EPA/600/8-90/038F
September 1990
Summary Review of Health Effects
Associated with Dimethylamine
Health Issue Assessment
Environmental Criteria and Assessment Office
Office of Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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Disclaimer
This document has been reviewed in accordance with US. Environmental
Protection Agency policy and approved for publication. Mention of trade
names or commercial products does not constitute endorsement or
recommendation for use.
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Preface
The Office of Health and Environmental Assessment has prepared this
summary health assessment to serve as a source document for EPA use. The
summary health assessment was developed for use by the Office of Air
Quality Planning and Standards to support decision making regarding possible
regulations of dimethylamine as a hazardous air pollutant.
In the development of the summary health assessment document, the
scientific literature has been inventoried through December 1989, key studies
have been evaluated, and summary/conclusions have been prepared so that
the chemical's toxicity and related characteristics are qualitatively identified.
Observed effect levels and other measures of dose-response relationships are
discussed, where appropriate, so that the nature of the adverse health
responses is placed in perspective with observed environmental levels.
Any information regarding sources, emissions, ambient air concentrations,
and public exposure has been included only to give the reader a preliminary
indication of the potential presence of this substance in the ambient air. While
the available information is presented as accurately as possible, it is
acknowledged to be limited and dependent in many instances on assumption
rather than specific data. This information is not intended, nor should it be
used, to support any conclusions regarding risk to public health.
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Abstract
Chemical properties, sources, environmental fate, biodistribution,
biometabolism and toxicity studies for dimethylamine (DMA) are reviewed. At
25°C, DMA is a colorless, alkaline, flammable gas which is readily soluble in
water. Sources of DMA are both natural and anthropogenic. Atmospheric
concentrations near plants emitting DMA range from 0 to 0.13 ppm (0 to 242
ng/m3). in the atmosphere, this amine reacts in daylight with hydroxyl radicals,
and-in darkness with nitric acid or nitrate. Estimates of half-life of DMA in the
lower troposphere are 3 to 6 hrs. Additional hydroxyl-related reactions form
dimethylnitrosamine, N-nitrodimethylamine (NNDA), amides, and
formaldehyde. Inhalation, ingestion, and endogenous production account for
the body burden of DMA. DMA is readily absorbed when ingested or inhaled
with 80 to 90 percent excreted unmetabolized in urine. Nasal and liver
microsomes convert some DMA to formaldehyde. In the presence of nitrite
and acidic conditions (e.g., stomach), DMA can be converted to nitrosamines;
although it appears that the amounts required exceed reasonable dietary
conditions. Acute toxicity in animals is due to ocular and sensory irritation. The
inhalation LC50 in mice has been estimated to be 7,650 ppm and in rats 4,540
ppm. The slope of the dose/percent mortality curve for both species is steep;
for rats, the lowest level for mortality is 3,983 ppm. The oral LD50 in animals
(250 to 700 mg/kg b.wt.) is dependent on its alkalinity. Inhalation studies of up
to 2 yrs in 2 or more species indicate concentration-dependent toxicity,
primarily in nasal mucosa, with no other tissues affected except for a 10
percent decrease in body weight at 175 ppm. There is no evidence for
carcinogenicity or mutagenicity. No data were found on teratogenic or
reproductive effects. Human data related to DMA exposure were not located
except for secondary reports of eye irritation at low concentrations, with nose,
throat, and lung irritation at 100 ppm DMA. Skin or eye contact produces,
severe, sometimes permanent burns. Further data are needed on ambient
levels and human health effects.
IV
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Table of Contents
Preface '"
Abstract iv
Tables v!l
Figures YJ|
Authors, Contributors, and Reviewers viii
1. Summary and Conclusions 1
2 Background Information 5
2.1 Physical and Chemical Properties 5
2.2 Organoleptic Properties 5
2.3 Natural Sources of Dimethylamine 5
2.4 Production, Use, and Occupational Exposure 7
2.4.1 Production 7
2.4.1.1 Manufacturing Process 7
2.4.1.2 Production Volume 7
2.4.1.3 Producers and Importers 8
2.4.1.4 Technical Product Composition 8
2.4.1.5 Storage, Handling, and Disposal 9
2.4.2 Use 9
2.4.3 Occupational Exposure 9
2.5 Quantitation and Analysis 10
2.6 Environmental Levels and Fate 14
2.6.1 Sources of Dimethylamine in the Environment .... 14
2.6.2 Environmental Levels 15
2.6.3 Environmental Chemistry 15
2.6.3.1 Reaction of DMA with Hydroxyl Radicals in Air 16
2.6.3.2 Reactions of DMA with Ozone 16
2.6.3.3 Aqueous Reaction of DMA with Nitrite .... 17
2.6.3.4 DMA Reactions with Nitrogenous Compounds 17
V
3. Metabolism 23
3.1 Inhalation Exposure 23
3.2 Oral Administration ' 25
3.2.1 Dimethylamine Biochemistry 25
3.2.2 Absorption 26
3.2.3 Distribution 26
3.2.4 Excretion and Secretion 27
3.2.5 Metabolism 30
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Contents (Continued)
3.3 Summary of Dimethylamine Metabolism 33
4. Animal Toxicology 35
4.1 Inhalation Toxicity . . . . 35
4.1.1 Acute Toxicity 35
4.1.2 Subchronic Toxicity 38
4.1.3 Chronic Toxicity 39
4.1.4 Carcinogenicity 41
4.2 Oral Toxicity 42
4.2.1 Acute Toxicity 42
4.2.2 Subchronic Toxicity 42
4.2.3 Chronic Toxicity 43
4.2.4 Carcinogenicity v. . . 43
4.2.5 Interactions and Synergistic Toxicity 43
4.2.5.1 Acute Exposure 43
4.2.5.2 Subchronic and Chronic Exposure 44
4.3 Mutagenicity 46
4.3.1 Gene Mutatation Assays 46
4.3.1.1 Reverse Mutation in Prokaryotes 46
4.3.1.2 Mammalian Cell Gene Mutation . . 47
4.3.1.3 In Vivo Gene Mutation (Host-Mediated Assays) 47
4.3.2 Chromosomal Aberration Assay 48
4.3.3 Other Mutagenic Mechanisms 48
4.3.3.1 Sister Chromatid Exchange (SCE) 48
4.3.3.2 DNA Repair'in Rat Hepatocytes 48
4.3.4 Conclusions 49
4.4 Teratogenicity and Reproductive Effects 49
4.5 Summary of Animal Toxicology 49
5. Human Health Effects 51
6. References . 53
VI
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List of Tables
No.
2-1 Physical and Chemical Properties of Dimethylamine 6
2-2 Production Volume, Imports, and Exports of Dimethylamine
for 1980-1985 7
2-3 Analytical Methods for Dimethylamine : . 11
2-4 Reported Atmospheric Concentrations of Dimethylamine .. 15
2-5 Conditions for DMA Conversion to DMNA 21
3-1 Disposition of Radioactivity in Rats Exposed to
[14C]Dimethylamine 23
3-2 Tissue Distribution of Inhaled [14C]Dimethylamine
Immediately Postexposure 24
3-3 Dimethylamine Balance in Rats 29
4-1 Acute Toxicity Values for Dimethylamine in Laboratory
Animals 36
List of Figures
3-1 Proposed scheme for the formation of methylamine,
dimethylamine, and trimethylamine in the mammalian
gut 25
3-2 Tissue distribution of [14C]dimethylamine 4 hours after
intravenous administration at 10 mg (20 viCi)/kg 28
3-3 Concentrations of nitrosatable compounds in human saliva
after ingestion of dimethylamine-hydrogen chloride in
solution or wafer form 31
4-1 Anatomical diagram of the nasal cavity of a 10-wk-old rat
exposed to 175 ppm DMA for 1 or 9 days 37
4-2 Anatomical diagram of the nasal cavity of an old rat
following 2 years.of exposure to 175 ppm DMA 38
VII
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Authors, Contributors, and Reviewers
This document was prepared by Dynamac Corporation under contract to
ECAO/ RTP U.S. Environmental Protection Agency (Winona Victery, Ph.D.,
Project Manager).
The following personnel of Dynamac Corporation were involved in the
preparation of this document: Nicolas P. Hajjar, Ph.D. (Project Manager);
Charles E. Rothwell, Ph.D. (Principal Author); Patricia Turck, Duane Parker,
Ph.D., Jess Rowland, and Tom England (Authors); Laura Chen and Anne
Gardner (Technical Editors); Leonard Keifer, Ph.D. (Reviewer); and Gloria Fine
(Information Specialist).
This document was reviewed for technical and scientific merit by W. P.
Dubinsky, Ph.D., Department of Physiology and Cell Biology, University of
Texas, Houston, TX; D. Stedman, Ph.D., Department of Chemistry, University
of Denver, Denver, CO; K. T. Morgan, Ph.D., CUT, Research Triangle Park,
NC; and L. T. Cupitt, Ph.D., B. Tilton, Mark Greenberg, and Harriet Ammann,
Ph.D. of the U.S. EPA.
VIII
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1. Summary and Conclusions
Dimethylamine (DMA) is a flammable, alkaline, colorless gas at room
temperature and atmospheric pressure. It is volatile due to its high vapor
pressure (at 25°C, vapor pressure is 1,500 Torr). It is a somewhat stronger
base than ammonia and dissolves rapidly in water to yield alkaline solutions.
DMA has a characteristic fishy odor at lower concentrations, whereas at higher
concentrations (100 to 500 ppm), its odor is more like that of ammonia. Odor
detection thresholds for DMA in air and water are approximately 0.3 and 0.7
ppm, respectively.
DMA enters the atmosphere from both natural and anthropogenic sources.
It has been found in the excreta of humans, pigs, cattle, and poultry. DMA also
occurs naturally in fruit, vegetables, grains, and especially seafood. Anthro-
pogenic sources of DMA include production losses, losses from dispersive
uses, automobile emissions, and emissions from garbage dumps and waste
treatment facilities. Data on atmospheric levels of DMA in the United States
were not found. However, DMA levels ranging from 0 to 0.13 ppm (0 to 242
have been measured in an industrial area with plants that emit DMA.
From several studies of the atmospheric reactions of DMA, it can be
estimated that the reaction with the hydroxyl radical is the most important
process that degrades this amine during daylight, while reactions with nitric
acid or nitrate (NO3) are significant in the dark, according to some
researchers. Based on reaction rate measurements, the half-life of DMA in the
lower troposphere was estimated to be 3 to 6 hours in daylight. No rate data
were found for the suggested dark processes. The hydroxyl radical (HO) is
reported to form dimethylamino radicals that react further with nitrogen oxides
(NOX) and oxygen to form dimethylnitrosamine (DMNA), N-nitrodimethylamine
(NNDA), amides, and formaldehyde. The highly carcinogenic DMNA is
destroyed by sunlight with a half-life of approximately one hour, wKile the
carcinogenic NNDA is relatively stable to this radiation. Reactions of DMA with
ozone (O3) and nitrogen tetroxide (N2O4) have also been studied; based on
the typical concentrations of these pollutants in ambient air, such reactions are
not important to the degradation of DMA.
DMA can be introduced into the body via ingestion or inhalation.
Additionally, studies have shown that DMA can be synthesized within the body
from other dietary constituents by microorganisms in the gut and by
unidentified endogenous pathways. It has been suggested that DMA is an
important nutrient, acting as a stimulator of postprandial gastrin secretion and
directly as a stimulator of gastrointestinal mucosal growth.
Quantitative absorption studies with single doses of labeled DMA have not
been performed; however, data from other studies indicated that DMA is
readily absorbed following inhalation or ingestion. The major site of absorption
in adult male rats following inhalation of [14C]DMA at 10 or 175 ppm for 6
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hours was the nasal mucosa. Very little, if any, of the inhaled [14C]DMA
reached the lung directly. Following ingestion, the major site of DMA
absorption appears to be the upper small intestine; absorption from the
stomach is barely detectable, as expected for an ionized substance.
After absorption, DMA travels via the blood to the various internal organs
and tissues. Tissue distribution studies performed in adult male rats and
guinea pigs Indicate that 4 hours following an intravenous dose of 10 mg/kg
[14C]DMA, concentrations of radioactivity are highest in the kidneys. Levels of
[14C] in most other tissues were less than half the kidney levels. A similar
distribution pattern was observed in adult male rats immediately following a 6-
hour inhalation exposure to [14C]DMA at 10 or 175 ppm.
DMA is excreted mainly via the urine. After inhalation of P4C]DMA at 10
ppm for 6 hours, male rats excreted mean levels of 78, 12.5, and 1.5 percent
of the recovered [14C] in the 0- to 72-hour urine, feces, and expired air,
respectively. After 6-hour exposures to 175 ppm [14C]DMA, mean levels of
86.7, 5.1, and 1.5 percent of the recovered [14C] were found in the 0- to 72-
hour urine, feces, and expired air, respectively . After intravenous injection of
60 iimol of [14C]DMA, adult male rats excreted 85 to 90 percent of the dose
into the 0- to 24-hour urine as unmetabolized DMA. Less than 0.1 percent of
the dose was expired as [14C]DMA and 0.5 percent as radiolabeled carbon
dioxide.
Balance studies indicate that urinary excretion accounts for 95 percent of
the DMA excreted in combined urine and feces. DMA excretion can range
from 1.5 to 14.7 times intake, depending on the amount of DMA ingested. The
excess DMA is considered to arise from in vivo synthesis by the host and/or
gastrointestinal flora. DMA can be absorbed from the gut into the bloodstream;
from there, it can be secreted into the bile, gastric juice, and saliva. Therefore,
DMA does undergo a certain amount of enterohepatic circulation.
It has previously been suggested that DMA is an end metabolite, i.e., that
it is not metabolized. However, it has been shown that DMA can be
metabolized in vitro to formaldehyde, albeit slowly, by rat hepatic and nasal
microsomes. Perhaps as much as 8 percent of inhaled DMA may be
converted to formaldehyde by rats in vivo. No information was found in the
available literature on potential DMA metabolites other than formaldehyde nor
on DMA metabolites in urine or feces. However, 98.7 percent of the
radioactivity in the 0- to 24-hour urine of male rats injected intravenously with
DMA was shown to be unmetabolized parent compound, indicating that little, if
any, DMA metabolites are excreted in the urine. There is evidence to show
that DMA can be chemically converted to DMNA in the presence of nitrite and
acidic conditions and that this conversion can take place in the mammalian
stomach when the compounds are administered by gastric intubation.
However, it has not been demonstrated that significant levels of DMNA are
formed in the stomach under reasonable dietary conditions or that absorption
of DMNA from the gastrointestinal tract occurs under these conditions. The
experimental doses used in these studies are relatively high when'compared
to air exposure routes.
The high water solubility and alkalinity of DMA contribute greatly to the
compound's toxicity. Acute inhalation exposures in rats and mice produce
immediate signs of ocular and sensory irritation. Under experimental
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conditions, the decrease in respiratory rate at particular air concentrations is
determined. The air concentration for 50% depression is the RD50. The RD50
values'for rats and mice, 573 and 511 ppm, respectively, are much lower than
the LC50 values (4,540 and 7,650 ppm for rats and mice, respectively).
Although no LOEL was actually determined, a TLV for sensory irritation for
humans was estimated to be between 0.01 RD50 and 0.1 RD50, with 0.1 RD50
the ceiling value. This range is between 5 and 51 ppm DMA. In rats exposed
to DMA concentrations of 600 ppm for 6 hours, pathological lesions were
limited mainly to the eyes and nasal mucosa. As the DMA concentration
approached lethal levels, greater toxicity to the lung and liver were observed.
For all doses tested, however, the tissues of the nasal cavity were most
severely affected, and a distinct anterior-to-posterior severity gradient was
observed; the lung was minimally affected.
The irritant properties of aqueous DMA also appear to be mainly
responsible for its acute oral toxicity. The oral LD50 values for aqueous DMA in
mice, rats, guinea pigs, and rabbits are 5 to 11 times lower than for neutralized
DMA. DMA is also highly irritating to the eyes of rabbits.
The results from studies on subchronic and chronic inhalation toxicity of
DMA in rodents show the same basic trends as those found with acute
exposures. In mice and rats exposed to DMA at 0, 10, 50, or 175 ppm for 6
hours/day, 5 days/week for up to 12 months, the most sensitive tissue was the
nasal mucosa. No other tissue, including liver and lung, was affected. Body
weights, however, were approximately 10 percent lower in the 175-ppm group
than in controls. Slight pathological lesions were observed in the olfactory
sensory cells of animals in the 10-ppm groups; this concentration, however is
considered to be the NOAEL, with 50 ppm, the LOAEL concentration. The
NOAEL data at 10 ppm from this,chronic study were used to calculate a RfDi
for DMA for humans of 2 vg DMA/mS (1.0 ppb) of air. This value has been
verified by the RfD work-group in 11/89. Reports of hepatic, testicular,
pulmonary, immunological, and central nervous system effects from long-term,
low-level exposure of animals to DMA have been made, but are questionable
because they are from studies that would be considered inadequate by
today's standards.
No evidence for carcinogenicity resulting from exposure to DMA has been
found. A 2-year toxicity/oncogenicity study in rats and mice has been
completed, but the results have not been published in full; there was no
evidence of increased tumors in these animals. The available genetic
toxicology studies are mostly inadequate and tend to show that DMA is
nonmutagenic. Several studies indicate that combined administration of DMA
and nitrite produces signs of toxicity similar to those observed after DMNA
administration. These include liver damage, mutagenicity, and carcinogenicity.
However, the doses of nitrite and DMA required to produce these effects are
extremely high, making the theory of DMA conversion to the carcinogenic
DMNA under normal dietary or inhalation exposure conditions questionable.
No information was found in the available literature on teratogenic and
reproductive effects of DMA.
A search of the primary literature failed to produce any reports on the
human health effects associated with exposure to DMA. However, several
secondary sources have reported a variety of acute toxic effects associated
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with DMA exposure. All reported effects of DMA in humans are related to the
compound's irritancy. Exposure to DMA vapors produces irritation of the eyes
with conjunctivitis and corneal edema. Inhalation of concentrations higher than
100 ppm can cause irritation of the nose and throat and lung irritation with
dyspnea and cough. The vapors may also produce primary skin irritation and
dermatitis. Direct contact with the liquid can produce severe and sometimes
permanent eye damage or skin burns. The effects of long-term, low-level
exposure to DMA are not known.
In conclusion, adequate data on practically all aspects of the environ-
mental levels and fate and the toxicity of DMA are lacking. Atmospheric levels
of DMA in the United States are not known. The percentage of atmospheric
DMA arising from natural or anthropogenic pathways has not been fully
characterized. Although a sustained level of DMNA does not apparently result
from the degradation of DMA in normal atmospheres, the concentrations of
NNDA that result have not been determined. No 2-year chronic
toxicity/oncogenicity, teratology, or reproductive studies in animals were found
although a 2-year study has been completed, but not published. Additionally,
no epidemiology studies or case histories of DMA exposure to humans were
found. Finally, evidence for the chemical conversion of DMA to DMNA in the
atmosphere, in vitro, and in vivo has been found, but the potential health
effects associated with combined exposure to DMA and nitrites after ingestion
has not been adequately demonstrated.
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2. Background Information
2.1 Physical and Chemical Properties
DMA (CAS No. 124-40-3) is a flammable, alkaline, colorless gas at room
temperature and atmospheric pressure. At relatively high concentrations (i.e.,
over 2 percent), the vapors are heavier than air and can travel a considerable
distance to reach an ignition source and flashback (Air Products and
Chemicals, Inc., 1983). Concentrated DMA vapors are also corrosive and have
been reported to damage the boots, gloves, and face shields of firefighters
attempting to plug a leaking tank car (Howard, 1984). Contact of DMA vapors
with strong oxidizers, chlorine, or mercury can cause fires and explosions
(Mackinson et al., 1981). DMA can be compressed into a clear, water-white
liquid (E. I. du Pont de Nemours & Company, 1984).
DMA is a somewhat stronger base than ammonia. It dissolves rapidly in
water to yield alkaline solutions ranging from water-white to pale straw in color
(E. I. du Pont de Nemours & Company, 1984). Several physical and chemical
properties of DMA are presented in Table 2-1.
2.2 Organoleptic Properties
DMA has a characteristic fishy odor at lower concentrations. However, at
higher concentrations (100 to 500 ppm), the fishy odor is no longer detectable
and the odor is more like that of ammonia (Braker and Mossman, 1980).
Following a review of the literature, Amoore and Hautala (1983) reported the
odor detection threshold of DMA in air to be 0.34 ppm. The original data
sources were not referenced. Based on a TLV of 10 ppm for DMA, an odor
safety factor (TLV/detection threshold) of 29 was calculated. According to the
authors, this means that 50 to 90 percent of distracted persons can smell DMA
at its TLV level. However, Braker and Mossman (1980) stated that prolonged
exposure to DMA may result in a loss of odor detection.
The organoleptic properties of DMA in water were studied by Dzhanashvili
(1967). Threshold concentrations for odor and aftertaste were investigated on
a group of 11 subjects in 14 series of experiments. DMA was found to impart
an ammoniacal odor to water with a detection threshold concentration of 0.67
mg/L. However, the taste and color of water were not affected by DMA
concentrations 10-fold higher. Water became undrinkable at DMA
concentrations as low as 20 mg/L due to its strong ammoniacal odor. Amoore
and Hautala (1983) reported an odor detection threshold of 0.29 mg/L for DMA
in water.
2.3 Natural Sources of Dimethylamine
DMA is a naturally occurring chemical that is abundant and widespread in
our ecosystem. It has been found in the manure of beef cattle and in the air
surrounding piggeries, poultry houses, and dairy cattle barns (Zimnal, 1979;
Kliche et al., 1978; Mosier and Torbit, 1976). DMA is also found at relatively
high concentrations in seafood. Lin et al. (1984) purchased samples of 25
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Table 2-1. Physical and Chemical Properties of Dimethylamine
Parameter Value Reference
Molecular formula
Molecular weight
Vapor pressure at:
20°C
21.1 °C
25°C
52°C
Boiling point
Melting point
C2H7N
45.085
24.7 psi
(1 ,280 Torr)
26.0 psi
(1 ,344 Torr)
29.0 psi
(1 ,500 Torr)
66.7 psi
(3,448 Torr)
6.9°C
-93 °C
Braker and Mossman (1980)
Braker and Mossman (1980)
Air Products and Chemicals
Incorporated (1983)
Braker and Mossman (1980)
E. I. du Pont de Nemours &
Company (1984)
Air Products and Chemicals
Incorporated (1983)
Braker and Mossman (1980)
Air Products and Chemicals
Freezing point -92.2°C
Vapor density (air = 1) 1.55
1.6
Solubility in water at
60°C
Base equilibrium
constant, kb; in water
Specific gravity at:
6.9°C
25°C
Flash point
23.7 percent
(by weight)
6.03 x 10-4
0.671
0.65
Incorporated (1983)
U.S. Coast Guard (1984)
Air Products and Chemicals
Incorporated (1983)
E. I. du Pont de Nemours &
Company (1985)
Braker and Mossman (1980)
Schweizer et al. (1982)
U.S. Coast Guard (1984)
E. I. du Pont de Nemours &
Company (1985)
20°F (-6.7°) U.S. Coast Guard (1984)
different dried seafoods from local (Taipei, Taiwan) markets and 25 different
fresh seafoods from local fisheries. DMA ranging from 3 to 2,043 ppm was
, found in 48 of the 50 samples. Highest DMA levels were found in dried squid
(956 to 2,043 ppm), dried cod (1,105 ppm), and dried octopus (972 ppm).
Because of the high levels of DMA in seafood diets common to the Orient and
because DMA is known to be converted to DMNA, concerns have been raised
that the high incidence of stomach cancer in Orientals may be related to high
dietary DMA (Lin et al., 1984). In addition to being present in seafood,
measurable quantities of DMA have been found in fresh fruit, vegetables, and
grains obtained at retail stores (Neurath et al., 1977). This natural occurrence
is not due to pesticide use, but natural synthesis and degradation of the
chemicals in the material.
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2.4 Production, Use, and Occupational Exposure
2.4.1 Production
2.4.1.1 Manufacturing Process
DMA is produced by the interaction of methanol and ammonia over a
catalyst at high temperature (Schweizer et al., 1982).
2.4.1.2 Production Volume
The public portion of the Toxic Substances Control Act (TSCA) Chemical
Substance Inventory (TSCA Inventory) reported the production of between 71
and 210 million pounds (32 to 95 million kilograms) of DMA in 1977. This
volume was the output of five manufacturers (CICIS, 1987).
The U.S. International Trade Commission (1986, 1985, 1984, 1983, 1982)
reported that 28 to 35 million kilograms of DMA were produced annually
during 1981 through 1985 and approximately 0.01 to 0.50 million kilograms
were imported annually during 1980 through 1983 (Table 2-2). Export volumes
have been reported for all methylamines (mono-, di-, tri-) combined, and these
volumes have steadily decreased since 1980 (SRI International, 1985a; Table
2-2). '
Table 2-2. Production Volume, Imports, and Exports of
Dimethylamine (million kilograms) for 7980-
7985
Year
1980
1981
1982
1983
1984
1985
Productions
volume
-
32.97
30.45
27.75
32.22
29.89
Imports3
0.50
0.29
0.01
0.01
—
-
Exports3-6
7.47
6.46
5.62
3.73
—
-
aU.S. International Trade Commission (1986, 1985, 1984, 1983,
1982).
These values represent export volumes for all methylamines
(mono-, di-, and tri-) combined (SRI International, I985a).
SRI International (1985b) listed four domestic producers of all three
methylamines (mono-, di-, tri-). Producers and the combined annual
production capacity of the methylamines they manufacture are as shown at
the top of the next page:
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Producer
E. I. du Pont de Nemours and Co., Inc.
Belle, WV
Air Products and Chemicals, Inc.
Pensacola, FL
International Minerals and Chemicals Corp.
Terre Haute, IN
GAP Corp.
Calvert City, KY
Annual Production Capacity
(million kilograms)
75
68
10
. 5
2.4.1.3 Producers and Importers
2.4.1.3.1 Producers. The following companies were listed in the public
portion of the TSCA Inventory as manufacturers of DMA (CICIS, 1987):
Air Products and Chemicals, Inc.
Pace, FL
American Bio-Synthetics Corporation
Milwaukee, Wl
American Cyanamid Company
Bound Brook, NJ
E. I. du Pont de Nemours and Co., Inc.
Belle, WA and La Porte, TX
GAF Corporation
Calvert City, KY
IMC Chemical Corporation
Terre Haute, IN
2.4.1.3.2 Importers. The following importers of DMA were identified in the
public portion of the TSCA Inventory (CICIS, 1987)
BASF Wyandotte Corporation
Parsippany, NJ
ICI Americas, Inc.
Wilmington, DE
2.4.1.4 Technical Product Composition.
Grades of DMA available are technical anhydrous, a 99 percent grade,
and technical aqueous (25 and 40 percent) (Hawley, 1981). DMA solutions are
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available in glass bottles, drums, tank cars, and trucks while liquefied gas is
available in steel cylinders, tank cars, and tank trucks (National Fire Protection
Association, 1986; Hawley, 1981).
2.4.1.5 Storage, Handling, and Disposal
It is recommended that DMA should be stored in a cool dry place;
containers should be protected against physical damage. Outside or detached
storage is preferable. Inside storage of liquid solutions should be in a standard
storage room or cabinet for flammable liquids. Inside storage of gas cylinders
should be in cool, well-ventilated areas away from oxidizing agents, heat,
sparks, or open flames. Accidental contact with mercury must be avoided
(Genium Publishing Corporation, 1986; National Fire Protection Association,
1986).
Protective clothing such as impervious gloves, face shields, aprons, boots,
and plastic coveralls should be worn to prevent possible skin contact; splash-
proof safety glasses should be worn to prevent any possibility of eye contact
(Genium Publishing Corporation, 1986; Mackison, et al., 1981). Eyewash
stations and safety showers should be readily available in use and handling
areas (Genium Publishing Corporation, 1986).
Bulk quantities of DMA may be disposed of by burning at a safe location
or by incineration in incinerators equipped with a scrubber or thermal unit to
reduce NOX emissions (Mackison et al., 1981; Sittig, 1981). Small quantities
should be allowed to evaporate if local, state, and Federal regulations permit
doing so (Genium Publishing Corporation, 1986).
2.4.2 Use
DMA is used as a chemical intermediate for producing dimethylformamide
and dimethylacetamide. It is also used in the production of pesticides such as
Pestox and ziram (Schweizer et al., 1982). Other miscellaneous uses include
the production of an anesthetic (Pontocaine), an antihistamine (Benadryl),
rubber accelerators (Monex, Thionex), a propellant for rockets (UDMH), a
catalyst (DMP-30), water treatment chemicals and a surfactant (Triton X-400)
(Schweizer et al., 1982). It also has potential applications as an acid gas
absorbent, an antioxidant, in dyes and other textile chemicals, in
pharmaceutical prescriptions, in textile chemicals, as a dehairing agent for
leather, and as a reagent for magnesium determination (Hawley, 1981).
2.4.3 Occupational Exposure
Estimates of occupational exposure to DMA have been reported in
industrial hygiene surveys performed by the National Institute for Occupational
Safety and Health (NIOSH). According to the National Occupational Hazard
Survey (NOHS), conducted by NIOSH from 1972 to 1974, 27,364 workers in
1,914 plants were potentially exposed to DMA in the domestic workplace
environment (Stanford Research Institute, 1976). The largest number of
exposed workers were involved in general building, chemicals and allied
products, heavy construction, rubber and plastic products, primary metals, and
medical and other health services industries.
Preliminary data from the National Occupational Exposure Survey
(NOES), conducted by NIOSH from 1980 to 1983, indicated that 8,700 workers
including 952 women at 183 sites were potentially exposed to DMA in the
workplace in 1980 (NOES, 1984). The largest number of exposed workers
were involved in chemicals and allied products, business services, health
-------
services, and primary metals industries. Unlike NOHS, the NOES estimates
were based only on direct observation by the surveyor of the actual use of the
compound.
The current time-weighted average (TWA) TLV for DMA exposure in the
workplace is 10 ppm (18 mg/m3) (American Conference of Governmental
Industrial Hygienists, 1986). This same level, 10 ppm, has also been adopted
by the National Institute for Occupational Safety and Health V(NIOSH) as an 8-
hour TWA permissible exposure limit for DMA (Mackison et al., 1981).
No data were available on DMA concentrations in U.S. plants. In two
studies from Germany, DMA has been found in two workplaces at
concentrations in the air of 0.61 to 1 ppm (Bretschneider and Matz, 1973) and
at 0.65 to 18 ppm (Bittersohl and Heberer, 1980).
2.5 Quantitation and Analysis
DMA can be detected and analyzed in air, water, and soil by several
methods, but because of its chemical properties, careful attention to assay
technique is necessary to obtain accurate, quantitative results. Because of
DMA's low acute toxicity (see Sections 4.1.1 and 4.2.1) and its easily
detectable odor, few sensitive methods for its analysis in air were developed
until it was recognized that carcinogenic DMNA could be formed from DMA in
the environment. NIOSH (in a report 'prepared for NIOSH by Stanford
Research Institute, 1976) does recommend a method of analysis for DMA in
air. In this method, air is sampled by drawing a known volume through a tube
that contains silica gel to trap the organic vapors present. The silica gel is then
extracted with an acid-methanol solution and the solution is neutralized with
potassium hydroxide. The DMA is quantified by gas chromatography (GC).
The method has been validated with the use of a 48-L air sample for the range
of 3.8 to 16 ppm. Specific methods for DMA are not included in U.S.
Environmental Protection Agency's methods for the analysis of municipal and
industrial wastewater (Longbottom and Lichtenberg, 1982) or in test methods
for the evaluation of solid waste (SW-846) (U.S. Environmental Protection
Agency, 1982), although methods for the determination of DMNA appear in
both of these publications.
Some of the recently developed methods of analysis are described in
Table 2-3. DMA's volatility allows it to be analyzed by GC, but its reactive
nature causes it to adsorb on many column-packing materials. To overcome
adsorption and the consequent peak broadening, specially treated column
materials must be used or the amines must be chemically converted to
derivatives that may be more easily chromatographed. Although the common
flame ionization detector (FID) can be used to measure DMA or its derivatives,
a greater sensitivity can be attained by the use of a nitrogen-phosphorus FID
(NP-FID, the alkali salt bead type) (Kuwata et al., 1980). Since Boehm et al.
(1983) have been able to detect as little as 1 ppb with the use of an FID, it
may be possible to detect DMA at 1 ppb in air with the use of the more
sensitive NP-FID. Fuselli et al. (1982) adsorbed amines from ambient air on
charcoal and analyzed them by an NP-FID detector following desorption using
heat. However, they were unable to detect levels of DMA below 5 ppb,
because they could not completely desorb the amines.
Several other methods use a derivatization procedure before the
measurement technique is applied. Derivatization usually forms a material that
highly absorbs ultraviolet (UV) radiation or that fluoresces. These methods
have been used for the analysis of DMA in air, biological fluids, water, and
foodstuffs. As shown in Table 2-3, DMA can be quantitated at levels in the
10
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Comments
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etection
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DMA found at 52-241
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„ S
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Table 2-3 Continued
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13
-------
parts-per-million (mg/kg) to parts-per-trillion (ng/kg) range. Many of the
methods use concentration techniques such as absorption in solid or liquid
matrices, then a distillation step, followed sometimes by extraction. If
distillation of a material with an alkali solution is used, DMA may be spuriously
generated by hydrolysis of a chemical precursor such as dimethylacetamide
(Ripley et al., 1982; Neurath et al., 1977).
Infrared (IR) spectroscopic methods for analyzing vapors, usually with the
use of the Fourier transform technique, requires such complex, expensive
equipment that they have been applied only in smog chamber research
studies of .reactions of DMA in air (Glasson, 1979; Pitts, 1978; and Tuazon et
al., 1978). This method does allow simultaneous detection of N- nitro- and N-
nitrosodimethylamines, but such mixtures cannot be quantitated because their
spectra overlap. No reports of the use of FT-IR to measure DMA
concentrations in ambient air were found. The very different properties of
these substances do not normally allow their combined determination by
chromatography or derivatization by the same reagents.
2.6 Environmental Levels and Fate
2.6.1 Sources of Dimethylamine in the Environment
Total environmental releases from manufacturing processes have been
estimated at approximately 630,000 kg in 1975 (1.4 million Ib/year) (Brown et
al., 1975). The fraction that enters the atmosphere was not estimated, but from
the manufacturing process (Schweizer et al., 1982) we expect that most of the
release will be into waste water. Since methylamine plants have generated
strong odors during operation (Keko, 1975), some gas emissions are known to
have occurred. Losses from the dispersive uses will be considerably less than
this quantity because less than 15 percent of the DMA produced is used
dispersively. DMA from herbicides such as diuron, monuron, and fenuron and
fungicides such as thiram and ziram may also enter the environment due to
hydrolytic or microbial degradation after agricultural use. However, no
estimates of the amounts of DMA released from pesticides have been found.
DMA is also generated by catalyst-equipped automobiles at approximately
0.11 mg/mile in the exhaust gases (Cadle and Mulawa, 1980). As much as
95,000 kg/year of DMA may enter the atmosphere from this source, if we
assume that 50 percent of the miles driven by motor vehicles are equipped
with catalytic converters (1/2 of 1.77 x 1012 miles/yr in 1985; Motor Vehicles
Manufacturers Association, 1987).
Several biogenic sources of DMA have also been reported. DMA has
been reported to be present at 1 to 7 ppm in some fresh vegetables such as
corn, kale, lettuce, and peas (Ripley et al., 1982; Neurath et al., 1977). DMA
may enter the environment from these materials as they are used or
degraded. Since human and animal metabolism apparently produces small
concentrations of DMA in the urine (10 to 25 mg/L) (Zeisel et al., 1985;
Bittersohl and Heberer, 1980; Beal and Bryan, 1978), some of the DMA in the
environment may be from this source. Humans and animals excrete creatinine,
and it has been reported that this material is partially transformed to DMA in
sewage treatment plants (Thomas and Alexander, 1981). DMA has been
detected in the effluent air from garbage units in Russia (Sidorenko et al.,
1978), and from air over cattle manure in barns (Kliche et al., 1978; Zimnal,
1979), or feed lots (Mosier and Torbit, 1976; Mosier et al., 1973).
14
-------
2.6.2 Environmental Levels
Although there are apparently a wide variety of sources of DMA in the
environment and there is concern that DMA may be converted into DMNA in
the atmosphere, very few published reports of studies were found that
measured concentrations of the DMA in general urban or rural areas. All of the
reports found in recent literature are from outside the United States. In
contrast, several studies of the concentration of DMNA in urban areas have
been reported (Pellizzari et al., 1986; Chuong et al., 1978; Fine et al., 1977;
U.S. Environmental Protection Agency, 1977; Fine et al., 1976). As shown in
Table 2-4, atmospheric levels of DMA as high as 0.13 ppm (242 ng/m3) were
found at industrial sites in Italy (Fuselli et al., 1982), and DMA has been
detected at levels at 0.0004 ppm (0.65 ug/m3) near office buildings in Russia
(Sidorenko et al., 1978). DMA has been measured at 0.09 ppm (17 ug/m3) in
air outside a rendering plant in Japan (Kuwata et al., 1983).
Table 2-4. Reported Atmospheric Concentrations of Dimethylamine
DMA Concentration
Location
liglm3
ppm
References
Sidorenko, et al.,
(1978)
Kuwata etal., (1983)
Fusselli et al., (1982)
Kuwata etal., (1983)
Kliche et al., (1978)
Air from residences, Russia 51-57 0.028-0.031
Air from garbage chutes, Russia . 667 0.370
Air from office buildings, Russia 8,73 0.00484
Air outside office buildings, 0,65 0.00035
Russia
Ambient air around rendering 17 0.0094
plant, Japan
Industrial area3, site A, Italy 120-148 0.065-0.080
Industrial area3, site B, Italy 212-242 0.115-0.131
Industrial area3, site C, Italy 0-52 0-0.030
Air in cow shed, Japan ND (< 0.24)& < 0.00013
Air around poultry waste unit, ND (<0.45)b < 0.00025
Japan
Air in large dairy cattle barn ND-1,500= ND-810°
(1,000-2,000 cattle)
aAn area with industrial plants that emit DMA and other methylamines.
bND :none detected. Air was sampled in the farm areas shown and assayed for low
molecular weight amines. TMA at 0.5 to 11 [ig/m3 and MMA at 0 to 1.8 [ig/m3
were found. However, DMA (at the detection limits shown) was not found.
cFrom 126 air samples taken over a 12-month period (3 samples per day) DMA was
selected on four days (85 samples). The detection limit varied from 0.1 to 0.7 ppm.
Because DMA is highly soluble in water and easily absorbed by acidic
materials, one would expect that releases of the amine into the environment
would disperse into air, water, and soil easily. Its concentration in the
environment is often rapidly reduced by further reactions (see Section 2.6.3).
2.6.3 Environmental Chemistry
Studies of the reactions of DMA with other constituents in air and water,
and by microbial systems have been performed in the last several years to
15
-------
determine the fate of DMA in the environment. Since DMNA has been shown
to be carcinogenic in animals, many of these studies have measured the
reactions of DMA with environmental levels of nitrogen oxides (NOX) or nitrites
to form DMNA. Reactions that have been studied are shown below:
2.6.3.1 Reaction of DMA With Hydroxyl Radicals (HO*) in Air.
The first step is formation of two types of DMA radicals:
i) HO» + CH3NHCH3 -> .CH2NHCH3 + H2O (2-1)
[Atkinson, 1985]
ii) HO» + CH3NHCH3-> CH3NCH3 + H2O
(2-2)
[Atkinson, 1985]
Both processes are important and competitive. The DMA radicals formed
above can react further with 02, NO, and ,NO2 to form formaldehyde and
methylformamide (Atkinson, 1985). The CH3NCH3 radical subsequently reacts
with NO, NO2, and O2, with reactions with N02 and NO predominating:
• hu
CH3NCH3 + O2 -* CH3(NOO)CH3 -» CH3N = CH2 + HO2
(2-3)
[Atkinson, 1985]
• hu
CH3NCH3 + NO -» CH3(NNO)CH3
(2-4)
[Atkinson, 1985]
• hu
CH3NCH3 +NO2 -» CH3(NNO2)CH3 -+ CH3N = CH2 + HONO
(2-5)
[Atkinson, 1985]
The •CH2NHCH3 radical reacts with O2:
•CH2NHCH3 + O2 -» CH2=N-CH3 + HO2
(2-6)
[Atkinson and
Carter, 1984]
2.6.3.2 Reactions of DMA With Ozone
DMA reacts with ozone in the gas phase; the general form of the reaction
O
(CH3)2NH + O3 -> H-C-H + N2 + H2O
(2-7)
[Dushutin and
Sopach, 1976]
This reaction which is discussed below indicates that formaldehyde is
produced with no observed N-nitroso, nitrate or nitrite compounds.
16
-------
(CH3)2NH + O3 -» CH3N=CH2 + O2 + H2O
DMA also reacts with ozone in aqueous solutions:
O O
(2-8)
[Atkinson and
Carter, 1984]
(CH3)2NH + 03
CH3-NH-C-H + H-C-H + CH,NHOH + other products
(2-9)
[Elmghari-Tabib
etal., 1982]
2.6.3.3 Aqueous Reaction of DMA with Nitrite.
Reactions with nitrite (NO2') ion in aqueous solution:
(CH3)2NH + H* + NO2' -> (CH3)2N-NO + H2O (2-10)
[Blatt, 1943]
2.6.3.4 DMA Reactions with Nitrogenous Compounds
DMA reacts with nitrogen oxides and nitrogen acids in the gas phase, with
and/or without light:
(CH3)2NH + ON-NO3 -+ (CH3)2N-NO + HNO3 (2-11)
(CH3)2NH + HONO -> (2-14)
O O
II II
(CH3)2N-NO2 + (CH3)2NC-H + HC-H + (CH3)2NN(CH3)2 +Others
[Grosjean,
1980; Glasson,
1979; Pitts,
1978; Tuazon
et al.,
1978;Dushutin
and Sopach,
1976; Hanstet
al., 1977]
Reactions with nitrogen acids as aqueous solutions of nitrogen oxides:
NO + NO2 +H2O -> 2HONO (2-15)
CH3NHCH3 + HONO -> CH3N(NO)CH3 + H2Q
(2-16)
[Blatt, 1943;
Glasson, 1979]
17
-------
Reaction with atmospheric HN03 in air:
CH3NHCH3 + HNO3 -> products not specified
(2-17)
[Atkinson
1985)
All of these reactions may contribute to the degradation of DMA in the environ-
ment. The importance of these reactions in the various compartments of the
environment has not been completely defined; pertinent reported studies are
discussed below.
Atkinson (1985) proposed that the reaction with HO is the primary
mechanism for degradation of most atmospheric organic pollutants, but notes
that for certain amines, reaction with gas phase HN03 "may be the dominant
loss process In urban environment." No rate data are reported for this
reaction.
The reactive HO» is formed in the atmosphere by the action of sunlight
(estimated concentration is given below). Because of its high reactivity, it does
not accumulate, but reaches a very low equilibrium concentration durmg
daylight. From Atkinson's (Atkinson et al., 1979) measured rate of the reaction
of DMA with HO» (6.5 x 10-11 cm3/molecules-sec) and estimates of boundary
layer (the atmosphere nearest the planet extending from the surface to a few
thousand meters altitude) HO* concentrations, one can calculate the half-life of
DMA removal from the lower atmosphere by reaction 1. Values of 3 to 6 hours
are obtained with the use of the HO» concentrations of 1 x 106 to 0.5 x 106
molecules/cm3 suggested for the tropospheric boundary layer, (see Cupitt,
1987). Other processes of DMA removal from the atmosphere (reactions Nos.
2-7, 2-8, 2-11 through 2-14, and 2-17, or absorption in rain; see Brimblecombe
and Dawson, 1984) are probably negligible (as discussed in the following
paragraph.) since they are much slower than the reaction with HO«.
Pitts and his co-workers (Pitts, 1978; Tuazon et al., 1978) studied the
reactions of 0.1 to 5 ppm levels of nitrogen oxides in air with equal concen-
trations of methyl and ethyl amines, including DMA and diethylamine (DBA).
Their experiments were performed in "smog chambers" of 16 to 50 m3
volume to minimize reactions on the surfaces. Using the larger chambers, the
reaction was observed for a 4-hour period, 2 hours in the dark and then 2
hours in sunlight. A small yield of N-nitrosoamine is rapidly formed from the
dialkylamine during the dark period (2.8 percent yield with diethylamine), while
only 20 percent of the amine was consumed. During exposure to sunlight, 90
to 95 percent of the dialkylamine was degraded (half-life, 30 to 65 minutes)
and a mixture of products was formed. The major product found was the
diakylamine-nitramine (R2N-NO2, R = CH3 in the DMA case). Aldehydes,
amides, peroxyacetylnitrate, and carbon monoxide were also found in
significant yields. The N-nitrosoamine formed initially in the dark was
destroyed by the sunlight with a half-life of approximately 1 hour. In the larger
chamber, in which 0.1 ppm of amine was introduced, the mixture was
analyzed by GC-MS after absorption on Tenax, while FT-IR spectrometry was
used to determine concentrations in the smaller chamber. In the latter case the
initial concentrations of the amines were 3 to 5 ppm. The FT-IR procedure
does not allow the quantitative differentiation of N-nitramines from N-
nitrosoamines in air mixtures. Pitts concludes that N-nitrosoamines may form
from a rapid reaction of nitrous acid (HONO) and the amine in air, but at the
typical ppb levels of NO2 and nitrous oxide (NO) present in the air the
18
-------
conversion will be very low. The nitrous acid is formed in the equilibrium
reaction below,
NO2 + NO + H2O £» 2HONO
(2-18)
but since the rate of the forward reaction does not become significant until the
NO concentrations equal 1 to 20 ppm the direct reaction of HONO with
dialkylamines does not normally occur to any extent. Therefore, reactions (2-1)
and (2-2) describe the primary reaction in sunlight; reactions (2-3) through (2-
5) then occur to form a series of products, but the N-nitrosoamine so formed is
destroyed in the sunlight.
Other groups have also studied the gas phase reaction of DMA at ppm
concentrations (Hanst et al., 1977; Dushutin and Sopach, 1976; Glasson,
1979). Such gas phase reactions are very difficult to study because reactions
on surfaces of reaction chambers used or reactions on aerosol particles may
occur that make it difficult to evaluate properly the gas phase processes.
Glasson (1979) reported such problems when studying the reaction of 3.7 to
13.5 ppm DMA with 2 ppm of NO and 2 ppm of NO2 in a 614-liter stainless
steel chamber. With no light introduced, 6 to 7 percent of the DMA was
converted to DMNA after 6.7 hours, while the DMA concentration decreased
by approximately 80 percent. The results were similar with or without excess
water vapor added. Since 80 percent of the DMA is also lost when the
experiment was performed without NOX present, Glasson suggested that
adsorption of DMA on the chamber surface accounted for the loss and
furthermore, that the DMNA formation occurred primarily by reaction 2-5.
Hanst et al. (1977) also found low yields of DMNA in a similar study, but
they did not consider surface reactions that may have degraded DMA.
In studies of the gas phase reaction of 6 to 3,600 ppm of DMA with ppm
levels of nitrogen tetroxide in a 120-liter chamber, DMNA, dimethylnitramine,
and dimethylammonium nitrate were found as products (Dushutin and Sopach,
1976). Absorption of the gases followed by wet-chemical methods was used to
follow quantitatively the course of the reactions. At 5 ppm concentrations of
each reactant the reaction was found to exhibit a half-life of less than ten
minutes. Even though an aerosol formed in the chamber, the authors did not
consider the importance of heterogenous reactions.
The reaction of O3 with DMA was also studied by Dushutin and Sopach
(1976). They were able to detect formaldehyde as a product of the reaction
and found that the reaction was quite fast at the concentrations studied (5
ppm). Tuazon and co-workers (1978) (reported by Atkinson and Carter, 1984)
determined the rate of the reaction of DMA with O3 in air. They found a
second order rate constant of 2.61 x 10-"18 cms/molecules-sec that is
consistent with Dushutin and Sopach's result. Tuazon's group found that the
major product was N-methylmethyleneamine, CH3N = CH2. Because of the
typical low concentration of O3 in the atmosphere, this reaction is too slow
(half-life = 4.4 days at ca. 30 ppb of ozone) to be a significant process that
would consume DMA under normal conditions.
From the above results one can suggest that ppb levels of DMA are
destroyed within hours with formation of negligible levels of DMNA in the
daytime, while removal of DMA by reaction with nitric acid or NO3 radicals
19
-------
may predominate at night (Atkinson, 1985; Atkinson and Carter, 1984). Pitts
(1978) summarizes the results of these studies as follows: "Thus, even though
ambient NOX and HONO concentrations from mobile and stationary sources
may be quite high under certain meteorological conditions (and high primary
emission levels), the risk of forming significant amounts of nitrosoamines or
nitramines in the urban or suburban atmosphere seems correspondingly low.
However, in specialized industrial cases, where sub-ppm concentrations of
amines may be released into ambient polluted air, within and immediately
downwind from the facility, the possibility of formation of nitrosoamines and, in
sunlight, of nitramines and amides, seems real." A study of the levels of,
DMNA in the air of Paris, France (Chuong et al., 1978) is consistent with this
suggestion. In 25 percent of the air samples taken, DMNA was found at 0.005
to 0.11 ppb, and the concentrations were lower after periods of sunshine.
Reactions of DMA with other substances in the atmosphere are apparently
not the only possible source of DMNA in the atmosphere. Two specific
sources from industry have been found (see Fine et al., 1976); these were
from a chemical factory manufacturing unsymmetrical dimethylhydrazine
which affected air and salt water concentrations of DMNA. Nitrosoamines can
also be formed from NOX and trialkylamine in the atmosphere (Pitts, 1978).
The carcinogens, DMNA and dimethylnitramine, are physically and
chemically quite different from DMA; these compounds are neutral rather than
alkaline, and since they have boiling points of 154°C and 187°C, respectively
(Weast, 1986), they are much less volatile than DMA, which is a gas at
standard temperature. DMNA is easily synthesized by treating DMA, as its
hydrochloride, with sodium nitrite in water at 70 to 75°C at slightly acid pH.
Under these conditions, over 88 percent yields of DMNA can be obtained
(Blatt, 1943). From a kinetics study of this reaction (Mirvish, 1975), it has been
found that the rate of formation of DMNA would be slow at environmental
concentrations of DMA and nitrite ion. First, Mirvish reports that the reaction
rate is dependent on pH, with the maximum rate occurring at 3.4, the rate
became very slow at pH less than 1.5, and too slow to measure at pH's above
7. At any particular pH, the rate of the reactions was found to depend on the
first power of the DMA concentration and the second power of the NO2"
concentration, as shown:
Rate = kx [DMA] x[N02-]2
(2-19)
This dependence is the result of the following series of reactions that occur:
N02' + H+ -» HONO (2-20)
2 HONO -> N203 + H20 (2-21)
(CH3)2NH + N203 -> (CH3)2N-NO + HONO (2-22)
Certain other materials such as the thiocyanate (NCS"), chloride, or bromide
ions can modify this mechanism at pH's below 2.5 (Mirvish, 1975), by the
following reactions:
HONO"+
NCS- -» ON-NCS + H2O
(2-23)
20
-------
ON-NCS + (CH3)2NH -*(CH3)2N-NO + H+ + NCS'
(2-24)
From these data it can be calculated that 0.125 percent of the DMA in an
aqueous solution of equal concentrations of DMA and sodium nitrite at 1.0
mg/L would be nitrosated within one hour at 25°C if the pH is 3.4. Further,
estimates of the DMNA formation at other concentrations change considerably
with pH or reactant concentrations because of the effects of pH and the third
order of the reaction, as shown:
Table 2-5. Conditions for DMA Conversion to DMNA
Concentration
DMA, gmIL
NaNO2, gm/L
Conversion to DMNA
pH in 1 hour, %
1.0
0.1
0.1
0.1
0.1
1.0
1.0
1.0
0.1
0.1
3.4
3.4
6.0
3.4
6.0
0.125
0.012
0.0001
0.0001
0.000001
Keefer and Roller (1973) found that this nitrosation is catalyzed by formalde-
hyde or chloral at pH's above 6, but yields do not exceed 1 percent after 17
hours when 0.05 M amine is allowed to react with 0.2 M sodium nitrite in the
presence of 0.05 M formaldehyde. In the absence of one of these aldehydes,
no nitrosation was detected. In other work at similar concentrations (900 mg/L
of DMA, with excess NO"2), the yield of DMNA was found to be less than 15
percent after 6 hours at 37° C and a pH of 3 (Ziebarth, 1974). Others report
that no nitrosamines are formed at pH values above 6, at environmental
concentration, unless microbial materials are present (Tate and Alexander,
1976; Ayanaba and Alexander, 1973) or actinic light is used as a catalyst (Ohta
etal., 1982).
21
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-------
3. Metabolism
3.1 Inhalation Exposure
McNulty and Heck (1983) and McNulty et al. (1983) studied the
metabolism of inhaled [^CIDMA in rats. McNulty and Heck (1983) exposed
groups of four male Fischer 344 rats for 6 hours to either 10 or 175 ppm
[1<»C]DMA. The [14CJDMA (Amersham Corp.) had a specific activity of 57
mCi/mmol and a radiochemical purity of 98 to 99 percent. Immediately after
exposure, the rats were placed in individual metabolism cages for the separate
collection of urine, feces, and expired air. Seventy-two hours after termination
of exposure, the disposition of the recovered radioactivity was similar for each
airborne concentration, with more than 90 percent in the urine and feces, 7 to
8 percent in the tissues and carcass, and 1.5 percent in the exhaled air (Table
3-1).
Table 3-1. Disposition of Radioactivity in Rats Exposed to [14C]
Dimethylamine3
Percent Disposition at Exposure Concentrations of
[14C] Distribution
10 ppm
175 ppm
Urine
Feces
Expired air
Tissues and carcass
78.0 ± 1.0
12.5 ± 0.8
1.5 ± 0.1
8.0 ± 0.9
86.7 ± 2.8
5.1 ± 1.5
1.5 ± 0.3
6.7 ± 1.1
Disposition is expressed as a percentage of the total recovered radioactivity.
Percentages represent the mean ± standard error (±SE) for four rats
Source: McNulty and Heck (1983).
When groups of rats were similarly exposed and killed immediately after
exposure, the highest concentration of radioactivity was in the respiratory and
olfactory mucosa, whereas concentrations of [14C3 in liver, lung, kidney, brain,
and testes were approximately 2 orders of magnitude less than in the nasal
mucosal tissues (Table 3-2). When tissues were radioassayed 72 hours after
being exposed to 10 or 175 ppm [14CJDMA, appreciable concentrations of
radioactivity remained only in the nasal mucosa, where respiratory tissue
contained 73.0 ± 8.3 and 336.2 ± 96.6 nmol equivalents of DMA per gram of
tissue, respectively (olfactory concentrations were not determined). Following
exposure to 175 ppm [1<»C]DMA, radioactivity in plasma was eliminated in a
biphasic manner. The relatively long half-life for the slow phase (44.6 and 63.6
hours for two rats) was similar to the half-lives of some plasma proteins and
23
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was postulated to be due to incorporation of [14C] into protein subsequent to
metabolism of [14C]DMA.
Table 3-2. Tissue Distribution of Inhaled ["CJDimethylamine
Immediately Postexposure
nmol Equivalents
of DMA/g Tissue3 at Exposure Levels of
Tissue
10 ppm
175 ppm
Respiratory mucosa
Olfactory mucosa
Liver
Lung
Kidney
Brain
Testes
19,500 ± 3,200
6,200 ± 1,400
43.1 ± 9.7
32.3 ± 7.8
96.1 ± 19.2
24.4 ± 7.1
27.6 ± 6.8
72,200 ± 6,100
29,000 ± 4,900
758.0 ± 21.1
689.8 ± 72.7
1,708.5 ± 120.9
465.8 ± 2.3
542.8 ± 27.8
aJhe values represent the mean ± SE for four rates.
Source: McNulty and Heck (1983.
DMA can be introduced into the body via ingestion or inhalation.
Additionally, studies have shown that DMA can be synthesized within the body
from other dietary constituents by microorganisms in the gut and by
unidentified endogenous pathways. It has been suggested that DMA is an
important nutrient, acting as a stimulator of postprandial gastrin secretion and
directly as a stimulator of gastrointestinal mucosal growth.
Several studies were conducted to determine the identity of the DMA
metabolites. Groups of three rats were injected intravenously (iv) with 20 iiCi
of the commercial [1<>C]DMA or commercial [14C]DMA further purified by ion
chromatography to remove any ^CO2 prior to injection. Rates of [14C]
exhalation were identical for both groups, indicating that the expired
radioactivity was due to metabolic breakdown of [14C]DMA to ™CO2 and not
from the injection of radiolabeled contaminants. Analysis of 0- to 24-hour urine
samples from these animals indicated that 98.7 ± 0.2 percent of the
radioactivity was the parent compound as determined by chromatography.
The remaining radioactivity (<2%) was unidentified and eluted at two separate
chromatographic positions.
McNulty et al. (1983) performed additional experiments to identify the
metabolites of DMA in the nasal mucosa of rats (see Section 3.2.5 for details).
Experiments were performed in vitro using microsomes prepared from liver
and from respiratory and olfactory nasal mucosa. All microsomal preparations
metabolized DMA to formaldehyde, although DMA was a poor substrate for
the N-demethylation reaction. The data also showed that DMA is metabolized
in vitro to formaldehyde by both cytochrome P-450 and flavin adenine
dinucleotide (FAD)-containing mono-oxygenases. In vivo, unextractable
radioactivity was observed in DNA, RNA, and protein isolated from respiratory
and olfactory mucosa of rats exposed to either 10 or 175 ppm of
24
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The authors concluded that as much as 8 percent of the absorbed DMA may
be converted to formaldehyde in vivo and, subsequently, may be, incorporated
into tissue macromolecules or further metabolized to carbon dioxide and.
exhaled (McNulty and Heck, 1983; McNulty et al., 1983).
3.2 Oral Administration
3.2.1 Dimethylamine Biochemistry
DMA can be introduced into the mammalian gastrointestinal tract in
several ways. In the diet, DMA is present in substantial amounts in a number
of foods, especially certain seafoods (see Section 2.3). In addition, DMA is
produced from other dietary components, such as creatinine, lecithin, and
choline, by bacterial metabolism in the lower gut (Asatoor and Simenhoff,
1965). .A general scheme,for the formation of aliphatic amines in the
mammalian gut has been proposed by Lowis et al. (1985) (Figure 3-1).
Choline, Lecithin
TMA
-> TMA Oxide
DMA ^ Kidney Excretion
Sarcosine
Creatinine
Figure 3-1. Proposed scheme for the formation of methylamine (MMA),
dimethylamine (DMA), and trimethylamine (TMA) in the
mammalian gut.
Source: Lowis et al. (1985).
25
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Experiments using germ-free rats and control rats consuming the same
methylamine-free diet indicated that gut bacteria were not essential for the
formation of DMA (Zeisel et al., 1985). Consequently, the authors concluded
that endogenous pathways that are capable of forming DMA must exist, but
these endogenous mechanisms remain unidentified.
It has been suggested that DMA is an important nutrient, acting as a
stimulator of postprandial gastrin secretion (Lichtenberger et al., 1982) and to
stimulate growth of the gastrointestinal mucosa (Dembinski et al., 1984).
3.2.2 Absorption
The gastrointestinal absorption of DMA has been studied in 15- to 20-
week-old male Wistar rats by Ishiwata et al. (1984a,b) using ligated gut
sections in situ. Additionally, blood samples were taken via heart puncture
from rats which had been injected with DMA into the ligated upper intestine.
The rates of disappearance of DMA from the ligated sections of gut were
monoexponential over 30 minutes. Disappearance half-lives were 8.3, 11.6,
31.5, and 11.0 minutes for the upper small intestine, lower small intestine,
cecum, and large intestine, respectively. Absorption of DMA from the stomach
was scarcely detectable (disappearance half-life, 198 minutes). Following
injection of DMA into the ligated upper small intestine, DMA levels in the blood
increased from 0.28 ± 0.06 to 3.0 ± 1.0 ppm within 5 minutes and then
decreased to 1.2 ± 0.21 ppm by 30 minutes.
Similar experiments have been performed with guinea pigs (Ishiwata et
al., 1977). As with the rats (Ishiwata et al., 1984a,b), no loss of DMA from the
stomach of the guinea pigs was detected after 20 minutes. However, only 15.4
± 6.1 percent of the injected DMA remained in the upper small intestine after
20 minutes. The rate of DMA disappearance from the small intestine was
monoexponential over the sampling period. These data may not be as
conclusive as those for the rat because blood levels of DMA were not
monitored, and, according to the authors, the injection solution contained
DMA, DMNA, nitrite, and nitrate, and not DMA alone.
A weak organic base, such as DMA, is present in ionized form in the
stomach. In such an ionized state, it is unlikely,to be absorbed. However, in
the small intestine, the opposite is true.
3.2.3 Distribution
The gastrointestinal distribution of DMA in rats fed diets containing normal
(23.6 ppm) or low (1 ppm) levels of DMA was studied by Ishiwata et al.
(1984a,b; 1982). Groups of five adult male Wistar rats were killed after 1 week
on the appropriate diet. Their gastrointestinal tracts were excised and the
contents of the stomach, small intestine (divided into four equal lengths),
cecum, and large intestine were removed and assayed for DMA content by
GC. For rats fed diets containing 23.6 ppm DMA, DMA levels were highest in
the contents of the stomach, and tended to decrease in the more distal
sections of the gastrointestinal tract. The authors attributed the relatively
higher DMA concentrations in the contents of the large intestine to the
absorption of water from the gut. Gastrointestinal levels of DMA in this group
of rats were higher than DMA levels in the diet. In rats fed diets low in DMA,
26
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the distribution pattern was different. The stomach contained the lowest DMA
levels, approximately 1 ppm, whereas the other sections of the gut contained
DMA concentrations higher than were in the diet. The authors attributed this
distribution pattern to the synthesis of DMA in the lower gut with subsequent
absorption into the blood followed by secretion into the small intestine via the
bile.
Chaudhari and Dutta (1981) studied the tissue distribution of DMA in male
Hartley guinea pigs and male Sprague-Dawley rats weighing between 300 and
400 g. Animals were anesthetized and a cannula was inserted into each
external jugular vein. [14C]DMA, 10 mg (20 nCi)/kg, was injected into one
cannula, and blood samples were removed from the other cannula at 0.5, 1, 2,
3, and 4 hours postinjection. At the end of 4 hours, the animals were killed and
samples of heart, liver, spleen, adrenal, kidney, brain, lung, pituitary, and
abdominal fat were radioanalyzed. The biological half-life and apparent volume
of distribution were calculated from a plot of blood concentration of DMA
against time based on the assumption that the rate of DMA disappearance
from the blood was first order.
The biological half-life and volume of distribution of [14C]DMA in the rat
were 3.92 ± 0.59 hours and 1.76 ± 0.17 L/kg, respectively. The
corresponding values in the guinea pig were 4.62 ± 0.48 hours and 1.58 ±
0.26 L/kg, respectively. There was no statistically significant difference
between corresponding rat and guinea pig values, indicating that there were
no species differences for these parameters. The volume of distribution values
are not especially high, and the binding was nonspecific rather than covalent.
The results of the tissue distribution studies are presented in Figure 3-2.
No species differences were apparent except that mean [14C] concentrations
in the abdominal fat of the guinea pigs were significantly higher than those in
the rats. The authors could not explain the biological significance of this
difference. Levels of DMA equivalents were highest in the kidneys of both
species, and tissue-to-blood ratios were greater than 1 for kidney, spleen,
adrenal, and pituitary. The concentration of [14C]DMA equivalents in the blood
was not reported.
3.2.4 Excretion and Secretion
Beal and Bryan (1978) studied the excretion of [14C]DMA in male
Sprague-Dawley rats weighing 200 to 250 g. Each of eight rats was injected
intraperitoneally (ip) with 60 iimol (6.2 nCi) of [14C]DMA and immediately
placed in metabolism cages. Urine, but not feces, was analyzed for [14C]DMA
content. The authors reported that 85 to 90 percent of the dose was excreted
in the 0- to 24-hour urine as unmetabolized DMA. They apparently did not
analyze the urinary radioactivity for DMA metabolites. Less than 0.1 percent of
the dose was excreted as expired DMA, and only 0.5 percent was excreted as
expired carbon dioxide. No other data on this experiment were provided.
DMA excretion by adult male Wistar rats maintained on a normal diet
containing 7.4 ppm DMA was studied by Lowis et al. (1985). Eight rats
weighing 300 to 400 g each were placed in individual metabolism cages. Urine
and feces were collected and analyzed for amine content. Over the course of
the 14-day experimental period, the rats consumed approximately 12 g of
food/day (88.8 ng DMA/day). DMA excretion showed a large variation, ranging
27
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16
ffl ,,
s
W 3
,<2
0
re
CD
S
a.
I'2
2
C o
-------
Table 3-3. Dimethylamine Balance in Rats
Ingestion and Excretion of DMA (tig/day) by Rats
Fed Diets Containing DMA at
23.
7.4 ppmb
1.0 ppma
Ingestion
Excretion
Urine
Feces
Total
300.1 ± 49.4
432.6 ± 49.3
21.7 ± 7.4
453.9 ± 47.9
88.8
506.4
20.6
527.0
19.2 ± 4.6
272.5 ± 12.5
10.3 ± 2.2
282.8 ± 12.5
aMean ±SD for five rats over 7 days (Ishiwata et al., 7982).
bMeans are estimated from data reported by Lowis et al. (1985).
21.1 ± 9.3 mg of nitrosatable compounds, primarily DMA, are ingested and
excreted in the daily urine, respectively (Ishiwata et al., 1978).
Ishiwata et al. (1984a,b) have also reported data that indicate that DMA
undergoes enterohepatic circulation. Five adult male Wistar rats were fasted
overnight and anesthetized, and their bile ducts were cannulated. After
recovering from the anesthetic, each animal was administered 250 ng of DMA
intravenously (iv). Bile was collected at various times postinjection and
analyzed.for DMA content. Before the injection, the biliary DMA concentration
was 0.59 ± 0.050 ppm. After injection, biliary DMA increased to a maximum
of 3.7 ± 1.9 ppm at 30 minutes postinjection. A second, smaller peak was
observed 3 hours postinjection. Thereafter, levels remained relatively constant
between 0.3 and 0.6 ppm. The cumulative 24-hour biliary excretion was 6.2 ±
2.2 ng. Thus, biliary excretion, uncorrected for background excretion,
accounted for less than 2.5 percent of the dose.
DMA may enter the gut via secretion from blood into the upper small
intestine, gastric juice, and/or saliva. The secretion of DMA into the upper
small intestine was studied by Ishiwata et al. (1984a,b). Groups of five adult
male Wistar rats were fasted overnight and then anesthetized. Their abdomens
were opened, and a 5-cm section of the small intestine was ligated 10 cm
below the pylorus. Each rat was then administered 250 ng of DMA iv. At
various times postinjection, the animals were killed and several samples were
taken: blood samples were taken via heart puncture; urine samples were taken
from the bladder; and the ligated section of intestine was excised, and its
contents removed. All samples were analyzed for DMA by GC.
According.to the authors, the data indicate that following an intravenous
injection, DMA in blood is excreted into the urine and secreted into the upper
small intestine. The initial half-life of DMA in blood was 12.5 minutes, followed
by a rise in DMA levels between 15 and 20 minutes, and then a second phase
of monoexponential disappearance with a half-life of 15.2 minutes. The
temporary second rise in blood DMA was attributed to absorption of the DMA
secreted into the gut.
29
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The half-lives reported here for the disappearance of DMA from the blood,
12.5 to 15.2 minutes, are considerably shorter than those reported by
Chaudhari and Dutta (1981) of 3.92 to 4.62 hours. However, the values
reported by Chaudhari and Dutta were based on the disappearance of [14C]
from the blood following intravenous injection of [14C]DMA, and their
calculations were based on measurements taken over 4 hours instead of 30
minutes, with the assumption that the rate of DMA disappearance from the
blood was first order. Therefore, .these data would not account for the rise in
blood DMA that Ishiwata et al. (1984b) attributed to reabsorption from the
small intestine and would incorporate the slow-phase disappearance of
[14C]DMA metabolites bound to plasma proteins (see Section 3.1).
Ishiwata et al. (1978) have demonstrated that DMA can also be secreted
into human saliva. A 32-year-old male volunteer ingested 100 mg of DMA'HCI
dissolved in water or in wafer form. Total nitrosatable compounds, primarily
DMA, were then measured at various times in samples of saliva. A definite
increase in salivary DMA was observed (Figure 3-3); the initial rise in DMA
after drinking the solution was due to traces of DMA remaining in the mouth.
Levels of nitrosatable compounds in the saliva of 11 untreated people (con-
trols) were extremely low 0.3 ± 0.2 ppm (mean ±SD) of DMA equivalent;
range, <0.1 to 0.6 ppm.
DMA has been observed in the gastric juices of adult male Sprague-
Dawley rats at 33.5 ± 10.5 nmol/mL (Zeisel et al., 1985). Experiments
performed in ferrets and dogs demonstrated that DMA enters the gastric juice
via the blood (Zeisel et al., 1986).
3.2.5 Metabolism
Concerns have been raised over the possibility of DMA being a
procarcinogen because it can be converted to DMNA under a variety of
conditions. Mirvish (1970) demonstrated that DMA nitrosation by nitrite can
occur in buffered aqueous solutions. DMNA formation was maximal at pH 3.4
and was proportional to the DMA concentration and to the square of nitrite
concentration. The formation of DMNA from DMA and nitrites has been
demonstrated in vitro in human saliva (Tannenbaum et al., 1978; Ishiwata et
al., 1975); both nitrite and DMA occur naturally in saliva (Ishiwata et al., 1978).
Furthermore, nitrosation has been shown to occur in the stomach of dogs
(Lintas et al., 1982), rats (Frank et al., 1985), and monkeys (Hayashi et al.,
1980) given large oral doses of DMA and nitrite. Krull et al. (1979) also
reported that 0.04 percent of a 250-ng oral dose of DMA was converted to
DMNA in the stomachs of mice; the nitrite dose, however, was not reported.
With the exception of the abstract by Krull et al. (1979), most reports of
DMNA formation in vivo have involved relatively massive doses of DMA and
nitrite. Therefore, the production of DMNA at normal dietary levels of DMA and
nitrite has not been clearly demonstrated. Furthermore, the effects of other
dietary factors such as food, ascorbic acid, and phenolic and sulfhydryl
groups, which tend to reduce the nitrosation reaction, have not been fully
investigated (Lintas et al., 1982; Cantoni et al., 1974).
Some investigators believe that formation of DMNA from DMA in vivo
under normal conditions may be negligible because of a low rate of reaction or
30
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0.1
Figure 3-3.
10
20 30 40
Time After Ingestion, Min
50
60
Concentrations of nitrosatable compounds in human saliva after
ingestion of dimethylamine-hydrogen chloride (100 mg) in
solution or wafter form.
Source: Ishiwata wt at. (1978)
because of interferences from other dietary components (Meier-Bratschi et al.,
1983; Cantoni et al., 1974; Mirvish, 1970).
Although the metabolism of DMA, as opposed to its chemical reactions,
has not been extensively investigated, McNulty et al. (1983) have performed
several experiments in vjfro to study the metabolism of DMA to formaldehyde.
In one set of experiments, DMA or benzphetamine (a cytochrome P-450
31
-------
substrate used as a positive control) was incubated with hepatic microsomes
from untreated rats. The N-demethylation of DMA to yield formaldehyde did
occur but at a slow rate, 0.80 ± 0.04 nmol of formaldehyde/mmute/mg
protein as compared to the N-demethylation of benzphetamine, 9.80 ± 0.37
nmol formaldehyde/minute/mg protein. When hepatic microsomes from rats
induced with phenobarbital were used as the enzyme source, the rate of N-
demethylation of DMA was reduced 40 percent whereas that of
benzphetamine was nearly doubled. The reasons for this finding were not
discussed Boiling the microsomes or omitting reduced nicotinamide adenme
dinucleotide phosphate (NADPH) prevented the N-demethylation of both
substrates. The metabolism of N,N-dimethylaniline, a substrate for FAD-
containing mono-oxygenases, was similar to that of DMA in the above
experiments. These results suggested that DMA could be metabolized by both
cytochrome P-450 and FAD-containing mono-oxygenases.
Additional experiments using hepatic microsomes from untreated rats
were carried out. When n-octylamine, a cytochrome P-450 inhibitor, was
added to the incubation mix, the N-demethylation of DMA and benzphetamine
was significantly reduced (p <0.01) when compared to controls. When the pH
of the system was raised to 8.4, maximal for FAD-containing mono-oxygenase
activity the metabolism of DMA was not reduced whereas that of
benzphetamine was. Finally, heat inactivation of FAD-containing mono-
oxygenases decreased, but did not eliminate N-demethylation of DMA (data
were not shown); this treatment had no effect on benzphetamine metabolism.
These studies also show that DMA is metabolized in vitro to some extent by
both cytochrome P-450 and FAD-containing mono-oxygenases in rat hepatic
microsomes with the subsequent release of formaldehyde.
Metabolism of DMA to formaldehyde was also studied in vitro using
microsomes isolated from the respiratory or olfactory mucosa of untreated
rats Turnover rates were very low, 0.20 ± 0.02 and 0.48 ± 0.04 nmol
formaldehyde/ minute/mg protein (mean ±SE) for respiratory and olfactory
mucosal microsomes, respectively. Indirect evidence was reported that
indicated that this metabolism is also a combination of cytochrome P-450 and
FAD- containing mono-oxygenase activities.
In vivo studies were conducted in male Fischer 344 rats exposed to
[HCIDMA at a level of 10 or 175 ppm for 6 hours. Immediately after exposure,
the rats were killed, the nasal and olfactory mucosae were removed, and both
tissues, were fractionated. Bound radioactivity was found in FINA, protein, and
DNA of both tissues after exposure at both levels. However, [14C] bound to
DNA was so low that it could not be accurately quantitated. The authors con-
cluded that these results show that oxidative metabolism of inhaled DMA does
occur in vivo in the nasal mucosa. They further suggested that DMA is N-
demethylated in vivo by cytochrome P-450 to yield formaldehyde and,
possibly converted to N,N-dimethylhydroxylamine by FAD-containing mono-
oxygenases. The N,N-dimethylhydroxylamine, being an unstable intermediate,
would be further oxidized to formaldehyde; formaldehyde derived from both
pathways could be covalently bound or otherwise incorporated into tissue
macromolecules. Formaldehyde could also undergo further oxidation to
carbon dioxide and be exhaled.
The binding of [14C] to tissue macromolecules in vivo after administration
of [14C]DMA (10 mg (80 nCi)/kg, iv) to rats and guinea pigs was studied by
32
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Chaudhari and Dutta (1981). They found radioactivity bound to DNA isolated
from lung and liver of both species. The amounts bound 4 hours postinjection
were extremely low, averaging 32 to 109 pmol DMA equivalents/mg DNA.
These levels were much less than those observed after [14C]DMNA
administration, 529 to 4,196 pmol DMNA equivalents/mg DNA. Experiments
performed in vitro indicated that the in vivo binding of [14C] to DNA after
[14C]DMA injection could have been due to nonspecific binding or to binding
of a radiolabeled contaminant. The in vivo binding of [14C] to DNA in liver was
not increased above control when guinea pigs were administered 80 uCi
[14C]DMA, iv, and were exposed to 50 ppm nitrogen dioxide for 4 hours
postinjection, indicating that DMNA was not formed in vivo under those
conditions.
3.3 Summary of Dimethylamine Metabolism
DMA introduced into the body via ingestion or inhalation can be distrib-
uted and/or metabolized in various tissues. Additionally, studies have shown
that DMA can be synthesized within the body from other dietary constituents
by microorganisms in the gut (Asatoor and Simenhoff, 1965) and by
unidentified endogenous pathways (Zeisel et al., 1985). It has been suggested
that DMA is an important nutrient, acting as a stimulator of postprandial gastrin
'secretion (Lichtenberger et al., 1982) and to stimulate growth of the
gastrointestinal mucosa (Dembinski etal., 1984).
Quantitative absorption studies with single doses of labeled DMA have not
been performed; however, data from other studies indicate that DMA is readily
absorbed following inhalation or ingestion. The major site of absorption in adult
male rats following inhalation of P4C]DMA at 10 or 175 ppm for 6 hours was
the nasal mucosa (McNulty and Heck, 1983). Very little, if any, of the inhaled
[14C]DMA reached the lung directly. Following ingestion, the major site of
DMA absorption is apparently the upper small intestine. Ishiwata et--al.
(1984a,b; 1977) injected DMA into ligated sections of the gastrointestinal tracts
of anesthetized adult male guinea pigs and rats, respectively, and followed the
disappearance of the compound from those sections. In both species, the rate
of disappearance occurred in the upper small intestine; absorption from the
stomach was barely detected, as expected for an ionized substance.
After absorption, DMA travels via the blood to the various internal organs
and tissues. Tissue distribution studies performed in adult male rats and
guinea pigs indicate that 4 hours following an intravenous dose of [14C]DMA at
10 mg/kg, concentrations of radioactivity are highest in the kidneys (Chaudhari
and Dutta, 1981). Levels of P4C] in most other tissues were less than half the
kidney levels. A similar distribution pattern was observed in adult male rats
immediately following a 6-hour inhalation exposure to [14C]DMA at 10 or 175
ppm (McNulty and Heck, 1983).
DMA is excreted mainly via the urine. After inhalation of [14C]DMA at 10
ppm for 6 hours, male rats excreted mean levels of 78, 12.5, and 1.5 percent
of the recovered P4C] in the 0- to 72-hour urine, feces, and expired air
respectively. After 6-hour exposures to 175 ppm [14C]DMA, mean levels of
86.7, 5.1, and 1.5 percent of the recovered [14C] were found in the 0- to 72-
hour urine, feces, and expired air, respectively (McNulty and Heck, 1983)
After intravenous injection of 60 jimol of P4C]DMA, adult male rats excreted
85 to 90 percent of the dose into the 0- to 24-hour urine as unmetabolized
33
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DMA Less than 0.1 percent of the dose was expired as [1"C]DMA and
approximately 0.5 percent as radiolabeled carbon dioxide (Beal and Bryan,
1978).
Balance studies indicate that urinary excretion accounts for 95 percent of
the DMA excreted in combined urine and feces. DMA excretion can range
from 1.5 to 14.7 times intake, depending on the amount of DMA ingested. The
excess DMA is considered to arise from in vivo synthesis by the host and/or
gastrointestinal flora. DMA can be absorbed from the gut into the bloodstream;
from there, it can be secreted into the bile, gastric juice, and saliva. Therefore,
DMA does undergo a certain amount of enterohepatic circulation.
It has previously been suggested that DMA is an end metabolite, i.e., that
it is not metabolized (Asatoor and Simenhoff, 1965). However, McNulty et al.
(1983) have shown that DMA can be metabolized in vitro to formaldehyde,
albeit slowly by rat hepatic and nasal microsomes containing P-450 and FAD
monooxygenase enzyme activities. McNulty and Heck (1983) have suggested
that as much as 8 percent of inhaled DMA may be converted to formaldehyde
by rats in vivo. No information was found in the available literature on potential
DMA metabolites other than formaldehyde or on DMA metabolites in urine or
feces However, 98.7 percent of the radioactivity in the 0- to 24-hour urine of
male rats injected with DMA, iv, was shown to be unmetabolized parent
compound, indicating that little, if any, DMA metabolites are excreted in the
urine (McNulty and Heck, 1983). There is evidence to show that DMA can be
chemically converted to DMNA in the presence of nitrite (large doses of both
DMA and nitrite were used) and acidic conditions and that this conversion can
take place in the mammalian stomach. However, it has not been demonstrated
that significant levels of DMNA are formed in the stomach under reasonable
dietary conditions or that absorption of DMNA from the gastrointestinal tract
occurs under these conditions.
34
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4. Animal Toxicology
4.1 Inhalation Toxicity
4.1.1 Acute Toxicity
The acute inhalation toxicity of DMA has recently been studied by
scientists at the Chemical Industry Institute of Toxicology. Steinhagen et al.
(1982) determined the RD50 of DMA (the DMA concentration that causes a 50
percent decrease in respiratory rate) in groups of male Fischer 344 rats and
male Swiss-Webster mice. Animals were exposed in a head-only exposure
chamber for 10 minutes to DMA concentrations ranging from 49 to 1,575 ppm.
Maximal decreases in respiratory rate were reached after 2 to 7 minutes of
exposure The RD50 values were similar for rats and mice, 573 and 511 ppm,
respectively (Table 4-1), and were comparable to the RD50 value for ammonia
in Swiss-Webster mice. The authors stated that their RD50 values for rats and
mice support the current TLV of 10 ppm as being protective of DMA-induced
sensory irritation.
It should be noted, however, that the RD50 technique is a screening tool
for comparing the sensory irritation of various chemicals. It has been useful in
predicting unacceptable occupational exposure concentrations due to
intolerable sensory irritation and possible respiratory tract injury in humans.
Steinhagen et al. (1982) also determined the LC50 of DMA in groups of
male Fischer 344 rats weighing 158 to 218 g each. Rats were exposed for 6
hours (whole-body) to DMA concentrations ranging from 600 to 6,119 ppm
and mortality was observed for 48 hours postexposure. An LC50 value of 4,540
ppm was calculated (Table 4-1). The authors stated that, based on the
pathology observed in the lungs of the survivors, the LC50 value would have
been lower if mortality had been mo'nitored for 14 days postexposure. The
lowest concentration at which mortality occurred in rats was 3,983 ppm. The
concentration versus percent mortality curve has a very steep slope, indicating
a narrow range of response rates at all concentration studies. An estimate of
LC-I was derived from this graph; for rats, LCi is estimated at 2,800 ppm.
Clinical signs observed in the Steinhagen et al. (1982) study included eye
irritation, gasping, and secretion of bloody mucus from the nose. Exposure at
the levels tested resulted in severe nasal congestion, ulcerative rhinitis, and
necrosis of the turbinates. In the lungs, ulcerative lesions of primary and
secondary bronchioles occurred at 4,000 ppm and higher, while emphysema,
bronchial hyperplasia, and pneumonitis occurred at 1,000 ppm and higher.
Mild emphysema in peripheral areas of the lung was noted at 600 ppm. Other
organs affected were the eyes and liver. Corneal edema was noted at 1,000
ppm. Fatty degeneration and focal necrosis of the liver and corneal ulceration,
35
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Table 4-1. Acute fox/city Values for Dlmethylamine in Laboratory Animals
Species/
Sex
Mouse(M)
Mouse (M)
Rat (M)
Rat (M)
Mouse
Rat
Guinea pig
Rabbit
Route of
Administration
Inhalation
Inhalation
Inhalation
Inhalation
Oral
Oral
Oral
Oral
Acute Toxicity Value
LC50: 7,650 ppm
(6,687-8,75? ppmfi
RDSO:511 ppm
(414-654 ppm)
LC5(f 4,540 ppm
(4,208-4,899)
RD50: 573 ppm
(460-747 ppm)
LD50: 316 mg/kg b. wt.
LD50: 698 mg/kg b. wt
8,100 mg/kg b. wt.c
LDSO: 240 mg/kg b. wt.
1,070 mg/kg b. wt. c
i.D50.- 240 mg/kg
1,600 mg/kg b. wt. c
Reference
Mezentseva
(1956)a
Steinhagen et al.
(1982)
Steinhagen et at.
(1982)
Steinhagen et al.
(1982)
Dzhanashvili (1967)
Dzhanashvili (1967)
Dzhanashvili (1967)
Dzhanashvili (1967)
LC50 value was calculated from the raw data reported by Mezentseva (1956).
Mice were exposed for 2 hours.
bValues in parentheses are 95 percent confidence limits.
°These oral LD50 values are for DMA solutions titrated with hydrochloric acid to pH8.
keratitis, edema, and loss of Descemet's membrane occurred at 2,500 to
6,000 ppm.
Buckley et al. (1984) exposed male Swiss-Webster mice (weighing
approximately 30 to 40 g) 6 hours/day for 5 days to RD50 concentrations of
DMA (511 ppm) to evaluate the extent of damage to the respiratory tract.
Twenty-four mice were exposed in glass aquarium chambers (102-L capacity)
with airflow ranging from 25 to 38 I/minute. DMA concentrations were
achieved by direct metering into the chamber and were analyzed at least once
an hour by IR spectrometry. Half of the mice were killed by exsanguination
and necropsied immediately after the last exposure; the others were killed and
necropsied 72 hours postexposure.
Body weights for all mice were decreased from 10 to 25 percent of control
values and three mice died during exposure. In mice killed immediately post-
exposure, severe exfoliation, erosion, ulceration, and necrosis of the
respiratory epithelium in the nasal area were noted. In addition, severe
ulceration and necrosis of olfactory epithelium and moderate degeneration of
olfactory nerves in the lamina propria were noted. No lung lesions were
observed. Mice killed 72 hours postexposure exhibited a reduction in nasal
inflammation. However, there was little change in ulceration or degeneration of
tissues. The 72-hour period was insufficient for recovery from the observed
lesions.
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Morgan et al. (1985) studied the effects of inhaled DMA on the nasal
mucociliary apparatus in rats as examined in rapidly excised tissue by video
analysis. Rats were exposed to 175 ppm DMA 6 hours/day for 9 days. Results
indicated that DMA inhibited mucociliary function in the dorsal half of the
maxilloturbinate, with normal ciliary activity persisting in the ventral meatus.
Mucus flow patterns on the lateral wall were altered by DMA. This may explain
in part the mechanism responsible for the nasal toxicity of DMA.
Gross et al. (1987) have recently reported additional histologic and video
analysis of effects on the mucociliary apparatus at additional time points after
175 ppm DMA exposure (1, 2, 4, or 9 days and at 2 years). Acute and chronic
DMA exposure produced erosion of anterior margins and fenestrations of the
adjacent septum. Ciliastasis and mucostasis were observed only on the
anteromedial aspect of the maxilloturbinate (see Figure 4-1). In the 2-year-old
= Areas of Fenestration and Erosion
= Ciliastasis
Figure 4-1. Anatomical diagram of the nasal cavity of a 10-wk-old rat exposed
to 775 ppm DMA for 1 or 9 days. Arrows indicate direction of
mucous flow. The asterisk indicates rotational flow over the
posterior wall. The solid arrow indicates a region in which mucus
flowed from the naso- to the maxilloturbinate over areas of
Ciliastasis following 9 days of exposure to DMA.
Source: Gross et al. (1987).
chronically DMA-exposed rats (study described in detail in Section 4.1.3),
mucociliary activity was present in areas adjacent to erosions of the turbinates
and septum (see Figure 4-2). Abnormal mucus flow patterns, including altered
or reversed direction of flow and "whirlpool-like" formation were observed in
all treated rats, but were more severe following chronic exposure. The authors
concluded that the mucociliary apparatus continues to function in nasal
passages of rats having localized destruction of nasal epithelium induced by
DMA exposure; this clearance system responds to alterations of nasal struc-
ture by modification of- mucus flow patterns. Additional note was made of the
dissimilar toxic cellular response to DMA when compared to formaldehyde
37
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fjgj = Respiratory Metaplasia
H = Areas of Fenestration and Erosion
IBB3 = Mucostasis
Wfa = Ciliastasis
Figure 4-2. Anatomical diagram of the nasal cavity of an old rat following 2
years of exposure to 175 ppm DMA. Areas of Ciliastasis and mucus
flow patterns are similar to those seen from acute exposure. The
asterisk marks an area of altered mucus flow on the lateral wall.
There are areas of respiratory metaplasia on the ethmoid
turbinates. The areas of fenestration and erosion are slightly
larger than those observed after acute exposure.
Source: Gross et al. (1987).
(which had been proposed as a metabolite of DMA in the nasal mucosa). The
epithelial vacuolation and severe subepithelial destruction observed with DMA
suggest that an alternative mechanism may be responsible for DMA toxicity,
which appears to be related to DMA directly rather than formaldehyde per se.
4.1.2 Subchronic Toxicity
Hollingsworth et al. (1959) exposed groups of 10 rats, 6 guinea pigs, and
1 rabbit of each sex and 5 female mice (age, weight, and strain were not
reported) to 97 or 183 ppm of DMA vapor for 7 hours/day, 5 days/week, for 18
to 20 weeks. Additionally, one male monkey was exposed to 97 ppm DMA and
one female monkey was exposed to 183 ppm. Galvanized sheet-metal boxes
having a 1760-L capacity served as the inhalation chambers. Anhydrous DMA
gas was mixed with air and injected into the inhalation chamber. DMA
concentration was maintained using a dual-syringe feeder pump and analyzed
periodically during the exposure period. Actual DMA concentrations ranged
from 152 to 195 ppm for the high-dose group (183 ppm) and 92 to 98 ppm for
the low-dose group (97 ppm).
The eyes of rats, guinea pigs, and rabbits were examined 9 and 45 days
after the start of exposure. Slight to moderate corneal damage to the eyes of
guinea pigs and rabbits exposed to 97 or 183 ppm DMA was observed after 9
38
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days, but did not progress through 45 days of exposure. However, no adverse
effects of treatment were noted in body weights, organ weights, or clinical
chemistry and hematology parameters. Histopathological evaluation revealed
centrilobular fatty degeneration and necrosis of the liver parenchyma! cells of
rats, rabbits, and mice at both dose levels. These lesions were also noted in
female guinea pigs exposed to 183 ppm. The authors also reported testicular
tubule degeneration in one rabbit (at 183 ppm) and in the monkey (exposed to
97 ppm). The available hematoxylin and eosin-stained slides were reexamined
by Quast (1981). Because of lost slides, inadequate animal coding, and other
problems, Quast could not conclude that the observed testicular pathology
was primarily the result of subchronic DMA inhalation.
In studies conducted by Coon et al. (1970), male and female Sprague-
Dawley and Long-Evans rats and Princeton-derived guinea pigs and male New
Zealand albino rabbits, squirrel monkeys, and beagle dogs (age and weights
were not specified) were exposed to 9 mg/m3 (approximately 4.9 ppm) DMA
continuously for 90 days. A modified Rochester-type inhalation chamber
containing 15 rats, 15 guinea pigs, 3 rabbits, 3 monkeys, and 2 dogs was
loaded in a typical experiment. DMA concentrations were continuously
monitored using a hydrogen flame-ionization detector. No signs of toxicity or
mortality were observed during the exposure period. Animals were killed by an
overdose of pentobarbital immediately after exposure. No changes in
hematology parameters were observed. Histological evaluation of the lung
revealed only minor interstitial inflammation in all species tested. Dilation of
the bronchi was noted in rabbits and monkeys. These effects were not
considered to be chemically induced. Apparently, sections of the nasal
turbinates were not collected; therefore, evidence of possible lesions of the
respiratory and. olfactory epithelia was not obtained. However, this study does
support earlier cited evidence of only minor lung involvement during inhalation
of DMA (Buckley et al., 1984).
Although no subchronic studies reporting nasal epithelial findings after
DMA inhalation were found in the literature, Lynch et al. (1986) studied the
effects of diethylamine (DEA) exposure on Fischer 344 rats. One hundred rats
per sex were exposed to 25 or 250 ppm DEA for 6 hours/day, 5 days/week for
6 months. Body weight gains of the 250-ppm rats were decreased throughout
the exposure period when compared to control animals. Sneezing, tearing, and
reddened noses were also noted in the 250-ppm animals. Histological
evaluation revealed squamous metaplasia, suppurative (pus containing)
rhinitis, and lymphoid hyperplasia of the respiratory epithelium. Therefore,
although lesions of the nasal or olfactory epithelium were not reported in the
DMA subchronic studies reviewed, the possibility that they occur cannot be
ruled out.
4.1.3 Chronic Toxicity
A 2-year chronic toxicity study was conducted in rats and mice (interim
report - Buckley et al., 1985; Chemical Industries Institute of Toxicology,
1987). Male and female Fischer 344 rats and B6C3F1 mice were exposed by
inhalation to 0, 10, 50, or 175 ppm DMA for 6 hours/day, 5 days/week for 1
year. Ninety-five animals (6-10 wk old)/sex/species were randomly assigned to
groups. Rats were individually housed and mice were group-housed five/cage
in suspended stainless steel wire cages within the exposure chambers, which
39
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were described as stainless steel and glass whole-body inhalation chambers
(8 m3). Airflow was maintained at 2,200 L/minute. DMA concentrations were
generated by metering "pure" DMA directly from the cylinder into the
chambers using a flow meter. Concentrations were analyzed four times/hour
using IR spectrometry. Results of the chamber DMA analyses indicated that
the average analytical concentrations of DMA were approximately 142, 44, and
8 ppm for the 175-, 50- and 10-ppm chambers, respectively.
Necropsies were performed on fasted animals after 6, 12, and 24 months
of exposure. No male mice were killed at the 12-month interval because of
unexpectedly high mortality in all groups. Prior to necropsy, blood was
collected for hematology and serum chemistry analyses. Specified tissues and
gross lesions were collected. The lung, liver, kidneys, and brain were weighed.
The nasal passages were flushed and the lungs were inflated with formalin
prior to fixation.
Body weight gains for rats in the 175-ppm group were consistently and
significantly decreased (by approximately 10%) when compared to controls
after 3 weeks of exposure. In addition, mice exposed to 175 ppm DMA
exhibited sporadic, significantly decreased body weight gains. No clinical
signs of toxicity or treatment-related mortalities were noted. The high mortality
throughout all groups observed in male mice was attributed to fighting.
Possible treatment-related changes observed in hematology parameters were
decreased platelet count in 175-ppm male rats, increased numbers of atypical
lymphocytes in 175-ppm female rats, and decreased mean red blood cell
volume in 175-ppm female mice when compared to controls. Statistically
significant changes in serum chemistry values after 12 months of exposure
consisted of decreased protein concentration and increased alkaline
phosphatase activity in 175-ppm female rats and increased glucose levels in
175-ppm female mice.
Histological evaluation revealed that exposure-related lesions were
confined to the nasal passages and were similar in nature for rats and mice. In
rats, there was a progression in severity of degeneration of the olfactory
epithelium with increasing exposure time whereas in mice, no apparent
progression was observed between 6 and 12 months of DMA exposure. Areas
of involvement included the respiratory epithelium and underlying tissues
adjacent to the vestibule and the olfactory epithelium in the mid portion of the
dorsal meatus with variable involvement of more posterior olfactory areas. In
the animals exposed to 175-ppm, variable destruction of the anterior portions
of the naso- and maxilloturbinates and fenestration of the nasal septum were
observed. The surfaces of the turbinates and septum were covered with
nonkeratinizing squamous epithelium. There were both focal and diffuse
mucosal and submucosal infiltration of mononuclear leukocytes and
neutrophils, indicating an inflammatory response. Little exudate was present.
Epithelial hypertrophy and hyperplasia, focal epithelial ulceration, and focal to
diffuse squamous metaplasia were observed. In rats, mild to severe goblet cell
hyperplasia on the ventral portion of the nasal septum was also observed. The
lesion of the olfactory region most frequently observed in rats and mice was
degeneration of olfactory sensory cells with variable vacuolation of the
olfactory epithelium. Atrophy of olfactory nerves in the lamina propria usually
accompanied these lesions. Accumulation of hyaline eosinophilic material in
the sustentacular cells, which were markedly hypertrophic, was also frequently
noted. This eosinophilic material was also observed in the associated airway
40
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(possibly a secretory product of the sustentacular cells) and in large
submucosal glands at the junction of the olfactory and respiratory epithelium.
Hypertrophy and focal hyperplasia were also noted in Bowman's glands.
Severe degeneration of the olfactory epithelium was followed by replacement
with well-differentiated, ciliated respiratory epithelium, which was sometimes
continuous with ciliated ducts of hypertrophic and hyperplastic Bowman's
glands. In rats, foci of fusiform cells were observed near the basal layer in
areas of respiratory metaplasia in the dorsal meatus. The basement
membrane of the underlying, edematous connective tissue appeared to be
thickened and separated from the epithelium. Basal cell hyperplasia in the
olfactory epithelium was also frequently observed in rats.
In the 50-ppm groups, changes in the respiratory nasal epithelium were
• confined to focal squamous metaplasia in the free margins of the turbinates
after 6 months and to epithelial hypertrophy and hyperplasia after 12 months
of DMA exposure. The majority of animals exposed to 50 ppm DMA exhibited
olfactory epithelial lesions. These lesions consisted of loss of sensory cells
and olfactory nerves.
In the 10-ppm groups, chronic inflammation of the vestibule and respira-
tory nasal epithelium was noted. Lesions consisting of focal degeneration of
olfactory epithelium located in the dorsal meatus were observed. These results
indicate that the olfactory sensory cell is highly sensitive to the toxic effects of
DMA, with minor lesions being produced in rats and mice even at 10 ppm
which is the current TLV for humans.
Chronic inhalation exposure of Wistar rats to 0, 0.005, 0.033, or 0.93
mg/m3 (0, 0.003, 0.02, and 0.5 ppm, respectively) of DMA was reported by
Artem'eva and Dobrinskii (1973). It should be noted that very few details of the
experimental procedure were reported and especially the length of exposure
was not specified. The authors reported that DMA levels of 0.93 and 0.033
mg/m3 caused changes in the normal ratio of muscle-antagonist chronaxy, a
decrease in blood cholinesterase activity, a decrease in -SH groups in serum,
an increase in urinary elimination of coproporphyrins, a disturbance of immune
reaction of the body, and a decrease in ascorbic acid in the organs.
Histological evaluation revealed infiltration of lung perivascular connective
tissue and thickening of interalveolar septa with congestive hyperemia of veins
and alveolar capillaries. Vacuolization of the cytoplasm with partial tigrolysis
was noted in some neurons and subcortical ganglia of the cerebral cortex in
the brain. No changes were observed in the 0.005-mg/m3 group when
compared with controls. These experimental findings need confirmation by
additional well-conducted studies.
4.7.4 Carcinogenicity
Groups of Fischer 344 rats and B6C3F1 mice of both sexes were exposed
to nominal concentrations of 0, 10, 50, or 175 ppm DMA for up to 24 months
(Chemical Industries Institute of Toxicology, 1987). Decreases in body weight
were noted in either sex of both rats and mice at exposure levels of 175 ppm.
The complete report giving specific body weights for both species is not yet
available (December 1989), but a few animals from this study were used by
Gross et al. (1987). Control 2 yr rats weighed an average of 355.8 ± 11.92g
(SEM) compared to exposed rats' weight of 346.50 ± 9.82g. Nasal toxicity
characterized by dose-related increases in incidence of inflammatory,
41
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degenerative, and hyperplastic lesions at the nasal passages was noted. There
were no increased incidences of tumors that could be attributed to DMA
exposure. The authors concluded that DMA is not carcinogenic to rats or mice.
Further information will have to await the release of the full experimental
docket by CUT.
4.2 Oral Toxicity
4.2.1 Acute Toxicity
The acute effects of oral administration (method not specified) of aqueous
DMA in rats, mice, guinea pigs, and rabbits (strain, sex, age, and weight were
not specified) were reported by Dzhanashvili (1967). In addition, because of
the severe irritating effects of aqueous DMA, the dosing solution neutralized
with hydrochloric acid was also given to rats, rabbits, and guinea pigs to
determine LD50 concentrations. The LD50 values for mice, rats, guinea pigs,
and rabbits given aqueous DMA were 316, 698, 240, and 240 mg/kg body
weight, respectively (Table 4-1). The LD50 values for the neutralized DMA
were 5- to 11-fold higher.
Clinical signs noted included transient excitation followed by
sluggishness, prostration, and disturbances in motor coordination. At
necropsy, extensive hemorrhage of the stomach and intestinal walls was noted
in animals receiving the unneutralized DMA solutions, indicating that the acute
oral toxicity of aqueous DMA was largely due to local action on the
gastrointestinal mucosa.
4.2.2 Subchronic Toxicity
The subchronic oral toxicity of DMA neutralized with hydrochloric acid
was described by Dzhanashvili (1967). Dose levels of 107 and 160 mg/kg
body weight of DMA (1/10 of the reported LD50) neutralized with hydrochloric
acid were administered orally to 30 guinea pigs and 15 rabbits, respectively,
daily for 6 weeks (animal strain, sex, weight, and age were not reported).
Increases in blood hemoglobin, blood cholinesterase activity, blood urea
nitrogen (BUN) concentration, and coproporphyrin excretion in urine were
reported. Some statistical differences were indicated. Relative liver weight was
increased and vitamin C content in the organs was decreased.
In addition, Dzhanashvili (1967) reported the effects of oral administration
(method not specified) of neutralized DMA to rats and guinea pigs for 8
months. Albino rats received 0.007, 0.035, or 0.35 mg/kg body weight of DMA
and guinea pigs received 0.035, 0.35 or 3.5 mg/kg body weight of DMA daily.
Again, strain, age, weight, and sex of the animals were not specified. No
control values were determined or reported. In guinea pigs, 3.5 mg/kg body
weight of DMA caused increases in BUN concentrations, relative liver weight,
and coproporphyrin excretion in the urine. There were also decreases in
vitamin C content in the adrenals. Daily doses of 0.35 mg/kg body weight
resulted in transient (noted in first 4 months) increases in BUN and the
number of white blood cells and decreases in vitamin C content in the
adrenals. No other changes were noted for guinea pigs.
42
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In rats, daily doses of 0.35 mg/kg body weight resulted in decreases in
the phagocytic activity of blood leukocytes and increases in absolute liver
weight. The authors also reported a higher nervous activity in the animals. This
was evaluated using the motor-alimentary method, which tests the animal's
capacity to develop new temporary nerve connections. This test is reported to
be widely used in the Soviet Union to determine hygienic standards for water,
but does not appear frequently in the U.S. literature. The rats were grouped
according to their conditioned reaction to a single positive stimulus
represented by a bell. The effect of DMA on the conditioned reflexes was then
evaluated. A dose of 0.035 and 0.35 mg/kg body weight resulted in higher
nervous activity of the rats. No other changes were noted.
4.2.3 Chronic Toxicity
No pertinent data on the chronic oral toxicity of DMA were found in the
literature.
4.2.4 Carcinogenicity
No pertinent data on the carcinogenicity of DMA after exposure via the
oral route were found in the literature.
4.2.5 Interactions and Synergistic Toxicity
4.2.5.1 Acute Exposure
The effects of combined DMA-nitrite administration have been investigated by
several laboratories. The acute effects of sodium nitrite (NaNO2) and DMA'HCI
in adult male HaM/ICR mice was studied by Asahina et al. (1971). Dose levels
of administered DMA were 500, 1,000, 2,000, or 2,500 mg/kg body weight,
whereas doses of NaNO2 were 100 or 150 mg/kg body weight. No mortality
was noted in mice receiving NaNO2 or DMA alone. Toxicity in the form of
relative weight losses, mortality, and liver necrosis was evidenced in animals
given NaN02 and DMA simultaneously or DMA followed by nitrite at time
intervals of up to 3 hours. Toxicity was decreased when nitrite was
administered prior to DMA at increasing time intervals. Livers from animals
receiving 2,500 mg/kg body weight of DMA and 150 mg/kg body weight of
NaNO2 were swollen, mottled, hemorrhagic, necrotic, and fragile. Microscopic
examination revealed widespread centrilobular and midzonal parenchymal liver
necrosis, sinusoidal and portal congestion, and hemorrhage. The authors
stated that these findings were consistent with the \n vivo formation of DMNA.
The influence of intestinal microflora on acute hepatotoxicity of DMA and
nitrite was studied in 30-day-old germ-free and conventional CFW and Swiss-
Webster mice by Pollard et al. (1972). Mice were fed NaNO2> DMA, or NaNO2
and DMA (doses of DMA were 2,500 or 3,500 mg/kg body weight and doses
of NaNO2 were 75 or 100 mg/kg body weight) and observed for mortality for 3
days. Conventional and germ-free mice demonstrated similar patterns of
susceptibility. Increased doses of DMA and NaNO2 caused increases in
deaths and hepatic necrosis. From these results, the authors concluded that
intestinal microflora do not play a role in the synthesis of the toxic agent,
which probably was DMNA. Sumi and Miyakawa (1983) conducted studies
comparing the effects of DMA and nitrite on liver necrosis and serum
43
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glutamic-oxaloacetic transaminase (SGOT) and serum glutamic-pyruvic
transaminase (SGPT) levels of treated conventional and germ-free Wistar rats.
Administration of DMA and nitrite or DMNA alone by stomach tube produced
hepatic necrosis; after 48 hrs, 30- to 40-fold elevations in SGOT and SGPT
levels were'found in germ-free rats with no changes in conventional rats. DMA
and NaNO2 administered simultaneously to male Swiss albino mice produced
synergistic acute inhibition of liver protein and nuclear RNA synthesis (Fried-
man et al., 1972). These findings provide further evidence of in vivo
nitrosamine synthesis since similar effects have been noted after
administration of DMNA.
Several acute studies have • been conducted to evaluate the possible
inhibition of DMA-NaNO2 hepatotoxicity by antioxidants. Cardesa et al. (1974)
reported complete inhibition of DMA-nitrite-produced liver necrosis and
associated marked increases in SGOT and SGPT in male Wistar rats (250-400
g) by oral doses of 90 to 720 mg/kg body weight of ascorbic acid (1,500
mg/kg body weight of DMA and 125 mg/kg body weight NaNO2). Propyl
gallate and tert-butylhydroquinone at equimolar levels to nitrite were also
shown to inhibit the effects of hepatotoxicity elicited by DMA-NaN02 (enzyme
induction and hepatic necrosis) in male Sprague-Dawley rats (Astill and
Mulligan, 1977). Antioxidants are thought to inhibit the formation of
nitrosamines.
4.2.5.2 Subchronic and Chronic Exposure
The combination of DMA and NaNO2 has been shown to cause acute toxicity
in rats and mice, presumably due to the formation of DMNA in vivo. Several
studies have been conducted to determine the long-term toxicity of DMA and
NaNO2 and the possible carcinogenicity of the combination of these
chemicals.
Kunisaki et al. (1974) fed rats (strain, age, weight, number, and sex were
not specified) NaNO2, DMA, or NaNO2 and DMA (10 mg/day) for 6 months.
Administration of DMA and NaN02 resulted in fatty degeneration of the liver
and hemorrhagic lesions in the kidney. DMA or NaNO2 alone had no effect.
In another study, male Wistar rats, five per group, were given the following
concentrations of DMA and NaNO2 simultaneously in their drinking water for
78 days: 0.5, 2.5, or 5.0 g/L NaNO2 plus 4 mL/L DMA (Oka et al., 1974). Also,
three groups of five male rats were given 1 g/L salicylic acid in addition to the
concentrations of DMA and NaNO2 given above. Vitamin A content and histo-
pathology of the liver were evaluated. Mean body weights of the high-dose
animals (5.0 g/L NaN02, 4 mL/L DMA with and without salicylic acid) were
significantly lower than controls, and vitamin A was decreased when compared
to other dose groups. The authors reported that the high-dose animals
developed a skin disorder described as loss of luster and "disturbance" of the
body coat after 10 days on study; this disorder persisted to study termination.
The skin disorder was attributed to decreases in vitamin A. Addition of salicylic
acid had no effect. Because of the significant decrease in hepatic vitamin A
observed in this study, additional experiments were conducted to test the
potential hepatic carcinogenicity of combined DMA-nitrite administration.
Oka et al. (1974) performed a study with male albino Wistar rats weighing
approximately 100 g (five rats/group) which were given 5, 15 or 30 g/L NaN02
44
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plus 4 mL/L DMA in the drinking water for 410 days. Vitamin A content and
histopathology of the liver were evaluated. All animals in the 15- and 30-g/L-
NaN02:4-mL/L-DMA groups exhibited the skin disorder described earlier and
died within 14 days of study initiation. Death was attributed to NaNO2 toxicity.
No liver changes were noted in these animals. In the 5-g/L- NaN02: 4-mL/L-
DMA group, there were decreases in body weight and vitamin A content in the
liver. Two of four rats in this group developed sarcomas of the liver. One rat,
dying on day 318, had what was described as a large metastatic liver sarcoma
with involvement of the mesentery and spleen. The other tumor-bearing rat
was sacrificed on schedule (day 410); its tumor was not metastatic. The
authors concluded that combined oral administration of DMA and nitrite to rats
over a long period of time was carcinogenic.
The validity of the authors' conclusion, however, is questionable because
of numerous deficiencies with the study protocol. Only four rats survived
longer than 2 weeks. Only one dose level of DMA was tested. Control groups
receiving DMA or NaNO2 alone were not included; therefore, the toxicity noted
could have been due to NaNO2. Analyses of test solutions were not
performed; therefore, chemical conversion of DMA to DMNA could have
occurred in the drinking water. Therefore, the study performed by Oka et al.
(1974) is an unacceptable study, and the evidence for carcinogenicity is
questionable.
Garcia Roche et al. (1983) studied the effects of DMA and NaNO2 on
male Wistar rats. Six groups of eight rats each were given oral doses of 10 or
20 mg of DMA'HCI (110 or 220 mg/kg body weight, respectively), 10 mg
NaNO2, 10 mg NaNO2 and 10 mg DMA'HCI, or 10 mg NaNO2 and 20 mg
DMA'HCI for 30 days. The rats were 30 to 40 days of age and weighed
approximately 90 g at study initiation. At the end of exposure, body and liver
weights were measured, and SGPT analysis and histopathologicai evaluation
of the liver and kidneys were performed. No significant differences were found
in any of the parameters evaluated. Histopathologicai evaluation did not reveal
any significant changes in the liver or kidneys of any exposed animals. The
only exposure-related observation noted upon necropsy was ascites fluid in
the abdomen of three animals from the 10 mg NaNO2:20 mg DMA group.
In another experimental study, groups of 30 weanling male Wistar rats
were given DMA (0.2 percent), NaNO2 (0.2 percent), DMA and -NaNO2,
butylated hydroxytoluene (BHT, 0.5 percent), or BHT, DMA, and NaNO2 in the
drinking water for 9 months (Darad et al., 1983). At study termination, the
animals were killed and hepatic microsomes were isolated for in vitro analysis
of lipoperoxidation and lysosomal enzyme activities (acid phosphatase and
cathepsin). Results indicated that NaNO2 or DMA alone caused significantly
higher peroxidation, but when administered simultaneously, there was no
increase in peroxidation when compared to controls. BHT administration
resulted in a significant reduction in peroxidation of lipids. However, BHT,
DMA, and NaNO2 administered simultaneously had no effect on peroxidation;
values were comparable to controls. In rats given DMA or NaNO2, the free
activities of both lysosomal enzymes were increased while the total activities
were decreased. The reasons for this were not clear. In rats receiving BHT, the
free activities of both enzymes were decreased while the total activities were
increased. Rats given DMA and NaNO2 had increases in free activities and
decreases in total activities of the lysosomal enzymes while animals given
DMA, NaNO2, and BHT had free activities that were comparable to controls.
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The authors concluded that DMA and NaN02 may induce toxicity through
some free radical reactions and BHT can provide some protection against
.toxicity.
Karpilovskaya and Rubenchik (1977) studied the effect of DMA, NaN02,
and the combination of the two on DMNA demethylase activity in the rat liver.
Young male rats weighing 140 to 200 g (strain not reported) were fed 150
mq/kg DMA, 38 mg/kg NaNO2, DMA and NaNO2 (concentrations equal to
above levels), DMA plus NaNO2 plus ascorbic acid (150 mg/kg), or DMNA (6
mg/kg) in the diet (supplemented with casein, 2 g/rat) for 3.5 months. Animals
were then killed, and hepatic rnicrosomes were isolated to determine DMNA
demethylase activity. Results indicated that administration of DMA caused a
significant increase (p <0.01) in DMNA demethylase activity when compared
to controls, suggesting that DMA is a demethylase inducer and may, therefore,
increase endogenously-formed DMNA toxicity.
4.3 Mutagenicity
Several in vitro and in vivo genetic toxicology assays on DMA have been
published. These have been categorized into gene mutation (category 1) and
chromosomal aberration assays (category 2) and those studies that assess
other mutagenic mechanisms (category 3). The findings from the studies are
discussed below.
4.3.1 Gene Mutation Assays (Category 1)
4.3.1.1 Reverse Mutation in Prokaryotes.
Three reverse mutation assays with Salmonella typhimurium were reported.
Takeda and Kanaya (1982) exposed S. typhimurium TA98 and TA100 to the
nitroso derivative of DMA (50 mM DMA reacted with 500 mM NaNO2 at pH
3.4). The assay was conducted in the absence and presence of an S9 mix
(hepatic rnicrosomes from rats induced with polychlorinated biphenyls plus
appropriate cofactors in buffered solution). No response was seen in S.
typhimurium TA98 (±S9). It was stated that the effect observed in S.
typhimurium TA100 in the presence of S9 was comparable to that observed
with DMNA. However, no data were reported and consequently the results of
this study are considered inconclusive.
When tested at concentrations of 1 to 5 mg/plate and in the absence of an
S9 mix, DMA was not mutagenic in S. typhimurium TA1530, TA1531, TA1532,
or TA1964 strains (Green and Savage, 1978). However, since DMA was spot
tested rather than incorporated into the medium, these results provide only
preliminary qualitative evidence of a negative response. In the presence of
mouse S9, 0.005 to 0.5 M DMA in suspension with these four tester strains
produced a dose-related increase in the mutation frequency (MF) of only S.
typhimurium TA1530 at 0.05, 0.15, and 0.5 M DMA. These doses were slightly
cytotoxic (>80 percent survival). Although this study provides acceptable
evidence of an S9-activated mutagenic response in the base-pair substitution
strain TA1530, the findings should be interpreted with caution because activity
was only'seen at very high doses (i.e., 0.5 M DMA, which is equivalent to
22,540 yg/plate) and the results have not been confirmed.
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4.3.1.2 Mammalian Cell Gene Mutation.
A survey study of 101 chemicals that included DMNA and DMA as a
carcinogenic/noncarcinogeriic pair, respectively, listed DMA as negative in the
Chinese hamster ovary cell (CHO) hypoxanthine guanine phosphoribosyl
transferase (HGPRT) assay with and without .rat S9 activation (Hsie et al.,
1978). Similarly, DMA was also reported to be negative by San Sebastian et
al. (1979) in a blind CHO/HGPRT assay of carcinogenic/noncarcinogenic
compound pairs. However, it appears that the reports of Hsie et al. (1978) and
San Sebastian et al. (1979) are abstracts of results from the same study; no
data were presented.
4.3.1.3 In Vivo Gene Mutation (Host-Mediated Assays).
Several investigators conducted mouse and/on rat host-mediated assays with
either DMA or DMA and NaNO2; the indicator organisms, which in all cases,
were histidine-deficient strains of S. typhimurium (Edwards et al., 1979; Whong
et al., 1979; Green and Savage, 1978; Braun et al., 1977; Couch and
Friedman, 1975). None of the assays conducted with. DMA were considered
acceptable. The study by Edwards et al. (1979) was reported in an abstract
and lacked sufficient data for evaluation, whereas the other four assays
showed no evidence of overt animal toxicity or bacterial cytotoxicity. However,
the data collectively suggest that DMA administration by. oral gavage or
intramuscularly at nontoxic doses up to 2 g/kg did not induce a mutagenic
response in the indicator organisms. In contrast, mutagenic effects were
achieved when DMA was administered orally either in combination or in
sequence with.NaNO2 to female mice or rats (Edwards et al., 1979; Whong et
al., 1979; Couch and Friedman, 1975). The results further suggest that activity
was detected at high doses of DMA ranging from 0.2 to 2 g/kg in the presence
of high doses of NaNO2- The study by Whong et al. (1979) was noteworthy
because the assays were conducted with mice and rats. Test animals (female
CD1 mice or CD rats) received intravenous inoculations of S. typhimurium G
46 10 minutes prior to gavage with 0.4 g/kg DMA or 0.2 g/kg NaNO2 or
sequential gavage with 0.07 to 0.4 g/kg DMA and 0.1 g/kg NaNO2. An
additional group of mice and rats were dosed with 0.4 g/kg DMA and 0.2 g/kg
NaNO2. Bacterial cells were harvested 2 hours posttreatment and plated for
total survivors and mutants. Mutation frequencies (MFs) were then calculated.
Results for both mice and rats showed that neither DMA nor NaN02, tested
separately, induced a mutagenic response. However, dose-related increases in
the MFs for both species were observed with increasing concentrations of
DMA + 0.1 g/kg NaNO2. At comparable doses, the response was
approximately 50 percent higher in rats than mice and the mutagenic effect
was enhanced in both species at the highest test dose by doubling the
concentration of NaNO2.
Although the data clearly show a dose-related mutagenic response
associated with DMA-nitrite interaction, the results should be viewed with
caution for the following three reasons. (1) If DMA in the presence of NaNO2
was converted to nitrosamines, as suggested by the authors, the marked
increase in the mutagenic response of bacterial cells harvested from rats
rather than mice is both unexpected and inconsistent with other studies. Prival
et al. (1979) have shown that In vitro conversion of DMNA to a reactive
mutagenic metabolite is species specific and S9 microsomal fractions derived
from mice are more effective in metabolizing DMA than are rat S9 fractions.
47
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(2) The findings with DMA in the presence of NaNO2 conflict with the results
presented by the authors from host-mediated assays with DMNA. In these
studies, higher mutagenic activity was observed in bacterial cells recovered
from mice than from rats. (3) Both DMA and NaNO2, tested separately, were
negative; however, in combination,' an interactive mutagenic effect was noted.
In general, the effect was proportionate to the dose of DMA (2-fold increase in
MF with doubling concentrations of DMA) while the level of NaN02 was held
constant. However, increasing the concentration of NaNO2 by 50 percent at
the highest DMA dose in both rodent species (0.4 g/kg + 0.2 g/kg NaNO2)
caused a 4- to 5-fold increase in mutagenesis. Although the higher
concentration of NaNO2 may have enhanced the rate of nitrosation of DMA,
NaN02 is also a direct-acting base-pair substitutional mutagen in the S.
typhimurium G 46 derivative strains TA1535 and TA100 (McCann et al., 1975)
and is frequently used as a positive control in the S. typhimurium microsome
mutagenicity (Ames) assay.
Thus, while the study of Whong et al. (1979) discussed above was
technically sound, the relevance of the findings is unclear.
Braun et al. (1977) also performed host-mediated assays with DMA and
DMA + NaN02 using male mice as the host and S. typhimurium TA1950
(derivative strain of G 46). The authors reported that DMA, at doses ranging
from 0.1 to 0.2 g/kg, was not mutagenic. In contrast to previous studies
showing an- interreactive mutagenic effect for DMA and NaNO2, Braun et al.
(1977) reported no mutagenic activity when 2 g/kg DMA was administered
orally to mice with 0.2 g/kg NaNO2. However, no data were presented.
4.3.2 Chromosomal Aberration Assay (Category 2)
San Sebastian et al. (1979) tested DMA as the nonclastogenic (negative
control) analogue for DMNA in a blind in vitro CHO S9-activated and
nonactivated chromosomal aberration assay. DMA was reported negative;
however, no data were presented. Thus, this study provides only supportive
evidence of a nonclastogenic response.
4.3.3 Other Mutagenic Mechanisms (Category 3)
4.3.3.1 Sister Chromatic! Exchange (SCE)
DMA was also reported negative at unspecified doses in an S9-activated
and nonactivated CHO sister chromatid exchange assay by San Sebastian et
al. (1979).
4.3.3.2 DNA Repair in Rat Hepatocytes
Groups of three partially hepatectomized male rats were gavaged with
DMA (doses not reported) or 160 to 640 mg/kg DMA plus 80 mg/kg NaNO2
(Hosokawa and Miyamoto, 1976). Hepatocytes were harvested 2 hours
posttreatment and assayed for increased DNA-repair activity using the alkaline
elution method. The authors reported that DMA alone (no data presented) was
negative in this assay. No toxic, cytotoxic, or genotoxic effects were observed
in primary rat hepatocytes harvested from animals exposed to 160, 320, or
640 mg/kg DMA in the presence of 80 mg/kg NaNO2. Histopathological
examination of the livers from the test animals revealed no cellular damage.
48
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Although DMA and nitrosated DMA were negative, the lack of evidence
suggesting compound interaction with the target organ precludes full
acceptance of this study.
4.3.4 Conclusions
Based on the limited number of available genetic toxicology studies, it
was concluded that the data were insufficient to establish a genotoxic profile
for DMA. Numerous data gaps exist and none of the reviewed studies were
considered valid by current standards of acceptability. Collectively, the weight
of evidence from in vivo gene mutation host-mediated assays suggests that
DMA is probably not mutagenic and a mutagenic response can only be
achieved if DMA, at high doses, is reacted with high doses of NaNO2. While it
is known that secondary amines can be converted intragastrically to
nitrosamines, the excessive doses pf both DMA and NaNO2 required to
demonstrate synthesis of a mutagenic' product cast doubts on the relevance of
this conversion under normal dietary conditions. In addition, although Whong
et al. (1979) presented data showing that the interactive mutagenic product
' was more readily detected in rats than in mice, this result conflicts with the
findings of others and suggests that a mutagenic product other than
nitrosamines may have been formed.
4.4 Teratogenicity and Reproductive Effects
No pertinent data on the teratogenicity or reproductive effects of DMA
were available in the literature.
4.5 Summary of Animal Toxicology
DMA, a gas at room temperature and atmospheric pressure, is highly
water soluble. Aqueous solutions of DMA are strongly basic. These two
physical properties of DMA contribute greatly to the compound's toxicity.
Acute inhalation exposures in rats and mice produce immediate signs of
ocular and sensory irritation (Buckley et al., 1984; Steinhagen et al., 1982).
The RD50 values for rats and mice, 573 and 511 ppm, respectively, are much
lower than the LC50 values (4,540 and 7,650 ppm for rats and mice,
respectively) with mortality at 3,983 ppm in rats. In rats exposed to DMA
concentrations of 600 ppm for 6 hours, pathological lesions were limited
mainly to the eyes and nasal mucosa. As the DMA concentration approached
lethal levels, greater toxicity to the lung and liver were observed. For all doses
tested, however, the tissues of the nasal cavity were most severely affected,
and a distinct anterior-posterior severity gradient was observed; the lung was
minimally affected (Buckley et al., 1984; Steinhagen et al., 1982).
The irritant properties of aqueous DMA also appear to be mainly
responsible for its acute oral toxicity. The oral LD50 values for aqueous DMA in
mice, rats, guinea pigs, and rabbits are 5 to 11 times lower than for neutralized
DMA (Dzhanashvili, 1967). Liquid DMA is also highly irritating to the eyes of
rabbits (Mellerio and Weale, 1966).
The results from studies on subchronic and chronic inhalation toxicity of
DMA in rodents show the same basic trends as those found with acute
exposures. In mice and rats exposed to DMA at 0, 10, 50, or 175 ppm for 6
hours/day, 5 days/week for up to 24 months, the most sensitive tissue was the
49
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nasal mucosa (Chemical Industries Institute of Toxicology, 1987; Buckley et
al., 1985). No other tissue, including liver and lung, was affected. Body
weights, however, were approximately 10 percent lower in the 175-ppm group
than in controls. Slight pathological lesions were observed in the olfactory
sensory cells of rats and mice in the 10-ppm groups. Effects of long-term
exposure to DMA that were different from those reported by Chemical
Industries Institute of Toxicology (1987) and Buckley et al. (1985) have been
reported by Artem'eva and Dobrinskii (1973), Coon et al. (1970), and
Hollingsworth et al. (1959). However, these latter studies would not be
considered adequate for determining the subchronic or chronic toxicity of
DMA by today's standards. Therefore, reports of hepatic, testicular,
pulmonary, immunological, and central nervous system effects from long-term,
low-level exposure to DMA are questionable.
The 2-year CUT study was used to calculate a preliminary value for a
chronic inhalation reference concentration (RfC) for humans. At 25°C and 760
mmHg, the 10 ppm NOAEL gives a duration-adjusted (6 hrs/day and 5
days/wk), for human equivalent concentrations = 3.3 mg/m3. After dosimetric
adjustment for the respective surface areas of the respiratory tract involved, a
Respiratory Gas Dosimetric Ratio of 0.18 was applied. Uncertainty factors
used to calculate RfC for humans are 10 for extrapolation of animal data to
man; 10 for individual sensitivity, and 3 for quality of data base. The inhalation
RfC for DMA for humans is 2.0 pg DMA/m3 (1.1 ppb) of air, as verified by the
11/89 RfC workgroup.
No evidence for carcinogenicity or mutagenicity resulting from exposure
to .DMA has been found. A 2-year chronic inhalation study revealed that DMA
is not carcinogenic to rats or mice (Chemical Industries Institute of Toxicology,
1987). The available genetic toxicology studies are mostly inadequate and
thus the data are inconclusive for determining mutagenic potential. Several
studies indicate that combined administration of DMA and nitrite produces
signs of toxicity similar to those observed after DMNA administration. These
include liver damage, mutagenicity, and carcinogenicity. However, the doses
of nitrite and DMA required to produce these effects are extremely high,
making the theory of DMA conversion to the carcinogenic DMNA under normal
dietary or inhalation exposure conditions questionable.
No information was found in the available literature on teratogenic and
reproductive effects of DMA.
50
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5. Human Health Effects
A-search of the primary literature failed to produce any reports on the
human health effects associated with exposure to DMA. Similarly, no reports
on the human health effects of DEA were found. However, several secondary
sources have reported a variety of acute toxic effects associated with DMA
exposure (Mackinson et al., 1981; Sittig, 1981; Braker and Mossman, 1980).
All reported effects of DMA in humans are related to the compound's
irritancy. After short-term exposure to DMA vapors produces irritation of the
eyes with conjunctivitis and corneal edema. Inhalation of concentrations higher
than 100 ppm can cause irritation of the nose and throat and lung irritation with
dyspnea and cough. The vapors may also produce primary skin irritation and
dermatitis. Direct contact with the liquid can produce severe and sometimes
permanent eye damage or skin burns. The effects of long-term, low-level
exposure to DMA are not known.
51
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