petrol additive 1,2-Dibromoethane has been added to scavenge the inorganic lead compounds (e.g., lead oxide and sulfate) remaining after fuel combustion. Lead accumulation is prevented by the reaction of 1,2-dibromoethane with lead oxide to form volatile lead bromide, which can pass from the combustion chamber to the atmosphere (IARC, 1977). In 1981, use as a lead scavenger represented 83% of the 1,2-dibromoethane consumed (SRI International, 1982). In 1972, 122 000 tonnes 1,2-dibromoethane was added to petrol formulations in the USA; this figure declined to 73 000 tonnes in 1980 and to 24 000 tonnes in 1992 (Roskill, 1992). In 1992, sales of unleaded petrol accounted for more than 90% of petrol in the USA. In the European Community, all new vehicles must be fitted with three-way convertors that can only use unleaded petrol by the mid-1990s. This is also true of Japan, where almost all cars run on unleaded petrol (Roskill, 1992). In 1992, demand for 1,2-dibromoethane as a gasoline additive in the USA was 24 000 tonnes and consumption outside the USA, principally in Europe, was 25 000 to 30 000 tonnes, giving an estimated world demand of 49 000 to 54 000 tonnes. The amount of 1,2-dibromoethane used in Germany in 1989 was 980 tonnes, calculated on the basis of the petrol consumed in the Federal Republic of Germany in 1989 (BUA, 1991). Legislation banning the use of lead in gasoline and controlling the agricultural use of 1,2-dibromoethane has reduced world demand for 1,2-dibromoethane by at least 75% (Roskill, 1992). 188.8.131.52 Fumigant The volatility of 1,2-dibromoethane allows it to be distributed as a gas through substances such as soil in sufficiently high concentrations to kill target pests. Its chemical and biocidal properties allowed it to be effectively utilized in a wide range of applications. Its primary pesticidal use has been as a soil nematocide (Pignatello & Cohen, 1989). 1,2-Dibromoethane has been used in the spot fumigation of grain milling machinery, post-harvest fumigation of grain, and in the control and prevention of infestations in produce. Additional minor uses have been the control of bark beetles in felled logs, moths in stored furniture and clothing, termites under concrete slab foundations and porches, Japanese beetles in balled ornamental trees and grass sod, and wax moths in stored honeycombs and beehive superstructures. In post-harvest grain fumigation of barley, maize, oats, rice, rye, sorghum and wheat, 1,2-dibromoethane has often been used in conjunction with 1,2-dichloroethane (ethylene dichloride) or carbon tetrachloride. Residues of 1,2-dibromoethane in tropical fruits, imported wheat and beans have been prohibited in Japan (MHW, 1985, 1987, 1988). Use of 1,2-dibromoethane for agricultural purposes has been prohibited in Egypt, Kenya, the Netherlands, Sweden, the United Kingdom and the USA (BUA, 1991; IRPTC, 1993). However, it is still used for quarantine purpose in some countries. 4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION 4.1 Transport and distribution between media The use of 1,2-dibromoethane on a field contaminated both the field and crops for 2 years (Yuita, 1984). About 10% of bromine- containing pesticides was retained, in the form of bromine, in the soil and crops. The remaining 90% seemed to have moved to underground water and rivers. 4.1.1 Air The atmospheric chemistry of bromine compounds has received attention because of the role that they play in the depletion of the stratospheric ozone layer. Wofsy et al. (1975) suggested that bromine atoms can be more effective than chlorine atoms in the catalytic destruction of ozone. A major uncertainty is the absolute concentration of bromine compounds in both the troposphere and the stratosphere. 4.1.2 Soil Injection of 1,2-dibromoethane as a soil fumigant at 70 kg/ha into fine sandy loam resulted in a concentration of 130 µg/kg nearly one year later (Steinberg et al., 1987). The disappearance with time of 1,2-dibromoethane was measured in a sediment-water mixture (ratio 0.075) and a half-life of 55 h was calculated (Jafvert & Wolfe, 1987). Important factors influencing the movement of soil fumigants include their physical and chemical characteristics, temperature, moisture, presence of organic matter, soil texture and soil profile variability (Munnecke & Van Gundy, 1979). 1,2-Dibromoethane is moderately hydrophillic, having a calculated octanol-water partition coefficient of 58 (Lyman, 1982). At environmental levels (10-1000 ppb), 1,2-dibromoethane has a soil organic carbon partition coefficient of 66 ml/g (Rogers & McFarlane, 1981). 1,2-Dibromoethane has a low vapour pressure and moves slowly in the vapour phase. Little, if any, mass flow occurs except in extremely warm soil or when water is applied. Soil temperature is important and may affect 1,2-dibromoethane movement in several ways. A rise in temperature increases the vapour pressure and decreases the solubility. This alters the phase distribution and results in an increase in the rate of diffusion of 1,2-dibromoethane through soils. Fumigation of warm soils (25°C) results in a faster rate and greater distance of nematicide diffusion. In colder soils (5°C), the rate of diffusion is slower and the persistence of the chemical is longer, but the total distance of diffusion of an effective dosage is decreased. The approximate movement and fate of 1,2-dibromoethane in two soils were predicted using extrapolations from laboratory experiments and soil-vapour phase concentrations obtained from simulated field experiments. The most far-reaching diffusion patterns in mineral soils are those obtained in soils whose moisture content is nearest the wilting point of plants (15 bars moisture tension). As the moisture content of the soil is increased, the diffusion pattern gradually becomes more limited. The soil texture and type determine to a large extent the amount of soil moisture present and the size of the connecting air spaces. Soil air space and the size of pores are important because these chemicals move primarily in the vapour phase and smaller pores are most easily blocked when water is present. A material balance for 1,2-dibromoethane was surveyed when 1,2-dibromoethane (equivalent to 47 litres/ha) was applied under various conditions to several soils using a soil fumigation technique in both field and laboratory experiments. Most of the 1,2-dibromoethane was accounted for; the remainder was mostly irreversibly adsorbed or lost during sampling. The 1,2-dibromoethane not accounted for represented between 10 and 40%. After 3 days at 15°C, about 40% of the 1,2-dibromoethane was absorbed in the soil-particle phase, 25% was in the soil-water phase, and 20% remained in the liquid state (McKenry & Thomason, 1974). 1,2-Dibromoethane soil fumigation is used for the control of plant parasitic nematodes on high value crops. In Ontario, Canada, soil types fumigated varied from loamy sand to muck. Three soils differing in texture (Fox loam sand, Vineland silt loam and Lincoln clay) were studied for penetration of 1,2-dibromoethane (Townshend et al., 1980). Fox loam sand (highest content of sand and lowest of organic matter) showed the most rapid penetration; moisture level, temperature and their interactions had the greatest effects on movement of 1,2-dibromoethane. On Vineland silt loam (medium-textured soil) the degree of penetration was dependent on moisture, temperature and bulk density, and there were relatively small interaction effects. On Lincoln clay (high content of organic matter and fine-textured soil) 1,2-dibromoethane did not move in the soil, regardless of edaphic factors, thus explaining the difficulty of using 1,2-dibromoethane fumigation to control nematodes in clay. 1,2-Dibromoethane persists in top soil at µg/kg levels for at least 20 years, despite its predicted lability in the environment (high water solubility and low soil-water partition coefficient). Misleading results were obtained when studies of microbial degradation, sorption, desorption and analytical recovery were conducted with freshly spiked soils or sediments (Pignatello, 1986). 1,2-Dibromoethane can serve as a C1 unit and energy source for some soil aerobic or anaerobic microorganisms. However, residual 1,2-dibromoethane is strongly bound to soils and can only be extracted from them by warming with polar solvents. Surfactants showed no enhanced extraction ability. Thermal desorption at temperatures as high as 200°C in an N2 stream resulted in more decomposition than desorption, while a fresh spike of 14C-labelled 1,2-dibromoethane was recovered quantitatively. Diffusion of residual 1,2-dibromoethane from soil to water is very slow and highly temperature-dependent (diffusion coefficient: 10-16 cm2/sec) (Pignatello et al., 1987). 1,2-Dibromoethane, when present as a groundwater contaminant in areas where it had been used as a soil fumigant, was degraded anaerobically by microorganisms in two types of soils from 1,2-dibromoethane-contaminated groundwater discharge areas. At initial concentrations of 6 to 8 µg/litre, 1,2-dibromoethane was degraded in a few days to near or below the detection limit (0.02 µg/litre). At 15 to 18 µg/litre degradation was slow. Bromide ion released at the higher concentration was 1.4 ± 0.3 and 23.1 ± 0.2 molar equivalents for the two soil types. A study using 14C-1,2-dibromoethane showed that 1,2-dibromoethane was converted to approximately equal amounts of CO2 and cellular carbon; only small amounts of 14C were not attributable to these products. However, 1,2-dibromoethane was not degraded in autoclaved soil water samples. The results suggested that, initially, microbial degradation of 1,2-dibromoethane in the topsoil was too slow to prevent leaching of large quantities to groundwater. With continued application the microbial community may have adapted to the higher levels and degradation rates increased; this has been observed with other agricultural chemicals. The results of acetate incorporation studies suggested that the highest application rates of 1,2-dibromoethane are definitely toxic to topsoil microbial communities. 5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE 5.1 Environmental levels 5.1.1 Air 1,2-Dibromoethane enters the atmosphere from its use as a petrol additive to scavenge the lead oxide resulting from the combustion of alkyllead antiknock additive, and from its use in agriculture as an insecticidal and fungicidal fumigant. Nilsson et al. (1987) reported that the exhaust gas of chain saws fuelled with petrol contained a mean 1,2-dibromoethane level of 0.0008 (0.0001-0.001) mg/m3 under snow-free conditions and 0.002 (0.0001-0.005) mg/m3 with snow on the ground during the winter. 1,2-Dibromoethane levels are around 45% higher in cold start than in hot start conditions and have a tendency to decrease with increasing vehicle speed (see Tables 4 and 5). Concentrations of 1,2-dibromoethane in raw, undiluted exhaust from vehicles using leaded petrol are in the range of 55-146 µg/m3 (7.2-19 ppb), 46-122 µg/m3 (6.0-16 ppb) and 38-115 mg/m3 (5.0-15 ppb) under the conditions of USA Federal test driving, idle, and a steady speed of 30 mph, respectively (Jacobs, 1980). Based on these levels, 1,2-dibromoethane concentrations in air alongside roads due to vehicle exhaust emissions may range from 0.04 to 122 µg/m3 (0.005-0.19 ppb). These results are similar to the observations of Leinster et al. (1978). Table 4. 1,2-Dibromoethane produced by motor vehicles (petrol engine) under constant speed test conditions Vehicle speed km/h Concentration (µg/m3) Engine not Vehicle with Vehicle with defineda 3 litre engineb 0.85 litre engineb Cold start (idle) 70 878 332 10 78 30 62-70 618 165 40 61 50 2 669 155 64 180 139 80 98 135 a Leinster et al. (1978) b Tsani-Bazaca et al. (1981) Table 5. 1,2-Dibromoethane in the exhaust emission of motor vehicles (petrol engine) (µg/m3)a Conditions 3 litre engine 0.85 letre engine ECEb cold start 292-560 733-538 hot start 200-234 533-538 ECD/CVSc 14-25 26-34 USA Federald cold start 48 29 hot start 22 a From: Tsani-Bazaca et al. (1981) b standard European driving cycle c ECE driving cycle under constant volume sampling condition d 1973 driving cycle 1,2-Dibromoethane levels in air have been measured at several sites around the world (Table 6). Leinster et al. (1978) concluded that the lower levels during the autumn were the result of a reduction in evaporative loss particularly from parked vehicles (the calculated evaporation rate for 1,2-dibromoethane at 5°C is less than one third of that at 30°C). An indication of the magnitude of evaporative loss from parked vehicles was provided by levels of 0.02-0.05 µg/m3 measured in a car park. It was also probable that an opposite trend would be produced by a change in driving conditions. For example, cold starts and driving speeds of vehicles have a marked influence on the 1,2-dibromoethane content of exhaust emissions. The 1,2-dibromoethane added to leaded petrol contributes to a large amount of methyl bromide in urban atmospheres. IPCS (1995) estimated that per annum between 7000 and 18 000 tonnes of methyl bromide could be emitted from car exhausts. Reactions in the lower troposphere with hydroxyl radicals and other chemical species are the most important of the possible removal mechanisms within the atmosphere (UNEP, 1992). The end-products of both photodissociation of methyl bromide and reactions with hydroxyl radicals in the atmosphere include bromide species (BUA, 1987). Active bromine species react with ozone mainly in the lower stratosphere and are thought to be partly responsible for the destruction of the ozone layer. However, 1,2-dibromoethane was not included as a controlled substance in the "Montreal Protocol on Substances that Deplete the Ozone Layer". Table 6. Environmental concentrations of 1,2-dibromoethane Location Measuring period Concentration (µg/m3) Reference London August 1976a 0.08-0.09 µg/m3 Leinster et al. (1978) December 1976b 0.001-0.01 µg/m3 12 Canadian cities 1989-1992 mean 0.05 ± 0.05 µg/m3 Environment Canada range n.d.-1.73 µg/m3 (1994) Busy streets at 2 m height 0.07-1.26 µg/m3 Tsani-Bazaca et al. and 5 m from kerbside (1981) Los Angeles, California, USA 9-21 April 1979 0.25 ± 0.20 ng/m3 (33.2 ± 26.2 ppt) Singh et al. (1981) range 0.041-1.4 ng/m3 (5.4-187.2 ppt) Oakland, California, USA 28 June-10 July 1979 0.12 ± 0.10 ng/m3 (15.8 ± 12.5 ppt) Singh et al. (1981) range 0.018-0.65 ng/m3 (2.4-84.5 ppt) Phoenix, Arizona, USA 23 April-6 May 1979 0.31 ± 0.29 ng/m3 (40.3 ± 38.3 ppt) Singh et al. (1981) range 0.018-1.6 ng/m3 (2.4-204.4 ppt) Background 38 ng/m3 Various cities (7) 1-2 weeks in 1980 0.122-0.453 ng/m3 (0.016-0.059 ppt)c Singh et al. (1982) 2.826 ng/m3 (0.368 ppt)d Denver, Colorado, USA 1-2 weeks n.d.-2.304 µg/m3 (0.3 ppb) Going & Spigarelli (1976); Leinster et al. (1978) Sites in New Jersey, USA late 1983-Spring 1984 0.077-5.4 µg/m3 Harkov et al. (1985) Summer 1981 < 0.038 µg/m3 Harkov et al. (1983) Winter 1982 < 0.038 µg/m3 Harkov et al. (1983) Table 6 (cont'd) Location Measuring period Concentration (µg/m3) Reference Central London Summer 1982 0.23 µg/m3 (0.03 ppb)e,f Clark et al. (1984a,b) Exhibition Road May-August 1983 0.23 µg/m3 (0.03 ppb)e Rural site Summer 1982 0.12 µg/m3 (0.015 ppb)e,g Clark et al. (1984a,b) Silwood Park, United Kingdom May-August 1983 0.15 µg/m3 (0.019 ppb)e Motorway outside London, Summer 1982 0.39 µg/m3 (0.05 ppb)e,h Clark et al. (1984a,b) Toddington May-August 1983 0.31 µg/m3 (0.04 ppb)e Central London Summer 1982 1.0 µg/m3 (0.13 ppb)i Clark et al. (1984a,b) May-August 1983 0.62 µg/m3 (0.08 ppb)i Motorway site Summer 1982 2.0 µg/m3 (0.26 ppb)i Clark et al. (1984a,b) May-August 1983 1.2 µg/m3 (0.15 ppb)i Anchorage (Alaska) March 1983 31-177 ng/m3 (4-23 ppt) Berg et al. (1984) Barrow (Alaska) March 1983 n.d.-177 ng/m3 (n.d.-28 ppt) Berg et al. (1984) Mould Bay Coast (Alaska) March 1983 38-284 ng/m3 (5-37 ppt) Berg et al. (1984) Thule (Greenland) March 1983 15-246 ng/m3 (2-32 ppt) Berg et al. (1984) North Pole March 1983 92.2 ng/m3 (12 ppt) Berg et al. (1984) Ny-Alesund (Norway) March-April 1983 31-150 ng/m3 (4-20 ppt) Berg et al. (1984) Table 6 (cont'd) Location Measuring period Concentration (µg/m3) Reference Bear Island (Norway) March-April 1983 23-100 ng/m3 (3-13 ppt) Berg et al. (1984) Bodo (Norway) March-April 1983 38-110 ng/m3 (5-14 ppt) Berg et al. (1984) a temperature range 28-30°C b temperature range 4-8°C c average level for each city d maximum concentration found in Houston, Texas, USA e mean hourly concentrations f range 0.078-1 µg/m3 (0.01-0.13 ppb) g range ND-0.78 µg/m3 (ND-0.01 ppb) h range 0.07-2.0 µg/m3 (0.009-0.26 ppb) i maximum hourly concentrations 1,2-Dibromoethane levels of 0.07-1.26 µg/m3 have been found in busy streets. Higher levels were found in a road tunnel and were associated with poor ventilation (Tsani-Bazaca et al., 1981). Three field studies on the measurement of selected potentially hazardous organic compounds in urban environments were conducted in the USA in 1979 (Los Angeles, California, 9-21 April; Oakland, California, 28 June-10 July; and Phoenix, Arizona, 23 April-6 May). These studies were performed to characterize the atmospheric abundance, fate and human exposure to these compounds (Table 6). The background concentration of 1,2-dibromoethane was 38 ng/m3 (5 ppt). Assuming an average respiratory volume of 23 m3 at 25°C and 1 atm for a 70-kg male, the average daily dose (µg/day) of 1,2-dibromoethane at these locations can be calculated as 6.0 ± 2.7 for Los Angeles, 2.9 ± 0.8 for Oakland and 7.0 ± 2.7 for Phoenix. The ratios of 1,2-dibromoethane to total haloethane and VHH (volatile halogenated hydrocarbons) in the average daily doses were 2.7% and 0.57%, 5.6% and 1.14%, and 2.8% and 1.03%, respectively. The chemical loss rate of 1,2-dibromoethane was 2.8% per day (sunlight = 12 h). There was diurnal variation in 1,2-dibromoethane levels at the three locations. The afternoon minimum at Phoenix was attributed to deep vertical mixing associated with hot and dry weather. The afternoon maximum at Oakland was most likely a result of transport from upwind sources (Singh et al., 1981). Other studies measuring 1,2-dibromoethane in the ambient atmosphere of urban and rural areas have been performed (Going & Long, 1975; Going & Spigarelli, 1976). Sources of 1,2-dibromoethane in air were considered to be emissions from stations dispensing leaded petrol and evaporative emissions from motor vehicles using leaded petrol. Atmospheric levels of 1,2-dibromoethane were low (0.046 to 3.5 µg/m3) (0.006 to 0.45 ppb) in worst case conditions near petrol stations and with heavy traffic in cities. These levels are 10 to 10 000 times less than the occupational exposure level of 1 mg/m3 (0.13 ppm) for 15 min recommended by the US National Institute of Occupational Safety and Health (Jacobs, 1980). Tsani-Bazaca et al. (1981) monitored the concentrations of VHH collected in 1979 at several locations and utilizing vehicles operating under various conditions on a busy road in central London (2000 vehicles/h), a poorly ventilated tunnel (1600 vehicles/h at peak traffic flow), and a semi-rural industrialized area. The concentration of 1,2-dibromoethane varied between 0.07 and 1.26 µg/m3. There was a good correlation between 1,2-dibromoethane and benzene concentrations (correlation coefficient : 0.93) at the three locations and a higher correlation between 1,2-dibromoethane and 1,2-dichloroethane (correlation coefficient : 0.94). In 1983, 54 air samples at 6 urban sites and 54 air samples at 6 mountainous sites were collected in Japan and were analysed for the presence of 1,2-dibromoethane. A total of 35 samples from 5 urban sites contained 1,2-dibromoethane at concentrations of 0.008-0.322 µg/m3 (0.001-0.042 ppb). The detection limit was 0.005-0.008 µg/m3 (0.0007-0.001 ppb). A total of 36 samples from 5 mountainous sites contained 1,2-dibromoethane at concentrations of 0.008-0.515 µg/m3 (0.001-0.067 ppb). The detection limit was 0.002-0.008 µg/m3 (0.0003-0.001 ppb) (Environment Agency Japan, 1985). Urban 1,2-dibromoethane levels at seven sites in selected cities in the USA in 1980, using on-site and real-time measurement instrument following a 24-h measurement schedule for a period of 1-2 weeks, were 0.12-0.45 µg/m3 (16-59 ppt) (Singh et al., 1982). The average concentration of 1,2-dibromoethane did not exceed 0.015-0.46 µg/m3 (0.06 ppb) (average range 0.002-0.06 ppb) at any study site and average levels ranged from 0.122 µg/m3 (0.016 ppb) at St. Louis, Missouri, to 0.46 µg/m3 (0.059 ppb) at Houston, Texas. The maximum concentration of 2.83 µg/m3 (0.368 ppb) was found at Houston. In general, the highest average levels were found during the night and early morning. In the case of Denver, Colorado, typical ambient concentration data suggested a range of not detectable to 2.3 µg/m3 (0.300 ppb) (Going & Spigarelli, 1976; Leinster et al., 1978). The Office of Science and Research (USA) monitored VHH in ambient air at listed abandoned hazardous waste sites and sanitary landfills in New Jersey (Harkov et al., 1985). 1,2-Dibromoethane was found at mean levels of 2.1 µg/m3 (0.27 ppb), 2.2 µg/m3 (0.288 ppb), 3.6 µg/m3 (0.47 ppb), 5.4 µg/m3 (0.7 ppb), 0.38 µg/m3 (0.05 ppb), 0.077 µg/m3 (0.01 ppb) and 0.15 µg/m3 (0.02 ppb) at different sites during late 1983 and early 1984. It was below the detection limit 0.038 µg/m3 (0.005 ppb) at three sites during the summer of 1981 (Harkov et al., 1983) and the winter of 1982 (Harkov et al., 1984). Ambient air monitoring survey of VHH at a busy road in central London, a rural site and a motorway location near London showed mean hourly 1,2-dibromoethane concentrations of 0.23, 1.2 and 0.39 µg/m3 (0.03, 0.15 and 0.05 ppb), respectively, in summer 1982 and 0.23, 0.15 and 0.31 µg/m3 (0.03, 0.019 and 0.04 ppb) between May and August 1983 (Clark et al., 1984a,b). The maximum hourly concentrations of 1,2-dibromoethane at the urban and motorway sites were 1.0 and 2.0 µg/m3 (0.13 and 0.26 ppb) in 1982, and 0.61 and 1.2 µg/m3 (0.08 and 0.15 ppb) in 1983, respectively. 1,2-Dibromoethane concentrations at the urban site were in the same ranges 0.07-0.31 ng/m3 (0.01-0.04 ppt) as those measured by other workers (Leinster et al., 1978; Tsani-Bazaca et al., 1981; Singh et al., 1982). The low concentrations found at the rural site were primarily related to the low incidence of vehicular pollutant sources in the area. However, the site was near the urban fringe of London and near several small towns and this may explain occasional elevated concentrations. 1,2-Dibromoethane concentrations were measured at Point Arena, California between 1979 and 1981; the background level of 1,2-dibromoethane in the troposphere was found to be less than 0.023 µg/m3 (3 ppt) (Singh et al., 1983). Berg et al. (1984) measured atmospheric 1,2-dibromoethane concentrations at eight arctic sites in 1983. Concentrations at three sites in Alaska (Anchorage, Barrow, Mould Bay Coast) in March were 0.031-0.177 µg/m3 (4-23 ppt), not detectable to 0.22 µg/m3 (29 ppt) and 0.038-0.284 µg/m3 (5-37 ppt), respectively. 1,2-Dibromoethane levels in Greenland (Thule) and at the North Pole in March were 0.015-0.246 µg/m3 (2-32 ppt) and 0.096 µg/m3 (12 ppt), respectively. Those at Norwegian sites (Ny-Alesund, Bear Island, Bodo) during March-April were 0.031-0.15 µg/m3 (4-20 ppt), 0.023-0.10 µg/m3 (3-13 ppt) and 0.038-0.11 µg/m3 (5-14 ppt), respectively. The mean concentration ± standard deviation was 0.084-0.77 µg/m3 (11 ± 10 ppt). Other organobromine compounds, such as methyl bromide, methylene dibromide and bromoform, were detected at similar concentrations. Monthly monitoring of the atmosphere of Barrow, Alaska (72 °N), showed that the 1,2-dibromoethane concentration was higher in winter than in other seasons, although the monthly average concentrations did not differ greatly (7.68-10.7 ng/m3) (1.0-1.4 ppt) except in January. From the results of atmospheric VHH monitoring, Rasmussen & Khalil (1984) suggested that VHH in arctic air might be an indicator of polluted air transported from industrial mid-latitude sources. 5.1.2 Water Widespread use of 1,2-dibromoethane as a soil fumigant in the USA resulted in its detection in both groundwater and surface water in California, Florida, Georgia, and Hawaii (Sun, 1984), Connecticut (Isaacson et al., 1984) and New Jersey (Page, 1981), and in wells used for irrigation in Georgia (Martl et al., 1984). 1,2-Dibromoethane was reported in groundwater in Georgia, California, Florida, and Hawaii by US EPA (1986). Laboratory studies have shown that 1,2-dibromoethane photohydrolyses rapidly in aqueous solutions when irradiated. The degradation is a two-stage process in which 1,2-dibromoethane is converted to bromoethanol (half-life, 7.6 min) and then to ethylene oxide (half-life, 64 min). Further degradation to ethylene glycol was less influenced by light, as shown by a half-life of 10 days (Castro & Belser, 1978). While the above study provides some understanding of aqueous degradation, Logan (1988) cautions that the efficiency of the photo-reactions were not reported in terms of quantum yield. 1,2-Dibromoethane was found in ground- and surface water in New Jersey (over 1000 different wells and 600 different sites) during 1977-1979; the highest levels were 0.2 µg/litre in surface water and 48.8 µg/litre in groundwater (Page, 1981). Analyses of 350 well water samples from Connecticut in 1984 revealed concentrations of up to 2 µg/litre. 1,2-Dibromoethane was rapidly lost from water samples exposed to the atmosphere or boiled for few minutes. It could not be detected in water samples purged with nitrogen for 10 min (Isaacson et al., 1984). In southwest Georgia, USA, agricultural practices involve intensive use of groundwater for irrigation and pesticides for control of plant and insect pests. 1,2-Dibromoethane was found at levels of between 1 and 90 µg/litre in water samples from three irrigation wells collected between 1981 and 1983. Application at ratios of 14-19 litres/ha) near wells showed that 1,2-dibromoethane concentrations in the aquifer did not appear to be directly related to the application rate of the compound to the surface. The concentrations in the wells may reflect application of the compound at sites some distance from the wells (Martl et al., 1984). In 1982, 27 water samples and 27 bottom sediment samples were collected at nine sites in Japan and were analysed for the presence of 1,2-dibromoethane. None of the water or bottom sediment samples contained 1,2-dibromoethane. The detection limit was 0.3-2 µg/litre for water and 0.0016-0.01 µg/kg for bottom sediment (Environment Agency Japan, 1985). In 1983, 1,2-dibromoethane surveillance of the water of six rural wells in Ibaraki prefecture, Japan, where 1,2-dibromoethane was used for soil fumigation or as a pesticide on pine tree, showed no 1,2-dibromoethane contamination (detection limit, 5 µg/litre) (Nemoto et al., 1984). Groundwater samples from nine sites in and around vegetable- growing areas in Gifu Prefecture, Japan, were collected twelve times between July 1983 and December 1984. 1,2-Dibromoethane levels ranged from 0.06 to 0.55 µg/litre at seven sites and the mean values of 1,2-dibromoethane at each site varied between 0.15 and 0.28 µg/litre. 1,2-Dibromoethane levels in groundwater around the vegetable-growing areas did not differ from those within the areas, where 1,2-dibromoethane application was limited to once a year in the first two weeks of July. Sites where 1,2-dibromoethane were detected around these areas overlapped completely the stream of groundwater coming from these areas (Terao et al., 1985). The annual variation of concentrations in the groundwater was small. 1,2-Dibromoethane concentration showed good correlation with bromine ion concentration and bromine ion/chlorine ion ratio at each site (Terao et al., 1984). Mayer et al. (1991) studied 1,2-dibromoethane concentrations in detail in water from a domestic well, approximately 10 m deep, in a fruit growing area of Whatcom County, Washington, USA where 1,2-dibromoethane had been used extensively prior to its 1983 ban. Additional wells (n = 107) were also sampled over a 4-year period; no details of well depths were given. Correlation analysis showed no relationship between 1,2-dibromoethane concentration in water and temperature but significant negative correlation between precipitation and 1,2-dibromoethane. The analysis allowed lag times of between 0 and 12 months; a 3-month lag was found to give the best relationship between precipitation and 1,2-dibromoethane in the water. The dilution effect of precipitation was followed by slow 1,2-dibromoethane infiltration from overlying soils which tended to re-establish prior concentrations over about 3 months. The authors stated that water contamination can result from such continuing infiltration of soil-matrix-derived 1,2-dibromoethane long after agricultural use has ceased. 5.1.3 Food Beckman et al. (1967) reported that part of the inorganic bromine in foods and raw agricultural commodities comes from the soil. 1,2-Dibromoethane was applied annually at 54 kg/ha and samples from 40 crops grown in soil treated with 1,2-dibromoethane were analysed over a 3-year period. In general, leafy portions of plants contained the highest levels of bromide on the basis of weight. Residue levels were calculated as inorganic bromide ion present in the crop after harvest. Levels in crop samples from untreated soil were less than 1.6 mg/m3 (0.2 ppm), and the highest level in crops from treated soil was 137 mg/kg (17.8 ppm) in sugar beet tops. Most of the crops were harvested about 100 days after soil treatment but time from treatment to harvest ranged from 55 days for strawberries to 10 years for walnuts. 1,2-Dibromoethane was absorbed strongly by cereal, grains, cereal products and other produce during the fumigation period. Even when normal ventilation procedures were followed, residues of 1,2-dibromoethane disappeared very slowly. Nearly all the 1,2-dibromoethane was physically sorbed and at normal temperatures there was little formation of inorganic bromide. However, occasionally in produce at higher temperatures and moisture content there was rapid breakdown to inorganic bromide (Heuser & Scudamore, 1967). Levels of 1,2-dibromoethane in wheat were between 10 and 20 mg/kg, and, for its products, between 2 and 4 mg/kg in flour, 0.002-0.04 in white bread and 0.006-0.16 in wholemeal bread. When flour was treated directly with 1,2-dibromoethane, ventilated thoroughly, and then baked into loaves, there were residues of 20-24 mg/kg in the flour and 0.33-0.47 mg/kg in the bread (FAO/WHO, 1972). Desorption of 1,2-dibromoethane occurred at low (14-17°C) rather than high (30-37°C) temperatures, and was abolished by grinding the grain (Bielorai & Alumot, 1975). Rappaport et al. (1984) reported that the decay of the outgassing rate over time from fumigated oranges was approximately first order. Outgassing was significantly slowed by reducing either the temperature or the ventilation rate. In laboratory trials, ventilation at 0.6 air changes/h removed 1,2-dibromoethane vapours from the surface of oranges, and prevented reabsorption onto the fruits. A pesticide formulation, consisting of carbon tetrachloride (CT), 1,2-dichloroethane (EDC), 1,2-dibromoethane in 63 : 30 : 7 w/w proportions, was applied to 27.3 tonnes of wheat stored in a paper laminate bin (Berck, 1974). The CT-EDC-1,2-dibromoethane distribution- persistence patterns were monitored at 16 bin locations over a 14-day period by GC. Fumigant residues in the wheat, in flour, bran, and middlings derived from the wheat, and in bread baked from the flour were determined over a 7-week period. 1,2-Dibromoethane residues in the wheat varied, depending on the bin location and contact time, and ranged from 0 to 3.3 mg/kg. Residues in bran and middlings were greater than those in flour, and ranged from 0 to 0.4 mg/kg. No 1,2-dibromoethane residues were found in any of the bread tested (detection limit, 10 ng/kg). 1,2-Dibromoethane levels were studied in biscuits (22 samples) and flour (22 samples), the biscuits being baked from each of the flour samples for 12 min at 268°C. After baking, the samples were sealed in plastic bags and frozen to prevent any further loss of 1,2-dibromoethane. Flour samples were also sealed in plastic bags and frozen. Levels of 1,2-dibromoethane in flour and biscuits ranged from non-detectable to 4.2 mg/kg and to 0.26 mg/kg, respectively. There was poor correlation between the levels of 1,2-dibromoethane in flour and biscuits. 5.2 Occupational exposure Air concentrations of 1,2-dibromoethane in ventilated containers dropped from several ppm immediately after fumigation to a few ppb after 5-10 days; levels remained between 15 and 23 mg/kg (2 and 3 ppm) for 15-20 days during unventilated, refrigerated storage. Results of experiments on a laboratory scale (0.25 carton) and a large scale (400 cartons) suggested that workers transporting and distributing fumigated citrus fruit could routinely be exposed to airborne 1,2-dibromoethane at concen trations greater than 998 µg/kg (130 ppb) (OSHA, 1983). The US National Institute for Occupational Safety and Health (NIOSH) estimated that approximately 108 000 workers in the USA were potentially exposed to 1,2-dibromoethane in their workplaces (Table 7) and that another 875 000 workers handling leaded petrol were exposed to very low levels (NIOSH, 1981). There is no estimate of the number of motorists exposed to 1,2-dibromoethane during self-service operations at filling stations. Table 7. Occupations with potenial exposure to 1,2-dibromoethanea Antiknock compound makers Motor fuel workers Cabbage growers Oil processors Corn growers Organic chemical synthesizers 1,2-Dibromoethane workers Petrol blenders Drug makers Resin makers Fat processors Seed corn maggot controllers Fire-extinguisher makers Soil fumigators Fruit fumigators Termite controllers Fumigant workers Tetraethyllead makers Grain elevator workers Waterproofing makers Grain fumigators Waxmakers Gum processors Wood insect controllers Lead scavenger makers Wool reclaimers a From: NIOSH (1977) In the 1970s, US EPA examined the exposure of professional pesticide applicators involved with 1,2-dibromoethane soil fumigation. It was estimated that applicators applying 1,2-dibromoethane for 30-40 days/year would receive a total annual inhalation dose of 3-40 mg/kg and farmer-applicators applying 1,2-dibromoethane for 7-10 days/year would receive a total annual inhalation dose of 0.7-10 mg/kg (US EPA, 1977). 1,2-Dibromoethane exposures were measured in a plant where lead antiknock blends for petrol were prepared (Jacobs, 1980). The antiknock blend constituents were mixed in tanks under enclosed-system conditions and the only manual operations were connecting and disconnecting hoses while loading and unloading tank cars, taking quality control samples, and processing and loading drums. The levels of worker exposure to 1,2-dibromoethane in antiknock blending and storage areas were 0.77 µg/m3 (0.1 ppb) (laboratory technician) to 6.3 µg/m3 (0.82 ppb) (raw maternal blender). In addition to long-term personal sampling, some short-term monitoring of specific tasks was conducted. The results are shown in Table 8. Table 8. Short-term air levels of 1,2-dibromoethane in antiknock blending plant tank cars (Jacobs, 1980) Taska Sampling time Concentration mg/m3 ppm Quality control sample 13 min, 10 sec 5.38 0.7 Loading tank car 7 min 1.07 0.14 a Respirator worn during these tasks Personal air monitoring during vehicle refuelling at a petroleum laboratory 10 m downwind of the fuel pump and fuel-handling facilities was performed at a USA plant in July, 1975 (Table 9). The average exposure of filling station attendants to 1,2-dibromoethane during refuelling was 1.8 µg/m3 (0.24 ppb). Measurements at the car fuel tank filler pipe showed maximum instantaneous 1,2-dibromoethane concentrations of 105 µg/m3 (13.7 ppb), with an average for four samples of 10.0 µg/m3 (1.3 ppb). This represented the maximum for a short-term exposure. The concentration of 1,2-dibromoethane in air at the fuel pump island was similar to values measured at upwind and downwind sites. Overall, the very low 1,2-dibromoethane air levels measured in this study indicated that the potential for filling station attendant exposure to 1,2-dibromoethane while refuelling cars was low and less than the current or proposed USA occupational air standard for 1,2-dibromoethane exposure (Jacobs, 1980). Exhaust emissions from various types of internal combustion engines, including four-stroke Otto engines and diesel engines, are a major source of environmental and occupational exposure to 1,2-dibromoethane (Hasanen et al., 1981). There are few data on the composition of and exposure to exhaust emissions from two-stroke engines. Table 9. Petrol station attendant exposure to 1,2-dibromoethane during vehicle refuelling (Jacobs, 1980) Sample Concentration mg/m3 ppb Upwind background < 0.77 < 0.1 Downwind background < 0.77 < 0.1 Fuel pump island 0.99 0.13 Near vehicle fuel pipe 9.98 1.3a during refueling 105.2 13.7b Personal air sampler 2.15 0.28 a Average b Maximum Seven chain saws fuelled with 93-octane standard petrol- containing tetramethyllead (lead content 0.15 g/litre) and 1,2-dibromoethane as a scavenger were tested on a test-bench permitting a variable load to be applied by an electric power brake (Nilsson et al., 1987). 1,2-Dibromoethane emissions were low (2.5 mg/m3). Exposure to chain saw exhaust during logging was studied under snowy and snow-free conditions. The time-weighted average exposure to 1,2-dibromoethane was lower in the snow-free conditions (0.0008 (0.0004-0.001) mg/m3) than in the snowy conditions (0.002 (0.0001-0.005) mg/m3). 1,2-Dibromoethane is mainly used as a scavenger in tetraalkyllead petrol and antiknock preparations, as a soil and grain fumigant, as an intermediate in the synthesis of dyes and pharmaceuticals and as a solvent for resins, gums and waxes (Alexeeff et al., 1990). Rumsey & Tanita (1978) performed an industrial hygiene survey of two manufacturing and two user facilities involving 1,2-dibromoethane. Samples were taken from more than 69 potentially-exposed workers in 17 job classifications. Median 1,2-dibromoethane exposure (by similar job types) in the manufacturing process ranged from 0.076 to 3.8 mg/m3 (0.010 to 0.5 ppm) (35 TWA personal samples). General area samples collected at breathing zone heights had median TWA levels of 1.5 mg/m3 (0.2 ppm) for 10 samples at process sites, and 3.8 mg/m3 (0.5 ppm) for 3 samples at laboratory sites. Papaya workers in Hawaii were exposed to a geometric mean of 676 mg/m3 (88 ppb), and peaks up to 2.01 mg/m3 (262 ppb) were measured (Steenland et al., 1986). 6. KINETICS AND METABOLISM 6.1 Absorption 1,2-Dibromoethane was found in the blood of rodents almost immediately after dermal and oral exposure. Jakobson et al. (1982) reported that during a 6-h dermal exposure of guinea-pigs of both sexes (weighing between 600 and 1000 g) with undiluted 1,2-dibromoethane applied to 3.1 cm2 of shaved skin on the back (1.0 ml/animal), the blood concentration of 1,2-dibromoethane increased rapidly during 1 h to a level of 2 mg/litre and then slowly decreased. The influx of 1,2-dibromoethane into the blood after 1 h was largely in equilibrium with its disappearance. In male Sprague-Dawley rats given 15 mg/kg body weight of [14C-1,2] 1,2-dibromoethane in corn oil by gavage, the blood levels at 24 h and 48 h were 0.90 and 0.64 mg/litre, respectively (Plotnick et al., 1979). The excretion of radioactivity in faeces within 24 h was 1.7% of the dose. The remainder was recovered either in the urine (72%) or in the tissues (2.8%) (Table 10). The results indicated rapid 1,2-dibromoethane absorption from the gastrointestinal tract. No absorption information regarding inhalation exposure exists. Table 10. The distribution of 14C in selected tissues and body fluids of male rats 24 h after a single oral dose of 14C-1,2-dibromoethane (15 mg/kg)a Tissue Tissue concentrationsb Percentage of dose (mg equivalent/kg or mg/litre) (%) Liver 4.78 ± 0.24 1.7 ± 0.07 Kidneys 3.32 ± 0.42 0.21 ± 0.02 Spleen 1.00 ± 0.03 0.22 ± < 0.01 Testes 0.49 ± 0.05 0.04 ± < 0.01 Brain 0.41 ± 0.04 0.02 ± < 0.01 Fat 0.35 ± 0.04 0.15 ± 0.02 Blood 0.90 ± 0.05 0.59 ± 0.03 Plasma 0.46 ± 0.04 Urinec 72.38 ± 0.98 Faecesc 1.65 ± 0.28 a From: Plotnick et al. (1979) b Values represent mean concentrations (expressed as parent compound) ± S.E.M. of duplicate determinations for six animals. c n = 12 6.2 Distribution Plotnick et al. (1979) compared levels of 14C in selected tissues of male Sprague-Dawley rats following oral administration of 14C-1,2-dibromoethane. One day after the administration, the highest levels of radioactivity were found in the liver and kidneys (Table 10). Distribution of 14C-1,2-dibromoethane (30 mg/kg body weight) after intraperitoneal administration to male guinea-pigs was studied by Plotnick & Conner (1976). The liver and kidneys contained the highest levels of radioactivity followed by the adrenal glands (Table 11). Table 11. Distribution of 14C-1,2-dibromoethane in selected tissues of male guinea-pigs at various time intervals following intraperitoneal administrationa Tissues/organs 4 h 8 h 24 h 72 h Liver 129.0 104.9 38.0 15.6 Kidneys 286.6b 236.5 3.5 10.5 Adrenals 60.7 60.8 28.6 10.4 Pancreas 35.0 36.8 18.7 6.0 Spleen 15.8 14.0 14.9 7.0 Heart 14.0 15.6 9.5 3.3 Lungs 20.9 19.0 15.4 5.8 Testes 10.7 10.7 8.3 4.0 Brain 6.2 7.6 6.5 2.5 Fatc 21.4 7.9 3.2 2.1 Muscle 5.5 5.0 4.2 2.2 Blood 10.0 3.4 5.0 2.8 a From: Plotnick & Conner (1976) b Values represent mean levels in mg equivalent/kg of tissue or litre of fluid for three animals at each time interval c Suprarenal fat Kowalski et al. (1985) reported epithelial binding of 1,2-dibromoethane in the respiratory and upper alimentary tracts of C57BL mice, Sprague-Dawley rats and Fischer-344 rats after intravenous and intraperitoneal injection of 14C-1,2-dibromoethane. In C57BL mice, there was a high level of radioactivity in the nasal and bronchial mucosa and liver 5 min after intravenous injection of 14C-1,2-dibromoethane. In the nose, the highest labelling was present in a spotty band beneath the epithelium of the ethmoturbinates. The radioactive labelling of the mucosa of the respiratory tract was persistent, and 10 days after injection a selectively bound radioactivity remained. High labelling was also present in the mucosa of the forestomach, whereas there was no selective uptake of radioactivity in the glandular stomach or intestine. Similar distribution patterns were observed in the intraperitoneally injected mice killed after 30 min or subsequently. 6.3 Metabolic transformation The metabolism of 1,2-dibromoethane has been extensively studied and metabolites have been identified in in vivo and in vitro studies (Table 12, Fig. 1). Table 12. Metabolites of 1,2-dibromoethane (a) In vivo Metabolite Animal; route; substrate Reference Bromide Swiss-Webster mice; White et al. intraperitoneal; plasma (1983) N-acetyl-S-(2-hydroxy male Wistar rat; oral; Van Bladeren et ethyl)-L-cysteine urine al. (1981b) GS-CH2-CH2SG female white rat; oral; Nachtomi (1970) liver GSCH2CH2OH sulfoxide liver Nachtomi (1970) GSCH2CH2OH liver and kidney Nachtomi (1970) S-(2-hydroxyethyl) kidney Nachtomi (1970) mercapturic acid (b) In vitro Metabolite Tissue Reference GSCH2CH2SG rat liver and kidney extract Nachtomi (1970) GSCH2CH2OH rat liver and kidney extract Nachtomi (1970) Bromide (1984) rat liver cytosols White et al. Bromide (1983) mouse liver cytosols White et al. Inorganic bromide may be formed as a consequence of attack by GSH or oxidative catabolism. In the first case, the expected intermediate would be S-(2-bromoethyl)-GSH, which can be converted to bis-GSH or S-(2-hydroxyethyl)-GSH. Sulfoxidation of S-(2-hydroxyethyl)-GSH would yield S-(2-hydroxyethyl)-GSH- S-oxide or further metabolism would produce S-(2-hydroxyethyl)-cysteine, which in turn may undergo sulfoxidation to yield N-acetyl- S-(2-hydroxyethyl)-cysteine- S-oxide. The oxidative metabolism of 1,2-dibromoethane by cytochrome P-450-dependent mixed function oxidases would be expected to yield 2-bromoacetaldehyde as the initial product. This may be converted by dehydrogenase to 2-bromoacetic acid or undergo attack by GSH and subsequent dehydrogenase activity to give rise to S-carboxymethyl-GSH. S-carboxymethyl-cysteine may be further metabolized to thioglycolic acid. A reactive intermediate binds mainly to DNA guanyl remnants and may be responsible for the genotoxicity. White et al. (1983) reported a deuterium isotope effect on the metabolism of 1,2-dibromoethane. The metabolism of 1,2-dibromoethane and tetradeutero-1,2-dibromoethane (d4-1,2-dibromoethane) was compared in male Swiss-Webster mice. Three hours after intraperitoneal administration of 1,2-dibromoethane or d4-1,2-dibromoethane (50 mg/kg), there was 42% less bromide in the plasma of d4-1,2-dibromoethane-treated mice than in the plasma of 1,2-dibromoethane-treated mice. This difference demonstrated a significant deuterium isotope effect on the metabolism of 1,2-dibromoethane in vivo. In in vitro studies, which measured bromide ion released from the substrate to monitor the rate of metabolism, hepatic glutathione- S-transferase was unaffected. Since the decreased metabolism of d4-1,2-dibromoethane was apparently due to a reduced rate of microsomal oxidation, these data supported the hypothesis that conjugation with GSH is responsible for the genotoxic effect of 1,2-dibromoethane. White et al. (1984) studied metabolism in isolated rat hepatocytes. Cytosolic metabolism of 1,2-dibromoethane was not affected by deuterium substitution. Both compounds caused DNA single-strand breaks, as measured by the alkaline elution technique, when incubated at a concentration of 0.1 mM with hepatocytes. No difference in the degree of DNA damage was demonstrated between hepatocytes incubated with 1,2-dibromoethane and those incubated with d4-1,2-dibromoethane. 1,2-Dibromoethane can be metabolized by freshly isolated rat hepatocytes to S-(2-hydroxyethyl)glutathione, S-(carboxymethyl) glutathione and S,S'-(1,2-ethanediyl)bis(glutathione). These three metabolites account for 84% of the total intracellular glutathione depletion (Jean & Reed, 1992). These reactions were negligible in the presence of rat glutathione- S-transferase, but conjugation was catalysed by the rat alpha class enzyme 2-2 and, to a lesser extent, the rat µ class enzyme 3-3. Of the three classes of human cytosolic glutathione- S-transferases, 1,2-dibromoethane conjugation was catalysed by the alpha class enzymes (Cmarik et al., 1990). Human fetal liver appears to be especially active (several times higher specific activity of glutathione- S-transferase, compared to adult liver, as reported by Wiesma et al., 1986) in metabolizing 1,2-dibromoethane in vitro (Kulkarni et al., 1992). 1,2-Dibromoethane-induced lipid peroxidation and cytotoxicity were increased upon concomitant exposure to carbon tetrachloride. Similarly, the amount of 1,2-dibromoethane metabolites bound covalently to proteins was enhanced. The effect of carbon tetrachloride has been related to a shift in the 1,2-dibromoethane metabolism from GSH-dependent to P-450-dependent (Chiarpotto et al., 1993). Oral administration of large doses of 1,2-dibromoethane (37.6 mg/animal) to male Wistar rats (weighing around 200 g), following a single dose of disulfiram (12 mg/kg), led to decreased excretion of the mercapturic acid metabolite, a phenomenon associated with a decrease in cytochrome P-450 levels (van Bladeren et al., 1981a). In an additional reaction, 1,2-dibromoethane is debrominated by an oxidative process catalysed by an enzyme in hepatic microsomes. This system requires NADPH and oxygen and is inducible by phenobarbital but not by methyl-cholanthrene (Hill et al., 1978). Simula et al. (1993) reported an increased mutagenicity of 1,2-dibromoethane in the Salmonella typhimurium strain TA100 expressing human glutathione- S-transferase A1-1, indicating that human glutathione- S-transferases are able to metabolize 1,2-dibromoethane to reactive intermediates. In a study with isolated human hepatocytes (Cmarik et al., 1990), it was found that concurrent treatment with diethylmaleate reduced the intracellular glutathione level and inhibited 1,2-dibromoethane concentration-dependent unscheduled DNA synthesis. 6.4 Elimination and excretion in expired air, faeces and urine When 14C-1,2-dibromoethane (30 mg/kg body weight) was given intraperitoneally to male guinea-pigs of the Hartley strain, 66% of the radioactivity was excreted in the urine within 72 h of administration (Plotnick & Conner, 1976). Faecal excretion was relatively insignificant, representing less than 3% of the dose. The excretion of unchanged 1,2-dibromoethane in the expired air was significant (10-12% of dose). Plotnick et al. (1979) reported that urinary extraction of radioactivity from male rats of the Sprague-Dawley strain, 24 h after a single oral dose of 14C-1,2-dibromoethane (15 mg/kg), was 72.4%. Faecal radioactivity was 1.7%. Concomitant exposure to dietary disulfiram significantly depressed urinary excretion of 1,2-dibromoethane. 6.5 Retention and turnover Following intraperitoneal administration of [1,2-14C]- 1,2-dibromoethane (40 mg/kg) to RF/Hiraki mice, the circulating radiolabel was mainly accounted for by S-(2-hydroxyethyl) cysteine- N-acetate. Less than 1% of the dose was present in the blood as a volatile component (Edwards et al., 1970). Jakobson et al. (1982) reported that the elimination curve for 1,2-dibromoethane from blood after a 4-h dermal exposure of guinea-pigs was non-linear and corresponded to a kinetic model involving at least two compartments. 6.6 Reaction with body components Radioactivity from [1,2-14C]-1,2-dibromoethane is bound irreversibly to macromolecules in rat tissues after intraperitoneal injection. For protein, DNA, and RNA, the largest amounts of bound radioactivity were found to be present in the liver and kidney. Lung, testis, stomach and the large and small intestines showed less radioactivity (Hill et al., 1978). Ozawa & Guengerich (1983) reported the formation of an S-[2-(N7-guanyl)ethyl]glutathione adduct. 1,2-Dibromoethane and GSH were irreversibly bound to calf thymus DNA in equimolar amounts when in vitro incubation was carried out in the presence of glutathione- S-transferase. The labelled DNA was enzymatically digested to deoxyribonucleosides and separated by HPLC. The level of adducts in DNA isolated from human hepatocytes incubated with 0.5 mM 1,2-dibromoethane was about 40% of the value obtained for rat hepatocytes (Cmarik et al., 1990). S-[2-(N7-guanyl)ethyl]glutathione was the only major DNA adduct formed in vivo in rat (male Sprague-Dawley) liver (1.3 nmol/mg DNA) or kidney (0.95 nmol/mg DNA) 8 h after intraperitoneal administration of 37 mg 1,2-dibromoethane/kg body weight. The in vivo half-life of S-[2-(N7-guanyl)ethyl] glutathione in rat liver, kidney, stomach and lung was estimated to be between 70 and 100 h (Inskeep et al., 1986). Following intraperitoneal injection of 1,2-dibromoethane (37 mg/kg) in rats and mice of several strains, it was found that more of the S-[2-(N7-guanyl)ethyl]glutathione adduct of DNA was formed in the livers of rats than in those of mice (Kim & Guengerich, 1990). Incubation of 1,2-dibromoethane with calf thymus DNA and cytosol from rats or mice did not result in different adduct levels, whereas the level of adduct formation by human liver cytosol was about half of those values for rats or mice. Induction of glutathione- S-transferase in rat liver by phenobarbital or ß-naphthoflavone did not increase DNA adduct levels, whereas cytochrome P-450 inhibition by disulfiram did increase DNA adducts without altering the transferase activity. Depletion of reduced glutathione in vivo by diethylmaleate correlated with a reduction in DNA adduct levels. Bromine atoms generated upon reductive degradation of 1,2-dibromoethane have been shown to react with polyunsaturated fatty acids via both abstraction of bisallylic hydrogen and addition to the double bond. Bromine atoms may be a potential initiator for lipid peroxidation and provide a chemical basis for the toxic action of 1,2-dibromoethane (Guha et al., 1993). The cytotoxic action of 1,2-dibromoethane has been studied by Khan et al. (1993). They found that both cytochrome P-450- and GSH-dependent metabolism of 1,2-dibromoethane contributed to its cytotoxic effect in hepatocytes. Antioxidants or removal of oxygen delayed the cytotoxicity. Furthermore, cytotoxicity could be increased markedly if aldehyde dehydrogenase was inhibited with disulfiram. In addition, cytotoxicity could be reduced if the hepatocytes were depleted of GSH before the addition of 1,2-dibromoethane. 1,2-Dibromoethane has also been shown to cause cytotoxicity in rabbit pulmonary cells (Nichols et al., 1992), being cytotoxic to Clara cells, type II cells and alveolar macrophages. The irreversible binding of radioactivity from [1,2-14C]- 1,2-dibromoethane to protein, DNA and RNA in rats was measured 24 h after an intraperitoneal injection of 14C-1,2-dibromoethane (2.6-3.2 mg/kg) (Hill et al., 1978). For each of these classes of macromolecules, the largest amounts of bound radioactivity were found in the liver and kidneys. Botti et al. (1982) evaluated the effect of 1,2-dibromoethane on GSH levels and cytosolic glutathione- S-transferase activity following administration by gavage to male rats. Doses of either 75 or 150 mg/kg were found to decrease GSH and glutathione- S- transferase activities. Maximal effects were observed 2 h following exposure, although a significant decrease in GSH levels was observed within 15 min. Mann & Darby (1985) also noted GSH depletion in both male and female rats, the maximum effect occurring 2 h after an intraperitoneal 1,2-dibromoethane dose of 80 mg/kg. A greater effect was observed in males. Brandt et al. (1987) used autoradiography and 14C-labelled 1,2-dibromoethane to study the tissue distribution of 1,2-dibromoethane following an intraperitoneal injection to a cynomolgus monkey. 1,2-Dibromoethane was found to bind preferentially to the liver and renal tubules, particularly the adrenal zona reticularis. Kaphalia & Ansari (1992) measured the rate of incorporation of label into albumin and other large plasma proteins following exposure to [14C]-1,2-dibromoethane either in vivo or in vitro. About 37% of the total label, administered by gavage (25 mg/kg body weight in mineral oil over a 12-day period), was estimated to be bound to plasma proteins, the majority (72%) being bound to albumin. In the case of in vitro exposure, the incorporation of label to human albumin or plasma after incubation with radioactive 1,2-dibromoethane could be increased by the addition of either microsomal enzymes or an NADPH-generating system. 7. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS 7.1 Single exposure Toxic effects of 1,2-dibromoethane have been mainly observed in the liver and kidneys. Inhaled 1,2-dibromoethane vapour produces nasal irritation and depression of the central nervous system. In solution, 1,2-dibromoethane causes skin irritation on the shaved abdomen, and eye irritation. 7.1.1 Oral 184.108.40.206 Rat 1,2-Dibromoethane (99% pure) in olive or corn oil was given by gavage to albino rats, guinea-pigs, rabbits, mice and chickens. The difference in LD50 of 1,2-dibromoethane in male and female rats was statistically significant; rabbits appeared to be the most sensitive and mice the least sensitive (Rowe et al., 1952) (Table 13). Adult male albino rats (weight 140-160 g) were given 110 mg 1,2-dibromoethane/kg in olive oil by gavage and were killed 2, 4, 8, 12, 17 or 22 h later. During the first 4 h, no changes in the liver were detectable by light microscopy. From 8 h after administration, 1,2-dibromoethane induced sinusoidal dilatation and centrilobular necrosis in the liver (Broda et al., 1976). 220.127.116.11 Chicken Leghorn chickens of both sexes were given 1,2-dibromoethane (110 mg/kg body weight) in soybean oil by gavage. There was an increase in liver weight and NAD concentration, and a decrease in liver and blood alkaline phosphatase activity (Nachtomi et al., 1968). Five-week-old male Leghorn chicks (weight 580-620 g) were given 1,2-dibromoethane (110 mg/kg body weight) in olive oil by gavage and were killed 8, 12 or 22 h later. The central areas of the liver were not changed, but portal areas were affected by 1,2-dibromoethane. The concentration of eosinophilic granulocytes was much greater in 1,2-dibromoethane-treated livers than in controls (Broda et al., 1976). 7.1.2 Inhalation 18.104.22.168 Rat When rats were exposed to concentrations of 770, 1540, 3080, 6610, 12 300, 23 100, 38 500 or 77 000 mg/m3 (20 males and females per group in most concentrations, and no control group) for durations Table 13. Acute toxicity of 1,2-dibromoethane Species Route Vehicle Parameter Value Reference Rat (M) oral olive oil LD50 146 mg/kg Rowe et al. (1952) Rat (F) oral olive oil LD50 117 mg/kg Rowe et al. (1952) Rat (M,F) oral corn oil LD50 140 mg/kg McCollister et al. (1956) Mouse (F) oral olive oil LD50 420 mg/kg Rowe et al. (1952) Rabbit (F) oral olive oil LD50 55 mg/kg Rowe et al. (1952) Guinea-pig oral olive oil LD50 110 mg/kg Rowe et al. (1952) (M,F) Chicken (M,F) oral olive oil LD50 79 mg/kg Rowe et al. (1952) Rabbit skin LD50 450 mg/kg Rowe et al. (1952) Rat inhalation vapour by LC50 4620 mg/m3 Rowe et al. (1952) aeration 1 h Rat (M,F) inhalation vapour by LC50 2304 mg/m3 McCollister aeration 4 h et al. (1956) Mouse (ICR) intraperitoneal corn oil LD50 205 mg/kg Kluwe et al. (1981) ranging from 0.01 to 16.0 h (exposure time varied at different concentrations), slight anaesthetic actions and depression of the central nervous system were observed in rats exposed to 1540 mg/m3 or more. Deaths occurred within 24 h at concentrations between 1540 and 3080 mg/m3, related to exposure duration, due to respiratory or cardiac failure. The LC50 concentration for a 2-h exposure was 3080 mg/m3. Deaths occurring from exposures at lower concentrations were almost always delayed, sometimes as long as 12 days after exposure. The majority of these deaths were due to pneumonia. The animals usually lost weight, appeared rough and unkempt, became irritable, had a bloodstained nasal discharge, and died. Animals surviving the exposure at the lower concentrations exhibited a typical progression of symptoms for several days before recovery took place. Rats exposed to concentrations producing mortality, which were sacrificed and autopsied 16-24 h after exposure, showed an increased weight of lungs, liver and kidneys. The lungs showed congestion, oedema, haemorrhages and inflammation; the liver cells had cloudy swelling, centrilobular fatty degeneration and necrosis; the kidneys showed slight interstitial congestion and oedema, with slight cloudy swelling of the tubular epithelium in some cases (Rowe et al., 1952). 22.214.171.124 Guinea-pig All guinea-pigs (20 males and females per group) exposed to 1540 or 3080 mg/m3 (no control group) for 2 to 7 h died, whereas all those exposed to 770 mg/m3 for 7 h or 1540 mg/m3 for 2 h survived (Rowe et al., 1952). 7.1.3 Intraperitoneal injection 126.96.36.199 Mouse Intraperitoneal injection (46.8 and 93.7 mg/kg; 0.25 and 0.5 mmol/kg) of 1,2-dibromoethane (> 99.9%) in corn oil in male B6C3F1 mice (weight 20-26 g) produced hepatic damage. The mice were killed 4 h later and in vivo genotoxicity was determined by a sensitive in vivo/in vitro alkaline DNA unwinding assay for the presence of single-strand breaks and/or alkali-labile sites in hepatic DNA. Significant hepatic DNA damage was found with a dose of 0.5 mmol/kg. In an assessment of the acute hepatotoxicity and nephrotoxicity of 1,2-dibromoethane, male B6C3F1 mice were given intraperitoneal injections (93.7, 140, 187.7 or 281.6 mg/kg; 0.5, 0.75, 1.0 or 1.5 mmol/kg) of 1,2-dibromoethane in corn oil and sacrificed 24 h later. Serum L-iditol dehydrogenase (IDH), alanine aminotransferase (ATT), and blood urea nitrogen were determined. At a dose of 187.7 mg/kg 1,2-dibromoethane produced statistically significant increases in relative liver and kidney weights, serum IDH and ATT levels, and blood urea nitrogen levels. Four out of five animals given a dose of 281.6 mg/kg died (Storer & Conolly, 1983). 188.8.131.52 Rat Adult male Fischer-344 rats were given a single intraperitoneal injection of 99% 1,2-dibromoethane (50 mg/kg; 0.27 mmol/kg) in corn oil; they were sacrificed 2, 12, 24, 48 or 96 h later and the kidneys were removed. Histopathological alterations in the kidney were most prominent 48 h after 1,2-dibromoethane injection, and consisted of acute proximal tubular degeneration (proximal tubular swelling and vacuolation) (Kluwe et al., 1982). 7.2 Short-term exposure 7.2.1 Oral 184.108.40.206 Chicken In a study by Schlinke (1970), 1,2-dibromoethane (formulation which contains 83% of active ingredient) was administered orally at doses of 50, 100 or 200 mg/kg per day to groups of five unsexed SPF White Leghorn chickens (6-7 weeks old) for 10 days. There was an untreated control group. All five chickens given 200 mg/kg per day showed lack of appetite and depression, and died after the third dose. Chickens which died had inflamed crops, excess pericardial fluid, and congestion of the liver. Chickens given 50 or 100 mg/kg per day showed no toxic effects. 7.2.2 Inhalation 220.127.116.11 Mouse B6C3F1 mice (10 males and 10 females per group) were exposed by inhalation to 23.1, 115.5 and 577.5 mg/m3 (3, 15 and 75 ppm) of 1,2-dibromoethane (6 h/day, 5 days per week) for 13 weeks. Four male mice in the low dose group died before the end of the exposure period. At 13 weeks, mice showed severe necrosis and atrophy of the olfactory epithelium in the nasal cavity after inhaling the highest concentration. Lower concentrations induced squamous cell metaplasia, hyperplasia and cytomegaly of the epithelium of the respiratory nasal turbinals. Squamous metaplasia, hyperplasia and cytomegaly of the epithelium were also seen in larynx, trachea, bronchi and bronchioles. The NOEL, based on histopathological alterations in the nasal cavity, was 23.1 mg/m3 (3 ppm) (Reznik et al., 1980). 18.104.22.168 Rat A group of 10 female rats (strain unknown) exposed to a concentration of 768 mg/m3 (100 ppm) of 1,2-dibromoethane vapour for 7 h/day, lost weight steadily and three died after 1, 5 and 7 exposures, respectively. Surviving rats were thin and unkempt after 7 exposures in 9 days. At autopsy the stomachs were full of food, and the contents were bloodstained. Lung, liver and kidney weights were significantly elevated. Microscopic examination revealed some thickening of the alveolar walls, with slight leukocytic infiltration of the lungs, widespread cloudy swelling of the liver (but no fatty degeneration), and slight congestion and haemosiderosis of the spleen (Rowe et al., 1952). F-344 rats (five males and five females per group) were exposed by inhalation to 23.1, 115.5 and 577.5 mg/m3 (3, 15 and 75 ppm) of 1,2-dibromoethane (6 h/day, 5 days per week) for 13 weeks. At 13 weeks, they showed severe necrosis and atrophy of the olfactory epithelium in the nasal cavity after inhalation of 577.5 mg/m3. Lower concentrations induced squamous cell metaplasia, hyperplasia and cytomegaly of the epithelium of the respiratory nasal turbinals. Squamous metaplasia, hyperplasia and cytomegaly of the epithelium were also seen in the larynx, trachea, bronchi and bronchioles. Other compound-related toxic lesions in rats were seen in the liver, kidney and testes. At 115.5 mg/m3, 1,2-dibromoethane induced only minor changes in the nasal cavity. No lesions were seen in other tissues. The NOEL based on histopathological alterations in the nasal cavity was 23.1 mg/m3 (3 ppm) (Reznik et al., 1980). Nitschke et al. (1981) conducted a 13-week inhalation study on 1,2-dibromoethane in rats. Male and female F-344 rats were exposed to 0, 23, 77 or 307 mg/m3 (0, 3, 10 or 40 ppm) (6 h/day, 5 days per week) for 13 weeks. Those exposed to 307 mg/m3 (40 ppm) of 1,2-dibromoethane exhibited a decrease in body weight gain, an increase in liver and kidney weight, and hyperplasia and metaplasia of the respiratory epithelium of the nasal turbinates. A slight epithelial hyperplasia of the nasal tubinates was also noted at 77 mg/m3 (10 ppm). A recovery period of 88 days resulted in regression of the lesions in all but one animal. 22.214.171.124 Guinea-pig Guinea-pigs (8 of each sex per group) that were administered 385 mg/m3 (50 ppm) of 1,2-dibromoethane for up to 7 h, 57 times in 80 days, had decreased final body weight and increased lung, liver and kidney weights. Microscopic examination of the tissues showed slight central fatty degeneration in the liver, and slight interstitial congestion and oedema, with some parenchymatous degeneration of the tubular epithelium in the kidney. Blood urea nitrogen values were normal. In females, the total lipid content in the liver revealed no significant variation. Guinea-pigs (4-8 of each sex per group) tolerated without toxic effects 145 exposures (7 h each) in 205 days at a 1,2-dibromoethane concentration of 193 mg/m3 (25 ppm). However, four out of eight males and two out of eight females died of pulmonary infection during the experiment (Rowe et al., 1952). 126.96.36.199 Rabbit When four female rabbits were exposed by inhalation to 770 mg/m3 (7 h/day) for 4 days, two of the rabbits died after the second exposure. Microscopic examination of tissues revealed widespread central fatty degeneration of the liver with areas of necrosis. Rabbits given 59 exposures each lasting 7 h (385 mg/m3) in 84 days showed no evidence of adverse effects except for a slight increase in liver and kidney weights; those given 152 exposures (each 7 h) (192.5 mg/m3) in 214 days showed no adverse effects (Rowe et al., 1952). 188.8.131.52 Monkey When one male and one female monkey were given 7-h exposures (385 mg/m3) 49 times in 70 days, they appeared ill, nervous and unkempt throughout the experiment. Liver weights were increased with slight central fatty degeneration and increased total lipid values. No significant changes were observed in other organs except for a slight increase in kidney weight. Another pair (one male and one female) of monkeys received 7-h exposures (193 mg/m3) 156 times in 214 days. This group showed no evidence of adverse effects and the NOEL was established as 193 mg/m3 (25 ppm) (Rowe et al., 1952). 7.3 Eye and skin irritation 7.3.1 Rabbit 1,2-Dibromoethane (undiluted, 1% and 10% in propylene glycol, quantity not stated) was introduced into both eyes of a rabbit and after 30 seconds one eye was flushed for 3 min with copious amounts of running water. Conjunctival irritation occurred in both eyes, and there was slight superficial necrosis of the cornea. However, healing was prompt and complete 12 days after exposure; there was no corneal scarring and no apparent injury to the iris or the lens. A 1% 1,2-dibromoethane solution in propylene glycol elicited a response very similar to undiluted 1,2-dibromoethane (Rowe et al., 1952). A 1.0% solution of 1,2-dibromoethane in butyl carbitol acetate was applied 10 times in 14 days to the rabbit ear and also to the shaved abdomen where it was then protected by a bandage. On the ear, it caused slight irritation (erythema and exfoliation), whereas on the shaved abdomen there was marked irritation with erythema and oedema progressing to necrosis and sloughing of the superficial layers of the skin. Healing was complete without scarring within 7 days after termination of exposure (Rowe et al., 1952). 7.4 Long-term exposure Designs of long-term/carcinogenicity studies are given in Table 14 and tumorigenic effects seen in these studies are summarized in Table 15. 7.4.1 Oral 184.108.40.206 Mouse Groups of 50 male and 50 female B6C3F1 mice (5 weeks old) were given technical-grade 1,2-dibromoethane (99.6% pure) in corn oil by gavage on 5 consecutive days per week. The time-weighted average high and low doses of 1,2-dibromoethane were 107 and 62 mg/kg per day for Table 14. Carcinogenicity studies on 1,2-dibromoethane Route Species Number of animals Sexa Dose and dosing scheduleb Durationc Reference (strain) per group Gavage Mouse 50 M 62 mg/kg body weight TWAd 78 weeks(53) NCI (1978) (B6C3F1) (treated) 107 mg/kg body weight TWAd 77 weeks(53) F 62 mg/kg body weight TWAd 90 weeks(53) 107 mg/kg body weight TWAd 78 weeks(53) 20 M,F (control)e Rat 50 M 38 mg/kg body weight TWAd 49 weeks(47) NCI (1978) (Osborn- (treated) 41 mg/kg body weight TWAd 49 weeks(34) Mendel) F 37 mg/kg body weight TWAd 61 weeks(57) 39 mg/kg body weight TWAd 61 weeks(44) 20 M,F (control)e Drinking-water Mouse 30 M 117 mg/kg body weight per day 15 months Van Duuren et (B6C3F1) (treated) F 103 mg/kg body weight per day 17 months al. (1985) 50 M,F (control) Inhalation Mouse 60 F 154 mg/m3 6 h/day, 5 days/week 6 months Adkins et al. (A/J) (treated) 384 mg/m3 6 h/day, 5 days/week 6 months (1986) 60 F 154 mg/m3 6 h/day, 5 days/week 6 months (control)e 384 mg/m3 6 h/day, 5 days/week 6 months 90 F (treatead) 60 (control) Table 14 (cont'd) Route Species Number of animals Sexa Dose and dosing scheduleb Durationc Reference (strain) per group Mouse 50 M 77 mg/m3 6 h/day, 5 days/week 78 weeks NTP (1982) (B6C3F1) (treated) 307 mg/m3 6 h/day, 5 days/week 78 weeks 50 F 77 mg/m3 6 h/day, 5 days/week 103 weeks (treated) 307 mg/m3 6 h/day, 5 days/week 90 weeks 50 M,F (control) Mouse 50 M 77 mg/m3 6 h/day, 5 days/week 103 weeks Stinson et (B6C3F1) (treated) 307 mg/m3 6 h/day, 5 days/week 90 weeks al. (1981) 50 F 77 mg/m3 6 h/day, 5 days/week 103 weeks (treated) 307 mg/m3 6 h/day, 5 days/week 90 weeks 50 M,F 104 weeks (control) Rat 50 M 77 mg/m3 6 h/day, 5 days/week 103 weeks NTP (1982) (Fisher-344) (treated) 307 mg/m3 6 h/day, 5 days/week 88 weeks 50 F 77 mg/m3 6 h/day, 5 days/week 103 weeks (treated) 307 mg/m3 6 h/day, 5 days/week 90 weeks 50 M,F (control) Rat 48 M,F disulfiramf (0.05% in diet) 18 months Wong et (Sprague- (treated) ± EDB (119-167 mg/m3 TWAb) al. (1982) Dawley) 7 h/day, 5 days/week 48 M,F (control) Table 14 (cont'd) Route Species Number of animals Sexa Dose and dosing scheduleb Durationc Reference (strain) per group Dermal Mouse 30 F 25 mg/mouse, 3 times/week 400-594 days Van Duuren et (Ha:ICR (treated) 50 mg/mouse, 3 times/week al. (1979) Swiss) 100 F (control)g a M = male, F = female b TWA = time-weighted average c observation period: treated and untreated weeks (exposed weeks) d doses changed in the course of the experiment with intermitting untreated weeks e the controls consisted of vehicle (corn oil) & untreated controls f This combination was chosen to examine effects of disulfiram used for alcoholism control programmes on workers who were exposed to 1,2-dibromoethane occupationally. g controls consisted of vehicle (acetone) & untreated controls Table 15. Summaries of results of carcinogenicity studies on 1,2-dibromoethane Study Route Animal Statistically significant effects dose (numbers of animals with effects/total numbers of animals) NCI (1978) gavage mouse squamous cell carcinoma of the forestomach control (M: 0/20, F: 0/20), 62 mg/kg (M: 45/50, F: 46/49) 107 mg/kg (M: 29/49, F: 28/50) alveolar/bronchiolar adenoma control (M: 0/20, F: 0/20), 62 mg/kg (M: 4/45, F: 11/43) 107 mg/kg (M: 10/47, F: 6/46) rat squamous cell carcinoma of the forestomach control (M: 0/20, F: 0/20), 38 mg/kg (M: 45/50), 37 mg/kg (F: 40/50) 41 mg/kg (M: 33/50), 39 mg/kg (F: 29/50) hepatocellular carcinoma control (M: 0/20, F: 0/20), 39 mg/kg (F: 6/48) haemangiosarcoma control (M: 0/20, F: 0/20), 38 mg/kg (M: 11/50), 41 mg/kg (M: 4/50) Van Duuren et al. (1985) drinking- mouse squamous cell carcinoma water 117 mg/kg (M: 26/30), 103 mg/kg (F: 22/30) oesophageal papilloma 103 mg/kg (F: 3/30) squamous cell papillomaa 115 mg/kg (M: 9/30, F: 10/30) Adkins et al. (1986) inhalation mouse (A/J) i) pulmonary adenoma (all females) control (F: 0/60), 154 mg/m3 (F: 60/60), 384 mg/m3 (F: 60/60) ii) pulmonary adenoma control (F: 0/60), 154 mg/m3 (F: 75/90), 384 mg/m3 (F: 90/90) Table 15 (cont'd) Study Route Animal Statistically significant effects dose (numbers of animals with effects/total numbers of animals) NTP (1982) inhalation mouse alveolar/bronchiolar carcinoma control (M: 0/41, F: 1/49), 77 mg/m3 (M: 3/48, F: 5/49), 307 mg/m3 (M: 19/46, F: 37/50) alveolar/bronchiolar adenoma control (M: 0/41, F: 3/49), 77 mg/m3 (F: 7/49), 307 mg/m3 (M: 11/46, F:13/50) haemangiosarcoma of the circulatory system control (F: 0/50), 77 mg/m3 (F: 11/50), 307 mg/m3 (F: 23/50) subcutaneous fibrosarcoma control (F: 0/50), 77 mg/m3 (F: 5/50), 307 mg/m3 (F: 11/50) nasal cavity carcinoma, or adenoma control (F: 0/50), 307 mg/m3 (F: 6/50, 8/50) mammary gland adenocarcinoma control (F: 2/50), 77 mg/m3 (F: 14/50), 307 mg/m3 (F: 8/50) inhalation rat nasal cavity carcinoma, adenocarcinoma, adenoma control (M: 0/50, F: 0/50), 77 mg/m3 (M: 1/50, 20/50, 11/50, F: 0/50, 20/50, 11/50), 307 mg/m3 (M: 21/50, 0/50, 28/50, F: 25/50, 29/50, 3/50) haemangiosarcoma of the circulatory system control (M: 0/50, F: 0/50), 307 mg/m3 (M: 15/50, F: 5/50) tunica vaginalis mesothelioma control (M: 0/50), 77 mg/m3 (M: 7/50), 307 mg/m3 (M: 25/50) alveolar/bronchiolar adenoma, carcinoma (combined) control (F: 0/50), 307 mg/m3 (F: 5/47) nasal cavity adenomatous polyps control (M: 0/50), 77 mg/m3 (M: 18/50), 307 mg/m3 (M: 5/50) mammary gland fibroadenoma control (F: 4/50), 77 mg/m3 (F: 29/50), 307 mg/m3 (F: 24/50) Table 15 (cont'd) Study Route Animal Statistically significant effects dose (numbers of animals with effects/total numbers of animals) Stinson et al. (1981) inhalation mouse nasal cavity carcinoma (squamous carcinoma, adenocarcinoma) control (M: 0/45, F: 0/50), 77 mg/m3 (M: 0/44, F: 0/49) 307 mg/m3 (M: 0/46, F: 7/49) sarcoma control (M: 0/45, F: 0/50), 77 mg/m3 (M: 0/44, F: 1/49) 307 mg/m3 (M: 0/46, F: 2/49) benign neoplasms (squamous papilloma, adenoma) control (M: 0/45, F: 0/50), 77 mg/m3 (M: 0/44, F: 0/49) 307 mg/m3 (M: 3/46, F: 7/49) Wong et al. (1982) inhalation rat hepatocellular tumour control (M: 0/48, F: 0/48), EDB (M: 3/46, F: 1/48) EDB+DSb (M: 36/48, F: 32/48) kidney (adenoma and adenocarcinoma) control (M: 0/48, F: 0/48), EDB (M: 3/46, F: 1/48) EDB+DSb (M: 17/48, F: 7/48) Van Duuren et al. (1979) skin mouse lung tumours control untreated (F: 30/100) control acetone (F: 11/100) 25 mg/mouse (F: 24/30), 50 mg/mouse (F: 26/30) skin carcinoma control untreated (F: 0/100) control acetone (F: 0/100) 25 mg/mouse (F: 2/30), 50 mg/mouse (F: 8/30) a carcinogenicity study on bromoethanol b DS: disulfirum given in diet both sexes. All surviving male mice and high-dose female mice were killed on week 78, and low-dose females were killed on week 90. In low-dose females, body weight depression was apparent after the first 10 weeks. Soft faeces, alopecia and body sores were observed in all surviving animals at week 14. In mice receiving the high dose, acanthosis of the forestomach was observed in 5/49 males and 9/50 females, compared with 1/50 in low-dose females. Hyperkeratosis occurred in the stomachs of 13/49 high-dose males, 12/50 high-dose females, and 1/48 low-dose females. There was testicular atrophy (10/47) related to compound administration in males receiving the high dose (NCI, 1978). 220.127.116.11 Rat Groups (50 of each sex per group) of Osborne-Mendel rats (8 weeks old) were administered technical-grade 1,2-dibromoethane in corn oil by gavage on five consecutive days per week. The time-weighted average high and low doses of 1,2-dibromoethane in treated groups were 41 and 38 mg/kg per day for male rats, and 39 and 37 mg/kg per day for females. Body weight depression was apparent in the treated rats after the first 10 weeks. Reddened ears, a hunched appearance, firm distended abdomens and abdominal urine stains were observed in treated groups. There was high mortality in both the high- and low-dose groups. All surviving treated male (24 out of 100) and female (3 out of 100) rats were sacrificed on weeks 49 and 61, respectively. In rats given the high dose, hyperkeratosis and acanthosis of the forestomach were observed in 12/50 males and 18/50 females, and in low-dose females the value was 4/50. In the treated rats, degenerative changes in the liver and adrenal gland and early development of testicular atrophy were reported (NCI, 1978). However, total development of testicular atrophy in controls, low-dose group and high-dose group were 11/20, 14/49 and 18/5, respectively. 7.4.2 Inhalation 18.104.22.168 Mouse In an NTP carcinogenicity study (NTP, 1982), groups of 50 male and 50 female B6C3F1 mice were exposed to 1,2-dibromoethane (> 99% pure) concentrations of 0, 77 or 308 mg/m3 (0, 10, or 40 ppm) for 6 h/day, 5 days per week, for 78 to 103 weeks, throughout the study. Mean body weights of high-dose male and female mice were lower than those of the untreated controls. Survival of high-dose female mice was significantly reduced compared with controls. Survival was also reduced in both control and treated male mice, the principal cause of death being an ascending suppurative urinary tract infection unrelated to compound administration. Surviving male mice were killed at 79 weeks, while female mice were killed at 104-106 weeks, except for the high-dose group (killed at 91 weeks). The NTP also reported inflammation of the nasal cavity and epithelial hyperplasia of the respiratory system in both sexes (NTP, 1982). Stinson et al. (1981) reported similar findings in mice using data from a 2-year study. Epithelial hyperplasia of the urinary bladder and inflammation of the prostate gland were also observed in dosed male mice. 22.214.171.124 Rat Groups of 50 male and 50 female inbred Fischer-344 rats were exposed to 1,2-dibromoethane (> 99% pure) concentrations of 0, 77 or 308 mg/m3 (0, 10 or 40 ppm) for 6 h/day, 5 days per week, for 78 to 103 weeks, throughout the study. Mean body weights of high-dose rats were lower than those of untreated controls. Survival of high-dose male and female rats was significantly reduced compared with the controls. Surviving female and male rats were killed at 104-106 weeks, except for the male high-dose group (5 out of 50 alive, killed at 89 weeks) and female high-dose group (8 out of 50 alive, killed at 91 weeks). Among the observed compound-related non-neoplastic lesions were hepatic necrosis and toxic nephropathy in both sexes, testicular degeneration and atrophy in males, and retinal degeneration in females (NTP, 1982). Four groups of 48 male and 48 female Sprague-Dawley rats were exposed to either control air, 154 mg 1,2-dibromoethane/m3, 0.05% disulfiram in the diet, or 20 mg 1,2-dibromoethane/kg and 0.05% disulfiram in the diet for 18 months. Disulfiram which is used in alcohol control programmes is known to inhibit acetaldehyde dehydrogenase. It may therefore alter the biotransformation of 1,2-dibromoethane and cause the accumulation of 2-bromoacetaldehyde, one of the possible toxic metabolites of 1,2-dibromoethane. The average starting weights ranged from 131 to 134 g for male rats and 118 and 124 g for females. Between inhalation exposures (7 h/day, 5 days/week), rats were permitted free access to water and food. Rats receiving 0.05% disulfiram showed reduced body weight gain compared with control rats or those given 20 mg 1,2-dibromoethane/kg or the control diet. Rats exposed to 154 mg/m3 of 1,2-dibromoethane alone and those receiving a combination of 20 mg 1,2-dibromoethane/kg and 0.05% disulfiram had high mortality compared with control and disulfiram-treated rats. In rats exposed by inhalation to 154 mg 1,2-dibromoethane/m3 alone, mortality was 90% in males and 77% in females at 18 months. Haematological parameters were within the normal range for moribund rats in this group. Male rats receiving 20 mg 1,2-dibromoethane/kg with 0.05% disulfiram had a high incidence of testicular atrophy and there was atrophy of the spleen in 30/48 males and 19/48 females (Wong et al., 1982). 7.5 Developmental toxicity 1,2-Dibromoethane causes testicular effects and mating failure in rats at high inhalation levels that result in mortality. It also causes temporary malformation of sperm cells in bulls and rams, but not in chickens. In laying hens, it causes decreased egg size. In rats and mice there is no evidence of embryotoxicity and teratogenicity. In rats, paternal exposure causes behavioural changes in F1 progeny. 7.5.1 Reproduction Male Sprague-Dawley rats (3-4 per group) were exposed by inhalation to average daily concentrations of 146, 300 or 684 mg/m3 (19, 39 or 89 ppm) of 1,2-dibromoethane for 7 h/day, 5 days/week, for 10 weeks. There was reduced weight gain in the 300 and 684 mg/m3 groups with mortality (21%) and morbidity in the 684 mg/m3 group. Animals in this group had reduced testicular weights, reduced serum testosterone levels, and atrophy of the testes (10/10), epididymis (10/10), prostate (10/10), and seminal vesicles (9/9). When mated with untreated females none of the males exposed to 684 mg/m3 impregnated any females, while 90% of those exposed to the low and intermediate concentrations impregnated females who produced litters that were normal in terms of total implants, viable implants and resorptions. In female Sprague-Dawley rats, inhaling average daily concentrations of 154, 300 or 614 mg/m3 (20, 39 or 80 ppm) of 1,2-dibromoethane for 7 h/day, 7 days/week, for 3 weeks, there was reduced weight gain, morbidity and mortality (20%) in the 614 mg/m3 group. At the end of the 3-week exposure, females were mated with untreated males. Females in the 614 mg/m3 group were in diestrus and did not cycle normally until 3-4 days later; consequently fewer females mated during a 10-day mating period than in the case of the other two groups. The vaginal smears from females exposed to 154 or 300 mg/m3 were normal. In all three groups the reproductive performance (total implants/dam, viable implants/dam and resorptions/ dam) was unimpaired. Histopathological examination of the ovaries and uterus did not reveal any significant lesions (Short et al., 1979). It was considered that the NOEL for reproductive performance was 300 mg/m3 for male and female rats. Weanling male albino rats (10 rats per group) were fed 1,2-dibromoethane in the diet at levels of 100 or 500 mg/kg (equivalent to 10 or 50 mg/kg body weight per day) for 90 days. There was no evidence of toxicity; serum enzyme activities were unchanged. Five rats from each group were mated with untreated virgin females. There was no impairment of reproductive performance in the male rats. At the end of the 2-week mating period the males were sacrificed. Histology of the testis was normal. The pregnant females were allowed to go to term, and the mean number of litters per group, mean pup weight at birth, and sex ratio were found to be similar to the values for a control group mated with untreated males (Shivanandappa et al., 1987). The NOEL for male rat reproductive performance was considered to be 50 mg/kg body weight per day. In a study of sperm quality and fertility, mature (12 months old) male New Zealand White rabbits (8-10 group) were injected subcutaneously with 1,2-dibromoethane in corn oil at dose levels of 15, 30 or 45 mg/kg body weight per day for 5 days. There were also untreated and vehicle control groups. Male fertility was assessed before exposure, and at 4 and 12 weeks after injection, by artificial insemination of three females/male per time point with one million motile sperm. The percentage of pregnant females, litter size, fetal body weights and structural development were assessed. In the highest dose group there was 30% mortality and liver damage in 43% of the survivors, indicated by increased levels of serum enzymes. There were also changes in some sperm parameters (see 126.96.36.199). The percentage of pregnant females and mean litter sizes were similar to those produced by sperm from vehicle control animals, demonstrating that fertilizing capacity and gestational outcome were unaffected (Williams et al., 1991). 188.8.131.52 Effects on sperm Four bull calves of the Israel-Friesian breed were administered 1,2-dibromoethane orally at a dose of 2 mg/kg body weight from the age of 4 days by adding 1,2-dibromoethane to milk or feed concentrates. When the calves reached an age of about 12 months, 1,2-dibromoethane was administered in gelatin capsules. The treatment did not affect the growth or health of the treated animals, and their libido was similar to that of untreated animals. However, sperm density in treated bulls was low, and sperm motility was poor. Semen showed abnormally shaped spermatozoa (tailless, coiled tail, pyriform head). Recovery after discontinuation of treatment varied from 10 days to about 3 months in different animals. In a further study, 1,2-dibromoethane (4 mg/kg body weight) was administered orally to a previously untreated bull. Two weeks after the start of the treatment the semen exhibited abnormalities (Amir & Volcani, 1965). Other studies also showed that 1,2-dibromoethane caused reversible abnormalities of sperm cells in bulls (Amir, 1973, 1975; Amir et al., 1979; Courtens et al., 1980) and in rams (ElJack & Hrudka, 1979), but not in chickens (Alumot et al., 1968). In a study by Williams et al. (1991), male New Zealand White rabbits (8-10/group) were injected subcutaneously with 1,2-dibromoethane in corn oil (0, 15, 30 or 45 mg/kg body weight for 5 days). Weekly semen samples (for 6 weeks before exposure, during treatment and 12 weeks after dosing) were analysed for sperm concentration, number, morphology, viability and motion parameters (velocity, linearity, beat cross-frequency, amplitude of lateral head displacement (ALH) and circularity), and for semen pH, osmolality, volume, and levels of fructose, citric acid, carnitine, protein and acid phosphatase (AP). In the 45-mg/kg dose group, 1,2-dibromoethane produced significant decreases in sperm velocity, percentage motility and ALH (up to 25% at various times after dosing). There were also dose-related decreases in semen pH (up to 2%) and total ejaculate volume (up to 23%, 15 and 30 mg/kg groups only). Acid phosphatase activities were significantly elevated (up to 116%) 2 weeks after dosing in the 45 mg/kg dose group. All other semen parameters evaluated were unaffected. Rabbits appear less sensitive than humans to the reproductive effects of 1,2-dibromoethane, since semen parameters were affected only at doses close to the LD50 and some parameters (sperm numbers, viability and morphology) were unaffected. A NOEL was not obtained in this study. 184.108.40.206 Effects on ova Feeding studies with laying hens showed that 1,2-dibromoethane absorbed by grain adversely affected egg production. When hens were fed grain containing 200 mg/kg (corresponding to 25 mg/kg per day) for 56 days or grain containing 300 mg/kg (corresponding to 38 mg/kg per day) for 46 days, the hens ceased laying completely. Feeding of grain containing 10 mg/kg (corresponding to 12.5 mg/kg per day) caused a diminution of egg size after 12 weeks (Bondi et al., 1955). 7.5.2 Teratogenicity Pregnant Sprague-Dawley rats and CD-1 mice inhaled 1,2-dibromoethane concentrations of 146, 292 or 614 mg/m3 (20, 38 or 80 ppm) (23 h/day for 10 days) from day 6 to day 15 of gestation. Adverse effects on maternal animals, measured by body weight gain and food consumption, were observed in both species at all doses tested. A marked increase in maternal mortality occurred in rats exposed to 614 mg/m3 and in mice exposed to 292 or 614 mg/m3. Some morphological changes, such as haematomas, exencephaly and skeletal variations, were observed in the fetuses of rats and mice. However, these changes occurred only at high concentrations that caused maternal toxicity (Short et al., 1978). The embryotoxic effects of 1,2-dibromoethane bioactivation, mediated by purified rat liver glutathione- S-transferases (GST), were investigated using rat embryos in culture (Mitra et al., 1992). Significant 1,2-dibromoethane metabolism was observed with rat liver GST purified by affinity chromatography. 1,2-Dibromoethane activation caused a significant reduction in general development as measured by crown-rump length, yolk sac diameter, somite number, and the composite score for different morphological parameters. Structures most significantly affected were the central nervous and olfactory systems as well as the yolk sac circulation and allantois. The results of this study clearly indicate that under in vitro conditions, bioactivation of 1,2-dibromoethane by GST can lead to embryotoxicity. GST isozymes from human fetal liver were purified and used to investigate the toxicity of 1,2-dibromoethane in an in vitro model of rat embryos in culture as passive targets (Mitra et al., 1992). 1,2-Dibromoethane bioactivation by the GST isozyme P-3 resulted in toxicity to cultured rat embryos. Significant reductions in crown rump length, yolk sac diameter, and the composite score of morphological parameters were observed. The central nervous, optic and olfactory systems, and the hind limb were most significantly affected. When pregnant Sprague-Dawley rats were injected intraperitoneally with 1,2-dibromoethane at a dose of 50 mg/kg body weight from day 1 to day 15 of gestation, there was no evidence of embryotoxicity or teratogenicity, although there were maternal toxic effects (change in organ weights) (Hardin et al., 1981). 220.127.116.11 Effects on neonatal behaviour Pregnant Long-Evans rats (16 animals/group, litter size 8-10) were exposed to 3.3, 51.2 or 512 mg/m3 by inhalation (4 h/day, 3 days/week) from day 3 to day 20 of gestation. The highest concentration produced enhanced rotorod performance and T-maze brightness discrimination acquisition in the offspring. Similar behavioural changes were noted in the offspring of mothers exposed to 51.2 mg/m3, but the magnitude of the effect was reduced. Exposure to 3.3 mg/m3 produced no effects. DRL-20 acquisition (differential reinforcement of low rates), straight alley running speed, and passive avoidance were not affected at any dose level (Smith & Goldman, 1983). In a study by Fanini et al. (1984), adult male Fischer-344 rats were injected intraperitoneally with 1,2-dibromoethane at daily doses of 0, 1.25, 2.5, 5 or 10 mg/kg body weight for 5 days. The treated males were then mated with untreated female rats 4 or 9 weeks after treatment. A total of 19 litters composed of 172 animals, 84 males and 88 females were obtained from breeding the exposed males with untreated females. Behavioural assessments of all F1 progeny were carried out up to 21 days of age. Assessment of behavioural development was made by means of an extensive testing battery. Pre-weaning behavioural assessment included simple reflexes (surface righting, cliff avoidance and negative geotaxis), motor coordination (e.g., swimming and open field activity) and locomotor activity. Significant impairment in the development of motor coordination and motor activity was observed in the F1 progeny of males of all treated groups. A NOEL was not found in this study. The effects of 1,2-dibromoethane exposure on several neurotransmitter enzymes in male rats were examined in various brain regions of the F1 progeny (from 7 to 90 days of age) (Hsu et al., 1985). Significant increase of choline acetyltransferase in the cerebellum, corpus striatum, hippocampus and hypothalamus, alterations of acetylcholinesterase in various brain regions, and an increase of glutamic acid decarboxylase activity in the corpus striatum may be related to early-development behavioural abnormalities. 7.6 Mutagenicity and related end-points Mutagenicity assays are summarized in Table 16. Table 16. Mutagenicity studies on 1,2-dibromoethane Test method Species (route Strain/cell type Resultsb Reference of administration)a In vitro Gene mutation Salmonella E503 - Alper & Ames (1975) typhimurium G46(-S9) + Ames & Yanofsky (1971); Von Buselmaier et al. (1972) TA1530(-S9) + Ames & Yanofsky (1971); Brem et al. (1974); Rosenkranz (1977); Buijs et al. (1984) TA1535(+/-S9) +l Brem et al. (1974); McCann et al. (1975); Rannug & Beije (1979); Shiau et al. (1980); Barber et al. (1981); Principe et al. (1981); Moriya et al. (1983); Buijs et al. (1984); Dunkel et al. (1985); Tennant et al. (1986, 1987); Zoetemelk et al. (1987); Barber & Donish (1982) TA98(+/-S9) +l Barber et al. (1981); Moriya et al. (1983);Dunkel et al. (1985); Tennant et al. (1986) TA100(+/-S9) +l McCann et al. (1975); Barber et al. (1981); Stolzenberg & Hine (1980); van Bladeren et al. (1980, 1981b); Principe et al. (1981); Moriya et al. (1983); Buijs et al. (1984); Dunkel et al. (1985); Kerklaan et al. (1985); Guobaitis et al. (1986); Tennant et al. (1986); Hughes et al. (1987); Zoetemelk et al. (1987); Barber & Donish (1982) TA1535(GSH-) + Kerklann et al. (1983) (-S9,+ GSH) Zoetemelk et al. (1987) TA100(GSH-) + Kerklaan et al. (1985) (-S9,+GSH) Zoetemelk et al. (1987) TA100W(Str',8AGr')(-S9) +g Ong et al. (1989) TA1535 (bile of rats) + Rannug & Beije (1979) TA1537(+/-S9) - Principe et al. (1981); Moriya et al. (1983); Dunkel et al. (1985); Tennant et al. (1986) TA1538(+/-S9) - Brem et al. (1974); Principe et al. (1981); Moriya et al. (1983); Dunkel et al. (1985) TA98 (+/-S9) - Principe et al. (1981); Wildeman & Nazar (1982) TA100(+/-S9) - Shiau et al. (1980); Wildeman & Nazar (1982) Table 16 (cont'd) Test method Species (route Strain/cell type Resultsb Reference of administration)a Serratia a21 (-S9) - Von Buselmaier et al. (1972) marcescens Escherichia coli WP2 (+/-S9) + Scott et al. (1978); Hemminki et al. (1980); Moriya et al. (1983); Dunkel et al. (1985) CHY832 (-S9) + Hayes et al. (1984) 343/286 (+/-S9) + Mohn et al. (1984) KI201, KI211 (-S9) + Izutani et al. (1980) uvrB5 + Foster et al. (1988) 343/113 (-S9) - Mohn et al. (1984) Bacillus subtilis TKJ5211, TKJ6321 (+S9) + Shiau et al. (1980) Streptomyces (-S9, spot test) + Principe et al. (1981) coelicolor (-S9, plate method) - Principe et al. (1981) Aspergillus methG1BiA1 + Scott et al. (1978) nidulans (+/-plant extract) haploid strain 35 (-S9) + Principe et al. (1981) Neurospora crassa ad-3 (forward mutation) + de Serres & Malling (1983) Tradescantia clone 02, 0106, 4430 +g Sparrow et al. (1974); Nauman et al. (1976); Vant'Hof & Schairer (1982) Mouse L5178Y (+/-S9) + Clive et al. (1979); Tennant et al. (1986, 1987) Chinese hamster CHO-K1 (+/-S9) + Tan & Hsie (1981); Brimer et al. (1982) Human cell line AHH-1, TK6 + Crespi et al. (1985) (-S9) Human cell line EUE (-S9) + Ferreri et al. (1983) Table 16 (cont'd) Test method Species (route Strain/cell type Resultsb Reference of administration)a Unscheduled Rat hepatocytes + Williams et al. (1982); Tennant et al. (1986) DNA synthesis Opossum lymphocytes + Meneghini (1974) Human lymphocytes (+/-S9) + Perocco & Prodi (1981) Mouse (C3Hfx101)F1, + Sega & Rene (1980) germ cells Sister-chromatid Fish lymphocytes (- S9) + Ellingham et al. (1986) exchange Chinese hamster V79 cl-15 (-S9) + Tezuka et al. (1980) Chinese hamster CHO (+/-S9) + Tennant et al. (1987) Human lymphocytes (-S9) +g Ong et al. (1989); Tucker et al. (1984) Chromosome Fish lymphocytes (- S9) + Ellingham et al. (1986) aberrations Chinese hamster V79 cl-15 (-S9) + Tezuka et al. (1980) CHO (+/-S9) + Tennant et al. (1987) Micronuclei Tradescantia clone 03, 4430 +l Ma et al. (1978, 1984) DNA damage E. coli polA1-/polA+ (-S9) +w Brem et al. (1974) B. subtilis TKJ5211, TKJ6321 - Shiau et al. (1980) (+/-S9) SOS induction S. typhimurium TA1535/pSK1002 +g Ong et al. (1987) (+/-S9) E. coli PQ37 (-S9) + Ohta et al. (1984); Quillardet et al. (1985) Mitotic gene Saccharomyces ade2, trp5 + Fahrig (1974) conversion cerevisiae Somatic A. nidulans diploid 35 x 17 (-S9) +g Crebelli et al. (1984) segregation Table 16 (cont'd) Test method Species (route Strain/cell type Resultsb Reference of administration)a DNA binding E. coli Q13 (+/-S9) - Kubinski et al. (1981) Mouse Ehrlich ascites (+/-S9) - Kubinski et al. (1981) Cell Human lymphocyte + Channarayappa et al. (1992) proliferation DNA strand Rat hepatocytes + Sina et al. (1983) breaks Cell Mouse Balb/c 3T3 (-S9) - Tennant et al. (1986); Perocco et al. (1991) transformation In vivo Gene mutation S. typhimurium G46 (host-mediated) + Von Buselmaier et al. (1972) Serratia a21 (host-mediated) - Von Buselmaier et al. (1972) marcescens Barley + Ehrenberg et al. (1974) Silkworm (egg color mutation) - Sugiyama (1980) Drosophila (wing spot) +g Graf et al. (1984) melanogaster Recombination D. melanogaster (wing spot) +g Graf et al. (1984) Sex-linked D. melanogaster +l Kale & Baum (1979a,b, 1981, 1982, 1983); Yoshida & Inagaki recessive lethal (1986); Vogel & Chandler (1974) mutations D.melanogaster spermatozoa + Ballering et al. (1993) Table 16 (cont'd) Test method Species (route Strain/cell type Resultsb Reference of administration)a Specific Mouse - Russell (1986) locus test Mouse DBA/2J - Barnett et al. (1992) Chromosome Barley root tips + Ehrenberg et al. (1974) aberration Mouse (ip) CD1, (bone marrow) - Krishna et al. (1985) Sister-chromatid Mouse (ip) CD1, bone marrow - Krishna et al. (1985) exchange Dominant lethal Rat (ih, po) CD, SD - Short et al. (1979); Teramoto et al. (1980) Mouse (po) BDF1 - Teramoto et al. (1980) Mouse (ip, po) ICR/Ha - Epstein et al. (1972) Mouse DBA/2J - Barnett et al. (1992) DNA strand Rat (po) hepatocytes + Nachtomi & Sarma (1977) breaks Mouse (ip) hepatocytes + Storer & Conolly (1983) breaks Mouse (ip) hepatocytes + White (1982) Micronuclei Amphibians: erythrocytes Fernandez et al. (1993) Pleurodeles waltl + (newt) Ambystoma + mexicanum (axolotl) Anuran: Xenopus + laevis (toad) Mouse ddY(peripheral blood - Asita et al. (1992) reticulocytes) Mouse(ip) CD1, bone marrow - Krishna et al. (1985) Tradescantia tetrads of + Ma et al. (1978) microsporogenesis Table 16 (cont'd) Test method Species (route Strain/cell type Resultsb Reference of administration)a Sperm Bull Friesian + Amir et al. (1977) abnormality a ip = intraperitoneal administration; ih = inhalation exposure; iv = intravenous administration; po = oral administration b g = test in gaseous phase; l = test in liquid or gaseous phase; w = weak positive results 7.6.1 In vitro assays 1,2-Dibromoethane was mutagenic in reverse mutation assays (Ames test) using Salmonella typhimurium strains G46, TA1530, TA1535, TA98, TA100 and TA100W, and in the host-mediated assay using strain G46. Bile from mice and rats injected intraperitoneally with 1,2-dibromoethane or following liver perfusion was mutagenic in a test using strain TA1535. Gene mutation assays using Escherichia coli, strain WP2 and several other strains, were positive. A positive response was reported in assays using Bacillus subtilis, Streptomyces coelicolor, Aspergillus nidulans and Neurospora crassa. A requirement for intracellular activation of 1,2-dibromoethane was observed for a mutagenic response in S. typhimurium TA1535. Glutathione- S-transferase 5-5 transfected into the bacteria allowed the induction of base-pair mutations on exposure to 1,2-dibromoethane, whereas a 20-fold extracellular excess of the enzyme did not permit 1,2-dibromoethane-induced mutations in non-transfected bacteria in the presence of reduced glutathione (Thier et al., 1993). 1,2-dibromoethane failed to induce reverse mutations in a number of assays using S. typhimurium E503, TA1537 and TA1538, with or without S9 mix. A negative response was reported in several assays using E. coli, Serratia marcescens and silkworms, and in the mouse specific locus test. Chromosomal aberrations were induced by 1,2-dibromoethane in cultured fish lymphocytes (Ellingham et al., 1986), Chinese hamster V79 and CHO cell lines (Tezuka et al., 1980; Tennant et al., 1987). 1,2-Dibromoethane was negative in a test for dominant lethal and specific locus mutations in germ cells from DBA/2J male mice (Barnett et al., 1992). 1,2-Dibromoethane increased significantly the frequency of sister chromatid exchanges in cultured fish lymphocytes (Ellingham et al., l986), Chinese hamster cell line (V79) and cultured human lymphocytes (Tucker et al., 1984; Ong et al., 1989), but not in bone marrow cells of mice injected intraperitoneally (Krishna et al., 1985). In isolated human mononucleated and binucleated peripheral lymphocytes, 1,2-dibromoethane caused an increased frequency of micronuclei in vitro (Channarayappa et al., 1992). A positive response was obtained in the unscheduled DNA synthesis assay using cultured rat hepatocytes (Williams et al., 1982; Tennant et al., 1986), cultured opossum lymphocytes (Meneghini, 1974), cultured human lymphocytes (Perocco & Prodi, 1981) and mouse germ cells (Sega & Rene, 1980), and in the DNA strand break assay using rat or mouse hepatocytes (Nachtomi & Sarma, 1977; White, 1982; Sina et al., l983). Tests for DNA damage using E. coli (Brem et al., 1974), SOS induction using S. typhimurium and E. coli (Ohta et al., 1984; Quillardet et al., 1985; Ong et al., 1987), mitotic gene conversion using Saccharomyces cerevisiae (Fahrig, 1974), somatic segregation using A. nidulans (Crebelli et al., 1984), recombinant DNA synthesis using D. melanogaster (Graf et al., 1984), and sperm abnormality in bulls (Amir et al., 1977) were positive. However, there was a negative response in a test for DNA damage using B. subtilis (Shiau et al., 1980), in DNA-binding tests using E. coli and Ehrlich ascites tumour cells (Kubinski et al., 1981), and in the cell transformation assay using mouse Balb/c 3T3 cells (Tennant et al., 1986). 7.6.2 In vivo assays 1,2-Dibromoethane did not induce chromosomal aberrations or sister chromatid exchanges in occupationally exposed papaya fruit packers (Steenland et al., 1986). 1,2-Dibromoethane was negative in tests for specific locus mutations in germ cells in male mice (Russell, 1986; Barnett et al., 1992). It did not induce dominant lethal mutations in mice (Epstein et al., 1972; Teramoto et al., 1980; Barnett et al., 1992) or rats (Short et al., 1979; Teramoto et al., 1980), chromosomal aberrations in mice (Krishna et al., 1985) or micronuclei in bone-marrow cells of mice (Krishna et al., 1985); there was a weak sister chromatid exchange response that was not dose-related (Krishna et al., 1985). Tests for recombinant DNA synthesis using D. melanogaster (Graf et al., 1984) and sperm abnormality using bulls (Amir et al., 1977), and a sex-linked recessive lethal test using D. melanogaster with exposure to 1,2-dibromoethane in the gaseous phase (Kale & Baum, 1982) were all positive. The frequency of micronuclei in pollen mother cells of Tradescantia was significantly increased by exposure to 1,2-dibromoethane in the liquid or gaseous phase (Ma et al., 1978, 1984). Gene mutation was demonstrated in barley (Ehrenberg et al., 1974) and Drosophila melanogaster (wing spot) (Graf et al., 1984). It induced DNA strand breaks in rat (Nachtomi & Sarma, 1977) and mouse (White, 1982) hepatic cells. 1,2-Dibromoethane was negative in a gene mutation assay (egg colour mutation) in silkworms (Sugiyama, 1980). 7.6.3 Other studies Two doses of 1,2-dibromoethane with dose levels ranging between 10 and 300 µmol/kg body weight (1.8-56 mg/kg body weight) were given by gavage to 90-day-old female Sprague-Dawley rats, 21 and 4 h before sacrifice. 1,2-Dibromoethane caused marked DNA damage. The fraction of DNA eluted from samples of blood, bone marrow, liver, kidney, spleen or thymus of the rats given 1,2-dibromoethane doses of 100 µmol body weight (18 mg/kg body weight) 21 and 4 h before sacrifice was higher than in controls. However, the difference was statistically significant only for kidney and liver (Kitchin & Brown, 1986). Intraperitoneal injection (0.25 and 0.5 mmol/kg) of 1,2-dibromoethane (> 99 9%) in corn oil in B6C3F1 mice (weight 20-26 g) produced hepatic damage. The mice were sacrificed 4 h later and in vivo genotoxicity was determined by a sensitive in vivo/ in vitro alkaline DNA-unwinding assay for the presence of single-strand breaks and/or alkali-labile sites in hepatic DNA. Significant hepatic DNA damage was found with a dose of 0.5 mmol/kg. Although 1,2-dibromoethane is a direct-acting mutagen, its mutagenicity is generally enhanced by metabolic activation. Two different pathways have been postulated for its activation to the ultimate mutagenic form. One is mediated by the mixed-function oxygenases of liver microsomes, in which 1,2-dibromoethane is converted to bromoacetaldehyde and 2-bromoethanol, both of which are potential DNA-damaging agents (Hill et al., 1978; Banerjee et al., 1979). The other pathway is mediated by enzymes present in liver cytosol, in which glutathione conjugation can yield a half-sulfur- mustard or an episulfonium ion as reaction products (Rannug, 1980; Van Bladeren et al., 1980). Glutathione conjugation also contributes to the binding of 1,2-dibromoethane to DNA, and an S-[2-(N7-guanyl)ethyl] glutathione adduct has been identified (Ozawa & Guengerich, 1983; Inskeep & Guengerich, 1984). Foster et al. (1988) reported that the majority of mutations induced by 1,2-dibromoethane consist of GC to AT and AT to GC base changes, suggesting that it acts like an alkylating agent. This glutathione conjugate accounts for > 95% of the total DNA adducts formed by 1,2-dibromoethane. S. typhimurium TA100 and sequence analysis were used to determine the type, site and frequency of mutations in a portion of the lacZ gene resulting from in vitro modification of bacteriophage M13mp18 DNA with S-(2-chloroethyl) glutathione, an analogue of the 1,2-dibromoethane-glutathione conjugate. An adduct level of approx.8 nmol per mg DNA resulted in a 10-fold increase in mutation frequency. The mutations were mainly base substitutions in which GC to AT transitions accounted for 75% (70% of the total mutations) (Cmarik et al., 1992). The steady-state levels of c-fos, c-jum, and c-myc mRNA were investigated in male Wistar rat liver following oral dosing with 100 mg 1,2-dibromoethane/kg body weight. This dose induced hyperplasia. Increases in the expression of c-myc and c-jum genes were observed in the absence of c-fos expression (Coni et al., 1993). Sundheimer et al. (1982) examined the relationship between glutathione metabolism and the rate of DNA alkylation by 1,2-dibromoethane in cultured hepatocytes. The rate of alkylation was decreased by the addition of diethyl maleate and increased by the addition of cytosolic microsomal enzymes. While high concentrations of 1,2-dibromoethane were capable of depleting glutathione in the hepatocytes, depletion did not appear to be necessary for binding to occur. On the basis of these results, the authors concluded that glutathione- S-transferases are involved in the bioactivation of 1,2-dibromoethane to an alkylating species. Working et al. (1986) assessed the ability of 1,2-dibromoethane to cause DNA damage by quantifying the rate of unscheduled DNA synthesis (UDS) in F-344 rat hepatocytes and spermatocytes exposed to 1,2-dibromoethane in vivo and in vitro. Pretreatment of cells with inhibitors of cytochrome-P450-mediated oxidation had no effect on the induction of UDS by 1,2-dibromoethane (10-100 µmol/litre) in vitro, whereas depletion of cellular glutathione strongly inhibited UDS induction in both cell types. Pretreatment of rats with metyrapone (an inhibitor of hepatic mixed-function oxidases) in vivo had no effect on 1,2-dibromoethane-induced UDS in hepatocytes, but produced a positive UDS response in spermatocytes. This suggests that the mixed-function oxidase pathway in metabolism is the primary route of clearance of 1,2-dibromoethane and the inhibition of this enzyme system leads to more extensive tissue distribution of the parent compound. The data also suggest that the pathway which produces genotoxic metabolites from 1,2-dibromoethane in hepatocytes and spermatocytes, in vivo and in vitro, involves the conjugation of 1,2-dibromoethane to glutathione and its subsequent metabolism. In studies of DNA adducts, Kim & Guengerich (1989) measured urinary excretion of S-[2-( N7-guanyl)ethyl]- N-acetyl-cysteine, derived from the nucleic acid adduct, S-[2-( N7-guanyl) ethyl]glutathione, in rats treated with 1,2-dibromoethane. A good correlation was found between the excretion of this mercapturic acid and the in vivo formation of the DNA adduct in liver and kidney DNA. Inskeep et al. (1986) determined that the major DNA adduct formed upon exposure to 1,2-dibromoethane, S-[2-( N7-guanyl)ethyl]glutathione, had a half-life in rat liver, kidney, stomach and lung between 70 and 100 h. Inskeep & Guengerich (1984) measured the rate of formation of 1,2-dibromoethane adducts to calf thymus DNA in vitro. Adduct formation was dependent on the presence of both glutathione and glutathione- S-transferase. 7.7 Carcinogenicity 1,2-Dibromoethane has been tested for carcinogenicity by oral administration and inhalation in mice and rats, and by skin application in mice (IARC, 1987) (see Table 14). It has been shown to cause tumours in various organs, by several dosage routes and, in some cases, with a latency of less than 12 months (Table 15). The following tumours have been observed: a) By oral administration hepatocellular carcinomas and neoplastic nodules in female rats haemangiosarcomas in various circulatory system organs in male rats alveolar/bronchiolar adenomas in male and female mice b) By inhalation exposure nasal cavity carcinomas and adenocarcinomas in male and female rats alveolar/bronchiolar carcinomas in female rats alveolar/bronchiolar carcinomas in male and female mice haemangiosarcomas in the circulatory system of male and female rats mesotheliomas in male rats mammary fibroadenomas in female mice subcutaneous fibrosarcomas in female mice c) By skin administration skin papillomas and lung papillomas in female mice 7.7.1 Administration by gavage 18.104.22.168 Mouse When technical grade 1,2-dibromoethane (99.1% pure) in corn oil was administered on 5 consecutive days per week by gavage to B6C3F1 mice (groups of 50 males and 50 females in the treated groups, and 20 of each sex in the untreated and vehicle control groups) at time- weighted average dose levels of 62 and 107 mg/kg per day, early development of squamous cell carcinomas of the forestomach was observed in both sexes. The incidence of alveolar/bronchiolar adenomas was significantly higher in treated mice of both sexes than in controls (NCI, 1978). 22.214.171.124 Rat Osborne-Mendel rats (50 animals of each sex in the treated groups and 120 animals of each sex in the untreated and vehicle control groups) were given on 5 consecutive days per week, by gavage, technical grade 1,2-dibromoethane (99.1% pure) in corn oil at time- weighted average dose levels of 38 or 41 mg/kg per day for males, and 37 or 39 mg/kg per day for females. Squamous cell carcinomas of the forestomach were observed in more than half the male and female rats at both dose levels, while none were observed in controls. The lesions, seen as early as week 12, were locally invasive and eventually metastasized. Significantly higher incidences of hepatocellular carcinomas and haemangiosarcomas were observed in treated males and females, respectively (NCI, 1978). Ledda-Columbano et al. (1987b) examined the interaction of an intragastric dose of either 1,2-dibromoethane or carbon tetrachloride (CCl4) with diethylnitrosomine (DENA). The administration of either 1,2-dibromoethane or CCl4 resulted in similar increases in cell proliferation. However, while pretreatment with CCl4 caused an increase in the incidence of hepatic foci resulting from subsequent DENA administration, pretreatment with 1,2-dibromoethane did not. This difference in the ability of the two compounds to act as a promoter was attributed to the nature of cell proliferation response. The authors concluded that the cell proliferation induced by 1,2-dibromoethane, unlike the compensatory cell proliferation induced by CCl4, is not an effective process for increasing the rate of tumour initiation. 7.7.2 Administration in drinking-water 126.96.36.199 Mouse 1,2-Dibromoethane (> 99% purity) and its metabolites, bromoethanol or bromoacetaldehyde, were administered to B6C3F1 mice (groups of 30 males and 30 females) at a concentration of 4 mmol/litre in distilled drinking-water (equivalent to 116 mg/kg body weight for males and 103 mg/kg body weight for females), for 450 days in the case of 1,2-dibromoethane and for 560 days in the case of the metabolites. A control group (60 males and 60 females) was given distilled drinking-water. 1,2-Dibromoethane induced squamous cell carcinomas of the forestomach in 26/30 males and 27/30 females, and squamous cell papillomas of the oesophagus in 3/30 females. Bromoethanol in drinking-water at a concentration of 4 mmol/litre (equivalent to 76 mg/kg body weight for males and 71 mg/kg body weight for females) induced squamous cell papillomas of the forestomach in 9/29 males and 10/29 females, but bromoacetaldehyde at the same concentration (equivalent to 62 mg/kg body weight for females and 62 mg/kg body weight for males) did not induce a significant incidence of forestomach tumours. The incidence of tumours in the control group was not significant. Bromoethanol and bromoacetaldehyde were not considered likely to be active intermediates of 1,2-dibromoethane carcinogenicity (Van Duuren et al., 1985). 7.7.3 Inhalation 188.8.131.52 Mouse Groups of 50 male and 50 female B6C3F1 mice were exposed in inhalation chambers to air containing 77 or 308 mg/m3 (10 or 40 ppm) of 1,2-dibromoethane (99.3-99.4% pure) for 78-106 weeks. The incidences of alveolar/bronchiolar carcinomas and alveolar/bronchiolar adenomas were significantly higher in exposed male and female mice than in controls. Haemangiosarcomas of the circulatory system, fibrosarcomas in subcutaneous tissue, carcinomas of the nasal cavity, and adenocarcinomas of the mammary gland were significantly increased in females. Exposure to 1,2-dibromoethane was also associated with epithelial hyperplasia of the respiratory system (NTP, 1982). 184.108.40.206 Rat Groups of 50 male and 50 female F-344 rats were exposed in inhalation chambers to air containing 77 or 308 mg/m3 (10 or 40 ppm) of 1,2-dibromoethane (99.3-99.4%) for 88-106 weeks. Carcinomas, adenocarcinomas and adenomas of the nasal cavity, and haemangiosarcomas of the circulatory system were significantly increased in exposed male and female rats. The incidences of mesotheliomas of the tunica vaginalis and adenomatous polyps of the nasal cavity in males, and of fibroadenomas of the mammary gland and alveolar/bronchiolar adenomas and carcinomas (combined) in females were significantly increased (NTP, 1982). Wong et al. (1982) reported that the coadministration of dietary disulfiram increases the rate of tumour incidence in rats exposed to 1,2-dibromoethane (153.6 mg/m3, 20 ppm) by inhalation. There is evidence to suggest that the synergistic effect of disulfiram may be the result of increased liver glutathione- S-transferase activity in animals treated with this drug (Elliot & Ashby, 1980). 7.7.4 Dermal application 220.127.116.11 Mouse Doses (25 mg or 50 mg) of 1,2-dibromoethane (> 99% pure) dissolved in 0.2 ml acetone were applied 3 times/week to the shaved dorsal skin of female Ha:ICR Swiss mice (groups of 30 animals). There were an acetone only and untreated control groups. The times to first appearance of skin tumour (papilloma) were 434 days for the 25-mg group and 395 days for 50-mg group. By comparison with controls, both groups showed a statistically significant increase in skin papillomas, and in the 50-mg group there was also a significant increase in lung papillomas. Both groups also had dermal squamous carcinomas and stomach, tumours but these were not statistically significant (Van Duuren et al., 1979). 7.7.5 Cell transformation 1,2-Dibromoethane caused transformation of BALB/C 3T3 cells both in the presence and absence of an exogenous metabolism system (Perocco et al., 1991). 7.8 Biochemical studies and species specificity 1,2-Dibromoethane (75-100 mg/kg body weight) given by gavage to non-fasted Wistar rats induced DNA synthesis and cell division in the liver. The peak of DNA synthesis, as measured by 3H-methyl thymidine incorporation, was attained at or shortly after 24 h. The mitotic waves measured with the aid of colchicine occurred at 24-30 h and 48 to 54 h after 1,2-dibromoethane treatment. Increase in DNA synthesis was confirmed by autoradiography. The stimulation of liver cell mitosis occurred in non-fasted animals without any apparent cell necrosis. 1,2-Dibromoethane was an effective mitogen for liver under these experimental conditions (Nachtomi & Farber, 1978). In a study by Ledda-Columbano et al. (1987a) 1,2-dibromoethane in corn oil was administered by gavage at a dose of 100 mg/kg body weight to male Wistar rats (weight 250-280 g). The rats were given an intraperitoneal injection of 3H-thymidine 1 h prior to sacrifice, 10, 20, 30, 36 and 48 h after the treatment. No mortality attributable to 1,2-dibromoethane was observed in the treated rats. The body weights of 1,2-dibromoethane-treated rats were similar to those of controls. No changes in the specific activity of DNA were observed in kidney 10 h after treatment. There was an increase in labelled thymidine incorporation into DNA and this was maximal after 20-30 h. At 48 h the extent of incorporation of labelled thymidine decreased rapidly even though it was still higher than in controls. When effects on the kidneys were investigated, mitotic activity was noted predominantly in the proximal tubular epithelium of the renal cortex. Histological examination of the kidney did not reveal any signs of necrosis. Of possible significance for the prediction of species differences in response to 1,2-dibromoethane are the observations (Dibiasio et al., 1991) that hepatic cytosolic glutathione- S-transferase activities are similar in rats and mice, but about 40% of these values in rhesus monkeys. In addition, cytosolic glutathione- S-transferase activities in rhesus monkey and human testis are only about 5% of the activities in rat and mouse testes. 8. EFFECTS ON HUMANS 8.1 Acute toxicity 1,2-Dibromoethane is strongly irritant to the eyes, skin, and respiratory tract (Peoples et al., 1978; Letz et al., 1984). Deaths from acute exposure to high concentrations of 1,2-dibromoethane are usually due to pneumonia following damage to the lungs. In addition, acute inhalation exposure may lead to liver and kidney damage. Six people who attempted suicide by ingesting 1,2-dibromoethane suffered from vomiting, nausea and burning throat; death followed in two cases. The characteristic pathological lesions were present in liver, lungs and kidneys. Intense jaundice was observed and was due to massive necrosis of the liver (Sarawat et al., 1986). It is estimated that 200 mg/kg is lethal to humans, based on the observation that 12 g caused the death of a woman weighing about 60 kg (Alexeef et al., 1990). 8.2 Occupational exposure In cases of poisoning following occupational exposure, headache, severe vomiting, diarrhoea, respiratory tract irritation and death have been reported. Exposure to 1,2-dibromoethane in air at concentrations above 384 mg/m3 (50 ppm) caused nasal and throat irritation. Two deaths were reported after exposure by inhalation to a mean concentration of 215 mg/m3 (28 ppm) for 30 and 45 min, respectively, during the cleaning of a storage tank containing residues of 1,2-dibromoethane (Letz et al., 1984, Jacobs, 1985). There was also absorption from dermal exposure to the 0.1-0.3% solution in the tank (Letz et al., 1984). The first worker collapsed while working inside the tank and died 12 h later with metabolic acidosis, depression of the CNS, and laboratory evidence of liver damage. A supervisor attempting to rescue the worker also collapsed inside the tank and died 64 h later with intractable metabolic acidosis, hepatic and renal failure, and necrosis of skeletal muscle and other organs. Coughing, vomiting, diarrhoea, eye, skin and respiratory irritation, coma, metabolic acidosis, delirium, confusion, nausea, low urine output, renal failure, tachycardia and asystole were noted. Autopsy revealed pulmonary oedema, liver damage and extensive autolysis in the kidney. Inhalation exposure to concentrations over 154 mg/m3 (20 ppm) for more than 30 min is considered fatal to humans. 8.2.1 Cancer incidence Mortality in employees exposed to 1,2-dibromoethane in two production units operated from 1942 to 1969 and from the mid-1920s to 1976 was investigated (Ott et al., 1980). The study population was 161 employees. In the first production unit two deaths from malignant neoplasms were observed against 3.6 expected, and in the second unit, where there was potential exposure to various organic bromide products, there were five deaths from malignant neoplasms against 2.2 expected (p < 0.072). However, no statistically significant increase in total deaths or malignant neoplasms relatives to duration of exposure was observed. Epidemiological studies of four worker populations did not show any increase in cancer that could be attributed to 1,2-dibromoethane (Ter Haar, 1980) 8.2.2 Reproductive effects In an investigation of possible sterility from exposure to 1,2-dibromoethane, sperm levels in workers exposed to 1,2-dibromoethane were not affected, and there was no evidence of effects on offspring (Ter Haar, 1980). Ratcliffe et al. (1987) and Schrader et al. (1987) conducted a cross-sectional study of semen quality in 46 men employed in the papaya fumigation industry in Hawaii, with an average duration of exposure of 5 years and a geometric mean breathing zone exposure to airborne 1,2-dibromoethane of 0.68 mg/m3 (88 ppb) (8-h time-weighted average). The control group consisted of 43 unexposed men from a nearby sugar refinery. Statistically significant decreases in sperm count per ejaculate and percentage of viable and motile sperm, together with increases in the proportion of sperm with specific morphological abnormalities, were observed among exposed men, compared to controls, after consideration of smoking, caffeine and alcohol consumption, subject's age, abstinence, history of urogenital disorders, and other potentially confounding variables. The data indicated that 1,2-dibromoethane could cause reproductive inpairment in males exposed to this concentration. Schrader et al. (1988) conducted a short-term longitudinal study on the effect of 1,2-dibromoethane exposure on male reproductive potential in ten forestry workers and six unexposed men in Colorado. The time-weighted average inhalation exposure over 6 weeks was 0.46 mg/m3 (peak exposure of 16 mg/m3) and there was extensive skin exposure. Sperm velocity and semen volume were decreased significantly in the exposed workers. Both studies suggested that 1,2-dibromoethane has multiple sites of action on male accessory sex glands and testes. In five studies on the reproductive effects of occupational exposure to 1,2-dibromoethane, four showed potential reproductive impairment but this was not large enough to be statistically significant. The power of all of the studies was low and they were considered inconclusive for assessing reproductive risk (Dobbins, 1987). A retrospective study of four plants in the United Kingdom where male workers were exposed to 1,2-dibromoethane revealed statistically marginally reduced fertility rates (i.e., live births to their wives). The average exposure was probably below 38.5 mg/m3 (5 ppm), although actual concentrations were not measured (Wong et al., 1985). 9. EFFECTS ON ORGANISMS IN THE ENVIRONMENT 9.1 Aquatic organisms 9.1.1 Invertebrates Nishiuchi (1980, 1981) studied the acute toxicity of 1,2-dibromoethane in aquatic larvae of insects and aquatic invertebrates, such as a mayfly (Cloeon dipterum), two dragonflies (Sympetrum frequens and Orthetrum albistylum speciosum), a Japanese diving beetle (Eretes sticticus) and a water boatman (Micronecta sedula) (Table 17). The toxicity threshold (48-h LC50 values) of 1,2-dibromoethane machine oil formulation for the above aquatic invertebrates and that of 1,2-dibromoethane for mayfly were greater than 40 mg/m3. In mayfly the reported 48-h toxicity thresholds for two mixed formulations, which consisted of 1,2-dibromoethane, malathion, diazinon and machine oil (3:1:1:80), and 1,2-dibromoethane, diazinon and O-sec-butylphenyl methylcarbamate (25:5:3) were 28 and 65 mg/m3, respectively (Nishiuchi & Asano, 1979). There was no apparent difference in toxicity of technical 1,2-dibromoethane and an oil-based formulation at least up to 40 mg/litre. Table 17. Acute toxicity of 1,2-dibromoethane to aquatic invertebrates (From: Nishiuchi, 1980) Species Test material Temperature 48-h LC50 (°C) Mayfly Technical material 25 > 40 (Cloeon dipterum) (in acetone) Dragonfly 1,2-dibromoethane (oil) 25 > 40 (Sympetrum frequens) Dragonfly 1,2-dibromoethane (oil) 25 > 40 (Orthetrum albistylum speciosum) Japanese diving beetle 1,2-dibromoethane (oil) 25 > 40 (Eretes sticticus) Water boatman 1,2-dibromoethane (oil) 25 > 40 (Micronecta sedula) Herring et al. (1988) evaluated the toxicity of 1,2-dibromoethane to Hydra oligactis in a series of three experiments. Study 1 evaluated lethality, feeding behaviour and mobility in a series of concentrations ranging from 7.5 to 75 mg/litre. In Study 2, adult Hydra were pre-treated for 14 days with a sublethal dose of 1,2-dibromoethane (5 mg/litre) prior to exposure to a range of 1,2-dibromoethane concentrations (25-300 mg/litre) for a total of 72 h. In the third study, the F1 offspring of pre-treated adult Hydra were also exposed to a series of 1,2-dibromoethane concentrations. The 48-h LC50 for Hydra was determined to be 70 mg/litre. When adult Hydra were pre-treated with sublethal concentrations of 1,2-dibromoethane, the 48-h LC50 was increased to 200 mg/litre. Furthermore, the F1 offspring of pre-treated adult exhibited mortalities of only 10% and 20%, respectively, after 24-h and 48-h exposures to 200 mg 1,2-dibromoethane/litre. These results suggest that Hydra and first-generation offspring are capable of developing tolerance to 1,2-dibromoethane. Adams & Kennedy (1992) exposed first-stage budding Hydra oligactis to 1,2-dibromoethane at 5 mg/litre. The 1,2-dibromoethane was dissolved using acetone at 15 mg/litre, and an acetone control was used. Exposure was for 24, 48 or 72 h. Following exposure, the animals were washed several times with the medium, sectioned through the gastric region, and the base/apical sections were grafted. Regeneration was significantly affected by all exposures to 1,2-dibromoethane but not by acetone. The severity of the effect increased with increasing exposure. Adams et al. (1989) reported dose-sensitive relationships for the loss and recovery of locomotor response, chromatophore expansion and lethality in three species of laboratory-reared octopus. Three species of octopus (Octopus bimaculoides, O. joubini, and O. maya) were exposed to 25, 50, 75 and 100 mg 1,2-dibromoethane/litre for either one hour, followed by transfer to chemical-free water, or continuously for a period of 72 h. Generally, responses by the octopuses were evident after only 1 min of exposure. Chromatophore expansion and loss of locomotor response occurred at 25 mg/litre after 30 min, but recovery was noted 6 h after transfer to chemical-free water. Lethality occurred in all three species at 25 mg/litre after 48 h of exposure. O. maya was the most sensitive species, exhibiting 100% mortality after 3 h of exposure. The acute LC50 values for O. bimaculoides, O. joubini and O. maya were 42.7, 35.3 and 30.6 mg/litre respectively (Table 18). Although the authors reported a chronic LC50 of 100 mg/litre occurring within 12 h, the Task Group considered this to be an acute exposure. Table 18. Acute LC50 values approximated for lethality data (Adams et al., 1989) using either the moving average, binomial or probit methods Test species Estimated 48-h LC50 95% confidence (mg/litre) limits Octopus bimaculoides 42.7 28.1-58.8a Octopus joubini 35.3 -b Octopus maya 30.6 0-52.02c a moving average method b confidence limits exceeded 95%, therefore the limits would range from 0 to infinity c probit method used 9.1.2 Fish There are few data for the acute toxicity of 1,2-dibromoethane in fish. A study of the effect of pH on the acute toxicity of 1,2-dibromoethane in killifish (Oryzias latipes) was carried out in open static systems. Altering the pH of the breeding water between pH 5.0 and pH 10.0 had no effect on 48-h LC50 values (Nishiuchi, 1982). Goldfish quickly absorbed 1,2-dibromoethane from water (at 1 mg/litre) and quickly eliminated it. The concentration in the goldfish (1.75 ± 0.041 mg/kg) was in equilibrium with the concentration in the water 1.5 h after the initiation of exposure. From the results of the elimination study, the biological half-life was calculated to be less than 30 min (Ogino, 1978). Landau & Tucker (1984) found the 48-h LC50 values for sheepshead minnow Cyprinodon variegautus and snook Centropomus undecimatis, both estuarine fish, to be 4.8 and 6.2 mg/litre, respectively. Nishiuchi & Asano (1979) measured toxicity thresholds for carp (Cyprinus carpio) exposed to pesticide mixtures containing various concentrations of 1,2-dibromoethane (Table 19). After 24 h of exposure at 24°C, no difference in the toxicity threshold (> 40) could be detected at unit pH increases between 5 and 9. Table 19. Toxicity threshold after 48 h exposure of Cyprinus carpio to mixtures containing 1,2-dibromoethane at 25°C (Nishiuchi & Asano, 1979) Mixture constituents Concentrations Toxicity threshold 1,2-Dibromoethane 2.5% oil > 100 Fenitrothion 0.5% oil 1,2-Dibromoethane 2.5% oil 86 Fenitrothion 0.5% oil 1,2-Dibromoethane 1.5% emulsion Fenitrothion 10% emulsion 45 Carbaryl 5% emulsion Diazinon 20% emulsion 28 1,2-Dibromoethane 10% emulsion Cyanophos 10% emulsion 32 1,2-Dibromoethane 10% emulsion 1,2-Dibromoethane 25% oil Diazinon 5% oil 65 O-sec-butylphenyl 3% oil methylcarbamate 9.2 Terrestrial biota Data on the effects of 1,2-dibromoethane on terrestrial biota (other than mammals) are limited. In a study on the effects of different foods on the susceptibility of the adzuki bean weevil (Callosobruchus chinensis Linn.) to 1,2-dibromoethane, the 24-h LC50 at 29°C was 4.40, 7.232, 6.130, 5.249 and 4.951 mg/litre for chickpea, pea, green gram, black gram, and pigeon pea, respectively (Mundhe & Pandey, 1980). Exposure of the nematode Aphelenchus avenae to low concentrations of 1,2-dibromoethane resulted in a very small conversion of the halide just before death. A study with 14C-labelled 1,2-dibromoethane showed that two primary products were ethylene (5%) and O-acetylserine (> 95%). These transformations were indicative of two primary modes of intoxication of the nematodes, postulated to be a direct reaction of 1,2-dibromoethane with an iron centre in the respiratory sequence and the substitution of a serine at the active site of an esterase or protease (Castro & Belser, 1978). 9.3 Microorganisms The toxicity of 1,2-dibromoethane to microsclerotia of Verticillium dahliae in air and in soil was determined in a sealed container. At concentrations of 470 mg/litre in air or 12.5 mg/kg in soil, 1,2-dibromoethane killed 97% of the microsclerotia, after incubation for 16 days in both cases. The toxicity of 1,2-dibromoethane increased with increasing temperature and with increase in soil moisture (0-80%) (Ben-Yephet et al., 1981). Pignatello (1986) investigated 1,2-dibromoethane effects on microorganisms from two soils/sediments taken from a 1,2-dibromoethane-contaminated groundwater discharge area. Labelled potassium acetate was added to slurries of soil, which had been shaken with added 1,2-dibromoethane (up to 1000 mg/litre), for 3 or 12 h. Incorporation of acetate into microbial lipids was used as the end-point. The EC50 for inhibition of acetate incorporation following 12-h incubation with 1,2-dibromoethane was 50 and 100 mg/litre for the two soils; soil 1 showed an EC50 of 100 following 3 h of incubation. Both soils showed "slight" inhibition at 10 mg 1,2-dibromoethane/litre and > 94% at 1000 mg/litre. Soil 1 was a muddy soil with a total organic carbon (TOC) content of 14%, whereas soil 2 was a stream-bed soil with a TOC of 0.24%. 9.4 Plants 1,2-Dibromoethane was phytotoxic to fruit after they had been fumigated against several species of fruit flies. Fumigation with 1,2-dibromoethane at a concentration of 4 g/m3 stimulated fruit respiration and ethylene evolution. A higher concentration (32 g/m3) increased respiration rate and ethylene evolution in the fruits and increased tissue leakage. Fruits stored at 1°C after fumigation with 32 g/m3 suffered more severe damage than those stored at 20°C. Storage at 1°C abolished the increases in gas exchange observed in fumigated fruits at 20°C. The injurious effect of cooling might be ascribed to a higher residue of unchanged fumigant persisting in the cooled fruits or to a decreased capacity of the fruits to repair cellular damage at low temperatures (Wade & Rigney, 1979). 10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT 10.1 Evaluation of human health risks 1,2-Dibromoethane is carcinogenic for rats and mice causing tumours (adenomas and carcinomas) in a variety of organs including the nasal cavity, lung, stomach, liver, skin, and mammary gland, as well as haemangiosarcomas. In many cases, a reduced latency period for developing tumours was observed. 1,2-Dibromoethane has been shown to be mutagenic in various in vivo and in vitro assays and to cause single-strand DNA breaks in vitro. Some metabolites have been shown to covalently bind to DNA. Based on these data, 1,2-dibromoethane is thought to be a genotoxic carcinogen to rodents. Although adequate studies in humans are not available, the extensive evidence for carcino genicity in animal studies indicates that 1,2-dibromoethane is a potential human carcinogen. 10.2 Evaluation of effects on the environment The high volatility of 1,2-dibromoethane makes the atmosphere the predominant environmental sink. Consequently, measured concentrations in surface waters are low (< 0.2 µg/litre). Air concentrations of < 0.2 µg/litre have been measured in cities, while concentrations of up to 90 µg/litre in irrigation wells reflect the mobility of the compound in soil. Persistent contamination of irrigation wells may result from the slow release of 1,2-dibromoethane from the soil matrix many years after its use as a soil fumigant. There is a lack of information on the degradation of 1,2-dibromoethane in the aquatic and soil environments. Stratospheric photodegradation occurs and potentially leads to breakdown products with ozone-depleting capacity. However, 1,2-dibromoethane is not listed in the Montreal Convention. Few aquatic ecotoxicity tests have been conducted with 1,2-dibromoethane. Those reported show LC50s greater than 5 mg/litre. There is a difference of at least 4 orders of magnitude between measured water concentrations and these toxic concentrations, indicating that 1,2-dibromoethane poses no risk to aquatic organisms. 11. CONCLUSIONS AND RECOMMENDATIONS Considering the toxicological characteristics of 1,2-dibromoethane, both qualitatively and quantitatively, it was concluded that an exposure that would not cause adverse effects in humans after any route of exposure could not be estimated. Consequently, all appropriate measures should be taken to eliminate or minimize human exposure to 1,2-dibromoethane. 12. FURTHER RESEARCH Further information from epidemiology studies on 1,2-dibromoethane would be useful. 13. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES IARC (1977, 1982, 1987) concluded, from biological data relevant to the evaluation of carcinogenic risk, that 1,2-dibromoethane is carcinogenic in mice and rats after oral administration, and by inhalation, producing squamous cell carcinomas of the forestomach. 1,2-Dibromoethane given orally or by intraperitoneal injection did not produce dominant lethal mutations in mice. Prolonged contact with 1,2-dibromoethane causes skin irritation. However, no case reports or epidemiological studies were available to the Working Group. IARC has classified 1,2-dibromoethane as a Group 2A carcinogen (probably carcinogenic to humans). WHO has not established a drinking-water quality guideline for 1,2-dibromoethane. This is because 1,2-dibromoethane appears to be a genotoxic carcinogen and the studies are inadequate for mathematical extrapolation (WHO, 1993). 1,2-Dibromoethane was evaluated by the Joint FAO/WHO Expert Committee on Pesticide Residues in 1965 (FAO/WHO, 1965) and 1966 (FAO/WHO, 1967). The 1965 evaluation concluded that 1,2-dibromoethane should be used for fumigation of food only on the condition that no residue of the unchanged compound reached the consumer. In the 1966 evaluation an Acceptable Daily Intake (ADI) of 1 mg/kg body weight as bromide was established. In 1991 the Codex Alimentarius Commission deleted the Guideline Levels for 1,2-dibromoethane in food commodities (FAO/WHO, 1992). 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Identité, propriétés physiques et chimiques, et méthodes d'analyse Le 1,2-dibromoéthane (dibromure d'éthylène) est un liquide incolore d'odeur chloroformique dont le point de fusion est de 9,9°C et le point d'ébullition de 131,4°C. Il est assez volatil, avec une tension de vapeur de 1,47 kPa (11 mmHg) à 25°C et une densité de vapeur par rapport à l'air de 6,1. Le 1,2-dibromoéthane est miscible à la plupart des solvants organiques. Sa solubilité dans l'eau est de 4,3 g/litre à 30°C. Dans l'air ambiant, l'analyse s'effectue par chromatographie en phase gazeuse après absorption sur polymères poreux puis désorption thermique rapide. Pour les échantillons d'eau, on utilise un système avec piège et purgeur. Les résidus de 1,2-dibromoéthane présents dans les denrées alimentaires et d'autres milieux peuvent être soit extraits par solvent, soit soumis à une analyse par la technique de l'espace de tête dans des conditions cryogéniques, après quoi on prépare un dérivé et on poursuit par chromatographie en phase gazeuse ou chromatographie liquide à haute performance. 2. Sources d'exposition humaine et environnementale Le 1,2-dibromoéthane est utilisé comme agent d'épuration des agents antidétonnants à base de plomb ajoutés à l'essence. On l'emploie aussi pour la fumigation du sol ou de certains fruits ou céréales. L'essence additionnée de plomb étant moins utilisée dans certains pays et les homologations pour les usages agricoles ayant été annulées, l'exposition humaine à ce produit a diminué. Il reste cependant encore en usage dans certains pays comme épurateur de l'essence au plomb, comme fumigant, au fins de quarantaine, comme solvent et comme intermédiaire dans l'industrie chimique. 3. Concentrations et dégradation dans l'environnement Dans l'air, on mesure des concentrations qui vont de zéro à des teneurs de l'ordre du ng/m3 en zone urbaine. On a trouvé du 1,2-dibromoéthane dans des eaux souterraines à des concentrations allant jusqu'à 0,2 µg/litre, la teneur pouvant atteindre 50 µg/litre dans les eaux superficielles des zones d'exploitation agricole intensive. Bien qu'il y ait lessivage du 1,2-dibromoéthane à travers le sol, il en reste une certaine quantité dans la matrice édaphique,d'où risque de contamination ultérieure de la nappe phréatique. On connaît mal les conditions de dégradation microbienne du 1,2-dibromoéthane dans le sol. Le composé étant très volatil, c'est l'atmosphère qui en est le principal réceptacle. Par photolyse dans la stratosphère, il peut se former des produits de décomposition susceptibles d'attaquer la couche d'ozone. 4. Cinétique et métabolisme chez les animaux de laboratoire Le 1,2-dibromoéthane est rapidement absorbé par la voie orale, percutanée et respiratoire. On pense que la toxicité du composé est largement due à ses métabolites. La métabolisation s'effectue soit par une voie oxydative (cytochrome P-450), soit par conjugaison (glutathion- S-transférase). Deux métabolites réactifs, le bromoacétaldéhyde formé par la voie oxydative, et l'ion thiiranium, formé par conjugaison, interagissent avec les macromolécules cellulaires (protéines, ADN), pour donner naissance à divers produits par l'établissement de liaisons covalentes. 5. Effets sur les mammifères de laboratoire et les systèmes d'épreuve in vitro Le 1,2-dibromoéthane est fortement toxique pour les animaux (DL50 par voie orale pour le rat égale à 146-417 mg/kg de poids corporel; CL50 inhalatoire pour le rat égale à 3080 mg/m3 après 2 h d'exposition; mortalité observée chez des lapins à la suite d'une application cutanée à raison de 210 mg/kg). Les effets toxiques observés se sont produits principalement au niveau des reins et du foie. L'inhalation de vapeurs provoque une irritation de la muqueuse nasale et une dépression du système nerveux central. Chez des groupes de rats exposés à des concentrations comprises entre 1540 et 77 000 mg/m3 (200-10 000 ppm) pendant 0,1 à 16,0 h, on a observé dans tous les groupes une mortalité qui était fonction de la durée d'exposition et de la concentration. En solution à 1,0%, le 1,2-dibromoéthane a provoqué une irritation sur la peau abdominale de lapins après rasage ainsi qu'une irritation oculaire. Chez des rats et des souris qui avaient reçu du 1,2-dibromoéthane par voie orale de manière subchronique, on a observé une certaine mortalité et une baisse du gain de poids à la dose quotidienne de 100 mg/kg de poids corporel. Chez des rats exposés au composé à la dose de 115 mg/m3 (578 ppm), 6 h par jour, 5 jours par semaine et ce, pendant 13 semaines, on a noté un moindre gain de poids et des effets pathologiques au niveau du nez. Cette étude a permis d'établir que la dose sans effets histopathologiques observables au niveau de la cavité nasale était égale à 23 mg/m3 (3 ppm). Lors d'une étude analogue sur des souris, on a observé le même genre d'effets histopathologiques avec la même dose sans effets observables (23 mg/m3, 3 ppm). On a administré du 1,2-dibromoéthane par gavage à des rats selon les modalités suivantes: 37-107 mg/kg de poids corporel (moyenne pondérée par rapport au temps) tous les jours pendant 49-90 semaines; de même des souris en ont reçu pendant 15-17 mois dans leur eau de boisson à raison de 103-117 mg/kg de poids corporel. A la suite de cela, on a observé des anomalies non malignes telles qu'une dégénérescence hépatique, une atrophie testiculaire, ainsi qu'une acanthose et une hyperkératose au niveau de la portion cardiaque de l'estomac. Après exposition par la voie respiratoire de rats et de souris à des doses de 77-388 mg/m3 pendant 6 à 18 mois, on a observé une inflammation de la trachée et de la cavité nasale, une dégénérescence testiculaire et une nécrose hépatique. Après exposition par la voie respiratoire, le 1,2-dibromoéthane ne se révèle pas tératogène pour le rat ou la souris. Chez des rats qui en avaient reçu par la voie intrapéritonéale une dose quotidienne de 1,25 mg/kg de poids corporel (mâles) ou de 509 mg/m3 (voie respiratoire, femelles, 4 h/jour, 3 jours par semaine, du jour 3 au jour 20 de la gestation), on a constaté une action toxique sur le développement (anomalies de la coordination motrice). Le 1,2-dibromoéthane a également eu une action délétère sur la fonction de reproduction de rats (chez les mâles, dans les conditions d'exposition suivantes: 684 mg/m3, 7 h/jour, 5 jours par semaine, pendant 10 semaines; chez les femelles, aux doses et pendant les durées suivantes: 614 mg/m3, 7 h/jour, 7 jours par semaine, pendant 3 semaines). La dose sans effet observable pour ce paramètre était égale à 300 mg/m3 chez les deux sexes. Lors d'une étude où des rats mâles ont reçu pendant 90 jours une alimentation contenant le composé, on a constaté que la dose sans effet observable sur la capacité de reproduction était égale à 50 mg/kg et par jour. On a observé une atteinte de la spermatogénèse chez des taureaux après administration du composé par voie orale à la dose quotidienne de 2 mg/kg pendant moins de 21 jours et chez des lapins après injection sous-cutanée du produit à raison de 15 mg/kg pendant 5 jours. Chez des poules qui avaient reçu pendant 12 semaines une nourriture contenant du 1,2-dibromoéthane à la dose de 12,5 mg/kg, on a constaté une diminution du calibre des oeufs. Le composé n'a pas entraîné de mutations léthales dominantes chez des souris ou des rats, ni produit d'aberrations chromosomiques ou de micronoyaux dans les cellules de la moëlle osseuse de souris traitées in vivo. Toutefois, il s'est révélé mutagène dans les épreuves sur bactéries et a provoqué des ruptures de l'ADN monocaténaire. On a constaté in vivo comme in vitro, que les métabolites du 1,2-dibromoéthane étaient fixés à l'ADN par des liaisons covalentes. Des échanges entre chromatides soeurs, des mutations et une synthèse non programmée de l'ADN, ont été observées dans des cellules humaines in vitro. Des études de cancérogénicité ont été effectuées selon le schéma suivant: souris et rats ayant reçu par gavage une dose quotidienne de 1,2-dibromoéthane égale à 37-107 mg/kg de poids corporel (en moyenne pondérée par rapport au temps), pendant 49-90 semaines; souris ayant reçu dans leur eau de boisson une dose de 1,2-dibromoéthane de 103-117 mg/kg de poids corporel, quotidiennement pendant 15-17 mois; souris et rats exposés à une dose de 10-40 ppm pendant 6-18 mois par voie respiratoire ou encore, souris badigeonnées au 1,2-dibromoéthane pendant 400-594 jours, 3 fois par semaine à raison de 25-50 mg/souris. Ces études ont montré que le 1,2-dibromoéthane était cancérogène pour les rats et les souris et provoquait l'apparition de tumeurs au niveau de divers organes, soit au point d'application, soit à distance de ce point: cavité nasale, poumons, estomac, foie, peau, système circulatoire et glandes mammaires. Dans de nombreux cas, il y avait réduction du temps de latence des tumeurs. 6. Effets sur l'homme Le 1,2-dibromoéthane peut avoir des effets nocifs sur le système respiratoire, le système nerveux et les reins. Ainsi, une seule exposition, par la voie respiratoire, à ce composé (215 mg/m3, soit 28 ppm) pendant 30 min ou davantage, s'est révélée mortelle pour l'homme. L'ingestion d'une dose de 140 mg/kg de poids corporel s'est également révélée mortelle. Chez des travailleurs exposés de par leur profession, une exposition de longue durée au 1,2-dibromoéthane (5 ans), à la concentration de 0,68 mg/m3 dans la zone de respiration, a provoqué une diminution sensible du nombre de spermatozoïdes et une baisse de la fécondité. 7. Effets sur les êtres vivants dans leur milieu naturel Peu d'études d'ecotoxicité aquatique ont été consacrées au 1,2-dibromoéthane. Les valeurs de la CL50 pour les organismes aquatiques sont supérieures à 5 mg/litre. On ne possède aucune donnée au sujet des organismes terrestres. RESUMEN 1. Identidad, propiedades físicas y químicas y métodos analíticos El 1,2-dibromoetano (dibromuro de etileno) es un líquido incoloro (punto de fusión: 9,9°C; punto de ebullición: 131,4°C) con olor similar al del cloroformo. Es muy volátil, con una presión de vapor de 1,47 kPa (11 mmHg) a 25°C y una densidad de vapor, en comparación con el aire, de 6,1. El 1,2-dibromoetano es invisible en la mayor parte de los disolventes orgánicos. Su solubilidad en el agua es de 4,3 g/litro a 30°C. El 1,2-dibromoetano existente en el aire ambiental se analiza por cromatografía de gases tras su absorción por polímeros porosos, seguida por una rápida desasorpción térmica. Para las muestras de agua se utiliza un método de «purge-and-trap». Los residuos de 1,2-dibromoetano presentes en los alimentos y en otros medios pueden extraerse mediante disolventes o ser sometidos a un análisis automatizado de la fase gaseosa superior en condiciones criogénicas, seguido de análisis por cromatografía de gases y cromatografía líquida de alta resolución, previa derivación. 2. Fuentes de exposición humana y ambiental El 1,2-dibromoetano se utiliza para eliminar las sustancias antidetonantes derivadas del plomo presentes en la gasolina. Asimismo, se utiliza como fumigante de suelos y para la fumigación de granos y frutas. El consumo reducido de gasolina con plomo en algunos países y la anulación de inscripciones para la utilización de 1,2-dibromoetano con fines agrícolas ha reducido la exposición humana a esa sustancia. Sin embargo, aún se utiliza para eliminar el plomo de la gasolina en algunos países, como fumigante, para fines de cuarentena, como disolvente y como producto intermedio en las sustancias químicas industriales. 3. Niveles ambientales y degradación Las concentraciones de 1,2-dibromoetano medidas en el aire abarcan desde niveles indetectables hasta otros expresados en ng/m3 en las zonas urbanas. En zonas de explotación agrícola extensiva se han detectado concentraciones de 1,2-dibromoetano superiores a 0,2 µg/litro en aguas subterráneas y a 50 µg/litro en aguas superficiales. Aunque el 1,2-dibromoetano se filtra a través de la tierra, parte de él queda retenido en la matriz del suelo y puede contaminar posteriormente los pozos de riego. Se carece de información suficiente sobre la descomposición microbiana en los suelos. La alta volatilidad del 1,2-dibromoetano determina que el principal receptor ambiental sea la atmósfera. La fotólisis estratosférica puede dar lugar a la formación de productos de descomposición potencialmente destructores del ozono. 4. Cinética y metabolismo en animales de laboratorio El 1,2-dibromoetano se absorbe rápidamente por vía oral y cutánea y por inhalación. Se cree que los metabolitos desempeñan una función importante en la toxicidad de esa sustancia para los seres humanos. El 1,2-dibromoetano se puede metabolizar por vía oxidativa (sistema del citocromo P-450) y por vía conjugada (sistema de la glutatión S-transferasa). Según parece, dos metabolitos reactivos, el bromacetaldehído formado por oxidación y el ion de tiranio formado por conjugación interactúan con las macromoléculas celulares (proteínas, ADN) para formar productos de enlace covalente. 5. Efectos en mamíferos de laboratorio y en sistemas de pruebas in vitro El 1,2-dibromoetano tiene una toxicidad aguda para los animales (DL50 por vía oral en ratas de 146-417 mg/kg de peso corporal, CL50 por inhalación en ratas de 3080 mg/m3 tras una exposición de 2 h, y una mortalidad observada tras la aplicación cutánea de 210 mg/kg a conejos). Los efectos tóxicos del 1,2-dibromoetano se observaron principalmente en el hígado y en los riñones. La inhalación de vapor de 1,2-dibromoetano produjo irritación nasal y depresión del sistema nervioso central. En ratas expuestas a concentraciones de 1540 mg/m3 a 77 000 mg/m3 (200 a 10 000 partes por millón), con una duración de la exposición de 0,1 a 16,0 h, se produjeron muertes en todos los grupos, en función de la concentración y del tiempo. El 1,2-dibromoetano (solución al 1,0%) causó irritación de la piel abdominal afeitada e irritación ocular en conejos. Tras la exposición oral subcrónica, se observaron efectos mortales y menor adquisición de peso en ratas y ratones con dosis de 100 mg/kg de peso corporal al día. Asimismo, se observaron reducciones en la adquisición de peso y efectos patológicos nasales en ratas expuestas al 1,2-dibromoetano en una proporción de 115 mg/m3 (578 partes por millón) durante 6 h al día y 5 días por semana a lo largo de 13 semanas. El NOEL relativo a las alteraciones histopatológicas de la cavidad nasal fue de 23 mg/m3 (3 ppm) en ese estudio. En otro similar realizado en ratones se observaron los mismos cambios patológicos, también con un NOEL de 23 mg/m3 (3 ppm). Tras la administración por sonda a ratones o ratas de 1,2-dibromoetano en dosis de 37 a 107 mg/kg de peso corporal al día (promedio ponderado por el tiempo) durante un periodo de 49 a 90 semanas, o la administración a ratones en dosis de 103 a 117 mg/kg de peso corporal al día en el agua de beber durante un periodo de 15 a 17 meses, se observaron cambios no carcinogénicos tales como degeneración hepática, atrofia testicular, y acantosis e hiperqueratosis del preestómago, además de mortalidad. Tras la exposición por inhalación (ratones o ratas expuestos a dosis de 77 a 388 mg/m3 durante un periodo de 6 a 18 meses), se observaron inflamación de la tráquea y de la cavidad nasal, degeneración testicular y necrosis hepática. El 1,2-dibromoetano no resultó teratogénico en ratas o ratones tras la exposición por inhalación. Se observó toxicidad para el desarrollo (daños en el desarrollo de la coordinación motora) en la descendencia de ratas macho tratadas por vía intraperitoneal con 1,25 mg/kg de peso corporal al día y en la descendencia de ratas hembra tratadas mediante la inhalación de 509 mg/m3 durante 4 h al día y 3 días por semana desde el día 3 al día 20 de la gestación. El 1,2-dibromoetano influyó en el comportamiento reproductivo de las ratas (en los machos, con un nivel de exposición de 684 mg/m3 durante 7 h al día y 5 días/semana a los largo de 10 semanas, y en las hembras con un nivel de exposición de 614 mg/m3 durante 7 h al día y 7 días por semana a lo largo de 3 semanas). El NOEL para ese parámetro fue de 300 mg/m3 en ambos sexos. El NOEL para el comportamiento reproductivo de las ratas macho en un estudio de alimentación fue de 50 mg/kg al día tras una exposición de 90 días. La espermatogénesis resultó afectada en toros tras la administración de dosis orales de 2 mg/kg al día durante menos de 21 días, y en conejos tras la inyección subcutánea de 15 mg/kg durante 5 días. La administración de 1,2-dibromoetano a gallinas a través de la alimentación causó una disminución del tamaño de los huevos tras la exposición a 12,5 mg/kg al día durante 12 semanas. El 1,2-dibromoetano no indujo mutaciones dominantes letales en los ratones o las ratas, ni produjo aberraciones cromosómicas o micronúcleos en las células de médula ósea de ratones tratados in vivo. Sin embargo, resultó mutagénico en análisis bacterianos y causó roturas del ADN de una sola hebra. Los metabolitos del 1,2-dibromoetano se fijaron al ADN mediante enlaces covalentes, in vivo e in vitro. En células humanas in vitro se observó intercambio de cromátides hermanas, mutaciones y síntesis de ADN no programada. Los estudios de carcinogenicidad en los que se administró la sustancia por vía oral (ratones y ratas sometidas mediante sonda a dosis de 37 a 107 mg/kg de peso corporal al día (promedio ponderado por el tiempo) durante un periodo de 49 a 90 semanas; y ratones a los que se administró 1,2-dibromoetano en el agua de beber en dosis de 103 a 117 mg/kg de peso corporal al día durante un periodo de 15 a 17 meses), mediante exposición inhalacional (ratones y ratas expuestos a dosis de 10 a 40 partes por millón durante un periodo de 6 a 18 meses) o por vía cutánea de 25 a 50 mg/ratón, 3 veces por semana durante un periodo 400 a 594 días) mostraron que el 1,2-dibromoetano es carcinogénico para las ratas y los ratones y causa tumores en diversos órganos (tanto en la zona de aplicación como en zonas distantes, entre ellas, la cavidad nasal, los pulmones, el estómago, el hígado, la piel, el sistema circulatorio y las glándulas mamarias). En muchos casos reduce el periodo de latencia de tumores en desarrollo. 6. Efectos en el ser humano El 1,2-dibromoetano puede producir efectos adversos en los sistemas respiratorio, nervioso y renal. La exposición aguda (única) a la inhalación de 1,2-dibromoetano en dosis de 215 mg/m3 (28 ppm) durante 30 minutos o más ha resultado mortal para el ser humano. La ingestión de 140 mg/kg de peso corporal resultó asimismo mortal. La exposición duradera (5 años) de la zona respiratoria al 1,2-dibromoetano a una concentración de 0,68 mg/m3 redujo notablemente la densidad de espermatozoides y la fecundidad en los trabajadores expuestos en su entorno laboral. 7. Efectos en otros organismos en el medio ambiente Se han realizado pocos estudios sobre la ecotoxicidad acuática del 1,2-dibromoetano. La CL50 para los organismos acuáticos es superior a 5 mg/litro. No se dispone de información acerca de los organismos terrestres.