EPA/600/8-89/052F
                                    June 1989
Summary Review of Health Effects
     Associated with Ammonia

      Health Issue Assessment
  Environmental Criteria and Assessment Office
 Office of Health and Environmental Assessment
      Office of Research and Development
     U.S. Environmental Protection Agency
      Research Triangle Park, NC 27711

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                           Disclaimer

    This document has been reviewed in accordance with U.S. Environmental
Protection  Agency policy and approved for publication.  Mention of  trade
names or commercial  products  does not constitute  endorsement or
recommendation for use.

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                               Preface

    The  Office of Health  and Environmental Assessment has prepared this
health assessment-to serve as a source document for EPA use. The summary
health assessment was developed for use by the Office of Air Quality Planning
and  Standards to  support decision making  regarding possible regulation  of
ammonia as a hazardous air pollutant.
    In the development of the assessment document, the scientific literature
has been inventoried through January 1989, key studies have been evaluated,
and summary/conclusions  have been prepared so that the chemicals' toxicity
and related  characteristics  are qualitatively identified. Observed effect  levels
and  other measures  of dose-response relationships are discussed, where
appropriate,  so that the nature of the adverse health responses is placed in
perspective with observed environmental levels.
    Any  information regarding sources, emissions, ambient air concentrations,
and public exposure has been included only to give the reader a  preliminary
indication of the potential presence of this substance in the ambient air.  While
the available  information   is  presented as  accurately  as  possible, it  is
acknowledged to be limited and dependent in many instances on assumption
rather than specific data. This information  is not intended, nor should it be
used, to support any conclusions regarding risk to public health.
    If a  review of the health information  indicates that  the  Agency should
consider  regulatory action for  this substance, considerable  effort  will  be
undertaken to obtain  appropriate information regarding sources,  emissions,
and ambient air concentrations. Such data will provide  additional  information
for drawing  regulatory conclusions  regarding the extent  and significance  of
public exposure to this substance.
                                   in

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                              Abstract

    Ammonia is a colorless  gas with  a repellent odor. It  is  a naturally
occurring compound in the environment; however, it is also released into the
environment from ammonia production  facilities and  during the manufacture
and use of ammonia-containing products.
    Ammonia is a central compound in  the environmental cycling of nitrogen
and is involved  in major  processes  such as  mineralization, nitrification, and
nitrogen fixation.  In  the  atmosphere, ammonia may undergo  many
transformations and is  expected to have a relatively short residence time of 5
to 10 days.
    Ammonia is a key metabolite in  mammals and plays an essential role in
acid-base  regulation and biosynthesis  of purines, pyrimidines, and  non-
essential amino  acids.  However, ammonia is a toxic gas and in experimental
animals, effects  from acute exposure to  ammonia gas have ranged from mild
irritation of the respiratory system and  mucous membranes to convulsions,
acute pulmonary edema, coma, and  death. Continuous or repeated exposure
of animals to sublethal  concentrations of  ammonia gas have produced adverse
effects on the respiratory tract, liver, kidneys, and spleen.
    Quantitative data on the toxic effects of ammonia in humans is  limited.
Accidental exposure of humans to unspecified concentrations of ammonia has
resulted in burns of the eyes, skin, and respiratory tract and in death. Chronic
exposure of humans to 40 ppm  ammonia has resulted in headache, nausea,
and  reduced appetite.  A  definite  conclusion  regarding  the  possible
reproductive/teratogenic,  mutagenic,  or carcinogenic potential  of ammonia
cannot be drawn because of the lack of adequate studies.
                                  IV

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                        Table of Contents
 Preface   	   ijj
 Abstract  	\[\\   jv
 Tables   	'.'.'.'.'.'.'.'.'.''   vi
 Figures	'.'.'.'.'.'.'.'.'.   vi
 Authors, Contributors, and Reviewers  	   Vii

 1.  Summary and Conclusions  	  1-1

 2.  Background Information  	  2-1
    2.1   Chemical Characterization and Measurement 	  2-1
    2.2  Sources and Emissions   	   2-2
    2.3  Environmental Release and  Exposure  	'.'.'.'.'.'.'.  2-2
    2.4  Environmental Effects	  2-6

 3.  Health Effects  	  3.!
    3.1   Pharmacokinetics and Metabolism  	'.'.'.'.'.'.'.  3-1
    3.2  Biochemical Effects  	  3.3
    3.3  Acute Toxicity  	     3.7
    3.4  Subchronic Toxicity  	  3-10
    3.5  Chronic Toxicity   	\ .  3-14
    3.6  Carcinogenicity	'.'.'.'.'.'.  3-14
    3.7  Mutagenicity  	    3-14
    3.8 Teratogenicity and Reproductive Effects	  3-15
    3.9  Neurotoxicity  	  3_15
    3.10 Effects on Humans	 ' " ^  3-15
         3.10.1  Ocular Toxicity  	  3-15
         3.10.2 Respiratory Toxicity  	       3-15
         3.10.3 Burns of the Skin   	                    3-17
         3.10.4 Other Effects	   3-17
         3.10.5 Experimental Studies  	'.'.'.'.'.'.'.   3-17
         3.10.6 Epidemiology  	   3-19

4.  References  	        4_1

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                           List of Tables
No.

2-1
2-2
2-3

3-1
3-2
Occupations with potential exposure to ammonia 	
Acute lethal concentration values for ammonia in fish  . .  .
Acute lethal concentration values for unionized ammonia
   in aquatic invertebrates   	
Acute toxicity values for ammonia in laboratory animals   ,
Results of subchronic exposures to ammonia gas in
   several species   	
 2-7
 2-8

2-11
 3-8

3-11
                          List of Figures
2-1
   Generalized representation of the nitrogen cycle  	  2-3
                                   VI

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           Authors, Contributors, and Reviewers

    The following personnel  of Dynamac  Corporation were involved in the
preparation of this document: Finis Cavender, Ph.D.' (Department  Director);
Nicolas P. Hajjar,  Ph.D. (Project Manager/Principal Author); Dana Cazzulino,
Cyrus Hamidi, Y'vonne  Jones-Brown, Ph.D., Lawrence Kaufman, Ph.D.,
Leonard Keifer, Ph.D.,  and  Kumar  D.  Mainigi, Ph.D.  (Authors);  William
McLellan, Ph.D. (Reviewer); Anne Gardner (Technical Editor); and Gloria Fine
(Information Specialist). This document was prepared under contract with the
Environmental Criteria and Assessment Office, EPA, Research Triangle Park,
NC (Beverly Comfort, Project Manager).
    This document has been reviewed for scientific and technical merit by the
following scientists: Professor William J. White,  Department of Comparative
Medicine, Milton S. Hershey  Medical Center,  Pennsylvania State University,
Hershey,  PA, 17033;  Professor  I. W.  Waters,  Research Institute  of
Pharmaceutical Sciences, University of Mississippi, University, MS 38677; Dr.
D. Burrows Schaub, Burrows Associates, Ltd., Fredrick, MD 21701. In addition,
it has been reviewed by members of the Human Health  Assessment Group
(HHAG) and the Exposure Assessment Group (EAG) of the Office of Health
and Environmental Assessment (OHEA), EPA, Washington, DC.
                                 VII

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                1.  Summary and Conclusions

    Ammonia (CAS No. 7664-41-7) is a colorless gas with a repellent odor. It
is very soluble in water with a high vapor pressure and a low vapor density.
Ammonia was ranked fourth  among  the  chemicals produced  in  the  United
States in 1987. It is used in the manufacture of fertilizers, fibers and plastics,
and explosives.
    Ammonia is released into the environment  from ammonia  production
facilities via industrial gaseous emissions and aqueous waste streams as well
as during the manufacture and use of ammonia-containing products. It  is also
a naturally occurring compound and a product of animal,  fish,  and microbial
metabolism. Ambient air concentrations range from 0.1 to 9.0 pg/ms, although
higher levels may be found in the vicinity of point sources.
    The Occupational Safety and Health Administration has established an 8-
hour TWA permissible  exposure limit for ammonia of 50 ppm (35 mg/m3).
Analytical methods used to determine  ammonia include colorimetry, titrimetry,
conductimetry,  specific  ion  electrode,  ion  chromatography,
chemiluminescence, absorption spectroscopy, gas chromatography, and mass
spectrometry.
    Ammonia is  a central compound in the environmental cycling  of nitrogen
and is involved  in  major  processes such as  mineralization, nitrification, and
nitrogen fixation. Under  most environmental  conditions,  the ammonium ion
(NH4 + ) is expected to predominate. The ammonium ion  is less mobile than
unionized ammonia (NH3) in soil and water. In the  atmosphere, ammonia may
undergo  many transformations  and  is  expected  to have a relatively short
residence time of  5 to  10  days.  The  most  important transformation  is its
solution  in water  droplets together with sulfur dioxide or other gases to form
aerosols, with up  to 75 percent removal by rainout.
    Ammonia is moderately toxic to aquatic organisms and is more toxic than
the ammonium ion. The acute toxicity  of unionized ammonia to  fish has been
extensively studied. The 24- and 96-hour acute LDSO values for fish  range from
0.07 to  12.7 mg/L,  with  salmonid species generally  being  more sensitive.
Aquatic invertebrates have a range of sensitivity comparable to that of fish and
show a varying sensitivity  with developmental stages.
    Ammonia gas  is readily  absorbed through the lungs as indicated by
increased ammonia concentrations in the blood following exposure. However,
the increase in  blood levels  is not exposure-related,  so that only modest
increases  are noted at  higher exposures.  Retention of ammonia  in the
respiratory tract of dogs exposed to 450 to 1,500 ppm and humans exposed to
up to 500 ppm is  >80 percent. Following absorption, ammonia is incorporated
into the amino acid pool and other organic molecules. However, the route of
administration drastically  alters the distribution of  ammonia between  alpha-
amino, amidine, and amide  nitrogen  of organ  proteins.  Ammonia is
metabolized largely by  pathways involving hepatic  glutamic dehydrogenase
and  carbamyl   synthetase  following  intragastric  and intraperitoneal
administration, whereas the glutamic  synthetase route is  involved following
subcutaneous and  intravenous administration. Approximately 90  percent of
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15N-labeled ammonia administered intravenously to rats was incorporated into
glutamic amide nitrogen  (80  percent) and urea (10 percent). Low levels of
labeled  15N (expressed as glutamme and ureas) were found in various tissues
and organs. Ammonia is excreted as urea in mammals, but excretion was also
found to occur via the lungs in expired air of several experimental animals and
human subjects exposed to NH3 vapor or injected intravenously with ammonia
acetate.
    Ammonia is a key metabolite in mammals and .plays an  essential role in
acid-base regulation  and  biosynthesis  of purines,  pyrimidines, and
nonessential amino  acids. Elevated levels of endogenous ammonia resulting
from  metabolic and genetic  disease have caused liver failure,  neurologic
disorders, and encephalopathy. There is no information on the potential risk to
humans  with genetic or  metabolic disorders  as a result  of exposure to
exogenous ammonia.  In experimental  ammonia toxicity studies with animals,
alteration  in metabolic and functional  aspects  of the brain,  changes in
neurotransmitter levels, involvement of glial cells,  and alterations in the blood-
brain  barrier have been noted.
    Ammonia is a toxic, gaseous  compound  at  relatively  moderate
concentrations. In animals, compound-  and concentration-related effects of
acute exposure to ammonia gas progress from mild irritation of the respiratory
system  and mucous  membranes  to  convulsions,  acute  pulmonary  edema,
coma, and death. The acute inhalation LC50 values for a 60-minute exposure
period are 4,230 ppm in mice and 14,140 and 19,770 ppm in male and female
rats, respectively. The data on acute exposure to low  levels  of ammonia are
conflicting; however, no signs of irritation or histological changes were seen in
the respiratory  tract of rats exposed  to 4 ppm ammonia  for up  to 7 days.
Continuous or repeated exposure of  animals to sublethal concentrations of
ammonia has produced adverse effects in the tissues of the  respiratory tract,
liver,  kidneys, and spleen. It may  also increase the tendency towards, and/or
severity of, respiratory tract infections  by reducing trachea! ciliary  activity and
the phagocytic activity of pulmonary alveolar macrophages and may produce
anorexia.  No clinically significant  effects  were noted  in  rats, guinea pigs,
rabbits,  dogs, or  monkeys continuously  exposed  to  ammonia  at  a
concentration of 57 ppm for 114 days.
    No adequate information was  found on the effects  of chronic  exposure to
ammonia in  animals. Ammonium hydroxide administered in drinking water to
Swiss mice at levels of 0.1, 0.2, or 0.3  percent or to C3H mice at a level of 0.1
percent was not carcinogenic. In another study a significant  increase in lung
tumors was not found in mice after administration of 42 mg/kg ammonia twice
a week for 4 weeks. Limited data suggest that ammonium  hydroxide may be
mutagenic to  Escherichia  coli and  Drosophila  melanogaster.  Ammonium
chloride was also found to reduce multiplication of 3T3 and SV-40  transformed
3T3 mouse  fibroblasts. Teratogenicity or  reproductive studies in  mammals
were  not reported for ammonia in  the available literature. Additional data are
needed to determine the chronic effects and mutagenic,  teratogenic, and
reproductive potential of ammonia.
    Accidental exposure of humans to unspecified concentrations  of ammonia
has resulted in burns of the eyes, skin, and respiratory tract and in death. Both
immediate and  long-term effects have  been  associated with  ammonia
exposure. Chronic  exposure to 40  ppm  ammonia vapor  has  resulted in
headache,  nausea,  and reduced  appetite.  In  experimental  studies,
hyperventilation,  lacrimation,  and  nasal irritation were  noted   in subjects
exposed at 500 ppm for 30 minutes, but no changes were noted for blood urea
and nonprotein nitrogen, although  increases in nonprotein nitrogen levels were
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observed with longer (4-hour) exposure periods. In another study, exposure at
concentrations of 50 ppm  or less did not cause  irritation or discomfort. In
repeated exposure studies (25, 50, or 100 ppm for 6-hour sessions once a
week for 6 weeks), no apparent changes were noted in respiratory rate, blood
pressure, pulse,  or forced vital capacity. The frequency of mild eye irritation
decreased in the later sessions, suggesting adaptation. No adequate studies
were found  on  the  adverse effects  of chronic occupational exposure to
ammonia.  Ammonia  is classified  as group D  "not  classifiable as to  human
carcinogenicity"  based on the weight-of-evidence approach in the current EPA
guidelines for carcinogen risk assessment.
                                  1-3

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                  2.  Background Information

    This overview provides a brief summary of the data available on the health
effects from  exposure to  ammonia.  Emphasis  is  placed  on determining
whether there is evidence to suggest  that ammonia exerts effects  on human
health under  conditions and at concentrations commonly experienced by the
general  public.  Both  acute  and  chronic  effects are  addressed,  including
general toxicity, teratogenicity, mutagenicity, and carcinogenicity. To place the
health effects discussion in perspective, this report also reviews  certain air
quality  aspects of ammonia in  the United States,  including  sources,
distribution, fate, and concentrations associated with rural, urban,  and point-
source areas.

2.1. Chemical Characterization and Measurement

    Ammonia (CAS No. 7664-41-7) has the empirical and molecular formula
NH3. It is a colorless gas at room temperature with a sharp and repellent odor
and a molecular weight of 17.03. Ammonia is very soluble in water (34 percent
at 20 °C or about 531 g/L at 20 °C) and has a high vapor pressure (8.7 atm at
20°C) and a low vapor density (0.6 g/L) (TDB; Verschueren, 1983).
    For  determination of ammonia  in  air,  it is  first necessary to absorb  the
ammonia  in  a liquid. Sampling air for determination of trace amounts  of
ammonia  has several inherent problems: minimization of human ammonia
contamination, the propensity of ammonia to adsorb to all surfaces,  especially
at low concentrations, differentiation of aerosol  ammonia  and gaseous
ammonia, and inefficiency  of bubbler samplers. After  sample  collection,
ammonia  concentrations are determined by established  methods including
colorimetry,  titrimetry,  conductimetry, specific  ion electrode,  ion
chromatography, chemiluminescence, absorption spectroscopy, or  gas
chromatography and mass spectrometry (National Research Council, 1977).
    Ammonia is determined in water or wastewater using one of the standard
methods developed for examination  of water and wastewater; i.e., colorimetry,
titrimetry, or the ammonia-selective electrode (Franson, 1981).
    Variations of the  basic methods have also  been instituted in an effort to
overcome difficulties inherent in  the  established methods.  Such  variations
include  automated colorimetry (Skjemstad and  Reeve,  1978; Bos,  1980;
Canelli,  1976), ion chromatography (Bouyoucos and  Melcher,  1983),  gas
chromatography (Hutchinson et a!.,  1982), nonautomated colorimetry (Bower
and Holm-Hansen, 1980; Boo and  Ma, 1976;  Hampson, 1977), specific  ion
electrode  (Ferm, 1979), ring oven  (Cattell and Du  Cros, 1976),  automated
distillation-spectrophotometry  (Crowther   and  Evans, 1980),
chemiluminescence (McClenny and  Bennett, 1980; Hales and Drewes, 1979),
air sampling techniques (Braman et al., 1982), coated piezoelectric crystals
(Guilbault, 1981; Hlavay and Guilbault,  1978),  fluorescence  (Abbas  and
Tanner, 1981; Aoki et al., 1983; Aoki  et al., 1986), teflon beads (Harward et al.,
1982), and harmonic diode laser system (Cappellani et al., 1985).
                                 2-1

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2.2.  Sources and Emissions

    Domestic production capacity of ammonia in 1984 was approximately 18
million  tons  (Chemical  and Engineering News, 1985). As  of March 1985,
ammonia was produced domestically by  62 companies  at 99  plant sites.
Ammonia was ranked fourth among the chemicals  produced  in the United
States in 1987 (Reisch, 1988) with a production volume of 16.2 million tons, an
increase of 15.4 percent from 1986 (Reisch, 1988).
    Ammonia is manufactured primarily  by a modified  Haber reduction
method using atmospheric nitrogen and a hydrogen source (TDB). The major
producers of ammonia in  the  U.S.  are CF Industries, Columbia Nitrogen,
Farmland Industries,  Union Oil  Company,  and the Williams  Companies
(Agrico). Major end uses for ammonia are  in the manufacture of fertilizer (80
percent), fibers and  plastics  (10 percent),  and  explosives (5 percent)
(Chemical & Engineering News,  1985).

2.3.  Environmental Release and Exposure

    Ammonia is released  into the environment from  ammonia  production
facilities via industrial gaseous  emissions  and  aqueous waste streams.  It is
also released during direct application of anhydrous ammonia and urea to soil
(National Research Council, 1977; Denmead  et al. 1982; Reynolds and Wolf,
1987),  the production of urea and  ammonium nitrate, application of animal
waste  as a fertilizer (National  Research  Council,  1977)  and from  animal
feedlots (Hutchinson et al.,  1982), vegetation  decay (Alkezweeny et al., 1986),
in process  gas condensate from coal gasifiers (Hanson  et al., 1985),  and
automobile exhausts (Pierson and Brachaczek, 1983).
    Ammonia is a product of animal metabolism as well as a chemical that is
manufactured and  used  in commerce.  Ammonia is ubiquitous  in  the
environment, existing in equilibrium in two forms, mostly as a result of the
nitrogen cycle (Figure 2-1).
             NH/  +
           Ammonium
           ion
H2O
NH3   +
Ammonia
Therefore, the fate of anthropomorphic ammonia in the environment should be
considered in the context that the compound is central to the environmental
cycling  of nitrogen. A network of active and efficient, natural inorganic and
organic processes has trapped, transformed, produced, and/or used ammonia
before there were  contributions from human sources. Consequently, the
ammonia that enters the environment from human sources  enters a system
already adapted to the  presence of ammonia and would be  subject to the
same  processes  as naturally occurring ammonia. Some  of  the major
processes of the nitrogen cycle that involve ammonia include, with associated
reactions (unbalanced), the following (National Research Council, 1977):
    Mineralization:

    RNH2   +   O2   ->      CO2
    Organic     Oxygen        Carbon
    nitrogen                   dioxide
                     H2O
                  Water
               +
              Ammonia
              ion
                                  2-2

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        Fixation by
         Ionizing
       Phenomena
       (Lightning)
   Juvenile  (
   Addition  j
 (Volcanoes) I
                              Atmospheric N2
                         Biologic Fixation
              Industrial
               Fixation
                                                Denitrification
                                                   Shunt
                            Symbiotic

                               y  Nonsymbiotic
       Soil
                                      Biosphere
                                         I
              Ammonium -»-  Nitrite —»- Nitrate •
                     Nitrification Sequence
                       \ Sediments \
Figure 2-1. Generalized representation of the nitrogen cycle.
Source: National Research Council (1977).
Nitrification:
           NH/
       Ammonium
       +    O2
      Oxygen
   H2O
   Water
Nitrogen fixation:
       N2
       Nitrogen
       gas
+       [HCHO]
        Organic
        matter
NH4
 NO2"
 Nitrite
CO2
 Ammonium Carbon
 ion         dioxide
    Ammonia is an important intermediate in the assimilation of nitrogen from
the soil by plants. Nitrogen is present in the soil  largely in the organic form.
Before being assimilated  by plants, it is normally mineralized by microbial
processes.  The formation of  ammonium ion  is the  first step  in  the
mineralization process.  Most plants can assimilate ammonium  ion, but the
ammonium ion may also be oxidized to the nitrate ion, the most common form
of mineralized nitrogen  in soil, which may be assimilated by plants as  well
(Andersson  and Hooper, 1983;  Cullimore and Sims,  1981; Lemon and  Van
Houtte, 1980; Kholdebarin and Oertli, 1977; National Research Council, 1977).
                                   2-3

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    Nitrification is a two-step, energy-yielding process exploited for metabolic
energy by two specific genera of microorganisms.  Ammonia is converted to
nitrite by Nitrosomonas, and nitrite is converted to nitrate by Nitrobacter. This
process occurs in soil and  water (Andersson  and Hooper,  1983; American
Petroleum Institute, 1981; Kholdebarin and Oertli, 1977).
    Another source of mineralized  nitrogen  is from nitrogen fixation, where
gaseous  nitrogen is transformed to ammonium ion,  usually by metabolic
processes.  Nitrogen fixation  occurs  in blue-green algae and  a few genera of
microorganisms, which include aerobic organisms  such as Azotobacter spp.,
anaerobic organisms such as Clostridium spp., and organisms  in symbiotic
association with higher plants such as Rhizobium spp. (Bailey and Ollis, 1977;
National Research Council, 1977).
    Industrial sources of ammonia are also a form of nitrogen fixation  and are
included in the nitrogen cycle shown in Figure 2-1. Because the nitrogen cycle
is dynamic, no dramatic buildup  of ammonia is expected to occur as  a result
of these additional inputs.  Also, volatilization,  adsorption,  and chemical
transformation will affect the fate of ammonia (American  Petroleum Institute,
1981; Weiler, 1979; National Research Council, 1977).
    In the atmosphere, ammonia may  undergo many transformations and  is
expected to have a relatively short residence time of 5 to 10 days. Probably
the most important  removal mechanism  is its solution  in water droplets
together  with sulfur dioxide  or other gases to  form aerosols, with  up to 75
percent removal by  rainout and washout. The principal  product formed  is
ammonium sulfate, but a number of secondary products can also be  formed.
Reactions of ammonia with nitric acid or nitrogen dioxide may yield other
aerosols  with the ammonium nitrate as the principal product. Other reactions
of ammonia, such as with OH radical, yield NH2 radical. The products of NH2
radical reaction are not clearly known (Mearns and Ofosu-Asiedu,  1984; Tang,
1980; Doyle  et al.,  1979;  Weiler, 1979; Esmen and  Fergus, 1977;  National
Research Cancer, 1977).
    Nitrification and  volatilization are  the important and competitive  fate
processes in surface waters. Volatilization rates are highest at the sources of
industrial inputs of  ammonia,  whereas nitrification  processes are more
significant  in lakes, slow  moving rivers,  and  estuaries. Nitrification  is
responsive to high inputs of  ammonia, although conditions of high nitrification
may contribute to low levels of dissolved oxygen and the eutrophication  of a
body of water. Adsorption to particles may also play a role in the aquatic fate
of ammonia.  Once bound to a particle, ammonia may settle to the sediment
where soil-type fate  processes  will take over (Orhon and Goneng, 1982;
American Petroleum  Institute, 1981; Bouwmeester and Vlek, 1981;  Weiler,
1979).
    In water, the ammonium ion is expected  to  be predominant; however,
equilibrium is affected  by pH  and temperature.  The  fraction  of  ammonia
increases tenfold with each unit increase in pH and increases  to a lesser
degree  with  increasing temperature (Erickson, 1985;  Burkhalter and Kaya,
1977).
    The  general  population may be potentially exposed  to ammonia via
inhalation of contaminated air from industrial  plants, farms, and numerous
other natural sources, including water supplies from wells. Ammonia has been
detected in emissions from  oil refineries at concentrations up to 470 mg/m3
(U. S. Miner,  1969; National Research Council, 1977). Ammonia concentrations
of  1,900 iig/m3 and 42  iig/m3 were  measured in  emissions from  two
pulverized-coal power plants (Bauer and Andren, 1985). Urban ammonia levels
in air as high as 280 jig/m3 have  been measured in  Italy, while an urban-
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 industrial area in  Japan had  ammonia levels of 7 to 210  pg/mS (National
 Research Council, 1977).
     Several studies in California indicated measured ammonia levels of 3 to
 60 ng/m3. One sample in  the  vicinity of a dairy farm had  an ammonia
 concentration of 315 pg/ms. Hutchinson et al. (1982) reported  that air samples
 taken 1.2 meters above a large cattle feedlot in Colorado contained ammonia
 levels ranging from 290 to 1,200 ng/m3.  Alkezweeney et al.  (1986) reported
 ambient ammonia concentrations of 0.04 to 5.6 ng/m3 for the summer of 1983,
 in an area surrounded by horse and cattle farms near Lexington, KY. Ambient
 ammonia levels ranging from  6,500 to  29,800 n/m3 have been reported in
 confinement structures  of swine-producing farms  (Donham  and Popendorf
 1985).
    Ammonia  levels in nonurban air samples in Seattle, WA have ranged from
 2.0 to 8.0 iig/m3 and urban air contained 0.8 to 77.0 ng/m3. Ambient ammonia
 concentrations in coastal Virginia ranged from 1.4 to 3.5 ng/m3 (Harward et al.,
 1982).  Analysis of air  samples from  the  Allegheny Mountain Tunnel  in
 Pennsylvania for ammonia showed mean concentrations of 3.0 yg/mS in  the
 tunnel and 0.44 ng/m3 outside the tunnel (Pierson and Brachaczek, 1983) and
 air samples in a rural  area in Pennsylvania have reportedly ranged from 0.01
 to 0.137 ng/m3 (Lewin et al., 1986). Analysis of air samples from Commerce
 City, CO, Abbeville, LA, and Luray, VA showed average ammonia levels of 2.4,
 0.57, and 1.34 jig/ms,  respectively. Ambient ammonia levels ranging from  1.4
 to 5.6 iig/m3 were reported on a smoggy day in Los Angeles, CA (Hanst et al.,
 1982). Hunt et al. (1984) reported ambient ammonia levels ranging from 3.0 to
 9.0 ng/m3 in various locations in Texas. In air samples taken from June 1981
 to June  1982  in Warren, Ml, average ammonia levels ranged from 0.10   to
 0.85 ng/m3. The highest average annual ammonia level was found during the
 summer months (Cadle,  1985).
    Ammonia  may also  be  present  in  the atmosphere  as particulate
 ammonium salts. In 1976 a mean ammonium level  of 1.2 ng/m3 was measured
 in Washington, D.C. (Kowalczyk et al., 1982). Urban ammonium concentrations
 ranging  from 0 to 15.1 ng/m3 were reported in  1968 for various air monitoring
 stations  throughout the  United States.  Nonurban ammonium concentrations
 ranged from 0 to 1.2 iig/m3 (National Research Council, 1977).
    Ammonia  concentrations in precipitation  (the source of  surface  water)
 have averaged from 0.2  to 1.0 ppm in snow in the United States and Canada
 (Feth, 1966). Mean ammonium ion concentrations deposited in precipitation at
 three  sites in  Minnesota ranged from  33.6 to 47.9 peq/L (Munger,  1982).
 Ammonium ion concentrations in  rain ranging from 0.5 to 28.0 ppm  were
 reported for Israel and average  yearly concentrations of 0.17 to 1.5 ppm were
 reported in Sweden. High ammonium ion concentrations have been measured
 in some natural waters, including levels up to 485 ppm in a group of California
 springs and 1,400 ppm in one hotspring.
    Determination of the ammonium-nitrogen concentrations in  groundwater,
taken  from wells located  in North  Carolina under various  soil and  crop
conditions, ranged from 0.01 to  8.85 ppm with average quarterly levels of 0.01
to 5.10 ppm (Gilliam et al., 1974). Wells in Michigan contained an average of
0.18 ppm ammonia-nitrogen in a marshy environment and 0.16 ppm in  an
agricultural area. A sampling of water from four elementary school sites, each
with a well for its  water supply, indicated  ammonia-nitrogen  concentrations
ranging   from  0.01 to  0.57 ppm  (Rajagopal,  1978). Ammonia-nitrogen
concentrations  as high as 38 ppm  were measured in groundwater obtained
from beneath corrals (Stewart et al., 1967).
                                 2-5

-------
    Estimates of occupational exposures to ammonia have been reported  in
industrial hygiene surveys performed by the National Institute for Occupational
Safety and Health (NIOSH). According to the National Occupational Hazard
Survey (NOHS),  2,524,078 workers were potentially exposed  to ammonia  in
domestic workplace environments in 1970. Preliminary data for 1980 in the
National Occupational Exposure Survey (NOES) indicate that 417,358 workers,
including 120,599 women, were exposed to  the  compound.  Table 2-1  lists
occupations having  potential exposure to  ammonia levels higher than  that
normally found in the environment.
    Atmospheric workplace concentration  limits  have been  established for
ammonia. The  Occupational  Safety  and  Health Administration  (Code  of
Federal Regulations, 1989) established  an  8-hour time-weighted average
(TWA) permissible exposure limit of 50 ppm (35 mg/m^) for ammonia, and the
American Conference of Governmental Industrial  Hygienists  (ACGIH, 1984)
recommended an 8-hour TWA threshold  limit value (TLV) of 25  ppm (18
mg/m3) and a  15-minute short-term  exposure limit (STEL) of 35  ppm (27
mg/m3).

2.4.  Environmental Effects

    Ammonia is highly  toxic  to aquatic organisms,  and  its concentration  in
U.S. waters has been regulated  to a  maximum of 0.02  mg/L (as unionized
ammonia) (U.S. Environmental Protection Agency, 1977).  In aqueous solution,
ammonia is present in unionized (NH3)  and ionized  (NH4 + )  forms.  The
percentage of total ammonia present in the unionized form and its toxicity to
aquatic organisms  is highly dependent upon the pH and temperature of the
media (Thurston et al., 1981c).  As  pH  and temperature  increases, the
ammonia equilibrium is shifted toward the NH3 chemical species (Emerson et
al.. 1975).

    The acute toxicity of ammonia to fish has been studied extensively and is
well summarized in the literature (Thurston et al., 1984; Ruffier et al., 1981;
European Inland Fisheries Advisory Commission,  1973). The reported median
lethal concentrations of unionized  ammonia for 22 species of fish are given in
Table 2- 2.
    Data on the effect of increasing water pH upon the  toxicity of unionized
ammonia are mixed. Thurston et  al. (1984) reported increasing acute toxicity
of  unionized ammonia  to rainbow  trout as the  pH increased  to  pH 7.5.
Conversely, Broderius et al. (1985) reported decreasing  toxicity of unionized
ammonia to smallmouth bass as water pH increased from 6.55 to 8.71.
    Limited data on the subacute and chronic effects of ammonia upon fish
are available.  The estimated 32-day no-observed-effect concentrations
 (NOEC) for growth effects in smallmouth  bass are 17.4, 14.4, 14.6, and  2.4
 mg/L  total  ammonia and 0.0437, 0.148,  0.599, and 0.612  mg/L  unionized
 ammonia at pH values of 6.60, 7.25, 7.38, and 8.68, respectively (Broderius et
 al., 1985). Exposure of carp fry (Cyprinis carpio) to 0.1 mg NH3/L for 3 weeks
 resulted in significant  (p <0.01) changes  in leukocyte, erythrocyte, and
 erythroblast counts as well as increases in brain  and muscle free amino acid
 levels (Dabrowska and Wlasow, 1986).
     Aquatic invertebrates are generally less sensitive than fish to  exposure to
 ammonia. The reported  median lethal concentrations of unionized ammonia for
 nine  species of aquatic invertebrates are given in Table 2-3. Several studies
 show varying sensitivity with developmental stage (Watton and Hawkes,  1984;
                                   2-6

-------
   Table 2-1.   Occupations with Potential Exposure to Ammonia
    Acetylene worker
    Aluminum worker
    Amine worker
    Ammonia worker
    Ammonium salt maker
    Aniline maker
    Annealer
    Boneblack maker
    Brazier
    Bronzer
    Calcium carbide maker
    Case hardener
    Chemical-laboratory worker
    Chemical manufacturer
    Coal-tar worker
    Coke maker
    Coke-oven byproduct extractor
    Compressed-gas worker
    Corn grower
    Cotton finisher
    Cyanide maker
    Decorator
    Diazo reproducing-machine operator
    Drug maker
    Dye-intermediate maker
    Dye maker
    Electroplater
    Electrotyper
    Explosive maker
    Farmer
    Fertilizer worker
    Galvanizer
    Gas purifier
    Glass cleaner
    Glue maker
    Ice cream maker
    Ice maker
    Illuminating-gas worker
    Ink maker
    Janitor
Lacquer maker
Latex worker
Manure handler
Metal extractor
Metal-powder processor
Mirror silverer
Nitric acid maker
Organic-chemical synthesizer
Paper maker
Perfume maker
Pesticide maker
Petroleum-refinery worker
Photoengraver
Photographic-film maker
Plastic-cement mixer
Pulp maker
Rayon maker
Refrigeration worker
Resin maker
Rocket-fuel maker
Rubber-cement mixer
Rubber worker
Sewer worker
Shellac  maker
Shoe finisher
Soda ash maker
Solvay-process worker
Stableman
Steel maker
Sugar refiner
Sulfuric  acid worker
Synthetic-fiber maker
Tannery worker
Transportation worker
Urea maker
Varnish maker
Vulcanizer
Water-base-paint worker
Water treater
Wool scourer
  Source: National Research Council (1977).
Armstrong et al.,  1978; Jayasankar and Muthu,  1983; Reddy and  Menon
1979).
    Ammonia can cause various kinds of injury to terrestrial  plants including
necrosis, growth reduction, and increased frost sensitivity. Growth reduction
may result from uncoupling photophosphorylation, which lowers carbohydrate
                                    2-7

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production. Necrosis and frost injury may occur from ammonia saturation of
membrane lipids (Van Haut and Prinz, 1979; Van der Eerden, 1982).

    Table 2-3.    Acute Lethal Concentration Values for Unionized
                Ammonia in Aquatic Invertebrates
             Organism
LC50 (mg/L)
                                                  Exposure conditions
Asellus vacovitzai
(Isopol adult)
Callibaetis skokianus
(Mayfly nymph)
Crangonyx pseudogracilis
(Amphipod adult)
Helisoma trivolvis
(Snail adult)
Musculium transversum
(Fingernail clam adult)
Orconectes immunis
(Crayfish adult)
Philartcus quaeris
(Caddisfly larvae)
Physa gyrina
(Snail adult)
Simocephalus vetulus
(Cladocevan adult)
5.02
3.09
3.12
2.37
1.10
18.3
10.1
1.95
1.71
Flowthrough, 96 h
Flowthrough, 96 h
Flowthrough, 96 h
Flowthrough, 96 h
Flowthrough, 96 h
Flowthrough, 96 h
Flowthrough, 96 h
Flowthrough, 96 h
Flowthrough, 48 h
   Source: Arthur et al. (1987)
                                 2-11

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-------
                         3.  Health Effects

 3.1  Pharmacokinetics and Metabolism

     The essential  role of  ammonia and nitrogen in amino acid,  protein, and
 nucleic acid metabolism by living organisms has been extensively discussed
 in standard textbooks and  monographs.  This section summarizes the available
 information on  the metabolism of exogenous  ammonia by  mammals. The
 metabolic activities leading to  the production and elimination of  endogenous
 ammonia, as well  as the possible chemical reactions leading  to ammonia
 toxicity are discussed in the section on biochemical effects
     Egle (1973) studied  the  uptake  and retention  of  ammonia  in  both the
 upper  and  lower  respiratory tract of dogs exposed  to ammonia  at
 concentrations ranging from 346 to 1,076 mg/m3 (459 to 1,522 ppm). He found
 that ammonia retention in the lower respiratory tract was slightly less  than that
 of the upper respiratory tract. Retention  ranged  from 79.8 to 84.0 percent but
 was not concentration-related.  Ammonia retention by the respiratory tract  of
 humans was reported by  Landahl and Hermann (1950) and Silverman  et al.
 (1949). When subjects were exposed to  ammonia concentrations varying from
 40 to 355 mg/m3 (57 to 502 ppm), approximately 92 percent was retained  in
 the lungs but without any concentration-related effect (Landahl and Hermann,
 1950). Silverman et al. (1949) found that exposure  of human  subjects  to
 ammonia vapors at 353 mg/m3 (500 ppm) for a  period of 30 minutes resulted
 in a steady increase in  ammonia concentrations in exhaled air. At equilibrium,
 about 80 percent of the inhaled ammonia was released in expired air.
     Schaerdel et al. (1983) studied the pulmonary absorption of ammonia gas
 by male rats by exposing  the rats from  11 to 818 mg/m3 (15 to  1,157 ppm)
 ammonia for 1 day. They found a significant increase in blood ammonia levels
 with an increase in the ammonia exposure level, but blood  levels decreased
 with time, suggesting that the body in some way compensates for the increase
 in blood ammonia.  There were  no significant effects noted on pH,  pCO2, pO2,
 liver cytochrome  P-450   concentration,  or  ethylmorphine-N-demethylase
 activity. In another  study, blood and brain ammonia levels,  blood glutamate,
 glutamine, creatinine,  and urea nitrogen levels,  and alkaline phosphatase
 activity were not affected in male rats  exposed to 3.1 ± 0.21, 0.35 ± 0 07 or
 0.14 ± 0.21 mg/m3 (4.4  ± 0.3, 0.5  ±  0.1,  or  0.2 ±  0.3 ppm) of ammonia
 generated from  decomposing urine and feces  in animal rooms  (White and
 Mans,  1984).
    Cooper and Lai (1987) studied the metabolism \n vivo of ammonia by rat
 brain.  Male Wistar rats (normal,  acutely hyperammonemic,  or  chronically
 hyperammonemic)  were treated with  13N-ammonia via  a  carotid artery
cannula. In  both normal and  hyperammonemic rats, the major portion of the
 13N-ammonia nitrogen was present as the amide nitrogen of glutamine. The
rate of conversion of blood-denied ammonia to glutamine was rapid in normal
rats  (t1/2 s3 seconds only) and slower  in hyperammonemic rats (t1/2  £10
seconds only).  Hyperammonemia  did not induce  increased  glutamine
synthetase activity in rat brain.
                                 3-1

-------
    Manninen et al. (1988) exposed groups  of  five female Wistar rats 6
hours/day  for  5,  10,  or  15  days to each  of  the  following ammonia
concentrations in air: 0,  18, or 212 mg/ms (0, 25, or 300 ppm). On day 5 of
exposure, a  concentration-dependent increase in blood ammonia and an
increase of blood and brain glutamine were observed in rats exposed at 212
mg/m3 compared with  controls.  By day 10, blood  ammonia  and blood and
brain glutamine levels were similar to those of controls.
    The initial biochemical reactions involved in the incorporation of ammonia
into organic molecules in mammals involve the following: (1) the biosynthesis
of glutamic acid from ammonia and alpha-ketoglutarate; (2) the biosynthesis of
glutamine;  (3) the  formation of carbamyl phosphate; (4) the  biosynthesis of
asparagine; and  (5) some  other relatively rare processes. However, it appears
that the  route of administration drastically alters the distribution  of ammonia
(15NH4+) between  alpha-amino,  amidine,  and  amide nitrogen  of  organ
proteins. Vitti et al. (1964) found that when 15N-ammonium citrate was  given
intragastrically or intraperitoneally  to  untreated and growth-hormone-treated
hypophysectomized female  Sprague-Dawley rats, extensive  labeling  of
alanine,  arginine,  glutamic acid, and  other amino acids of  liver  protein
occurred. In contrast, subcutaneous injection resulted in extensive labeling of
the amide  nitrogen of glutamine. In addition, various levels of   N label were
found in proteins of the heart, kidneys, and  spleen, although the distribution
varied among the  various amino acids analyzed.  The relative  rate  of
incorporation of  15N was highest in the liver and lowest in the heart and varied
with the  route of administration (subcutaneous intraperitoneal intragastric). The
authors suggested that ammonia administered   intragastrically  or
intraperitoneally was metabolized  largely by  pathways involving  hepatic
glutamic dehydrogenase  and carbamyl synthetase, whereas  subcutaneously
administered ammonia  is  metabolized, to a great extent,  by the  glutamine
synthetase route.
    Following intravenous administration of 15N-ammonia  in male  rats,
ammonia was incorporated mainly  into the amide position of glutamine  (Duda
and Handler, 1958). Approximately 90 percent of the isotope was incorporated
into glutamine and urea 30 minutes after administration of 52.2 micromoles
(mol) of i5N-ammonia, with 80 percent being glutamine amide nitrogen. Urea
synthesis represented  a fixed percentage of available ammonia  over a large
concentration range. Incorporation into glutamine, urea, and glutamic acid
reached a maximum at 20 minutes, but the specific activity of glutamine was
approximately seven times that of either urea or glutamic acid. The distribution
of labeled  glutamine and urea  in the tissues of rats  following intravenous
administration of 47.5 mol of 15N-ammonium lactate was also determined by
these investigators. The  residue  levels in  glutamine   and  urea in  various
organs,  expressed  as  nmol of glutamine and  urea,  respectively, were as
follows:  carcass (25.85, 5.60); liver (1.37, 0.39); heart (0.30, 0.03);  kidneys
(0.11, 0.15); spleen (0.10,  0.023); brain (0.08, 0.01); and testes (0.051, 0.028).
    A fraction of exogenous ammonia is excreted via the lungs in expired air.
 Measurable amounts (about 269 g/m3; 377 ppb) of free ammonia were found
in the  expired  air  of dogs  injected intravenously  with ammonium acetate
 (Robin et  al., 1959). Exposure of  human  subjects  to ammonia vapor at 353
 mg/m3 (494 ppm) for a period of 30 minutes  also resulted in a steady increase
 in ammonia concentrations in exhaled  air. At equilibrium, about 80 percent of
the inhaled ammonia was released in expired air (Silverman et al., 1949).
     Like exogenous ammonia, endogenous ammonia is also  excreted via the
 lungs in expired  air.  For instance,  Barrow and Steinhagen  (1980)  found
 endogenous ammonia in the expired air of rats at concentrations ranging from
                                   3-2

-------
 7 to 250 ug/m3 (10 to 353 ppb) in nose-breathing animals and 24 to 526 ng/m3
 (34  to  744 ppb)  in tracheal-cannulated animals. They attributed these
 differences to the absorptive effect of moisture in the respiratory tract of nose
 breathers.
     Ammonia is also excreted in the urine as urea. A study by Minana et al.
 (1988) indicated that in groups of 18 male Wistar rats given a diet containing
 20  percent  (w/v) ammonium  acetate for  15  days  and then a  single
 intraperitoneal injection  of 7 mmol ammonium  acetate/kg, ammonia  was
 initially  sequestered  and finally  eliminated in the  urine as urea. Saul and
 Archer (1984) also showed that repeated oral administration  of 15N-ammonium
 chloride to male Sprague-Dawley rats resulted in low but significant amounts
 of excess 15N-nitrate in the urine. Rats were gavaged with 1,000 iimol of 15N-
 ammonium chloride daily for 5 days. Nitrate was detected in the urine during
 the exposure period and on 5 subsequent days; approximately 0.008 percent
 of the  dose  was  converted to  nitrate. The authors  suggested  that
 hydroxylamine was a possible intermediate in the ammonia  oxidation process,
 and  postulated that ammonia is oxidized in vivo by a nonenzymatic process
 that  involves active oxygen species such as the  hydroxyl radical. Similar
 results were reported by Wagner et al. (1985) after continuous intravenous
 infusion of 15NH3 to male Sprague-Dawley rats over a 96-hour period.

 3.2   Biochemical Effects

    Ammonia  is  a key metabolite in  mammals and plays an essential
 biochemical role in acid-base regulation and in the biosynthesis  of purines,
 pyrimidines, and nonessential amino acids  (Kvamme, 1983;  Visek, 1984;
 Stryer, 1981). A high concentration of endogenous ammonia, however, is quite
 toxic to mammals and may lead to life-threatening conditions.
    The gastrointestinal (Gl)  tract is a major site of  ammonia production.
 Amino acid deaminases and ureases of bacterial flora  in the  colon  liberate
 ammonia from dietary amino acids  and urea. Newly generated ammonia is
 transported to the liver through the portal circulation, where it is converted to
 urea. The urea is then transported by the blood to the kidneys for excretion:

     a-ketoglutarate + NH3 + NADH + H* ^ glutamate +  NAD*  + H2O

     NH3 + CO2 + 2ATP + H2O ^ carbamoylphosphate + 2ADP +  Pi

            Carbamoylphosphate ^ urea

    The kidneys produce ammonia from the deamination of glutamine (Good
and  DuBose,  1987; Dass and  Welbourne,  1986; Eriksson et  al.,  1985;
Windmueller and Spaeth, 1978; Visek, 1984).  The ammonia produced by the
kidneys acts  as an urinary buffer  (Windmueller and  Spaeth, 1978). The
metabolic activity of skeletal muscle also generates ammonia (Eriksson et al.,
 1985). In the central nervous system, the purine nucleotide  cycle appears to
be the  main  generator  of ammonia,  which  under normal conditions is
incorporated into glutamine (Kvamme, 1983).

     NH3 + a-ketoglutarate + NADH +  H+ ^ gfutamate +  NAD*  + H2O

            ATP + glutamate + NH3 ^ glutamine + ADP  + Pi
                                 3-3

-------
    The liver is the only organ that has a complete urea cycle that converts
ammonia to urea.  In other organs,  ammonia is  incorporated into glutamine.
Muscle tissue comprises the largest glutamine pool in humans (Lund, 1980;
Windmueller and Spaeth, 1978).
    The importance of the urea cycle is not restricted to detoxifying ammonia;
it also exchanges substrates with the citric acid cycle and provides substrates
for the synthesis of pyrimidines and  polyamines that regulate RNA and protein
synthesis. For this reason, deficient or abnormal operation of the urea cycle
may have serious metabolic consequences (Grisolia et al., 1976).
    In humans,  excretory mechanisms  for  detoxification  and removal of
ammonia are very rapid.  For  instance, under normal  conditions,  the  hepatic
portal circulation assures  that all  of the ammonia from the Gl  tract is
transported  to the liver for detoxification. Fifty  percent of the arterial blood
ammonia is  detoxified by the skeletal muscle in healthy individuals (Freed and
Gelbard, 1982; Lockwood et  al., 1979). At the same time, the urea cycle
normally operates  at about 60 percent capacity (Hems et al., 1966); thus it is
the availability of the substrate that  may limit the rate of urea production. Fico
et al. (1986)  studied the rate of  urea  synthesis  in human  liver  samples
obtained by biopsy. They found that increasing the ammonia concentration in
the incubation medium from 0 to 5.0 mM produced a 200  percent increase in
urea synthesis.
    Inherited conditions in children have been reported in which all or some of
the enzymes participating in the urea cycle were defective (Hjelm et al., 1986;
Brusilow,  1985; Shambaugh, 1978;  Zimmermann et al., 1985). Such subjects
exhibited  various  neurologic  disorders,  hyperammonemia, inhibited  growth,
and protein intolerance. Several acquired diseases can also affect the urea
cycle enzymes  (Zimmerman  et  al.,  1985; Glasglow, 1983;  Boutros et  al.,
1980), causing  severe  hyperammonemia, hyperaminoaciduria (Hilty et  al.,
1974), hepatic failure, and encephalopathy. In pathologic  conditions such as
alcoholic hepatitis, uremia,  and liver cirrhosis, defective urea-cycle enzymes
are also present (Muting et al., 1986; Swendseid et al.,  1975; Maier et al.,
1974; Brown et al., 1967).
     It is possible that exogenous ammonia may cause a  potential health risk
under certain conditions to man (e.g., genetic or  metabolic disorder). However,
since ammonia is  severely irritating to sensitive  areas such as the eyes, skin,
lungs, and throat,  it  is likely that humans will avoid exposure  to quantities of
"environmental" ammonia that can produce metabolic toxicity.
     Acute exposure  of mice  for 2 days to ammonia vapors (50,000  ppm)
increased the activity of sodium  ion  (Na+) and  potassium ion (K*)-activated
ATPase of the brain,  resulting  in an  increased  concentration  of adenine
derivatives  (Sadasivudu et al., 1979, 1977), and decreased the activity of
adenosine  deaminase,  thus  reducing  the  degradation  of adenosine
(Sadasivudu et  al.,  1981).  Since adenosine  has been  implicated both as  a
cerebral depressant as well as a sleep-inducing agent (Haulica et al., 1973), its
accumulation could be a major factor  in the  depression  of brain function.
Alternatively, a  rise  in  ATPase activity may lead  to  stabilization of neuronal
 membranes and increased transport of NH4+  into glial  cells,  exceeding the
 detoxifying ability of the cells. Increased transport of NH4* into glial cells may
 possibly  be due  to its  similarity  to hydrated  K+,  whose concentration is
 normally maintained by these cells (Lewis, 1976). Hence, this could  produce  a
 gross disturbance in ionic  fluxes possibly leading to depression of neuronal
 transmission, the  degree of which  would depend on the extent of damage to
 the glial cells (Sadasivudu et al., 1979).
                                    3-4

-------
     Chronic exposure to 50,000 ppm ammonia also alters the metabolism of
 amino acids belonging to the glutamic acid family (gamma-aminobutyric acid,
 alanine, glutamic acid, aspartic acid, glutamine) by increasing the activities of
 aspartate  aminotransferase,  glutamate dehydrogenase,  and glutamine
 synthetase. This change facilitates greater removal of ammonia ultimately in
 the form of glutamine, thus  compensating for a rise in the level of  ammonia
 (Sadasivudu et al., 1979). The process occurs in the astroglial cells, which are
 known to possess most of glutamine synthetase activity in the brain (Martinez-
 Hernandez et al., 1977).
     Hepatic encephalopathy has been  linked with a derangement  in  the
 metabolism of  a number of  neurotransmitters like catecholamines, serotonin,
 gamma-aminobutyric  acid (GABA),  and acetylcholine  (Fischer  and
 Baldessarini,  1976; Biebuyck  et al., 1975;  Walker  et al., 1971). Increased
 ATPase and  decreased   monoamine oxidase  (MAO)  and  glutamate
 decarboxylase (GD) activities in all three regions of the  brain were observed in
 mice intraperitoneally injected  with  200 mg/kg  ammonium  chloride
 (Sadasivudu and Murthy, 1978). Glutamate decarboxylase (GD) and GABA-
 aminotransferase (GABA-T) are involved  in the  production  and metabolism of
 GABA,  whereas  MAO  degrades catecholamines and serotonin. While  an
 increase in ATPase activity leads to membrane stabilization, GABA  is known
 to bring  about  hyperpolarization (Krnjevic et al.,  1966). Decreased GD and
 GABA-T activities may be regarded as  compensatory because  they reduce
 the GABA level. A decrease  in MAO activity  would tend to raise the levels of
 catecholamines and serotonin. An increase in catecholamine concentration, in
 particular, would promote consciousness in  the  animal.  However,  following
 exposure to 50,000 ppm ammonia  vapors for 2 and 5 days, increased MAO
 levels in the  cerebellum were observed. A  greater destruction of  biogenic
 amines  may  lead to a  state of unconsciousness (Sadasivudu and Murthv
 1978).
    During the  last three decades,  several mechanisms have been proposed
 to explain the biochemical basis for ammonia  neurotoxicity. Because the brain
 is highly vulnerable to decreases in  the ATP level, these hypotheses postulate
 an eventual decrease  in available cerebral  energy due  either to  reduced
 production  or  enhanced  utilization of ATP  during  ammonia  detoxification
 and/or due to ammonia-induced stimulation  of ATPase activity  (McCandles
 and Schenker, 1981; Walker  and  Schenker, 1970). Other theories include the
 formation or accumulation of  GABA, an inhibitory neurotransmitter (Goetcheus
 and Webster, 1965), and depletion of acetylcholine  (Braganca et al.,  1953).
 However, none  of these hypotheses  has been  conclusively  proven. It  is
 possible  that  ammonia  intoxication produces  a  multiplicity of biochemical
 injuries. The following theories are briefly discussed.
    McKhann and Tower (1961)  suggested  that  ammonia reduces the
 incorporation of pyruvate into the tricarboxylic acid (TCA) cycle, thus slowing
the oxidative  metabolism. This  conclusion  was drawn  from  an  in  vitro
observation that high concentrations of ammonium  chloride  (15  mM)  inhibit
oxygen consumption in cat cortex mitochondria, indicating  impaired pyruvate
decarboxylation.  However,  tests  conducted  on the brain of  ammonia-
intoxicated  rats  and from brains incubated with  ammonium chloride  or
ammonium  acetate (2 to 18  mM) failed  to reveal any alteration  in pyruvate
decarboxylation (Walker and Schenker, 1970; Ratnakumari et al., 1986).
    Based on in vitro studies with high ammonia  concentrations,  Worcel and
Erecinska  (1962) suggested that  cerebral  detoxification of ammonia  to
glutamate depletes the NADH pool,  resulting in  decreased amounts of NADH
available for ATP formation in the mitochondria.  However, results from in vivo
                                 3-5

-------
studies indicated that the cerebral cytoplasmic NADH:NAD+ ratios increased
during acute  ammonia  intoxication  due  to  a  marked  increase  in  the
lactate:pyruvate ratio (Hawkins et al.,  1973; Hindfelt, 1973). Moreover, there
was  an  apparent decrease in NADH:NAD+  ratio in the  mitochondria,
suggesting a failure to transport reduced equivalents from the cytoplasm to
the mitochondria (Hindfelt et al.,  1977).
    The  "Energy Depletion Hypothesis" was suggested  by  Bessman  and
Bessman  (1955). According to  this hypothesis, ammonia entering  the brain
reacts with  alpha-ketoglutarate  (alpha-KG)  and  NADH, forming glutamate.
Glutamate would deplete the  TCA cycle of  one  of its dicarboxylic  acids,
resulting  in a drop in the cerebral oxygen utilization observed in hepatic coma.
This reduction in oxidative metabolism would also  result  in a drop in ATP
formation in the  brain, eventually leading  to coma.  It has been observed  that
the brains of hepatic coma patients often exhibit ammonia uptake (Bessman
and  Bessman,  1955) and  decreased oxygen  consumption (Fazekas  et al.,
1956). Further, after ammonia injections, the concentrations of alpha-KG were
decreased in  the cerebral cortex and  whole brain  of  dogs and  mice,
respectively (Bessman, 1961;  Clark and  Eiseman, 1958). However, other
studies with animals have failed  to  detect any significant change in  the
concentrations of alpha-KG or ATP in the brain during the induced ammonia
intoxication  (Ratnakumari et al., 1986; Raabe and  Lin,  1984;  Hawkins et al.,
1973; Hindfelt and Siesjo,  1970, 1971).  Bessman and  Pal (1982) suggested
that the major problem with the acceptance of this hypothesis  in the past was
the lack  of exact correlation between  levels of ammonia concentration in the
blood and the mental state of the patient. In fact, correlation between cerebral
symptoms and  CSF glutamine  content was somewhat better  than  the
correlation with  ammonia concentration.  However,  they  have now
demonstrated the presence of  a relation between  ammonia concentration  in
the blood and the state of consciousness.
    Another theory explains the depletion of cerebral ATP through  enhanced
synthesis of glutamine (Nakazawa and Quastel, 1968).  A fourfold increase  in
cerebral  glutamine  was  found  within 15 minutes  after administration of an
acute  dose of ammonium  acetate to rats (du Ruisseau et al.,  1957). Other
investigators have reported similar findings  (Berl et al., 1968).  However, it has
been suggested that glutamine synthesis alone cannot  utilize  enough ATP  to
affect cerebral function, unless a "vital" ATP pool is involved (Bessman, 1961).
Administration  of methionine  sulfoximine,  a potent inhibitor of  glutamine
synthetase, caused a  marked decrease in ammonia toxicity  in mice. It was
concluded that ammonia intoxication does not depend on the mere presence
of high cerebral ammonia content, but is related to a metabolic process that
occurs directly  or indirectly through the major known pathway of cerebral
ammonia detoxication,  i.e., synthesis of glutamine (Warren  and  Schenker,
 1964). Hindfelt (1973) failed to  support the  sparing mechanism of methionine
 sulfoximine through  ATP-saving inhibition of glutamine  synthesis. In addition,
 Hawkins et al. (1973) found no significant arteriovenous difference in glutamate
 or glutamine  concentration  in  acutely  intoxicated mice.  Although   a
 considerable amount of ammonia was incorporated into glutamine, it was not
 rapidly released from the brain into the circulatory system.
     Hawkins et al.  (1973) suggest  that the general  increase  in  nerve cell
 excitability  and  activity that results in convulsions, as  well as the increased
 metabolic rate of the brain, may be due to Na* and K* stimulation  of ATPase
 activity produced by ammonia. After an injection of ammonium acetate, the
 plasma  K* concentration increased from 3.3 to 5.4 mol/L, with  no significant
 increase in Na* concentration. A  possible  decrease of 15 mV  in the resting
                                   3-6

-------
 transmembrane potential was calculated. Accordingly, the likely mechanism
 for pharmacologic action of ammonia is the effect on the electric properties of
 nerve  cells.  Extracellular ammonia-like  K*  decreases  the  resting
 transmembrane potential, and, therefore, the resting potential is closer to the
 threshold for nerve conduction.  This could then cause a general increase in
 nerve-cell excitability leading to convulsions.
     Ulshafer (1958)  suggested that the depletion of ATP may cause  a
 decrease in cerebral acetylcholine, which  requires ATP  for  its  synthesis.
 Administration  of sufficient ammonium carbonate  to produce convulsions in
 rats caused  a  decrease in the brain content of acetylcholine. Ammonia also
 inhibits the synthesis of  acetylcholine  in brain cortex slices, which can  be
 relieved by the addition of glutamine  synthetase  inhibitors (Braganca  et al
 1953).  However,  Walker et al.  (1971) failed to  detect any change  in
 acetylcholine, serotonin, or norepinephrine during  the  development of acute
 ammonia-induced coma.
     Raabe  and  Lin  (1983:1984)  found that systemic  ammonia  toxicity
 inactivates the  extrusion of the chloride ion (CI') from  the  neurons and thus
 decreases the  hyperpolarizing action of postsynaptic inhibition, producing the
 first signs of ammonia neurotoxicity.  The  decrease in  the  hyperpolarizing
 action of postsynaptic inhibition was without a concurrent decrease in energy
 metabolism (decrease of pyruvate, a-ketoglutarate,  glutamate,  or ATP) as had
 been suggested by Bessman and  Bessman (1955). Similar results were also
 reported by lies and Jack (1980).

 3.3   Acute Toxicity

    Several  studies  have been  conducted  with  laboratory  animals  to
 determine the  effects of acute exposure to ammonia.  Acute  toxicity values,
 presented in Table 3-1, suggest that ammonia is very toxic at high exposure
 levels.
    In animals, compound- and concentration-related effects resulting from
 exposure to ammonia progress from mild irritation  of the respiratory system
 and mucous membranes to convulsions, acute pulmonary edema, coma, and
 death. Typical signs of toxicity associated with exposure to ammonia include
 initial excitation, closed  eyes,  labored  respiration, mouth  breathing,  nose
 pawing, scratching, ocular and nasal discharge, and coughing (Kapeghian  et
 al., 1982; Silver and McGrath, 1948; Appelman et al.,  1982; Boyd et al   1944-
 Weedon et al.,  1940;  Dodd and  Gross,  1980; Cralley, 1942; Dalhamn,  1956;
 Dalhamn and Sjoholm, 1963; Drummond et al., 1978).
    Exposure to sublethal and lethal concentrations  of ammonia has produced
 adverse effects  in the respiratory tract and liver in some species.  Kapeghian et
 al. (1982) studied the effect of inhalation of ammonia gas in mice exposed to
 ammonia levels ranging from 0 to  3,436 mg/ms (0 to 4,860 ppm) for 1 hour
followed by an observation period of  14 days. Exposed  animals exhibited
 irritant effects (excitation,  rapid, vigorous tail revolutions,  eye blinking,  nose
scratching, and  dyspnea) immediately following  exposure. At exposure  levels
of 2,793, 2,984,  3,188, and 3,450  mg/m3 (3,950,  4,220, 4,490, and 4,860  ppm)
there  was 25,  42, 67,  and  100  percent mortality,  respectively.  Diffusely
hemorrhagic  lungs were noted  in  animals  that died during exposure. No
deaths were noted at exposure levels lower than 2,792 mg/mS. Appelman et al.
(1982) found that exposure to ammonia levels ranging from  21,353 to 38,547
mg/m3 (30,075  to  54,292  ppm) for 10  minutes;  18,642 to 23,641 mg/m3
(26,256  to 33,305 ppm) for 20 minutes; 12,862 to  17,164 mg/m3 (18,116 to
24,175 ppm) for 40 minutes; and 10,059 to 13,491  mg/m3 (14,169 to 19,002
                                  3-7

-------
Table 3-1.    Acute Toxicity Values for Ammonia in Laboratory Animals
Route/species,
sex
Inhalation
Mouse, M

Mouse
Rat,M

Rat,F
Rat,M

Rat,F

Cat
Rabbit

Acute
toxicity value

LC50 = 2,991 mg/m3
(4,230 ppm)
LC50 = 6,988 mg/m3
(9,884 ppm)
LC50 = 26,327 mg/m3
(37,238 ppm)
LC50 = 31,899 mg/m3
(45,119 ppm)
LC50 = 9,997 mg/m3
(14,1 40 ppm)
LC50 = 13,977 mg/m3
(19,770 ppm)
LC50 = 7,1 27 mg/m3
(10,080 ppm)
LC50 = 7,1 27 mg/m3
(10,080 ppm)
Exposure
duration,
min

60

10
10

10
60

60

60
60

Reference

Kapeghian et al. (1982)

Silver and McGrath
(1948)
Appelman et al. (1982)

Appelman etal. (1982)
Appelman et al. (1982)

Appelman et al. (1982)

Boydetal. (1944)
Boyd etal. (1944)

 Oral
     Guinea piga  LD7s = 900-1,200 mg/kg
 Intravenous
     Chicken
     Mouse

 Intraperitoneal
     Rat"

     Chicken0
     Mouse0
LDSO = 46.3 mg/kg
LD50 = 95.9 mg/kg
LD100 = 400 mg/kg

LD50 = 177.5 mg/kg
LDSO = 184.3 mg/kg
                         NA"     Koenig and Koenig
                                     (1949)
NA      Wilson et al. (1968)
NA      Wilson et al. (1968)
NA      Koenig and Koenig
            (1949)
NA      Wilson etal. (1968)
NA      Wilson etal. (1968)
 aAmmonium chloride used.
 bNA = Not applicable.
 °Ammonium acetate used.

 ppm) for 60 minutes produced excitability and nasal and eye irritation in rats.
 Macroscopic examination revealed hemorrhagic lungs in all exposed animals.
 Exposure-related deaths occurred in all exposure groups except those animals
 exposed to 21,353  mg/mS ammonia for 10 minutes. Exposure to ammonia gas
 levels of 6,063 to 8,946 mg/m3 (8,540 to 12,600 ppm) for 10 minutes resulted
 in  25  to 80  percent mortality. Of 180  mice tested,  100 died within the 10
 minute  exposure period (Silver  and McGrath, 1948). An increase in the
 hexobarbital sleeping time was  reported  by Kapeghian  et al.  (1985)  after
 exposing mice to 3,110 mg/ms (4,380 ppm) ammonia for 4 hours; however,
 this exposure level was  lethal to  4 of the 12 animals. No effect was noted on
 the hexobarbital-induced sleeping time in animals exposed to 958 mg/m3
 (1,350  ppm)  ammonia  for  4  hours;  however,  the  latent periods  were
 significantly reduced in both exposure groups.
     The results of acute exposure to lower levels of ammonia are conflicting.
 Schaerdal et al. (1983) saw no signs of irritancy or histological changes  in the
                                    3-8

-------
respiratory tract of rats exposed to ammonia levels of 11 to 818 mg/m3 (15 to
1,157 ppm) for 1 day or 3 to 507 mg/m3 (4 to 714 ppm) for 3 or 7 days. The
National Research Council (1977) reported no signs of ill effects in 4 mice and
7 rats exposed to 707 mg/m3 (1,000 ppm) ammonia for 16 hours; however, 1
rat died during the exposure period. Gross examination revealed congestion,
hemorrhage, and edema  of the  lungs. Slight  irritation was  reported in rats
exposed  to from 339 to 403 mg/m3 (480 to 570 ppm) ammonia for 4 hours
(Carson et al.,  1981). Exposure  to 71 to  212 mg/m3  (110  and 300  ppm)
ammonia for 6 hour intervals reduced  free access wheel running in rats and
mice. Reductions in wheel  running during exposure to irritants  may be
interpreted to reflect sensory  irritation (Tepper et al.,  1985). Wood (1981)
calculated the aversive concentration  at  which  50 percent  (AC50) of the
ammonia exposures were terminated using an operant conditioning procedure.
His calculations  indicate that ammonia produces irritant effects in mice at
levels <243 mg/m3 (344 ppm).  In a later work, Tepper and Wood (1985) using
a similar operant conditioning procedure, calculated an  AC50 value for mice of
303 ± 92 mg/m3 (428 ± 130 ppm). After repeated exposures to high levels of
ozone prior to ammonia exposure, the AC50 value  decreased from 303 to 165
mg/m3 (428 to 233 ppm). Exposure to  198 mg/m3  (280 ppm) ammonia for 36
hours resulted in frothing of the mouth  and excessive secretions from the
noses of pigs. After the  exposure period, convulsions occurred and respiration
was  short and  irregular (Stombaugh  et al., 1969).  Merilan  (1973) saw  a
significant decrease in respiratory rates in calves exposed to  35 to 71 mg/m3
(50 and 100 ppm) ammonia for  7.5 hours. Exposure to 35 to 71 mg/m3 for 2.5
hours did not produce  this  effect (Mayan  and  Merilan, 1976). Vesell et al.
(1973) reported that the ammonia produced from fecal  matter in animal cages
could produce  hepatic microsomal enzyme inhibition (ethylmorphine N-
demethylase and aniline hydroxylase  activity) in  rats. This finding  was not
confirmed by Schaerdal et  al. (1983) and Kapeghian et  al. (1985)  after
exposing rats to 505 mg/m3 (714 ppm) ammonia for 7 days and mice to 248
mg/m3 (350 ppm) ammonia for  4 days.  Dodd and  Gross (1980) detected
necrosis and sloughing of the airway mucosal surface in cats exposed to 707
mg/m3 (1,000 ppm) ammonia for 10 minutes. A cessation of tracheal ciliary
activity was seen in rats 7 to 8 minutes after exposure to 2  mg/m3 (3 ppm)
ammonia, 150 seconds after exposure to 4 to 5 mg/m3 (6 to 7 ppm), 20
seconds after exposure  to 14 mg/m3 (20 ppm), 10 seconds after exposure to
32 mg/m3 (45 ppm), and 5 seconds after exposure to 64 mg/m3 (90 ppm)
(Dalhamn, 1956). A reduction in  ability to clear pulmonary bacteria (scherice in
cats exposed to  707 mg/m3 (1,000 ppm) ammonia for 10 minutes. A cessation
of tracheal ciliary activity was seen in rats 7 to 8 minutes after exposure to 2
mg/m3 (3 ppm) ammonia, 150 seconds  after exposure to 4 to 5 mg/m3 (6 to 7
ppm), 20 seconds after exposure to 14 mg/m3 (20 ppm), 10 seconds  after
exposure to 32 mg/m3 (45 ppm), and 5 seconds after exposure to 64 mg/m3
(90 ppm) (Dalhamn, 1956). A reduction in ability to clear pulmonary bacteria
(Escherichia coli) was found in pigs exposed to 35 to 53 mg/m3 (50 to 75
ppm) ammonia for 2 hours (Drummond  et al., 1978). While ammonia had little
effect on performance or respiratory tract structure, the authors suggested that
exposure to ammonia  could be a  contributing  factor  in pulmonary  tract
infection.
    Buckley et  al. (1984) exposed via inhalation  groups of  16 to 24 male
Swiss-Webster mice to ammonia at the  RD50 concentration of 214 mg/m3  (303
ppm)  6 hours/day,  for 5 days. An evaluation  of the ammonia-induced
histopathological  lesions of  the respiratory  tract indicated mild to moderate
epithelial exfoliation, erosion, ulceration,  necrosis, inflammation, and squamous
                                 3-9

-------
metaplasia  in the nasal cavity. No  lesions were observed  in the olfactory
epithelium.
    Rothenberg et al. (1986) exposed five male and three female beagle dogs
(nose only) to 1 mg/m3 ammonium sulfite mixed with sulfate for 1 hour. The
levels of sulfur dioxide and  ammonia were  <0.5  ppm and <5.0  ppm,
respectively. No  statistically significant differences were observed in the
tracheal mucosal clearance rate between preexposure and postexposure. In a
separate experiment,  inhalation exposure  (nose  only)  of 12  male and 12
female guinea pigs  to  aerosol concentrations  of  50, 250, or 450 mg/m3 of
ammonium sulfite (60 to 80 percent) for 1 hour produced no deaths at any
level.
    Minana  et  al. (1988)  investigated  the protective  effect of  long-term
ammonium  ingestion  against  acute  ammonium  intoxication in
hyperammonemic rats. Groups of 18 male Wistar rats were fed either a control
diet or a diet containing 20 percent (w/v) ammonium acetate for 15 days. Both
the control and the treated rats  were then given a  single intraperitoneal
injection of 7 mmol  ammonium acetate/kg. Blood ammonia,  blood  urea, and
glutamine  levels were determined at various  intervals  (1  to  8  hours
postinjection). Survival was higher (nine survivors) for hyperammonemic rats
than  for control  rats  (one survivor). In addition,  of the nonsurvivors,
hyperammonemic rats died within 31  ± 10 minutes, and the  control rats died
within 18 ± 5 minutes postexposure. Ingestion of ammonium-containing diet
for 15 days had a protective  effect  against a  single  high dose of  ammonia.
Blood ammonia levels were the same (2 mM) for both  groups; the  maximum
was  reached after 15 and 30 minutes for hyperammonemic  and control rats,
respectively, suggesting a more rapid detoxification in hyperammonemic rats.

3.4   Subchronic Toxicity

    Subchronic exposure to ammonia levels higher than those encountered in
ambient air produces  adverse  effects on the tissues of the  respiratory  tract
and  impairs the pulmonary defense system. It may also produce anorexia;
increase the  tendency towards,  or  severity of,  respiratory  tract infections;
and/or produce degenerative changes in the lungs, liver, kidneys, and spleen.
    Coon et al. (1970)  in four experiments studied the effects of repeated or
continuous exposure to varying  concentrations  of ammonia gas in several
species. Table 3-2 gives the results  of those experiments.  In summary, nasal
and ocular effects were associated with repeated exposure to ammonia at 778
mg/m3  (1,100  ppm) in dogs and  rabbits; however, these  signs disappeared
during the  second week of exposure.  No clinically  significant effects were
detected in guinea pigs, rabbits, dogs, and monkeys continuously exposed to
ammonia at a concentration of 40 mg/m3 (57 ppm) for  114 days. There were
inflammatory changes noted in the lungs and kidneys of rats exposed to 127
mg/m3 (181 ppm) ammonia continuously for 90 days. However, these changes
were reported  in 50  percent  of the control and exposed  animals. In rats
exposed to 262 mg/m3 (374 ppm) ammonia there  were  nonspecific circulatory
and  degenerative changes  in  the lungs and kidneys that, according to the
authors, were difficult to  specifically relate to  ammonia exposure. Deaths
occurred at concentrations of 460 and 455 mg/m3 (650 and 672 ppm).
     Numerous  other  subchronic toxicity  studies have also been reported.
Weatherby (1952) found that exposure of male guinea pigs to 120 mg/m3 (170
ppm) (range 99 to 141 mg/m3; 140 to 200 ppm) ammonia for 6 hours/day, 5
days/week for up to 18 weeks resulted in congestion of the spleen, liver, and
kidneys and  early  degenerative changes in the  suprarenal  gland. No
                                  3-10

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 significant effects were detected following exposure of guinea pigs and mice
 to an ammonia concentration of 14 mg/m3 (20 ppm)  for 28 days. When the
 exposure duration was increased  to  42  days or  when  the  ammonia
 concentration was  increased to 35 mg/m3 for guinea pigs, pulmonary edema,
 congestion,  and hemorrhage were  seen in  both species (Anderson et al.,
 1964). Richard et  al.  (1978)  found  nasal irritation and severe inflammatory
 lesions in rats exposed to 353 mg/m3 ammonia for 3 weeks which were not
 present after  8 weeks  of  exposure. The  authors believed this finding
 suggested the occurrence of an adaptive process. Mayan  and Merilan (1972)
 found  no pathologic" changes in the liver, lungs,  spleen,  or kidneys after
 exposing female white rabbits to 35  mg/m3 ammonia for  2.5 to  3 hours  (22
 exposures) or 71  mg/m3 for. 16 exposures (duration of each exposure  not
 indicated).  Examination  of guinea  pig alveolar  macrophages  after
 subcutaneous  inoculation  with  Mycobacterium bovis  BCG and  intradermal
 injection of 2.5 g of tuberculin-purified protein derivative (PPD) and exposure
 to 35  or 64 mg/m3 (50  or 90  ppm) ammonia for 3  weeks  resulted in no
 significant alterations  in  bactericidal or  phagocytic  activities. However,  the
 addition of ammonia to cultures of alveolar macrophages from normal animals
 significantly  inhibited the bactericidal activity  of those cells (Targowski et al.,
 1984). An increase in the severity  of rhinitis,  otitis media, tracheitis,  and
 pneumonia was seen  by Broderson  et al. (1976) after inoculating rats  with
 Mycoplasma pulmonis and exposing them for 4 to 6 weeks to ammonia levels
 routinely found in animal cages 18 to 177 mg/m3 (25 to 250 ppm). The authors
 also found pathologic  changes in the nasal passages of animals exposed to
 106 mg/m3 (150 ppm) ammonia for 75  days and 177 mg/m3 for 35 days.
 Schoeb et al. (1982) found that ammonia  had a direct growth-promoting effect
 on  Mycoplasma pulmonis  which was responsible for  respiratory disease
 syndromes in rats.
    In commercial animal species, Deaton et al. (1982; 1984) showed  that
 exposure of laying hens to ammonia at  a concentration of 141 mg/m3 (200
 ppm) for  17 days resulted in a significant reduction in egg production. Deaton
 et al. (1982), Oyetunde et al. (1978), and  Reece  et  al.  (1981)  found  that
 exposure of chickens to sublethal  concentrations of  ammonia  (18 to  141
 mg/m3) for up to  28  days significantly  reduced  body weight gain.  Mild to
 moderate macroscopic and microscopic changes in the lungs and air sac were
 seen in chickens  exposed  to 71  mg/m3 (100 ppm) ammonia for 4 weeks
 (Oyetunde et al.,  1978).  No significant effects were detected following the
 exposure of chickens to ammonia at a concentration of 14 mg/m3 (20 ppm) for
 up  to 28 days and turkeys for up to 6 days; however, pulmonary  edema,
 congestion, and  hemorrhage  were detected  in chickens  exposed  at  141
 mg/m3 for 17 to 21  days or 707 mg/m3 (990 ppm) for 14 days, and in turkeys
 exposed  at 35 mg/m3 for  10 to 14 days.  Also, chickens  maintained in
 environments containing  14 mg/m3 ammonia for 72 hours  or 35 mg/m3 (50
 ppm) for  48 hours  were  found to be  more susceptible  to Newcastle disease
 virus (Anderson et al., 1964). Like Dalhamn  (1956), Nagaraja et al. (1983)
found that exposure  to  ammonia produced  a reduction  in  tracheal ciliary
activity. After exposure to 7 to 28 mg/m3 (10 to 40 ppm) ammonia for 1 to 7
 weeks, turkeys exhibited deterioration of the  mucociliary apparatus which is
thought to reflect a breakdown in the defense mechanism of the respiratory
tract against an accumulation of pathogenic  bacteria  and viruses. With the
exception of mild conjunctivitis and blepharitis in one pig, Curtis et al. (1975),
found no evidence of structural aberrations in any organ or tissue of pigs'
exposed to ammonia levels of 35 to 53 mg/m3 for up to 75 days. The National
 Research  Council (1977)  reported  an increased  thickness of tracheal
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epithelium and goblet cells in pigs after  exposure to 75  mg/m3 (106  ppm)
ammonia for 2 weeks.

3.5  Chronic Toxicity

    No adequate information was found on the effects of chronic exposure to
ammonia in animals.

3.6  Carcinogenicity

    No  information was  found on the carcinogenic potential  of  inhaled
ammonia in animals.  However, oral administration of ammonium  hydroxide
and  ammonia was not carcinogenic  in mice.  Toth (1972)  investigated  the
carcinogenic  potential of ammonium  hydroxide  in  Swiss and C3H  mice.
Ammonium hydroxide was administered daily in the drinking water of  Swiss
mice at levels of 0.1, 0.2, or 0.3 percent (1,000, 2,000, or  3,000 ppm) and to
C3H mice at a level of 0.1. percent over the  normal  life span of the animals.
Ammonium hydroxide was  not carcinogenic in either species,  and did  not
affect the development of breast adenomas in C3H females. The incidences of
breast adenomas in the treated and control groups were 60 and 76 percent,
respectively.  In another study, no significant increase in lung tumors was
found in mice with  a  high  sensitivity to lung  tumorigenesis after  the
administration of 42 mg/kg ammonia twice a week  by  stomach tubes for 4
weeks (UzvSlgyi and Bojan,  1980).

3.7   Mutagenicity

     Limited data  suggest that ammonia may be mutagenic. Demerec et al.
(1951)  tested  ammonia for  its ability to induce back-mutations  from
streptomycin dependence  (Sd-4) to nondependence  in Escherichia coli.
Bacterial suspensions  were added to ammonia solutions  ranging from 0.025 to
0.500 percent (250 to  5,000 ppm)  in distilled water, and incubated at 37°C for
3 hours. Control  cultures were incubated in distilled water only. A definite
mutagenic  activity was observed  at concentrations of 0.25 and 0.50 percent
(2,500 and 5,000 ppm); however, the proportion of survivors was lower than 2
percent.
     Lobashev and Smirnov (1934) reported that 95 percent mortality occurred
in larvae of Drosophilia melanogaster (100-120 hr old) exposed to the  fumes
of 1 percent (10,000  ppm) ammonium hydroxide solutions. The  offspring of
the  survivors showed a mutation rate of 0.54  percent while control cultures
showed only 0.05 percent, which was a statistically significant effect.
     Visek et al. (1972) examined  the effect of ammonia in cultures of normal
and transformed 3T3  cells.  Normal 3T3 and SV-40 transformed  3T3 mouse
fibroblasts  were cultured in  media with serum and  antibiotics plus ammonia
added as ammonium  chloride. The amount of ammonia added was 0, 10, 20,
or 35 ug/mL (0, 10, 20 or 35 ppm) of culturing medium. Normal  morphology
and cell multiplications were seen in both cell lines when ammonia was not
added. However, when ammonia was added both cell  lines showed distinct
changes in the morphology and highly  significant (p < 0.001) reductions in cell
multiplications. These changes increased progressively as  the concentration of
ammonia increased.  Control 3T3 cultures  released significantly (p  < 0.001)
 greater quantities of  ammonia per cell than control cultures  of  transformed
 cells, but their multiplication was  more adversely affected with the addition of
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ammonia. The affect of ammonia on cell multiplication was independent of the
pH of the medium.

3.8   Teratogenicity and Reproductive Effects

    No information was found on  the teratologic or reproductive effects of
ammonia in animals.

3.9   Neurotoxicity

    Elevated levels of ammonia in the blood of animals and humans have
been  known to  cause  neurologic  disorders  and  encephalopathy.
Hyperammonemia may result from  liver failure or metabolic and  genetic
diseases that affect the synthesis  of urea and/or removal of ammonia. The
biochemical basis for ammonia neurotoxicity is discussed in Section 3.2.

3.10  Effects on Humans

    Most of the available literature on the effects of ammonia on  humans
consisted of case  reports following accidental exposure via  inhalation;
consequently, exposures were not well quantified. The major effects of acute
exposure to ammonia  are burns of the eyes, skin, and respiratory tract. Since
ammonia is highly  water soluble,  these effects are likely the result of  the
formation of ammonium hydroxide in situ.
3.10.1
Ocular Toxicity
    Eye injuries are the most common cause of permanent disability due to
accidental acute exposure to  ammonia (Helmers  et  al., 1971; Jarudi and
Golden, 1973). Ammonia, in the form of ammonium hydroxide, forms soaps as
it reacts with the fatty epithelial layer of the cornea, after which it traverses the
stroma and disrupts the endothelium. Edema of the cornea can  appear  a few
minutes after exposure. In a severe exposure, ammonia may reach the iris and
start cataractous changes in the lens. The trabecular meshwork  may become
edematous and plugged with  iris pigment and inflammatory cells. Following
these changes, an increase in  intraocular pressure can be detected a few
hours after exposure. Weeks after exposure, infiltration  of the cornea may
result in fibrosis and neovascularization. Ulceration of the conjunctiva! surfaces
may cause adhesion of the lids to the globe. The  inflammatory progression
may continue until the cornea, iris, and lens are fused into a mass of vascular
granulation tissue.
    Gaseous ammonia is slightly irritating to the human eye at a concentration
of 99 mg/m3 (140 ppm) and immediately irritating at 495 mg/ms (700  ppm)
(National Research  Council, 1977; Griffiths  and  Megson,  1984).  Reported
ocular effects following exposure to ammonia are inflamed eyes, lacrimation,
swelling of the eyelids (O'Kane,  1983; Ward et al., 1983; Hoeffler et al.,  1982;
Close et al., 1980; Montague and  Macneil,  1980;  Ferguson et al., 1977;
Verberk,  1977;  Helmers et al.,  1971;  Silverman et al.,  1949; Caplin, 1941),
hyperemic conjunctiva (Hatton et al.,  1979;  Sobonya,  1977;  Helmers et  al.,
1971; Levy  et  al., 1964;  Caplin, 1941;  Slot, 1938), and sustained  corneal
damage (Birken et al., 1981; Kass et al.,  1972; Osmond and Tallents,  1968;
Caplin, 1941).  Highman  (1969) described two cases in  which ammonia was
squirted in the face and eyes. The presenting signs mimicked those of acute
angle closure  glaucoma; i.e.,  oval, semidilated, nonreacting  pupils;  corneal
edema; and a rapid rise  in intraocular pressure (to 60 mmHg in the damaged
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eye of one patient and 36 mmHg in the damaged eye of the other patient).
(The normal range for intraocular pressure is  10 to  30 mmHg.) Continued
medication was  necessary to  decrease and  maintain intraocular pressure.
Other signs observed in the two patients were burns of the eyelids, chemosis,
and corneal ulcers.
    Moeller (1974)  examined ophthaimologic  changes  due  to  chronic
exposure in 109 persons working  in an ammonia plant. The average exposure
time was  7.6  years.  The following examinations were  carried  out:  vision
determination,  slit lamp examination,  ophthalmoscopy, examination of the
central and peripheral visual fields, and anomaloscope examination. No ocular
effects due to chronic ammonia exposure were noted.
3.10.2
Respiratory Toxicity
    The range of odor threshold concentrations for ammonia in humans was
reported to be  from 0.5 to 35.0 mg/m3 (0.7 to 50  ppm),  with the average
threshold concentration estimated at 4.0 mg/m3 (5 ppm) (National Research
Council, 1977).  Many case report studies of accidental  ammonia inhalation
have classified  the  exposures  as mild, moderate, or severe. Mild exposure
usually  results  in temporary,  irritating  respiratory symptoms;  moderate
exposure,  in more insidious and prolonged effects; and severe exposure, in
death and  long-  term irreversible respiratory changes.  Close  et  al.  (1980)
reported that in moderately exposed persons,  initial  chest findings may be
normal but may worsen with time due to insidious penetration of ammonia into
the lower airways.
    Immediate  signs of accidental ammonia inhalation are dyspnea (Flury et
al., 1983; O'Kane, 1983; Hoeffler et al., 1982; Close et al., 1980; Montague and
Macneil, 1980; Dalton and  Bricker, 1978; Sobonya, 1977; Walton, 1973; Kass
et al.,  1972; Levy et al., 1964; Caplin, 1941),  wheezing, rhonchi,  and rales
(Flury et al., 1983; O'Kane, 1983; Montague and Macneil, 1980; Helmers et al.,
1971; Sobonya, 1977; Levy et  al., 1964; Caplin, 1941), chest pain (Montague
and Macneil, 1980; Walton,  1973), nonproductive  cough  (O'Kane,  1983;
Hoeffler et al., 1982; Montague and Macneil, 1980; Walton,  1973), productive
cough  (Price et al.,  1983; Hoeffler et al., 1982; Caplin, 1941), nasal discharge
and bronchial  secretions (O'Kane, 1983;  Helmers et al., 1971; Levy et al.,
1964),  acute upper airway obstruction (Close et al., 1980), aphonia (Montague
and Macneil, 1980), laryngopharyngeal edema (Griffiths  and  Megson,  1984;
Flury et al., 1983; O'Kane, 1983; Montague and Macneil,  1980;  Dalton and
Bricker, 1978;  Osmond and  Tallents,  1968;  Levy  et al.,  1964), cyanosis
(O'Kane, 1983;  Dalton and  Bricker,  1978; Walton,  1973;  Caplin,  1941),
hypoxemia and hypercapnia (Price et al.,  1983; Flury et al., 1983; Hoeffler et
al., 1982),  decreased blood gas levels (O'Kane,  1983;  Close  et al.,  1980;
Montague and  Macneil,  1980), pulmonary  edema  (Hoeffler  et al., 1982; Chu,
1982; Griffiths and Megson, 1984; Birken et al., 1981;  Sobonya, 1977; Helmers
et  al.,  1971;  Capiin,  1941),  bronchospasm (O'Kane, 1983; Sobonya,  1977;
Walton, 1973;  Levy et al., 1964), and pseudomembranous covering of the
pharynx wall (Flury et al., 1983).
     Long-term  effects of accidental  ammonia  inhalation are hypoxemia
(Sobonya,  1977;  Kass et  al.,  1972), pulmonary  edema (Price et al.,  1983;
O'Kane, 1983), emphysema (Kass et al., 1972),  bronchiectasis (Price  et al.,
1983;  Kass et  al., 1972),  mucopurulent  exudate  arising  from  the
tracheobronchial  tree (Flury et al., 1983;  Sobonya, 1977; Kass et al., 1972),
infection with Nocardia asteroides (Sobonya, 1977), pneumonia  or pneumonia
infiltrate (Flury  et al, 1983; O'Kane, 1983; Hoeffler et al., 1982; Kass  et al.,
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 1972; Osmond and Tallents, 1968; Caplin, 1941; Slot, 1938), chronic infectious
 lung disease (O'Kane, 1983), and a prolonged decrease in pulmonary function
 (Price et al., 1983; Birken et al., 1981; Close et al., 1980; Kass et al., 1972).
    Reported pathologic findings in deceased victims 2 to  120 days following
 excessive ammonia inhalation have been loss of cartilage in both lungs (Birken
 et al., 1981); cystic bronchiectasis (Hoeffler et al.,  1982; Birken et al.,  1981;
 Sobonya, 1977); distended, congested lungs  (Arwood et al., 1985; Birken et
 al., 1981; Sobonya,  1977; Walton, 1973; Caplin, 1941; Slot, 1938); denudation
 of epithelium from bronchial walls (Arwood et al.,  1985; Burns et  al.,  1983;
 Sobonya, 1977; Walton, 1973; Caplin, 1941); edema (Burns et al.,  1983;
 Walton,  1973;  Caplin, 1941;  Slot, 1938); bronchopleural  fistula,  thickened
 bronchial wails, fibrous tissue growths (Sobonya, 1977),  and  hemorrhage
 (Burns et al., 1983).
3.70.3
Burns of the Skin
    Chemical burns of the skin constitute the remaining major consequence of
accidental exposure to high concentrations of ammonia. Upon contact with the
skin,  ammonia forms ammonium hydroxide,  which causes burns similar to
those caused by other alkalies. A concentration of 7,070 mg/m3 (10,000 ppm)
is sufficient to evoke skin  damage  (Birken  et al.,  1981). The maximal
concentration of vapor tolerated  by the skin for more than a few seconds is
14,140  mg/m3  (20,000  ppm), whereas  21,210 mg/m3  (30,000  ppm) may
produce blisters in a few minutes (National Research Council, 1977). Several
case  reports of chemical burns as a result  of  acute exposure have  been
reported (Flury et al., 1983; Close et al.,  1980; Hatton et al., 1979; Walton,
1973; Kass  et al.,  1972; Helmers et al.,  1971; Osmond and Tallents  1968-
Levy et al., 1964; Slot, 1938).
3.10.4
Other Effects
    Chronic exposure to 28 mg/m3 (40 ppm) ammonia vapor has resulted in
headache, nausea, and reduced appetite (National Research Council, 1977).
Other reported effects of exposure to ammonia vapor are convulsions (Kass et
al., 1972), shock (Osmond and Tallents, 1968; Slot, 1938), gastritis (Dupuy et
al., 1968; Slot, 1938), urticaria (Morris, 1956), leukocytosis (Ward et al., 1983),
and inflammatory bronchoconstriction (Bernstein,  1982).  Herrick and Herrick
(1983) described a case of allergic  reaction  in  a female weight lifter who
inhaled  an aromatic  ammonia inhalant.  Shortly after  inhalation, the woman
presented  with  rhinitis,  rhinorrhea, conjunctivitis,  dizziness,  headache,
dyspnea, wheezing, periorbital swelling,  and urticaria. Ingestion of  ammonia
(usually in the form of household ammonia, a 15 M solution of 28 percent
ammonia) has resulted in acute corrosive esophagitis and gastritis followed by
esophageal and gastric stenosis (Ernst et al., 1963; Norton, 1960).
    Shimkin et al. (1954) reported a case in which epidermoid carcinoma of
the upper lip was diagnosed 2 months after the patient spilled an oil-ammonia
mixture  on the area. The authors suggested  that the case was "acceptable as
an instance of a single-exposure, chemical-trauma exteriorization of a latent
cutaneous carcinoma in man." However,  no  similar reports were found in the
available literature.

3.70.5      Experimental Studies
    Several studies have been carried out in human subjects exposed to low
levels of ammonia. Schmidt  and Vallencourt  (1948)  exposed  one subject
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(Schmidt) to 375 to 396 mg/m3 (530 to 560 ppm) of ammonia for 4 hours and
found no significant changes in the pulse, pH, urea and creatinine levels, or
CO2-binding power (the amount of  CO2 that can exist in serum or plasma as
HCO ' at a PCO2 of 40 mm/Hg) of the blood over the exposure period. The
systolic blood pressure stayed constant for the first 35  minutes of exposure,
then decreased from  127 mmHg at 35 minutes to 102 mmHg at 180 minutes.
There was a marked linear increase in nonprotein nitrogen from 27 to 57 mg%
at 4  hours  when  exposure  was  ended.  After  termination  of  exposure,
nonprotein  nitrogen levels decreased  linearly, approaching the preexposure
level 3 hours after exposure cessation. However, later studies disputed these
findings; i.e., the reported blood nitrogen levels reached 36.4 mg%  after 4
hours, exceeded maximum theoretical retention levels (Silverman et al., 1949)
and were inordinately higher than levels sufficient to induce death in rats and
rabbits (Ting, 1950).
    In a study by Silverman et al. (1949), all exposed persons (7) experienced
hyperventilation  ranging from 150  to 250 percent  above normal values after
being exposed to 354 mg/m3 (500 ppm) ammonia for 30 minutes. Lacrimation
and nasal irritation were noted  in two subjects. No changes were observed in
blood urea, nonprotein nitrogen, or  CO2-binding power in two subjects tested.
In one of the two subjects, a slight  elevation in pulse and blood pressure was
noted.
    Verberk (1977) exposed 16 volunteers to 42, 57, 78, and 99 mg/m3 (60,
80, 110, and 140 ppm) ammonia for 2 hours at each exposure level over a 4-
week period. The subjects consisted of eight  "experts,"  persons familiar with
the effects  of ammonia, and  eight "students," persons who  were  not.  No
changes in vital capacity, forced  expiratory volume,  or  forced inspiratory
volume were noted. The "students" were  more responsive  than the "experts"
for subjective effects; e.g., smell; irritation of the eyes, throat, or nose;  urge to
cough; and general discomfort. The effect of ammonia exposure on "students"
seemed to be concentration-dependent.
    In another study with six volunteers, two subjects were exposed to 18, 35
or 71 mg/m3 (25, 50, or 100 ppm)  ammonia for 6-hour sessions once  a week
for 6 weeks (Ferguson et al., 1977). No apparent changes  in respiration rate,
blood pressure,  pulse, or forced vital capacity were noted.  An increase in  the
1-second forced expiratory volume occurred with  increasing concentrations.
The frequency  of mild  eye  irritation  decreased in  the  later sessions,
suggesting an adaptation to the exposure. However, the authors stated that  the
exposure concentrations were  not constant,  with  excursions to  106  to 141
mg/m3  (150 to 200 ppm) occurring, which produced lacrimation and transient
discomfort.
     Cole et al. (1977) examined minute volume, tidal volume,  and heart rate
during submaximal exercise in  18  male volunteers exposed to  ammonia. The
exposure took place in two periods during which  the volunteers exercised at
20 to 120 W for 8 minutes and 20 to  180 W for 11 minutes. The exposure
level was 50 to  79 mg/m3 (71 to 113 ppm) ammonia gas  for the first period
and 115 to 158 mg/m3 (165 to 226 ppm) for  the  second period. Reported
subjective responses consisted of a  prickling sensation in  the  nose and  a
slight dryness of the mouth but no real discomfort. There was no significant
difference in heart rate, but there were significant decreases (p <0.05) in
minute volume (from 25 to 22.5 liters/minute), tidal volume (from 1.57 to 1.43
liters),  and an  increase  in  mean  respiratory frequency (from 19.1  to 21.0
breaths/minute)  with exposure  at the higher  level. There were no significant
changes in these parameters  with exposure at  the lower  level (50 to 79
mg/m3). The authors suggested that the ventilatory responses  to ammonia
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 occurred a few minutes after exposure onset and were reversible, indicating a
 reflex rather than a structural reaction.
     Eleven of 23 subjects complained of nasal irritation after exposure to  71
 mg/m3 ammonia for up to 30 seconds in each nostril (McLean et al., 1979).  All
 of  the  subjects  showed increased  nasal airway  resistance, which  was
 suspected to be due  to vascular dilation in the nasal mucosa, and/or edema
 resulting from increased vessel permeability.
     In a study by an independent testing laboratory reported in Johnston  et
 al., (1979), 10 subjects were sequentially exposed for 5-minute intervals to 23,
 35,  51, and 95  mg/ms  (32, 50,  72, and 134 ppm) ammonia. At  23 and  35
 mg/m3, 1 of  10 and 2 of 10, respectively, noted dryness of the nose. At  51
 mg/m3 eye irritation (3 of 20), nasal irritation (2 of 10), and throat irritation (3 of
 10) were experienced. At 95 mg/ms, lacrimation accompanied by eye irritation
 (5  of 10), nasal irritation (7 of 10),  throat irritation (8 of 10),  and chest
 discomfort (1 of  10) were  reported  by  the  subjects.  These  subjective
 symptoms were  the  only   effects  investigated.  The laboratory  workers
 concluded that concentrations of 35 mg/m3 or less did not  cause  irritation  or
 discomfort.
     Increased incidences of  upper respiratory tract disease, skin changes, and
 alterations in  lipoprotein  and protein metabolism  were  reported  in  140
 adolescents exposed to ammonia and nitrogen oxides for 3 hours/day for 2  to
 3 years while enrolled in a vocational training program, when compared  to a
 control group. However,  the  exposure concentrations were reported as  "not
 exceeding maximal permissible concentrations," and it was not stated whether
 these increased incidences  were statistically significant (National Research
 Council, 1977).
     Donham  et al. (1984) evaluated the  acute respiratory effects of the work
 environment in swine confinement workers. Workers were  selected  from 21
 swine confinement operations with a history of spending at  least 5 hours/day
 in  the buildings. Controls were nonsmoking office workers and students  with
 no  previous occupational  exposure  to swine  confinement and no history  of
 chronic respiratory disease. Both groups were subjected to a 4-hour exposure
 period inside  a swine confinement  building  for two separate exposures.
 Pulmonary function tests were taken immediately before and after exposure  A
 decrease  in FEV1; FVC, FEV^FVC,  and FEF25.75  was  seen in all exposed
 subjects. However, a greater decrease in the pulmonary function parameters
 was seen in the swine confinement workers. Further, these effects were more
 significant in workers that had  been employed in  the swine  confinement
 operation for >6 years  compared to workers employed for  <6 years.  The
 levels of  respiratory irritants found in the swine confinement building were not
 given; however, levels of ammonia ranging from  14 to 30 mg/m3 (20.3 to 42.2
 ppm) in  addition  to  high  levels  of other, respiratory irritants in swine
 confinement buildings  have recently been reported by Donham and  Popendorf
 (1985).

 3.70.6      Epidemiology
    The  earlier data on the adverse effects associated with chronic
occupational  exposure to ammonia have  been discussed  by  the National
 Research  Council  (1977) and Carson et al. (1981).  Most  of these studies
involve chronic exposure  to a mixture  of  substances  and lack  adequate
experimental design to abstract any meaningful information. More recently,  in
a case control study of renal cancer mortality at a Texas chemical plant,'an
increased  incidence of renal  cancer mortality from  exposure to a variety of
                                 3-19

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physical agent exposures for 26 former employees deceased of renal cancer
and two matched control groups. There was  however,  an elevated risk for
"chlorine" workers but those workers were exposed  to other compounds as
well (Bond et al., 1985).
    There are no adequate epidemiology studies or animal carcinogenicity
studies for ammonia in the present data base. However, since  ammonia is a
key metabolite in mammals and plays an essential role in acid-base regulation
and in the biosynthesis of purines, pyrimidines and nonessential amino acids,
it is  unlikely that ammonia is a  human carcinogen.  Comprehensive assays
however, have not been done and therefore, ammonia should be classified as
group D "not classifiable  as to human carcinogenicity" based on the weight-
of-evidence  approach in  the current EPA guidelines  for carcinogen risk
assessment.
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                          4.  References

 Abbas, R.; Tanner, R. L (1981) Continuous determination of gaseous ammonia
    in the ambient atmosphere using fluorescence  derivatization.  Atmos
    Environ. 15:277-281.

 Alabaster, J. S.; Shurben, D. G.; Mallett, M. J. (1983) The acute lethal toxicity
    of mixtures of cyanide and ammonia to smolts of salmon, Salmo  salar L.
    at low concentrations of dissolved oxygen. J. Fish Biol. 22: 215-222.

 Alkezweeny,  A.  J.; Laws,  G.  L.; Jones,  W.  (1986) Aircraft and  ground
    measurements of ammonia in Kentucky. Atmos. Environ. 20: 357-360.

 American Conference  of Governmental  Industrial Hygienists.  (1984) TLVs:
    threshold limit values for chemical substances and physical agents in the
    work environment and biological exposure indices with intended changes
    for 1984-85.  Cincinnati, OH:  American Conference of Governmental
    Industrial Hygienists; p. 10.

 American Petroleum Institute. (1981) The sources, chemistry, fate, and effects
    of ammonia  in  aquatic environments. Washington,  DC:  American
    Petroleum Institute.

 Anderson, D. P.; Beard, C.  W.; Hanson, R. P.  (1964)  The adverse effects of
    ammonia on  chickens  including  resistance to infection with  Newcastle
    disease virus. Avian Dis. 8: 369-379.

 Andersson, K. K.; Hooper, A. B.  (1983) O2 and H2O are each the source of one
    O in  NO2" produced from NH3 by Nitrosomonas:  ISN-NMR evidence
    FEBS Lett. 164: 233-240.

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