U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
PB378 182
Ammonia
National Research Council, Washington, DC
Prepared for
Health Effects Research Lab, Research Triangle Park, N C
Nov 77
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rEPA-680/1-77-S54
November 1377
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RESEARCH REPORTING SERIES
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TECHNICAL REPORT DATA
(Please read Imtructions on the reverse before completing)
REPORT NO.
' EPA-600/1-77-054
4. TITLE AND SUBTITLE
AMMONIA
5. REPORT DATE
November 1977
6. PERFORMING ORGANIZATION CODE
'TTAUTHOR(S)
Subcommittee on Ammonia
87PERFORMING ORGANIZATION REPORT NO.
9 PERFORMING ORGANIZATION NAME AND ADDRESS
'Committee on Medical and Biologic Effects of
Environmental Pollutants
National Academy of Sciences
Washington, D.C. 20460
10. PROGRAM ELEMENT NO.
1AA601
11. CONTRACT/GRANT NO.
68-02-1226
12
. SPOt4SQRLNGJAGENCYr.NAME AND ADDRESS .
Health Effects Research laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
- RTP.NC
14. SPONSORING AGENCY CODE
EPA 600/11
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This document summarizes the available information on ammonta as it relates
to its effects on man and his environment.
Ammonia is a ubiquitous substance and is known widely as a household cleaning
agent and as a fertilizer. It plays an important role in the nitrogen cycle-- in
the life processes and in the death processes. It is both a "friendly" molecule
and a hazardous one. This report has the objective of presenting a broad
coverage of the available knowledge on ammonia and discusses its physical and
chemical properties; the practical methods of measuring it; and the effects of its
presence in the environment on man, animals, plants, materials, and the ecology of
the environment. The information presented is supported by references to the
scientific literature whenever possible or is based on a consensus of the members
of the Subcommittee on Ammoni.a
17.
KEY WORDS AND DOCUMENT ANALYStS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. cos AT I Field/Group
ammonia
air pollution
toxicity
health
ecology
chemical analysis
06 H, F, T
. DISTRIBUTION STATEMEf
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report!
UNCLASSIFIED
21
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
.EPA Form 2220-1 (9-73)
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PORTIONS OF THIS REPORT ARE NOT LEGIBLE.
HOWEVER, IT IS THE BEST REPRODUCTION
AVAILABLE FROM THE COPY SENT TO NTIS.
-------
EPA-600/1-77-054
November 1977
Ammonia
by
Subcommittee on Ammonia
Committee on Medical and Biologic Effects of
Environmental Pollutants
National Research Council
National Academy of Sciences
Washington, D.C.
Contract No. 68-02-1226
Project Officer
Orin Stopinski
Criteria and Special Studies Office
Health Effects Research Laboratory
Research Triangle Park, N.C. 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
HEALTH EFFECTS RESEARCH LABORATORY
RESEARCH TRIANGLE PARK, N.C. 27711
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DISCLAIMER
This report has been reviewed by the Health Effects Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection
Agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
NOTICE
The project that is the subject of this report was approved by the
Governing Board of the National Research Council, whose members are
drawn from the Councils of the National Academy of Sciences, the National
Academy of Engineering, and the Institute of Medicine. The members of
the Committee responsible for the report were chased for their special
competences and with regard for apropriate balance.
This report has been reviewed by a group other than the authors
according to procedures approved by a Report Review Committee consisting
of members of the National Academy of Sciences, the National Academy of
Engineering, and the Institute of Medicine.
ii
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FOREWORD
The mnny honofits of our modern, developing, industrial society are
accompanied by certain hazards. Careful assessment of the relative risk
of existing and new man-made environmental hazards is necessary for the
establishment of sound regulatory policy. These regulations serve to
enhance the quality of our environment in order to promote the public
health and welfare and the productive capacity of our Nation's population.
The Health Effects Research Laboratory, Research Triangle Park,
conducts a coordinated environmental health research program in toxicology,
epidemiology, and clinical studies using human volunteer subjects. These
studies address problems in air pollution, non-ionizing radiation,
environmental carcinogenesis and the toxicology of pesticides as well as
other chemical pollutants. The Laboratory develops and revises air quality
criteria documents on pollutants for which national ambient air quality
standards exist or are proposed, provides the data for registration of new
pesticides or proposed suspension of those already in use, conducts research
on hazardous and toxic materials, and is preparing the health basis for
non-ionizing radiation standards. Direct support to the regulatory function
of the Agency is provided in the form of expert testimony and preparation of
affidavits as well as expert advice to the Administiator to assure the
.adequacy of health care and surveillance of persons having suffered imminent
ami substantial endangerment of their health.
To aid the Health Effects Research Laboratory to fulfill the functions
listed above, the National Academy of Sciences (NAS) under EPA Contract
No. 68-02-1226 prepares evaluative reports of current knowledge of selected
atmospheric pollutants. These documents serve as background material for
the preparation or revision of criteria documents, scientific and technical
assessment reports, partial bases for EPA decisions and recommendations
for research needs. "Ammonia" is one of these reports.
John H. Knelson, M.D.
Director
Health Effects Research Laboratory
jii
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SUBCOMMITTEE ON AMMONIA
HENRY KAMIN, Duke University Medical Center, Durham, NC,
Chairman
JAMES c BARBER, James C. Barber & Associates, Florence, AL
STUART I. BROWN, University of Pittsburgh School of Medicine,
Pittsburgh, PA
C. C. DELWICHE, University of California, Davis, CA
DANIEL GROSJEAN, University of California, Riverside, CA
JEREMY M. HALES, Battelle, Pacific Northwest Laboratories
Field Office, Muskegon, MI
L. W. KNAPP, Jr., University of Iowa, Oakdale, IA
EDGAR R. LEMON, U.S. Department of Agriculture, Ithaca, NY
CHRISTOPHER S. MARTENS, University of North Carolina,
Chapel Hill, NC
ALBERT H. NIDEN, Charles H. Drew Postgraduate Medical
School, Martin Luther King, Jr. General Hospital,
Los Angeles, CA
ROBERT P. WILSON, Mississippi State University,
Mississippi State, MS
JAMES A. FRAZIER, National Research Council, Washington, DC,
Staff Officer
COMMITTEE ON MEDICAL AND BIOLOGIC EFFECTS
OF ENVIRONMENTAL POLLUTANTS
REUEL A. STALLONES, University of Texas, Houston, TX,
Chairman
MARTIN ALEXANDER, Cornell University, Ithaca, NY
ANDREW A. BENSON, University of California, La Jolla, CA
CLEMENT A. FINCH, University of Washington School of
Medicine, Seattle, HA
EVXLLE GORHAH, University of Minnesota, Minneapolis, MN
ROBERT I. BENKIN, Georgetown University Medical Center,
Washington, DC
IAH T. 1. HIGGINS, University of Michigan, Ann Arbor, MI
HOB W. HIGHTQWER, Rica University, Houstaon, TX
HENRY KAMIN, Duke University Medical Center, Durham, NC
ORVJLLS A. LEVANDER, Agricultural Research Center,
Beltsville, MD
ROGER P. SMITH, Dartmouth Medical School, Hanover, NH
T. D. SQA3, JR., National Research Council, Washington, DC,
Executive Director
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SUBCOMMITTEE ON AMMONIA
HENRY KAMIN, Duke University Medical Center, Durham, NC,
Chairman
JAMES C BARBER, James C. Barber & Associates, Florence, AL
STUART I. BROWN, University of Pittsburgh School of Medicine,
Pittsburgh, PA
C. C. DELWICHE, University of California, Davis, CA
DANIEL GROSJEAN, University of California, Riverside, CA
JEREMY M. HALES, Battelle, Pacific Northwest Laboratories
Field Office, Muskegon, MI
L. W. KNAPP, Jr., University of Iowa, Oakdale, IA
EDGAR R. LEMON, U.S. Department of Agriculture, Ithaca, NY
CHRISTOPHER S. MARTENS, University of North Carolina,
Chapel Hill, NC
ALBERT H. NIDEN, Charles H. Drew Postgraduate Medical
School, Martin Luther King, Jr. General Hospital,
Los Angeles, CA
ROBERT P. WILSON, Mississippi State University,
Mississippi State, MS
JAMES A. FRAZIER, National Research Council, Washington, DC,
Staff Officer
v
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COMMITTEE ON MEDICAL AND BIOLOGIC EFFECTS
OF ENVIRONMENTAL POLLUTANTS
REUEL A. STALLONES, University of Texas, Houston, TX,
Chairman
MARTIN ALEXANDER, Cornell University, Ithaca, NY
ANDREW A. BENSON, University of California, La Jolla, CA
CLEMENT A. FINCH, University of Washington School of
Medicine, Seattle, WA
EVILLE GORHAM, University of Minnesota, Minneapolis, MN
ROBERT I. HENKIN, Georgetown University Medical Center,
Washington, DC
IAN T. T. HIGGINS, University of Michigan, Ann Arbor, MI
JOE W. HIGHTOWER, Rice University, Houstaon, TX
HENRY KAMIN, Duke University Medical Center, Durham, NC
ORVILLE A. LEVANDER, Agricultural Research Center,
Beltsville, MD
ROGER P. SMITH, Dartmouth Medical School, Hanover, NH
T. D. BOAZ, JR., National Research Council, Washington, DC,
Executive Director
VI
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ACKNOWLEDGMENTS
Dr. Henry Kamin, Chairman of the Subcommittee on Ammonia,
which prepared this document, wrote the preface and overview
and drafted the summary and recommendations (Chapters 9 and
10) on the basis of information prepared by the Subcommittee
members and their collaborators.
Dr. Jeremy M. Hales drafted Chapter 1, which describes
the properties of ammonia.
The sections of Chapter 2 dealing with the nitrogen
cycle, fixation and denitrification, and interactions in
the soil were written by Dr. C. C. Delwiche; the section on
water by Dr. Christopher S. Martens; that on nitrogen assimi-
lation and ammonia metabolism by Dr. Kamin; those on compara-
tive ammonia metabolism, transport, distribution, and excretion
by Dr. Robert P. Wilson; and that on atmospheric transformation
by Dr. Daniel Grosjean. In collaboration with the Subcommittee,
Dr. Winston Brill (University of Wisconsin) contributed informa-
tion on the current status of genetic manipulation of plants for
nitrogen fixation, Dr. Aubrey W. Naylor (Duke University) wrote
the section on ammonia in plant nutrition, and Dr. Gene Likens
contributed information for the discussion of the role of ammonia
in acid precipitation.
Vll
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Dr. Hales wrote Chapter 3 with Dr. Martens, who prepared
the section dealing with natural waters, Dr. Edgar R. Lemon
that on soils, and Dr. Kamin that on determination of ammonia
in blood and tissue.
For Chapter 4, Dr. James C. Barber wrote material on
production and uses of ammonia; Dr. Wilson on ammonia from
animal wastes; Dr. Grosjean on the more general atmospheric
sources, concentrations, and particle formation; Dr. Lemon
on fixation by plants; and Dr. Martens on nitrogen dynamics
in varous marine environments.
Mr. L. W. Knapp, Jr., prepared Chapter 5, which discusses
the safety of transporting ammonia and gives some examples of
accidents related to its handling and transportation.
For Chapter 6, Dr. Kamin prepared the discussions on
metabolic toxicity in man; Dr. Wilson prepared several sections
that concern toxicity in ruminants, fishes, and bats, the ad-
verse effects of ammonia in confined housing for domestic ani-
mals, and the cerebral effects of ammonia intoxication;
Dr. Albert H. Niden the section on acute and chronic exposure
of animals to gaseous ammonia; and Dr. Lemon the information
on plant toxicity, in collaboration with Dr. Patrick Temple
(Ontario Ministry of the Environment).
Chapter 7 deals with human health effects. Dr. Stuart I.
Brown, in collaboration with Drs. Lee Shahinian and Bartly J.
Mondino (University of Pittsburgh School of Medicine), prepared
the discussions on ammonia burns of the eye; and Dr. Niden
Vlll
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prepared those on the effects on skin, lungs, and gastro-
intestinal tract.
Effects of ammonia on materials are covered briefly in
Chapter 8, which was written by Dr. Hales.
The preparation of the report was assisted by the com-
ments of anonymous reviewers chosen by Dr. Ralph P. Smith,
who served as Associate Editor. The members of the Committee
on Medical and Biologic Effects of Environmental Pollutants
(MBEEP) were very helpful in reviewing and commenting on the
report. In addition, several liaison representatives to the
MBEEP Committee, both inside and outside the National Academy
of Sciences-National Research Council, provided helpful comments.
Dr. Robert J. M. Horton of the Environmental Protection
Agency gave valuable assistance by providing the Subcommittee
with various documents and other sources of information.
Informational assistance was obtained from the National Research
Council's Advisory Center on Toxicology, the National Academy of
Sciences Library, the National Library of Medicine, the National
Agricultural Library, the Library of Congress, the Department of
Commerce, the Department of Transportation (U.S. Coast Guard and
Hazardous Materials Division), and the Air Pollution Technical
Information Center.
The staff officer for the Subcommittee was Mr. James A.
Frazier. The editor was Mr. Norman Grossblatt, and the refer-
ence assistant was Ms. Joan Stokes. The report was typed by
Mrs. Eileen Brown.
IX
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PREFACE AND OVERVIEW
In the spring of 1970, the Division of Medical Sciences,
National Research Council, entered into a contract with what
has since become the Environmental Protection Agency to pro-
duce reports that document the available scientific information
on the effects of selected environmental pollutants on man,
animals, plants, and the ecology of the environment. Since
the beginning of this project, a series of reports have been
prepared on a variety of pollutants. Among the substances now
being studied is ammonia. A subcommittee of the Committee on
Medical and Biologic Effects of Environmental Pollutants was
formed to study ammonia and met for the first time in July 1975.
Ammonia is a ubiquitous substance and is known widely as
a household cleaning agent and as a fertilizer. It plays an
important role in the nitrogen cycle—in the life processes and
in the death processes. It is both a "friendly" molecule and
a hazardous one. This report has the objective of presenting
a broad coverage of the available knowledge on ammonia and
discusses its physical and chemical properties; the practical
methods of measuring it; and the effects of its presence in the
environment on man, animals, plants, materials, and the ecology
of the environment. The information presented is supported by
references to the scientific literature whenever possible or is
based on a consensus of the members of the Subcommittee on Ammonia,
XI
Preceding page blank
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In this report, the distinction between ammonium i°n (NH4 >
and ammonia (NH3) is not made, except where the distinction is
specifically important. Thus, the term "ammonia" is used to
describe either or both of these molecules; where quantities or
concentrations are given, the term "ammonia" designates the sum
of NH4+ and NH3.
At the first meeting of the Subcommittee on Ammonia, the
chairman, a biochemist, pointed to the novelty of the notion that
ammonia might be considered as an environmental pollutant.
Ammonia, had always been regarded by life scientists as a friendly
molecule, as a food rather than a hazard, as essential to life
as carbon dioxide, water, and energy. It was wondered whether
this attitude would survive the thorough examination of the sub-
ject that the Subcommittee was about to undertake.
On the whole, this attitude has survived. Ammonia is an
important industrial and agricultural hazard, but not a major
pollutant of the environment, with the possible exception of
the aspects that will be discussed shortly. We have not recom-
mended establishment of any new environmental standards. The
fundamental reason why ammonia is not itself a major pollutant
is that mechanisms for taking up ammonia in nature are plentiful
and effective. Ammonia is a base, and it will be readily se-
questered by ubiquitous acidic substances. In addition, plants
and animals have active, efficient, and rapidly operating enzyme
systems to trap ammonia and to channel it into metabolic pathways.
Xll
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Ammonia as a "potential pollutant" occupies an unusual,
perhaps unique, niche. It may sometimes be a deleterious by-
product of current civilization, but it is also the stuff of
life itself. The amount of life that the earth can support
is determined by how much nitrogen, usually in the form of
ammonia, can be made available. This is emphatically true of
human populations. The apparent question of whether food
energy (expressed as calories) or nitrogen (expressed as
protein) is limiting to the nutriture of the human popula-
tion is not really a question. In general, populations subject
to famine eat simple diets, and the staple food determines both
the caloric and the protein intake. The protein content of
the cereal or tuber determines the protein content of the diet,
and the amount of plant grown is, in turn, often determined by
the availability of soil nitrogen. If the crop fails, both
calories and protein will become insufficient, and deprivation of
one will exaggerate the effects of deprivation of the other. If
the world will have more people, it must have more ammonia, not
less. In recognition of this basic truth, the 1977 report,
"World Food and Nutrition Study," of the National Research Council
has recommended a high priority for research to improve the
Xlll
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sources of nitrogen fertilizer, stressing particularly the need
for research to increase biologic nitrogen fixation in seed and
forage legumes, cereals, and other grasses.
Questions have recently been raised about possible ill
effects of rapid increases in the use of fertilizer, be it syn-
thetic ammonia or ammonia formed by biologic processes. It has
been suggested that, after cycling, nitrous oxide formed by bac-
terial denitrification will increase and will deplete the ozone
of the upper atmosphere. This Subcommittee did not come to grips
with that question, but this report notes that the data are not
sufficient to quantify or locate nitrous oxide formed, or to
assess the potential effects of increased fertilizer application
on the magnitude of the process. Our response to this problem
was set, in part, by subcommittee boundaries and by the fact
that the various valence states of nitrogen are in a dynamic re-
lationship with each other. Should the fertilizer-ozone question
be addressed by panels on ammonia, on nitrates, on "NO.,," on ozone,
JC
or on what? The nitrogen atom defies administrative categorization
Perhaps the best approach is to convene a group of scientists care-
fully selected for appropriate expertise and instructed to deal
specifically with the question of fertilizer and ozone.
But the Subcommittee cannot ignore what it has learned of
the societal context within which ammonia is made and used.
This context will be highly pertinent to the question of the
XIV
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importance to be assigned to the fertilizer-ozone relationship.
We have learned that ammonia is expensive to make, in both money
and energy. In a world that is short of both, ammonia will be
applied not randomly, but to areas where it can best be converted
into food for human consumption. Any projection of the effect of
fertilizer application on ozone must be made within the context
of that assumption.
But there is yet another assumption that must be taken into
account: If there is much more fertilizer and much more food,
there will be many more humans. These humans will compete for
space and resources; within the context of the enormous problems
of the increased human population that would accompany increased
fertilizer use, how does one assess the importance of ozone de-
pletion and of skin cancer that may arise from increased ultra-
violet radiation? Should one wear long sleeves and a broad-
brimmed hat and at the same time eat more protein and have more
children? Would all societies give the same answers to those
questions? These considerations may be beyond the purview of the
Subcommittee on Ammonia, but we feel it our duty to call atten-
tion again to the boundless complexities of environment
interrelationships.
xv
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Finally, we call attention to suggestions that production
of ammonia and fertilizer may have a directly beneficial, rather
than a deleterious, effect on the atmosphere. It is now gener-
ally agreed that the provision of extra nitrogen enhances the
ability of plants to absorb atmospheric carbon dioxide and fix
it into photosynthetic products. If the carbon dioxide in the
atmosphere is indeed increasing with the massive recent use of
fossil fuels, and if increased atmospheric carbon dioxide, via
a "greenhouse effect," causes an increase in the world's temper-
ature, then perhaps the action of ammonia and ammonia-derived
fertilizer in sequestering this carbon dioxide would be a useful
counterbalance.
The Subcommittee has attempted to restrain itself in making
recommendations, but it has made some that urge the acquisition
of information of broad environmental importance and others that
are in more specialized subjects or that deal with environmental
problems considered less likely to represent hazards. There are
many unanswered ammonia-related questions, including those raised
about nitrous oxide, ozone, carbon dioxide, nitrosamine (formed
from amines that generally accompany ammonia emission), and radi-
ative climatic effects of ammonium-containing aerosols. The most
important recommendation is simple and obvious: One should monitor
No amount of predictive theory can substitute for the continuous
and intelligent analysis of the atmosphere for such materials as
nitrous oxide, and carbon dioxide, and ozone, to see whether the
changes predicted by theory are actually occurring, and to s.ee
xv i
-------
whether alarm is necessary. Inappropriate complacency can be
disastrous, and excessive alarm can be fearfully expensive.
xvii
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CONTENTS
1 Physical and Chemical Properties of Ammonia
2 Chemical Interactions: Transformations and
Transport Mechanisms
3 Measurement and Monitoring
4 Sources, Concentrations, and Sinks of Atmospheric
Ammonia
5 Transportation of Ammonia
6 Toxicology
7 Human Health Effects
8 Effects on Materials
9 Summary
10 Recommendations
XIX
Preceding page blank
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CHAPTER 1
PHYSICAL AND CHEMICAL PROPERTIES OF AMMONIA
HYSICAL PROPERTIES OF AMMONIA
Ammonia, NH3, is a colorless gas under standard conditions,
hose pungent odor is easily discernible at concentrations above
bout 50 ppm. Its molecular weight is 17.03. It represents the
3 valence state of nitrogen, which can exist in a number of addi-
ional valence states, as indicated in Table 1-1.
The thermodynamic properties of ammonia are summarized in
'ables 1-2 and 1-3. Vapor pressures of ammonia gas over pure
imr:ionia liquid may be calculated with Eq. 1-1:'
log1QP = 9.95028 - 0.003863T - 1473.17/T, (1-1)
where P = partial pressure, mm Hg, and
T = temperature, K.
Enthalpies, free energies of formation, and standard entropies
of ammonia and other nitrogen compounds of interest in air pollution
are given in Table 1-4.
The ammonia molecule has a pyramidal structure with the nitrogen
atom at the apex and hydrogen atoms at the base. The H-N-H bond angles
have been observed to be 106° 47'. '8 This structure arises as a
natural consequence of the nitrogen atom's ground-state electronic
configuration (Is^, 2s^, 2p3), which promotes sigma bonding between
the three mutually perpendicular p orbitals and the s electrons of
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TABLE 1-1
Valence States of Nitrogen
Valence
State Typical Compound (s)
-3 Ammonia, NH.,
-2 Hydrazine, NH2NH2
-1 Hydroxylamine, H2NOH
0 Nitrogen, N2
+1 Nitrous oxide, N2O
+2 Nitric oxide, NO
+ 3 Nitrogen trioxide, N-^Oo ;
nitrous acid, HN02; nitrites, M+NO "
+4 Nitrogen dioxide, N02
+5 Dinitrogen pentoxide, N20g;
nitric acid, HN03; nitrates, M+NO3~
+6 Nitrogen trioxide, NOo
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TABLE 1-2
Physical Properties of Ammonia^
Boiling point at 1 atm
Triple-point temperature
Triple-point pressure
Triple-point density of
liquid
Critical temperature
Critical pressure
Heat of vaporization at
normal boiling point
Heat of formation of gas
at 25° Ck
Free energy of formation
of gas at 25° ck
Entropy of gas at 25° C
Specific heat at constant
pressure of gas at 25° C
-33.37 C
-77.69° C
0.05997 atm
0.735 g/ml
132.45° C
112.3 atm
5,581 cal/mole
-11,040 cal/mole
-3,976 cal/mole
46.01 entropy units
8.523 cal/mole-deg
—Data from Jolly and Jones.°
standard states of nitrogen and hydrogen.
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TABLE 1-3
Thermodynamic Properties of Saturated
and Superheated Ammonia5.
Saturated Ammonia*
Temp.,
•F.
i
-60
-50
—40
-30
-20
-16
-12
- 8
- 4
0
4
g
12
16
20
Abt
pro-
sure,
Ih./iq.
in.
T>
5.55
? 67
10.41
13 90
18.30
20.34
22 56
24 97
27.59
30.42
33 47
36 77
40.31
44.12
48 21
Volume,
cu- ft./lb.
Liquid
»/
0 02278
.02299
.02322
"62369
02419
02474
Vapor
It
44.73
33 08
24 86
18 97
14.68
13.29
12 06
10 97
9.991
9.116
8.333
7 629
6.9%
6.425
5 910
Enthalpy,
B.t.u./lb.
Liquid
A/
-21.2
-10.6
0.0
10.7
21.4
25.6
30 0
34.3
38.6
42.9
47.2
51.6
56 0
60 3
64 7
Vapor
A,
589 6
593.7
597.6
601.4
605.0
606.4
607.8
609.2
610.5
611.8
613.0
614.3
615.5
616 6
617 8
Eotropy.
B.t.u./(Ib.)('R-)
Liquid
if
-0.0517
- 0256
.0000
.0250
.0497
,0594
.0690
.0786
.0880
0975
.1069
.1162
.1254
.1346
1437
Vapor
««
4769
.4497
.4242
.4001
.3774
.3686
.3600
.3516
.3433
.3352
.3273
.3195
.3118
.3043
2969
Temp.,
'¥
t
24
28
32
36
40
50
60
70
80
90
100
110
120
125
Ate.
pres-
sure.
lb./iq.
in.
t>
52.59
57.28
62.29
67.63
73.32
89.19
107.6
128.8
153.0
180.6
211.9
247.0
286.4
307.8
Volume.
cu. fu/lhu
Liquid
V
.02533
.02564
.02597
.02632
.02668
.02707
.02747
.02790
.02836
.02860
Vapor
•t
5.443
5.021
4.637
4.289
3.971
3.294
2.751
2.312
.955
.661
.419
.217
.047
0.973
Enthalpy.
B.tWlb.
Liquid
*/
69.1
73.5
77.9
B2.3
86. S
97.9
109.2
120.5
132.0
143.5
155.2
167.0
179.0
183.9
Vapor
k,
618.9
619.9
621.0
622.0
623.0
623.2
627.3
629.1
630.7
632.0
633.0
633.7
634.0
634.0
Entropv.
B.t.u./(lb.)CTU
Liquid
V
.1618
.1708
.1797
.1885
.2105
.2322
.2537
.2749
.2958
.3166
.3372
.3576
.3659
Vipor
*
2825
!2755
2686
:26I8
.2453
.2294
.2140
.1991
.1846
.1705
.1566
.1427
.1372
• U. S. Bar. ShuutardM Circ. 142. 1923.
Superheated Ammonia*
r, volume, cu. ft./lb.; k, enthalpy. B.t.u./lb.; «. entropy. B.t.u./(lb.)(*R.)
Absolute preasure, Ib. per aq. in. (aaturation temperature. °F., in parentbesea)
Temp.,
•F.
Sit.
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
5 (-63.11)
i
49.31
51 05
52.36
53.67
54.97
56.26
57.55
58.84
60.12
61.41
62.69
63.96
65.24
66 51
67 79
A
588.5
595.2
600.3
605.4
610.4
615.4
620.4
625.4
630.4
635.4
640.4
645.5
650.5
655,5
660 6
*
.4857
.5025
.5149
.5269
.5385
.5498
.5608
.5716
.5821
.5925
.6026
.6125
.6223
.6319
6413
7 (-52.SB°)
t
36.01
36.29
37.25
38.19
39.13
40.07
41.00
41.93
42.85
43.77
44 69
45 61
46.53
47 44
48 36
A
592.5
594.0
599.3
604.5
609.6
614.7
619.8
624.9
629.9
635 0
640 0
645.0
650 1
655 2
660 2
t
.4574
.4611
.4739
.4861
.4979
.5094
.5206
.5314
.5421
.5525
.5627
5727
.5825
5921
6016
101-41.34)
;
25.81
26.58
27.26
27.92
28.58
29.24
29.90
30.55
31.20
31.85
32.49
33.14
33.78
A
597.1
603.2
608.5
613 7
618 9
624.0
629.1
634.2
639 3
644.4
649.5
654 6
659 7
t
1.4276
.4420
.4542
.4659
.4773
.4684
.4992
.5097
.5200
.5301
.5400
.5497
.5593
14 (-29.761
t
18.85
19.33
19 82
20.30
20.78
21.26
21.73
22.20
22.67
23.14
23 60
24 06
A
601.4
606. S
612.2
617 6
622 8
628.0
633.2
638 4
643 6
648 7
653 9
659 0
i
1.3996
1.4119
.4241
.4358
.4472
4582
.4688
.4793
48%
4996
5094
.5191
18 (-20.61)
D
14.90
14.93
15.32
15.70
16.08
16.46
16.83
17.20
17.57
17.94
18.30
18.67
A
604.8
605.1
6,10.7
616.2
621.6
626.9
632.2
637.5
642.7
647.9
653.1
658.4
t
1.3787
1.3795
1.3921
1 4042
.4158
.4270
.4380
4486
.4590
.4691
.4790
.4887
• 0.3. Bur. Standard. Circ. I4Z 1923.
Phillipa, WMte, il aL. Okie Stall Unit. Reft.. August, 1952. p. 176.
A wall-nied
Air Conditioning
.mm, 5 to 200 Ib./tq.
" -.7.172 (1943) give
pplied itudin in
-Reprinted with permission from Perry.14
-------
TABLE 1-4
Standard Entropies (S°), Enthalpies CAH^),
and Free Energies
(AF0:) of Formation of
Selected Nitrogen-Containing
Gas
NH3
N2
NO
N02
N2°4
N20
N00
AH°,
kcal/mole
-11.04
0
21.60
8.09
2.31
19.49
3.6
AF°,
kcal/mole
-3.98
0
20.72
12.39
23.49
24.76
_
Gases5
eu
46.01
45.77
50.34
57.47
72.73
52.58
—
—Based on standard states of oxygen, nitrogen, and hydrogen,
-------
the hydrogen atoms. Natural tetrahedral bond angles of 109 28'
are modified to the observed value of 106° 47' by a combination of
repulsive forces from the hydrogen atoms and the nonbonding electrons,
Ammonia is transparent in the visible and near-ultraviolet
regions and exhibits a progression of diffuse absorption bands be-
tween about 2168 & and 1700 &.6 A second, weaker system of bands
appears from 1700 8 down to 1400 A* and is accompanied by much stronge
overlapping progressions of bands starting at wavelengths below 1450
Below 1400 A, the absorption bands become intense, merging into a
o
strong continuum below about 1150 A. The lonization potential of
—18
ammonia is 10.15 electron volts (1.626 x 10 J) , corresponding to
a wavelength of 1222 A.
Absorption of radiation in the infrared region is character-
ized by complex series of bands, as indicated by the near-infrared
spectrum shown in Figure 1-1. Microwave absorption by ammonia, dis-
cussed at length by Townes and Shawlow,20 is of particular interest,
because it reflects a vibrational inversion caused by the nitrogen
atom's shifting back and forth across the plane formed by the three
hydrogen atoms. Ammonia is also of prime interest to workers in
microwave spectroscopy, because of its richness of rotational ab-
sorption modes and its behavior as a classical example of a molecule
with a symmetrical-top configuration.
-------
10OO 4QQO CM, MOO 2VX> 20OO
I1OO lOpO 950900850 6OO 750 7OO CM"-
FIGURE 1-1.
Absorption spectrxim of ammonia gas in the
near-infrared. A, partial pressure = 700 mm
Hg; B, partial pressure = 45 mm Hg. Reprinted
with permission from Pierson et al. ->
-------
CHEMICAL PROPERTIES
Formation Reactions
Ammonia may be formed as the product of a number of chemical
reactions. The most convenient means for laboratory preparation is
simply reaction of an ammonium salt with a strong base, such as sodium
hydroxide:
NH4+ -I- OH" J NH3 t + H20 . (1-2)
An additional method for ammonia preparation, particularly important
because of its significance in the conversion of animal wastes in the
global nitrogen balance, is the hydrolysis of urea:
(NH2)2CO + H2O ->• 2NH3 + C02 . (1-3)
On an industrial scale, the most important means for formation
is the direct reaction of nitrogen with hydrogen in.the presence
of catalyst:
%N2 + lhH2 £ NH3 + 11 kcal/mole. (1-4)
The Haber process for ammonia production, based on Reaction 1-4,
can operate with a variety of catalytic materials. Although the
exact nature of these catalysts is the subject of considerable
industrial secrecy, it is apparent that iron-potassium aluminate
mixtures are used most often for this purpose.
Equilibrium yield data for Reaction 4 are given in Table 1-5,
which indicates that ammonia yield at equilibrium is favored by low
temperatures and high pressures. These data may be used to formulate
the following expression for free energy of formation:
-------
TABLE 1-5
Percentages of Ammonia at Equilibrium—
Tcmpiralure,
«C.
200
250
300
350
400
450
500
550
COO
650
700
Ammoni*. So : •
At 10 aim. | At 30 aim. | Al SO »tm.
50. CO
28.34
14.73
7.41
3.85
2.11
1.21
0.70
0.49
0.33
0.23
07.50
47.22
30.25
17.78
10.15
5. 86
3.49
2.18
1.39
0.96
O.C8
74.38
56.33
39.41
25.23
15.27
9.15
5.56
3.45
2.26
1.53
1.05
.At IUO »tm.
81.54
67.24
52.01
37.35
25.12
16.43
10.61
At 3(JO Mm.
89.94
81.38
70.96
59.12
47.00
35.82
26. 44
G.82 • 19.13
4.52
3.11
2.18
13.77
9.92
7.28
At GOO Htm,
95.37
90.66
84.21
75.62
65.20
53.71
42.15
31.03
23.10
16.02
12.60
At 1000 «tm.
98.2
-------
AF° = -9500 + 4.96T InT + 0.000575T2
-0.00000085T3 - 9.16T; (1-5)
F°25°C = -3-91 kcal/mole. (l
A second process for the commercial production of ammonia is
formation as a byproduct of coking. Fixed nitrogen in coal reacts
with available hydrogen under the reducing atmosphere of the coke
oven, and the resulting ammonia is separated from other off-gases
by absorption in water.
An additional ammonia production process, less important than
the previous two, is based on the following reaction sequence:
CaC2 + N2 J CaNCN + C; (1-6)
CaNCN + 3H20 J CaC03 + 2NH3 t; U~7)
CaO + 3C ^ CaC2 + CO t. (1-8)
Termed the "cyanamide process," this reaction scheme has been largely
replaced by the more economical Haber process since the end of World
War I.
Acid-Base Properties: lonization Reactions
Because of its asymmetric structure, ammonia is a polar substance
(dipole moment, 1.47 debyes) and exhibits a strong hydrogen-bonding
character. An ammonia molecule binds a proton to form the ammonium
ion. This binding can be expressed as an acidic dissociation, i.e.,
NH + + NH, + H+. (1-9)
4 j
10
-------
The dissociation constants at various temperatures are provided in
Table 1-6; these can be calculated numerically with the semiempirical
o
equation: *•
log,nK = -0.09018 - 2729.92/T (K). (1-10)
_LU a
The magnitude of the dissociation constant is such that, in aqueous
solution, a substantial concentration of hydroxyl ions is formed:
NH3 + H20 + NH4+^OH~. (1-11)
The hydroxyl ion concentration can be calculated from Table 6-1:
[NH +] [OH']
KK = -r_ , = d-12)
In addition, ammonia can undergo a further, much weaker, acidic
dissociation, i.e.,
NH 1 NH ~ + H+, (1-13)
•3 ^
to form the strongly basic amide ion. This dissociation is too
weak to occur in aqueous solution.
Jolly quoted conductance and solvent-extraction studies in
support of the existence of two nondissociated ammonia species in
aqueous solution, a hydrated and a nonhydrated form:
NH, | = NH, + NH^-H90 . (1-14)
j aq j j z
Relative amounts of these two species can be expressed in terms of
an equilibrium constant for the reaction,
NH3 + H20 £ NH3'H20 , (1-15)
11 ;
-------
TABLE 1-6
lonization Constants for Ammonia Dissociation in Aqueous Solution—
Temperature, K
°C b
0
5
10
15
1.
1.
1.
1.
374
479
570
652
x 10 5
x 10~5
x 10~5
x 10~5
Ka
7.278
6.76
6.369
6.053
Temperature, K,
°c
x 10~
x 10"
x 10~
x 10"
10
10
10
10
20
25
30
35
1
1
1
1
.710 x
.774 x
.820 x
.849 x
10"
10"
10"
10"
5
5
5
5
K
a
5.
5.
5.
5.
848 x
637 x
495 x
408 x
io-10
10"10
io-10
ID"10
—Data from Bates and Pinching.
-------
which is about 0.21. The available evidence suggests that the struc-
ture of the NH3'H20 complex takes the form H3N-"H-OH, rather than
that of "ammonium hydroxide," NH4"I"'-'OH~. Nuclear magnetic resonance
measurements have indicated that the forward and reverse reactions
in Reaction 1-11 take place very rapidly7 and usually can be neglected
as rate-controlling steps in the dissolution process.
The solubility of ammonia in water has been investigated over a
wide range of conditions.5'9'13'16'19 At moderate concentrations
and temperatures, solubility data can be obtained most easily from
graphic19 and tabular14 compilations and empirical formulas. At
low concentrations, solubility may be calculated with reasonable
accuracy by assuming that the dissolution process occurs by a gas-
liquid step,
TT
NH,| + NHo I . • a. ^ f /-i in
j gas •«- J dissolved, undissociated (1-16)
plus the dissociation given by Reaction 1-11.5 Mathematical combina-
tion of these two steps results in the form
Molarity of total = H [NH3 | ] + J K, H [NH3| ] , (1-17)
dissolved ammonia o i yas» j D -3 gas
where [NH3|gasJ is the molar concentration of gas-phase ammonia, K^
is the dissociation constant given in Table 1-6, and H is a Henry's
law constant, given by
loglft H = 1477.8 _ l 693? (1-18)
10 T J--03J/.
It should be noted here that the simple formulas given above
are insufficient to describe ammonia's solubility if impurities are
present.
13
-------
More complicated expressions have been derived on the basis of
equilibrium theory in attempts to describe the solubility of ammonia
in water in the presence of other ionizing materials. Of particular
interest in this regard are the gases sulfur dioxide and carbon dioxi|
which have been examined because of their importance as interactants
with ammonia in the atmosphere and in chemical process systems. The
atmospheric interaction among ammonia, carbon dioxide, and sulfur
dioxide in water has been analyzed by several authors, including
in 17 iR
Junge and Scott and co-workers. /J-0
Addition Reactions
Addition, or "ammoniation," reactions are those in which ammonia
by virtue of the unshared pair of electrons on the nitrogen atom,
forms covalent bonds with another molecule or ion. This can be illus
trated by the reaction of ammonia with sulfur trioxide:
.. • •
: o • H : o : H
*•*• •• ••••••
: o : s> t : N : H j : o : s ' N : H d-is)
• • • , •• ••„,«•
°o: H : o : H
* 9 * •
Similar reactions occur with other electron-accepting molecules, such
as boron trifluoride and sulfur dioxide. Ammonia's high solubility
in water can be explained in part by addition interactions with water
molecules to form the hydrate, NH3«H20. Addition reactions are also
responsible for formation of a number of ionic species in solution,
for example,
CU2+ + 4NH3 ^ Cu- (NH3)42+ (1-20)
14
-------
Substitution Reactions
Substitution, or "ammonolysis, " reactions are those in which an
amide group, NH , an imide group, NH, or a nitrogen atom is substi-
tuted for another group on a given molecule. An example is the reac-
tion of aqueous ammonia with mercuric chloride:
2NH
H
gCl2
ClHgNH2
1-21)
A variety of substitution reactions involving organic molecules can
occur. Particularly important in this respect are H\e> teca Ves
halide, sulfonate. hydroxyl, and nitrite radicals. Examples of
such reactions are-.
2NH
O
II
O
O
Oxidizing
3 "•
Agent -
,,„
H
NH.
NaNH.SO.
4 4
H2°
(1-24)
15
-------
I -*
!0'
Oxidation-Reduction Reactions
Ammonia participates in a number of important oxidation-reducti
reactions. One of the best known of these is the combustion of aim
with oxygen:
4NH3 + 302 -* 2N2 4- 6H20 . (1-2
In the presence of a platinum catalyst, this reaction forms nitric
oxide, i.e.,
4NH3 + 502 -> 4NO + 6H20 . (1-271
Oxidation-reduction reactions are also important in reducing a
number of metal oxides to free metals, for example,
3CuO + 2NH3 ^ 3Cu + 3H 0 + N . (1-28)
Furthermore, some pure metals react directly to change the oxidation
state of the nitrogen:
3Mg + 2NH, £ Mg,N0 + 3H0 . (1-29)
J J £• 2.
16
-------
An oxidation- reduction reaction occurring between ammonium and
nitrite ions that may be of particular importance to global balance
considerations is
NH + + NO2~ -»- 2H20 + N2t . (1-30)
Electrochemistry
The electrochemical properties of ammonia and its compounds can
be summarized best in a chart of standard electrode potentials. Table
1-7 provides such a chart, giving values for selected other nitrogen-
containing species for comparison.
Photochemistry
In concordance with its previously mentioned transparency in the
visible and near-ultraviolet regions of the electromagnetic spectrum,
ammonia does not undergo any primary photochemical reactions under
^normal tropospheric conditions. Ammonia does decompose when exposed
to radiation in the far-ultraviolet by two reactions : ^ >^
NH3 + hv + NH2 4- H; (1-31)
NH + hv -> NH + 2H. (1-32)
Ammonia is known to undergo secondary reactions with photochemi-
1 9
cally excited species. For example,
NH3 + OH -> NH2 + H20; (1-33)
NH3 + 0 -> NH2 + OH; (1-34)
NH3 + 03 -v Products. (1-35)
17
-------
TABLE 1-7
Single Electrode Potentials of Selected
Reactions of Nitrogen Compounds^.
Reaction
NO2~ + H20 + e = NO + 20H~
N2O + H2O + 6H+ + 4e = 2NH OH+
2H+ + 2e = H0
z
NO-." + H9O + 2e = NO?" + 20H~
J ^ ^-
2NO2~ + 3H20 + 4e = N2O + 60H~
NH2OH + 2H20 + 2e = NH4OH + 20H~
2NH-OH + 2e = N0H, + 20H~
L, £ *±
2NO + H20 + 2e = N2O + 20H~
2N03~ + 4H+ + 2e = N2O4 + 2H20
N2°4 + 2e = 2N02~
N03~ + 3H+ + 2e = HN02 + H20
N03" + 4H+ + 3e = NO + 2H20
N204 + 2H+ + 2e = 2HN02
N2H + + 3H+ + 2e = 2NH.+
2HN02 + 4H+ 4- 4e = N20 + 3H 0
NH3OH+ + 2H+ + 2e = NH4+ + H20
2NH3OH+ + H+ + 2e = N2H5+ + 2H20
E°, V
-0.46
-0.05
0.0000
0.01
0.15
0.42
0.74
0.76
0.81
0.88
0.94
0.96
1.07
1.24
1.29
1.35
1.46
from Lange.11
18
-------
Some of these reactions may be important in atmospheric nitrogen
balance, and they are discussed further in this context in a later
chapter.
19
-------
REFERENCES
1. Bates, R. G. , and G. D. Pinching. Dissociation constant of aqueous
ammonia at 0 to 50° from E. m. f. studies of the ammonium salt of
weak acid. J. Amer. Chem. Soc. 72:1393-1396, 1950.
2. Emerson, K. , R. C. Russo, R. E. Lund, and R. V. Thurston. Aqueous aoq
equilibrium calculations: Effect of pH and temperature. J. Fis|
Res. Board Can. 32:2379-2383, 1975.
, Jones, R. M., and R. I. Baber. Ammonia, pp. 771-810. In R. E. Kirk a(
~> •
D. F. Othmer, Eds. Encyclopedia of Chemical Technology. Vol. 1,
New York: The Interscience Encyclopedia, Inc., 1947.
4. Green, M. Bonding in nitrogen compounds, pp. 1-71. In C. B. Colburn,
Developments in Inorganic Nitrogen Chemistry. Vol. 1. New York
Elsevier Publishing Company, 1966.
5. Drewes, D. R., and J. M. Hales. Removal of Pollutants from Power Pla»|
Plumes by Precipitation. Report to the Electric Power Research
Institute. Richland, Washington: Battelle-Northwest, (in prepari|
6, Herzberg, G. Molecular Spectra and Molecular Structure., III. Electro!
Spectra and Electronic Structure of Polyatomic Molecules. Princetd
N. J. : D. Van Nostrand Company, Inc., 1966. 745 pp.
7. Jolly, W. L. The Inorganic Chemistry of Nitrogen. New York: W. A.
Benjamin, Inc., 1964. 124 pp.
8. Jones, K. Ammonia, pp. 199-227. In J. C. Bailar, Jr., H. J. Emeleus,
R. Nyholm, and A. F. Trotman-Dickenson, Eds. Comprehensive Inorganic
Chemistry. Vol. 2. New York: Pergamon Press, 1973.
20
-------
9. Jones, M. E. Ammonia equilibriu:.. between vapor and liquid aqueous phases
at elevated temperatures. J. Phys. Chem. 67:1113-1115. 1963.
10. Junge, C. E. Air Chemistry and Radioactivity. New York: Academic Press,
1963. 382 pp.
11. La.nge, N. A., Ed. Single electrode potentials at 25 C, pp. 1244-1249.
In Handbook of Chemistry. (8th ed.) Sandusky, Ohio: Handbook
Publishers, Inc., 1952.
12. McConnell, J. C. Atmospheric ammonia. J. Geophys. Res. 78:7812-7821,
1973.
13. Morgan, 0. M., and 0. Maass. An investigation of the equilibria existing
in gas-water systems forming electrolytes. Can. J. Res. 5:162-199,
1931.
14. Perry, J. H., C. H. Chilton, and S. D. Kirkpatrick, Eds. / Properties of
ammonia_/ p. 3-151. In Chemical Engineers' Handbook. (4th ed.)
New York: McGraw-Hill Book Company, 1963.
15. Pierson, R. H., A. N. Fletcher, and E. St. Claire Gantz. Catalog of
infrared spectra for qualitative analysis of gases. Anal. Chem.
28:1218-1239, 1956.
16. Polak, J., and B. C.-Y. Lu. Vapor-liquid equilibria in system ammonia-
water at 14.69 and 65 psia. J. Chem. Eng. Data 20:182-183, 1975.
17. Scott, W. D., and P. V. Hobbs. The formation of sulfate in water droplets.
J. Atmos. Sci. 24:54-57, 1967-
18. Scott, W. D., and J. L. McCarthy. The system sulfur dioxide - ammonia -
water at 25°C. Ind. Eng. Chem. Fundam. 6:40-48, 1967.
19. Sherwood, T. K. Solubilities of sulfur dioxide and ammonia in water.
Ind. Eng. Chem. 17:745-747, 1925.
20. Townes, C. H,, and A. L. Schawlow. Microwave Spectroscopy. New York:
McGraw-Hill Book Company, Inc., 1955. 698 pp.
21
-------
CHAPTER 2
CHEMICAL INTERACTIONS: TRANSFORMATION AND TRANSPORT MECHANISMS
THE NITROGEN CYCLE
Ammonia is a ubiquitous constituent of the soil, the
atmosphere, and the waters of the earth. Treatment of its
cycling and reactions is best preceded by a brief discussion
of the nitrogen cycle, of which ammonia, is a part.
Nitrogen is present in the soil largely in the organic form.
Before it is assimilated by plants, it is normally changed by
microbial processes to a "mineralized" form, such as ammonium or
nitrate4"^ This nitrogen is assimilated into the organic fraction
of plant tissue, which is then consumed by animals or returned
directly to the soil. This constitutes a comparatively rapid
cycle—from soil to living organisms and back to soil—that is
similar to the cycles of other elements. The organic nitrogen
of plants and animals is normally in its "reduced" form, the same
oxidation state as ammonia, so the first mineralized form of
nitrogen to appear in the soil is usually ammonia . Because
ammonium can be oxidized, with an energy yield, to produce nitrate
ion, nitrate is the more common form found in soil; this compli-
cates the cycle somewhat.
Superimposed on this fundamental cycle is a cycle resulting
from the process of denitrification, wherein nitrate ion can
22
-------
serve as an oxidizing agent in the absence of oxygen for some
microorganisms to metabolize organic materials. In denitrifica-
tion, gaseous nitrogen, N2—or in some cases nitrous oxide, ^0--
is released to the atmosphere and thereby lost from the pool of
"available" nitrogen. The atmosphere is by far the largest reser-
voir of nitrogen (other than the crust of the earth) and would be
the ultimate sink for most of the nitrogen of the biosphere were
it not for the processes of nitrogen fixation, which returns
nitrogen to the mineral pool. Nitrogen fixation requires energy,
which is provided mainly by metabolic processes, although there
is some fixation in the atmosphere by lightning discharge and
other ionizing phenomena.
This second process of cycling nitrogen from the biosphere
to the atmosphere and back is a much slower one, requir-
ing perhaps 30 million years for an "average" nitrogen atom.
When the two processes are combined (with some additional complex-
ities that will be discussed in turn), the overall nitrogen cycle
is considerably more involved than the cycles of most soil minerals
required by plants and animals. The cycle is shown in simplified
form in Figure 2-1, and Table 2-1 summarizes the principal reactions,
When the nitrogen cycle is considered in greater detail, it is
necessary to recognize processes of long-term significance, such
as the transport of nitrogen compounds from the land to the sea
and back, the loss of nitrogenous compounds to sediments, the
fixation of nitrogen by ionizing processes in the atmosphere, the
23
-------
ho
U)
Fixation by
ionizing
phenomena
Juvenile
addition
industrial
fixation
SOIL
ATMOSPHERIC N,
Riologic fixation
Symbiotic
1
Nonsymbibtic
BIOSPHERE
J
4 I
Ammonium'
Nitrite
Nitrification sequence
Denitrification
shunt
SEDIMENTS
Figure 2-1. Generalized Representation of the Nitrogen Cycle.
-------
TABLE 2-1
Processes of the Nitrogen Cycle
Mineralization, an energy-yielding process, e.g.:
RNH.
organic nitrogen
°2
oxygen
CO.
carbon dioxide
2
water
NH
ammonium
Nitrification, an energy-yielding process, e.g.:
ammonium
2
oxygen
H90
4b
water
NO.
nitrite
Nitrite oxidation, an energy-yielding process, e.g,
NO,
nitrite
oxygen
N03~
nitrate
Denitrification, an energy-yielding process, e.g.:
[HCHO;
NO-
organic matter nitrate
CO,
carbon dioxide
H2°
N
water nitrogen gas
Nitrate reduction, an energy-requiring process, e.g.:
NO + [HCHO]
organic matter
H20
nitrate
ammonium
(or amino or
amide nitrogen)
water
Nitrogen fixation, an energy-requiring process, e.g.:
N,
nitrogen gas
[HCKOJ
organic matter
CO,
carbon dioxide
NH
H-
ammonium
(or amino or
amide nitrogen)
CO 2
carbon dioxide
24
-------
^These are unbalanced schematic reactions intended to show only
the overall process; reactants and products may vary- For
example, nitrous oxide, N^O, is sometimes a product of denitri-
fication; free ammonium, NH^+, need not appear in the reduction
process; and nitrous oxide may serve as an "electron acceptor"
in the denitrification reaction. "Energy-yielding" and "energy-
requiring" in the usage of the table are not thermodynamic ex-
pressions, but rather reflect the relationship of a reaction to
the energy economy of the organism effecting the reaction. Thus,
the reduction of nitrate in the denitrification reaction yields
energy to an organism at the expense of some exogenous supply of
organic substrate; and the assimilatory reduction of nitrate in
plants or microorganisms requires energy, inasmuch as organic
substrate or energy that could otherwise be used for growth or
other functions is expended in the reduction.
25
-------
appearance of new (juvenile) nitrogen in volcanic events, and the
introduction of new fixed nitrogen by man, including that fixed
intentionally and that fixed inadvertently by combustion reactions.
These processes are shown in schematic form in Figure 2-1.
In evaluating the influence of any unnatural input on the
nitrogen cycle and the biosphere, it is necessary to have some
quantitative estimate of what the natural cycle is like. Consider-
ation of natural cyclic processes conventionally involves the con-
cepts of "pools" or "compartments" and transfer rates between them.
The pool descriptions and sizes and the transfer rates used in
this report are summarized in Figure 2-2. These values, compiled
from various sources and adjusted to give balances for bookkeeping
purposes, are in some cases very uncertain. Although two and
sometimes three significant figures are given, this reflects compu-
tation results for balancing purposes, and not confidence levels.
Human activities have had a considerable impact on the nitro-
gen cycle. The fixation of nitrogen in industrial processes, by
the use of leguminous plants, and in combustion reactions (par-
ticularly internal-combustion engines) exceeds our best estimates
of the annual rate of fixation before the intervention of man.
Although the large reservoir of atmospheric nitrogen would not be
measurably depleted in thousands of years of fixation at present
rates, it might be anticipated that this input of new combined
nitrogen would influence biologic processes or other terrestrial
or atmospheric processes.
26
-------
/PLANTS\
<& ANIMALS
INORGANICT* ,. . / ORGANIC \
. _ / V r. I \ _ itr I
ORGANIC/INORGANIC'
FIGURE 2-2.
Pool sizes and transfer rates between pools of the nitrogen cycle. '''''
Some figures, such as those for industrial nitrogen fixation and size of the
atmospheric nitrogen pool, are known with reasonable precision; others, such
as those for the size of the organic nitrogen pool and the rate of nitrogen
fixation (and denitrification) in the ocean, are supported by only limited
data and are therefore uncertain. Pools are in units of gram-atoms of nitrogen.
Transfer rates shown (arrows) are in units of 10^ gram-atoms of nitrogen per
second (1 gram-atom/s = 441 metric tons/year). Transfer rates are as follows:
-------
Figure 2-2 continued
Reaction
(a) Nitrogen fixation, land
(b) Nitrogen fixation, ocean
(c) Nitrogen fixation, atmospheric
(d) Nitrogen fixation, industrial
(e) Nitrogen fixation, combustion
(f) Weathering processes
(g) Runoff, organic
(h) Runoff, inorganic
(i) Assimilation, land
(j) Assimilation, sea
(k) Mineralization, land
(1) Mineralization, sea
(m) Denitrification, land
(n) Denitrification, sea
(o) Ammonium fallout, rainout, and washout, land
(p) Ammonium fallout, rainout, and washout, sea
(q) Nitrogen from fossil fuel (largely ammonium!
(r) Ammonium volatilization, plants and animals
(s) Ammonium volatilization, soil
(t) NOX fallout, rainout, and washout, land
(u) NOX fallout, rainout, and washout, sea
(v) To organic pool, land
(w) To organic pool, sea
Process rate,
1()4 gram-atoms/s
22
7
1.7
9
4.1
1
5
3
400
320
430
320
27
9
15
2.9
0.8
12
5
5.7
2
430
320
28
-------
Nitrogen fixation is an energy-requiring reaction, and
denitrification (in an anaerobic system with organic substrate)
is an energy-yielding reaction; so it is not surprising that most
of the nitrogen of the world (exclusive of that contained in the
earth's crust) is in the atmosphere.
The industrial fixation of nitrogen involves the catalytic
reaction of hydrogen (obtained from fossil fuels) with gaseous
nitrogen to produce ammonia. The energy consumed (i.e., the
energy equivalent if the fossil fuel were burned in an oxygen-
containing atmosphere) is high—about 7 x 10 calories/kg of
nitrogen fixed. For this reason and others, the use of nitrogen
fertilizers has energy limitations.
The energy requirement for plants and microorganisms is also
high—apparently about the same as the industrial requirement.
Leguminous plants are generally less productive than cereals,
per unit of area, and higher yields can be obtained by applying
nitrogenous fertilizers to legumes than by requiring them to fix
nitrogen. However, the energy source for fixation by legumes is
photosynthetic; in many circumstances, therefore, this is the pre-
ferred means of supplying nitrogen.
In addition to soil, the atmosphere, groundwater, and surface
water are the three environmental components most commonly recognized
as subject to influence by processes or products of the nitrogen
cycle. The principal water contaminant normally is nitrate; when
ammonia appears in the system under normal conditions (aerobic),
29
-------
it is rapidly converted to nitrate by nitrification. The princi-
pal sources of these nitrogenous contaminants are usually considered
to be agriculture,10'11 some industrial point sources, and the more
diffuse sources of internal-combustion engines and other combustion
processes. The point sources include major industries and in-
dustrial centers, municipal sewage-disposal systems, and animal
feed lots.3'6'14
Ammonia has a comparatively short residence time in the
atmosphere—5-10 days—and its concentration in the troposphere
varies over a wide range with location and weather conditions. ' • *•*>^
Estimates of nitrous oxide emission are exceedingly uncertain.
When emission rates or residence times for nitrous oxide and
ammonia are considered collectively in the context of present assump-
tions that these are of biologic origin, it is difficult to recon-
cile them with some figures for nitrogen fixation and denitrifica-
tion, the presumed source of nitrous oxide. Even if low figures
for nitrous oxide production are used, reasonable balance can be
obtained only if a long residence time or a higher fixation rate
is assumed.8'9
30
-------
REFERENCES
1. Council for Agricultural Science and Technology. Effect of Increased
Nitrogen Fixation on Stratospheric Ozone. Report No. 53. Ames:
Department of Agronomy, Iowa State University, 1976. 33 pp.
2. Delwiche, C. C. The nitrogen cycle. Sci. Amer. 223(3):137-146, 1970.
3. Elliott, L. F., G. E. Schuman, and F. G. Viets, Jr. Volatilization of
nitrogen-containing compounds from beef cattle areas. Soil Sci.
Soc. Amer. Proc. 35:752-755, 1971.
4. Hardy, R. W. F., and U. D. Havelka. Nitrogen fixation research: A key
to world food? Science 188:633-643, 1975.
5. Hitchcock, D. R. , and A. E. Wechsler. Biological Cycling of Atmospheric
Trace Gases. Final Report Prepared for National Aeronautics and
Space Administration. (Contract No. NASW-2128) Cambridge, Mass.:
Arthur D. Little, Inc., 1972. 419 pp.
6. Hutchinson, G. L., and F. G. Viets, Jr. Nitrogen enrichment of surface
water by absorption of ammonia volatilized from cattle feedlots.
Science 166:514-515, 1969.
70 Junge, C. E. The distribution of ammonia and nitrate in rain water over
the United States. Trans. Amer. Geophys. Union 39:241-248, 1958.
8. Junge, C. The cycle of atmospheric gases - natural and man made. Q. J.
Roy. Meteorol. Soc. 98:711-729, 1972.
9. Junge, C. E. Residence time and variability of tropospheric trace gases.
Tellus 26:477-488, 1974.
10. Kimball, B. A., and E. R. Lemon. Theory of soil air movement due to
pressure fluctuations. Agric. Meteorol. 9:163-181, 1972.
31
-------
11. Kimball, B. A., and E. R. lemon. Air turbulence effects upon soil gas
exchange. Soil Sci. Soc. Amer. Proc. 35:16-21, 1971.
12. McConnell, J. C. Atmospheric ammonia. J. Geophys. Res. 78:7812-7821,
1973.
13. McKay, H. A. C. Ammonia and air pollution. Chem. Xnd. 1969:1162-1165.
14. Porter, L. K., F. G. Viets, Jr., and G. 1. Hutchinson. Air containing
nitrogen-15 ammonia: Foliar absorption by corn seedlings. Science
175:759-761, 1972.
15. Robinson, E., and R. C. Robbins. Gaseous nitrogen compound pollutants
from urban and natural sources. J. Air Pollut. Control Assoc. 20:
303-306, 1970.
16. Soderlund, R., and B. H. Svensson. The global nitrogen cycle. Ecol.
Bull. (Stockholm) 22:23-73, 1976.
17. Wo 1 aver, T. G. Distribution of Natural and Anthropogenic Elements and
Compounds in Precipitation Across the U. S. : Theory and Quantitative
Models. (Prepared for the U. S. Environmental Protection Agency)
Chapel Hill: University of North Carolina, 1972. 75 pp.
Nitrogen Fixation
When, as a first approximation, the distribution of nitrogen
compounds in their various biologic and geochemical compartments
is viewed as a steady state, this distribution reflects the ener-
getic realities of the system more than it does most of the other
variables. The largest compartment is atmospheric nitrogen, N2,
32
-------
and this reflects the potency of the denitrification reaction and
therefore a marginal nitrogen "hunger" in most ecosystems—a hunger
that is met by the processes of nitrogen fixation. There is a
small input of nitrogen compounds to the biologic system by ioniza-
tion in the atmosphere, but most of it comes from biologic fixa-
tion. Fixation reactions have a comparatively large energy re-
quirement, particularly in an aerobic system; therefore, there is
a limit to the extent to which a species can support nitrogen fixa-
tion without competitive disadvantage relative to other less prodi-
gal species.
The biologic fixation of nitrogen occurs in relatively few
genera of microorganisms, which are either "free-living" or in
symbiotic association with higher plants. The free-living orga-
nisms obtain their energy from organic materials liberated or lost
to the soil by plant roots, from the decomposition of organic
t
residues in the soil, or (in the case of photosynthetic organisms)
|
directly from the sun.
Although the fixation of nitrogen requires strongly reducing
conditions, a number of aerobic organisms can fix nitrogen.
Such organisms as those of the genus Azotobacter have a high
metabolic rate, and, particularly in fast-growing cultures of
high density, their high oxygen consumption may assist in lowering
the availability of oxygen and in providing locally reducing con-
ditions within cell organelles. In blue-green algae, the special-
ized formation of a heterocyst may serve an analogous function by
33
-------
limiting oxygen input. A number of anaerobic organisms, notably
some ciostridia, readily fix nitrogen.
In symbio-cic associations with higher plants, the energy in-
put for nitrogen fixation is from the photosynthetic activity of
the plants. The type of microorganism-plant association and the
nature of the specialized organs accommodating this association
can be quite different from one species to another,26 In most
cases, however, as with the nodules of Rhizobium-legume associa-
tion, the organ developed limits the rate of entry of oxygen into
the system, thereby helping to maintain the microaerophilic en-
vironment in which strongly reducing reactions can take place.
The quantity of nitrogen fixed annually by biologic and other
means is not known with certainty. Some of the estimates that
have been made are shown in Table 2-2. Although agreement is
not close on the amount of biologic fixation, the quantity of
nitrogen fixed annually by the use of legume crops and by industrial
processes approximately equals that fixed "naturally" before the
influence of human activity. Moreover, the recent development of
industrial fixation has greatly changed the balance of input of
new fixed nitrogen, compared with historic (geologically speaking)
figures. This change poses no threat to the vast atmospheric
reservoir, but it can potentially influence other features of
the nitrogen cycle, including phenomena of eutrophication of fresh-
water bodies and coastal waters and injection of nitrous oxide
into the atmosphere„
34
-------
Estimates of Quantities of Nitrogen Fixed
Process Nitrogen Fixed,5- moles/s x 10~4
Hutchinson-'--'
Natural processes, agriculture
Forest and unused land
Oceans
Legume crops
Total biologic 4.2-21
Atmospheric
Juvenile addition
Terrestrial historic
Industrial
Combustion
Total
Delwiche^
10
2.
(3.
12.
1.
0.
(10.
6.
20.
3
2)
3
7
045
8)
8
9
Garrels
pt al 11
CL. fiLL-
9.8
2.3
12.1
1.75
7.97
1.3
23.1
Hardy and
Havelka13
20.
13.
0.
(7.
34.
2.
12.
4.
53.
2
6
23
9)
0
3
9
5
7
Siderlund and Cast
Svensson22 Report
20
14
(18
34
5
9
4
53
.4
.2
.1)
.6
.7
.0
.5
.8
20.
11.
20.4-2
(7.
31.
8.
4.
48.5-7
5
13
3
1.4
9)
5
16
30
3.4
—Parentheses indicate amounts that are included in other amounts.
-------
Nitrogen fixation by microorganisms (particularly the
Rhizobium-legume association) is inhibited by inorganic nitrogen
compounds, so biologic fixation is probably suppressed to some
extent by the use of fertilizer nitrogen.
Much of the uncertainty regarding total biologic fixation
stems from our lack of knowledge of processes in the oceans,10'24
particularly in deep-sea oozes. Direct observations on seawater
demonstrate that some nitrogen fixation occurs in the ocean.
However- no accurate estimate of the amount is yet possible.
Figures for terrestrial nitrogen fixation are based on a
combination of nitrogen-balance figures for soils or soil-plant
systems, direct measurement of fixation rates with isotopic
nitrogen, and estimates made by the acetylene reduction tech-
nique. Estimates made by difference methods could be in
error, if there were a large loss of nitrogen by denitrifica-
tion or by volatilization of ammonia to the atmosphere.
McConnell18 attributes a little over 20% of atmospheric
ammonium to pollution sources, with a total annual input of
1.74 x 1014 g, or about 39 x 104 moles/s. Much of this is re-
turned directly as ammonia in rainout, washout, or dry deposi-
tion; the remainder, including that transported to the strato-
sphere, is returned as NOX or decomposed to nitrogen gas.18a/20a
Industrial processes are recognized as contributors of
ammonia to the atmosphere, but there are still many uncertainties
related to the sources of ammonia. Atmospheric concentrations
36
-------
are generally higher over land than over the oceans, so it is
assumed that land sources predominate. Washout and rainout
patterns, however, are not completely consistent with this
idea.12'16'26 One example of this is shown in Figure 2-3, modi-
fied from the data of Wolaver and Lieth,2^ which shows total wet
fallout of ammonium ion over the conterminous United States.
Concentrations over the southern coast of California are attributed
to vehicles and industrial and agricultural activity in the Los
Angeles basin. Concentrations over other areas are likewise
explained as resulting from industrial activity or agriculture.
Of interest in this connection are the comparatively high con-
centrations over northern Michigan, northern Maine, and the
Mississippi delta area. Although these areas undoubtedly have
a sizable industrial input of ammonia, the air over other heavily
industrialized areas does not have correspondingly high concen-
trations, and the air over a number of agricultural areas that
use nitrogen fertilizers likewise do not have correspondingly
high ammonia concentrations.
Healy et aJ^. ,14 in a survey of ammonia and ammonium sulfate
in the troposphere over the United Kingdom, found little geo-
graphic or seasonal variation. The usual concentration was
about 4 ng/m^, which would be equivalent to a mixing ratio of
_q
5.4 x 10 . They concluded that hydrolysis of urea in animal
urine was by far the largest contributor of ammonia to the
troposphere. The lack of correlation, either geographically
37
-------
00
W^WO 4M
0000-if»n i 1 ! M 1)1 (4 (l(t! ( ...
-
nO'""r'1< 1 1 H * 1 f |l H 4 i' 1 1 1
-n-nr 'no .,,,., ,4 , )( | ( 1 i4 t,.t
. imnc* I 1 1 Ml 1 U 1 M I ft (I
-HID"1 i »44i| *f M [ Ml ' 1 1
• MQ90W19B
-
-. ...
-|»p«a0fic3a ppie»a*-«t nrjr-n t 1.4. ____
•B««9BSQBei f fa 8+ 9*1 HOOD tl-l. ___
pe««ae«oo vitt ...
•avaeoovoaa A-IM-IP* onn Li.it . .
tge«oe«eceB »opgee» on Ul ..
•aefla«e«oB«e ««««<=•* ooo H * .
•««ve«3R^BMB PPf"W 00 it J_i
!W«
jp«i!ni
inflnn'
SPBRrl
' i
: i
HH '.
"unHflflRRB
)!pppPtfljJn4Hi)B
{faptiRnnn^nna
qnnrp?iftRi|nni>
flBPp«PBflnBHfl
PPFPflP.»"JIBH
Br"rHPflHrinPB
-pprpnimn^n
Rnnipp-nnnnqni
SSRF^iJSSn""!!""!!"
•pFippRTRppppprnip.RHp.
xtinnp^RPtninnBiinRitR
rn
as
Finn
JMJIjj
Bllfl]
•-* > 4 • + 5 1 * * f- * •"-
rreoopjcr Di5T°tBOT")> rr DI*» pfr«i ?uuus rw «CP LW|t
,.ttJtii
T «
IBWLUTf^Hnr iB<»Ct^»PPLT1
MIN. 30 52 107 161 215 HG/tf/n (NH*)
MAX. 52 107 161 215 277 *
;o»
; ^J
FIGURE
2-3. Total wet fallout of ammonium ion over the conterminous United States,
(Modified from data of Wolaver and Lieth.26)
-------
or in time, with industrial activity and the diffuse nature of
the source were in part responsible for this conclusion. The
possibility of decaying organic matter as a contributor of
atmospheric ammonia was considered, but was not regarded as
significant.
Current Status of Genetic Manipulation Of Plants For Nitrogen
Fixation
Dixon and Postgate6 were able to transfer nitrogen-fixation
(nif) genes via a plasmid from Klebsiella pneumoniae to
Escherichia coli. The resulting E. coli strain was capable of
fixing nitrogen from the atmosphere. This experiment was successful
because the nif genes are all closely clustered in K. pneumoniae
and thus were easy to manipulate onto the plasmid.
These results created excitement, because of the possibility
of transferring this cluster of nif genes to plant cells and pro-
ducing a plant, such as corn or wheat, that would require less or
no fertilizer nitrogen. Bacterial genes have been reported to be
expressed in cultured plant cells, '^' and cultured plant cells
have been induced to form mature plants.4,20 j^ therefore seemed
possible to transfer nif genes to a callus or cell culture of a
plant, such as corn, and then to produce a vigorous nitrogen-fixing
crop.
Examination of the specific requirements that must be met
if a cell is to fix nitrogen shows that the possibility of pro-
ducing such a plant genetically is remote. The most obvious
barrier is the extreme oxygen lability of nitrogenase.2 All
nitrogenases that have been examined are inactivated rapidly
39
-------
by oxygen, and no oxygen-stable enzymes have yet been obtained
by mutation. Azotobacter is one of the few bacterial genera
that fix nitrogen aerobically. Organisms of this genus seem
to protect their nitrogenase by having an extremely high respira-
tory rate,-21 presumably, the oxygen is reduced to water be-
fore it reaches nitrogenase. Aerobic blue-green algae have
specialized structures, heterocysts, that keep oxygen from in-
o *} t
activating nitrogenase. Root nodules in legumes contain a
plant-coded protein, leghemoglobin, that prevents free oxygen
from inactivating nitrogenase in the Rhizobium symbionts.25
Klebsiella pneumoniae will fix nitrogen only under anaerobic
conditions, although it grows equally well aerobically on fixed
nitrogen. The hybrid nitrogen-fixing 13. coli also will not fix
nitrogen aerobically. In fact, when the plasmid containing the
nif genes was introduced to organisms of Agrobacterium, which
are strict aerobes, the nitrogenase synthesized was immediately
inactivated by oxygen.7 These examples demonstrate that a mecha-
nism for oxygen protection needs to be included in the design of a
nitrogen-fixing corn. This is especially difficult in plant cells,
because oxygen is produced intracellularly by photosynthesis.
If the problem of oxygen sensitivity of nitrogenase is sur-
mounted, the nif gene products would still require an intracellu-
lar environment suitable in other aspects to the survival, control,
and function of nitrogenase. The organism must function as an
integrated whole, and the problem is complex.
40
-------
Other plans for increasing nitrogen fixation in plants in-
clude optimizing genes (by plant breeding) in legumes and bring-
ing about stable associations between ammonium-excreting bacterial
mutants and carbohydrate-excreting cereal plants.
An important problem that should be worked on is why some
strains of Rhizobium compete well in a particular soil, whereas
other strains are unable to compete. If we understood these
complexities, there would be a better chance that laboratory-
derived strains would be useful in agriculture.
Thousands of different legumes growing wild around the
world have not been tested for their potential in agriculture.
It is important to screen these plants and determine their
value for enriching poor soils and for their potential as new
and valuable foods.
41
-------
REFERENCES
1. Brill, W. J. Biological nitrogen fixation. Sci. Amer. 236(3):68-81, 1977.
2. Bulen, W. A., and J. R. LeComte. The nitrogenase system from azotobacter:
Two-enzyme requirement for N2 reduction, ATP-dependent HZ evolution,
and ATP hydrolysis. Proc. Nat. Acad. Sci. U.S.A. 56:979-986, 1966.
3. Carlson, P. S. The use of protoplasts for genetic research. Proc.
Nat. Acad. Sci. U.S.A. 70:598-602, 1973.
4. Carlson, P. S., H. H. Smith, and R. D. Bearing. Parasexual interspecific
plant hybridization. Proc. Nat. Acad. Sci. U.S.A. 69:2292-2294, 1972.
5, Council for Agricultural Science and Technology. Effect of Increased
Nitrogen Fixation on Stratospheric Ozone. Report No. 53. Ames:
Department of Agronomy, Iowa State University, 1976. 33 pp.
6. Delwiche, C. C. The nitrogen cycle. Sci. Amer. 223(3): 137-146, 1970.
7. Dixon, R., F. Cannon, and A. Kondorosi. Construction of a P plasmid
carrying nitrogen fixation genes from Klebsiella pnfeumoniae. Nature
260:268-271, 1976.
8. Dixon, R. A., and J. R. Postgate. Genetic transfer of nitrogen fixation
from Klebsiella pneumoniae to Escherichia coli. Nature 237:102-
103, 1972.
9. Doy, C. H. , P. Gresshoff, and B. G. Rolfe. Biological and molecular evi-
dence for the transgenesis of genes from bacterial to plant cells.
Proc. Nat. Acad. Sci. U.S.A. 70:723-726, 1973.
10. Dugdale, R. C., and J. J. Goering. Uptake of new and regenerated forms
of nitrogen in primary productivity. Limnol. Oceanogr. 12:196-
206, 1967.
42
-------
11. Carrels, R. M., F. T. MacKenzie, and C. Hunt. Chemical Cycles and the
Global Environment. Assessing Human Influences. Los Altos, Calif.:
William Kaufmann, Inc., 1973. 206 pp.
12. Georgii, H.-W. Oxides of nitrogen and ammonia in the atmosphere. J.
Geophys. Res. 68:3963-3970, 1963.
13. Hardy, R. W. F., and U. D. Havelka. Nitrogen fixation research; A key
to world food? Science 188:633-643, 1975.
14. Healy, T. V., H. A. C. McKay, A. Pilbeam, and D. Scargill. Ammonia and
ammonium sulfate in the troposphere over the United Kingdom. J.
Geophys. Res. 75:2317-2321, 1970.
15. Hutchinson, G. E. Nitrogen in the biogeochemistry of the atmosphere.
Amer. Sci. 32:178-195, 1944.
16. Junge, C. E. The distribution of ammonia and nitrate in rain water over
the United States. Trans. Amer. Geophys. Union 39:241-248, 1958.
17. Ledoux, I., and R. Huart. DNA-mediated genetic correction of thiamineless
Arabidopsis thaliana. Nature 249:17-21, 1974.
18. McConnell, J. C. Atmospheric ammonia. J. Geophys. Res. 78:7812-7821,
1973.
18a. McKay, H. A. C. The atmospheric oxidation of sulphur dioxide in water
droplets in presence of ammonia. Atmos. Environ. 5:7-14, 1971.
19. MacRae, I. C., and T. F. Castro. Nitrogen fixation in some tropical rice
soils. Soil Sci. 103:277-280, 1967.
20. Melchers, G., and G. Labib. Somatic hybridisation of plants by fusion of
protoplasts. I. Selection of light resistant hybrids of "Haploid"
light sensitive varieties of tobacco. Mol. Gen. Genet. 135:277-
294, 1974.
43
-------
20a. Pearson, F. J., Jr., and D. W. Fisher. Chemical Composition of Atmospheric
Precipitation in the Northeastern United States. Geological Survey
Water-Supply Paper 1535-P. Washington, D.C.: U. S. Government
Printing Office, 1971. 23 pp.
21. Phillips, D. A., and M. J. Johnson. Aeration in fermentations. J. Biochem.
Microbiol. Tech. Eng. 3:277-309, 1961.
22. Soderlund, R., and B. H. Svensson. The global nitrogen cycle. Ecol.
Bull. (Stockholm) 22:23-73, 1976.
23. Stewart, W. D. P. Nitrogen fixation by photosynthetic microorganisms.
Annu. Rev. Microbiol. 27:283-316, 1973.
24. Williams, P. M. Sea surface chemistry: Organic carbon and organic and
inorganic nitrogen and phosphorus in surface films and subsurface
waters. Deep-Sea Res. 14:791-800, 1967,
25. Wittenberg, J. B., F. J. Bergersen, C. A. Appleby, and G. L. Turner.
Facilitated oxygen diffusion, The role of leghemoglobin in nitrogen
fixation by bacteroids isolated from soybean root nodules. J. Biol.
Chem. 249:4057-4066, 1974.
26. Wolaver, T. G. Distribution of Natural and Anthropogenic Elements and
Compounds in Precipitation Across the U. S.: Theory and Quantitative
Models. (Prepared for the U. S. Environmental Protection Agency)
Chapel Hill: University of North Carolina, 1972. 75 pp.
44
-------
Nitrogen Assimilation
Nitrogen enters the biosphere in the ammonia oxidation
state and remains almost exclusively in that oxidation state
during the life of all organisms. The source of this nitrogen
is, ultimately, the vast reservoir of molecular nitrogen in
the atmosphere. The immediate precursor of ammonia can be the
same diatomic atmospheric nitrogen, N2, reduced to ammonia by
"nitrogen fixation," which proceeds via Reaction 2-1:
N2+ 2H+ +6 [H- ] ->• 2NH4+. (2-1)
The other biologic process for converting relatively oxi-
dized forms of nitrogen to the ammonia oxidation state is called
"nitrogen assimilation," or (because this is the predominant
mode) "nitrate assimilation."3i6,11 This proceeds via the over-
all reaction,
NO3~ + 8 [H- ] •> NH4+ + H2O + 2OH~, (2-2)
and can now be considered to proceed via two enzymatic steps:
the reduction of nitrate to nitrite in a two-electron process
(Reaction 2-3) and the six-electron, reaction that converts nitrite
to ammonia (Reaction 2-4):
N03~ + 2H+ + 2e -»• NC>2~ + H2O; (2-3)
N02~ + 6H+ + 6e -> NH4+ + 20H~. (2-4)
45
-------
The organisms that conduct the 6-electron reduction do so with
an enzyme, i.e., an assimilatory nitrite reductase, that char-
acteristically catalyzes Reaction 2-4 without free nitrogenous
intermediates, although added intermediates can usually be
reduced.•*
The process of nitrogen fixation may be considered "pri-
mary," in that it can involve nitrogen that did not originate
in or cycle through a living organism. However, the bulk of
nitrate assimilation may be considered a "secondary" or "re-
cycling" process, because the nitrate in nature is predominantly
either a product of bacterial oxidation of ammonia or of the
nitrogen compounds of deceased organisms or their excreta or
a result of man's activity in the synthesis of nitrate from
atmospheric nitrogen (see Chapter 4).
Although the biologic process of nitrate assimilation has
ammonia as its end product, the reduction of nitrate itself
does not necessarily constitute an assimilatory process:
nitrate reduction can be dissimilatory.6/11 in the latter
case, the primary function of nitrate is to serve as an electron
acceptor in anaerobic organisms (or in other organisms under
anaerobic conditions). This "dissimilatory" nitrate reduction
can also be termed "nitrate respiration"; nitrate takes the
place of the oxygen of aerobic life to serve as the terminal
electron acceptor in a respiratory chain. In nitrate respira-
tion, nitrogen compounds other than ammonia (nitrite, nitric
46
-------
oxide, nitrous oxide, and molecular nitrogen) are the usual
products; in some cases, ammonia is indeed formed,-^ but it
is difficult to prove that this is not part of a simultaneous
assimilatory pathway. Because the products of nitrate respira-
tion are often gaseous, they constitute a part of the process
of denitrification. Thus, although respiratory (or dissimilatory)
nitrate reduction may be an important part of the mass movement
of nitrate, it is probably not a quantitatively important source
of ammonia. This process therefore will not be dealt with in
detail in this report.
Assimilatory and dissimilatory nitrate reduction processes
serve different biologic roles and are therefore coordinated by
different sets of controls.3/H The enzymes of nitrate respira-
tion tend to be induced by anaerobiosis and are unaffected by
the presence of ammonia or amino acids. The enzymes catalyzing
these reactions tend to be particulate and to be localized in
manners and structures analogous to those of the respiratory
chains that terminate in oxygen; indeed, most bacteria prefer
oxygen respiration to nitrate respiration, and the dissimilatory
nitrate reductases are generally induced, rather than constitutive,
The enzymes that catalyze nitrate assimilation have character-
istics quite different from those which catalyze nitrate respira-
tion. In general, their production is not affected by oxygen
tension, and their biosynthesis tends to be repressed by ammonia
and amino acids. Both the nitrate and the nitrite reductases
47
-------
(see Reactions 2-3 and 2-4) are soluble. It should be noted
that some sulfite reductases can utilize nitrite as an alter-
nate substrate; these can be distinguished from "true" nitrite
reductases, in that their formation is not repressed by ammonia
or amino acids, but is repressed by sulfur amino acids. Thus,
these enzymes are on the pathway of sulfate, rather than nitrate,
assimilation.13 But assimilatory sulfite and nitrite reductases
do have many features in common: both are furnished electrons
either by an "internal" electron transport system that is part
of the enzyme molecule or by an "external" electron transport
system; both seem to have (without known exception in sulfite
7 9
reductases, ' but with possible exceptions in nitrite re-
ductaseslO,12) a characteristic heme prosthetic group8 termed
"siroheme,"''8 '-^ an iron tetrahydroporphyrin of the isobac-
o
teriochlorin type with eight carboxylic acid side chains.
The process of nitrate assimilation is initiated by a nitrate
reductase, which catalyzes Reaction 2-3. This enzyme is found in
many bacteria, fungi, yeasts, and plants; it has been extensively
studied in fungi and has been shown to contain a flavin moiety,
a molybdenum atom in an undefined oxidation state, and a cyto-
chrome of the b type.3'6 Reducing power is generated from metab-
olism via the coenzyme reduced nicotinamide adenine dinucleotide
phosphate (NADPH); the nitrate ion is believed to interact with
the molybdenum site.
48
-------
The nitrite reductase of the assimilatory nitrate reduction
pathway has been less extensively studied, but a number of recent
studies1'2'4'10'15^16 have considerably elucidated its nature
and mechanism of action. The nitrite reductases that have been
studied are relatively small proteins (molecular weight,
60,000-63,000).4,10,15 The assimilatory nitrite reductases of
such plants as spinach1^'15' -^ and marrow,5 of Neurospora,14 and
of the green alga Chlorella,16 have been shown to contain siro-
heme. In addition, several of these enzymes have been shown to
have an iron-labile sulfide cluster.2'15 Although some studies
o
have reported the presence of two iron atoms (one of which is
assignable to siroheme), more recent and detailed studies have
established, for the spinach enzyme, that each enzyme molecule
contains one iron-sulfur cluster of the composition Fe2~S2 and
one siroheme.15 It has been established that the site of inter-
action of nitrite is the siroheme grouping.14/15 There is evi-
dence that the nitrogen atom changes its valence state during
enzyme turnover, but that no intermediate is released until all
six electrons have been taken up to form the ammonia molecule.15
The source of reducing power for the reduction of nitrite
to ammonia is variable.3,6,11 jn green plants and algae, the
source is photosynthetic: light energy cleaves the water molecule
and transfers the hydrogen via NADPH, the flavoprotein NADPH-
ferredoxin reductase, and ferredoxin. Reduced ferredoxin appears
to be the immediate electron donor to these assimilatory nitrite
49
-------
reductases. Although in green plants and photosynthetic algae,
water cleaved by light energy represents the ultimate electron
source, the dark organisms** have their ultimate source of
reducing power in other metabolic processes. The nature of the
pathways that bring electrons to the nonphotosynthetic assimi-
latory nitrite reductases have been less well-defined.
Photosynthetic organisms Cplants and photosynthetic algae)
constitute the major portion of the world's biomass, these plants
derive most of their nitrogen through nitrogen fixation or nitro-
gen assimilation. It is therefore, instructive to compare the
quantitative aspects of these processes. It is estimated that
about 1.2 x 10*3 moles (2.04 x 10^ tonnes, or metric tons) of
ammonia are fixed per year (8 x 1012 moles, or 1.36 x 108 t, by
bacterial or symbiotic nitrogen fixation and other natural pro-
cesses and 4.2 x 1012 moles, or 7.1 x 107 t, by industrial pro-
cesses and combustion). This quantity of fixed nitrogen, al-
though small compared with the annual uptake of nitrogen by plants
(approximately 2 x 1014 moles, or 3.4 x 109 t), replenishes that
lost to the atmosphere by denitrification or to sediments.
50
-------
REFERENCES
1- Aparicio, P. J., D. B. Knaff, and R. Malkin. The role o£ an iron-sulfur
center and siroheme in spinach nitrite reductase. Arch. Biochem.
Biophys. 169:102-197, 1975.
2. Cardenas, J., J. I. Barea, J. Rivas, and C. G. Morena. Purification and
properties of nitrite reductase from spinach leaves. FEES Lett.
23:131-135, 1972.
3. Hewitt, E. J. Assimilatory nitrate-nitrite reduction. Annu. Rev. Plant
Physiol. 26:73-100, 1975.
4. Ho, C.-H., and G. Tamura. Purification and properties of nitrite reductase
from spinach leaves. Agric. Biol. Chem. 37:37-44, 1973.
5. Hucklesby, D. P., D. M. James, M. J. Banwell, and E. J. Hewitt. Proper-
ties of nitrite reductase from Cucurbita pepo. Phytochemistry 15:
599-603, 1976.
6. Losada, M. Metalloenzymes of the nitrate-reducing system. J. Mol.
Catal. 1:245-264, 1976.
7. Murphy, M. J,. and L, M, Siegel. Siroheme and sirohydrochlorin. The
basis for a new type of porphyrin-related prosthetic group common
to both assimilatory and dissimilatory sulfite reductases. J.
Biol. Chem. 248:6911-6919, 1973.
8. Murphy, M. J., L. M. Siegel, H. Kamin, and D. Rosenthal. Reduced nicotin-
amide adenine dinucleotide phosphate-sulfite reductase of enterobac-
teria, II. Identification of a new class of heme prosthetic groups:
An iron-tetrahydroporphyrin (isobacteriochlorin type) with eight
carboxylic acid groups. J. Biol. Chem. 248:2801-2814, 1973.
51
-------
9. Murphy, M. J. , L, M. Siegel, H. Kamin, D. V. DerVartanian, J.-P. Lee,
J. LeGall, and H. D. Peck, Jr. An iron tetrahydroporphyrin prosthetic
group common to both assimilatory and dissimilatory sulfite reduc-
tases. Biochem. Biophys. Res. Commun. 54:82-88, 1973.
10. Murphy, M. J. , L. M. Siegel, S. R. Tove, and H. Kamin. Siroheme: Anew
prosthetic group participating in six-electron reduction reactions
catalyzed by both sulfite and nitrite reductases. Proc. Nat. Acad.
Sci. U.S.A. 71:612-616, 1974.
11. Payne, W. J. Reduction of nitrogen oxides by microorganisms. Bacteriol.
Rev. 37:410-452, 1973.
12. Prakash, 0., and J. C. Sadana. Purification, characterization and proper-
ties of nitrite reductase of Achromobacter fischeri. Arch. Biochem.
Biophys. 148:614-632, 1972.
13. Siegel, 1. M. Biochemistry of the sulfur cycle, pp. 217-286. In D. M.
Greenberg, Ed. Metabolic Pathways. (3rd ed.) Vol. 7. Metabolism
of Sulfur Compounds. New York: Academic Press, 1975.
14. Vega, J. M. , R. H. Garrett, and L. M. Siegel. Siroheme: A prosthetic
group of the Neurospora crassa assimilatory nitrite reductase. J.
Biol. Chem. 250:7980-7989, 1975.
15. Vega, J. M. , and H. Kamin. Spinach nitrate reductase. Purification and
properties of a siroheme-containing iron-sulfur enzyme. J. Biol.
Chem. 252:896-909, 1977.
16. Zumft, W, G. Ferredoxin: Nitrite oxidoreductase from Chlorella. Purifi-
cation and properties. Biochim. Biophys. Acta 276:363-375, 1972.
52
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Denitrification
"Denitrification" commonly refers to the conversion of
nitrogen compounds to a gaseous form, either diatomic nitrogen
or nitrous oxide. Recognized as a largely biologic process
since the latter part of the nineteenth century, it is the
principal means by which combined nitrogen is returned to the
large atmospheric reservoir of diatomic nitrogen. The effective-
ness of the denitrification reaction is emphasized by the fact
that this atmospheric reservoir constitutes more than 97% of the
total nitrogen of the earth, exclusive of that contained in sedi-
ments or buried in or beneath the rock of the earth's crust. The
denitrification reaction therefore is the ultimate sink for nitro-
gen of the biosphere; only through the energy-requiring fixation
reaction can nitrogen again be returned to the active biosphere
pool.
For energetic reasons, denitrification is characteristic of
anaerobic or microaerophilic environments. A thermodynamic con-
sideration of the denitrification process as related to other
reactions of nitrogen explains the potency of the process and
the tendency for nitrogen to move to the atmospheric pool.
In the presence of a suitable substrate and in the absence
of oxygen, nitrate ion, nitrite ion, or the oxides of nitrogen
or their oxyacids can serve as electron acceptors for the oxi-
dation of the substrate.
Reactions 2-5 through 2-7 are generalized reactions showing
the oxidation of a theoretical carbohydrate substrate, with nitrate
as electron acceptor, resulting in the production of nitrogen
gas, nitrous oxide, or ammonium.
53
-------
NO-
[HCHO] - 0.5N20 + 0.5H20 + C02 + OH~; (2-5)
A G° = - 133.92 kcal;
298
A G' = - 143.48 kcal.
298
NO ~ + 1.25[HCHOJ + 0.5N2 + 0.75H2O + 1.25CO2 + OH"; (2-6)
A G° = - 140.92 kcal;
298
A G^ = - 150.47 kcal.
298
N03 + 2 [HCHO] + H+ -»• NH4+ + 2CO2 + OH"; (2-7)
A G° = - 169.73 kcal
298
A G° is standard free-energy change, and A G' Q is free-
298 ^y°
energy change at a pH of 7. All three of these are considered
"dissimilatory" reduction. This usage implies that the functional
role of nitrate reduction is in the support of an energy-yielding
reaction, as contrasted with "assirailatory" reduction, in which
nitrate is reduced to the level of ammonia, amino, or amide nitro-
gen entering the anabolic pool. Only Reactions 2-5 and 2-6,
resulting in the production of nitrogen gas and nitrous oxide,
respectively, are normally considered "denitrification."
Although a carbohydrate substrate is indicated in these
generalized reactions, a wide variety of organic compounds—
including fats, fatty acids, amino acids, and methane (and prob-
ably other hydrocarbons)—can be utilized. Some inorganic compounds
54
-------
can also serve as suitable substrate for some organisms, in-
cluding reduced compounds of sulfur, elemental sulfur, and
hydrogen gas.
Although many organisms, including higher plants, can re-
duce nitrate to the level of amino nitrogen in assimilatory
reactions, fewer can denitrify. Most of these are facultative
and can use oxygen as an electron acceptor, and many can partici-
pate in various fermentative reactions in the absence of both
oxygen and nitrate. Denitrifiers are to be found among both
spore-forming and non-spore-forming organisms; a number of
denitrifying pseudomonads are particularly characteristic of
soils.
The oxidation of reduced sulfur compounds with concomitant
denitrification, the classical reaction of Thiobacillus deni-
trificans, is of particular interest, because of the similar
behavior of nitrogen and sulfur compounds in microaerophilic
environments. Sulfate, like nitrate, can serve as an electron
acceptor for the oxidation of organic substrates in a manner
completely analogous to the denitrification reaction and with
significant energy yield. The energy yield is less than in
the denitrification reaction, however, and the oxidation of
reduced sulfur compounds with nitrate as an electron acceptor
therefore is yet another denitrifying reaction.
55
-------
H+ + No3- + 0.'625H2S - 1.25H+ + 0.625SO42- +
A G° = - 112.56 kcal;
298
A G" = - 114.94 kcal.
298
Some of the oxidation states of nitrogen and sulfur are shown in
Figure 2-4, with a diagramatic representation of the processes
of nitrification, denitrification, assimilatory nitrate reduction,
sulfate reduction and the oxidation of sulfur compounds.
The sequence of reactions in denitrification is probably
variable and depends on the organisms involved and the culture
conditions. Although nitrogen gas is commonly considered to be
the principal gaseous product of denitrification, nitrous oxide
often can be formed in large quantities. At low pH, nitric oxide
is also produced. Field studies of the distribution of gaseous
products have given a wide range of results, with nitrous oxide
usually constituting 10% or less of the total denitrified gas,
the remainder being nitrogen. With heavy fertilization and
periodic flooding, extensive denitrification can take place in
soils, often with the production of considerable quantities of
nitrous oxide.
It is possible that the reduction of nitrogen compounds and
emission of ammonia to the atmosphere take place in marsh areas
and tidal flats.3'4'5 Although it is generally assumed that
nitrate in these environments would be reduced to nitrogen or
nitrous oxide in the denitrification reaction, the further reduction
56
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VALENCE
+6 +5 +4 +3 +2 +1 0 -1 -2 -3
NH,
NO [HNO]
NO2 N O -NH
| ---- . ------ DENITRIFICATION — -»| ------ -
j ------------- _>J ----------- NITRATE REDUCTION ------------ ->{
j ---- N-FIXATION ------ ->j
------------ 1«- ------------- NITRIFICATION --------------- 1
S04 SO SO
so2
SULFATE REDUCTION ----------- -»| ------------- ->J
SULFUR OXIDATION ------------- |«- ------------- 1
FIGURE 2-4. Some oxidation-reduction states of nitrogen and
sulfur, showing the relationship of these oxidation
states to the nomenclature of various biologic pro-
cesses. Note that the net processes of "assimilatory"
and "dissimilatory" reduction to ammonia are the
same--the difference in nomenclature refers only to
the primary functional role, or "reason," for the
reduction.
57
-------
to ammonia may be a heretofore underestimated phenomenon. This
process can be readily demonstrated in the laboratory. Reducing
muds—such as those characteristic of salt marshes, tidal flats,
and swamps—are particularly active ammonia-producers, provided
that there is an input of nitrate ion. The dissimilatory reduc-
tion of nitrogen gas to ammonia concomitant for the oxidation of
some organic substrate is an unlikely source of ammonia (Reaction
2-9) .
N2 + 3H2 -> 2NH3(aq); (2-9)
AG298 = -12-75 (-4-25 per H2) .
A typical reaction, such as Reaction 2-9, has a small energy
yield; however, the high activation energy of the dinitrogen
molecule makes the yield of useful energy to any organism im-
probable—particularly in light of what is known of the energy
requirement for nitrogen fixation by organisms that are capable
of fixation. Moreover, the coexistence of nitrogen and organic
material in marsh environments emphasizes that the reaction is
not a common one.
Tsunogai° has compared atmospheric ammonium concentrations
over land areas and the ocean and concluded that atmospheric
ammonia sources are primarily terrestrial and that the combined
nitrogen transported from the land to the ocean (in rainwater)
is 1.5 x 1012 moles/year (4.76 x 104 moles/s).
58
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Georgii and Miiller-'- examined ammonia concentrations in the
troposphere at various continental European locations and found
2
concentrations similar to those reported by Healy et al. --about
0.25 ymoles/m^ (approximately 5.4 x 10~9 mixing ratio) near the
ground surface and approximately one-fourth of that at an alti-
tude of 3 km. The sharp negative tropospheric gradient is con-
sistent with the viev/ of a short residence time for ammonia in
the troposphere, as is the typical accumulation of ammonia below
an inversion layer. They also found lower atmospheric concentra-
tions over lakes and the North Sea than over land areas.
The reduction of nitrous oxide does take place in these
anaerobic environments, however, and the product need not be
nitrogen.
N20 + 4H2 -> 2NH3(a) + H20; (2-10)
AG298 = ~94-19
Reaction 2-10 has an appreciable energy yield and is a possible
reaction for the production of ammonia in salt marshes and tidal
flats.
The competitive dissimilatory reduction of nitrous oxide to
nitrogen gas — would indeed appear to be less likely, were it not
N20 + H2 -»> N2 + H20; (2-11)
AG298 = ~78'73 kcal
59
-------
for the gaseous nature of the product nitrogen, its comparatively
low solubility, and its high activation energy. Because little
is known of the kinetic properties of the terminal nitrogen
enzyme in the denitrification reaction, no theoretical model can
be devised on which to predict the likelihood of one reaction's
being favored over the others.
Denitrification with the production of nitrogen gas or
nitrous oxide is probably also limited by the nature of the
microflora. Highly reducing conditions and the production of
hydrogen sulfide may well suppress the development of denitrifying
organisms, as well as others with a terminal electron transport
system that depends on a cytochrome. In the presence of sulfide
ion, any reduced iron probably would be precipitated as ferrous
sulfide, resulting in a low availability of iron; this in itself
perhaps limits the synthesis of cytochromes and therefore the
population of organisms with such a requirement.
It is hazardous to draw any sweeping conclusions concerning
the extent of nitrous oxide reduction in anaerobic muds; however,
it appears that a closer examination of tidal flats, salt marshes,
and other anaerobic environments is justified, in that they are
possible additional sources of atmospheric ammonia.
60
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REFERENCES
1. Georgii, H.-W., and W. J. Muller. On the distribution of ammonia in the
middle and lower troposphere. Tellus 26:180-184, 1974.
2. Healy, T. V. , H. A. C. McKay, A. Pilbeam, and D. Scargill. Ammonia and
ammonium sulfate in the troposphere over the United Kingdom. J.
Geophys. Res. 75:2317-2321, 1970.
3. Lodge, J. P., Jr., P. A. Machado, J. B. Pate, D. C. Sheesley, and A. F.
Wartburg. Atmospheric trace chemistry in the American humid tropics.
Tellus 26:250-253, 1974.
4. Porter, L. K., and A. R. Grable. Fixation of atmospheric nitrogen by
nonlegumes in wet mountain meadows. Agron. J. 61:521-523, 1969.
5. Richards, F. A. Anoxic basins and fjords, pp. 611-645. In J. P. Riley
and G. Skirrow, Eds. Chemical Oceanography. Vol. 1. New York:
Academic Press, 1965.
5a. Schlegel, H. G. Production, modification, and consumption of atmospheric
trace gases by microorganisms. Tellus 26:11-20, 1974.
6. Tsunogai, S. Ammonia in the oceanic atmosphere and the cycle of nitrogen
compounds through the atmosphere and hydrosphere. Geochem. J. 5:57-
67, 1971.
61
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Fertilizer Nitrogen and Stratospheric Ozone
Attention has recently been focused on the possible relation
of fertilizer nitrogen to the stratospheric ozone layer. • • • >
To the extent that the nitrogen in fertilizer is lost in denitri-
fication and nitrous oxide is produced in the process, some nitrous
oxide will be released into the atmosphere and will eventually
appear in the stratosphere and serve to catalyze ozone destruction.
This appearance may be deferred if the fertilizer nitrogen is
transferred to plants and animals; it would reappear after the
death and dissolution of the organisms.
The subject has been reviewed elsewhere-^ and will not be
dealt with in detail here, except for some general comments in
connection with ammonium.
It is generally assumed that atmospheric nitrous oxide is
largely a product of denitrification, but the rate of natural
input to the atmosphere—the fraction from the soil, the sea,
and other processes—is not known.
Current estimates suggest that perhaps 10% of the total
nitrogen lost in denitrification^''° may be lost as nitrous
oxide, but the matter is the subject of some controversy.
Extensive research will be needed to resolve the question.
Likewise, it is not known how much fertilizer nitrogen is
lost owing to denitrification or where or how soon the nitrogen
from this source (or from legume crops) is introduced into the
fixed nitrogen pool.
62
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The amount of fertilizer nitrogen assimilated by the plants
in a crop varies with the rate of application and with the type
of plants in the crop, but ranges from 20 to 80%-13 Of the nitrogen
harvested with the crop, a large portion later appears in the
urban sewage disposal systems, in animal feed lots, and in
other concentration centers with an uncertain final disposition,
but undoubtedly much of the nitrogen is eventually denitrified.
Again, quantitative data are lacking.
In the final analysis, management of nitrogen input at the
field and nitrogen management at the disposal site are both re-
quired. The problem requires solution in manageable socioeconomic
dimensions and on a global scale, as well as in its technical
aspects; but before any rational solutions can be effected, the
problem must be defined. Present information does not permit
any confident definition.
Pending the acquisition of more adequate information, reason-
able steps should be taken to minimize what may be an undesirable
process by improved management of nitrogen at both ends of the
sequence from field to waste disposal, preferably in such a manner
as to return discarded nitrogen to the production end of the
sequence.
63
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REFERENCES
1. Crutzen, P. J. Estimates of possible variations in total ozone due to
natural causes and human activities. Ambio 3:201-210, 1974.
2. Crutzen, P. J. Upper limits on atmospheric ozone reductions following
increased application of fixed nitrogen to the soil. Geophys.
Res. Lett. 3:169-172, 1976.
30 Delwiche, C. C. , and B. A. Bryan. Denitrification. Annu. Rev. Microbiol.
30:241-262, 1976.
4. Hahn, J. N20 measurement in the northeast Atlantic Ocean. "Meteor11
Forschungsergeb. Reihe A 16:1-14, 1975.
5o Johnston, H. W. Analysis of the independent variables in the perturbation
of stratospheric ozone by nitrogen fertilizers. J. Geophys. Res. 82:
1767-1772, 1977.
60 McElroy, M. B. , J. W. Elkins, S. C. Wofsy, and Y. L. Yung. Sources and
sinks for atmospheric ^0. Rev. Geophys. Space Phys. 14:143-150,
1976.
7. Myers, R. J. K. , and J. W. McGarity. Factors influencing high denitri-
fying activity in the subsoil of solodized solonetz. Plant Soil
35:145-160, 1971.
8. Stefanson, R. C. Soil denitrification in sealed soil-plant systems. I.
Effects of plants, soil water content and soil organic matter content.
Plant Soil 37:113-127, 1972.
64
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AMMONIA METABOLISM
Incorporation of Ammonia into Organic Linkage
With few exceptions, the nitrogen of all living organisms
is in the ammonia state of oxidation. Most of the nitrogen atoms
are in the constituent amino acids of proteins and in the other
major nitrogen-containing macromolecules, the nucleic acids.
Much smaller quantities are found in smaller molecules: amines,
amides, and heterocyclic compounds. In many cases, these small
molecules are transient intermediates in the biosynthesis and
degradation of the major protein and nucleic acid pools of the
organisms.33,51
The precursor molecule in which nitrogen enters organic
linkage in the biosphere is ammonia, and the large-scale processes
of nitrogen fixation and nitrogen assimilation funnel into the
formation of this key molecule. Nitrogen metabolism in living
organisms may be considered to begin with the fixation of an
ammonia molecule to a carbon compound; this nitrogen will ulti-
mately find its way into the amino group of the amino acid of
which proteins are composed, into the purines and pyrimidines
constituting the nucleic acids, and into other biologic compounds
that appear in smaller quantities. -1-
Thus, the ammonia molecule is essential to life, and the ad-
verse effects of insufficient or excess ammonia represent the
extremes of "insufficient" or "excessive" availability of
ammonium compounds. Insufficient ammonia is inevitably trans-
lated into insufficient biosynthesis of protein—protein starva-
tion, a major public-health problem in many developing nations.60
Ammonia serves as a nutrient. If ammonia is in excess, the
processes that ultimately funnel into protein and nucleic acids
65
-------
may become overloaded, and free ammonia may accumulate and cause
secondary effects, some of them damaging, by either diverting
metabolism in the whole organism7'12'20 or trapping protons and
thereby raising the local pH to damaging values (see Chapter
7). Ammonia excess can be produced either by such phenomena as
ammonia spills, accidents, and excessive ammonia in air, soil,
or water, or by defective mechanisms for the uptake of ammonia
by tissues (i.e., metabolic defects in ammonia uptake by liver,
etc.).12,20
This section reviews briefly the dynamics of ammonia metab-
olism in living organisms, so that the pathways of ammonia metab-
olism (and the limitations imposed by rates of various processes)
can be presented as a basis for the understanding of derangements
in the relationship between ammonia and living materials. Ammonia
metabolism is discussed in chapters dealing with amino acid and
protein metabolism in standard biochemistry texts29 ' 32 ' 37 / 61 an(j
in monographs on the subject.2'13'33'43'50'56
The initial reactions that fix ammonia in organic linkage
are remarkably few:26/34 the biosynthesis of glutamic acid
from ammonia and a-ketoglutarate, the biosynthesis of glutamine,
the formation of carbamyl phosphate, the biosynthesis of aspar-
agine, and some relatively rare processes.
Glutamic Acid Biosynthesis. The link between the metab-
olism of carbon compounds and the nitrogen atom involves pri-
marily the glutamic acid dehydrogenase reaction.10'23'33'38'52/59
66
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The carbon chain for glutamic acid is furnished from carbo-
hydrate precursors by a variety of pathways described in most
biochemistry textbooks, this chain, a-ketoglutarate, is a key
component of the Krebs citric acid cycle, wherein the carbon
atoms of foodstuffs become converted to carbon dioxide and the
hydrogen atoms are transported to the "electron transport
system," ultimately to be oxidized by oxygen under circum-
stances where the energy of the oxidation can be conserved as
adenosine triphosphate (ATP). a-Ketoglutarate reacts with
ammonia in a reaction catalyzed by glutamic dehydrogenase:
a-Ketoglutarate + NAD(P)H + H+ + NH4+ v glutamate + NAD(P}+
+ H20.* (2-12)
Depending on the tissue, species, or subcellular organelle,
NAD+ or NADP+ can serve as a cofactor. In most cases, the iso-
lated enzyme can utilize either or both.52,59 Glutamic dehydro-
genase is widely distributed in plants, animals, and micro-
organisms; 52 it is found in both mitochondria and cytosol and
can participate in a number of biologic processes directed toward
biosynthesis or energy production.
At physiologic pH, the equilibrium constant for Reaction
2-12, as written, strongly favors the reductive amination of
*NADH = reduced nicotinamide adenine dinucleotide; NADPH =
reduced nicotinamide adenine dinucleotide phosphate; NAD =
nicotinamide adenine dinucleotide; NADP = nicotinamide
adenine dinucleotide phosphate.
-------
a-ketoglutarate to glutamate; Keq = 6 x IQ^.l1'52 Thus, the
synthesis of glutamic acid serves as an effective ammonia trap,
and at equilibrium, only small quantities of ammonia can co-
exist with a-ketoglutarate.26,52 Reaction 2-12 is therefore a
key reaction in the biosynthesis of amino acids from free ammonia.
Nevertheless, despite the apparently large equilibrium
constant for Reaction 2-12, the reaction is biologically readily
reversible, inasmuch as (reading from right to left) it fcan be
"pulled" by the even more energetically favorable oxidation of
the hydrogen of NADH or NADPH by molecular oxygen in mitochondria!
oxidation. Thus, in effect, Reaction 2-12 is freely reversible
and serves as a key step in the uptake of ammonia or the produc-
tion of ammonia, depending on the metabolic circumstance.61
The glutamic dehydrogenases observed in nature tend to be struc-
turally complex with many subunits.^9/52 Elaborate systems of
biologic control have been described for these enzymes; but the
control process, undoubtedly important in protein biosynthesis
and degradation, is still imperfectly understood.2/50,52
The glutamic dehydrogenase reaction is crucial in nitrogen
metabolism, not only because it is one of the primary reactions
in which the ammonia molecule is either combined into or re-
leased from organic linkage, but because its chief molecules,
glutamate and a-ketoglutarate, can serve as distribution points
or gathering points for the nitrogen of a wide variety of amino
acids. This gathering and release of amino acid nitrogen thus
68
-------
makes the glutamate and a-ketoglutarate molecules transfer
agents that serve as "brokers" in the movement of ammonia into
and out of the amino acid molecule . ->!/ 61 The " transaminase"
reaction participating in this transfer is shown as Reaction
2-13.
/R,\ O ,'R -•.
Ui) I 1R?' H
-Glutamate +\R,/- C - COO ^ a-ketoglutarate + 1 -- C - COO . (2-13)
(various keto acids) (various amino acids)
Depending on the direction in which these biologically re-
versible reactions occur, a combination of glutamic dehydrogenase
and transaminase can serve in the degradation of amino acids to
yield ammonia and a carbon skeleton that can be further metabolized
for energy . -^ ' ^9 / 61 This ammonia release occurs via the reaction
sequence shown below
Transaminase: Amino acid + a-ketoglutarate ->• a-keto acid
+ glutamate. (2-14)
Glutamic dehydrogenase: Glutamate + NAD(P)+ ->• a-ketoglutarate
+ NAD(P)H + H+ + ammonia. (2-15)
Sum: Amino acid + NAD(P)+ ->• keto acid + NAD(P)H + H
+ ammonia. (2-16)
69
-------
These reactions can, conversely, serve to synthesize a
variety of amino acids from ketoacid carbon skeletons synthesized
by many pathways, plus ammonia, to yield the amino acids required
for protein synthesis. This "synthetic" sequence is shown as
Reactions 2-17 through 2-19.
Transaminase: a-Keto acid + glutamate ->• amino acid
+ a-ketoglutarate. (2-17)
Glutamic dehydrogenase: a-Ketoglutarate + NAD(P)H+
+ ammonia -> glutamate + NAD(P) + . (2-18)
Sum: a-Keto acid + NAD(P)H + H+ + ammonia -> amino acid
+ NAD(P)+. (2-19)
Thus, the sum of the actions of glutamic dehydrogenase and
transaminases is the fundamental biologic funnel for the channeling
of inorganic nitrogen, as ammonia, into and out of organic linkage
in amino acids ' and, by other (but analogous) pathways, the
purines and pyrimidines of nucleic acids and other nitrogen com-
pounds present in smaller quantities.61
Transaminases are ubiquitous in nature,3 and this emphasizes
the biologic importance of the reaction sequences shown above.
The capacity of the glutamic dehydrogenase reaction to absorb
ammonia is, on the basis cf enzyme content of various cells,
large. In mammals, it is difficult to demonstrate the potenl
rate at which this enzyme can operate, because an experimental
70
-------
limitation in the whole animal is the relatively low rate of
entry of the glutamic acid molecule into cells.24,26 Neverthe-
less, it is likely that intracellular reactions can occur rapidly,
and the equilibrium point of Reaction 2-12 is one of several bio-
chemical factors that decree that the normal intracellular con-
centration of ammonia must be very low.
Glutamine Biosynthesis. Glutamic acid is important not
only because it can represent (see Reaction 2-12) a primary
product of the chemical fixation of ammonia into organic linkage,
but because it can itself, in an extremely active secondary step,
accept a molecule of ammonia to form the compound glutamine, the
amide of glutamic acid. This reaction, catalyzed by the enzyme
glutamine synthetase,33'36 ' 54'55 is shown as Reaction 2-20.
1-Glutamic acid + NH3 + ATP ->• 1-glutamine + ADP + pi.
(adenosine
diphosphate) (2-201
The equilibrium constant for this reaction lies well to the right,
and the ATP hydrolysis that accompanies the reaction provides the
thermodynamic driving force.29,48 Thus, it can be observed that
yet another reaction, active in virtually all biologic systems,
tends to ensure low steady-state intracellular ammonia concentra-
tions.
Glutamine is a component of proteins, is a potential source
of ammonia via hydrolysis (which can also regenerate glutamic
acid), and can serve as an agent to transfer a nitrogen atom
71
-------
from its amide linkage to a wide variety of acceptors for many
biologic purposes.5'33'34'43 Glutamine is a remarkable mole-
cule.26'33 Because at physiologic pH the molecule bears no net
charge, it permeates cell membranes freely and indeed is the
only molecule other than glucose that can cross the blood-brain
barrier with ease in substantial quantities. Once it is in a
cell, it can release or transfer its amide group and yield
glutamic acid, which, in the cell, can be metabolized rapidly.
Thus, glutamine can serve as a transport form for both ammonia
nitrogen and glutamic acid, penetrating the cell membrane, which
is but poorly permeable to glutamic acid itself.
In mammals, glutamic acid seems to serve as an ammonia
"buffer" with a large capacity for the uptake of ammonia into
the amide of glutamine.9 Rapid processes can, when needed,
re-release or transfer the nitrogen atom of the amide group. Of
the potential reactions that bind ammonia into organic linkage,
the one that seems to occur most rapidly both in plants and in
animals is the synthesis of glutamine.9'26'36 With the short-
lived nitrogen-13 isotope, Wolk et. al.63 showed that glutamine
was the first rapidly formed organic nitrogen compound formed
in the cyanobacterium Anabaena cylinderica. In mammals, Duda
and Handler9 showed, with nitrogen-15, that the first detectable
pool of isotopic nitrogen (either from free ammonia or from amino
acids) was in the amide group of glutamine.
72
-------
Glutamine may be looked at as a "detoxified" ammonia
molecule, which differs from ammonia itself not only in being
attached, in a biologically controllable manner, to a carbon
skeleton, but in losing its basic properties once the nitrogen
atom is carried into the amide linkage; the nitrogen atom re-
sists protonation and retains its unshared electron pair even
at low pH.
It is perhaps for this chemical reason that glutamine
serves so effectively, by transfer reactions, as a source of
nitrogen to a wide variety of acceptors. ^ • ^6 i 33 ,43 j^_ j_s tjie
direct nitrogen donor in the biosynthesis of aminosugars,
nicotinamide coenzymes, histidine, carbamyl phosphate, purines,
pyrimidines, and many other specialized compounds. -* > 33, 34 Q£
particular quantitative importance is its role in the biosyn-
thesis of purines: ' in all living organisms, purines make
up one of the two types of bases in nucleic acids; and in such
animals as birds and reptiles, whose mass nitrogen excretion
occurs in the form of uric acid (instead of urea, as in mammals),
the purine biosynthesis pathway has been adapted into a large-
scale nitrogen-disposal process in the catabolism of protein.
Glutamine directly furnishes two of the four nitrogen atoms of
the purine molecule. -^ The process of purine biosynthesis may
be considered to start with the formation of 5-phosphoribosyl-
amine,^ which obtains its nitrogen from glutamine and serves
as the nucleus around which the purine ring is constructed; the
73
-------
nitrogen atom N-9 of purines also comes from glutamine, by nitro-
gen transfer to N-formylglycinamide ribonucleotide.
In most cases in which glutamine transfers its nitrogen,
ammonia can serve as a substitute, but only at much higher total
concentrations.5'33/42 In that case, it can be calculated that
only uncharged ammonia, with its unshared pair of electrons, can
serve as an ammonia donor; ammonium ion cannot. Thus, at physio-
logic pH, at which only about 1% of the total of ammonia and
ammonium exists as ammonia, these processes are unlikely to use
ammonia. But the amide nitrogen of glutamine, which remains
unprotonated even at physiologic or lower pH, can serve as the
biologic nitrogen donor.
The role of glutamic acid and glutamine may be summarized
as follows: Glutamate is the organic molecule in which ammonia
first appears, bound to carbon derived from carbohydrate metabo-
lism; it serves as a transfer agent of ammonia to other amino
acids. Glutamine is the product of ammonia uptake by the pre-
viously formed glutamic acid molecule and serves as a transfer
agent of nitrogen to a variety of acceptors; it can also serve
as a readily available source of free ammonia when the release
of ammonia from a storage pool is biologically advantageous.
Because the glutamine synthetase reaction is rapid and wide-
spread, glutamine can serve as a "storage" form of ammonia.
74
-------
Carbamyl Phosphate Biosynthesis.* The carbamyl phosphate
molecule, H2N - C - 0-PO3H~, is composed of the basic moieties
0
carbon dioxide, ammonia, and phosphate.23,44,45 There is no
evidence that the carbon dioxide that enters this molecule comes
from any special source; indirect evidence in mammals suggests
that its composition and origin reflect the general carbon dioxide
pool.^ The nitrogen can originate either as free ammonia or as
the amide nitrogen of glutamine. The phosphate moiety can arise
from inorganic phosphate or, more commonly, from ATP- The di-
verse origin of these moieties reflects the occurrence of
different types of carbamyl phosphate-synthesizing enzymes,
which in turn reflects the different biologic uses for which
the carbamyl phosphate molecule is destined.44'45 Two major
biologic pathways receive nitrogen from carbamyl phosphate: the
synthesis of pyrimidines, which is initiated by transfer of the
carbamyl group to an aspartic acid molecule to form carbamyl
aspartic acid16'19'21'45 (Reaction 2-21);
*An enzyme catalyzing the biosynthesis of carbamyl phosphate
can be referred to as a "carbamate kinase" or as a "carbamyl
phosphate synthetase." Raijman and Jones44 suggested the use
of "carbamate kinase" when carbamyl phosphate is formed from
carbon dioxide, ammonia, and 1 mole of ATP, and the use of
"carbamyl phosphate synthetase" when the reactants are carbon
dioxide, ammonia, and 2 moles of ATP. They recognized and
discussed the possibilities of ambiguity in this nomenclature.
-------
o
H-y\
O H2N CH2
I 2—
H^ _ c - 0-P-032~ + HOOC - CH2 - CH - COOH * O = C H?C + HP04 (2-21)
NH2 N COOH
(carbamyl phosphate) (aspartic acid) H (inorganic
phosphate)
(N-carbamyl
aspartic acid)
. . 23,44,45 .
and the biosynthesis of the amino acid arginine, in
which the carbamyl moiety is transferred to the 6-group of
ornithine to form citrulline, an arginine precursor (Reaction
2-22) .
NH2
C = 0
NH9
1 ^
C = 0
1 +
0
1
0~-P-0~
0
(carbamyl
phosphate)
NH0
i ^
(CH,),
1 t
H-C-NH.
2
COOH
(ornithine)
i
NH,
1
- (CH2) 3 +
1
H-C-NH,
i
COOH
(citrulline)
OH
0~-P-O~.
0
(inorganic
phosphate)
(2-22)
Arginine biosynthesis can itself serve in two biologic pathways
of fundamentally different objectives and mass magnitudes. '
When carbamyl phosphate is used in the synthesis of arginine
destined for protein synthesis, the rate of reaction is low and
76
-------
is controlled to limit the quantity of product to that required
«
for growth. However, in ureotelic (urea-forming) animals, such
as mammals (including man), most arginine synthesis is destined
for the large-scale synthesis of urea:
Precursors . . . .> arginine H2° >_ ornithine + urea. (2-23)
arginase
Urea formation, a device for discarding extra nitrogen in
a metabolically innocuous form, utilizes a portion of the arginine
biosynthesis pathway (Figure 2-5). However, after the arginine is
formed, its guanido group is cleaved hydrolytically by arginase
to yield urea and regenerate ornithine, which can then accept
another molecule of nitrogen from carbamyl phosphate, etc. The
essentials of the urea cycle27,45 are shown in Figure 2-5. The
sources of nitrogen for this cycle (the structures of the com-
ponents and intermediates can be found in any biochemistry text-
book) are thus ammonia (via carbamyl phosphate) and aspartate;
the latter in turn regenerates its amino group by transamination
from glutamic acid to the precursor of the aspartic acid carbon
chain, oxaloacetic acid.45
Reflecting the plurality of roles of carbamyl phosphate, its
biosynthesis is catalyzed by different enzymes in various organisms
and in various subcellular fractions;^'" it is clear that differ-
ent sets of biologic controls modulate the various processes.
Several enzymes catalyze the synthesis of carbamyl phosphate.
In mammals, two types of carbamyl phosphate synthetases have
11
-------
Pi
CARB/Wr/. P//05P//AF£
H H j v.-a
GLUUMIC ACfD
ClTRUllIHE
KSPARTATE
+ KJP
ARCIWlKf
tAD?
FIGURE 2-5. The urea cycle.
78
-------
been observed. ^'^ one of these, Type I, is present in liver
mitochondria and appears to be the enzyme that catalyzes the
synthesis of phosphate for urea synthesis^ (Reaction 2-24).
carbamyl phosphate
C0? + NH, + 2ATP synthetase I ^ carbamyl phosphate (2-24)
N-acetylglutamate + 2ADP + P^
N-Acetylglutamate is required for this reaction, probably as an
allosteric ef fector. ^ ' *•-> Because of the use of 2 moles of ATP
for the formation of one mole of carbamyl phosphate, the reaction
is essentially irreversible. Thus, this reaction, like the glu-
tamic dehydrogenase and glutamine synthetase reactions, has an
equilibrium that ensures the removal of ammonia from solution,
Mammalian cells have another carbamyl phosphate synthetase,
but it is present in the cytosol, rather than in the mito-
chondria, and, because it is repressed by pyrimidines, is pre-
sumed to serve on the pathway of pyrimidine biosynthesis. Gluta-
mine, rather than ammonia, is the nitrogen source; N-acetylgluta-
mate is not required. The glutamine-dependent reaction^ is
catalyzed by a class of enzymes designated carbamyl phosphate
synthetase II (Reaction 2-25).
carbamyl phosphate
Glutamine + C02 + 2ATP synthetase II \ carbamyl phosphate
+ Glutamic Acid + 2ADP + P1. (2-25)
79
-------
In Escherichia coli, a carbamyl phosphate synthetase, also
repressed by pyrimidines, is found; this enzyme, like the mam-
malian carbamyl phosphate synthetase II, utilizes glutamine
rather than ammonia.I'57 Neurospora crassa has a carbamyl
phosphate synthetase that operates with the same stoichiometry
and in the same reaction as does the liver mitochondrial carbamyl
phosphate synthetase I, but N-acetylglutamate is not required.
This enzyme is repressed by arginine and is thus presumed to be
fi 2
a part of the arginine biosynthetic pathway.
In addition to these carbamyl phosphate synthetases—which
synthesize this material from carbon dioxide, ATP, and a nitro-
gen source--carbamyl phosphate can be formed by the reversal of
the reaction of ornithine transcarbamylase (Reaction 2-22) of
the urea cycle4^,45 or of the aspartic transcarbamylase (Reaction
2-21) of the pyrimidine biosynthetic pathway. Although both
these reactions can, in theory, yield carbamyl phosphate, it is
more likely that their actual biologic role is almost exclusively
biosynthetic, inasmuch as each of these enzymes is present in
the mammalian cell in a tight complex with the carbamyl phosphate
synthetase of its biosynthetic pathway. Nevertheless, ornithine
transcarbamylase ' 4 (Reaction 2-22) can indeed serve an energy-
yielding role in bacteria grown on arginine; here, the reversal
of Reaction 2-22 can serve as an intermediate step in arginine
degradation; the carbamyl phosphate formed in this reaction can
react with ADP to form ATP in a reaction catalyzed by an enzyme
80
-------
called carbamate kinase (Reaction 2-26),
Carbamyl phosphate + ADP ^- -~--v carbamic acid + ATP- (2-26)
in which part of the energy of arginine degradation can be
stored in ATP formed by the carbamate kinase reaction.
In mammals, the reactions of glutamic dehydrogenase, glutamine
synthetase, and carbamyl phosphate synthetase all proceed in the
direction of ammonia uptake, and their activity and equilibrium
points account for the low steady-state concentration of ammonia
in tissues and body fluids. In addition, the total capacity of
these enzymes is high: ammonia can be administered to dogs
intravenously, and urea synthesis can be as fast as 2 mg of
nitrogen per kilogram per minute.24,26 When glutamine is simi-
larly administered, the rate of urea formation is even higher;
this must reflect potentially high rates of glutamine hydrolysis
and carbamyl phosphate synthesis. Thus, mammals have the enzy-
matic capabilities of metabolizing ammonia at high rates; under
normal conditions, these mechanisms are overwhelmed only under
very unusual circumstances; however, if there are defects in
the enzymes of ammonia uptake, then the picture changes, and
ammonia can have a high degree of metabolic toxicity. (This
problem is dealt with elsewhere in this report.)
Asparagine Biosynthesis.35 Although, formally, the process
of asparagine biosynthesis can utilize ammonia as in glutamine
synthesis (Reaction 2-20), this process appears to be much more
81
-------
narrowly distributed and quantitatively less important, particu-
larly in animals. In microbial and plant biosynthesis, asparagine
may be formed not by an analogue of the glutamine synthesis reac-
tion, but by transfer of the amide group from glutamine to
aspartic acid or (possibly via e-cyanoalanine) by utilizing
both the carbon and the nitrogen of cyanide.35'47
Relatively Rare processes. Other processes can fix ammonia;
these probably occur in small-scale reactions or in organisms in
highly specialized ecologic niches.33 It is unlikely that they
are of quantitative significance in the transfer of ammonia during
the nitrogen cycle. Ammonia can be fixed by amino acid dehydro-
genases that can operate in a manner analogous to that of glu-
tamic dehydrogenase, but with a different ketoacid as an analogue
for a-ketoglutarate. In addition, some of the previously cited
glutamine transfer reactions might, under special circumstances
(and probably at high ammonia concentrations or high pH), utilize
ammonia, rather than glutamine, in biosynthetic pathways.5'33
Again, the role of these processes in nitrogen economy has not
been systematically explored.
Release of Ammonia from Organic Linkage
Most of the nitrogen in the biosphere is contained in pro-
teins and nucleic acids; in some specialized or artificial
systems, such as feed lots and sewage systems, excreta provide
substantial quantities of other compounds in which nitrogen at
82
-------
the ammonia oxidation level can be found. Urea in particular
may be present in some places in high concentrations and con-
tribute substantial quantities of nitrogen.
When an organism dies, its proteins and nucleic acids are
degraded to amino acids, purines, and pyrimidines. This degra-
dation may be initiated by the organism's own intracellular
proteases and nucleases; but proteases and nucleases of bacteria
are interjected into this process, so it is impossible to de-
scribe precisely the relative contributions of external and
intracellular proteases and nucleases in the depolymerization
of the major nitrogen-containing compounds of organisms.
Once the process of proteolysis or nucleic acid degrada-
tion is well in progress, an enormous variety of types of reac-
tion can release the nitrogen of amino acids, purines, and
pyrimidines, with the formation of ammonia. Again, it is
difficult or impossible to measure amounts of ammonia that are
produced by the various bacterial processes. Certainly, the
sum of glutamic dehydrogenases and transaminases (see Reaction
2-16) must have substantial input. In addition to such enzymes
as glutamic dehydrogenase,^2 specific amino acid oxidases^ can
catalyze the overall reaction,
H
R - C - COOH + ijO2 cofactors ^ R _ c _ COOH + NH,, (2-27)
11 3
NH2
0
83
-------
leading to release of ammonia. Deamination can also take place
hydrolytically and reductively-33 Specialized enzymes, either
induced or constitutive, degrade (probably for use as energy
sources) the wide variety of specific amino acids, purines,
pyrimidines, and other nitrogenous materials found in the re-
mains of organisms.
Ureases may sometimes play an important role. These enzymes,
which catalyze Reaction 2-28,
CO(NH2)2 + H20 -»• 2NH3 + CO2, (2-28)
are not normal constituents of animals, but are widely distributed
among microorganisms and plants.^6 The ureases may play a role in
mammalian generation of free ammonia, inasmuch as enteric bacteria
contain urease; in some circumstances, bacterial intestinal
hydrolysis of urea generated in the liver may have some clinical
impact. There are other ureases in the plant world, in soil
constituents, and in plant residues; those commonly encountered
in the laboratory are prepared from plant materials, such as soy-
beans and jack beans. Nevertheless, it is likely that plants
that utilize urea from fertilizer do so by utilizing ammonia
formed by urease-containing microorganisms, rather than by their
own urease; this ammonia is probably assimilated after it has
undergone "nitrification" to nitrate.
84
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Formation of Ammonia in Mammals
The steady-state concentration of free ammonia (or ammonium
ion) in the cells and extracellular fluid of mammals is governed
by the relative velocities of processes that release and take up
ammonia. The previous section described the processes for taking
up ammonia and demonstrated that the equilibrium points of the
major ammonia-fixing reactions were such that the equilibrium
concentration of ammonia could be expected to be quite low. The
reactions that release ammonia are relatively few. ' ' ' ' ^'
' ' ' Because mammals, including man, do not limit their
intake of protein by metabolic or permeability devices, but
forage freely and use protein (beyond that needed for protein
synthesis) as a source of energy, the degradation of ingested
amino acids is a process of quantitative importance. In
Americans, the degradation of amino acids can provide 10-25%
(or even more) of total caloric needs. In this event, nitrogen
is released from the amino acids--the bulk of it as ammonia by
transaminase and glutamic dehydrogenase reactions (Reaction 2-16).
Although direct amino acid oxidases (Reaction 2-27) have been de-
scribed, 4,33 they either are of low activity or operate on the
unnatural optical isomer of amino acids; the enzyme that cata-
lyzes the latter process, D-amino acid oxidase,^ has long been
known, but its function remains obscure.
The ammonia formed from amino acids during the degradative
process is either immediately funneled into the biosynthesis of
85
-------
carbamyl phosphate on the pathway of urea biosynthesis (Reaction
2-24 and Figure 2-5) or temporarily stored in the amide group
of glutamine.9'26'33 The latter process is rapid and is of
considerable metabolic importance (Reaction 2-20) . The hydrolysis
of glutamine18 furnishes a ready source of ammonia, re-releasing
it for urea synthesis or for the biosynthesis of amino acids or,
in specialized tissues like the kidney,25'30'58'61 providing
ammonia to serve as an acceptor for hydrogen ions in the regula-
tion of acid-base balance. The hydrolytic release of ammonia
from glutamine is catalyzed by enzymes called "glutaminases"18
that catalyze the following reaction:
0
O
H
HOOC - C - CH - CH - C -
NH
H H2 H2
H9O -> HOOC - C -C-C-C-OH+ NH3
(glutamic acid)
Glutaminase is particularly important in renal metabolism,58'61
where it can release ammonia in the tubular epithelium to serve
as an acceptor of hydrogen ions. In acidosis, the renal con-
centration of this enzyme increases markedly over a period of
several days,8'26'39'61 in parallel with the increased excretion
of ammonium ion. In acidosis, it can be demonstrated that about
two-thirds of urinary ammonia can be accounted for on the basis
of the arterial-venous glutamine difference in the plasma passing
through the kidney. 58 The other one-third can be accounted for
86
-------
by the net deamination of amino acids and by the direct clearance
of plasma ammonia and ammonium ion by the kidney.^0,41
Thus, one can envision mass flow of the ammonia formed
from amino acids by Reaction 2-16 as being temporarily stored
in the amide of glutamine, where it can be delivered to various
tissues by that freely permeable molecule, utilized in nitrogen
transfer reactions, or re-released as ammonia either for urea
synthesis or as a renal "buffer" in the regulation of acid-base
balance.
Compared with the quantitative importance of the glutaminase
and glutamic dehydrogenase reactions as immediate sources of
ammonia, other reactions occur to but a limited extent. Ammonia
can be released hydrolytically from some amino acids, such as
cysteine, serine, and histidine. The degradation of purines can
also lead to ammonia formation, catalyzed by such enzymes as
adenine deaminase (which catalyzes the hydrolytic conversion of
adenine to hypoxanthine and ammonia), guanine deaminase (which
catalyzes the conversion of guanine to xanthine and ammonia),
and adenylic acid deaminase (which catalyzes the formation of
inosinic acid and ammonia). The nitrogen-containing pyrimidines
can also yield ammonia during their degradation. These reactions
are not of high quantitative significance; the ammonia formed in
them may be expected to be stored temporarily in glutamine and
then transferred or released in the processes involving glutamine
that have been previously described.4'17'18'33•46'52'61'64 - 65
-------
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16b. Hager, S. E. , and M. E. Jones. A glutamine-dependent enzyme for the syn-
thesis of carbamyl phosphate for pyrimidine biosynthesis in fetal
rat liver. J. Biol. Chem. 242:5674-5680, 1967.
17. Hanson, K. R., and E. A. Havir. The enzymic elimination of ammonia, pp.
75-167. In P. D. Boyer, Ed. The Enzymes. (3rd ed.) Vol. VII.
New York: Academic Press, 1972.
18. Hartman, S. C. Glutaminases and )f—glutamyltransferases, pp. 75-100. In
P. D. Boyer, Ed. The Enzymes. (3rd ed.) Vol. IV. New York:
Academic Press, 1971.
19. Henderson, J. P., and A. R. P. Paterson. Nucleotide Metabolism. An Intro-
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20. Hsia, Y. E. Inherited hyperammonemic syndromes. Gastroenterology 67:
347-374, 1974.
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21. Jacobson, G. R. , and G. R. Stark, ^spartate transcarbamylases, pp. 226-
308. In P. D. Boyer, Ed. The Enzymes. (3rd ed.) Vol. IX, Part B.
New York: Academic Press, 1973.
22. Jones, M. E. , and S. E. Hager. Source of carbamyl phosphate for pyrimidine
biosynthesis in mouse Ehrlich ascites cells and rat liver. Science
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23. Jones, M. E. , L. Spector, and F. Lipmann. Carbamyl phosphate, the carbamyl
donor in enzymatic citrulline synthesis. J. Amer. Chem. Soc. 77:
819-820, 1955. (letter)
24. Kamin, H. , and P. Handler. The meta". olism of parenterally administered
amino acids. II. Urea synthesis. J. Biol. Chem. 188:193-205, 1951.
25. Kamin, H, , and P. Handler. The metabolism of parenterally administered
amino acids. III. Ammonia formation. J. Biol. Chem. 193:873-
880, 1951.
26. Kamin, H. , and P. Handler. Amino acid and protein metabolism. Annu. Rev.
Biochem. 26:419-490, 1957.
27. Krebs, H. A., and K. Henseleit. Untersuchungen uber die Harnstoffbildung
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influence of ADP, GTP, and L-glutamate on the binding of the reduced
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29. Lehninger, A. L. Biochemistry. (2nd" ed.) New York: Worth, 1975.
pp. 559-586, 693-728.
30, Lotspeich, W. D., and R. F. Pitts. The role of amino acids in the renal
tubular secretion of ammonia. J. Biol. Chem. 168:611-622, 1947.
31. MacKenzie, C. G., and V. du Vigneaud. The source of urea carbon. J.
Biol. Chem. 172:353-354, 1948. (letter)
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32. McGilvery, R. W. The nitrogen cycle, pp. 357-399. In Biochemical Concepts,
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33. Meister, A. Biochemistry of the Amino Acids. (2nd ed.) Vols. I and II.
New York: Academic Press, 1965. 1084 pp.
34. Meister, A. On the synthesis and utilization of glutamine. Harvey Lect.
63:139-178, 1968.
35. Meister, A. Asparagine synthesis, pp. 561-580. In P. D. Boyer, Ed. The
Enzymes. (3rd ed.) Vol. X. New York: Academic Press, 1974.
36. Meister, A. Glutamine synthetase of mammals, pp. 699-754. In P. D. Boyer,
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York: Academic Press, 1977.
38. Miller, R. E., and E. R. Stadtman. Glutamate synthase from Escherichia
coljL. An iron-sulfide flavoprotein. J. Biol. Chem. 247:7407-7419,
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39. >Muntwyler, E., M. lacobellis, and G. E. Griffin. Kidney glutaminase and
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Amer. J. Physiol. 184:83-90, 1956.
40. Owen, E. E., and R. R. Robinson. Amino acid extraction and ammonia metab-
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ammonium chloride. J. Clin. Invest. 42:263-276, 1963.
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42. Preiss, J., and P. Handler. Biosynthesis of diphosphopyridine nucleotide.
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43. Pruisiner, S., and E. R. Stadtman, Eds. The Enzymes of Glutamine Metab-
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44. Raijman, L., and M. E. Jones. Carbamate kinase, pp. 97-119. In P. D.
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45. Ratner, S. Enzymes of arginine and urea synthesis. Adv. Enzymol. 39:
1-90, 1973.
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Biochim. Biophys. Acta 184:578-582, 1969.
48. Rosing, J. , and E. C. Slater. The value of AG° for the hydrolysis of
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13
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Comparative Ammonia Metabolism
It has been well established that ammonia, which is produced
as a byproduct of various phases of protein metabolism, can be
highly toxic. Therefore, mechanisms are required by which
organisms can detoxify and dispose of this substance. In verte-
brates in a water environment, this problem is handled by simple
diffusion of ammonia into the environment. But the adaptation of
higher vertebrates to a terrestrial environment requires the ex-
cretion of excess ammonia in a nontoxic form, such as urea or
uric acid. Vertebrates may be divided into three classes accord-
ing to the manner in which they excrete excess nitrogen or de-
toxify ammonia: the ammonotelic, which excrete free ammonia;
the uricotelic, which excrete uric acid; and the ureotelic,
which excrete urea.
Mammals. In mammals, the collective action of glutamic de-
hydrogenase, glutamine synthetase, and carbamyl phosphate syn-
thetase has been suggested as responsible for the extremely low
tissue concentrations of ammonia; -^ /34 this would indicate that
these enzyme systems are utilized in the detoxification of
exogenous ammonia. Duda and Handler17 used [15N]ammonia and
reported that glutamine synthesis was the major fate of exogenous
ammonia in rats, accounting for 80% of the intravenously ad-
ministered ammonia in 30 min, followed in importance by carbamyl
phosphate synthetase and glutamic dehydrogenase.
-------
Foster et al.19 investigated the utilization of [l5N]ammonium
citrate fed to rats on a low-protein diet. The animals were
sacrificed after 5 days, and the following amino acids were found
to contain nitrogen-15: creatine, glycine, proline, histidine,
arginine, glutamic acid, and aspartic acid; the last two had the
highest concentrations of nitrogen-15. However, the ammonia
liberated during protein hydrolysis ("amide nitrogen") had a
nitrogen-15 concentration much higher than that of the amino
groups of any amino acid. The arginine from the animals was
hydrolyzed into ammonia and ornithine, of which only the ammonia
contained nitrogen-15, indicating that it was in the guanido group
of the arginine.
Duda and Handler-^ investigated the metabolic fate of intra-
venously administered [ 1% ] ammonium lactate in rats. The incorpora-
tion of nitrogen-15 into liver urea, glutamine, glutamic acid and
aspartic acid, and alanine and glycine, as well as total-body
glutamine and urea, was determined at various intervals. Glutamine
synthesis was the major fate of ammonia. Urea synthesis, per
unit time, represented a fixed percentage of available ammonia over
a large concentration range. The incorporation of nitrogen-15 into
glutamine-amide-N, urea, and glutamic acid reached a maximum at
20 min; however, the specific activity of glutamine was approxi-
mately 7 times that of either urea or glutamic acid. These workers
also reported the distribution of labeled urea and glutamine after
intravenous administration of [15^]ammonia. The rats received
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injections of 47.5 ymoles of [ -^Njammonium lactate (36.7 atoms %
excess), and the nitrogen-15 (in umoles) in urea and glutamine-
amide in various organs was determined as follows: carcass,
5.6 and 25.85; testes, 0.028 and 0.0509; liver, 0.392 and
1.365; kidney, 0.145 and 0.107; heart, 0.03 and 0.301; spleen,
0.0226 and 0.0985; and brain, 0.0095 and 0.0815.
Takagaki et a_l. ,^4 after intravenous infusion of [ 15]sj]ammonium
acetate in cats, determined the nitrogen-15 concentration in brain
and liver tissue. Although the concentrations of the amino acids
measured in the various tissues remained constant or decreased
slightly, the concentration of glutamine in the brain increased
by at least 50%. They observed that the nitrogen-15 content of
the amide group of cerebral glutamine was higher than that of
liver or blood. The a-amino group of glutamine isolated from
the brain had 10 times the specific activity found in glutamic
acid. However, the a-amino group of glutamine isolated from the
liver had a lower specific activity than that of glutamic acid.
These differences were suggested as due to the brain glutamine's
being derived from a compartment of glutamic acid that was not
in equilibrium with the total tissue content of glutamic acid,
whereas this compartmentalization did not exist in the liver.
The initial fate of [15N]ammonia administered to cats by
carotid infusion has also been reported by Berl et al.5
Ammonia, glutamic acid, glutamine, aspartic acid, glutathione,
and urea from cerebral cortex, liver, and blood, as well as
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cerebral y-aminobutyric acid, were isolated and analyzed. Next
to free ammonia, the highest nitrogen-15 concentration in cere-
bral cortex was in the amide group of glutamine, followed by its
a-amino group. In liver, glutamic acid, glutamine, aspartic acid,
and urea all contained appreciable concentrations of the isotope.
However, liver aspartic acid contained an isotope concentration
that exceeded, in most experiments, that of glutamine. Gluta-
thione in liver and y-aminobutyric acid in cerebral cortex also
contained appreciable amounts of the isotope.
Incorporation of nitrogen-15 from ammonium citrate into pro-
teins of liver, heart, kidney, spleen, and three fractions of
quadriceps muscle was studied in untreated and growth-hormone-
treated hypophysectomized rats by Vitti et. a^.68 Three successive
lots of animals received the same dose of nitrogen-15 per unit of
body weight intragastrically, intraperitoneally and subcutaneously.
Changing the route of administration drastically altered the
distribution of nitrogen-15 between a-amino, amidine, and amide
groups of organ proteins. Subcutaneous injection apparently
facilitated incorporation of ammonia into glutamine. When this
route was used, marked labeling of amide in both control and
growth-hormone-treated rats reduced the difference between the
two groups, with respect to total nitrogen-15 incorporation.
This was particularly true for liver protein, in which labeling
of a-amino and amidine groups decreased. When [15N]ammonium
citrate was given intragastrically or intraperitoneally, labeling
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of arginine, glutamic acid, and other amino acids of liver protein
was extensive, and growth hormone augmented total nitrogen-15 in-
corporation into all proteins examined. The effect of the hormone
on ammonia utilization appeared to be related to its effect on
utilization of the amino acids to which ammonia was transferred.
There were also significant differences in the distribution of
nitrogen-15 in the various organs, depending on the route of ad-
ministration. In all organs tested (liver, heart, kidney, and
spleen), the specific activity of nitrogen-15 after 72 h was
highest after subcutaneous, next highest after intraperitoneal,
and lowest after intragastric administration.
Other Vertebrates. The distribution of glutamine synthetase
in 12 tissues of 17 species of vertebrates (seven species of
mammals, four species of birds, and two species each of reptiles,
amphibians, and fishes) has been reported by Wu. The brain was
unique: it had the enzyme activity in all vertebrate species
studied, and in the lower animals it was the only tissue with
activity. In general, the brains of the lower animals had higher
specific activities than those of the higher animals. The highest
activity observed in any tissue occurred in the brain of the blue-
gill. In mammals, the activity in the cerebrum was always greater
than that in the cerebellum; however, the reverse was true in the
birds. The enzyme was found in liver of all species above reptiles
on the phylogenetic scale.
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Janssens and Cohen33 studied glutamine synthetase in the
African lungfish, Protopterus aethiopicus, and found enzyme
activity in the brain, but not in the liver; the negative liver
52
results are questionable, in that Pepquin et al. and Lund and
Goldstein40 used an ATP-regenerating system4 in their assays to
remove ADP (an inhibitor of glutamine synthetase produced pri-
marily by tissue ATPase), and were able to detect low concentra-
52
tions of the enzyme in other tissues of the fish. Pequin et al.
found activity in brain, liver, kidney, spleen, and intestinal
mucosa of the carp, Cyprinus carpio, and Lund and Goldstein^O
reported activity in the brain, liver,- and kidney of the dogfish,
Squalus acanthias; the eel, Anquilla rostrata; and the shorthorn
sculpin, Myoxocephalus scorpius. However, Vorhaben et al.70
showed that the ATP-regenerating system used by the workers just
mentioned (which includes phosphoenolpyruvate plus pyruvate
kinase, producing ATP and pyruvate) leads to an overestimation of
glutamine synthetase activity, owing to an artifact produced in
the assay; and they recommended the use of creatine phosphate plus
creatine kinase as the ATP-regenerating system.
Wilson and Fowlkes77 improved the glutamine synthetase assay
and used it to determine the activity of this enzyme in selected
tissues of the channel catfish, Ictalurus punctatus. They con-
firmed the finding of Vorhaben et. al.,70 that the pyruvate kinase
ATP-regenerating system resulted in tissue activities 2-7 times
higher than those observed with the creatine kinase system.
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They also found that glutamine synthetase is apparently a mito-
chondrial enzyme in the fish. Maximal tissue activity was ob-
tained by homogenization in 0.5% Triton X -100.* Tissue homog-
enates prepared in 0.9% sodium chloride^^'^9 or in 0.25 M
sucrose33/52 did not provide maximal solubilization of the enzyme.
Vorhaben and Campbell69 found that glutamine synthetase was local-
ized in the mitochondrial fraction of uricotelic species, but was
extramitochondrial in rat liver. This enzyme has also been shown
to be an extramitochondrial enzyme in rat brain.61 The brain of
the catfish was found to have the highest activity, and there was
significant activity in the liver, kidney, and gill tissue. The
specific activity of the enzyme in gill tissue was about twice
that in kidney tissue; however, the actual tissue activities were
about the same. Enzyme activity had previously been reported in
liver, kidney, and brain; because of the problems of assay, it is
difficult to compare the tissue concentrations of the previous re-
ports with those obtained by the more refined method.
A Km value of 3.93 x 10~3 M was determined for L-glutamate
in the glutamine synthetase of catfish brain homogenate;77 this
value is close to the 2.5 x 10"-^ M obtained for the purified sheep
f\
brain enzyme.50 But both are lower than the 1.5 x 10 M and
1.3 x 10~2 M for the rat liver and rat brain, respectively,
A detergent used to make membrane-bound enzymes soluble.
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obtained by radiochemical assay-39 Wu79 also found a relatively
high apparent Km for glutamate (1.1 x 10~2 M) in a crude rat
liver extract, and Richterich-van Baerle et al_.58 reported
5.5 x 10~2 M in a crude guinea pig kidney preparation.
In addition to serving as a source of glutamine for various
metabolic pathways, it has been suggested that glutamine synthe-
tase has a role in ammonia detoxification in fish.74'76'77'79
Because fishes are ammonotelic, and therefore subjected to a
constant endogenous ammonia load, it seems reasonable to suggest
that the high activity associated with brain tissue is related to
detoxification. The role of the kidney enzyme of the catfish is
unclear, inasmuch as fishes (unlike mammals) apparently do not
utilize renal ammonia production for acid-base regulation.18
The comparative biochemistry of carbamyl phosphate synthe-
tase has received considerable attention. This enzyme is present
in all mammals and is responsible for urea synthesis and excretion
in the ureotelic species. Kennan and Cohen36 found that carbamyl
phosphate synthetase activity, and the activity of the other three
enzymes of the urea cycle, did not appear in the rat until late
fetal life; however, all four enzymes were found at significant
concentrations in the liver of the youngest pig embryo studied
(28 days) .
In general, a functional ornithine-urea cycle has not been
detected in the true ammonotelic or uricotelic species.8'13'14'45'
Two enzymes of the cycle, carbamyl phosphate synthetase and
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ornithine transcarbamylase, have been reported to be absent from
teleost liver.11 However, Huggins et al. found low concentra-
tions of all five enzymes of the urea cycle in several species
of teleostean fishes, from both freshwater and marine habitats.
Ornithine transcarbamylase has been reported in the liver of the
marine teleost Opsanus beta, 4 2. ancj Read has reported fairly
high activities for all five of the urea-cycle enzymes in
Opsanus tau. Arginase, another enzyme of the urea cycle, has
long been known to be present in the teleost liver, kidney,
heart, and, to a lesser extent, spleen, gills, ovaries, testes,
and muscle.15,16,28 Significant concentrations of carbamyl
phosphate synthetase, ornithine transcarbamylase, and arginase
have been detected in liver tissue of the channel catfish,
Ictalurus punctatus, whereas only ornithine transcarbamylase and
arginase were detected in kidney tissue. "75 NO arginine synthesis
could be demonstrated in the catfish liver or kidney; therefore,
it was concluded that this species does not have a functional
urea cycle.
The Km values for L-arginine of 8.0 and 11.1 mM for catfish
liver and kidney arginase, respectively,75 are of considerable
interest, because they are similar to those obtained for ureotelic
species.^5,46 Mora et al.^5,46 have suggested that two types of
arginase are found, owing to the different Km values: all the
arginases from liver of ureotelic animals had Km values of
10-20 nM, whereas the enzymes from uricotelic animals had Km
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-------
values of 100-200 mM. They also indicated that the "ureotelic"
arginase is able to hydrolyze endogenous L-arginine with great
efficiency, whereas the "uricotelic" arginase is present in the
livers that do not have the enzymes of arginine biosynthesis,
and thus its specific role in intermediary metabolism is un-
certain. They also found that high concentrations of arginine
resulted in substrate inhibition of the liver arginases from
the ureotelic species, but not the uricotelic species. No sub-
strate inhibition was detected in either the liver or kidney
arginase from the catfish.75 However, inasmuch as the Km values
obtained from the catfish tissues are similar to those of the
''ureotelic" arginase, it appears that these implications may not
apply to fish arginase.
It is of interest that nitrogen excretion changes in the
developing tadpole. As an infant, this animal lives in an
aquatic environment and excretes predominantly free ammonia;
during metamorphosis, carbamyl phosphate synthetase develops,
and the urea cycle becomes functional, as the frog changes its
environment from aquatic to terrestrial.10'45 A similar change
has been described for glutamic dehydrogenase: Wiggert and
Cohen73 found that the specific activity of glutamic dehydro-
genase increased by a factor of approximately 10 during
metamorphosis.
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Transport and Distribution of Ammonia and the Effect of pH
Early work by Jacobs and Stewart-^ found that ammonium salts
of strong acids fail to enter most cells, whereas those of weak
acids enter readily. There was evidence that the penetration in
the latter case was due to the hydrolyzed products of the salt,
i.e., ammonia and free acid. It was theorized on the basis of
the chemical properties of ammonium compounds, that, in a mixture
of a nonpenetrating and a penetrating ammonium salt, the penetrating
salt may be so distributed as to lead to a considerable excess of
its internal- over its external-equilibrium concentration, and
thus cause an osmotic swelling of the cell. With sufficiently
weak acids, however, the internal-equilibrium concentration
theoretically may be equal to or even less than the external
concentration, and swelling in such cases should not occur.
Jacobs and Stewart found the behavior of the sea urchin egg to
be in agreement with this theory. Although it failed to swell
in isotonic ammonium chloride alone, it did swell in an originally
hypertonic mixture of ammonium chloride (but not potassium chloride)
and ammonium acetate. Furthermore, the addition of sodium acetate
to ammonium chloride caused swelling of the cell, but the addition
of sodium borate did not, even though the cell was apparently
freely permeable to ammonium borate.
Jacobs and Parpart^*-1 compared the effects of sodium hydroxide
and ammonium hydroxide on red-cell volume changes. There was a
considerable difference: whereas sodium hydroxide added to a
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suspension of cells in sodium chloride solution produced only
shrinkage, ammonium hydroxide produced first pronounced swelling
and then shrinkage. To explain these differences, it was stated
that a red cell theoretically is freely permeable to undissoci-
ated ammonia, somewhat less permeable to anions, and impermeable
to cations, including the ammonium ion.
Milne et al.43 summarized the theoretical and experimental
evidence of the nonionic diffusion of weak acids and bases in
the stomach, kidney, and pancreas. Ammonia was included in this
investigation and was also shown to follow the pH-gradient-drug-
distribution hypothesis, indicating that the cell membranes are
relatively impermeable to one form (ionized ammonia, NH^+),
whereas the other (unionized ammonia, NH^) passes tissue barriers
with ease.
Warren and Nathan'^ postulated that a greater proportion
of a given dose of ammonia may enter the brain as the blood pH
rises, because of an increase in the amount present as unionized
ammonia. They based their postulation on the distribution
hypothesis of Milne et a_l.43 for ammonia and on the reported
pKa for ammonia of approximately 8.90 at 37° C at a blood pH of
7.4.2 Warren and Nathan determined simultaneous blood and brain
ammonia concentrations and blood pH values after intravenous in-
jections of LD50 doses of five ammonium salts that were known to
have different blood pH effects. In spite of appreciable differ-
ences in the nitrogen content of the LD50 dose of each salt, there
106
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were remarkably small differences among the brain ammonia nitrogen
concentrations. The sole exception was ammonium hydroxide, which
was shown to be primarily a cardiotoxic, rather than cerebrotoxic,
drug. The different diffusion rates of ammonium salts across the
blood-brain barrier were related to their different effects on
blood pH. As the blood pH was increased by the salt, the amount
of unionized relative to ionized ammonia increased.
Numerous investigators have produced evidence to support the
pH-gradient-drug-distribution hypothesis for the distribution of
ammonia in the body.9'31'32'37'44'59'63'71 In general, the best
evidence can be found in the summary by Stabenau e_t al_. 63 In
an effort to delineate the role of pH in the distribution of
ammonia between blood and various other tissues, temporary pH
gradients between blood and cerebrospinal fluid, brain, and
muscle were experimentally induced by intravenous infusion of
hydroxide solutions or by increasing and decreasing the partial
pressure of carbon dioxide by respiratory means. Simultaneous
brain, muscle, and cerebrospinal fluid ammonia concentrations
were serially determined during steady-state conditions and were
related to arterial whole-blood ammonia concentrations at corres-
ponding times. There was a direct relation between the diffusion
of ammonia into cerebrospinal fluid and the magnitude and direction
of a gradient in pH between blood and cerebrospinal fluid. There
appeared to be a direct and predictable correlation between altera-
tion of blood pH and tissue ammonia concentration. During metabolic
107
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and respiratory alkalosis, brain and muscle ammonia concentrations
increased by a factor of 2-3; during metabolic and respiratory
acidosis, brain and muscle concentrations remained at or decreased
to below control concentrations. These findings may be explained
by the pH-gradient-drug-distribution hypothesis.
On the basis of the mathematical and biologic aspects of
the pH-gradient-drug-distribution hypothesis, Moore et al.44
presented the following derivations pertinent to the distribution
of ammonia:
NH4+ ; - — *• NH, + H+; (2-30)
<* 5
= [NH3][H+], (2-31)
a .
[NH4+]
Yielding the Henderson-Hasselbalch equation:
PH = PKa + log
[NH4+]
or [NH4+] = [NH3]10(PKa~PH) . (2-33)
Because the blood (Bl) and cerebrospinal fluid (CSF) compartments
are separated by a semipermeable membrane (blood-brain barrier)
and the total measured ammonia in each compartment (Ccsf and CB]_
equal the concentration in cerebrospinal fluid and blood, re-
spectively) is equal to [NH + + NHU ] ,
108
-------
Ccsf
CB1
Substitute for [NH4+1:
Ccsf .
_ _ _ _ " ^ '
CB1 [NH3]B110Pa-PBl + CNH3]B1
Because tNHJ = tNHJ at equilibrium,
C , 1 + lo(PKa-PH)csf
CSt = . (2-36)
cB1 i + i
Therefore, it can be seen that, because the pKa is assumed to be
equal in both compartments, pH is the only variable determining
the steady-state distribution ratio of ammonia.
Warren presented a general equation based on similar
derivations for the distribution of ammonia between intracellular
and extracellular fluids:
Concentration intracellular 1 + 10 jPICa"P^ ln^.} (2-37)
Concentration extracellular I + 10 (P^a-pn extra;
Hogan26 examined the effect of pH on the passage of ammonia
from the rumen in sheep. When an ammonia-containing buffer at
109
-------
a PH of 6.5 was placed in the rumen, transport increased with the
concentration gradient. At a pH of 4.5, however, the concentra-
tion of ammonia in the rumen did not affect its rate of passage
across the epithelium. The net loss of ammonia nitrogen from
the rumen at a pH of 6.5 was more than 3 times that at a pH of
4.5. Additional support for the effect of pH on ammonia absorp-
tion across the ruminal epithelium in sheep has been reported
by Bloomfield et al.6 As they changed the pH of the ruminal
contents from 6.21 to 6.45, no ammonia was absorbed; however,
as they increased the pH up to 7.55, 7.58, and 7.65, the ab-
sorption became 26,11, and 11 mmoles/liter-h. One sheep with
a ruminal pH of 7.7 died of ammonia toxicity within 30 min.
These workers concluded that the free ammonia may penetrate the
lipid layers of the ruminal epithelium, in contrast with the im-
permeability of the charged ammonium ion.
Mossberg,47 not considering the pKa of ammonia, studied the
absorption of ammonia from isolated intestinal loops of the golden
hamster. Mossberg concluded that, although some movement of
ammonia from mucosa to serosa occurs in the jejunum, preferential
transport of ammonia takes place in the ileum of the golden
hamster. Active transport could not be inferred, however, be-
cause there was no attempt to demonstrate ionic movement against
an electrochemical gradient. The positive transference of
ammonia, even in the presence of minimal or negative water trans-
port, indicated that solvent drag (movement with the solvent, in
110
-------
this case water) was not the cause of the observed changes. The
author also stated that inhibition by cyanide and dinitrophenol
points to an energy-dependent transport system; so it is reason-
able to suspect that aerobic metabolism is essential for ammonia
movement against a concentration gradient.
In addition to the previously discussed diffusion of free
ammonia across membranes, there is evidence that the ammonium ion
can be transported across membranes. The ammonium ion was found
to substitute directly for potassium ion in the active transport
system for the removal of sodium ions from the human red cell.55
A concentration of ammonium ions 3-7 times that of potassium was
required to cause a comparable effect. Ammonium ions have also
been shown to replace potassium in producing sodium extrusion in
toad skeletal muscle. The effect of ammonium ions was completely
abolished by ouabain; this indicates that the mechanism of ammo-
nium ion involvement was the same as that known for potassium in
the sodium-ion- and potassium-ion-dependent ATPase system.
Albano and Francavillal studied the concentration of ammonia,
potassium ion, and sodium ion in red cells of rats during ammo-
nia intoxication. Ammonia, if injected intraperitoneally, was
rapidly taken up by red cells. The accumulation of ammonia was
accompanied by a specific decrease in the cellular potassium ion
content, with no significant change in the cellular sodium ion
content. The authors suggested that the ammonium ion is readily
transported from plasma into red cells in exchange with sodium ion
111
-------
and in competition with potassium ion, that the decrease in the
potassium content of the red cells was correlated chronologically
with the neurologic signs of intoxication, and that the accumu-
lation of ammonia in the brain may be accompanied by a decrease
in the intracellular potassium-ion content in a manner similar
to that in red cells. Hawkins et_ all.23 have suggested that a
likely mechanism of the pharmacologic action of ammonium ions
is an effect on the electrical properties of nerve cells. They
indicated that, when presented extracellularly, ammonium ions,
like potassium ions, decrease the resting transmembrane potential,
bringing the potential closer to the threshold for firing. This
could cause a general increase in nerve-cell excitability and
activity, resulting in convulsions.
Ammonia Excretion
H. W. Smith reported that the urinary nitrogen of the
freshwater carp and goldfish constitutes only a small fraction
of the total nitrogen excreted by these fish. Approximately
6-10 times as much nitrogen was excreted by the gills as by the
kidneys. The branchial excretion consisted largely.- if not en-
tirely, of the readily diffusible substances—ammonia, urea,
and amide or amine oxide derivatives. The less diffusible sub-
stances—creatine, creatinine, and uric acid—were excreted by
the kidneys.
112
-------
However, Goldstein et a^.2^ studied ammonia excretion in
the marine teleost, Myoxocephalus Scorpius, and accounted for
about 60% of the excreted ammonia as coming from blood ammonia;
the remainder was accounted for by the deamination of plasma
a-amino acid. They did not observe a net removal of glutamine
from plasma and concluded that the previously observed glutaminase
activity21 probably does not serve as the source of excreted
ammonia. Pequin^l perfused carp livers with ammonia to study
glutamine synthesis and ammonia excretion. He concluded that
the carp fixes the exogenous ammonia in the liver as glutamine
and then deamidates the glutamine to glutamate and free ammonia
before it reaches the gill tissue, where the ammonia is rapidly
excreted. However, Wilson and Fowlkes77 suggested that glutamine
plays an important role in ammonia metabolism of the gill, inas-
much as glutamine synthetase, glutamic dehydrogenase, and glutam-
inase are all present.21,75
Makarewicz and Zydowo41 investigated the activities of four
ammonia-producing enzymes--adenosine aminohydrolase, 5'-nucleotidase,
AMP-aminohydrolase,* and glutaminase--in the kidneys of fifteen
vertebrate species and in the gills of carp. The kidneys of lower
vertebrates, like fishes and amphibia, were able to produce more
ammonia from AMP than from glutamine. The same was true for the
gills of carp. About equal amounts of ammonia were produced from
*AMP = adenosine monophosphate.
113
-------
AMP and glutamine in the kidneys of the tortoise and chick,
but glutamine was the major source in mammals.
A substantial amount of free ammonia has been shown to be
excreted by the kidneys of uricotelic species. O'Dell et al.
reported that, in urine of chicks fed a commercial diet, about
81% of the total nitrogen was in uric acid, 10% in free ammonia,
and the rest in urea and amino acids.
Mammalian urine can contain substantial quantities of ammonia,
but excretion is not obligatory. Thus, a 24-h sample of human
urine can contain 0-2 g of ammonia. Ammonia in mammalian urine
responds to the acid-base regulatory function of the kidney.
Plasma glutamine"^ supplies a substantial portion of urinary
ammonia, but other sources may contribute. The stimulus for the
excretion of free ammonia has been well established—an acidic
pH of the urine. However, the exact mechanism is still under
extensive investigation.20'24'25'38 ,49,53,54,57,60,78
Kamin and Handler35 found that intravenous infusion of amino
acids into dogs led to a marked increase in ammonia excretion,
even in the absence of acidosis. Higher rates of ammonia formation
followed infusion of L-glutamine, L-asparagine, DL-alanine,
L-histidine, and casein hydrolysate. L-Glutamic acid, L-lysine,
and L-arginine infusion had little effect. It appears that the
kidney has the capacity to effect the net deamination of a variety
of amino acids.
114
-------
Robin et a^L.59 have reported that the intravenous administra-
tion of ammonium acetate to dogs resulted in measurable amounts of
free ammonia in expired air. Jacquez et a_l. 31,32 also found free
ammonia in expired air from normal dogs and from humans with
hepatic-induced ammonia toxicity. They concluded that it is likely
that ammonia is equilibrated between alveolar air and blood during
its passage through the pulmonary capillaries. These findings
were supported by Bloomfield et aj^. ,7 who reported the presence of
free ammonia in expired air from sheep during experimentally in-
duced urea toxicity.
-------
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123
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Ammonia in Plant Nutrition
Nitrogen constitutes approximately 2% of the dry weight of
plants, and plants supply the bulk of the nitrogen intake by
animals. On an annual basis, approximately 10 billion tons
(9 x 109 t) of nitrogen are incorporated into plants. Among
the nitrogen substances most readily assimilated by plants are
organic nitrogen, ammonia, nitrate, and diatomic nitrogen.
Relatively few present-day species are adapted to use all these
forms. Today, the major portion of plant nitrogen is derived
from nitrate produced through reduction on the part of soil
microorganism. But it has not always been thus. When the
earth had a reducing atmosphere, ammonia was undoubtedly the
major form of nitrogen utilized, and indeed the bulk of the
plant kingdom can still assimilate ammonia to some degree. As
long as ammonia was plentiful, there was little or no selective
advantage in the ability to utilize diatomic nitrogen, and it is
unlikely that nitrogenase developed.
Evolution of the Ability to Utilize Different Forms of
Nitrogen. Robbins attempted to classify plants according to
their genetic plasticity to nitrogen utilization (Table 2-3).
Although a few species (confined essentially to a few genera
of bacteria and algae) can assimilate all four major forms of
nitrogen, most plants are restricted to nitrate, ammonia, and
various forms of organic nitrogen. Only a comparatively small
group of plants can utilize only ammonia and/or organic nitrogen.
As the atmosphere became less reductive, and the pO2 began
to increase, organisms evolved with a capacity to oxidize ammonia
124
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and utilize the energy of oxidation in driving their biosynthetic
reactions. One major group of bacteria, Nitrosomonas, in the
soils of the world catalyzes the reaction
NH4+ + 3/2 O2 > N02~ + 2H+ + H20 (A g = -65 kcal/mole NH4+), (2-38)
Nitrobacter, another large group living with them, catalyze the
reaction
N02~ + 1/2 O2 > N03~ U g = - 18 kcal/mole N02~). (2-39]
These bacteria are collectively known as the nitrifying bacteria.
Under early earth conditions, the net effect of the nitrifying
bacteria was to cause nitrate to amass at the expense of ammonia.
The great nitrate deposits of the world, such as those in Chile,
TABLE 2-3
Groups of Plants by Forms of Nitrogen Utilized—
Grout
II
III
IV
Plants
Some fungi (Endomyces,
Phycomyces) , some bac-
teria, some species
of Euglena
Some fungi (Mucor,
Rhizopus) , some bacteria
Organic
Nitrogen Ammonia
X
X X
N Molecular
Nitrate Nitrogen
Most bacteria, fungi,
algae, and higher plants
Some bacteria, actinomy-
cetes, and blue-green
algae
X
X
X
a 74
Derived from Robbins.
125
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are attributed to the activity of nitrifying bacteria. Distri-
bution of the nitrifying bacteria is such that, when ammonium
salts are added to the soil as fertilizer, there is a very rapid
conversion to nitrate. Chemical examination shows that compara-
tively little ammonium or nitrite is present in soil; nitrates
predominate. The speed with which ammonium compounds are trans-
formed to nitrates depends largely on moisture supply, temperature,
and pH.
Ammonium is constantly being formed in the soil as a result
of the action of ammonifying bacteria on organic matter. But
the quantity present is generally only a few parts per million
of soil. Nitrates produced from the ammonia are all dissolved
in the soil water and readily lost through leaching, unless the
soil dries out; but much of the ammonia can be held as ammonium
ion in the soil particles, which serve as an ion-exchange matrix.
One can calculate the total quantity of inorganic nitrogen in
the soil by determining the difference between the rate of produc-
tion from organic matter by soil organisms and the rate of re-
moval by leaching, by growing plants, and by other nitrogen-
assimilating organisms of the soil. Correspondingly, the ratio
of nitrate to ammonia depends on the rate of oxidation of ammonia
to nitrates, the uptake of nitrates by plants, and the loss of
nitrates through leaching.
In native grassland soils, the bulk of the readily assayable
mineral nitrogen is present as ammonia; both the ammonia and
126
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nitrate concentrations remain relatively constant year around.
In contrast, cultivated soils, particularly if they are not too
acid, have a fairly constant but low concentration of ammonia
nitrogen and a nitrate content of 2-20 mg/kg of farmland soil,
up to 60 mg/kg of rich garden and flood plain soil, and up to
100 mg/kg of some tropical soils during the first days of the
dry season. Nitrification requires a good oxygen supply;
consequently, the process occurs most readily in well-aerated
and well-drained soils.
Gaseous Ammonia, Ammonium Salts, and Nitrate Utilization by
Plants. Gaseous ammonia at low concentrations can be assimilated
by plants. This is most readily shown in nitrogen-deficient
plants, because the yellow-green leaves turn green soon after
exposure to ammonia. 57 , 76 , 90 , 92 Although it was thought for a
time in the nineteenth century that gaseous ammonia was the chief
source of nitrogen used by plants, Boussingault12' helped to
lay that notion to rest by showing the value of nitrate for sun-
flower (Helianthus) and cress (Lepidium). He also detected it
in the sap of banana (Muca), beech (Fagus), hornbean (Carpinus),
grape (Vitis), and walnut (Juglans). In a comparative study,
ViHe^ demonstrated that potassium nitrate is a better nitrogen
source, for a number of species, than are ammonium salts. During
the last century, this discovery was verified many times. For
example, Bineau10 showed that many freshwater algae utilize both
ammonia and nitrate. Pasteur67 reported that yeast can utilize
127
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ammonia in the biosynthesis of protein; but some yeasts, including
Saccharomyces acetoethylicus8 and Hansenula anomala, utilize
nitrate.
It has been known since the carefully controlled experiments
of Muntz59 that many seed plants—including beans (Vicia, Phaseolus)
maize (Zea), barley (Hordeum), and hemp (Cannabis)—can be grown
satisfactorily with ammonium salts.. Similar findings were re-
ported soon after for mosses, diatoms, green algae, and duckweed
(Lemna minor).88 Hutchinson and Miller38 extended the earlier
work and demonstrated direct utilization of ammonia from sterile
nutrient and sand cultures. Resolution of the problem of vari-
ability in results of different investigators came later.66
It is not known that absorption and assimilation of nitrate
and ammonium are sensitive to many environmental factors. Inter-
pretation and comparison of results are difficult, owing to
genetic or species differences, pH, nonnitrogenous nutrients,
stage of development of the plant, and nature of carbohydrates
in the plant.2'62'63'86
Plants that grow better with ammonia than with nitrate include
potato (Solanum tuberosum), pineapple (Ananas comosus), screw
pine (Pandanus veitchii), and rice (Oryza sativa) seedlings.
However, rice gains the ability to assimilate nitrate when
mature.11 In suspension-cultured rice cells, Yamaya and Obira98
have found a protein that inactivates nitrate reductase. Further-
more, activity of this factor fluctuated during the growth period.
128
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Chenopodium album seems to utilize only ammonium; the nitrate
that it accumulates is not utilized. Several other members of
the Chenopodiaceae also accumulate nitrate and have little or
no ability to reduce it.55
Although the normal concentration of nitrate in most plants
rarely exceeds a few hundred parts per million, species from all
major groups of the plant kingdom, native and cultivated, have
been reported to accumulate it. Accumulation is a natural and
usually temporary occurrence that results from uptake of nitrate
in excess of capacity to reduce and assimilate it. A buildup
depends on the genetic makeup of the plant, the nitrate-supplying
power of the soil, and environmental conditions under which the
plant is grown. Furthermore, nitrate concentrations differ with
age and organs of the plant sampled. It has been known since
189553 that fodder plants accumulating excessive nitrates can be
toxic to animals that ingest them.
"Cornstalk poisoning" and "oat hay poisoning" of cattle was
clarified by Davidson e_t al_. ,27a wjrio showed that nitrate was re-
duced to nitrite after ingestion. On absorption of nitrite into
the bloodstream, it reacts with hemoglobin to form methemoglobin.
Signs of hypoxia may follow.
Concern over human ingestion of nitrate/nitrite arose in
1945, when Comly described methemoglobinemia in babies given
formula prepared with well water of high nitrate content.24
Additional reports followed rapidly; within 5 years, nitrate/nitrite
129
-------
ingestion through food, feed, and water was recognized as poten-
tially hazardous for man and livestock.47 Extensive experimenta-
tion has resulted in a clear confirmation of the acute effects of
nitrates and nitrites in livestock. Attempts, however, to induce
chronic poisoning with nitrates and nitrites have generally been
unsuccessful. In sum, there is insufficient experimental evidence
to relate any chronic condition to long-term consumption of sub-
lethal quantities of nitrate/nitrite.28 Several reviews on the
importance of nitrate accumulation in plants have helped to
clarify the issue. 52 ' 8^ ' 97
Reduction of nitrate to ammonia is achieved in two steps in-
volving nitrate reductase and nitrite reductase. Nitrate reductase
is currently considered to be a complex consisting of at least two
components. One of these components transfers electrons from
NADH to the flavin-containing component, and a subunit then trans-
fers electrons by way of molybdenum to nitrate. Recently, it has
been proposed19 that this monomer exists as a tetrahedral trans-
membrane tetramer functioning both in nitrate transport and in
reduction. An ATPase is visualized as being closely associated
with each member of the nitrate reductase tetramer. The tetramer
is presumed to be oriented so that one monomer is exposed to the
outside of the plasmalemma and the other three are exposed to
the cytoplasmic side. This orientation can yield a reaction mecha-
nism in which the transport and reduction of one nitrate ion are
accompanied by the transport of two additional nitrate ions (i.e.,
130
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a 3:1 transport-reduction ratio). The proportion of transported
nitrate actually reduced could be modulated by thiol-reversible
ADP inhibition of reduction. More likely, however, the inhibition
is the result of adenylate binding on the nitrate-activated ATPase
to which nitrate reductase is tightly coupled. To account for the
lack of accumulation of nitrate in some tissues, in some algae,
and in chloroplasts, Butz and Jacksonl9 suggested that an analogous
system consisting of a nitrate reductase dimer plus an ATPase
spans the membrane. According to this model, only transported
nitrate acts as a substrate for reduction, and intracellular
nitrate is not readily reduced. Furthermore, adequate means are
provided for environmental impact and age on the system.
Although leaves can accumulate nitrate when there is little
or no reduction of nitrate, there is good evidence that the stems
often accumulate approximately three-fourths of the free nitrate.
Presumably, nitrate reaching the leaves becomes reduced as leaf
growth progresses. This has been found to be the case in several
species of Amaranthus, Avena sativa, Borago officinalis, Triticum
sativum, buckwheat (Fagopyrum escudentum), Bryophyllum calycinum,
pineapple (Ananus comosus), sunflower (Helianthus annuus), celery
(Apium graveolens), rye grass (Lolium perenne), and Salvia refLexa. 5
Many planktonic algae utilize ammonia and nitrate equally well.^2
Chlorella, however, has been found to utilize ammonia only, even
when nitrate is present in the same nutrient medium.25 This is
probably the result of ammonia's blocking of nitrate reductase
131
-------
activity. In some fungi such as Scopulariopsis brevicaulis and
Myrothecium verrucaria, even very low concentrations of ammonia
inhibit the uptake of nitrate. Cultures grown with ammonium
nitrate will not utilize nitrate until the ammonium has been
practically exhausted.573 The same is true for sweet potatoes.31
But this pattern of suppression is not universal; thus, uptake of
nitrate by radish root tissue is unaffected by the presence of
ammonia in the growth medium. As noted earlier, ammonia nitrogen
is utilized better than nitrate by pineapple roots78 and potato
sprouts.8^ The reason for this is still obscure.
The pH of the growing medium affects the absorption of both
ammonium and nitrate. As a result of ion-exchange reactions
during uptake by roots, pH changes occur in the growing medium
of plants grown with either ammonium or nitrate. Growth media
with ammonium become more acid, and those with nitrates become
more basic. The tendency toward acidification of soils supplied
with ammonium salts was recognized and explained more than a
century ago.72 The only method yet devised to maintain a steady
pH when ammonium is supplied is to use a continuous-flow nutrient
culture technique; the flow must.be fairly rapid, because of the
massive hydrogen-ion exchange taking place in large root systems.
The optimal pH range for the growth of most plants is approximately
5.6-6.5. More plants tolerate relatively high pH than relatively
low pHs. However, some plants, such as tomato, continue to absorb
appreciable amounts of ammonium at a pH of 4.0.
132
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The inorganic ion composition of nutrient solution in the
soil has a significant effect on the uptake of both ammonium
and nitrate by plants. For example, maize, vetch, and oats sup-
plied with ammonium salts in the nutrient solution have lower
fi 9
calcium and magnesium contents than when nitrate is present.
Higher calcium concentrations are required in nutrient solutions
containing ammonia than in those with nitrate. The calcium re-
quirement is lower at low pHs; the net effect is a widening of
the range of pH at which good growth can be obtained with ammo-
nium. Similar results have been recorded for cotton, maize,
barley, citrus trees, and tomato. The beneficial effect
of calcium is well shown by cotton: with adequate calcium in
the nutrient medium, it utilizes ammonium at a pH of 3.0, whereas
39
increasing the magnesium content decreases the uptake of ammonium.
Phosphate-nitrogen source concentrations are also important, as
is illustrated by the fact that barley seedlings grown with am-
monium contain more phosphate than those grown with nitrate.
Micronutrient requirements differ with the nitrogen source.
58 1
For example, tomato and barley, cauliflower, Aspergillus
Q o o o 96
niger, ' and Anabaena cylindrica all require more molybdenum
with nitrate than with ammonium. This is probably related to the
fact that nitrate reductases are molybdoproteins.
Oxygen tension is also an important factor in nitrogen
utilization in plants, as shown in experiments with cotton
seedlings. At oxygen tensions of 10-15% of atmospheric pres-
48
sure, nitrate is assimilated much more readily than is ammonia.
133
-------
Plants supplied with nitrate commonly require less oxygen than
.50
those receiving ammonia.
A high intake of nitrogen is required for rapid growth of
young seedlings. Several plant species have been tested to deter-
mine which form of nitrogen is preferentially assimilated during
^ „ 21,23,70,77,80,81
the life cycle. It has been found repeatedly
that more ammonium than nitrate is removed by young seedlings
from solutions that contain both ions. As seedlings develop,
nitrate is preferentially removed from such solutions. Rice is
an excellent example and has often been studied in an effort to
27 40 43
understand this form of biochemical differentiation. ' '
Although the biochemical reason for the developmental shift from
ammonia preference to nitrate preference has not been ascertained,
progress has been made. Rice seedlings, 4-6 days old, grown with
ammonium salts contain no nitrate reductase; in comparison, seed-
lings grown only with nitrate produced nitrate reductase. A
protein-like inhibitor of nitrate reductase has been found in
40 98
rice roots and rice cells in suspension culture. Cultured
cells of soybean and peanut also appear to be very rich in the
98
same inhibitor. The factors that promote the production of the
inhibitor are not known.
Deficiency or absence of enzymes associated with inorganic
nitrogen utilization has been demonstrated in the young embryos
*3 c "7 T
of several species. ' Rijven35 found that young embryos of
Anagallis arvensis, Anabidopsis thaliana, Capsella bursa-pastorijs,
Sisymbrium orientale, and wheat were unable to utilize either
134
-------
ammonium or nitrate, but could grow well with alanine, glutamic
acid, and glutamine. Nitrate reductase was often produced before
95
nitrite reductase. Wetherell and Dougall have determined the
nitrogen requirements for in vitro embryogenesis in Caucus carota.
Nitrate at concentrations of 5-95 mM (potassium nitrate) was asso-
ciated with very low embryogenesis. As little as 0.1 mM ammonium
chloride added to the nitrate medium allowed some embryogenesis,
and 10 mM ammonium chloride was near optimal when potassium ni-
trate was at 12-40 mM. Glutamine, glutamic acid, urea, and
alanine could individually partially replace ammonium chloride
as a supplement to potassium nitrate<. It was concluded that a
reduced nitrogen source is required, at least as a supplement to
nitrate, for iri vitro embryogenesis of cultured wild carrot
tissue.
The Nature of Ammonia Toxicity. The carbohydrate concentra-
tion of the whole plant is crucial in inorganic nitrogen utili-
zation. Unlike nitrate, ammonia requires no reduction and is
toxic at relatively low concentrations. Unless it is quickly
combined with a carbon compound (a-ketoglutarate, glutamate, etc.)
and not allowed to accumulate, toxic symptoms are likely to
develop. The symptoms may be as mild as tipburn or as drastic
as death. Common symptoms of 15- to 22-day-old tomato seedlings
exposed to unbuffered solutions containing nitrogen solely in
the ammonium form show weakly developed, thickened, sparsely
branched, discolored root systems, marginal necrosis of some
135
-------
leaves, wilting, very dark green foliage, easily bruised stems,
r o
and restricted growth.
Ammonia toxicity symptoms are probably traceable to several
metabolic perturbations. Both photosynthetic and respiratory
pathways can be caused to malfunction by ammonia. In 1960, Vines
and Wedding demonstrated the poisoning effect of ammonia on
steps in the tricarboxylic acid cycle. Their work has been ex-
tended, and it is now clear that there is a close interrelation
between the ammonia concentration and respiratory metabolism,
including oxygen uptake, glycolysis, and the TCA cycle. With
respect to photosynthesis, Gibbs and Calo showed that ammonium
salts uncouple photophosphorylation in isolated spinach chloro-
plasts, and their finding was confirmed by Avron with Swiss
41
chard chloroplasts and by Kanazawa et al. with intact Chlorella
cells.
It has not been clearly established whether ammonia enters
root cells in an ionic or undissociated molecular form. In
intact maize plants, Becking showed , that uptake of ammonium at
low concentration is accomplished by an equivalent loss of hydro-
gen ions from the roots. But at higher concentrations of ammonia,
hydrogen-ion exchange accounts for only 75-80% of the ammonium
uptake. Presumably, there is an increased transport of anions
to balance the charge difference. In agreement with'the hypo-
thesis that ammonia is taken up by corn as the ionic species,
Becking found that the rate of ammonia uptake is ,the same at a
pH of 4.6 as it is at a pH of 6.0. When the ammonium concentration
136
-------
was varied at either pH, the relationship between concentration
and rate of uptake was hyperbolic, indicating a saturable up-
take system.
49
MacMillan concluded that ammonia uptake by the mycelia
of Scopulariopsis versicolor occurs by diffusion of the undis-
sociated molecule, inasmuch as the rate, of uptake was independent
of the rate of removal by assimilation. In addition, ammonia
was lost rapidly (up to 50% within 15 min) when mycelia were
transferred to an ammonia-free buffer. Respiratory poisons had
little effect on the concentration of ammonium in the mycelia.
MacMillan reasoned that, if ammonia diffuses passively into a
mycelium as the undissociated molecule, the uptake rate would
depend on the concentration gradient between the external nutrient
solution and the inside of the mycelium. Because pH affects the
degree of dissociation, MacMillan kept the mycelia in a medium
of constant ammonium concentration, varied the pH of the nutrient
solution, and determined the ammonium content and pH of the
mycelial cells. The pH in the protoplasm rose only slowly while
the pH of the bathing nutrient solution rose from 5.0 to 9.0.
Thus, this experiment provided supporting evidence for the dif-
fusion hypothesis.
Symbiotic Nitrogen Fixation. In nature, biologic nitrogen
fixation is essential in maintaining a balance that supports
plant and animal life. Both symbiotic and nonsymbiotic nitrogen-
fixing agents reduce nitrogen from the air and serve in supplying
137
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the requirements of land and aquatic plants. Although estimates
of the amounts of nitrogen fixed by symbiotic and nonsymbiotic
organisms are available, the accuracy of such figures is highly
debatable, because the list of species known to fix nitrogen is
being added to continuously.17 Furthermore, worldwide sampling
for distribution of known nitrogen-fixing organisms has not been
systematic. The most intensively studied symbiotic nitrogen-
fixing contributors are leguminous plants. Approximately 13,000
species of the Leguminosae have been described; most of those
tested for nitrogen fixation have been found to possess root
nodule bacteria--usually a species of Rhizobiura--and are
variously capable of fixing nitrogen.
Such leguminous crops as peas, beans, alfalfa, clover, and
soybeans often fix nitrogen at over 100 kg/ha per year. The
physiologic and biochemical nature of the symbiosis has been
under investigation for some time, and great strides have been
made since 1975 in understanding this form of mutualism. One
can only infer how rhizobia normally incapable of fixing nitrogen
in the laboratory are converted to nitrogen-fixing bacteroids in
plants, but several strains of free-living Rhizobium species
have been induced by environmental manipulations to produce
nitrogenase and fix nitrogen wholly independently of the green
plant. tiii, Thus, the higher plant's contribution
to the induction of nitrogenase is being clarified.
138
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Until the 1940's, the processes of nitrogen fixation were
studied chiefly in root nodules of leguminous plants. With
application of the concepts of comparative biochemistry to the
problem, however, it was presumed that free-living nitrogen-
fixing forms probably carry out the process in the same or an
analogous manner. This assumption is proving to be correct.
In reality, the symbiotic rhizobia and even the endophytic
nodule-forming actinomycetes that fix nitrogen in Alnus,
Ceanothus, and Myrica are separated from their host cells by
a membrane. In a sense, therefore, the endophytes are outside the
cell, and the exchange between the symbionts takes place across
the "host's" membranes. Goodchild and Bergersen34 documented
this view by demonstrating with the electron microscope that
nodulation by rhizobia in soybean is initiated by infection
threads that penetrate cell walls and push back the plasmalemma.
Thus, when a cell is traversed by an infection thread, the thread
is encased in a plasmalemma tubule. Ultimately, a tetraploid
cell is reached in the root cortex; bacteria are released from
the infection thread. They then attach themselves to the enveloping
host membrane, and the membrane folds around each bacterium as
it floats free into the cytoplasm of the tetraploid host cell.
The host cell or cells proceed to divide and produce the core
of the nodule. Meanwhile, the bacteria divide within their sacs
and begin to produce the complex enzyme nitrogenase. Similarly,
the actinomycete endophytes of Alnus, Ceanothus, and Myrica are
surrounded by a membrane of apparent host plant origin.79
139
-------
The nitrogenases from symbiotic and free-living forms of
bacteria and algae seem to have a great deal in common. Cell-
free fixation of nitrogen has been achieved with extracts from
Clostridium pasteurianum,2° Azotobacter and Rhodospirilum rubrum,15
heterocysts of blue green algae,36 and Rhizobium bacteroids from
soybean nodules.45 Thus far, details of the properties of nitro-
9 ft
genase are available only from C. pasteurianum and Azotobacter
vinelandi,. 16/44 but it is now clear that nitrogenase consists of
two easily separable components: an iron-molybdenum protein of
molecular weight approximately 200,000 and an iron protein of
molecular weight approximately 40,000 that is cold-labile. The
enzyme and its subunits from all examined sources are oxygen-
sensitive. The substructures of the two major components are
still unclear.
For technical reasons, it was not possible to determine
the product of nitrogen fixation definitively until nitrogen-15
methods were developed. Newton e_t a_1.61 in 1953 demonstrated
directly that ammonium is the first product of nitrogen fixation.
Furthermore, they and others who have since tried could not detect
any other free intermediates in the reductive sequence. Bergerson
and Turner^ showed that all nitrogen-15 reduced by Rhizobium
japonicum bacteroids appeared rapidly as [15N]ammonium in super-
natant fractions, supporting the conclusion of involvement of
plant-ammonium assimilatory enzymes in utilization. O'Gara and
Shanmugam64 used free-living Rhizobium japonicum and reported
that 94% of the ammonium ion is exported as such.
140
-------
Because the process of ammonium formation from nitrogen
involves the transfer of three electron pairs, it had been
assumed that at least two intermediates might be involved.
They have not been found, so it may be that all the inter-
mediates remain tightly bound to nitrogenase until ammonium is
produced. A second possibility is that the molybdenum-iron
protein, which contains an abundance of iron, could serve as a
reductant, storing sufficient electrons to effect an almost
instantaneous reduction of nitrogen to ammonia. A third possi-
bility is that the N=N bond is disrupted at the active site of
nitrogenase, with the positively charged nitrogen units being
immediately reduced to ammonia.-^
Once ammonium is produced within the endophyte, it can be
rapidly used in the formation of glutamine.29,60,85 This is
important, because, if ammonium is allowed to accumulate, it
inhibits nitrogenase biosynthesis. Once ammonium is stabilized
in glutamine, it can be utilized in different ways. It soon
finds its way into glutamic acid and later into aspartate,
alanine, and citrulline—the latter via carbamyl phosphate. Any
or all of these forms of nitrogen can be exported from the cells
of the nodule and utilized by green plants, either in the root,
stem, leaves, or fruits; glutamine and glutamic acid are the most
frequently exported. Interestingly, glutamic acid, alanine,
asparagine, lysine, histidine, and phenylalanine are better
sources of nitrogen for aseptically grown red clover (Trifolium
141
-------
pratense) than either ammonium salts or nitrates; glutamic acid
n *-\
and asparagine are the best nitrogen sources tried.-3
Glutamine synthetase has been proposed as a positive regulator!
of nitrogenase in nitrogen-fixing bacteria. In enteric bacteria,
glutamine synthetase has both catalytic and regulatory functions.
In Klebsiella pneumoniae, which is capable of fixing nitrogen in
culture, nitrogenase expression is regulated by glutamine syn-
thetase. A Rhizobium cowpea 32H1 strain deficient in glutamine
synthetase activity is also deficient in nitrogenase activity.
Recently, Ludwig and Signer^3 have reported evidence that
glutamine synthetase plays a role in the regulation of nitro-
genase activity in both free-living rhizobia and bacteroids,
but the mechanism is not yet known. The results of Brown and
Dilworthl4 with bacteroid preparations suggest that ammonia
assimilation directed at glutamine synthetase and glutamate
synthetase does not occur in the bacteroid, but rather in the
associated plant cell, where the same two plant enzymes are
present in abundance, as well as NAD-linked glutamate dehydro-
genase activities.
142
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ATMOSPHERIC TRANSFORMATIONS
Five types of reactions that are relevant to the atmospheric
chemistry of ammonia are reviewed in this section: aqueous-phase
reactions, with emphasis on the role of ammonia in the formation
of sulfate aerosols; heterogeneous reactions involving ammonia
interactions with soot particles; thermal reactions of ammonia
153
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with sulfur dioxide and ozone; photochemical reactions that result
in formation and further reactions of the amino radical, NH2;
and reactions by which ammonia is involved in acid precipitation.
Several other important aspects of the atmospheric chemistry of
ammonia are not reviewed here: the formation of ammonium nitrate
aerosols by reaction of ammonia with photochemically produced
nitric acid (this has been extensively reviewed in the NRC report
on nitrates71) and the atmospheric chemistry of such ammonia-
related pollutants as amines and nitrosamines (despite growing
concern and active research on them, adequate review of these
pollutants would greatly exceed the scope of this section).
Aqueous-Phase Reactions
The liquid-phase oxidation of sulfur dioxide, leading to
the formation of particulate sulfate, has been extensively studied
for over 50 years. Among the major factors that affect the rate
of aqueous sulfur dioxide oxidation in the atmosphere are the
relative humidity, the temperature, the pH, and the presence of
trace-metal ions that catalyze the reaction.3'17'20'35 Because
of the increasing solubility of sulfur dioxide in aqueous solu-
tions of decreasing acidity, the rate of aqueous sulfur dioxide
oxidation increases with pH. (It should be noted here that the
pH of water droplets in unpolluted air is close to 5.6, which is
expected from the natural carbon dioxide buffer.) Not surprisingly
the role of ammonia in the aqueous oxidation of sulfur dioxide has
been studied in detail, because traces of ammonia in the atmosphere
directly affect the pH of water droplets.
154
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Junge and Ryan^6 first investigated the effect of ammonia
in the metal-catalyzed oxidation of sulfur dioxide in water.
They concluded that the maximal sulfate formation is a linear
function of the sulfur dioxide partial pressure in the air and
that the presence of ammonia enhanced sulfate formation. They
estimated that sulfate at about 3 ug/m would be formed in a
"clean" atmosphere containing ammonia at 3 ug/m3 and sulfur dioxide
at 20 pg/m3. Increasing the ammonia and sulfur dioxide concen-
trations to 10 and 500 ug/m , respectively, would result in the
formation of sulfate at 26 pg/m^--nearly a tenfold increase.
Ambient measurements of sulfate, sulfur dioxide, ammonia, and
water content in urban atmosphere conducted by Tomasi et al. ^8
were found to be satisfactorily accounted for by Junge and Ryan's
model. The formation of ammonium sulfate in water droplets ex-
posed to sulfur dioxide and ammonia was experimentally studied
by van den Heuvel and Mason^l at much higher sulfur dioxide and
ammonia concentrations than those encountered in polluted air.
Extrapolation of their data to atmospheric concentrations indi-
cates a sulfur dioxide conversion rate of several percent per
minute, which is rather large in comparison with available
atmospheric data.
Scott and Hobbs^ investigated the uncatalyzed aqueous oxi-
dation of sulfur dioxide in the presence of ammonia and carbon
dioxide. They proposed the following mechanism:
155
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S02(g) + H20 * S02-H20,
S02-H20 J HS03~ + H+, (2-41)
- en 2- + H+ (2-42)
NH3(g) + H2° - NH3'H2° (2~43)
NH3-H20 t NH4+ + OH~, (2-44)
C02(g) + H2° " C°2'H2°' (2"45)
C02-H20 ^ HC03~ + H+, (2-46)
HC03~ ^ C032~ + H+, (2-47)
H20 ^ H+ + OH~. (2-48)
From this and van den Heuvel and Mason's data, they deduced the
rate law (time in seconds):
d(S042-)/dt = 1.7,x 10~3 (S032~) , (2-49)
which was used in calculations of sulfate formation in the
atmosphere. These calculations indicated atmospheric rates of
sulfur dioxide oxidation of about 2-3%/h. Similar rates were
156
-------
obtained by Miller and de Pena.^9 AS opposed to those of Junge
and Ryan, Scott and Hobb's calculations did not predict the
linear dependence of sulfate formation on sulfur dioxide partial
pressure.
With the mechanism of Scott and Hobbs modified so as to
include sulfite oxidation data of Fuller and Crist,20 McKay^6
predicted much higher sulfate formation rates, up to 13%/h.
McKay's calculations also indicated that the rate of ammonium
sulfate formation is significantly higher at lower temperature,
owing in part to the increasing solubility of sulfur dioxide and
ammonia at lower temperatures. The same temperature dependence
has been reported by Freibergl^ for the iron-catalyzed oxidation
of sulfur dioxide in water. (It is well known that severe pollu-
tion episodes in the Meuse Valley of Belgium, in Donora, Pennsylvania,
and in London, England, were all associated with high relative
humidity and low temperatures.) The effect of ammonia concentra-
tion on ammonium aerosol formation, as calculated by McKay, is
shown in Figures 2-6 and 2-7. Figure 2-6 shows the effect of
ammonia for constant partial pressures of ammonia and sulfur
dioxide, i.e., assuming that ammonia and sulfur dioxide concentra-
tions are not significantly depleted as sulfate builds up. Cal-
culations made with the assumption of progressive depletion of
ammonia are shown in Figure 2-7. They apply to droplet: air
volume ratios of 3 x 10~8:1 and 10~7:1. The time necessary for
the conversion of 50% of the ammonia to ammonium sulfate is indi-
cated in Table 2-4 for various typical ammonia and sulfur dioxide
157
-------
FIGURE 2-6
Effect of temperature and ammonia
concentration on sulfate buildup.
Initial concentrations: sulfur
dioxide, 20 ug/m ; ammonia,
2.7 ug/m3 (A,D), 5.3 ug/m3 (B,E),
and 10.6 ug/m3 (c,F). Temperature:
25°C (A,B,C) and 15°C (D,E,F). Re-
printed with permission from McKay -
66
158
-------
Asymptote
'of curvt G
FIGURE 2-7.
Effect of a limited supply of ammonia
and sulfur dioxide at 15°C, with vary-
ing initial ammonia concentration.
Reprinted with permission from McKay.66
Droplet:Air
Volume
Ratio
0
3 x 10~8:1
Sulfur Dioxide at 20 ug/m3
Ammonia Concentration,
2TT "571 IoT6
ABC
D E F
GUI
159
-------
TABIE 2-4
Time Required for Conversion of 50% of Arcngnia
to Anmonium Sulfate3.
Time, h. and min
Artmonia Concentration,
Droplet : Air
Temperature , Volume
°C Fatio
25 10~7:1
3 x 10"8:1
15 10-7:1
3 x 10~8:1
yg/rn^
2-7 5-3 10-6 5-3
Sulfur Dioxide Concentration,
20
0,35
>5
0,10
2,05
20
1,20
>5
0,17
4,15
20
3,30
>5
0,36
>5
20_
1,20
>5
0,17
4,15
5-3
yg/m3
40___
0,38
>5
0,10
2,00
5-3
IOC?.
0,20
5
0,07
1,05
5-3
20°
0,10
2,15
0,05
0,32
a£ata from McKay.
66
160
-------
concentrations and for two temperatures and volume ratios. For
comparison, sulfate aerosol concentration-time profiles calculated
by Beilke et. al. from the model of Scott and Hobbs are shown in
Figure 2-8.
Despite the more recent work of Beilke, Lamb, and Muller,^
who also reviewed the pertinent literature on the oxidation of
sulfur dioxide in water solution without the participation of
metal catalysts, there is still no agreement about the "best"
rate constant that one should adopt for the aqueous oxidation
of sulfur dioxide in the presence of ammonia. However, the data
indicate that this reaction is one of the major pathways for the
formation of ammonium sulfate particles in the atmosphere.
Heterogeneous Reactions
Novakov and co--workerslO, 73 investigated the role of ammonia
in the formation of particulate compounds by nitric oxide-soot
and ammonia-soot surface reactions. Soot particles formed in the
combustion of fossil fuels consist of finely divided carbon with
graphite-like structure. Surface discontinuities in the graphite
structure constitute active sites on which polar functional groups-
such as carboxyl, -COOH, and hydroxyl, -OH—are retained by chemi-
sorption. Using X-ray photoelectron spectroscopy, Novakov and
co-workers examined the thermal and vacuum behavior of ambient
particulate samples and identified a third form of ammonium in
addition to ammonium nitrate and sulfate. This more volatile
form of ammonium was later generated in laboratory experiments
161
-------
FIGURE 2-8.
Formation of sulfate as a function of time for
various concentrations of sulfur dioxide and
ammonia at 3 and 25°C, from the model of Scott
and Hobbs. Reprinted with permission from
Beilke et al.5
162
-------
conducted with nitric oxide-soot and ammonia-soot systems at
ambient temperature, which led to the formation of carboxyl and
hydroxyl ammonium surface complexes. Reaction of nitric oxide
and ammonia with soot at higher temperature led to the formation
of amine, amide, and nitrite-surface complexes (Figure 2-9).
These heterogeneous reactions are undoubtedly important in com-
bustion processes (for example, automobile exhaust) that generate
relatively high concentrations of soot, nitric oxide, or ammonia.
However, the importance of these heterogeneous reactions in the
atmosphere, where both soot particles and ammonia are present
at low concentrations, remains to be determined.
Thermal Reactions
Only one thermal reaction involving ammonia seems to be
relevant to the formation of ammonium sulfate in the atmosphere:
the anhydrous reaction between ammonia and sulfur dioxide,
+ S00 i (NH^)n so? (s) • (2-50)
-J/v Z / \ J 1 1 ^-
(g) (g)
Kushnir e_t a_1.50 observed the formation of solid compounds when
ammonia and sulfur dioxide reacted in the absence of water over
a temperature range of - 70 to + 30°C Further reaction of these
solid products with traces of water yielded ammonium sulfate.
These products were identified by Scott e_t al.85 to be amidosul-
furous acid, NH3S02/ and ammonium amidosulf ite , (NH3)2SO2. The
former product was favored when sulfur dioxide was in excess, and
9
the latter when ammonia was in excess. Carabine et al. and
163
-------
ONHd
phenolic hydroxyl
ammonium complexes
carboxyl
ammonium
complexes
amides
amines
nitriles
FIGURE 2-9.
Formation of particulate nitrogen compounds on soot
particles. Reprinted with permission from Chang and
Novakov . 10
164
-------
Arrowsmith et al . further investigated the nucleation rate and
size distribution of these aerosol products; Lamb^l suggested
that these compounds might be stable at low temperature under
conditions that prevail in the lower stratosphere (- 70°C) . With
Scott's estimate of the vapor pressure of amidosulf urous acid
at - 70°C to be about 10~7 torr, Kiang, Stauffer, and Mohnen48
concluded that the highly deliquescent amidosulfurous acid may
undergo heteromolecular nucleation--and therefore compete with
NH + S0. + NHS02. . , (2-51)
NH3S02. . ,
J (9)
NH3S02(g) + H2°(g) - NH3S02 (aqueous droplet)
the oxidation of sulfur dioxide followed by heteromolecular
nucleation of water and sulfuric acid into sulfuric acid droplets
oxidation _ ,. __.
S02 -y S03, (2-53)
+ HoO, . -»• H2SO. , (2-54)
(g) 2 (9) 2 4(g)
H SO9 + H9O + H7O, v -> H7S04 (2-55)
^ (g) (g) (g) (aqueous droplets)
and with the incorporation of gaseous ammonia and sulfur dioxide
into previously formed sulfuric acid droplets. For these three
mechanisms, further oxidation (reactions 2-51 and 2-52) and reac-
tion with ammonia in the liquid phase would result in the formation
165
-------
of ammonium bisulfate, NH4HS04, or ammonium sulfate, (NH4)2SO4.
Mechanisms similar to reactions 2-51 and 2-52 may also account
for the formation of ammonium chloride aerosol,38'42'48'89 which
has been observed at trace concentrations in the polluted tropo-
sphere (see Chapter 4).
Despite the availability of more recent data on the thermo-
chemistry52,53,67 and dynamics36'90 of the aerosol-forming thermal
reaction between ammonia and sulfur dioxide, there is no consensus
as to its possible importance in the atmosphere.18 Until more
definitive studies—especially at realistic concentrations of
sulfur dioxide and ammonia (i.e., parts per billion)—are con-
ducted, this reaction should not be dismissed as a possible route
in the formation of atmospheric ammonium sulfate.
The formation of ammonium nitrate, NH^NOo, aerosols has been
studied by Heicklen and co-workers, who investigated the thermal
reactions involving ammonia and nitric acid, HONC>2, and ammonia
and ozone. 3;'->f'° They showed that ammonia and ozone react to
produce ammonium nitrate according to the overall stoichiometric
reaction:
2NH + 40 -> 402 + H2O + NH4NO3. (2-56)
Minor amounts of nitrous oxide and nitrogen were also reported.
In the vapor phase, the monomer ammonium nitrate is mainly dis-
sociated into nitric acid and ammonia:
NH4NO3 + NH3 + HONO2. (2-57)
166
-------
After an induction period, particle production occurs according to:
+ 8HONO,, -> 8NHN03 . (2-58)
The multiple stoichiometry indicates the size of the molecular
cluster required for nucleation. Ammonium nitrate particles then
grow by condensation according to the following mechanism:
HON02 + (NH4N03)n £ (NH4N03)n HON02, (2-59)
NH3 + (NH4N03)n HON02 -> (NH4NO3)n + -,_, (2-60)
in which Reaction 2-59 is rate-determining.
In this comprehensive study, crystals of ammonium nitrate
were produced at atmospheric pressure in nitrogen and at 25°C
from ozone and ammonia at pressures ranging from 8 x 10 to
12 x 10 torr and 0.11 to 1 torr, respectively. The possible
significance of the reaction as a route for ammonium nitrate
aerosol production in the atmosphere was not discussed by the
authors.
Hamilton and Naleway32,33 observed that the atmospherically
important recombination reaction of the hydroperoxyl radical, HC>2,
H02 + H02 ->- H202 + O2, (2-61)
is increased by a factor of - 2.5 at ambient temperature when
water or ammonia is added at a few torr. This is due to the
167
-------
formation of 1:1 complexes--
H02 + H20 1 H02 ' H20, (2-62)
H02 + NH3 + H02 • NH3 (2-63)
—which are more reactive than hydroperoxyl radical toward a
second hydroperoxyl radical. Although the HC>2 ' NH3 complex is
more stable than the HO2 • H20 complex, this mechanism should
not be important at the low ammonia concentrations typical of
the atmosphere.
Photochemical Reactions
There is no known photochemical reaction that leads to the
production of ammonia in the atmosphere. Photochemical reactions
that account for the destruction of ammonia include:
• Photolytic dissociation at wavelengths < 2200 A,
which results in the production of amino and ammonia
radicals--
NH3 + hv -y NH2 + H, (A < 2200 8) (2-64)
NH3 + hv -> NH + 2H (X < 1600 A) (2-65)
--where the amino and NH radicals are produced in various
energetic states, depending on the wavelength used.74
Because wavelengths that may dissociate ammonia into
excited products do not penetrate much below 75 km,
the main photolytic process in the stratosphere is
NH3 + hv -> NH2 (2B1) + H, (2-66)
which leads to the production of amino radical in its
fundamental state with a quantum yield of - 100%.74
168
-------
• Reaction with" ozone, atomic oxygen, and the hydroxyl
radical, OH:
NH3 + 0(3P) -> NH2 + OH, (2-67)
NH3 + 0(1D) + NH2 + OH, (2-68)
NH3 + 03 -> products, (2-69)
NH3 + OH -+ H20 + NH2. (2-70)
On the basis of atmospheric concentration data of McConnell
and McElroy64 for hydroxyl radical, O(3P), and 0( D) and available
rate constants for the above reactions, McConnell63 concluded that
the reaction of ammonia with the hydroxyl radical is the most im-
portant radical destruction mechanism for ammonia in the tropo-
sphere (Figure 2-10).
The hydroxyl-ammonia reaction rate constant has been measured
by Stuhl,87 Kurylo,49 Heck et al.,37 Zellner and Smith,86'94
Gordon and Mulac,25 Cox et a^.1J- and Perry et al.78 (Table 2-5).
In the recent study of Perry, Atkinson, and Pitts,78 a flash
photolysis-resonance fluorescence technique was used to determine
the hydroxyl-ammonia rate constant over the temperature range
297-427 K. The temperature dependence of the rate constant was
given by:
k (cm3/molecule • s) = 2.93 x 10"12 e ~ (171° ± 300)/RT' (2-71)
the reaction rate at 298 K being
169
-------
eo
IO° IO6 IOr IOa IO? IO
FLOW AND LOSS TIME CONSTANTS (SEC)
K>
FIGURE 2-10.
Time constants for chemical destruction and flow.
The chemical time constant is given by T chem =
1/[J1 + k2(OH) + k3 (O) + k^fO^-D) ], where Jj, is
the frequency of the photolytic process (NH^ +
hv -> NH2 + H) and kj_ is the rate constant for
the reaction of ammonia with OH (k2) , with
0(3p)(k3), and with O(lD)(k4). The dashed line
is the time constant of ammonia removal by hydroxyl
radical if k2 is assumed to be temperature-
independent. Reprinted with permission from
McConnell. °3
170
-------
TABLE 2-5
Rate Constants, k, and Activation Energies, E, for
the Reaction of Anrrionia with Hydroxyl Radical
k, x 10^3, cm-Vmolecuie ~
(at room temperature)
1.5+0.4
0. 41 + 0. 06
1.58
2.5 +0.8
1.2+0.4
1.64 + 0.16
E, kcal/mole
1.6
1.83
-
1.71 + 0.30
Reference
87
49
86,94
37
11
78
171
-------
k (cm3/molecule • s) = (1.64 + 0.16) x 10 13 (2-72)
With their rate constant and Levy's56 and Crutzen's12
estimates of the hydroxyl-radical concentration in the lower
troposphere ( 3 x 106 molecule/cm3), Perry, Atkinson, and Pitts
estimated the tropospheric ammonia half-life to be about 16 days.78
Levy's and Crutzen's estimates of the hydroxyl-radical concentra-
tion apply to unpolluted tropospheric air where hydroxyl radical
is produced mainly through the reactions:
03 + hv -> 02 + 0(1D), (2-73)
0(1D) + H20 \ 20H. (2-74)
In the polluted troposphere, many other reactions account for
the production and destruction of the hydroxyl radical, resulting
in higher hydroxyl-radical concentrations than in unpolluted air.
Therefore, although many species compete with ammonia for the
highly reactive hydroxyl radical, one would expect the half-life
of ammonia to be substantially shorter in photochemically polluted
air.
Both photolysis of ammonia in the stratosphere and reaction
IH
of ammonia with hydroxyl radical the troposphere lead to the
formation of the amino radical, whose fate is essentially unknown.
Possible reactions of NH2 include the following:
NH2 + 0 -> NH + OH, (2-75)
172
-------
NH2 + O + HNO + H, (2-76)
NH2 + OH -> NH + H2O, (2-77)
NH2 + OH ->- HNO + H2, (2-78)
NH2 + 02 -* HNO + OH, (2-79)
NH2 + NO -»• NH2NO + N2 + H20. (2-80)
Further reactions of the NH and HNO formed in Reactions
2-75 and 2-77 and Reactions 2-76, 2-78, and 2-79, respectively,
include the following:
NH + OH -> N + H20, (2-81)
NH + OH -> HNO + H, (2-82)
NH + 0 -> N + OH, (2-83)
NH + 02 -> NO + OH, (2-84)
NH + NO -> N2 + OH, (2-85)
HNO + 0 + NO + OH, (2-86)
HNO + OH -> NO + H20, (2-87)
HNO + 02 -> HO2 + NO. (2-88)
Rate constants for Reactions 2-75 and 2-76,l 2-79,40 2-80,26
2-85,26 and 2-8731 have been measured. The possible atmospheric
signifiance of Reactions 2-75 through 2-88 has been discussed by
McConnell.63
173
-------
in addition, an oxidation scheme analogous to that proposed
for the oxidation of methane to carbon monoxide12 may be proposed
for ammonia:
NH3 + OH + NH2 + H20, (2-70)
NH2 + 02 + M + NH202 + M, (2-89)
NH202 + NO + NH20 + N02, (2-90)
N02 + hv -> NO + 0, (2-91)
Q + 02 + M + 03 + M, (2-92)
NH20 + O2 -> HNO + H02, (2-93)
HO2 + NO -»• OH + N02> (2-94)
HNO + hv -» NO + H, (2-95)
with a net production of water, ozone, and oxides of nitrogen
The key issue with respect to the tropospheric budget of
ammonia and the global nitrogen cycle is the relative importance
of Reaction 2-80, which indicates that ammonia destruction repre-
sents a sink for nitric oxide, and Reactions 2-79 and 2-89 which
ultimately lead to the production of nitric oxide. Reaction 2-80
was first proposed by Gesser24 to account for the observed forma-
tion of molecular nitrogen when ammonia was irradiated in the
presence of oxygen. In a later study by Jayanty et al.,41 it
174
-------
was postulated that the amino radical reacts almost exclusively
with oxygen via Reaction 2-89.
Despite considerable discussion,12'63'64'65'72'87'92 it is
not clear whether the amino radical undergoes reactions that pro-
duce nitrogen oxides or acts as a sink for nitrogen oxides.
Kinetic studies26 of Reaction 2-80 yielded a reaction -rate con-
stant of 2.7 x 10"-'--'- cm /molecule, which suggests a rapid reac-
/)
tion at atmospheric nitric oxide and ammonia concentrations.
In a recent study of the photooxidation of ammonia in the presence
of nitric oxide and nitrogen dioxide, Cox e_t al. concluded that
ammonia oxidation acts as a net sink for nitric oxide in the
troposphere and the stratosphere. Another recent kinetic study54
with flash photolysis also indicated that the amino radical is
unreactive toward oxygen,
kl 5
NH2 + O2 -»• products (k1 <_ 10 liter/mole, s) , (2-96)
but highly reactive toward nitric oxide,
NH2 + NO +1 products (k2 - 1.2 x 1010 liter/mole, s). (2-97)
k R
The rate-constant ratio, _2 >_ 1.2 x 10 , indicates that the
kl
NH2 + NO pathway is important, even when nitric oxide is present
at parts-per-million concentrations in the air. Recent calcula-
tions carried out by Levine and Calvert also indicate the im-
portance of the NH2 + 02 pathway and support the mechanism pro-
posed by Gesser.24 Only a more precise determination of the
175
-------
NH2 + 02 reaction rate constant will permit establishing whether
ammonia oxidation is a source or a sink for nitric oxide in the
atmosphere.
The Role of Ammonia in Acid Precipitation
The generic term "acid precipitation" is applied to precipi-
tation, either rainfall or snow, -that contains an unusually high
concentration of hydrogen ion. Because the minimal pH for pure
water in equilibrium with atmospheric carbon dioxide is 5.6,
"acid precipitation" can be defined as rain or snow having a pH
of less than 5.6. The pH of rain and snow in much of the eastern
United States and northern Europe averages between 4.0 and 4.2
and pH values of 2.1-3.0 have been measured during individual
storms at various locations.
Although natural processes without the intervention of man
would be expected to contribute some acidity to rainfall, there
is strong evidence that the contribution of human activities has
increased greatly since the industrial revolution and more par-
ticularly within the last two decades.21'22'59 The subject of
acid precipitation has received extensive treatment the last
several years and is not reviewed in detail here, but dealt with
only to the extent that the circulation of atmospheric ammonia
may contribute to the phenomenon.
Major constituents of acid precipitation are sulfate and
nitrate ions originating from sulfur oxides and nitrogen oxides,
respectively. Oxides of sulfur appear to be the major contributor
176
-------
to acidity in precipitation (other than that arising from dis-
solved carbon dioxide from the atmosphere). Various estimates
of the contribution of oxides of sulfur to the atmosphere by
human activities, although they vary over a wide range, support
this contention.7/8,23,79 Estimates of biologic sources of
atmospheric sulfur also vary considerably, but are of the same
order of magnitude as the estimated anthropogenic contribu-
tions .3'^'' " i'0 Biologic sources of sulfur emission include
hydrogen sulfide, I^S, and other reduced forms.^9'^1'62,80,83
The comparative significance of anthropogenic and natural sources
of sulfur compounds in the atmosphere is not certain, but without
question the anthropogenic sources are increasingly large and in
most cases concentrated. The interpretation of the significance
of this additional acid component in precipitation is a matter
of some controversy -^•21/60 Oxides of sulfur and other sulfur
compounds, when they reach the atmosphere, have a comparatively
short residence time and are eventually oxidized to sulfate
ion.6,30,70,79,82
The other major acidic constituent of acid precipitation is
nitrate ion, which is often present in concentrations roughly
equivalent to that of sulfate ion (on a gram-atom basis)• '
The contribution of nitrate to ambient acidity has significantly
increased in the last 10 years. For example, measurements con-
ducted at a forest station in New Hampshire showed that the
nitrate contribution increased from 15% in 1964-1965 to 30% in
1973-1974.59
177
-------
Nitrate, like much of the sulfate, is assumed to be from
human sources and is formed by oxidation of nitric oxide and
nitrogen dioxide emitted in combustion reactions, including
the high-temperature reactions of internal-combustion engines.
Nitrate concentrations in the atmosphere have shown an increase
with increased compression ratios of internal-combustion engines,
particularly in portions of the world where the use of automobiles
has expanded greatly in recent decades.58 Other important con-
tributors to atmospheric emission of nitrogen oxides are stationary
combustion sources, such as power plants, and soil nitrogen (see
discussion in this chapter).
There are some anomalies, however, in the trends of ionic
constituents of acid precipitation that suggest that further
examination should be given to the problem, to determine the
comparative significance of different sources. The residence
time of ammonium ion in the atmosphere is comparatively short, "^ ,88,93
and it is commonly assumed that combination with sulfate ion in
the atmosphere or washout by rainfall results in a rapid return of
ammonia to the soil. It is possible that oxidation of at least
part of this ammonium ion to oxides of nitrogen and nitrate ion
could represent a more significant contribution to the total
acidity of rainfall than had heretofore been considered likely.
The problem, therefore, is to determine the extent of the
competitive processes of ammonia oxidation and ammonia removal
by fallout, rainout, and dry fallout. The relative importance
of these processes is unknown.
178
-------
Ammonium ion is an important trace constituent of rainwater
and plays a significant role in influencing pH. '^ ' ' Of
major importance in an assessment of the role of ammonia in acid
precipitation are the various chemical reactions of ammonia in
clouds and rainwater. Interactions of ammonia with other chemical
species in clouds and rainwater can be classified roughly in three
categories. The first is the dissolution interaction and the re-
sulting influence on acid-base chemistry. The second, usually
strongly related to the first, is ammonia's role as a promoter
of chemical reactions of other compounds in the aqueous phase.
The third category includes the processes in which ammonia itself
is converted by chemical reaction.
Dissolution Chemistry and Acid-Base Phenomena. In Chapter 1,
formulas were provided to calculate the solubility of ammonia in
pure water at low concentrations. These were based on the assump-
tion that the dissolution process occurs by a physical absorption
step,
TT
NH3'gas N NH3 dissolved, undissociated' d-14)
followed by an ionization reaction,
K
b
NH.
3 dissolved, undissociated -
+ OH . (1-10)
Consolidation of the equilibrium expressions for these two reac-
tions lei to the solubility equation:
179
-------
Molarity of
total dissolved = H [NH.I J + J KbH [NH3 qasJ/ d-15)
-> i gd& » -*
ammonia
1477.8 _ 1.6937
where Iog10 H = T(°K)
2729.92
and lognn K, = 0.09018.
10 10 T (oR)
The formation of hydroxide ions by the reversible Reaction
1-10 can play a significant role in influencing the acid-base
chemistry of clouds and rainwater. A typical ammonia concentra-
tion of 10™^ M in otherwise "clean" rainwater would, for example,
result in a pH shift from 7 (at 25° C) to about 9.
Any number of acid- and base-forming impurities can exist
in natural rainwater, so the equilibrium depicted in Reaction
1-10 can be shifted significantly, resulting in a radical departure
of actual behavior from the solubility equation (Eq. 1-15), and a
concurrent displacement of the pH. Carbon dioxide is undoubtedly
the most important interactant in this regard on a global basis;
its dissolution in pure water can be depicted by the following
equilibrium reactions:
Hc
C°2 gas ^ C02 dissolved, undissociated (2-98)
i
H 0 + CO,,,. . , . . •*• HCO ,~ + H+, (.2-99)
2 2. | dissolved, undissociated 3
ISO
-------
K
HC03~ ^ H+ + CO . (2-100)
Appropriate values for H , K, , and K0 can be obtained for the
C -L ^
34 81
literature ' and may be expressed by the following relations:
H = (0.08206T) antilog_n (2385. T3/m - 14.0184 (2-101)
c 10 T
+ 1.52642 x 10~2T)
Iog10 Kl = " O + 14.8435 - 0.032786T, (2-102)
Iog10 K2 = - . + 6.4980 - 0.02379T. (2-103)
Although no actual measurements of ammonia's solubility at
ambient carbon dioxide and ammonia concentrations are available,
a number of investigator14'45'66'68'84'91 have combined the
equilibrium expressions given above to provide solubility esti-
mates. These have been extended to account for additional acid-
and base-forming impurities; for example, an expression for the
solubility of ammonia in water containing a dissolved, doubly
dissociating, acid-forming gas (e.g., carbon dioxide) plus a
strongly dissociating acid (e.g., sulfuric acid) as follows, in
which X is the molarity of total dissolved ammonia and [A~] is
the normality of strong acid:
181
-------
TNH I 1 = X [OH"] (2-104)
L lJ H ([OH'] + K)
A "3
[OH"] + b [OH~] + c [OH"] + d [OH~] + e = 0 (2-105)
where
&K.+ ot + i
[A"] + a
b =
C =
d= |A JKb - Kw- KbX }
K, K
_ b w
6 — "" ^r
gas
and
K
K
a = - . B = - _. , (2-106)
TT ir^
W K
W
: = [H+~| foH~l (2-107)
w L J L J •*
The solubility of ammonia under these circumstances can be cal-
culated directly from Eq. 2-104 once the hydroxide ion concentra-
tion is known. The hydroxide ion concentration can be calculated
from Eqs. 2-105 and 2-106, where an iterative approximation is
usually the most expedient approach. Because of this, this procedure
182
-------
provides a means for estimating rain pH, in addition to the
solubility of such systems.
Very recently, some actual measurements of solubility in
low-concentration ammonia-carbon dioxide systems in the presence
of strong acid (sulfuric acid) have become available.28 Two
major conclusions obtained from these measurements are that, in
the absence of carbon dioxide, Eqs. 2-104, 2-105, and 2-106
predict actual solubilities and acidities of systems of ammonia,
strong acid, and water with good accuracy, and that, at atmos-
pheric concentrations of carbon dioxide (about 320 ppm),
Eqs. 2-104, 2-105, and 2-106 predict solubilities that are
much higher than those actually observed.
Although the reason for the discrepancy between predicted
and actual behavior of systems containing carbon dioxide is
uncertain, it seems possible that formation of a volatile
ammonia-carbon dioxide adduct is the major contributing factor.
In a discussion of solubility and dissociation phenomena,
a few qualitative aspects should be emphasized. These can be
evaluated in large part by examination of the solubility equa-
tions and the fundamental equilibrium expressions.
• Ammonia is highly soluble in water, and its solubility
increases with acidity. Thus, typical partition
coefficients (expressed as ammonia concentration in
water divided by that in the gas phase) are around
10,000 for pure water and higher by many orders of
183 !
-------
magnitude in acid rain. The presence of atmospheric
carbon dioxide also appears to decrease the ammonia
partition coefficient by about a factor of 50.
• Ammonia is almost completely dissociated in water at
atmospheric concentrations; thus, it can, in many
respects, be considered a "strong" base under these
circumstances.
• Carbon dioxide is weakly dissociated in water. Because
carbon dioxide is relatively abundant in the atmosphere,
this allows it to have a considerable buffering effect
on the influence of ammonia on rain pH.
• Ammonia's solubility depends heavily on its concentra-
tion when a strong acid is present. This dependence
arises from an acid-base titration effect, and there
is typically an increase of six orders of magnitude in
solubility per decade of decrease in concentration (for
ammonia concentrations in the region of the strong acid
concentration).
184
-------
Ammonia's Role as a Chemical Promoter. Primarily because
of its role as a base-forming substance, ammonia has been con-
sidered a key factor in promoting the aqueous-phase chemistry
of acidic compounds, such as sulfur dioxide. As described in
more detail earlier in this chapter, this is primarily because
ammonia enhances the solubility or dissociation of such sub-
stances. Sulfur dioxide's solubility, for example, is known
to depend heavily on pH,29 and the aqueous-phase reactions of
sulfur dioxide are strongly influenced by the presence of ammonia.
As noted previously in this chapter, this influence has been
examined by many authors. In addition, there have been several
investigations of aqueous-phase conversion via specific agents,
such as metal ions and dissolved ozone. Many of these have not
considered the influence of ammonia directly; one would certainly
expect, however, that added ammonia would enhance these reactions
through an increase in the solubility of sulfur dioxide.
In summary, there appears to be a diversity of opinion with
regard to the important mechanisms for aqueous-phase conversion
of sulfur dioxide and other acidic compounds. Regardless, there
is general agreement that, although ammonia is not essential for
these reactions, it is an important promoter.
Aqueous-Phase Conversion of Ammonia. Precipitation chemistry
analyses have indicated that ammonium ion is relatively stable in
precipitation samples; this suggests that it is not oxidized or
reduced rapidly in clouds or rainwater. Oxidation-reduction
185
-------
reactions are, of course, possible; for example the reaction,7?
NH4+ + N02~ -» N2 + 2H20, (2-108)
may be partially responsible for the typically low nitrite con-
tent of rain. Other possibilities include oxidation by ozone
and bacterial oxidation. However, destruction or formation of
ammonium in rainwater has not been considered an important
atmospheric mechanism, and relatively little material addressed
to this subject appears in the literature.
186
-------
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45. Junge, C. R. Air Chemistry and Radioactivity. New York: Academic Press,
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46. Junge, C. E. , and T. G. Ryan. Study of the S02 oxidation in solution and
its role in atmospheric chemistry. Q. J. Roy. Meteorol. Soc. 84:
46-55, 1958.
47. Kellogg, W. W. , R. D. Cadle, E. R. Allen, A. L. Lazrus, and E. A. Mart ell.
The sulfur cycle. Science 175:587-596, 1972.
48. Kiang, C. S., D. Stauffer, and V. A. Mohnen. Possibilities for atmos-
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49. Kurylo, M. J. Kinetics of the reactions OH(V=0) -(- NH —> H20 + NH
and OH(1/=0) 4 C>3 -7" H02 4- 02 at 298°K. Chem. Phys. Lett. 23:
467-471, 1973.
5°. Kushnir, J. M. , H. I.Malkin, V. A. Mohnen, A. J. Yencha, and E. H. McLaren.
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51. Lamb, D. An implication of a model of ammonia-sulfur dioxj.ue reactions
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196
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SOIL
Organic matter is the major soil reservoir of nitrogen.
Only a small portion of the total is mineralized and transferred
to plants each year; this amount is highly variable, owing to
soil and climatic differences, e.g., in temperature and rainfall,
Soils in cooler climates and in high-rainfall areas tend to be
higher in organic matter than those in warmer or drier regions.
There is no "typical" residence time of nitrogen in the soil
organic fraction. Nitrogen in the soil in a highly soluble and
readily metabolized organic compound may be rapidly mineralized
and returned to the inorganic fraction (where it is again avail-
able for plant absorption); or, if it is in a more recalcitrant
organic compound or in a compound tightly bound to the soil
colloid, it may remain in the soil for years, or even centuries,
before being released in some metabolic event.
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Once nitrogen is liberated to the soil as ammonium ion, as
a result of the breakdown of organic material, there are several
possible routes for it to take. The ammonium ion is comparatively
immobile in soil. Being cationic, it tends to be adsorbed on the
negative adsorption sites of clay colloids, with only a small
fraction of the total ammonium being in solution. The ammonium
ion is chemically quite similar to that of potassium and may
substitute for potassium in the lattice structure of a clay
mineral.
The most likely fate of the ammonium ion is "nitrification"
or oxidation by microorganisms to nitrite ion and thence to
nitrate ion. Both reactions are energy-yielding, and ammonium -, j,i
is the obligatory substrate for some nitrifying autotrophic
organisms. Once oxidized to nitrate ion, the nitrogen is more
mobile in the soil and will be transported downward to the
rhizosphere, where it is available for uptake by plants, or
through the rhizosphere to groundwater, where it may reappear
in irrigation water pumped from wells or in domestic water
supplies. Otherwise, it may be transported to local streams
or rivers and eventually to the ocean.
In relatively anaerobic soils, as nitrate ion is trans-
ported downward into a region of limited oxygen supply and
available organic substrate, other organisms (denitrifiers) can
utilize the nitrate as electron acceptor for metabolic purposes,
liberating nitrogen gas or nitrous oxide to the soil. If nitrous
198
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oxide is the product, it may escape to the atmosphere or be
further denitrified to nitrogen gas.
Nitrogen taken up by the plant (normally as nitrate ion,
inasmuch as this is its more likely form in the soil solution)
will probably be reduced again to ammonia or amino radical,
entering one or another synthetic sequence. Nitrate reduction
is an energy-requiring process; in most plants, metabolic feed-
back controls suppress reduction of nitrate in excess of that
required for the synthesis of plant tissues. For this reason,
if nitrogen is available in quantities that exceed metabolic
needs or if the plant is under stress of some other sort, such
as a deficiency of another ion or drought, nitrate ion can
accumulate in large quantities in the plant tissues.
As plant material is returned to the soil, either directly
or after processing through an animal, the transformations are
repeated; the nitrogen appears as a product of metabolism of
microorganisms or perhaps is for a time incorporated into the
tissues of a microorganism, is eventually released as ammonia,
is oxidized to nitrate, and again becomes available to plants
or possibly is lost from the system.
Thus, the soil can be viewed (see Figure 2-11) as a large
organism with the distribution of chemical species representing
a steady state, but with continuous processing of nitrogen through
the system. Normally, some nitrogen is lost from the system by
leaching or denitrification and replenished by processes of
199
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INPUT OF NEW FIXED
NITROGEN
ATMOSPHERIC NITROGEN (N )
POOL 2
ORGANIC PLANT & ANIMAL
RESIDUES
DENITRIFICATId
LOSS
N ,N 0
. 2 2
I Iff''If(
SOIL ORGANIC NITROGEN POOL
' /
/ / / /
/
MINERALIZATION
FIGURE 2-11.
The soil can be looked on as a complex organism with a
large organic pool. Nitrogen is cycled through this
system to plants (and possibly animals) and back to
the soil. There is a continuous loss of nitrogen
through leaching, denitrification, and cropping and
a continuous replenishment by fixation reactions,
rainfall, and activities of man.
200
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fixation, rainout, washout, or fallout. Any process that jolts
the system (such as the addition of a large amount of nitrogen
fertilizer) shifts it to a new steady state; but, because it is
a dynamic system, it has a large buffering capacity for any
change--a given percentage change in a single form of input
does not necessarily mean that there will be a comparable change
in any given form of output.
The transformations and cyclic processes outlined above
are those of a "typical" ecosystem. They assume a soil that
is well aerated, receives moisture in moderate amounts at regular
intervals, and has a moderate cation-exchange capacity that
carries a large spectrum of cationic elements required by plants.
Many soils do not meet this ideal, however, and transformation
of soil nitrogen might take quite different paths. For example,
a soil that has a relatively low ion-exchange capacity, receives
frequent and large amounts of water, or both may have nitrogen
leached from it more rapidly and may require a larger continuing
supply by nitrogen fixation, if there is to be adequate nitrogen
for vegetation. In such a soil, plants that can fix nitrogen
will tend to have a competitive advantage, and there will be a
greater flow of nitrogen through the soil.
In agricultural soil, new nitrogen might be introduced by
fertilization, and more nitrogen removed by cropping. If the
timing of addition of new nitrogen is not careful or if too much
nitrogen is added, there can be an excessive flow of nitrogen
201
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into groundwater or an excessive loss by denitrification, depend-
ing on the water input and the degree of aeration. When a native
ecosystem, such as a prairie, is converted to agricultural uses,
there is a large part of the season after the crop has been re-
moved when there is no input of organic material and yet there
is continuing microbial activity. Nitrogen released by this
microbial activity can be leached downward; the net result will
be that the soil will reach a new (and lower) organic content
and some nitrogen will be lost by leaching. Conversely, an arid
soil in a warm climate, when converted to irrigation agriculture,
may have a larger input of organic matter and move toward a higher
mean organic content, with a higher retention of combined nitro-
gen. If the crop is one of continuous coverage, such as irri-
gated alfalfa, this increase in organic content can be quite
large.
A large fraction of the earth's soil is poorly permeable to
oxygen, because of waterlogging. This is true of marshes, tidal
areas, and the bottoms of some lakes, rivers, and oceans. The
surfaces of these muds or oozes, in most cases, are aerated; but,
if there is any significant metabolic activity, conditions be-
come anaerobic, sometimes within a few millimeters of the surface.
In the sharp oxygen gradient from the surface to the anaerobic
zone, conditions change abruptly: at the surface, oxidative
processes comparable with those described above, including nitri-
fication, are taking place; immediately below this., denitrif ication
202
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is possible; at greater depths, decomposition of organic matter
is greatly slowed, and any nitrogen released by the fermentative
decomposition of organic matter remains as ammonia.
In arid climates, where evapotranspirative loss of water
exceeds rainfall, the net movement of salts (including nitrate)
will be upward, particularly if there is a net transport of salts
from adjacent areas of higher rainfall, such as a mountain range.
Under these circumstances, "fossil" nitrogen can accumulate in
the soil. When such soil is converted to irrigation, this accumu-
lated nitrate, as well as other salts, will be moved downward at
a rate proportional to the net downward movement of excess water—
usually less than a meter per year. Eventually, these salts will
appear in groundwater.
WATER
A description of important chemical and biologic transforma-
tions and transports of ammonia in natural water requires inte-
gration of key aspects of the nitrogen cycle—including rates of
input, biogeochemical transformations, utilization, and output—
with information on other important chemical species in repre-
sentative environments. Discussions of processes that control
the nitrogen chemistry of natural water can be found in works
on lakes by Hutchinson,12 and Wetzel,28 On rivers and streams
by Hynes,13 and on impounded water by Neel.22
Discussions of coastal and open-ocean marine systems appear
in Chapter 4.
203
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Sources of Ammonia in Freshwater
Sources of ammonia in natural water include precipitation
and dry fallout, nitrogen fixation in water and sediment, dis-
I
solved and particulate material from surface runoff and ground-
water, direct excretion, organic-matter decomposition, sewage
(in the absence of tertiary treatment), and a wide variety of
industrial activities.2i The ammonia present in unpolluted
freshwater is generated primarily by heterotrophic bacteria
as the major end product of organic-matter decomposition,12,28
either directly from proteins or from other nitrogenous organic
substances. Intermediate compounds are quickly transformed by
bacteria. Animal excretion is generally not a major source,
in comparison with decomposition in freshwater; however, in
some eutrophic marine ecosystems, such as coastal upwelling
areas, zooplankton excretion may be a major source of nitrogen
(see Chapter 4).
Input of ammonia and other forms of nitrogen from runoff,
groundwater, and agricultural activities can be expected to vary
widely as a reflection of climate, geography, and land use. In
general, a relationship between concentration of dissolved species
and direct surface runoff can be expected, as described by
Eq. 2-109:13'17
C = KDf, (2-109)
where c = concentration of dissolved material,
K = constant,
D = discharge rate, vol/time, and
f = number < 1.0.
204
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Greater rainfall in a given region generally increases the
fraction of the total erosional load that occurs as dissolved
material, because of water retention and percolation associated
with more foliage. The fraction of particulate material in-
creases as rainfall decreases.13 The effect of agriculture and
other land-clearing is therefore to increase the turbidity of
natural water and thereby increase the fraction of adsorbed
ammonia.
Rainfall data from the National Precipitation Sampling
Network spatially modeled by Wolaver and Lieth-^O suggested
characteristic ammonia concentrations ranging from 0.03 to
0.2 mg/liter in the continental United States. Atmospheric
sources of nitrogen have generally been considered minor, in
comparison with runoff sources;^8 however, this may not be the
case in oligotrophic water in mountainous land regionslS and
in oligotrophic marine water.20 Highly variable atmospheric
input also includes poorly quantified dry fallout.
Nitrification in Natural Water
Nitrification represents the conversion of reduced forms of
nitrogen to an oxidized state. The series of oxidation states
involved can be listed as follows:
NH + -> NH2OH -> K2N2°2 ~" N°2~
ammonia hydroxylamine pyruvic nitrite
oxime
205
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An excellent review of nitrification processes can be found in
Alexander.2 Little if any of the intermediate compounds between
ammonia and nitrite has been found either in lakes (e.g., Baxter
et al.3) or in oceans (e.g., Fiadeiro et al. ). The bacteria
carrying out nitrification are largely of the genus Nitrosomonas,
which operate optimally at near neutral pH with a wide temperature
tolerance.28 The oxidation of nitrite to nitrate—
N02~ + 1/2 02 + N03~ (2-110)
--is carried out primarily by the genus Nitrobacter, which is
less tolerant of low temperatures and high pH. The overall con-
version of ammonia to nitrate consumes 2 moles of oxygen per mole
of ammonia--
NH4+ + 202 ->• N03~ + H2O + 2H+. (2-111)
In addition to being inhibited by anoxic conditions, nitri-
fication is severely reduced in acidic water (pH < 5), and by
some dissolved inorganic substances. The significance of this
is discussed below.
Ammonia Adsorption on Particles
Ammonia is strongly adsorbed on soil and sediment particles
and colloids.1'24'28 This results in high concentrations of
sorbed ammonia in oxidized sediments (e.g., Keeney14). Kemp and
Mudrochova15 reported concentrations of exchangeable ammonia
ranging from approximately 15 to 85 yg/g (dry wt) of sediment
in a Lake Ontario core. Under anoxic conditions, the adsorptive
206
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capacity of sediments is less, and this results in the release
of ammonia either to the water column or to an oxidized sediment
layer above.
Ammonia Uptake by Freshwater Plants
There is some disagreement as to whether lake plants grow
better with nitrate or ammonia as a nitrogen source. Wetzel28
suggested that most algae and macrophytes prefer nitrate.
Hutchinsonl2 pointed out that ammonia is as good or better as
a source, on the grounds that nitrate must be reduced to ammonia
during assimilation (see Chapter 4), and cited evidence of
phytoplankton blooms during which sudden decreases in ammonia
occurred with little decrease in nitrate concentration.
Dugdale and Dugdale^ showed that algal nitrate uptake,
but not growth, was inhibited by ammonia in Sanctuary Lake,
Pennsylvania.
Ammonia in Lakes
Ammonia concentration in unpolluted surface water of lakes
is generally much less than 5 mg/liter, extreme concentrations
of over 10 mg/liter are found only in the hypolimnion of anoxic
or periodically anoxic lakes.28 The rapid rise in ammonia con-
centration is associated with regeneration from organic materials
in bottom water and sediment.12'25'28 Important factors con-
trolling regional, spatial (within a lake), and seasonal ammonia
distribution thus include productivity, rates of biogeochemical
-------
transformations,28 vertical mixing,27,28 and flushing rate.5
Wetzel28 has reviewed the seasonal and spatial concentration
ranges observed in lakes ranging from oligotrophic well-mixed
lakes to hypereutrophic poorly mixed lakes and has found highest
bottom-water and overall concentrations in the latter. The high
concentrations are associated not only with relatively rapid
decomposition of organic material, but also with complete lack
of nitrification under anoxic conditions and release of sorbed
ammonia under anoxic conditions.
The importance of an oxidized bottom layer in controlling
adsorption of ammonia in lake sediment has been linked to
hypolimnion ammonia concentration by Hutchinsonl2 ancj others.
The degree of oxidation of the uppermost sediment layers plays
a major role in controlling potentially large releases of ammonia
through desorption. An oxidized layer even only a few centimeters
thick may trap desorbed ammonia diffusing up from lower sediment
layers.I4 Under anoxic bottom-water conditions, substantial
release into the hypolimnion may occur. Serruya et al.25 re-
ported sediment-water ammonia fluxes as high as 61 ymole/m2-h
for Lake Kinneret, Israel. This value is comparable with ammonia
fluxes reported for coastal organic-rich marine sediment (e.g.,
Nixon et aJL.23 and Hartwig10; see Chapter 4).
Seasonal variations in hypolimnion redox conditions, and
thus adsorption-desorption processes, may account for part of
the observed seasonal changes in lake nitrogen budgets.
208
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Nitrogen budgets of lakes based on close-interval measure-
ments of input, metabolic dynamics, and output are not avail-
able for lakes.28 In seasonally stratified productive lakes,
the ammonia supply resulting from decomposition of organic
materials in bottom sediment competes in importance with input
o
from land drainage (e.g., Gorham et al. ). Seasonal varia-
tions in such lakes feature ammonia concentration increases in
bottom water during periods of stratification and nitrification
and uptake by algae after water-column mixing.28 Nitrification
can be severely inhibited by some dissolved inorganic substances
in soils, especially humic substances; thus, relatively higher
ammonia concentrations may be associated with water rich in
such substances.
Nitrogen introduced by man to lake surface water through
runoff from agricultural land or sewage in the form of ammonia
should appear as pulse inputs. The response of the lake eco-
system to nitrogen pulses should be in proportion to the volume
of receiving water, mixing and flushing rates, and redox condi-
tions. A higher nitrate:ammonia ratio would be expected in un-
polluted lakes.12
Ammonia in Rivers and Streams
Chemical characteristics of flowing water are highly variable
as a result of patterns in runoff, precipitation, and other factors
discussed above. Much of the water in rivers and streams enters
as subs irface runoff; surface runoff becomes relatively more
important during heavy precipitation or snow melt.
209
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Turbulent mixing in flowing water generally results in a
relatively uniform distribution of dissolved substances. Lateral
differences in large rivers result from entry of tributaries or
point sources of materials (e.g., industrial wastes), because
inflowing water tends to follow the bank along which it enters.
Physical models dealing with lateral mixing incorporate such
factors as river-bed roughness, attached-plant distribution,
flow rate, sinuosity, and the angle of entry of the new water.13
Rodina (cited in Hynesl3) observed increased concentrations of.
microorganisms along the banks of major polluted Russian rivers
as a result of such lateral inhomogeneities.
Vertical mixing may be incomplete, owing to flow character-
istics and water-temperature variations, especially during the
summer. Depletion of oxygen in the bottom water of large rivers,
such as the Neuse River of North Carolina,11 and smaller channel-
ized streamsJ-6 is not uncommon. Although the stratification is
less stable than that of stratified lakes, similar biogeochemical
effects are to be expected under such circumstances, including
release of adsorbed ammonia and lack of nitrification.
In general, smaller and more turbulent streams have oxygen
concentrations close to equilibrium values, although seasonal
variations may be introduced by primary productivity and leaf
decay. -^
High water input would be expected to lower oxygen content,
because of both increased heterotrophic decomposition activity
210
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associated with increased organic materials and lower photosyn-
thesis associated with higher turbidity. Diel variations in
oxygen content are generally dominated by daytime photosynthetic
production. Other factors influencing oxygen content, and thus
nitrification processes, include the input of ground water with
low oxygen content and the addition of bubble entrainment devices,
such as wiers and waterfalls, which restore equilibrium oxygen
content.
Under well-oxygenated conditions, nitrification should
rapidly convert ammonia introduced to rivers and streams to
nitrite and nitrate. Matulewich and Finsteinl9 have suggested
that the rate of disappearance of ammonia through nitrification
is related to the amount of rock surface area, all other factors
being equal. Rain that enters flowing water usually has a low
pH associated with high carbon dioxide and sulfuric acid content.
If this pH is not neutralized through mineral-water interactions
or goes through boggy soils where base exchange with soils leads
to incorporation of humic materials, water with both low pH and
high humic content will occur. Examples are Scottish rivers
(e.g., Sholkovitz2^) and southeastern U.S. rivers (e.g., Beck
e_t al. ) . Nitrification in such water is inhibited by both the
low pH and the high organic content, and relatively high concen-
trations of ammonia would be expected.
Sorbed ammonia entering on particles that are deposited
and buried as sediment represents a potential later source.
211
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Changing redox conditions leading to desorption could provide
new ammonia to a watershed.
The effect of lakes associated with flowing waters is to
retain nitrogen and thereby to act as nutrient traps. If nitro-
gen fixation processes are active, however, a significant frac-
tion of the incoming nitrogen will be retained in the water
column and thus be available for export.
Ammonia in Impounded Water
The damming of any watercourse, however small, results in
the creation of a reservoir. Most reservoirs are created through
inundation of rich bottom land and river slope topsoil, thus
ensuring high nitrogen content during the initial stages of a
reservoir's existence.22
With the exception of a general decline with time in produc-
tion of nutrients from initially nutrient-rich sediments, as
discussed above, the ammonia budget of reservoir water and sedi-
ment will be controlled by many of the same factors as control
lakes. Ammonia distribution and transport will be related to
the magnitude of input, the volume and concentration ratios of
receiving-water volume to new-water, differences in biogeochemi-
cal transformations resulting from changes in redox potential,
$
and stratification characteristics.
~~
Stratification will lead to^anoxic conditions in the
hypolimnion of the reservoir, and maximal ammonia concentrations
generated there will depend on the stratification time and the
depth and magnitude of hypolimnial outflow from the reservoir.
212
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Control of ammonia release to water downstream from a
reservoir can be achieved through regulation of both depth and
amount of water released. The ammonia concentration of hypo-
Limnial water releases will not be proportional to that of
water entering the reservoir, but will reflect the addition
of contributions from organic-matter decomposition in bottom
water and sediment.
Ammonia in Wetlands
Little is known about the nitrogen cycle of wetlands.
Estuaries and coastal wetlands are a sink for nitrogen (e.g.,
Harrison and Hobble") and transform 50% or more of newly intro-
duced nitrogen to particulate organic nitrogen by phytoplankton;
a considerable fraction of this is eventually deposited in
sediment, as witness the buildup of organic nitrogen. (Estu-
aries and coastal wetlands are discussed further in Chapter 4.)
Inland marshes may be expected to take up nitrogen species,
including ammonia, from associated water during the summer growth
period and release them to the water primarily in the form of
nitrate after the dieoff period in the fall (e.g, Whigham and
Simpson ^). Experiments designed to assess the potential of
such wetlands for removing nitrogen from sewage and converting
it into plant material are going on.
213
-------
Ammonia in Surface Water of the United States
This section demonstrates the usefulness of a nationwide
data set for ammonia concentration in U.S. surface water. Data
from a consistent, dense monitoring system can be combined with
computer mapping and modeling techniques (e.g., Wolaver and
Lieth30) to provide an excellent tool for use in identification
of regional concentration distribution and change.
A small data set provided by the Geological Survey, U.S.
Department of the Interior, illustrates the potential yield
from these techniques. The data were recorded in monthly
intervals and include total ammonia measurements at approxi-
mately 100 stations in the conterminous United States. Close
stations reduce the number of useful entry points for regional
mapping to about 70 stations, as shown in Figure 2-12. Sparse
data are available for the midwestern region and far western
states; nevertheless, the data set can be mapped in using a
relatively large "search radius" for interpolation in order to
demonstrate the technique.
Maps generated from data on total ammonia concentration at
the stations shown in Figure 2-12 for the annual, winter, and
summer averages are shown in Figures 2-13, 2-14, and 2-15,
respectively. Five concentration intervals for total ammonia
between 0.1 and 0.5 ppm and two categories, for low (L) and high
(H) values, outside this range are used in these figures.
214
-------
-5 1 6-
5 I nit
FIGURE 2-12. Distribution of data points. S = superimposed loci.
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-------
A regional analysis of the stations across the United
States shows that most average total ammonia concentrations
are below 0.18 ppm. Obvious deviations are found in the
metropolitan areas of New York-Baltimore and Boston. The
"background" ammonia concentration across the United States
thus appears to be below 0.2 ppm.
An ammonia washout distribution map derived from precipi-
tation network data by Wolaver and Lieth-^O is shown in Figure
2-16. The background precipitation concentration appears to
fall in the range of 0.01-0.15 ppm, in agreement with the
surface-water background concentration of less than 0.2 ppm.
A consistent, dense monitoring system will be required
to generate maps with truly regional capabilities for detecting
concentration changes resulting from seasonal or other controlling
factors. The limited exercise presented here, however, makes it
clear that valuable insights may be gained through such monitoring
and modeling.
219
-------
to
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vFIGURE 2-16. Ammonia washout map generated from National Precipitation
Sampling Network data by Wolaver and Lieth.30 Reprinted
from Wolaver a.nd Lieth. ^0
-------
REFERENCES
1. Ahlrichs, J. L., A. R. Fraser, and J. D. Russell. Interaction of ammonia
with vermiculite. Clay Miner. 9:263-273, 1972.
2. Alexander, M. Nitrification. Agronomy 10:307-343, 1965.
3. Baxter, R. M., R. B. Wood, and M. V. Prosser. The probable occurrence of
hydroxylamine in the water of an Ethiopian lake. Limnol. Oceanogr.
18:470-472, 1973.
4. Beck, K. C., J. H. Reuter, and E. M. Perdue. Organic and inorganic geo-
chemistry of some coastal plain rivers of the southeastern United
States. Geochim. Cosmochim. Acta 38:341-364, 1974.
5. Dillon, P. J. The phosphorus budget of Cameron Lake, Ontario: The impor-
tance of flushing rate to the degree of eutrophy of lakes. Limnol.
Oceanogr. 20:28-39, 1975.
6. Dugdale, V. A., and R. C. Dugdale. Nitrogen metabolism in lakes. II.
Role of nitrogen fixation in Sanctuary Lake, Pennsylvania. Limnol.
Oceanogr. 7:170-177, 1962.
^
1. Fiadeiro, M., L. Solorzano, and J. D. H. Strickland. Hydroxylamine in
seawater. Limnol. Oceanogr. 12:555-556, 1973.
8. Gorham, E., J. W. G. Lund, J. E. Sanger, and W. E. Dean, Jr. Some rela-
tionships between algal standing crop,, water chemistry, and sediment
chemistry in the English lakes. Limnol. Oceanogr. 19:601-617, 1974.
9- Harrison, W. G., and J. E. Hobbie. Nitrogen Budget of a North Carolina
Estuary. UNC-WRRI-74-86. Raleigh: Water Resources Research Insti-
tute of the University of North Carolina, 1974. 172 pp.
221
-------
10. Hartwig, E. 0. The impact of nitrogen anJ phosphorus release from &
siliceous sediment on the overlying water, pp. 103-117. In
Estuarine Processes. Vol. 1. New York: Academic Press, 1976.
11. Hobbie, J. E. , and N. W. Smith. Nutrientd in the Neuse River Estuary,
North Carolina. Sea Grant Publication UNC-SG-75-21. Chapel Hill,
University of North Carolina, 1975.
12. Hutchinson, G. E. A Treatise on Limnology. Vol. 1. Geography, Physics,
and Chemistry. New York: John Wiley & Sons, Inc., 1957. 1015 pp.
13. Hynes, H. B. N. The Ecology of Running Waters. Toronto: University of
Toronto Press, 1970. 555 pp.
14. Keeney, D. R. The nitrogen cycle in sediment-water systems. J. Environ.
Qual. 2:15-29, 1973.
15. Kemp, A. L. W., and A. Mudrochova. Distribution and forms of nitrogen
in a Lake Ontario sediment core. Limnol. Oceanogr. 17:855-867, 1972.
16. Kuenzler, E. J. Seasonal patterns of water quality in natural and channel-
ized swamp streams of eastern North Carolina. In Abstracts of Papers
Submitted for the 39th Annual Meeting , American Society of Limnology
and Oceanography Inc., Savannah, Georgia, June 1976.
17. Leopold, L. B., M. G. Wolman, and J. P. Miller. Fluvial Processes in
Geomorphology. San Francisco: W. H. Freeman and Company, 1964.
522 pp.
18. Likens, G. E., and F. H. Bormann. Nutrient cycling in ecosystems, pp. 25-
67. In J. A. Wiens, Ed. Ecosystem Structure and Function. Proceed-
ings of the 31st Annual Biology Colloquium, 1970. Corvallis: Oregon
State University Press, 1972.
19. Matulewich, V. A., and M. S. Finstein. Water phase and rock surfaces M
the site of nitrification, p. 189. In Proceedings of the Annual
Meeting of the American Society of Microbiologists, 1975.
222
-------
20. Menzel, D. W., and J. P. Spaeth. Occurrence of ammonia in Sargasso Sea
waters and rain water at Bermuda. Limnol. Oceanogr. 7:159-162, 1962.
21. National Academy of Sciences, National Academy of Engineering. Environ-
mental Studies Board. Water Quality Criteria 1972. A Report of the
Committee on Water Quality Criteria. Washington, D. C.: U. S.
Government Printing Office, 1974. 594 pp.
22. Neel, J. K. Impact of reservoirs, pp. 575-593. In D. G. Frey, Ed.
Limnology in North America. Madison: The University of Wisconsin
Press, 1963.
23. Nixon, S. W., C. A. Oviatt, and S. S. Hale. Nitrogen regeneration and the
metabolism of coastal marine bottom communities, pp. 269-283. In J.
M. Anderson and A. Macfadyen, Eds. The Role of Terrestrial and Aquatic
Organisms in Decomposition Processes. London: Blackwell Scientific
Publishers, 1976.
24. Rosenfeld, J. K., and R. A. Berner. Ammonia adsorption in nearshore
anoxic sediments, p. 1076. In Abstracts with Program, 1976 Annual
Meeting, Geological Society of America, Denver, 1976.
25. Serruya, C., M. Edelstein, U. Pollingher, and S. Serruya. Lake Kinneret
sediments: Nutrient composition of the pore water and mud water
exchanges. Limnol. Oceanogr. 19:489-508, 1974.
26. Sholkovitz, E. Interstitial water chemistry of the Santa Barbara Basin
sediments. Geochim. Cosmochim. Acta 37:2043-2073, 1973.
27. Weimer, W. C., and G. F. Lee. Some considerations of the chemical limnology
of meromictic Lake Mary. Limnol. Oceanogr. 18:414-425, 1973.
28. Wetzel, R. G. Limnology. Philadelphia: W. B. Saunders Company, 1975.
743 pp.
223
-------
29. Whigham, D. I"., and R. L. Simpson. Sewage spray irrigation in a Delaware
River ireshwater tidal marsh, pp. 119-144. In Freshwater Wetlands
and Sewage Effluent Disposal. University of Michigan School of
Natural Resources and College of Engineering, 1976.
30. Wolaver, T. G. Distribution of Natural and Anthropogenic Elements and
Compounds in Precipitation Across the U. S. : Theory and Quantitative
Models. (Prepared for the U. S. Environmental Protection Agency)
Chapel Hill: University of North Carolina, 1972. 75 pp.
224
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CHAPTER 3
MEASUREMENT AND MONITORING
DETERMINATION OF AMMONIA AND AMMONIUM ION IN AIR
Sampling
Collection of air samples for determination of ammonia is
complicated by a number of difficulties. One major problem is
the possibility of contamination of samples by ammonia emitted
by man. (Indeed, ammonia monitors have been tested as personnel
detectors by the military.) This problem has been noted by a
number of investigators, such as Breeding et al.5 Although there
is little published material specifically addressed to avoidance
of contamination by humans, experience indicates that reasonable
measures can control this factor to within tolerable limits in
most cases--e.g., placing the samplers at some distance from
routine human activity and exercising moderate care in sampler
servicing. The operator should remain near the sampler only
for the time necessary for servicing to be completed and should
attempt to position himself downwind from active samplers during
servicing.
An additional problem involves ammonia's propensity to sorb
on almost any available surface. This makes it essential to
minimize contact of the sample stream with solid surfaces before
collection. As with most other trace gases, the magnitude of
this type of error may be expected to increase with decreasing
225
-------
ammonia concentration, because the proportion of airborne mater.
that is sorbed usually increases under these conditions.
Sampling air for ammonia involves differentiating between
ammonia gas and ammonium aerosol. Many wet-chemical techniques
of analysis do not distinguish between the two; indeed, mostpn
mote conversion of ammonia to ammonium ion during the sampling
process. Ostensibly, this problem can be overcome simply by
filtering ammonium aerosol from the sampled air stream before
collection. Kadowaki e_t
-------
> z
H- a
lonization
Release
As NH-.
in sampler
Oxidation
Escape from sampler by
gas or liquid entrain-
ment in air stream
FIGURE 3-1.
Potential interactions of ammonia and ammonium aerosol
on a prefilter sampling train.
227
-------
of the sampling medium. Ammonia is extremely soluble in acidi-
fied water, and in principle it should be collectible with
simple bubbler techniques. Efficiency measurements of such
bubbler systems, however, have had rather uncertain results.
Morgan et al.49 reported efficient collection of ammonia in
bubbler samplers containing 50 ml of a 0.05 N sulfuric acid solu-;
tion. Somewhat different results were reported by Okita and
Kanamori,53 who found that, although 0.02 N sulfuric acid bubbler
solutions retain higher concentrations (7 ppm) of airborne ammonal
they are unsuccessful at capturing the gas quantitatively at low :
concentrations.
Uncertainties in bubbler sampling efficiency have prompted
researchers to apply alternative collection techniques. The
most prominent involves the use of impregnated filter media for
collection of total ammonia (NH^+ + NH,) on filter substrates.
The most successful applications have involved filters impregnated!:
with sulfuric acid53 an(j oxalic acid-ethanol solutions.64 Oxalic.
acid has also been used as an ammonia-trapping reagent in packed-
column samplers, in which glass beads in a sampling tube are coate
with the reagent, the sample air is passed through the tube, and
the oxalic acid-ammonium residue is extracted and analyzed. Quant,,
tative retention of ammonia by samplers of this type has been re- ,
C rj
ported; the possibility of ammonium-aerosol capture by such unit!
however, renders their use questionable for most applications.
228
-------
Analytic Techniques
The most common analytic methods for ammonia and ammonium ion
in air are summarized in Table 3-1. It is evident that a number
of sensitive wet-chemical methods are available; once valid
samples of ammonium ion are obtained in solution, it is rela-
tively simple to use these techniques to arrive at final analytic
results.
Of the wide variety of colorimetric techniques available for
ammonia analysis, three general methods have accounted for the
overwhelming majority of practical use. These are the Nessler,
indophenol, and pyridine-pyrazolone techniques, each of which
has modifications and adaptations. The Nessler method^ is
usually considered the classical technique for ammonia analysis
and has been used for the longest period. It is based on the
development of a yellow-brown color by reaction of ammonium ion
with Nessler's reagent, which is a solution of mercuric potassium
iodide and sodium hydroxide in water. This method is currently
falling from favor, because of noted interferences from trace
species, although these effects can be alleviated at least partly
by predistillation of the sample. The technique is also trouble-
some in practice, in that its use of mercury-salt solutions pre-
sents a toxicity and disposal problem.
The indophenol method, based on the colorimetric determina-
tion of indophenol blue ion concentration, has emerged as a
sensitive alternative to the Nessler technique and is relatively
229
-------
TABLE 3-1
Summary of Analytic Methods for Ammonia and Ammonium Ion
Method of Analysis Medium Sensitivity
Colorimetry-Nessler Aqueous 0.02 ing/liter
Comments
References
Traditional method, widely used in past; 7,49,69
numerous interferences, including alde-
hydes, sulfur dioxide, amines, and met-
als; prepurification by distillation
often recommended
Colorimetry-indophenol Aqueous 0.01 mg/liter
Colorimetry-pyridine-
pyrazolone
Titrimetry
NJ
o Conductimetry
Specific-ion
electrode
Ion chromatography
Ring oven
Aqueous 0.05 mg/liter
Aqueous 1 mg/liter
Aqueous 0.1 mg/liter
Aqueous <0.1 mg/liter
Aqueous <0.1 mg/liter
Filter 0.05 ug
substrate
Widely used; adapted for automated
analysis; less sensitive to interfer-
ences from Nessler method; pH-dependent
Some metals interfere, as do cyanate,
cyanide, and thiocyanate
All acids and bases interfere
Potential interferences from other re-
dox species
Slight interference by amines; commer-
cial units fast and easy to use, but
response slows at lower concentrations
New technique, now available in com-
mercial units; virtually interference-
free; requires little sample prepara-
tion
Adaptable for analysis of ammonia and
ammonium ion deposited on filters, as
well as for aqueous solutions; formal-
dehyde interferes, but can be separated
from sample
25,39,43,69,
71
36,53
7,48,64
17
4,69
66
64
-------
Method of Analysis Medium
Chemiluminescence Gaseous
Aerosol formation
Absorption spectros- Gaseous
copy
Gas chromatography Gaseous
Mass spectroscopy Gaseous
Sensitivity
1 ppb
Comments
Gaseous 0.01 ppb
Best results from combined chromato-
graphic application
Poor stability in past applications;
new device under development
20-20,000 ppb, Low sensitivity with simple unitsj
depending on can be improved substantially with
technique advanced adaptations, such as second-
derivative techniques
1 ppm
Sensitivity depends on detector
Sensitivity depends on unit and
sample preconcentration techniques
References
18,27
10
40
18,35,42,75
16,59
-------
free from interferences. It is also readily adaptable for auto-
mated analysis. In this method, ammonia and "hypochlorite ion
react to form monochloroamine, which reacts in alkaline solu-
tion with phenol to form the intense indophenol blue ion via
the intermediate quinone chlorimide:
NH3 + HOC1 F=^ NH2C1 + H20
C1H N + {"VoH + 2HOC1 —>• C1-N=^^=0 + ZQ.fi + 2HC1,
HO—/^V-N.=( /-O ^^ 0-v^ /~N-\_/~0 + IT"
indophenol
blue
The chief disadvantages of this method are its alleged pH depend-
ence and the rather cumbersome steps involved in preparing and
maintaining the necessary phenol and hypochlorite reagent solution.
The pyridine-pyrazolone method offers some advantages, al-
though it appears to be less sensitive. This technique is based
on the formation of a purple color by reaction of ammonium ion
with pyridine-pyrazolone reagent (3-raethyl-l-phenyl-5-pyrazolone
and pyridine in water solution). The method has been used com-
paratively little.so far.
Noncolorimetric wet-chemical techniques that have been
applied to ammonia analysis include acid-titration and con-
ductimetry. In general, these tend to be less sensitive than
the colorimetric methods and are subject to a host of interferences
232
-------
Relatively new "quasiwet" chemical methods that are finding
icreased application in ammonia analysis include the use of
b
>ecific-ion electrodes, ion chromatography, and ring ovens.
3.
jecific-ion electrodes for ammonia analysis are based on the
i;
referential migration of ammonia molecules (as contrasted to
nmonium ions) through a hydrophobic plastic membrane, which
2parates an ammonium chloride solution from the aqueous sample
3 be analyzed. Entrance of ammonia into the ammonium chloride
n:
Dlution until equilibrium is reached between the sample and the
I
lectrode solution results in a shift in pH, which can be used
I*
irectly as a measure of ammonia concentration. Specific-ion
lectrodes are especially attractive, because they are sensitive,
elatively free from interferences, and extremely easy to use.
on chromatography requires more costly and elaborate apparatus
! hhan the use of specific-ion electrodes, but has the advantage
an!')f allowing analysis of multiple species if cations in addition
lfflt".o ammonium ion are present in the aqueous sample. The ring-
f;>ven technique, described at length by West74 for analysis of
^articulate materials, has been adapted by Shendrikar and
fcodge°4 for ammonia determination. This adaptation shares the
[.'advantages of high sensitivity and selectivity with reasonably
ifigood accuracy- It is somewhat more involved than the use of
specific-ion electrodes, but certainly no more complex than most
i'Of the colorimetric methods listed in Table 3-1.
As seen in Table 3-1, a number of techniques allow the
.analysis of ammonia directly in the gas phase. Many of these
233
-------
have been rather successful in permitting the assessment of
ammonia at high concentrations; their performance at ambient
concentrations, however, has been marginal at best.
One of the more promising techniques for measuring ambient;'
ammonia involves adaptation of the conventional chemiluminescent
nitric oxide monitor. The air sample is passed over a catalyst!
that promotes quantitative oxidation of ammonia to nitric oxide,
and the resulting gas stream is fed directly to the chemilumi-
nescent analyzer. Early adaptations of this principle^ re-
quired concurrent measurements of ambient nitric oxide for sub-
traction to determine the ammonia contribution to the nitric
oxide content of the oxidized gas stream. Errors caused by
this subtraction process limited analytic sensitivity to about
20 ppb. Farber and Rossano^-S appear to have improved on this
situation a great deal, however, by providing a chromatographic
column for separation of ammonia from nitric oxide before oxi-
dation. This technique has allowed detection of ambient ammonia
with sensitivities approaching 0.5 ppb.
Gas chromatography has received more general application
with numerous other types of detectors for determination of
ammonia at higher concentrations.35,38,42,75 A standard diffi-
culty for all gas-chromatographic determinations of ammonia is
the selection of an appropriate column, which often presents sub-
stantial problems associated with the basicity of the ammonia
molecule.
234
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An additional method that has been examined for possible
36 as a sensitive atmospheric ammonia detector involves genera-
ion of an aerosol by gas-phase reaction of ammonia with hydro-
en chloride and detection with condensation nucleus counting,
'it
eta attenuation, or any other suitable aerosol-sensing technique.
il-
Ithough commercial instrumentation using these methods has been
!•
vailable, the results so far have been poor, with regard to both
"alibration and reliability. An improved apparatus being de-
promises to avoid these difficulties.
1
Absorption and mass spectroscopy have also been used for
'malysis of ammonia in the gas phase. Although both are generally
''restricted to concentrations above 1 ppm, their sensitivities
li:;an be improved by special adaptations.
*•' Commercial absorption-photometric detectors are available
'-for determination of ammonia at high concentrations , 40 and con-
itfcentrations of several parts per billion can be detected by such
adaptations as second-derivative ultraviolet spectroscopy.
((Standard mass-spectrometry techniques have been enhanced by such
adaptations as sample preconcentration and photoionization, 16 , s9
;;although these methods typically require considerable effort and
Expense .
: Remote-sensing applications for detection of atmospheric
ammonia are at a rather limited stage of development. Rapid
advances currently being made in the general field of remote
sensing, however, lead to the expectation that such techniques
235
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will soon find extensive use for ammonia detection. The variety
of remote-sensing methods for analysis of atmospheric trace gases
has been reviewed in several documents.30'37'43'51 These tech-
niques can be divided according to whether they provide integral,
long-path measurements or have ranging capability; further divi-
sions based on spectral regions and special adaptations (e.g.,
interferometry and correlation spectroscopy) are also possible.
Most remote-sensing applications for ammonia analysis
have involved the infrared region of the electromagnetic
spectrum.-^' ^O , 33 , 34 , 47 These have involved both active and
passive applications of simple absorption spectroscopy (sensi-
tivities reported in the region of a few parts per billion over
pathlengths of several kilometers) and special adaptations, such
as correlation spectroscopy and laser-acoustic techniques. Thus
far, most of these attempts have yielded integral results; as
with most similar applications, development of ranging capability
is much more difficult.
Microwave spectroscopy has been investigated as a means for
remote sensing of ammonia, but to a more limited extent than its
infrared counterpart.15 This portion of the electromagnetic
spectrum offers some interesting advantages in the case of
ammonia, because of this molecule's characteristic inversion
spectra (see Chapter 1). Applications of ultraviolet ranges
of the spectrum for remote ammonia sensing have been minimal
and should not be expected to become important, primarily
236
-------
jcause of the behavior of the spectrum, which is, for all
ractical purposes, occluded by absorption characteristics
f common atmospheric gases.
IL
^TERMINATION OF AMMONIA AND AMMONIUM ION IN NATURAL WATER
Analysis of the ammonia and ammonium ion content of water
Djis straightforward, because water is the preferred medium for
»;iany standard analyses (see Table 3-1) . The primary difficulty
Associated with analysis of ammonia in natural water is related
•PS
j,;o interference caused by other constituents. This problem may
36 countered by using such techniques as distillation^ for
.separating the impurities before analysis or by choosing an
analytic method that is insensitive to the specific impurities
at hand.
Measurements of ammonium in seawater are generally more
difficult than freshwater measurements, because of both lower
concentrations and higher interferences, particularly with
alkaline earth metals.57 por example, the classical Nessler
method still used for freshwater cannot be used in seawater
determinations. Seawater methods have evolved from distilla-
tion procedures to direct colorimetric determinations, some
of which have been automated.22,26,32,44,65 ^^e four principle
methods in recent use are discussed below. (Much of this dis-
cussion is based on the recent comprehensive review by Riley, '
to which the reader is referred for further details.)
237
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Indophenol Blue
For use with seawater, there have been many investigations51
of the indophenol blue method, with respect to optimal pH, reager
concentrations, and reaction times. The slow conversion of the
intermediate quinone to indophenol blue is catalyzed by sodium
nitroprusside2^ or potassium ferrocyanide.41
The primary turbidity interference resulting from precipita-
tion of calcium and magnesium compounds at the high pH used for
color development is best avoided through addition of complexing
agents, such as citrate.^2'°'
Koroleff^2 has modified the indophenol blue method for
at-sea analysis and discussed interferences with hydrogen sulfidf
in anoxic waters. In his method, phenol and-sodium nitroprussick
are added directly to a seawater sample as a single reagent, and
then an alkaline hypochlorite solution is added. The turbidity
interference is avoided by rapid settling of the precipitate.
Total sulfide can be present at up to 0.06 mM (2 mg/liter) with-
out interference. Samples with higher sulfide content (e.g.,
from the Black Sea) can be diluted; their ammonium content is
very high.
Solorzano's67 method using sodium nitroprusside and citrate
has been widely adopted, but lacks reproducibility 'and has high
blanks.41 Liddicoat et a.!.41 have linked part of the problem
to the sodium nitroprusside and have substituted potassium
ferrocyanide for it. Variations in commercial hypochlorite
238
-------
solutions, for which they recommend substitution of sodium
dichloro- iso-cyanurate , have also been cited as part of the
problem.
Day-to-day variations in color development noticed by
Liddicoat et_ a_1.41 were attributed to differences in light
intensity and overcome by irradiation with ultraviolet lamps
- 365 nm) during color development.
Oxidation to Nitrite
A very sensitive ammonium determination method based on
oxidation of ammonium to nitrite has been developed by Richards
and Kletsch.55 The oxidation is carried out in highly alkaline
solution with hypochlorite and bromide as catalysts. Nitrite
is determined after removal of excess hypochlorite with sodium
arsenite and acidification. The major source of error is
variable decomposition of nitrite after acidification.
A problem is interference from amino acid nitrogen. The
technique is useful primarily in determination of ammonium plus
biologically useful amino acids, rather than ammonium alone.
Hypobromite Oxidation
A less specific method for ammonium plus other organic com-
pounds uses an oxidation step with excess hypobromite. The ex-
cess hypobromite remaining after oxidation is determined colori-
metrically with starch or iodide.54 The major problem is that
other nitrogen-containing organic compounds, such as urea and
239
-------
amino acids, will also reduce hypobromite. This method could
be combined with a distillation step.
Rubazoic Acid
Practical details of the pyridine-pyrazolone method de-
veloped by Kruse and Mellon36 and later applied to seawater were
described by Strickland and Parsons. The original method witl
pyridine has been modified by Prochakova54 into a two-stage
process. Ammonium reacts with chloramine T at a pH of 6.5. The
solution is then buffered to a pH of 10 with sodium carbonate,
and bispyrazolone and pyrazolone are added- When formation of
rubazoic acid is complete, it is extracted with trichloroethylene
for colorimetric analysis.
DETERMINATION OF AMMONIA AND AMMONIUM ION IN SOILS
The measurement of ammonia and ammonium in soils can be
divided into measurement of the gas phase (evolved gas or that
in the interstitial area between soil particles) and the con-
densed phases (groundwater, solids). The gas-phase fraction is
particularly important, because of its relationship with the
rate of ammonia loss from soils.
In nitrogen-balance studies of agricultural and natural
land ecosystems, less attention has been given to gaseous losses
than to other components of the budget, because of sampling and
analytic problems. Most studies arrive at gaseous losses by
difference; thus, all the accumulated errors are in this estimatic
240
-------
Ammonia gas evolved from the ground is one of the simpler
gaseoub components to deal with; yet the determination of
liquid-phase ammonia in a chunk of soil is elusive, because of
the dynamic character of the numerous reactions going on in
such a living system.
Gas Phase
Analytic procedures for ammonia in air have been dealt with
earlier in this chapter. Procedures for collecting and evaluating
ammonia evolved from the land are considered here first. (Much
of this, subject is covered in a thorough review by McGarity and
>;
Rajaratnam.^6)
Whether single or multiple components of the gaseous nitro-
gen lost are collected from the field, three provisions have to
be met to maintain natural integrity of the system:
• In either long- or short-term studies, the imposed
environment must represent the natural cyclic con-
ditions of the field site.
• The soil substrate must represent the natural proper-
ties and inherent heterogeneity of the field site.
• The confining, monitoring, and measuring devices and
sampling methods must not produce artifacts or create
artificial conditions likely to influence the natural
processes under study.
241
-------
The classification of methods in Table 3-2 is a McGarity
and Rajaratnam46 modification from Ross et al.58
In Table 3-2, two major categories are "open" and "closed"
systems. In the latter, the soil, plant, and atmosphere are
completely enclosed, and concentration changes are measured
either by accumulation or by input-output difference. In "open"
systems, the soil-plant components are unconfined or only
partially confined, and only particular products may be monitored.
In both kinds of system, gaseous change may be desirable to main-
tain the natural integrity of the system.
Volatilization Chambers. Many different types of chambers
or covers have been placed directly over field sites, with simple
equipment, such as an absorption sink, placed inside. Released
gases may be purged by an external input-output system with an
absorption train outside the chamber or cover. There are dis-
advantages in this system: water condenses on the cover, gas
is adsorbed in the liquid, and the liquid later drips back to
the soil; and control of air, soil, and plant temperatures in
the chamber is difficult.
Soil-Air Reservoirs. Small air reservoirs may be placed in
the field, either in the soil or above the soil, and connected
to the soil profile by wells. Well design depends on the shrink-
ing properties of the soil, the depth of insertion, and the volume
of the gas to be removed. Reservoir air is periodically sampled,
242
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TABLE 3-2
Apparatus used in Studies of Gaseous-Nitrogen Loss—
item
Apparatus
Site
Gases Measured—
Tontinuous flow Volatilization
r chamber
Field NH , N02
liDiffusion
*!
Diffusion
Air reservoir (Van Field
Bavel well)
Aerometric
apparatus
Field
N20,
/ N0
N20, 15N2, N02 ,
NH3
osed:
^Continuous flow Volatilization
chamber
'Diffusion
Diffusion
Electrolytic
respirometer
Gas lysimeter
Glasshouse^ NH^ , NO2
Growth chamber Cabinet?, NH3 , NG>2
Cabinet
15
NH3 , N2O, N2/
NO, NO2
Glasshouse NH-j , N20, N2
NO, N02
Data from McGarity and Rajaratnam.46
Italics indicate gases measured in experimentation; apparatus
appears suitable for other gases listed, with analytic tech-
niques now available.
Controlled indoor environment.
243
-------
yielding an equilibrium concentration for the depth sampled.
Concentration differences in relation to depth allow rough cal-
culation of gas fluxes with diffusion theory. Accuracy is not
very great, but the depth of activity can be identified and
correlated with other characteristics.
Aerometric Apparatus. This device is a combination of the
two methods just noted, with a cover over the soil and access
wells in the soil. It allows control of gas (i.e., oxygen and
carbon dioxide) in the cover or chamber, so that the influence
of gas on soil processes below the ground can be studied. Accesi1
wells and air reservoirs permit soil-profile sampling for fluxes;
and activities in the ground.
Closed Volatilization Chambers. These chambers are similar
to the open chambers or covers, except that the soil is also
enclosed. Such a system affords controlled soil environment,
if this is desired. It also allows moving the whole unit to a
glasshouse or growth chamber. Obviously, natural conditions
become harder to simulate.
Respirometers. Electrolytic respirometers allow maintenance
of predetermined oxygen concentrations in a restricted volume
above the soil, so that evolved gases can accumulate to concen-
trations suitable for measurement. Oxygen consumption is measured.,
continuously- The chief disadvantage is the requirement of close
temperat-re control.
244
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Gas Lysimeters. This unit is similar to the closed volatiliza-
'<•;
.on chamber, with more rigid control of the environment and gas-
*''
cchdiHje system, as well as enclosure of a sizable "undisturbed"
jil core in a more or less natural state. Small amounts of gas
an accumulate to measurable concentrations, and major safeguards
re taken against leaks. The idea behind this unit is that un-
..isturbed soil of sufficient depth includes biologically active
,iubsoil horizons (layers); this helps to avoid limitations in-
lerent in the use of only surface horizons.
liquid Phase
It was mentioned earlier that the determination of ammonia
and ammonium in the liquid phase of soil present difficult
problems, because of their dynamic nature. Not only do life
processes constantly change the content of dissolved ammonia and
ammonium, but physical processes of the soil colloidal system
render these compounds "fixed" in the system over a wide range
of "availability." The instability of nitrogen compounds plagues
the analyst all the way along—in adequately sampling the soil
in time and in space, in transporting and storing the soil before
extraction, in extracting the soil for the various forms or degrees
of fixation, in storing the extracts until analysis, and in main-
taining integrity during analysis. Bremner^ clearly described
the problems of sampling, extracting, and analyzing for inorganic
combined nitrogen in the form of ammonium in soil.
245
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Until recent, it was generally assumed that only a small
proportion of the total nitrogen in soils was in the inorganic
form. It is now well established that soils have the capacity
to fix ammonia (i.e., to absorb ammonium in such a manner that
it is not readily exchangeable). Both organic and inorganic
soil constituents can fix ammonium, but it is assumed that most
of it is fixed in the lattices of silicate minerals.
Bremner^ defined exchangeable ammonia as that which is
extracted by a 2 N potassium chloride solution, and nonexchange-
able (or fixed) ammonia as that which is released by a 5 N
hydrofluoric acid—1 N hydrochloric acid solution after treat-
ment with potassium oxybromide-potassium hydroxide solution to
remove both exchangeable ammonia and labile organic nitrogen
compounds.
Current data indicate that the proportion of soil nitrogen
in nonexchangeable ammonium is usually 5% or less in the surface
soil. It may exceed 30%, however, in some subsoils.
The determination of exchangeable ammonium is complicated
by the fact that it is subject to rapid change due to ammonifi-
cation, nitrification, and other microbial processes. Samples
should be analyzed immediately after collection, lest the results
be invalid. Because this is sometimes impractical, reagents may
be added to inhibit microbial activity. Other methods of preser-
vation are more satisfactory, such as very rapid drying at 55° C,
then sealing of the sample in airtight containers to prevent
246
-------
contamination from the natural background ammonia in the air.
Even rapid drying and careful storage create changes, so early
analysis soon after sample collection is preferred, if it is at
all possible.
Direct colorimetric methods of analyzing soil extracts for
ammonia have been attempted with little success, so distillation
methods have generally been used. In the distillation methods,
ammonium is estimated from the ammonia liberated by distillation
of the extract with an alkaline reagent. Rapid steam distilla-
tion now seems to be the preferred method. Direct steam dis-
tillation without preliminary extraction is a recent attractive
method that avoids many of the disadvantages inherent in soil
extraction.
DETERMINATION OF AMMONIA IN BLOOD AND TISSUES
Simple and reliable methods for the determination of ammonia
in biologic materials would be of considerable clinical value.
Hsia28 began his review of inherited hyperammonemic syndromes
with the statement that "the detection of disturbances of ammonia
concentration in biological tissues has been hampered by the lack
of a convenient, sensitive, and accurate technique for measuring
ammonia in small volumes of blood."
The difficulty in analyzing biologic materials for ammonia
is not the inherent difficulty or insensitivity of the methods
for detecting and quantifying the ammonia molecule (these general
methods have been discussed previously in this chapter), but
247
-------
rather the problem of avoiding interference provided by ammonia
generated during the course of analysis from both protein and
nonprotein glutamine. The amide group of glutamine is labile,
both chemically and enzymatically (see Reaction 2-29); bio-
logic materials contain ammonia at low concentrations in the
presence of relatively high concentrations of glutamine. Even
slight hydrolysis of glutamine amide can produce a large error
in the estimation of ammonia.
Colombo-'--'- tabulated methods for determining ammonia in
blood (see Table 3-3). The stability properties of glutamine
have been summarized in detail by Greenstein and Winitz.
The heart of the problem of ammonia analysis in biologic
materials is the selection of conditions that can provide com-
plete recovery and detection of free ammonia while minimizing
the contribution of the amide nitrogen of glutamine. The in-
stability of glutamine has long been known and was noted almost
simultaneously with the discovery of glutamine.62,63 it was
found that a material that reacted with Nessler's reagent (and
therefore presumably ammonia) appeared when glutamine solutions
were permitted to stand. Chibnall and Westall8 and Vickery
et al.72 studied the loss of amide nitrogen from glutamine and
described the formation of the cyclic product of glutamine de-
amination, pyrrolidonecarboxylic acid. Their studies provided
a thorough description of this process; pyrrolidonecarboxylic
acid is formed best in neutral solution, whereas glutamic acid
248
-------
TABLE 3-3
Method of Determining Ammonia in Blood5.
Normal Concentration
of Ammonia Nitrogen
'•«!• in Venous Whole Blood,
E Determination yjg/100 ml Reference
% "
n of ammonia (by distillation,
:liion, or diffusion) and determination by:
-titration 0 14
ljt:r reaction for colorimetry:
:th Nessler's reagent 50-120 56
,th ninhydrin 47-102 50
.th phenol-hypochlorite 73+13 73
!!f.th hypobromite-phenosafranin reaction —b 70
'.onbmetric jtitration —£ 9
)li:
ion of ammonia on ion-exchange resin
jjjjtermination in the eluate by color
Ion:
i,n Nessler's reagent 39+11 29
S phenol-hypochlorite 6-50 19
colorimetric determination of ammonia
,otein-free e:
-------
is the product of glutamine hydrolysis in strong acid or alkali,
Thorough studies of the chemical examination of glutamine have
been performed by Hamilton,24 who found that in neutral solution
pyrrolidone-carboxylic acid formation was stimulated by inorganic*
P
phosphate, and by Gilbert et ail. ,21 who studied the effects of
phosphate and arsenate on this process. The formation of
pyrrolidone-carboxylic acid in neutral solution explains the
observation that the glutamine amide nitrogen is more stable in
protein linkage than with free glutamine; the formation of the
cyclized derivative provides additional thermodynamic driving
force for the removal of ammonia.
The prevention of glutamine interference has been approached
by investigators in several fashions; usually, these have focused
on the control of pH and temperature, Conway-^ measured blood
ammonia by diffusion techniques at room temperature and extrapo-
lated his values back to zero time of diffusion. He concluded
that ammonia was completely absent in blood—a conclusion not
verified by later workers. Archibald^ •• 3 used vacuum distilla-
tion, keeping the temperature of the solution below 38°C and
using a pH of 10.1 to minimize glutamine hydrolysis. In analyzing
both ammonia and glutamine in tissue, he assayed glutamine first
by distilling free ammonia and then adding a crude kidney homogenat
(which contained glutaminase) to release ammonia from glutamine;
this ammonia was then distilled, and the distillate was analyzed
by various techniques. Speck,68 who studied the biosynthesis of
250
-------
tamine, analyzed ammonia and glutamine simultaneously by
I;
hniques based largely on the studies of Archibald.
i'<
The various techniques used in blood ammonia analysis and
ted by Colombo11 ultimately incorporate the same ammonia-
.ection methods previously described, but with various analytic
I:
iditions to minimize interference.
!:
Because cells have higher protein concentrations than tissue
);
lids, ammonia analyses in cells are even more subject to
(•
itamine-caused errors than are analyses, in cell-free materials.
i
is questionable whether reliable analyses have ever been per-
t 1 T
rmed. Conn has presented data from analyses of plasma and
Die blood and has calculated from these data the ammonia con-
'ntration in red cells. Red-cell ammonia varies with plasma
"monia in a systematic fashion (plasma average, 136 yg/100 ml;
'd-cell average, 258 yg/100 ml) , but a correlation plot of
".ole-blood ammonia (ordinate) versus plasma ammonia (abscissa)
"ies not go through the origin. The possibility must be enter-
'iined that this discrepancy represents a red-cell pool of a
"ibile ammonia precursor, perhaps glutamine.
251
-------
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General Dynamics Corporation, 1969. 160 pp.
44. Maclsaac, J. J., and R. K. Olund. An automated extraction procedure for
the determination of ammonia in seawater. Invest. Pesq. 35:221-232,
1971.
45. McCullough, H. A simple micro technique for the determination of blood
ammonia and a note on the effect of exercise, Clin. Chim. Acta
19:101-105, 1968.
46. McGarity, J. W., and J. A. Rajaratnam. Apparatus for the measurement of
losses of nitrogen as gas from the field and simulated field envir-
onments. Soil Biol. Biochem. 5:121-131, 1973.
47. Menzies, R. T., and M. S. Shumate. Air pollution: Remote detection of
several pollutant gases with a laser heterodyne radiometer. Science
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48. U. S. Environmental Protection Agency. Water Quality Office, Analytical
Quality Control Laboratoratories. Methods for Chemical Analysis of
Water and Wastes 1971. Washington, D. C. : U. S. Government Printing
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256
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^Morgan, G. B., C. Golden, and E. C. Tabor. New and improved procedures
for gas sampling and analysis in the national air sampling network.
J. Air Pollut. Control Assoc. 17:300-304, 1967.
Nathan, D. G., and F. L. Rodkey. A colorimetric procedure for the deter-
mination of blood ammonia. J. Lab. Clin. Med. 49:779-785, 1957.
National Aeronautics and Space Administration. Remote Measurement of
Pollution. NASA-SP-285. Langley Station, Va. : NASA Langley
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Ohira, T. , M. Takeda, T. Ishiguro, and 0. Koyama. Offensive odors. 7.
Gas chromatographic analysis of offensive odors at plants handling
fish entrails and bones. Taiki Osen Kenkyu (J. Jap. Soc. Air Pollut.)
2:49-50, 1967.
Okita, T. , and S. Kanamori. Determination of trace concentration of
ammonia in the atmosphere using pyradine-pyrazolone reagent. Atmos.
Environ. 5:621-627, 1971.
Prochazkova, L. Spectrophotometric determination of ammonia as rubazoic
acid with bispyrazolone reagent. Anal. Chem. 36:865-871, 1964.
Richards, F. A., and R. A. Kletsch. The Spectrophotometric determination
of ammonia and labile amino compounds in fresh and sea water by oxida-
tion to nitrite. Recent Res. Fields Hydrosphere, Atmos. Nuclear
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Richterich, R., J. P. Colombo, and H. Weber. Ultramikromethoden im
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ii
Bestimmung von Harnstoff und Ammoniak in Blut und Urin. Arztl. Lab.
8:259-267, 1962.
Riley, J. p. Analytical chemistry of sea water, pp. 193-514. In J. P.
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it
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S
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259
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CHAPTER 4
SOURCES, CONCENTRATIONS, AND SINKS OF ATMOSPHERIC AMMONIA
PRODUCTION AND USE OF AMMONIA
This section deals with the historical events and technical
developments that have led to the present-day industrial produc-
tion of ammonia. Ammonia is the source of the nitrogen in fer-
tilizers, although it may first be converted into other nitrogen
products, such as urea, nitrates, or ammonium phosphates. Most
of the 14,870,000 tonnes* of ammonia produced in the United
States in 1975 went into fertilizers or was used to supply the
nutrient nitrogen in animal food. Nitrogen fertilizer is applied
directly to the soil as both anhydrous and aqueous ammonia and
as various ammonium and nitrate compounds. More nitrogen is applied
to the soil as anhydrous ammonia than as any other compound. Ammonia
is used to make synthetic fibers, plastics, and glues, in the treat-
ment and refining of metals, and in the production of explosives.
At the beginning of the twentieth century, arable land in
the united States was plentiful, and the nation's growing food
requirements were met by cultivating more land. In the 1930's
and 1940's, crop yields began to be increased, and the exploitative
use of land for growing the nation's food was averted. Industrial
*A tonne (abbreviated t), or metric ton, is 1,000 kg. A ton, or
short ton, is 2,000 Ib. 1 tonne - 1.1 tons.206
260
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processes for combining atmospheric nitrogen with hydrogen have
constituted one of the more important technologic innovations
leading to the reduction in the land needed to produce a given
quantity of food. Ammonia requirements used to be met by the
carbonization of coal; today, only about 134,000 t of ammonia
per year are produced by this, method in the United States.30
Origin of the Ammonia Industry
At the end of the nineteenth century, industrial nitrogen-
fixation processes were being sought to obtain nitrates for the
manufacture of explosives and to capture nitrogen in a nutrient
form suitable for use in growing crops. Nitrate explosives were
being used in industry and as munitions. The United States did
not have adequate indigenous mineral nitrates, but depended on
imported sodium nitrate (Chilean saltpeter). With increasing
consumption of mineral nitrates throughout the world, it appeared
unwise to continue to rely on the imported mineral, particularly
as a source of nitrates for munitions. Thus, there was much in-
centive to develop processes for fixation of the virtually limit-
less supply of atmospheric nitrogen.
Industrial fixation of nitrogen began at Niagara Falls,
New York, in 1902 with a process22 whereby an electric arc was
used to form nitrogen oxides from air and these oxides were con-
verted into nitric acid. The early attempt to fix nitrogen in-
dustrially was short-lived: the plant was shut down in 1904,
mainly because the nitric acid produced was impure. Similar
nitrogen-fixation plants, constructed at places where electric
261
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energy was abundant, were more successful. Perhaps the best known
was the Birkeland-Eyde process plant built in Norway to make sodiun
nitrate. Another electric-arc plant built at Niagara Falls con-
tinued to operate until 1927.
About 1902, in Germany, Wilheln Ostwald developed a process
for making nitric acid from ammonia.8'29 A nitric-acid plant
using his process was built in Gerthe, Germany, in 1908. At
first, Ostwald's process did not work well, because the ammonia
used was made by carbonizing coal and was impure. Ammonia pro-
duced later by the fixation of nitrogen contained few impurities
and was better suited for making nitric acid by Ostwald's process.
In 1895, Adolf Frank and Nikodem Caro in Germany had developed
the cyanamide method for the fixation of atmospheric nitrogen. 10»22,
Atmospheric nitrogen was captured by having it react with calcium
carbide to form calcium cyanamide, and treatment of calcium cyan-
amide with water produced ammonia. (Calcium cyanamide could al-
so be used as fertilizer without proceeding to the production of
ammonia.) The ammonia produced in this way was amenable to the
production of nitrates by the Ostwald process. .A plant was built
in Canada at Niagara Falls in 1907 to produce calcium cyanamide.
The electric energy requirements were high—about 22,000 kWh/t
of atmospheric nitrogen fixed, and this limited nitrogen-fixation
plants that used the cyanamide process to locations where electric
energy was cheap and plentiful; nevertheless, some calcium cyan-
amide plants were constructed in several countries.
262
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Fritz Haber, another German scientist, proceeded to make
ammonia directly by combining atmospheric nitrogen with hydrogen
(see Chapter I).13 In 1913, a small (30 tons/day, or 27 t/day)
32
ammonia plant went onstream in Ludwigshafen-Oppau, Germany;
ammonia is still being produced at this site.
When it became apparent that World War I would extend beyond
the depletion of the Chilean saltpeter stockpile, the Haber ammonia
plant was enlarged and another ammonia plant was built. The am-
monia produced was converted into nitric acid by Ostwald's method,
and nitrates needed for munitions were made from the nitric acid.
In the United States, as importation of Chilean saltpeter
became threatened by submarine warfare, a small (27 t/day), largely
experimental Haber-process plant was built. This early attempt
to adopt the Haber process was unsuccessful. A plant was started
at Muscle Shoals, Alabama, in the latter part of 1917 to fix nitro-
gen by the better-known cyanamide process, with the objective of
producing ammonium nitrate for munitions in World War I. The
plant began production on November 12, 1918, the day after the
Armistice. The plant's capacity was 136 t of ammonia per day
(150 tons/day). It operated for a short test period only, be-
cause the product was no longer needed for munition.
After World War I, research and development continued in
the United States on the Haber process for the production of
ammonia by combining hydrogen and nitrogen.1® This work led to
the construction of a Haber-process ammonia plant at Niagara
Falls, New York; a small plant at Syracuse, New York, operating
263
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at the end of the war, was improved and enlarged. Large ammonia
plants were constructed at Belle, West Virginia, Hopewell,
Virginia, and various other locations throughout the world. By
1930, ammonia was being produced in eight plants in the United
States, with an annual capacity of about 146,000 t of nitrogen,
and 79 plants throughout the world, with a total annual capacity
of 1.8 x 106 t of nitrogen.
Ammonia Production Trends
World War II brought a further increase in ammonia produc-
tion: 10 new plants were constructed during the early 1940's,
with a combined capacity of 726,000 t of nitrogen per year. Indi-
vidual plant capacities ranged from 45,000 to 181,000 t/year.
One of these, at Muscle Shoals, Alabama, was built by the Tennessee
Valley Authority; it started operation in August of 1942 and
operated for nearly 29 years.
The growing need for fertilizer nitrogen brought about another
rapid expansion of ammonia production in the 1950's and 1960's.
By 1962, U.S. production was 4.3 x 106 t of nitrogen per year,
and world production was 14.0 x 106 t. U.S. and worldwide pro-
duction for the period 1962-1975 and expected production through
1980 are plotted in Figure 4-1.
From 1962 to 1975, the average annual increase in production
in the United States was 8.3% and, worldwide, 10.1%. Over the
last 5 years of that period, the annual average increase in the
U.S. was 3.5% and, worldwide, 7.2%.
264
-------
801—
0
1962 1964 1966 1968 1970 1972 1974 1976 1978 1980
FISCAL YEAR
FIGURE 4-1. U.S. Worldwide nitrogen production.
265
-------
In 1975, ammonia was produced in some 93 plants in the
United States; annual U.S. production capacity was 13.7 x 106 t
of nitrogen,7'37 and about 11.8 x 106 t of nitrogen were pro-
duced. The worldwide production capacity was 69.1 x 10 t of
nitrogen, with 457 plants operating. The United States has
20% of the world's capacity and the same percentage of the
world's ammonia plants. The USSR is second, with 14% of the
world's capacity and 13% of the plants.
Various TVA publications1^/16,17,19 nave given estimates
of future production of ammonia and trends in its consumption
in fertilizers. A study by an international group-^3 predicted
in 1975 that worldwide production in 1985 would be about
83.9 x 106 t of nitrogen.
Figure 4-2 shows the locations and capacities of the U.S.
plants. Louisiana, Texas, and California lead the states in
ammonia production capacity. The capacity at a given site ranges
from 6,000 t/year in a plant at Portland, Oregon, operated by
Pennsalt Chemicals, to 535,000 t/year in a plant at Texas City,
Texas, operated by Amoco Oil Company.
Figure 4-3 shows the distribution of plant capacity in the
United States. The median capacity is 119,000 t of nitrogen per
year (396 t of ammonia per day), but the median capacity may
increase as small plants are phased out and larger plants are
put into production. A capacity of 907 t of ammonia per day
(1,000 tons/day) is generally taken as typical in making economic
calculations of ammonia production.
266
-------
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93 PLANTS IN 30 STATES
CAPACITY 13.7 MILLION METRIC
TONS N PER YEAR
* I
FIGURE 4-2. Number, location, and capacity of ammonia plants in the United States (1975)
-------
oo
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FXOSUKE 4-3.
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PLANT CAPACITY IN IOOO METRIC TONS NITROGEN PER YEAR
Size of ammonia plants in the United States.
-------
Ammonia Production Technology
An iron catalyst was used in the original Haber process to
increase the rate of reaction between nitrogen and hydrogen to
form ammonia. The iron catalyst had to be unusually pure to be
effective, and all impurities—such as phosphorus, sulfur, and
chlorine--that permanently poison the iron catalyst had to be
removed from the nitrogen-hydrogen mixture. Oxygen and oxygen
compounds (including water vapor) will form iron oxide that will
poison the catalyst temporarily or, if formed repeatedly, per-
manently- Much of the early work on ammonia production involved
perfecting the engineering processes to cleanse the nitrogen-
hydrogen mixture of impurities to avoid catalyst poisoning.
The earlier ammonia plants built in the United States used
electrolytic hydrogen or water gas (a mixture of hydrogen and
carbon monoxide) and atmospheric nitrogen as feedstocks.
Electrolytic-hydrogen ammonia plants are now uncommon, owing to
their large energy requirements. Byproduct hydrogen from the
production of other chemicals is commonly converted into ammonia.
Water gas produced from coke gasification required extensive
cleaning to remove impurities.
At first, ammonia-plant gases were cleaned by absorbing the
impurities in aqueous solutions and by filtering. Gaseous im-
purities driven from the absorbing solutions were discharged into
the air, causing some pollutant emission. After the mixture
hydrogen-nitrogen was cleaned, it was compressed to about
300-350 atm (about 30,400-35,500 kN/m2) to make the elements
269
-------
combine and form ammonia. The ammonia-plant gases were com-
pressed at various steps of purification to decrease the size
of equipment required.
In the 1940's ammonia-producers began using natural gas
as a feedstock and the reaction of hydrocarbons (mainly methane)
with steam to make a mixture of hydrogen, carbon monoxide, and
carbon dioxide. This process is called "steam reforming." A
mixture of steam and natural gas flowed through heated metal
tubes filled with a nickel catalyst. The tubes were suspended
in a furnace, and fuel (usually natural gas) was burned in the
furnace to heat the tubes. Air was then added to the process
gas stream to furnish nitrogen, and some of the gases burned to
provide additional heat needed for the reforming reactions. The
carbon monoxide in the hot gas reacted with water to produce
additional hydrogen, and the last traces of oxygen and oxygen
compounds were removed. Natural gas is a relatively clean fuel,
but sulfur, if present, must be removed before reforming, to pro-
tect the catalyst and to protect the reformer tubes from corrosion.
An ample supply of low-cost natural gas in the 1950's in
the United States resulted in its widespread use to make ammonia.
Hydrogen produced from natural gas cost less than hydrogen made
from coke and water, and reformers were simpler to operate and
caused less air pollution than either coke or coal gasification
equipment. Naphtha is widely used as a feedstock; coke-oven
gas can also be used. Methods were recently developed to use
municipal solid waste as a feedstock.
270
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The recent natural-gas shortage has threatened the continued
use of this fuel for making ammonia, although only about 2.5% of
the nation's natural gas is used for this purpose. During the
winter of 1975-1976, natural-gas shortages caused the loss of
production of 185,000 t of ammonia.
Fuel oil was used in the reformer furnaces built in the
1950's as a substitute fuel for firing the furnaces. The later
development of the pressure reforming process precluded the use
of such liquid fuels. However, methods have recently been de-
2 6
veloped that permit vaporized fuel oil to be used. This will
permit the replacement of about one-third of the natural gas
with fuel oil and thereby help to relieve the natural-gas shortage,
The following developments merit special mention, because
they affect the emission of air pollutants.
• Processes to remove carbon monoxide by internal
methanation, instead of aqueous scrubbing; Before
the adoption of methanation, carbon monoxide was
removed from the process gas stream by scrubbing
the gas with an ammoniacal copper solution at
about 0° C. The copper solution was heated to drive
out absorbed carbon monoxide gas, and some ammonia
was emitted with the carbon monoxide. With methana-
tion, carbon monoxide and carbon dioxide in the gas
both react with steam in the presence of a catalyst
to produce methane, and the methane flows through the
synthesis system as an inert gas without adverse ef-
fect on the ammonia catalyst. Consequently, methanation
271
-------
has eliminated the emission of carbon monoxide
and ammonia in this part of the purification
system at ammonia plants.
Use of purge gas as fueJ: Hydrogen, nitrogen, and
some uncondensed ammonia can be lost to the atmo-
sphere when the inert gases are vented. In modern
ammonia plants, the purge gas is burned to supply
part of the heat needed in the natural-gas reformer.
In some plants, the purge gas is burned at nitric
acid production facilities nearby for the abatement
of NOV emission.
J\.
Pressure reforming of natural gas; The first natural-
gas reformers operated at slightly above atmospheric
pressure. In the late 1950's, ammonia-plant reformers
began to be operated at increased pressures. Opera-
tion at high pressure was made possible by improved
metallurgy, which permitted reformer tubes to with-
stand both high pressure and high temperature.
Pressure reforming substantially decreases equipment
size, improves heat transfer-, and thereby decreases
the fuel requirement and the emission of pollutants
resulting from fuel combustion. Although operation
at 30 atm (3,040 kN/m2) is now common, the trend
toward increased reformer pressure appears to be
continuing.5 Further improvement in ammonia-plant
efficiency may be achieved as metallurgy permits
operation of reformers at even higher pressures.
272
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• Improved carbon monoxide shift catalyst; Improved
catalysts now give greater carbon monoxide conver-
sion at low temperature; this decreases the amount
of unreacted carbon monoxide gas that remains in
the gas stream and makes it possible to use methana-
tion to remove the last traces of carbon monoxide
in the gas stream before the synthesis of ammonia.
However, the combination of contact of the gases
with iron and copper catalysts and pressure causes
some ammonia and organic compounds (mainly methanol)
to be formed. The ammonia and methanol come out in
the condensate, and this causes a water pollution
problem, if the condensate is discharged as an effluent
without treatment.
• Refrigerated storage of ammonia at atmospheric
pressure: This essentially eliminates storage losses
at manufacturing plants and terminals. Ammonia may be
transferred from storage tanks to transporting equipment
with little loss of ammonia vapor.
Ammonia production requires a source of hydrogen. The
production of this hydrogen from hydrocarbons or from reaction
of water with coal or coke can itself be a source of pollution
as an accompaniment to ammonia synthesis. Therefore, the en-
vironmental effects of hydrogen-producing processes will be
examined.
273
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The TVA first produced ammonia in August 1942 from a mixture
of water gas and producer gas—obtained by the gasification of
coke. Environmental problems encountered in the gasification of
coke were inadvertent leakage of carbon monoxide gas into the
workroom, disposal of spent scrubber solution obtained at a
sulfur removal facility, and disposal of ash from the coke.
Leakage of carbon monoxide gas into the working area caused a
hazard to employees. The EPA has recognized the environmental
problems associated with the gasification of solid fuels and is
actively pursuing the development of appropriate new-source
performance standards, in anticipation of the construction of
commercial-scale coal-gasification processing facilities. In
1951, the TVA ammonia plant was modified, and the feedstock was
changed to natural gas.4 A natural-gas reformer was installed
and operated at approximately atmospheric pressure, because
methods for pressure reforming had not been developed. The
conversion to natural gas as a feedstock significantly decreased
ammonia production cost and diminished the formidable environ-
mental and safety problems associated with solid-fuel gasifica-
tion. A refrigerated ammonia storage facility was installed in
1965 and decreased ammonia losses that occurred when ammonia was
stored or loaded for shipment.
In January 1972, a modern ammonia plant, illustrated in
Figure 4-4, was put into operation. By this time, methods for
pressure reforming of natural gas had been developed, and a
30-atm (3,040-kN/m2) pressure reformer was installed. Carbon
monoxide and carbon dioxide are removed by methanation; thus,
274
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Compressor
Stack
Process
Air
\ ^v A \ A '
\' \' \ \'\'
Low Temp.
By-Product Shjft Conv
C02 ^ __
CO2
Absorber
Regenerator
Steam
-c
•E
Low Temp.
Sulfur Guard
Secondary
Reformer
High Temp.
Shift
Conv.
X
\/
Natural
Gas
Feedstock
Separator
Recirculating
Compressor
Figure 4-4 Diagram of anhydrous ammonia production process.
-------
the air pollution associated with their emission has been elimi-
nated. The purge gas emitted at the ammonia synthesis converters
is burned as fuel in the reformers, to form nitrogen and water
vapor—both nonpollutants.
Emission from Ammonia Plants
Natural gas contains small amounts of sulfur compounds—a
minor source of air pollution. The sulfur in natural-gas feed-
stock present as hydrogen sulfide or mercaptan is normally re-
moved from the gas stream by adsorption on metal-impregnated
carbon. The sulfur compounds are discharged in the air when
the treated carbon is regenerated. The sulfur emission, calcu-
lated as sulfur dioxide, is 0.1 kg/t of ammonia produced, but
it would be 0.7 kg/t if the natural gas contained the maximal
sulfur content allowed under interstate gas contracts. When
natural gas is the process fuel for the reformer, the sulfur
dioxide emission will be 0.03 kg/t, but could be up to 0.3 kg/t
if the natural gas contained the maximal allowable sulfur con-
tent. At some ammonia plants, fuel oil supplies the process heat
for the reformers; reformers fired with No. 2 fuel oil result in
a sulfur dioxide emission of about 3.3 kg/t of ammonia. Some
nitrogen oxides are formed during combustion in the reformer,
and these oxides are emitted in the exhaust gases. An analysis
of the reformer exhaust gases at the TVA showed an NOV concen-
X
tration, calculated as nitrogen dioxide, of 229 mg/m3 of exhaust
gas, and the mass emission rate was 0.6 kg/t of ammonia produced.
276
-------
Alkaline scrubbing is used to remove the bulk of the carbon
dioxide when gas is purified for ammonia synthesis. A small
amount of carbon monoxide is absorbed in the scrubbing solution
and is emitted when the absorbent is regenerated. The amount is
estimated to be 0.03 kg/t of ammonia produced.
Ammoniacal copper liquor is used at a few plants to remove
residual carbon monoxide, carbon dioxide, and oxygen from the
process gas. The absorbed gases are expelled when the copper
liquor is regenerated, resulting in the following emission of
carbon monoxide and ammonia at 91.5 and 3.2 kg/t of ammonia pro-
duced, respectively. These figures apply to the old TVA ammonia
plant. Part of the expelled ammonia was recovered in the TVA plant
as dilute ammonium carbonate solution, which could be recovered
by using it in another production process. -^ it was assumed that
this recovery method was not available at other ammonia plants
that used copper-liquor scrubbing.
Ammonia emission at the synthesis section of the old TVA
ammonia plant was 1.6 kg/t of ammonia produced. This emission
came from purge gas and leakage.
Some ammonia is lost as vapor during ammonia loading for
shipment. This loss was estimated to be 0.5 kg/t of ammonia at
the TVA plant.
Condensate is trapped from the process gas at ammonia plants,
and this condensate may contain ammonia and cause a water pollu-
tion problem.2 The waste effluent may be steam stripped to drive
out most of the ammonia and correct the water pollution problem;
however, steam stripping of the effluent before discharge will
277
-------
cause ammonia to be emitted in the air at about 0.7 kg/t of
ammonia produced. New methods being developed are expected to
provide a water treatment process that does not cause emission
to the air.
Table 4-1 summarizes emission from old and modern ammonia
plants. As can be seen, there has been little change in sulfur
dioxide and nitrogen dioxide emission, but carbon monoxide emis-
sion has been virtually eliminated, and ammonia emission has been
diminished by two-thirds. Table 4-2 shows emission factors and
estimated quantities of emission from existing plants,
The Environmental Protection Services, Province of Alberta,
Canada, has promulgated an ammonia emission guideline for new
plants of 1.5 kg/t of ammonia produced (3 Ib/ton), but plant
managers must strive to achieve an ammonia emission rate of
1.0 kg/t (2 Ib/ton). The Alberta emission guidelines were selected
to be compatible with current ammonia plant technology, in which
the normal practice is to limit ammonia emission as much as is
economically possible to conserve the product. In the develop-
ment of the Alberta standards, ammonia emission was not considered
noxious or particularly harmful by the Environmental Protection
Services, except at high concentrations. Ammonia emission was
considered only a nuisance at normal discharge rates.14
The estimated ammonia emission for modern plants (Table 4-1)
is consistent with the findings of the Alberta Environmental Pro-
tection Services. Another set of estimates23 of ammonia and
carbon monoxide emission are substantially higher than values
estimated for this report.
278
-------
TABLE 4-1
Emission from Ammonia Production Facilities
Emission, kg/t of ammonia produced
Old plants^ Modern plants^.
Ission Source S02 N02 CO NH3 S02 NO2 CO NH3
!t;ural-gas cleaning 0.05-0.7 - - - 0.05-0.7 -
former 0.03-0.3 0.6 - - 0.03-0.3 0.5
jrbon dioxide removal - - 0.03- - - 0.03 -
^oer-liquor scrubbing - -91.53.2
nonia synthesis - - -1.6 - - -1.6
l/nonia loading - - -_ 0.5 - - - 0.2
tal 0.1-1.0 0.6 91.5 5.3 0.1-1.0 0.5 0.03 1.8
lants using copper-liquor scrubbing for carbon monoxide removal.
lants using methanation for carbon dioxide removal; ammonia-synthesis
urge gas is burned as fuel.
279
-------
TABLE 4-2
Pollutant Emission from Ammonia Production—
Emission Factor
kg/t of ammonia Total Emission,
Pollutant produced t/yr
Sulfur dioxide 0.4 5,900
Nitrogen dioxide 0.6 8,900
Carbon monoxide 6.0 89,200
Ammonia 1.3 19,300
^Calculated from 1975 ammonia production of 14,370,000 t.
280
-------
Ammonia concentrations in the working area at the new TVA
ammonia plant illustrated in Figure 4-4 were measured; the results
are given in Table 4-3. Instantaneous analyses in the compressor
building showed concentrations of up to 72 mg/m , with an average
value of 35 mg/m . Impinger samples taken over a 2-h period showed
lower values, as would be expected. Concentrations in the outside
plant area were lower than those in the compressor building. At
the old TVA ammonia plant, the average ammonia concentrations were
usually 7-22 mg/m , and maximal concentrations were about 72 mg/m^.
During the 10-year period from 1964 to 1974, consumption of
ammonia nitrogen for fertilizer increased from 3.6 to 7.3 x 10^ t
in the United States-^ (about a 100% increase), and worldwide con-
sumption of ammonia nitrogen for fertilizer increased from about
16 to 39 x 10^ t-^ (about a 140% increase). There is also a sig-
nificant demand for ammonia in industrial chemicals.
When coal is carbonized, ammonia may be recovered at 2.7-3.3
kg/t as byproducts--ammonium sulfate, ammonium phosphate, and
28 9
ammonia liquor. In 1974, 110,000 t of nitrogen (as ammonia
byproducts) came from the carbonization of coal, and this was
only about 1% of the total ammonia nitrogen produced. The U.S.
energy program may call for up to 270 x 106 t of additional coal
per year to provide clean fuel equivalent to 20% of current U.S.
oil consumption,24 but gasification of coal by existing methods
would not produce enough byproduct ammonia to make any significant
impact on the ammonia industry.
Coal is being used as ammonia-plant feedstock in South Africa, ^
an area in which indi.genous natural gas is unavailable. From the
-------
TABLE 4-3
Ammonia Concentrations in Working Environment
at New TVA Ammonia Plant
Concentration in air, mg/m
Sampled by
Detector Tubes-
Sample Point
Compressor building
Outside
No.
10
3
Avg.
35
17
Range
Trace-72
14-36
Sampled by
Impingers—
No.
21
1
Avg. Range_
8 0.2-24
0
—Instantaneous concentrations.
—Measurements over a 2-h period.
282
-------
reported results of the operation in South Africa and the experi-
ence at the TVA with gasification of coke to produce ammonia, an
ammonia-from-coal process would be expected to have several dis-
advantages. The investment cost has been reported to be 1.9
times as much as it is for a plant using natural gas to produce
ammonia. Environmental and safety problems may further increase
the investment cost at ammonia-from-coal plants. Energy consump-
tion at such plants is greater than that at plants using natural
gas; this represents a waste of natural resource and increased
cost for abatement of thermal pollution.
Development is being carried out to adapt coal gasification
to ammonia production and thereby utilize the coal as a feedstock.
In the ammonia-from-coal process, the coal would be gasified
under pressure, and sulfur would be removed from the gas mixture.
The composition of the gas mixture would be about the same as the
composition at the secondary reformer outlet at an ammonia-from-
natural-gas plant (Figure 4-4); that is, the gas would contain
about 56% hydrogen, 23% nitrogen, 14% carbon monoxide, and 7%
carbon dioxide. The ammonia production process would be unchanged
downstream from the reformer.
From 75 to 113 kg of ash residue will be obtained per tonne
of ammonia produced. At coal-fired power plants and at large coal-
gasification plants, the handling, storage, and disposal of the
ash cause significant problems. Inadvertent spills sometimes occur
at ash ponds and cause serious water pollution problems. Some
metals in the ash limit utilization of the material on agricultural
lands, and other methods of utilization may be subject to limitations,
283
-------
When natural gas or naphtha is used as ammonia-plant feedstock,
the environmental problems and the byproduct disposal problems
associated with the ash are not encountered. Therefore, develop-
ment to use coal as ammonia-plant feedstock should include studies
of coal-ash handling, storage, and disposal. Thermal pollution
may be a greater problem at ammonia-from-coal plants than it is at
plants that use natural gas or naphtha as feedstock. The develop-
ment should include studies of ways to utilize the surplus heat
or to discharge the heat in an environmentally acceptable manner.
Naphtha is used as a feedstock for ammonia production at some
places where natural gas is unavailable, and it is used to produce
30-40% of the world's ammonia supply. In the United States, naphtha
is not used as a feedstock, because it costs more than twice as
much as natural gas. However, naphtha is replacing natural gas
as a feedstock in some petrochemical production processes. A
naphtha reforming plant consumes about the same energy as a natural-
gas reforming plant—about 9.6 x 106 kilocalories/t of ammonia
produced (34.4 x 106 BTU/ton, or 40.2 x 106 kJ/t). The investment
cost for a naphtha plant is about 1.13 times as much as it is for
a natural-gas plant.3 Furthermore, naphtha plants have no serious
environmental or safety problems such as exist at ammonia-from-coal
plants. Consequently, naphtha plants may be built in the United
States, if the costs of natural gas and naphtha become competitive.
Electrolytic hydrogen and coal may be long-range feedstocks.
284
-------
Industrial Emission of Ammonia
From 65 to 70% of ammonia produced goes into fertilizers,
and about 20% is believed to be consumed in the chemical industry
in the United States.11 From 10 to 15% (1-1.6 x 106 t) of nitro-
gen is unaccounted for, but the actual loss is believed to be
much less than the amount unaccounted for, because field inventory
not included in producers' stocks introduces inaccuracies in the
overall nitrogen balances. Consequently, each major use of ammonia
products was examined to estimate losses.
A study was made for the EPA by The Research Corporation of
o -5
New England^-3 to develop estimates of air emission of ammonia
from industrial sources. The sources of emission identified were
ammonia plants, petroleum refineries, diammonium phosphate fertil-
izer, nitrate fertilizer, byproduct coke ovens, sodium carbonate
(in the Solvay process), and beehive coke ovens. Additional
sources should be considered in estimating total ammonia emission,
as follows:
• Direct application of anhydrous ammonia to soil; The
amounts of fertilizers applied to the soil have been
reported, 1-5 and about 37% of the total nitrogen, or
2.8 x 10^ t/year, is applied as anhydrous ammonia.
Losses that occur during direct application of ammonia
are about 5% of the ammonia handled. This loss is
attributed to the emission of ammonia vapor at local
storage and nurse tanks, transportation to fields, and
field application. Loss of ammonia vapor during trans-
fer of liquid ammonia from local storage tanks to
285
-------
applicator tanks has been measured at 2.5%,35
Ammonia emission from these sources was estimated
at 168,000 t/year. In addition to loss of ammonia
during direct application to the soil, a safety
hazard was recently identified in the use of addi-
tives, such as chlorinated pyridine, which are put
into the nurse tanks. The additive may result in
electrolytic corrosion of aluminum in valves and
gauges; this problem is serious enough to merit
the issuance of a bulletin.3"
Production of urea; Ammonia and carbon dioxide are
combined to make urea, and unreacted ammonia is re-
covered and recycled. Venting of the byproduct
inert gases carries out some ammonia and results
in ammonia emission. At the TVA urea facility,
ammonia is emitted at about 0.6 kg/t of ammonia
used in the process. Jojima and Sato27 gave the
range of ammonia emission from urea plants; the
midpoint of this range is 0.6 kg/t of ammonia
used. The Province of Alberta guideline for new
urea plants calls for a maximal ammonia emission
equivalent to 2.7 kg/t of ammonia used (3.5 Ib/ton
of product).14 About 4.1 x 106 t of urea is pro-
duced per year,15 and urea production will consume
about 2.4 x 10 t of ammonia. Review of these data
led to an assumed ammonia emission from urea produc-
tion of 4,000 t/year.
286
-------
t Ammoniation-granulation plants; From reported emission
rates at ammoniation-granulation plants, it is esti-
mated that the annual ammonia emission rate is 10,000 t.
• Miscellaneous ammonia emission during production of
fertilizers; This includes emission during production
of aqueous ammonia, ammoniation of triple superphos-
phate, and production of liquid fertilizer. Data were
not available to calculate ammonia emission from these
sources, but an emission rate of 2,000 t/year was
assumed. Table 4-4 summarizes ammonia emission rates
from the various sources and indicates a total annual
emission of 300,000 t of ammonia, with emission during
the direct application of anhydrous ammonia contributing
more than half the total. A relatively large amount
of ammonia is also emitted during the production of
ammonium nitrate. Methods are needed to decrease the
losses from these sources, to improve recovery of a
valuable chemical.
Total estimated ammonia emission in the United States is
thus 319,000 t/year--300,000 t from production and use of fertil-
izers and industrial chemicals, and 19,000 t from ammonia manu-
facture. This rate is considered relatively small, compared with
the emission of other pollutants. For example, nationwide emis-
sion of nitrogen oxides (calculated as nitrogen dioxide) is
21 x 106 t/year,6 66 times the rate for ammonia on a weight basis,
or about 30 times on a molar basis.
287
-------
TABLE 4-4
Ammonia Emission from Production of
Fertilizers and Industrial Chemicals
Source of Emission
Direct application of
anhydrous ammonia3.
Ammonium nitrate
Petroleum refineries
Sodium carbonate
(Solvay process)
Diammonium phosphate
Ammoniator-granulators
Urea
Miscellaneous emission
from fertilizer pro-
duction
Beehive coke ovens
Total
Ammonia Emis-
sion Rate
t/yr
168,000
59,000
32,000
14,000
10,000
10,000
4,000
2,000
1,000
300,000
Basis of Estimate
Calculated from reported shrinkage^
during handling, transportation,
and use of anhydrous ammonia
Calculated from ammonium nitrate
production and reported ammonia
emission rate2^
TRC estimate23
TRC estimate23
TRC estimate23
Calculated from reported emission
rates at ammoniation-granulation
plants-1-
Calculated from measurements at
TVA plant and reported emission^?
Assumed
TRC estimate
23
—"Direct application" is the term used in agriculture when a chemical
fertilizer is applied to the soil without combining or mixing it
with any other chemical. Direct application of anhydrous ammonia
involves transportation of ammonia to a storage area and to nurse
tanks, metering, and injection into soil.
288
-------
When nitrogen fertilizers are applied to the soil, reactions
occur that result in substantially larger nitrogen losses than
the ammonia losses reported above. About 15% of the fertilizer
nitrogen is lost in air or ground water.20,21 prom 25 to 45% of
applied nitrogen remains in the soil after cropping during the
year of application, and there can be further nitrogen loss to air
and ground water. The ultimate loss may reach 20-25% of the nitro-
gen applied as fertilizer. About 9.4 x 10^ t of nitrogen was con-
sumed as fertilizer in 1976, and a loss of 20-25% would be equiva-
lent to an annual ammonia loss of 2.3-2.8 x 10^ t. These losses
might be reduced by developing improved fertilizer materials or by
improving agricultural practices.
289
-------
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11. Council for Agricultural Science and Technology. Effect of Increased
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13. Goran, M. The Story of Fritz Haber. Norman: University of Oklahoma
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15. Harre, E. A. Fertilizer Trends 1973. National Fertilizer Development
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16. Harre, E. A., and J. N. Mahan. The supply outlook for blending materials,
pp. 9-21. In Tennessee Valley Authority Fertilizer Bulk Blending
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17. Harre, E. A., J. D. Bridges, and J. T. Shields. Worldwide fertilizer
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31. Partridge, L. J. Coal processing: Coal-based ammonia plant operation.
Chem. Eng. Prog. 72(8):57-61, 1976.
32. Slack, A. V., and G. R. James, Eds. Ammonia. (In four parts) Fertilizer
Science and Technology Series, Vol. 2. New York: Marcel Dekker, Inc.,
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33. Unico International Corporation. Long-Term Forecast for World Nitrogenous
Fertilizer Demand and Supply. Tokyo, October 1975.
34. Walkup, H. G., and J. 1. Nevins. The cost of doing business in agricul-
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96-100, 1966.
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36. Wheller, E. M., and R. L. Gilliland. Ammonia additives. Pert. Prog.
7(5):28, 1976.
37. World Fertilizer Production Capacity, Ammonia. A Compilation Prepared
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294
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AMMONIA VOLATILIZATION FROM CATTLE FEEDLOTS AND ANIMAL WASTES
SPREAD ON THE SOIL SURFACE
Feedlots
The methods of producing beef for slaughter in the United
States have changed dramatically during recent years. Animals
are being produced in large concentrated feedlots, in contrast
with the small individual farms of a few years ago. The rapid
increase in animal production is due not only to increased popu-
lation, but also to increased per capita beef consumption, which
21
has increased by about 3.5%/year for the last 20 years. Of the
131.8 million cattle in the United States in 1975, about 10.2
million at any given time were being fed in feedlots throughout
the country.19 Because of the abundance and proximity of feed-
grain supplies, cattle-feeding is concentrated in four major
areas: southern California and Arizona, the panhandles of Texas
and Oklahoma, the central Corn Belt, and an area from eastern
Colorado through Nebraska to the North Dakota line.21 The trend
in recent years has been to increase the size of the feedlots, as
shown in Table 4-5. The density of animals in the feedlots has
also increased, e.g., 352 to 2,150 animals/ha, or 4.6 m2/animal,
in dry California and Arizona.21 The density is much lower in
other areas; e.g., two Colorado cattle feedlots each have capac-
ities of 100,000 head, with about 890 head/ha.
Table 4-6 gives some estimation of the overall composition
of the waste from a 453.6-kg bovine on a daily and feeding-period
basis and on an annual basis with 890 head/ha. The feeding period,
average animal weight, and stocking rate were taken from a
295
-------
TABLE 4-5
Number and Size of Cattle Feedlots in the United States—
No. Feedlots
Animals per Feedlot 1962 1963
<1,000
1,000-2,000
2,000-4,000
4,000-8,000
8,000-16,000
16,000-32,000
>32,000
234^ 231^
752 785
373 388
179 215
105 114
26 28
5 7
1964
223^
808
421
242
120
34
10
1965
220^
895
459
250
131
44
8
1966
215^
938
486
298
136
55
8
1967
210^
960
510
313
153
59
13
1968
206^
967
522
316
176
80
19
1969
188^
932
498
319
188
101
31
1970
182-
991
543
331
210
105
41
(Ti
—Data from NAS; ^ original source, Statistical Reporting Service (1963-1971). Some lots
from larger groups are included in smaller groups to avoid disclosing individual operations,
Data are for 35 states, except for 1969-1970, for which time 12 or 13 states were excluded
because operations were minor.
—In thousands. All others are actual numbers of feedlots.
-------
TABLE 4-6
Some Constituents of Waste of 453.6-kg Bovines
on Daily and Feeding-Period Bases and on an
Annual Basis with 890 Head/ha
Per Head Per Head for 890 Head, Per
Constituent Per Day, kg 140 Days, kg Hectare Per Year, 1
Wet manure and urine 29.03 4,064 9,430
Dry mineral matter 0.95 133 309
Dry organic matter 3.72 521 1,208
Water 24.36 3,410 7,913
Total nitrogen 0.17 23.8 55
Total phosphorus 0.02 2.3 6
Total potassium 0.12 16.8 39
-Data from Viets.21
297
-------
successful 100,000-head Colorado feedlot operation. 2 On the
basis of these values, Viets20 calculated that, on a hectare of
this feedlot stocked with 890 head of cattle, 5.5 t of nitrogen
would be excreted per year. Therefore, for the total of 112.5
ha of the feedlot, 6,188 t of nitrogen would be produced per
year, or 17 t/day. These data point out the magnitude of the
problem of disposal, as well as pollution abatement, associated
with large-scale feedlot operations.
Previous reports on the pathways of nitrogen removal have
been concerned primarily with surface runoff and the deep per-
colation of nitrate into underground water supplies.15 & third
pathway of nitrogen loss from feedlots—volatilization of nitro-
genous gases, primarily as ammonia, into the atmosphere—has
been ignored as a contributor to air, soil, and water pollution
until quite recently.
Hutchinson and Viets' demonstrated that volatilization of
ammonia from beef-cattle feedlots contributed significant quanti-
ties of ammonia to the atmosphere and to the nitrogen enrichment
of surface water in the vicinity of the feedlots. Ammonia traps
were installed near several cattle feedlots and in appropriate
control areas, as well as on the surface of two lakes near the
feedlots. Although weekly rates of absorption of ammonia fluctu-
ated widely, absorption at sites near the feedlots was always
substantially higher than that at the control sites. Site 7
(about 0.4 km west of 90,000-unit feedlot) differed from site 1
(control) on the average by a factor of nearly 20. The mean
absorption rate at site 7 was 2.3 kg of ammonia nitrogen per
298
-------
hectare per week, with individual values up to 5.7 kg. At 5
times as great a distance from the same feedlot (2 km east of
it), the mean ammonia absorption rate was lower by about half.
These workers also found that a significant amount of ammonia
volatilized from the surface of cattle feedlots was absorbed
from the air by water surfaces in the vicinity. Nitrogen enrich-
ment of lakes by this route was large, compared with other sources.
Their measurements indicated that a lake 2 km from a feedlot con-
taining 90,000 units absorbed enough ammonia from the air in a
year to raise its nitrogen concentration by 0,6 mg/liter. This
amount of inorganic nitrogen was suggested to be adequate to
contribute to the eutrophication of the lake. Sawyer et, al.
(cited in Hutchinson and Viets ) suggested that 0.3 mg/liter is
the critical concentration of inorganic nitrogen beyond which
algal bloom can normally be expected in a lake.
The release of ammonia plus steam-distillable organic
nitrogen compounds to the atmosphere from a small beef feedlot
and a pasture has been measured by Elliott et. al. Acid traps
placed next to the feedlot and 0.8 km from the feedlot averaged
ammonia plus steam-distillable organic nitrogen compounds at
148 and 16 kg/ha per year, respectively. The same traps averaged
organic nitrogen compounds that were not recovered by a 3-min
steam distillation procedure at 21 and 3.3 kg/ha per year, re-
spectively. Feedlot disturbances, such as manure mounding, in-
creased volatilization of nitrogen compounds. Ammonia plus steam-
distillable organic nitrogen compounds trapped near a cattle
pasture and cropland averaged 15 and 11 kg/ha per year, respectively.
299
-------
Organic nitrogen compounds not recoverable by a 3-min steam
distillation were very low in this area. Somewhat greater
nitrogen loss from a pasture grazed with sheep has been reported
o
by Denmead et al. They used a micrometeorologic technique to
measure the flux of ammonia and related gaseous nitrogen compounds
from the pasture. During a 3-week period in late summer, the
average daily flux density of nitrogen in these forms was 0.26
kg/ha, for an annual figure of about 95 kg/ha.
Studies in the Chino-Corona dairy area of southern California
by Luebs e_t a^L.11 reported that 143,000 head of dairy cattle
located in an area of about 150 km caused considerable enrich-
ment of the air with ammonia and volatile amines over an area
o
of more than 560 km . The area within the dairy area contained
20-30 times more ammonia and distillable bases than the non-
dairy area.
About 62 kg of nitrogen is excreted per animal per year in
a typical feedlot (Table 4-6). About half, or 32 kg, is present
as urinary urea, which is rapidly hydrolyzed to ammonia and carbon
dioxide.18 The fate of the released ammonia has been studied by
Stewart.18 When cattle urine was added to soil columns every 4
days for 8 weeks to simulate a dry feedlot with 7 m2/animal, the
soil pH rose to 9.9 from about 7, and about 90% of the added nitrogen:
was lost as ammonia. However, when urine was added every 2 days
to an initially wet soil at 5 ml per 21 cm2, less than 25% of
the added nitrogen was lost as ammonia, and about 65% was converted
to nitrate. Therefore, it appears that the moisture of the feed-
lots is important in the volatilization of the ammonia, the problem
being more severe in dry regions.
300
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14
Mosier et al. attempted to identify the basic organic
nitrogen-containing compounds volatilized from a cattle feedlot.
Previous work on measuring the ammonia volatilized from feedlot
areas had indicated the presence of other volatile amines in
their acid traps. '' Mosier et a_l.14 identified seven amines
by gas chromatography in the acid used to trap feedlot volatiles
and confirmed their presence by gas-chromatographic identification
of their pentafluorobenzoyl derivatives. The amines identified
were methyl-, dimethyl-, ethyl-, n-propyl-, isopropyl-, n-butyl-,
and n-amyl-. On a nitrogen basis, these amines collectively
amounted to about 2-6% of the ammonia of the basic volatiles
from a feedlot. Many other amines were present, but unidentified
and unmeasured.
Viets pointed out that the amines are of concern for two
reasons that make them liabilities to the environment. First,
they are very bad-smelling substances that are persistent in
sticking to clothing and most other surfaces; the odor threshold
for some amines is very low—0.021 ppm for methylamine and 0.047
ppm for dimethylamine--but it is not known how much these com-
pounds contribute to the overall odor problem of animal wastes,
inasmuch as other organic compounds may be involved. Second,
the secondary amines have been shown to combine with nitrate under
favorable conditions of high acidity and temperature to produce
the highly carcinogenic, teratogenic, and mutagenic nitrosamines.
However, the surfaces of feedlots are generally highly alkaline,
so reactions leading to the formation of nitrosamines are highly
improbable; therefore, the concern about the potential presence
301
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of nitrosamines in or around large feedlots has apparently not
been substantiated.
A marked diurnal fluctuation in the atmospheric content of
ammonia and related gases has been recorded in the vicinity of
a large dairy area.10 Meteorologic factors, particularly tempera-
ture inversions in the atmosphere and wind, and proximity to the
waste greatly affected atmospheric concentrations of distillable
nitrogen. Low concentrations of the gases were frequently recorded
in the afternoon and high concentrations at night in , the large dairy
area. The higher nighttime values were related to temperature in-
versions. A reverse diurnal pattern—with high afternoon and low
nighttime concentrations—was recorded at an isolated dairy site.
Proximity to the source and a high horizontal flux of distillable
nitrogen with afternoon winds were important factors in this diurnal
pattern. Winds averaging 9.3 km/h transported distillable nitrogen
500 m from the isolated dairy at an altitude of 1.2 m.
Several possible techniques of odor control have been investi-
gated in cooperation with a 24,000-head-capacity cattle feedlot
in southeastern Idaho.12'13 Nine commercially available products
for feedlot odor control were applied to one or more pens each,
to determine their effectiveness. Ammonia release rates and odor
intensities of the feedlot litter were used as measures of success.
Four of the products—sodium bentonite, Odor Control Plus, and two
natural zeolites—were found consistently to reduce the rate of
ammonia release from the treated areas, compared with nearby un-
treated areas. Two materials were added to the feed ration to con-
trol odor. Neither material proved effective, on the basis of
302
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ammonia release rate or odor intensity. Preliminary data have
also been presented on a greenbelt odor barrier (tree and shrub
windbreak) and a water spray system that would provide a mist in
areas downwind of the feedlot.12
Soil Surface
The value of using animal waste as fertilizer for various
crops has been known for centuries. Animal waste from live-
stock and poultry production in the United States was estimated
to be about 1.7 x 109 tons (1.5 x 109 t) per year in 1974.22
As indicated in the previous section, large numbers of animals
are for various reasons being raised in rather confined arisas,
magnifying the volume of waste to be disposed of in these areas.
At the same time, specialization has often eliminated cropland
that would be available for land disposal of this waste. These
factors have contributed to a renewed interest in the economical
disposal of animal waste on land. This would aid in solving the
disposal problem as well as provide, valuable nutrients to enhance
crop production.
The problem of nitrogen loss by ammonia volatilization from
animal waste spread on the soil surface has been known for several
years. Salter and Schollenberger,^-^ quoting Danish data from 34
field experiments with fermented manure high in ammonia content,
reported mean total nitrogen losses of 15% in 6 h, 27% in 12 h,
and 42% in 4 days. Other Danish data showed total nitrogen losses
of 2-21% in 24 h and 10-29% in 4 days, depending on the season when
the manure was spread. These data indicate ammonia half-lives
303
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(times of 50% loss) of between 1 and 4 days. Heck reported
initial rates of ammonia volatilization with half-lives of
0.5-2.0 days. He also found that two stages were exhibited in
the ammonia loss from manure after spreading: the first stage
with loss at a half-life of 0.5-2.0 days, and the second stage
with a slower loss. These early workers estimated that up to
50% of the total nitrogen in manure at the time of spreading
could be lost as volatile ammonia after spreading. '-*•'
Laboratory studies have demonstrated that a considerable
amount of the nitrogen in animal waste was lost as ammonia, even
when the material was mixed with soil. 1? 18 Adriano et_ al.
studied the rate of nitrogen loss for manure applied at different
rates under greenhouse conditions at two soil moistures and two
soil temperatures. Fresh feces was mixed, air-dried, and ground
to pass a No. 40 mesh sieve. The dried feces was then mixed at
various concentrations with soil in a concrete mixer. The
moisture content was adjusted as desired with a urine-water
mixture to resemble a fresh urine-feces mixture. The manure rate
did not have a significant effect on the percentage of loss of
applied nitrogen. At 10° C, the average losses of applied nitrogen
were 26 and 39% for 60 and 90% moisture, respectively. At 25° C,
losses were 40 and 45% for 60 and 90% moisture, respectively.
The results suggest that these losses occurred largely through
18
volatilization of ammonia. Stewart reported somewhat higher
losses, as discussed in the previous section,
Lauer et aJL. have determined the volatilization of ammonia
from dairy manure spread and left on the soil surface under natural
304
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field conditions. Manure was applied at 34 and 200 t/ha. Ammonia
volatilization was determined after spreading by periodically
measuring the total ammonia nitrogen content of manure samples
collected from the soil surface. Corrections were made for
increases in ammonia nitrogen in the soil. The experiments lasted
for 5-25 days, and total losses ranged from 61 to 99% of the total
ammonia nitrogen content. Quantities of nitrogen volatilized as
ammonia ranged from 17 to 316 kg/ha, depending on the application
rate and the total ammonia nitrogen content of the manure. In
a winter trial, ammonia volatilization was precluded by subfreezing
temperatures, snow cover, and a rapid thaw that leached the ammonia
nitrogen into the soil. In the other experiments, for a period
of 5-7 days after spreading, rates of ammonia loss were repre-
sented by mean half-lives of 1.86 and 3.36 days for the low and
high rates of manure application, respectively. After the initial
period of loss, the ammonia volatilization slowed in most cases.
The 34-t/ha manure application dried more rapidly, because of its
thinner ground cover, which increased the rate of ammonia loss
(mean half-life, 1.86 days) from the manure. Volatilization of
ammonia was maximal under sustained drying conditions. These
workers hypothesized three stages of ammonia volatilization from
bovine manure. The first stage is a very rapid initial loss of
ammonia driven by very high partial pressure (pNH3) resulting
from urea hydrolysis in the manure. Half-lives of less than 1
day characterize first-stage losses. Second-stage ammonia
volatilization losses, characterized by half-lives of 2-4 days,
begin as manure is subjected to drying, either in the facility
305
-------
or after spreading. Drying maintains a pNH3 somewhat below that
of the first stage, but sufficient for continuous ammonia vola-
tilization. The third-stage ammonia volatilization loss is
characterized by a decrease in pNH3 and half-lives of over 4 days.
This stage occurs after a large fraction (over 75%) of the ammonia
has been lost. Owing to these high losses of nitrogen, the ap-
plied manure should be immediately incorporated into the soil.
Plowing of the manure within 6 days in one study did not prevent
a loss of 85% of the total ammonia nitrogen.
Studies have also shown considerable loss of nitrogen through
ammonia volatilization from poultry waste^ and liquid sewage
sludge^ spread on the soil.
The ammonia volatilized from the soil surface has been
assumed to be lost; however, studies have suggested that green
plants are avid scavengers of ammonia in the air. Porter et al.16
and Hutchinson et al. have shown that such plants as corn, cotton
soybeans, and sunflowers can absorb considerable quantities of
ammonia from the atmosphere. Hutchinson et al.6 estimated that
annual ammonia absorption by plant canopies could be about
20 kg/ha. The ammonia appears to enter into metabolism and growth
like ammonium ions absorbed through roots or produced by nitrate
reduction in plant cells.
306
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REFERENCES
1. Adriano, D. C. , A. C, Chang, and R. Sharpless. Nitrogen loss from manure
as influenced by moisture and temperature. J. Environ. Qual. 3:258-
261, 1974.
2. Denmead, 0. T., J. R. Simpson, and J. R. Freney. Ammonia flux into the
atmosphere from a grazed pasture. Science 185:609-610, 1974.
3. Elliott, L. F., G. E. Schuman, and F. G. Viets, Jr. Volatilization of
nitrogen-containing compounds from beef cattle areas. Soil Sci.
Soc. Amer. Proc. 35:752-755, 1971.
4. Giddens, J., and A. M. Rao. Effect of incubation and contact with soil
on microbial and nitrogen changes in poultry manure. J. Environ.
Qual. 4:275-278, 1975.
5. Heck, A. F, The availability of the nitrogen in farm manure under field
conditions. Soil Sci. 31:467-481, 1931.
6. Hutchinson, G. L., R. J. Millington, and D. B. Peters. Atmospheric
ammonia: Absorption by plant leaves. Science 175:771-772, 1972.
7. Hutchinson, G. L., and F. G. Viets, Jr. Nitrogen enrichment of surface
water by absorption of ammonia volatilized from cattle feedlots.
Science 166:514-515, 1969.
8. King, L. D. Mineralization and gaseous loss of nitrogen in soil-applied
liquid sewage sludge. J. Environ. Qual. 2:356-358, 1973.
?. Lauer, D. A., D. R. Bouldin, and S. D. Klausner. Ammonia volatilization
from dairy manure spread on the soil surface. J. Environ. Qual. 5:
134-141, 1976.
'• Luebs, R. E., K. R. Davis, and A. E. Laag. Diurnal fluctuation and move-
ment of atmospheric ammonia and related gases from dairies. J.
Environ. Qual. 3:265-269, 1974.
307
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11. Luebs, R. E., K. R. Davis, and A. E. Laag. Enrichment of the atmosphere
with nitrogen compounds volatilized from a large dairy area. J
Environ. Qual. 2:137-141, 1973.
12. Miner, J. R. Evaluation of Alternate Approaches to Control of Odorc
from Animal Feedlots. Final Report to National Science Foundation
Grant No. ESR74-23211. Moscow, Idaho: Idaho Research Foundation,
1975. 83 pp.
13. Miner, J. R,, and R. C. Stroh, Controlling feedlot surface odor emission
rates by application of commercial products. Paper Presented at the
1975 Winter Meeting of the American Society of Agricultural Engineers,
Chicago, Illinois, 1975. 16 pp.
14. Mosier, A. R., C. E. Andre, and F. G. Viets, Jr. Identification of
aliphatic amines volatilized from cattle feedyard. Environ. Sci.
Technol. 7:642-644, 1973.
15. National Research Council. Agricultural Board. Accumulation of Nitrate.
Washington, D. C.: National Academy of Sciences, 1972. 106 pp.
16. Porter, 1. K. , F. G. Viets, Jr., and G. I. Hutchinson. Air containing
nitrogen-15 ammonia: Foliar absorption by corn seedlings. Science
175:759-761, 1972.
17. Salter, R. M., and C. J. Schollenberger. Farm manure, pp. 445-461. In
U. S. Department of Agriculture. Soils and Men. Yearbook of Agri-
culture 1938. Washington, D. C.: U. S. Government Printing Office,
1938.
18. Stewart, B. A. Volatilization and nitrification of nitrogen from urine
under simulated cattle feedlot conditions. Environ. Sci. Technol.
4:579-582, 1970.
19. U. S. Department of Agriculture. Agricultural Statistics, 1975. Washing-
ton, D. C.: U. S. Government Printing Office, 1975. 621 pp.
308
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20. Viets, F. G. Fate of nitrogen under intensive animal feeding. Fed.
Proc. 33:1178-1182, 1974.
21. Viets, F. G., Jr. The mounting problem of cattle feedlot pollution.
Agric. Sci. Rev. 9(l):l-8, 1971.
22. Young, R. A. Crop and hay land disposal areas for livestock wastes, pp.
484-492. In Processing and Management of Agricultural Wastes. Pro-
ceedings of the 1974 Cornell Agricultural Waste Management Conference,
Rochester, New York, 1974.
309
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SOURCES AND CONCENTRATIONS OF ATMOSPHERIC AMMONIA
More than 99.5% of atmospheric ammonia is produced by natural
biologic processes.57 According to Junge, the main biologic
source of ammonia emitted in the troposphere is the decomposition
of organic waste material. Therefore, ammonia is a "natural"
constituent of the troposphere, where it exists in concentrations
well below those which are hazardous to humans, animals, and
plants.
Ammonia produced as a result of human activities, although
a minor fraction of the total ammonia emitted in the atmosphere,
may nevertheless reach, in confined environments, concentrations
at which adverse health effects occur. Moreover, concentrations
of particulate ammonium compounds that are believed to have ad-
verse health effects may result from gas-to-particle conversion
of ammonia emitted in the atmosphere by sources related to human
activities (such as automobile exhaust, cattle feedlots, and
production and use of fertilizers).
Natural biologic processes also constitute the major sink
for atmospheric ammonia, either directly or after conversion of
gaseous ammonia to particulate ammonium compounds via a variety
of physical and chemical transformations in the atmosphere. To
avoid redundancy with other parts of this document, this section
deals mainly with the sources and concentrations of ammonia in
urban, industrial, and rural atmospheres. Ammonia emission
associated with production and use of ammonia and with feedlot
operations has been reported earlier in this chapter.
310
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Anthropogenic Sources
The following are among the major anthropogenic sources
of atmospheric ammonia:
• Combustion processes in urban areas, as in municipal-
waste incineration, domestic heating, and internal-
combustion engines.
• Industrial sources, such as fertilizer plants, re-
fineries, organic-chemical process plants, and strip
mining.
• Miscellaneous sources, such as cattle feedlots,
food processing plants, and use of ammonia in
industrial and household cleaning.
According to a 1974 report from the National Institute for
Occupational Safety and Health (NIOSH), ammonia was produced in
1971 by approximately 80 companies in the United States in as
many as 100 plants.16 NIOSH also estimated that about one-half
million U.S. workers have potential exposure to ammonia. ° A
number of occupations with potential exposure to ammonia are
listed in Table 4-7.
Ammonia emission resulting from these and other human ac-
tivities are discussed in the following sections. Most foreign
references cited here were available through the EPA APTIC
Literature Search and the original publications were not con-
sulted. A useful compilation of data from before 1969 was found
in a literature review published by the U.S. Department of Health,
Education, and Welfare.
3U
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TABLE 4-7
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
Farmers
Fertilizer worker
Galvanizer
Gas purifiers
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
-Derived from NIOSH.16
312
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O o
Waste Incinceration. Gardner^-* estimated that about 7GO Ib
(345 kg) of ammonia was discharged daily into the atmosphere in
a metropolitan area of 100,000 persons in 1968. Domestic dis-
posal (such as by backyard burning and apartment incinerators)
accounted for about 370 Ib (168 kg) of the ammonia daily emitted,
the remaining 390 Ib (177 kg) resulted from municipal disposal
and incineration.
The United States produced about 170 x 106 tons (153 x 106
t) of refuse in 1969, of which about 15% was incinerated. In
1980, about 260 x 106 tons (234 x 106 t) of refuse will be pro-
duced, and the fraction to be incinerated is expected to in-
crease by about 50%.^5 Ammonia emission from various incinera-
tion processes is summarized in Table 4-8.
Domestic Heating. The rate of emission of ammonia from
various categories of fossil fuels is presented in Table 4-9.
Evans e_t a_1.20 estimated the amounts of ammonia discharged daily
from domestic heating sources in a metropolitan area of 100,000
persons to be 2,000, 800, and 0.3 Ib (907, 363, and 0.14 kg)
for coal, oil, and gas, respectively. Obviously, the increasing
changeover from natural gas to fuel and coal resulting from cur-
rent energy constraints will have a substantial impact on ammonia
emission in urban areas.
Internal-Combustion Engine. Substantial amounts of ammonia
are emitted in automobile exhaust.30 The emission of ammonia
from internal-combustion engines has been estimated at 2.0 lb/1,000
gal (0.24 kg/m3) burned for gasoline-powered and diesel-powered
313
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TABLE 4-8
Ammonia Emission from Incineration^
Emission Factor
Concentration
u>
H
Combustion Source
Gas-fired domestic incinerators—
shredded paper and domestic wastes
Older units--
shredded paper
Municipal incinerators:
Spray chamber (Alhambra, Calif.)
Multiple chamber
Other incinerators:
Single chamber
Wood waste
Backyard paper and trimmings
Backyard 6 ft^ of paper
Backyard 6 ft3 of trimmings
Open dump burning
Large gas-fired industrial units
Flue-fed apartment incinerators
<4,000
4,000
20,000
400
800
45,000
3 ,000
100,000
400
Ib/ton of
Material Burned
kg/t of
Material Burned
0.3
0.4
0.3-0.5
1.8
0.1
4.4
2.3
0.4
0.15
0.2
0.15-0.25
0.9
0.005
2.2
1.15
0.2
-Derived from U.S. DREW.55
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TABLE 4-9
Ammonia Emission from Combustion-
Combustion Source
Emission Factor
Coal
Fuel oil
Natural gas
2 Ib/ton (1 kg/t)
1 lb/1,000 gal (0.12 kg/m3)
0.3-0.56 lb/106 ft3 (0.000005-0.00001 kg/m3)
Bottle gas (butane) 1.7 lb/106 ft3 (0.00003 kg/m3)
Propane 1.3 lb/106 ft3 (0.00002 kg/m3)
Wood 2.4 Ib/ton (1.2 kg/t)
Forest fires 0.3 Ib/ton (0.15 kg/t)
^Derived from U.S. DHEW.55
315
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engines.12'34'48 As early as 1953, the total ammonia emitted
into the Los Angeles atmosphere from the combustion of gasoline
was estimated at 5 tons/day (4.5 t/day).55 More recently, large
quantities of ammonia were measured in the exhaust of automobiles
equipped with dual-catalyst emission control systems. 6 Thus,
in metropolitan areas, the contribution of automobile exhaust to
the total anthropogenic ammonia burden could exceed that from
stationary sources and become important in air pollution.
Industry-Related Sources. Ammonia is generated as a byproduct
in a wide variety of industrial processes and related activities,
such as the conversion of coal to coke in coke plants; metal-
lurgic operations, as in foundries; '" ceramic plants ;55 strip
r n
mining; synthesis of ammonia-derived chemicals, such as nitric
acid, synthetic monomers, and plastics;-^ treatment of waste
gases;36/51 sewage plants; ammonium nitrate explosives;^ diazo
reproducing;47 refrigeration equipment; household cleaning;21 and
food processing, as in fishmeal plants65 (Table 4-10).
Large amounts of ammonia are also emitted by oil refineries,
mainly from the use of catalyst regenerators in fluid-bed catalytic-
cracking units. A study conducted at various oil refineries in the
Los Angeles area showed that up to 4.2 tons/day (3.8 t/day) can be
emitted by fluid-bed catalytic-cracking units.2 Thus, oil re-
fineries appear to be one of the most important industrial cate-
gories contributing to ammonia pollution in the United States.
However, ranking of the various industry-related sources listed
above in terms of their contribution to the total ammonium burden
316
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TABLE 4-10
Ammonia Concentrations Associated with Various
Industrial Processes!?.
Operation Ammonia Concentration, ppm
Machinery manufacturing
(cleaning operations) 15
Use of diazo reproducing machine 8
Mildewproofing 125
Electroplating 55
Galvanizing, ammonium
chloride flux 10-88
Use of blueprint machine 10-35
Use of printing machine 1-45
Etching 36
Use of refrigeration equipment 9-37
^Derived from NIOSH.16
317
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in the atmosphere appears difficult, in view of the scarcity of
data on the corresponding ammonia emission factors.
Atmospheric Concentrations*
Because of its relatively low concentration, even in urban
communities (in the parts-per-billion range), and the unavailability
of a continuous, reliable method for measuring ammonia at such
low concentrations (see Chapter 3), ammonia has not been routinely
measured by federal and state air monitoring networks. However,
atmospheric concentrations of ammonia have been measured inter-
mittently for many years in both rural and urban air, and specific
measurements of particulate ammonium have been reported in the
last few years.
Ammonia Concentrations in Nonurban Areas. Georgii^^ reviewed
data on atmospheric ammonia from before 1963, including concentra-
tions of 2-5 yg/m3 at maritime stations (such as Westerland on the
North Sea, 4 Vesima on the Italian coast, ^ and Hawaii3^*) and'"con-
centrations of about 5-8 yg/m at various rural and mountain loca-
tions in Switzerland and Germany. Transport of continental ammonia
to the maritime atmosphere was further studied by Tsunogai,^^ who
concluded that most of the ammonia in oceanic air is of continental
*Ammonia concentrations are reported in this section in parts per
billion (1 ppb = 10~3 ppm) or micrograms per cubic meter (yg/m ) .
Exact conversion from ppb to yg/m3 (and vice versa) is not possible
if atmospheric temperature and pressure at the time of the measure-
ment (s) are not known, but an approximate conversion factor of 0.7
for ammonia (1 ppb _ 0.7 yg/m3) can be used in most cases.
318
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origin. In later studies, 4-5 pg/m was generally considered to
be representative of ammonia concentrations outside of urban-
industrial areas.49,57
Breeding et al.6 measured the concentrations of several
gaseous trace contaminants in the central United States. Ammonia
was determined by the indophenol blue method in 1-h and 2-h samples
collected at four rural sites in Illinois and Missouri in October
1971 and 1972. They reported ammonia concentrations of 2-6 ppb
(about 1.4-4.2 yg/m3), with variations within that range depend-
ing largely on natural mechanisms. Axelrod and Greenberg^ con-
ducted five experiments in July 1975 in Boulder, Colorado, with
0.01 N sulfuric acid bubblers and a particle prefilter. They
measured ammonia at 2.9, 3.8, and 4.5 ppb in Boulder air on rela-
tively pollution-free days. These results compared well with
r Q
those of Shendrikar and Lodge, who also measured ammonia in
the vicinity of Boulder in February and March 1974 with the ring-
oven technique.
Lodge et. aJL.44 investigated trace substances, including
ammonia, in the atmosphere of the American tropics. Their ex-
tensive study inclxided diurnal profiles from 1-h averaged samples,
as well as seasonal patterns for the years 1967 and 1968. Measured
ammonia concentrations ranged from 5 to 31 ppb, with an average
(termed a "generalized tropical value") of 15 ppb, i.e., twice the
typical concentrations encountered in the temperate zone.
The atmospheric concentrations and transformations of ammonia
and related pollutants in the United Kingdom were investigated by
319
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Stevenson,62 Eggelton,19 and Healy and co-workers.32 Ammonia
concentrations measured at rural locations in the U.K. were
generally about 4 yg/m3. Healy31 also conducted a comprehensive
program at a rural site (Harwell) and measured diurnal profiles
for ammonia, sulfur dioxide, and ammonium over a 2-week period
in September 1969. Ammonia was present typically at 0.85-1.7
yg/m , with peaks of up to 5.1 yg/m .
Ammonia concentrations were measured at two nonurban sites
in California13 where ammonia diurnal profiles were established
from 4-h samples collected in November 1972. Both the desert
site (Goldstone) and the coastal site (Point Arguello) showed
little variation in the diurnal pattern, with ammonia averaging
4.6 + 0.9 and 9.7 + 2.8 yg/m3, respectively-
" 25
Georgii and Muller conducted an extensive study of the
distribution of ammonia in the middle and lower troposphere.
From November 1969 to September 1972, they conducted 75 aircraft
ascents over different areas of the Federal Republic of Germany
that were not directly influenced by pollution sources and
measured, with the indophenol blue method, the concentration of
atmospheric ammonia from ground level to an altitude of 4,000
m. Ammonia vertical distribution profiles thus obtained (Figure
4-5) are typical of that of a trace gas with its source at ground
level. Ground-level concentrations ranged from about 7 to 20
yg/m and were directly proportional to ground temperature, as
expected because the ammonia production rate at the ground is
controlled by bacterial activity. Thus, ground-level ammonia
concentrations and vertical profiles exhibit strong seasonal
320
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4000-jm above ground
\!
11) Ground temperature < * 10°C
(2) Ground temperature >« 18°C
13) Vertical distribution of SO?
la) Summer
15 20 25/igmm1
FIGURE 4-5. Vertical distribution of ammonia over the
Federal Republic of Germany. Reprinted
with permission from Georgii and Muller.2b
321
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variations, reaching constant "background" values of H 1-2 yg/m3
at — 1,500 m above the ground on winter days and — 5 yg/m at
3,000 m during the summer. These results are discussed further
with respect to particulate ammonium formation in the atmospheric-
chemistry section of Chapter 2.
Ammonia Concentrations in Urban and Industrial Areas.
Georgii measured ammonia at up to 20 yg/m3 in the atmosphere
of Frankfort on the Main, Germany. The concentrations were 4-5
times higher than those obtained by the same method at nonurban
locations and exhibited a marked maximum in the winter, owing to
the increasing contribution from combustion processes, especially
for domestic heating.
Later studies conducted in western Europe also indicated
high ammonia concentrations at urban locations. Spinazzola and
co-workers^O'61 measured ammonia in the atmosphere of Cagliari,
Italy. In a first study conducted at four sites, hourly samples
were collected during the day and analyzed with the Jacobs method.
Ammonia concentrations ranged from 88 to 400 ppb (2. 62 to 280
yg/m ), with no detectable diurnal peak. The study was extended
to 18 locations in Cagliari; again, high concentrations, 53-304 ppb
were reported. The highest concentrations were measured in the
vicinity of the port; this was attributed to the presence of
wastes from ships and sewers. Haentach and Lehmann analyzed
West Berlin air for ammonia (with the indophenol method) from
samples collected at residential and industrial sites over a 1-
year period. Ammonia averaged 17-6 yg/m3, reaching up to
322
-------
97 ug/m / and exhibited a strong seasonal pattern (winter greater
than summer), but no definite diurnal pattern.
Studies of ammonia in urban-industrial areas were conducted
iin Japan by Okita and Kanamori53 and by the Tokyo^-64 an(^ Tsuruga
air pollution networks. Concentrations of up to 6.8 yg/m were
measured in Tsuruga35 (with the electroconductivity method) and
up to 300 ppb d 210 yg/m3) in an industrial suburb of Tokyo down-
wind from two major pharmaceutical plants.64
Okita and Kanamori53 measured ammonia in the atmosphere of
downtown Tokyo, Japan, during the period January 20-May 27, 1969.
They performed comparative measurements with Nessler's procedure
and their own pyridine-pyrazolone method. They found a signifi-
cant positive interference due to formaldehyde, CH-jCHO, with
Nessler's method. The 2-h averaged ammonia values with the
pyridine-pyrazolone method ranged from 4.0 to 25.8 yg/m . (Be-
cause ammonium-containing particles were also assumed to be
present, but were not measured separately, these values represented
the total concentration of gaseous and particulate ammonia.) The
correlation between total ammonia concentration and air tempera-
ture was nearly linear; this suggested that atmospheric ammonia
is produced mainly by biologic activity.
Ammonia has been routinely measured in the United States since
i
1967 as part of the National Air Surveillance Networks.50 Measure-
ments have also been reported by Hidy et al., Hanst and co-
O Q T ^ 11
workers, Farber and Rossano, the California Air Resources Board, J-
Pitts et al.,54'67 and Breeding and co-workers.5 These data re-
sulted from the recent development and use of more sensitive and
323
-------
reliable techniques for measuring atmospheric ammpnia, such
29 67
as Fourier-transform long-path infrared spectroscopy, '
second-derivative spectroscopy and the combination of gas
"? 0
chromatography and chemiluminescence. z The measurements were
in Seattle, St. Louis, and southern California.
Farber and Rossano^ report ammonia concentrations of
1.2-110 ppb d 0.8 to 77 yg/m ) in air samples collected in
May 1975 on the campus of the University of Washington, Seattle.
Six of these samples yielded ammonia at 30 ppb or more. Breeding
e_t al. measured ammonia as part of a comprehensive pollutant
study conducted by the National Center for Atmospheric Research
(NCAR) in the St. Louis area. The urban plume 80 and 120 km
from the urban center was measured at ground level and in air-
craft. Measurements conducted in October 1972 and April 1973
yielded ammonia at up to 20 and 25 ppb, respectively. The
typical ammonia concentration outside the urban plume was about
4 ppb.
Ammonia has been measured at various urban locations in
California as part of the California Aerosol Characterization
Experiment (ACHEX) , by Hidy e_t al.13 On the basis of 2-h and
4-h samples, ammonia diurnal profiles were established at Fresno
(10-30 yg/m3; average, - 15 pg/m3), San Jose (4-60 yg/m3; average,
- 25 yg/m ), Riverside (3-60 yg/m3; average, - 20 yg/m3), Pomona
(10-60 yg/m ; average, :_ 30 yg/m3), and the vicinity of the
Harbor freeway in downtown Los Angeles (8-16 yg/m3; average,
- 10 yg/m ). As shown in Figures 4-6 and 4-7, no definite diurnal
pattern was observed, although ammonia concentration exhibited
324
-------
20
SAN JOSE
9/13
60
40
20
10
10/12 -
10/5
10/20
2000
2400
0400
0800
HOURS (
1200
1600
2000
FIGURE 4-6.
Diurnal patterns of ammonia concentration,
San Jose, California. Reprinted with per-
mission from Hidy et al.i3c
325
-------
-i 1 1 r
i 1—
RIVERSIDE
60
SO,
9/27
40
30
20
10
10
10/14
10/12
10/20
-I 1
J L
2400 0400
0800 1200 1600
HOURS (PST)
2000 2400
FIGURE 4-7.
Diurnal patterns of ammonia concentration,
Riverside, California. Reprinted with per-
mission from Hidy et al. c
326
-------
wide variations (from a few micrograms per cubic meter up to
60 yg/m ) over the period studied.
Long-path infrared spectroscopic studies of gaseous pol-
lutants, including ammonia, have been conducted by Hanst et al.29
and Tuazon and co-workers67 in Pasadena and Riverside, California,
respectively. Ammonia was not present in Pasadena air at con-
centrations higher than 5 ppb (the detection limit of the in-
strument) , but was found in Riverside air at up to 23 ppb.
Another study conducted in the California southern coastal
air basin (SCAB) by the California Air Resources Board11 showed
that higher ammonia concentrations are encountered in the
eastern inland part of the SCAB (i.e., Riverside) than at coastal
and western locations (Santa Monica, Los Angeles, and El Monte).
This difference has been attributed to important ammonia emission
from feedlots concentrated inland in the Chino-Corona area.
Measurements in December 1975 in this area showed ammonia con-
centrations as high as 450 ppb (— 315 pg/m ) in the immediate
vicinity of a major dairy farm.
Particulate Ammonium Concentrations in Nonurban Areas.
Despite the obvious relation between atmospheric particles and
radiation balance and the increasing concern about the impact
of particulate air pollution on global climate, the distribution
of nonurban atmospheric aerosols with respect to size and chemi-
cal composition is still poorly documented. This is especially
true for particulate ammonium, which has received much less atten-
tion than other important inorganic particulate pollutant species,
such as sulfates and nitrates.
327
-------
According to a 1972 EPA report,1 the 1968 annual ammonium
averages for 28 nonurban stations of the NASN throughout the
United States ranged from 0 to 1.2 yg/m3 (see Table 4-11).
Averages for the same year for 149 NASN stations in urban areas
ranged from 0 to 15.1 yg/m .
In their previously cited study, Georgii and Muller
measured simultaneously the vertical distribution profile of
ammonia, ammonium, sulfur dioxide, and sulfate from ground level
to an altitude of about 3,000 m over Bavaria, Germany (Figure 4-8).
The vertical profile of ammonium closely followed that of ammonia,
3
with ammonium reaching a constant value of 2_ 1 yg/m at an alti-
tude of 1,000 m. As shown in Figure 4-8, the vertical profiles
of sulfur dioxide and sulfate are different, owing to anthropo-
genic sources at ground level and the resulting accumulation of
sulfur dioxide and sulfate under the inversion level.
Data from the NASN and the study of Georgii and Muller, as
well as more recent measurements from Point Arguello (ammonium
0.36 yg/m3) and Goldstone (0.71 yg/m3) in California as part of
1 o ,o
the ACHEX-1- seem to indicate a "background" value of — 1 yg/m
for ammonium in nonurban atmospheres. Healy,3-'- however, re-
ported somewhat higher values at Harwell, U.K., with "background"
ammonium of 3-4 yg/m3 and peaks of up to 12 or 13 yg/m3. These
higher values may reflect the contribution of nearby anthropogenic
and related sources, such as cattle and the use of fertilizers.
The recent study of Reiter, Sladkovic, and Potzl56 provided
detailed information on the chemical composition and concentra-
tions of nonanthropogenic aerosols in the troposphere. Particulate
328
-------
TABLE 4-11
National Range of 1968 Annual Average Concentrations
of Major Particulate Pollutants^.
Maximal Station
Average
Concentration, ug/m
Minimal Station
Average
Concentration, ug/m
al suspended particles
Irban
lonurban
,ctions of suspended particles:
lenzene-soluble organics:
239
49
26
6
Urban
Nonurban
braion ium :
Urban
Nonurban
"Nitrate:
Urban
Nonurban
Sulfate:
Urban
Nonurban
23.8
3.0
15.1
1.2
13.0
1.2
48.7
14.1
1.3
0.8
0.0
0.0
0.6
0.1
1.6
0.9
Derived from EPA.1 Annual averages are arithmetic means for all pollutants
total suspended particles, for which geometric means were reported. Urban
^measurements were conducted at 149 stations. Nonurban measurements were
conducted at 28 stations.
329
-------
iOOO-i
3000-
2000-
1000-
10
20/jg/Nm3
FIGURE 4-8.
Vertical distribution of trace substances over
Bavaria. Reprinted with permission from Georgii
and Muller.25
330
-------
samples were collected at Wank Peak (1,780 m.) in the Garmish-
Partenkirchen area and were analyzed for water-soluble ions
(sodium, potassium, calcium, ammonium, chloride, sulfate, and
nitrate), insoluble materials (silica, ferric oxide, aluminum
trioxide, and calcium oxide), and trace elements (zinc, cadmium,
copper, phosphorus, and vanadium). Results obtained over the
2-year period, November 1971-December 1973, are summarized in
Table 4-12, which shows a mean ammonium concentration of
1 1.3 ug/m^. A comprehensive monitoring of meteorologic and
other characteristics permitted the conclusion that higher
ammonium concentrations (>3 ug/m3 in 15 of the 202 cases studied)
were associated with incursions of polluted air masses of con-
tinental origin. Because most measurements were conducted in
unadulterated air masses having no ground contact above the
European continent, the value of 1.3 ug/m-* can be considered
as representatives of "background" ammonium in nonanthropogenic
aerosols.
Particulate Ammonium Concentrations in Urban Areas.
Certainly one of the most comprehensive studies of the chemical
composition, size distribution, and origin of atmospheric acid
particles was that of Brosset and co-workers,7,8,9 who investi-
gated in Sweden the transport of anthropogenic aerosols originating
in England and other countries in northern and central Europe.
Particulate samples collected at Rao, a location free of local
pollutant sources on the Swedish west coast, were analyzed for
sulfate, ammonium, and hydrogen ions. Combining inorganic
331
-------
TABLE 4-12
Chemical Composition and Concentrations of
Nonanthropogenic Aerosols^
Jo
Aerosol Constituent Mean Concentration, yg/nr Fraction of Total.
Na+ 0.053 0.8
K+ 0.062 0.9
CaO + Ca2+ 0.322 4.8
Fe203 0.145 2.1
Si02 0.663 9.8
Pb2+ 0.033 0.5
Cl" 0.112 1.7
S042" 3.147 46.6
N03 0.924 13.7
NH4+ . 1.295 19.2
Total 6.756 100.1
Important Atmospheric Characteristics Mean
Temperature, °C +4.05
Relative humidity, % 68.8
Exchange intensity, kg/(m)(s) 13.13
Wind velocity, m/s 4.05
o
Aitken nuclei, no./cm 1062
Size distribution parameter 2.0
Precipitation, mm/100 m3 2.22
Radioactivity in air, pCi/m3 61.93
a sfi
"Derived from Reiter et a1.
b
-For 202 cases studied from Nov. 1971 to Dec. 1973.
332
-------
analysis, size distribution measurements in the optical range,
x-ray diffraction studies, and air trajectory analyses, Brosset
ct al- identified two major types of particulate pollution on the
Swedish west coast. The first type consists of dark particles of
low acidity accumulating between 0.5 and 1.5 pm in diameter. The
water-soluble part of these particles contains mainly (NH4)2S04
and some (NH4) 3 HCSC^^- Particles of this type are observed
frequently, originate in the South (northern central Europe),
and are generated by oxidation of sulfur dioxide dissolved in
water droplets. The second type (Table 4-13) consists of smaller,
almost colorless particles of high acidity accumulating below
0.4 urn in diameter. The water-soluble fraction of these particles
contains mainly NH4 H SO4 and some (NH
-------
u>
U)
TABLE 4-13
Ammonium and Other Particulate Species during Type 2
(High-Acidity) Pollution
Sample
No.
Stan
Slop
r.h.,
P;irl. cone.
/'B "'' ''
S04"
nimilc m
Nil,'
innolc in" J
II'
niiiolo m"1
Episodes3
May episode
1
dale 21
lime 15:25
dale 22
lime 12:15
87
•/. yj
94
392
\\ijr.
2-1.1
180
2
22
12:25
23
14:00
85
71
94
353
153
209
.15-0
3
23
14:30
2.1
21:00
89
91
59-9
241
402
26-6
4
23
21:00
24
09:10
91
96
4.V5
166
292
22-7
5
24
09:15
25
14:00
92
87
91
202
103
135
450
6
25
15:30
28
15:20
78
70
45
270
124
175
20-4
7
28
15:20
28
24.00
45
48
537
2.10
177
219
8
29
00:00
29
06:00
48
71
55H
234
I9H
212
9
29
06:00
29
12:00
71
37
5K-9
224
214
214
10
29
12:00
30
12:00
42
60
33
359
149
217
28-1
II
30/5
13:00
1/6
09:00
33
57
86
370
102
121
UK
July episode
in
14:25
.1/7
15:00
4-1
•11
71
MB
I'M
M.1
7lil
3. 9
—Reprinted with permission from Brosset et al.
-------
•specially dense mist with extremely low-visibility. Visibility
reduction correlated well with both sulfate and ammonium concen-
trations throughout the period studied.
Demuynck et aj^.°a reported the chemical composition of air-
borne particulate matter during a period of severe pollution in
Ghent, Belgium, in September 1972. Selected data for this pollu-
tion episode are listed in Table 4-14, which indicates a tenfold
or greater increase in ammonium (highest concentration measured,
33 yg/m3) over its usual concentration range of 1-3 pg/m3.
Ammonium and other particulate pollutants measured during this
pollution episode were shown to be anthropogenic.
Particulate ammonium has also been routinely measured at
various urban locations throughout the United States. Data for
the year 1968 are listed in Table 4-11. The 1970-1972 average
annual concentrations of the three major inorganic ions—ammonium,
nitrate, and sulfate—are listed in Table 4-15 for selected U.S.
cities.
Because of their widespread accumulation in the atmosphere
of northern Europe and in most of the eastern United States,
sulfate aerosols have been extensively studied in the last few
years. Although sulfuric acid has been found in the atmosphere
of eastern cities, most sulfate aerosols exist in the air as
various combinations of ammonium salts. Charlson et. al.14'15
identified both (NH4)2 504 and NH4HS04 in and near St. Louis,
Missouri. Acid ammonium sulfate was also measured at Brookhaven
(Upton, N.Y.) by Tanner et al.63
335
-------
TABLE 4-14
Atmospheric Concentrations of Major Particulate Pollutants
during Severe Pollution Episode in Ghent* Belgium^.
Sampling
date
(1972)
Sept. 16-17
Sept. 18-19
Sept. 19-20
Sept. 21-22
Sept. 22-23
Sept. 23-24
3
Concentration, yg/m
Total
Suspended 2_
Particles NH4 SO^
44 1.3 5.4
70 3.4 9.9
144 10.0 24.8
366 33.0 81
194 21.0 41.7
84 1.9 8.4
Benzene-
soluble
N03 Na Cl Pb Organics
1.8 1.69 2.71 0.31 2.0
3.4 0.53 1.26 1.17 3.9
11.1 0.75 2.07 1.27 6.3
24.2 1.78 4.35 3.01 42.9
17.0 1.21 2.91 2.76 9.7
3.26 2.67 4.20 0.43 2.8
— Derived from Demuynck et al.
336
-------
TABLE 4-15
Average Annual Concentration of Chemical Components
Derived from NASN High-Volume Sampling
Chicago:
S04"2
N03"
NH4+
Cincinnati:
so4~2
N03
NH4+
Philadelphia:
N03
NH4+
Denver:
so4"2
N03~
NH4+
St. Louis:
so4"2
N03"
NH4
Average
1970
14.8
2.7
1.1
12.4
3.5
0.2
21.9
3.6
2.1
4.5
3.1
0.1
b
b
b
Annual Concentration,
1971
16.1
4.4
0.9
11.8
3.7
0.4
15.2
3.8
0.7
5.0
3.1
0.0
12.2
2.7
0.1
a
3
1972
17.4
4.4
0.3
11.9
3.7
0.3
16.1
3.5
0.5
6.6
3.6
0.1
16.3
3.9
0.2
—Derived from Lee and Goranson.
43
—Insufficient data.
337
-------
Keese, Hopf, and Moyers40 reported the concentrations of
sulfate, ammonium, and 22 metals in samples collected over a
1-year period (December 1973-December 1974) at 11 locations in
and around Tucson, Arizona. They found high and similarly
correlated sulfate and ammonium concentrations at both urban
locations (ammonium =0.29 times sulfate; r = 0.944) and rural
locations (ammonium = 0.28 times sulfate; r = 0.931), with
24-h averaged ammonium concentrations ranging from 0 to
6.5 yg/m3. The slopes of the obtained correlations (0.29) also
suggested the existence of sulfate to a large extent in the
form of (NH,)SC> (ammonium: sulfate molar ratio, R, of 0.38) and
NH4HS04 (R = 0.19) .
The distribution of ammonium with respect to particle size
has been recently investigated by Kadowaki,39 who analyzed size-
resolved samples (eight-stage cascade impactor) collected in
Nagoya, Japan, during the period December 1973-October 1974.
As shown in Table 4-16, ammonium in Nagoya air ranged from 2.7
to 4.2 yg/m3, with an average mass median diameter of 0.55 urn.
The mass median diameter showed very little seasonal variation.
Most of the ammonium accumulated with sulfate in particles less
than 1 ym in diameter (Figure 4-9); this indicates the anthro-
pogenic nature of particulate ammonium.
Another study of the distribution of ammonium with respect
to particle size has been conducted by Cunningham et al . ,17/18
who used Fourier-transform infrared spectroscopy to determine
ammonium and other aerosol constituents in size-resolved samples
collected at Argonne, Illinois, during the spring of 1973. They
338
-------
TABLE 4-16
Average Concentration and Mass Median Diameter of
Components in Urban Air at Nagoya, Japan ^L
Total acroinK Sullalc
Samphne No com m m d No con, mmd Sn con, m m d So com ^ mmd
ptnod sample,. (M m 'i l^mi Mmpl-.-s ing n> 'i ipmt sample- |/ig m^^ ^mi jdmnlc^iwj^ J "'""
Winter
(Dec -71 F,-h '74,
Spring
(Ma. Ma> ">4l
Summer
(June AuE -14,
Autumn
(Od Nm '^i
(Sepi Oci "J41
a 39
—Reprinted with permission from Kadowaki.
339
-------
FIGURE 4-9.
£
CT
a.
e
<3
Cone. 4-2 /ig m"3
(23-29 July 1974)
1 i r
J_
008 O43 O65 II 21 334770
Particle dia , /im
30
Histogram and size distribution curve of
ammonium in Nagoya. Reprinted with per-
mission from Kadowaki.39
340
-------
found ammonium sulfate to be the major ammonium salt associated
with small particles (stage IV of the cascade impactor used,
0.3-1.2 ym) . Also of interest is their observation of ammonium
halide (chloride and/or bromide) in samples with an "excess"
of ammonium over sulfate.
Particulate ammonium in California air has been the subject
of several recent studies. Large samples of airborne particulate
matter were collected by Gordon and Bryan26 at four locations in
the Los Angeles area and analyzed for nitrogenous constituents
after successive extraction with benzene, methanol, and water.
Particulate ammonium in downtown Los Angeles averaged 2.8, 3.4,
and 3.2 yg/m over the 1-year periods August 1969-August 1970,
August 1970-August 1971, and June 1971-June 1972, respectively.
The methanol extract was found to contain principally ammonium
nitrate, which accounted for 10-15% of the total airborne particles
over the 1-year period studied (June 1971-June 1972) . Lundgren45
also found ammonium nitrate to be a major constituent of sub-
micrometer particles collected at Riverside, California, during
severe episodes of photochemical smog.
The chenical composition of Pasadena, California, aerosol
was investigated by Novakov et. al.52 Analysis of 4-h particulate
samples collected on September 3-4, 1969, by x-ray photoelectron
spectroscopy revealed four major chemical states for particulate
nitrogen—two organic states (amino nitrogen and pyridino nitrogen)
and two inorganic states (nitrate and ammonium, the latter rang-
ing from 0.1 to 1.8 yg/m3). The diurnal profile of particulate
ammonium in particles smaller than 2 ym exhibited a strong morning
341
-------
peak associated with automobile traffic (motor vehicles are known
to emit mixed ammonium and lead halides33}. The diurnal profile
of ammonium in larger particles closely followed the profiles
of sulfate and nitrate; this indicated significant gas-to-particle
conversion of gaseous ammonia.
The ACHEX13 provided detailed information about particulate
ammonium in California atmospheres. From data on 24-h samples
collected at various urban and nonurban locations in California
and analyzed for ammonium nitrate, and sulfate it was concluded
that an average of 85% of the two major anions (nitrate and
sulfate) can be accounted for in ammonium salts. Although in
these calculations sulfate was assumed to be present as ammonium
sulfate and nitrate as ammonium nitrate (Table 4-17), assuming
sulfate to be present as N^HSC^ would further improve the
balance between measured and calculated ammonium.
Results from the ACHEX first pointed out that, as opposed
to ammonium sulfate (and/or bisulfate), which is somewhat evenly
distributed throughout the California southern coastal air basin,
ammonium nitrate is found at much higher concentrations in the
eastern inland part of the SCAB. Further studies by the California
Air Resources Board25 and the Statewide Air Pollution Research
Center Riverside group27 confirmed this trend in the geographic
distribution of ammonium nitrate in the SCAB. Simultaneous
measurements of sulfate, nitrate, ammonium, and gaseous ammonia
conducted at four sites arranged approximately on a west-east
transverse of the SCAB revealed a significant increase in ammonium
nitrate and ammonia concentrations at the inland sites (Figure 4-10)
342
-------
TABLE 4-17
Comparison of Theoretical and Experimental Ammonium Concentrations
ampline Site
Harbor Freeway
•ii'asadena
lilies t Covina
Pomona - 1972
,'omona 1973
Riverside
i&ubidoux
Dominguez Hills
Pt. Arguello
Goldstone
d
Hunter Liggett
ii
'S.F. Airport
' Richmond
' Fresno
' San Jose
Average
at Urban Sites
No. Samples
2
6
4
5
2
7
3
2
1
1
1
1
2
2
7
in California fL
Ammonium
Expected on Basis
N03~ and S042"
Present, MK/m
4.0
4.0
10.3
8.9
6.6
7.9
15.5
7.9
2.7
0.9
1.9
1.0
1.7
3.6
3.0
6.2
Concentration
of
Observed, °L of
Expected
103
82
76
94
75
93
73
62
131
79
125
71
59
106
78
85
-Derived from Hidy et a_l.13d Analyses on high-volume samples collected on
Whatman-41 filters.
-Assumes composition to be
and
343
-------
NH,.
1500
1250 -
o
oo
o 1000 —
o
CO
.E
LU
_J
O
O
750 -
500 -
250 •>
(gas-phase)
Santa
Monica
Riverside
FIGURE 4-10.
Comparison of molar concentrations of gas-phase
ammonia and particulate ammonium, nitrate, and
sulfate ions at four stations in the southern
coastal air basin; average values for 4 moderate-
smog days in October 1974. Reprinted with Pf?~
mission from California Air Resources Board.
344
-------
Rapid reaction of ammonia emitted by feedlots with nitric acid
produced in photochemical smog results in the observed sharp in-
crease in inland concentration of particulate ammonium nitrate.
High concentrations of ammonium nitrate were also measured
by Grosjean et al_. , 7 who analyzed 24-h particulate samples
collected daily during the 6-month period May 1-October 31, 1975,
at Riverside, California, a smog receptor site in the eastern part
of the SCAB. During the 6-month summer period studied (176 24-h
samples), particulate ammonium averaged 7.63 yg/m , with a highest
24-h averaged value of 30.1 ug/m (Table 4-18). The concentra-
tion frequency distributions for total suspended particles, sulfate,
nitrate, and ammonium over the period studied are shown in Figure
4-11. On the average, ammonium accounted for all the measured
nitrate (as ammonium nitrate) and half the sulfate (as ammonium
sulfate) ; this suggests that ammonium sulfate and/or other acidic
ammonium and sulfate salts are the major constituents of sulfate-
containing particles in Riverside air.
345
-------
TABLE 4-18
Highest 24-Hour Total Suspended Particles> Sulfate,
Nitrate, Ammonium, and Organic Carbon Concentrations,
Riverside, California, May-October 1975 —
• b ,r/m3
Concentration,— yg/m
Month
May
June
July
August
September
October
Total
Suspended
Particles
218(3)
185(10)
218(26)
254(22)
277(13)
269(2)
NH4+
17.5(31)
24.9(10)
15.7(22)
16.1(15)
30.1(13)
22.4(1)
N03"
30.44(3)
38.6(10)
40.9(26)
46.4(22)
70.2(13)
61.3(1)
S(V2
33.0(31)
29,7(13)
23.5(25)
31.1(21)
48.7(14)
34.9(2)
Organic
Carbon
14.7(3)
16.3(11)
20.9(25)
21.3(2)
22.8(21)
26.7(2)
a 27
^Derived from Grosjean et al.
-Numbers in parentheses indicate, for stated month, the day on which maximum
concentration occurred.
346
-------
ro
i
o>
3OO
200
100
NOB
NH4
S0|
10
NUMBER OF DAYS
FIGURE 4-11. Frequency distribution of total suspended particles (TSP) and sulfate,
nitrate, and ammonium ions, Riverside, California, May-October 1975
(176 days). Reprinted with permission from Grosjean et al.27
-------
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356
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PLANT AMMONIA ABSORPTION
De Saussure published his observation of ammonia in the air
in 1804 Liebig reported in 1847 that soil colloids would ab-
sorb ammonia from the atmosphere and theorized that plants thus
gain most of the nitrogen they need from the air. He was later
proved wrong, but attention is being focused again on the gas-
phase exchange of nitrogen compounds between plants, soil, and
atmosphere. This recent interest has several reasons:
• Despite recent advances in understanding of various
components of the nitrogen budget of agricultural
and natural ecosystems, gained through the use of
nitrogen-15, there is still considerable uncertainty
about the balance. This is especially true under
field conditions, where the measurement of gas flux
is difficult. Imbalances as high as 50% of the
total nitrogen budget are often encountered, and
they are attributed to gas losses--!.e., nitrogen,
nitrous oxide, nitrogen dioxide, and ammonia.
• Man's activities may be increasing the turnover
rate of these gases in soil, air, and water
through increased use of commerical fertilizers
and nitrogen fixation by leguminous crops.
Increased volatilization of ammonia into the
atmosphere could result from extensive use of
anhydrous ammonia and urea.
357
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• The large numbers of animals in feedlots produce
locally high concentrations of ammonia in the
atmosphere. This can be carried to soil, water,
and plants.
e There is some evidence that, in regions of high
atmospheric ammonia concentration, bodies of
water absorb the gas and that this leads to
eutrophication.
e Evidence is accumulating that soil and plants may
absorb more ammonia from the air than previously
recognized. These gains are relatively small in
comparison with agricultural crop needs, but they
may play some role in supplementing crops. More
important, absorption from the air could be sig-
nificant to natural ecosystems when nitrogen is
a limiting factor in plant growth. Thus, the
absorption of ammonia from the air could be re-
lated to the amount of carbon dioxide also ab-
sorbed from the air during photosynthesis.
Ammonia uptake and improved nitrogen nutrition
of plants play a role in damping the atmospheric
buildup of carbon dioxide (about which there is
concern), through storage of more carbon in the
biosphere. Plants and soils can also damp
atmospheric buildup of ammonia. Obviously, all
358
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these factors are tightly coupled in the complex
modern world.
The fact that there is a substantial vertical gradient of
ammonia in the troposphere (higher at the earth's surface)
lends support to the argument that the surface is an active
exchange site. Ammonia concentrations in the air are higher
over land than over the sea; this leads to speculation that
the sea is a sink. Williams ^ has questioned this. He has
found that sea-surface films are extremely rich in organic
and inorganic ammonia compounds that become airborne as
359
-------
aerosols from bubbles that burst in wave action. Thus, aerosol
cycling of ammonia could be from sea to land, as well as re-
cycling with the sea again. Unfortunately, current analytic
methods and available data do not allow evaluation of the pro-
portions of ammonia in the gaseous and aerosol forms, and it
is still an open question whether the seas are a net source
or net sink for ammonia.
Aerosol formation of ammonium salts is also important on
land. Man's industrial activity contributes to the quantities
of ammonia in this nongaseous form. The relative proportions
of direct gaseous ammonia adsorption by land plants and soil and
wet and dry deposition of particulate forms of ammonia have not
been determined. The particulate form would probably not be>so
reactive in plant adsorption through leaf stomata. However,
salts would be adsorbed through the leaf cuticle when surfaces
became wet with dew, rain, or irrigation.
Plants have a high affinity for gaseous ammonia when the
leaf stomata are open in daylight. Three successive processes
are involved: physical adsorption, chemical exchange, and meta-
bolic assimilation. Absorbed ammonia in a leaf is rapidly metab-
olized to amino acids and proteins, according to Porter et al.9
and Hutchinson et al.5 These authors speculated that the ammonia
is initially metabolized via glutamic acid or carbamyl phosphate.
Recently, Lewis and Berry,6 have shown that glutamine is a major
acceptor of reduced nitrogen in leaves and that the role of
glutamine as a nitrogen storage compound and as an ammonia "4e-
toxifier" in many plants extends to the incorporation of
360
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photosynthetically produced ammonia in leaves. Chloroplasts
were proved to be the site of this activity.
Hutchinson e_t al.5 reported leaf uptake rates for young
vigorous plants in bright light, as shown in Table 4-19.
The uptake rate depended heavily on stomatal opening, and
there was no hint of saturation during the active light period.
The authors therefore conclude that species difference in ab-
sorption rate must be explained by species differences in in-
ternal leaf geometry, which determines the diffusion of ammonia
across the air spaces in the leaves. It is surprising that the
authors did not mention that species difference could be
attributed to differences in stomatal diffusive resistance,
especially because their experiments demonstrated remarkable
stomatal control of ammonia uptake between light and dark
periods.
Plants sometimes give off ammonia, but the factors contributing
to the phenomenon are unclear.^ in any event, losses are likely
to be small. Denmead et. al.2 recently reported on the uptake of
ammonia by a pasture composed of 67% Wimmera ryegrass (Lolium
rigidum Goud) and 33% subclover (Trifolium subterraneum L.).
They used a micrometeorologic approach in the field: vertical
gradients of ammonia were measured in the natural airstream
above and through the vegetation. Thus, the system was not
disturbed, and the results reflected what was going on in the
natural state. The results for various periods of the day are
shown in Table 4-20. Upward flux intensity is the amount of
ammonia gas passing up through a unit area of a horizontal plane
361 .
-------
TABLE 4-19
Leaf Uptake of Ammonia in Bright Light5.
Plant
Soybean (Glycine max.)
Sunflower (Helianthus annuus)
Corn (Zea mays)
Cotton (Gossypium hirsutum)
NH3 Uptake Rate,
mg/m^-h
0.40
0.49
0.56
0.35
NH3 Air Concentration,
ug/m3
24
31
24
44
-Data from Hutchinson et al.5
362
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TABLE 4-20
Ammonia Uptake in an Ungrazed Ryegrass-Subclover Pasture-
Ammonia Nitrogen Upward
Flux Intensity, mg/m -h
Time At Ground
Nov. 21, 1974:
0845-1047
1052-1300
1305-1505
1510-1715
1717-1922
Nov. 22, 1974:
0835-1036
1039-1242
1247-1447
1452-1652
5.
3.
2.
1.
0.
2.
2.
1.
0.
6
2
9
8
3
2
8
7
9
At Crop Top
0.
0.
0.
0.
0.
0.
0.
0.
0.
1
1
4
2
3
2
1
1
0
5.5
3.1
2.5
1.6
0
2.0
2.7
1.6
0.9
from Denmead et al.
363
-------
in a unit of time. Here, there are two horizontal planes, the
upper and lower boundaries of the crop canopy. The difference
between the flux intensities through the two planes shows the
net gain or loss of ammonia by the crop. The concentration of
ammonia averaged 13.5 ug/m in the air near the ground and about
1 yg/m^ in the air immediately above the vegetation.
Obviously, the mixed pasture plants were absorbing ammonia
from the air. The source of ammonia was the soil, the detritus
at the base of the vegetation, or both. Net-crop-uptake data
are based on ground area and are about 10 times greater than the
leaf data reported by Hutchinson et. al. ^ This is entirely
reasonable, in that the Australian mixed pasture could easily
have had a leaf area of 10 m^/m^ of ground area. The authors,
however, believed that absorption was too high to be through the
stomata alone. They speculated that ammonia was dissolved in
leaf surface dew and then became absorbed in ionic form.
Although the methods used by Denmead et. al.2 are not very
accurate and could be in error by a factor as large as 2, the
results nonetheless clearly demonstrated that plants can scrub
the air of ammonia. If their results are extrapolated to a
yearly basis, they amount to about 10 kg/ha-yr, perhaps 10-25%
of the nitrogen balance of the pasture.
When ambient ammonia concentration is increased and the
upward flux from the soil is small, it is reasonable to expect
that ammonia can flow downward into the vegetation when the
stomata are open in daylight.
364
-------
We have mentioned the significance of ammonia's originating
at the base of the Australian ryegrass-subclover pasture and
later being absorbed by the plants. This absorption may in
the past have caused underestimation of the amount released
from the soil or from the detritus under vegetation. This
problem deserved investigation, because it had been assumed
that the ammonia from the soil or at the surface was a minor
contributor to the atmosphere, compared with that from urine
and feces deposited by grazing animals.
In an earlier study, Denmead et al. used meteorologic
techniques to measure ammonia flux from a 4-ha alfalfa pasture
being grazed by 200 sheep. The results are given in Table 4-21.
Air concentration measured 20 cm above the ground averaged 15.7
ug/m3, with a range of 3.4-51.5 pg/m ; 95 cm above the ground,
the average was 10.1 pg/m , with a range of 1.6-28.4 pg/m3.
The authors attributed the wide variation in atmospheric
ammonia to local air turbulance. In any event, the upward flux
intensities of ammonia from the top of the grazed alfalfa pasture
(1.9 mg/m2-h) were about equal to the upward flux intensities at
the base of the ungrazed mixed pasture (2.4 mg/m2-h). It is safe
to assume that the urine and feces from the animals grazing in the
pasture contributed a large amount of ammonia at ground level, be-
low the vegetation canopy; this explains why some ammonia was escapinc
through the vegetation and out of the top of the canopy (0.2 mg/m2-h).
Unfortunately, there are no data for estimating the portion of the
ammonia coming from the ground surface that was absorbed on its
passage upward through the vegetation. In the mixed-pasture
365
-------
TABLE 4-21
Ammonia Flux from a Grazed Alfalfa Pasture —
NH3 Upward Flux Intensity above Pasture,
Time mg/m -h
March 14,
1130 -
1330 -
1600 -
1800 -
2000 -
March 15,
0630 -
0830 -
1030 -
1230 -
1974:
1330
1550
1800
2000
2200
1974:
0830
1030
1230
1430
3.7
1.5
1.3
1.0
0.8
1.0
2.1
3.2
2.7
a 3
— Data from Denmead et al.
366
-------
experiment, however, comparisons can be made between a grazed
area and an adjacent ungrazed area where ammonia flux was
measured simultaneously. Daytime losses from the top of the
two pastures averaged 1.3 mg/m2-h for the grazed area and
0.3 mg/m2-h from the ungrazed one. No data were given on the
amount of leaf area in these two pastures, so comparisons are
somewhat questionable.
Soil and its associated vegetation and detritus can serve
as either a source or a sink for ammonia. For example, Malo
and Purvis7 and Hanawalt4 considered that absorption of ammonia
by the soil in New Jersey contributed to crop productivity. In
their studies of absorption by six different dry soils exposed
to air ammonia concentrations of 57 pg/m^ (average), they sug-
gested that factors governing diffusion (i.e., wind, temperature,
soil porosity, air concentration, and soil moisture) played a
more important role than pH in absorption. Allison^ concluded
that low soil pH enhanced absorption of atmospheric ammonia.
(Soil organic matter also plays a role.) The low pH of laterite
soil has been suggested by Allison as the cause of lower ambient
concentrations of ammonia over the southern United States.
Alternatively, one can speculate that the lush vegetation growing
over a longer period in this region creates a greater sink for
ammonia.
It is evident that the mechanisms and dynamics of ammonia
exchange on land are not well understood. The fact that pasture-
land can absorb ammonia at 10 kg/ha-yr suggests that this exchange
can play an important role in regulating atmospheric ammonia con-
centration and may, under sone conditions, contribute to crop
productivity. 367
-------
REFERENCES
1. Allison, F. E. The enigma of soil nitrogen balance sheets. Adv. Agron.
7:213-250, 1955.
2. Denmead, 0. T., J. R. Freney, and J. R. Simpson. A closed ammonia cycle
within a plant canopy. Soil Biol. Biochem. 8:161-164, 1976.
3. Denmead, 0. T., J. R. Simpson, and J. R. Freney. Ammonia flux into the
atmosphere from a grazed pasture. Science 185:609-610, 1974.
4. Hanawalt, R. B. Environmental factors influencing the sorption of atmos-
pheric ammonia by soils. Soil Sci. Soc. Amer. Proc. 33:231-234, 1969.
5. Hutchinson, G. L., R. J. Millington, and D. B. Peters. Atmospheric
ammonia: Absorption by plant leaves. Science 175:771-772, 1972.
6. Lewis, 0. A. M., and M. J. Berry. Glutamine as a major acceptor of
reduced nitrogen in leaves. Planta 125:77-80, 1975.
7. Malo, B. A., and E. R. Purvis. Soil absorption of atmospheric ammonia.
Soil Sci. 97:242-247, 1964.
8. McKee, H. S. Nitrogen Metabolism in Plants. Oxford: Clarendon Press,
1962. 728 pp.
9. Porter, L. K., F. G. Viets, Jr., and G. I. Hutchinson. Air containing
nitrogen-15 ammonia: Foliar absorption by corn seedlings. Science
175:759-761, 1972.
10. Williams, P. M. Sea surface chemistry: Organic carbon and organic and
inorganic nitrogen and phosphorus in surface films and subsurface
waters. Deep-Sea Res. 14:791-800, 1967.
368
-------
OCEANS
Fixed Nitrogen as a Limiting Nutrient
Availability of dissolved inorganic nutrients in coastal and
open-ocean surface water frequently controls the amount and rate
of photosynthetic primary productivity- Some form of nitrogen is
often scarce, and thus the critical limiting factor in algal
growth in both coastal water and the surface layers of the open
13 45,48
ocean. ' ' In the open ocean, primary productivity is limited
by the most slowly regenerated nutrient. Nitrogen becomes limiting,
because organic phosphorus is converted to inorganic phosphate far
more rapidly. In coastal water and estuaries, low fixed nitrogen
concentrations, often associated with large phosphorus surpluses,
result from the generally low nitrogen-to-phosphorus ratio of
land contributions relative to growth requirements, as well as
the more rapid recycling of phosphorus.45
Sources of Nitrogen in Marine Systems
Sources of nitrogen in various marine systems are listed in
Table 4-22. Both newly introduced and recycled forms of nitrogen
are included, to illustrate that chemical transformations between
many chemical forms of nitrogen—including ammonia, nitrate, dis-
solved organic nitrogen, and nitrogen-containing organic materials—
are important. It is also important to note that discharge of
municipal sewage and runoff from agricultural areas have a poten-
tially major effect on the near-shore marine environment.
369
-------
4-92
TABLE 4-22
Potential Nitrogen Sources in Marine Systems-
Marine System
Nitrogen
Source
Regeneration
Seasonal mixing
Diffusion from
deep water
Rainfall
Runoff
Fixation
Periodic
intrusions
Near -shore
Coastal Continental
Upwelling Estuary Shelf
X XX
X
X
X XX
X X
X XX
X
Off-shore
Continental
Shelf
X
X
X
X
X
X
Oligo-
trophic
Central
Gyres
X
X
X
X
X
Upwelling
—Derived from Smith.
370
-------
In the absence of tertiary treatment,* the amount of sewage
nitrogen released is directly related to the human population.
Unit emission rates and population figures therefore provide an
estimate of the load imposed on a particular estuary or near-
shore area. Average total nitrogen and phosphate in municipal
sewage emission for a densely populated area ^ are summarized
in Table 4-23, with estimates of other constituents, including
dissolved solids, suspended solids, and BOD (biologic oxygen
demand). Recently, Duedall e_t cQ.1J- have shown that ammonium in
municipal sewage effluent discharged into the New York Bight area
is a major source of ammonia nitrogen, for that water supplies
5-10 times more ammonia than barge-dumped sludge during a typical
summer.
Agricultural runoff may become more important in estuarine
marine systems with the advent of large-scale farming operations
on formerly undeveloped coastal land areas, such as those found
along the southeastern United States. Nitrogen utilization in
U.S. agriculture has increased fourteenfold between 1945 and
1970, while the amount of nitrogen released via sewage has in-
creased by a factor of 1.7.9 in most cases, the discharge of
sewage is intentional, and both the source and magnitude of re-
sulting nitrogen emission can be described more accurately than
agricultural or industrial emission.
*Wastewater treatment beyond the biologic stage (secondary)
that removes phosphorus, nitrogen, and a high percentage
of suspended solids.
371
-------
TABLE 4-23
Average Sewage Emission for a Densely Populated Areag.
Unit emission rate
Constituent
Ib/capita-day kg/capita-day
Total nitrogen
Phosphate
Dissolved solids
Suspended solids
BOD
0.047
0.029
1.03
0.162
0.160
0.021
0.013
0.467
0.073
0.073
^Derived from NAS.3^
371-
-------
Other sources of newly arrived nitrogen for near-shore
coastal water include river runoff, rainfall and upwelling of
deeper nitrogen-rich water. The relative significance of the
different sources—including regeneration, periodic intrusions
of deeper nitrogen-rich off-shore water, seasonal mixing, and
diffusion from deeper water—and the role of ammonia in estuarine
and other marine systems is discussed below.
Ammonium Distribution in Various Marine Environments
The typical distribution of ammonium in the water column of
various marine environments is illustrated in Figure 4-12. The
roles of both fluxes from bottom sediments and regeneration in
the water column are seen in the estuarine and continental shelf
profiles, whereas the important role of water-column regeneration
is emphasized by the coastal upwelling and open-ocean system
profiles.
The relatively high concentrations of ammonium found in the
interstitial water of organic-rich fine-grained marine sediments
often found in coastal marine environments or areas underlying
water bodies with restricted circulation (Figure 4-13) reflect
the importance of bottom sediments as a probable ammonia source
for estuarine and shelf waters.
Role of Ammonia in Marine Nitrogen Dynamics
Uptake of Ammonia by Primary Producers. The uptake of
limiting fixed-nitrogen compounds can be described by saturation
kinetics in a way similar to descriptions of nutrient-limited
growth of a bacterial population.37'52 An expression derived for
371- &.
-------
100 r—
50
0
(a) o
10
(b)
i.o
2.0
100i—
1.0
2.0
AMMONIUM (Mmole/litec)
Figure 4-12. Typical ammonium distributions in various marine environments:
(a) estuary (Barber and Kirby-Smith 1), (b) continental shelf
(Rowe et al. *), (c) coastal upwelling system (Friebertshauser
et al."1") . and (d) Atlantic Ocean (Friebertshauser et al. ).
372
-------
800i-
700
600
500
u
I 400
t
lit
D
300
200
100
(a)
150
100
50
1.0
2.0 0» °0
1.0
2.0
100
I
a.
LU
Q
50
(0 °0
150
100
50
0.5
1.0
(d)°0
AMMONIUM (mmole/liter)
Figure 4-13. Ammonium concentration depth profiles in interstitial water of
organic-rich sediments: (a) West African continental margin,
2,066-m water depth (Hartmann et al. ) , (b) Devil's Hole, Bermuda
(Thorstenson and Machenzie 49), (c) Santa Barbara Basin
(Sholkovitz 4S), and (d) Long Island Sound, 2 km off shore
(Goldhaber et al 21).
373
-------
enzymes can also formally describe a hyperbola for ammonia
uptake in marine organisms (Figure 4-14) via the equation:
V = V.
max K + S (4-1)
where V = specific uptake rate of limiting nutrients, units
in time ,
V = maximal specific uptake rate,
max
S = concentration of limiting nutrient (substrate) , juK1
K = limiting nutrient concentration for V = vmax/2, also
referred to as "half-saturation concentration."
Ammonia uptake by natural populations of marine phytoplankton
has been shown to follow this type of kinetics (e.g., Maclsaac
-30 cr
and Dugdale and Caperon and Meyer ). The half-saturation concen-
tration, KM, is expected to be constant for any given uptake mecha-
nism,^ thereby justifying its use for description of uptake kinetics
by a mixed natural phytoplankton population expected to have the
same uptake mechanism (i.e., for algae). Variability in Vmax
would be expected, for example, in populations with different;
concentrations of nutrient uptake sites per unit population. A
review of KM values for batch-culture phytoplankton experiments
can be found in Eppley e_t a.1. ,16 and limited data for continuous
culture experiments have been presented by Caperon and Meyer.5
The metabolic pathway of nitrate assimilation (see Chapter
2) involves the stepwise reduction of nitrate to nitrite followed
by nitrite reduction to ammonia (e.g., Lui and Roels2^). in the
presence of sufficient ammonia concentrations, the synthesis of
374
-------
FIGURE 4-14.
Nutrient uptake as a function of nutrient
concentration, according to the Michaelis-
Menten expression. Reprinted with per-
mission from Dugdale.
375
-------
nitrate and nitrite reductase enzymes in phytoplankton is pre-
vented.12'17/29 When ambient ammonia concentrations are around
1 ymole/liter, nitrate uptake is strongly affected. Figure 4-15
illustrates the partitioning of nitrogen uptake between ammonium
and nitrate, as observed in the plume of the Peruvian upwelling
system.12
Importance of Ammonia in Marine Primary Productivity.
Ammonia is the preferred nitrogen source of phytoplankton.1^'1^
The proportion of ammonium incorporated into particulate form by
phytoplankton to total nitrogen demand (ammonia plus nitrate
nitrogen incorporation), i.e.,
(NH4+)incorp.
(NH3 + N03-)incorp.
ranges from approximately 98% in oligotrophic (nutrient-poor),
central ocean gyres* to as low as 28% in coastal upwelling
areas.13'54 The oligotrophic central gyre systems and eutrophic
(nutrient-rich) upwelling systems set the boundaries for nitrogen
dynamics in a spectrum of marine systems. Characteristic values
of this ratio for continental shelves having productivities between
the two extremes, and represented by the Gulf of Maine and North-
east Pacific, range from 61 to 76%.13 The relatively greater
*Large, closed circulatory bodies formed by semiclosed current
systems. Subtropical current gyres are centered at 30° N and
30° S latitude. Gyres are a surface feature vertically isolated
from deeper waters by density differences and are several thousand
kilometers in diameter.
376
-------
Sediment-Water
I nterface
SEDIMENTS
FIGURE 4-15.
Approximate pathways of nitrogen circulation, and
biologic uptake and regeneration in Peruvian up-
welling region. Adapted from Dugdale.12
377
-------
importance of regenerated nitrogen in the oligotrophic central
gyres accounts for their higher ammonia incorporation.
Coastal upwelling systems differ from the central gyres
primarily in the importance of newly arrived nitrogen in the form
of nitrate upwelled with deep water. Nitrogen available to phyto-
plankton in central gyres comes mostly from regeneration processes,
with zooplankton ammonia release being an important source, along
with bacteria and nekton (free-swimming fishes). 3
Zooplankton ammonia release supplies approximately half the
ammonia nitrogen demand in both upwelling and central gyre systems.
However, the proportion of the total nitrogen demand supplied by
zooplankton is lower in the upwelling system, because of the new
nitrate nitrogen source. The relative significance of ammonia in
these marine systems is discussed below.
• Estuaries. The primary sources of nitrogen in an
estuary are regeneration, fixation, tidal exchange,
and runoff. ' In situ regeneration by zooplankton
and from bottom sediments probably supply more than
80% of the total nitrogen demand.13 In shallow
estuaries, it appears that ammonium regeneration
from bottom sediments is more important than that
from zooplankton47 and thus may be the primary con-
trol on nitrogen-limited productivity. The estimates
of zooplankton regeneration in the form of ammonia
ignore urea, which may represent up to 44% of the
total nitrogen release from well-fed populations.47
McCarthy35 has shown that urea is a source of nitrogen
378
-------
for many marine phytoplankton species; however, its
importance as a nitrogen source in marine systems is
not well understood.
Coastal upwelling systems. Coastal upwelling areas on
the eastern side of the major oceans (e.g., Peru, West
3 8
Africa, and the U.S. West Coast) are eutrophic owing
to the more abundant nitrate nitrogen from upwelled
water. The nitrogen pathway in the Peruvian upwelling
system is shown in Figure 4-15. Approximately half
the nitrogen primary productivity is newly introduced
(based on nitrate uptake), and the other half is
"regenerated" productivity (based' on ammonia uptake).
The regeneration of nitrogen occurs at or near the
sediment-water interface and in the water column near
the foraging activities of herbivores, primarily the
anchoveta population.
Changes in ammonia concentration along the axis of the
upwelling plume resulting from biologic uptake, regenera-
tion, and additional upwelling limit the usefulness of
calculating stoichiometric relationships between seawater
nutrient composition and phytoplankton growth and compo-
sition,41 although these models are applicable for con-
sideration of interactions over long periods in large
areas of the ocean.
Partitioning of nitrogen assimilation between
ammonia and nitrate shows that, as regenerated
ammonia concentration increases downplume, nitrate
assimilation is reduced and nitrate is replaced
379
-------
by ammonia,12 as a result of ammonia inhibition
of nitrate reductase.
Continental shelf areas. The amount of nitrogen
cycling in continental shelf coastal areas varies
widely; this results in productivity between the
extremes of upwelling (eutrophic) and central
gyre systems (oligotrophic). Recent studies of
the North Carolina continental shelf by Smith47
have shown that off-shore shelf areas resemble
oligotrophic systems, in that nitrogen supplied
by zooplankton ammonium regeneration amounts to
66% of the total nitrogen demand, whereas, in
the near-shore shelf areas, zooplankton supply
only 9% of the total nitrogen demand of phyto-
plankton. Increased primary productivity in the
near-shore shelf is thought to result from other
sources of regenerated nitrogen, such as deep-
water and surface marine organisms.
Open ocean. Oligotrophic central gyre systems repre-
sent terminal receptors of nitrogen. Ammonia accounts
for as much as 92% of the total nitrogen assimilated
into primary food-chain producers.13 Seasonal changes
in the depth of vertical mixing result in seasonal
patterns of productivity, as deeper pools of regenerated
nitrogen are reincorporated. The sources of newly
arrived nitrogen (Table 4-22) include rainfall, diffu-
sion from deeper water, and fixation.6/47
380 !
-------
Ammonia Regeneration and Flux from Marine Sediments
Regeneration of ammonia from sediments and its return to
overlying water can supply a substantial fraction of the total
biologic nitrogen demand in the productive near-shore areas
where the mixed layer is bounded by the bottom.44 Efforts to
measure transformations among nitrogenous compounds in sedi-
ments controlling ammonia concentrations and to assess fluxes
out of the sediments have recently received much attention.
Microbial Metabolism in Marine Sediments. Ammonia in
marine sediments is formed by bacterial decomposition of organic
materials. Concentrations of 0.1 to greater than 1.0 mmole/liter
are not uncommon in the upper meter of the interstitial water of
organic-rich marine sediments^4> 46 (see Figure 4-13). Microbial
ammonium production and kinetic analysis of transport processes
across the sediment-water interface are discussed below. Empha-
sis is placed primarily on the near-shore environment.
In near-shore sediments, oxygen is the preferred and most
efficient electron acceptor in bacterial decomposition of organic
material. When oxygen is exhausted, alternate electron acceptors—
such as nitrate, sulfate, and bicarbonate—must be utilized, with
successively lower energy yield, as shown in Table 4-24. In the
competition for organic substrate, microbial organisms capable of
deriving the greatest energy yield will dominate. The competitive
exclusion arising from more efficient substrate utilization leads
to a succession of microbial ecosystems, as shown in Figure 4-16,'
each characterized by a dominant and apparently mutually exclusive
set of metabolic processes.
381
-------
TABLE 4-24
Baterial Energy-Yielding Metabolic Processes
Utilizing "Carbohydrate" as _ Substrate^-
Respiration Process A G , kcal/mole
Aerobic respiration:
CH20 + 02 -* C02 + H20 -686
Nitrate reduction:
5CH20 + 4N03" + 4HT1" ->• 2N2 + 5C02 + 7H20 -579
Sulfate reduction:
2CH20 + S042~ -> H2S + 2HC03" -220
Carbonate reduction:
2CH20 + 2H20 -+ 2C02 +4H2
4H2 + HC03" + H+ -> CH4 + 3H20
C02 + H20 -> HC03 + H
+
Net: 2CH20 -> CH4 + C02 - 57
a
"Derived from Goldhaber and Kaplan.
382
-------
water-sedimenfary
column
(biogeochem-
icol zones)
h.
o
i
^
V
o
t
j
c
•5
a>
in
0
sc
Hc
HC
CH
H
i '
i >
2
K
5
r)j
4,
Z
photic zone
"-V _" ."(aerobic'" "zOne)
(anaerobic
reducing •
zone)
\ \ \ \ \
\ \ \ (anaerobic
\ \ \carbonate
. reducing
\ \ \ zone)
\ \ \ \ \
\ \ \ \ \
\ \\\ \
*
^
\. photo-
f synthesis
t
o
ffi
I aerobic ^
respiration uj
<
O
O
UJ
2
y anaerobic <
respiration .
T
FIGURE 4-16.
Idealized cross section of marine organic-
rich sedimentary environment. Note the
sequence of biogeochemical zones resulting
from ecologic succession. Reprinted with
permission from Claypool and Kaplan.7
383
-------
Buried nitrogen-containing organic matter moves downward
through this succession of microbial ecosystems. When anoxic
conditions occur, the next best electron acceptor is nitrate.
This zone is not shown in Figure 4-16, because only small
amounts of nitrate are normally present in seawater. Nitri-
fication of ammonia to nitrate is carried out by distinctive
groups of bacteria in two steps :•*"
(Nitrosomonas) NH4+ -I- 1.502 -* NO2~ + 2H+ + H20; (4-2)
(Nitrobacter) NG>2~ + 0.502 -" N03~. (4-3)
Another group of bacteria utilize the nitrate for coenzyme
oxidation through denitrification:36
5CH20 + 4N03~ + 4H+ -> 2N2 + 5CO2 + 7H2
-------
are found in organic-rich fine-grained sediments (as shown in
Figure 4-13) , where the aerobic zone is restricted to shallow
areas near the sediment-water interface and the nitrate reduc-
tion zone is virtually missing.46'49
Kinetic Model for Early Diagenesis of Nitrogen in Anoxic
Near-shore Sediments. Depth distributions of ammonia and other
dissolved nitrogen species in interstitial water are sensitive
indicators of time-dependent chemical processes and thus amenable
to kinetic interpretation. Stoichiometric models for ammonium
regeneration during sulfate reduction42 ? 43 have been used to de-
scribe ammonium regeneration during sulfate reduction in the
interstitial water of marine sediments, ^ ' 4° as shown below:
(CH20)c(NH3)N(H3P04)p +
(C02)c + (H20)c + (NH3)N + (H3P04) + (S2~)o.5C- (4~5)
These models ignore the effects of diffusion, adsorption, and
other processes potentially important for ammonium itself or
other chemical components of the model. The time-dependent
changes in ammonium concentration are controlled by a number
of processes, including diffusion, rapid (equilibrium) adsorp-
tion, decomposition of biologic organic matter, and compaction
resulting from burial. Mathematically, these processes can be
described with the terms shown in Eq. 4-6:
385
-------
Ds ilc _ dc + dc _ co 9c _ 0 .
S 3^ dt, dt, . , 9z ~ ° ' C4~6>
adsorp biol
where z = vertical depth in sediments,
t = time,
c = concentration of ammonium,
c = concentration of chemical species on sediment
surfaces that can rapidly exchange with ammonium
ions,
D = whole-sediment diffusion coefficient (differs
from normal diffusion coefficient in aqueous
solution, because of tortuosity in sediments),
and
u) = sedimentation rate.
In combination with information on the sedimentary
content of nitrogen-rich proteinaceous organic matter,
solutions to these tentative equations and more sophisti-
cated models in the future should yield predicted ammonium
concentrations with respect to depth. The model thus provides'
a tool with which the effects of variations of important processes
can be quantitatively checked. Fitting actual field data to the
model allows an understanding of the relative importance of
these processes in any given environment. Berner's model^ is
intended for sediments where macrobenthic activity (e.g., irri-
gation of sediments by organisms) or other process leading to
sediment disturbance is missing or limited. More recent efforts
have led to models incorporating the effects of mixing processes,
such as irrigation21 and sediment resuspension by currents.24 /"
Solutions to these models both explain concentration gradients
observed in interstitial water and yield information about
386
-------
diffusion or "mixing" coefficients useful for understanding
transfer processes across the sediment-water interface,
Ammonium Flux from Marine Sediments. Production of ammonium
in interstitial water results in concentration gradients described
kinetically by the model discussed above. The concentration
gradient results in ammonium transport into overlying water by
molecular diffusion or mixing. The importance of processes at
or adjacent to the sediment-water interface should be noted, be-
cause of the known concentration of microbial activity and rela-
tively fresher nature of organic materials undergoing initial
diagenesis there. It appears that a significant fraction is re-
generated very close to the interface, leaving organic matter
depleted in nitrogen, 25 , 46 relative to average marine plankton
4 1
composition.
In the coastal environment, where benthic respiration
processes are viewed as an important ammonium source, at least
two approaches to determining the flux across the sediment-water
interface are being attempted. The first involves measuring
concentration gradients, as well as diffusion or stochastic
mixing coefficients, and then applying Pick's first law modi-
fied for interstitial water :^
_
s 3 z
(4-7)
where JNH + = flux of ammonia, moles/(area) (time),
= sediment porosity,
D = whole-sediment diffusion coefficient (or
o
Dm for stochastic mixing coefficient) , and
387
-------
3c = depth-concentration gradient.
3~z
Estimates of Dc or D can be obtained by measuring natural
s m
tracers, such as radon, for which the flux can be assessed
directly24 or by solving equations similar to Eq. 4-6.
The second approach involves direct measurement of ammonium
fluxes by enclosing a portion of the sediment in a box corer or
similar device with bottom water, sealing the enclosure, and
monitoring changes in ammonium concentration in the bottom water
over the sediment (for several hours) that result from ammonium
exchange across the sediment-water interface. Workers using
this approach have measured ammonium fluxes from Buzzard's Bay
(Mass.) sediment seasonally ranging from 2.56 (January) to
124 pmole/m2-h (June) and correlated these fluxes with bottom
oxygen demand. Nixon et a_l. " reported fluxes from Narragansett
Bay sediment of up to 300 ymole/m2-h during warmer months.
Hartwig26 reported a mean flux of 36.3 umole/m2-h from a sub-
tidal siliceous sediment off La Jolla, California. Seasonal,
as well as geographic, variations in microbial degradation rates
and irrigation activities of organisms will have large effects
in regulating these fluxes.21'33
Nitrogen Exchange Between Ocean and Atmosphere
The exchange of nitrogen between ocean and atmosphere is
probably the largest transfer in the nitrogen cycle;51 however,
neither exchange rates nor mechanisms are well defined. The
amount of nitrogen supplied to the oceans appears to be in excess
of that trapped by sediment, according to steady-state budgets.10'14'27
388
-------
With constant nitrogen content (steady state), the annual nitrogen
excess added by oceanic rain and rivers, estimated to range from
10 to 70 x 10 t/year, would be assumed to have been denitrified.1
It should be noted that the rainfall nitrogen flux estimate is
based on little information and is poorly known. On the basis
of Richard's summary (cited in C.A.S.T.10), denitrification must
occur, not in stagnant sulfide-bearing water and sediment, but
in other low-oxygen, less stagnant water, such as the eastern
tropical Pacific. This hypothesis is in agreement with the above
discussion, in that denitrification should occur before sulfate
reduction. Estimates of total denitrification are so uncertain
that no conclusions can be drawn as to the validity of the assump-
tion. Further investigations of the role of nitrous oxide as
a product of denitrification in the oceans and a nitrogen source
for the atmosphere may help to resolve this problem.
Ammonia in the Marine Atmosphere
The concentration of atmospheric ammonia is much lower over
the ocean than over land.28'50 Tsunogai observed concentra-
tions of total (gaseous plus particulate) ammonia decreasing
from about 0.2 ymole/m3 (STP) near Tokyo to a mean of 0.05 + 0.02
-i O o
ymole/m^ (STP) over the Pacific Ocean at 30 N, 170 W. He con-
cluded, in agreement with previous investigations, that ammonia
in marine air was of continental origin, with a residence time of
approximately 5-10 days.51 The proportion of total (gaseous plus
particulate) ammonia in the aerosol phase was observed by Tsunogai
to increase from 30% in the North Pacific to 80% in the South
Pacific. This result was interpreted as indicating incorporation
389
-------
of ammonia gas into aerosols as the gas migrated away from the
land source.
It is possible that ammonium found in organic-rich sea sur-
face films or microlayers55 is a source for the atmosphere.
Bubbles produced by wave action rising through this microlayer
act as a surface microtome, preferentially skimming off a layer
of a thickness that is 0.0005 times the bubble diameter,31 The
high ammonia concentrations in microlayers found by Williams
at stations off Peru and California were associated with high
nitrate and phosphate, as well as organic matter. Ammonia con-
tent in the microlayer collected by the screen technique of
Garrett1^ ranged from 8.2 to 14.4 pinole/liter. The screen col-
lects the upper 150 pm of water; thus, concentrations in a
thinner microlayer, if actually present, would be considerably
higher. Microlayer ammonia concentrations were 7-14 umole/liter
higher than that in samples from a depth of 15-20 cm.
One possible implication of these results is that an unknown
fraction of the nitrogen input to the ocean, particularly that
in rain, may be cyclic and associated with ammonia injected by
bubble microtome action at the sea surface.55 Such a closed
recycling system would greatly reduce the net input of nitrogen,
as reported by Emery et al.14
Williams55 suggested that the "ammonia" in the microlayer
was largely labile organic nitrogen or was formed from organic
nitrogen in situ. The high nitrate and ammonia concentrations
in organic-rich microlayer on the sea surface off Peru correlates
well with the known high-nitrogen-content waters there.
390
-------
REFERENCES
1. Barber, R. T., and W. Kirby-Smith. The Water Quality Ramifications of
Converting Forest to Intensive Agriculture. Water Resources Research
Institute Data Report No. 1. Chapel Hill: University of North
Carolina, 1975.
2. Barnes, R. 0., K. K. Bertine, and E. D. Goldberg. N2:Ar, nitrification
and .denitrification in southern California borderland basin sediments.
Limnol. Oceanogr. 20:962-970, 1975.
3^ Berner, R. A. Kinetic models for the early diagenesis of nitrogen, sulfur,
phosphorus, and silicon in anoxic marine sediments, pp. 427-450. In
E. D. Goldberg, Ed. The Sea. Ideas and Observations on Progress in
the Study of the Seas. Vol. 5. New York: John Wiley & Sons, 1974.
4. Berner, R. A. Principles of Chemical Sedimentology. New York: McGraw-
Hill, 1971. 240 pp.
5. Caperon, J., and J. Meyer. Nitrogen-limited growth of marine phytoplank-
ton. II. Uptake kinetics and their role in nutrient limited growth
of phytoplankton. Deep-Sea Res. 19:619-632, 1972.
6. Carpenter, E. J., and C. C. Price. Nitrogen fixation, distribition and
production of Oscillatoria (Trichodesmium) spp. in the western Sargasso
and Caribbean Seas. Limnol. Oceanogr. 22:60-72, 1977.
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in marine sediments, pp. 99-139. In I. R. Kaplan, Ed. Natural Gases
in Marine Sediments. New York: Plenum Press, 1974.
8. Cline, J. D. , and F. A. Richards. Oxygen deficient conditions and nitrate
reduction in the eastern tropical North Pacific Ocean. Limnol.
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9, Commoner, B. Threats to the integrity of the nitrogen cycle: Nitrogen
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New York: Springer-Verlag New York Inc., 1970.
10. Council for Agricultural Science and Technology. Effect of Increased
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Department of Agronomy, Iowa State University, 1976. 33 pp.
11. Duedall, 1. W, , M. J. Bowman, and H. B. O'Conners, Jr. Sewage sludge and
ammonium concentrations in the New York Bight apex. Estuarine Coastal
Mar. Sci. 3:457-463, 1975.
12. Dugdale, R. C. Chemical oceanography and primary productivity in upwell-
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of nitrogen in primary productivity. Limnol. Oceanogr. 12:196-
206, 1967.
14. Emery, K. 0., W. L. Orr, and S. C. Rittenberg. Nutrient budgets in the
ocean, pp. 299-310. In Essays in the Natural Sciences in Honor of
Captain Allan Hancock on the Occasion of his Birthday, July 26, 1955.
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15. Eppley, R. W. , A. F. Carlucci, 0. Holm-Hansen, D. Kiefer, J. J. McCarthy,
E. Venrick, and P. M. Williams. Phytoplankton growth and composition
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nitrogen source. Limnol. Oceanogr. 16:741-751, 1971.
16. Eppley, R. W. , j. N.
Half.saturation
stants for uptake of nitrate and ammonium by marine phytoplankton.
Limnol. Oceanogr. 14:912-920, 1969.
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17. Eppley, R. W., J. I. Coatsworth, and L. Solorzano. Studies of nitrate
reductase in marine phytoplankton. Limnol. Oceanogr. 14:194-205,
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1975. 243 pp.
19. Garrett, W. D. Collection of slick-forming materials from the sea
surface. Limnol. Oceanogr. 10:602-605, 1965.
20. Goering, J. J. Denitrification in the oxygen minimum layer of the eastern
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21. Goldhaber, M. B., R. D. Aller, J. K, Cochran, J. K. Rosenfeld, C. S. Martens
and R. A. Berner. Sulfate reduction, diffusion and bioturbation in
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22. Gctldhaber, M. B. , and I. R. Kaplan. The sulfur cycle, pp. 569-655. In
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the Study of the Seas. Vol. 5. New York: John Wiley & Sons, 1974.
23. Guillard, R. R. L., and J. H. Ryther. Studies on marine planktonic
diatoms. I. Cyclotella nana Hustedt, and Detonula confervacea
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in the Hudson River estuary, pp. 119-132. In T. M. Church, Ed.
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15. Hartmann, M., P. Muller, E. Suess, and C. H. van der Weijden. Oxidation
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26. Hartwig, E. 0. The impact of nitrogen and phosphorus release from a sili-
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Processes. Vol. 1. New York: Academic Press, 1976.
27. Holland, H. D. Ocean water, nutrients and atmospheric oxygen, pp. 68-71.
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28. Junge, C. E. Air Chemistry and Radioactivity. New York: Academic Press,
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29. Lui, N. S. T, and 0. A. Roels. Nitrogen metabolism of aquatic organisms.
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30. Maclntyre, F. Bubbles: A boundary-layer Microtome11 for micro-thick
samples of a liquid surface. J. Phys. Chem. 72:589-592, 1969.
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pp. 245-299. In E. D. Goldberg, Ed. The Sea. Ideas and Observations
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uptake by natural populations of marine phytoplankton. Deep-Sea
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33. Martens, C. S. Control of methane sediment-water bubble transport by
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36 Mechalas, B. J. Pathways and environmental requirement? for biogenic gas
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Quality Criteria 1972. A Report of the Committee on Water Quality
Criteria. Prepared for the U. S. Environmental Protection Agency.
Washington, D. C.: U. S. Government Printing Office, 1974.
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M. Anderson and A. Macfadyen, Eds. The Role of Terrestrial and Aquatic
Organisms in Decomposition Processes. London: Blackwell Scientific
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organisms on the composition of sea-water, pp. 26-77. In M. N. Hill,
Ed. The Sea. Ideas and Observations on Progress in the Study of
the Seas. Vol. 2. New York: Interscience Publishers, 1963.
42 Richards, F. A. Anoxic basins and fjords, pp. 611-645. In J. P. Riley
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nutrient regeneration and its coupling to primary productivity in
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coastal waters. Nature 255:215-217, 1975.
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Systems. Ph.D. Thesis. Durham, N. C.: Duke University, 1976.
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48. Thomas, W. H. On nitrogen deficiency in tropical Pacific oceanic phyto-
plankton: Phytosynthetic parameters in poor and rich water. Limnol.
Oceanogr. 15:380-385, 1970.
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compounds through the atmosphere and hydrosphere. Geochem. J. 5:57-
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• Tsunogai, S., and K. Ikeuchi. Ammonia in the atmosphere. Geochem. J.
2:157-166, 1968.
52. Vaccaro, R. F., and H. W. Jannasch. Studies on heterotrophic activity in
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Huntsman. Spin-up of the Baja California upwelling ecosystem.
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56. ZoBell, C. E. The assimilation of ammonium nitrogen by Nitzschia
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U. S. A. 21:517-522, 1935.
397
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CHAPTER 5
TRANSPORTATION OF AMMONIA
The vulnerable points in the transportation of ammonia,
regarding loss of material to the environs and consequent
danger to people, appear to be associated primarily with
portions of the transportation system nearest the consumer.
However, because there is a potential for the release of
large quantities of ammonia (although few cases of serious
injury or property damage have been reported), the complete
system needs scrutiny.
PRODUCTION AND STORAGE
The production of ammonia has been described as having
three basic steps: gas preparation; gas purification; and
ammonia synthesis, wherein ammonia is produced, compressed,
and placed in storage. A typical modern manufacturing plant
demonstrating these steps is illustrated in Figure 5-1.12
There are three main systems for storage of large
volumes of ammonia: the pressurized hortonsphere, aqua
ammonia low-pressure storage, and the low-pressure refrigerated
storage tank. The pipelines used to move ammonia from producer
to distributor (for example, those shown in Figures 5-2 and
5-3) should also be considered as storage.
398
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Start
Air
Air
Compressor
Stage I Gas Preparation
Reformer
Secondary
Reformer
Start
i Natural Gas
Desulfurization|
Drums
Co-Shift
Converter
C^tfc^
LHeat
Recovery
and Cooling
Water
Stage II Purification
Refrig.
Compression
and Synthesis
Product
NH3
Product
Stage III Synthesis
FIGURE 5-1.
Simplified ammonia process flow diagram.
Reprinted with permission from Proceedings
of Agronomy Workshops on Anhydrous Ammonia.
399
-------
SOUTH
/ DAKOTA
I ! mapco
I ' 1 WH i T i NG
MINNESOTA
FARMLAND - MANKATO )
S~"T^JWiSCOMSOM
|FARMLAND-GARNER,
fCAMEX-GARNER
SERGEANT BLUFF
NEBRASKA
mapco
' GREENWOOD
CAMEX -EARLY :
| AGRICO- BLAIR
mapco
CLAY CENTER
COLORADO
mapco
CON WAY
AGRICO
VERDIGRIS ! JEFFERSON en
MIS SOUR
FARNSWORTH
OKLAHOMA
OKLAHOMA CITY
ARKANSAS
LITTLE ROCK
EX )C O I CAMEX
~ BORGER
LEGEND
. Ammonia Plant Location
Delivery Point B Terminal
Figure 5-2. Mid-America pipeline system.
400
-------
^-STi
-p,—--
= ^=-..— v-^/b?., y
C4--^°^T.
,,— % W " - -- . Ui-
' " s«-7=V-i-sr " i
GULF CENTRAL PIPELINE COMPANY
SYSTEM MAP
Figure 5-3. Gulf Central pipeline system.
Reproduced from
best available copy.
401
-------
The storage tanks at transportation terminals may have
capacities of up to about 30,000 tons (27,216 t) of ammonia.
The tanks found at the "dealer's" storage area are much
smaller, although most are large enough to hold a jumbo
tank car containing 70 tons (63.5 t) of ammonia.
Little information is available on the effects of the
rupture of one of the large storage vessels, such as a barge,
where there might be a major spill that creates a "hazard
envelope" affecting the surrounding area. A "hazard envelope"
is an area with a concentration of gas sufficient to produce
acute respiratory responses. This lack of data appears to be
related to the small number of such occurrences, but this does
not obviate the examination of current design standards and
transportation regulations.
CURRENT SPECIFICATIONS
The desirability of providing some form of mechanical con-
tainment for entrapment or recovery of ammonia or neutraliza-
tion of its effects on the environment and its inhabitants
should be considered.
Dikes can probably be used to contain spills from ruptured
tanks; such dikes are required or standard practice in the
storage of petroleum products and other hazardous liquids.
More expensive double-wall construction might also be con-
sidered. Whatever the design or method, the principle of con-
tainment in case of natural or accidental release of ammonia
402
-------
into the environment, where it would flow to the nearest water-
course, should be considered. Simultaneously with the release
of the liquid there will be vapor formation, so the location of
storage with respect to surrounding residential areas should be
considered. In a draft statement, "Guidelines for the Location
of Stationary Bulk Ammonia Storage Facilities," prepared by the
Alberta Department of Environment Standards & Approval Division,
Nov. 1975, minimal distances from permanently occupied residential
buildings were suggested (Figure 5-4). Other distance figures
are found in American National Standard K61.1-1972,16 subsection
2.5, "Location of Containers," paragraph 2.5.4. Container loca-
tions are to comply with Table 5-1, according to K61.1-1972.
The pressure tanks used for storage of ammonia and delivery
to the consumer and farmer may vary in capacity from a few
gallons to thousands of gallons and are manufactured with a
minimal design pressure (working pressure) of 250 psig per the
ASME (American Society of Mechanical Engineers) construction
code for unfired pressure vessels. Although these tanks are
designed for a maximal working pressure of 250 psig (about
1,720 kN/m2), they are hydrostatically tested at the time of
manufacture to about 1.5 times the design pressure, or about
375 psig (2,580 kN/m2).12 The internal pressures of stored
anhydrous ammonia in these tanks may vary according to tempera-
ture, as shown in Table 5-2.
403
-------
1,250
1,000
S 750
CD
LU
o
250
Over 500
to 2,000
Over 2,000
to 20,000
Over 20,000
to 30,000
Over 30,000
to 100,000
Over
100,000
STORAGE TANK CAPACITY (gal.)
FIGURE 5-4.
Minimum recommended distance of ammonia
storage facilities from permanently
occupied residential buildings. Re-
printed with permission from Alberta
Department of Environment.1
404
-------
TABLE 5-1
Safe Location of Ammonia Containers-
Minimal Distance, ft (m), from Container to;
Nominal Capacity Line of Adjoin-
of Container, ing Property that
gal (m3) May Be Built on Place of
Highways and Main Public Institution
Line of Railroad Assembly Occupancy
Over 500 to 2,000
(over 1.9 to 7.6)
Over 2,000 to
30,000
(over 7.6 to 114)
Over 30,000 to
100,000
(over 114 to 379)
Over 100,000
(over 379)
25
(7.6)
50
(15)
50
(15)
50
(15)
150
(46)
300
(91)
450
(137)
600
(183)
250
(76)
500
(152)
750
(229)
1,000
(305)
-Data from American National Standard K61.1-1972, paragraph 2.5.4.
405
-------
TABLE 5-2
Vapor Pressure of Anhydrous Ammonia at Various Temperatures-
Temperature, °F (°C) Vapor Pressure, psig (kN/m2)
-28 (-33.3) 0 (0)
0 (-17.8) 15.7 (108.2)
32 (0) 47.6 (328.2)
60 (15.6) 92.9 (640.5)
100 (37.8) 197.2 (1,359.6)
125 (51.7) 293.1 (2,020.9)
130 (54.4) 315.6 (2,176.0)
—Data from Proceedings of Agronomy Workshop on Anhydrous
Ammonia.12
406
-------
The tanks are also to be equipped with pressure-relief
valves (American National Standard K61.1-1972, subsection
2.9, "Safety Relief Devices"), to direct the vented material
away from the container upward and without obstruction to the
atmosphere. Such devices, to operate with relation to the
design pressure of the container, are as listed in Table 5-3.
American National Standard K61.1-1972, Safety Requirements
for the Storage and Handling of Anhydrous Ammonia, ^ a consensus
standard, also covers many other topics, including first aid
and personal protection equipment and its use, identification
and marking of equipment, operational procedures, location of
containers, various kinds of storage containers (including
refrigerated and portable), transport systems mounted on trucks,
and farm application.
The Code of Federal Regulations (CFR 29-1910:111) estab-
lishes requirements for the storage and handling of anhydrous
ammonia.-1-1 Section (a), General (1) Scope, states that this
standard is intended to apply to the design, construction,
location, installation, and operation of anhydrous ammonia
storage systems and not to manufacturing or refrigeration plants
where ammonia is used as a refrigerant. Section (b), "Basic
Rules," deals with such items as approval of equipment and
systems; requirements for construction; original test and re-
qualification of nonrefrigerated containers; marking of non-
refrigerated and refrigerated containers; container appurtenances;
407
-------
TABLE 5-3
Start-to-Discharge Pressures of Relief Devices of Ammonia Container1
Relief Pressure, % of
Container Design Pressure
Containers Minimum Maximum
ASME-U-68, U-69 110% 125%
ASME-U-200, U-201 95% 100%
ASME 1952, 1956, 1959, 1962, 1965, 95% 100%
1968 or 1971
API-ASME 95% 100%
U.S. Coast Guard as required by USCG
regulations
DOT as required by DOT
regulations
-Data from American National Standard K61.1-1972, paragraph
^ • _/ * £ •
408
-------
piping, tubing, and fittings; hose specifications; safety relief
devices; charging of containers; tank car unloading points and
operations; liquid-level gauging device; painting of containers;
and electric equipment and wiring. Subsection (10) of this por-
tion of the requirements mentions training of personnel and
specifies personal protective devices, including first aid water
supplies for permanent and transport vehicles, except the farm
applicator. (Stationary storage installations must have an
easily accessible shower or 50-gal—0.2-m—drum of water avail-
able, and each vehicle transporting ammonia in bulk must have
a container carrying 5 gal--0.02 m^—of water and a full-face
mask.) Section (c) describes systems that use stationary non-
refrigerated storage containers; Section (d), refrigerated storage
systems; Section (e), systems that use portable DOT containers;
Section (f) , tank motor vehicles for the transportation of
ammonia; Section (g), systems mounted on farm vehicles other
than for the application of ammonia; and Section (h), systems
mounted on farm vehicles for the application of ammonia. Specific
points and requirements are made concerning the safe handling
and movement of ammonia in these sections to minimize or eliminate
the development of hazards related to liquid or gaseous ammonia.
SCOPE OF ACCIDENTS INVOLVING AMMONIA
The transportation of ammonia may be divided into two
parts: from the manufacturing facility to the distribution
point and from the distribution point to the consumer.
409
-------
Transportation problems and risks associated with the move-
ment of ammonia from factory to distributor have been recognized
by industry and government, which have established standards and
regulations to minimize the dangers to the public and employees.
Whether the ammonia is to be transported by refrigerated or
pressurized vessel on the high seas, by barge on canals or along
the coast, or by pipelines and trains or tank truck, there are
design specifications, work rules, and emergency procedures to
limit exposures in accidents. Still, there are situations where-
in an accident may have a catastrophic effect, even though all
contingencies appear to have been covered.
The rupture of a ship on the high seas would have a limited
effect on numbers of persons affected—i.e., only those on board
ship—and the envelope of gas or liquid would soon be dissipated.
However, a similar accident in a harbor, inland waterway, or
canal could have serious effect on both man and the environment.
Because the quantity (tons) is large in many cases, such an
accident could produce an envelope of gas and liquid expanding
to surrounding shore areas, thereby affecting people and live-
stock. On a river or small canal, such a spill could have a
deleterious effect on aquatic life.
With the rapid increase in transportation of ammonia on
inland and coastal water of the United States, the Coast Guard
in 1972 sponsored research into the effect of ammonia spills on
and beneath the surface of water. The findings indicated that
410
-------
a reasonable estimate of the partitioning value (fraction, by
weight, of spill that goes into water solution) of a liquid
surface spill would be 0.6; the remaining fraction, 0.4, goes
into vapor. For an underwater spill, the tests showed a par-
titioning value of 0.85-0.90 and no observable vapor liberation.
In underwater spills, a temperature rise was noted in the
vicinity of the spill discharge.
The tests demonstrated that surface reaction on water is
rapid and generally confined to a small area and that the vapor
liberated is relatively bouyant and rises rapidly. "Prediction
of Hazards of Spills of Anhydrous Ammonia on Water, Arthur D.
Little, Inc., March 1974 - Prep, for U.S. Coast Guard"13 showed
that, in underwater release, depending on the depth and size of
release, all the liquid may go into solution with the water.
Two major points unresolved in the research conducted for
the Coast Guard are the effects of continuous release versus
instantaneous release of ammonia on the surface and the possi-
bility of underwater explosions in the case of instantaneous
underwater release of large quantities of ammonia.
The NRC prepared a tentative guide for use in developing
a hazard evaluation system for bulk cargoes and assigning
ratings to specific commodities.7 In 1975, the NRC published
for the Coast Guard a report describing a system for classifi-
cation of the hazards of bulk water transportation of industrial
chemicals.8 The Coast Guard has instituted CHRIS, or Chemical
411
-------
Hazards Response Information System (essentially a handbook),
to assist its officers in dealing with incidents associated
with hazardous chemicals. One of its main purposes is to ,
provide a method for predicting dispersion of chemicals in
water and the hazards that they pose after a spill. It covers
methods for estimating air concentrations, handling spills,
and cleaning up.
Accidents involving the manufacturer-to-distributor portion
of ammonia transport are few. But some have produced traumatic
situations, such as the railroad accident several years ago
at Crete, Nebraska, where the gas envelope covered a portion of
the town and there were serious results. Railroad and auto-
motive transport accidents in urban areas are obviously dangerous,
not only to those involved in the transport system and those in
the immediate vicinity, but also to policemen, firemen, and
rescue teams called to the accident site.
Pipelines have been said to rupture owing to faulty
assembly procedures or structural damage resulting from digging
or trenching. However, there are few reports of injuries associ-
ated with such ruptures. This may be due in part to their general
remoteness from populated areas.
AGRICULTURAL APPLICATION
Agriculture consumes the largest portion of ammonia pro-
duced, so special concern should be directed toward agricultural
aspects of delivery and application. Of all the forms of ammonia
412
-------
applied by the agriculturalist, aqua and anhydrous are the only
ones considered here and discussed regarding the potential hazard
envelopes associated with their use.
Aqua ammonia solutions (ammonium hydroxide) used in various
parts of the United States are usually manufactured at a fertil-
izer dealer's plant. Such solutions generally contain 18-30%
ammonia by weight and have a vapor pressure of 0-10 psig
(0-69 kN/m2) at 104°F (40°C).
The Fertilizer Institute,5 on September 23, 1970, published
standards for the storage and handling of nitrogen fertilizer
solutions containing more than 2% free ammonia and specifications
for 3,000- to 21,000-gal (11.4- to 79.5-m3) steel tanks for the
storage of field-grade aqua ammonia containing 20-25% ammonia.
This standard in many ways follows the pattern of requirements
for anhydrous ammonia covering similar subjects, but it has few
requirements for transportation to and application by the custom
applicator or farmer. This use of ammonia, although it has a
minimal potential hazard in most instances (because the liquid
is usually handled in nonpressurized tanks), is a case in which
material loss can be observed. Transfer, which generally in-
volves pump operations, often permits a loss of liquid to the
ground at the dealer's station and in the field when ammonia
is being loaded and placed in the applicator. An accident with
a delivery truck, although it could constitute a major spill,
might produce its greatest effect on the environment as it flowed
into the nearest waterway.
413
-------
The application of anhydrous ammonia, however, because it
is stored, transported, and applied under pressure, has a poten-
tial hazard envelope whose size depends on the activity between
dealer and soil application.
The first hazard of concern here is that associated with
the filling of the dealer-to-farm delivery tank (nurse tank).
There must be several couplings to attach the nurse tank to
the storage supply tank, wherein through a two-hose closed
system (fill hose and gas recovery hose) the tank is charged
to approximately 85% of capacity (the remaining 15% permits
expansion due to temperature changes, thereby minimizing venting
through the safety relief valve and mechanical damage to the
system).
Typically, nurse tanks are of 1,000-gal (3.8-m ) capacity
and mounted on a four-wheel chassis for transportation. Accord-
ing to ANSI Standard K61.1-1972,16 they are supposed to have
safety tow chains and 5-gal (19-dm3) water tanks. The cross-
section diagram in Figure 5-5 (taken from Agricultural Anhydrous
Ammonia Operators Manual M-7, 1973 Fertilizer Institute,
Washington, D.C. ) shows the nurse tank configuration. The
diagrams in Figures 5-6, 5-7, and 5-8, from the same publication,
depict a variety of agricultural delivery systems (distributor
to dealer), all having the same potential worker hazard envelope
at the nurse tank filling station.
414
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- LIQUID WITHDRAWAL VALVE
, LIQUID FILL VALVE
- PRESSURE GAGt
I—fIXED LIQUID ItVLl GAGt
I ,—- VAPOR RETURN VALVE
1 : j-- FLOAT GAGt
SAFETY RELIEF
VALVE
FIGURE 5-5. Typical ammonia nurse tank, excluding running gear.
Reprinted with permission from The Fertilizer Institute.
415
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TRANSPORT TRUCK
To fill storage tank from truck
1. Opm vltvn no. 1, 2, 3, 4, 5, and 7
2 CtOM vilvM na 6, 8, and 9
TRANSPORT TRUCK
To fill nurse tank from storage tank
1. Open v»nrm no. 8, 9, 1 3, 6, 2
2 Clow valvM no. 7, 4, 5
FIGURE 5-6.
Arrangement of facilities at an ammonia plant, illustrating
method of operating system with liquid pump. Reprinted
with permission from The Fertilizer Institute.4
416
-------
.To compressor --
INLET
To fill storage tank from tank car (or truck)
Open valve. 1, 2, 3. 4, 5, 6
Clow valvei 7, 8, 9,10, 11
-To comprise' ' H& I '-From ro
INLET - ' OUHET
To recover vapor from tank car (or truck)
Open valvm 2, 4, 6, 7
CtoM vilvm 1, 3, 5. 8, 9, 10, 11
FIGURE 5-7.
Arrangement of facilities at an ammonia plant, illustrating
method of operating system with compressor. Reprinted with
permission from The Fertilizer Institute.^
417
-------
To load nurse tank from storage tank
Optfivifcw 10,11,3,5,5,4
Qottvttm 1,2,6,7,8
FIGURE 5-8. Arrangement of facilities at an ammonia plant, illustrating
method of operating system with compressor. Reprinted with
permission from The Fertilizer Institute.^
418
-------
The nurse tank is shown attached to a farm tractor in
these diagrams, but delivery is usually accomplished by towing
the nurse tank with a truck to the farm application site. The
nurse tank may also be pulled behind the tractor-applicator
(without its own tank) for field application, in lieu of a
field applicator with tank attached. This is often done in
larger operations, where the applicator tanks usually have
only a 250-gal (0.9-m ) capacity, thereby reducing the number
of transfer operations for the operator.
If the farmer is using a field applicator unit (a two-
wheeled trailer with applicator knives attached, all pulled
by a tractor) and the nurse tank serves as a stationary supply
station, the farmer must proceed somewhat similarly in filling
the nurse tank, in that hoses must be connected to transfer
the liquid from tank to tank (see Figure 5-9). The major dif-
ference in this operation from that of filling the nurse tank
is that a venting method will probably be used, instead of a
closed two-pipe method, for filling the applicator tank. If
the farmer connects the nurse tank delivery hose to the appli-
cator liquid fill valve and then opens the vapor bleeder valve
on the applicator, the pressure difference between the nurse
tank and the applicator will permit the liquid to flow into
the applicator tank. (Obviously, appropriate delivery hose
valves will have been opened.) The potential hazard envelope
in this operation usually involves only one or two people
during each transfer.
419
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Vapor Bleeder Valve
Fixed Liquid Level Gage
Safety Relief Valve
Liquid Withdrawal Valve
Pressure Gage -Liquid Fill Valve
Liquid Level Float Gage
FIGURE 5-9-
Four-opening applicator tank, excluding
chassis and applicator knife assemblies.
Reprinted with permission from The Fertilizer
Institute.4
420
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ACCIDENTS
Ammonia containers and appurtenances in general are
covered by manufacturing standards, but there can be no
absolute guarantee that the chemical will never escape from
containers or their fittings during movement from production
to applications.
The most common accident appears to be associated with
operations involving transfer from container to container,
wherein the worker must connect hoses (from nurse tank to
applicator tank). In a typical transfer, there are usually
two to four valve connections that must be operated in a proper
sequence. The opportunities for faulty equipment, human error,
and carelessness are many and varied.
The safety department of an anhydrous ammonia distributor,
for its worker training program, lists the following protective
equipment to be checked before a nurse tank leaves the bulk
plant premises for farm use:
• Goggles, clean and tight-fitting.
• Respirator for ammonia, with good cartridges; or
full-face mask with ammonia cartridge.
• Gloves for ammonia.
• A 5-gal (19-dm3) can of fresh water.
• Proper markings (show placards).
421
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In addition, there must be an overall equipment inspec-
tion regarding leaks, worn parts, tires, etc.
Safety experts suggest that the saddle-shaped water tank
with its dispersing hose is a more satisfactory first aid
water source, in case of accidental spill or spray of anhydrous
ammonia on the worker (especially in the eyes or on the face) ,
than the 5-gal (19-dm ) water can usually attached to the running
gear. They also suggest that workers carry a small squeeze
bottle of water to be used immediately, especially for ammonia
in the eyes.
Although much has been printed that describes how to be
safe around and while using ammonia, agricultural work patterns
often change and are modified by workers as the occasion "dictates.
Such "normal" changes in work patterns must also be anticipated
and considered with regard to equipment design, suggestions of
alternative work procedures, and development of new rules, regu-
lations, and standards affecting worker safety.
In agricultural regions, most small communities have storage
areas with numerous nurse tanks available to move ammonia from
the dealer to the farm. In a three-state region in the Midwest,
the fertilizer industry reports an inventory of 40,000 such
tanks .
Specific numbers of dealers or equipment were not dis-
covered, but a 1974 survey of fertilizer manufacturers indicated
that, of 5,023 plants reporting, 1,985 said that they distributed
422
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ammonia for agricultural purposes (Fertilizer Institute, personal
communication).
In a survey of 9,537 retail dealers, 4,214 indicated that
they sold ammonia and 4,931 that they sold nitrogen solutions.6
No figures' were available to determine how many independent
dealers and custom applicators there are.
Reports involving the overturn of nurse tanks on the high-
way or involving other vehicles can be found in newspapers and
police records, but usually indicate a small envelope of danger
with few injuries, in most instances involving only the driver
or people engaged in rescue or cleanup. Statistics on such
accidents were not found and indeed appear to be unobtainable.
In agricultural areas, local doctors are seeing the re-
sults of on-the-farm exposure of farmers to ammonia. Reports
of accidental exposure to a minimal envelope of danger (a spray
of liquid, ruptured hose, leaky valve, etc.) have involved loss
of eyesight, respiratory problems, and skin burns.
A 40-year-old employee of an anhydrous ammonia distributing
company was injured while transferring liquid from a rail car
to a nurse tank. The employee was standing on the side walkway
of the rail car. The nurse tank filled more rapidly than ex-
pected; before the employee realized how full it was, the safety
relief valve emitted a spray of ammonia. (This valve is designed
to prevent the tank from being overfilled--it relieves at 85% of
capacity—and ensures that there is space for the anhydrous
423
-------
ammonia to expand when the temperature rises, without bursting
the tank.) The victim, standing about 6 ft above the valve,
was sprayed on the face and chest. He immediately jumped to
the ground and began to wash his face in a water tank that was
on the premises for such emergencies. He was taken to a local
hospital, but quickly transferred to a larger hospital. Facial
burns were not extremely serious, and both eyes were unaffected;
but pulmonary edema and pneumonitis resulting from inhalation
developed quickly, with inflammation and edema of the upper
airways. A tracheostomy was performed, and aspiration was
necessary. Treatment included pressurized oxygen, aminophylline,
and several antibiotics. Recovery was gradual, and the patient
was discharged after 11 days in the hospital. There was no
residual lung damage.
A 17-year-old farm boy who applied fertilizer for a
commercial concern was injured during transfer of aqua
ammonia (25% ammonia in water). He and his employer were
installing a new transfer pump when the accident occurred.
With the new pump in place, they started to move the liquid
from the nurse tank to the applicator tank. One hose had not
been tightened sufficiently and began to leak. Without shutting
off the machine, the boy grasped the hose and began to rotate
it to make a tight connection. As he did so, the opposite end
of the hose flipped out of the applicator tank and sprayed him
with several gallons of aqua ammonia. Knocked down but not
424
-------
panicking, he scrambled to his tractor and used his jug of
water to wash his eyes. He then ran 70 yards to a nearby
creek and immersed himself, but he did not remove his ammonia-
soaked clothing. He noted some tightness of his throat during
the first few minutes after the accident. He was driven home
by his employer, removed his clothing, and rested. He soon
noticed, however, that he had received burns to the buttocks
from contact with his clothing during the 2-mile ride home.
Taken to a local hospital, the victim was treated for second-
degree burns and recovered completely within a few days. No
eye injury was sustained.
A 36-year-old manager of an anhydrous ammonia retail
operation was injured in a farmer's field to which he had
been summoned because of improperly functioning equipment.
The farmer was using a 1,000-gal (3.8-m-^) nurse tank connected
by direct supply to a seven-row tool bar applicator. Anhydrous
ammonia runs from the nurse tank through a hose and quick-
coupling device to a flow regulator on the tool bar and from
there out through the individual knives into the ground. The
coupling device had been leaking, so the manager installed a
new one. When the new device was tested, by opening the liquid-
out valve at the supply tank and permitting ammonia to pass
through the hose, leakage occurred again. The man closed the
liquid-out valve and attempted to make a tighter connection
by jiggling the coupler. The coupler flew apart, and the man
425
-------
was sprayed in the face with anhydrous ammonia that had re-
mained under pressure in the portion of the hose between the
coupler and flow regulator. Immediate blepharospasm prevented
him from seeing clearly as he got away from the escaping amijionia
stream. The farmer who was with him at the time took him to
the rear of the nurse tank and helped him pour a 5-gal emergency
water supply over his face. He washed with water from a Thermos
bottle while being driven 25 miles to a doctor's office, where
his eyes were irrigated for several minutes. During the washing,
the victim concentrated on the left side of his face, believing
that only that part had been affected. His right eye, which in
fact had also been sprayed, was thus somewhat neglected and sus-
tained the greater damage, with resulting irritative conjun,cti-
vitis and superficial corneal ulceration. Second-degree facial
burns were also sustained, and palpebral edema of the left eye
developed of such magnitude as to swell the eye shut several
times during the following week. Recovery took a week, and
there were no known sequelae.
During the period 1971-1975, 239* incidents involving
transportation accidents with anhydrous ammonia were reported
to the U.S. Department of Transportation. From 1971 to April
1977, there were 61 incidents that caused injury or death re-
lated to the handling or transportation of anhydrous ammonia.
*Data from Office of Hazardous Materials Operations, U. S
Department of Transportation, Washington, D.C.
426
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Quantities too small to be measured (owing to pressure
release before a safety-valve shutoff caused by defective or
accidentally ruptured fitting valves or by closures of the
container) are the predominant cause of injuries during trans-
portation of anhydrous or aqua ammonia. Usually, hospitalization
is not required—the injured having received exposure sufficient
to cause eye irritation, minor skin burns, or fume inhalation—
and the injured are released after treatment.
A number of accidents involving the transportation of
anhydrous ammonia have resulted in injuries and death from
exposure to it. Some incidents involved transfer of the
product at storage facilities or transportation by truck,
train, and pipeline.
In 1976, during the unloading of a tractor-trailer at
a bulk storage plant, a 2-in. (5-cm) liquid transfer hose
burst. The^ failure of the safety devices to shut down resulted
in the discharge of 5,500 gal (14.2 t) of anhydrous ammonia.
Nine townspeople were treated for inhalation of the fumes and
released. Two persons who assisted in the rescue had to be
hospitalized, owing to exposure to the fumes.
In another incident, involving the unloading of a tank-
truck in 1971 in Indiana, the driver had completed unloading,
had bled off the pressure, and had disconnected the hoses and
laid them on the ground. While capping the unloading pipe, he
accidentally opened the valve for the unloading line, allowing
42T
-------
the anhydrous ammonia between this valve and the safety valve
to escape. He was not wearing safety clothing. He ran to a
water tank and placed his head and shoulders in the water. By
the time a witness ran to him, he was limp; he never regained
consciousness.
18
In 1973, a cylinder used in servicing air-conditioning
equipment and containing 2.2 gal (5.7 kg) was being transported
in the cargo space of a half-ton van truck. The cylinder
ruptured (for unknown reasons) as the truck was moving at
approximately 60 mph on a freeway in Industry, California.
The driver stopped the truck, opened the door, and fell out.
Although attended by highway patrol and a fire rescue squad,
he died either at the scene or en route to the hospital.
A catastrophic accident ^ involving a truck occurred in
May 1976 in Houston, Texas, when the semitrailer containing
7,509 gal (19.3 t) of anhydrous ammonia overturned owing to
the lateral surge of the liquid and excessive speed of the
truck on a curve of a freeway overpass, and plunged, 15 ft to
the freeway below. The truck's tank exploded, and the explosion
split one of the overpass support columns. A 100-ft-high cloud
of ammonia developed. Rescue was hampered by the absence of
wind under the overpass, which prevented the dispersion of the
gas; the danger persisted for approximately 2% h. Five deaths
and 178 injuries were caused by inhalation of the ammonia fumes.
428
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An accidental involving two trains occurred in Glen
Ellyn, Illinois, in May 1976. It was caused by a faulty
outside rail of a curved track that did not comply with
federal track safety standards. The locomotive and 27 cars
of a freight train overturned, owing to the lateral force on
the faulty track. When a second train traveling in the same
direction on an adjacent track collided with the derailed
train, a tank car in the second train ruptured, releasing
20,000 gal (51.5 t) of anhydrous ammonia. The accident
occurred in the early morning, and 3,000 residents were
evacuated and kept away for more than 16 h. There were no
deaths, and the injuries suffered by 15 people were not
serious.
Some 8,800 gal (22.7 t) of anhydrous ammonia leaked
from the tank car of a train over approximately a mile of
track in Reese, Michigan, in April 1976. ^ The accident
occurred when a train unloaded one of its cars onto the
track where the tank car was being unloaded. The cars
coupled, and the conductor pulled the cutting lever and
signaled the engineer; however, the cars failed to uncouple,
and the discharge pipes on the tank car were pulled away, pulling
the hoses apart. Local residents were notified to evacuate, and
only two people were injured.
In February 1969,10 a catastrophic train accident occurred
in Crete, Nebraska. A train derailed on a curve, and the
429
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derailed cars struck cars standing on a siding; a tank car
was fractured by the impact and released 29,200 gal (75.2 t) of
anhydrous ammonia. At 6:30 a.m., when the accident occurred,
the temperature was 4° F (-15.6° C), and there was ground fog,
with thin scattered clouds at 12,000 ft and no wind. A tempera-
ture inversion had occurred in the area. Several houses close
to the railroad were damaged by flying parts from derailed cars
and from the burst tank car. Those houses quickly filled with
ammonia gas, forcing the residents to abandon them and try to
escape. Several residents of other houses smelled the gas,
left their homes, and sought shelter. Any person who ventured
into the vapor cloud without adequate protection was either
killed or seriously injured. Five people were killed immediately
by ammonia, another died later, and 53 were injured (28 of them
seriously).
The anhydrous ammonia pipeline of the Mid America Pipeline
Company (MAPCO)9 ruptured at Conway, Kansas, in December 1973,
releasing 89,800 gal (231.1 t) of anhydrous ammonia into the
atmosphere (Figure 5-2). The accident was caused by excessive
pressure due to the failure of a remote-controlled valve to
open when the station at Borger, Texas, began pumping. Pumping
was stopped after 9,660 gal (24.9 t) of anhydrous ammonia had
been pumped into the line, and the indicator light on the console
in Tulsa, Oklahoma, still showed that the valve had not opened.
The 8-in. (20.3-cm) pipeline ruptured under an initial pressure
430
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of at least 1,200 psig (8,275 kN/m2), At the time of the acci-
dent, the ground was covered with snow, ice, and sleet. The
temperature was near 20° F (-70° C), the sky was clear, and
the wind was at 5-10 mph. The injured were the drivers of
two trucks on U. S. Highway 56, within a half-mile (0.8 km)
of the ruptured line; they were hospitalized because of
ammonia burns to the eyes, nose, throat, and lungs. The
ammonia vapor was visible a half-mile from the leak, and
invisible but very irritating to the eyes, nose, and throat
for another 3.5 miles (5.6 km). Beyond that point, ammonia
odor was detectable for another 4 miles (6.4 km), but did not
irritate the eyes, nose, or throat.
A review of the U.S. Coast Guard records from 1971 to mid-
1977 revealed few accidents or spills involving ammonia-carrying
vessels (U.S. Coast Guard, personal communication). The inci-
dents on record involved tank barges, rather than ships, and
involved mostly spills from leaky fittings, valves, or hoses
during transfer. During this period, the only catastrophic
accident occurred in October 1974. A barge containing 9,000
tons (8,160 t) of anhydrous ammonia and 4,500 (4,080 t) of
bulk urea broke from the towline during a storm and grounded
and sank off Kekur Peninsula, Baranof Island, Alaska. The
entire cargo of anhydrous ammonia and urea escaped to the
marine environment and the atmosphere. There was no exposure
of humans. Some mussels and starfish died, and approximately
a square mile (2.6 km2) of forest in the immediate vicinity
was laid waste by ammonia fumes.
431
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REFERENCES
l. Alberta Department of the Environment. Standards and Approvals Division.
Guidelines for the Location of Stationary Bulk Ammonia Storage
Facilities. Edmonton, Canada: Alberta Department of the Environment,
1977. 9 pp.
2. American Society of Mechanical Engineers. ASME Boiler and Pressure Vessel
Code. Section 8. Rules for Construction of Unfired Pressure Vessels
1962 Edition. New York: American Society of Mechanical Engineers,
1962. 228 pp.
3- Helmers, S., F. H. Top, Sr., and L. W. Knapp, Jr. Ammonia injuries in
agriculture. J. Iowa Med. Soc. 61:271-280, 1971.
4. Fertilizer Institute. Agricultural Ammonia Operator's Manual M-7-1973.
Washington, D. C.: The Fertilizer Institute, 1973. 44 pp.
!
5- Fertilizer Institute. Standards for Storage and Handling of Nitrogen
Fertilizer Solutions Containing More Than 2% Free Ammonia and
Specification for 3,000 to 21,000 Gallon Steel Tanks for Storage of
Field Grade Aqua Ammonia Containing 20% to 25% NHL. Washington,
D. C.: The Fertilizer Institute, 1970. 32 pp.
6. Fertilizer Institute. Fertilizer Progress Data Sheet. Compilation of
Survey Information of Retail Details. Washington, D. C.: The
Fertilizer Institute _/ not dated_/.
7. National Research Council. Committee on Hazardous Materials. Evaluation
of the Hazard of Bulk Water Transportation of Industrial Chemicals.
A Tentative Guide. 1970 Edition with Additions to July 30, 1973.
Prepared for the U. S. Coast Guard. Washington, D. C.: National
Academy of Sciences, 1974. 58 pp.
432
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8. National Research Council. Committee on Hazardous Materials. System for
Classification of the Hazards of Bulk Water Transportation of Indus-
trial Chemicals. A Report to the Department of Transportation, U. S.
Coast Guard. Washington, D. C.: National Academy of Sciences,
1975. 42 pp.
9. National Transportation Safety Board. Pipeline Accident Report. Mid
America Pipeline System Anhydrous Ammonia Leak, Conway, Kansas,
December 6, 1973. Report No. NTSB-PAR-74-6. Washington, D. C.
National Transportation Safety Board, 1974. 29 pp.
10. National Transportation Safety Board. Railroad Accident Report. Chicago,
Burlington, and Quincy Railroad Company Train 64 and Train 824 Derail-
ment and Collision with Tank Car Explosion, Crete, Nebraska, February
18, 1969. Report No. NTSB-RAR-71-2. Washington, D. C.: National
Transportation Safety Board, 1971. 79 pp.
11. U. S. Department of Labor, Occupational Safety and Health Administration.
Storage and handling of anhydrous ammonia. Code of Federal Regulations
29-1910.111.
12. Sutherland, W. N., and N. L. Case. Anhydrous ammonia product information,
pp. 1-8. In Proceedings of Agronomy Workshops on Anhydrous Ammonia,
North Platte, Nebraska and Licoln, Nebraska, July 1968. Sponsored by
College of Agriculture, University of Nebraska, Agricultural Ammonia
Institute, and Nebraska Ferlilizer Institute, Inc., 1968.
13. Raj, P. K., J. Hagopian, and A. S. Kalelkar. Water dispersion, pp. 182-
188. In Prediction of Hazards of Spills of Anhydrous Ammonia on
Water. (Prepared for U. S. Coast Guard under contract DOT-CG-22, 182-A)
Cambridge, Mass.: Arthur D. Little Inc., 1974.
14. Risks of shipping chemicals studied. Chem. Eng. News 54(14):15, 1976.
433
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15. FS Services, Inc. What inspections should be made before going on the
road, pp. 40-':2. In Safety Phase "8". Ammonia. _/ Training Course
for FS Employces_/ Bloomington, Illinois: FS Services, Aiot dated]
16. Compressed Gas Association, Inc., and The Fertilizer Institute. American
National Standard Safety Requirements for the Storage and Handling
of Anhydrous Ammonia. ANSI K61.1-1972. Approved February 4, 1972 bj
the American National Standards Institute, Inc. New York: Com-
pressed Gas Association and Washington, D. C.: The Fertilizer
Institute, 1972. 32 pp.
17. U. S. Department of Transportation. Office of Hazardous Materials.
Operations. Hazardous Materials Incidence Reporting System.
Hazardous Materials Incident Report 1050085. Washington, D. C.:
U. S. Department of Transportation, 1971.
18. U. S. Department of Transportation. Office of Hazardous Materials
Operations. Hazardous Materials Incidence Reporting System.
Hazardous Materials Incident Report 3110085. Washington, D. C.:
U. S. Department of Transportation, 1973.
19. U. S. Department of Transportation. Office of Hazardous Materials
Operations. Hazardous Materials Incidence Reporting System.
Hazardous Materials Incident Report 6040588. Washington, D. C.:
U. S. Department of Transportation, 1976.
20. U. S. Department of Transportation. Office of Hazardous Materials
Operations. Hazardous Materials Incidence Reporting'System.
Hazardous Materials Incident Report 6050911. Washington, D. C.:
U. S. Department of Transportation, 1976.
434
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21. U. S. Department of Transportation. Office of Hazardous Materials
Operations. Hazardous Materials Incidence Reporting System.
Hazardous Materials Incident Report 6060004. Washington, D. C.
U. S. Department of Transportation, 1976.
22. U. S. Department of Transportation. Office of Hazardous Materials
Operations. Hazardous Materials Incidence Reporting System.
Hazardous Materials Incident Report 6060028. Washington, D. C.
U. S. Department of Transportation, 1976.
435
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CHAPTER 6
TOXICOLOGY
METABOLIC TOXICITY OF AMMONIA IN MAN
General aspects of the metabolism of ammonia in various
species are described in Chapter 2. The circumstances, symptoms,
and causative mechanisms of toxicity in a number of animals are
presented elsewhere in this chapter. The purposes of this sec-
tion are to describe how these general mechanisms apply specifi-
cally to man, under what circumstances metabolic toxicity of
ammonia can be observed, the bases of this toxicity, and the
current approaches to therapy.
As mentioned in Chapter 2, metabolic toxicity of ammonia
can, in theory, have two classes of causes: the presentation
of excessive ammonia to man and the presence of defective mecha-
nisms for ammonia removal.
It is highly unlikely that a human can be exposed to sufficien
quantities of "external" ammonia long enough for its metabolic
toxicity to become manifest. First, as mentioned in Chapter 2,
the biochemical mechanisms for removal of ammonia are extra-
ordinarily rapid and efficient. Second, the reaction of sensi-
tive target organs — such as skin, eyes, and lungs (Chapter 7) —
is sufficiently severe that these deleterious effects would
drive away the victim long before symptoms of metabolic toxicity
436
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could become evident. Thus, there are no reliable reports of
the metabolic toxicity of ammonia as a result of spill, acci-
dent, or excessive external exposure.
When ammonia toxicity is observed, the toxicity is most
likely to be from ammonia generated by the metabolism of the
victim. Biologic defects can cause the accumulation of ammonia
in tissues and extracellular fluid, with a resulting constellation
of symtpoms that can be called "ammonia toxicity"; this toxicity
is not fundamentally different from that found in other animals.
Almost all known cases of ammonia toxicity stem from defects
in ammonia uptake; these defects can be placed in two broad
categories: general hepatic insufficiency and congenital (or
genetic) disorders of specific enzymes, particularly those
involved in the uptake of ammonia. General heptatic insufficiency,
which probably represents a combination of toxic effects of in-
sufficent circulation through the liver with deficiencies in
essential hepatic enzymes, is included in the syndrome known as
"hepatic coma"; this subject has been extensively reviewed, and
only the more recent or valuable references are cited
here. ->' ^ ' ^11 30 / 51, 71 More and more of the congenital disorders
are becoming recognized; two useful summaries are those by
Colombo -* and Hsia.
Although a distinction has been made between toxic effects
of "excessive ammonia" and of "defective mechanisms for ammonia
removal," the distinction is not absolute. "Excessive ammonia"
43-7
-------
may not be a primary cause of ammonia toxicity, but a "normal"
or "close to normal" production of ammonia may have the effect
of an excess in a person with defective removal mechanisms.
Indeed, therapy for metabolic toxicity of ammonia is in,part
designed to minimize internal generation of ammonia. Neverthe-
less, the primary defect appears generally to be in the uptake,
rather than in the production mechanisms.
Hepatic Coma
Hepatic coma (or hepatic encephalopathy) is a clinical syn-
drome whose etiology has long been associated with "ammonia
toxicity." The term "hepatic coma" describes a continuum of
clinical states whose symptoms can range from irritability,
inappropriate behavior, convulsions, and decerebrate rigidity
to gradually developing stupor and deep coma. 9'51 It j_s con_
sidered to be a disease of metabolic, rather than cerebral,
origin, inasmuch as pathologic changes in the brain generally
follow the onset of cerebral symptoms, rather than preceding it.
Two broad classes of hepatic coma are recognized: the coma that
results from catastrophic acute liver disease, such as massive
hepatic necrosis from a variety of causes, and diseases that
produce gradual deterioration of liver function.9 Chronic liver
diseases, such as cirrhosis, produce both a decrease in the mass
of functional liver tissue and a gradual shunting of enteric
blood flow around the liver, rather than through it.21 The sub-
ject of hepatic coma has been amply reviewed.5,9/21,30,51, 71
438
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One of the chief questions in evaluating the status of
hepatic coma is whether to seek a "unitary" cause or to con-
sider the process as representing the end state of a broad
variety of metabolic inputs that in various proportions, com-
bine to produce an overall derangement of consciousness.
Whether a "unitary" hypothesis or a "multiple" hypothesis is
adopted, ammonia is a leading candidate for consideration as
a primary precipitating cause.
Authorities differ, however, in the emphasis that they
place on ammonia. Hindfelt stated^O that "it seems reasonable
to conclude that most evidence favors the role of ammonia and
its metabolism in the pathogenesis of hepatic coma." Other
authorities (such as Fischer2^) tend to emphase other etiologic
aspects, point out that serum ammonia concentrations are not
increased in all patients with hepatic encephalopathy, and seek
alternative or additional explanations. These viewpoints are
not necessarily contradictory, and the complexity of the physio-
logic and biochemical functions of the liver permits a broad
and perhaps continuous range of etiologies. This can become
evident through review of the functions of the liver.
Biochemically, liver is enormously complex and contains a
variety of cell types. Its metabolism can affect that of brain:
liver has the enzymatic capability of both synthesizing cerebral
stimulants and metabolizing or "detoxifying" cerebral depressants,
Given a particular amount of loss of hepatic enzymatic function,
439
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one cannot predict a. priori which of these functions is more
damaged, and common clinical tests of liver function do not
distinguish.
Of at least equal importance is the role of the liver as
a filter-barrier that protects the entire organism against the
outside world. This protection is afforded not only by the
liver microsomal hydroxylation system recently recognized as
predominant in the metabolism of drugs and foreign compounds, '
but also by the liver's anatomic location, whereby it serves as
a barrier between the gut and the organism itself. The gut can
be considered as a portion of the "external" world, where extra-
cellular digestive enzymes degrade the polymers of food into
assimilable oligomers or monomers and where a rich bacterial
flora that is foreign to "internal" man resides. Under normal
conditions, the hepatic portal circulation ensures that the
products of gut biochemical action are presented to and filtered
by the liver before their release into the general circulation.
In many forms of liver disease, the blood supply draining the
intestine bypasses the liver; this provides a portocaval shunt
that permits the products of gut metabolism to be presented
directly, without filtration by liver, into the general circu-
lation. 21/28,63 under these circumstances, the organism re-
ceives an "uncensored" mixture of products of the metabolism of
the "external" world of the gut. Many of these products are
toxic; and one of them is ammonia. The clinical importance of
440
-------
the products of gut metabolism is made readily evident by the
therapeutic effectiveness in hepatic coma of attempts to
"sterilize" the gut17/19> 23• 51r54/59 Or to decrease the amount
of protein available to the bacterial and other enzymatic
processes that occur within its lumen.3i51,54
Therefore, the diseased liver may, in theory, be deficient
in any or all of its cerebrally relevant enzymatic and "barrier"
functions, and it is not unreasonable to assume that the clinical
and laboratory manifestations in a given patient may reflect the
peculiar and individual combination of actual defects. These
defects can include a failure to produce an essential substance,
to detoxify a material formed from the metabolism of the indi-
vidual, (owing to enzymatic or circulatory deficiencies or both)
to detoxify the products of gut metabolism. It is not surprising,
therefore, that a broad spectrum of laboratory and clinical find-
ings can be observed in hepatic encephalopathy or that there is
disagreement as to the relative importance of various etiologic
factors.
It is not the function of this report to discuss the pre-
cipitating causes of hepatic coma, but a classification may be
useful, and one is presented in Table 6-1. Special attention
should be given to the third item in the table, "Sedatives and
Anesthetics." Most patients in hepatic coma are seen in a
hospital environment; many have been subjected to a large array
of drugs and other therapeutic regimens. In the face of defective
441
-------
TABLE 6-1
Precipitating Causes of Hepatic Coma—
Cause
1. Gastrointestinal hemorrhage
2. Diuretics
3. Sedatives and anesthetics
4. Uremia
Presumed Mechanisms Leading to Coma
Provides substrate for increased anunc
production (100 ml blood = 15 to 20 g
protein)
Hypovolemia may compromise hepatic an
renal function, the latter leading to3
increased activity of the enterohepat
urea nitrogen cycle and increased aitun
production
Contribution from ammonia in stored b
Role of shock and/or hypoxia
Induce hypokalemic alkalosis, increas<
renal vein ammonia concentration, and
enhanced transfer of ammonia across b
brain barrier
Overvigorous diuresis (and paracentes
may lead to hypovolemia and prerenal
uremia
Separate role of acetazolamide . . . ,
Direct depressive effect on brain . .
Hypoxia
Increased enterohepatic circulation oi
urea nitrogen with increased ammonia
production
Direct cerebral effect of uremia per s
a. n
Reprinted with permission from Breen and Schenker.
442
-------
Table 6-1 - continued
Cause
5. infection
6. Constipation
Presumed Mechanisms Leading to Coma
Increased tissue catabolism, leading to
increased endogenous nitrogen load and ;
creased ammonia production
Dehydration and diminished renal functic
Hypoxia, hyperthermia may potentiate
ammonia toxicity
Increased ammonia production and
absorption
443
-------
liver metabolism, these drugs may have unexpected effects;
interpretation of clinical and laboratory data is always subject
to the possibility that observed derangements stem from the
9 SI
therapy, as well as from the disease. ' Some of the disagree-
ment in the field may well result from inability to separate, meta-
bolic and therapeutic effects.
The Role of Ammonia. Ammonia is implicated in the patho-
genesis of hepatic coma, not only because of observed abnormal-
ities of ammonia metabolism in humans, but because of the large
body of experimental animal work that describes the toxic (and
coma-producing) effects of ammonia, the toxicity of amino. acids
when rates of administration are high enough to increase
plasma ammonia content, and the susceptibility to increased
toxicity of oral ammonium compounds in animals subjected to
portacaval shunts.°'^0,51 There are thus ample animal models
for at least some of the clinical manifestations of the human
hepatic coma syndrome. These experimental models are more fully
described later in this chapter.
A large body of observations implicates ammonia in the
etiology of hepatic coma in humans. ^ .If a person's hepatic
function is compromised, increased dietary protein, ammonia-
releasing resins, and ammonium salts may produce precoma or
coma;45 the effects of "dietary" protein would include at least
in part the effects of gastrointestinal hemorrhage, which presents
the intestine with substantial quantities of protein. Hyperammonemia
444
-------
is a prominent laboratory finding in most patients with hepatic
coma,44 and the ammonia concentration in the spinal fluid of
persons in hepatic coma is usually increased.11 Congenital
abnormalities of the urea cycle 3 are also associated with
hyperammonemia and with stupor or coma.15/33 The glutamine
content in cerebrospinal fluid is usually increased in hepatic
coma;32 because glutamine is a diffusible "detoxified form" of
ammonia (see Chapter 2, Reaction 2-20), this finding may indicate
the cumulative effect of prior ammonia exposure. Knowledge of
general and especially brain metabolism permits the conjecture
(not always confirmed by observation) that ammonia can be ex-
pected to interfere with the respiratory and energy metabolism
of brain.4'5
Correlations are undoubtedly imperfect, and exceptions to the
observations just cited are frequently observed. These exceptions
are important enough to prevent the unequivocal conclusion that
ammonia is the sole etiologic factor in hepatic coma.21 For
example, the ammonia concentration in plasma and in cerebrospinal
11 21
fluid may not correlate with the state of consciousness. •LJ-> ^•L
Indeed, correlation between cerebral symptoms and cerebrospinal
fluid glutamine content is somewhat better than the correlation
with ammonia concentration.32 In this regard, it is of interest
that coma arising from causes other than hepatic insufficiency
is usually not associated with an increase in cerebrospinal
fluid glutamine.26
445
-------
What is the source of the ammonia associated with hepatic
coma? Clearly, there must be a disturbance in the balance
between ammonia production and ammonia removal. There is no
special reason for proposing an actual increase in ammonia pro-
duction in the liver, and attention is therefore focused on de-
fects in ammonia removal. The hepatic capability of synthesizing
urea is high,35 and hepatic dysfunction virtually equivalent to
removal of the liver is required to reduce blood urea content
substantially- From the enzymatic standpoint, it may be con-
jectured (but it is by no means proven) that the enzymatic path-
ways of ammonia removal (see Chapter 2) are more deranged than
are the enzymes for ammonia production. But data providing in-
ventories of the activity of ammonia-producing and ammonia-
utilizing reactions in liver disease are sparse, and reliable
reports on humans have not appeared. Nevertheless, it is not
necessary to postulate an imbalance between enzymatic mechanisms
of ammonia production and utilization in liver to account for
hyperammonemia. Certainly, the rapid appearance of increased
blood ammonia after experimental creation of portacaval shunts
argues against the necessity of invoking specific enzymatic de-
fects; it may be enough to have insufficient removal of intestinally
produced ammonia as the blood supply from intestine bypasses the
liver and enters the systemic circulation.9/21,51
Intestinal ammonia may have two general classes of sources.-3
One is the bacterial deamination of dietary amino acids; intestinal
446
-------
flora has substantial capacity for carrying out deamination
reactions, which have been described in Chapter 2. The other
source is urea.60/61,69 intestinal microorganisms contain
urease and are capable of splitting urea to ammonia and carbon
dioxide. This process can go on to a surprisingly large extent.
Walser and Bodenlos,66 using doubly labeled urea, found that at
least one-fourth of the urea produced was degraded to ammonia in
the intestine; if the intestine was "sterilized" by oral ad-
ministration of neomycin, the hydrolysis of urea ceased. Thus,
there appears to be an enterohepatic circulation of urea and
ammonia:34 urea, synthesized in the liver and freely diffusible
in body water, enters the intestine, where some of it is
hydrolyzed by intestinal microorganisms; the ammonia is normally
returned to the liver by the portal circulation and is there con-
verted to urea. In the portacaval shunting that accompanies much
liver disease, intestinal ammonia bypasses the liver and appears
in the general circulation. Thus, the sources of intestinally
produced ammonia can be either ingested protein (including pro-
tein released into intestine by gastrointestinal hemorrhage) or
tissue urea. The importance of intestinal ammonia is emphasized
by the relative success of therapy directed either at minimizing
the access of protein to intestine by dietary restriction or con-
trol of hemorrhage or at sterilizing the intestinal contents. ' ' '
441
-------
Another potential source of ammonia is the kidney. The
kidney is usually a net ammonia producer, and renal venous
ammonia concentration is usually higher than renal arterial
concentration.^>46,53 Alkalosis and associated hypokalemia
C Q
increase net ammonia formation;-30 the combination can often
be seen in patients with hepatic coma, in whom it can result
from administration of diuretics without adequate administration
of potassium.
The data on the effects of ammonia on brain metabolism, as
obtained in experimental animals, are reviewed in'Chapter 6.
The original hypothesis proposed by Bessman and Bessman^ was
attractive: it proposed, in summary, that excess ammonia in-
creased the formation of glutamic acid and glutamine, creating
a unidirectional drain on the keto acid components of the
citric acid cycle. Because these components could be replenished
only from carbohydrate precursors, by a series of carbon dioxide-
fixing reactions that required energy and whose activity in brain
was not clearly documented, one could expect decreased brain
respiration, with coma secondary to decreased cerebral oxidation
and energy storage. This attractive hypothesis has eluded ex-
perimental verification.2 For example, depletion of brain
a-ketoglutarate has not been demonstrated, 31/ 52 , 55 , 67 an(j
searches for substantial changes in the brain concentration of
high-energy phosphate compounds have failed to produce striking
results, although slight alterations have been found in the brain
448
-------
stem. The ratio of NADH to NAD+ has been calculated to be in-
creased in brain in acute hyperammonemia,31 but the relation-
ship between this ratio and brain respiration is not clear.
The least equivocal findings are that glutamine concentration
is indeed increased in the cerebrospinal fluid of patients
with hepatic coma and that brain nonprotein glutamine is in-
creased in experimental animals subjected to hyperammonemia.^
But these increases in glutamine do not appear to be associated
with net decrease in the free glutamic acid of brain.^1 Thus,
the "energy-depletion" hypothesis—a correlation between coma
and depleted energy sources — is not strongly supported by actual
measurements. Coma is always associated with a decrease in
brain oxygen metabolism. °' but this is generally true of coma
from any source, so it is difficult to separate cause and effect.
In hepatic coma, one study suggested a decrease in brain respira-
tion before coma,20 one study was equivocal,-^ and two others
showed no early decrease in brain oxygen uptake. '
Nevertheless, the failure to confirm directly the "energy-
depletion" hypothesis of the effect of ammonia on hepatic coma
does not necessarily make the hypothesis incorrect.5< 9i 30 if
alterations of consciousness stem from highly localized meta-
bolic changes in the brain, these changes could be expected to
be only poorly detectable and could be lost in the "background"
of general brain metabolism. Metabolic sequences, including
those pertaining to ammonia and oxidative metabolism, can be
449
-------
compartmentalized in specific loci.1'2'30'41'64 Recent studies
have placed increasing emphasis on the importance of compart-
mentalization. Thus, Martinez-Hernandez et a^-4-*- have demon-
strated that glutamine synthetase of brain is localized in glial
cells; they called attention to correlation with a glial altera-
tion known as Alzheimer Type II change, which is characteristically
observed in chronic hyperammonemia. These types of studies and
(perhaps more importantly) the continuing observation of associa-
tion of hyperammonemia with hepatic coma^>^> 30r51 indicate that
the Bessman hypothesis must continue to be seriously considered.
Additional or Alternative Etiologies of Hepatic Coma.
Materials other than ammonia have been suggested as causing, at
least in part, some of the symptoms of hepatic coma.9'21,51,71
These may be considered to act synergistically with ammonia.
Most are thought to be products of gut metabolism, and the re-
newal of interest in these materials evokes, possibly in more
rational form, the old concept of "autointoxication" by intestinal
contents.
• Mercaptans and methionine: These materials have
long been suspected of accumulating during hepatic
coma. In patients with hepatic coma, there is
frequently a fetor hepaticus, a "characteristic
sweetish, musty odor which has suggested to some
observers the presence of indoles or mercaptans." ->
450
-------
Methylmercaptan and dimethylsuflide have been
identified in the urine of a patient with ful-
minant hepatitis. ^ Mercaptans are found in
the breath of cirrhotic patients in higher
concentrations than in normal. When methionine
was administered to cirrhotic patients, there
was a selective increase in urinary dimethyl-
sulfide that was correlated with the presence
of fetor hepaticus.14 zieve and associates have
observed that administration of mercaptans causes
reversible coma in animals and increases the
toxicity of ammonia. ' It may be presumed
that, "normally, mercaptans formed in the gut
and the liver are readily metabolized and only
small amounts of mercaptans are released in the
breath. In patients with liver disease, in-
creased amounts of mercaptans or their deriva-
tives are exhaled due to their decreased hepatic
metabolism. Oral antibiotics often eliminate
fetor hepaticus, supporting the role of intestinal
bacteria in mercaptan formation. It should be
noted that the administration of methionine leads
to the production not only of mercaptans, but of
additional ammonia, because the latter can be
formed from methionine by intestinal bacteria.
451
-------
Fatty acids; Zieve e_t aJ.70 have reported
that simultaneous injections of ammonium
salts and a fatty acid into normal rats or
cats caused coma at lower plasma concentra-
tions of ammonia and free fatty acids than
separate injections.
X-Aminobutyric acid: A-Aminobutyric acid, an
inhibitory neurotransmitter, is a product of
the decarboxylation of glutamic acid. It has
been suggested that this material may be formed
as a result of amination of a-ketoglutaric acid
and then decarboxylation of the resulting glutamic
acid. However, no increase of this material in
rat brain has been noted after liver damage or
27
administration of ammonia.
False neurotransmitters; The possible importance
of these materials as etiologic agents in hepatic
coma has been reviewed and discussed by Fischer.21
Fischer and Baldessarini^ have suggested that
biogenic amines, such as octopamine and
6-phenylethanolamines, may be produced from
ingested protein by intestinal bacteria. These
materials would be expected normally to be de-
toxified by liver but, in the presence of impaired
hepatic circulation, they could bypass this filter
452
-------
and accumulate in the brain. These amines can
function as weak neurotransmitters.21^51 jf
they accumulate in synaptosomes, they may
interfere with normal synaptic impulse trans-
mission. This hypothesis is based on observa-
tions of increased concentrations of biogenic
amines in serum and urine of hepatic coma pa-
tients and in the brain of animals with experi-
mental hepatic damage. Antibiotic therapy de-
creases the accumulation of these substances
in experimental animals. Administration of
L-dopa is sometimes effective in temporarily
reversing hepatic coma, ^ and it is presumed
that it acts by serving as a precursor of the
normal catecholamine neurotransmitters or by
competing for the false neurotransmitters at the
synaptosomes. Related to this hypothesis is the
possibility of derangement in metabolism of the
amino acid tryptophan; this could occur either
through inadequate hepatic synthesis of
5-hydroxytryptophan8 (a precursor of the neuro-
transmitter serotonin) or through excessive
formation of intestinal bacterial degradation
products of tryptophan (skatoles and indoles).
The latter materials at high concentrations have
fi Q
been found to inhibit brain respiration.00
453
-------
The hypothesis that defects in production of
potential neurotransmitters contribute to
the syndrome of hepatic coma is not unattractive, 1
but requires experimental verification in liver
disease.
Thus, there are a wide variety of "toxic substances" that
can impair cerebral function; ammonia is the best known, best
documented, and most extensively studied. There is no reason
to rule out the possibility that ammonia toxicity can act addi-
tively or synergistically with other toxic materials in pro-
ducing the symptoms of coma.
* Failure to provide materials essential to brain;
In principle, hepatic coma may result from the
failure of liver to provide an essential material,
rather than from its inability to detoxify toxic
materials. Some support for this hypothesis is
provided by the observation that addition of
cytidine and uridine to perfusion fluid appears
to protect isolated cat brain preparations partially
against the impaired metabolic and electric activity
that result from removal of the liver from the per-
fusion fluid.25 A factor so essential that it is
often taken for granted, and possibly overlooked,
is glucose. Liver glycogen is an immediate pre-
cursor of blood glucose, the preferred substrate
454
-------
for brain oxidation. In hepatic insufficiency,
glucose release by liver may occasionally be
seriously impaired, and hypoglycemia may result,
with consequent decrease in consciousness. 51
Drugs: The hospitalized patient is exposed
to a plethora of new and foreign substances.
Reviews of hepatic coma9-51 have pointed out
the impaired ability of liver to metabolize
and detoxify a wide variety of drugs. The
condition of a patient with hepatic insufficiency
may reflect not only his own metabolic state, but
the modulations imposed by his therapy. This
substratum of response to drugs makes it dif-
ficult to distinguish "spontaneous" from
"iatrogenic" symptoms.
The effect of net long-term depletion and the
problem of "increased cerebral sensitivity":
The concept of "increased cerebral sensitivity""'5-
suggests that a patient who has had long-term
chronic liver disease is more susceptible to
some stresses and responds to them with a greater
decrease in consciousness than would a healthy
person. The response of patients with liver
disease to sedatives, infection, hypoxia,
electrolyte disturbances, etc., is greater
455
-------
than that of normal people. This increased
sensitivity can itself be due to the long-
term accumulation of toxic materials in brain,
in which case the next increment will have a
greater effect; or it may reflect the long-term
depletion of essential materials in the brain.
For example, the continuous production of
glutamine over long periods might deplete some
sensitive locus of metabolic precursors. Need-
less to say, the theories of accumulation of
toxic materials and of depletion of essential
substrates are not mutually exclusive, and
these factors may combine to provide a basis for
an apparent increase in the sensitivity of the
cerebrum to further insults or injury -
It can be seen that hepatic coma can result from combina-
tions of various stimuli, such as the depletion of essential
metabolites and the accumulation of toxic materials. There
is no doubt that ammonia plays a prominent role and that the
failure of the liver to shield the systemic circulation from
ammonia and other products of intestinal bacterial activity
also plays a prominent role. The most consistently effective
therapy51 is that directed toward the removal of intestinal
bacteria (or the change of intestinal bacterial flora to
varieties that are less active in producing ammonia from urea)
456
-------
Feeding of lactulose6 has recently been used with some success;
it may act by lowering the pH of colon, or by shortening the
transit time of colon contents. Therapy has also been directed
at limiting access of protein to the gastrointestinal tract by
restriction of dietary protein or control of gastrointestinal
hemorrhage. The restriction of dietary protein in a debilitated
patient retards achievement of nitrogen balance and recovery, so
the decision to minimize protein intake is not taken lightly.
It is of interest that intravenously administered amino acids
appear to be less toxic than orally administered amino acids,
and perhaps this route of administration holds some therapeutic
promise.
Inborn Errors of Ammonia Metabolism
A number of inborn errors of ammonia metabolism have been
recognized, and excellent reviews are available.15,33 These
defects result in hyperammonemia, some of whose symptoms may
be ascribed to ammonia toxicity. "Hyperammonemia may be lethal
in the newborn, may cause severe symptoms in infancy, or may
cause chronic remittent symptoms in older children and adults."
In the newborn, symptoms may appear rapidly, deterioration
may be swift, and death may occur before laboratory measurements
have been made.12 Some of the features of the disease may re-
semble those of hepatic coma in adults; suspicion of hyper-
ammonemic disease may be aroused by a history of unexplained
neonatal deaths in siblings or other relatives12'33 and is
457
-------
strengthened if symptoms are precipitated by feeding of protein-
containing milk. Depending on the specific defect, either meta-
bolic acidosis^O Or metabolic alkalosis^-^ can accompany hyper-
ammonemia.
In older infants, children, and adults, the clinical syn-
drome may be characterized by a remittent course, with episodes
of vomiting, neurologic derangements, seizures, or coma. These
episodes may be precipitated by high-protein foods; when they
occur in infants and children, an intolerance to such foods can
often be described by the parents. "With correct diagnosis
and effective treatment, these patients will escape repeated
attacks of hyperammonemia, and may recover partial or complete
neurological and intellectual function."33
Recognition of a heterozygous state is useful in permitting
genetic counseling.33 Heterozygous females with deficiency in
ornithine transcarbamylase^^ or argininosuccinic acidurea^
or with familial protein intolerance have been recognized.
As adults, they may have a history of feeding difficulties in
infancy and of aversion to protein-rich meals.
It is of interest that, even with inborn errors of urea cycle
enzymes (defects have been described in each of the five enzymes
that constitute the cycle), no patient has been described who
completely lacks blood urea. It has been suggested that a total
block in the urea cycle is incompatible with full fetal develop-
ment; an alternative possibility is the catalysis of urea cycle
458
-------
reactions by enzymes of different biologic "purpose" and
different genetic origin. Thus, the genetically distinct
carbamyl phosphate synthetase of the pyrimidine biosynthesis
pathway (see Chapter 2) may take over some of the functions
of the urea synthesis-directed synthetase.33 Similarly, it
is conceivable that urea can be formed by the relatively weak
arginase activity of transamidinase.^'^ ' ^^
The diseases that stem from defects of urea cycle enzymes
are listed in Table 6-2, reprinted from Hsia.33 The author
described the various characteristics of the relatively small
number of patients who had these defects. The most extensively
studied group of diseases, with almost 50 patients described, is
a series of defects in ornithine transcarbamylase. The presence
of hyperammonemia in the patients cited in Table 6-2 is, at least
in theory, consistent with known metabolic pathways. Because
the urea cycle can be considered as an integrated ammonia-
utilizing mechanism, defects in its components can lead to de-
fects in ammonia removal, with consequent hyperammonemia and the
symptoms resulting from it.
Hyperammonemia is also observed in several other metabolic
derangements involving amino acids. Here, the relationship
between the metabolic defect and the hyperammonemia is less
clear. These defects are summarized in Table 6-3, also re-
printed from Hsia. Hyperammonemia is a common but not in-
variable finding; in ornithinemias, hyperammonemia was observed
459
-------
Table 6-2. Inborn Errors of Urea Cycle Enzymes
1 l\irl>.im\l |ilin:,pli,iif
stlllhflJ^f I
''T^lmmTl'i'hM,
phaie ->>ni lii'i a.ie
Cjrh.imv 1 pliii"-
phaie synllu'ia.so
2 Ornil hme t ran>i .ir
OriiilliniKrJM-.
carli.um Ulse
'Ormlhinrlr.iiu.-
j. COrllHlml.lM'
cK
o
Ornithuu- lran.s-
carhiim>l;j.se
3. ArKimi-succiniilfsyn-
thetase
ft Artfinase
Possible variant
Arginase
" CSK. cerebrospina)
';;,;;;;;;:' , K >
i '
I.IV1T Illllll C' AWllll KfMllll.ll
choiulrui a rn.iv lie
carhann 1 |»tiu^
plultfbvnlhflj'.L-II
I.IVIT CM",I
L.VCT ,l:,'-.W.,
(A in in n , i }
. malr-. Kinei ics
' uiu-ban^ed
Liver , ('>'"• 1 Km Ormihme U.
shiti m pH
optimum
Liver a'^ioSO1;) K^Car-
bum> 1 prufophfiK1 I
altered isoeletlru
point
Liver ('2fr, ai pH 7 I)).
("')' • i.t normal at
pHH.IM K»Cur-
bamyl phosphate |
Lwer. kidney (U V;» K, fitrul
brain, tul- line 1 1
tured tellb
cells, t ul- : kidney)
lured i elk
Liver. Imim. tAlwi-nl in mi blond
bliHid cells. telK and t olliired
cultured cellM
cells ;
Li\er. brain. I Absent in.red and
blm.d tells. | white blood cells)
cultured
cells i
1 - u,
luid.
.-MM MM •>! in hroiher
1 mlanl ^ir!
•1 children with *e
dainuKC
Let i m ne i n
severity in
tein.iles
Lethal m 1 newborn
hoy, similar hii
lory in brothers
and maternal
uncles
Lethal in '1 inlanl
yirl>. 1 mother
mildly allected
Moderately severe
in 1 hoy
Lethal in 2 newborn
babies; moderate-
ly severe in 3
infants
May be severe.
chnnuc. May
ha\t- 1 nchorrht'xis
nodosa
Moderate in 1)
Mslcrs
Mink-rale m 1
child
'Tllrv ;;;"''
Severe
Moderate
Moderate
able in
females
Severe
Moderate in
girls, mild
in mother
Moderate
Moderate
Variable
Moderate
Moderate
h'™'
Extreme
Moderate
Moderate
ulre lem
able m
females
Severe
Moderate in
Kirls, mild
in mother
Mdd
Moderate
moderate,
post pran-
dial
Moderate.
l»oM pran-
dial
None
Olli>Tl,.,nlu< ,KJ|
None
Keiutit hy pert;ly-
cinemia
None
undine)
Orotic aciduna
(also uracil
undine)
Orotic aciduna
(alsourjol
uridmej
Elevated citrulline
in blutid. CSK/
and urine
evate arKinino-
CSF. bliMHl and
urine; al^o
citrulline
Elevated ar^inine
in blood. (*SK
and urine Cys-
tinunc paitern of
annntiat iduria
Elevated artfinine
inbliHid.CSK.
and urine: aUo
citrulline in
blood and CSF
M-^nh.,,
~K,t"esM«
9
? Reproduced from |P
best available copy, ^f
X-linked
X linked
dominant
X-linked
dominant
•j
? AulHMimal
receaMve
utn&oma
? Autosomal
recessive
9
Reprinted with permission form. Hsia
33
-------
Table 6-3 Other Inborn Errors Associated with Hyperammonemia
Disorder
1. Ornithine
Ornithine
Ormthinemia
2. Hyperlysinemia
Hyperlysinemia with
homocitrullinemia and
homoargininemia
Hyperlysinemia
Saccharopinuria
3. Hyperlysinuria with
Metabolic error
9
9
Ornithint'transammase
deficiency
Lysine dehydrogenase
deficiency
9
? Defective utilization
of Ivsine for protein
synthesis
i
s
? Transport defect in
hyperammonemta intest ine and kidney
Lvsinuria 9 Transport defect in
intestine and kidney
Severitv ol clinical
features
1 boy with moderate
retardation
Gyrate atrophy of
choroid and retina
in 9 patients
2 siblings with liver
damage and retar-
dation
1 infant girl with
severe retardation
Severely retarded
patients
Svniploms ot
protein
intolerance
Moderate
None
Mild
Moderate
None
One family reported. None
Resembles lysine-
deficient animals
Mildly retarded short None
women
Decree of h\ per-
ammonemia
Mild
None
None
Moderate
None
None
None
1 boy with growth re- Mild Moderate post-
tardation and se- ' prandial
vere mental retar-
dation
2 retarded siblings None
with growth
failure, vomiting
and diarrhea
None
Other biochemical features
Elevated blood ornithine;
also urine homocitrul-
line
Ornithine elevated in
blood, CSF," aqueous
humor.
Elevated blood ornithine;
with generalized amino-
aciduria
Elevated blood lysine.
arginine
Elevated blood, CSF,
urine, and stool Ivsine;
also homocitrullinuria
and homoargininuna
Elevated blood, CSF,
urine, and stool Ivsine,
ornithine; also pipecola-
turia, homocitrulli-
nuria, homoargininemia
Elevated blood and urine
lysine: with citrulli-
nuria, homocitrullinuria.
homoargininuria.
saccharopinuria
Low plasma lysine,
Modeol
inheritance
9
? Autosomal
recessive
? Autosomal
recessive
9
? Autosomal
recessive
9
'
9
arginine; elevated urine j
lysine, arginine,
glutamate
Low serum lysine,
arginine, ornithine.
elevated urine lysine,
arginine, ornithine with
homocitrullinuria
? Autosomal
recessive
a oo
Reprinted with permission from Hsia.
-------
Table 6-3. (Continued)
Dibasic aniinoat idemia
4. Lysinuric protein intoler-
ance (familial prolein
intolerance with diba-
sicamino aciduria)
Disorders ol branched-chain
a mi no acid metabolism
Maple s\ rup urine disease
and variants
Hypervalmemia
Isovaleric acidemia
0-methylcrotonyl plycin-
uria with /}-hydroxyiso-
valeric aciduria
Defective isoleucine me-
tabolism with ketotic
hyperglycinemia
0 Transpori defect in
intestine ;md kidney
Familial occurrence
with no retarda-
tion
? 1 Not ^lutaminase I ) Finnish and Lapp
Hranched-chain keto-
pat ienls with diar-
rhea and vomiting
usually without
retardat ion
Severe in classical
acid decarboxylase form, variable in
variants
Mild
Mild to mod-
erate
Severe, vari-
able
0 Vahnetransammase i 1 severely retarded ' Severe
deficiency , infant
lso\aleryl dehydro- Mildly retarded
genase deficiency j children with per-
sistent odor of
sweaty feet
i
Moderate
None
Mild post-
prandial
Not recorded
Not recorded
None
Low plasma lysine,
arginine; elevated urine
lysine, arginine.
sometimes cystine
? Aulosomal
dominant
Autosomal :
recessive
Severe ketoacidosis: Uri- Aulosomal
nary- n-ketoaciduria recessive
Hypervalinemia ?
i >
Severe ketoacidosis; ele- ? Autosomal
vated isovalerate in i recessive
blood and urine
!
/3-methylcrotonyl car- j 2 children, 1 with Mild Not recorded Severe ketoacidosis; ele- :
boxylase deficiency ' muscular atrophy; vated^-methyl-
odorof cat's urine
9
Infant girl with mild
retardation
Propionicacidemia Propionyl carboxylase Severe in classical
Moderate
Moderate
Severe ; May be severe
form
Methyl malonic acidemia Methylmalonyl mutase Severe Severe Not recorded
and errors in vitamin
B, , metabolism
Methylmalonic acidemia Methylmalonyl race- Severe in 1 male
! mase i neonate
Severe
Severe
crotonyl-glycine.
i8-hydroxy isovalerate
in urine
Ketotic hyperglycinemia
Ketotic hyperglycinemia; Autosomal
propionicacid in blood recessive
and urine i
Ketotic hyperglycinemia; ? Autosomal
methylmalonate in \ recessive
blood and urine
Metabolic acidosis,
methylmalonate in
blood and urine
7
' CSF, cerebrospinal fluid.
-------
in one patient, and protein restriction proved beneficial. In
other patients, there was no strong correlation between protein
feeding and exacerbation of symptoms. In ornithinemia, few
studies appear to have been performed on the activity of the
urea cycle enzymes. It is possible that the increased steady-
state ornithine concentration causes secondary derangement of
the rates of biosynthesis of urea cycle enzymes. The only
enzymatic abnormality actually observed was a defect in hepatic
ornithine-ketoacid transaminase.
Another class of defects that has been observed is the
hyper lysinemias . -"-^, 33 In this class of diseases, a rationale
for hyperammonemia can be entertained: lysine is a competitive
inhibitor of arginase, and, at the lysine-to-arginine ratio in
extracellular fluids, it was calculated-^ that substantial
inhibition of arginase could occur. Nevertheless, the argument
is not compelling, inasmuch as the apparent liver content of
arginase is far in excess of normal requirements for urea
synthesis .7/35
Another, largely unexplained syndrome called "lysinuric
protein intolerance" has been found in Finnish and Lapp pa-
tients.37'57 This condition is characterized by postprandial
hyperammonemia with low-normal blood urea, low plasma lysine
and arginine, and lysinuria, arginuria, and sometimes cysti-
nuria. The rise in blood urea after administration of a test
load of alanine is slower than normal, but is made normal by
463
-------
administration of arginine. Long-term administration of
arginine appears to be of clinical benefit. The basic enzy-
matic defect in this disease, clustered in a close ethnic and
familial group, is not understood.
Several of the many disorders of branched-chain amino acid
metabolism have been associated with hyperammonemia. These
metabolic defects are also summarized in Table 6-3; the relation-
ship of these conditions to defects in ammonia metabolism is not
understood.
It should be noted that a specific defect in the metabolism
of an amino acid may have secondary effects on the metabolism
of other amino acids. This can occur not only because of the
potential effects of abnormal concentrations of a single amino
acid on the biosynthesis of other amino acids in mammals (the
control mechanisms for amino acid biosynthesis are far better
understood in bacteria than in mammals), but because of competi-
tion of amino acids for renal transport sites. It has been ob-
served that the administration of single amino acids profoundly
alters the excretion of other amino acids. ° Considerable data
on the amino acid compositions of urine in patients with congenital
disorders of urea and ammonia metabolism have been presented else-
where.
464
-------
Relationship Between Exposure to External Ammonia and Defect
in Ammonia Metabolism.
In theory, patients with impaired ability to metabolize
ammonia can be expected to be more sensitive than normal persons
to exposure to external ammonia and therefore to be more prone
to risk in industrial or agricultural accidents or excessive
exposures. No systematic literature in this field has come to
the attention of the Subcommittee, and the chance encounter of
an ammonia-sensitive person with an ammonia-excessive environ-
ment is statistically improbable. Nevertheless, it is apparent
that a greater than usual degree of caution should be exercised
in the exposure of patients with metabolic hyperammonemia to
environments that may contain abnormally high ammonia concentra-
tions.
465
-------
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4-73
-------
AMMONIA TOXICITY IN GENERAL
Ammonia has been known to be toxic in animals for nearly a
century. Hahn e_t al. •* observed that a dog with Eck's fistula
could not tolerate a high-protein diet; a characteristic syndrome
known as "meat intoxication" developed after a short time.
Marfori10 in 1893 first described the principal effects of in-
jected ammonium chloride as twitches, tremors progressing to
tetany, convulsions, opisthotonos, irregular respiration,
salivation, somnolence, and lassitude. Matthews^ reported that
during the meat intoxication syndrome blood ammonia content
reached 1.8-2.2 mg/100 ml, compared with 0.1-0.2 mg/100 ml in
474
-------
the control. It was also found that, when ammonium chloride was
injected to induce a blood ammonia content of 1.5-2.0 mg/100 ml,
similar nervous signs were observed. Similar results were found
after intravenous injection of ammonium carbonate in dogs and
cats. Therefore, it was suggested that at least one of the
causative factors in meat poisoning in Eck's fistula dogs is
the absorption of ammonia from the stomach due to food decom-
position. It was not until 1927 that a disorder in ammonia
metabolism was suspected of causing similar symptoms in man.2
Five years later, Van Caulaert and his associates18'19'20'21
presented a series of papers that related the ingestion of
ammonium chloride by patients with hepatic cirrhosis to signs
of drowsiness, confusion, and coma.
Early studies on the relative toxicity of ammonium com-
pounds were inconclusive.1-^ it was reported that the toxicity
of different ammonium salts had little or no relation to the
ammonia content of the compounds. However, Underhill and
Kapsinow reported that the intraperitoneal toxicity of 21
different inorganic and organic ammonium salts in rats was
directly proportional to the amount of ammonia in the compounds
and that, the greater the ratio of ammonia to the salt, the
smaller the minimal lethal dose. The time required to produce
death was inversely proportional to the amount of ammonia in
the compound.
475
-------
Karr and Hendricks8 investigated the intravenous toxicity
of ammonium chloride, ammonium acetate, ammonium bicarbonate,
and ammonium carbonate in dogs. They reported that the
occurrence of toxicosis depended on the rate of intravenous
administration and was virtually independent of the total amount
administered. They also found that the toxic effects of ammonium
chloride were due to the ammonium ion, and not to the acidifying
effect of the compound, inasmuch as the same effects were pro-
duced by the carbonate or acetate salt without accompanying
acidosis.
Torda found that the dose of ammonium chloride, administered
intraperitoneally, required to induce convulsions in rats was
40 mg/100 g of body weight. Convulsions occurred only when the
ammonium content of the brain reached 10 times the normal value.
He concluded that the accumulation of the ammonium ion in the
brain may be a result of increased cerebral activity, and not
necessarily the factor that initiates convulsions.
The intravenous and intraperitoneal LD and LDgg g
values for several ammonium compounds have been reported in
various species and are summarized in Table 6-4. In general,
the toxicity of the ammonium compounds increases in relation
to their effect in raising blood pH. This change appears to
be related to the effect of pH on the ammonia-to-ammonium ratio
and the ability of ammonia to cross the blood-brain barrier or
to a direct effect of increased pH on the barrier.22 The toxic
476
-------
TABLE 6-4
Toxicity of Several Ammonium Compounds in Selected Species
Ammonium
Compound
Acetate
Animal.3.
"ticarbonate
carbamate
Carbonate
Chloride
Hydroxide
Intravenous Dose,
mmoles/kg of body wt
Rat
Mouse
Mouse
Chick
Rainbow
Channel
Channel
Goldfish
trout (15.6
catfish (23.
catfish (32.
(23.3°C)£
Goldfish (36.6°C)-
Mouse
Mouse
Mouse
Mouse
Mouse
Mouse
Mouse (38.8°C)k
Mouse (40.4°C)b
Mouse (27.9°C)b
Mouse
—Water temperature.
HBody temperature.
LD
50
6.23
5.64
2.72
LD
5.05
3.10
0.99
4.47
1.02
6.75
6.62
5.17
10.21
2.53
99.9
7.67
4.87
3.80
1.34
1.36
Intraperitoneal Dose,
mmoles/kg of body wt
LD5Q LD9g>9
8.2
10.84
10.44
17.74
25.73
14.66
29.34
20.57
10.8
18.00
26.20
40.70
41.00
20.40
70.50
40.00
References
4
22
29
29
27
27
27
27
27
22
28
28
22
28
22
25
25
25
22
-------
syndrome appears to be very similar, if not the same, in all
species studied. The syndrome after intravenous injection can
be characterized by hyperventilation and clonic convulsions that
begin immediately after administration. This is followed by either
a fatal tonic extensor convulsion or the gradual onset of coma
over the course of 3-5 min. The animals remain in a comatose
state for approximately 30-45 min, showing no response to touch
or light, but moving convulsively in response to sound stimuli.
At this stage, a tonic convulsion and death can occur at any
time, but animals that survive usually recover rapidly and com-
pletely.22'25/28'29 The syndrome after intraperitoneal injection
is very similar, except that the onset of toxic signs usually
does not appear until 15-20 min after administration. Death
or recovery usually occurs within 45-60 min. ' ' °
Navazio e_t a_.L. ^2 observed that, after the intraperitoneal
injection of ammonium acetate at 7.8 mmoles/kg of body weight
in rats, the ammonia concentration in the blood increased to
twice the basal value in 8-10 min. None of the characteristic
toxic signs were detected before this concentration was attained,
and no substantial increase in brain ammonia was observed. However
when the blood ammonia concentration reached more than 20 times
the basal value, there was a sudden rise in brain ammonia con-
tent, which reached a maximum of approximately 100 ug of ammonia
nitrogen per gram between 10 and 26 min after injection. This
observation was explained by assuming that brain ammonia is
478
-------
regulated by the blood-brain barrier; when high blood ammonia
content is reached, the regulatory mechanism is altered and a
sudden rise in brain ammonia may be observed. When the concen-
tration of ammonia in the brain reached approximately 50 pg/g,
contractions and occasional tetanus occurred, and then coma.
Although the animals started to recover from the comatose state
approximately 70 min after onset, basal blood and brain ammonia
concentrations were not observed until 2 h after the injection
of the ammonium acetate. The blood pH rose during the first
few minutes and then dropped to 7.1 after 18 min, the time of
the most severe contractions. Alkalosis developed later, and
the pH returned to normal after 2 h.
Contrary to the above findings, an immediate increase in
brain ammonia has been observed after intraperitoneal injections
of ammonium acetate in rats. ' ' Various workers found dra-
matic increases in brain ammonia content 2-5 min after adminis-
tration of ammonium acetate. Salvatore et al. suggested that
there is no critical blood ammonia concentration necessary for
diffusion through the blood-brain barrier.
Hypoxia has been reported to increase ammonia toxicity in
mice.25 Three main factors were suggested as being responsible
for the increased ammonia toxicity resulting from hypoxia: in-
creased permeability of the blood-brain barrier due to a change
in blood pH, which increases the freely permeable form of am-
monia, or due to a direct effect of anoxia; decreased detoxification
-------
of ammonia due to the effect of anoxia on cerebral and liver
enzymes; and an effect of anoxia on the brain, directly ;in-
creasing ammonia toxicity.
Ammonia toxicity has been shown to be increased at high
body temperature, whereas hypothermia affords marked protection
against ammonia. 25 The LD,-n values for ammonium chloride in
mice at various body temperatures are shown in Table 6-4. The
increased toxicity of ammonia at high body temperature was sug-
gested to be due to a direct metabolic effect of hyperthermia
on the brain unrelated to dehydration or stress. The protective
effect of hypothermia against ammonia toxicity was suggested to
be due to a decreased influx of ammonia into the brain and the
reduction of cerebral metabolism and oxygen demand. Zuidema
ejt al. ° also found a protective effect of hypothermia in ammonia
intoxication; they reported that whole-body hypothermia signifi-
cantly reduced blood ammonia content after administration of
whole blood by gastric tube to Ecks-fistula monkeys. Kierle
e_t al.9 have advocated hypothermia for the treatment of hepatic
coma in humans.
Warren and Schenker^1* investigated the effects of equivalent
plasma pH changes induced by hydrochloric acid infusion and
carbon dioxide inhalation on ammonia toxicity in mice. Acidosis
induced by hydrochloric acid had a significant protective effect,
whereas acidosis resulting from carbon dioxide inhalation either
had no effect or tended to increase the toxic effect of intra-
venously administered ammonium bicarbonate.
480
-------
Intravenous LD50 and LDg9 values have been determined for
ammonium carbamate, ammonium carbonate, and ammonium bicarbonate
2 8
in mice. The values for ammonium carbamate and ammonium carbonate
were the same (Table 6-4); that for ammonium bicarbonate was higher,
even allowing for the difference in ammonia content of the com-
pounds. The lethal intravenous dose of ammonium carbamate was
about the same in mice, dogs, and sheep. Wilson et a_l. ex-
tended their investigation to study the physiologic effects of
the injected ammonium compounds in dogs and sheep. Electrocardio-
grams recorded during the toxic syndrome indicated that the ani-
mals died from ventricular fibrillation. There was also evidence
that death was due to a direct effect of ammonia on the heart.
These findings were in agreement with the effects noted by
Berl e_t al. -*- during the infusion of ammonium chloride in cats.
They recorded electrocardiograms and found them to be altered
in a complex manner. However, the results were not in agreement
with earlier results reported by Warren and Nathan^3 who were
unable to demonstrate a cardiotoxic effect of the ammonium com-
pounds in mice and concluded that the toxicity syndrome was due
primarily to a cerebral effect, and not a direct effect on
cardiac or skeletal muscle. Failure to find the ventricular
fibrillation observed by Wilson et. a_l.28 in the electrocardio-
grams may have been due to the difference in cardiac physiology
of the smaller laboratory animals.
481
-------
To study the relative importance of the major metabolic
pathways of ammonia detoxification, Wilson et jil. compared
the toxicity of ammonium acetate in mice (a ureotelic species)
and chicks (a uricotelic species). The intravenous LD5Q and
LD99 9 values are shown in Table 6-4 and Figure 6-1. These data
indicate that ammonium acetate is about twice as toxic in chicks
as in mice. However, when the intraperitoneal LD5Q and LDgg^g
values were determined, they were very similar for both species
(Table 6-4 and Figure 6-2). On the basis of these data, it
appears that the intraperitoneal route of administration pro-
vides a better index of detoxification capabilities of the ani-
mal. As the capabilities of the detoxification enzyme systems
are surpassed, systemic blood concentrations increase to a point
that is toxic to a critical organ, perhaps the heart. Therefore,
the findings of this study indicate that the avian liver may be
able to detoxify exogenous ammonia as readily as the mouse liver,
even in the absence of one of the major detoxification pathways
functional in the mouse—the urea cycle. These workers suggested
that some other pathway in the chick, possibly the uric acid
pathway, may be as efficient in detoxification of ammonia as
the urea cycle in the mouse.
Wilson and co-workers^' have also determined the intra-
peritoneal LD^0 and LD^n g values for ammonium acetate in three
species of fish--rainbow trout, channel catfish, and goldfish.
Fishes were selected to include ammonotelic, as well as ureotelic
482
-------
CD
Dose, nttolesAg °f
weight
H 9
/// ID50 = 5.64 + 0.083
10
vrrtlRE 6-1 The LD50 curves for arttnonium acetate intravenously administered to mice and chicks.
" The doses that gave 0% and 100% observed nortality are indicated as + and t, re-
spectively Arrows on the left refer to chicks; those on the right, to mice.
ThTdashed lines indicate the 95% confidence intervals. Reprinted with permission.
-------
§
o
s,
o
I
99.9
99
95
90
80
60
40
20
10
5.0
1.0
0.1
99.9
99
95
90
80
60
40
20
10
5.0
1.0
0.1
LD 50= 10.44 ± 0.405
LD50= 10.84 ±0.203
i
10
6 7 8 9 10 15 20 25
Dosage, mrrttlea/kg body weight
30 35 40 45
i
i
FIGURE 6-2. The LD50 curves for anroonium acetate intraperitoneally administered
to mice and chicks. The doses that gave 0% and 100% observed
mortality are indicated as 4- and i, respectively. The dashed lines
indicate the 95% confidence intervals. Reprinted with permission
fron Wilson et al.29
484
-------
and uricotelic, species. There was a direct relationship be-
tween the LD,-Q values for ammonium acetate and the relative
resistance of the fishes to environmental conditions; i.e., the
trout were the most sensitive, the channel catfish intermediate,
and the goldfish the most resistant. A comparison of the intra-
peritoneal LD5n values in millimoles per kilogram for all spe-
cies studied is presented in Table 6-4 and Figure 6-3. It is
evident from these data that the fishes were more tolerant to
the intraperitoneally administered ammonia than either the
v«.
ureotelic or uricotelic species. These results were not pre-
dicted, on the basis of the distribution of ammonia detoxification
enzyme systems in the three general classes of nitrogen excretors.
An increase in the aquarium temperature considerably decreased
the fishes' tolerance to injected ammonia (Table 6-4). These
observations are in agreement with the general concept that
hyperthermia increases ammonia toxicity and hypothermia reduces
it.15
485
-------
REFERENCES
1. Berl, S., G. Takagaki, D. D. Clarke, and H. Waelsch. Metabolic compart-
ments jLn vivo . Ammonia and glutamic acid metabolism in brain and
liver. J. Biol. Chem. 237:2562-2569, 1962.
2. Burchi, R. I. Cited in McDermott, W. V., Jr. Metabolism and toxicity of
ammonia. N. Engl. J. Med. 257:1076-1081, 1957.
3. du Ruisseau, J. P., J. P. Greenstein, M. Winitz, and S. M. Bimbaum.
Studies on the metabolism of amino acids and related compounds
in ivo . VI. Free amino acid levels in the tissues of rats pro-
tected against ammonia toxicity. Arch. Biochem. Biophys. 68:
161-171, 1957.
4. Greenstein, J. P. , M. Winitz, P. Gullino, S. M. Birnbaum, and M. C. Otey.
Studies on the metabolism of amino acids and related compounds. ui_
vivo. III. Prevention of ammonia toxicity by arginine and related
compounds. Arch. Biochem. Biophys. 64:342-354, 1956.
5. Hahn, M. , 0, Massen, M. Nencki, and J. Pawlow. Cited in Stauffer, J. C.,
and B. H. Scribner. Ammonia intoxication during treatment of alkalosi
in a patient with normal liver function. Amer. J. Med. 23:990-994,
1957.
6. Hoffman, B. F. , and P. F. Cranefield. /"inducement of fibrillation_7, p.
102. In Electrophysiology of the Heart. New York: McGraw-Hill
Book Company, Inc., I960.
7. Jacobson, C. The concentration of ammonia in the blood of dogs and cats
necessary to produce ammonia tetany. Amer. J. Physiol. 26:407-
412, 1910.
486
-------
8. Karr, N. W., and E. L. Hendricks. The toxicity of intravenous ammonium
compounds. Amer. J. Med. 218:302-307, 1949.
9. Keirle, A. M. , J. J. McGloin, R. W. Buben, and W. A. Altemeier. Blood
ammonia. Experimental and clinical reduction by hypothermia. Arch.
Surg. 83:348-355, 1961.
lO Marfori, P. Cited in Sollmann, T. Ammonium salts, pp. 774-778. In
A Manual of Pharmacology and Its Applications to Therapeutics and
Toxicology. (7th ed.) Philadelphia: W. B. Saunders Company, 1948.
Hf Matthews, S. A. Ammonia, a causative factor in meat poisoning in Eck-
fistula dogs. Amer. J. Physiol. 59:459-460, 1922. (abstract)
12. Navazio, F, , T. Gerritsen, and G. J. Wright. Relationship of ammonia
intoxication to convulsions and coma in rats. J. Neurochem. 8:
146-151, 1961.
13. Rachford, B. K., and W. H. Crane. Cited in Underbill, R. P., and R.
Kapsinow. The comparative toxicity of ammonium salts. J. Biol.
Chem. 54:451-457, 1922.
14. Salvatore, F. , V. Bocchini, and F. Cimino. Ammonia intoxication and its
effects on brain and blood ammonia levels. Biochem. Pharmacol. 12:
1-6, 1963.
•,r Schenker, S. , and K. S. Warren. Effect of temperature variation on tox-
icity and metabolism of ammonia in mice. J. Lab. Clin. Med. 60:
291-301, 1962.
16. Torda, C. Ammonia ion content and electrical activity o£ the brain during
the preconvulsive and convulsive phases induced by various convulsants
J. Pharmacol. Exp. Ther. 107:197-203, 1953.
17. Underbill, F. P., and R. Kapsinow. The comparative toxicity of ammonium
salts. J. Biol. Chem. 54:451-457., 1922.
487
-------
/ *r v.
18. Van Caulaert, C., and C. Deviller. Ammoniemie experimentale apres
%. ^
ingestion de chlorure d'ammonium chez 1'homme a 1'etat normal et
pathologique. C. R. Seances Soc. Biol. Paris 111:50-52, 1932.
19. van Caulaert, C., C. Deviller, and M. Halff. Le taux de 1'ammoniemie
dans certaines affections hepatiques. C. R. Seances Soc. Biol.
Paris 111:735-736, 1932.
/
20. Van Caulaert, C., C. Deviller, and M. Halff. Troubles provoques par
1"ingestion de sels ammoniacaux chez 1'homme atteint de cirrhose de
laennec. C. R. Seances Soc. Biol. Paris 111:739-740, 1932.
s /
21. Van Caulaert, C., C. Deviller, and J. Hofstein. Epreuve de 1 ammoniemie
provoquee: Repartition de I1 ammoniaque dans le sang et les humeurs.
C. R. Seances Soc. Biol. Paris 111:737-738, 1932.
22. Warren, K. S. The differential toxicity of ammonium salts. J. Clin.
Invest. 37:497-501, 1958.
23. Warren, K. S., and D. G. Nathan. The passage of ammonia across the
blood-brain-barrier and its relation to blood pH. J. Clin.
Invest. 37:1724-1728, 1958.
24. Warren, K. S., and S. Schenker. Differential effect of fixed acid and
carbon dioxide on ammonia toxicity. Amer. J. Physiol. 203:9,03-
906, 1962.
25. Warren, K. S., and S. Schenker. Hypoxia and ammonia toxicity. Amer.
J. Physiol. 199:1105-1108, 1960.
26. Wilson, R. P. Comparative Ammonia Toxicity and Metabolism. Ph.D. Thesis.
Columbia: University of Missouri, 1968. 208 pp.
27. Wilson, R. p., R. 0. Anderson, and R. A. Bloomfield. Ammonia toxicity
in selected fishes. Comp. Biochem. Physiol. 28:107-118, 1969.
488
-------
28, Wilson, R. P., 1. E. Davis, M. E. Muhrer, and R. A. Bloomfield. Toxico-
logic effects of ammonium carbamate and related compounds. Amer.
J. Vet. Res. 29:897-906, 1968.
29- Wilson, R. P., M. E. Muhrer, and R. A. Bloomfield. Comparative ammonia
toxicity. Comp. Biochem. Physiol. 25:295-301, 1968.
30. Zuidema, G. D., W. D. Gaisford, R. S. Kowalczyk, and E. F. Wolfman, Jr.
Whole-body hypothermia in ammonia intoxication. Effects on monkeys
with portacaval shunts. Arch. Surg. 87:578-582, 1963.
489
-------
UREA AND AMMONIA TOXICITY IN RUMINANTS
Urea and various ammonium salts have been used for several
years as nonprotein nitrogen sources in ruminant nutrition. Urea
is used much more widely for this purpose than are the ammonium
compounds. Urea is hydrolyzed to ammonia and carbon dioxide by
the ruminal bacteria. The released ammonia is then utilized by
the ruminal microorganisms to synthesize microbial protein. The
microbial protein is then digested in the small intestine of the
490
-------
I
C
4)
99.9
99
95
90
80
70
60
50
40
30
20
10
5.0
1.0
0.1
Mice LD 50 - 10.84+0.203
Chick LD 50 = 10.4440.405
Trout LD50 = 17.74+1.02
Catfish LD 50- 25.73+1.01
Goldfish LD 50 = 29.34+1.01
T—I I I II I I I I I t I I II I III 1 1 1 1—I—I I I I I I I
Mice
Chonne
Catfish/'GO Id
fish
I I I I I I I I III Illl
I
10
9
I
6 7 8 9 10 15 20
Dosage, m-moles/kg body weight
25 30 35 40 45 50 60 70 80 90
FIGURE 6-3. LD50 values for armonium acetate intraperitoneally administered in mice, chicks,
rainbow trout (15.6° C) , channel catfish (23.3° C), and goldfish (23.3° C).
Reprinted with permission from Wilson.26
5 o.
4
3
2
-------
ruminant and utilized as a source of dietary amino acids. These
aspects of ruminant nutrition are beyond the scope of this re-
view and are presented elsewhere.4r1^>29
The use of urea as a partial source of nitrogen in ruminant
nutrition is limited by its toxicity. The urea toxicity syndrome
has been described as being characterized by restlessness, ataxia,
•j -5
dyspnea, collapse, muscle spasm, tetany, and death. J Severe
pulmonary congestion and edema have also been observed.1»15,23,24
The toxicity has been shown electrocardiographically to result
7 92 2^ 32
in arrythmias and abnormalities of the heart; ''' Wilson
o o
et a_l. concluded that the death of an animal poisoned with either
ammonia or urea is a direct effect of ammonia on the heart. Some
adverse effects have also been observed on electroencephalograms
recorded during urea toxicity in sheep.22
High ruminal fluid ammonia content and then high blood
ammonia and urea concentrations are major signs of urea tox-
icity.8,13,14,15,16,17,22,23,24,31,33 Ifc wag initially believed
that the toxic signs were caused by severe nerve poisoning,
severe pulmonary congestion, and edema,-'-' ^/ 21 an(j that finally
death was due to circulatory collapse with generalized venous
stasis.5,21 Lewis1^ concluded that the toxic effects of urea in
ruminants were related to high ammonia content in the blood.
This increased circulating ammonia is believed to be due to a
rapid liberation of ammonia in the rumen by the action of
bacterial urease on ingested urea. Bloomfield et al.2 reported
492
-------
that the enzymatic hydrolysis of urea to ammonia and carbon
dioxide proceeded 4 times more rapidly than the corresponding
uptake of ammonia nitrogen for bacterial protein synthesis.
The absorption of this excess ammonia was shown to depend on the
pH of the nominal contents.3 These data supported the hypothesis
that the unionized ammonia penetrates the lipid layers of the
ruminal epithelium, in contrast with the impermeability of these
lipid layers to the charged ammonium ion.6
Clark et al.5 failed to produce signs of urea toxicity by
injecting dilute solutions of ammonia in sheep. For this
reason, they suggested that some toxic intermediate was pro-
duced in the rumen by the excess ammonia. It has been shown
that ammonium carbamate is an intermediate in the hydrolysis
of urea by urease.10'28'30 Kaishio e_t al.12 suggested that
ammonium carbamate may be produced in the rumen by incomplete
hydrolysis of ingested urea or by complete hydrolysis followed
by the establishment of the equilibrium known to exist in aqueous
solutions between ammonium carbamate and ammonium carbonate.
Injections of ammonium carbamate produced intoxication similar
to that observed when urea solutions were placed directly in the
abomasum.12 Hale and King also produced typical signs of urea
toxicity in sheep by intravenous injections of ammonium carbamate.
Wilson et al.32 confirmed that ammonium carbamate, when admin-
istered intravenously, resulted in typical signs of urea toxicity,
but they also found that the ammonium carbamate decomposes to
493
-------
ammonium carbonate or bicarbonate below a pH of 10,4. They re-
ported that the pharmacodynamic effects of ammonium carbamate,
ammonium carbonate, and ammonium bicarbonate were the same as
those observed in experimentally produced urea toxicosis in
sheep; this indicated that the ammonia was the toxic entity in-
volved with each of three compounds. These results agreed with
earlier work by Clark et a_l. and Coombe et a_l.,6 who observed
circulatory collapse during urea toxicosis in sheep. However,
in a more recent report, Singer and McCarty^S observed that
only one sheep died of ventricular fibrillation, and the re-
mainder of respiratory failure.
The lethal oral dose of urea is only about 0.5 g/kg of
body weight for either sheep or cattle that are unaccustomed
to dietary urea.7/9,18,20 Toxic signs become apparent as the
blood ammonia nitrogen increases to 1 mg/100 ml, with tetanic
spasms occurring at about 2 mg/100 ml; death follows.13'14'16'17'
Hemograms from acutely poisoned sheep have been de-
scribed.13 In addition to about a 15-fold increase in blood
ammonia nitrogen concentration, the following hemic changes were
recorded at death: red-cell count and hemoglobin concentration
increased by 7.9%, white-cell count decreased by 27.5%, and
packed-cell volume increased by 11.4%. Mean corpuscular volume,
mean corpuscular hemoglobin, and mean corpuscular hemoglobin
concentration were not changed substantially.
494
-------
The pathologic effects of ammonia toxicity in sheep have
recently been described. ' The changes were similar when sheep
received intraruminal injections of ammonium chloride, ammonium
sulfate, or a mixture of ammonium chloride, carbonate, phosphate,
and sulfate. General passive hyperemia and numerous petechial
and ecchymotic hemorrhages in the musculature, thymus, and
lungs were constant gross alterations. The lungs were distended
and severely congested. On microscopic examination, the pul-
monary lesions included severe hyperemia, hemorrhage, alveolar
edema, and alveolar emphysema. In the thymus, there were de-
generation and necrosis of Hassall's corpuscles and centrilobular
hemorrhages. Lesions in kidneys included severe generalized
cloudy swelling and multiple foci of early coagulative necrosis
of the proximal convoluted tubules, general hyperemia of the
glomerular tufts, and degeneration of the glomerular tuft cells.
495
-------
REFERENCES
1. Annicolas, D., H. Le Bars, J. Nugues, and H. Stmonnet. Toxicite de
1'uree chez les petits ruminants. Bull. Acad. Vet. Fr. 29:225-
230, 1956.
2. Bloomfield, R. A., G. B. Garner, and M. E. Muhrer. Kinetics of urea
metabolism in sheep. J. Anim. Sci. 19:1248, 1960. (abstract)
3. Bloomfield, R. A., E. 0. Kearley, D. 0. Creach, and M. E. Muhrer.
Ruminal pH and absorption of ammonia and VFA. J. Anim. Sci. 22:
833, 1962. (abstract)
4. Chalupa, W. Problems in feeding urea to ruminants. J. Anim. Sci. 27:
207-219, 1968.
5. .Clark, R., W. Oyaert, and J. I. Quin. Studies on the alimentary tract of
the Merino sheep in South Africa. XXI. The toxicity of urea to sheep
under different conditions. Onderstepoort J. Vet. Res. 25(1):73-
78, 1951.
6. Coombe, J. B., D. E. Tribe, and J. W. C. Morrison. Some experimental
observations on the toxicity of urea to sheep. Austral. J.
Agric. Res. 11:247-256, 1960.
7. Davis, G. K., and H. F. Roberts. Urea Toxicity in Cattle. Agricultural
Experiment Station Bulletin 611. Gainesville: University of Florida,
1959. 16 pp.
8. Dinning, J. s., H. M. Briggs, W. D. Gallup, H. W. Orr, and R. Butler.
Effect of orally administered urea on the ammonia and urea concen- •
tration in the blood of cattle and sheep, with observations on blood
ammonia levels associated with symptoms of alkalosis. Amer. J.
Physiol. 153:41-46, 1948.
496
-------
9. Gallup, W. D. L. S. Pope, and C. K. Whitehair. Urea in Rations for
Cattle and Sheep. A Summary of Experiments at the Oklahoma Agri-
cultural Experiment Station 1944 to 1952. Agricultural Experiment
Station Bulletin B-409. Stillwater: Oklahoma A. & M. College,
1953. 35 pp.
10. Gorin, G. On the mechanism of urease action. Biochim. Biophys. Acta
34:268-270, 1959.
11. Hale, W. H., and R. P. King. Possible mechanism of urea toxicity in
ruminants. Proc. Soc. Exp. Biol. Med. 89:112-114, 1955.
12. Kaishio, Y., S. Higaki, S. Horii, and Y. Awai. On the transition of
the given urea in the body of ruminants. Bull. Nat. Inst. Agric.
Sci. Ser. G. (No. 2):131-139, 1951.
13. Kirkpatrick, W. C., M. H. Roller, and R. N. Swanson. Hemogram of sheep
acutely intoxicated with ammonia. Amer. J. Vet. Res. 34:587-589,
1973.
14. Kirkpatrick, W. C. , M. H. Roller, and R. N. Swanson. Serum and tissue
ammonia nitrogen and tissue water values in ammonia-intoxicated
sheep. Amer. J. Vet. Res. 33:1187-1190, 1972.
15. Lewis, D. Ammonia toxicity in the ruminant. J. Agric. Sci. 55:111-117,
1960.
16. McBarron, E. J., and P. Mclnnes. Observations on urea toxicity in sheep.
Austral. Vet. J. 44:90-96, 1968.
17. Morris, J. G., and E. Payne. Ammonia and urea toxicoses in sheep and
their relation to dietary nitrogen intake. J. Agric. Sci. 74:
259-271, 1970.
18. Nix, R. R., and W. B. Anthony. Urea-lethal dose and toxic syndrome for
sheep. J. Anim. Sci. 24:286, 1965. (abstract)
19. Oltjen, R. R. Effects of feeding ruminants non-protein nitrogen as the
only nitrogen source. J. Anim. Sci. 28:673-682, 1969.
497
-------
20. Oltjen, R. R., G. R. Waller, A. B. Nelson, and A. D. Tillman. Ruminant
studies with diammonium phosphate and urea. J. Anim. Sci. 22:36-
42, 1963.
21. Pierson, R. E., and W. A. Aanes. Urea poisoning in ruminants: Report
of a case in feeder lambs. Allied Vet. 30:136-139, 156, 1959.
22. Rash, J. J. Physiological Chemistry of Ammonia Toxicity. M.S. Thesis.
Columbia: University of Missouri, Columbia, 1967.
23. Repp, W. W., W. H. Hale, E. W. Cheng, and W. Burroughs. The influence of
oral administration of non-protein nitrogen feeding compounds upon
blood ammonia and urea levels in lambs. J. Anim. Sci. 14:118-131, 195
24. Rummler, H. J., W. Laue, and F. Berschneider. Untersuchungen uber die
biochemischen Vorgange und uber therapeutische Massnahmen bei der
Harnstoffvergiftung der Kinder. Monatsh. Veterinaermed. 17:156-
161, 1962.
25. Rumsey, T. S., J. Bond, and R. R. Oltjen. Growth and reproductive pre-
formance of bulls and heifers fed purified and natural diets; II.
Effect of diet and urea on electrocardiograph and respiratory
patterns. J. Anim. Sci. 28:659-666, 1969.
26. Singer, R. H., and R. T. McCarty. Acute ammonium salt poisoning in sheep.
Amer. J. Vet. Res. 32:1229-1238, 1971.
27. Singer, R, H. and R. T. McCarty. Pathologic changes resulting from
acute ammonium salt poisoning in sheep. Amer. J. Vet. Res. 32:
1239-1246, 1971.
28. Sumner, J. B., D. B. Hand, and R. G. Holloway. Studies of the intermedi-
ate products formed during the hydrolysis of urea by urease. J.
Biol. Chem. 91:333-341, 1931.
29. Tillman, A. D., and K. S. Sidhu. Nitrogen metabolism in ruminants: Rate
of ruminal ammonia production and nitrogen utilization by ruminants
-- a review. J. Anim. Sci. 28:689-697, 1969.
498
-------
30. Wang, J. H., and D. A. Tarr. On the mechanism of urease action. J.
Amer. Chem. Soc. 77:6205-6206, 1955.
31. Webb, D. W., E. E. Hartley, and R. M. Meyer. A comparison of nitrogen
metabolism and ammonia toxicity from ammonium acetate and urea in
cattle. J. Anim. Sci. 35:1263-1270, 1972.
32. Wilson, R. P., I. E. Davis, M. E. Muhrer, and R. A. Bloomfield. Toxicologic
effects of ammonium carbamate and related compounds. Amer. J. Vet.
Res. 29:897-906, 1968.
33. Word, J. D., L. C. Martin, D. L. Williams, E. I. Williams, R. J. Panciera,
T. E. Nelson, and A. D. Tillman. Urea toxicity studies in the bovine.
J. Anim. Sci. 29:786-791, 1969.
499
-------
AMMONIA TOXICITY TO FISH
Ammonia is normally found in most natural water, owing
primarily to the normal biologic degradation of proteins. The
endogenous concentration is usually very low, because of the
continuous conversion of ammonia to nitrate (nitrification).
However, the ammonia concentration in polluted water may be
high enough to be lethal to fish. There is evidence that sub-
lethal concentrations of ammonia are also harmful to fish over
a long period. The major sources of exogenous ammonia in
500
-------
polluted water are sewage effluent, industrial effluent, and
various agricultural practices.
Several environmental factors affect the toxicity of
ammonia to fish. The major factor determining the aqueous
toxicity of ammonia is the pH of the water;9'46 only the unionized
ammonia was toxic, whereas the ammonium ion had little or no
toxic effect on fish. Other factors that affect the toxicity
are water temperature,16'45 dissolved oxygen concentration,9'24/27,3$
carbon dioxide content,1'26 salinity,18 acclimation to low ammonia
concentration,27'28'38 physical activity,17 and sex,15 The
specific effects of each of these factors have been critically
., 41 44
reviewed. '
Several reports on ammonia toxicity in fish have failed to
state the water pH, temperature, or oxygen concentration. These
reports indicate a wide range of ammonia concentration—2-25 mg/liter
(1.18 x 10~4 to 1.47 x 10~3 M)—as lethal for various fishes.8'40
But these factors, mainly pH and temperature, are necessary to
determine the concentration of the unionized ammonia, so such
data are often inconsistent with those obtained in more definitive
studies. Similarly, confusion in the terminology used to de-
scribe concentration ha.s caused considerable problems in com-
paring data, as well as in setting up guidelines for safe
limits of ammonia in water. For example, the concentration
has often been expressed as the amount of ammonia per liter or
as ammonia or ammonia nitrogen in parts per million, with no
501
-------
regard to the amount of unionized ammonia (the toxic entity)
present. Chemical analysis gives a value only for total
ammonia (ionized plus unionized), and the concentration of
unionized ammonia must be calculated on the basis of the pH
and temperature of the solution. For example, an increase of
0.3 in pH (from 7.0 to 7.3) or an increase of 10°C in tempera-
ture would double the concentration of unionized ammonia in
solution.11' 37
Toxicity in Salmonids
No adverse effects were observed after fertilized eggs,
embryos, and alevins (embryos after hatching) of rainbow trout
(Salmo gairdnerii) were exposed to unionized ammonia at 3.58 mg/
liter (2.11 x 10~ M) for 24 h, until about the fiftieth day of
development.33 At that time, the susceptibility (as indicated
by mortality) increased dramatically and continued to increase
until most of the yolk was absorbed (when alevins became fry).
The median tolerance limit (24-h TLm) for 85-day-old fry was
0.068 mg/liter (4.0 x 10~6 M)—slightly less than the 0.097 mg/
liter (5.71 x 10~" M) value determined by the same workers for
adult trout under similar conditions. All bioassays were carried
out at 10°C with a pH of 8.3. Fertilization of eggs was not
prevented in unionized ammonia solutions at up to 1.79 mg/liter
(1.05 x 10™ M), the highest concentration tested. These find-
ings as to the rather high resistance of eggs and alevins of
rainbow trout to ammonia exposure are consistent with earlier
observations on eggs and "yolk fry" of brown trout (Salmo trutta) .3Q
502
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f) Q
Merkens and Downing''* compared the effects of two concen-
trations of dissolved oxygen on the lethality of unionized
ammonia at about 2.43-10.70 mg/liter U. 43-6.28 x 10~4 M) on
rainbow trout, perch (Perca fluviatilis), roach (Rutilus rutilus),
and gudgeon (Gobio gobio). The period of survival decreased in
all species tested with increasing concentrations of unionized
ammonia. Decreasing the oxygen tension increased the toxicity
of unionized ammonia, except in gudgeon, in which there was no
change. The resistance of perch and roach to lack of oxygen was
unaffected by the presence of low nontoxic concentrations of
ammonia, whereas that of rainbow trout was significantly reduced.
In an additional experiment on rainbow trout, these workers^
reported the concentrations of ammonia required to produce com-
plete mortality at 20.1°C with increasing exposure periods and
two concentrations of dissolved oxygen. The ammonia concentra-
tions at 100% air saturation for 2, 8, 36, 168, and 312 h were
4.82, 2.66, 2.32, 2.14, and 2.1 mg/liter (2.84, 1.56, 1.36, 1.26,
and 1.24 x 10~4 M). The concentrations at 45.7% air saturation
for 2, 8, 36, 168, and 312 h were 1.27, 0.96, 0.96, 0.76, and
0.76 mg/liter (7.47, 5.65, 5.65, 4.47, and 4.47 x 10~5 M). The
concentrations of ammonia that resulted in no mortality in the
above study decreased from 2.6 to 1.53 mg/liter (1.53 to 0.90
x 10~4 M) over the same periods for the higher oxygen content and
from 0.72 to 0.38 mg/liter (4.24 to 2.24 x 10~5 M) for the lower
oxygen content.
503
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Lloyd and Herbert26 reported that the toxicity of ammonia
in rainbow trout in different dilution waters (i.e., containing
different amounts of carbonate alkalinity and free carbon dioxide)
had a variation not entirely related to the concentration of the
unionized ammonia.. The evidence indicated that this variation
could be attributed to the increase in concentration of free
carbon dioxide at the gill surface, which causes decreases in pH
and in the concentration of unionized ammonia. The extent of
these decreases would depend on the initial concentration of
free carbon dioxide in the bulk of the solution. These workers
then estimated the 500-min ammonia TLm to be 0.49 mg/liter
(2.88 x 10 M) at the gill surface. These data agreed with
previous work that indicated that increasing concentrations of
carbon dioxide up to 30 ppm decreased the toxicity of ammonia
in rainbow trout; above 30 ppm, the carbon dioxide itself became
toxic to the fish.
o 5
Lloyd" presented a series of graphs based on earlier data
from which the threshold LC^Q of ammonia for rainbow trout could
be calculated. The graphs could be used to predict the threshold
LC^Q at various pH, temperature, dissolved oxygen, and free carbon
dioxide values. There was a high correlation between the pre-
dicted and observed LC values over a wide range of water condi-
tions. However, recent experiments by Ball^ gave a 24-h (asymptotic)
ammonia LC value of 0.50 mg/liter (2.94 x 10~5 M) for rainbow
trout—the same as that reported by Herbert and Shurben17 and
504
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similar to the 0.49 mg/liter (2.88 x 10~5 M) reported by Herbert
and Shurben.18 Lloyd and Orr27 also reported a 24-h ammonia
LC50 of 0.47 mg/liter (2.76 x 10~5 M) for rainbow trout fitted
with urinary catheters. These values were all lower than those
predicted by the use of the graphs of Lloyd25 for the experimental
conditions; Lloyd and Orr27 suggested that the differences may
be due to variations in test procedures. For example, the data
used by Lloyd in preparing the graphic predicting method were
obtained by transferring the fish from clear water into the test
solutions. The later experiments were conducted without trans-
fer of the fish. Even lower threshold ammonia LC5Q values of
0.2 mg/liter (1.18 x 10 M) have been given for rainbow trout
fry by Liebmann23 and for rainbow trout finger lings by Danecker,-6
but no suggestion was made to account for the increased suscepti-
bility of the fish, except that Danecker used diluted liquid
manure to produce the required ammonia concentrations.
Atlantic salmon (Salmo salar)smolts in freshwater were
found to be more susceptible to ammonia poisoning than rainbow
trout of the same size, with a 24-h LC5Q of 0.28 mg/liter
(1.65 x 10~5 M), but this difference in sensitivity was lost
at increased salinity.^°
Brown et al.3 studied the effects of fluctuating concentra-
tions of ammonia on rainbow trout, to simulate field conditions,
where the pK or ammonia concentration may vary in natural water.
The data indicated that concentration fluctuating between 1.5
505
-------
and 0.5 times the 48-h ammonia LC5Q on a 2-h cycle caused a
greater mortality than was the case for fish kept constantly at
a concentration equivalent to the 48-h LC5Q. However, exposure
of fish to the same concentration fluctuation at 1-h intervals
resulted in mortality similar to that obtained with constant
exposure to the 48-h LC5Q. It was noted that the increased
mortality with the 2-h cycle was observed when the fish were
transferred from the low to the high concentration of ammonia.
It has been suggested that it took 1-2 hr for the ammonia to
have a definite physiologic effect on the fish.41 This suggestion
was based on the work of Lloyd and Orr,27 which indicated that
sublethal concentrations of ammonia induce a marked diuretic
effect in rainbow trout. These workers and others28'38 have
shown that fish can acclimate to some extent to sublethal con-
centrations of ammonia. It was suggested that the fish may be
able to increase their rate of ammonia detoxification during
acclimation by an increase in their permeability to water, thus
increasing the urinary removal of ammonia.27
Toxicity in Other Species
Ball2 studied the acute toxicity of ammonia in rainbow trout
and four species of coarse (cyprinid) fish—bream (Abramis brama) ,
perch (Perca fluviatilis), roach (Rutilus rutilus), and rudd
CScardinius erythrophthalmus). The rainbow trout responded more
quickly than the coarse fish, so a longer period than expected
(24 h for rainbow trout) was necessary to obtain asymptotic LC50
506
-------
o for the coarse fish. The asymptotic ammonia LC5Q values
for roach, rudd, bream, and perch were 0.42, 0,44, 0,50, and
0.35 mg/liter C2.47, 2.59, 2.94, and 2,06 x 10~5 M), respectively.
To obtain the asymptotic LC5Q values, median lethal concentra-
tions (LC5Q) were determined for increasing intervals until the
curvilinear plot of LC5Q against time on double-logarithm paper
became asymptotic to the time axis. For the coarse fish, this
time ranged from 2.5 to 4 days. Although the coarse fish showed
a greater resistance to the ammonia within 24 h, the resulting
asymptotic LC5Q values were quite similar to the 0.50 mg/liter
(2.94 x 10 M) determined for rainbow trout. These values are
of considerable interest for field application, but it is diffi-
cult to compare them with other data, because most LC,-_ values
have been determined en a short-term (24-h) basis.
The toxicity of unionized ammonia has been determined for
striped bass (Morone saxatilis) and stickleback (Gasterosteus
aculeatus) by static bioassay at 15°C and 23°C in freshwater,
brackish water (33% seawater), and seawater.14 The 96-h ammonia
TLm values for striped bass in milligrams per liter were as
follows: at 15°C, 1.36 (8.0 x 10~5 M) in freshwater, 1.36
(8.0 x 10~5 M) in brackish water, and 0.97 (5.71 x 10~5 M) in
seawater; and at 23°C, 0.92 (5.41 x 10~5 M) in freshwater, 1.02
(6.0 x 10~5 M) in brackish water, and 0.73 (4.29 x 10~5 M) in
seawater. The 96-h TLm values for sticklebacks were as follows:
15°C, 1.02 (6.0 x 10~5 M) in freshwater, 2.52 (1.48 x 10~4 M)
-------
in brackish water, and 5,05 (2.97 x 10~4 M) in seawater; and at
23°C, 0.88 (5.18 x 10~5 M) in freshwater, 1.16 (6.82 x 10"5 M)
in brackish water, and 1.12 C6.59 x 10~5 M) in seawater. The
authors pointed out the need to determine the TLm values for
several species before ammonia waste discharge requirements
could be made. For example, they cited that an objective of
one-tenth the 96-h TLm for ammonia waste in seawater at 15°C,
based on stickleback data, may permit concentrations of
unionized ammonia much greater than one-tenth of the 96-h TLm for
striped bass determined under similar conditions. Therefore,
on the basis of this toxicity bioassay application factor, the
striped bass would not be adequately protected. When the problem
is compounded by natural variations in pH and difficulties in
assaying ammonia, the protection of all fish is even more un-
certain.
Several other reports have dealt with the toxicity of
ammonia in fish; however, because of inconsistencies in reporting
and lack of information concerning the pH, temperature, and oxygen
content of the water during the tests, these reports offer little
assistance in making recommendations concerning the toxic concen-
trations of ammonia in freshwater f ish. 8 ,10 ,12 ,13 ,15, 22 ,34,38,40
Toxicity of Ammonia in the Presence of Other Materials
Several tests of the toxicity of mixtures of ammonia and
other toxic materials in rainbow trout have been reported.
Wuhrmann and Woker46 found that a mixture of ammonia and hydrocyanic
508
-------
acid was more toxic than either substance alone. Experimental
results have indicated that the toxicity of some mixtures—
such as ammonia and phenol, ammonia and zinc sulfate,^ and
ammonia and copper sulfate19—was additive; i.e., the toxicities
of the individual poisons could be added together to yield the
toxicity of the mixture. Brown et al.3 found that mixtures of
zinc, phenol, and ammonia yielded LC50 values similar to the
sums of the individual toxic fractions of components. However,
when zinc predominated in the mixture, this approach tended to
overestimate the toxicity of the mixture.
Vamos and Tasnadi™ reported using cupric sulfate success-
fully in reducing the toxicity of ammonia in carp ponds.
Effects of Sublethal Exposure to Ammonia
12 ~~
Flis studied the short-term morphologic changes induced
in various tissues of carp by toxic concentrations of ammonia.
The ammonia caused regressive changes in the carp, mainly in the
organs directly exposed, such as the skin, gills, and intestine;
these changes were necrobiotic and induced necrosis, as well as
disturbances in the circulatory system, such as congestion and
hemorrhage. In another study, Flis found that prolonged ex-
posure of carp (up to 35 days) to sublethal concentrations of
ammonia resulted in more harmful effects than the short-term
treatment with a toxic concentration. Severe necrobiotic and
necrotic changes with tissue disintegration occurred in the
carp organs. Various defense reactions were also observed, in
the form of abundant mucus secretion and profuse cell infiltration.
509
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Burrows4 reported that concentrations of unionized ammonia
as low as 0.002 mg/liter (1.18 x 10~7 M) in continuous exposure
for 6 weeks produced extensive hyperplasia of the gill epithelium
in chinook salmon (Oncorhynchus tshawytscha) fingerlings. He
also found that prolonged but intermittent exposure to unionized
ammonia reduced growth rate and physical stamina. It was postu-
lated that continuous ammonia exposure is the precursor of
bacterial gill disease.
Sigel e_t al_. ^ observed that high concentrations of total
ammonia, 0.65-0.70 M, in a recirculating seawater system reduced
serum protein and caused bulbous skin lesions in the shark.
Sharks exposed to total ammonia at less than 0.01 M showed no
adverse effects. Because the pH and temperature of the water
were not reported, it is not possible to calculate the concen-
tration of unionized ammonia in the system; however, these are
extremely high concentrations of ammonia.
Use of Ammonia in Fishery Management
Ammonia has been studied as a repellent of green sunfish.^
A concentration of 1.7 mg/liter (1.0 x 10~4 M) had no effect,
but the fish were repelled at 8.5 (5.0 x 10~4 M) ; at 10. and 22
mg/liter (.5.88 and 12,94 x 10"4 Ml, the; fish died before they
could move out of the area containing the ammonia. At 1,7
mg/liter (1.0 x 10~4 M), the green sunfish were observed gulping
near the surface, although the water contained oxygen at 5.2
mg/liter, Jones20 reported that the three-spined stickleback
510
-------
avoided high concentrations of ammonia, but was attracted to
low concentrations. Shelford34 reported that fish did not
avoid toxic concentrations of ammonia. It was concluded from
the above study36 that ammonia, at the concentrations needed
to repel fish, is so rapidly fatal that it would not be suitable
for use as a fish repellent.
Anhydrous ammonia has been used experimentally in fishery
management in attempts to develop a technique for simultaneous
control of fish populations, control of submerged vegetation,
and fertilization.7'21'31'32'42'43 Ammonia was chosen for this
purpose because it is a naturally occurring compound that does
not leave a persistent nonbiodegradable residue. On the basis
of a review of the previous work, Champ and co-workers pre-
sented a detailed study of the various effects of anhydrous
ammonia treatment of impounded water. In addition to the
effects on fish and other aquatic organisms, they determined
the effects on pond pH; concentrations of total and phenol-
phthalein alkalinity (bicarbonate, carbonate, and hydroxide),
carbon dioxide, oxygen, nitrate, and ammonia; total hardness
(Ca and Mg2+); and water temperature. A pond with a surface
area of 1.78 ha was treated with 1,158 kg of anhydrous ammonia
(for a calculated ammonia concentration of 28.8 mg/liter, or
1.69 x 10~3 M) in November 1968. The substance was bubbled
from a mobile farm fertilizer tank through plastic tubes placed
0.6 m from the bottom of the lake at three points. Chemical,
511
-------
physical, and biologic data were taken 1 week before, on the
day of, and at selected intervals for 12 months after treatment.
Ammonia nitrogen concentrations before treatment were 0.2-0.4
mg/liter (ammonia at 1.43-2.86 x 10~5 M) . On the day after
treatment, the ammonia nitrogen stabilized at 37.7 mg/liter
(ammonia at 2.68 x 10 M); it gradually declined to 5,0 ppm
(ammonia at 3.57 x 10 M) after 3 months. The pH before treat-
ment was 6.9. A maximal pH of 10.3 was recorded during treatment,
and it stayed above 9.0 for 2 weeks after treatment. Titratable
carbon dioxide decreased as the pH and carbonates increased.
Phytoplankton counts were reduced by 96% and zooplankton counts
by 99% after treatment. Rooted aquatic vegetation was destroyed.
Dead frogs and tadpoles were seen. The most adversely affected
macroinvertebrates were crayfish and freshwater shrimp. The
fish kill (16 species) seemed to be total: no live fish were
taken by trawl or seine and none were seen after treatment.
Champ et al. concluded that anhydrous ammonia was an
effective fish poison. In this study, a toxic concentration
of ammonia persisted for several months. These workers suggested
that the low water temperatures contributed to the persistence
of the ammonia, inasmuch as, in experimental applications to
smaller ponds in the warm months,21 the ammonia fell to nontoxic
concentrations in less than a month. The ammonia content had
declined in the spring, so the pond could be restocked. Although
the phytoplankton was initially decimated, it had regained to
512
-------
about a threefold increase over the initial population by July.
The zooplankton community was slow and erratic in its recovery,
with a population below the pretreatment quantity persisting
for about 11 months. The species composition of the zooplankton
was also altered. The most noticeable effect was a complete
eradication of rooted vascular plants, even at the end of the
12-month sampling period.
513
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REFERENCES
1. Alabaster, J. S., and D. W. M. Herbert. Influence of carbon dioxide on
the toxicity of ammonia. Nature 174:404, 1954.
2. Ball, I. R. The relative susceptibilities of some species of fresh-water
fish to poisons. I. Ammonia. Water Res. 1:767-775, 1967.
3, Brown, V. M., D. H. M. Jordan, and B. A. Tiller. The acute toxicity to
rainbow trout of fluctuating concentrations and mixtures of ammonia,
phenol and zinc. J. Fish Biol. 1:1-9, 1969.
4. Burrows, R. E. Effects of Accumulated Excretory Products on Hatchery-
Reared Salmonids. U. S. Bureau of Sports Fisheries and Wildlife
Research Report No. 66. Washington, D. C.: U. S. Government Print-
ing Office, 1964. 12 pp.
5. Champ, M, A., J. T. Lock, C. D. Bjork, W. G. Klussmann, and J. D.
McCullough, Jr. Effects of anhydrous ammonia on a central Texas
pond, and a review of previous research with ammonia in fisheries
management. Trans. Amer. Fish. Soc. 102:73-82, 1973.
6. Daneeker, E. Cited in Water Quality Criteria for European Freshwater
Fish. See reference 41.
7. DiAngelo, S., and W. M. Spaulding, Jr. Cited in Champ jat a±. See
Reference 5.
i
8. Doudoroff, P., and M. Katz. Critical review of literature on the toxicity
of industrial wastes and their components to fish. I. Alkalies,
acids, and inorganic gases. Sewage Ind. Wastes 22:1432-1458, 1950.
9. Downing, K. M., and J. C. Merkens. The influence of dissolved-oxygen
concentration on the toxicity of un-ionized ammonia to rainbow trout
(Salmo gairdnerii Richardson). Ann. Appl. Biol. 43:243-246, 1955.
514
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10. Ellis, M. M. Detection and measurement of stream pollution. Bull. U. S.
Bur. Fish. 48:365-437, 1940.
11. Emerson, K., R. C. Russo, R. E. Lund, and R. V. Thurston. Aqueous ammonia
equilibrium calculations: Effect of pH and temperature. J. Fish.
Res. Board Can. 32:2379-2383, 1975.
12> Flis, J. Anatomicohistopathological changes induced in carp (Cyprinus
carpio L.) by anmonia water. Part I. Effects of toxic concentra-
tions. Acta Hydrobiol. 10:205-224, 1968.
13. Flis, J. Anatomicohistopathological changes induced in carp (Cyprinus
carpio L.) by ammonia water. Part II. Effects of subtoxic concentra-
tions. Acta Hydrobiol. 10:225-238, 1968.
14. Hazel, C. R., W. Thomsen, and S. J. Meith. Sensitivity of striped bass
and stickleback to ammonia in relation to temperature and salinity.
Calif. Fish Game 57:138-153, 1971.
15. Hemens, J. The toxicity of ammonia solutions to the mosquito fish
(Gambusia affinis Baird & Girard). Inst. Sewage Purif. J. Proc.
1966:265-271.
16. Herbert, D. W. M. The toxicity to rainbow trout of spent still liquors
from the distillation of coal. Ann. Appl. Biol. 50:755-777, 1962.
17. Herbert, D. W. M., and D. S. Shurben. A preliminary study of the effect
of physical activity on the resistance of rainbow trout (Salmo
gairdnerii Richardson) to two poisons. Ann. Appl. Biol. 52:321-
326, 1963.
18. Herbert, D. W. M. , and D. S. Shurben. The susceptibility of salmonid
fish to poisons under estuarine conditions. II. Ammonium chloride.
Int. J. Air Water Pollut. 9:89-91, 1965.
19. Herbert, D. W. M., and J. M. Vandyke. The toxicity to fish of mixtures of
poisons. II. Copper-ammonia and zinc-phenol mixtures. Ann. Appl.
Biol. 53:415-421, 1964.
515
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20. Jones, J. R. E. The inorganic gases, pp. 100-105. In Fish and River
Pollution. London: Butterworths, 1964.
21. Klussmann, W. G., M. A. Champ, and J. T. Lock. Utilization o£ anhydrous
ammonia in fisheries management, pp. 512-520. In J. W. Webb, Ed.
Proceedings of the Twenty-third Annual Conference, Southeastern Assoc
ation of Game and Fish Commissioners, Mobile, Alabama, October 1969.
22. Knepp, G. L., and G. F. Arkin. Ammonia toxicity levels and nitrate toler-,
ance of channel catfish. Prog. Fish Cult. 35:221-224, 1973.
23. Liebmann, H. Cited in Water Quality Criteria for European Freshwater
Fish. See reference 41.
24. Lloyd, R. Effect of dissolved oxygen concentrations on the toxicity of
several poisons to rainbow trout (Salmo gairdnerii Richardson). J.
Exp. Biol. 38:447-455, 1961.
25. Lloyd, R. The toxicity of ammonia to rainbow trout (Salmo gairdnerii
Richardson). Water Waste Treat. J. 8:278-279, 1961.
26^ Lloyd, R., and D. W. M. Herbert. The influence of carbon dioxide on the
toxicity of un-ionized ammonia to rainbow trout (Salmo gairdnerii
Richardson). Ann. Appl. Biol. 48:399-404, 1960.
27. Lloyd, R., and L. D, Orr. The diuretic response by rainbow trout to
sub-lethal concentrations of ammonia. Water Res. 3:335-344, 1969.
28. Malacea, I. Cited in Lloyd and Orr, 1969. See reference 27.
29. Merkens, J. C., and K. M. Downing. The effect of tension of dissolved
oxygen on the toxicity of un-ionized ammonia to several species of
fish. Ann. Appl. Biol. 45:521-527, 1957.
30. Penaz, M. Cited in Water Quality Criteria for European Freshwater Fish.
See reference 41.
31. Ramac hand ran, V. Observations on the use of ammonia for the eradication
of aquatic vegetation. J. Sci. Ind. Res. 19C:284-285, 1960. (letter)
516
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32. Ramachandran, V. Cited in Champ et al., 1973. See reference 5.
33. Rice, S. D., and R. M. Stokes. Acute toxicity of ammonia to several devel-
opmental stages of rainbow trout, Salmo gairdnerii. Fish. Bull. U. S.
Nat. Mar. Fish. Serv. 73:207-211, 1975.
34. Shelford, V. E. An experimental study of the effects of gas waste upon
fishes, with especial reference to stream pollution. Bull. 111.
State Lab. Nat. Hist. 11:381-412, 1917.
35. SLgfil, H. M., G. Ortiz-Muniz, and" R. B. Shouger. Toxic effect of ammonia
dissolved in sea water. Comp. Biochem. Physiol. 42A:261, 1972.
36 Summerfelt, R. C., and W. M. Lewis. Repulsion of green sunfish by certain
chemicals. J. Water Pollut. Control Fed. 39:2030-2038, 1967-
37. Trussell, R. P. The percent un-ionized ammonia in aqueous ammonia solu-
tions at different pH levels and temperatures. J. Fish. Res. Board
Can. 29:1505-1507, 1972.
s
38. Vamos, R. Ammonia poisoning in carp. Acta Biol. (Szeged) 9:291-297, 1963.
39. Vamos, R. , and R. Tasnadi. Ammonia poisoning in carp. 3. The oxygen con-
tent as a factor in influencing the toxic limit of ammonia. Acta
Biol. (Szeged) 13(3-4):99-105, 1967.
40. Wallen, I. E., W. C. Greer, and R. Lasater. Toxicity to Gambusia affinis
of certain pure chemicals in turbid waters. Sewage Ind. Wastes 29:
695-711, 1957.
41. European Inland Fisheries Advisory Committee. Water Quality Criteria
for European Freshwater Fish. Report on Ammonia and Inland Fish-
eries. EIFAC Technical Paper 11. Rome: Food & Agricultural
Organization of the United Nations, 1970. 12 pp.
42. Whitley, J. R. , 1964. Cited in Champ .et al., 1973. See reference 5.
43. Whitley. J. R. , 1965. Cited in Champ et al., 1973. See reference 5.
517
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44. Willingham, W. T. Ammonia Toxicity. Control Technology Branch, Water
Division, U. S. Environmental Protection Agency, Region VIII.
EPA-908/3-76-001. Denver: U. S. Environmental Protection Ag«ncy,
1976. 103 pp.
45. Woker, H. Cited in Water Quality Criteria for European Freshwater Fish.
See reference 41.
46_ Wuhraann, K., and H. Woker. Experiment el le Untersuchungen uber die
Ammoniak- und Blausaurevergiftung. Schweiz. Z. Hydrol. 11: 210-
244, 1948.
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ADVERSE EFFECTS OF ATMOSPHERIC AMMONIA ASSOCIATED WITH CONFINED
HOUSING OF DOMESTIC ANIMALS
Poultry
Laboratory studies have indicated that poultry generally
are less susceptible to air pollution than other farm animals.
The reported toxic effects in poultry can be largely prevented
through proper management practices. Thus, air pollution does
not appear to constitute a serious health hazard to commercial
poultry operations.-^ However, several pollutants do have toxic
effects. Most of these are due to bacterial conversion of poultry
waste into ammonia, hydrogen sulfide, carbon dioxide, and
methane.24
In colder climates, many poultry houses cannot maintain proper
ventilation rates; therefore, gas production in the manure may
build up to a harmful point. Ammonia has been found at over
50 ppm in modern poultry houses and up to 200 ppm in poorly
o 9 p
ventilated poultry houses. '
519
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An idiopathic ocular disorder, designated as keratoconjuncti-
vitis, in young chicks was first described by Bullis et al.,
who attributed it to environmental factors in the rearing facili-
ties „ Affected birds tended to group together in the darker
corners of the pens. There appeared to be marked photophobia
and evidence of ocular irritation. Some birds kept their eye-
lids closed almost continuously, and there was considerable
rubbing of the eyes, as shown by the soiled condition of the
wing feathers. Exposure to direct sunlight appeared to increase
the irritation. Only rarely were exudates noted, but these were
attributed to secondary infections; in an occasional severely
affected chick the eyelids stuck together in the presence of
considerable exudate. Lacrimation was minimal, but increased
when the eyelids were manipulated during examination. After
removal from the contaminated area, affected birds exhibited
almost complete anorexia for 7-10 days with a rapid weight loss.
The most prominent lesion of this disturbance was an erosion of
the surface of the cornea. The periphery of the eroded area was
irregular, and the shape was extremely variable. The involvement
was usually bilateral, but varied widely in severity from one
eye to the other. The eroded area varied from a small focus
of 2-3 mm in diameter to nearly the entire surface of the central
portion of the cornea. When the eroded area was small, it was
posterior to the center of the cornea. Perforation was rarely
noted. There was marked congestion of the conjunctiva with
520
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various degrees of edema. Panophthalmitis was not noted. The
lesions persisted for from a few days to 3 months, with an
average of about a month in birds held under observation at the
laboratory. A slight cloudiness of the cornea, attributed to
cicatricial tissue, persisted for a while in some birds. In-
filtration and irregularity of the iris, suggested to be due to
concurrent lymphomatosis, was noted occasionally. There was
some distortion of the eyelids in advanced cases, giving the
appearance of an enlargement of the eye.
Initial attempts to transmit this condition were unsuccess-
ful. Both the transfer of ocular exudates from the eyes of
affected chicks to healthy birds with cotton swabs and contact
exposure in cages for a month or more failed to produce the
disease. Ammonium hydroxide was applied to the litter (no con-
centration reported) in a paper-covered cage 1-3 times a day
over a 2-week period; it produced discomfort after each appli-
cation, but no lesions appeared in the young chicks. Later
workers have been able to induce the syndrome by exposing young
chicks to atmospheric ammonia.2'6'8'16'25'28'29 In general,
ammonia concentrations of about 60 ppm or above caused kerato-
conjunctivitis. When the concentration fell below this, the
9 o
speed of recovery depended on the severity of the ulcers. °
Anderson et al.2 reported that chickens exposed continuously
to ammonia at 20 ppm had some signs of discomfort, including
rubbing of the eyes, slight lacrimation, anorexia, and later
521
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weight loss. Chickens exposed to ammonia at 20 ppm for as short
a period as 72 h were more susceptible to aerosol injection of
Newcastle disease virus. Gross and microscopic damage to the
respiratory tract could be detected after 6 weeks of continuous
28
exposure of ammonia at 20 ppm. Valentine reported tracheitis
in chicks exposed to ammonia at 60-70 ppm. The breathing of the
birds was audible as moist rales with bubbling sounds. At post-
mortem examination, some of the birds had slight congestion of
the lungs with excess mucus in the respiratory tract. The mucous
membranes of the trachea were much thicker than in the control
birds, and there was leukocytic infiltration of the tissue. It
was suggested that this tracheitis may predispose the affected
birds to respiratory diseases, with the added risk of secondary
infections.
Charles and Payne reported that ammonia at 100 ppm caiised
reductions in carbon dioxide production and depth of respira-
tion and a 7-24% decrease in the respiration rate of laying hens.
These workers also observed that broilers reared to 28 days of
age in atmospheres containing high concentrations of ammonia
consumed less food and grew slower. Pullets reared in high-
ammonia atmospheres matured up to 2 weeks later than pullets
reared in ammonia-free atmospheres.
Airsacculitis, one of many respiratory diseases in poultry,
has been associated with high ammonia concentrations in poultry
houses.15 High concentrations of dust were also noted during
522
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periods of winter confinement, when the high ammonia concentra-
tions were observed. Anderson et al.4 found that high concen-
trations of dust (0.6-1.0 mg/ft3, or 21-35 mg/m3) in the
atmosphere significantly increased the incidence and severity
of air sac lesions in turkeys. Flocks with a high rate (47%)
or a low rate (2%) of infection with Mycoplasma meleagridis
were similarly affected. No significant interaction between
dust and ammonia concentrations (up to 30 ppm) with regard to
effect on the development of air sac lesions was found.
Mortality and feed conversion were not significantly affected
by exposure to dust and ammonia. There was considerable loss
of cilia from the epithelium of the tracheal lumen and an in-
crease in mucus-secreting goblet cells in turkeys exposed to
high concentrations of dust and ammonia. Areas of consolidation
and inflammation were frequently observed in lungs of these
turkeys. The air sac lesions ranged from mild (lymphocytic
infiltration) to severe (masses of caseous material).
Airsacculitis has also been experimentally induced in
chickens exposed to atmospheric ammonia and the stress of
1 7
infectious bronchitis vaccination. Air sac lesions were
observed and several severe cases of airsacculitis were seen
in chickens maintained in chambers containing ammonia at 25
and 50 ppm for 8 weeks. Chickens receiving ammonia at 25 ppm
had a total air sac score of 46; chickens receiving 50 ppm had
a total score of 64. These scores indicated that ammonia stress
523
-------
and infectious bronchitis vaccination may cause airsacculitis
in Leghorns, even if they respond negatively to tests for
Mycoplasma gallisepticum and M. synoviae. The severity of the
air sac involvement was directly related to the concentration
of ammonia to which the birds were exposed.
Kling and Quarles-^ also studied the effect of atmospheric
ammonia and the stress of infectious bronchitis vaccination on
Leghorn male chicks. Ammonia at 0, 25, or 50 ppm was introduced
into 12 controlled-environment chambers containing the birds.
Ammonia was introduced continuously into the test chambers from
the fourth to the eighth week of the experiment. An infectious
bronchitis vaccination was administered to all chicks at 5 weeks
of age. Body weights and feed efficiencies were determined at
4, 6, and 8 weeks of age. At 4, 5, 6, and 8 weeks of age, lung
and bursae of Fabricius weights, hematocrits, and air sac scores
were determined. Body weights and feed efficiencies were signifi-
cantly reduced in the ammonia chambers. The bursae of Fabricius
of the ammonia-stressed chickens were significantly larger than
those of controls at 5 weeks of age and significantly smaller
at 8 weeks of age. Chickens grown in ammoniated environments
had significantly larger lungs at 8 weeks. Hematocrits were not
significantly different among the treatments. Tbtal air sac
scores were significantly higher in the ammonia-stressed chickens
at 8 weeks. The results indicated that chickens were affected
by the stress of ammonia at 25 or 50 ppm and the added infectious
bronchitis vaccination.
524
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A similar set of experiments with broilers have been
reported. 3 Eighty broiler chicks were randomly assigned to
each of 12 chambers in a controlled-environment building.
Anhydrous ammonia gas was introduced into the test chambers
from 4 to 8 weeks of age; treatments consisted of ammonia at
0, 25, and 50 ppm. Chicks were vaccinated at 5 weeks of age
with a commercial strain of infectious bronchitis dust vaccine.
Eight-week body weights and feed efficiencies of broilers ex-
posed to ammonia were significantly reduced. At 6 and 8 weeks
of age, severe airsacculitis was observed in the ammoniated
broilers. During the 8-week period, airborne bacteria were
significantly greater in the chambers with ammonia at 25 and
50 ppm. Ammonia and infectious bronchitis vaccination stress
did not affect meat flavor, tenderness, or juiciness, but sig-
nificantly increased condemnations and undergrade carcasses.
Charles and Payne^ studied the effects of graded concen-
trations of atmospheric ammonia on the performance of laying
hens. At 18°C and 67% relative humidity, ammonia at 105 ppm
significantly reduced egg production after 10 weeks of exposure.
No effects were observed in egg quality. Food intake was reduced,
and weight gain was lower. No recovery in egg production occurred
when the treated groups were maintained for an additional 12
weeks in an ammonia-free atmosphere. Similar results were ob-
served at 28°C under similar conditions. Earlier work had
indicated that egg quality could be affected by ammonia exposure.9
525
-------
Freshly exposed laid eggs were exposed to various concentrations
of ammonia in a desiccator for 14 h at room temperature and then
moved to normal atmosphere for another 32 h at 50°C before ex-
amination. There was evidence of ammonia absorption into the
eggs and significant impairment of interior egg quality, as
measured by Haugh units, pH, and transmission of light. The
authors suggested that the quality of eggs left all day in hen-
houses containing high concentrations of ammonia might be affected.
Swine
The following hypothetical situation has been presented by
Curtis^ to illustrate the potential hazards of rearing swine
over a waste collection pit with inadequate ventilation:
Consider a pig held for a day in a closed box.
Assume that the box is a 1.5 m cube, that its
sides are impervious to everything but heat,
water vapor and 0- and that it has mechanisms
to maintain standard conditions of atmospheric
pressure and temperature. Assume that the pig
weighs 80 kg and consumes 3.5 kg daily of a
13% crude protein (thus 2.1% N) corn-soybean
meal diet. If the diet is 85.5% corn and
12.5% soybean meal, and if corn consists 0.2%
and soybean meal 0.4% of S, then the diet will
be about 0.22% S. Assume that 70% of the N and
S ingested is excreted..., that the pig excretes
526
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0.5 kg of volatile solids daily, of which
40% eventually becomes C02 and 60% CH4-..and
that the excreta accumulates and decomposes
in the box. Assume that at equilibrium
half of the daily excreta is microbially
decomposed each day, producing NH3, H2S,
C02 and CH4- Assume that the pig [excretes]
1,000 liter of C02 daily via respiration....
It can be shown that—-under these assumptions —
about 40 liters of NH3, 2 of H2S, 85 of C02
and 125 of CH^—plus respiratory C02—would
be evolved daily. Thus these amounts .would
have accumulated in the box by the end of the
day, increasing (at constant pressure) the
volume of the pig's atmosphere from the
original 3,375 liters to 4,617 liters. The
approximate concentrations of pollutant gases
(volume/volume basis) which would consequently
obtain in the atmosphere, if the gases did not
interact, would be:
NH3—8,700 ppm; H2S — 435 ppm; C02 — 235,000 ppm
and CH.—27,000 ppm. Since in humans NH3 at
around 700 ppm irritates eyes and nose, H2S
at 500 ppm causes nausea and C02 at 40,000
ppm causes drowsiness, and since CH^ is
521
-------
explosive at 50,000 ppm..., we might guess
that—-if the pig survived the day—it would
be a pitiably teary-eyed, wet-nosed, en-
auseated, dizzy beast in a potentially ex-
plosive environment. Enclosure of an animal
in a house over a waste pit is a precarious
situation.
The increased use of confined housing of swine has caused
concern about the purity of the air within the buildings and
its effects on performance. Bacterial decomposition of excreta
collected and stored beneath slotted floors in enclosed buildings
produces a number of gases, including ammonia, carbon dioxide,
hydrogen sulfide, and methane.-^ Miner and Hazen^2 reported a
range of ammonia concentrations of 6-35 ppm determined 1 ft
(30.5 cm) above the floor level in a swine-rearing facility.
The normal range in solid-floor confinement units was found
to be less than 50 ppm, but it could be higher during cold
months, when ventilation was at a minimum, particularly if the
f\ "7
floor was heated. ' The normal ammonia concentration in the air
above slotted floors was said to be about 10 ppm, but this could
be increased by a factor of 5-10 by stirring the stored manure.
Ammonia at 280 ppm was found to be toxic to swine.^6 when a
30-kg gilt was placed in a chamber containing ammonia at 280 ppm,
frothing of the mouth and excessive secretions about the nose
and mouth were observed. Aftei^ approximately 3 h, the frothing
528
-------
disappeared, but the excessive secretions and occasional sneezing
and shaking of the head persisted. After 36 h in this environ-
ment, convulsions occurred and breathing was extremely short and
irregular. The ammonia supply was then turned off, and the com-
partment was completely ventilated. Although the pig continued
to have convulsions for at least 3 h, her condition improved.
Seven hours after the convulsions ceased, she appeared completely
normal, except for occasional sneezing and head-shaking.
26
Stombaugh et al. exposed pigs to atmospheric ammonia at
10, 50, 100, and 150 ppm for 5 weeks at 21.1°C and 77% relative
humidity. The ammonia concentration had a highly significant
adverse effect on feed consumption and average daily gain.
During the trials, the high ammonia concentrations appeared to
cause excessive nasal, lacrimal, and mouth secretions. This
was more pronounced at 100 and 150 ppm than at 50 ppm. After
3 or 4 days on trial, the pigs exposed to 50 ppm apparently
adjusted, and the secretory rate was only slightly above that
in the control animals. After 1 or 2 weeks of exposure, the
signs observed in all animals appeared to lessen gradually.
The frequency of coughing was observed to be higher in the
animals exposed to the higher ammonia concentrations. Examina-
tion of the respiratory tract from some of the animals revealed
no significant gross or microscopic differences related to the
ammonia.
529
-------
Because organic dust reduces air quality in hog barns,
Doig and Willoughby1^ studied the adverse effects on pigs
1-7 weeks old exposed in environmental chambers to ammonia at
100 ppm, organic dust, and combinations of ammonia and organic
dust. Conjunctival irritation was evident after the first day
of ammonia exposure and persisted for 1 week, whereas it was
apparent for 2 weeks during the ammonia and dust exposure.
Changes were not detected in appetite, mean daily gain, fre-
quency of coughing, hemograms, or total serum lactic dehydro-
genase activity- Histopathologic changes were limited to the
nasal and tracheal epithelium. A 50-100% increase in the
thickness of the tracheal epithelium with a concomitant decrease
in the number of tracheal epithelial goblet cells was detected
in pigs exposed to ammonia at 100 ppm for 2-6 weeks. Similar
lesions were detected in the nasal epithelium of pigs exposed
to ammonia and organic dust. There was no evidence of structural
damage in the bronchial epithelium or alveoli of exposed pigs.
Curtis j|t al. exposed pigs to ammonia, hydrogen sulfide,
and swine-house dust individually and in various combinations
for 17-109 days. Ammonia at 50 and 75 ppm, hydrogen sulfide
at 2 and 8.5 ppm, and dust at 10 and 300 mg/m3 were used in the
various treatments. As opposed to some of the previous reports,
ammonia alone at 50 or 75 ppm had little effect on the pigs'
performance. Only when aerial dust was applied at a very high
concentration (300 mg/m3) did it affect performance; at the
530
-------
concentration more commonly encountered under normal conditions
(10 mg/m ), it had no effect. Effects of aerial dust and
ammonia tended to be additive, but they did not interact; in
particular, aerial dust apparently did not increase the effect
of ammonia on the pigs. Hydrogen sulfide, either alone at 2
or 8.5 ppm or in combination with ammonia at 50 ppm, had little
effect on the growth rate of the pigs. With the exception of
mild conjunctivitis and blepharitis in one of the pigs exposed
to ammonia at 50 ppm, there was no evidence of structural
alterations due to experimental treatment in any organ or
tissue studied. Turbinates, tracheas and lungs of all pigs
were classified as normal after both gross and microscopic
examination. The authors concluded that rate of gain and
respiratory tract structure of growing swine, which are free
of respiratory disease, are not directly influenced by ammonia,
hydrogen sulfide, and dust at the concentrations and in the
combinations commonly encountered in the air enclosed houses
in commercial swine-production operations.
Cattle
Reports dealing with the adverse effects of toxic gases on
cattle appear to be limited to the European literature. This
is apparently because there is limited if any mass rearing of
cattle in total confinement in the United States. Albright and
Alliston have reviewed some of the problems of toxic gases
531
-------
associated with totally enclosed livestock facilities and
slotted floors with liquid-waste handling systems. They
pointed out that such manure gases as ammonia, hydrogen sul-
fide, carbon dioxide, and methane have caused acute poisoning
in cattle in Sweden and other parts of Europe in poorly ventilated
barns. They cited Swedish workers who suggested that the simul-
taneous exposure of cattle to ammonia and hydrogen sulfide re-
sults in a more pronounced effect than exposure to hydrogen
sulfide alone. The effect of ammonia and hydrogen sulfide is
said to be the same as that of ammonium hydrogen sulfide, NH4SH,
which has the ability to soften a horny substance. The chronic
manure-gas poisoning could be due to ammonium hydrogen sulfide,
but it was pointed out that other gas components may also be
contributing factors.
Marschang and Crainiceanu ^ measured the air ammonia content
(sampled at nose level of the animals) in calf stables at four
dairy farms around Temesvar, Rumania. The ammonia ranged from
0.001 to 0.20 vol % (10 to 2,000 ppm). Most of the observed values
greatly exceeded the admissible upper limits of 0.026 vol %
(260 ppm). During these periods of high ammonia concentrations,
a very high morbidity rate and a rather high mortality rate
I
were observed in the calves. These workers suggested that the
high ammonia content weakened the resistance of the animals
and thus created the conditions for development of secondary
infections. The deaths were caused mainly by various respiratory
532
-------
diseases. Autopsy indicated mainly various degrees of changes
in the lungs, mainly inflammations. Bacteriologic investigations
always concluded "nothing specific."
In a second study, Marschang and Petre measured the
ammonia content in the air of three cattle-fattening facilities
in Rumania. These animals were being fed in total confinement;
the capacities of the three operations were 300, 3,000, and
4,900 animals. The ammonia ranged from 0.003 to 2.0 vol %
(30 to 20,000 ppm). In general, the ammonia content was below
the admissible upper limit of 0.026 vol % (260 ppm) during the
summer months, but exceeded this during the winter months, when
extremely high concentrations were observed. These very high
concentrations were due primarily to blocking of the ventilation
system to maintain the necessary stall temperature. In addition,
the highest value (20,000 ppm) was observed when the cleaning
mechanism of the manure canals malfunctioned. The highest
morbidity, mainly from respiratory diseases, and mortality rates
simultaneously increased with ammonia concentration in the stalls
and decreased as some of the toxic gas concentrations decreased
to admissible points. These workers suggested that ammonia is
the most important environmental factor in producing damage in
cattle-fattening stalls. They did not refer to the growth rate
of the cattle; however, in an additional report, Marschang19
observed a marked decrease in growth rate of fattening cattle
when the ammonia content of the stable air was high.
533
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Wild Birds and Mice
Anhydrous ammonia gas has been used to exterminate wild
birds and mice from farm buildings.13 The building were sealed
one evening after removal of the livestock and then gassed with
anhydrous ammonia at 1 lb/10,000 ft3 (0.0016 kg/m3) of air space.
After 7 min of exposure, the barns were reopened. After approxi-
mately 30 min, the following wild birds and mice were removed
from two buildings: 618 starlings, 290 sparrows, 24 mice, and
two pigeons. No birds survived the ammonia treatment. Cattle
were allowed to reenter the buildings within an hour of their
reopening. This technique was recommended by these workers
because of its low cost, ease of application, and lack of
persistent residue.
534
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REFERENCES
1. Albright, J. L., and C. W. Alliston. Effects of varying the environment
upon the performance of dairy cattle. J. Anim. Sci. 32:566-577,
1971.
2. Anderson, D. P., C. W. Beard, and R. P. Hanson. The adverse effects of
ammonia on chickens including resistance to infection with Newcastle
disease virus. Avian Dis. 8:369-379, 1964.
3. Anderson, D. P., F. I. Cherms, and R. P. Hanson. Studies on measuring
the environment of turkeys raised in confinement. Poult. Sci. 43:
305-318, 1964.
4. Anderson, D. P., R. R. Wolfe, F. I, Cherms, and W. E. Roper. Influence
of dust and ammonia on the development of air sac lesions in turkeys.
Amer. J. Vet. Res. 29:1049-1058, 1968.
5. Bullis, K. L., G. H. Snoeyenbos, and H. Van Roekel. A keratoconjunctivitis
in chickens. Poult. Sci. 29:386-389, 1950.
6. Carnaghan, R. B. A. Keratoconjunctivitis in broiler chicks. Vet. Rec.
70:35-37, 1958.
7. Charles, D. R., and C. G. Payne. The influence of graded levels of
atmospheric ammonia on chickens. I. Effects on respiration and
on the performance of broilers and replacement growing stock.
Brit. Poult. Sci. 7:177-187, 1966.
8. Charles, D. R., and C. G. Payne. The influence of graded levels of
atmospheric ammonia on chickens. II. Effects on the performance
of laying hens. Brit. Poult. Sci. 7:189-198, 1966.
9- Cotterill, 0. J., and A. W. Nordskog. Influence of ammonia on egg white
quality. Poult. Sci. 33:432-434, 1954.
535
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10. Curtis, S. E. Air environment and animal performance. J. Anim. Sci. 35:
628-634, 1972.
11. Curtis, S. E., C. R. Anderson, J. Simon, A. H. Jensen, D. L. Day, and
K. W. Kelley. Effects of aerial ammonia, hydrogen sulfide and
swine-house dust on rate of gain and respiratory-tract structure in
swine. J. Anim. Sci. 41:735-739, 1975.
12. Devore, A. L., D. W. Maxson, J. L. Albright, and R. W. Taylor. How about
anhydrous ammonia for bird control? Pest. Control 35(2):24,26, 1967.
13. Day, D. I., E. L. Hansen, and S. Anderson. Gases and odors in confinement
swine buildings. Trans. Amer. Soc. Agric. Eng. 8:118-121, 1965.
14. Doig, P. A., and R. A. Willoughby. Response of swine to atmospheric
ammonia and organic dust. J. Amer. Vet. Med. Assoc. 159:1353-
1361, 1971.
15. Ernst, R. A. The effect of ammonia on poultry. Feedstuffs 40(32):40, 1968.
16. Faddoul, G. P., and R. C. Ringrose. Avian keratoconjunctivi'tis. Vet.
Med. 45:492-493, 1950.
17. Kling, H. F., and C. L. Quarles. Effect of atmospheric ammonia and the
stress of infectious bronchitis vaccination on Leghorn males.
Poult. Sci. 53:1161-1167, 1974.
18. Lillie, R. J., Ammonia, pp. 14-19. In Air Pollutants Affecting the Per-
formance of Domestic Animals. A Literature Review. Agricultural
Handbook No. 380. Washington, D. C. : U. S. Government Printing
Office, 1970.
19. Marschang, F. Der NH3-Gehalt der Stalluft und die Mastfahigkeit
erwachsener Kinder. Dtsch. Tieraerztl. Wochenschr. 79:214-216,
1972.
536
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20. Marschang, F., and E. Crainiceanu. Untersuchungen uber die Zusammenhange
zwischen Stallklima und Kalbersterblichkeit. Berl. Munch. Tierarztl.
Wochenschr. 84:417-420, 1971.
2i. Marschang, F., and C. Petre. Der NH3-Gehalt der Stalluft und sein Einfluss
auf die Morbiditat und die Tierverluste in Rindermaststallen.
Zentralbl. Veterinaermed. B18:646-654, 1971.
22. Mine*, J. R., afcd T. E. Hazen. Ammonia and amines: Components of swine-
building odor. Trans. Amer. Soc. Agric. Eng. 12:772-774, 1969.
23. Quarles, C. L., and H. F. Kling. Evaluation of ammonia and infectious
bronchitis vaccination stress on broiler performance and carcass
quality. Poult. Sci. 53:1592-1596, 1974.
24. Ringer, R. K. Adaptation of poultry to confinement rearing systems. J.
Anim. Sci. 32:590-598, 1971.
25. Saunders, C. N. Kerato-conjunctivitis in broiler birds. Vet. Rec. 70:
117-119, 1958.
26. Stombaugh, D. P., H. S. league, and W. L. Roller. Effects of atmospheric
ammonia on the pig. J. Anim. Sci. 28:844-847, 1969.
27. Taiganides, E. P., and R. K. White. The menace of noxious gases in animal
units. Trans. Amer. Soc. Agric. Eng. 12:359-362, 1969.
28. Valentine, H. A study of the effect of different ventilation rates on
the ammonia concentrations in the atmosphere of broiler houses.
Brit. Poult. Sci. 5:149-159, 1964.
29 • Wright, G. W., and J. F. Frank. Ocular lesions in chickens caused by
ammonia fumes. Can. J. Comp. Med. Vet. Sci. 21:225-227, 1957.
537
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BATS
Large colonies of Mexican free-tailed or guano bats, Tadarida
brasiliensis Mexicana, have been reported to roost in several
caves of the Southwest. These great numbers of bats (up to
100,000} produce large amounts of guano, which, on bacterial de-
composition, results in very high atmospheric ammonia concentra-
tions in the caves. The combination of ammonia with high relative
humidity has been shown to bleach the pelage of some species of
bats.1'4 Mitchell4 measured the annual fluctuation of atmospheric
ammonia in a guano bat cave and reported a range of 85-1,850 ppm.
It was impossible to enter the caves without proper gasmasks at
the higher ammonia concentrations. However, no adverse physiologic
538
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effects were noted in the bats at the high ammonia concentrations,
except for the bleaching of the hair pigments. This apparent
high tolerance to inhaled ammonia has led to studies on the
mechanism of ammonia tolerance by the guano bat^/7 and the
California leaf-nosed bat, Macrotus californicus.3
Mitchell measured several physiologic characteristics in
California leaf-nosed bats that were exposed to increasing
ammonia concentrations of 500-5,500 ppm for 9 h in gas chambers.
All concentrations above 3,000 ppm were lethal in 9 h; at 5,500
ppm, the animals died in 40 min. The blood nonprotein nitrogen
almost doubled in the exposed animals, with no significant in-
crease in urinary urea or ammonia. There was a linear decrease
in both heart rate and respiratory rate with increasing ammonia
content. Table 6-5 compares some physiologic responses to various
concentrations of ammonia by man and bats. The major pathologic
conditions attributed to ammonia toxicity in bats were marked
visceral damage, corrosion of the skin and mucous membranes,
and pulmonary edema.
Studier reported that guano bats exposed to atmospheric
ammonia at 3,000 ppm apparently filtered about 30-35% of the
ammonia during respiratory passage. This investigator suggested
that the filtering process is facilitated by the mucous lining
in the respiratory passage. He also observed that, when the
bats were removed from the ammoniated air to normal air, they
exhaled measurable amounts of ammonia. The blood pH of 7.66
539
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TABLE 6-5
Physiologic Response to Various Concentrations of Ammonia by Man and Bats3.
Physio-logic Response
Odor is detectable
Causes immediate irritation of throat
Causes irritation of eyes
Causes coughing
Maximal concentration allowable for prolonged exposure:
1-9 hb
v.
Maximal concentration allowable for short exposure: 1 h£
0.5-1 h
Dangerous for even very short exposure (0.5 h)
Rapidly fatal for short exposure (0.5 h)_
Ammonia Concentration, ppm
Man£Bat
>.53
1408
^69 8
>1,720
85-100
f^approx. 100
Unknown
^approx. 1,350
^approx. 3,500
3,000
50-100
300-500
2,500-6,500
5,000-10,000
3,000
5,000
5,500
30,000
—Derived from Henderson and Haggard and Mitchell.
—Periods used in bat study.3
-------
remained constant during extended exposure to high concentrations
of atmospheric ammonia.
Studier et al. compared the effects of increasing concen-
trations of ammonia in air on the metabolic rates and ammonia
tolerances of three species of bats—Tadarida brasiliensis
mexicana, Myotis lucifugus, and Eptesicus fuscus—and rats and
mice. Rats and mice exhibited increased oxygen consumption
when exposed to increased ammonia. Oxygen consumption in rats
ranged from 0.8 to 1.2 cm /g-h in gradients of ammonia ranging
from 0 to 5,0.00 ppm, whereas mice exhibited a rise in oxygen
consumption from 3.7 to 4.7 cm-Vg-h when exposed to 0-3,000 ppm.
Two species of bats, M. lucifugus and 13. fuscus, did not exhibit
a consistent pattern in oxygen consumption during exposure.
However, T. brasiliensis mexicana exhibited a decreased oxygen
consumption ranging from 8.8 to 2.3 cm /g-h in air containing
ammonia at 0-7,000 ppm. Table 6-6 compares the tolerance of
these animals to gaseous ammonia. One can readily observe that
the various species of bats are more tolerant to ammonia than
other mammals. Studier e_t al.7 suggested that the difference
in tolerance between M_ lucifugus and T. brasiliensis mexicana
may be explained by adaptation, inasmuch as M. lucifugus has
never been found in areas where ammonia was noticeable, whereas
T. brasiliensis mexicana is normally found in caves with very
high ammonia concentrations.
541
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TABLE 6-6
Ammonia Tolerance of Selected Mammals—
Animal
Man-
Laboratory mouse
Laboratory rat
M. californicus—
M. lucifugus
E. fuseus
T. brasiliensis
Elapsed Exposure Time until Death at Various Ammonia Concentrations
500 ppm 1,000 ppm 3,000 ppm 5,000 ppm 7,000 ppm 10,000 ppm
0.5-1 h
16 h-
16 h-
2.5-3 h
1-9 h
10-20 min
30-40 min
> 4 daysli
35-45 min
1-2 h
2-3 h
10-20 min
10-20 min
a 7
"Derived from Studier et al.
b -
—Data from Henderson and Haggard.
C R
—Data from Weedon et al.
-Data from Mitchell.3
from Studier.
-------
REFERENCES
Constantine, D. G. Bleaching of hair pigment in bats by the atmosphere
in caves. J. Mammal. 39:513-520, 1958.
Henderson, Y., and H. W. Haggard. Ammonia gas, pp. 125-126. In Noxious
Gases and the Principles of Respiration Influencing Their Action.
(2nd ed.) American Chemical Society Monograph 35. New York:
Reinhold Publishing Corporation, 1943.
Mitchell, H. A. Ammonia tolerance of the California leaf-nosed bat. J.
Mammal. 44:543-551, 1963.
Mitchell, H. A. Investigations of the cave atmosphere of a Mexian bat
colony. J. Mammal. 45:568-577, 1964.
Studier, E. H. Physiological Respiratory Adaptations to High Ammonia
Levels by Tadarida brasiliensis. the Mexican Free-Tailed Bat. Ph.D.
*
Thesis. Tucson: University of Arizona, 1967- 73 pp.
Studier, E. H. Studies on the mechanisms of ammonia tolerance of the
guano bat. J. Exp. Zool. 163:79-85, 1966.
Studier, E, H(> L. R. Beck, and R. G, lindeborg. Tolerance and initial
metabolic response to ammonia intoxication in selected bats and
rodents. J. Mammal. 48:564-572, 1967-
Weedon, F. R., A. Hartzell, and C. Setterstrom. Toxicity of ammonia,
chlorine, hydrogen cyanide, hydrogen sulphide, and sulphur dioxide
gases. V. Animals. Contrib. Boyce Thompson Inst. 11:365-385, 1940.
543
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RESPIRATORY EFFECTS OF AMMONIA IN ANIMALS
Acute Exposure
Surprisingly few animal studies have been reported in the
English literature on the acute toxic effects of ammonia on the
respiratory tract.2,5,11,12,16,17,18,21
Six rabbits exposed to ammonia at 2,200 ppm (1,540 mg/m3)
were found to have tracheal concentrations of approximately 100 ppm
(70 mg/m ) ; i.e., 95% of the ammonia was absorbed by the naso-
pharynx. This animal study confirmed earlier studies demon-
strating 78-88% retention in the nasopharynx and 92% absorption
in the mouth of human subjects. In another study, rabbits
and cats were exposed for 1 h to initial ammonia concentrations
of 5,000-12,400 ppm (3,500-8,700 mg/m ), which were considered
to approximate the LC50 of 10,000 ppm (7,000 mg/m3).2 Because
of the static method of exposure, the average exposure was esti-
mated at half or less of the intial concentrations. One group
of animals breathed normally through nose, mouth, and .throat, and
a second group inhaled directly through a tracheal cannula. In-
haling normally through the nose and mouth almost doubled the
mean survival time—to 33 h, compared with 18 h for animals in-
haling directly through a tracheal cannula. The tracheas were
normal and the bronchi only slightly hyperemic and edematous
in the former group, whereas the tracheas and to a lesser degree
the bronchi were severely congested, edematous, and necrotic in
the latter group. This demonstrates the protective absorption
544
-------
of ammonia by the upper respiratory tract. The bronchioles
and alveoli were identical in the two groups—congested, edema-
tous, and atelectatic.2 It appears that small airways and
alveoli are not protected by absorption in the upper respiratory
tract, but not enough details were presented to assess this
aspect of the study adequately.
Only one ultrastructural study on the acute toxic effects
of ammonia on the bronchioles and alveoli has been reported.^
Mice were exposed to acute lethal concentrations of ammonia
(concentrations not given) that resulted in striking alterations
in the terminal airways. The terminal bronchiolar cells demon-
strated a marked increase in secretory granules and a ballooning
of cell apex with disruption suggesting stimulation of merocrine
and apocrine secretion. There was marked edema and disruption
of alveolar type I epithelial cells, with an increased number of
empty lamellar bodies in alveolar type II epithelial cells.
Alveolar basement membrane and capillary endothelial cells
appeared normal, although there was increased clumping of intra-
capillary platelets. The effects on the large airways were not
described.
Two pairs of guinea pigs were exposed to ammonia at
5,000-6,000 ppm (3,500-4,200 mg/m3) for 5, 30, 60, or 120 min,
and then observed for 10 days.17 Within 30 sec, all exhibited
rhinorrhea and labored breathing. By 5 min, their eyes and
noses were affected and respiration was irregular. Breathing
545
-------
became shallow at 60 min, and barely perceptible at 120 rain.
The severity of respiratory distress depended on duration of
exposure. All the animals survived and appeared free of
respiratory difficulties at 10 days. However, there was no
pathologic examination of their lungs. Of four guinea pigs
exposed to ammonia at 20,000-25,000 ppm, two were removed after
5 min and recovered within a week; one of them was permanently
blind. One died with reflex apnea at 9 min, and the fourth,
exposed for 30 min, recovered (except for blindness) after
marked respiratory distress. The animals' lungs were not ex-
amined microscopically.
In contrast, when 180 mice were exposed for 10 min to
ammonia at 8,770-12,940 ppm (6,140-9,060 mg/m3), death with
convulsions began to occur after 5 min of exposure; 100 mice
died before completion of the experiment. The 80 surviving
animals recovered rapidly, but seven died between the sixth
and tenth days after exposure. Their lungs were not examined.
Mice were exposed to acute toxic concentrations of ammonia
(2,500-15,000 ppm) either alone or in combination with carbon
monoxide,, carbon dioxide, or both, as might occur during a fire.
The inhalation of two gases prolonged the time required for
animal collapse after the beginning of exposure. Inhalation
of all three gases further protected the animals by increasing
the time necessary for collapse. The mechanism for this phenomenon
is not understood.
546
-------
Chronic and Subacute Exposure
Eight rats and four mice were exposed to ammonia concentra-
tions of 1,000 ppm (700 mg/m3) for 16 h.21 One rat died after
12 h of exposure with congestion, hemorrhage, and edema of the
lungs. The others showed no ill effects, and results of gross
examination of the lungs from two mice and two rats 5 months
after exposure were normal.
In another study, 12 guinea pigs were exposed to ammonia
at 140-200 ppm (98-140 mg/m3) for 6 h/day, 5 days/week.20
Autopsy findings were normal in the four animals sacrificed
at 6 and 12 weeks. Slight but definite changes were noted in
the guinea pigs autopsied at 18 weeks. These consisted of
congestion in the spleens, livers, and kidneys and early de-
generative changes in the adrenal glands. The lungs were normal.
One pig exposed to ammonia at 280 ppm (196 mg/m ) developed
19
severe respiratory distress and convulsions by 36 h. There
was apparent complete recovery within several hours. The
lungs were not examined microscopically. In addition, four
groups of nine pigs each were continuously exposed for 5 weeks
to ammonia at 12, 61, 103, and 145 ppm (8, 43, 72, and 102
mg/m3). Signs of respiratory irritation appeared only after
exposure to the three higher concentrations, and increased with
concentration. Food intake and weight gain were inversely re-
lated to concentration. Results of gross and microscopic ex-
amination of the lungs were normal in five animals sacrificed
from each group.
541
-------
A species variation in resistance to the effects of ammonia
has been reported.12 Rabbits continuously exposed to ammonia
at 5,000 ppm (3,500 mg/m ) or 15,000 ppm (10,500 mg/m ) lived
for 53 days, compared with the 4-15 days of guinea pigs exposed
to identical concentrations. In the same study, younger ani-
mals appeared more sensitive than older animals of the same
species.
A series of studies on rats, guinea pigs, rabbits, dogs,
and monkeys revealed evidence of increasing respiratory distress
and nonspecific inflammatory changes with increasing concentra-
tions of ammonia, as well as with continuous, compared with
intermittent, exposure.33 Ammonia at 220 ppm (155 mg/m } for
8 h/day, 5 days/week, for 6 weeks produced no pathologic ab-
normalities, except focal pneumonitis in one monkey. Similar
exposures at 1,110 ppm (770 mg/m3) resulted in respiratory
distress only in the rabbits and dogs; evidence of respiratory
distress disappeared by the second week of exposure. Pathologic
examination at the end of 6 weeks of exposure revealed nonspecific
inflammatory changes only in the lungs of the rats and guinea
pigs. Continuous exposure of the animals to only 60 ppm
(40 mg/m ) for 114 days produced no evidence of toxicity or
microscopic abnormalities at necropsy. When the animals were
exposed to 680 ppm (470 mg/m3) continuously for 90 days, four
of 15 guinea pigs and 13 of 15 rats died. All animals examined
had focal or diffuse interstitial inflammation in the lungs.
548
-------
Additional studies performed only on rats revealed no tissue
abnormality in 48 rats continuously exposed to ammonia at 180
ppm (127 mg/m3) for 90 days, mild nasal irritation in 12 of 49
rats exposed to 380 ppm (262 mg/m3) for the same duration, and
death by the sixty-fifth day in 50 of 51 rats exposed to 650 ppm
(455 mg/m ) ; no necropsy was performed on the last two groups of
animals. a
Of six weanling pigs, one was sacrificed each week during
continuous exposure to ammonia at 106 ppm (74 mg/m3}.9 In-
creased thickness of tracheal epithelium and increased goblet
cells were seen by the second week of exposure. Bacterial
flora in the trachea of exposed animals did not differ from
that of controls. Simultaneous exposure to ammonia with corn
dust or cornstarch dust inhibited the effects of ammonia on the
trachea.9
Exposure to ammonia at 50 ppm (35 mg/m ) and 100 ppm
(70 mg/m3) for 2.5-3 h decreased the rate of breathing in rabbits
and increased their depth of breathing with time of exposure.15
In five rabbits exposed to 100 ppm (70 mg/m3), blood urea nitro-
gen increased from 19.4 to 24.6 mg/100 ml, and blood bicarbonate
increased from 14.3 to 18.9 mEq/liter of plasma; these altera-
tions were statistically significant. Blood pH did not change.
No microscopic abnormalities were^noted in lungs, liver, spleen,
or kidneys.
549
-------
Although pathologic alterations in the airways may not be
detected in the lungs after low exposure to ammonia, functional
alterations might occur that would make animals more susceptible
to infection. Indeed exposure to ammonia at 20-50 ppm (14-35 mg/m
significantly increased the infection rate of chickens later ex-
posed to Newcastle disease virus. Chicks exposed continuously
to 25-50 ppm (18-35 mg/m3) from the age of 4 weeks to 8 weeks were
vaccinated with an infectious bronchitis vaccine at 5 weeks of
age. Ammonia stress and vaccination resulted in reduced chicken
performance (i.e., decreased body weight and feed efficiency)
and increased incidence of respiratory disease (airsacculitis) .
Finally, pathogen-free rats were inoculated intranasally with
murine respiratory mycoplasma and exposed for 4-6 weeks to
ammonia at. 25-250 ppm (18-175 mg/m3).3 All concentrations of
ammonia increased the severity of rhinitis, otitis media,
tracheitis, and lung lesions. Ammonia exposure alone produced
only changes in the nasal mucosa consisting of thickening of
the epithelium with submucosal edema.
To determine whether the functional changes accounted, at
least in part, for the increased incidence of infection associ-
ated with low ammonia exposure, a number of investigators studied
the direct effect of ammonia on tracheal ciliary activity -4'5'6/
Because approximately 90-95% of inhaled ammonia is absorbed by
the mucous membrane of the upper respiratory tract,5'14 it would
be necessary to inhale 10-20 times the concentration of ammonia
550
-------
to which the tracheas were directly exposed in these experi-
ments, to produce the equivalent effect in the intact animal.
Permanent cessation of ciliary activity was observed in excised
rabbit tracheas exposed to ammonia at 500 ppm (350 mg/m ) for
5 min and 400 ppm (280 mg/m3) for 10 min. Temporary cessation
of activity was noted at 200 ppm (140 mg/m ) after 9.5 min.
A number of studies on the direct effect of ammonia on rat
respiratory tract ciliary activity, as observed microscopically,
demonstrated cessation of activity after exposure at 90 ppm
(63 mg/m3) for 5 s, at 45 ppm (32 mg/m ) for 10 s, at 20 ppm
(14 mg/m ) for 20 s, at 6.8 ppm (4.5 mg/m3) for 150 s, and at
O /- C Q
3 ppm (2 mg/m ) for 7-8 min. Later studies by the same author '
failed to show this marked sensitivity of ciliary activity to
ammonia. Cessation of ciliary activity occurred after 5 min
of exposure to 500-1,000 ppm (350-700 mg/m ). Exposure to
270-400 ppm (190-280 mg/m3) stopped or decreased activity; be-
low 260 ppm (182 mg/m3), ciliary beats had to be counted to de-
tect any decrease. There was a 7.5% decrease in rate of ciliary
beat when the trachea was exposed to 112-169 ppm (78-118 mg/m ).
Below 100 ppm (70 mg/m3), no effect on ciliary activity was
noted. Therefore, assuming 90% absorption of inhaled ammonia
by the naso-oro-pharynx, the inhalation of less than 1,000 ppm
(700 mg/m3) should produce no effect on tracheal ciliary ac-
tivity in the rat. Finally, exposure to ammonia (119 ppm)
plus activated charcoal (carbon at 3.5 mg/m3) for 5 h/day.
551
-------
5 days/week, for 60 days produced effects substantially greater
than those of ammonia or charcoal alone, as measured by a re-
duction in ciliary activity and pathologic alterations in
tracheal mucosa. Presumably, the increased toxicity of in-
haled ammonia plus activated charcoal results from the adsorp-
tion of ammonia on the carbon and their deposition on the tra-
chea, where they act as an alkali irritant.
552
-------
REFERENCES
1. Anderson, D. P., C. W. Beard, and R. P. Hanson. The adverse effects of
ammonia on chickens including resistance to infection with Newcastle
disease virus. Avian Dis. 8:369-379, 1964.
2. Boyd, E. M. , M. L. MacLachlan, and W. F. Perry. Experimental ammonia gas
poisoning in rabbits and cats. J. Ind. Hyg. Toxicol. 26:29-34, 1944.
3. Broderson, J. B.> J. lindsey, and J. E. Crawford. Role of Environmental
Ammonia in Respiratory Mycoplasmosis of Rats. Personal communication.
Sa.Coon, R. A., R. A. Jones, I. J. Jenkins, Jr., and J. Siegel. Animal
inhalation studies on ammonia, ethylene glycol, formaldehyde,
dimethylamine, and ethanol. Toxicol. Appl. Pharmacol. 16:646-655,
1970.
.4. Cralley, L. V. The effect of irritant gases upon the rate of ciliary
activity. .J. Ind. Hyg. Toxicol. 24:193-198, 1942.
5. Dalhamn, T. Effect of ammonia alone and combined with carbon particles
on ciliary activity in the rabbit in vivo, with studies of the
absorption capacity of the nasal cavity. Int. J. Air Water Pollut.
7:531-539, 1963.
6. Dalhamn, T. Mucous flow and ciliary activity in the trachea of healthy
rats and rats exposed to respiratory irritant gases (SO , HoN, HCHO).
VIII. The reaction of the tracheal ciliary activity to single expo-
sure to respiratory irritant gases and studies of the pH. Acta
Physiol. Scand. 36(Suppl. 123):93-105, 1956.
Z. Dalhamn, T., and L. Reid. Ciliary activity and histologic observations in
the trachea after exposure to ammonia and carbon particles, pp. 299-
306. In C. N. Davies, Ed. Inhaled Particles and Vapours. II. Pro-
ceedings of an International Symposium, 1965. New York: Pergamon
Press, 1967.
553
-------
8. Dalhamn, T.. and J. Sjoholm. Studies o£ S02, N02 and NH3: Effect on cil-
iary activity in the rabbit trachea of single in vitro exposure and
resorption in rabbit nasal cavity. Acta Physiol. Scand. 58:287-
291, 1963.
9. Doig, P. A., and R. A. Willoughby. Response of swine to atmospheric
ammonia and organic dust. J. Amer. Vet. Med. Assoc. 159:1353-
1361, 1971.
10. Gaume, J. G. , P. Bartek, and J.H. Rostand. Experimental results of time
of useful function (TUF) after exposure to mixtures of serious con-
taminants. Aerosp. Med. 42:987-990, 1971.
11. Horvath, A. A. The action of ammonia upon the lungs. Proc. Soc. Exp.
Biol. Med. 22:199-200, 1924/1925.
12. Horvath, A. A. The action of ammonia upon the lungs. (Part I). Jap.
Med. World 6:17-29, 1926.
13. Kling, H. F., and C. L. Quarles. Effect of atmospheric ammonia and the
stress of infectious bronchitis vaccination on Leghorn males.
Poult. Sci. 53:1161-1167, 1974.
14. Landahl, H. D., and R. G. Herrmann. Retention of vapors and gases in the
human nose and lung. Arch. Ind. Hyg. Occup. Med. 1:36-45, 1950.
15. Mayan, M. H. , and C, P. Merilan. Effects of ammonia inhalation on respir-
atory rate of rabbits. J. Anim. Sci. 34:448-452, 1972.
16. Niden, A. H. Effects of ammonia inhalation on the terminal airways.
Aspen Emphysema Conf. 11:41-44, 1968.
17- Underwriters Laboratories. Report on the Comparative Life, Fire and
Explosion Hazards of Common Refrigerants. Miscellaneous Hazard No.
2375, pp. 26-28. Chicago: Underwriters Laboratories, 1933.
18. Silver, S. D., and F. P. McGrath. A comparison of acute toxicities of
ethylene imine and ammonia to mice. J. Ind. Hyg. Toxicol. 30:7-
9, 1948.
554
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19. Stombaugh, D. P., H. S. Teague, and W. 1. Roller. Effects of atmospheric
ammoria on the pig. J. Anim. Sci. 28:844-847, 1969.
20. Weatherby, J. H. Chronic toxicity of ammonia fumes by inhalation. Proc.
Soc. Exp. Biol. Med. 81:300-301, 1952.
21. Weedon, F. R., A. Hartzell, and C. Setterstrom. Toxicity of ammonia,
chlorine, hydrogen cyanide, hydrogen sulphide, and sulphur dioxide
gases. V. Animals. Contrib. Boyce Thompson Inst. 11:365-385, 1940.
CEREBRAL EFFECTS OF AMMONIA INTOXICATION
Several possible mechanisms have been proposed to explain
cerebral effects observed during ammonia intoxication. Figure
6-4 diagrams and identifies the principal pathways of ammonia
detoxification in the brain and the major biochemical sites
implicated in ammonia neurotoxicity.^8 In general, these mecha-
nisms postulate an eventual decrease in available cerebral
energy, ultimately in the form of ATP. This concept was based
on the following formulations: the oxidative metabolism stage
in the Krebs cycle is the major source of ATP in the brain;
depletion of ATP in vital areas of the brain may have func-
tional significance, inasmuch as ATP is believed to be essential
for proper electric activity (repolarization) and metabolism
of the brain; and the various mechanisms of ammonia toxicity
given in Figure 6-4 either appear to interfere with key processes
of the Krebs cycle or may enhance the utilization of ATP during
ammonia detoxification and via ammonia-induced stimulation of
555
-------
Phosphofruciokinose
Acetylcholine
NAD NADH Ch°lir"
Acetyl CoA"±^Ac«toacetate
t t« '
Laclot«
FIGURE 6-4. Postulated biochemical sites of armonia
toxicity in brain, I, impaired oxidative
decarboxylation of pymvic acid. II, NAEH
depletion slows electron-chain generation
of ATP. Ill, depletion of ct-ketoglutarate.
IV, utilization of ATP in glutamine forma-
tion. V, stimulation of membrane ATPase.
VI, decreased synthesis of acetylcholine.
Reprinted ..with permission from Walker and
Schenker.18
556
-------
ATPase activity.!8 other hypotheses that have been presented
include the formation or accumulation of an inhibitory neuro-
transmitter, a-aminobutyric acid,9 and depletion of a trans-
mitter, such as acetylcholine,5
According to one theory shown in Figure 6-4 as site I,
ammonia may interfere with the entry of pyruvate into the Krebs
cycle, thus slowing the cycle.14 This concept was based on the
in vitro observation that high concentrations of ammonium chloride
(15 mM) inhibited oxygen consumption in cat cortex mitochondria;
the effect would be similar to that of impaired pyruvate decar-
boxylation. However, studies with mitochondria obtained from
cortex and brain stem of ammonia-intoxicated rats and brain in-
cubated with ammonium chloride and ammonium acetate over a range
of 2-18 mM failed to show an impairment of pyruvate decarboxyla-
tion. ° Ammonia has also been reported not to exert a primary
? 1
effect on pyruvate utilization in rat liver.
Another theory (site II), also based on in vitro investiga-
tions with high concentrations of ammonia, suggests that, during
the detoxification of cerebral ammonia by glutamic dehydrogenase,
the supply of available NADH is depleted.21 This would result in
a decreased amount of NADH available for mitochondrial generation
of cerebral energy. However, in vivo studies have found that the
cerebral cytoplasmatic NADH:NAD+ ratios increase during acute
ammonia intoxication, owing to a marked increase in lactate:pyruvate
ratios,10'11'13 as well as an apparent decrease in NADH:NAD+
557
-------
ratio in the mitochondria, which suggests a failure to transport
1?
reduced equivalents from the cytoplasm to the mitochondria. *•
The most widely studied hypothesis suggests that ammonia
toxicity depends on the depletion of cerebral a-ketoglutarate
(by amination to glutamic acid and then conversion to glutamine) ,
resulting in impairment of the Krebs cycle (site III) and later
decrease in ATP synthesis. This theory has been supported by
the observations that the brains of patients in hepatic coma
often exhibit ammonia uptake^ and decreased oxygen consumption; &
that concentrations of a-ketoglutarate were decreased in cere-
bral cortex and whole brain of dogs and mice, respectively,
that received ammonia injections; 3,6 ancj that the prevention
of glutamine formation by methionine sulfoximine resulted in
decreased ammonia toxicity in mice. 20 shorey e_t al. measured
both a-ketoglutarate and ATP in the cortex and brain stem of
mice and rats that received ammonia injections. Brief ammonia
intoxication in rats failed to decrease cortical or brain stem
a-ketoglutarate, whereas ATP was significantly decreased only
in the brain stem. A 5.5-h period of hyperammonemia (without
stupor) in mice resulted in a significant decrease in cortical,
but not brain stem, a-ketoglutarate, whereas ATP decreased a
little, but only in the brain stem. The acute studies in rats
did not support the a-ketoglutarate-depletion hypothesis. How-
ever, Shorey et al. pointed out that a-ketoglutarate is present
in brain in at least two metabolic pools: a smaller one
558
-------
accounting for 20% of the total and turning over every 60 min,
and a larger one with a lower metabolic rate. They suggested
that a 50% depletion of the smaller pool would result in only
a 10% decrease in the total a-ketoglutarate, which could not
have been detected under their conditions. The mice data
tended to support the hypothesis, owing to a detectable de-
crease in a-ketoglutarate; however, because there was no
detectable change in the cortical ATP, Shorey e_t al. questioned
the significance of the a-ketoglutarate change. Hindfelt and
»* 1 o
Siesjo-1--5 found the concentrations of a-ketoglutarate to be
about the same or higher in the supratentorial or infraten-
torial cerebral structures of rats during ammonia toxicosis.
They concluded that the ammonia itself does not cause any change
in the energy balance of the cerebral tissue during ammonia
intoxication. Hawkins e_t a^. also were unable to detect any
significant change in a-ketoglutarate concentration in brain
tissue of rats during ammonia intoxication.
Another possible site for the depletion of cerebral ATP
(site IV) has been suggested to involve the glutamine synthetase
reaction.-*--* Several workers have shown that the brain synthe-
sizes an appreciable amount of glutamine after ammonia loading.
A fourfold increase in cerebral glutamine was found within 15 min
after administration of a rather large dose of ammonium acetate
to rats.7 The in vivo synthesis of glutamine in brain has been
studied by Berl e_t al.2 by infusion of [15N]ammonium acetate
559
-------
into the carotid arteries of anesthetized cats. A high concen-
tration of nitrogen-15 appeared in the amide group of glutamine,
with lower concentrations in glutamate and aspartate. The
a-amino group of glutaraine was more heavily labeled than that
of glutamate. Because glutamate is the direct precursor of
glutamine, these workers postulated the existence of two
distinct pools of glutamate: a small, rapidly metabolizing
pool, which supplies glutamate for glutamine synthesis, and
a larger, less active pool. Analogous results and conclusions
were obtained in guinea pig brain cortex slices.-'- It has been
suggested, however, that glutamine synthesis alone could not
drain off enough ATP to affect cerebral function, unless a
vital ATP pool were involved.^ warren and Schenker^O used
methionine sulfoximine, a competitive inhibitor of glutamine
synthetase, to study the relative importance of this enzyme
in ammonia toxicity. They found that this compound provided
a marked decrease in ammonia toxicity in mice. The peak brain
ammonia concentration after the injection of the LD,.- for un-
treated mice was significantly higher in the methionine sul-
foximine-treated mice, because of an increased baseline brain
ammonia concentration, whereas no deaths were observed in the
treated group. Methionine sulfoximine had an effect on endoge-
nous ammonia metabolism, as evidenced by a doubling of the
brain ammonia concentration, 2 h after its administration,
that lasted for at least 24 h. The inhibitor of glutamine
560
-------
synthetase also interfered with the detoxification of the
exogenous dose of ammonia and the formation of glutamine from
this ammonia load. These workers concluded that ammonia in-
toxication does not depend on the mere presence of high cere-
bral ammonia content, but is related to a metabolic process
that occurs directly or indirectly through the major known path-
way of cerebral ammonia detoxication—the synthesis of glutamine.
Hindfelt11 has also studied the effects of methionine sulfoximine
on the energy state of the brain of rats treated with ammonia
and concluded that the results were not consistent with the
hypothesis that this compound was exerting its effects by the
ATP-saving inhibition of glutamine synthesis. Hawkins et al.10
found no significant arteriovenous difference in glutamate or
glutamine concentration in acutely intoxicated mice. Although
considerable ammonia was incorporated into glutamine, it was
not rapidly released from the brain into the circulation.
These workers concluded that ammonia stimulates oxidative
metabolism, but does not interfere with brain energy balance.
They also indicated that the increased rate of oxidative
metabolism could not be accounted for only on the basis of
glutamine synthesis.
Hawkins e_t a..!.10 have suggested that the general increase
in nerve-cell excitability and activity that result in convul-
sions, as well as the increased metabolic rate of the brain,
may be due to sodium and potassium stimulation of ATPase activity
561
-------
brought about by ammonia (site V). These workers found that,
after an ammonium acetate injection, the plasma potassium con-
centration increased from 3.3 to 5.4 moles/liter, with no de-
tectable change in sodium concentration. On the basis of that,
they calculated a possible decrease of 15 mV in the resting
transmembrane potential. They suggested that a likely mecha-
nism of the pharmacologic action of ammonia is the effect on
the electric properties of nerve cells. When present extra-
cellular ly, ammonia, like potassium, decreases the resting
transmembrane potential, therefore bringing the potential closer
to the threshold for firing. This could then cause a general
increase in nerve-cell excitability and activity and result in
convulsions.
Finally, it has been suggested that a depletion of ATP
may cause a decrease in cerebral acetylcholine (site VI), which
requires ATP for its synthesis. Ulshafer17 has shown that ad-
ministration of sufficient ammonium carbonate to produce convul-
sions in rats caused a decrease in the brain content of acetyl-
choline. It has also been shown that ammonia inhibits the syn-
thesis of acetylcholine in brain cortex slices and that the in-
hibition is relieved by addition of glutamine synthetase in-
cr 19
hibitors.13 However, Walker et al. were unable to detect any
change in acetylcholine, serotonin, and norepinephrine during
the development of acute ammonia-induced coma.
562
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REFERENCES
Berl, S., W. J, Nicklas, and D. D. Clarke. Compartmentation of glutamic
acid metabolism in brain slices. J. Neurochem. 15:131-140, 1968.
Berl, S., G. Takagaki, D. D. Clarke, and H. Waelsch. Metabolic compart-
ments in vivo. Ammonia and glutamic acid metabolism in brain and
liver. J. Biol. Chem. 237:2562-2569, 1962.
Bessman, S. P. Ammonia and coma, pp. 370-376. In J. Folch-Pi, Ed.
Chemical Pathology of the Nervous System. Proceedings of the Third
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Bessman, S. P., and A. N. Bessman. The cerebral and peripheral uptake of
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Braganca, B. M. , P. Faulkner, and J. H. Quastel. Effects of inhibitors of
glutamine synthesis on the inhibition of acetylcholine synthesis in
brain slices by ammonium ions. Biochim. Biophys. Acta 10:83-88, 1953
Clark, G. M., and B. Eiseman. Studies in ammonia metabolism. IV. Bio-
chemical changes in brain tissue of dogs during ammonia-induced coma.
N. Engl. J. Med. 259:178-180, 1958.
du Ruisseau, J. P., J. P. Greenstein, M. Winitz, and S. M. Birnbaum.
Studies on the metabolism of amino acids and related compounds in
vivo. VI. Free amino acid levels in the tissues of rats protected
against ammonia toxicity. Arch. Biochem. Biophys. 68:161-171, 1957.
Fazekas, J. F., H. E. Ticktin, W. R. Ehrmentraut, and R. W. Alman. Cere-
bral metabolism in hepatic insufficiency. Amer. J. Med. 21:843-
849, 1956.
DO J
-------
9. Goetcheus, J. S., and L. T. Webster, Jr. \ -Aminobutyrate and hepatic
coma. J. Lab. Clin. Med. 65:257-267, 1965.
10. Hawkins, R. A., A. L. Miller, R. C. Nielsen, and R, 1. Veech. The acute
action of ammonia on rat brain metabolism in vivo. Biochem. J.
134:1001-1008, 1973.
11. Hindfelt, B. The effect of acute ammonia intoxication upon the brain
energy state in rats pretreated with L-methionine D-L-sulphoximine.
Scand. J. Clin. Lab. Invest. 31:289-299, 1973.
12. Hindfelt, B., F. Plum, and T. E. Duffy. Effect of acute ammonia intoxi-
cation on cerebral metabolism in rats with portacaval shunts. J.
Clin. Invest. 59:386-396, 1977.
13. Hindfelt, B., and B. K. Siesjo. Cerebral effects of acute ammonia intox-
ication. II. The effect upon energy metabolism. Scand. J. Clin.
Lab. Invest. 28:365-374, 1971.
14. McKhann, G. M., and D. B. Tower. Ammonia toxicity and cerebral oxidative
metabolism. Amer. J. Physiol. 200:420-424, 1961.
15. Nakazawa, S. , and J. H. Quastel. Inhibitory effects of ammonium ions
and some amino acids on stimulated brain respiration and cerebral
amino acid transport. Can. J. Biochem. 46:543-548, 1968.
16. Shorey, J., D. W. McCandless, and S. Schenker. Cerebral cK-ketoglutarate
in ammonia intoxication. Gastroenterology 53:706-711, 1967.
17. Ulshafer, T. R. The measurement of changes in acetylcholine level (ACh)
in rat brain following ammonium ion intoxication and its possible
bearing on the problem of hepatic coma.. J. Lab. Clin. Med. 52:
718-723, 1958.
18. Walker, C. 0., and S. Schenker. Pathogenesis of hepatic encephalopathy -
with special reference to the role of ammonia. Amer. J. Clin. Nutr.
23:619-632, 1970.
564
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19. Walker, C. 0., K. V. Speeg, Jr., J. D. Levinson, and S. Schenker. Cerebral
acetylcholine, serotonin, and norepinephrine in acute ammonia intox-
ication. Proc. Soc. Exp. Biol. Med. 136:668-671, 1971.
20. Warren, K. S., and S. Schenker. Effect of an inhibitor of glutamine
synthesis (methionine sulfoximine) on ammonia toxicity and metabo-
lism. J. Lab. Clin. Med. 64:442-449, 1964.
21. Worcel, A., and M. Ereeinska. Mechanism of inhibitory action of ammonia
on the respiration of rat-liver mitochondria. Biochim. Biophys.
Acta 65:27-33, 1962.
565
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PROTECTIVE AGENTS AGAINST AMMONIA TOXICITY
Intraperitoneal LD50 and LDg9>g values for the L- and D-
forms of arginine hydrochloride, histidine hydrochloride, iso-
leucine, allo-isoleucine, leucine, lysine hydrochloride, meth-
ionine, phenylalanine, threonine, allo-threonine, tryptophan,
9 I
and valine in rats have been reported. x Among the L-amino
acids, allo-isoleucine was the least toxic and tryptophan the
most toxic; among the D-arnino acids, although allo-isoleucine
was still the least toxic, arginine hydrochloride was the most
toxic. Mixtures of the 10 essential L-amino acids had toxicities
considerably less than those calculated from the means of the
toxicities of the individual components. This was found to be
due to the presence of L-arginine hydrochloride; a mixture of
nine L-amino acids from which L-arginine hydrochloride was ex-
cluded had a toxicity not far from that calculated from the mean
of the toxicities of the individual components. This protective
effect of L-arginine was further demonstrated by adding it to
a lethal mixture of nine L-amino acids; mortality was reduced
from 100% to 24%. It was postulated by these workers that the
L-arginine exerts its protective effect in part to an increased
mobilization of the hepatic urea cycle.
Greenstein et a_1.17 reported the intraperitoneal toxicity
of ammonium acetate in rats and the protective effect of arginine
and related compounds. The LDso and LDg9 9 values were 8.2 + 0.8
and 10,8 + 0,8 mmoles/kg of body weight, respectively. Injection
566
-------
of L-arginine hydrochloride at 2 mmoles/kg of body weight 60
min before an LDgg g dose of ammonium salt resulted in complete
protection of the animals. A comparable degree of protection
with L-citrulline and L-ornithine hydrochloride was achieved
at 8 mmoles/kg. L-arginine methylester hydrochloride, neutral-
ized to a pH of 7.0, conferred nearly complete protection at
4 mmoles/kg of body weight. Compounds that protected some but
not all of the animals when injected I h before an LDgg g dose
of ammonium acetate included the D- isomers of arginine hydro-
chloride, citrulline, ornithine hydrochloride, and arginine
methylester hydrochloride, as well as a-keto-6-guanidovaleric
acid (the ct-keto acid analogue of arginine) and a-acetyl-L-
ornithineo Compounds that were completely nonprotective under
the same conditions included acetyl-L- and -D-arginine,
a-acetyl-D-ornithine, 6-acetyl-L-ornithine, and the L forms
of lysine, homocitrulline, and homoarginine. Liver slices pre-
pared from animals that received injections of various protective
compounds 60 min earlier showed, when incubated with ammonium
chloride, an accelerated consumption of ammonia and formation
of urea; with nonprotective compounds under the same conditions,
there was either a smaller acceleration or none at all. These
workers concluded that the effect of the previously injected
protective substances consisted at least in part of a mobiliza-
tion and acceleration of the classic Krebs-Henseleit urea syn-
thesis mechanism in the liver.
-------
The effect of L-arginine and related compounds on reduction
of blood ammonium acetate intoxication has been investigated by
du Ruisseau et al.10 They found that the injection of amino
acids and ammonium acetate at the LD99>9 was followed by a
rapid increase in blood ammonia and a moderate increase in blood
urea before death. In the presence of protective amounts of
arginine, ornithine, or citrulline, the rise in blood ammonia
was quickly checked, its concentration rapidly decreased to
normal as the blood urea markedly increased, and the animals
survived.
Winitz et a_1.45 investigated the effect of mixtures of
L-arginine hydrochloride and several other compounds that might
serve as possible substrates in nitrogen metabolism. A mixture
of L-arginine hydrochloride and each of the following—none of
i
which by intraperitoneal injection will protect rats against an
intraperitoneal injection of an LDgg g dose of ammonium acetate—
will confer such protection: monosodium L-glutamate, L-glutamate,
disodium a-ketoglutarate, monosodium L-aspartate, L-asparagine,
disodium oxaloacetate, L-alanine, sodium pyruvate, glucose, and
sodium chloride. Survial of all animals was observed when
L-arginine hydrochloride at 1 mmole/kg of body weight was mixed
with glutamate, a-ketoglutarate, or glucose at 4 mmoles/kg.
Aspartate and its derivatives were less effective, and replace-
ment of the 1-mmole/kg dose of L-arginine hydrochloride with
an equivalent amount of L-ornithine hydrochloride led to no
568
-------
protection whatever against ammonia toxicity. Each of the
effective components of the mixtures, such as L-arginine hydro-
chloride at 1 mmole/kg and L-glutamate at 4 mmoles/kg, signifi-
cantly reduced the blood ammonia of animals given a lethal dose
of ammonium acetate, but only when they were used together was
the blood ammonia reduced to normal with survival of the animals.
It was suggested that the effective partners in such mixtures
detoxify the ammonia by separate mechanisms.
The protective action of arginine was observed independently
at about the same time by Harper et a^L.22 They observed that,
during the toxicosis that developed from glycine infusion in
dogs, blood ammonia concentrations became extremely high. How-
ever, when a mixture of amino acids (i.e., casein hydrolysate)
was infused, the blood ammonia content was lower and the blood
urea increased. Najarian and Harper found that arginine ad-
ministered simultaneously with the glycine prevented the in-
crease in blood ammonia and thus the toxicity- Monosodium
glutamate was not found to be very effective against the ammonia
toxicity from glycine infusion. The increase in blood urea that
accompanied the decrease in blood ammonia was interpreted to mean
that the arginine was exerting its effect by influencing urea
production.
Manning and Delp27 reported the successful use of L-arginine
in the treatment of hepatic coma in man. Three patients in
hepatic coma were treated with intravenous L-arginine hydro-
chloride; all three recovered. A decrease in blood ammonia was
569
-------
observed in each case after treatment. The use of arginine was
recommended for the management of hepatic coma. Manning26 later
postulated that the arginine exerts its effect by adding sub-
strate to increase the capacity of the urea cycle for the re-
moval of ammonia. On the contrary, other workers11'12'32 have
been unable to produce any consistent clinical improvement or
decrease in blood ammonia in human subjects with advanced liver
disease and hepatic encephalopathy with the administration of
L-arginine. L-arginine was similarly without significant effect
when blood ammonia was increased in subjects with normal liver
function by intravenous administration of ammonium salts. Fahey
e_t a]..12 suggested that L-arginine plays an important role in
preventing or reducing increased blood ammonia content when it
acts at the site of ammonia release, but has little effect when
the ammonia is exogenous. In support of the conclusions of
Fahey et a_l.,12 Nathans et a_l.31 found that L-arginine injected
intravenously during glycine infusion produced an abrupt cessation
of ammonia release by the liver and caused the liver to remove
ammonia from incoming blood. Arginine did not affect ammonia
release or removal by any other organ tested. Similar results
have been reported by Barak et al.3
Greenstein et aj..16 reported that L-arginine hydrochloride
and mixtures of L-arginine hydrochloride with sodium L-glutamate,
which were effective in protecting all or nearly all normal rats
of the same weight from an LD99>9 dose of ammonium acetate, were
570
-------
less effective in animals subjected to laporotomy and completely
ineffective in animals subjected to partial hepatectomy. Blood
ammonia nitrogen and urea nitrogen concentrations in partially
hepatectomized animals at the point of death from an LDQQ Q
y y. y
dose of ammonium acetate were the same as in normal animals sub-
jected to the same treatment; when the partially hepatectomized
animals were treated first with arginine and then with the LD9g g
dose of ammonium acetate, they died with the same blood ammonia
nitrogen content, but with a moderately increased blood urea
nitrogen content.
Various routes of administration of L-arginine have been
investigated by Gullino e_t a_l. 0 in an attempt to find the most
effective route in preventing ammonia intoxication in rats. The
most effective routes, as measured by the proportion of survivors
of the injection of the LDgg g dose of ammonium acetate, were the
intraperitoneal and the intrasplenic. Subcutaneous and oral routes
were the least effective, and the intravenous route was only
moderately effective.
Gershenovich and Krichevskaya14 reported the lowering of
blood ammonia content induced by high oxygen pressure in rats
by the intraperitoneal administration of arginine. The ammonia
content of the liver was reduced by 38% after administration of
arginine.
.Salvatore and Bocchini reported that a mixture of L-
aspartic acid and L-ornithine had a protective effect against
5-71
-------
hyperammonemia in rats comparable with that of arginine. When
given intraperitoneally, the mixture afforded optimal protection
at 2.0 mmoles/kg of body weight; at 1.0 mmole/kg, 95% of the
animals survived. Aspartic acid alone (at 3.0 mmoles/kg} had
almost no effect, and the addition of ornithine in rather low
concentration (0.5 mmoles/kg) sufficed to raise the survival
rate to 90%. In the protected rats, the increase in blood
ammonia was quickly checked, and the concentration rapidly de-
creased to normal, whereas blood urea content showed a marked
increase.
DL-Potassium and magnesium aspartates, either alone or as
a mixture, have been shown to protect rats against ammonium
34
acetate intoxication. Potassium aspartate was more effective
than magnesium aspartate on a weight-to-weight basis. Relatively
ineffective doses of each, when used together, afforded a high
degree of protection. The aspartate moiety was shown to be
necessary, as well as the potassium and magnesium cations. The
mechanism whereby these two cations increased the protective
effect of aspartate is unknown.
a-D,L-Methylaspartic acid has been described by Braunshtein
e_t al." as a strong inhibitor of hepatic argininosuccinate syn-
thetase, and thus an inhibitor of the urea cycle i_n vitro with
rat liver slices. Cedrangolo e_t al.8 confirmed the inhibition
of urea synthesis in vitro by a-D,L-methylaspartic acid, but
were unable to show this inhibitory effect in vivo. However,
572
-------
Saivatore et al. ' found that the a-methylaspartate did in-
/hibit the urea cycle in vivo. When rats totally protected by
the ornithine-aspartate mixture against an LD5~ dose of ammonium
acetate were given injections of a-raethylaspartate, their liver
argininosuccinate synthetase was completely inhibited; 50% of
the animals died, and 95% had convulsions. Moreover, in com-
parison with controls (not given a-methylaspartate), their
blood ammonia concentrations increased markedly, whereas their
urea concentrations correspondingly decreased. The above re-
sults led to the conclusion that ornithine-aspartate effects
its protection through an enhancement of urea biosynthesis from
ammonia. Results obtained in similar experiments with L-arginine
as a protective agent seemed to show that it protects through a
different mechanism. Furthermore, in an appropriate dose,
arginine partially removed the a-methylaspartate inhibition of
argininosuccinate synthetase in the liver.
The mechanism whereby the ornithine-aspartate mixture
protects against ammonia intoxication has also been studied by
Balestrieri et al.1 They measured the incorporation of [15Njammonia
into urea in intact mice as affected by ornithine-aspartate pre-
treatment. About 30% of the injected ammonia could be recovered
in the urea from the control mice, whereas 60% of the injected
ammonia was incorporated into urea in the pretreated group.
These data indicate that the pretreatment with the ornithine-
aspartate mixture exerts its effect by a marked increased in urea
biosynthesis.
513
-------
Gross! e_t al..19 have found that an equimolar mixture of
aspartic acid and ornithine was effective in reducing blood
ammonia in acute ammonia toxicosis in dogs. The same amino
acid mixture was also effective in preventing toxic blood con-
centrations of ammonia in Eck's fistula dogs when given 1 h
before an acute ammonia load. These workers have also shown
some beneficial effect of treatment of Eck's fistula dogs with
ATP before an acute ammonia load.18 Ten dogs were given ammonium
acetate loads (4.1 mmoles/kg) into the duodenum. ATP (2 mg/kg)
was given intravenously 1 h before the ammonia load. The ATP
was found to prevent an increase in venous ammonia in nine of
the dogs. The authors suggested that the administered ATP in-
creases the rate of ammonia detoxification.
Arginine or arginine-glutamate has been shown to assist
isolated perfused normal rat livers and livers made abnormal
experimentally in detoxifying administered ammonia.2 This de-
toxification was reflected both in removal of ammonia from the
perfusate and in the stimulation of urea production. In general,
fatty livers and azo dye-fed livers were not as efficient as
normal livers in producing urea from ammonium salts, amino acids,
or combinations of these supplements placed in the blood per-
fusate. Addition of glutamate to the perfusate of fatty livers
did not increase urea, as in normal and precancerous livers.
The effects of arginine, glutamate, and aspartate on ammonia
detoxification has been studied in the perfused bovine liver.15
574
-------
Ammonia removal from the perfusate was greatly accelerated by
arginine, arginine plus aspartate, and arginine plus glutamate,
accelerated only slightly by aspartate, and not accelerated at
all by glutamate. These data supported the conclusion that
hepatic removal of excess ammonia occurs primarily through the
Krebs-Henseleit ornithine-urea cycle. It was suggested that
the acceleration of ammonia removal by glutamate, as reported
to occur in intact animals, must take place elsewhere than in
the liver.
Pyrrolidonecarboxylic acid (a possible metabolite produced
by glutamine synthetase) and arginine, alone or as mixtures,
have been investigated as protective agents against acute ammonia
intoxication in rats. 3 Pyrrolidonecarboxylate alone did not
reduce mortality, but did result in a significant decrease in
blood ammonia content with no increase in blood urea. A mixture
of pyrrolidonecarboxylate and arginine resulted in a greater pro-
tective effect than arginine alone. This increased effect was
accompanied by an increase in urea production greater than that
observed with arginine alone. The beneficial effect of the
pyrrolidonecarboxylate was thought to involve increased glutamine
synthesis and then conversion of the glutamine amide nitrogen
into urea.
Two other amino acids have been shown to exert a protective
effect against ammonia intoxication, but their mechanisms are
unknown. Various combinations of a-aminobutyric acid and glucose,
575
-------
when given intraperitoneally 1 hr before an intraperitoneal in-
jection of the LD75 dose of ammonium acetate, have shown defi-
nite protective effects,28 and Cittadini ejt a 1.9 showed evidence
that carbamylaspartate was able to protect rats against ammonia
intoxication when given intraperitoneally 1 h before ammonia
challenge.
In addition to the previously discussed metabolites, the
effects of several drugs on ammonia toxicity have been studied.
Warren and Schenker'*^ studied the influence of 12 drugs related
to the exacerbation or amelioration of hepatic coma on the mouse
intravenous LD5Q of ammonium chloride. Of the drugs tested,
four (cortisone, paraldehyde, morphine, and 5-hydroxytryptophan)
had no effect, seven (monosodium glutamate, phenobarbital,
iproniazid, pentobarbital, acetazolamide, arginine hydrochloride
and chlorothiazide) provided protection, and one (formaldehyde)
exacerbated acute ammonia toxicity. These workers concluded
that there was no direct relationship between the exacerbation
of hepatic coma by a drug and its effects on ammonium chloride
toxicity. Diphenhydramine hydrochloride (benadryl) has been
shown to prevent hyperammonemia in Eck's fistula dogs given
whole blood by gastric tube.25 The mechanism of action'Of this
drug in lowering increased blood ammonia content has not been
clearly defined.
Several other types of therapy have been used to reduce
either the production of ammonia or its absorption from the gut
576
-------
during acute or chronic hepatic encephalopathy. Such anti-
biotics as neomycin, succinylsulfathiazole, and phthalylsulfa-
thiazole have been administered orally or rectally to reduce
intestinal bacterial urease activity. Oral administration of
a urease inhibitor, acetohydroxamic acid, has shown only limited
success. Antibody formation against urease has also been at-
tempted, to decrease ammonia production in the gut. Lactulose,
a disaccharide that is not absorbed by human intestinal mucosa,
has been used successfully in decreasing both ammonia produc-
tion and absorption in the gut of humans. This compound is
degraded by the bacterial flora in the large bowel to acetic
and lactic acids. It therefore lowers the fecal pH, which
reduces ammonia absorption, as well as suppressing some urease-
producing bacteria. For a more detailed discussion of these
24
various treatments, see the reviews by Jacobson and Bell,
IT 0-5
Fischer, and Hsia. ° Oral administration of various types
of ion-exchange resins has also been used, with various degrees
of success in reducing the absorption of ammonia from the but
of humans with hepatic failure.
3 8
Snetsinger and Scott have investigated the role of arginine
and glycine in overcoming the growth depression due to dietary
excesses of single supplemental amino acids in chicks. Glycine
and sometimes arginine, either singly or in combination, were
demonstrated to be capable of partially alleviating the growth
of depression of chicks fed either a soybean-glucose, sesame-
glucose, or corn-soybean meal diet supplemented with excess
577
-------
lysine and a soybean-glucose ration supplemented with excess
histidine or phenylalanine. Substantially greater quantities
of supplemental glycine (in excess of 2%) were required than
of arginine (less than 0.6%) to alleviate the growth depress!
Glycine and arginine were shown to have an additive effect an
it was assumed, independent means of overcoming the amino aci
intoxication. High gain:feed ratios were observed when suppl
mental glycine was added either singly or in combination with
arginine to semipurified diets containing an excess of lysine
phenylalanine, or histidine. It was postulated that glycine
and arginine function in overcoming the amino acid toxicities
by increasing the excretion of excess nitrogen via the uric
acid and urea cycles, respectively. However,- Snetsinger and
Scott-^9 were unable to show any protective effect of either
glycine or arginine against the toxicity of injected amino ac
or ammonium sulfate. Recent investigators have been unable t
detect carbamylphos.phate formation in the avian liver5'29/41'
and attribute the urea present to the action of arginase on
dietary arginine.7 Salvatore et a_l.36 reported evidence that
arginine protects against ammonia toxicity through some mecha
nism other than that involved in urea synthesis. Therefore,
n o
the protective effect indicated by Snetsinger and Scott may
be attributed to a similar non-urea-synthesis mechanism in th
chick.
578
-------
A more extensive study of all the various substrates for
urea and uric acid synthesis with respect to their protective
effects against acute ammonia intoxication in chicks and mice
has been reported.4 Glycine and a mixture of glucose and
glycine were shown to exert a significant protective effect
against ammonia intoxication in chicks, with no comparable
effect in mice. The urea-cycle substrates showed no protective
*
effects in the chicks. It was suggested that glycine and glu-
cose are the limiting substrates for purine synthesis in chicks
during ammonia stress. Evidence was presented that the mixture
of glucose and glycine exerts its effect by increasing uric acid
synthesis.
The sodium salts of some metabolizable fatty acids has also
been shown to exert a protective effect against acute ammonia
intoxication in chicks. The following compounds were found
to exert a significant protective effect in chicks when ad-
ministered intraperitoneally 1 h before ammonia challenge:
sodium acetate at 2, 3, and 4 mmoles/kg; sodium propionate at
3 mmoles/kg; sodium butyrate at 3 mmoles/kg; sodium bicarbonate
at 3 mmoles/kg; potassium acetate at 3 mmoles/kg. These com-
pounds had no comparable effect in mice. There was evidence
that the sodium ion of the metabolizable sodium salts exerts
its effect by increasing uric acid transport or excretion. The
data were consistent with previous work indicating that salt of
metabolizable acids (such as potassium acetate, potassium
bicarbonate, sodium acetate, and sodium bicarbonate), but
not neutral salts, stimulate growth in chicks.40
579
-------
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synthesis in growing chicks. Arch. Biochem. Biophys. 102:259-269,
1963.
42. Tamir, H., and S. Ratner. Enzymes of arginine metabolism in chicks.
Arch. Biochem. Biophys. 102:249-258, 1963. '
43. Warren, K. S., and S. Schenker. Drugs related to the exacerbation or
amelioration of hepatic coma and their effects on ammonia toxicity.
Clin. Sci. 25:11-15, 1963.
44- Wilson, R. P1
-------
45. Winitz, M., J. P. du Ruisseau, M. C. Otey, S. M. Birnbaum, and J. P.
Greenstein. Studies on the metabolism of amino acids and related
compounds in vivo. V. Effects of combined administration of non-
protective compounds and subprotective levels of L-arginine-HCl on
ammonia toxicity in rats. Arch. Biochem. Biophys. 64:368-374, 1956
46. Zuldema, G. D. , D. Cullen, R. S. Kowalczyk, and E. F. Wolfman, Jr. Blood
ammonia reduction by potassium exchange resin. Arch. Surg. 87:296-
300, 1963.
585
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PHYTOTOXICITY OF AMMONIA
Ammonia has been known as a phytotoxic air pollutant since
the late nineteenth century, primarily because of localized
vegetation injury in the vicinity of accidental releases of
Q "
gaseous or liquefied ammonia. Vegetation injury was most fre-
quently associated with the release of ammonia from refrigeration
systems, but, with the replacement of ammonia as a heat trans-
fer fluid by Freons, this source of ammonia injury to vegetation
has declined in importance. Nevertheless, incidents of ammonia
injury to vegetation in the field have increased in recent years,
because of increased agricultural use of anhydrous ammonia. Of
12 major episodes of ammonia injury to vegetation investigated
in Ontario in recent years, 11 involved the manufacture, storage,
transportation, or application of anhydrous ammonia fertilizer.
One case involved spillage of ammonia from a refrigeration
system (P. J. Temple et al., personal communication).
Symptom Expression
Foliar injury symptoms on broad-leaved woody plants exposed
to high concentrations of ammonia usually begin as large, dark
green, water-soaked areas that after several hours darken into
brownish-gray or black necrotic lesions. Necrotic areas are
bifacial on severely injured foliage, but lesions and dark
586
-------
discolorations are predominantly on the upper surface on lightly
injured leaves. Although patterns of interveinal or marginal
necrosis arc occasionally seen on lightly injured plants,
ammonia injury more often produces large, irregular, necrotic
lesions or discolorations widely scattered over the leaf sur-
face. On trees or shrubs with crowded or overlapping leaves,
injury may be confined to particular sections of the leaf.
The uninjured portion may have been protected by the overlapping
1 ?
of adjacent foliage. Although foliage of woody species
normally darkens on exposure to high concentration of ammonia,
foliar lesions can occasionally turn orange, purple, or reddish-
brown, mimicking fall coloration. Conifer foliage injured by
exposure to ammonia darkens to shades of gray-brown, purple,
or black. The entire part of the needle exposed to the gas is
usually affected. Abscission of severely injured leaves is
observed often in both broad-leaved and conifer species.
Symptoms of injury are more variable on herbaceous plants
than on woody species, ranging from irregular, bleached, bifacial,
necrotic lesions to reddish interveinal streaking or dark upper-
surface discoloration. Upper-surface glazing or bronzing has
also been reported.17 Grasses and cereal grains developed tan
to reddish-brown, marginal or interveinal necrotic lesions, and
broad-leaved weeds showed red-brown to dark-brown upper-surface
discolorations on terminal and marginal portions of the leaf.
The variegated leaves of coleus (Coleus sp.) were reported to
587
-------
lose their brilliant color after exposure to ammonia; thereafter
1 R
appearing green. °
Parts of plants other than foliage are far less susceptible
to injury by ammonia,13 but injury to apples, peaches, and other
fruits and vegetables in cold storage has been reported.!5 The
gas apparently entered the fruit through lenicels and other
breaks in the epidermis and caused browning or blackening of
red-pigmented tissues and dark-brown discoloration of yellow
tissues. The outer skin of red onions became greenish-black,
and the skin of yellow and brown onions became dark brown.
These color changes took place almost immediately .after exposure
Tl,
to ammonia and were usually permanent, lowering the marketability
of the stored produce.
Ammonia injury to flowers is rarely observed in the field,
although the development of small necrotic spots on azalea
(Rhododendron sp.) flowers has been reported.17
Phytotoxic Concentration of Ammonia
Concentrations of ammonia during accidents or spills have
not been reported, so data on toxic exposures of plants to
ammonia have been derived from controlled-fumigation studies.
16
Thornton and Setterstrom exposed tomato (Lycopersicon
esculentum Mill.), tobacco (Nicotiana glutinosa L.), and
buckwheat (Fagopyrum esculentum Moench) to ammonia at 1, 4,
588
-------
16, 63, 250, and 1,000 ppm* for short periods. They recorded
50% foliar necrosis on tomato after exposure to 250 ppm for
4 min. Buckwheat and tobacco were more resistant, and 50%
foliar injury was obtained after exposure to 1,000 ppm for 5
and 8 min, respectively. The authors ranked the toxicity of
ammonia in relation to other phytotoxic gases as chlorine
>sulfur dioxide >ammonia >hydrogen cyanide >hydrogen sulfide.
Zimmerman18 reported that fumigation with ammonia at 40 ppm
for 1 h injured tomato, sunflower (Helianthus annuus L.), and
coleus. The same species were only slightly injured after
exposure to 16.6 ppm for 4 h, and 8.3 ppm for 5 h had little
or no effect.
Benedict and Breen^ exposed 10 species of weeds to ammonia
at 3 and 12 ppm for 4 hr and recorded symptom expression and
relative susceptibilities of the plants: 3 ppm severely injured
mustard (Brassica juncea (L,). Coss) , but caused little or no
injury to other species; pigweed (Amaranthus retroflexus L.)
and goosefoot (Chenopodium murale L.) were the most resistant,
and were only slightly injured by 12 ppm for 4 h.
Other plant parts have far higher thresholds of injury
than foliage. Thornton and Setterstrom16 found 50% injury to
4
tomato stems after exposure to 1,000 ppm for 1 h. Brennan et al.
*1 ppm = 700 yg/m ,
589
-------
fumigated apples and peaches with ammonia and reported that, at
200 ppm, peach fruit developed a temporary overall darkening of
the skin that became permanent at higher concentrations. Apples
developed transitory dark discoloration around the lenticels at
300 ppm that became permanent at concentrations above 400 ppm.
Symptoms of injury were similar to those observed on fruit that
had been injured by accidental releases of ammonia in cold
storage. Barton-'- exposed radish (Raphanus sativus L.) .and
spring rye (Secale cereale L.) seeds to ammonia at 250 and
1,000 ppm. Moist rye seeds were killed after exposure to
1,000 ppm for 4 h but moist radish seeds required 16 h at
1,000 ppm for complete kill. Exposure to 250 ppm for 16 h
reduced germination of rye seeds by 52%, but had no effect on
radish seeds. McCallan and Setterstrom13 summarized an extensive
series of fumigation experiments with ammonia conducted on a
variety of plant organs and other organisms by ranking their
relative susceptibilities to ammonia as leaves > stems, fungi,
and bacteria > seeds and sclerotia and animals.
Uptake of Ammonia by Plants
Environmental and physiologic factors affecting the uptake
of ammonia by plants and the later development of injury symptoms
7 8
have not been studied systematically. ' At the very high con-
centrations of ammonia (e.g., above 1,000 ppm) likely to be
found after accidents or spills, the gas is probably absorbed
directly into the leaf through the cuticle and epidermis, rather
590
-------
than through the stomata. Thornton and Setterstrom16 found that
the increases in the pH of tomato leaves exposed to ammonia at
1,000 ppm in darkness were the same as the increases in those
exposed in the light, although increases in the pH of stem tissue
were greater in light than in darkness. Bredemann and Radeloff3
found that night fumigations were just as effective as daytime
exposures in producing ammonia injury in plants. Temple et al.
(unpublished data) also observed that accidental nighttime re-
leases of ammonia and daytime fumigations produce vegetation
injury of equal severity. Both symptom expression and relative
susceptibility were the same in daytime and nighttime exposures
to the gas.
Absorption of ammonia by the bark of dormant deciduous
trees has been demonstrated, and the total nitrogen content
of leaves from trees fumigated during the winter was greater
than that of foliage from control plants. Large increases in
the nitrate nitrogen content of conifer foliage exposed to
ammonia from a ruptured pipeline transporting anhydrous ammonia
have also been reported.^ Foliar absorption and assimilation
of ammonia were demonstrated in corn (Z_ea mays L.) seedlings at
concentrations of 1-20 ppm14 and for soybean (Glycine max (L.)
Merr.), sunflower, corn, and cotton (Gossypium hirsutum L.)
at concentrations of 0.034-0.06 ppm. Rates of foliar absorption
of ammonia appeared to be relatively unaffected by nitrogen con-
tent within plant species.
591
-------
Relative Susceptibilities
Heck et aj..10 listed the relative susceptibilities of 16
plant species to ammonia, on the basis primarily of fumigation
experiments cited previously. Table 6-7 lists 96 plant species
arranged according to relative susceptibility to ammonia, on the
basis of observations of plants injured in the field. Data were
derived from 12 major episodes of ammonia injury to plants in
Ontario, Canada, and most of the species were observed in six or
more of the episodes. Relative susceptibility was assessed by
comparison of foliar injury symptoms on plants growing at equal
distances from the point of the spill and equally vulnerable to
exposure. The rankings in Table 6-7 are based on plant species
observed under a variety of environmental and physiologic condi-
tions, and the table is intended only as an approximate guide
to the relative susceptibilities of the species listed.
592
-------
TABLE 6-7
Relative Susceptibilities of Plant Species to Acute Ammonia Injury
(Species within Each Group are Listed in Order of Increasing;
Resistanceto Ammonia)
Trees and Shrubs
Red mulberry
(morus rubra L.)
Balsam poplar
(Populus balsamifera L.)
Hop hornbeam (Ostrya virginica
(Mill.) K. Koch)
y. Butternut
5 CJuglans cinerea L.)
Snowberry
(Symphoricarpos albus L.)
White birch
(Betula papyrifera Marsh.)
SUSCEPTIBLE
Cultivated Plants
Pea
(Pisum sativum L.)
Sweet pea
(Lathyrus odoratus L.)
Pole bean
(Phaseolus vulgaris L.)
Scarlet runner
(Phaseolus coccineus L.)
Radish
(Raphanus sativus L.)
Peony
CPaeonia suffruticosa
Haw,)
"Weedy" Plants
Catnip
(Nepeta cataria L.)
Wild teasel (Dipsacus sylvestris
Huds.)
White-flowered sweet clover
(Melilotus alba L.)
Common ragweed
(Ambrosia artemisiifolia L.)
Common burdock
(Arctium minus (Hill) Bernh.)
Black mustard
(Brassica nigra (L.) Koch.)
Lamb's-quarters
(Chenopodium album L.)
Daisy fleabane
(Erigeron annuus L.)
-------
TABLE 6-7 - continued
Trees and Shrubs
Oval-leaf or California
privet (Ligustrum
ovalifolium Hassk.)
Catalpa
(Catalpa bignonioides
Walt.)
Sweet mock orange
(PhiladeIphus
coronarius L.)
Cultivated Plants "Weedy" Plants
Periwinkle Oxeye daisy
(Vinea minor L.) (Chrysanthemum leucanthemum L.)
Barley
(Hordeum vulgare L.)
Soybean Woodland goldenrod
(Glycine max (L,) Merr.) (Solidago nemoralis Ait.)
Motherwort
(Leonurus cardiaca L.)
Canada thistle
(Cirsium arvense L.)
Climbing nightshade
(Solanum dulcamara L.)
(Pyrus Malus L.)
Sour cherry
(Prunus cerasus L.)
Flowering crabapple
(Pyrus sieboldii Regel)
INTERMEDIATE
Potato
(Solanum tuberosum L.)
Asparagus
(Asparagus officinalis
L,)
Tomato
(Lycopersicon esculentum
Mill.)
Common chickweed
(Stellaria media (L.)
Cyrillo)
Black medick
CMedicago lupulina L.)
Common milkweed
CAsclepias syriaca L.)
-------
TABLE 6-7 - continued
Trees and Shrubs
Cultivated Plants
Flowering dogwood
(Cornus florida L.)
Sunflower
(Helianthus annuus L.)
Strawberry
(X Fragaria Ananassa
Duchesne)
"Weedy" Plants
Bird peppergrass (or pepperweed)
(Lepidium' virginicum L.)
Dogwood
(Cornus racemosa Lam.)
Lilac
(Syringa vulgaris L.)
Staghorn sumac
(Rhus typhina L.)
Eastern hemlock
CTsuga canadensis (L.)
Carr.}
Quaking aspen
(Populus tremuloides
(Michx.I
Northern red oak
(Quercus rubra L.)
Carrot
(Daucus carota L,, or
sativa)
Lily of the valley
(Convallaria majalis L.)
Cucumber
(Cucumis sativus L.)
Cabbage
(Brassica oleracea L.
var. capitata L.)
Beet
(.Beta vulgaris L.)
Hollyhock
(Althaea rosea Cav.)
Sraartweed (Lady's thumb)
(Polygonum persicaria L.)
Dandelion
(Taraxacum officinale
Weber)
Galinsoga
CGalinsoga ciliata
(Raf.) Blake)
Quack grass
(Agropyron jrepens Beauv.)
Ground ivy
(Glechoma hederacea L.)
Bird's-foot trefoil
(Lotus corniculatus L.)
-------
TABLE 6-7 - continued
Trees and Shrubs
Cultivated Plants
Norway spruce
(Picea abies (L.) Karst.)
White spruce
(Picea glauca (Moench) Voss)
"Weedy" Plants
Spiny sowthistle
(Sonchus asper (L.) Hill)
Curly dock
(Rumex crispus L.)
RESISTANT
Forsythia
(Forsythia viridissima
Peach
(Prunus persica (L.)
Box elder
(Acer Negundo L.)
Silver maple
(Acer saccharjlnum L.)
Norway maple
(Acer platanoides L.)
Sugar maple
(Acer saccharum Marshall)
Black maple
(Acer nig .rum Michx.J
Corn
(Zea mays L.)
Kentucky bluegrass
(Poa pratensis L.)
Cornflower
(Centaurea cyanus L.)
Smooth brome
(Bromus inermis Leyss.)
St. Johns wort
(Hypericum perforatum L.)
Wild carrot
(Daucus carota L.)
Chicory
(Chichorium intybus L.)
Spotted spurge
• (Euphorbia maculata L.)
Pigweed
(Amaranthus hybridus L.)
-------
TABLE 6-7 - continued
Trees and Shrubs Cultivated Plants "Weedy" Plants
English ivy Onion
(Hederahelix L.) (Allium cepa L.)
Common chokecherry
(Prunus virginiana L.)
Japanese yew
(Taxus cuspidata Sieb.
and Zucc.)
White cedar
(Thuja occidentalis L.}
;£ Pfitzer juniper
-1 (Juniperus chinensis
Pfitzeriana Mast.)
-------
REFERENCES
1. Barton, L, V, Toxieity of ammonia, chlorine, hydrogen cyanide, hydrogen
sulphide and sulphur dioxide gases. IV. Seeds. Contrib. Boyce
Thompson Inst. 11:357-363, 1940.
2. Benedict, H. M., and W. H. Breen. The use of weeds as a means of evaluat-
ing vegetation damage caused by air pollution, pp. 177-190. In Pro-
ceedings of the Third National Air Pollution Symposium, Pasadena,
California, April, 1955.
3. Bredemann, G., and H. Radeloff. Ueber Schadigung von pflanzen durch
Ammoniakgase und ihran Nachweis. Z. Pflaneenkr. (Pflanzenpath.)
Pflanzenschutz 42:457-465, 1932.
4. Brennafij, E,, I. A. Leone, and R. H. Daines. Ammonia injury to apples and
peaches in storage. Plant Dis. Rep. 46:792-795, 1962.
5. Dale, E. E., Jr. The effects of anhydrous ammonia.on a forest ecosystem.
Bull. Ecol. 3oc» Ara^r. 57(1):17, 1976. (abstract)
H M
b' Garber, 1C Uber die Aufnahme von Schadstoffen durch die Rinde der Baume.
Wiss. Z. Tech. Univ. Dresden 11:549-552, 1962.
K
7. Garber, K. Uber die Physiologic der Einwirkung von Ammoniakgasen auf die
Pflanze. Landwirtsch. Vers.-Stn. 123:277-344, 1935.
8. Garber, K., and B. Schurmann. Wirkung und Nachweis von Ammoniak-
Iramissionnen in der Nahe von Grossstallungen. Landwirtsch. Forsch.
26(1):36-40, 1971.
9. Haselhoff, E., and G. Lindau. Ammoniak, pp. 279-287. In Die Beschadigung
der Vegetation durch Rauch. Leipzig: Verlag' von Gebruder Borntraeger,
1903.
598
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10. Heck, W. W. , R. H. Dairies, and I. J. Hindawi. Other phytotoxic pollutants,,
pp. F1-F24. In J. S. Jacobson and A. C. Hill, Eds. Recognition of
Air Pollution Injury to Vegetation: A Pictorial Atlas„ Pittsburgh:
Air Pollution Control Association, 1970.
11. Hutchinson, G. L., R. J. Millington, and D. B. Peters. Atmospheric
ammonia: Absorption by plant leaves. Science 175:771-772, 1972.
12. Linzon, S. N. Effects of air pollutants on vegetation, pp. 131-151. In
B. M. McCormac, Ed. Introduction to the Scientific Study of Atmos-
pheric Pollution. Dordrecht, Holland: D. Reidel Publishing Company,
1971.
13. McCallan, S. E. A., and C. Setterstrom. Toxicity of ammonia, chlorine,
$ hydrogen cyanide, hydrogen sulphide, and sulphur dioxide gkses, I.
General methods and correlations. Contrib. Boyce Thompson Inst.
11:325-330, 1940.
14. Porter, L. K., F. G. Viets, Jr., and G. L. Hutchinson. Air containing
nitrogen-15 ammonia: Foliar absorption by corn seedlings. Science
175:759-761, 1972.
15. Ramsey, G. B. Mechanical and chemical injuries, pp. 835-637. In U. S.
Department of Agriculture. Plant Diseases. The Yearbook of Agricul-
ture 1953. Washington, D. C.: U. S. Government Printing Office, 1953.
16. Thornton, N. C., and C. Setterstrom. Toxicity of ammonia, chlorine, hydro-
gen cyanide, hydrogen sulphide, and sulphur dioxide gases. III.
Green plants. Contrib. Boyce Thompson Inst. 11:343-356, 1940.
17. Treshow, M. Ammonia, pp. 362-363. In Environment & Plant Response.
New York: McGraw-Hill Book Co., 1970.
18. Zimmerman, P. W. Impurities in the air and their influence on plant life,
pp. 135-141. In Proceedings of the First National Air Pollution Sym-
posium, November 10 and 11, 1949, Pasadena, California* (sponsored
by Stanford Research Institute)
599
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CHAPTER 7
HUMAN HEALTH EFFECTS
The increased use of ammonia in a wide variety of industrial
processes and as a fertilizer will lead to consumption of 30 x 10
tons (21.2 x 106 t) by 1980.14 In addition, there is continued
growth in industries--e.g., chemical, coal, and oil-refining—that
emit ammonia as a side product. About half-million Americans are
employed in such industries,^^ •^5 and one may anticipate that in-
creasing numbers of Americans will be exposed accidentally to acute
toxic concentrations of ammonia. Although most atmospheric ammonia
is produced by diffuse biologic processes, ammonia produced by
industry and livestock can be important in air pollution in specific
areas. ° Thus, millions more people can be affected by chronic low
concentrations of ammonia above a safe threshold. Ammonia is also
available in most households as a cleaning agent with the potential
for acute toxic exposure in that environment.
Ammonia, a volatile va.ter-soluble alkali, is an irritant that
most commonly affects the skin, eyes, mucous membrane of the upper
respiratory tract,, arid lungs.79'83'84'85 When ingested, it has
corrosive effects on the mouth, esophagus, and stomach.56'152 And,
in some forms of liver disease, ammonia from protein metabolism can
accumulate to toxic concentrations and lead to more generalized
bodily dysfunction, especially of the central nervous and muscular
system. Necropsy findings in patients who died from acute toxic
inhalation of ammonia fumes have revealed diffuse cerebral hemorrhage,
hencrrhagic r^Dlrr •• t:i .<- and hemorrhagic liver-cell necrosis, in addition
600
-------
to effects on skin, eyes, and respiratory tract.144 The effects
of ammonia on human health can result from accidental acute toxic
exposure, from chronic exposure to low concentrations in the work-
place or as an air pollutant, and from endogenous accumulation in
liver disease. The degree and manifestation of dysfunction and
tissue damage depend on the concentration, duration, and type of
exposure, as well as on the presence of underlying disease processes.
Accidental release of high concentrations of ammonia from faulty
valve connections, containers, and handling by workers in agriculture
and industry results in numerous deaths and injuries each year.
There are no reports of human toxicity of the ammonium moiety
of ammonia-containing aerosols. Ammonium salt at 35 \\g/m has been
the highest recorded 24-h average concentration in heavily polluted
areas, this corresponds to an ammonia concentration of 0.05 pprn--
much less than the odor threshold of 5 ppm and the recommended time-
weighted average of 50 ppm. At concentrations likely to be en-
countered, the capacity for transport and metabolism of ammonium
aerosols will exceed the rate of presentation.
In guinea-pigs exposed to toxic concentrations of sulfuric
acid aerosol, the simultaneous presence of ammonia ameliorated
the irritant ef f ects. H«a in recent experiments, M. 0. Amdur
(personal communication; see also the references in Larson et al. ^
reported that, if the bronchoconstrictive effect of sulfuric acid
(at 0.5-9 mg/m3) were assigned the value of 100, the effect of
ammonium acid sulfate and ammonium sulfate would be given a value
in the range of 3-10. In addition, recent studies of Larson et al. a
have indicated that the ambient concentrations of free ammonia in the
601
-------
nasopharynx of humans is such that "H2S04 particles of 20 yg
per m3 with a diameter of 0.3 ym at 30 percent relative
humidity should be completely neutralized after about 0.5
seconds in the nose, and after about 0.1 seconds in the mouth."
Charles e_t aj..36a,36b introduced droplets of sulfate salts
intratracheally into perused or in situ rat and guinea pig lung
and reported that ammonium ion can facilitate lung transport of
the sulfate ion of sodium sulfate. They also found histamine
release from lung in in vitro experiments at 0.1 M ammonium
sulfate and in experiments involving perfusion and intratracheal
intubation. They suggested that this phenomenon, accompanied by
bronchoconstriction, results from ion exchange between the ca-
tionic forms of ammonia and histamine. It is unclear whether
these experiments can serve as valid models for effects of
ammonium-containing aerosols under actual atmospheric conditions.
In summation, the predominant evidence suggests that ammonia
mitigates, rather than exaggerates, the toxic effects of sulfuric
acid aerosols.™"a However, experiments on humans are sparse,
and the issue cannot be considered as closed.
BURNS OF THE EYE
The most devastating burns of the eye are those caused by
strong alkalis. These burns are corrosive, destroy the texture
and substance of the ocular tissue, and have marked tendency for
late complications and persistent morbidity. Although the
use of strong alkalis is widespread, the number of serious alkali
602
-------
burns in the United States is not known. Liquid ammonia and
solutions of ammonia are important offenders, others being
sodium hydroxide, potassium hydroxide, and calcium hydroxide.
The subject of this report is ammonia itself, but alkali
burns of the eye can be discussed as a group, because the cation
has little influence on the severity of the burn. Character-
istics peculiar to ammonia burns are mentioned when appropriate.
The emphasis is on the recent revolution in our biochemical
understanding of the pathogenesis and the effect of this under-
standing on the medical and surgical treatment of eyes severely
injured by such burns.
Chemistry
Gaseous ammonia is slightly irritating to human eyes at a
38 11
concentration of 140 ppm and immediately irritating at 700 ppm. '
In humans, chronic exposure to ammonia gas in the air has caused
only hyperemia of the conjunctiva and lids. However, a forceful
blast of concentrated ammonia gas directed into the eyes has
caused a severe ocular damage similar to that caused by liquefied
or aqueous ammonia, i.e., severe chemical burns,72(pp. 121-122)
Ammonia is very soluble in water, combining to form ammonium
hydroxide. This alkali is strongly dissociated and yields a
large excess of hydroxyl ions. The pH depends on concentration
and on the degree of dissociation. Table 7-1 shows the pH values
of the hydroxides of several bases at various concentrations.
603
-------
TABLE 7-1
pH Values of Bases at Various Concentrations—
pH at concentration of:
Base
Ammonium hydroxide
Sodium hydroxide
Potassium hydroxide
Calcium hydroxide
0,01
10.
12.
12.
PH
N
6
0
0
of
0.
11
13
13
1 N
.1
.0
.0
saturated
1.
11
14
14
0 N
.6
.0
.0
solution =
= 12.4
from CRC Handbook.43
604
-------
The amount of tissue damage is related to the pH or
hydroxyl ion concentration. With in vivo corneal stromal
preparations, -Friedenwald and co-workers64 found that a pH
of 11.5 was necessary for sodium hydroxide to cause irreversible
tissue damage. Grant and Kern73 showed that for a large variety
of alkalis, including ammonium hydroxide, minimal damage to
rabbit corneas (with the epithelium removed) occurred at a pH
of 11, whereas severe injury with stromal opacity occurred at
a pH of 12. The cation concentration in each case was the same,
the pH being adjusted with hydrochloric acid. Altering the
cation concentration by addition of the chloride without changing
the pH did not increase the tissue damage. These experiments
indicated that injury of the denuded corneal stroma is determined
by pH, rather than by the nature or concentration of the cation.
The corneal epithelium is an ineffective barrier against
liquid ammonia and ammonium hydroxide. The ammonium ion, owing
partly to its lipid solubility, penetrates the cell barriers of
the cornea very rapidly; traces are detectable in the anterior
chamber within 5 s, and considerable ion is present after 30 s.
It saponifies fatty acids, destroys cell membranes, and rapidly
penetrates the epithelium.55'72(PP- 97-98) Variations in manner
and rate of penetration of the epithelial tissue account for some
clinical differences between burns caused by calcium hydroxide,
sodium hydroxide, and ammonium hydroxide.72(PP- 97-98) Calcium
hydroxide is the slowest of the three in penetrating the
605
-------
epithelial tissue, possibly because the insoluble calcium
soaps that are formed provide a barrier to penetration. Thus,
calcium hydroxide initially causes superficial opacification,
sodium hydroxide leaves the cornea translucent, and ammonium
hydroxide tends to cause the deepest damage: the cornea often
looks deceptively benign for the first day, with loss of luster
but no signs of gross injury.
Several properties of ammonium hydroxide have no proven
relation to ocular tissue damage. The cations bind rapidly
and in great quantity to collagen at a high pH, and reversal
by dilution is very slow. But more rapid chemical removal of
the cation does not improve the clinical course. The importance
of hydroxyl ion regeneration during the slow release of cations
from the tissues is not known.73 Heat released by alkalis is
not sufficient to damage the eye.^5,81 Ammonia solutions are
hygroscopic and thus are said to withdraw essential water from
tissues; but there is no experimental evidence to support this
hypothesis.72(P- 125),85
Pathogenesis
The clinical and histopathologic course of alkali burns
has been well summarized elsewhere. 8.5,98 After topical appli-
cation, there is a rapid penetration of alkali through the
cornea into the anterior chamber, iris, ciliary body, and lens.
The rapidity of corneal penetration by ammonia was demonstrated
by Siegrist, who detected ammonia in the anterior chamber 5 s
606
-------
after topical application.136 Ammonia therefore tends to cause
more corneal endothelial damage, stromal edema, iritis, and lens
damage than other alkalis.72(PP• 121-122)
The conjunctival epithelium and corneal epithelium under-
go rapid necrosis and sloughing after exposure to alkali.
Within 10 min of the alkali burn, the cornea has become opa-
lescent and edematous, with disintegration of stromal and
endothelial cells. Within 30 min, conjunctival edema and
ischemia and segmentation of vessels in the limbal stroma are
noted, and blanching and translucency of the sclera are observed.
A polymorphonuclear cell infiltration becomes apparent in the
conjunctiva, episcleral tissues, and corneal periphery by
2 h. Corneal edema becomes prominent, with folds in Descemet's
membrane. Cells and flare in the anterior chamber and an acute
increase in intraocular pressure have been reported in cases of
ammonia burn'. 80 By 24 h, the mucopolysaccharides of the corneal
stroma are significantly reduced.32 The polymorphonuclear in-
filtration of the conjunctiva, cornea, and anterior chamber has
become more extensive. Anterior lens opacities are apparent.
Aqueous glucose and ascorbate concentrations are reduced in
anterior segments,121 and intraocular pressure decreases as a
result of reduction in aqueous secretion.
Experimental work in rabbits has indicated that the endo-
thelium is replaced in several days by multiple layers of cells
resembling fibroblasts.104 In rabbits, these fibroblasts seem
601
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to have the capacity to transform into endothelial cells. The
clinical counterpart of this finding has been observed in
retrocorneal membranes in humans shortly after alkali burns.
Fibroblasts also appear in the corneal periphery at this time.
In the absence of substantial limbal involvement, new blood
vessels begin to invade the cornea within a week. In rabbits
with only corneal burns, epithelial cells and fibroblasts have
kept pace with the neovascularization and have not been central
to it; the rabbit corneas were vascularized in 3 weeks, except
in the 28% that were perforated.32 In rabbits with both corneal
and limbal burns, neovascularization was delayed, and the perfora-
tion rate was 90%; this highlighted the poorer prognosis usually
associated with limbal burns in humans7.
In the second week, corneal ulcers develop and are central
to the advancing neovascularization. Neovascularization seems
to preserve the structural integrity of the cornea and assist
in the healing of corneal ulcerations. Symblepharon also
develops in the second week, and the iris may become atrophic.
Proliferation of fibroblasts in the cornea continues, and there
is fibrosis of the ciliary body, which, if severe enough, may
lead to phthisis bulbi. The healing of the corneal epithelium
is slow, and there is a tendency for recurrent breakdown and
ulcerations.
Hypopyon and hyphema make their appearance, usually in the
same eye, 9 days to 6 weeks after the alkali burn.31 The
608
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development of glaucoma, phthisis, and anterior synechiae seems
to be correlated with the presence of hyphema or hypopyon.
In summary, complications of severe alkali burns include
symblepharon, pannus, pseudopterygia, progressive or recurrent
corneal ulcerations that often lead to perforations, permanent
corneal opacification, corneal staphyloma, persistent iritis,
phthisis b.ulbi, secondary glaucoma, and dry eye.
It has been determined that collagenase is responsible for
the ulcer of the alkali-burned cornea, which, if not vigorously
treated, often progresses to perforation. Intralamellar
injections of harvested collagenase from the ulcerated tissues
of alkali-burned rabbit corneas cause full-thickness ulcers in
intact alkali-burned corneas. Collagenase is produced by the
advancing epithelium and the underlying stroma (most likely
from polymorphonuclear leukocytes, which have been shown to
contain collagenase) and is found 10 days after alkali exposure.
Substantial collagen production requires an interaction between
the regrowing epithelium and damaged stroma. The occurrence of
ulcerations central to the advancing border of epithelium and
new vessels is probably explained by the lack of serum proteins
that inhibit collagenase and by the scarcity of fibroblasts
that produce new collagen; both factors tilt the balance in
favor of further collagen degradation. The environment of the
peripheral cornea, however, with new vessels and many fibroblasts,
favors collagen production.
609
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The collagenase from alkali-burned corneas is typical of
mammalian collagenase.25 The viscosity of collagen solutions
is reduced by 40-50%, and aliquots of the reaction mixture
demonstrate limited breakdown of a- and g-tropocollagen chains,
which increases with time when studied by polyacrylamide gel
electrophoresis. The activity of the corneal collagenase de-
pends on calcium ions. Accordingly, chelators for calcium,
like disodium ethylenediamine tetraacetate (Na2~EDTA), inhibit
collagenase. Cysteine weakly chelates calcium, but also
irreversibly inhibits collagenase by attaching itself directly
to the collagenase molecule. These properties of cysteine and
Na2~EDTA have obvious therapeutic implications.
Treatment
Because of the extensive destruction of the anterior seg-
ment of the eye caused by liquid ammonia and ammonium hydroxide
burns, the outlook for severe burns of this type was uniformly
dismal as recently as 10 years ago. Many of these eyes were
lost after corneal perforation; at best, the corneas were totally
opaque and with vision consisted only of light perception. The
prognosis depends heavily on the severity of the burn and, more
specifically, on the amount of limbal ischemia. The classifica-
tion presented in Table 7-2 reflects the growing awareness that
corneal changes are not as important in the prognosis as are
ischemic changes of the limbal area.
610
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TABLE 7-2
Severity of Alkali Burns—
Burn
Grade Corneal Condition
1 Epithelial damage
2 Hazy, but iris detail
seen
3 Total epithelial loss,
stromal haze, iris
details observed
4 Opaque, no view of
iris or pupil
Limbal Ischemia Prognosis
None Good
< 1/3 Good
1/3 - 1/2
> 1/2
Vision reduced,
perforation
rare
Poor
-Data from Roper-Hall.128
611
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It is generally recognized that mild alkali burns heal
well with simple conservative measures. 1 Therefore, we con-
sider here only the treatment of severe burns.
Immediate treatment consists of copious irrigation with
water or saline. Because of the rapid penetration described
above, removal of the ammonia must be prompt, probably within
5-6 s to reduce tissue damage.136 Buffer solutions are not
superior to water or saline for irrigation.13'55 Although
immediate irrigation, starting within 5 s of injury, is prob-
ably of some benefit, the efficacy of prolonging irrigation
beyond a minute or so is questionable.55'^ However, in
calcium hydroxide burns, there is some rationale for more pro-
longed irrigation. Penetration of this alkali into the eye is
less rapid, and particulate alkaline material may be lodged in
the conjunctiva and require prolonged irrigation or direct
mechanical removal.
Because of the severe iritis, atropine should be used to
prevent the formation of posterior synechiae. Prophylactic
antibiotic drops are also recommended,55'^5 because of the in-
complete epithelial cover and poor blood supply of injured eyes.
Attempts to treat hypopyon have been frustrating. In one
series,31 this complication was seen in 40% of the severe alkali
burns, and the duration and amount of hypopyon seemed to be un-
affected by systemic or topical steroid treatment.
612
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The realization in the late 1960's that the alkali-burned
cornea produces collagenase led for the first time to a treat-
ment that could prevent corneal ulceration and perforation.
Brown and Weller33 showed that L-cysteine, a collagenase in-
hibitor, at 0.1 - 0.2 M prevented perforations in 80% of rabbit
eyes with severe alkali burns. In control animals treated with
sodium chloride, 14 of 15 eyes were perforated. Cysteine has
also been shown to be very effective in preventing corneal
ulceration in humans.29 Brown and coworkers31 were able to
heal 32 of 33 severely alkali-burned eyes with 0.2 M cysteine,
2 drops applied topically 6 times per day beginning on the
seventh day after injury- In contrast, five of seven severely
alkali-burned eyes not treated with cysteine were perforated.
Slansky e_t a].. showed that acetylcysteine is also effective
in preventing ulcerations in alkali-burned rabbit eyes. This
collagenase inhibitor is more stable in solution than cysteine.
The mechanism of action of these chelating agents has been
postulated by Hook and co-workers.^2 Chelators like sodium
EDTA are reversible inhibitors and presumably act by chelating
the calcium that was necessary for collagenase activity.29
The replacement of calcium by the surrounding tissues would
explain the short duration of action of these inhibitors.
Cysteine, in addition to binding calcium, also binds irreversibly
to the collagenase molecule and is therefore a more desirable
therapeutic agent.
613
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Brown^ recommended that the use of collagenase inhibitors
could be delayed until 7 days after exposure to alkali. At
this time, corneal vascularization accompanied by epithelial-
cell cover and stromal fibroblasts and granulocytes begins.
Treatment must be continued until the epithelium has covered
the cornea and the epithelial collagenase production has stopped
The stromal production of collagenase continues long after
epithelial healing,25,34 ku-|- does not cause stromal dissolution,
perhaps because of the inhibition of this enzyme by serum proted
Cysteine in therapeutic concentrations is well tolerated
by the human eye.^9,31 when 20% acetylcysteine or 1.25 M
L-cysteine was injected intrastromally in rabbits,!^! severe
inflammation resulted. Only transient damage occurred when
0.2 M L-cysteine was injected. The point should be made,
however, that intrastromal injection is not analogous to topi-
cal application. In addition, 20% acetylcysteine has been
used without problems in treating keratoconjunctivitis sicca. ^
Epithelial healing is slightly but significantly retarded in
rabbits treated topically with 20% acetylcysteine.98
Another critical problem in the medical management of
ammonia burns is epithelial healing. Stromal ulceratidn ceases
once the epithelium is intact, but the common sequelae.of
scarring—trichiasis, symblepharon, and eyelid deformation—
delay epithelial healing by mechanical trauma and alteration
of the tear film. Burned eyes also have decreased tear
614
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production, with scarring of ducts98 and destruction of goblet
19*?
cells. ^- one approach to the problem of drying has been trans-
position of the parotid duct into the conjunctival sac, in an
attempt to bring in parotid secretions to replace normal tears.37
Drawbacks to this approach include epiphora, lack of a mucin
component in the tears, and possible digestion of stromal
ground substance by the amylase in parotid secretions.2 Most
importantly, the mechanical factors so crucial to corneal wetting,
such as blinking, are completely ignored in this approach.
The use of soft contact lenses to promote epithelial heal-
ing has been more promising. Brown and co-workers treated
20 of 40 severely alkali-burned eyes with Griffin soft contact
lenses. A lens was worn continuously until epithelial healing
was complete in 14 of the 20 eyes. In the other six cases,
symblepharon or thick conjunctival overgrowths caused the lenses
to fit improperly, and they were discontinued. Modified pressure
dressings were used for the severely burned eyes not treated with
a soft contact lens. The eyes fitted with soft contact lenses
healed an average of 5 weeks sooner than those treated with
pressure dressings. However, this difference must be qualified,
in that the soft lenses had to be discontinued in six eyes that
were the slowest to heal. The soft contact lens appears to
facilitate epithelial healing and the maintenance of the healed
state in corneas, except when there are external irritating
factors, such as eyelid deformation, trichiasis, and altered
615
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tear production. The soft lens appears to be of particular
value in promoting quick healing of late epithelial erosions
and in preventing further erosions that otherwise consistently
recur in alkali-burned corneas.
The most serious complication associated with the use of
soft contact lenses in severely ammonia-burned eyes is infec-
f\ p
tion. Brown and co-workers^0 found that 17% of severely injured
eyes, many of them alkali-burned, developed corneal infections
after soft contact lenses were worn for 2 months or more, with
periodic cleaning of the lenses. All these patients were using
topical steroids or antibiotics or both for their eye disease.
The authors recommended cleaning the lenses semiweekly if not
daily, avoiding chronic use of topical steroids and antibiotics
if possible, and examining periodic conjunctival cultures, so
that pathogenic organisms can be treated if they appear.
Even when the problems of epithelial erosion and stromal
ulceration have been overcome, the patient is almost always
left with an opaque and vascularized cornea and vision limited
to perception of light or hand motion. Keratoprostheses have
been tried with some success, but no long-term followup is
available, and these devices eventually extrude with disappointing
regularity.98 Girard and co-workers69 reported improved vision
in 72% of patients with alkali burns treated with keratoprosthesis;
33% achieved vision of 20/40 or better, but length of followup
was not specified.
616
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Until 5 years ago, attempts at corneal transplantation for
severely ammonia-burned eyes was uniformly unsuccessful.6^
Poor epithelial healing led to stromal ulceration and graft
perforations. Grafts that survived the initial postoperative
period eventually opacified, and it was thought that grafting
into a vascularized bed made immune rejection inevitable.
But Capella and co-workers35 believed that vessels alone could
not explain the consistent late failures of grafts for severe
chemical burns:
In our experience, no cornea with extensive
chemical burns on which we have done a keratoplasty
has remained clear. In the past, it was assumed
grafts for chemical burns failed because of extensive
vascularization and homograft reaction. This has not
been established as fact, however, and we believe that
there are other reasons. Excluding those eyes in which
there are chemical burns, even eyes with severe vascu-
larization do extremely well after keratoplasty and
the prognosis for them does not appear to be greatly
different from that for eyes without vascularization.
Brown, Tragakis, and Pearce^O confirmed these suspicions
by showing that the late failure of keratoplasty in alkali burns
was indeed not a posterior failure or immune reaction, but rather
an anterior failure--that is, scarring and opacification caused
by persistent or repeated breakdown of the corneal epithelium.
They demonstrated that penetrating keratoplasty with fresh
donor material could be successful in rehabilitating the healed
but opaque cornea of severe alkali burn. In two later reports,26'27
Brown and his collaborators expanded on the surgical techniques,
the postoperative management, and the results of followup. The
617
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conjunctival overgrowth was dissected from the cornea and freed
from the thickened subconjunctival tissue. The thickened sub-
conjunctival tissue was excised en bloc, and the conjunctiva
recessed 6 mm from the limbus, leaving a smooth scleral surface.
Symblepharon were repaired by freeing the eyelids from the globe
and mobilizing conjunctival flaps to cover bare areas of sclera
and extraocular muscle. Iris adhesions to the corneal button
were carefully freed with blunt dissection. Whenever an iridot-
omy was indicated, the iris was first crushed with a needle
holder to minimize bleeding. If a cataract were present, it
was removed. Anterior vitrectomy was performed if there was
*.
vitreous fluid in the anterior chamber. In an important de-
parture from previous techniques, the epithelium of the donor
corneal button was left intact, and the button was sutured in
place with a running 10-0 nylon suture. Although most corneal
surgeons remove the epithelium from the donor eye, Brown's re-
sults indicated that incomplete epithelial healing with stromal
ulceration occurred often if the epithelium were not left intad
In the postoperative period, cysteine was of questionable value,
but the soft contact lens proved to be invaluable in treating
erosions of the graft epithelium. Various lenses had to be
tried again and again to effect epithelial healing. Epithelial
erosions were observed in this series for up to 2 years after
surgery. in 25 eyes followed for more than 5 years, 14 grafts
have remained transparent.
618
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EFFECTS ON SKIN
Although odor is the first detectable sign of atmospheric
ammonia, low concentrations of ammonia are irritating to the
skin and thus provide an additional warning. Ammonia gas
quickly dissolves on moist body surfaces and results in an
alkali burn; contact with liquid anhydrous ammonia also pro-
duces a burn by its freezing effect.78'80'90'101/116/118'160/164
Two cases of possible skin sensitization have been reported.108
Contact with liquid anhydrous ammonia or ammonia gas under
pressure results in second-degree burn, with formation of
blisters, that, if extensive, may be fatal.
The relation between skin response and concentration of
ammonia has not been well described. A concentration of
10,000 ppm (7,000 mg/m ) produces skin damage. The maximal
concentration of vapor tolerated by the skin for more than a
•5 p C
few seconds is 20,000 ppm (14,000 mg/m ). Although no spe-
cifics of the experiment were given, one study indicated that
10,000 ppm (7,000 mg/m3) is mildly irritating to the skin,
20,000 ppm (14,000 mg/m3) causes increased irritation, and
30,000 ppm (21,000 mg/m3) may produce blisters in a few minutes.118
Therefore, skin should be protected in air with a concentration
of over 10,000 ppm.
Immediate management after skin contact consists of flushing
of the skin with water, showering, and changing clothes; clothing
and perspiration absorb ammonia, thus extending the duration of
619
-------
contact. Salves and ointments, which apparently increase pene-
tration of ammonium hydroxide, should not be used for 24 h.78
EFFECTS ON UPPER RESPIRATORY TRACT AND LUNGS
Odor
Ammonia vapor has a sharp, irritating, pungent odor that
acts as a warning of potentially dangerous exposure. The odor
threshold concentration for ammonia has been reported to be as
low as 0.7 ppm (0.5 mg/m^) in the most sensitive people-"0,131,132
and as high as 50 ppm (75 mg/m^).62,99 one study indicated that
the average threshold concentration is approximately 5 ppm
(3.5 mg/m ). Ammonia is acceptable up to 20 ppm (14 mg/rn^),
a concentration that some people find annoying ("complaint
level"!. Chronic exposure to higher concentrations (40 ppm)
results in headache, nausea, and reduced appetite.HO Acclim-
atization occurs with chronic exposure to low concentrations
of ammonia,'*'* resulting in an increase in the odor threshold
concentration.
Acute Toxic Exposure
Effects of ammonia on the respiratory tract include mild
irritation, hoarseness, excess salivation, sneezing, cough,
productive cough, hemoptysis, rales, and the more severe
respiratory symptoms of laryngeal edema with asphyxia, pulmonary
edema, and bronchopneumonia.15•16'36'41'70'77'78'90•10°•101'109'
116,129,134,135,144,160,164,167 High concentrations Of ammonia
620
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produce laryngeal spasm and reflex bronchoconstriction. A
concentration of 400 ppm (280 mg/m3) produces immediate throat
irritation;78'79 1,700 ppm (1,200 mg/m3), cough; 2,400 ppm
(1,700 mg/m3), a threat to life after 30 min;118 and 5,000-10,000
ppm (3,500-7,000 mg/m3), a high mortality rate.78 Laryngeal
edema may develop several hours after acute exposure; such
exposure often results in an initial impression of less severe
damage.ll6
Because ammonia is water-soluble and thus absorbed by
A-J
the upper respiratory tract, the lungs are protected from the
effects of exposure to low concentrations of ammonia.22,75,96
The most common cause of death after acute exposure to ammonia
from leakage of ammonia gas under pressure or from spray with
liquid anhydrous ammonia is laryngeal edema and asphyxia or the
development of pulmonary edema. In all but one reported case, ^9
the ammonia concentration and the duration of the acute acci-
dental exposure were not stated. Although it is poorly docu-
mented, the greater the exposure (according to historical de-
scriptions of distance from the source and duration of exposure),
the more pronounced the symptoms and physical findings and the
higher the mortality rate. °
Immediate treatment consists of removal from exposure and
l
ventilation with warmed, humidified air or oxygen. If laryngeal
edema (stridor) develops, treatment consists of tracheostomy.
In the presence of pulmonary congestion and edema with associated
621
-------
hypoxemia, the treatment is administration of oxygen and, if
necessary, artificial ventilation; arterial blood gases must
be carefully monitored.78
There have been few studies in man on the respiratory
sequelae of acute toxic exposure to ammonia. Some of the
survivors gradually became asymptomatic, and their pulmonary
function returned to normal in 1-2 years, even after nearly
fatal respiratory changes.63,101 in other patients, moderate
chronic airway obstruction with or without a reduction in
diffusing capacity persisted or gradually worsened over the
next few years.^,100,160 In some patients, the changes were
&
attributed to continued cigarette-smoking.160 TWO qases>of
bronchiectasis,90 one case of subatrophic pharyngolaryngitis, -
and three cases of chronic bronchitisl44 > 164 were reported after
exposure to ammonia at unspecified concentrations.
There are two major limitations regarding assessment of
incidence and significance of the late respiratory sequelae
of acute toxic exposure to ammonia fumes: few patients have been
studied, and the pulmonary-function tests used (vital capacity,
forced vital capacity, and diffusing capacity) are relatively
insensitive for the detection of early small-airway obstruction.
It is apparent from the available case reports that documented
acute lower respiratory tract involvement (acute tracheitis,
bronchitis, bronchopneumonia, and pulmonary edema) does not
necessarily lead to chronic respiratory disease. However, all
622
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patients with residual lung dysfunction or chronic respiratory
symptoms had had such involvement.
Human Inhalation Experiments
The first experiments in humans on the effects of ammonia
inhalation were reported in 1886. The author exposed himself
to ammonia at 330 ppm (220 mg/m3) for 30 min and concluded
that concentrations of 300-500 ppm (210-350 mg/m3) could be
tolerated for protracted periods.97 In a later study, six
volunteers exposed for 10 min to 30 ppm (21 mg/itr) and 50 ppm
(35 mg/m3) reported little irritation and a highly penetrating
odor at the lower concentration and moderate irritation at the
higher concentration.1^
-------
assuming 100% absorption of inhaled ammonia, the serum ammonia
content would have to have exceeded what was theoretically
possible.138 In the second study, seven volunteers were exposed
to ammonia at 500 ppm (350 mg/m3) for 30 min.139 Ammonia reten-
tion decreased progressively, with equilibration at 24% reten-
tion. As opposed to the previous study, blood urea nitrogen,
nonprotein nitrogen, urinary urea, and urinary ammonia remained
normal. Symptoms were limited to the nose and throat; this
suggested that, at the concentration used, ammonia was primarily
absorbed by the upper respiratory tract. Indeed, approximately
83% of ammonia inhaled through the nose (at 60-500 ppm) is re-
tained in the nasal passages.""
Chronic Low-Concentration Exposure
A number of studies have been reported on the adverse
effects of chronic low-concentration exposure to ammonia on
man>18,19, 20, 21,54, 57,58, 68,71,91,106,110,112,113,135,141,158,159,16
However, most of those reported have dealt with chronic exposure
to a mixture of irritating air pollutants, such as nitrogen oxides,
sulfur dioxide, and ammonia. In addition, these epidemiologic
studies lacked adequate controls or documented poorly the exposure
to ammonia, the characteristics of the populations studied, and
the objective alterations. For example, 250 household members
living within a 0.5-km radius of a sanitation center were sur-
veyed. Mixed respiratory irritants of nitrogen oxides and
624
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ammonia were not identified, nor were concentrations measured.
Although no control population was studied, it was concluded
that there was a high incidence of headache, nervousness, loss
of appetite, and chronic fatigue in the population studied.
Although 46 people were examined in detail, there was no indi-
cation of the basis for selection. Of the 46, 34 (74%) had
"respiratory disorder." Pulmonary function was measured in
six patients—again with no indication of how or why they were
selected—and all had evidence of chronic obstructive lung
disease.
In another study, 41 persons employed in an ice manu-
facturing plant were questioned.57 The concentration of ammonia
in the ambient air was not measured. No difference was noted
in pulmonary function and respiratory symptoms between control
and exposed, groups of workers.
Workers exposed to ammonia, hydrogen chloride, and hydrogen
sulfide in a hydrometallurgic plant had a high incidence (52%)
of upper respiratory tract disease.71 The peak ammonia concen-
tration in the working area was greater than 100 ppm (70 mg/m3),
but exact concentrations were not given.
A well-controlled study involving 140 adolescents exposed
to ammonia and nitrogen oxides at concentrations not exceeding
"maximum permissible concentration" 3 h/day for 2-3 years of
vocational training revealed increased incidences of upper
respiratory tract disease, skin changes, and alterations in
625
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lipoprotein and protein metabolism, compared with those in a
control group of unexposed students at the same school.68
Workers in a fertilizer factory exposed to ammonia alone
as well as in combination with carbon monoxide and nitrogen
oxides were found to have decreased tissue vitamin B concen-
6
trations and required an increased dietary intake of the vitamin
to maintain a positive balance.112'113
Finally, a few reports have suggested a relationship between
ammonia exposure and malignancy. ' ' ' ' ' An increased
incidence of lung, urinary tract, gastric, and lymphatic neo-
plasia was reported in persons exposed to ammonia at 2-3 times
the maximal allowable concentration of 35 ppm (25 mg/m3) in a
chemical plant.1°'19'2® However, adequate background material
(with reference to characterization of the population studied
and environmental exposure to other agents) was not included
to allow proper assessment of the conclusions. A detailed epi-
demiologic study of gasworkers exposed to the byproducts of
coal carbonization indicated an increased risk of lung and bladder
cancer.-* Some 300 female pharmacists exposed in drug rooms to
ammonia (at 10-200 ppm), antipyretics, sulfonamides, zinc, and
talc dusts were found to have 2-4 times the incidence of cervical
precancerous lesions as a control group of 262 women.159 And,
one case of epidermoid carcinoma of the nasal septum was re-
ported after an acute ammonia and oil burn of the area.135
None of these reports clearly linked exposure to ammonia to
neoplasia in a cause-effect relationship.
626
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Thus, the lack of carefully performed epidemiologic studies
makes it impossible to assess properly the long-term health
effects of chronic exposure to low concentrations of ammonia
in the environment. Not only is ammonia normally present in
small amounts in plasma and in expired air, ^, 94,127 but j_t ^s
also found in cigarettes (36-153 ng/cigarette).17'143 What role
ammonia in cigarette smoke plays in the development of the lung
changes and respiratory symptoms seen in chronic cigarette-
smokers is not known.
EFFECTS ON GASTROINTESTINAL TRACT
Ingestion of ammonia may produce acute corrosive esophagitis
and gastritis, followed by the late development of esophageal
and gastric stenosis.50/59,114,140 There has been one report
of severe acute gastritis after inhalation of ammonia at an
unknown concentration.56
ENVIRONMENTAL AIR STANDARDS
Definitions
• Maximal allowable concentration (MAC): the average
concentration of a given agent in the air that will
not (except in cases of hypersensitivity) provoke
any signs or symptoms of disease or poor physical
condition that can be revealed by tests interna-
tionally accepted as the most sensitive in any
worker continuously exposed to the agent in the
course of his daily work.
627
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• Ceiling concentration; the concentration that
must never be exceeded, even for short periods.
4 Time-weighted average (TWA): the average con-
centration of exposure over a 6- to 8-h working
day, 5-7 days/week.
» Threshold limit value (TLV): the concentration
at which it is believed that nearly all workers
may be repeatedly exposed day after day without
adverse effect.
Basis of Standards
The current U.S. federal standard for exposure to ammonia
is an 8-h time-weighted average of 50 ppm (35 mg/m3). The
first toxic limit of ammonia established by the U.S. Public
Health Service was published in 1943; on the basis of the most
widely accepted value, a time-weighted average of ammonia was
stated to be 100 ppm (70 mg/m3).23 This value was apparently
based on the original poorly controlled self-exposure studies
of Lehman in 1886.39'97 On the basis of current practice in
several states39 and exposure studies in an ammonia plant where
ammonia at 100 ppm (70 mg/m3) produced irritation of the upper
respiratory tract and eyes, the American Conference of•Governmental
Industrial Hygienists (ACGIH) recommended an MAC of 100 ppm
(70 mg/m3) , H which later became a threshold limit value.
628
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As a result of animal studies that showed pathologic
changes in spleens, livers, and kidneys after chronic exposure
to ammonia at 140-200 ppm (100-140 mg/m3)162 and direct toxic
effects on isolated trachea after exposure at 100 ppm (70 mg/m3),46
it was recommended that the TLV be reduced to 50 ppm (35 mg/m3),3'6
specifically to protect against respiratory irritation and elimi-
nate discomfort. The ACGIH published an intent to recommend that
the TWA of 50 ppm (35 mg/m3) be changed to a ceiling value—a
limit that should not be exceeded.7 However, a TWA of 25 ppm
(18 mg/m3) was later recommended"'^ on the basis of unpublished
plant surveys by the Detroit Department of Health that indicated
that 25 ppm (14-18 mg/m3) was the maximal acceptable ammonia
concentration with an acceptable incidence of complaints. It
is noteworthy that the U.S. Navy set 25 ppm (18 mg/m3) as the
limit for continuous exposure and 400 ppm (280 mg/m ) as the
maximal concentration for 1 h in a submarine. Official
occupational MAC's set by foreign countries range from 30 ppm
(20 mg/m3) in Russia148 to 100 ppm (70 mg/m3) in Great Britain
, „ . . . _ . . _ ,. 4,45,52,65,119,123,148,165
and Yugoslavia (see Table 7-3) . ' ' ' ' '
Whereas the current U.S. recommended but unofficial TLV of
25 ppm (18 mg/m ) is based on upper respiratory tract and eye
symptoms and animal morphologic studies,153 the recommended but
unofficial Russian limit of 15 ppm (10 mg/m3) is based in part
on physiologic studies of reflex activity related to the central
nervous system—namely, changes in higher central nervous activity,
629
-------
TABLE 7-3
Maximal Allowable Ammonia Concentrations in Several Countries
MAC for Ammonia
Country ppm mg/m^
Czechoslovakia 60 40
France 50 35
Great Britain 100 7Q
Hungary 30 20
Japan 50 35
Poland 30 20
United States 50 35
USSR 30 20
Yugoslavia 100 70
630
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i.e., changes in eye sensitivity to light and changes in EEC
evoked response. For example, eye sensitivity to light was
found to be reduced in humans exposed to ammonia at 0.45 ppm
(0.32 mg/m3) and an EEC evoked response on exposure to as little
as 0.50 ppm (0.35 mg/m3), so 0.30 ppm (0.2 mg/m3) was considered
the subthreshold concentration for the most sensitive person.130'131'
The data from the Russian studies must be interpreted with care.
They represent protective, rather than pathologic, responses to
the stimuli. However, the Russians claim that this protective
response indicates that the subject is being adversely affected
by the environment. Although it was only an abstract without
details of methodology, a report from Russia on the effects on
human subjects of exposure to ammonia at 20 ppm for 8 h re-
vealed significant increases in blood urea nitrogen (from 23.9
to 30 mg%) , urinary urea nitrogen (from 15,9 to 29.9 mg%), and
urinary ammonia (from 65 to 99.1 mg/ml). In addition, brady-
cardia, decreased oxygen uptake, and mild respiratory depression
were noted.^^ This report needs confirmation.
Industrial exposure to ammonia is often associated with
exposure to other air pollutants, such as nitrogen oxides,
hydrogen sulfide, and sulfur dioxide. These mixtures may occur
at acute toxic concentrations during a fire in habitable spaces
or at chronic low concentrations in industry- Studies on the
effects of such exposures are uncommon.67'93 On the basis of
the threshold for olfactory perception and reflex effects on
631
-------
biopotentials of the brain (EEC) , the threshold for the combina-
tion of sulfuric acid aerosol, sulfurous anhydride, nitrogen
oxides, and ammonia (a common atmospheric combination of
pollutants) was compared with the thresholds for the individual
pollutants. The threshold for the mixture could be character-
ized by a simple summation of thresholds for the individual
components. 93 in the absence of information to the contrary,
the effects of different hazards should be considered additive —
i.e., when the sum of the ratios of concentration to TLV for
each observed pollutant equals unity, one has reached the TLV
of the mixture (Cj + C2 . . . .CN = I).93'165 Thus, the total
TLV 2 TLVN
concentration of such a mixture expressed in parts of TLV of
each of the components must not exceed 1.
The TLV, MAC, and ceiling concentrations discussed above
are intended to define the limits of exposure in a work area.
They are meant to be guides in the control of health hazards
of workers and are intended for use in industrial hygiene
specifically. They are not meant to be applied in evaluation
or control of concentration of ammonia in the community. The
MAC and ceiling concentration of ammonia in the air of populated
areas in Russia are both 0.3 ppm (0.2 mg/m3).148 This value is
based on the threshold concentration as ascertained from central
nervous system reflex activity.130'131'132
632
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A guide for short-term public limits (STPL) for the United
States has been proposed. 74 Tne following concentrations were
considered tolerable for the duration of the exposure: 20 ppm
(14 mg/m3), ceiling for 10 min; 10 ppm (7 mg/m3), for 30 min;
10 ppm (7 mg/m3) for 60 min; and 5 ppm (3.5 mg/m3), as a TWA
not to exceed ceiling limits, for 5 h/day, 3-4 days/month.
More chronic exposure limits have not been defined for the
western world. Public emergency limits (PEL) have also been
defined: 100 ppm (70 mg/m ) for 10 min, 75 ppm (52 mg/m3) for
30 min, and 50 ppm (35 mg/m3) for 60 min.74
633
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118. Patty, F. A. Alkaline materials, pp. 859-869. In D. W. Fassett and D. D.
Irish, Eds. Industrial Hygiene and Toxicology. Vol. 2. Toxicology.
(2nd ed.) New York: Interscience Publishers, 1963.
Hq Permissible levels of Toxic Substances in the Working Environment. Sixth
Session of the Joint ILO/WHO Committee on Occupational Health, Geneva
4-10 June 1968. Geneva: International Labour Office, 1970. 405 pp.
120. Delete.
121. Pfister, R. R., J. Friend, and C. H. Dohlman. The anterior segments of
rabbits after alkali burns. Metabolic and histologic alterations.
Arch. Ophthalmol. 86:189-193, 1971.
122. Ralph, R. A. Conjunctival goblet cell density in normal subjects and in
dry eye syndromes. Invest. Ophthalmol. 14:299-302, 1975.
123. Japanese Association of Industrial Health. Recommendation for permissible
concentrations of hazardous substances in working environment. Sangyo]
Igaku (Jap. J. Ind. Health) 13:475-484, 1971. (in Japanese)
124. Delete.
125. Underwriters Laboratories. Report on the Comparative Life, Fire and
Explosion Hazards of Common Refrigerants. Miscellaneous Hazard No.
2375, pp. 26-28. Chicago: Underwriters Laboratories, 1933.
646
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126. American Conference of Governmental Industrial Hygienists. Report of the
Subcommittee on Threshold Limits, pp. 54-56. In Proceedings of the
*!
Eighth Annual Meeting of the American Conference of Governmental
Industrial Hygienists, Chicago, Illinois, April 7-13, 1946.
127. Robin, E. D., D. M. Travis, P. A. Bromberg, C. E. Forkner, Jr., and J. M.
Tyler. Ammonia excretion by mammalian lung. Science 129:270-271,
1959. (letter)
128. Roper-Hall, M. J. Thermal and chemical burns. Trans. Ophthalmol. Soc.
U. K. 85:631-646, 1965.
129. Savic, D. , B. Mihaljevic, and M. Janjic". Une grave lesion des voies
respiratoires avec issue letale. Ann. Otolaryngol. Chir. Cervicofac,
86:339-341, 1969.
130. Sayfutdinov, M. M. Experimental data proposed as a .basis for the deter-
mination of maximal allowable ammonia concentration in atmospheric
air, pp. 67-76. In B. S. Levine, (Translator). U.S.S.R. Literature
on Air Pollution and Related Occupational Diseases. A Survey. Vol.
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131. Saifutdinov,- M. M. Maxiumum permissible concentration of ammonia in the
atmosphere. Hyg. Sanit. 31(4-6):171-176, 1966.
132. Sayfutdinov, M. M. Sanitary characteristics o£ ammonia and validation of
its maximum permissible concentration in atmospheric air, pp. 58-61.
In M. Y. Nuttonson, Ed. AICE Survey of U.S.S.R. Air Pollution Liter-
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133. Schmidt, F. C., and D. C. Vallencourt. Changes in the blood following
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134. Sestier, F., J. Bernier, and R. Charbonneau. Bronchopneumopathie d'origii
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toxique par inhalation de vapeurs ammoniacales. A propos d'un cas.
Union Med. Can. 98:1903-1910, 1969.
135. Shimkin, M. B., A. A. de Lorimier, J. R. Mitchell, and T. P. Burroughs.
Appearance of carcinoma following single exposure to a refrigeration
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1954.
136. Siegrist, A. Konzentrierte Alkali- und Saurewirkung auf das Auge. Z.
Augenheilkd. 43:176-194, 1920.
137. Silver, S. D., and F. P. McGrath. A comparison of acute toxicities of
ethylene imine and ammonia to mice. J. Ind. Hyg. Toxicol. 30:7-
9, 1948.
138. Silveman, L. , and J. L. Whittenberger. Blood changes due to ammonia
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74-78, 1949.
140. Sinha, K., B. Das, and A. Charan. Cicatricial gastric stenosis caused by
ingestion of corrosives. Indian J. Chest Dis. 14:90-95, 1972.
141. Sinitsyna, E. L. Investigations into certain aspects of the health of
people working in the main shops of tanneries. Hyg. Sanit. 30(4-6):
336-340, 1965.
142. Slansky, H. H. , M. B. Berman, C. H. Dohlman, and J. Rose. Cysteine and
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Sloan, C. H., and G. P. Morie. Determinations of ammonia in tobacco and
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247, 1974.
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144. Slot, G. M. J. Ammonia gas burns. An account of six cases. Lancet 2:
1356-1357, 1938.
145. Smelyanskiy, Z. B., and I. P. Ulanova. New standards for permissible
levels of toxic gases, fumes, and dust in the air of work areas.
Gig. Tr. Prof. Zabol. 3 (5):7-15, 1959. (in Russian)
146. Smirnova, N. A., and N. P. Granik. Late after-effects of occupational
acute damage to respiratory passages by irritating gases. Gig. Tr.
Prof. Zabol. 15 (11):16-19, 1971. (in Russian, summary in English)
147. Smyth, J. F., Jr. Improved communication -- hygienic standards for daily
inhalation. Amer. Ind. Hyg. Assoc. J. 17:129-185, 1956.
148. U.S.S.R. State Committee of the Council of Ministers for Construction.
Maximum allowable concentrations of harmful substances in the air of
a work zone. In Sanitarnyye Normy Proyektirovaniya Promyshlennykh
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151- Sugar, A., and S. R. Waltman. Corneal toxicity of collagenase inhibitors.
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152. Taylor, A. S. Poisoning by ammonia, pp. 299-303. In On Poisons in Rela-
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8
old Limit Values for Chemical Substances and Physical Agents in the
Workroom Environment with Intended Changes for 1974. Cincinnati:
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i
167. Zygadlowski, J. Acute burns with ammonia vapors. Otolaryngol. Pol. 22:
773-780, 1968. (in Polish, summary in English)
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CHAPTER 8
EFFECTS ON MATERIALS
The influence of ammonia on a variety of metallic and non-
metallic materials has been well documented, ^-r 3/ 4» 7' 8 Ammonia
corrodes a number of metals and alloys, and the corrosive ef-
fects are generally increased by the presence of water. Copper,
tin, zinc, and their alloys corrode rapidly in the presence of
ammonia at ordinary and high temperatures. Metals recommended
for use in the presence of anhydrous ammonia include aluminum
and its alloys, iron and steel, essentially all stainless steels,
and the noble metals. Aluminum and the stainless steels have
low corrosion rates in the presence of ammonia-water.mixtures
as well. Contact of ammonia with mercury leads to reaction
products that are highly explosive and detonate easily. Equip-
ment containing mercury should therefore be avoided in laboratory
or industrial circumstances that involve ammonia.
Steels are generally recommened for use in ammonia-containing
environments, but some ammonia storage tanks fabricated from
carbon steels have experienced severe stress-corrosion cracking,
leading to vessel failure under some circumstances. Investiga-
t
? ft
tions of this effect ' have shown that trace quantities of air
i
accelerate the phenomenon and that the presence of water inhibits
it. Accordingly, such behavior can be controlled by the use of
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stress-relieved vessels with air-free ammonia containing trace
quantities of water.
Although ammonia is most generally associated with increased
corrosion effects, it has also been applied as a corrosion in-
Q
hibitor.0 This application has involved introduction of ammonia
into burner fuels to reduce corrosion of cast-iron firebox
interiors. This inhibition probably occurs because of neutral-
ization of the acidic sulfur-containing species normally present
in flue gases.
Ammonia has some rather pronounced effects on nonmetallic
materials. One of the best known is wood-softening, which
occurs because of an interaction of ammonia and cellulose fibers.
This effect has been applied to some advantage in the wood-
forming industry. Ammonia swells natural rubber, but some syn-
thetic rubbers appear to resist this effect.
Ammonia has an adverse effect on aerated concrete, whenever
it is exposed with high concentrations of carbon dioxide.
Ammonium hydroxide corrodes glass slowly, but this effect is
insufficient to preclude recommendation for use of glass with
ammonia solutions.
Most plastics resist ammonia and ammonium hydroxide corro-
sion. Exceptions are epoxy fiberglass, nylon, and polyvinyl-
chloride, which deteriorate under some conditions of temperature
and concentration.
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REFERENCES
1. Dasgupta, D. Mechanism of atmospheric corrosion of steel - a review.
Brit. Corros. J. 4:119-121, 1969.
2. Deegan, D. C., and B. E. Wilde. Stress corrosion cracking behavior
of ASTM A517 Grad F steel in liquid ammonia environments. Corrosion
29:310-315, 1973.
3. Fabian, R. J., and J. A. Vaccari, Eds. How materials stand up to corrosion
and chemical attack. Mater. Eng. 73(2):36-59, 1971.
4, Hamner, N. E. (Compiler) _/ Ammonia cotnpounds_/, pp. 40, 402. In Corrosion
Data Survey. Non-metals Section. (5th ed.) Houston: National
->
Association of Corrosion Engineers, 1975.
5. Kvatbaev, K. K., and £. A. Roizman. Protection of aerated concrete
structures from corrosive media. Tr. Alma-At. Nauchno-Issled.
Proektn. Inst. Stroit. Mater. 8:8-226, 1967. (in Russian)
6. Loginow, A. W. , and E. H. Phelps. Stress-corrosion cracking of steels
in agricultural ammonia. Corrosion 18:299t-309t, 1962.
7. Perry, J. H., C. H. Chilton, and S. D. Kirkpatrick, Eds. -Continuous
countercurrent operations, pp. 16-20--16-23. In Chemical Engineers'
Handbook. (4th ed.) New York: McGraw-Hill Book Company, 1963.
8. Uhlig, H. H., Ed. Corrosion Handbook. New York: John Wiley & Sons,
Inc., 1948. 1188 pp.
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CHAPTER 9
SUMMARY
CHEMICAL INTERACTIONS: TRANSFORMATIONS AND TRANSPORT MECHANISMS
Ammonia is the first inorganic nitrogen compound resulting
from the degradation of plant and animal tissues and is a central
and active participant in the nitrogen cycle. In the soil (and
in seawater), it is oxidized to nitrate by "nitrifying" micro-
organisms as their energy source. The nitrate thus produced is
again taken up by plants and reduced to the level of ammonium
nitrogen, which is incorporated into protein and other nitrogenous
compounds, completing this portion of the nitrogen cycle.
Nitrate ion can also serve as oxidant for other microorganisms
(in the absence of available oxygen) in the metabolism of organic
compounds, resulting in the production of nitrogen gas and nitrous
oxide, which are released to the atmosphere. This could result
in the delivery of essentially all available nitrogen to the
atmosphere as nitrogen gas, were it not for the processes
(largely biologic) of "nitrogen fixation," whereby the relatively
inert nitrogen gas is again converted to combined nitrogen usable
by plants or microorganisms. This constitutes another feature of
the nitrogen cycle—operating much more slowly (because of
the large nitrogen pool) than the comparatively rapid transport
from soil to plant and back to soil.
-------
The assimilation of nitrogen by plants has two principal
features: the uptake of nitrate by roots and the reduction of
nitrate to ammonium or amino nitrogen, which is incorporated
into plant tissues. Plants can also utilize ammonia directly,
but, because it is rapidly nitrified in the soil, the more common
soil form is nitrate. Nitrate assimilation requires energy pro-
vided directly or indirectly by photosynthesis.
Nitrogen fixation also requires energy and is carried on
by a limited number of microorganisms, sometimes in symbiotic
association with higher plants or fungi. Nitrogen fixation
need not require large amounts of energy from a thermodynamic
standpoint, but in practice it does. Much of this energy is
expended in splitting the nitrogen molecule.
Although it has now been shown to be possible to insert
nitrogen-fixing (nif) genes into several types of organisms,
the production thereby of an enzyme that is viable and functional
in the organism under normal field conditions has not yet been
achieved. Of the many obstacles involved, the requirement of an
anaerobic microenvironment for nitrogenase appears to be the most
immediate. Thus, although the possibilities for this approach
are, in principle, attractive and exciting, the problem is far
from solved.
In plants, nitrogen is generally transported into cells in
the form of nitrate from the soil: it is reduced to nitrite
by the enzyme nitrate reductase. Nitrite is then reduced to
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the ammonia level of oxidation by a single enzyme, nitrite re-
ductase. The ammonia formed is available for further assimilation.
Ammonia is an active metabolite, central in both the bio-
synthesis and the degradation of amino acids. It is fixed into
organic linkage by reactions with appropriate acceptors, to
form glutamic acid, glutamine, carbamyl phosphate, and, to a
lesser extent, other compounds. This ammonia-derived nitrogen
can enter a variety of biologic pathways; the amino nitrogen
of amino acids arises from ammonia via the combined reactions
of glutamic dehydrogenase plus transaminase. The equilibrium
constants of the reactions catalyzed by glutamic dehydrogenase,
glutamine synthetase, and carbamyl phosphate synthetase dictate
that the concentration of free ammonia in animal tissues must
be low, and these three enzymes are therefore of major im-
portance in the detoxification of either exogenous or metabolically
generated ammonia. Capacity to assimilate ammonia in living sys-
tems is high; glutamine synthesis and degradation are particu-
larly rapid processes, and glutamine serves as a labile "pool"
for trapping and release of ammonia.
In amino acid degradation, ammonia is formed by the com-
bined action of transaminases and glutamic dehydrogenase. In
the various species of animals, this nitrogen is then excreted
either as free ammonia (in fishes), as uric acid (in birds and
reptiles), or as urea (in mammals and some other animals). Thus,
ammonia is a central intermediate in both the biosynthetic and
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the degradative pathways of amino acids, which are the subunits
of proteins.
Transport of ammonia across cellular membranes is rapid
and efficient. Unionized ammonia readily traverses cell
membranes, but recent evidence indicates that ammonium ions
are transported by an enzyme—a sodium-potassium-dependent
ATPase.
Ammonia is present in the atmosphere as a result of
natural and anthropogenic emission. There is no known chemi-
cal reaction by which ammonia is produced in the atmosphere.
Chemical reactions relevant to the atmospheric transformations
of ammonia can be divided into four groups: aqueous-phase,
heterogeneous, thermal, and photochemical reactions.
Ammonia contributes to the formation of atmospheric aero-
sols. It reacts with acids formed from oxides of sulfur and
nitrogen. Sulfur dioxide is further oxidized in the presence
of ammonia, forming aerosols of ammonium sulfate. Aerosol
formation increases substantially at high relative humidity,
high ammonia concentrations, and low temperature. Although
the complex reaction mechanism involved seems to be adequately
described, there is considerable discrepancy in the reported
sulfur dioxide oxidation rates, which range from 2 to 13%/h.
Reaction of ammonia with soot particles results in the
heterogeneous formation of particulate ammonium complexes.
The atmospheric significance of this reaction in the polluted
troposphere remains to be established.
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Thermal reaction between ammonia and sulfur dioxide leads
to the formation of the condensable products amidosulfurous
acid and ammonium amidosulfite, which may undergo heteromolecular
nucleation. More definitive studies conducted at atmospheric
ammonia and sulfur dioxide concentrations (i.e., parts per
billion) are needed, to assess the possible importance of the
ammonia-sulfur dioxide thermal reaction in the formation of
ammonium sulfate aerosols in the troposphere. The studies of
Heicklen and co-workers suggest that thermal reactions of ammonia
with ozone and with nitric acid to form ammonium nitrate particles
are not significant causes of ozone depletion, in that the former
is at least second-order and should proceed at substantial rates
only at ammonia and ozone concentrations much higher than those
found in the atmosphere.
Two photochemical reactions, the photolytic dissociation
of ammonia (which prevails in the stratosphere) and the reac-
tion with the hydroxyl radical in the troposphere, are of
major importance for atmospheric removal of ammonia. The
latter reaction controls the half-life of ammonia, which is
about 16 days in the unpolluted troposphere and certainly shorter
in photochemically polluted areas. Both photolytic dissociation
and reaction with hydroxyl radical produce the amino radical,
whose further reactions in the atmosphere are poorly understood.
Kinetic and mechanistic studies are needed, to establish whether
ammonia oxidation results in a significant source or sink for
nitric oxide in the troposphere.
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There is only limited information on the relative im-
portance of the various reactions reviewed here in the global
atmospheric ammonia budget. It has been reported that about
half the atmospheric ammonia is destroyed by reaction with the
hydroxyl radical, the other half being accounted for by hetero-
geneous removal processes, dry deposition of ammonia, and wash-
out as particulate ammonium.
The"biochemical and geochemical mechanisms of transformation
of the nitrogen atom in natural waters through its various valence
V
ft
states have been described. Quantitative descriptions of the
rates and extents ("budgets") of these processes are sparse.
Thus, nitrogen budgets for natural waters based on closely-
spaced measurements of inputs, dynamics, and outputs are not
available.
Reservoirs impounding natural waters will influence the
concentration and distribution of ammonia through curtailment
of mixing processes and stratification of the water column.
Populations of nitrifying bacteria may be expected to increase
in such environments. These processes will alter the pattern
of nitrogen cycling in the previously free-flowing natural waters.
The transfer of nitrogen in the coastal wetlands is poorly
understood, and little information is available. An accurate
assessment of nitrogen exchanges will be required to establish
the flux into the atmosphere from the nitrogen-limited coastal
waters.
659
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Models are available for geographic mapping of the seasonal
variations in the concentration of dissolved ammonia or ammonium
in precipitation and surface waters. The available data sets
for many of the regional distribution patterns are too sparse
for quantitative purposes.
SOURCES, CONCENTRATIONS, AND SINKS
Production and Use
In 1975, 14.3 x 10 t of ammonia was produced in the United
States, almost all by the fixation of atmospheric nitrogen. About
1% of the total came from the carboniation of coal. Ammonia is
the source of nitrogen in fertilizer and of the chemical nitrogen
added to animal feed, and it is used widely in the chemical
industry.
Industrial fixation of atmospheric nitrogen began before
World War I, and methods were developed for production of nitrates
from ammonia. Synthetic ammonia began to replace imported Chilean
saltpeter as a nitrogen source late in the 1920s; by 1930, annual
ammonia production was 177,000 t. Production capacity was sig-
nificantly increased during World War II, when there was a great
need for nitrates to make munitions. Ammonia from the wartime
plants went into fertilizers when hostilities ceased. Since
1962, the average annual increase in ammonia production has been
8.5%, and continuing increase is expected to meet growing food
requirements.
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The conversion of nitrogen to ammonia requires both energy
and the hydrogen atom. Natural gas is currently the feedstock
and fuel in ammonia production in the United States. Significant
improvements have been made in the production process, and most
of the improvements have resulted in decreased energy consump-
6
tion. About 9.6 x 10 kilocalories of energy are required to
produce a tonne of ammonia. Emission of ammonia from the produc-
tion process was also decreased by technologic improvements.
Total annual emission of ammonia during manufacture of the chemical
is estimated to be 19,300 t.
The natural-gas shortage has resulted in a search for
alternative fuels for feedstock and for process heat. Vaporized
fuel oil can be used in the reformer, and this will reduce the
natural-gas requirement by about one-third. A suitable alternative
fuel for use as a feedstock has not been developed.
An aqueous effluent at ammonia plants results from the con-
densation of steam from the process gas stream. The effluent
contains ammonia and methanol and must be treated to avoid water
pollution. The effluent is normally treated by steam stripping,
which causes ammonia and methanol to be emitted into the air.
Methods should be developed to recycle and utilize the water
and ammonia waste.
About 300,000 t of ammonia are emitted per year during the
production and use of fertilizers, industrial chemicals, and the
nitrogen products. One of the uses—direct application of ammonia
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to soil as fertilizer—results in the emission of about
168,000 t/year. Techniques should be developed to minimize
these losses.
Volatilization from Cattle Feedlots and Animal Wastes
Recent trends in livestock production in the United States
have resulted in large concentrated feedlots, in contrast with
the small individual farms of a few years ago. This marked in-
crease in the confinement feeding of animals in relatively small
areas has resulted in waste disposal problems and point sources
of various odors and ammonia volatilization. Several workers
have demonstrated that significant amounts of ammonia are
volatilized from the surface of feedlots, as well as from soil
surfaces on which animal waste has been applied. The atmospheric
ammonia content is much higher in and around the feedlots than
in other areas. The major source of the volatilized ammonia
appears to be urinary urea, which is readily hydrolyzed by urease
to ammonia and carbon dioxide.
The odors normally associated with feedlot areas have been
shown to be due to volatile amines. Owing to the alkalinity of
the soil surface in these areas, the formation of nitrosamines
from these volatile amines seems highly improbable.
The ammonia that is volatilized from the feedlot and soil
surfaces does not appear to be totally lost. Atmospheric ammonia
has been shown to be absorbed from air by water surfaces in the
vicinity of feedlots. In addition, a significant amount of the
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ammonia appears to be removed from the air by green plants.
Atmospheric ammonia appears to enter into metabolism like
ammonium ions absorbed through roots or produced by nitrate
reduction in plant cells.
Atmospheric Sources and Concentrations
Because of their high concentrations in polluted air and
their accumulation in the respirable range, particles contain-
ing ammonium and the associated anions, nitrate and sulfate,
must be evaluated as a potential health hazard to human popula-
tions in urban areas. These particles can contribute significantly
to the reduction of visibility- Furthermore, particulate ammonium
sulfate and nitrate compounds may affect the radiative climate of the
earth and are directly involved in acid rain precipitation. Despite
these potentially important effects, ammonium particles have received
more limited attention than other substances in air pollution researc
Although most atmospheric ammonia is produced by natural
biologic processes, anthropogenic sources of ammonia--such as
combustion and industrial processes, feedlot operations, produc-
tion and use of fertilizers, and automobile exhaust—account for
the observed substantial increase in gaseous ammonia and particu-
late ammonium concentrations in urban atmospheres.
Studies conducted in pollution-free areas (such as coastal,
maritime, desert, and mountain sites) all indicate a background
ammonia concentration of a few micrograms per cubic meter. The
fact that bacterial activity is the major source of ammonia
663
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production is reflected in the temperature dependence of
seasonal variations (summer > winter) and geographic variations
(tropical > temperature zone) in ammonia, as well as in its
vertical concentration gradient in the troposphere.
Ammonia concentrations of up to about 300 yg/m have been
measured in the vicinity of various types of anthropogenic
sources. Ammonia in industrial and urban areas and far down-
wind in urban plumes often reaches concentrations 5-10 times
higher than "background" values typical of unpolluted regions
and exhibits opposite seasonal variations, with a winter maximum
that reflects the increased contribution of combustion processes.
Particulate ammonium is a major constitutent of tropospheric
aerosols, in which it exists as ammonium nitrate, in various com-
binations with sulfate ions (ammonium sulfate, (NH4) 3!! (804) 2/
ammonium bisulfate, and possibly other intermediate combinations
of these salts), and in traces of ammonium halides (ammonium
chloride and ammonium bromide). Measurements conducted at un-
polluted sites and vertical distribution profiles in the
troposphere indicate a background ammonium concentration of
about 1 yg/m .
Particulate ammonium concentrations of up to about 35 yg/m^
(24-h averaged concentrations) have been measured in polluted
areas, where most ammonium associated with nitrate and sulfate
accumulates in particles smaller than 1 ym in diameter. Sulfate-
and ammonium-containing particles account for a major.fraction
664
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of the total particulate burden in the atmosphere of northern
Europe and the eastern United States, whereas high ammonium
nitrate concentrations are encountered in photochemically
polluted atmospheres, such as in southern California.
Plant Ammonia Fixation
Because more nitrogen is being fixed for agricultural enter-
prise, more ammonia may be leaking into the air. However, plant
life on the land and perhaps oceans has a great capacity to ab-
sorb ammonia from the air. Available data show that land plants
might complement their supply of nitrogen by 10 kg/ha-yr through
ammonia absorption at today's ambient concentrations. Unfortu-
nately, ammonia in the form of aerosols, although known to be
increasing in the terrestrial environment and recently recognized
in the marine environment, has not been adequately evaluated or
even distinguished from the gaseous form in many atmospheric
analyses. This raises questions about sources and sinks and
about the process involved.
Micrometeorologic methods of measuring ammonia gas coming
and going at the earth's surface have recently been used to de-
termine the roles of soil, plants, and animal manure as sources
and sinks. More ammonia may be coming from the soil or detritus
on the soil surface and being absorbed by vegetation growing
above ground than previously recognized. The latter is a daytime
phenomenon, inasmuch as ammonia gas is absorbed through leaf
stomata that open only in daylight. These amounts are small,
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compared with those needed for agricultural crops; however, they
could be a significant source for natural ecosystems when the
nitrogen available for plant growth is limited. Under these con-
ditions, ammonia uptake from the air plays a role in damping the
carbon dioxide buildup in the atmosphere through storage of more
carbon in the biosphere. Wet and dry deposition of ammonium
aerosols on plants could provide a pathway for plant absorption
through the leaf cuticle during both day and night. Little is
known about this phenomenon.
The fixation of nitrogen is probably increasing, thus lead-
ing to the leakage of more gaseous ammonia to the air; but the
land plant capacity to absorb and use the nitrogen will undoubtedly
prevent any significant increase in ammonia in the ambient atmos-
phere on a global scale. The status of ammonium aerosols is
much less understood. Whether and how plants absorb ammonia
through dry or wet deposition of aerosols is unknown.
Oceans
Ammonia is the preferred nitrogen source for phytoplankton.
Nitrogen availability frequently is the critical limiting factor
in plant growth in both near-shore and open-ocean water. Organic-
rich coastal sediment is an important, but unmeasured, source of
regenerated ammonia for near-shore waters.
Ammonia regeneration in the water column plays an important
role in the nitrogen dynamics of the entire spectrum of marine
systems. Sewage and agricultural nitrogen emission can play an
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important role in the nitrogen dynamics of near-shore water.
Assessments of ammonia or other nitrogen input and concentra-
tions in the.coastal zone must take note, not only of the con-
centrations in the water, but also of the fact that organisms
rapidly react to new input of nitrogen by banking it in the
form of standing stocks. The population expansions are often
represented by undesirable organisms capable of rapid growth.
Nitrogen exchanges between the ocean and the atmosphere are
difficult to measure and poorly understood; however, the ocean
does not appear to be a significant source of either particulate
or gaseous ammonia.
Atmospheric ammonia concentrations are higher over the land
than over the oceans. A quantitative assessment of the global
nitrogen cycle will require more accurate estimates of air-sea
and sediment-water exchanges of nitrogen compounds, in addition
to further work on chemical transformations within the water
column.
TOXICOLOGY
Ammonia Toxicology in General
The intravenous or intraperitoneal toxicity of several
ammonium compounds has been determined in various species,
including mice, rats, chickens, and fishes. The toxic syndrome
appears to be the same in all species studied and may be char-
acterized by hyperventilation and clonic convulsions followed
by a graduate onset of coma, with death occurring during a tonic
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extensor convulsion. The survivors also had hyperventilation,
clonic convulsions, hyperirritability, and coma for about
20-45 min; complete recovery was usually observed in 50-60 min.
Ammonium salts are more toxic at relatively alkaline,
rather than relatively acid, pH*s. This difference appears to
be due to the ability of ammonia to cross membranes more readily
>*>
and thus produce the toxic effect. Hypothermia has been shown
to protect animals against ammonia toxicity, whereas hyperthermia
potentiates it. Hypoxia has also been shown to increase ammonia
toxicity in mice. Death during ammonia toxicosis has been at-
tributed to a direct effect of ammonia on the heart and a more
generalized effect on the brain.
Comparative studies have shown that the intraperitoneal LD5Q
values for ammonium acetate are the same in mice (a ureotelic
species) and chicks (a uricotelic species), but higher in selected
fishes (ammonotelic species).
Urea and Ammonia Toxicity in Ruminants
Urea is a valuable source of nonprotein nitrogen that is
extensively used in ruminant nutrition. The amount of urea that
can be used in the diet is limited by its toxicity. The urea
toxicity syndrome is characterized by restlessness, ataxia,
dyspnea, collapse, muscle spasm, tetany, and death. The toxic
effects of urea in ruminants are due to ammonia toxicity. The
ammonia is released by the action of bacterial urease in the
rumen. When the ammonia is released too rapidly to be utilized
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in the synthesis of bacterial protein, it is absorbed through the
ruminal epithelium; if it exceeds the detoxification capacity of
the animal, it becomes toxic. Toxic signs are observed at a
blood ammonia nitrogen concentration of 1 mg/100 ml; death
occurs at 2 mg/100 ml.
Ammonia Toxicity in Fishes
Several environmental factors have been shown to affect the
toxicity of ammonia in fish. The major factors are the pH and
temperature of the water; these govern the concentration of
unionized ammonia in solution. The unionized ammonia appears
to be the toxic form of ammonia, in that relatively high concen-
trations of ammonium ions do not appear to be toxic. Several
reports have appeared in which the water pH or temperature was
not recorded; these reports are of little benefit in establishing
guidelines concerning safe ammonia concentrations for various
fishes. A concentration of 0.024 mg/liter has been suggested
as the highest concentration of unionized ammonia that will not
cause adverse effects on fishes. This value is based on sketchy
data and cannot yet be considered as authoritative.
Several laboratory experiments of relatively short duration
have demonstrated that the lethal concentration of ammonia for
a variety of fish species is 0.2-2.0 mg/liter. Rainbow trout
appear to be the most sensitive, and carp the most resistant,
to aqueous ammonia. The report that gave 24-h ammonia TLm
values of 0.068 mg/liter for fry and 0.097 mg/liter for adult
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trout seems questionable, because these concentrations are about
one-tenth those reported elsewhere. Sublethal exposure to
ammonia has been reported to cause adverse physiologic and histo-
pathologic effects in fish.
Anydrous ammonia has been used experimentally in fishery
management for simultaneous control of fish populations, control
of submerged vegetation, and fertilization.
Ammonia Associated with Confined Housing of Domestic Animals
A problem that has been encountered in confined housing of
domestic livestock is the accumulation of atmospheric ammonia
due to bacterial decomposition of animal waste and poor ventila-
tion. In most casesf this problem can readily be avoided by
proper management,. Atmospheric ammonia at 20-50 ppm has been
shown to result in reduced feed consumption, reduced weight gain,
airsacculitis, increased susceptibility to respiratory diseases,
and a general discomfort in poultry. Higher concentrations,
60-100 ppmp were found to result in reduced egg production,
tracheitis, and keratoconjunctivitis in poultry.
Atmosp.her.ic ammonia does not appear to be a problem in most
commercial confined swine or cattle operations, at least in the
United States. Laboratory studies have indicated that atmospheric
ammonia in excess of 100 ppm will result in reduced growth rate
of swine. However, this is about 10 times the concentration
normally encountered in properly managed swine operations.
Ammonia,, wi~h other manure gases, has been reported as the
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cause of reduced growth rate and death of young cattle in several
confined units in Sweden and other parts of Europe. Again, this
problem appears to be due to improper management.
Anhydrous ammonia has been used to exterminate wild birds
and mice in farm buildings. This technique has been recommended
because of its low cost, ease of application, and lack of per-
sistent residue.
Bats
Some species of bats that roost in caves in the southwest
United States have been found to have a very high tolerance to
atmospheric ammonia. The bats have apparently adapted to the
high concentrations of atmospheric ammonia that result from
decaying feces in the caves. Atmospheric ammonia ranged from
85 to 1,850 ppm in some of the caves. These concentrations
did not appear to have any adverse physiologic effects on the
bats.
Animal Toxicology (Gaseous Ammonia)
There have been few studies of animal exposure to gaseous
ammonia, and most have consisted of gross observations of ani-
mal response and mortality rate.
There appears to be species and individual susceptibility
to the effects of acute exposure to toxic concentrations of
ammonia. Increasing concentration or duration of exposure results
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in progressive injury and increasing mortality among exposed
animalso Mice appear more sensitive than guinea pigs, which
are more sensitive than rabbits, to acute toxic exposure to
ammonia gas.
As much as 95% of inhaled ammonia is absorbed onto the
mucous membranes of the naso-oro-pharynx. This protects the
tracheobronchial tree, but not the terminal airways and alveoli.
The tissue of the terminal airways appears more sensitive to
the effects of ammonia than the remainder of the tracheobronchial
tree.
The subacute or chronic exposure of animals to ammonia at
less than 300 ppm in inspired air does not appear to produce
light microscopic changes in the lung. In contrast, concentra-
tions greater than 600 ppm resulted in a high mortality rate,
with evidence of focal and diffuse interstitial pulmonary in-
flammation in all animals studied.
Direct exposure of the trachea to ammonia at less than 100 ppm
appears to have no effect on ciliary activity. Because 95% of
ammonia inhaled has been shown to be absorbed by the naso-oro-
pharynx, it would require exposure to approximately 2,000 ppm
to produce 100 ppm at the trachea in the intact animal—the con-
centration necessary to affect tracheal ciliary activity- In con-
trast, the inhalation of approximately 1-10% of that concentration
(25-250 ppm)—i.e., approximately 1.0-12 ppm at the trachea—has
been shown to increase the infection rate and severity when
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exposed chicks or rats were inoculated with virus or mycoplasma.
Thus, the effect of ammonia on ciliary activity of the tracho-
bronchial tree does not appear to be a factor in the apparent
increased susceptibility to infection that was noted in a few
studies of such exposure to low concentrations of ammonia.
Although industrial (chronic) and accidental (acute) ex-
posure of humans to ammonia fumes often occurs in association
with exposure to other potentially toxic gases—e.g., nitrogen
oxides, carbon monoxide, sulfur dioxide, and hydrogen sulfide—
animal studies on the effects of such exposure are rare.
Cerebral Effects of Ammonia Intoxication
Several possible mechanisms have been presented to explain
the cerebral effects observed during ammonia intoxication. The
following biochemical factors have been suggested to be responsi-
ble for the neurotoxicity of ammonia:
• Impaired oxidative decarboxylation of pyruvic acid.
• Slowing of electron chain generation of ATP by
NADH•depletion.
• Depletion of a-ketoglutarate.
• Utilization of ATP and glutamate in glutamine
formation.
• Stimulation of membrane ATPase.
• Decreased synthesis of acetylcholine.
In general, all these mechanisms postulate an eventual
decrease in available cerebral energy, ultimately in the form
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of ATP, or a depletion of citric acid^cycle intermediates. The
brain stem seems most susceptible to this depletion.
Protective Agents Against Ammonia Toxicity
Many compounds have been studied as possible protective
agents against ammonia intoxication. The most effective com-
pounds in mammals are substrates of the urea cycle: arginine,
ornithine, and citrulline. A mixture of ornithine and aspartic
acid is also very effective. These compounds, when administered
intraperitoneally 1 h before an intraperitoneal injection of the
LDgg g of ammonium acetate, gave total protection. The mecha-
nism whereby these compounds exert their protective effects is
postulated to be the stimulation of urea synthesis. The most
effective agents are the urea-cycle intermediates.
Glycine and a mixture of glucose and glycine exert a
similar protective effect against ammonia intoxication in
chicks, but no comparable effect in mice. These compounds exert
their protective effect through increased synthesis of uric acid,
the end product of nitrogen metabolism in birds.
HUMAN HEALTH EFFECTS
With ever-increasing industrialization and use of fertilizer,
one may anticipate increasing exposure of the population in work
areas and the community to ammonia. The acute toxic effects of
ammonia are well defined and include irritation of the eyes, skin,
and respiratory tract.
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Liquid ammonia and solutions of ammonia are important causes
of severe alkali burns of the eye. Because of its lipid solubility,
ammonia penetrates the intact cornea more easily than other
alkalis and therefore causes deeper damage. A pH greater than
11.5 is thought to be necessary for significant tissue destruc-
tion. Severe alkali burns cause corneal ulcerations, with a
tendency toward recurrence and perforation if untreated. Com-
plications associated with severe alkali burns include symble-
pharon, corneal neovascularization, secondary glaucoma, cataract,
dry eye, and phthisis.
The prognosis for severe alkali burns of the eye is directly
related to the amount of limbal ischemia. Irrigation with water
or saline is effective treatment only if begun within 5 s of
injury; the important factor is the rapidity with which eye irri-
gation is begun, rather than the duration of irrigation or the
type of irrigant used.
The role of collagenase in stromal ulceration and the im-
portance of the epithelium both preoperatively and postoperatively
for eyes with severe alkali burns have come to be understood only
in the last few years. With this understanding have come new
therapeutic approaches, both medical and surgical, that promise
visual rehabilitation of a substantial proportion of eyes with
severe alkali burns.
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Exposure to high concentrations of ammonia may result in
third-degree skin burns and death from respiratory injury.
Chronic eye and skin changes secondary to acute toxic exposure
to ammonia are well described. Late respiratory tract sequelae
are uncommon, even after nearly fatal acute pulmonary changes.
However, the limited number of patients so examined and the
relative insensitivity of the tests performed to detect altera-
tions in lung function make it difficult to be certain of the
true incidence and type of chronic lung changes that follow such
exposure. The results of the few studies of human inhalation of
ammonia at low or moderate concentrations for 5 min to 8 h are
conflicting and suggest that brief exposure (5-30 min) to 30-560
ppm has little effect other than mild eye and upper respiratory
tract irritation. Longer exposure—4-8 h at 560 and 20 ppm,
respectively—may induce metabolic changes. Certainly more such
studies are warranted. The three studies that suggested a possi-
ble relationship of ammonia exposure and cancer need verification.
It is apparent that environmental air standards for work areas
are based on a paucity of data mostly from poorly controlled
studies. The recommended TLV is an arbitrary value designed
to eliminate most complaints of irritation of the eyes and upper
respiratory tract. Empirically, it appears that the TLV for
ammonia of 35 ppm (25 mg/m^) would result in no health hazard
to workers. However, this needs verification with well-designed
epidemiologic studies.
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There is little information on concentrations of ammonia
encountered in .the workplace or on the farm. What is available
suggests that such ammonia is not a problem—if the current TLVs
are truly safe over a work-life exposure. Finally, there is
even less information on the effects of ammonia encountered in
the urban environment on the general population.
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CHAPTER 10
RECOMMENDATIONS
It is easy to make recommendations, particularly for re-
search. If all recommendations of all committees were given
equal priority, nothing would happen. We have therefore placed
our recommendations into two categories; the more urgent of
these are printed in italics. The word "urgent" is used in a
special sense: Italicized recommendations are those of broad
current importance, as well as those which deal with subjects
in which there is substantial public interest. In addition,
italics are used for recommendations that involve important
questions or uncertainties about potential health or environ-
mental effects. The nonitalicized recommendations are not less
real, but they encompass narrower subjects, and those with pri-
mary interest in them may be groups, individuals, or agencies
with objectives different from those of the Environmental Pro-
tection Agency. Other broad environmental recommendations are
; \
nonitalicized because the Subcommittee feels that, although the
questions raised are of interest, the environmental problems
addressed are of less immediate public importance.
X
To illustrate: Sections on the nitrogen cycle\and denitri-
fication are italicized, because there is at the moment a public
question of whether fertilizer application, followed by
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denitrification, leads to ozone depletion, A definitive answer
cannot yet be given, so relatively high priority is attached
to acquiring information on the subject. However, although
studies of the inflammatory response to ammonia burns of the
eye are of great importance to both patient and doctor, they
are of less general public interest and are perhaps better
addressed by more specialized agencies.
NITROGEN CYCLE
The evaluation of the interrelationship of ammonia and
ammonium relative to other components and processes in the
nitrogen cyele necessitates more quantitative information on
a number of processes and reactions. Particular needs are:
0 Global figures on nitrogen fixation by all
biologic and other processes in terrestrial and
oceanic environments.
• Estimation of the amount of ammonia produced and
volatilized from tidal areas, estuaries, and
marshland.
• Determination of the comparative significance of
nitrification and denitrification as sources of
nitrous oxide on land and in the sea.
0 Accurate estimates of the emission, movement, and
degradation of ammonia in the atmosphere.
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GENETIC MANIPULATION OF PLANTS FOR NITROGEN FIXATION
Research in genetic manipulation of plants to insert
nitrogen-fixing genes should continue to be pursued actively,
although success is by no means ensured. In addition, the
survey of existing species should continue: some strains of
Rhizobium compete better in a particular soil than other strains.
Understanding the basis of soil-plant interaction would improve
chances for the development of more useful agricultural strains.
Thousands of different species of legumes grow wild around the
world. It is important that these be screened, to determine
their value for food and for enriching poor soils.
DENITRIFICATION
Additional information is needed regarding denitrification.
This process can result, ultimately, in the production of nitrous
oxide from nitrogen fertilizer. Atmospheric nitrous oxide con-
centrations should be monitored, and field, aquatic,' and waste-
disposal sources should be evaluated as nitrous oxide sources.
The rates of natural processes of nitrous oxide production and
destruction should be better assessed.
ATMOSPHERIC TRANSFORMATIONS
Several subjects should be further explored, to improve our
understanding of the physical and chemical transformations of
ammonia in the atmosphere. More specifically, the following
studies are recommended:
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• Kinetic and mechanistic studies of the ammonia-nitric
oxide-oxygen system should be directed to establishing
whether destruction of ammonia in the atmosphere repre-
sents a 'Source of nitric oxide or a sink for nitric
oxide. The rate constants for the reaction of the
amino radical with oxygen and nitric oxide should be
established.
• To understand better the formation and fate of acid
rain and of ammonia-containing particles, the dynamics
of ammonia gas-to-particle conversion processes should
be further investigated. This would require field
measurements of aerosol and particulate concentrations
and study of the thermodynamics and physics of aerosols.
• The processes for the removal of ammonia from the
troposphere should be better described. These processes
include reactions of gaseous ammonia with receptors
and washout as particulate ammonium-containing materials,
• Global nitrogen budgets for the troposphere should be
refined to include a broad spectrum of often-neglected
nitrogen compounds.
WATER
The capability of monitoring ammonia in surface and ground
waters in the United States is inadequate for obtaining good
descriptions of ammonia concentrations in various regions.
Such information should be obtained, mapped (with available
computer mapping techniques) , and utilized in combination
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with mapping of rainfall data, to show nationwide trends in
ammonia concentrations.
The growth of organisms in coastal waters is nitrogen-
limited. A knowledge of nitrogen budgets in wetland areas
would improve our understanding of life in coastal waters.
Reservoirs can cause stratification of ammonia concen-
trations in surface waters. The effect of this phenomenon
on plants, animals, and nitrifying bacteria should be assessed.
PRODUCTION AND USES OF AMMONIA
Ammonia production requires a source of energy and of
hydrogen. Natural gas can furnish both and can be both a
fuel and a feedstock. The shortage of natural gas has led
to studies of alternative feedstocks for ammonia production.
It is recommended that priority be given to a search for
potential feedstocks that will minimize pollution problems
or safety hazards during ammonia production and that will
permit industry to meet pollution abatement and safety
standards with relatively low capital investment. Naphtha
and electrolytic hydrogen are feedstocks that create environ-
mental problems comparable with those related to natural gas.
Other feedstocks should be sought. No changes in current air-
pollution standards are considered necessary for emission from
ammonia plants that use natural gas as a feedstock and natural
gas or light fuel oil (No. 2) as fuel for the reformers.
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At modern ammonia plants, about 972 kg of water condensate
is obtained per tonne of ammonia produced. The condensate con-
tains about 1 kg of ammonia per tonne of ammonia produced.
Effluent guidelines limit the amount of ammonia that can be
discharged, and about 98% of the ammonia must be removed before
the effluent can be discharged as a waste. With present water-
treatment technology, ammonia-plant condensate is steam-stripped,
and ammonia removed from the wastewater is emitted into the air.
It may be possible to recycle the condensate in the ammonia-
plant process and thereby eliminate emission of ammonia to the
air. Furthermore^ recycling the condensate would decrease the
consumption of energy in the steam-stripping operation. It is
recommended that studies be undertaken to investigate recycling
of the ammonia-plant condensate in the process.
Of all ammonia losses from production and application in
industry and agriculture, the major portion occurs during the
direct application of ammonia to soil. Although this process
is relatively efficient (only 5% of ammonia applied is lost to
air), the loss accounts for 60% of the total industrial-
agricultural loss. For resource conservation, efforts should
be directed toward reducing further the loss of ammonia during
production, distribution, and application. The amount of total
nitrogen lost in air and ground water when nitrogen fertilizers
are applied to the soil is about 8 times as much as the loss,
as ammonia, during the production and distribution of fertilizers,
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The nitrogen losses in air and ground water result from denitri-
fication and leaching, respectively, of soil nitrogen. It is
recommended that major effort be directed toward development of
improved nitrogen fertilizers that are less susceptible to such
losses. This should be part of a continuing effort to improve
agricultural practices and decrease nitrogen losses in air and
ground water.
AMMONIA VOLATILIZATION FROM ANIMAL WASTES
Methods should be developed to reduce the volatilization of
ammonia from feedlot surfaces, to conserve nitrogen for agricultural
use. Study of the ammonia flux from feedlot areas into surface
water and plant leaves would provide useful background data.
ATMOSPHERE
Polluted air contains particles and droplets that in turn
contain nitrate and sulfate, which may constitute a health
hazard to human populations in urban areas and contribute sig-
nificantly to the reduction of visibility. Some of these particles
contain ammonium ion, but it is not known whether the ammonium
moiety lessens or heightens toxicity. Present evidence suggests
that ammonia lessens toxicity. Furthermore, particulate ammonium,
sulfate, and nitrate compounds may affect the radiative climate
of the earth and are directly involved in acid-rain precipitation.
Ammonium-containing particles have received more limited
attention than other substances in air-pollution research.
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Specific recommendations related to the atmospheric concentra-
tions of ammonia are as follows:
• An improved inventory of ammonia emission from
stationary and automotive sources should be
developed.
• Methods should be developed or refined for the
routine measurement of ambient ammonia at parts-
per-billion concentrations. These methods should
be suitable for continuous measurement of ambient
ammonia as part of a limited monitoring network.
• Simultaneous measurements of ammonia and of
particulate hydrogen (acidity), ammonium, sulfate,
and nitrate content are needed, to elucidate further
the role of ammonia in the formation of particulate
ammonium, nitrate, and sulfate and to formulate im-
proved strategies for the control of these major
inorganic pollutants.
PLANT AMMONIA FIXATION
Plants may play a role in absorption of ammonia and ammonium
aerosols. Research is needed to distinguish gaseous and particu-
late components in the cycling of ammonia between the atmosphere
and vegetation.
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OCEANS
Ammonia is important in the nitrogen dynamics of coastal
waters. Municipal sewage effluent is a major source of ammonia
in these waters. The effects of municipal sewage on the nitrogen
economy of coastal waters should be examined.
Ammonium fluxes across the sediment-water interface should
be measured for the range of sedimentary conditions found in
coastal water.
TOXICOLOGY AND HEALTH EFFECTS
Despite much effort, the metabolic basis of ammonia toxicity
is insufficiently understood. Sound research in this area should
be encouraged. The basis of hepatic coma should continue to be
studied, and the functional importance of depletion of citric
acid-cycle intermediates and ATP depletion should be examined.
The possible role of ATPase, acetylcholine, and other neurotrans-
mitters requires further investigation.
The treatment of urea toxicity in ruminants is not as
effective as could be desired, and additional studies are needed
on the causes of death due to urea feeding or rumen ammonia
production.
Both short- and long-term tolerance limits for ammonia in
fish should be established, so that guidelines can be developed
for safe concentrations in natural waters.
Proper ventilation and waste management can prevent the
buildup of ammonia in the ambient air in confined livestock
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facilities. Information about proper technical construction and
utilization is available and should be disseminated to livestock
producers.
Bats can tolerate extremely high concentrations of atmospheric
ammonia; their mechanism of tolerance should be studied, in the
hope that the information could be used to protect more sensitive
species, including man.
Animal studies of pulmonary effects have been limited in
number and sometimes inadequately controlled. Additional studies
of physiologic and biochemical effects of ammonia on pulmonary
ultrastructure and function would therefore be useful.
Studies of late sequelae of acute toxic inhalation of
ammonia and of responses to chronic low exposure to ammonia
need to be performed. Ammonia needs to be investigated as a
sole pollutant and in mixtures with other pollutants, such as
carbon monoxide, nitrogen oxides, sulfur dioxide, and hydrogen
sulfide. Because studies of the synergistic effects of various
combinations of pollutants at various concentrations could in-
volve a large number of permutations and require a tremendous
expenditure of effort and resources, these studies should be
carefully selected and designed. Available empirical observa-
tions on man suggest that gaseous ammonia as encountered in
air pollution adds little to the toxicity of other pollutants.
Thus, it appears appropriate to suggest here, as well as for
some of the recommendations to follow, that such studies be
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preceded by careful, well-controlled epidemiclogic surveys.
This will permit proper identification of the problem, if
present, and of the specific combinations of pollutants that
need be investigated. The following subjects warrant evalua-
tion, to determine threshold and safe limits for acute and
chronic exposure to ammonia (alone or with carefully selected
synergists) with respect to age:
• Functional changes of the terminal airways, i.e.,
frequency-dependent compliance, closing volume,
and flow rates at low lung volume.
• Structural changes, as studied by ultrastructural
techniques, scanning electron microscopy, auto-
radiographic techniques of cell turnover in the
lung and bronchial tree, and electron microscopic
tracer studies of pulmonary capillary permeability.
• Biochemical changes -in vivo and in vitro, particularly
with respect to collagen and elastin metabolism; mucin
production; protein, carbohydrate, and lipid (sur-
factant) metabolism; histamine and serotonin release;
lysosomal enzyme alterations; and effects on other
enzyme systems.
• Changes in lung defenses, as manifested by changes
in humoral and cell-mediated immunologic function,
macrophage function, and in vivo and in vitro re-
sponses to bacterial and viral challenge.
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The continued study of metabolic ammonia toxicity, and of
hepatic encephalopathy should be encouraged, to elucidate the
various intracerebral biochemical mechanisms and assess their
significance for human hepatic coma and other types of ammonia
intoxication.
The initiation and perpetuation of the acute inflammatory
response to ammonia burns of the eye should be studied further.
Study is also needed of the various cellular interactions that
result in protease degradation of the cornea and of the question
of why ammonia-burned eyes are slow to epithelialize.
Monitoring of the industrial environment and workplace
should continue, to accumulate accurate measurements of ammonia
in air and, if necessary, to refine industrial standards.
Additional well-controlled human inhalation studies should
be conducted. They should last at least a few hours and should
include monitoring of such metabolic and respiratory character-
istics as blood urea nitrogen, urinary urea nitrogen, serum
and urinary ammonia, closing volume, frequency-dependent com-
pliance, alveolar-arterial oxygen gradient, maximal midexpiratory
flow, and flow rates at low lung volumes.
Epidemic/logic studies on selected industrial-rural popula-
tions chronically exposed to accurately monitored ammonia con-
centration are recommended. Other air pollutants, if present,
should be identified and monitored. Detailed and accurate epi-
demiologic histories and tests of respiratory and metabolic
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characteristics are necessary, and there should be well-studied
control groups. Smokers and nonsmokers should be specifically
identified, because the effect of cigarette smoke may obscure
the effects of air pollutants. The incidence of neoplasm in
the group should also be determined.
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