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    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY


    ENVIRONMENTAL HEALTH CRITERIA 91




    ALDRIN AND DIELDRIN









    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.

    Published under the joint sponsorship of
    the United Nations Environment Programme,
    the International Labour Organisation,
    and the World Health Organization

    World Health Orgnization
    Geneva, 1989


         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

    Aldrin and Dieldrin.

        (Environmental health criteria ; 91)

        1.Aldrin  2.Dieldrin  I.Series

        ISBN 92 4 154291 8        (NLM Classification: WA 240)
        ISSN 0250-863X

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CONTENTS

ENVIRONMENTAL HEALTH CRITERIA FOR ALDRIN AND DIELDRIN

 1. SUMMARY                    

     1.1. General           
     1.2. Environmental transport, distribution, and transformation    
     1.3. Environmental levels and human exposure   
     1.4. Kinetics and metabolism   
     1.5. Effects on organisms in the environment   
          1.5.1. Accumulation   
          1.5.2. Toxicity for microorganisms    
          1.5.3. Toxicity for aquatic organisms 
          1.5.4. Toxicity for terrestrial organisms 
          1.5.5. Population and ecosystem effects   
     1.6. Effects on experimental animals and  in vitro test systems           
     1.7. Effects on man    

 2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

     2.1. Identity          
          2.1.1. Primary constituent: aldrin    
          2.1.2. Primary constituent: dieldrin  
     2.2. Physical and chemical properties  
          2.2.1. Aldrin     
          2.2.2. Dieldrin   
     2.3. Analytical methods    
          2.3.1. Sampling methods   
          2.3.2. Analytical methods 

 3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE    

     3.1. Natural occurrence    
     3.2. Man-made sources  
          3.2.1. Production levels and processes; uses  
                 3.2.1.1  World production figures  
                 3.2.1.2  Manufacturing processes   
                 3.2.1.3  Release into the environment during
                          normal production 
          3.2.2. Uses       
                 3.2.2.1  Aldrin    
                 3.2.2.2  Dieldrin  

 4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION      

     4.1. Transport and distribution between media  
          4.1.1. Leaching of aldrin and dieldrin    
          4.1.2. Surface run-off    

          4.1.3. Loss of aldrin and dieldrin from soils -
                 volatilization 
                 4.1.3.1  Movement within the soil profile - mass 
                          flow  
                 4.1.3.2  Movement within the soil profile - 
                          diffusion  
                 4.1.3.3  Actual volatilization losses - laboratory 
                          studies    
                 4.1.3.4  Actual volatilization losses - field 
                          studies  
          4.1.4. Losses of residues following treatment of soil
                 with aldrin    
          4.1.5. Losses of residues from water  
          4.1.6. Aldrin and dieldrin in the atmosphere  
          4.1.7. Aldrin and dieldrin in water   
     4.2. Translocation from soil into plants   
     4.3. Models of the behaviour of water and chemicals in soil     
     4.4. Biodegradation of aldrin and dieldrin 
          4.4.1. Epoxidation of aldrin  
          4.4.2. Other metabolic pathways of aldrin     
          4.4.3. Biotransformation of dieldrin  
          4.4.4. Conclusions    
     4.5. Abiotic degradation   
          4.5.1. Photochemistry 
                 4.5.1.1  Photochemistry of aldrin and dieldrin in 
                          water  
                 4.5.1.2  Photochemistry of aldrin and dieldrin in 
                          air    
                 4.5.1.3  Photochemistry of aldrin and dieldrin on 
                          plant surfaces 
                 4.5.1.4  Photochemistry of aldrin and dieldrin in 
                          soils  
                 4.5.1.5  Conclusions   
          4.5.2. Other abiotic processes    
                 4.5.2.1  Reaction with ozone   
                 4.5.2.2  Clay-catalysed decomposition  
     4.6. Bioaccumulation   
     4.7. The fate of aldrin and dieldrin in the environment    
          4.7.1. Aldrin and dieldrin in soils   
          4.7.2. Aldrin and dieldrin in the atmosphere  
          4.7.3. Conclusion 

 5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE    

     5.1. Environmental levels  
          5.1.1. Air and rainwater  
                 5.1.1.1  Aldrin    
                 5.1.1.2  Dieldrin  
          5.1.2. Concentrations in houses   
                 5.1.2.1  Aldrin used for subterranean termite
                          control   
                 5.1.2.2  Aldrin and dieldrin used for remedial
                          treatment of wood 
          5.1.3. Aquatic environment    
          5.1.4. Soil       

          5.1.5. Drinking-water 
          5.1.6. Food and feed  
                 5.1.6.1  Joint FAO/WHO food contamination
                          monitoring programme  
                 5.1.6.2  Information summarized by GIFAP (1984)    
                 5.1.6.3  United Kingdom (UK MAFF, 1983-1985)   
                 5.1.6.4  USA   
                 5.1.6.5  Appraisal of intake studies   
          5.1.7. Concentrations of dieldrin in non-target species       
                 5.1.7.1  Occurrence of dieldrin in birds of prey 
                          and fish-eating birds    
     5.2. General population exposure   
          5.2.1. Adults     
                 5.2.1.1  Aldrin    
                 5.2.1.2  Concentrations of dieldrin in adipose 
                          tissue  
                 5.2.1.3  Concentrations of dieldrin in blood   
                 5.2.1.4  Concentrations of dieldrin in other 
                          tissues   
          5.2.2. Babies, infants, and mother's milk 

 6. KINETICS AND METABOLISM    

     6.1. Absorption        
          6.1.1. Aldrin     
                 6.1.1.1  Ingestion 
                 6.1.1.2  Inhalation    
          6.1.2. Dieldrin   
          6.1.3. Photodieldrin (and other metabolites of dieldrin)  
     6.2. Distribution      
          6.2.1. Aldrin     
                 6.2.1.1  Mouse 
                 6.2.1.2  Rat   
                 6.2.1.3  Dog   
                 6.2.1.4  Human studies 
          6.2.2. Dieldrin   
                 6.2.2.1  Laboratory animals    
                 6.2.2.2  Transplacental transport  
                 6.2.2.3  Domestic animals  
                 6.2.2.4  Human volunteers  
                 6.2.2.5  General population    
          6.2.3. Photodieldrin (and major metabolites of dieldrin)  
                 6.2.3.1  Laboratory animals    
                 6.2.3.2  Human beings  
     6.3. Metabolic transformation  
          6.3.1. Aldrin and dieldrin    
                 6.3.1.1  Laboratory animals    
                 6.3.1.2  Human studies 
                 6.3.1.3  Non-domestic organisms    
          6.3.2. Photodieldrin (and major metabolites of dieldrin)  
                 6.3.2.1  Rat   
                 6.3.2.2  Monkey    
     6.4. Elimination and excretion 
          6.4.1. Aldrin     
                 6.4.1.1  Rat   

          6.4.2. Dieldrin   
                 6.4.2.1  Laboratory animals    
                 6.4.2.2  Human studies 
          6.4.3. Photodieldrin (and major metabolites of dieldrin)  
                 6.4.3.1  Rat   
                 6.4.3.2  Monkey    
     6.5. Retention and turnover    
          6.5.1. Non-domestic organisms 
          6.5.2. Biological half-life in human beings   
          6.5.3. Body burden and (critical) organ burden; indicator 
                 media   
     6.6. Appraisal         

 7. EFFECTS ON ORGANISMS IN THE ENVIRONMENT    

     7.1. Microorganisms    
     7.2. Aquatic organisms 
          7.2.1. Aquatic invertebrates  
                 7.2.1.1  Acute toxicity    
                 7.2.1.2  Short-term toxicity, reproduction, and 
                          behaviour 
          7.2.2. Fish       
                 7.2.2.1  Acute toxicity  
                 7.2.2.2  Long-term toxicity
                 7.2.2.3  Reproduction    
          7.2.3. Amphibia and reptiles  
     7.3. Terrestrial organisms 
          7.3.1. Higher plants  
          7.3.2. Earthworms 
          7.3.3. Bees and other beneficial insects  
          7.3.4. Birds      
                 7.3.4.1  Acute toxicity    
                 7.3.4.2  Short- and long-term toxicity 
                 7.3.4.3  Reproductive studies  
                 7.3.4.4  Eggshell thinning 
                 7.3.4.5  Concentrations of dieldrin in tissues of 
                          experimentally poisoned birds  
          7.3.5. Mammals    
     7.4. Effect on populations and ecosystems  
          7.4.1. Exposure to dieldrin   
          7.4.2. Effects on populations of birds    
          7.4.3. Effects on populations of mammals  

 8. EFFECTS ON EXPERIMENTAL ANIMALS AND  IN VITRO TEST SYSTEMS      

     8.1. Single exposures  
          8.1.1. Aldrin and dieldrin    
                 8.1.1.1  Oral  
                 8.1.1.2  Dermal    
                 8.1.1.3  Inhalation    
                 8.1.1.4  Parenteral    
          8.1.2. Formulated materials   
                 8.1.2.1  Oral and dermal   
                 8.1.2.2  Inhalation    

     8.2. Short-term exposures  
          8.2.1. Oral       
                 8.2.1.1  Rat   
                 8.2.1.2  Dog   
                 8.2.1.3  Domestic animals  
          8.2.2. Dermal     
          8.2.3. Inhalation 
     8.3. Skin and eye irritation; sensitization    
          8.3.1. Skin and eye irritation    
          8.3.2. Sensitization  
     8.4. Long-term toxicity and carcinogenicity    
          8.4.1. Mouse      
                 8.4.1.1  Appraisal 
          8.4.2. Rat        
                 8.4.2.1  Appraisal 
          8.4.3. Hamster    
          8.4.4. Monkey     
          8.4.5. Mode of action 
     8.5. Reproduction, embryotoxicity, and teratogenicity  
          8.5.1. Reproduction   
                 8.5.1.1  Mouse 
                 8.5.1.2  Rat   
                 8.5.1.3  Dog   
                 8.5.1.4  Appraisal 
          8.5.2. Embryotoxicity and teratogenicity  
                 8.5.2.1  Mouse 
                 8.5.2.2  Rat   
                 8.5.2.3  Hamster   
                 8.5.2.4  Rabbit    
                 8.5.2.5  Appraisal 
     8.6. Mutagenicity and related end-points   
          8.6.1. Microorganisms 
          8.6.2. Mammalian cell point mutations 
          8.6.3. Dominant lethal assays and heritable translocation 
                 assays in mice   
          8.6.4. Micronucleus test  
          8.6.5. Chromosome and cytogenicity studies    
          8.6.6. Host-mediated assays   
          8.6.7. Cell transformation in mammalian cell systems      
          8.6.8.  Drosophila melanogaster and other insect systems       
          8.6.9. Effects on DNA 
          8.6.10. Cell to cell communication 
          8.6.11. Appraisal  
     8.7. Special studies   
          8.7.1. Liver enzyme induction 
          8.7.2. Nervous system 
                 8.7.2.1  Rat   
                 8.7.2.2  Dog   
                 8.7.2.3  Monkey    
          8.7.3. Weight loss and stress 
                 8.7.3.1  Rat   
          8.7.4. Immunosuppressive action   
     8.8. Toxicity of photodieldrin and major metabolites   

          8.8.1. Photodieldrin  
                 8.8.1.1  Acute toxicity    
                 8.8.1.2  Short-term toxicity   
                 8.8.1.3  Long-term toxicity    
                 8.8.1.4  Reproduction, embryotoxicity, and 
                          teratogenicity  
                 8.8.1.5  Appraisal 
          8.8.2. Major metabolites of dieldrin  
                 8.8.2.1  Acute toxicity    
                 8.8.2.2  Short-term toxicity   
     8.9. Mechanisms of toxicity; mode of action    
          8.9.1. Central nervous system 
          8.9.2. Liver      

 9. EFFECTS ON HUMAN BEINGS    

     9.1. General population exposure   
          9.1.1. Acute toxicity - poisoning incidents   
          9.1.2. Effects of short- and long-term exposure -
                 controlled human studies   
                 9.1.2.1  Accidental poisoning  
                 9.1.2.2  Controlled human studies  
          9.1.3. Tissue concentrations of dieldrin in hospitalized 
                 people    
                 9.1.3.1  Pathological findings 
                 9.1.3.2  Influence of weight loss and stress on
                          dieldrin concentrations in tissues    
          9.1.4. Exposure in treated homes  
     9.2. Occupational exposure 
          9.2.1. Acute toxicity - poisoning incidents   
                 9.2.1.1  Blood levels diagnostic of 
                          aldrin/dieldrin poisoning 
                 9.2.1.2  Electroencephalography    
          9.2.2. Effects of short- and long-term exposure   
          9.2.3. Epidemiological studies    

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  
     10.3. Conclusions       

11. RECOMMENDATIONS        

12. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES   

REFERENCES                      

APPENDIX I. NOMENCLATURE    

FRENCH TRANSLATION OF SUMMARY, EVALUATION, AND RECOMMENDATIONS

WHO TASK GROUP ON ALDRIN AND DIELDRIN

 Members

Dr G. Burin, Office of Pesticide Programs, US Environmental 
   Protection Agency, Washington DC, USA

Dr I. Desi, Department of Hygiene and Epidemiology, University 
   Medical School, Szeged, Hungary  (Vice-Chairman)

Dr S. Dobson, Institute of Terrestrial Ecology, Monks Wood 
   Experimental Station, Abbots Ripton, Huntingdon, United Kingdom 

Dr R. Goulding, Guy's Hospital, London, United Kingdom  (Chairman)

Dr A. Furtado Rahde, Ministry of Public Health, Porto Alegre, 
   Brazil 

Dr S.K. Kashyap, National Institute of Occupational Health, 
   Ahmedabad, India

Dr M. Takeda, Division of Environmental Chemistry, National 
   Institute of Hygienic Sciences, Tokyo, Japan

Dr H.G.S. Van Raalte, The Hague, Netherlands

 Observers

Dr R. Rimpau, European Chemical Industry, Ecology and Toxicology 
   Centre, Brussels, Belgium

Dr R.C. Tincknell, International Group of National Associations of 
   Agrochemical Manufacturers, Brussels, Belgium

Dr H.G.S. Van Raalte, International Commission on Occupational 
   Health, Geneva

 Secretariat

Dr J.R.P. Cabral, International Agency for Research on Cancer, 
   Lyons, France

Dr J. Copplestone, Pesticide Development and Safe Use Unit, World 
   Health Organization, Geneva, Switzerland

Dr M. Gilbert, International Programme on Chemical Safety, World 
   Health Organization, Geneva, Switzerland

Ms B. Goelzer, Office of Occupational Health, World Health 
   Organization, Geneva, Switzerland 

Dr H. Galal Gorchev, Food Safety Unit, World Health Organization, 
   Geneva, Switzerland

 Secretariat (contd.)

Dr K.W. Jager, International Programme on Chemical Safety, World 
   Health Organization, Geneva, Switzerland  (Secretary)

Dr G.J. van Esch, Bilthoven, Netherlands  (Rapporteur)

Dr N. Watfa, Safety and Health Branch, International Labour Office, 
   Geneva, Switzerland

NOTE TO READERS OF THE CRITERIA DOCUMENTS

    Every effort has been made to present information in the 
criteria documents as accurately as possible without unduly 
delaying their publication.  In the interest of all users of the 
environmental health criteria documents, readers are kindly 
requested to communicate any errors that may have occurred to the 
Manager of the International Programme on Chemical Safety, World 
Health Organization, Geneva, Switzerland, in order that they may be 
included in corrigenda, which will appear in subsequent volumes. 



                            * * *



    A detailed data profile and a legal file can be obtained from 
the International Register of Potentially Toxic Chemicals, Palais 
des Nations, 1211 Geneva 10, Switzerland (Telephone no. 7988400 -
7985850). 



                            * * *



    The proprietary information contained in this document cannot 
replace documentation for registration purposes because the latter 
has to be closely linked to the source, the manufacturing route, 
and the purity/impurities of the substance to be registered.  The 
data should be used in accordance with paragraphs 82 - 84 and 
recommendations paragraph 90 of the Second FAO Government 
Consultation (FAO, 1982). 

ENVIRONMENTAL HEALTH CRITERIA FOR ALDRIN AND DIELDRIN

    A WHO Task Group on Environmental Health Criteria for Aldrin 
and Dieldrin met in Geneva from 13 to 17 July 1987.  Dr K.W. Jager, 
IPCS, opened the meeting and welcomed the participants on behalf 
of the heads of the three IPCS cooperating organizations 
(UNEP/ILO/WHO).  The group reviewed and revised the draft criteria 
document and made an evaluation of the risks for human health and 
the environment from exposure to aldrin and dieldrin. 

    The first draft of this document was prepared by Dr G.J. VAN 
ESCH of the Netherlands on the basis of a review of all studies on 
aldrin and dieldrin including the proprietary information, made 
available to the IPCS by Shell International Chemical Company 
Limited, London, United Kingdom. 

    The second draft was also prepared by Dr van Esch, 
incorporating comments received following the circulation of the 
first draft to the IPCS contact points for Environmental Health 
Criteria documents. 

    Dr K.W. Jager and Dr P.G. Jenkins, both members of the IPCS 
Central Unit, were responsible for the technical development and 
editing, respectively, of this monograph. 

    The assistance of Shell in making available to the IPCS and the 
Task Group its toxicological proprietary information on aldrin and 
dieldrin is gratefully acknowledged.  This allowed the Task Group 
to make its evaluation on a more complete data base. 

    The efforts of all who helped in the preparation and 
finalization of the document are gratefully acknowledged. 



                             * * *



    Partial financial support for the publication of this criteria 
document was kindly provided by the United States Department of 
Health and Human Services, through a contract from the National 
Institute of Environmental Health Sciences, Research Triangle Park, 
North Carolina, USA - a WHO Collaborating Centre for Environmental 
Health Effects.  The United Kingdom Department of Health and Social 
Security generously supported the cost of printing. 

INTRODUCTION

    Aldrin and dieldrin are the common names of insecticides 
containing 95% HHDN and 85% HEOD, respectively. 

    Throughout this monograph the names aldrin and dieldrin are 
used, although concentrations determined in the different matrices 
are actually those of the active molecules HHDN and HEOD. 

    Aldrin is readily metabolized to dieldrin (HEOD) in plants and 
animals.  Only rarely are aldrin residues present in food or in the 
great majority of animals, and then only in very small amounts. 
Therefore, national and international regulatory bodies have 
considered these two closely related insecticides together.  The 
practicality of considering them jointly is further emphasized by 
the lack of significant difference in their acute and chronic 
toxicity and by their common mode of action. 

1.  SUMMARY

1.1.  General

    Aldrin and dieldrin, both organochlorine pesticides and 
manufactured commercially since 1950, were used throughout the 
world up to the early 1970s.  Both compounds were used as 
insecticides in agriculture for the control of many soil pests and 
in the treatment of seed.  Insects controlled by these compounds 
include termites, grasshoppers, wood borers, beetles, and textile 
pests.  Dieldrin has also been used in public health for the 
control of tsetse flies and other vectors of debilitating tropical 
diseases.  Both aldrin and dieldrin act as a contact and stomach 
poison for insects. 

    Since the early 1970s, both compounds have been severely 
restricted or banned, in a number of countries, from use, 
especially in agriculture.  Nevertheless, the use for termite 
control continues in other countries.  Global production, which was 
estimated to be 13 000 tonnes/year in 1972, decreased to less than 
2500 tonnes/year in 1984. 

    The purity of technical grade aldrin and dieldrin is 90% 
and > 95%, respectively.  Impurities for aldrin include 
octachlorocyclopentene, hexachlorobutadiene, and polymerization 
products, and for dieldrin polychloroepoxyoctahydrodimethano-
naphthalenes. 

    Both compounds are practically insoluble in water and 
moderately to highly soluble in most paraffinic, aromatic, and 
halogenated hydrocarbons, and in esters, ketones, and alcohols.  
The vapour pressure of aldrin is 6.5 x 10-5 mmHg at 25 C and that 
of dieldrin is 3.2 x 10-6 mmHg at 25 C. 

    Analytical methods for the determination of aldrin and dieldrin 
in food, feed, and the environment are described in section 2. 

1.2.  Environmental Transport, Distribution, and Transformation

    A major use of aldrin is as a soil insecticide.  Hence, aldrin-
treated soil is an important source of aldrin and its reaction 
product dieldrin in the environment. 

    Aldrin has a low propensity for movement away from treated 
areas, either through volatilization or by leaching.  It is mainly 
and rapidly adsorbed on soils with a high organic matter content, 
but only moderately adsorbed by clay soils.  Aldrin and dieldrin 
rarely penetrate more than 20 cm beneath the top treated layer of 
soil.  Aldrin adheres to soil particles to such an extent that only 
traces can be removed by water.  For this reason, contamination of 
ground water does not generally occur. 

    The disappearance of aldrin from soil resembles a first-order 
reaction.  Immediately after application, there is a short period 
of rapid loss due to volatilization and thereafter a second longer 

exponential period of decline, mainly due to conversion to 
dieldrin, which is slower to dissipate.  However, there is the 
possibility of migration by way of soil erosion, as wind drift, 
sediment transport, and surface run-off.  From data on residues of 
aldrin in the environment, it appears that it is mainly retained in 
the soil and that 97% of the primary residue is not the parent 
compound but its epoxide, dieldrin. 

    Photodieldrin is a photodegradation product of dieldrin and 
does not occur widely in the environment. 

    Aldrin applied to soils is lost slowly in temperate areas, 
three-quarters of the applied aldrin being lost during the first
year in a typical case.  The rate of loss slows later as aldrin is 
converted to dieldrin.  There is some evidence that the rate of loss
is greater under the anaerobic conditions of rice paddies than under
aerobic conditions.  Dieldrin is lost from the soil very rapidly in
tropical areas, up to 90% disappearing within 1 month, whereas the
half-life of dieldrin in temperate soils is approximately 5 years. 
Volatilization appears to be the principal route of loss from the
soil, though atmospheric levels of dieldrin and aldrin are generally
low.  Some dieldrin is washed from the atmosphere by rain, but
levels in ground water are very low because of strong adsorption to
soil particles.  Dieldrin has been detected, in small amounts, in
surface water contaminated by run-off from agricultural land. 

1.3.  Environmental Levels and Human Exposure

    Aldrin and dieldrin have been found in the atmosphere, in the 
vapour phase, adsorbed on dust particles, or in rainwater at 
variable levels according to the situation.  They have been 
detected mainly in agricultural areas, where the mean level in the 
air has been of the order of 1 - 2 ng/m3, with maximum levels of 
about 40 ng/m3.  In rainwater, concentrations of the order of 
10 - 20 ng/litre, or occasionally higher, have been found. 

    Concentrations found in the air in houses treated for the 
control of termites were much higher, ranging from 0.04 to 7 g/m3, 
depending on the time of sampling (i.e., the number of days of 
after application) and the type of house.  Within 8 weeks, the 
concentrations decreased rapidly.  Treatment of internal wood in 
houses resulted in dieldrin concentrations in the air ranging from 
0.01 to 0.5 g/m3.  Aldrin and dieldrin migrated into food from 
treated laminated timber and plywood, and by direct contact and/or 
sorption from the atmosphere. 

    The occurrence of dieldrin in the aquatic environment has been 
reported.  However, the concentrations were very low, mainly less 
than 5 ng/litre.  Higher levels have been generally attributed to 
industrial effluents or soil erosion during agricultural usage. 
River sediments may contain much higher concentrations (up to 1 mg/kg). 

    Aldrin is found only rarely in food, but dieldrin is more 
common, especially in dairy products, meat products, fish, oils and 
fats, potatoes, and certain other vegetables (especially the root 
vegetables).  Maximum residue limits (MRLs) in the range of 0.02 to 
0.2 mg/kg product have been recommended over the years by the 
FAO/WHO Joint Meetings on Pesticide Residues.  Recent studies in 
different countries have shown that the actual concentrations of 
dieldrin in these food commodities are generally lower.  Studies 
from the United Kingdom indicate this decrease clearly.  In 
1966 - 67, the mean level of dieldrin residues in a total diet 
study was 0.004 mg/kg food, whereas in the period 1975 - 77 it was 
0.0015 mg/kg, and in 1981, 0.0005 mg/kg.  This downward trend has 
been confirmed in other countries, for instance in the USA.  This 
may be due to the restriction or banning of the use of these 
compounds. 

    A large number of investigations has been reported in which the 
adipose tissue, organs, blood, or other tissues of the general 
population have been examined for the presence of dieldrin.  Over 
the last 25 years, surveys have been carried out in many countries 
all over the world.  Most of the mean values for adipose tissue 
have been in the range of 0.1 - 0.4 mg/kg.  Surveys in the 
Netherlands, the United Kingdom, and the USA have indicated a 
decline in concentrations in adipose tissue, since the mid-1970s. 
Blood concentrations range from 1 to 2 g/litre.  Levels in the 
liver are below 0.4 mg/kg, while those in other tissues, including 
the kidneys, brain, and gonads, are below 0.1 mg/kg tissue. 

    As a result of transplacental exposure, dieldrin is present in 
the blood, adipose tissue, and other tissues of the fetus and 
newborn infants.  The concentrations are one tenth to one half of 
those of their mothers.  There is no difference between infants and 
adults in the brain/liver/fat ratio of dieldrin concentrations. 
Dieldrin is also excreted in mother's milk.  Over the last 15 
years, samples of mother's milk have been analysed for the presence 
of organochlorine pesticides, including dieldrin, in various 
countries.  In most countries, the dieldrin concentration in milk 
amounts to 6 g/litre, though higher levels have occasionally been 
found. 

1.4.  Kinetics and Metabolism

    In both animals and human beings, aldrin and dieldrin are 
readily absorbed into the circulating blood from the 
gastrointestinal tract, through the skin, or through the lungs 
following inhalation of the vapour.  A study on human volunteers 
showed that absorption through the intact skin amounts to 7 - 8% of 
the applied dose.  Inhalation studies with human volunteers 
suggested that up to 50% of inhaled aldrin vapour is absorbed and 
retained in the human body.  After absorption, it is rapidly 
distributed throughout the organs and tissues of the body and a 
continuous exchange between the blood and other tissues takes 
place.  In the meantime, aldrin is readily converted to dieldrin, 
mainly in the liver but also to a much lesser extent in some other 
tissues, such as the lungs.  This conversion proceeds very rapidly. 

    When 1-day-old rats were given oral doses of 10 mg aldrin/kg 
body weight, their livers contained dieldrin 2 h after treatment. 
Over the course of the next few hours, dieldrin concentrated to a 
greater extent in the lipid tissues. 

    Numerous studies carried out with 14C-labelled aldrin and 
dieldrin have shown that part of the ingested material is passed 
unabsorbed through the intestinal tract and eliminated from the 
body, part is excreted unchanged from the liver into the bile, part 
is stored in the various organs and tissues particularly in the 
adipose tissue, and part is metabolized in the liver to more polar 
and hydrophilic metabolites.  In human beings and most animals, the 
metabolites are excreted primarily via the bile in the faeces.  It 
has also been shown that both aldrin and dieldrin are biodegraded 
into the same metabolites. 

    Most of the currently available information on the 
biodegradation metabolism in mammals is based on studies on 
dieldrin in the mouse, rat, rabbit, sheep, dog, monkey, chimpanzee, 
and in human beings.  The overall picture shows only quantitative 
variations between species, and the mechanisms in rats seem to be 
similar to those in primates. 

    The major metabolite, except in the case of the rabbit, is the 
9-hydroxy derivative.  This metabolite is found in the faeces and 
in a free or conjugated form in the urine.  Small amounts of three 
other metabolites have been found and identified in experimental 
animals.  These are the  trans-6,7-dihydroxy derivative, 
dicarboxylic acid derived from the dihydroxy compound, and the 
bridged pentachloroketone. 

    Only the 9-hydroxy compound has been demonstrated in the faeces 
of human beings and neither this nor the other metabolites have 
been found in human blood or other tissues.  Dieldrin was found to 
be present in the faeces of occupationally exposed workers, whereas 
the concentrations in the samples from the general population were 
below the limits of detection.  Examination of the urine of five 
workers indicated that urinary excretion of dieldrin and its four 
metabolites was minor compared to the elimination of the 9-hydroxy 
metabolite via the faeces. 

    The conversion of aldrin to dieldrin by mixed-function
monooxygenases (aldrin-epoxidase) in the liver and the distribution
and the subsequent deposition of dieldrin (mainly in lipid-
containing tissues, such as adipose tissue, liver, kidneys, heart, 
and brain) proceed much more rapidly than the biodegradation and 
ultimate elimination of unchanged dieldrin and its metabolites from 
the body.  Thus, at a given average daily intake of aldrin and/or 
dieldrin, dieldrin slowly accumulates in the body.  However, this 
accumulation does not continue indefinitely.  As dosing continues, 
a "steady state" is eventually reached at which the rates of 
excretion and intake are equal.  The upper limit of storage is 
related to the daily intake.  This has been demonstrated in rats, 
dogs, and human beings. 

    When the intake of aldrin/dieldrin ceases or decreases, the 
body burden decreases.  The biological half-life in man is 
approximately 9 - 12 months.  Significant relationships have been 
found between the concentrations of dieldrin in the blood and those 
in other tissues in rats, dogs, and human beings. 

    Numerous investigations of the concentrations of dieldrin in 
the blood, adipose tissue, and other tissues of members of the 
general population and from special groups, carried out in several 
different countries, have shown that at equilibrium the ratio of 
dieldrin concentrations in the adipose tissue, liver, brain, and 
blood is about 150:15:3:1. 

    Dieldrin is transported via the placenta and reaches the fetus. 
Accumulation takes place in the same organs and tissues as in the 
adult, but to a much lower level.  There seems to be an equilibrium 
between the levels in the mother and the fetus. 

    Photodieldrin is also metabolized into bridged pentachloroketone
in the rat and dog.  Both compounds were found in the adipose
tissue, liver, and kidneys when animals were administered high
levels of photodieldrin.  No residues of these compounds could be
detected in human adipose tissue, kidneys, or breast milk.  The
accumulation of photodieldrin in the adipose tissue of experimental
animals was much less than that of dieldrin. 

1.5.  Effects on Organisms in the Environment

1.5.1.  Accumulation

    Most residues in organisms are of dieldrin, since aldrin is 
readily converted to dieldrin in all organisms. 

    The uptake of dieldrin from medium into fungi, streptomycetes, 
and bacteria over 4 h has yielded concentration factors ranging 
from 0.3 to >100.  Protozoa take up more dieldrin than algae. 
Algae take up dieldrin from the culture medium very rapidly, maxima 
often being reached within a few hours. 

    Many species of aquatic invertebrates concentrate dieldrin from 
very low water concentrations, yielding high concentration factors. 
A steady state is reached within a few days.  On transfer to clean 
water, the loss of dieldrin is rapid, the half-life being 60 - 120 h. 

    Bioconcentration factors for whole fish are greater than 
10 000.  The half-life for loss of accumulated dieldrin was found 
to be 16 days for one species of fish. 

    The bioconcentration of dieldrin in aquatic organisms is 
principally from the water rather than by ingestion of food. 

    Earthworms take up dieldrin from the soil and concentrate it to 
a maximum of about 170 times.  There is little correlation between 
levels in earthworms and levels in most types of soil. 

    Many investigations have been carried out to estimate the 
occurrence of dieldrin in the tissues or eggs of non-target 
species.  The concentrations found cover a wide range from 0.001 
mg/kg up to 100 mg/kg tissue, but most are below 1 mg/kg tissue. 

    Both the body tissues and eggs of birds accumulate dieldrin 
readily.  Similarly, various mammal species have been shown to 
accumulate dieldrin, particularly in the fatty tissues. 

1.5.2.  Toxicity for microorganisms

    The effects of dieldrin on unicellular algae are very variable, 
some species being markedly affected by 10 g/litre and others 
unaffected even by 1000 g/litre.  Aldrin and dieldrin have only 
minor effects on soil bacteria, even at levels far exceeding those 
normally encountered.  Most studies have shown no effects at 
exposure levels of 2000 mg/kg soil.  Effects on photosynthesis have 
been reported in several different species of algae, with aldrin 
showing a more marked effect than dieldrin at the same 
concentration.  However, these slight effects on the biochemical 
processes of soil algae were only transitory. 

1.5.3.  Toxicity for aquatic organisms

    Aldrin and dieldrin are highly toxic for aquatic crustaceans, 
most 96-h LC50 values being below 50 g/litre.  However, a few 
reported results of up to 4300 g/litre illustrate species 
variability.  Daphnids are less sensitive to dieldrin than aldrin, 
with 48-h tests yielding LC50 values of 23 - 32 g/litre for aldrin 
and 190 - 330 g/litre for dieldrin.  Molluscs are significantly 
more resistant, with 48 h values ranging up to >10 000 g/litre. 
The results of studies over several weeks have confirmed the 
relative resistance of daphnids and molluscs.  The most susceptible 
aquatic invertebrates are the larval stages of insects with 96-h 
values of 0.5 - 39 g/litre for dieldrin and 1.3 - 180 g/litre for 
aldrin. 

    Both aldrin and dieldrin were highly toxic in acute tests on 
fish.  Values for 96-h LC50s in various fish species varied from 
2.2 to 53 g/litre for aldrin, and from 1.1 to 41 g/litre for 
dieldrin.  Several studies have revealed that toxicity increases 
with increasing temperature.  In a long-term study on  Poecilia 
 latipinna, there was 100% mortality at dieldrin concentrations of 
3 g/litre or more.  Dieldrin administered in the food of rainbow 
trout at up to 430 g/kg body weight per day did not have any 
effects on mortality, but enzymic changes were reported. 
Morphological changes in liver mitochondria were seen using the 
electron microscope.  The ammonia-detoxifying mechanism of fish is 
sensitive to dieldrin, the no-observed-adverse-effect level being 
less than 14 g/kg body weight per day.  Different life stages of 
fish have been found to have different susceptibilities to 
dieldrin.  Eggs were resistant and juvenile stages were less 
susceptible than adults. 

    The acute toxicity of both aldrin and dieldrin is high for 
larval amphibia with 96-h LC50s of the order of 100 g/litre. 

1.5.4.  Toxicity for terrestrial organisms

    The toxicity of dieldrin for higher plants is low, crops only 
being affected at application rates greater than 22 kg/ha.  Aldrin 
is more phytotoxic, to tomatoes and cucumbers particularly, but 
only at application rates many times greater than those 
recommended.  Cabbage is the most sensitive crop to aldrin. 

    Oral LD50s for honey bees ranging from 0.24 to 0.45 g/bee for
aldrin and from 0.15 to 0.32 g/bee for dieldrin have been reported.
Contact toxicity ranged from 0.15 to 0.80 g/bee for aldrin and from
0.15 to 0.41 g/bee for dieldrin.  Two studies have indicated that
dieldrin is relatively non-toxic for predatory insects eating pest
species.

    In laboratory studies, earthworms tolerated aldrin at a level 
of 13 mg/kg of artificial soil with <1% mortality.  The 6-week 
LC50 was 60 mg aldrin/kg soil. 

    The acute toxicities of aldrin and dieldrin have been found to 
vary by more than an order of magnitude for 13 species of birds, 
ranging from 6.6 to 520 mg/kg body weight for aldrin and from 6.9 
and 381 mg/kg body weight for dieldrin.  In four bird species, 
subacute oral toxicity varied between 34 and 155 mg/kg for aldrin 
and 37 and 169 mg/kg for dieldrin.  Repeated testing over a period 
of time did not indicate the development of resistance in these 
species.  Reproductive studies on several species of domestic birds 
have indicated that levels of dieldrin in the diet of more than 
10 mg/kg cause some adult mortality.  There are no reproductive 
effects on egg production, fertility, hatchability, or chick 
survival at levels of dietary dieldrin not causing maternal 
toxicity.  Eggshell thickness is not directly affected by dieldrin. 
However, reduced food consumption is a symptom of dieldrin 
poisoning, and eggshell thickness can be reduced by decreased food 
intake. 

    Among non-laboratory mammals, the response to dieldrin varies 
from species to species.  Four vole species showed acute LD50s 
ranging from 100 to 210 mg/kg body weight, making them less 
susceptible to dieldrin than laboratory species.  Shrews survived a 
diet containing 50 mg dieldrin/kg but died with a dietary level of 
200 mg/kg.  Blesbuck (antelope) survived for 90 days at 5 and 15 
mg/kg diet but all died within 24 days at levels of 25 mg/kg or 
more.  All blesbuck in an area sprayed with dieldrin at 0.16 kg/ha 
died, the calculated dietary intake being 1.82 mg/kg per day. Thirty
percent of springbok survived the spray with no after-effects. 
Toxicological signs of dieldrin poisoning were similar to those of
laboratory mammals. 

1.5.5.  Population and ecosystem effects

    It has been suggested that some mammal populations have been 
affected by dieldrin.  Small mammals were probably killed by eating 
dieldrin-dressed seed, but populations were replenished by 
immigration.  Bats have been killed by dieldrin in wood preservatives. 

    Residues of dieldrin have been reported in many species of 
birds.  Throughout the world, the highest residues have been found 
in birds of prey at the top of foodchains.  The dieldrin content of 
bird tissues and eggs has paralleled usage patterns and decreased 
with restrictions in the use of aldrin and dieldrin.  It is not 
easy to identify the effects of dieldrin, because residues occur 
together with residues of other organochlorines.  Dieldrin is more 
toxic to birds than DDT and probably has been responsible for more 
adult deaths that DDT.  However, the reproductive effects of 
dieldrin in the field are more difficult to prove.  There are 
seasonal changes in the contents of dieldrin in bird tissues. 
Furthermore, effects can occur long after exposure to the source of 
the pollutant. 

1.6.  Effects on Experimental Animals and  In Vitro Test Systems

    Aldrin and dieldrin are of a high order of toxicity; the oral 
LD50s for both compounds in the mouse and rat range from 40 to 70 
mg/kg body weight.  The dermal toxicity is in the range of 40 - 150 
mg/kg body weight, depending on the animal species and the solvent 
used.  Technical aldrin and dieldrin were found to produce slight 
to severe irritation in the rabbit skin, but this effect was mainly 
caused by the solvent.  In the Magnusson & Kligman guinea-pig 
maximization test, aldrin produced a sensitization effect.  
However, during 20 years of manufacture and formulation, no cases 
of skin sensitization occurred in a group of over 1000 workers. 

    The vapour pressures of both aldrin and dieldrin are low and 
acute inhalation effects do not normally arise.  The effects 
observed in acute toxicity studies by all routes involve the 
central nervous system and include hyperexcitability, tremors, and 
convulsions. 

    Short- and long-term oral studies have been carried out with 
aldrin and dieldrin on the mouse, rat, dog, hamster, and monkey. 
The liver is the major target organ in the rat and mouse, with an 
increased liver/body weight ratio and hypertrophy of the 
centrilobular hepatocytes occurring, which in the early stages may 
be reversible.  Microscopically these changes include increased 
cytoplasmatic oxyphilia and peripheral migration of basophilic 
granules.  These changes were not found in the liver of the hamster 
and the monkey.  In the dog, mild liver changes (fatty changes and 
slight hepatic cell atrophy) were accompanied by kidney changes 
consisting of vacuolization in the epithelia of distal renal 
tubules and tubular degeneration.  In the rat, the overall no-
observed-adverse-effect level from the available short-term and 
long-term studies is 0.5 mg/kg diet, equivalent to 0.025 mg/kg body 

weight.  With feeding levels equivalent to 0.05 mg/kg body weight 
or more, an increasing dose-related hepatomegaly and histological 
changes occurred.  In the dog, no-effect levels of 0.04 - 0.2 mg/kg 
body weight were found. 

    A number of long-term carcinogenicity studies on mice of 
different strains were carried out with aldrin or dieldrin.  In all 
studies, benign and/or malignant liver cell tumours were found. 
Females seemed to be less sensitive than males.  No other types of 
tumours were induced. 

    Long-term studies on the other animal species (rat, hamster) 
did not show any increase in tumour incidence.  Photodieldrin, fed 
at concentrations up to 7.5 mg/kg diet, did not induce tumours. 

    In addition, a number of special studies have been published 
that have so far failed to elucidate the mechanism of the induction 
of the liver tumours in mice. 

    In most of the reproduction studies (over 1 - 6 generations) 
carried out with aldrin or dieldrin on mice and rats, the major 
effect was an increased mortality rate in pre-weaning pups. 
Reproductive performance was only affected at doses causing 
maternal intoxication.  Studies on dogs were too limited to draw 
firm conclusions, apart from a consistent increase in pre-weaning 
pup mortality. 

    It can be concluded from the results of these reproduction 
studies that 2 mg dieldrin/kg in the rat diet and 3 mg dieldrin/kg 
in the mouse diet, equivalent to 0.1 and 0.4 mg/kg body weight per 
day, respectively, are no-observed-adverse-effect levels for 
reproduction. 

    No evidence of teratogenic potential was found in studies on 
the mouse, rat, or rabbit using oral doses of aldrin and dieldrin 
of up to 6 mg/kg body weight.  Single doses of aldrin and dieldrin, 
equal to about half the LD50, caused severe fetotoxicity and an 
increased incidence of teratogenic abnormalities in the mouse and 
hamster.  The significance of these findings in the presence of 
likely maternal toxicity is doubtful. 

    Many  in vivo and  in vitro mutagenicity studies have been 
carried out, but the results of nearly all these studies were 
negative. 

    The acute oral toxicity of photodieldrin is higher than that of 
dieldrin in the mouse, rat, and guinea-pig.  In acute and short-
term toxicity studies, the symptoms of intoxication and the effects 
on target organs are quantitatively and qualitatively similar to 
those of dieldrin.  Photodieldrin did not induce tumours in mice 
and rats. 

    Like most other chemical substances, aldrin and dieldrin do not 
have a single mechanism of toxicity.  The target organs are the 
central nervous system and the liver.  In human beings and other 

vertebrates, intoxication following acute or long-term overexposure 
is characterized by involuntary muscle movements and epileptiform 
convulsions.  Survivors recover completely after a short period of 
time of residual signs and symptoms.  In the liver there is an 
increased activity of microsomal biotransformation enzymes, 
particularly of the monooxygenase system with cytochrome P-450. 
This induction of the microsomal enzymes is reversible and, if it 
exceeds a certain level, it appears to be linked to cytoplasmic 
changes and hepatomegaly in the liver of rodents. 

    All the available information on aldrin and dieldrin taken 
together, including studies on human beings, supports the view that 
for practical purposes these chemicals make very little 
contribution, if any, to the incidence of cancer in man. 

1.7.  Effects on Man

    Aldrin and dieldrin are highly toxic for human beings.  Severe 
cases of both accidental and occupational poisoning have occurred 
but only rarely have fatalities been reported.  The lowest dose 
with a fatal outcome has been estimated to be 10 mg/kg body weight. 
Survivors of acute or subacute intoxications recovered completely. 
Irreversible effects or residual pathology have not been reported. 

    Adverse effects from aldrin and dieldrin are related to the 
level of dieldrin in the blood.  Determination of the level of 
dieldrin in the blood provides a specific diagnostic test of 
aldrin/dieldrin exposure.  The level of dieldrin in the blood of 
male workers below which adverse effects do not occur, (the 
threshold no-observed-adverse-effect level) is 105 g/litre blood. 
This corresponds to a daily intake of 0.02 mg dieldrin/kg body 
weight per day. 

    Environmental exposure (mainly dietary though also, to a small 
extent, respiratory) leads to the presence of dieldrin at very low 
levels in organs, adipose tissue, blood, and mother's milk.  As far 
as can be judged from the extensive clinical and epidemiological 
studies, there is no reason to believe that these prevailing body 
burdens constitute a health hazard for the general population.  In 
a continuing study lasting more than 20 years, involving more than 
1000 industrial workers in an aldrin/dieldrin insecticide-
manufacturing plant, no increase in cancer incidence occurred among 
workers who had been exposed to high levels of aldrin and dieldrin. 
More significantly, there were no signs of any premonitory change 
in liver function in these workers. 

    An epidemiological mortality study was carried out at a 
manufacturing plant in the USA on a cohort of 870 workers exposed 
to aldrin, dieldrin, and endrin.  With almost 25 000 man-years of 
observation, no specific cancer risk associated with employment at 
this plant could be identified. 

2.  IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

2.1.  Identity

2.1.1.  Primary constituent: aldrina

Chemical Structure

Chemical formula:         C12H8Cl6

Relative molecular mass:  364.9

IUPAC chemical nameb:     (1 R,4 S,4a S,5 S,8 R,8 R,a R)-1,2,3,4,10,
                          10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,
                          4:5,8-dimethanonaphthalene or 1,2,3,4,10,
                          10-hexachloro-1,4,4a,5,8,8a-hexahydro-
                           exo-1,4- endo-5,8-dimethanonaphthalene

Common synonyms
and trade names:          ENT 15 949 (compound 118), HHDN, 
                          Octalene, OMS 194

CAS registry number:      309-00-2

RTECS registry number:    I02100000

 Technical product

Common trade name:        Aldrin.  This is the common name of an
                          insecticide containing 95% of HHDN.

Purity:                   The minimum content of aldrin (as defined
                          above) in technical aldrin is 90%.

Impurities:               octachlorocyclopentene (0.4%), 
                          hexachlorobutadiene (0.5%), toluene (0.6%), 
                          a complex mixture of compounds formed by 
                          polymerization during the aldrin reaction 
                          (3.7%) and carbonyl compounds (2%) 
                          (FAO/WHO, 1968b)

-------------------------------------------------------------------
a From:  Worthing & Walker (1983).
b Other chemical names are given in Appendix I.

2.1.2.  Primary constituent: dieldrina

Chemical Structure

Chemical formula:         C12H8OCl6

Relative molecular mass:  380.9

IUPAC chemical nameb:     (1 R,4 S,4a S,5 R,6 R,7 S,8 S,8a R)-1,2,3,
                          4,10,10-hexachloro-1,4,4a,5,6,7,8,8a-
                          octahydro-6,7-epoxy-1,4:5,8-
                          dimethanonaphthalene or 1,2,3,4,10,10-
                          hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-
                          octahydro- endo-1,4- exo-5,8,-
                          dimethanonaphthalene

Common synonyms           ENT 16 225 (compound 497), HEOD, Alvit,
and trade names:          Octalox, OMS 18, Quintox

CAS registry number:      60-57-1

RTECS registry number:    I01750000

 Technical product

Common trade name         Dieldrin.  This is the common name of an
                          insecticide containing 85% of HEOD.

Purity:                   Technical dieldrin contains not less than
                          95% of dieldrin, as defined above.

Impurities:               other polychloroepoxyoctahydrodimethano-
                          naphthalenes, endrin 3.5% (FAO/WHO, 
                          1968b)

-------------------------------------------------------------------
a From:  Worthing & Walker (1983).
b Other chemical names are given in Annex I.

2.2.  Physical and Chemical Properties

2.2.1.  Aldrin

    Pure aldrin is a colourless crystalline solid.  It has a 
melting point of 104 - 104.5 C. 

    Technical aldrin (90%) is a tan to dark brown solid with a 
melting point of 49 - 60 C.  Its vapour pressure is 8.6 mPa at 
20 C (6.5 x 10-5 mmHg at 25 C).  Its density is 1.54 g/ml at 
20 C.  Its solubility in water is 27 g/litre at 27 C 
(practically insoluble), and in acetone, benzene, and xylene 
is > 600 g/litre.  Aldrin is stable at < 200 C and at pH 4 - 8, 
but oxidizing agents and concentrated acids attack the 
unchlorinated ring.  Aldrin is non-corrosive or slightly corrosive 
to metals because of the slow formation of hydrogen chloride on 
storage (Shell, 1976, 1984; Worthing & Walker, 1983). 

2.2.2.  Dieldrin

    Technical dieldrin (95%) consists of buff to light tan flakes 
(setting point > 95 C) with a mild odour.  Its melting point is 
175 - 176 C.  Its vapour pressure is 0.4 mPa at 20 C (3.2 x 10-6 
mmHg at 25 C).  Its density is 1.62 g/ml at 20 C.  Its solubility 
in water is 186 g/litre at 20 C (practically insoluble), but it 
is moderately soluble in most paraffinic and aromatic hydrocarbons, 
halogenated hydrocarbons, ethers, esters, ketones, and alcohols. 
Dieldrin is stable to alkali, mild acids, and to light.  It reacts 
with concentrated mineral acids, acid catalysts, acid oxidizing 
agents, and active metals (iron, copper).  It is non-corrosive or 
slightly corrosive to metals in the same way as aldrin (Shell, 
1976; Worthing & Walker, 1983). 

2.3.  Analytical Methods

2.3.1.  Sampling methods

    Methods of sampling and storage have been reviewed by Beynon & 
Elgar (1966).  Sample collection is broadly divisible into two types: 
adventitious sampling (particularly of wildlife) and systematic 
sampling (soil, total diet surveys) in which samples are collected 
in accordance with the principles of statistical design.  Surveys 
of dieldrin in human blood and adipose tissue are a partial 
combination of these two classes of sample collection.  The 
sampling methods for total diet surveys were reviewed by Cummings 
(1966), and the sampling of air for pesticide residues has been 
discussed in detail by Lewis (1976). 

2.3.2.  Analytical methods

    Since the introduction of the method of gas-liquid 
chromatography with electron capture detection (GLC/EC) (Goodwin et 
al., 1961), old methods, based on, for instance, total organic 
chlorine or the colorimetric phenyl azide procedure, have been 
abandoned.  The great majority of analytical data relating to the 

occurrence of residues of aldrin or dieldrin since that time have 
been based on GLC/EC procedures.  There has been considerable 
evolution of various aspects (especially extraction and clean up 
procedures) of the methodology.  The many publications on specific 
procedures are reviewed in the Codex Publication "Recommendations 
for methods of analysis of pesticide residues", CAC/PR 8-1986, 
(FAO/WHO, 1986b).  This review lists 22 individual publications, 
four of which refer to simplified methods.  It also lists the 
following compendia of methods which may also be consulted. 

-   Official methods of analysis of the Association of Official 
    Analytical Chemists, 14th Edition 1984.

-   Pesticide analytical manual, Food & Drug Administration, 
    Washington DC, USA.

-   Manual on Analytical methods for pesticide residues in foods, 
    Health Protection Branch, Health and Welfare, Ottawa, Canada,
    1985.

-   Methodensammlung zur Rueckstandsanalytik von 
    Pflanzenschutzmitteln (Methods for analysing residues of plant 
    protective agents) 1984 Verlag Chemie GmbH, Weinheim, Federal 
    Republic of Germany. 

-   Chemistry Laboratory Guidebook, USDA.

    Whatever procedure is adopted should be carried out within the 
requirements of the CAC publication "Codex Guidelines on Good 
Laboratory Practice in Pesticide Residue Analysis", CAC/PR 7-1984, 
(FAO/WHO, 1984). 

    It is important to recognize that the electron capture detector 
is not specific for aldrin and dieldrin and in the analysis of 
samples without a precise history of treatment, confirmation of the 
identity of the residue is an essential part of the analysis. 
Reports of the occurrence of aldrin in environmental samples in the 
past, are now thought, in many cases, to have been instances of 
misidentification.  The occurrence of PCBs in the same sample has 
been a particularly troublesome source of interference.  Many 
procedures for the confirmation of identity are available and 
include comparison of the position of the peak on different 
chromatographic columns, thin-layer chromatography, and 
derivatization.  The most definitive method, however, involves the 
uses of mass spectrography as the detector.  With this procedure, 
much of the uncertainty with regard to the identification of the 
residue has been eliminated.  The mass spectrography procedure 
described by Hargesheimer (1984) is effective for the determination 
of chlorinated hydrocarbon residues in the presence of PCBs.  The 
limit of determination of individual methods depends to a 
considerable extent on the amount of effort the analyst devotes to 
extraction and clean-up procedures.  With samples of food and 
feeds, for example, a limit of determination of 0.01 mg/kg is 
normally regarded as acceptable, but in water and air far lower 
levels are achievable, depending on the care and effort taken. 

    It should be recognized that there is considerable variation in 
the results that can be obtained on the same sample by different 
analysts and in different laboratories and variations of 100% are 
by no means uncommon at the lower end of the scale.  A valuable 
account of the variation found among 120 laboratories for a sample 
of butterfat containing known amounts of 11 different chlorinated 
hydrocarbon insecticides was given by Elgar (1979). 

3.  SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

3.1.  Natural Occurrence

    Aldrin and dieldrin are not known to occur as natural products. 

3.2.  Man-Made Sources

3.2.1.  Production levels and processes; uses

3.2.1.1  World production figures

    The first laboratory synthesis of aldrin and dieldrin was in 
1948 by J. Hyman & Co. (Thompson, 1976).  The method was licensed 
to Shell and manufacture began in 1950, first in the USA and later 
on in the Netherlands (IARC, 1974). 

    Production has decreased since the early 1960s.  The production 
capacity was 20 000 tonnes in 1971, and the estimated 1972 
production was 13 000 tonnes.  In 1984, less than 2500 tonnes of 
aldrin and dieldrin were manufactured, approximately one third of 
which was used in Australia, the United Kingdom, and the USA (Van 
Duursen, 1985). 

    Up to the late 1960s and early 1970s, aldrin and dieldrin were 
used throughout the world.  Since then, many countries have 
severely restricted or banned their use, especially in agriculture, 
because of their persistent character in the environment (IARC, 
1974).  The main remaining uses are in the control of disease 
vectors and termites and industrial applications. 

3.2.1.2  Manufacturing processes

    Aldrin is synthesized by the Diels-Alder reaction of 
hexachlorocyclopentadiene with an excess of bicycloheptadiene at 
100 C.  The yield is more than 80%, calculated on the 
hexachlorocyclopentadiene (Melnikov, 1971). 

    Commercial production of dieldrin is believed to be through 
epoxidation of aldrin with a peracid (e.g., peracetic or perbenzoic 
acid), but an alternate synthetic route involves the condensation 
of hexachlorocyclopentadiene with the epoxide of bicycloheptadiene 
(Galley, 1970). 

3.2.1.3  Release into the environment during normal production

    Loss of aldrin and dieldrin, together with isobenzan, in waste 
water from a manufacturing plant in the Botlek area of the 
Netherlands caused deaths among sandwich terns  (Sterna 
 sandvicentis), eider ducks  (Somateria mollissima), and, to a lesser 
extent, some other bird species, feeding on marine organisms 
containing high levels of these insecticides in the Wadden Sea 
during 1962 - 65.  Following improvement of the waste-water 
purification of the plant, the residue levels in the marine 
organisms decreased during subsequent years (Koeman, 1971). 

3.2.2.  Uses

3.2.2.1  Aldrin

    Aldrin is a highly effective broad-spectrum soil insecticide. 
It kills insects by contact and ingestion, and possesses slight 
fumigant action within the soil, which ensures distribution in the 
top soil where the pests are found. 

    It is used to control soil insects, including termites, corn 
rootworms, seed corn beetle, seed corn maggot, wireworms, rice 
water weevil, grasshoppers, and Japanese beetles, etc.  Crops 
protected by aldrin soil treatment include corn and potatoes; it is 
used as a seed dressing on rice.  Aldrin is also used for the 
protection of wooden structures against termite attack.  It is 
supplied mainly as an emulsifiable concentrate or wettable powder. 

3.2.2.2  Dieldrin

    Dieldrin is used mainly for the protection of wood and 
structures against attack by insects and termites and in industry 
against termites, wood borers, and textile pests (moth-proofing). 
It acts as a contact and stomach poison. 

    Dieldrin is no longer used in agriculture.  It has been used as 
a residual spray and as a larvacide for the control of several 
insect vectors of disease.  Such uses are no longer permitted in a 
number of countries. 

    It is available as an emulsifiable concentrate or wettable 
powder. 

4.  ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

4.1.  Transport and Distribution Between Media

4.1.1.  Leaching of aldrin and dieldrin

    As would be expected from their very low water solubility, 
hydrophobic character, and strong adsorption by soil, aldrin and 
dieldrin are very resistant to downward leaching through the soil 
profile. 

    Since one of the major uses of aldrin is as a soil insecticide, 
aldrin-treated soil is an important source of aldrin in the 
environment. 

    Bowman et al. (1965) studied the leaching of aldrin through six 
different types of soil, by passing water through them.  In five 
out of six soil types, only traces were recovered in the leachates. 
However, 16% of applied aldrin was found in the leachate from a 
sandy soil type.  Other studies indicate that leaching of aldrin 
through soil is minimal (Harris, 1969; Herzel, 1971; El Beit et 
al., 1981a,b). 

    A study was carried out to determine the possible involvement 
of aldrin applied for the control of termites around house 
foundations.  Seven types of soil collected from different 
geographical areas in the USA were investigated by placing the 
soils (adjusted to 0, 5, 10, or 15% water content) in glass 
columns.  The soil columns were separated into five layers of 5 cm 
by filter paper support cloth.  An emulsion of aldrin was placed on 
the top of the column, equivalent to 0.365 kg aldrin/m2.  The 
layers of soil were removed approximately 24 h after application of 
the emulsion and the concentration of aldrin determined. 
Penetration below 20 cm did not occur in any soil at any of the 
water contents.  In certain soils, penetration only took place in 
the first 5 cm and, in others, in the third layer (10 - 15 cm).  
Water content also plays a role in the penetration.  In another 
study, layers of 4 cm were used, with comparable results (Carter & 
Stringer, 1970). 

    Several field studies on the leaching of aldrin through 
different types of soil have been carried out.  In these studies, 
aldrin was applied to the surface or tilled to a depth of about 15 
cm at dose levels of 1.8 - 20.7 kg/ha.  From the results, it is 
clear that, even up to 5 years after application, aldrin and 
dieldrin were still present in the treated layer, with little 
penetration to layers immediately below the treated layer.  From 
these studies, it appears that there is little movement 
(Lichtenstein et al., 1962; Daniels, 1966; Park & McKone, 1966). 
However, Wiese & Basson (1966) found some movement, even in clay 
soil. 

    In studies by Powell et al. (1979), sandy soil in which tomato 
plants were growing was sprayed with an aldrin emulsion (2.2 kg/ha) 
on six occasions at intervals of 1 - 2 weeks.  Approximately one 

year after the final treatment, soil core samples were taken and 
the concentrations of aldrin and dieldrin in the 0 - 5, 5 - 10, 
10 - 15, 15 - 22.5 cm layers were determined.  About 73% of the 
total residue in the 0 - 22.5 cm layer was in the 0 - 15 cm layer.  
The ratio of aldrin to dieldrin in the four strata was similar.  
The remark should be made that in this study there were a number of 
confounding factors (e.g., the field was ploughed). 

    Stewart & Fox (1971) applied aldrin as a spray to four turf 
plots at doses of 3.3, 4.4, or 6.6 kg/ha.  Loam and silt soil core 
samples were taken to a depth of 30 cm 9 - 13 years after 
treatment.  Aldrin was not detected; 93 - 100% of the total 
dieldrin in the 30 cm core was in the top 15 cm layer of soil. 

    In studies by Lichtenstein et al. (1971), aldrin was applied to 
a silt loam at a rate of 4.4 kg/ha and rototilled to a depth of 
10 - 12.5 cm.  After 10 years, the percentage of the applied aldrin 
in the 0 - 22.5 cm layer was 0.18% as aldrin and 5.2% as dieldrin. 
The ratios of concentrations in the 0 - 15 cm layer relative to the 
15 - 22.5 cm layer were:  aldrin, 2.5; dieldrin, 4.9. 

    14C-Aldrin was incorporated to a depth of 15 cm in experimental 
plots in which potatoes were grown in the Federal Republic of 
Germany (sandy loam; equivalent to 2.9 kg/ha) and England (sandy 
clay loam; equivalent to 3.2 kg/ha).  After 6 months, the 
concentrations of aldrin in both cases were as follows:  at 0 - 10 
cm, 0.58 and 0.59 mg/kg; at 10 - 20 cm, 0.23 mg/kg and < 0.01 
mg/kg; at 20 - 40 cm 0.02 and < 0.01 mg/kg and at 40 - 60 cm, < 0.01 
mg/kg (in both locations) (Klein et al., 1973).  In a parallel 
study, the 14C activity in leach water collected at a depth of 60 
cm was determined over a 3-year period; the cumulative rainfall 
during this period was 160 cm.  About 10% of the 14C activity, 
applied initially to a depth of 15 cm, was found in the leachate 
over a period of 3 years.  Almost all the 14C activity was present 
as dihydrochlordene dicarboxylic acid (Moza et al., 1972). 

    In studies by Stewart & Gaul (1977), aldrin (5.6 and 11.2 
kg/ha) was incorporated to a depth of 15 cm into a sandy loam soil 
for three successive years.  Various crops were grown and soil 
samples were collected for 14 years.  Residues of aldrin and 
dieldrin below 15 cm were negligible in the tenth year after the 
initial application, whereas the residues of aldrin plus dieldrin 
in the 0 - 15 cm layer were 0.2 and 1.7 mg/kg, respectively, at the 
two different treatments levels. 

    The results of these leaching studies indicate the almost 
quantitative adsorption of aldrin by organic matter and clay 
minerals.  Water molecules compete with aldrin for the adsorption 
sites in clay minerals, and it has been found that aldrin is bound 
to a greater extent in dry soil (Baluja et al., 1975; Kushwaha et 
al., 1978b).  The adsorption and desorption of aldrin has been 
studied by Tejedor et al. (1974) in whole soil and in the clay and 
organic (humic) fractions.  It was concluded that the organic 
fraction was mainly involved in the adsorptive uptake of aldrin and 
that the clay fraction was the major factor affecting the retention 

of aldrin.  There does not appear to be a simple relationship 
between water solubility and leaching, presumably because of the 
variations in the adsorptive capacity of clay minerals in various 
types of soil (Yaron et al., 1967).  A chromatographic model of the 
movement of pesticides through soils has been proposed (King & 
McCarty, 1968; Oddson et al., 1970). 

    In the laboratory, the investigations by Eye (1968) and Harris 
(1969) of the transport of dieldrin by water through soil are 
particularly relevant and are consistent with the chromatographic 
model for chemicals in soil of King & McCarty (1968).  The elution 
of dieldrin from soil by 1600 ml water was investigated in a study 
of six types of soil placed in chromatographic columns.  The 
dieldrin content of the total eluate, as a proportion of the 
applied dieldrin, varied from 1% (loam soil) to 65% (soil 
containing 93% sand) (Bowman et al., 1965). 

    The leaching of dieldrin through soil columns (30 cm diameter) 
was studied by Thompson et al. (1970).  A dieldrin emulsion was 
applied to the surface (equivalent to 31 kg dieldrin/ha) of soil 
columns 35 cm deep, and water was added to the surface until about 
30 litres (equivalent to about 6 months rainfall) had passed down 
the columns in 120 h.  It was concluded that dieldrin did not 
readily leach from the three types of soil investigated into 
drainage water, and that cracks and crevices caused by drying or by 
earthworms and other animals favour the leaching of dieldrin.  The 
results of an investigation using sloping troughs gave results 
consistent with the soil column study. 

4.1.2.  Surface run-off

    Run-off from treated land caused by soil erosion is a potential 
source of dieldrin residues in surface waters in areas where 
erosion is not controlled by good farming practice.  Sediments 
bearing aldrin and dieldrin can result in low concentrations in 
aqueous solution, although these are limited due to adsorption onto 
the sediments.  Thus, rain-water run-off (without sediment) does 
not appear to be a major contributor. 

    Richard et al. (1975) and Sparr et al. (1966) sampled various 
surface waters in the USA and reported levels of dieldrin ranging 
from < 1 to 42 ng/litre and of aldrin in the region of 0.05 
g/litre. 

    To gain data on the erosion of treated land, Caro & Taylor 
(1971) and Caro et al. (1976) incorporated dieldrin into the soils 
of two small watersheds in Ohio, USA, and studied run-off losses 
over a three-year period.  In the first case, there was practically 
no surface soil erosion and the total loss of dieldrin was confined 
to run-off water.  The area was 1.07 ha and the loss over the 
period was less than 0.5 g dieldrin, the highest level in the water 
being 4 g/litre.  In the second study, there was a substantial 
loss of soil by erosion and the amount of dieldrin lost in the 
solid sediment was 77 g in only 8 months.  The loss in the water 
itself was just under 2.5 g and the highest water concentration was 

20 g/litre.  It should, however, be borne in mind that in this 
case the soil had been mechanically compacted to aggravate the 
effects of erosion, so that it is questionable whether the results 
bear much relation to normal agricultural practice.  The authors 
commented that there was only a poor correlation between rainfall 
events and the amounts of dieldrin lost. 

    Sediment-bearing residues of aldrin or dieldrin will yield some 
of their burden to true solution in the water which they enters. 
Sharom et al. (1980) showed that the ratio of dieldrin 
concentration in soil to that in water (in equilibrium with the 
soil) was between 100 and 500 for mineral soils, whilst that same 
ratio for aldrin was likely to be around 5 - 6 times higher.  Thus, 
with 1 mg dieldrin/kg sediment, one could expect a water 
concentration of about 10 g/litre. 

    The movement of aldrin and dieldrin by run-off and soil erosion 
was studied by Haan (1971).  Each pesticide was applied at 1.65 
kg/ha to the surface of small plots, mainly consisting of silt loam 
(slope, 1 - 2%), in a greenhouse.  Water was applied and the run-
off water, sediment, and surface soil (0.6 cm deep) were analysed. 
It was estimated that 94.8% and 95.4%, respectively, of the applied 
aldrin and dieldrin remained in the surface soil (0.6 cm depth).  
It was concluded that there was no difference in the potential for 
loss from soil by rainfall, whether the rainfall occurred shortly 
after aldrin application or several days later. 

4.1.3.  Loss of aldrin and dieldrin from soils - volatilization

    Most authors consider that the principal loss of aldrin and 
dieldrin from soils is by volatilization.  There is widespread 
evidence for this, although other mechanisms (sections 4.4.1 and 
4.4.2) may also play an important role. 

    Volatilization from soils was first demonstrated when it was 
shown that mosquitoes were killed by vapour emanating from treated 
soil blocks (Barlow & Hadaway, 1955, 1956; Gerolt, 1961). 

    When aldrin is incorporated into the soil, it is most readily 
lost from the surface layer.  Subsequently, material from deeper 
layers has to rise to the surface to replenish what was lost.  The 
position is somewhat complicated by its gradual conversion to the 
less volatile dieldrin, although this, too, behaves in a 
qualitatively similar manner. 

    There are two routes to the surface:  transport in ascending 
capillary water - analogous to the process of salinization - and 
vapour diffusion through the soil pores.  Both of these processes 
are strongly affected by hydrophobic adsorption, a phenomenon 
common to many hydrophobic pesticides of low water solubility. 
Adsorption by the soil has the effect, at practical rates of 
application, of reducing the vapour pressure and hence the 
saturation vapour density in the soil atmosphere.  It also reduces 
the maximum concentration in the soil solution. 

    There is a very extensive literature on soil adsorption, 
especially of dieldrin and the following general situation is now 
well established. 

    Adsorption, as measured by reduced vapour density, takes place 
in all soils but is greatest at low moisture levels; that is to say 
soils in equilibrium with air of relative humidity below around 
95%.  (Barlow & Hadaway, 1955, 1956; Gerolt, 1961; Harris, 1964, 
1972; Igue et al., 1972). 

    In dry soils, mineral components play the most important part, 
whereas in moist soils it is organic matter that dominates (Harris 
& Lichtenstein, 1961; Harris et al., 1966; Harris & Sans, 1967; 
Harris, 1972).  In fact, Harris demonstrated a linear relation 
between organic matter and adsorption in moist soils.  On the other 
hand, in a dry mineral soil with predominantly montmorillonitic 
clay and very low organic matter, practically no dieldrin 
volatilized until the relative humidity of the air in equilibrium 
with soil reached saturation.  At this point volatilization readily 
resumed. 

    In moist soils, Spencer et al. (1969) found that adsorption, 
expressed as a reduction in vapour density, became less marked as 
the dieldrin level increased.  At 20 C, 10% moisture in the soil, 
and 1 mg dieldrin/kg soil, the dieldrin vapour density was only 2 
ng/litre, compared with 52 ng/litre when the dieldrin level in the 
soil was increased to 25 mg/kg.  This level is close to the figure 
for free dieldrin.  Similar results were reported at 30 C and 
40 C by Spencer & Cliath (1973). 

    In dry soils, however, adsorption is far stronger.  At 100 mg 
dieldrin/kg moist soil (Spencer et al., 1969), the depression in 
vapour pressure was negligible.  However, as the moisture content 
of the soil fell to a critical level of 2.1%, there was a dramatic 
decrease in vapour density, so that below 2% moisture the vapour 
density was practically zero.  The same authors showed that the 
level of water in their soil needed to provide a monomolecular 
layer was 2.8%.  They concluded that the critical point at which 
adsorption increased was when the monomolecular layer started to be 
lost, leaving adsorption sites available for occupation by 
dieldrin.  Restoration of the moisture status of the soil, however, 
restored the vapour density to its original level. 

    Whilst most of these studies were carried out on one soil, Gila 
silt loam, and whilst the figures would be different for other 
soils, the qualitative conclusions are largely valid for all soils. 
Adsorption is expected to be least on sandy soils of low organic 
matter content. 

    Adsorption by soils can also be determined by measuring the 
reduction in the saturation concentration of the soil solution 
(Eye, 1968; Tejedor et al., 1974; Baluja et al., 1975).  As in the 
case of reduced vapour pressure caused by adsorption by moist 
soils, the organic matter content of the soil was the principal 
soil characteristic affecting adsorption from solution.  Eye (1968) 

also demonstrated the dominating influence of organic matter, 
whereas clay content, surface area, and cationic exchange capacity 
showed very little correlation.  These findings are compatible with 
those of Yaron et al. (1967). 

    In studies involving the percolation of dieldrin, dissolved in 
water, through columns of soils with differing contents of organic 
matter, Sharom et al. (1980) also showed that the soil capacity for 
adsorption was largely determined by its content of organic matter. 
Moreover, adsorption followed the Freundlich adsorption equation. 
They reported Freundlich adsorption constants for a range of soils 
and pesticides, including dieldrin, and showed that, for a given 
pesticide, adsorption was strongly dependent on the organic matter 
content of the soil.  Moreover, the strength of adsorption by a 
given soil depended mainly on the water solubility of the 
pesticide, so that dieldrin, with its low water solubility, was 
more strongly adsorbed than, for instance, the much more water-
soluble lindane.  Although aldrin was not studied, it may be 
inferred from these data that aldrin would be adsorbed 
correspondingly more strongly, owing to a much lower water 
solubility than that of dieldrin. 

4.1.3.1  Movement within the soil profile - mass flow

    Spencer & Cliath (1973) concluded from laboratory studies that 
dieldrin could ascend the soil profile by mass flow in capillary 
water moving up to the surface through a moisture gradient, and 
that this mechanism could account for 3 - 30% of the total upward 
movement.  However, with low solubility products such as dieldrin, 
Jury et al. (1983) pointed out that volatilization decreases with 
time, because ascent to the surface is rate limiting.  With high 
solubility compounds, however, the reverse is true as more material 
reaches the surface, dissolved in capillary water, to become 
available for evaporation.  However, it is not only water 
solubility that determines the behaviour, but the value of Henry's 
constant for the partition of the compound between air and water. 
These authors considered the critical value to be 2.7 x 10-5; above 
this value mass flow is progressively less important.  The value of 
Henry's constant for dieldrin (6.7 x 10-4) is substantially higher 
(Jury et al., 1983) and that for aldrin higher still, so that on 
this basis it is doubtful whether mass flow ever does play a 
significant role in the transport of aldrin or dieldrin up the soil 
profile. 

    In support of the view that transport by mass flow is not 
appreciable, the mathematical models that have been proposed to 
describe the loss of aldrin and dieldrin from soils (Farmer & 
Letey, 1974; Mayer et al., 1974; Jury et al., 1983) tend to 
demonstrate, in comparisons with laboratory data, that ascent to 
the surface is predominantly by vapour diffusion rather than mass 
flow. 

4.1.3.2  Movement within the soil profile - diffusion 

    Diffusion is regarded as the main route by which aldrin and 
dieldrin ascend the soil profile to reach the surface.  Diffusion 
increases with soil temperature, concentration, decreasing 
adsorption capacity (usually the same as decreasing organic 
matter), maintenance of moisture content above the wilting point, 
and the "tortuosity" of the soil pore system (a measure of the 
openness of the soil).  With regard to moisture content, Farmer & 
Jensen (1970) found that diffusion coefficients of dieldrin in 
three soils in equilibrium with air of 94% relative humidity were 
9.7, 4.4, and 3.8, but at 75% relative humidity the values were 
0.6, 0.4, and 0.4, respectively.  According to Farmer & Letey 
(1974), the critical moisture level is probably the "fifteen 
atmosphere percentage", usually considered to be a reasonable 
measure of the water content at the wilting point. 

    Tortuosity increases as soils are compacted.  Working with 
moist soils of differing bulk densities, Farmer et al. (1973), 
showed that diffusion of dieldrin was about twice as fast in a soil 
with a density of 0.75 g/cm3 as when it was compressed to a bulk 
density of 1.5 g/cm3. 

4.1.3.3  Actual volatilization losses - laboratory studies

    Lichtenstein & Schulz (1970) reported that aldrin was lost by 
volatilization from a silt loam soil about 20 times faster than 
dieldrin.  Helene et al. (1981) reported a 31% loss of aldrin from 
a highly humic soil after 120 days but 62% from a soil of low 
organic matter content. 

    In studies of moist soils in volatilization chambers, Farmer et 
al. (1972) and Igue et al. (1972) found that the rate of loss by 
volatilization gradually decreased with time.  However, if 
translated into terms of the open field, this could still represent 
a loss of between 0.2 and 1.4 kg/ha per year, depending on the 
depth of incorporation. 

    With a surface application of dieldrin in a microagroecosystem 
chamber, Nash (1983) reported loss of dieldrin at the rate of 1 - 4 
g/day, but this rate fell to about a half of its initial value 
within 6 - 7 h.  Incorporation of the dieldrin had the effect of 
greatly slowing this loss rate (Nash, 1983). 

4.1.3.4  Actual volatilization losses - field studies

    The data on volatilization losses in the field are limited and 
refer only to dieldrin.  Caro & Taylor (1971) reported loss by 
volatilization from an incorporated dieldrin application (5.6 
kg/ha) of 2.8% of that applied (after 18 weeks).  Spencer et al. 
(1973) cited unpublished studies by Caro & Taylor (1971) where a 
surface application was lost at the rate of 3% per hour.  In a 
later study, Caro & Taylor (1976) found that 4.5% of a dieldrin 
application was lost by volatilization in the first year after 
treatment.  By the autumn, the loss rate was only 0.2 g/ha per day, 

although this increased to 0.9 g/ha per day immediately after the 
land was cultivated, due, presumably, to the exposure of fresh 
soil. 

    Taylor et al. (1972, 1976) estimated a loss of dieldrin of 0.2 
kg/ha from an incorporated application of dieldrin.  However, only 
6% remained from a surface application after 16 weeks, although in 
this case a small amount was recovered as photodieldrin (Turner et 
al., 1977). 

    Willis et al. (1972) demonstrated an 18% loss from a very high 
application (22 kg/ha) of dieldrin after 5 months where the soil 
was kept moist by irrigation.  However, losses were substantially 
less when the soil was not irrigated or when maintained under flood 
conditions.  The maximum rate of loss by volatilization was 0.2 
kg/ha per day. 

4.1.4  Losses of residues following treatment of soil with aldrin

    One of the earliest systematic studies of the decline of aldrin 
and dieldrin residues in soils, arising from the application of 
aldrin to the soil, was by Decker et al. (1965), who sampled a wide 
range of soils of known treatment history from Illinois, USA.  They 
demonstrated the transformation of aldrin to dieldrin and 
considered that the loss of residues was a two-stage process.  
There was a comparatively rapid loss in the first year after 
treatment, a typical loss being 75% of the applied dose. 
Thereafter, residues declined with a half-life of 2 - 4 years, the 
reduced rate being apparently due to the greater proportion of 
dieldrin in the residues.  Elgar (1966) incorporated 2.2 kg 
aldrin/ha into soils in the United Kingdom and reported somewhat 
similar results for the decline of residues, although there were 
indications that the rate of decline slowed in later years as the 
level in the soil fell to around 0.3 mg/kg.  Further studies of 
this kind have been reported by Lichtenstein et al. (1970), Onsager 
et al. (1970), and Korschgen (1971).  Although the rates of decline 
were very variable, they were not inconsistent with the data of 
Decker et al. (1965), bearing in mind the inherent variability of 
soil data. 

    There are indications that loss rates are higher in tropical 
soils than in temperate climates.  Whilst Agnihotri et al. (1977) 
found that epoxidation was faster in tropical than temperate soils, 
leading to the possibility of slower decline because of higher 
dieldrin levels, Gupta & Kavadia (1979) found in India that 
declines were often much faster.  In one case, half of the aldrin 
applied had been lost in only 38 days.  Wiese & Basson (1966) also 
reported comparatively high loss rates in South Africa.  Using 
three rates of treatment and three soils, they found that half of 
the original application was lost between 1 and 2 months. 

    Elgar (1975) conducted a series of studies in temperate, warm 
temperate, and tropical soils and reported rates of decline that 
were compatible with those of Decker et al. (1965).  Again, losses 
from the tropical sites occurred more rapidly than from the 

temperate sites.  He deduced the following empirical expression to 
describe loss rates, expressed as the sum of aldrin and dieldrin 
residues surviving n years after a single application. 

    C(n) = fC(o)(1-p)n-1

In this expression, C(o) is the initial residue level, C(n) is the 
level after n years, f is the proportion remaining after the first 
year, and p is the proportion lost in each of the succeeding years. 
In Elgar's studies, the mean estimate of these latter two 
parameters was f = 0.25 and p = 0.44, but in the Decker work, the 
value of p was somewhat less.  It is also possible to derive an 
equation that describes the accumulation of residues in a soil 
subject to a regular routine of annual applications.  The 
implications of this equation are that residue levels do not 
continue to increase indefinitely, but reach a plateau.  In the 
case of Elgar's data, the plateau level, one year after the last of 
n applications, would be around 60% of the level observed 
immediately after the first application.  This prediction is well 
borne out by the soil monitoring data presented in Table 1. 

    Studies of the decline of residues arising from aldrin applied 
for the control of termites (Bess & Hylin 1970; Carter & Stringer, 
1970) reveal slower rates of decline than would be expected, 
considering the deep application. 

    Separate studies have been carried out on dieldrin residue 
losses.  These show considerably slower rates of decline than in 
the case of aldrin, but there is a very wide range in the data 
reported.  Thus, Edwards (1966) reported that the average time for 
the disappearance of 95% of the residues was 8 years, but Wiese & 
Basson (1966) found much faster rates.  Intermediate rates were 
reported by Stewart & Fox (1971) and Beyer & Gish (1980).  It seems 
probable that the rate of decline of dieldrin in the soil is 
reasonably well reflected by Elgar's equation for the years that 
succeed the first year of aldrin application. 

4.1.5.  Losses of residues from water

    The partition of dieldrin between the vapour phase and water 
was determined by a dynamic gas-flow method using 14C-dieldrin 
(Atkins & Eggleton, 1970).  The partition coefficient at 20 C 
(expressed on a weight/volume basis for air and water) was constant 
at 540, up to a concentration of 0.033 mg dieldrin/litre water.  At 
higher concentrations, there was a rapid increase in the partition 
coefficient, which was attributed to the aqueous solution becoming 
saturated at 0.033 mg/litre.  Using the values for vapour pressure 
(3.47 x 10-4 Pa) and water solubility found in this study, the 
wash-out ratio for the removal of dieldrin vapour from atmospheric 
air by rain was 0.65.  It was suggested that the concentration of 
dieldrin in the rainfall in London (Abbott et al., 1965) (Table 6) 
may indicate the presence of dieldrin in particulate matter in the 
atmosphere rather than in the vapour phase. 


                                                                 
Table 1.  Concentrations of aldrin and dieldrin in soila
------------------------------------------------------------------------------------------------------------------------------
Location       Year     Use                        Number    Mean concentration  Comments                      Reference
                                                   of        in mg/kg (maximum
                                                   sites     value in brackets)
                                                             aldrin    dieldrin
------------------------------------------------------------------------------------------------------------------------------
United                  aldrin: potatoes           21        0.02      0.09      LD < 0.03 mg/kg               Wheatley et
Kingdom                                                      (0.12)    (0.41)                                  al. (1962)

               1965     aldrin: potatoes;          10        0.15      0.48      LD not reported; apparently   Davis (1968)
                        dieldrin: seed-dressing,             (0.7)     (0.7)     < 0.02 mg/kg; various soil
                        carrots, and wheat;                                      types; residues in soil
                        cumulative applications                                  microfauna also determined
                        during 5 years prior to                                
                        sampling (0.14-3.4 
                        kg/ha)                 
                       
Canada

S.W. Ontario   1964-65  aldrin: various crops;     13        0.19      0.57      LD < 0.1 mg/kg; soil of       Harris et al.
                        known usage                          (0.8)     (1.3)     various types (sandmuck);     (1966)
                                                                                 aldrin used to a 
                                                                                 considerable extent
                                                                                 (1954-60) on 27 sites

                        no reported use 1961-64    14        0.18      0.25      
                                                             (2.1)     (1.6)

                        none used 1954-64          5         LD        LD
                                                                                                      
Atlantic       1965     aldrin: 1-5 applications                                 LD 0.01 mg/kg; no detectable  Duffy & Wong
provinces               during 15 years prior to                                 residues of aldrin or         (1967)
                        sampling; cumulative                                     dieldrin in orchard soils to
                        application 0.5-45 kg/ha;                                which aldrin/dieldrin had
                                                                                 not been applied
                                                                               
                        root crops                 18        0.46      0.41    
                                                             (1.5)     (1.45)

                        vegetables                 17        0.66      0.36
                                                             (2.5)     (1.35)
------------------------------------------------------------------------------------------------------------------------------

Table 1.  (contd.)
------------------------------------------------------------------------------------------------------------------------------
Location       Year     Use                        Number    Mean concentration  Comments                      Reference
                                                   of        in mg/kg (maximum
                                                   sites     value in brackets)
                                                             aldrin    dieldrin
------------------------------------------------------------------------------------------------------------------------------
Southern       1971     aldrin: tobacco            4 (50     ND        0.16      LD 0.001 mg/kg; woodlots      Frank et al.
Ontario                                            samples)            (0.19)    were adjacent to treated      (1974)
                                                                                 areas, but not directly
                                                                                 sprayed

                        cereals                    4 (60     ND        0.16      
                                                   samples)            (0.19)

                        woodlots                   12        ND        trace
                                                   samples

Saskatchewan   1970     soil from 21 vegetable     41        0.03      0.06      LD 0.005 mg/kg; aldrin found  Saha & Sumner
                        farms                      samples   (0.28)    (0.77)    in 25% of samples; dieldrin   (1971)
                                                                                 found in 55% of samples       
                                                                                 
Southern       1972-75  soil samples from                                        LD < 0.0004 mg/kg; dieldrin   Frank et al.
Ontario                 orchards                                                 had been used (1955-65)       (1976)
                                                                                 at recommended rates of
                                                                                 0.8-1.3 kg/ha

                        apple: 0-15 cm             31        ND        0.03     
                                                                       (0.38)
                               15-30 cm                      ND        0.001
                                                                       (0.03)

Southern       1972-75  sweet cherry:              16                                                          Frank et al.
Ontario                        0-15 cm                       ND        0.001                                   (1976)
                                                                       (0.01)
                               15-30 cm                      ND        LD

                        sour cherry:               12
                               0-15 cm                       ND        0.005
                                                                       (0.04)
                               15-30 cm                      ND        0.003
                                                                       (0.02)
------------------------------------------------------------------------------------------------------------------------------

Table 1.  (contd.)
------------------------------------------------------------------------------------------------------------------------------
Location       Year     Use                        Number    Mean concentration  Comments                      Reference
                                                   of        in mg/kg (maximum
                                                   sites     value in brackets)
                                                             aldrin    dieldrin
------------------------------------------------------------------------------------------------------------------------------
Southern                peach:                     11
Ontario                        0-15 cm                       ND        0.04
(contd.)                                                               (0.11)
                               15-30 cm                      ND        0.02
                                                                       (0.07)
                        vineyards:                 16
                               0-15 cm                       ND        0.009
                                                                       (0.035)
                               15-30 cm                      ND        0.004
                                                                       (0.023)

USA

Seven eastern  1965     aldrin and dieldrin in 3                                 LD 0.05 mg/kg; proportions    Seal et al.
states                  crops:                                                   of soil samples with          (1967)
                                                                                 measurable residues:

                        peanuts:                   5         ND        0.15      potatoes, 76%; carrots,
                                                                       (0.20)    21%; peanuts, 100%
                        carrots:                   19        ND        0.19
                                                                       (0.26)
                        potatoes:                  25        ND        0.10
                                                                       (0.20)

               1965-67  aldrin and dieldrin used   17 (278   0.02      0.21      LD 0.01 mg/kg; aldrin         Stevens et al.
                        regularly                  samples)  (0.47)    (2.84)    detected in 15% of samples    (1970)
                                                                                 and dieldrin in 67% of
                                                                                 samples from areas of
                                                                                 regular use

                        limited use                16        LD        0.001        
                                                                       (0.001)    

                        no known use               18        LD        LD
------------------------------------------------------------------------------------------------------------------------------

Table 1.  (contd.)
------------------------------------------------------------------------------------------------------------------------------
Location       Year     Use                        Number    Mean concentration  Comments                      Reference
                                                   of        in mg/kg (maximum
                                                   sites     value in brackets)
                                                             aldrin    dieldrin
------------------------------------------------------------------------------------------------------------------------------
USA (contd.)

Colorado       1967     aldrin: various soil       11        0.16      0.19      LD < 0.02 mg/kg; some         Mullins et al.
                        types (1-4.3% organic                (0.61)    (0.44)    fields had been treated       (1971)
                        matter); nominal                                         annually for 9 years; time  
                        concentrations in soil at                                of last treatment prior to
                        time of application:                                     sampling varied from 0-9
                        0.06-6.75 mg/kg                                          years
                      
                        dieldrin: nominal          9         ND        0.05
                        concentrations in soil at                      (0.30)
                        time of application:
                        0.13-0.63 mg/kg
                     
Arizona        1968     3 types of soil (organic   13        LD        0.0003    LD not defined; appears to    Laubscher et 
                        matter 0.5-6.6%) from                          (0.0013)  be about 0.0001 mg/kg; no     al. (1971)
                        area downwind of                                         relationship between   
                        an area of insecticide                                   concentration of dieldrin
                        use                                                      and distance from area of
                                                                                 application

10 major       1969     samples of soil            71        0.02      0.79      LD 0.01 mg/kg; aldrin in      Wiersma et al.
areas of                                                     (0.96)    (16.72)   4.2% of samples and           (1972)
onion growing                                                                    dieldrin in 73% of samples
                                                                                 
9 areas        1969     samples of soil            92        0.01      0.17      LD 0.01 mg/kg; aldrin in      Sand et al.
growing sweet                                                (0.11)    (2.18)    3.3% and dieldrin in 60.9%    (1972)
potatoes                                                                         of samples

Rice-growing   1972     samples of soil            99        0.01      0.04      LD 0.01 mg/kg; aldrin in      Carey et al.
areas                                                        (0.25)    (0.27)    39% and dieldrin in 85% of    (1980)
                                                                                 samples

USA National   1970     samples of soil            1506      0.02      0.04      LD 0.01 mg/kg; aldrin in      Crockett et al.
Monitoring                                                   (4.25)    (1.85)    13% and dieldrin in 31% of    (1974)
Program                                                                          samples
(35 states)
------------------------------------------------------------------------------------------------------------------------------

Table 1.  (contd.)
------------------------------------------------------------------------------------------------------------------------------
Location       Year     Use                        Number    Mean concentration  Comments                      Reference
                                                   of        in mg/kg (maximum
                                                   sites     value in brackets)
                                                             aldrin    dieldrin
------------------------------------------------------------------------------------------------------------------------------
USA (contd.)

12 states in   1970     average application of     12 (389   0.05      0.07      LD <0.01 mg/kg; dieldrin      Carey et al.
the cornbelt            dieldrin was 1.3 kg/ha     samples)  (2.98)    (2.04)    residues attributed           (1973)
region                                                                           primarily to the use of     
                                                                                 aldrin; aldrin had been
                                                                                 used in one or more years
                                                                                 from 1954

14 cities      1970     soil from urban areas      356       LD        0.1       LD < 0.03 mg/kg; aldrin       Carey et al.
                        sampled to a depth of                          (12.8)    not detected in any           (1976)
                        7.6 cm                                                   samples; dieldrin in
                                                                                 samples from 22 sites 
                                                                                 (6.5%) in 6 cities

Japan, S.W.  

Kyushu                                             99        0.07      0.29      LD 0.001 mg/kg                Suzuki et al.
district                                           samples   (1.01)    (1.73)                                  (1973)
------------------------------------------------------------------------------------------------------------------------------
a LD = limit of detection; ND = not determined.
    The rate of dry deposition of dieldrin (vapour phase) on grass, 
calculated from the results of wind tunnel studies, was 4 x 10-2
cm/second.  The average lifetime of dieldrin in the atmosphere, 
assuming loss by wash-out and dry deposition only, was estimated to 
be 28 weeks (Atkins & Eggleton, 1970). 

    The rate of transfer of dieldrin from water to air and vice 
versa has been determined (Slater & Spedding, 1981).  The transfer 
velocity from water, measured in a wind tunnel, increased as the 
air speed (measured at 6 cm above the water surface) increased. 
When there was no air movement, the transfer velocity was 2.6 x 
10-5 cm/second compared to 15 x 10-5 cm/second at an air velocity 
of 31.1 km/h.  The transfer velocity from air to water was measured 
by passing air through a column of downward-flowing water, and was 
found to increase as the interfacial velocity increased from 0.9 x 
10-2 cm/second (at 10 km/h) to 5.2 x 10-2 cm/second (at 34.2 km/h). 
It was suggested that the exchange of dieldrin between water and 
air was controlled by diffusive processes either in the air 
boundary or water boundary layers.  The Henry's law constant (ratio 
of the concentrations in air and aqueous phases at equilibrium) for 
dieldrin was 1.3 x 10-3 at 20 C.  It was concluded that the 
resistances to transfer of dieldrin from water to air and vice 
versa were similar. 

    The physical and thermodynamic principles of exchanges of 
chemicals between water and air have been discussed (Mackay & 
Wolkoff, 1973; Liss & Slater, 1974; Mackay & Leinonen, 1975; Mackay 
et al., 1979; Smith et al., 1981).  An estimate of the half-life of 
the evaporation of dieldrin at 25 C from a column of water of 1 m 
depth was derived by Mackay & Leinonen (1975).  Although this 
estimate (539 days) is not based on the most recent and reliable 
values for the vapour pressure and water solubility of dieldrin, it 
is probably of the right order. 

4.1.6.  Aldrin and dieldrin in the atmosphere

    Small amounts of dieldrin have been detected in the atmosphere 
(Table 6).  Baldwin et al. (1977) conducted a study at Bantry Bay 
on the west coast of Ireland, well away from point sources of 
emission.  They found concentrations of dieldrin between 0.06 and 
1.6 ng/kg, with an average of 0.36 ng/kg, but no aldrin, 
photodieldrin, or photoaldrin.  No dieldrin was detected on solid 
matter trapped on filter pads; the limit of determination ranged 
from 1.1 to 7.2 pg/kg (parts per thousand trillion of air). 

    The reason for the very low level of occurrence of dieldrin in 
the global atmosphere, if, as seems probable, a major part of the 
aldrin used in agriculture escapes from the soil by evaporation, 
has been the subject of considerable speculation.  It appears 
unlikely that direct photochemical reactions are involved, since 
there have been no reports of photodieldrin being detected.  
Washout by rain may be an important factor.  Indeed, Baldwin et al. 
(1977) cited literature figures for Hawaii of 1 - 97 ng/litre, and 
Abbott et al. (1965) reported 1 - 95 ng/litre in rainfall in London 
and other locations in the United Kingdom.  MacCuaig (1975), on the 

other hand, working in the vicinity of a dieldrin application in 
Ethiopia, reported 100 g/litre in rainwater.  These results 
support the suggestion of Atkins & Eggleton (1970) that, though 
washout of the atmosphere by rain would be inefficient in the case 
of dieldrin, it could lead to substantial losses.  If this were so, 
dieldrin deposits would be expected on soil adjacent to treated 
areas, but the fact that large areas of soil in the cornbelt of the 
USA (Carey et al., 1973) have no detectable levels of aldrin or 
dieldrin seems to cast doubt on the extent to which rain acts to 
disperse aldrin and dieldrin onto untreated land near to treated 
areas. 

    It would appear possible, therefore, that there are losses of 
aldrin and dieldrin in the atmosphere.  Glotfelty (1978) mentioned 
the high reactivity of free radical species in the atmosphere, in 
particular hydroxyl radicals.  These could presumably play an 
important role in the degradation of molecules occurring as vapour. 

4.1.7.  Aldrin and dieldrin in water

    The data regarding the occurrence of aldrin and dieldrin in 
both ground and surface waters are summarized in Table 7 (section 
5.1.3).  As would be expected from the extreme resistance of 
dieldrin and, especially, aldrin to leaching from soil, the 
occurrence of either compound in groundwater is rare.  Spalding et 
al. (1980) took a series of groundwater samples in Nebraska, USA, 
where aldrin had been used extensively for the control of corn 
rootworm and could not detect it in any of the samples.  Their 
limit of determination was between 5 and 10 ng/litre.  Junk et al. 
(1980) reported somewhat similar results from Nebraska.  Richard et 
al. (1975), in a wide-ranging study, examined the water supplied to 
a series of cities in Iowa, USA, from boreholes.  Again, no aldrin 
or dieldrin was reported; their limit of determination appears to 
have been 0.5 ng/litre. 

    Surface waters, by contrast, have often been reported to 
contain small amounts of dieldrin.  In a programme of sampling 
various surface waters in Iowa, Richard et al. (1975) reported 
levels of dieldrin ranging from 3 to 75 ng/litre in rivers and 
streams and levels in reservoirs from 3 to 18 ng/litre.  In rivers 
in Iowa and Louisiana, levels ranged from < 1 to 42 ng/litre. 
During the period 1976 - 80, dieldrin was found in 2.4% of samples 
from national surface waters in the USA, (maximum concentration of 
0.61 g/litre) and in 21.7% of national surface water sediments 
(maximum concentration of 5300 g/kg) (Carey & Kutz, 1985). 

    The dieldrin in surface water probably comes from run-off from 
treated land.  Sparr et al. (1966) sampled drainage ditches and a 
river in a maize growing area in northwest Indiana, USA.  Levels 
reached 0.6 g/litre in the river but, in the ditches from fields 
treated with aldrin at up to 5.6 kg/ha, levels seldom exceeded the 
limit of determination (0.05 g/litre).  Water draining from rice 
paddies that had been planted with aldrin-treated seed also 
contained small amounts of dieldrin (1 g/litre after seeding and 

falling by the 14th week to 0.07 g/litre).  The authors calculated 
that about 1 g of aldrin had been lost from the rice paddy surface 
water during the whole 14-week period. 

    Hindin et al. (1964) reported aldrin in irrigation water up to 
2.3 g/litre, but no dieldrin.  However, in view of the readiness 
with which aldrin is epoxidized to dieldrin in surface waters, 
there must be some doubt as to the identity of the residue they 
actually measured. 

    It does appear that dieldrin can occur in surface waters 
draining from agricultural areas, but the amounts are usually so 
small that they could not be expected to represent a major 
proportion of the product applied to the soil.  The ultimate fate 
of these small levels of dieldrin in water is not known.  It is 
probably that adsorption onto particulate matter, volatilization, 
and various degradation mechanisms all play a role. 

4.2  Translocation From Soil Into Plants

    The uptake of aldrin and dieldrin by plants is much higher in 
root crops than in grain crops.  It is influenced by the levels in 
soils, the strength of adsorption, and the depth of application. 

    In grain crops, it is rare for residues to reach detectable 
levels in the grain (FAO/WHO, 1970a; Gupta & Kavadia, 1979).  Root 
crops are much more prone to take up residues from treated soils, 
as observed by Harris & Sans (1967) who found that carrots, 
radishes, and turnips had the highest residues.  Onions, lettuce, 
and celery were intermediate and cole crops showed no detectable 
uptake at all (Lichtenstein, 1959). 

    The level of aldrin and dieldrin in the soil influences the 
degree of uptake as shown by Lichtenstein et al. (1970) and Edwards 
(1973a,b), who both reported on ratios of the concentrations in 
plants to those in the soil.  Further work by Onsager et al. 
(1970), Voerman & Besemer (1975), Bruce & Decker (1966), and Saha 
et al. (1971) provided compatible results. 

    The availability of aldrin and dieldrin for uptake by plants 
depends on the strength of adsorption by the soil and especially 
the organic matter fraction.  Harris & Sans (1967), Beall & Nash 
(1969), Beestman et al. (1969), and Nash et al. (1970) demonstrated 
that crops tend to take up more residues from soil of low than of 
high organic matter.  Adding activated charcoal to soil reduced 
dieldrin uptake by 70% or more in carrots and potatoes 
(Lichtenstein et al., 1971). 

    Deep application of dieldrin greatly reduces the uptake (Beall 
& Nash, 1972).  Residues in the plants from a deep (31 - 32 cm) 
application were only 1% of those from superficial application. 
The authors commented that a possible treatment for reducing the 
uptake of old soil residues by crops would be simply to plough them 
under. 

    The mechanism of uptake by crops is not entirely clear and 
appears to vary considerably from species to species.  Beall & Nash 
(1971), in work with soyabeans grown on soil treated with 14C-
labelled dieldrin, found that residues were taken up both by 
absorption through the roots and by absorption of vapour through 
the leaves.  In the case of cereals, it seems unlikely that root 
uptake occurs to any great extent (Powell et al., 1970; Gutenmann 
et al., 1972; Gupta et al., 1979).  This probably accounts for the 
very low levels found in cereal grains from treated crops.  On the 
other hand, it would seem almost certain that it is root uptake 
which accounts for the residues found in root crops. 

4.3.  Models of the Behaviour of Water and Chemicals in Soil

    Various models for the movement of water and chemicals in 
porous media have been developed, based on physical variables such 
as vapour pressure, diffusibility, and adsorption, etc. (Keller & 
Alfaro, 1966; Bresler & Hanks, 1969; Lindstrom et al., 1971; 
Davidson & McDougal, 1973; Pionke & Chester, 1973; Van Genuchten et 
al., 1974).  Models for run-off from soil have also been proposed 
(Crawford & Donigian, 1973; Bailey et al., 1974; Bruce et al., 
1975).  These models may be useful as a means of defining more 
precisely the behaviour of aldrin and dieldrin in soil. 

4.4.  Biodegradation of Aldrin and Dieldrin

    When used to protect crops from soil insects, aldrin is usually 
incorporated into the soil in which the plants are grown.  For this 
reason, most of the work on the biodegradation of aldrin in 
agriculture has been concerned with the soil system. 

4.4.1.  Epoxidation of aldrin

    The most important transformation of aldrin in the soil is its 
conversion by epoxidation to dieldrin (Fig. 2, section 6.3.1.1). 
Epoxidation, essentially biological in nature (Lichtenstein & 
Schulz, 1960), occurs in all aerobic and biologically active soils, 
and about 5