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    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

    ENVIRONMENTAL HEALTH CRITERIA 54







    AMMONIA








    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, 1986


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CONTENTS

ENVIRONMENTAL HEALTH CRITERIA FOR AMMONIA

1. SUMMARY

    1.1. Properties and analytical methods
    1.2. Sources in the environment
    1.3. Environmental transport, distribution and transformation 
    1.4. Environmental levels and human exposure
    1.5. Kinetics and metabolism
         1.5.1. Uptake and absorption
         1.5.2. Distribution
         1.5.3. Metabolic transformation
         1.5.4. Excretion and turnover
         1.5.5. Plant metabolism of ammonia
    1.6. Effects on aquatic organisms
    1.7. Effects on experimental animals and  in vitro test systems
         1.7.1. Single exposures
         1.7.2. Short-term exposures
         1.7.3. Skin and eye irritation; sensitization
         1.7.4. Long-term exposure
         1.7.5. Reproduction, embryotoxicity, and teratogenicity
         1.7.6. Mutagenicity
         1.7.7. Carcinogenicity
         1.7.8. Mechanisms of toxicity
    1.8. Effects on man
         1.8.1. Organoleptic effects
         1.8.2. Clinical, controlled human studies and accidental 
                exposure
         1.8.3. Endogenous ammonia
    1.9. Evaluation of the health risks for man and effects on the 
         environment
    1.10. Conclusions

2. PROPERTIES AND ANALYTICAL METHODS

    2.1. Physical and chemical properties of ammonia and ammonium 
         compounds
         2.1.1. Gaseous and anhydrous liquid ammonia
         2.1.2. Aqueous solutions
         2.1.3. Chemical reactions
         2.1.4. Ammonium compounds
    2.2. Sampling and analytical methods
         2.2.1. Air and water samples
         2.2.2. Soil samples
         2.2.3. Blood and tissue samples

3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

    3.1. Production and use
    3.2. Sources releasing ammonia into the air

    3.3. Sources discharging ammonia into water
         3.3.1. Point sources of ammonia
         3.3.2. Non-point sources of ammonia
         3.3.3. Comparison between point and non-point sources

4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

    4.1. Uptake and transformation in atmosphere
    4.2. Transport to the earth's surface
         4.2.1. Wet and dry deposition
         4.2.2. Contribution to acid rain
    4.3. Transformation in surface water
    4.4. Uptake and transformation in soils

5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

    5.1. Environmental levels
         5.1.1. Atmospheric levels
         5.1.2. Levels in water
         5.1.3. Levels in soil
         5.1.4. Food
         5.1.5. Other products
    5.2. General population exposure
         5.2.1. Inhalation
         5.2.2. Ingestion from water and food
         5.2.3. Dermal exposure
    5.3. Occupational exposure
    5.4. Exposure of farm animals
         5.4.1. Oral exposure
         5.4.2. Inhalation exposure

6. EFFECTS ON ORGANISMS IN THE ENVIRONMENT

    6.1. Microorganisms
    6.2. Plants
         6.2.1. Terrestrial plants
         6.2.2. Aquatic plants
         6.2.3. Fresh-water plants
         6.2.4. Salt-water plants
    6.3. Aquatic invertebrates
         6.3.1. Fresh-water invertebrates: acute toxicity
         6.3.2. Fresh-water invertebrates: chronic toxicity
         6.3.3. Salt-water invertebrates: acute and chronic toxicity
    6.4. Fish
         6.4.1. Ammonia metabolism in fish
                6.4.1.1  Ammonia production and utilization
                6.4.1.2  Ammonia excretion
         6.4.2. Fish: acute toxicity
                6.4.2.1  Salt-water fish
         6.4.3. Factors affecting acute toxicity
                6.4.3.1  pH
                6.4.3.2  Temperature
                6.4.3.3  Salinity
                6.4.3.4  Dissolved oxygen
                6.4.3.5  Carbon dioxide
                6.4.3.6  Prior acclimatization to ammonia

         6.4.4. Fish: chronic toxicity
    6.5. Wild and domesticated animals
         6.5.1. Wildlife
         6.5.2. Domesticated animals
                6.5.2.1  Oral exposure
                6.5.2.2  Inhalation exposure

7. KINETICS AND METABOLISM

    7.1. Absorption
         7.1.1. Respiratory tract
         7.1.2. Gastrointestinal tract
         7.1.3. Skin and eye
    7.2. Distribution
         7.2.1. Human studies
         7.2.2. Animal studies
    7.3. Metabolic transformation
    7.4. Reaction with body components
    7.5. Elimination and excretion
         7.5.1. Expired air
         7.5.2. Urine and faeces
    7.6. Retention and turnover
    7.7. Uptake and metabolism in plants

8. EFFECTS ON EXPERIMENTAL ANIMALS AND  IN VITRO TEST SYSTEMS

    8.1. Single exposures
         8.1.1. Inhalation exposure
         8.1.2. Oral exposure 
                8.1.2.1  Effects of metabolic acidosis induced by 
                         ammonium chloride  
                8.1.2.2  Organ effects following oral 
                         administration  
                8.1.2.3  Influence of diet on the effects of 
                         ammonia 
         8.1.3. Dermal exposure 
         8.1.4. Effects due to parenteral routes of exposure  
                8.1.4.1  Lethality 
                8.1.4.2  Central nervous system effects  
                8.1.4.3  Effects on the heart  
    8.2. Short-term exposures 
         8.2.1. Inhalation exposure 
         8.2.2. Oral exposure 
                8.2.2.1  Histopathological effects 
                8.2.2.2  Effects of ammonium as a dietary nitrogen 
                         supplement 
         8.2.3. Dermal exposure 
    8.3. Skin and eye irritation; sensitization 
    8.4. Long-term exposures  
         8.4.1. Inhalation exposure 
         8.4.2. Oral exposure 
    8.5. Reproduction, embryotoxicity, and teratogenicity
    8.6. Mutagenicity
    8.7. Carcinogenicity

    8.8. Factors modifying effects  
         8.8.1. Synergistic effects 
         8.8.2. Antagonistic effects  
    8.9. Mechanisms of toxicity 

9. EFFECTS ON MAN  

    9.1. Organoleptic aspects 
         9.1.1. Taste 
         9.1.2. Odour 
    9.2. Clinical and controlled human studies  
         9.2.1. Inhalation exposure 
         9.2.2. Oral exposure   
                9.2.2.1  Effects of acute oral exposure  
         9.2.3. Endogenous hyperammonaemia  
                9.2.3.1  Inborn errors of metabolism 
                9.2.3.2  Hepatic features

10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT

    10.1. Atmospheric exposure and effects
          10.1.1. General population exposure
          10.1.2. Occupational exposure
    10.2. Exposure through food and water
    10.3. Ocular and dermal exposure
    10.4. Accidental exposure
    10.5. Evaluation of risks for the environment
          10.5.1. The aquatic environment
          10.5.2. The terrestrial environment
    10.6. Conclusions  
          10.6.1. General population
          10.6.2. Sub-populations at special risk
          10.6.3. Occupational exposure
          10.6.4. Farm animals
          10.6.5. Environment

11. RECOMMENDATIONS

    11.1. Research needs

REFERENCES

ANNEX I

REFERENCES TO ANNEX I

ANNEX II

WHO TASK GROUP ON AMMONIA

 Members

Professor E.A. Bababunmi, Department of Biochemistry, University of 
   Ibadan, Ibadan, Nigeria  (Chairman)

Dr J.R. Jackson, Albright and Wilson, Ltd., Occupational Health and 
   Hygiene Service, Warley, United Kingdom  (Rapporteur)

Professor I. Kundiev, Research Institute of Labour, Hygiene, and 
   Occupational Diseases, Saksaganskogo, Kiev, USSR

Dr M. Piscator, Department of Environmental Hygiene, Karolinska 
   Institute, Stockholm, Sweden

Professor D. Randall, Department of Zoology, University of British 
   Columbia, Vancouver, British Columbia, Canada

Dr V.R. Rao, Department of Toxicology, Haffkine Institute, Parel, 
   Bombay, India

Dr J.A.A.R. Schuurkes, Laboratory of Aquatic Ecology, Faculty of 
   Natural Sciences, Catholic University, Nijmegen, The Netherlands

Dr J.R. Stara, Office of Research and Development, US Environmental 
   Protection Agency, Cincinnati, Ohio, USA

Dr H. Suzuki, Department of Hygiene, Fukushima Medical College, 
   Fukushima, Japan

Dr R.V. Thurston, Fisheries Bioassay Laboratory, Montana State
   University, Bozeman, Montana, USA

Dr E. Weisenberg, Institute for the Standardization and Control of 
   Pharmaceuticals, Ministry of Health, Jerusalem, Israel 
    (Vice-Chairman)

 Secretariat

Dr E. Smith, International Programme on Chemical Safety, World
   Health Organization, Geneva, Switzerland  (Secretary)

Mrs I.-M. Linquist, Occupational Safety and Health Branch,
   International Labour Office, Geneva, Switzerland

Dr C. Xintaras, Office of Occupational Health, World Health
   Organization, Geneva, Switzerlanda

-------------------------------------------------------------------
a Attended half day only.

NOTE TO READERS OF THE CRITERIA DOCUMENTS

    Every effort is made to present information in the criteria 
documents as accurately as possible.  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 data profile and information on the various limits set by 
countries can be obtained from the International Register of 
Potentially Toxic Chemicals, Palais des Nations, 1211 Geneva 10, 
Switzerland (Telephone No. 988400 - 985850). 





    Concentrations in this document are expressed in the terms used 
in original references. 

    1 mmol is equivalent to 14 mg ammonia-nitrogen/litre
                            17 mg NH3/litre
                            18 mg NH4+/litre

    1 mg ammonia-nitrogen is equivalent to 1.21 mg NH3
                                           1.29 mg NH4+

    In air, 1 mg/m3 is equal to about 1.42 ppm, depending on the 
temperature and pressure. 


ENVIRONMENTAL HEALTH CRITERIA FOR AMMONIA

    Following the recommendations of the United Nations Conference 
on the Human Environment held in Stockholm in 1972, and in response 
to a number of resolutions of the World Health Assembly and a 
recommendation of the Governing Council of the United Nations 
Environment Programme, a programme on the integrated assessment of 
the health effects of environmental pollution was initiated in 
1973.  The programme, known as the WHO Environmental Health 
Criteria Programme, has been implemented with the support of the 
Environment Fund of the United Nations Environment Programme.  In 
1980, the Environmental Health Criteria Programme was incorporated 
into the International Programme on Chemical Safety (IPCS), a joint 
venture of the United Nations Environment Programme, the 
International Labour Organisation, and the World Health 
Organization.  The Programme is responsible for the publication of 
a series of criteria documents. 

    A WHO Task Group on Environmental Health Criteria for Ammonia 
was held in Geneva on 8-13 July, 1985.  Dr E.M. Smith opened the 
meeting on behalf of the Director-General.  The Task Group reviewed 
and revised the draft criteria document and made an evaluation of 
the health risks of exposure to ammonia. 

    The original draft of this document was prepared by THE UNITED 
STATES ENVIRONMENTAL PROTECTION AGENCY ENVIRONMENTAL CRITERIA AND 
ASSESSMENT OFFICE under the direction of DR J.F. STARA.  Additional 
contributions were made by DR J.R. JACKSON, PROFESSOR D. RANDALL, 
and DR R.V. THURSTON. 

    The efforts of these contributors and 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. 

1.  SUMMARY

1.1.  Properties and Analytical Methods

    Ammonia (NH3) is a colourless acrid-smelling gas at ambient 
temperature and pressure.  It can be stored and transported as a 
liquid at a pressure of 10 atm at 25 C. 

    Ammonia dissolves readily in water where it forms, and is in 
equilibrium with, ammonium ions (NH4+).  The sum of ammonia and 
ammonium concentrations is termed "total ammonia" and, because of 
the slightly different relative molecular masses, may be expressed 
as "total ammonia-nitrogen (NH3-N)".  In most waters, NH4+ 
predominates, but increases in pH or temperature or decreases in 
ionic strength may materially increase levels of non-ionized 
ammonia. 

    Ammonia will adsorb on various solids.  At concentrations of 
between 16 and 27% by volume, it can form explosive mixtures with 
air.  Catalytic oxygenation is an important reaction in the 
manufacture of nitric acid.  Ammonia dissolves in dilute acids to 
form ionized ammonium salts, which are similar in solubility to 
alkali metal salts, and can be crystallized.  Some of these salts 
are found in nature.  Heating solutions or crystals of the salts 
yields gaseous ammonia.  Ammonia forms chloramines in water 
containing hypochlorous acid. 

    There are difficulties in sampling media for the determination 
of ammonia, and in preventing contamination and losses before 
analysis.  A variety of analytical techniques are available; many 
have interactions.  For measurements, the flourescent 
derivatization technique has advantages. 

1.2.  Sources in the Environment

    Ammonia is present in the environment as a result of natural 
processes and industrial activity, including certain types of 
intensive farming.  Atmospheric ammonia is volatilized from the 
earth's surface in quantities of about 108 tonnes/year, mostly from 
natural biological activity.  Industrial activity may cause local 
and regional elevations in emission and atmospheric concentrations.  
Surface waters receive ammonia from point sources, such as effluent 
from sewage treatment and industrial plants, in quantities 
estimated in the USA to be about half a million tonnes annually.  
Much more significant quantities arise from non-point sources, such 
as atmospheric deposition, the breakdown of vegetation and animal 
wastes, applied artificial fertilizers and urban runoff, and these 
are significant, even in industrial areas. 

1.3.  Environmental Transport, Distribution, and Transformation

    Ammonia in the environment is a part of the nitrogen cycle.  It 
volatilizes into the atmosphere where it may undergo a variety of 
reactions.  Photolytic reactions destroy some of the ammonia and 
reactions with sulfur dioxide or ozone produce aerosols, most 

importantly of ammonium sulfate or nitrate, which return to the 
earth's surface as wet or dry deposition.  In surface waters, 
ammonium may undergo microbiological nitrification, which yields 
hydrogen and utilizes oxygen so that, in certain systems, 
acidification and oxygen depletion may result.  In one study, one-
third of the acidifying effect of precipitation was attributed to 
ammonium deposition.  Ammonia may be assimilated by aquatic plants 
as a nitrogen source or transferred to sediments or volatilized.  
In soil, major sources of ammonia are the aerobic degradation of 
organic matter and the application and atmospheric deposition of 
synthetic fertilizers.  The ammonium cation is adsorbed on 
positively charged clay particles and is relatively immobile.  Most 
ammonium undergoes nitrification; the nitrate ion is mobile and is 
removed by leaching, plant root uptake, or denitrification. 

1.4.  Environmental Levels and Human Exposure

    Atmospheric concentrations vary according to underlying land 
usage.  Urban concentrations are typically in the range of 5 - 
25 g/m3 and rural concentrations, 2 - 6 g/m3.  Areas with 
intensive manure production or use may produce concentrations of 
100 - 200 g/m3.  Particulate ammonium concentrations above oceans, 
remote from land, have been found to be 10 - 115 ng/m3.  In most 
situations, atmospheric particulate ammonium concentrations are 
comparable to gaseous ammonia concentrations. 

    Surface waters contain concentrations of total ammonia that 
vary both regionally and seasonally.  In the USA, most surface 
waters contain less than 0.18 ng/litre, though those near large 
metropolitan areas may contain 0.5 ng/litre, as total ammonia.  In 
hydrologically isolated acidified small lakes, concentrations may 
reach 3 mg NH4+-N/litre, and values near intensive farms of 12 mg 
NH4+-N/litre have been recorded.  Ground water usually contains low 
concentrations of ammonia, because of ammonium adsorption and/or 
nitrification; this, and the conversion of ammonia to chloramines 
on chlorination, results in low levels of ammonia in most treated 
drinking-water. 

    Ammonia in soil is largely fixed; that in solution is in 
dynamic equilibrium with nitrate and is not directly available to 
plants.  Ammonia occurs in unprocessed foods, but ammonium salts 
are added to processed foods.  Acceptable Daily Intakes (ADIs), 
where specified, relate to the anion.  Cigarette smoking and 
certain medicines may contribute to intake, in some cases, but the 
intake from all sources is small in comparison with endogenous 
intestinal ammonia production. 

    Occupational exposure to low levels of ammonia is common, but, 
in certain occupations, work-place concentrations may exceed 
100 mg/m3.  At such levels, the daily ammonia intake is small in 
relation to endogenous production, but it is significant, since 
inhaled ammonia enters the systemic circulation. 

1.5.  Kinetics and Metabolism

1.5.1.  Uptake and absorption

    At low concentrations, inhaled ammonia dissolves in the mucous 
fluid lining the upper respiratory tract and little reaches the 
lower airways.  Initial retention is about 80% in both the dog and 
man, but, in man, it falls to less than 30% in less than 27 min.  
In rats, increases in blood-ammonia were measured following short-
term exposure to ammonia at 220 mg/m3 but not at 23 mg/m3.  The 
increases were less marked with longer exposure.  Calculated blood-
ammonia increases with exposure to air containing 18 mg/m3 are 
about 10% of fasting levels. 

    Ammonia is formed in the human intestinal tract by the 
biological degradation of nitrogenous matter, including secreted 
urea, in quantities of about 4 g/day.  Nearly all of this is 
absorbed (mainly passively) and is metabolized in the liver on 
first passage, so that only small amounts reach the systemic 
circulation. 

1.5.2.  Distribution

    Ammonia is normally present in all tissues constituting a 
metabolic pool.  Its distribution is pH dependent, since NH3 
diffuses more easily than NH4+.  Oral administration of ammonium 
chloride to healthy male and female volunteers at 9 mg/kg body 
weight produced transient increases in blood-ammonia in about half 
of the subjects.  Patients with cirrhosis showed a greater and more 
prolonged increase over a higher baseline.  This confirms 
substantial first pass metabolism in the liver. 

    Administration of 15N-labelled ammonium compounds to 
experimental animals indicated that the initial distribution of 15N 
depended on the route of administration and that, after parenteral 
administration, more was distributed to organs other than the 
liver. 

1.5.3.  Metabolic transformation

    Ammonia is taken up by glutamic acid in many tissues, and this 
will take part in a variety of transamination and other reactions, 
the nitrogen being incorporated in non-essential amino acids.  In 
the liver, ammonia is used in the synthesis of protein by the 
Krebs-Henseleit cycle. 

1.5.4.  Excretion and turnover

    The principal means of ammonia excretion varies between phyla.  
Mammals excrete urea and secrete ammonium in the kidney tubules as 
a means of hydrogen ion excretion.  Faecal and respiratory 
excretion are insignificant.  Exhaled air may contain volatilized 
ammonia from the microfloral degradation of salivary urea.  In man, 
on a 70 g protein/day diet, 70% of administered ammonium 15N is 
lost in a week; on a 20 g protein/day diet, 35% is lost. 

1.5.5.  Plant metabolism of ammonia

    Ammonia is toxic in plants and cannot be excreted.  It is 
detoxified by combination with carbon skeletons, and so excess 
ammonia may strain carbohydrate metabolism.  Some plants have 
special means of handling ammonia, enabling them to tolerate it or 
use it preferentially. 

1.6.  Effects on Aquatic Organisms

    Concentrations of ammonia that are toxic for aquatic animals 
are generally expressed as non-ionized ammonia (NH3), because, in 
the environment, NH3 and not the ammonium ion (NH4+) has been 
demonstrated to be the principal toxic form of ammonia. 

    Concentrations of ammonia, acutely toxic for fish, can cause 
loss of equilibrium, hyperexcitability, increased breathing, 
cardiac output, and oxygen uptake, and, in extreme cases, 
convulsions, coma, and death.  At lower concentrations, ammonia 
produces many effects in fish including a reduction in egg hatching 
success, a reduction in growth rate and morphological development, 
and pathological changes in the tissue of the gills, liver, and 
kidney. 

    Several factors have been shown to modify acute ammonia 
toxicity in fresh water.  Some factors alter the concentration 
of NH3 in the water by affecting the aqueous ammonia equilibrium, 
while other factors affect the toxicity of NH3 itself, either 
ameliorating or exacerbating its effects.  Factors that have been 
shown to affect ammonia toxicity include dissolved oxygen 
concentration, temperature, pH, previous acclimatization to 
ammonia, fluctuating or intermittent exposures, carbon dioxide 
concentration, salinity, and the presence of other toxic 
substances.  The best studied of these is pH; the acute toxicity 
of NH3 has been shown to increase as pH decreases.  Data on 
temperature effects on acute NH3 toxicity are limited and 
variable, but there are indications that NH3 toxicity is greater 
at low (< 10 C) temperatures. 

    Data concerning concentrations of NH3 that are toxic for fresh-
water phytoplankton and vascular plants, although limited, indicate 
that fresh-water plant species are appreciably more tolerant to NH3 
than invertebrates or fish. 

    (a)   Fresh-water organisms

    Mean 48- and 96-h LC50 values reported for fresh-water 
invertebrates and fish ranged from 1.10 to 22.8 mg NH3/litre for 
invertebrate species, and from 0.56 to 2.48 mg/litre for fish 
species.  Mean 96-h LC50 values ranged from 0.56 to 2.37 mg 
NH3/litre for salmonid fish and from 0.76 to 2.48 mg/litre for non-
salmonids.  In terms of LC50, Percidae and Salmonidae are 
considered to be the most sensitive families and walleye and 
rainbow trout are the most sensitive species within these families. 

    For fresh-water organisms, the families most sensitive in terms 
of chronic toxicity are Salmonidae and Catostomidae, pink salmon 
and white sucker being the most sensitive species within these 
families.  Limited chronic toxicity data for invertebrates, mostly 
cladocerans and one insect species, indicate that they are 
generally more tolerant than fish, although the fingernail clam 
appears to be as sensitive as salmonids. 

    (b)   Salt-water organisms

    Available acute and chronic ammonia toxicity data for salt-
water organisms are very limited.  Mean LC50 values for marine 
invertebrate species range from 0.94 to 18.3 mg NH3/litre and, for 
marine fish species, from 0.32 to 1.31 mg/litre.  The prawn, 
 Macrobrachium rosenbergii, appears to be the most sensitive 
invertebrate species tested, and the red drum, the most sensitive 
fish species. 

1.7.  Effects on Experimental Animals and  In Vitro Test Systems

1.7.1.  Single exposures

    There have been many estimates of inhalational toxicity in 
which the theoretical relationship between concentration, duration 
of exposure, and lethality has been observed.  Typical results are 
LC50 values in rats ranging from 31 612 mg/m3 for a 10-min exposure 
to 11 620 mg/m3 for a 60-min exposure.  The corresponding value for 
a 2-h exposure was 7600 mg/m3.  Exposed mice exhibited avoidance 
behaviour at concentrations above 350 mg/m3, and ciliary activity 
was arrested above this level in  in vitro studies on rabbit 
tracheal epithelium.  Other effects of exposure include bradypnoea 
and bradycardia, changes in various serum-enzyme levels, and 
histological changes in the lung.  At high concentrations, 
convulsions occurred. 

    There have been a number of studies on the oral toxicity of 
various ammonium salts, some of which have been complicated by the 
acidity or alkalinity of the preparations used.  Median lethal 
doses for ammonium sulfamate or sulfate were in the range 3 - 
4.5 g/kg body weight in both rats and mice.  Ammonium chloride 
causes substantial acidosis and has been reported to produce 
pulmonary oedema by a different mechanism by gavage, but not by 
intraperitoneal injection.  There is also evidence that ammonium 
ions exert a direct effect on the appetite by their effect on 
prepyriform cortical areas.  Ammonium chloride, even after 
administration for periods of a few days, produces hypertrophy of 
the kidney, but the extent to which this results from acidosis, a 
solute load, or a direct effect of the ammonium ion is not clear.  
Diet and the clinical condition of the liver are important 
modulators of ammonia toxicity, and it has been shown that the 
administration of ornithine, aspartic acid, or adenosine 
triphosphate (ATP) exerts a protective effect against ammonia 
toxicity. 


    No information is available regarding systemic toxicity from 
single dermal exposures to ammonia or ammonium compounds. 

    Symptoms after intravenous injection of ammonium salts are 
characterized by immediate hyperventilation and clonic convulsions, 
followed by either fatal tonic extensor convulsion or the onset of 
coma, in which tonic convulsions and death can occur at any time.  
After 30 - 45 min, surviving animals recover rapidly and 
completely.  After injection, neurological symptoms commenced when 
the blood-ammonia concentration doubled above basal values.  Brain-
ammonia levels did not increase until blood levels reached 20 times 
basal values; at this stage, brain levels suddenly increased to 
about 100 mg ammonia-nitrogen/kg wet weight.  However, immediate 
increases in brain-ammonia after intravenous injection have also 
been observed, and it has been suggested that there is no critical 
blood-ammonia concentration for diffusion of ammonia through the 
blood-brain barrier.  Some workers have demonstrated the induction 
of ventricular fibrillation of the heart following injections of 
ammonium salts. 

1.7.2.  Short-term exposures

    Ninety-day inhalation exposures of rats to 127 mg/m3 and 
262 mg/m3 did not produce any, or only minimal, changes.  Continuous 
exposure to 455 mg/m3 was fatal for 50 out of 51 rats by the 69th 
day of exposure.  Similar results were obtained in guinea-pigs.  
The principal pathological findings were eye irritation, corneal 
opacities, and diffuse lung inflammation.  Similar results have 
been published by a number of authors.  Concentration-dependent 
increases in susceptibility to infection during ammonia exposure 
have been reported.  Blood-ammonia levels increased with 
inhalational exposure to increasing concentrations of ammonia above 
70 mg/m3, for periods of 1 - 7 days. 

    Studies on the effects of ingestion of ammonium chloride 
(10 g/litre drinking-water - about 1 g/kg body weight per day) 
and ammonium sulfamate (5 g/kg body weight per day for 6 days 
per week) did not show any significant toxic effects.  Cyclical 
administration of various ammonium salts, at moderate doses, for 3 
weeks out of 4 affected the reproductive system of virgin female 
rabbits.  Ammonium salts have been given as a dietary supplement to 
animals on diets deficient in non-essential amino acids, with 
resultant increases in weight gain.  Ammonium salts can prevent and 
reduce the weight loss associated with 10% and 20% reduction of the 
crude protein content of the diet of pigs. 

    There is no information regarding the systemic effects of 
short-term dermal exposure. 

1.7.3.  Skin and eye irritation; sensitization

    There is little information on animals to complement the 
extensive human experience.  In rabbits, ammonia has been shown to 
penetrate the cornea rapidly and to cause corneal burns.  Ammonium 
persulfate is a recognized skin sensitizer in man.  No data on 
sensitization potential in animal models are available. 

1.7.4.  Long-term exposure

    Inhalation exposure studies did not extend beyond 130 days.  A 
130-day study demonstrated congestion of parenchymatous organs at 
18 weeks, but not at 12 weeks, in guinea-pigs exposed to about 
119 mg/m3 for 6 h/day, 5 days/week.  Long-term studies have not 
been carried out according to modern protocols, and observed 
effects have mainly been related to changes in acid-base balance. 

1.7.5.  Reproduction, embryotoxicity, and teratogenicity

    There have not been any formal studies based on modern 
protocols, but studies have been undertaken to investigate the 
effects of ammonia in hen-houses on the egg-laying performance of 
intensively reared poultry.  No systematic conclusions could be 
drawn. 

1.7.6.  Mutagenicity

    Ammonium sulfate has been reported non-mutagenic in  Salmonella
and  Saccharomyces test systems, but mutagenic in  E. coli at toxic 
levels and may affect mutagenic responses to other agents.  Various 
workers have described effects on  Drosophila, which were minimal 
or achieved only at toxic levels.  There is no evidence that ammonia 
is mutagenic in mammals. 

1.7.7.  Carcinogenicity

    There is no evidence that ammonia is carcinogenic, though it 
can produce inflammatory lesions of the colon and cellular 
proliferation, which could increase susceptibility to malignant 
change.  There was no evidence that ammonia was responsible for the 
increased incidence of tumours with increased dietary protein 
intake.  Ammonia did not either cause tumours or increase the 
spontaneous incidence of tumours in life-time studies on mice. 

1.7.8.  Mechanisms of toxicity

    Although there are a number of hypotheses, there is no 
established mechanism for the toxicity of ammonia or ammonium 
salts. 

1.8.  Effects on Man

1.8.1.  Organoleptic effects

    Ammonia can be tasted in water at levels above about 35 
mg/litre.  Odour thresholds have been variously reported according 
to the definition used and technique of measurement.  Most people 
can identify ammonia in air at about 35 mg/m3 and can detect it at 
about one-tenth of this level. 

1.8.2.  Clinical, controlled human studies and accidental exposure

    Exposure to ammonia in air at a concentration of 280 mg/m3
produced throat irritation; 1200 mg/m3 produced cough; 1700 mg/m3
was life-threatening, and more than 3500 mg/m3 caused a high 
mortality.  Respiratory symptoms were usually reversible, but 
chronic bronchitis has been reported to develop.  Volunteers 
exposed by oro-nasal mask experienced irritation and increased 
minute volumes.  Retention of inspired ammonia decreased 
progressively to about 24% after about 19 min of exposure.  The 
blood chemistry remained normal.  Respiratory indices were 
insignificantly altered at concentrations up to 98 mg/m3 (which was 
tolerable).  Other studies have demonstrated a high incidence of 
symptoms at this level.  Irritation occurred at 35 mg/m3, which was 
neither discomforting nor painful.  Industrial exposure at 88 mg/m3 
was described as "definitely irritating". 

    Ingestion of ammonia solutions has produced caustic burns of 
the upper gastrointestinal tract.  Ingestion of ammonium chloride 
produces metabolic acidosis and diuresis and is administered for 
these effects. 

1.8.3.  Endogenous ammonia

    Ammonia plays a key role in nitrogen metabolism, and its level 
in the body may be increased as a result, either of in-born errors 
of metabolism, or, as a result of impaired liver function.  The 
role of hyperammonaemia in causing the encephalopathy associated 
with the latter is not completely clear, but there is sufficient 
evidence to indicate a significant contribution. 

1.9.  Evaluation of the Health Risks for Man and Effects on the
Environment

    Atmospheric exposure of the general population is toxicologically 
insignificant.  Occupational exposure can give rise to symptoms, 
particularly in occupations exposed to decaying organic matter.  
Accidental exposure to ammonia in any of its forms produces 
irritant or caustic effects. 

    Exposure to ammonia in the water supply and food is 
insignificant in comparison with the nitrogen intake through the 
diet which becomes available as metabolic ammonia. 

    The most significant effects of ammonia are in the aquatic and 
terrestrial environments where, as a result of urbanization, 
industry, and farming and as a result of deposition to sensitive 
environments, significant toxic effects of ammonia may arise. 

1.10.  Conclusions

    Ammonia does not present a direct threat to man except as a 
result of accidental exposure, particularly in industry.  Farm 
animals may be adversely affected when reared intensively in closed 
conditions.  Localized effects of point-source emissions of ammonia 
and of deposition in sensitive environments is a cause of concern. 

2.  PROPERTIES AND ANALYTICAL METHODS

2.1.  Physical and Chemical Properties of Ammonia and Ammonium Compounds

2.1.1.  Gaseous and anhydrous liquid ammonia

    Ammonia (NH3) is a colourless gas at atmospheric pressure, 
which is lighter than air and possesses a strong penetrating odour.  
Some of the relevant physical properties of ammonia are summarized 
in Table 1. 

    The vapour pressure of ammonia gas over pure ammonia liquid can 
be calculated using the equation (NRC, 1979): 

    log10P = 9.95028 - 0.003863T - 1473.17/T,

    where P = partial pressure in mm Hg, and T = temperature at K.

    Ammonia may be liquefied under pressure at about 10 atm and is 
stored and transported in this state. 

2.1.2.  Aqueous solutions

    Ammonia dissolves readily in water where it ionizes to form the 
ammonium ion. 
                      \
    NH3 + H2O ========= NH4+ + OH-
             \     

    The solubility of ammonia in water is influenced by the 
atmospheric pressure, temperature, and by dissolved or suspended 
materials.  Solubility values at moderate concentrations and 
temperatures can be obtained from the graphic (Sherwood, 1925) and 
tabular (Perry et al., 1963) compilations, and from empirical 
formulae (Jones, 1973). 

    The total ammonia content of water is the sum of non-ionized 
(NH3) and ionized (NH4+) species.  Ammonia is readily soluble in 
aqueous systems (Table 1) and, at the pH of most biological 
systems, exists predominantly in the ionized form.  At low 
concentrations, the molarity of total dissolved ammonia is given by 
(Drewes & Hales, 1980): 

    [NH3] + [NH4+] = H[NH3(gas)] + KbH[NH3(gas)],

where [NH3(gas)] is the molar concentration of gas-phase ammonia, 
Kb is the dissociation constant given by: 

         [NH4+] [OH-]
    Kb = ------------ = 1.774 x 10-5 (at 25C)
            [NH3]

and H is a Henry's law constant given by (NRC, 1979): 

           log10H = 1477.8/T - 1.6937

Table 1.  Physical properties of ammoniaa
------------------------------------------------------------------
Properties                               Values
------------------------------------------------------------------
Boiling point at one atm                 -33.42 C

Melting point                            -77.74 C

Density (liquid) at -33.35 C and 1 atm  0.6818 gm/cm2

Density (gas)                            0.7714 g/litre

Viscosity at -33 C                      0.254 centipoise

Viscosity at 20 C                       9.821 x 109 poise

Refractive index at 25 C                1.325

Dielectric constant at 25 C             16.9

Surface tension at 11 C                 23.38 dyn/cm

Specific conductance at -38 C           1.97 x 10-7 cm-1

Thermal conductivity at 12 C            5.51 x 10-5 gcal/cm

Vapour pressure at 25 C                 10 atm

Critical temperature                     132.45 C

Critical pressure                        112.3 atm

Critical density                         0.2362 g/cm3

Solubility in water, 101 kPa

    at  0 C                             895 g/litre
       20 C                             529 g/litre
       40 C                             316 g/litre
       60 C                             168 g/litre
------------------------------------------------------------------
a From:  Jones (1973) and Windholz et al., ed. (1976).

The pKa for the ammonia/ammonium equilibrium  can be calculated at 
all temperatures, T(K), between 0 and 50 C (273 < T < 323) by 
the equation (Emerson et al., 1975): 

     Ka = [NH3] [H+]/[NH4+],
     pKa = 0.09018 + 2729.92/T

Theoretically, the fraction (f) of total ammonia that is non-
ionized depends on both water temperature and pH, according to the 

preceding and the following equations (Emerson et al., 1975): 

              (pKa-pH)
     f = 1/[10        + 1]

Thus, in water at 0 C and a pH of 6, less than 0.01% of the total 
ammonia present is in the non-ionized form, whereas, at 30 C and a 
pH of 10, 89% of total ammonia is non-ionized. 

    The above relationship holds in most fresh waters.  However, 
the concentration of non-ionized ammonia will be lower at the 
higher ionic strengths of very hard fresh waters or saline waters.  
Using the appropriate activity coefficients, in sea water of ionic 
strength = 0.7, the above relationship can be restated as follows 
(API, 1981): 

              (pKa-pH + 0.221)
     f = 1/[10                + 1]

    At 25 C, the pKa can be calculated to be 9.24, from the 
equation of Emerson et al. (1975).  Therefore, at pH 8, and at a 
temperature of 25 C, the above equation shows that 3.31% of the 
total ammonia in sea water exists in the non-ionized form.  The 
corresponding value in fresh water can be calculated to be 5.38%.  
Thus, at this pH and temperature, sea water with an ionic strength 
of 0.7 would contain 62% as much non-ionized ammonia as fresh 
water. 

2.1.3.  Chemical reactions

    Gaseous ammonia is readily adsorbed on certain solids.  The 
adsorption characteristics of ammonia on metal surfaces are 
important in its synthesis and other catalytic reactions (Cribb, 
1964).  Because of the adsorption of ammonia on charcoal, acid-
impregnated charcoal masks are used for protection against ammonia 
gas. 

    Ammonia can form explosive mixtures with air at atmospheric 
temperature and pressure, if present in concentrations of 16 - 27% 
by volume.  The products of combustion are mainly nitrogen and 
water, but small traces of ammonium nitrate (NH4NO3) and nitrogen 
dioxide (NO2) are also formed. 

    Another important reaction involving the oxidation of ammonia 
is its catalytic oxidation to nitric oxide (NO) and nitrous oxide 
(N2O) (Miles, 1961; Matasa & Matasa, 1968).  This reaction is an 
important step in the manufacture of nitric acid. 

    Under normal atmospheric conditions, ammonia does not undergo 
any primary photochemical reactions at wavelengths greater than 
290 nm. 

    When exposed to radicals or other photochemically excited 
species, ammonia undergoes secondary decomposition: 

    NH3 + -OH  ->  -NH2 + H2O

    NH3 + O  ->  -NH2 + -OH

Some of these reactions may be important in the balance of 
atmospheric nitrogen. 

    Ammonia also undergoes decomposition to nitrogen and hydrogen, 
when exposed to an electric discharge (Jones, 1973).  It reacts 
with sulfur dioxide gas to form ammonium sulfate in the atmosphere 
(Kushnir et al., 1970). 

    Aqueous ammonia can take part in substitution reactions with 
organic halide, sulfonate, hydroxyl, and nitro compounds, and, in 
the presence of metallic catalysts, it is used to produce amino 
acids from keto acids.  Ammonia reacts with hypochlorous acid 
(HOCl) to form monochloramine, dichloramine, or nitrogen 
trichloride (Morris, 1967; Lietzke, 1978).  The formation of these 
 N-chloramines depends on the pH, the relative concentrations of 
hypochlorous acid and NH3, the reaction time, and the temperature.  
When pH values are greater than 8, and when the molar ratio of HOCl 
to NH3 is 1:1 or less, the monochloramine predominates.  At higher 
Cl2:NH3 ratios or, at lower pH values, dichloramine and 
trichloramine are formed.  These, and various organic chloramines, 
are produced during the chlorination of water containing NH3 or 
organic amines.  The presence of these chloramines may contribute 
to the taste and odour of drinking-water, and to various 
associated health problems (Morris, 1978). 

2.1.4.  Ammonium compounds

    Ammonium compounds comprise a large number of salts, many of 
which are of industrial importance; ammonium chloride, ammonium 
nitrate, and ammonium sulfate are produced on a large scale.  With 
the exception of metal complexes, the ammonium salts are very 
similar in solubility to the salts of the alkali metals, but differ 
in that they are completely volatilized on heating or ashing. 

    Ammonium salts undergo slight hydrolysis in aqueous solution.  
Most dissociate at elevated temperatures to give ammonia and the 
protonated anion.  The physical and chemical properties of ammonium 
compounds of environmental importance are discussed below, and some 
of their physical properties are summarized in Table 2. 

    Ammonium chloride [NH4Cl] occurs naturally in volcanic
crevices as a sublimation product.  When it sublimes, the
vapour is completely dissociated into hydrogen chloride and
ammonia.  Like other ammonium salts of strong acids, the
chloride hydrolyses in aqueous solution to lower the pH of the
solution.  The solid tends to lose ammonia during storage.  Aqueous 
solutions of ammonium chloride have a notable tendency to attack 
ferrous metal and other metals and alloys, particularly copper, 

bronze, and brass.  Ammonium chloride can be oxidized to nitrosyl 
chloride and chlorine by strong oxidizing agents, such as nitric 
acid. 

    Ammonium nitrate [NH4NO3] does not occur in nature.  It is 
soluble in water and liquid ammonia and slightly soluble in 
absolute ethyl alcohol, methanol, and acetone.  Although ammonium 
salts of strong acids generally tend to lose ammonia during 
storage, ammonium nitrate can be considered a very stable salt.  It 
undergoes decomposition at elevated temperatures or under extreme 
shock, as in commercial explosives.  Ammonium nitrate acts as an 
oxidizing agent in many reactions, and, in aqueous solution, it is 
reduced by various metals.  Solutions of ammonium nitrate attack 
metals, particularly copper and its alloys. 

    Ammonium sulfate [(NH4)2SO4] is found naturally in volcanic 
craters.  It is soluble in water and insoluble in alcohol and 
acetone.  The melting point of ammonium sulfate is 230 C.  On 
heating in an open system, the compound begins to decompose at 
100 C, yielding ammonium bisulfate (NH4HSO4) that has a melting 
point of 146.9 C. 

    Ammonium acetate [CH3COONH4] is a deliquescent material that is 
highly soluble in cold water and in alcohol.  Solubility does not 
increase greatly with increasing temperature, at least up to 25 C.  
In aqueous solution at atmospheric pressures, ammonium acetate 
readily loses ammonia, especially in alkaline conditions. 

    Ammonium carbonate [(NH4)2CO3] and ammonium bi-carbonate 
[NH4HCO3] have long been known because of their occurrence in 
association with animal wastes.  Ammonium bicarbonate is the more 
readily formed and the more stable.  It decomposes below its 
melting point (35 C), dissociating into ammonia, carbon dioxide, 
and water.  Ammonium bicarbonate reacts with, and dissolves, 
calcium sulfate scale.  Ammonium carbonate decomposes on exposure 
to air with the loss of ammonia and carbon dioxide, becoming white 
and powdery and converting into ammonium bicarbonate.  Ammonium 
carbonate volatilizes at about 60 C.  It dissolves slowly in water 
at 20 C, but decomposes in hot water. 

2.2.  Sampling and Analytical Methods

2.2.1.  Air and water samples

    Measurement of ammonia levels in air is difficult.  Atmospheric 
levels are low, and samples can be contaminated by emissions from 
man; thus, the analyst should remain remote from the sampling 
device.  In addition, air samples are bubbled through acid media to 
form an aqueous solution of ammonia, predominately in its ionic 
form.  The extraction of ammonia is variable and both gaseous 
ammonia and that contained in aerosols will be extracted.  In some 
instances filters are used to remove aerosols from the gas stream 
so that only ammonia gas is sampled.  There are, however, some 
problems with aerosol filters as they may interact with gaseous 
ammonia when the aerosol is collected on the filter (NRC 1979). 


Table 2.  Physical properties of some ammonium compoundsa
-----------------------------------------------------------------------------------------------------------------
Property        Ammonium       Ammonium       Ammonium       Ammonium      Ammonium         Ammonium
                chloride       nitrate        sulfate        acetate       carbonate        bicarbonate
-----------------------------------------------------------------------------------------------------------------
Synonyms        ammonium       ammonium       ammonium       ammonium      ammonium         ammonium bicarbonate;
                chloride;      nitrate        sulfate;       acetate       carbonate;       ammonium hydrogen
                sal ammoniac                  mascagnite                   monohydrate      carbonate

Colour          colourless     colourless     colourless     white         colourless       colourless

Physical state  cubic          rhombic        rhombic        crystals,     cubic            rhombic or monoclinic
(25 C, 1 atm)  crystals       crystals       crystals       hygroscopic   crystals         crystals

Formula         NH4Cl          NH4NO3         (NH4)2SO4      CH3COONH4     (NH4)2CO3 x H2O  NH4HCO3

Relative        53.49          80.04          132.14         77.08         114.10           79.06
molecular mass

Melting point   340 sublimes   169.6          230            114           58               35
(C)                                          decomposes                   decomposes       decomposes

Boiling point   520            > 210                         decomposes                     sublimes
(C)                           decomposes

Density         1.527 (20 C)  1.725 (25 C)  1.769 (50 C)  1.17 (20 C)                   1.58 (20 C)

Refractive      1.642                         1.533                                         1.423, 1.555
index, nb20

Solubility in   370 (20 C)    1920 (20 C)   754 (20 C)    1480 (4 C)   1000 (15 C)     217 (20 C)
water 
(g/litre)
-----------------------------------------------------------------------------------------------------------------
a From:  Dean (1979) and Weast (1979).
                                                          
    Air samples collected by liquid impinger yield aqueous 
solutions.  Fabric filters used for collecting aerosols may be 
extracted with water for analysis.  Generally, air and water 
samples are analysed using similar techniques, which are summarized 
in Table 3. 

    Various methods for preventing interference can be used, but 
distillation at pH 9.5 is often carried out.  Care must be taken 
with water samples to prevent oxidation, volatilization, or 
microbiological assimilation of ammonia.  Thus, samples should be 
acidified and refrigerated in sealed containers (and may be treated 
with reagents) and analysed within 24 h (APHA, 1976; NRC, 1979; US 
EPA, 1979b; ASTM, 1980; API, 1981; Analytical Quality Control 
(Harmonised Monitoring) Committee, 1982). 

2.2.2.  Soil samples

    Soil samples are usually collected by the grab method.  To 
inhibit microbial activity during transport and storage, reagents 
(e.g., mercury (II) chloride) can be added to the soil (NRC, 1979).  
Rapid drying at 55 C, then sealing the samples in air-tight 
containers is a more satisfactory method of preservation for 
ammonium determination (NRC, 1979), but even this may not prevent 
erroneous results, and samples should be analysed soon after sample 
collection (NRC, 1979).  Analytical methods for the determination 
of ammonia and ammonium in soils have been reviewed by NRC (1979). 

2.2.3.  Blood and tissue samples

    The various techniques used for the determination of ammonia in 
blood and tissues ultimately incorporate the ammonia detection 
methods described in Table 3, but with various conditions, such as 
distillation, aeration, and diffusion to minimize interference 
(NRC, 1979).  Because of the higher protein concentration in 
tissues, determination of ammonia is subject to greater glutamine-
caused error than in body fluids (NRC, 1979). 


Table 3.  Ammonia detection methods
----------------------------------------------------------------------------------------------------------------------
Medium  Particular      Method            Principle                  Interferants         Sensitivity  Reference
        application
----------------------------------------------------------------------------------------------------------------------
Air     silo air NH3    alkalimetric      air is drawn through       other acidic or      70 - 700     Elkins (1959);
                                          sulfuric acid until        alkaline             mg/m3        Leithe (1971)
                                          bromophenol indicator      contaminants                      
                                          changes colour; volume                                       
                                          of air is inversely
                                          proportional to 
                                          ammonia concentration

Water   high            titrimetric       NH3 in water is distilled                       1 - 25       API (1981)
        concentrations                    off into distilled water                        mg/litre
                                          which is titrated with
                                          acid to a methyl red/
                                          methylene blue end-point

Air                     Nesslerization    NH3/NH4 in dilute          amines, cyanate,     14 - 95      Leithe (1971);
                                          sulfuric or boric acid     alcohols, aldehyde,  mg/m3 air    NIOSH (1977)
                                          is reacted with alkaline   ketones, colour,                  
Water                                     mercuric and potassium     turbidity, residual  1 - 25       Stern (1968);
                                          iodide solution (Hg I2 x   chlorine             mg/litre     API (1981)
                                          KI); absorbence at 440 nm                       water        
                                          is compared with a
                                          standard curve; distil-
                                          lation can preceed
                                          analysis

Air     low             indophenol        NH3 in solution is         monoalkyl amines,    7 - 7000     Leithe (1971)
        concentrations  reaction          reacted with hypochlorite  formaldehyde         g/m3        
                                          and phenol (slow-warm
                                          reagents)

Water                                                                turbidity, colour    10 - 2000    API (1981)
                                                                     salt (sea water)     g/litre

Air     measurement     ammonia           measurement of ionization  mercury, volatile    14 - 2100    Sloan & Morie
        of tobacco      electrode         potential of NH3 -->       amines               g/m3        (1974)
        smoke           (potentiometric)  NH+4                                                        
----------------------------------------------------------------------------------------------------------------------

Table 3.  (contd.)
----------------------------------------------------------------------------------------------------------------------
Medium  Particular      Method            Principle                  Interferants         Sensitivity  Reference
        application
----------------------------------------------------------------------------------------------------------------------
Water                                                                                     0.05 - 1400  API (1981)
                                                                                          mg/litre

Air     continuous      chemiluminescent  air is passed through                           3.5 - 3500   Spicer (1977)
        measurement                       high- and low-temperature                       g/m3        
                                          catalytic converters,
                                          which respectively
                                          measure NOx + NH3 and
                                          NOx; NH3 is obtained by
                                          subtraction
                                          

Air     tobacco         gas chromato-     gas chromatography with                         7 - 70       Sloan & Morie
        smoke           graphy            thermal conductivity                            mg/m3        (1974)
                                          detector                                                   

Air     continuous      UV spectro-       NH3(gas) exhibits several                       0.7 - 7      Leithe (1971)
        measurement     photometry        strong absorption bonds                         mg/m3        
                                          between 190 and 230 nm;
                                          absorption in 10 cm 
                                          quartz cells at 204.3 nm
                                          has been used (molecular
                                          extinction coefficient =
                                          2790)

Air     continuous      Fluorescent       1-phthaldehyde                                  0.07 g/m3   Abbas & Tanner
        measurement     derivatization    derivatization                                  upwards      (1981)
        high            technique                                                                      
        sensitivity
----------------------------------------------------------------------------------------------------------------------
3.  SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

    Ammonia is present in the environment as a result of natural 
processes and through the industrial activities of man.  It is 
generally accepted that, of the ammonia present in the atmosphere, 
99% is produced by natural biological processes.  Ammonia is 
continually released throughout the biosphere by the breakdown or 
decomposition of organic waste matter.  Thus, any natural or 
industrial process that concentrates and makes nitrogen-containing 
organic matter available for decomposition represents a potential 
source of high local concentrations of ammonia in water, air, and 
soil.  Industrially-produced ammonia, from non-biological nitrogen, 
also represents an environmental source, by release through 
agricultural fertilization and industrial emissions.  Coal 
gasification or liquefaction may provide a major local source of 
ammonia.  The natural occurrence of ammonia compounds is indicated 
in section 2.1.4. 

3.1.  Production and Use

    Ammonia is one of the most widely-used industrial chemicals.  
It is ranked fourth in production volume in the USA after sulfuric 
acid, lime, and oxygen (Chemical and Engineering News, 1980).  
Total production of ammonia-nitrogen in the USA increased from 
5.8 x 106 tonnes in 1964 to 11.5 x 106 tonnes in 1974 (Keyes, 
1975), and had further increased to 17.6 x 106 tonnes by 1979 
(Chemical and Engineering News, 1980).  The demand in the USA for 
the production of ammonia is projected to reach 25 x 106 tonnes by 
1990 (Mai, 1977). 

    Ammonia is mainly produced industrially by the Haber-Bosch 
process in which nitrogen and hydrogen are combined under high 
pressure in the presence of a catalyst (Harding, 1959; Matasa & 
Matasa, 1968).  Prior to the Haber-Bosch process, ammonia was 
produced by the hydrolysis of cyanamides or cyanides.  A smaller 
scale method for ammonia production is regeneration from ammonium 
salts by heating with a base.  Alkaline earth metal oxides and 
hydroxides have been used with the naturally-occurring ammonium 
chloride. 

    Most of the ammonia produced in the USA is consumed as 
fertilizers (80%), fibres and plastics (10%), and explosives (5%) 
(Chemical and Engineering News, 1980).  It is also used in the 
production of animal feed (1.5%), pulp and paper (0.6%), and rubber 
(0.5%) (Keyes, 1975) and in a variety of other chemical production 
processes.  Ammonia and ammonium compounds are used as cleaning 
fluids, scale-removing agents, and in food as leavening agents, 
stabilizers, and for flavouring purposes.  A survey by the US Food 
and Drug Administration (US FDA) indicated that about 6000 tonnes 
of ammonium compounds were used in food in 1970 (FASEB, 1974) 
comprising ammonium bicarbonate, 317 tonnes; ammonium carbonate, 
24 tonnes; ammonium hydroxide, 535 tonnes; monobasic ammonium 
phosphate, 52 tonnes; dibasic ammonium phosphate, 434 tonnes; and 
ammonium sulfate, 1468 tonnes.  Information for ammonium chloride 
was not available.  The use of ammonium compounds in food nearly 
doubled during the period 1960 - 70. 

3.2.  Sources Releasing Ammonia into the Air

    Ammonia is released into the atmosphere by agricultural, waste-
disposal, and industrial activities.  Ammonia global release has 
been estimated at 113 - 244 x 106 tonnes ammonia-nitrogen/year 
(Sderlund & Svensson, 1976).  In the USA, industrial emissions 
from ammonia and fertilizer production (anhydrous ammonia, aqueous 
ammonia, ammonium nitrate, ammonium phosphates, urea), from 
petroleum refineries, coke ovens, and sodium carbonate manufacture, 
and loss of anhydrous ammonia during distribution, handling, and 
application have been estimated to be approximately 328 x 103 
tonnes, annually (NRC, 1979; US EPA, 1981).  This figure does not 
include volatilization of ammonia after soil applications of 
nitrogen fertilizer, which may amount to 5 - 10% of the ammonia and 
urea fertilizer applied.  These losses were estimated to comprise 
another 285 x 103 tonnes, annually (US EPA, 1981). 

    Combustion processes release ammonia as a by-product in amounts 
that are dependent on the substance being burned and the conditions 
of combustion.  Assuming that 2% of the municipal wastes generated 
in the USA are incinerated, about 0.8 x 103 tonnes of ammonia would 
be emitted annually from this source.  On the other hand, fossil 
fuel combustion in the USA is estimated to release 783 x 103 
tonnes/year (US EPA, 1981). 

    On the basis of the number of cattle in the USA and an average 
excretion of 31 kg urea per animal per year, it has been estimated 
that 3400 x 103 tonnes/year of ammonia are produced by cattle in 
the USA (API, 1981).  Similar calculations made in the Netherlands 
on the basis of the manure production of cattle, pigs, and poultry 
give a figure of 114 x 103 tonnes/year (Buysman, 1984).  Estimates 
of atmospheric emissions from the Netherlands and the USA are shown 
in Table 4. 

    It must be emphasized that substantial uncertainties are 
associated with these estimates, which are given for rough 
comparison only.  Ammonia from sources that cannot be quantified 
includes that which volatilizes from livestock wastes or polluted 
water, and emissions from the combustion of wood.  These sources 
must be considered in perspective with natural sources, especially 
the microbial fixation of nitrogen and the mineralization of 
nitrogenous organic matter.  Emissions from these natural sources 
far outweigh those from man-made sources, on a global scale; 
however, man-made sources can result in locally elevated 
atmospheric concentrations. 


Table 4.  Estimated atmospheric emissions of 
ammonia in the USA and the Netherlands
--------------------------------------------------
Source                     Annual emission 
                           (103 tonnes NH3)
                           ----------------------
                           USAa  the Netherlandsb
--------------------------------------------------
animal manure              3400  114 (1)

fertilizer volatilization  285   6.1 - 10.6

industrial activities      1111  7.6

other sources              0.8   0.5
--------------------------------------------------
a From:  US EPA (1981).
b From:  Buysman (1984).

    The very high contribution to ammonia emission from animal 
manure production in the Netherlands is remarkable.  More than 80% 
of the annually emitted ammonia results from the production of 
manure on intensive livestock farms and its use as an agricultural 
fertilizer.  In all areas with intensive livestock farming, ammonia 
emission from animal manure production contributes 90 - 99% to the 
total NH3 emission.  The number of poultry and pigs used in 
livestock farms increased 3 - 5 times between 1950 and 1980, and it 
can be expected that the ammonia emission from animal manure 
production has increased similarly.  In only a few areas does most 
of the emitted ammonia result from industrial activities, such as 
the production of coke and fertilizers, and the combustion of 
fossil fuel. 

    In Denmark, Belgium, and some parts of the Federal Republic of 
Germany and France, animal manure production contributes 
significantly to atmospheric emissions of NH3 (Buysman et al., 
1985). 

3.3.  Sources Discharging Ammonia into Water

    Ammonia is released into the aquatic environment from a variety 
of man-made point source discharges and from natural and man-made 
non-point sources. 

3.3.1.  Point sources of ammonia

    Major man-made point sources discharging ammonia into surface 
waters include sewage treatment plants, and plants producing 
fertilizers, steel, petroleum, leather, inorganic chemicals, 
non-ferrous metals, and ferroalloys, and meat processing plants.  
Amounts of ammonia discharged annually by these industries in the 
USA were estimated to be nearly 5.6 x 105 tonnes (API, 1981) 
(Table 5).  These estimates show that the industries examined 
contribute < 5% of the total ammonia discharged into surface 
waters while publicly owned sewage treatment plants (POTWs) 

contribute > 95% of the total.  It is important to note that the 
POTW figure is based on an estimated actual discharge, while 
several of the industrial figures are based on Best Practicable 
Control Technology (BPT) guidelines and other industrial data. 

    An estimate of ammonia discharge by sewage treatment plants was 
based on an average ammonia concentration of 15 mg/litre in 
secondary treatment waste waters (Metcalf & Eddy, Inc., 1972) and a 
total discharge of 104 billion litres per day.  However, some 
sewage treatment plants discharge waste waters containing much 
higher ammonia concentrations.  Using data from Mearns (1981), the 
US EPA (1981) estimated that the mean effluent concentration of 
ammonia from 5 major POTWs in southern California was 107 mg NH3-
N/litre (130 mg NH3/litre). 

    The iron and steel industries release ammonia, as a by-product 
of the conversion of coal to coke, and during blast furnace 
operations.  The source estimate in Table 5 is based on proposed 
BPT effluent control limits and steel production data. 

    The estimated ammonia contribution from the fertilizer industry 
was based on 1978 production figures for ammonia, ammonium nitrate, 
urea solutions, and urea solids, and on BPT guideline limits.  This 
contribution may be underestimated because relatively few of these 
producers meet BPT limits and because production is increasing (US 
EPA, 1981). 

    The estimated contribution of ammonia for all other industry 
groups in Table 5, except the meat processing and leather 
industries, was based on production figures and BPT guideline 
limits.  The effluents of the meat processing and leather 
industries were reported to contain about 40 and 100 mg NH3/litre, 
respectively (API, 1981). 

3.3.2.  Non-point sources of ammonia

    Non-point sources of ammonia for surface waters are not as easy 
to quantify as point sources.  Non-point sources include releases 
not discharged by a discrete conveyance.  They are variable, 
discontinuous, diffuse, and differ according to specific land use.  
They may be the result of runoff from urban, agricultural, 
silvicultural, or mined lands.  Urban runoff may sometimes be 
considered a point source, as it is frequently collected and 
discharged from drainage systems.  Several hydrological models are 
available to predict runoff and estimate pollutant loading, but 
there is still difficulty with this subject.  Major non-point 
sources of ammonia for surface waters include fertilizer runoff, 
animal feedlots, animal wastes spread on the soil, urban runoff, 
and precipitation. 

Table 5.  Estimates of aquatic emissions of ammoniaa from
point sources in the USA
----------------------------------------------------------
Point source                       Estimated contribution
                                   (tonnes NH3-N/year)
----------------------------------------------------------
Sewage treatment plants (POTWs)    535 922.3b

Steel industry                     12 951.0c

Fertilizer industry                5955.9c

Petroleum industry                 2826.1c or 2767.2b

Meat processing industry           1099.3b

Leather industry                   687.1b

Inorganic chemicals industry       99.8c

Non-ferrous metals manufacturing   0.9c

Ferroalloy manufacturing industry  0.3c

                     Total         559 542.7 tonnes/year
----------------------------------------------------------
a Adapted from: API (1981).
b Estimated contribution based on reported or estimated 
  actual discharge concentrations.
c Estimated contribution based on production data and BPT 
  guidelines, not actual discharges.

    The ammonia content of urban runoff is variable, depending, in 
part, on specific land use.  In a study of urban runoff, the amount 
of ammonia present varied with the seasons of the year.  Ammonia 
concentrations ranged from 0.18 mg N/litre in the autumn to 1.4 mg 
N/litre in the early spring (Kluesener & Lee, 1974).  In another 
study, Struzewski (1971) reported that ammonia-nitrogen in urban 
storm water ranged from 0.1 to 2.5 mg/litre. 

    The ammonia content of rural runoff originates from natural 
and man-made sources, including wastes from wildlife and livestock, 
decaying vegetation, fertilizer applications, material originally 
present in the soil, and precipitation.  Estimating total rural 
runoff quantities and ammonia concentrations is extremely complex 
and no overall estimates are available.  Loehr (1974) reported 
that the ammonium-nitrogen concentrations in the drainage from 4 
forested watersheds ranged from 0.03 to 0.08 mg/litre.  The 
ammonium-nitrogen concentrations were 8 - 14% of the nitrate-
nitrogen concentrations. 

    Precipitation is also a significant non-point source of 
ammonia.  Concentrations may vary locally, reflecting local 
atmospheric sources.  The average concentration in rainfall at one 
rural location on Long Island, New York (0.18 mg NH3-N/litre) was 

less than half those at 2 other Long Island sites closer to the New 
York urban area (0.43 and 0.459 mg NH3-N/litre) (Frizzola & Baier, 
1975).  Among collection sites throughout Wisconsin, ammonia levels 
in urban rain samples differed little from those in rural samples 
not taken near barnyards (range, 0 - 3 mg NH3-N/litre); however, 
values for locations near barnyards were 4 - 5 times higher (range 
0 - 3 mg NH3-N/litre) indicating contamination from locally-
generated atmospheric ammonia (Hoeft et al., 1972). 

    Similar tendencies have been observed in the Netherlands, 
though the absolute data are much higher.  In agricultural areas 
with dense livestock farming, ammonia levels ranging from 2.9 mg 
NH4+-N/litre near slurry manured croplands to 5.4 mg NH4+-N/litre 
at a distance of 100 m from a poultry farm have been found.  In 
relatively unaffected areas along the northern coast, the average 
value was 1.2 mg NH4+-N/litre, because of the relatively high 
background levels of atmospheric ammonia.  The average 
concentration in wet deposition was 2.4 mg NH4+-N/litre (Schuurkes, 
in press). 

    Watershed studies from pristine forests (Fisher et al., 1968), 
rural wood and pasture lands (Taylor et al., 1971), and heavily 
fertilized crop lands (Schuman & Burwell, 1974) have all shown that 
rainfall nitrogen, including ammonia-nitrogen, accounts for a 
substantial proportion (50 - 100%) of nitrogen in surface runoff. 

3.3.3.  Comparison between point and non-point sources

    Little information is available for the accurate comparison of 
point and non-point sources of ammonia for surface waters.  In one 
study, Wilkin & Flemal (1980) examined 3 Illinois river basins to 
determine the relative sources of various pollution loadings (by 
mass balance accounting) and the possible extent of water quality 
improvement by controlling various types of sources.  The three 
river basins, showed differences in point sources, patterns of land 
use (which influences non-point sources), and ammonia-nitrogen 
concentrations.  The east DuPage basin (42% industrial and urban) 
contained 4.73 mg NH3-N/litre, the upper Sangamon basin (19% urban 
and industrial), 2.51 NH3-N/litre, and the west DuPage basin (2% 
urban and industrial), 0.22 mg NH3-N/litre.  The fraction of 
ammonia-nitrogen load from undefined (non-point) sources in the 
heavily-industrialized east branch DuPage was only 0.54 compared 
with 0.84 in the rural upper Sangamon.  The authors concluded that 
much of the pollution loading appeared to be related to undefined 
sources and that further restrictions on point-source contributions 
might not result in improved water quality. 

    These data indicate that, although point sources contribute a 
large fraction of ammonia loading to surface waters, the 
contribution of undefined non-point sources is also significant. 

4.  ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

    Ammonia in the environment is a part of the total biotic and 
abiotic nitrogen balance as represented by the nitrogen cycle.  The 
processes of the nitrogen cycle consist of nitrogen fixation, 
assimilation, ammonification, nitrification, and denitrification.  
Nitrogen fixation and ammonification are microbially-mediated 
processes that produce ammonium ions from nitrogen gas and organic 
nitrogen.  Assimilation is the uptake and incorporation of 
inorganic nitrogen into organic molecules by microbes and plants.  
Nitrification is the microbial oxidation of the ammonium ion to 
nitrite (NO2-) and nitrate (NO3-).  Denitrification converts 
nitrate to nitrogen gas or nitrous oxide. 

4.1.  Uptake and Transformation in Atmosphere

    Ammonia enters the atmosphere as a result of both natural and 
artificial processes on the Earth's surface; there is no known 
photochemical reaction by which ammonia could be produced in the 
atmosphere (NRC, 1979).  Atmospheric ammonia undergoes four main 
types of reaction, namely aqueous-phase reactions, thermal 
reactions, photochemical reactions, and heterogeneous reactions. 

    In the aqueous-phase reactions, oxidation of aqueous sulfur 
dioxide in the presence of ammonia results in the formation of 
atmospheric ammonium sulfate aerosols.  This process is favoured by 
high humidity, high ammonia concentrations, and low temperatures 
(NRC, 1979). 

    Thermal reactions involving anhydrous ammonia and sulfur 
dioxide may, via heteromolecular nucleation, also result in the 
formation of ammonium sulfate aerosols.  Thermal reactions of 
ammonia with ozone result in the formation of ammonium nitrate, but 
the importance of this mechanism in the production of atmospheric 
ammonium nitrate aerosols is not known (NRC, 1979). 

    Photolytic degradation and reaction with photolytically 
produced hydroxyl radicals (-OH) in the troposphere are major 
pathways for the removal of atmospheric ammonia.  While there is 
limited information on the relative importance of these different 
reactions, it has been suggested that one-half of the atmospheric 
ammonia may be destroyed by the reaction with hydroxyl radicals, 
with the balance being destroyed by reaction with soot particles or 
by deposition (wet and dry) as particulate ammonium (NRC, 1979). 

    In addition to the formation of ammonium sulfate and nitrate, 
various ammonium surface complexes may be formed by the 
heterogeneous reaction of atmospheric ammonia with nitric oxide-
soot surfaces in the atmosphere (NRC, 1979).  While these 
heterogeneous reactions are significant in combustion reactions, 
their importance in the atmosphere at much lower concentrations of 
both ammonia and soot particles, is not known (NRC, 1979). 

    Comparison of the findings of Robinson & Robbins (1971) and 
Sderlund & Svensson (1976) on global nitrogen balances for ammonia 
reveals differences and it is difficult to evaluate which is the 
more accurate. 

4.2.  Transport to the Earth's Surface

    Most of the ammonia entering the atmosphere will be transported 
back to the earth by both wet and dry deposition.  Wet deposition 
includes rainfall, snow, hail, fog, and dew, while dry deposition 
mainly concerns gaseous ammonia.  In the Netherlands, a comparison 
has been made between the total emission and total deposition of 
ammonia- and ammonium-nitrogen.  Almost 95% of the emitted ammonia 
(119 x 103 tonnes/year) is deposited back on the surface (van 
Aalst, 1984).  In this way, ammonia contributes 60 - 90% of the 
nitrogen loading of water and soil, with nitrogen oxides making up 
the other part. 

4.2.1.  Wet and dry deposition

    A part of the ammonia in the atmosphere is removed by washout 
and rainout.  Ammonium sulfate aerosols are produced by aqueous-
phase reactions.  Thus, wet deposition of ammonia can be estimated 
by measuring ammonium concentrations in precipitation.  Annual 
average concentrations in wet deposition at locations in 21 
European countries vary from 0.12 to 1.74 mg NH4+-N/litre (Fuhrer, 
1985).  In the Netherlands, the mean annual concentration for the 
period 1978 - 82 was 2.4 mg NH4+-N/litre, corresponding to a wet 
deposition of 12.2 kg/ha per year.  The wet deposition in Norway 
ranges from 1.3 kg/ha per year in the centre of the country to 
8.6 kg/ha per year in the south (calculated from Overrein et al., 
1980).  In the United Kingdom, it varies between 3.2 and 6.0 kg/ha 
per year (calculated from Warren Spring Laboratory, 1982). 

    A comparison has been made of the amounts of dry and wet 
deposition of ammonia and ammonium per area in the Netherlands.  
The data are summarized in Table 6. 

    Wet deposition plays only a minor part (1/3) in the total 
deposition of NH3 and NH4+.  On average, 28.4 kg NH3 + NH4+-N is 
deposited per ha per year.  However, in rural areas with dense 
livestock farming, values may reach up to 50 - 100 kg per year. 

Table 6.  Dry and wet deposition of NH3 + NH+4
per ha per year in the Netherlandsa
------------------------------------------------
                mol/ha per year  kg/ha per year
------------------------------------------------
dry deposition  1150             16.2

wet deposition  790              12.2

Total           1940             28.4
------------------------------------------------
a From:  Van Aalst (1984).

4.2.2.  Contribution to acid rain

    Although ammonia is a base and thus increases the pH of rain 
water, it contributes to the acidifying action of deposition.  In 
particular, the conversion of ammonium to nitrate appears to be 
important in the acidification of soil and water in carbonate-poor 
environments (Roelofs, in press; Schuurkes, in press).  This 
potentially-acidifying action has been implicated in the acid rain 
problem in the Netherlands. On average, NH3 contributes about 32% 
of the total deposition of potentially-acidifying substances (Table 
7). 

Table 7.  Average deposition of acid 
and acidifying substances (acid eq.,/ha 
per year) in the Netherlandsa
---------------------------------------
                  SO2    NOx    NH3
---------------------------------------
Total deposition  2750   1310   1940
                  (46%)  (22%)  (32%)
---------------------------------------
a From:  The Netherlands Ministry of 
  Housing, Physical Planning, and 
  Environment (1984).

4.3.  Transformation in Surface Water

    Nitrification is important in preventing the persistence or 
accumulation of high ammonia levels in waters receiving sewage 
effluent or runoff.  The overall reaction is: 

    NH4+ + SO2 ---> 2H+ + NO3- + H2O

It occurs in two steps, involving primarily two bacterial genera, 
and forming nitrite as an intermediate. 

         Nitrosomonas      
    NH4+ ------------>  NO2-

         Nitrobacter      
    NO2- ----------->  NO3-

The process depends on many factors, including the amount of 
dissolved oxygen, temperature, pH, the microbial population, and 
the nitrogen forms present.  Nitrification is an oxygen-consuming 
process, requiring 2 moles of O2 per mole of NH4+ consumed and 
yielding hydrogen ion (NRC, 1979).  Nitrification may thus lead to 
a depletion of dissolved oxygen and acidification, which may, in 
turn, inhibit microbiological nitrification (Knowles et al., 1965; 
Schuurkes et al., 1985). 

    Anthonisen et al. (1976) reported that, at high levels of 
total ammonia and a high pH, the resulting concentrations of free 
ammonia were toxic to both nitrifying forms, but especially to 
nitrobacters, occasionally leading to the accumulation of nitrite.  

Other authors (Kholdebarin & Oertli, 1977) have reported that high 
pH alone, in the absence of ammonia, can inhibit nitrite oxidation.  
At high nitrite levels, formation of free nitrous acid caused 
inhibition of nitrosomonad bacteria, resulting in the persistence 
of both ammonia and nitrite.  However, inhibitory conditions and 
persistence of reduced forms are usually transient (Anthonisen et 
al., 1976), and reports of high nitrite levels are rare (Ecological 
Analysts, Inc., 1981). 

    Other mechanisms also act to remove ammonia from natural 
waters.  Ammonia is assimilated by aquatic algae and macrophytes 
for use as a nitrogen source.  Ammonia in water may be transferred 
to sediments by adsorption on particulates, or to the atmosphere by 
volatilization at the air-water interface.  Both processes have 
been described as having measurable effects on ammonia levels in 
water; however, the relative significance of each will vary 
according to specific environmental conditions (API, 1981). 

4.4.  Uptake and Transformation in Soils

    Ammonia levels in soils are a function of the balance between 
natural and man-made activities.  As a result of aerobic 
degradation processes, ammonia is the first inorganic nitrogenous 
compound to be released from organic matter together with amines, 
which are rapidly converted to ammonia (Powers et al., 1977).  
Other important sources of ammonia in soil are fertilizers 
(primarily anhydrous ammonia, ammonium nitrate, and urea, which is 
rapidly converted to ammonia), wet and dry deposition, and animal 
wastes. 

    The ammonium cation is relatively immobile in soils, because 
it is adsorbed on the negatively-charged clay colloids present 
in all soils (Wallingford, 1977).  Ammonia may be lost from 
soils by volatilization, especially after the application of 
ammonia fertilizers (Walsh, 1977), sewage, or manures, and by 
uptake of ammonium ions into root systems.  However, the most 
likely fate of ammonium ions in soils is conversion to nitrate by 
nitrification.  Nitrate is, in turn, lost from soils by:  leaching, 
which occurs readily, since it is repulsed by the clay particles; 
denitrification, which occurs rapidly within a few days or weeks in 
warm, moist soils; and by uptake by the plant root system. 

5.  ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

5.1.  Environmental Levels

5.1.1.  Atmospheric levels

    Ammonia is present in the atmosphere in very low 
concentrations, which vary with underlying land use.  In most 
situations, urban atmospheres contain more than non-urban, but 
certain rural areas, for example, those characterized by intensive 
animal husbandry or use of organic manure, have atmospheric ammonia 
levels that exceed urban values.  Atmospheric ammonia levels also 
show a seasonal variation, the highest levels being attained during 
the winter and the lowest during the summer months.  In urban 
areas, the ammonia levels may increase substantially during 
pollution episodes.  However, they do not show any circadian 
patterns. 

    Urban and non-urban atmospheric levels of ammonia at some 
locations around the world are shown in Tables 8 and 9.  It can 
be seen that ammonia levels of 4 - 5 g/m3 and 20 g/m3 are 
typical of non-urban and urban sites, respectively.  Levels of 
particulate NH4+ ions in the atmosphere above the main oceans 
(Atlantic, Pacific, Indian, and Antartic) have been studied; in the 
southern hemisphere, remote from terrestrial sources, the NH4+ 
concentrations were found to be between 10 and 115 ng/m3.  The 
authors concluded that the oceans are a source of ammonia for the 
atmosphere (Servant & Delaporte, 1983). 

    Atmospheric levels of particulate ammonium at some non-urban 
and urban locations around the world are shown in Table 10.  It can 
be seen that concentrations of 1 g/m3 and 4 - 5 g/m3 are typical 
for non-urban and urban sites, respectively. 

5.1.2.  Levels in water

    The concentration of ammonia in surface waters varies 
regionally and seasonally.  Wolaver (1972) studied US Geological 
Survey data for total ammonia and reported average concentrations 
of < 0.18 mg/litre in most surface waters, and around 0.5 mg/litre 
in waters near large metropolitan areas.  Analysis of data from the 
Water Quality Control Information (STORET) System for the years 
1972 - 77 (US EPA, 1979a) showed that, although total ammonia-
nitrogen concentrations in surface waters in the USA tended to be 
slightly lower during summer months than during winter months, the 
percentage of areas in which non-ionized ammonia concentrations 
occasionally exceeded 0.02 mg/litre increased from 11% during 
winter to 23% during summer; these percentages were higher when 
waters had elevated pH values. 

Table 8.  Urban and industrial atmospheric levels of ammonia in a 
few global locationsa
--------------------------------------------------------------------
Location              Year      Concentration        Reference
                                (g/m3)
--------------------------------------------------------------------
 Germany, Federal 
 Republic of
 Frankfurt-am-Main    pre-1963  8 - 20               Georgii (1963)

 Italy
 Cagliari             -         37 - 280             Spinazzola et 
                                (highest conc.       al. (1966)
                                in the vicinity
                                of port)

 Japan
 Tokyo                -         up to 210 (down-     TMRI (1971)
                                wind from two major
                                pharmaceutical
                                plants)
 Tokyo                1969      4.8 - 25.8           Okita & 
                                                     Kanamori (1971)
 Tsuruga              -         up to 6.8            FEPCC (1972)

 Netherlands
 Bilthoven            1983      5                    Van Aalst 
                                                     (1984)
 Delft                1979-81   4.4                  Van Aalst 
                                                     (1984)

 USA
 Seattle, Washington  1975      0.8 - 77.0           Farber & 
                                                     Rossano (1975)
 St. Louis, Missouri  1972-73   up to 17.5           Breeding et al. 
                                                     (1976)
 Five urban sites     -         3 - 60               Hidy (1974)
 in California                  (average 20.0)

 Chino-Corona area,   1975      up to 315            Pitts & 
 California                     (vicinity of         Grosjean (1976)
                                dairy farm)

 USSR
 Environment of       1967      190                  Saifutdinov 
 metallurgical plant                                 (1966)

 West Berlin           -         up to 97             Hantzsch & 
                                (average 17.6)       Lahmann (1970)
-------------------------------------------------------------------- 
a Adapted from: NRC (1979). Industrial activities include intensive
  farming activities.

Table 9.  Non-urban atmospheric levels of ammonia in a few global 
locationsa
--------------------------------------------------------------------------
Location                  Year      Concentration   Reference
                                    (g/m3)
--------------------------------------------------------------------------
Harwell, England          1969      up to 5.1       Healy et al. (1970)
                                    (typical level
                                    0.85 - 1.7)

Maritime stations         pre-1963  2 - 5           Georgii (1963)
(North Sea, Italian
coast, and Hawaii)

Rural and mountain        pre-1963  5 - 8           Georgii (1963)
locations in Switzerland
and the Federal Republic
of Germany

Non-urban locations       -         4 - 5           Robinson & Robbins
                                                    (1968); McKay (1969)

Rural sites in USA        1971      1.4 - 4.2       Breeding et al. (1973)

Boulder, Colorado, USA    1975      2.0 - 3.1       Axelrod & Greenberg
                                                    (1976)

American tropic           1967-68   3.5 - 21.7      Lodge et al. (1974)
                                    (average 10.5)

Non-urban sites in        1972      4.6 - 9.7       Hidy (1974)
California, USA
--------------------------------------------------------------------------
a Adapted from: NRC (1979).

    In the Netherlands, enhanced ammonium levels are also present 
in waters that are not influenced by surface run-off.  In 
particular, in hydrologically-isolated acidified small lakes, 
concentrations may reach up to 3 mg NH4+-N/litre.  In rural areas 
with high atmospheric ammonia levels, the loading of these small 
lakes with airborne ammonia substances appears to be responsible.  
The highest measured value near intensive pig and poultry farms was 
12 mg NH4+-N/litre (Leuven & Schuurkes, 1984). 

    There are few data on the concentrations of ammonia in 
drinking-water.  This is possibly because of the conversion of most 
of the available ammonia to N-chloramines (mono-, di-, and tri-
chloramines) during the chlorination of drinking-water (Morris, 
1978), which reduces ammonia concentrations to levels below 
analytical detectability.  The presence of these N-chloramines may 
contribute to the taste, odour, and also the potential health 
problems of drinking-water. 

Table 10.  Urban and non-urban atmospheric levels of particulate
ammonium in some global locationsa
-------------------------------------------------------------------
Location              Year     Concentration  Reference
                               (g/m3)
-------------------------------------------------------------------
Non-urban:

 England
 Harwell              -        3 - 4          Healy (1974)
 (troposphere)        1971-73  1.3            Reiter et al. (1976)

 Germany, Federal
 Republic of
 Bavaria              -        1.0            Georgii & Muller
 (lower troposphere)                          (1974)

 USA
 28 non-urban sites   1968     0 - 1.2        US EPA (1972)
 Point Arguello,      -        0.36           Hidy (1974)
 California
 Goldstone,           -        0.76           Hidy (1974)
 California

Urban:

 Belgium
 Ghent                1972     1.3 - 33.0     Demuynck et al. 
                               (severe        (1976)
                               pollution
                               episode)
 Japan
 Nagoya               1973-74  2.7 - 4.2      Kadowaki (1976)

 Netherlands
 Delft                1979-81  4.6            Van Aalst (1984)
 Terschelling         1982     2.7            Van Aalst (1984
 Houtakker            1983     19             Van Aalst (1984)

 Sweden
 Rao                  -        2.2 - 7.2      Brosset et al. (1975)
                               (aerosol 
                               originating
                               from England)
 United Kingdom
 Tees River Valley    1967     up to 33.0     Eggelton (1969)
                               (severe 
                               pollution
                               episode)
-------------------------------------------------------------------

Table 10.  (contd.)
-------------------------------------------------------------------
Location              Year     Concentration  Reference
                               (g/m3)
-------------------------------------------------------------------
 USA
 Urban areas          1968     0 - 15.1       US EPA (1972)
 Five cities          1970-72  0 - 21         Lee & Goranson (1976)
 Tuscon, Arizona      1973-74  0 - 6.5        Keesee et al. (1975)
 Los Angeles,         1969-70  2.8 - 3.4      Gordon & Bryan (1973)
 California
 15 urban sites in    -        average 5.3    Hidy (1974)
 California
 Riverside,           1975     up to 30.1     Grosjean et al. 
 California                    (average 7.6)  (1976)
-------------------------------------------------------------------
a Adapted from:  NRC (1979).

    Ground water is frequently used as drinking-water, without 
prior chlorination.  Ammonia levels in ground water are usually low 
because the adsorption of the ammonium ion on clay minerals, or its 
bacterial oxidation to nitrate, limit its mobility in soil (Feth, 
1966; Liebhardt et al., 1979).  However, nitrogen fertilizers, 
livestock wastes, or septic tanks may contribute significant 
amounts of ammonia to shallow ground waters, especially those 
underlying poorly-drained soils (Gilliam et al., 1974; Rajagopal, 
1978).  In domestic tap water from Michigan wells averaging 20 m in 
depth, mean levels of ammonia-nitrogen were between 0.04 and 0.18 
mg/litre; the highest reported single value was 0.57 mg/litre from 
a well 12.5 m in depth (Rajagopal, 1978). 

    In wells drilled for research purposes and not supplying 
drinking-water, levels of ammonia-nitrogen in shallow (3 m) wells 
beneath wood and crop land usually averaged less than 2 mg/litre 
(Gilliam et al., 1974).  Levels in shallow (3 - 6 m) ground water 
beneath plots spread with poultry manure varied typically between 1 
and 15 mg NH3-N/litre (Liebhardt et al., 1979); those in ground 
water beneath 29 feedlots averaged 4.5 mg NH3-N/litre and ranged up 
to 38 mg/litre (Stewart et al., 1967).  Levels in hot springs and 
other ground waters have been reported to reach > 1000 mg NH3-
N/litre (Feth, 1966). 

    The ammonia levels present in the runoff of receiving surface 
waters have been measured in various studies.  Kluesner & Lee 
(1974) found that levels ranged from approximately 0.23 mg 
ammonia/litre in the autumn to 1.8 mg ammonia/litre in the early 
spring in the urban runoff of Madison, Wisconsin.  Struzewski 
(1971) reported that ammonia levels in urban storm water ranged 
from 0.1 to 3.2 mg/litre. 

    Only limited data are available on nitrogen pools in the ocean.  
Sderlund & Svensson (1976) used values of 5 g NH3-N/litre for 
deep areas and 50 g NH3-N/litre for near-shore areas and estimated 
an ammonia inventory of approximately 9 x 103 g/litre in coastal 
upwelling systems. 

    Interstitial water in sediments rich in organic matter contain 
higher concentrations of ammonia.  Sholkovitz (1973) reported 
values of 1.4 - 23.8 g ammonia/litre in the interstitial waters 
of the Santa Barbara Basin.  The interstitial water of the Long 
Island Sound, 2 km off shore, contained concentrations ranging 
from 11.2 to 42 g ammonia/litre (Gold-haber & Kaplan, 1974). 

5.1.3.  Levels in soil

    The quantity of ammonia bound to clay in soil has not been 
estimated.  The ammonia present in soil is in dynamic equilibrium 
with nitrate and other substrates of the nitrogen cycle and is 
difficult to measure as its concentration is in constant flux (NRC, 
1979). 

5.1.4.  Food

    There is very little ammonia in unprocessed food and in 
drinking-water derived from deep ground-water or chlorinated 
sources.  Various salts of ammonia are added to foods (Annex I). 

5.1.5.  Other products

    Ammonium chloride is a common ingredient in expectorant 
cough mixtures and is a component of tobacco smoke (about 
40 g/cigarette) (Sloan & Morie, 1974). 

5.2.  General Population Exposure

    Exposure via inhalation and ingestion must be compared to the 
endogenous production of ammonia in the intestinal tract, which is 
of the order of several grams per day (section 7.1.2).  The 
relative importance of the different sources is indicated in Table 
11. 

5.2.1.  Inhalation

    Assuming ammonia and ammonium concentrations in non-urban and 
urban air are 2 and 6 g/m3 and 24 and 25 g/m3, respectively, and 
that the amount of air breathed per day by an individual is 20 m3, 
the intake of total ammonia through inhalation can be calculated to 
be 0.1 - 0.5 mg/day; the amounts exhaled are considerably higher. 

    The average amount of ammonia inhaled from the smoking of one 
cigarette is approximately 42 g (Sloan & Morie, 1974).  Assuming 
an individual smokes 20 cigarettes per day, the inhalation of 
ammonia through cigarette smoking would be 0.8 mg/day. 

5.2.2.  Ingestion from water and food

    Most drinking-water in the USA is chlorinated, which 
effectively eliminates ammonia.  However, assuming the direct 
consumption of 2 litres per day of untreated surface water, at an 
average total ammonia concentration of 0.18 mg/litre (Wolaver, 
1972), the average human uptake from this source would be 0.36 mg 
per day. 

Table 11.  Intake of ammonia from 
different sources
------------------------------------
Source                       mg/day
------------------------------------
Endogenous                   4000

Exogenous

 Ingestion (food and drink)  ~18

 Inhalation                  < 1

 Cigarette smoking (20/day)  < 1
------------------------------------

    Although ammonia is a negligible natural constitutent of food, 
it is formed in the intestine by deamination of the amino groups of 
food proteins.  In addition, ammonium compounds are added in small 
amounts (< 0.01 - 20 g/kg) to various foods as stabilizers, 
leavening agents, flavourings, and for other purposes (FASEB, 
1974).  Information concerning the usual concentrations of ammonium 
salt additives in foods and the estimated total quantities of these 
compounds used for this purpose in the USA in 1970 has been used to 
estimate the average daily intake of 6 ammonium salt additives 
(FASEB, 1974).  The estimates for ammonium bicarbonate, carbonate, 
hydroxide, monobasic phosphate, dibasic phosphate, and sulfate were 
42, 0.3, 7, < 0.1, 6, and 20 mg, respectively.  No estimate was 
available for ammonium chloride.  On this basis, the average daily 
ammonia intake from these compounds has been calculated to be 
18 mg. 

5.2.3.  Dermal exposure

    Very few data are available concerning levels of dermal 
exposure to ammonia or ammonium compounds.  Dermal exposure of 
human beings mainly occurs through the use of household cleaning 
products, accidental spillage, or under occupational conditions. 

5.3.  Occupational Exposure

    Exposure to ammonia or ammonium compounds can occur in certain 
occupations involving their production, transportation, and use in 
agricultural and farm settings, during fertilizer application, or 
as a result of animal waste decomposition. 

    It is estimated that about half a million workers in the USA, 
in a wide variety of occupations, have potential exposure to 
ammonia (NIOSH, 1974). 

    Ammonia is generated as a by-product in a wide variety of
industrial activities, and workplace atmospheric concentrations 
are given in Table 12.  Municipal waste incineration and gas-fired 
industrial incinerators generate concentrations of 20 and 0.4 
mg/m3, respectively (NRC, 1979) and shipboard and quayside levels 

for natural gas tankers may be about 30 mg/m3 (Avot et al., 1977).  
Levels in intensive livestock-rearing buildings are frequently 
reported to be up to 30 mg/m3 (Poliak, 1981) or more (Anderson et 
al., 1964b; Taiganides & White, 1969; Marschang & Petre, 1971).  
Ammonia levels in dairy farms and cattle-fattening facilities in 
Romania have been reported to range from 0.7 mg/m3 to 140 mg/m3 
(Marchang & Crainiceanu, 1971; Marschang & Petre, 1971). 

    Maximum daily intake from work-place concentrations such as 
these would normally be less than 300 mg/day and this may be 
compared with endogenous production (Table 11). 

    Occupational exposure limits for some countries in the world 
are shown in Table 13. 

5.4.  Exposure of Farm Animals

    Farm animals are exposed to ammonia through feed containing 
urea or various ammonium salts and to atmospheric ammonia due to 
bacterial decomposition and volatilization of ammonia from animal 
wastes. 

5.4.1.  Oral exposure

    (a)   Non-protein nitrogen additives

    Urea and various ammonium salts have been used for several 
years as non-protein nitrogen sources in ruminant nutrition.  It is 
used much more widely for this purpose than the ammonium compounds.  
Urea is hydrolysed to ammonia and carbon dioxide by the ruminal 
bacteria and, therefore, represents a source of ammonia exposure.  
The ammonia released is used by the ruminal microorganisms to 
synthesize microbial protein, which is then digested in the small 
intestine of the ruminant and used as a source of dietary amino 
acids. 

    (b)   Refeeding of livestock wastes

    Results of studies on the refeeding of livestock wastes 
(Bhattacharya & Taylor, 1975; Arndt et al., 1979; Smith & Wheeler, 
1979) have indicated that manure could be of nutritive value, 
salvaging some nutrients ordinarily lost (Yeck et al., 1975).  The 
non-protein nitrogen (e.g., urea, uric acid) present in livestock 
wastes is available to ruminants because of microbial conversion in 
the rumen.  Wastes are of limited value for monogastrics such as 
swine. 

Table 12.  Ammonia levels in some industrial processesa
--------------------------------------------------------
Operation                             Level (mg/m3)
--------------------------------------------------------
Machinery manufacturing (cleaning)    10.5

Diazo-reproducing machine             5.6

Mildew-proofing                       87.5

Electroplating                        38.5

Galvanizing, ammonium chloride flux   7 - 61.6

Blueprint machine                     7 - 31.5

Printing machine                      0.7 - 31.5

Etching                               25.2

Refrigeration equipment               6.3 - 25.9

Cementing insoles                     5.6 - 19.6

Chemical mixing                       42 - 308

Fabric impregnating                   ND
--------------------------------------------------------
a From: NIOSH (1974).    
ND = Not detectable.

5.4.2.  Inhalation exposure

    (a)   Ruminants

    Marschang & Crainiceanu (1971) measured the ammonia 
concentrations in air (sampled at nose level of animals) in calf 
stables at 4 dairy farms in Romania.  The ammonia levels ranged 
from 0.7 to 140 mg/m3 (1 - 200 ppm).  Most of the observed values 
greatly exceeded the permissible upper limit of 18.2 mg/m3 (26 
ppm).  In a second study, Marschang & Petre (1971) measured the 
ammonia concentrations in the air of 3 cattle-fattening facilities 
in Romania in which the animals were being fed in total 
confinement; the capacities of the 3 operations were 3000, 3000, 
and 4900 animals.  The ammonia concentration ranged from 2 to 
1400 mg/m3 (3 to 200 ppm).  In general, the ammonia content was 
below the admissible upper limit during the summer months but 
exceeded it during the winter months, when extremely high 
concentrations were observed.  These high concentrations were 
primarily due to the blocking of the ventilation system, in order 
to maintain necessary stall temperatures.  The highest value 
(1400 mg/m3) was measured when the cleaning mechanism of the 
manure canals malfunctioned. 

Table 13.  Occupational exposure limits (mg/m3)a
-------------------------------------------------
Country                     Ammonia    Ammonium 
                   Ammonia  chloride   sulfamate
                   A   B    A   B      A   B
-------------------------------------------------
Australia          18       10         10

Belgium            18       10         10

Czechoslovakia     40  80

Finland            18

German Democratic      20       10
 Republic

Germany, Federal   35       10         15
 Republic of

Hungary            20

Italy              20                  10

Japan              18

Netherlands        18       10         10

Poland             20

Romania            20  30   5   10     10  15

Sweden             18  36

Switzerland        18       6          10

USA (NIOSH/OSHA)   35                  15
 (ACGIH)           18  27   10  20     10  20

USSR               20                  10

Yugoslavia         35                  15

Council of Europe  18                  15
-------------------------------------------------
a From:  ILO (1970).
Column A represents average values.
Column B is higher quoted limits, which may 
 variously be ceiling values, short-term exposure 
 limits, etc.

Note: Occupational exposure levels and limits are derived in 
      different ways, possibly using different data, and expressed 
      and applied in accordance with national practices.  These 
      aspects should be taken into account when making comparisons. 

    (b)   Swine

    The increased use of confined housing for swine has caused 
concern about the purity of the air within the buildings and its 
effects on swine growth.  Bacterial decomposition of excreta 
collected and stored beneath slotted floors in enclosed buildings 
produces a number of gases, including ammonia, carbon dioxide, 
hydrogen sulfide, and methane (Curtis, 1972).  Miner & Hazen (1969) 
reported a range of ammonia concentrations of 4.2 - 24.5 mg/m3 
(6 - 35 ppm) determined 30 cm above the floor level in a swine-
rearing facility.  Levels in solid-floor confinement units were 
normally found to be < 35 mg/m3 (< 50 ppm), but they could be 
higher during cold months, when ventilation was at a minimum, 
particularly when the floor was heated (Taiganides & White, 1969).  
The normal ammonia concentration in the air above slotted floors 
was reported to be ~7 mg/m3 (~10 ppm), but this was increased by a 
factor of 5 - 10 by stirring the stored manure. 

    (c)   Poultry

    Poultry are usually exposed to ammonia, together with hydrogen 
sulfide, carbon dioxide, and methane, in the air of poultry houses.  
These compounds result from bacterial action on poultry wastes 
(Ringer, 1971).  In cold climates, proper ventilation rates cannot 
be maintained in many poultry houses, and gas production in the 
manure may build up to toxic levels.  Ammonia has been found at 
concentrations exceeding 35 mg/m3 (50 ppm) in modern poultry 
houses, and at up to 140 mg/m3 (200 ppm) in poorly-ventilated 
poultry houses (Anderson et al., 1964b; Valentine, 1964).  The 
toxic effects in poultry can be prevented through proper management 
practices (Lillie, 1970). 

6.  EFFECTS ON ORGANISMS IN THE ENVIRONMENT

6.1.  Microorganisms

    Many microorganisms are able to use ammonia as a nitrogen 
source for cellular nutrition.  Nitrifying organisms derive energy 
from the oxidation of ammonia to nitrate.  High levels of ammonia 
and high pH, which may occur, for example, in waste waters or 
fertilized fields, may inhibit nitrification and cause persistance 
or accumulation of ammonia and/or nitrite.  Improper maintenance of 
conditions in waste treatment processes may result in ammonia 
overloading and inhibition of the nitrification process, with 
consequent ammonia and/or nitrite pollution of receiving surface 
waters.  Other soil microorganisms may also be inhibited; fungi 
reportedly are more sensitive than bacteria.  However, these 
inhibitory effects are temporary.  Aqueous and gaseous ammonia have 
been used to control microbial growth in stored fruits, hay, and 
grains.  Ammonia treatment has proved more effective against fungal 
than against bacterial spoilage of food. 

    The bacterial species  Escherichia coli and  Bacillus subtilis 
were found to be sensitive to ammonium chloride (NH4Cl) (Deal et 
al. 1975); exposure to 1100 mg NH3/litre killed 90% of an  E. coli  
population in 78 min.   B. subtilis, an aerobic, spore-forming 
bacterium, was destroyed in less than 2 h in a solution of 620 mg 
NH3/litre.  Anthonisen et al. (1976) and Neufeld et al. (1980) 
studied NH3 inhibition of the bacterium  Nitrosomonas (which 
converts ammonium to nitrite) and the bacterium  Nitrobacter (which 
converts nitrite to nitrate).  The nitrification process was 
inhibited by NH3 at a concentration of 10 mg/litre (Neufeld et al., 
1980).  Concentrations that inhibited  Nitrosomonas (10 - 150 
mg/litre) were greater than those that inhibited  Nitrobacter 
(0.1 - 1.0 mg/litre), and NH3, not NH4+, was reported to be the 
inhibiting chemical species (Anthonisen et al. 1976). 
Acclimatization of the nitrifying bacteria to NH3, temperature, 
and the number of active nitrifying organisms are factors that may 
affect the inhibitory concentrations of NH3 in a nitrification 
system. 

    Langowska & Moskal (1974) investigated the inhibitory effects 
of NH3 on bacteria during 24-h exposure periods.  Ammonifying and 
denitrifying bacteria were most resistant to NH3; proteolytic and 
nitrifying bacteria were the most sensitive.  Concentrations of up 
to 170 mg NH3/litre did not adversely affect denitrifying and 
ammonifying bacteria; a concentration of 220 mg/litre caused a 
reduction in metabolic processes.  Proteolytic bacteria were 
unaffected at concentrations of 0.8 mg NH3/litre, but were affected 
at 13 - 25 mg/litre. 

    Jones & Hood (1980) conducted studies on 2 species of 
 Nitrosomonas isolated from 2 wetland environments, one estuarine 
and the other fresh water.  At 30 C and pH 8.0, the estuarine 
isolate showed peak ammonium oxidation activity at 18 mg NH3/litre; 
activity gradually declined to 30% of the peak at 80 mg NH3/litre.  
However, the fresh-water isolate was not inhibited by ammonia 
concentrations of up to 80 mg NH3/litre. 

    Application of anhydrous ammonia to soil may strongly affect 
soil microorganisms; however, the effect has been attributed more 
to alterations in pH than to ammonia toxicity  per se.  Henis & Chet 
(1967) found that ammonia reduced sclerotial germinability of the 
fungus  Sclerotium rolfsii only when the soil pH rose to 9.8 or 
higher.  According to Mller & Gruhn (1969), fungi were more 
sensitive than bacteria to ammonia application, the fungi 
disappearing at pH values above 8.  At pH 8.38, bacterial numbers 
initially decreased but then increased above control levels, 7 days 
after application, with an increased number of protein-decomposing 
and nitrifying forms. 

    Ammonia has been used to control microbial growth in food and 
cattle feed.  The growth of mould  (Penicillium digitatum) on fresh 
fruit was inhibited by 70 - 300 mg ammonia/m3 in the air, either