Toxicity Profiles
Formal Toxicity Summary for 2,4-DINITROTOLUENE
NOTE: Although the toxicity values presented in these toxicity profiles were correct at the time they were produced, these values are subject to change. Users should always refer to the Toxicity Value Database for the current toxicity values.
- EXECUTIVE SUMMARY
- 1. INTRODUCTION
- 2. METABOLISM AND DISPOSITION
- 1. INTRODUCTION
- 2.1 ABSORPTION 2.2 DISTRIBUTION 2.3 METABOLISM 2.4 EXCRETION
- 3. NONCARCINOGENIC HEALTH EFFECTS
- 3.1 ORAL EXPOSURES 3.2 INHALATION EXPOSURES 3.3 OTHER ROUTES OF EXPOSURE 3.4 TARGET ORGANS/CRITICAL EFFECTS
- 4. CARCINOGENICITY
- 4.1 ORAL EXPOSURES 4.2 INHALATION EXPOSURES 4.3 OTHER ROUTES OF EXPOSURE 4.4 EPA WEIGHT-OF-EVIDENCE 4.5 CARCINOGENICITY SLOPE FACTORS
- 5. REFERENCES
Prepared by: Rosmarie A. Faust, Ph.D., Chemical Hazard Evaluation Group in the Biomedical and Environmental Information Analysis Section, Health Sciences Research Division, Oak Ridge National Laboratory*.
Prepared for: Oak Ridge Reservation Environmental Restoration Program.
*Managed by Martin Marietta Energy Systems, Inc., for the U.S. Department of Energy under Contract No. DE-AC05-84OR21400.
This report is an update of the Toxicity Summary for 2,4-Dinitrotoluene (CAS Registry No. 121-14-2). The original summary for this chemical was submitted in December 1991. The update was performed by incorporating any new human health toxicity data published since the original submittal of the report. Pertinent pharmacokinetic, toxicologic, carcinogenic, and epidemiologic data were obtained through on-line searches of the TOXLINE database from 1992 through April 1995. In addition, any changes to EPA-approved toxicity values (reference doses, reference concentrations, or cancer slope factors) from the Integrated Risk Information System (IRIS) (current as of May 1995) and/or the Health Effects Assessment Summary Tables, Annual FY-94; July Supplement No. 1; and November Supplement No. 2) for this chemical were incorporated in this update.
EXECUTIVE SUMMARY
2,4-Dinitrotoluene (2,4-DNT; 1-methyl-2,4-dinitrobenzene; CAS Reg. No. 121-14-2) is a yellow crystalline solid and one of six possible chemical forms of dinitrotoluene (DNT). Technical grade DNT (t-DNT) is typically composed of 78% 2,4-DNT, 19% 2,6-DNT, and small amounts of 3,4-DNT, 2,3-DNT, and 2,5-DNT (Dunlap 1978). 2,4-DNT is primarily used as a chemical intermediate in the manufacture of polyurethanes but also serves as a component of military and commercial explosives, as an intermediate in dye processes (Etnier 1987, Hawley 1981), and as a propellant additive (Sears and Touchette 1982).
The DNTs are absorbed through the gastrointestinal tract, respiratory tract, and skin in most species (EPA 1986). The initial acute toxic effects of 2,4-DNT in humans include methemoglobinemia, cyanosis, and headache. Symptoms indicative of neurotoxicity are impaired reflexes, tremors, nystagmus, dizziness, and sleepiness (EPA 1980). Subchronic and chronic oral toxicity studies with experimental animals indicate that the blood, liver, nervous system, and reproductive system are targets affected by 2,4-DNT. These effects were generally observed at doses of 5 mg/kg/day in rats and at 10 mg/kg/day in dogs. The most common hematological findings were methemoglobinemia, anemia, reticulocytosis, and an increase in Heinz bodies. Hepatotoxic effects included liver discoloration, and proliferative alterations of hepatocytes and bile duct epithelium. Neuromuscular effects, ranging from tremors and ataxia to convulsions, were more severe in dogs than in rodents. Reproductive effects consisted of decreased spermatogenesis, testicular atrophy, and ovarian dysfunction (Lee et al. 1985; Ellis et al. 1985, 1979; Lee et al. 1978).
The major route of exposure to DNT in the occupational setting is by inhalation. Effects reported in workers exposed to t-DNT and/or 2,4-DNT included ischemic heart disease, hematological effects characterized by cyanosis, anemia, and leukocytosis, and neurological effects such as dizziness, insomnia, nausea, and tingling pains in extremities (Levine et al. 1986a, McGee et al. 1942). The evidence for potential reproductive effects (reduction of sperm counts) in male workers exposed to a mixture of DNT isomers and diaminotoluene is equivocal (Hamill et al. 1982, Ahrenholz 1980).
An oral Reference Dose (RfD) of 2.00E-03 mg/kg/day has been calculated for chronic (EPA 1995a) and subchronic exposure to 2,4-DNT (EPA 1994), based on a NOAEL of 0.2 mg/kg/day derived from a chronic oral study with dogs conducted by Ellis et al. (1985). Data are inadequate for the calculation of an inhalation Reference Concentration (RfC) (EPA 1995a).
An association between DNT exposure and increased risk of hepatobiliary cancer was found in a retrospective mortality study involving 4989 workers exposed to DNT (isomer composition not specified) and 7436 unexposed controls at an U.S. Army munitions facility (Stayner et al., 1993). The carcinogenic activity of 2,4-DNT and t-DNT has been studied in several chronic bioassays and in less than lifetime studies (Leonard et al. 1987, CIIT 1982, Ellis et al. 1979, NCI 1978). 2,4-DNT (containing small amounts of 2,6-DNT) induced an increased incidence of hepatocellular carcinomas and subcutaneous tumors in rats and renal tumors in male mice (Ellis et al. 1979). In two rat studies t-DNT induced hepatocellular carcinomas (Leonard et al. 1987, CIIT 1982). However, conclusions drawn from the isomer-specific carcinogenicity study by Leonard et al. (1987) and tumor-initiation/promotion assays by Popp and Leonard (1982) suggest that 2,6- rather than 2,4-DNT is the primary hepatocarcinogen in t-DNT. Although EPA has not evaluated pure 2,4-DNT for evidence of human carcinogenic potential, the dinitrotoluene mixture (containing 2,4-DNT and 2,6-DNT) was classified as a B2 chemical carcinogen, probable human carcinogen (EPA 1995b). A slope factor of 6.8E-1 (mg/kg/day)-1 was calculated for oral exposure to the dinitrotoluene mixture. The drinking water unit risk is 1.9E-5 (µg/L)-1 (EPA 1995b).
1. INTRODUCTION
2,4-Dinitrotoluene (2,4-DNT; 1-methyl-2,4-dinitrobenzene; CAS Reg. No. 121-14-2) is a pale yellow crystalline solid and one of six possible chemical forms of dinitrotoluene (DNT). Having a molecular weight of 182.14, a melting point of 71C, and a boiling point of 300C, 2,4-DNT is soluble in alcohol, ether, acetone, and benzene, but only slightly soluble in water (Weast et al. 1988, Dean 1979). 2,4-DNT does not occur naturally. It is produced by dinitration of toluene with nitric acid in the presence of sulfuric acid, a reaction that produces a mixture of several DNT isomers (Etnier 1987). Technical grade DNT (t-DNT) is typically composed of 78% 2,4-DNT, 19% 2,6-DNT, and small amounts of 3,4-DNT, 2,3-DNT, and 2,5-DNT (Dunlap 1978).
2,4-DNT is primarily used as a chemical intermediate in the manufacture of polyurethanes. It is also used as a component of military and commercial explosives, as an intermediate in dye processes (Etnier 1987, Hawley 1981), and as a propellant additive (Sears and Touchette 1982). DNT isomers are formed as by-products during the manufacture of trinitrotoluene (TNT) (Etnier 1987) and are commonly found in wastewater released from TNT production facilities (Spanggord and Suta 1982). DNTs have also been identified in soil, surface water, and groundwater of hazardous waste sites that contain buried munition wastes (Etnier 1987).
2. METABOLISM AND DISPOSITION
2.1. ABSORPTION
The DNTs are absorbed through the gastrointestinal tract, respiratory tract, and skin in most species (EPA 1986). Lee et al. (1975) reported that female CD rats absorbed 80-90% of orally administered 2,4-DNT within 24 hours. Absorption was 90-100% in male and female CD rats following subchronic or chronic feeding (up to 20 months) of 2,4-DNT (Ellis et al. 1979). In contrast, mice absorbed only 17% of an orally administered dose of 2,4-DNT (Lee et al. 1978). 2,4-DNT metabolites that are excreted into the bile are subsequently reabsorbed from the intestine (Medinsky and Dent 1983).
The presence of 2,4-DNT metabolites in the urine of workers in DNT manufacturing plants, where inhalation was considered the major route of exposure (Levine et al. 1985, Woolen et al. 1985), indicates that inhaled 2,4-DNT can be absorbed. However, an excess of urinary 2,4-DNT metabolites compared with the amount of 2,4-DNT measured in inspired air suggested that dermal (Woolen et al. 1985) and possibly oral absorption contributed to the body burden of 2,4-DNT (Levine et al. 1985).
2.2. DISTRIBUTION
No data were available concerning the tissue distribution of 2,4-DNT in humans orally exposed to the compound. Trace amounts of 2,4-DNT were found in blood samples of workers employed at an explosives factory (Woolen et al. 1985).
Small amounts of radioactivity were found in the liver, blood, kidney, brain, and skeletal muscle of animals following oral exposure to radiolabeled 2,4-DNT (Etnier 1987). Peak levels of radioactivity were observed in the blood of male rats 6 hours after a single oral dose of 3H-2,4-dinitrotoluene (Mori et al. 1978). Concentrations of 2,4-DNT in rat and mouse liver and kidney were 2 to 10 times higher than in plasma or red blood cells, and about twice as high in the lung, spleen, fat, and brain (Schut et al. 1982, Rickert and Long 1980). 2,4-DNT has been shown to cross the placenta in rats (Rickert et al. 1980). Animal studies addressing the tissue distribution of 2,4-DNT following inhalation exposure were unavailable.
2.3. METABOLISM
2,4-DNT is metabolized by the reduction of the nitro group(s) and/or oxidation of the methyl group. One or both of the nitro groups may be reduced to the corresponding aminonitrotoluenes or diaminotoluenes, while the methyl group is oxidized to a benzyl alcohol or benzoic acid. These reductive and oxidative reaction products may undergo subsequent conjugation to form glucuronides, sulfates, and other compounds (ATSDR 1989, Lee et al. 1978). Metabolism of 2,4-DNT is extensive and occurs in the liver and also by the intestinal microflora. Both oxidized and reduced metabolites are excreted in the urine after oral administration of 2,4-DNT (ATSDR 1989).
Metabolites of DNT found in the urine of male workers at a DNT manufacturing plant (expressed as percent of total urinary metabolites) were 2,4-dinitrobenzoic acid (52.5%); 2-amino-4-nitrobenzoic acid (37%); and 2,4-dinitrobenzyl alcohol glucuronide (9.5%). Females excreted 28.8% as 2,4-dinitrobenzoic acid and 33.3% as 2,4-dinitrobenzyl alcohol glucuronide (Levine et al. 1985, Turner et al. 1985). Oral administration of 2,4-DNT to rats resulted in four major urinary metabolites: 2-amino-4-nitrobenzoic acid; 2,4-dinitrobenzoic acid; 4-acetyl-amino-2-nitrobenzoic acid; and 2,4-dinitrobenzyl alcohol glucuronide (Rickert and Long 1981). Similar metabolites were identified in the urine of mice following intraperitoneal or oral dosing with 2,4-DNT. In addition, small amounts of 2,4-diaminotoluene and the parent compound, 2,4-DNT, were identified (Schut et al. 1985).
2.4. EXCRETION
No information was available regarding the excretion of 2,4-DNT in humans orally exposed to 2,4-DNT. Rats excreted 55 to 90% of orally administered 2,4-DNT in the urine and 15 to 30% in the feces within 72 hours after dosing, with females excreting a greater percentage of the dose in the urine than males (Rickert and Long 1981). In contrast, mice eliminated most of orally administered 2,4-DNT in the feces and only about 10% in the urine (Lee et al. 1978).
Analysis of DNT metabolites in urine collected from workers at a DNT manufacturing plant indicated that the highest excretion rate of 2,4-dinitrobenzoic acid occurred at the end of the work shift. The calculated half-life for urinary excretion of 2,4-dinitrobenzoic acid was 2 to 5 hours. Three days after the last exposure, detectable levels of 2,4-dinitrobenzoic acid were still present in urine, suggesting a biphasic elimination of this metabolite (Woolen et al. 1985).
3. NONCARCINOGENIC HEALTH EFFECTS
3.1. ORAL EXPOSURES
3.1.1. Acute Toxicity
3.1.1.1. Human
EPA (1980) reports that the initial acute toxic effect resulting from ingestion of 2,4-DNT in humans most probably is methemoglobinemia followed by cyanosis. A number of other symptoms including headache, vertigo, fatigue, dizziness, weakness, nausea, vomiting, dyspnea, drowsiness, arthralgia, insomnia, tremors, paralysis, unconsciousness, chest pain, shortness of breath, palpitation, anorexia, and weight loss have been reported after varying doses of 2,4-DNT. Alcohol ingestion has a synergistic effect on 2,4-dinitrotoluene (EPA 1987).
3.1.1.2. Animal
Oral LD50 values for 2,4-DNT range from 268 to 650 mg/kg for rats and from 1250 to 1954 mg/kg for mice (Etnier 1987). Acute toxic effects in animals include central nervous system depression resulting in ataxia, respiratory depression, and death after a few hours (Ellis et al. 1980).
3.1.2. Subchronic Toxicity
3.1.2.1. Human
Information on the subchronic oral toxicity of 2,4-DNT in humans was unavailable.
3.1.2.2. Animal
Subchronic exposure of rats to dietary levels of 0.07, 0.2, or 0.7% 2,4-DNT (35, 100, or 350 mg/kg/day) for 13 weeks resulted in decreased weight gain at all dose levels. Increased relative liver, kidney, and brain weights, decreased spermatogenesis, reticulocytosis, and splenic hemosiderosis occurred at the two higher doses. Also observed was neuromuscular dysfunction associated with demyelination of the cerebellum and brain stem at 350 mg/kg/day (Lee et al. 1985). Kozuka et al. (1979) reported significant weight loss, high mortality, hepatic hypertrophy, testicular atrophy, and pronounced hemoglobinemia in rats administered a dietary concentration of 0.5% 2,4-DNT (250 mg/kg/day) for 6 months. The major adverse effect in dogs given daily doses of 25 mg/kg of 2,4-DNT in gelatin capsules for 13 weeks was neurotoxicity, characterized by incoordination, tremors, convulsions, ataxia, paralysis, and degeneration of the cerebellum (Ellis et al. 1985, 1979).
3.1.3. Chronic Toxicity
3.1.3.1. Human
Information on the chronic oral toxicity of 2,4-DNT in humans was unavailable.
3.1.3.2. Animal
2,4-DNT administered to CD rats at dietary concentrations of 0.0015%, 0.01%, or 0.07% (0.75, 5, or 35 mg/kg/day) for 2 years was not toxic at the lowest dose, but caused increased mortality, a progressive development of hyperplastic foci in the liver, atrophy of seminiferous tubules, decreased spermatogenesis, toxic anemia with reticulocytosis, and mild neuromuscular effects at the two higher dose levels (Lee et al. 1985). In a study with t-DNT (76% 2,4 DNT, 19% 2,6-DNT), F344 rats were fed doses of 3.5, 14, or 35 mg/kg/day for 104 weeks (CIIT 1982). General signs of toxicity included high mortality in the high-dose group and a dose-related decrease in body weight gain. In the mid- and high-dose groups, degenerative and proliferative alterations of hepatocytes and bile duct epithelium were observed in the first 26 weeks of treatment. These changes generally involved necrotic and vacuolated hepatocytes and necrosis and hyperplasia of the biliary epithelium. The high- and mid-dose males exhibited an increased incidence of testicular degeneration with decreased spermatogenesis. The high-dose group also had a low-grade regenerative anemia. In contrast, in a study performed by NCI (1978), decreased body weight gain was the only significant effect seen in F344 rats and B6C3F1 mice exposed to diets containing 200 ppm and 400 ppm 2,4-DNT, respectively, for 78 weeks.
Ellis et al. (1979) studied the chronic toxicity of 2,4-DNT in CD-1 mice by exposing them to 13.5, 95, or 900 mg/kg/day in the diet for up to 2 years. All of the high-dose males died by month 18 of the study and 95% of high-dose females died by month 21. After 1 year, anemia with decreased erythrocyte and hemoglobin levels, increased Heinz bodies and reticulocytes, and occasional methemoglobinemia were seen. Similar effects were observed in some moribund animals receiving 95 mg/kg/day. High-dose animals exhibited a greatly decreased weight gain, increased liver weight, hepatocellular dysplasia, nephropathy, decreased testis weight, testicular atrophy, and non-functioning ovarian follicles. Pigmentation of the spleen and liver was reported for all dose levels. Liver dysplasia and decreased body weights were observed in male but not female mice exposed to the lowest dose.
In a chronic study with dogs, administration of 10 mg/kg/day of 2,4-DNT for up to 2 years (Ellis et al. 1985, 1979) caused muscular incoordination, paralysis, and degeneration of the cerebellum. Other effects included cyanosis, methemoglobinemia with Heinz bodies, and reticulocytosis; pigmentation of liver, kidney, gall bladder, and spleen; and mild biliary tract hyperplasia. Administration of 1.5 mg/kg/day for 2 years caused some CNS effects, but no apparent adverse effects were observed at 0.2 mg/kg/day.
3.1.4. Developmental and Reproductive Toxicity
3.1.4.1. Human
Information on the developmental and reproductive toxicity of 2,4-DNT in humans following oral exposure was unavailable.
3.1.4.2. Animal
Male rats fed 35 mg 2,4-DNT/kg/day for 2 years exhibited severe atrophy of the seminiferous tubules and almost complete lack of spermatogenesis (Ellis et al. 1979). Effects in male mice administered dietary doses of 95 or 900 mg 2,4-DNT/kg/day for 1 year included decreased testis weight, aspermatogenesis, and testicular atrophy. Also observed were nonfunctioning ovarian follicles (lacking corpora lutea) in females administered the higher dose (Ellis et al., 1979). Testicular degeneration with reduced spermatogenesis was reported in dogs fed daily doses of 25 mg 2,4-DNT/kg/day for 13 weeks (Ellis et al. 1985, 1979).
No malformations were seen in rats administered t-DNT by gavage at doses ranging from 14 to 150 mg/kg/day on gestation days 7-20. However, there was evidence of embryo/fetal toxicity (increased resorptions and fetal deaths and hematological effects consistent with DNT toxicity) at 150 mg/kg/day, a dose that also produced high maternal mortality (Price et al. 1985). In an oral three-generation reproductive study of 2,4-DNT with CD rats, effects at the highest dose (34 mg/kg/day for males; 45 mg/kg/day for females) included decreased body weight, aspermatogenesis, and decreased neonatal viability resulting in the absence of an F2 generation and only few matings in the F1 generation. There was increased hemorrhaging and/or retention of placentas as well as increased mortality during parturition (Ellis et al. 1979).
3.1.5. Reference Dose
3.1.5.1. Subchronic
ORAL RfD: 2.00E-03 mg/kg/day (EPA 1994)
NOAEL: 0.2 mg/kg/day
UNCERTAINTY FACTOR: 100
PRINCIPAL STUDY: Ellis et al. 1985
COMMENTS: The same study was used for the derivation of subchronic and chronic RfD. The chronic RfD derived from this study was adopted as the subchronic RfD.
3.1.5.2. Chronic
ORAL RfD: 2.00E-03 mg/kg/day (EPA 1995a)
NOAEL: 0.2 mg/kg/day
UNCERTAINTY FACTOR: 100
PRINCIPAL STUDY: Ellis et al. 1985
CONFIDENCE
STUDY: High
DATA BASE: High
RfD: High
VERIFICATION DATE: 8/14/91
COMMENTS: The chronic RfD was based on a no-observed-adverse-effect level (NOAEL) of 0.2 mg/kg/day in dogs treated orally with 2,4-DNT for up to 2 years. Neurotoxicity, presence of Heinz bodies in erythrocytes, and biliary tract hyperplasia were observed at 1.5 mg/kg/day. The uncertainty factor includes two factors of 10 for intra- and interspecies variability.
3.2. INHALATION EXPOSURES
3.2.1. Acute Toxicity
3.2.1.1. Human
According to EPA (1980), the acute toxic effects of inhaled 2,4-DNT are the same as those described for oral exposure (see Sect. 3.1.1.1). Incidents of poisoning resulting from inhalation of 2,4-DNT are primarily described in the earlier literature. For example, one case report describes marked cyanosis, headache, palpitations, tightness in the chest, insomnia, lack of appetite, impaired reflexes, nystagmus, and tremors following exposure to 2,4-DNT (Floret, 1929). Dyspnea, dizziness, sleepiness, and pain in the joints were attributed to inhalation and dermal exposure to 2,4-DNT vapor during purification of 2,4-DNT cakes (Perkins 1919). Lewin (1921) reported that exposure to 2,4-DNT may result in temporary visual disturbances.
3.2.1.2. Animal
Information on the acute inhalation toxicity of 2,4-DNT in animals was unavailable.
3.2.2. Subchronic Toxicity
3.2.2.1. Human
Levine et al. (1986a) reported a significant increase in mortality due to ischemic heart disease and other circulatory diseases in workers involved in the manufacture and processing of t-DNT and/or 2,4-DNT at two separate plants during the 1940s and 1950s. The median time for employment
with potential exposure to DNT at the two plants was 0.4 and 1.2 years, respectively. According to Levine (1987), exposure to DNT occurred by inhalation as well as by dermal contact and frequently exceeded 1 mg DNT/kg/day.
McGee et al. (1942) conducted an epidemiological study of 154 workers at a plant where 2,4-DNT was used in the manufacture of explosives. The most frequently mentioned symptoms included unpleasant taste in the mouth, muscular weakness, headache, loss of appetite, dizziness, nausea, insomnia, and tingling pain in extremities. Primary clinical findings were pallor, cyanosis, anemia, and leukocytosis. There were no instances of permanent physical impairment.
There was no difference in hepatic or renal blood chemistry profiles of workers occupationally exposed to t-DNT and diaminotoluene compared to a non-exposed control group (Ahrenholz et al. 1980).
3.2.2.2. Animal
Information on the subchronic inhalation toxicity of 2,4-DNT in animals was unavailable.
3.2.3. Chronic Toxicity
3.2.3.1. Human
Information on the chronic inhalation toxicity of 2,4-DNT in humans was unavailable.
3.2.3.2. Animal
Information on the chronic inhalation toxicity of 2,4-DNT in animals was unavailable.
3.2.4. Developmental and Reproductive Toxicity
3.2.4.1. Human
Available data regarding human reproductive toxicity of 2,4-DNT are equivocal. Ahrenholz (1980) reported that male workers exposed to mixed DNT isomers and diaminotoluene in one facility exhibited a significant reduction in sperm counts and normal sperm morphology. However, the sperm count of a nonexposed group was abnormally high. There was also a slight, but not statistically significant, increase in the number of spontaneous abortions in the wives of exposed workers. Measured exposure levels at the plant were 0-0.10 mg/m3. In a study designed to corroborate these findings, Hamill et al. (1982) found no detectable reproductive effects among male workers exposed to DNT in another facility.
3.2.4.2. Animal
Information on the developmental and reproductive toxicity of 2,4-DNT in animals following inhalation exposure was unavailable.
3.2.5. Reference Concentration
The health effects data for 2,4-DNT were reviewed by EPA and determined to be inadequate for derivation of an inhalation RfC (EPA 1995a).
3.3. OTHER ROUTES OF EXPOSURE
3.3.1. Acute Toxicity
3.3.1.1. Human
According to EPA (1980), the acute toxic effects of dermally absorbed 2,4-DNT are the same as those resulting from ingestion (see Sect. 3.1.1.1).
3.3.1.2. Animal
Zieger (1913) reported that two dermal applications of 5 g each of 2,4-DNT were fatal to cats within 8 hours. 2,4-DNT was mildly irritating to the skin, but was not irritating to the eyes of rabbits (Lee et al. 1975).
3.3.2. Subchronic Toxicity
Information on the subchronic toxicity of 2,4-DNT in humans or animals by other routes of exposure was unavailable.
3.3.3. Chronic Toxicity
Information on the chronic toxicity of 2,4-DNT in humans or animals by other routes of exposure was unavailable.
3.3.4. Developmental and Reproductive Toxicity
Information on the developmental and reproductive toxicity of 2,4-DNT in humans or animals by other routes of exposure was unavailable.
3.4. TARGET ORGANS/CRITICAL EFFECTS
3.4.1. Oral Exposures
3.4.1.1. Primary Target Organ(s)
1. Blood: Hematologic effects observed in laboratory animals orally exposed to 2,4-DNT included methemoglobinemia with an increase of Heinz bodies, anemia, and reticulocytosis. In humans, the initial acute toxic effect of 2,4-DNT is methemoglobinemia followed by cyanosis.
2. Liver: Oral exposure of rats to 2,4-DNT produced increased liver weight and proliferative alterations of hepatocytes and bile duct epithelium. Pigmentation of liver and gall bladder and mild biliary tract hyperplasia was seen in dogs.
3. Testes and ovaries: Aspermatogenesis, testicular atrophy, and ovarian dysfunction were effects reported in laboratory animals orally exposed to 2,4-DNT.
4. Nervous system: Oral exposure of rats to 2,4-DNT resulted in increased relative brain weights and neuromuscular dysfunction associated with demyelination of cerebellum and brain stem. Neurotoxic effects were more severe in dogs and included muscular incoordination, tremors, convulsions, ataxia, paralysis, and degenerative changes in the cerebellum.
3.4.1.2. Other Target Organ(s)
1. Kidney: Oral exposure to 2,4-DNT produced nephropathy in mice and increased kidney weights in rats.
2. Spleen: Splenic hemosiderosis was seen in rats orally exposed to 2,4-DNT.
3.4.2. Inhalation Exposures
Although inhalation is considered the primary route of exposure to 2,4-DNT in the occupational setting, dermal exposure and/or inadvertent ingestion may also occur. Thus, it is not always possible to attribute the observed effects to a specific route of exposure.
3.4.2.1. Primary Target Organ(s)
1. Hematopoietic system: Pallor, cyanosis, anemia, and leukocytosis were reported in munitions workers exposed to t-DNT.
2. Cardiovascular system: A significant increase in heart disease mortality was reported in workers exposed to 2,4-DNT and/or t-DNT.
3. Nervous system: Muscular weakness, headache, dizziness, nausea, insomnia, and tingling pains in the extremities were reported in munitions workers exposed to t-DNT.
4. Reproduction: One occupational study suggested that exposure to 2,4-DNT may cause a reduction in sperm counts and normal sperm morphology.
3.4.2.2. Other Target Organ(s)
No other target organs following inhalation exposure to 2,4-DNT were identified.
3.4.3 Other Routes of Exposure
Target organs by other routes of exposure to 2,4-DNT were not identified.
4. CARCINOGENICITY
4.1. ORAL EXPOSURES
4.1.1. Human
Information on the carcinogenicity of 2,4-DNT in humans following oral exposure was unavailable.
4.1.2. Animal
Ellis et al. (1979) conducted a 2-year carcinogenicity study with male and female rats by exposing them to dietary concentrations of 0.0015, 0.01, or 0.07% 2,4-DNT (98% 2,4-DNT, 2% 2,6-DNT), corresponding to an average intake of 0.75, 5, or 35 mg/kg/day. The highest dose induced an increased incidence of hepatocellular carcinomas that was statistically significant only in females. Additionally, there was an increased incidence of subcutaneous tumors (mostly fibromas in males and mammary fibroadenomas in females). In a study with CD-1 mice similarly exposed to dietary concentrations of 0.01, 0.07, or 0.5% 2,4-DNT (13, 95, or 650 mg/kg/day) for 2 years, there was a significantly increased incidence of benign and malignant kidney tumors in mid-dose males (most high-dose males died before 12 months). Female mice exhibited no treatment-related increase of tumors in any tissue.
CIIT (1982) exposed F344 rats to dietary concentrations of 3.5, 14, or 35 mg/kg/day t-DNT (76% 2,4 DNT, 19% 2,6-DNT) for 2 years. After 1 year of treatment, the incidence of hepatocellular carcinomas was 100% in high-dose males and 55% in high-dose females. After 2 years, a high incidence of hepatocellular carcinomas was also reported in the mid-dose males and females. In addition, there was an increased incidence of hepatic neoplastic nodules in high-dose rats of both sexes after 1 year, and in low- and mid-dose rats of both sexes after 2 years of treatment. Also reported was an increased incidence of mammary gland fibroadenomas in low-dose male rats and in mid-dose rats of both sexes, and of subcutaneous fibroadenomas in high- and mid-dose rats of both sexes. Several cholangiosarcomas were seen in mid- and high-dose males.
In contrast to the two studies discussed above, a study with 2,4-DNT performed by NCI (1978) did not demonstrate hepatocarcinogenicity in male or female F344 rats. Dietary administration of 80 or 200 ppm 2,4-DNT (>95% purity, contaminants not specified) for 78 weeks induced benign tumors, i.e., fibromas of the skin and subcutaneous tissue in males and fibroadenomas of the mammary gland in females. The tumor incidence in male and female B6C3F1 mice similarly exposed to 80 or 400 ppm 2,4-DNT was not increased.
In a study designed to compare the carcinogenic potential of t-DNT, pure 2,4-DNT, and pure 2,6-DNT, 47% of male F344 rats fed 35 mg/kg/day t-DNT for 1 year developed hepatocellular carcinomas, compared with 85 or 100% of rats fed 7 or 14 mg/kg/day pure 2,6-DNT, respectively. No tumors were found in rats fed 27 mg/kg/day pure 2,4-DNT or in control groups (Leonard et al. 1987). Although the duration of this study was limited to 1 year, the data suggest that 2,6- rather than 2,4-DNT is the primary carcinogen in t-DNT.
Popp and Leonard (1982) tested 2,4-, 2,6-, and t-DNT using an in vivo hepatic tumor initiation/promotion protocol with rats. The presence of GGT+ (gamma-glutamyl transpeptidase positive) foci in the liver, indicative of initiating activity, was only observed for 2,6- and t-DNT. In the promotion assay, positive responses were observed for both the 2,4- and 2,6- isomers, with the 2,6-isomer yielding a stronger response.
Swenberg et al. (1983) demonstrated covalent binding of 2,6-DNT to rat hepatocyte RNA following oral dosing with 2,6-DNT, with hepatocytes of female rats showing slightly less binding than male rats. Rickert et al. (1983) reported similar hepatic binding of 2,6-DNT to protein, RNA, and DNA of rats.
4.2. INHALATION EXPOSURES
4.2.1. Human
A retrospective cohort mortality study conducted by Levine et al. (1986b) found no significant increases in cancer morality at two army munition plants that used t-DNT and/or 2,4-DNT. However, the study was limited by a small cohort size and could have detected only an eightfold or greater increase in some cancers (ATSDR 1989).
More recently, Stayner et al. (1993) conducted a retrospective mortality study of 4989 workers exposed to DNT and 7436 non-exposed workers at an U.S. Army munitions facility. The workers had been employed for at least 5 months between 1949 and 1980, but exposure concentrations and isomer composition of the DNT used in the facility were not available. An excess of hepatobiliary cancer was observed among workers exposed to DNT. The standardized rate ratio (SRR) for hepatobiliary cancer was 2.67 based on a comparison with the U.S. population and 3.88 based on a comparison with the internal non-exposed referent group. The study failed to demonstrate an exposure relationship between duration of DNT exposure and hepatobiliary cancer mortality.
4.2.2. Animal
Information on the carcinogenicity of 2,4-DNT in animals following inhalation exposure was unavailable.
4.3. OTHER ROUTES OF EXPOSURE
4.3.1 Human
Information on the carcinogenicity of 2,4-DNT in humans by other routes of exposure was unavailable.
4.3.2 Animal
In a lung tumor bioassay, intraperitoneal injections of 2,4-DNT administered at doses up to 1200 mg/kg, 3 times weekly for 8 weeks, did not elicit a tumorigenic response in male A/Jax mice (Slaga et al. 1985). When applied topically at doses of 1, 5, or 10 mg followed by weekly applications of a phorbol ester for 3 weeks, 2,4-DNT did not initiate the induction of skin tumors in SENCAR mice (Slaga et al. 1985).
4.4. EPA WEIGHT-OF-EVIDENCE
Pure 2,4-DNT (without 2,6-DNT as contaminant) has not been evaluated by EPA for evidence of human carcinogenic potential (EPA 1995a, 1987). However, a carcinogenicity assessment is available for the dinitrotoluene mixture, which includes both 2,4-DNT and 2,6-DNT (EPA 1995b).
Classification: B2--probable human carcinogen (EPA 1995b)
Basis: Increased incidence of multiple and malignant tumor types at multiple sites in both sexes of rats (2 strains) and malignant renal tumors in male mice. This classification is supported by mutagenicity data.
4.5. CARCINOGENICITY SLOPE FACTORS
4.5.1. Oral
SLOPE FACTOR: 6.8E-1 (mg/kg/day)-1
DRINKING WATER UNIT RISK: 1.9E-5 (µg/L)-1
PRINCIPAL STUDY: Ellis et al. (1979)
VERIFICATION DATE: 05/03/89
COMMENT: The DNT used in the principal study contained 98% 2,4- and 2% 2,6-DNT. The slope factor and drinking water unit risk value pertain to the dinitrotoluene mixture, which includes both 2,4- and 2,6-DNT (EPA 1995b).
4.5.2. Inhalation
A slope factor for inhalation exposure has not been assigned.
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