3.2.1.1. Death

No studies were located regarding death in humans and/or animals after inhalation exposure to trichlorobenzenes.

3.2.1.2. Systemic Effects

There is very limited information regarding health effects in humans following exposure to trichlorobenzenes. A review of the literature indicates that an adult male who inhaled trichlorobenzene for several hours during the repair of a pump suffered massive hemoptysis, and that some trichlorobenzene production workers developed chloroacne (IPCS 1991). There is also a case report of aplastic anemia in a woman with prolonged exposure through the soaking of her husband’s work clothes in trichlorobenzene (Girard et al. 1969). None of these reports provided exposure details or specified the isomer involved. Citing an unpublished source, ACGIH (2001) states that minimal eye and throat irritation could occur in some people exposed to 3–5 ppm 1,2,4-trichlorobenzene.

No information was located regarding systemic effects in animals following inhalation exposure to 1,2,3-trichlorobenzene.

The highest NOAEL values and all LOAEL values of 1,2,4-trichlorobenzene and 1,3,5-trichlorobenzene from each reliable study for systemic effects in each species and duration category are recorded in Tables 3-1 and 3-2 and plotted in Figures 3-1 and 3-2.

Respiratory Effects. Continuous exposure of male cynomolgous monkeys to up to 100 ppm 1,2,4-trichlorobenzene vapors for 26 weeks had no significant effect on results of pulmonary function tests (static compliance, diffusion capacity, distribution of ventilation, and lung volumes) conducted in anesthetized monkeys at termination (Coate et al. 1977). Measurements of mechanical properties of the lungs conducted in unanesthetized monkeys also were not significantly affected by exposure to 1,2,4-trichlorobenzene. Histological examination of the lungs showed no treatment-related effects.

Continuous exposure of male rats to up to 100 ppm 1,2,4-trichlorobenzene vapors for up to 26 weeks did not induce significant histological alterations in the lungs (Coate et al. 1977). Similar results were reported in rats exposed to up to 200 ppm 1,2,4-trichlorobenzene vapors 6 hours/day for 15 exposures (Gage 1970) or in male rats exposed 7 hours/day, 5 days/week to up to 100 ppm 1,2,4-trichlorobenzene vapors for a total of 30 exposures (Kociba et al. 1981). Two intermediate-duration studies in rabbits exposed to up to 100 ppm 1,2,4-trichlorobenzene vapors continuously (Coate et al. 1977) or intermittently (Kociba et al. 1981) also reported no significant alterations in the lungs upon microscopic examination. Similar results were reported in dogs following intermittent intermediate-duration exposure to up to 100 ppm 1,2,4-trichlorobenzene (Kociba et al. 1981). The nasal mucosa was also examined in rats and rabbits in the Kociba et al. (1981) study.

The only information regarding 1,3,5-trichlorobenzene is from a study in male and female CD rats in which the animals were exposed 6 hours/day, 5 days/week for 13 weeks (Sasmore et al. 1983). Exposure to up to 130 ppm 1,3,5-trichlorobenzene vapors did not induce significant histological alterations in the lungs, trachea, or nasal passages.

Cardiovascular Effects. Continuous exposure of male monkeys, rats, or rabbits up to 100 ppm 1,2,4-trichlorobenzene vapors for 26 weeks did not induce significant gross or microscopic alterations in the heart (Coate et al. 1977). Exposure of male rats, dogs, and rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors 7 hours/day, 5 days/week for a total of 30 exposures during a 40-day period did not induce significant gross or microscopic alterations in the heart or aorta (Kociba et al. 1981).

Table 3-1

Levels of Significant Exposure to 1,2,4-Trichlorobenzene - Inhalation.

Figure 3-1

Levels of Significant Exposure to 1,2,4-Trichlorobenzene - Inhalation. Intermediate (15-364 days)

Table 3-2

Levels of Significant Exposure to 1,3,5-Trichlorobenzene - Inhalation.

Figure 3-2

Levels of Significant Exposure to 1,3,5-Trichlorobenzene - Inhalation.

Exposure of rats to up to 130 ppm 1,3,5-trichlorobenzene vapors 6 hours/day, 5 days/week for 13 weeks did not induce histological changes in the heart (Sasmore et al. 1983).

Gastrointestinal Effects. Exposure of male rats, dogs, and rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors 7 hours/day, 5 days/week for a total of 30 exposures during a 40-day period did not induce significant gross or microscopic alterations in the gastrointestinal tract (Kociba et al. 1981). Similar results were reported for the gastrointestinal tract of rats exposed to up to 130 ppm 1,3,5-trichlorobenzene vapors 6 hours/day, 5 days/week for 13 weeks (Sasmore et al. 1983).

Hematological Effects. Complete blood counts performed on male monkeys, rats, and rabbits exposed continuously to up to 100 ppm 1,2,4-trichlorobenzene vapors for up to 26 weeks did not show any significant exposure-related differences from controls (Coate et al. 1977). Kociba et al. (1981) reported no significant alterations in total red blood cells, total differential leukocytes, packed cell volume or hemoglobin concentration in blood samples from male rats, rabbits, and dogs following 30 intermittent exposures to up to 100 ppm 1,2,4-trichlorobenzene vapors.

Exposure of rats to up to 130 ppm 1,3,5-trichlorobenzene 6 hours/day, 5 days/week for 13 weeks did not significantly alter blood cell counts and mean corpuscular values, differential counts, or platelet counts (Sasmore et al. 1983). Methemoglobin was slightly higher at 13 weeks than at 4 weeks, but values did not reach significant levels (data not shown).

Musculoskeletal Effects. No significant alterations were reported in skeletal muscle from male rats, rabbits, and dogs following 30 intermittent exposures to up to 100 ppm 1,2,4-trichlorobenzene vapors (Kociba et al. 1981).

In the 13-week inhalation study with 1,3,5-trichlorobenzene (Sasmore et al. 1983), there is no explicit indication that musculoskeletal tissues were examined, although the investigators stated that 34 specific organs and tissues from the control and the high-exposure groups (130 ppm) were examined microscopically. Therefore, it is reasonable to assume that evaluations were conducted and that no alterations were observed.

Hepatic Effects. Continuous exposure of male monkeys or rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors for 26 weeks did not induce significant gross or microscopic alterations in the liver (Coate et al. 1977). However, exposure-related liver changes were described in rats (only qualitative description provided). The changes were characterized as mild and were seen in all exposed groups (25, 50, 100 ppm) usually after 4 and 13 weeks but not at 26 weeks. Hepatocytomegaly occurred in all exposed groups but seemed more noticeable in the mid- and high-exposure groups. There was also a slight increase in the degree of vacuolization of hepatocytes in exposed rats that did not appear dose-related. Hepatocytomegaly was present in all exposed groups at 4 weeks and in the mid- and high-exposure groups at 13 weeks. Exposed rats also showed a slight increase in incidence of granuloma at 4 weeks, which did not appear to be dose-related. No histological alterations were reported in the liver from rats following 15 exposures to 200 ppm 1,2,4-trichlorobenzene each lasting 6 hours (Gage 1970).

Changes in liver weight were reported in rats, dogs, and rabbits exposed to 100 ppm 1,2,4-trichlorobenzene vapors 7 hours/day, 5 days/week for a total of 30 exposures during a 44-day period (Kociba et al. 1981). These changes were not accompanied by histological alterations or alterations in clinical chemistry tests for liver function. In rats, relative liver weight increased 11% relative to controls. Urinalyses conducted after 15 and 30 days of exposure showed statistically significant increased coproporphyrins and uroporphyrins in both the low- (30 ppm) and high-dose rats (100 ppm), which the investigators attributed to the ability of 1,2,4-trichlorobenzene to induce hepatic microsomal enzymes rather than to induce destruction of heme-containing cytochromes or inhibition of heme synthesis. In dogs, both absolute and relative liver weights were increased (27–30%). In rabbits, relative liver weight was decreased 16% relative to controls. Urinary porphyrins levels were not examined in dogs or rabbits.

Exposure of rats to up to 130 ppm 1,3,5-trichlorobenzene vapors 6 hours/day, 5 days/week for 13 weeks did not significantly affect liver weight or the gross or microscopic appearance of the liver (Sasmore et al. 1983). Urinary porphyrin levels were elevated in males at 13 weeks, but large variability rendered the differences with controls nonsignificant.

Renal Effects. Continuous exposure of male monkeys or rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors for 26 weeks did not induce significant gross or microscopic alterations in the kidneys (Coate et al. 1977). Male rats exposed in a similar manner showed kidney changes characterized as mild and present in all exposed groups usually after 4 and 13 weeks but not at 26 weeks of exposure (only a qualitative description was provided). Exposed male rats showed hyaline degeneration in the inner zone of the cortex, which appeared more severe at 4 weeks but was not dose-related; severity appeared increased at 13 weeks in high-dose rats. No histological alterations were reported in the kidneys from rats following 15 exposures to 200 ppm 1,2,4-trichlorobenzene each lasting 6 hours (Gage 1970), or in the kidneys from rats, rabbits, and dogs exposed to up to 100 ppm 1,2,4-trichlorobenzene vapors 7 hours/day, 5 days/week for 30 exposures during a 44-day period (Kociba et al. 1981).

Exposure of rats to up to 130 ppm 1,3,5-trichlorobenzene vapors 6 hours/day, 5 days/week for 13 weeks did not result in significant gross or microscopic alterations in the kidneys (Sasmore et al. 1983).

Endocrine Effects. Fifteen 6-hour exposures to up to 200 ppm 1,2,4-trichlorobenzene vapors did not induce significant gross or histological alterations in the adrenal glands from rats (Gage 1970). Exposure of rats, dogs, and rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors 7 hours/day, 5 days/week for a total of 30 exposures did not induce significant gross or microscopic alterations in the pituitary gland, adrenal gland, thyroid, or parathyroid (Kociba et al. 1981).

In the 13-week study of rats exposed intermittently to up to 130 ppm 1,3,5-trichlorobenzene vapors, the investigators stated that 34 organs were examined in the control and high-dose groups but did not specify the organs (Sasmore et al. 1983). However, there is mention that hemosiderosis was noted in the thyroid gland, which, by the distribution and nature in the different groups, appeared unrelated to the treatment. It seems reasonable to assume that other endocrine glands were also examined and that no alterations were observed.

Dermal Effects. Continuous exposure of male monkeys, rats, and rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors for 26 weeks did not induce significant gross or microscopic alterations in a section of abdominal skin that was examined (Coate et al. 1977).

No relevant data were located regarding 1,3,5-trichlorobenzene.

Ocular Effects. Gage (1970) reported that lacrimation occurred in rats initially during the 6-hour exposures to 70 ppm 1,2,4-trichlorobenzene but not during exposures to 20 ppm 1,2,4-trichlorobenzene. Continuous exposure of male monkeys, rats, or rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors for 26 weeks did not induce significant gross or microscopic alterations in the eyes (Coate et al. 1977). The eyes from rats, dogs, and rabbits were also examined in the intermediate-duration study by Kociba et al. (1981). In that study, exposure to up to 100 ppm 1,2,4-trichlorobenzene vapors did not induce alterations in the microscopic morphology of the eye.

Body Weight Effects. Continuous exposure of male monkeys, rats, and rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors for 26 weeks (Coate et al. 1977) or intermittent exposure of rats, dogs, and rabbits to up to 100 ppm for 44 days (Kociba et al. 1981) did not significantly alter body weight. Gage (1970) reported that rats exposed to 70 ppm 1,2,4-trichlorobenzene 6 hours/day for 15 exposures showed retarded weight gain, but no data were presented.

Exposure of rats to 1,209 ppm 1,3,5-trichlorobenzene vapors for 60 minutes resulted in 44 and 60% less body weight gain in males and females, respectively, 14 days after exposure (Jorgenson et al. 1976). Body weight was not affected in rats exposed intermittently to up to 130 ppm 1,3,5-trichlorobenzene vapors for 13 weeks (Sasmore et al. 1983).

Metabolic Effects. Intermittent exposure of rats to up to 130 ppm 1,3,5-trichlorobenzene vapors for 13 weeks did not significantly affect serum electrolyte levels or electrolyte balance (Sasmore et al. 1983).

No relevant data were located regarding 1,2,4-trichlorobenzene.

3.2.1.3. Immunological and Lymphoreticular Effects

No studies were located regarding immunological effects in humans after inhalation exposure to trichlorobenzenes.

Continuous exposure of monkeys, rats, and rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors for 26 weeks did not induce significant gross or microscopic changes in the spleen of the animals (Coate et al. 1977). Fifteen intermittent exposures (6 hours/day) of rats to up to 200 ppm 1,2,4-trichlorobenzene vapors also did not result in significant histological alterations in the spleen (Gage 1970). Similar experiments in rats, rabbits, and dogs exposed 7 hours/day, 5 days/week to up to 100 ppm 1,2,4-trichlorobenzene vapors for a total of 30 exposures during a 44-day period did not result in significant gross or microscopic alterations in the spleen, thymus, or lymph nodes (Kociba et al. 1981).

No histological alterations were observed in lymphoreticular tissues from rats exposed to up to 130 ppm 1,3,5-trichlorobenzene vapors 6 hours/day, 5 days/week for 13 weeks (Sasmore et al. 1983).

No relevant data were located regarding 1,2,3-trichlorobenzene.

NOAELs for lymphoreticular effects of 1,2,4-trichlorobenzene and 1,3,5-trichlorobenzene are presented in Tables 3-1 and 3-2 and are plotted in Figures 3-1 and 3-2.

3.2.1.4. Neurological Effects

No studies were located regarding neurological effects in humans after inhalation exposure to trichlorobenzenes.

Lethargy was reported in rats during 6-hour exposures to 70 ppm 1,2,4-trichlorobenzene vapors (Gage 1970). No such effect was observed during exposures to 20 ppm.

Continuous exposure of monkeys, rats, or rabbits to up to 100 ppm 1,2,4-trichlorobenzene vapors for 26 weeks did not induce significant gross or microscopic changes in the brain and spinal cord (Coate et al. 1977). Operant behavior tests conducted in the monkeys throughout the study showed no exposure-related alterations. Similar lack of gross or histological alterations were reported in the brain, spinal cord, and peripheral nerves from rats, dogs, and rabbits exposed intermittently to up to 100 ppm 1,2,4-trichlorobenzene vapors during a 44-day period (Kociba et al. 1981).

No histological alterations were observed in the brain and spinal cord from rats exposed to up to 130 ppm 1,3,5-trichlorobenzene vapors 6 hours/day, 5 days/week for 13 weeks (Sasmore et al. 1983).

No relevant data were located regarding 1,2,3-trichlorobenzene.

NOAELs and LOAELs for neurological effects are presented in Tables 3-1 and 3-2 and are plotted in Figures 3-1 and 3-2.

3.2.1.5. Reproductive Effects

No studies were located regarding reproductive effects in humans after inhalation exposure to trichlorobenzenes.

No significant gross or histological alterations were reported in the reproductive organs from male rats, dogs, and rabbits exposed intermittently to up to 100 ppm 1,2,4-trichlorobenzene vapors for 44 days (Kociba et al. 1981). It should be noted, however, that absolute and relative testes weights were significantly increased (30 and 43%, respectively) in rabbits exposed to 100 ppm (but not 30 ppm). The investigators considered this change unrelated to the test material since, as indicated above, microscopic examination did not reveal any significant histological changes.

No histological alterations were observed in the reproductive organs from male or female rats exposed to up to 130 ppm 1,3,5-trichlorobenzene vapors 6 hours/day, 5 days/week for 13 weeks (Sasmore et al. 1983).

No relevant data were located regarding 1,2,3-trichlorobenzene.

NOAELs for reproductive effects are presented in Table 3-1 and are plotted in Figure 3-1.

No studies were located regarding the following health effects in humans or animals after inhalation exposure to trichlorobenzenes:

3.2.1.6. Developmental Effects

3.2.1.7. Cancer

3.2.2.1. Death

No studies were located regarding death in humans after oral exposure to trichlorobenzenes.

Information regarding acute lethality is available for the three trichlorobenzene isomers. An LD₅₀ of 756 mg/kg was reported for 1,2,4-trichlorobenzene in CFE rats (Brown et al. 1969). In the same study, the investigators determined an oral LD₅₀ of 766 mg/kg for 1,2,4-trichlorobenzene in C57BL/6N mice. In both species, lower doses caused depression of activity, while lethal doses induced extensor convulsions. Another study reported an LD₅₀ of 880 mg/kg for 1,2,4-trichlorobenzene in Sprague-Dawley rats (Côté et al. 1988). In a developmental study, six out of six pregnant Sprague-Dawley rats died after 3 days of dosing with 1,200 mg/kg 1,2,4-trichlorobenzene (Kitchin and Ebron 1983).

Without providing further details, Côté et al. (1988) reported that the oral LD₅₀ for 1,2,3-trichlorobenzene in Sprague-Dawley rats was 1,830 mg/kg. In a brief report in which groups of two rats per group were administered 1,000 or 2,000 mg/kg 1,2,3-trichlorobenzene by gavage in corn oil, one rat in the high-dose group died within 2 days of dosing (Dow Chemical 1956). The investigators stated that slight pathology of the liver and spleen occurred, but no details were provided.

An oral LD₅₀ of 2,100 mg/kg was reported for 1,3,5-trichlorobenzene in Sprague-Dawley rats (Côté et al. 1988). In another study, Jorgenson et al. (1976) reported LD₅₀ values of 1,800 and 2,800 mg/kg for 1,3,5-trichlorobenzene in male and female Sprague-Dawley rats, respectively. All deaths except one occurred between 21 and 96 hours after dosing. Clinical signs observed included rough hair coat, passive tremors, depression, and inactivity leading to prostration, persistent tremor, coma, and death; necropsy revealed no gross abnormalities. The corresponding oral LD₅₀ values for 1,3,5-trichlorobenzene in male and female ICR mice were 3,350 and 3,402 mg/kg, respectively (Jorgenson et al. 1976). Clinical signs observed included rough hair coat, passive tremors, depression, inactivity, prostration, persistent tremors, coma, and death. Deaths occurred between 22 and 288 hours after dosing; necropsy revealed no gross abnormalities. Increased mortality rate was reported in male rats dosed with 66.5 mg/kg/day 1,2,4-trichlorobenzene for 104 weeks (Moore 1994a). Similar results were reported in male and female mice dosed with 519.9 and 572.6 mg/kg/day 1,2,4-trichlorobenzene, respectively, for 104 weeks (Moore 1994b).

The limited data available suggest that 1,2,4-trichlorobenzene has a stronger acute toxicity than the other two isomers, and that rats may be more susceptible than mice.

Lethal doses and LD₅₀ values are presented in Tables 3-3, 3-4, and 3-5 and plotted in Figures 3-3, 3-4, and 3-5.

3.2.2.2. Systemic Effects

No studies were located regarding systemic effects in humans after oral exposure to trichlorobenzenes.

The highest NOAEL values and all LOAEL values from each reliable study for systemic effects in each species and duration category are recorded in Tables 3-3, 3-4, and 3-5 and plotted in Figure 3-3, 3-4, and 3-5.

Respiratory Effects. No gross or microscopic alterations were observed in the lungs, bronchi, or trachea from rats administered up to 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3- or 1,3,5-trichlorobenzene on Gd 6–15 and sacrificed on Gd 22 (Black et al. 1988). In intermediate-duration studies, there were also no significant histological alterations in the lungs, trachea, or bronchi from rats exposed via the diet to up to 101 mg/kg/day (Côté et al. 1988) or 150.6 mg/kg/day (CMA 1989) 1,2,4-trichlorobenzene. A 13-week dietary study in mice reported no significant histological alterations in the lungs or trachea from animals dosed with up to 1,345 mg/kg/day 1,2,4-trichlorobenzene (Hiles 1989). Chronic-duration exposure to 1,2,4-trichlorobenzene also did not induce significant histological alterations in the lungs and trachea from rats dosed via the diet with up to 81.4 mg/kg/day 1,2,4-trichlorobenzene (Moore 1994a) or from mice dosed with up to 572.6 mg/kg/day 1,2,4-trichlorobenzene (Moore 1994b).

Table 3-3

Levels of Significant Exposure to 1,2,4-Trichlorobenzene - Oral.

Figure 3-3

Levels of Significant Exposure to 1,2,4-Trichlorobenzene - Oral.

Table 3-4

Levels of Significant Exposure to 1,2,3-Trichlorobenzene - Oral.

Figure 3-4

Levels of Significant Exposure to 1,2,3-Trichlorobenzene - Oral.

Table 3-5

Levels of Significant Exposure to 1,3,5-Trichlorobenzene - Oral.

Figure 3-5

Levels of Significant Exposure to 1,3,5-Trichlorobenzene - Oral.

Black et al. (1988) also studied the 1,2,3- and 1,3,5- isomers and reported no significant effects in the lungs, bronchi, and trachea of pregnant rats dosed by gavage with up to 600 mg/kg/day of either isomer on Gd 6–15 and sacrificed on Gd 22. Similar results were reported in rats treated with up to 113 mg/kg/day 1,2,3-trichlorobenzene or 146 mg/kg/day 1,3,5-trichlorobenzene in the diet for 13 weeks (Côté et al. 1988).

Cardiovascular Effects. No significant gross or microscopic alterations were observed in the heart of rats dosed by gavage with up to 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3- or 1,3,5-trichlorobenzene on Gd 6–15 and sacrificed on Gd 22 (Black et al. 1988). Similar results were reported regarding the heart and aorta from rats treated with up to 101 mg/kg/day 1,2,4-trichlorobenzene, 113 mg/kg/day 1,2,3-trichlorobenzene, or 146 mg/kg/day 1,3,5-trichlorobenzene in the diet for 13 weeks (Côté et al. 1988), or 150.6 mg/kg/day 1,2,4-trichlorobenzene for 14 weeks (CMA 1989). Treatment of mice with up to 1,345 mg/kg/day 1,2,4-trichlorobenzene for 13 weeks via the diet did not significantly alter the gross or microscopic appearance of the heart or aorta (Hiles 1989). Treatment of rats with up to 81.4 mg/kg/day 1,2,4-trichlorobenzene or mice with up to 572.6 mg/kg/day 1,2,4-trichlorobenzene through the diet for 104 weeks did not induce gross or microscopic changes in the heart (Moore 1994a, 1994b).

Gastrointestinal Effects. No significant gross or microscopic alterations were reported in the gastrointestinal tract of rats dosed by gavage with up to 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3- or 1,3,5-trichlorobenzene on Gd 6–15 and sacrificed on Gd 22 (Black et al. 1988). Similar results were reported in rats treated with up to 101 mg/kg/day 1,2,4-trichlorobenzene, 113 mg/kg/day 1,2,3-trichlorobenzene, or 146 mg/kg/day 1,3,5-trichlorobenzene in the diet for 13 weeks (Côté et al. 1988), or 150.6 mg/kg/day 1,2,4-trichlorobenzene for 14 weeks (CMA 1989). Examination of the gastrointestinal tract from mice dosed with up to 1,345 mg/kg/day 1,2,4-trichlorobenzene for 13 weeks via the diet did not reveal significant treatment-related gross or histological alterations (Hiles 1989). No gross or histological alterations were reported in the gastrointestinal tract from rats or mice dosed via the diet with up to 81.4 or 572.6 mg/kg/day 1,2,4-trichlorobenzene, respectively for 104 weeks (Moore 1994a, 1994b).

Hematological Effects. Changes in hematological parameters have been reported in some acute- and intermediate-duration studies. However, since the reductions in hemoglobin and hematocrit reported in some of these studies are within the normal range for these parameters, they are not listed as LOAELs in Table 3-2; instead, the highest doses tested are listed as NOAELs for hematological effects.

Treatment of pregnant rats with 150 or 300 mg/kg/day 1,2,4-trichlorobenzene during Gd 6–15 resulted in reductions in hemoglobin (6–7%) and hematocrit (6%) (Black et al. 1988). In the same study, doses of 300 and 600 mg/kg/day 1,2,3-trichlorobenzene reduced hemoglobin by 6–7% and doses of 600 mg/kg/day reduced the hematocrit by approximately 6%. Rats treated with 600 mg/kg/day 1,3,5-trichlorobenzene showed reduction in hemoglobin and hematocrit of approximately 10–11% (Black et al. 1988). In another acute-duration study in rats, doses of up to 40 mg/kg/day 1,2,4-trichlorobenzene by gavage for 14 days did not affect hemoglobin or hematocrit levels (Carlson and Tardiff 1976).

Some intermediate-duration dietary studies have reported mild hematological changes following exposure to 1,2,4-trichlorobenzene. For example, treatment of male rats with 133.7 mg/kg/day, but not 45.6 mg/kg/day, 1,2,4-trichlorobenzene in the diet for 14 weeks reduced mean erythrocyte count (5%), hemoglobin (1.2%), and hematocrit (6%) (CMA 1989). In female rats, doses of 150.6 mg/kg/day reduced hemoglobin and hematocrit by 3.6–4%. Platelets were increased in males dosed with 133.7 mg/kg/day. In a similar study, administration of doses of up to 82 mg/kg/day to male rats and 101 mg/kg/day to females did not alter hematological parameters (Côté et al. 1988). No significant hematological changes were observed in male mice dosed with up to 1,222 mg/kg/day 1,2,4-trichlorobenzene for 13 weeks (Hiles 1989). In the same study, female mice dosed with 1,345 mg/kg/day 1,2,4-trichlorobenzene had lower (5–9%) hemoglobin, hematocrit, mean corpuscular volume, and mean corpuscular hemoglobin; since the these changes occurred only in females, the investigator (Hiles 1989) did not consider them to be treatment-related.

Administration in the diet of up to 113 mg/kg/day 1,2,3-trichlorobenzene or 146 mg/kg/day 1,3,5-trichlorobenzene to rats for 13 weeks did not alter hematological parameters (Côté et al. 1988).

In the chronic-duration oral studies with 1,2,4-trichlorobenzene, cellular morphology and leukocyte differential were monitored on weeks 52, 78, and at termination (Moore 1994a, 1994b). The results showed no significant treatment-related alterations in the parameters monitored in rats dosed through the diet with up to 81.4 mg/kg/day or in mice dosed with up to 572.6 mg/kg/day 1,2,4-trichlorobenzene. No evidence of leukemia was seen in either study.

Musculoskeletal Effects. No significant gross or histological alterations were reported in skeletal muscle from pregnant rats dosed with up to 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3-trichlorobenzene or 1,3,5,-trichlorobenzene on Gd 6–15 and sacrificed on Gd 22 (Black et al. 1988).

Similar results were reported in rats dosed via the diet with up to 150.6 mg/kg/day 1,2,4-trichlorobenzene, 113 mg/kg/day 1,2,3-trichlorobenzene, or 146 mg/kg/day 1,3,5-trichlorobenzene for 3 months (CMA 1989; Côté et al. 1988). An intermediate-duration dietary study in mice dosed with up to 1,345 mg/kg/day 1,2,4-trichlorobenzene for 13 weeks also did not find morphological alterations in bone or skeletal muscle (Hiles 1989). Chronic-duration studies did not find morphological alterations in bone or skeletal muscle from rats or mice dosed with up to 81.4 or 572.6 mg/kg/day 1,2,4-trichlorobenzene via the diet, respectively, for 104 weeks (Moore 1994a, 1994b).

Hepatic Effects. Acute-, intermediate-, and chronic-duration oral studies in animals indicate that the liver is a target for trichlorobenzenes. An acute-duration study with 1,2,4-trichlorobenzene described intense necrosis and fatty change in rats following administration of 500 mg/kg/day 1,2,4-trichlorobenzene by gavage for 10 days (Rimington and Ziegler 1963). In a 14-day gavage study in male rats, 1,2,4-trichlorobenzene induced a dose-related increase in relative liver weight (all doses, 15.3% at 10 mg/kg/day, 28.9% at 40 mg/kg/day) (Carlson and Tardiff 1976). Moderate hepatocellular hypertrophy was reported in the liver from pregnant rats following administration of 360 mg/kg/day for 4 days; the NOAEL for this effect was 120 mg/kg/day (Kitchin and Ebron 1983). In another developmental study, mild hepatic changes consisting of increased periportal cytoplasmic eosinophilia and mild anisokaryosis of hepatocellular nuclei were reported in pregnant rats dosed with 150 and 300 mg/kg/day 1,2,4-trichlorobenzene on Gd 6–15 (Black et al. 1988). The same was reported in pregnant rats dosed with 300 and 600 mg/kg/day 1,2,3- or 1,3,5-trichlorobenzene. Because no quantitative histological data were presented in the latter study, this information is not listed in Tables 3-3, 3-4, and 3-5. Histological alterations in the liver were almost always accompanied by increases in liver weight.

In a 90-day study in male rats, gavage administration of 1,2,4-trichlorobenzene (10, 20, 40 mg/kg/day) increased relative liver weight 14% in high-dose rats after a 30-day recovery period; however, no significant histological alterations were seen in the liver (Carlson and Tardiff 1976). Dietary administration of ≥14.6 mg/kg/day 1,2,4-trichlorobenzene to male rats or ≥52.5 mg/kg/day to females for 14 weeks induced dose-related increases in absolute and relative liver weights (CMA 1989). Microscopic examination of the liver revealed an increased incidence of centrilobular hepatocyte hypertrophy in male rats dosed with ≥45.6 mg/kg/day 1,2,4-trichlorobenzene and in female rats dosed with 150.6 mg/kg/day; the corresponding NOAELs were 14.6 and 52.5 mg/kg/day (CMA 1989). Centrilobular hepatocyte hypertrophy was used as the basis for derivation of an intermediate-duration oral MRL for 1,2,4-trichlorobenzene. An additional intermediate-duration dietary study reported significant increases in relative liver weight in male rats dosed with 78–82 mg/kg/day of each trichlorobenzene isomer (Côté et al. 1988). The investigators stated that most treated groups (doses ranged from approximately 0.1 to 140 mg/kg/day) showed mild-to-moderate increases in cytoplasmic volume and anisokaryosis of hepatocytes mostly in perivenous and midzone areas. High-dose rats showed aggregated basophilia as well as widespread midzonal vacuolation due to fatty infiltration. However, since only a qualitative description of the histological changes was provided, it is impossible to determine with certainty NOAELs or LOAELs for the lesions; therefore, they are not listed in Tables 3-3, 3-4, or 3-5, but the organ weight changes are.

A significant increase in absolute and relative liver weight was reported in male mice dosed via the diet with ≥850 mg/kg/day 1,2,4-trichlorobenzene and female mice dosed with ≥1,183 mg/kg/day 1,2,4-trichlorobenzene for 13 weeks (Hiles 1989). These changes in liver weight correlated with microscopic changes characterized by hepatocellular cytomegaly with karyomegaly and multinucleation complex with adjacent hepatocellular compression, atrophy, anisocytosis, vacuolar degeneration, and necrosis. The NOAELs for these alterations were 67 and 86 mg/kg/day in males and females, respectively. In addition, changes in clinical chemistry that were considered treatment-related consisted of higher total protein in mid-dose males (850 mg/kg/day) and high-dose males (1,222 mg/kg/day) and females (1,345 mg/kg/day), increased albumin and globulin in high-dose males and females, increased serum alanine aminotransferase (ALT) in mid-dose males and in high-dose males and females, and increased sorbitol dehydrogenase (SDH) in mid- and high-dose males and females. According to the investigators, the higher protein was probably caused by dehydration.

In a 104-week dietary study with 1,2,4-trichlorobenzene in rats, doses of 66.5 mg/kg/day in males and 81.4 mg/kg/day in females produced significant increases in absolute and relative liver weight at termination (Moore 1994a). The corresponding NOAELs were 19.4 and 23.5 mg/kg/day. Significant increases in the incidence of liver lesions were reported in rats that received the highest doses, 66.5 mg/kg/day in males and 81.4 mg/kg/day in females. The histological alterations consisted of hepatocyte hypertrophy, focal cystic degeneration, and diffuse fatty change. The increased incidence of hepatocyte hypertrophy in male rats served as the basis for derivation of a chronic-duration oral MRL for 1,2,4-trichlorobenzene. In a similar study in mice, doses ≥21 mg/kg/day 1,2,4-trichlorobenzene induced a dose-related increase in absolute and relative liver weight in males, whereas doses ≥100.6 mg/kg/day 1,2,4-trichlorobenzene increased relative liver weight (Moore 1994b). In females, doses ≥26.3 mg/kg/day also increased absolute and relative liver weight. Histological examination of the liver showed a significant increase in the incidence of centrilobular hepatocytomegaly in males dosed with ≥101 mg/kg/day 1,2,4-trichlorobenzene. The neoplastic effects in mice are described in Section 3.2.2.7, Cancer.

In addition to inducing changes in liver weight and morphological alterations in the liver, 1,2,4-trichlorobenzene has been shown to be a potent inducer of phase I and phase II metabolic enzymes (Ariyoshi et al. 1975a, 1975b; Carlson and Tardiff 1976; Kato and Kimura 2002; Kato et al. 1988, 1993; Kitchin and Ebron 1983). For example, administration of ≥10 mg/kg/day 1,2,4-trichlorobenzene to rats by gavage for 14 days resulted in dose-related increases in cytochrome c reductase, cytochrome P-450, glucuronyltransferase, EPN detoxification, and azoreductase (Carlson and Tardiff 1976). Extending the dosing period to 90 days resulted in smaller increases in enzyme activities, except for glucuronyltransferase activity, which was reduced relative to controls (Carlson and Tardiff 1976). In rats, 1,2,4-trichlorobenzene also induced ALA synthetase, the rate-limiting enzyme in the biosynthesis of heme, which is consistent with the development of porphyria in rats administered 1,2,4- trichlorobenzene (Rimington and Ziegler 1963). For example, doses of 250–500 mg/kg/day significantly increased the urinary excretion of coproporphyrin and, to a smaller extent, the excretion of uroporphyrins. Liver uroporphyrin was also increased by 1,2,4-trichlorobenzene; liver coproporphyrin and protoporphyrin were increased in rats showing marked porphyrinuria. Studies by Kato and coworkers (Kato and Kimura 2002; Kato et al. 1988, 1993) have shown that both the induction of drug-metabolizing enzymes and ALA synthetase are not due to 1,2,4-trichlorobenzene itself but its metabolite 2,3,5-trichlorophenyl methyl sulfone. Further information on the mechanism of porphyria can be found in Section 3.5, Mechanisms of Action.

Renal Effects. No gross or microscopic alterations were reported in the kidneys from pregnant rats dosed on Gd 6–15 with up to 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3-trichlorobenzene or 1,3,5-trichlorobenzene and sacrificed on Gd 22 (Black et al. 1988).

In a 13-week dietary study in rats with trichlorobenzenes, the three isomers increased relative kidney weight in male rats in doses ranging between 78 and 82 mg/kg/day (no data on females were presented), but only 1,3,5-trichlorobenzene reportedly induced morphological alterations in the kidneys (Côté et al. 1988). The changes were characterized by eosinophilic inclusion, enlargement and anisokariosis of the epithelial lining cells, and hyperplasia of renal tubular epithelial cells. Only the changes associated with the highest dose levels, 78–82 mg/kg/day, were considered to be biologically significant by the investigators. Since only a qualitative description of the histology was provided, NOAELs and LOAELs for histological changes are not presented in Tables 3-3, 3-4, and 3-5, but the organ weight changes are. In a 14-week dietary study with 1,2,4-trichlorobenzene in rats, doses ≥45.6 mg/kg/day in males and ≥52.5 mg/kg/day in females significantly increased relative kidney weight, but morphological alterations were seen only in high-dose males (133.7 mg/kg/day) and consisted of dilated tubules, granular casts, hyaline droplets, and interstitial nephritis (CMA 1989). BUN was also significantly elevated in high-dose males and females (150.6 mg/kg/day). Mice administered up to 1,345 mg/kg/day 1,2,4-trichlorobenzene via the diet for 13 weeks did not show significant gross or microscopic alterations in the kidneys (Hiles 1989).

In the 104-week dietary studies with 1,2,4-trichlorobenzene in rats and mice, kidney alterations were reported only in rats (Moore 1994a). Gross necropsy at termination showed increases incidence of kidney abnormalities in mid- (19.4 mg/kg/day) and high-dose (66.5 mg/kg/day) males. Microscopically, there was an increased incidence in marked renal papilla mineralization in high-dose males and in transitional renal cell hyperplasia, also in males; only the latter effect showed dose-response. In addition, there was an increase in severity of chronic nephropathy in males. In mice, there were no significant gross or microscopic alterations in the kidneys following dosing with up to 572.6 mg/kg/day 1,2,4-trichlorobenzene (Moore 1994b).

Endocrine Effects. The only relevant information from acute-duration exposures is that from the study by Black et al. (1988) in which pregnant rats were administered trichlorobenzenes by gavage on Gd 6–15 and were sacrificed on Gd 22. No significant gross or microscopic alterations were reported in the pituitary, parathyroid, adrenals, or pancreas from dams following doses of up to 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3-trichlorobenzene or 1,3,5-trichlorobenzene. However, mild thyroid histopathology was reported in rats dosed with ≥300 mg/kg/day of each isomer; the NOAEL in each case was 150 mg/kg/day. The alterations were described as reduction of follicle size and increased epithelial height accompanied by cytoplasmic vacuolization. Since no quantitative data were presented, NOAELs and LOAELs for thyroid effects are not presented in Tables 3-3, 3-4, and 3-5.

Côté et al. (1988) examined the same organs in a 13-week study in Sprague-Dawley rats and reported similar results. Morphological alterations were limited to the thyroid and were described as mild and appeared to be more severe in males. Reported changes consisted of reduction in follicular size, increased epithelial height from flattened cuboidal cells to columnar shape, and reduced colloid density. Changes in the high-dose groups (78–82 mg/kg/day) varied from mild to moderate. Since no quantitative data were presented, NOAELs and LOAELs for histological alterations in the thyroid are not listed in Tables 3-3, 3-4, and 3-5. In contrast, CMA (1989) did not find significant histological alterations in the thyroid from Fisher-344 rats dosed with up to 150.6 mg/kg/day 1,2,4-trichlorobenzene in the diet for 14 weeks. Whether this can be attributed to differences in sensitivity between rat strains is unknown. No significant alterations were reported in endocrine glands from mice dosed via the diet with up to 1,345 mg/kg/day 1,2,4-trichlorobenzene for 13 weeks (Hiles 1989) or from rats or mice dosed with up to 81.4 or 572.6 mg/kg/day 1,2,4-trichlorobenzene, respectively, for 104 weeks (Moore 1994a, 1994b).

Dermal Effects. None of the studies that examined the skin of animals following oral administration of trichlorobenzenes reported treatment-related gross or microscopic alterations. These include the acute developmental study by Black et al. (1988) (300 mg/kg/day 1,2,4-trichlorobenzene; 600 mg/kg/day 1,2,3-trichlorobenzene and 1,3,5-trichlorobenzene), a 13-week dietary study (Côté et al. 1988) (78–82 mg/kg/day), and 104-week dietary studies with 1,2,4-trichlorobenzene in rats (Moore 1994a) (81.4 mg/kg/day) and mice (Moore 1994b) (572.6 mg/kg/day).

Ocular Effects. Examination of the eyes of animals exposed orally to trichlorobenzenes did not show treatment-related gross or histological alterations. These include the acute developmental study by Black et al. (1988; 300 mg/kg/day 1,2,4-trichlorobenzene; 600 mg/kg/day 1,2,3-trichlorobenzene and 1,3,5-trichlorobenzene), 3-month dietary studies in rats (Côté et al. 1988; 78–82 mg/kg/day, and CMA 1989; 150.6 mg/kg/day), a 13-week dietary study with 1,2,4-trichlorobenzene in mice (Hiles 1989; 1,345 mg/kg/day), and 104-week dietary studies with 1,2,4-trichlorobenzene in rats (Moore 1994a; 81.4 mg/kg/day) and mice (Moore 1994b; 572.6 mg/kg/day).

Body Weight Effects. Almost all studies of trichlorobenzenes monitored body weight of the animals. Pregnant rats administered 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3-trichlorobenzene on Gd 6–15 gained less weight than controls, but quantitative data for these isomers were not provided (Black et al. 1988). However, administration of 600 mg/kg/day 1,3,5-trichlorobenzene resulted in a reduction in weight gain of 34% relative to controls on Gd 22 (Black et al. 1988). In another developmental study, doses of 360 mg/kg/day 1,2,4-trichlorobenzene on Gd 9–13 induced weight loss; 120 mg/kg/day had no significant effect (Kitchin and Ebron 1983). Weight loss was also reported in a study in rats dosed by gavage with 500 mg/kg/day 1,2,4-trichlorobenzene for 10 days or with 780 mg/kg/day 1,2,3-trichlorobenzene for 7 day (Rimington and Ziegler 1963). None of these studies provided information on food consumption.

Fifteen days of dosing with 730 mg/kg/day 1,2,4-trichlorobenzene by gavage resulted in loss of appetite and weight loss in rats (Rimington and Ziegler 1963). Neither food consumption nor weight gain was significantly affected in rats dosed via the diet with up to 101 mg/kg/day 1,2,4-trichlorobenzene or 146 mg/kg/day 1,3,5-trichlorobenzene for 13 weeks (Côté et al. 1988). Similar results were reported in rats dosed through the diet with up to 150.6 mg/kg/day 1,2,4-trichlorobenzene for 14 weeks (CMA 1989). Male rats treated with 78 mg/kg/day 1,2,3-trichlorobenzene for 13 weeks gained 10.2% less weight than controls (Côté et al. 1988); the NOAEL was 7.6 mg/kg/day. Final body weight was significantly reduced in male mice dosed with 1,222 mg/kg/day 1,2,4-trichlorobenzene (9%) and in female mice dosed via the diet with 1,345 mg/kg/day 1,2,4-trichlorobenzene (8.3%) for 13 weeks (Hiles 1989). Cumulative body weight gain was significantly reduced in males dosed with 67 mg/kg/day 1,2,4-trichlorobenzene (27%), in males dosed with 1,222 mg/kg/day 1,2,4-trichlorobenzene (40%), and in females dosed with 1,345 mg/kg/day 1,2,4-trichlorobenzene (33%); these changes were associated with significant reductions in food consumption throughout the study.

Final body weight of rats dosed through the diet with up to 81.4 mg/kg/day 1,2,4-trichlorobenzene for 104 weeks was not significantly different than controls (Moore 1994a). Final body weight of male mice dosed with 519.9 mg/kg/day 1,2,4-trichlorobenzene in the diet for 104 weeks was 16% lower than controls; food consumption in this group was reduced during the first 52 weeks of the study (Moore 1994b). Final body weight was not significantly affected in female mice dosed with up to 572.6 mg/kg/day 1,2,4-trichlorobenzene. The NOAEL for body weight changes in male mice was 100.6 mg/kg/day.

Metabolic Effects. Administration of up to 300 mg/kg/day 1,2,4-trichlorobenzene or up to 600 mg/kg/day 1,2,3- or 1,3,5-trichlorobenzene to pregnant rats on Gd 6–15 did not significantly alter the concentration of electrolytes or glucose in blood (Black et al. 1988).

None of the intermediate-duration studies with trichlorobenzenes reported adverse metabolic effects. Treatment of rats with dietary doses of up to 150.6 mg/kg/day or mice with up to 1,345 mg/kg/day 1,2,4-trichlorobenzene for 3 months had no significant effect on serum electrolyte or glucose levels (CMA 1989; Côté et al. 1988; Hiles 1989). Similar results were reported in rats dosed via the diet with up to 113 mg/kg/day 1,2,3-trichlorobenzene or 146 mg/kg/day 1,3,5-trichlorobenzene (Côté et al. 1988).

3.2.2.3. Immunological and Lymphoreticular Effects

No studies were located regarding immunological and lymphoreticular effects in humans after oral exposure to trichlorobenzenes.

Information from studies in animals is limited to evaluations of the gross and microscopic morphology of lymphoreticular organs and tissues. In pregnant rats that were exposed to up to 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3-trichlorobenzene or 1,3,5-trichlorobenzene on Gd 6–15, there were no significant morphological changes in the spleen or thymus on Gd 22 (Black et al. 1988).

Intermediate-duration studies showed that exposure of rats to up to 150.6 mg/kg/day 1,2,4-trichlorobenzene, 113 mg/kg/day 1,2,3-trichlorobenzene, or 146 mg/kg/day 1,3,5-trichlorobenzene, or mice to up to 1,345 mg/kg/day 1,2,4-trichlorobenzene in the diet for 3 months did not alter the gross or microscopic morphology of the spleen, thymus, or lymph nodes (CMA 1989; Côté et al. 1988). Similar results were reported in rats and mice dosed with up to 81.4 and 572.6 mg/kg/day 1,2,4-trichlorobenzene, respectively, in the diet for 104 weeks (Moore 1994a, 1994b).

These values are presented as NOAELs for lymphoreticular effects in Table 3-3, 3-4, and 3-5 and are plotted in Figures 3-3, 3-4, and 3-5.

3.2.2.4. Neurological Effects

No studies were located regarding neurological effects in humans after oral exposure to trichlorobenzenes.

No gross or histological alterations were observed in the brain and peripheral nerves from rats exposed to up to 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3-trichlorobenzene or 1,3,5-trichlorobenzene on Gd 6–15 and sacrificed on Gd 22 (Black et al. 1988).

Côté et al. (1988) examined the brain, spinal cord, and sciatic nerve from rats following a 13-week exposure period via the diet to doses of up to 101 mg/kg/day 1,2,4-trichlorobenzene, 113 mg/kg/day 1,2,3-trichlorobenzene, or 146 mg/kg/day 1,3,5-trichlorobenzene and reported no significant gross or microscopic alterations in those tissues. Similar results were reported in rats dosed via the diet with up to 150.6 mg/kg/day 1,2,4-trichlorobenzene for 14 weeks (CMA 1989) and in mice dosed with up to 1,345 mg/kg/day 1,2,4-trichlorobenzene for 13 weeks (Hiles 1989). Dietary exposure of rats and mice to up to 81.4 and 572.6 mg/kg/day 1,2,4-trichlorobenzene, respectively, in the diet for 104 weeks also did not induce histological alterations in the brain, spinal cord, or sciatic nerve (Moore 1994a, 1994b).

The NOAELs for morphological changes in the central and peripheral nervous systems are listed in Tables 3-3, 3-4, and 3-5 and are plotted in Figures 3-3, 3-4, and 3-5.

3.2.2.5. Reproductive Effects

No studies were located regarding reproductive effects in humans after oral exposure to trichlorobenzenes.

Examination of the ovaries and uteri from rats dosed by gavage with up to 300 mg/kg/day 1,2,4-trichlorobenzene or 600 mg/kg/day 1,2,3-trichlorobenzene or 1,3,5-trichlorobenzene on Gd 6–15 and sacrificed on Gd 22 did not show significant gross or microscopic alterations (Black et al. 1988).

No treatment-related morphological alterations were reported in the reproductive organs from male or female rats dosed via the diet with 1,2,4-trichlorobenzene (82 mg/kg/day males, 101 mg/kg/day females), 1,2,3-trichlorobenzene (78 mg/kg/day males, 113 mg/kg/day females), or 1,3,5-trichlorobenzene (82 mg/kg/day males, 146 mg/kg/day females) for 13 weeks (Côté et al. 1988). No alterations were noted in the reproductive organs from male and female rats dosed via the diet with up to 133.7 and 150.6 mg/kg/day 1,2,4-trichlorobenzene, respectively, for 14 weeks (CMA 1989) or male and female mice dosed with up to 1,222 and 1,345 mg/kg/day, respectively, for 13 weeks (Hiles 1989).

Two-year dietary studies with 1,2,4-trichlorobenzene in rats (66.5 mg/kg/day males, 81.4 mg/kg/day females) and mice (519.9 mg/kg/day males, 572.6 mg/kg/day females) also did not find gross or microscopic alterations in the reproductive organs (Moore 1994a, 1994b).

Robinson et al. (1981) conducted a multi-generation reproductive study in rats in which the F0 and F1 generations were exposed to 1,2,4-trichlorobenzene via the mother’s milk until weaning and then directly through their drinking water. At approximately 90 days of age in the F0 and F1 generations, the rats were mated to produce the subsequent generation. The results showed that treatment of males and females with up to 33 or 53.6 mg/kg/day 1,2,4-trichlorobenzene, respectively, did not affect fertility. The doses correspond to the intake of test material by the F0 generation at 83 days of age and were estimated by the investigators.

The NOAELs for reproductive organs histology and the NOAEL for fertility from Robinson et al. (1981) are presented in Tables 3-3, 3-4, and 3-5 and are plotted in Figures 3-3, 3-4, and 3-5.

3.2.2.6. Developmental Effects

No studies were located regarding developmental effects in humans after oral exposure to trichlorobenzenes.

Black et al. (1988) examined the developmental effects of trichlorobenzenes in Sprague-Dawley rats. Rats were administered 0, 75, 150, or 300 mg/kg/day 1,2,4-trichlorobenzene or 0, 150, 300, or 600 mg/kg/day 1,2,3-trichlorobenzene or 1,3,5-trichlorobenzene by gavage in corn oil on Gd 6–15. Dams were sacrificed on Gd 22, and the uterus and ovaries were removed. Fetuses were examined grossly for birth defects and were also examined for skeletal and visceral anomalies. Also, entire fetuses were fixed, stained, and examined microscopically. Gestational exposure to the trichlorobenzenes did not significantly alter the number of pregnancies, fetal weight, litter size, resorptions, or dead fetuses, or the incidences of skeletal and visceral anomalies. However, fetuses from the 150 mg/kg/day 1,2,4-trichlorobenzene group and all groups exposed to 1,3,5-trichlorobenzene showed histological alterations in the lenses of the eye consisting of central areas of cellular disorientation and disaggregation with ballooning and granular degeneration. The investigators stated that autolysis and incomplete preservation made examination of other fetal tissues difficult, but there did not appear to be any significant treatment-related changes. In an additional study, pregnant rats were dosed with 0 or 360 mg/kg/day 1,2,4-trichlorobenzene on Gd 9–13 and were sacrificed on Gd 14 (Kitchin and Ebron 1983). Treatment did not increase resorptions or induce significant embryolethality or teratogenicity; however, it significantly retarded development as measured by reduced head length, crown-rump length, somite number, and protein content. It should be noted that dams administered 360 mg/kg/day 1,2,4-trichlorobenzene lost considerable body weight, which probably contributed to the delayed development of the offspring.

A series of studies were conducted with 1,2,4-trichlorobenzene in which pregnant mice were administered 0 or 130 mg/kg/day 1,2,4-trichlorobenzene by gavage on Gd 8–12 (Chernoff and Kavlock 1983; Gray and Kavlock 1984; Gray et al. 1986). Treatment with 1,2,4-trichlorobenzene had no significant effect on average litter weight, pup viability, or growth. Testing of the pups in a figure 8 maze for reactive locomotor activity levels on postnatal days 22, 58, and 200 showed no significant differences between pups from treated groups and controls. Examination of female pups at age 30 days showed no significant effect on percent vaginal patency. Breeding of the F1 pups resulted in no significant effects on percent pregnant, age at parturition, F2 litter size, or abnormalities in the F2 generation. Necropsy of F1 males at about 250 days of age showed no significant effects on body weight and weight of the liver, testes, seminal vesicles, or right kidneys.

In the multi-generation reproductive study conducted by Robinson et al. (1981), treatment with 1,2,4-trichlorobenzene did not affect neonates’ weight, litter size, or viability during the pre-weaning period in any generation. In addition, there were no treatment-related effects on locomotor activity in the F1 or F2 generation rats. Of the organs weighed in the pups (liver, lungs, heart, kidneys, adrenals, and gonads, as well as seminal vesicles in males), only the adrenals were affected by 1,2,4-trichlorobenzene. Absolute weight of the adrenals of high-dose F0 and F1 males and females were significantly increased relative to controls (7–12%), although with no clear dose-response relationship. Microscopic examination of liver and kidneys from F1 rats showed no histological damage. Results from blood chemistry tests in F0 and F1 rats did not reveal any treatment-related alterations. The dose levels of 1,2,4-trichlorobenzene at which the increase in adrenal weight were observed in F0 males and females were estimated by the investigators to be 33 and 53.6 mg/kg/day, respectively.

NOAELs and LOAELs for developmental effects are presented in Tables 3-3, 3-4, and 3-5 and are plotted in Figure 3-3, 3-4, and 3-5.

3.2.2.7. Cancer

Two long-term bioassays are available for 1,2,4-trichlorobenzene. Groups of F-344 rats (50/sex/group) were fed a diet containing 0, 100, 350, or 1,200 ppm 1,2,4-trichlorobenzene for 104 weeks (Moore 1994a). The diet provided doses of 0, 5.6, 19.4, or 66.5 mg/kg/day to males and 0, 6.9, 23.5, or 81.4 mg/kg/day to females. In the study in mice, groups of B6C3F₁ mice (50/sex/group) were fed a diet containing 0, 150, 700, or 3,200 ppm 1,2,4-trichlorobenzene (98.9% pure) for 104 weeks (Moore 1994b). The diet provided doses of 0, 21, 100.6, or 519.9 mg/kg/day to males and 0, 26.3, 127, or 572.6 mg/kg/day to females. Parameters evaluated in both studies included mortality (twice daily), clinical signs, body weight, and food consumption (weekly for 16 weeks and every 4 weeks thereafter), hematology (week 52 and 78 for cellular morphology and leukocyte differential, from control and highdose groups), organ weight (at termination, brain, brainstem, liver, kidneys, testes, and epididymis), and necropsy and histopathology findings (at termination, all major organs and tissues).

There was no evidence of treatment-related increases in the incidences of neoplasia in rats. In mice, treatment with 1,2,4-trichlorobenzene resulted in significant early mortality in both high-dose male and female groups. Percent survival on week 105 was 90, 88, 82, and 10% in males and 78, 76, 84, and 0% in females from the control, low-, mid-, and high-dose mice, respectively. Histological examination of tissue and organs from both unscheduled deaths and terminal sacrifice showed significantly increased incidence of hepatocellular carcinoma in mid- and high-dose groups (males: 8/50, 5/50, 27/50, and 50/50; females: 1/50, 1/50, 28/50, and 46/50). Neoplasms in other organs showed comparable incidences between the control and treated groups.

EPA classified 1,2,4-trichlorobenzene in Group D: not classifiable as to human carcinogenicity (IRIS 2010), or as a chemical for which there is “Inadequate Information to Assess Carcinogenic Potential” according to the Guidelines for Carcinogen Risk Assessment (EPA 2005a). EPA’s classification was done in 1988 and was last revised in 1991.

3.2.3.1. Death

No studies were located regarding death in humans after dermal exposure to trichlorobenzenes.

A dermal LD₅₀ of 6,139 mg/kg was reported for 1,2,4-trichlorobenzene in Sprague-Dawley rats (Brown et al. 1969). This value is presented in Table 3-6. The investigators noted that low doses caused depression of activity, whereas lethal doses induced extensor convulsions, and that all deaths occurred within 5 days of exposure. Dermal LD₅₀ values of 300 and 305 mg/kg were estimated for 1,2,4-trichlorobenzene in mice applied doses ranging from 122 to 769 mg/kg (Yamamoto et al. 1978). During the 7-day observation period, no deaths occurred in the group dosed with 122 mg/kg 1,2,4-trichlorobenzene. No information was located regarding 1,2,3-trichlorobenzene or 1,3,5-trichlorobenzene.

Application of 0.5 mL of undiluted 1,2,4-trichlorobenzene to a shaven area of the back of guinea pigs 6 hours/day, 5 days/week for 3 weeks resulted in the death of an unspecified number of guinea pigs; the time of death was also not specified (Brown et al. 1969).

3.2.3.2. Systemic Effects

The highest NOAEL values and all LOAEL values from each study for systemic effects in each species and duration category are recorded in Tables 3-6, 3-7, and 3-8.

No studies were located regarding systemic effects in humans after dermal exposure to trichlorobenzenes.

Respiratory Effects. Application of technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin of rabbits in doses of up to 450 mg/kg 5 days/week for 4 weeks did not induce histological alterations in the respiratory tract including the nasal turbinates (Rao et al. 1982).

Cardiovascular Effects. No histological alterations were observed in the heart from rabbits administered 0.2 mL of a 100% solution of technical-grade 1,2,4-trichlorobenzene (97 mg/kg) to the ear 3 times/week for 13 weeks (Powers et al. 1975). Similar results were reported in rabbits following application of technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin in doses of up to 450 mg/kg, 5 days/week for 4 weeks (Rao et al. 1982).

Gastrointestinal Effects. Application of technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin of rabbits in doses of up to 450 mg/kg 5 days/week for 4 weeks did not induce histological alterations in the gastrointestinal tract, including the nasal turbinates (Rao et al. 1982).

Hematological Effects. No treatment-related hematological alterations were reported in rabbits following application of technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin in doses of up to 450 mg/kg, 5 days/week for 4 weeks (Rao et al. 1982).

Musculoskeletal Effects. Histological examination of skeletal and bone from rabbits administered technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin in doses of up to 450 mg/kg, 5 days/week for 4 weeks did not show treatment-related effects (Rao et al. 1982).

Hepatic Effects. In an acute lethality study in mice applied single doses of 1,2,4-trichlorobenzene ranging from 123 to 769 mg/kg onto the skin, mice that survived the highest dose showed congestion and necrosis of the liver (Yamamoto et al. 1978). Guinea pigs that died following application of 0.5 mL of undiluted 1,2,4-trichlorobenzene to a shaven area of the back for 6 hours/day, 5 days/week for 3 weeks showed necrotic foci in the liver (Brown et al. 1969).

Table 3-6

Levels of Significant Exposure to 1,2,4-Trichlorobenzene - Dermal.

Table 3-7

Levels of Significant Exposure to 1,2,3-Trichlorobenzene - Dermal.

Table 3-8

Levels of Significant Exposure to 1,3,5-Trichlorobenzene - Dermal.

No histological alterations were observed in the liver from rabbits administered 0.2 mL of a 100% solution of technical-grade 1,2,4-trichlorobenzene (97 mg/kg) to the ear 3 times/week for 13 weeks (Powers et al. 1975). Application of technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin of rabbits in doses of up to 450 mg/kg, 5 days/week for 4 weeks did not induce histological alterations in the liver; grossly, however, the liver of rabbits treated with 450 mg/kg did show slight pallor (Rao et al. 1982).

Renal Effects. No histological alterations were reported in the kidneys from rabbits applied 0.2 mL of a 100% solution of technical-grade 1,2,4-trichlorobenzene (97 mg/kg) to the ear 3 times/week for 13 weeks (Powers et al. 1975). No histological alterations were reported in the kidneys from rabbits following application of technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin in doses of up to 450 mg/kg, 5 days/week for 4 weeks (Rao et al. 1982). However, urinalysis revealed a slight but significant increase in urinary coproporphyrin in high-dose males on day 24 of the study, which was considered only a slight or questionable effect of treatment.

Endocrine Effects. Microscopic examination of the pituitary gland, pancreas, adrenal gland, and thyroid and parathyroid glands from rabbits administered technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin in doses of up to 450 mg/kg, 5 days/week for 4 weeks showed no significant treatment-related alterations (Rao et al. 1982).

Dermal Effects. Application of 1,2,4-trichlorobenzene in concentrations of 70–100% to the skin of mice produced erythema, but histological examination of the skin showed no remarkable change (Yamamoto et al. 1978). Application of 0.05 mL of a 75% solution of 1,2,4-trichlorobenzene to the shaved intact shoulder of guinea pigs for 24 hours produced no to mild irritation in young animals, but moderate to severe irritation in older guinea pigs (E.I. DuPont 1971). In a repeated treatment study, 1 mL of undiluted 1,2,4-trichlorobenzene was applied in a patch of lint to the shaved skin of rabbits for 6 hours during 3 consecutive days (Brown et al. 1969). Seven days after the first application, histological examination of the skin showed spongiosis, acanthosis, and parakeratosis.

Repeated applications of a 10% solution of 1,2,3-trichlorobenzene to the abraded belly of rabbits caused questionable irritation and edema that healed normally (Dow Chemical 1956). When the solution was applied to intact skin, essentially no response was observed except for slight exfoliation after six applications. Application of undiluted 1,2,3-trichlorobenzene to the intact skin induced slight reddening to slight exfoliation after seven applications. However, in the abraded area, the undiluted chemical produced moderate reddening of the skin, slight edema, and trace of necrosis; healing was described as ordinary (Dow Chemical 1956).

In a study with 1,3,5-trichlorobenzene, 500 mg of the chemical was applied to the abraded or intact skin of six rabbits (Jorgenson et al. 1976). The test sites were covered and 24 hours later, the excess compound was removed and the sites were scored for erythema and edema. All treated rabbits showed erythema and edema at the 24-hour reading, and only three rabbits showed erythema at the 72-hour reading. The chemical was considered mildly irritating.

Intermittent application of 0.5 mL of undiluted 1,2,4-trichlorobenzene to guinea pigs or 1 mL to rabbits for 3 weeks produced spongiosis, acanthosis, and parakeratosis in both species (Brown et al. 1969). Rabbits applied 0.2 mL of a 5% solution of technical-grade 1,2,4-trichlorobenzene (4.8 mg/kg) onto the ventral surface of the ear 3 times/week for 13 weeks showed slight redness with slight scaling and desquamation that did not increase in severity after 39 exposures (Powers et al. 1975). Rabbits applied 25 or 100% solutions (24 or 97 mg/kg) showed moderate to severe irritation characterized by slight to severe erythema, severe scaling, desquamation and encrustation with slight enlargement of the follicles, some hair loss, and scarring. There was no evidence of acne form dermatitis.

A study was conducted in rabbits in which the animals were applied technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin in doses of 0, 30, 150, or 450 mg/kg, 5 days/week for 4 weeks (Rao et al. 1982). At termination, the skin of all treated rabbits showed localized effects considered slight at the low- and mid-dose levels and moderate at the high-dose level. The effects consisted of an area where regrowing fur was matted by a white bran-like scale, slight thickening of the skin, fissures which progressed to erosions and shallow ulcers, and erythema. Increasing dose increased the affected area. Microscopically, the skin site showed changes including inflammation, focal erosion and ulcers, and accumulation of inflammatory cells with varying degrees of exudation. Some rabbits showed slight superficial edema with slight fibrosis.

Painting 0.03 mL of a 30% solution of 1,2,4-trichlorobenzene 2 times/week for 2 years induced thickening and keratinization of the epidermis followed by inflammation (Yamamoto et al. 1982).

Ocular Effects. Instillation of a 10% solution of 1,2,3-trichlorobenzene to the eyes of rabbits followed by washing with water produced marked pain, slight conjunctival irritation, and trace of corneal injury (Dow Chemical 1956). The corneal injury almost completely healed in 24 hours, and irritation almost completely healed in 48 hours. In the unwashed eye, there was marked pain, conjunctival irritation and no corneal injury; complete healing occurred in 24 hours. In unwashed eyes instilled with undiluted 1,2,3-trichlorobenzene, there was a trace of pain, slight conjunctival irritation, and no corneal injury; healing occurred in 48 hours. The same was found in the washed eye, but healing occurred in 24 hours.

In a study with 1,3,5-trichlorobenzene, an amount of 100 mg of the chemical was applied into the eyes of rabbits (Jorgenson et al. 1976). Some rabbits had the compound washed out at 30 seconds or 5 minutes after application, or did not have the compound washed out. The eye was graded for ocular lesions at 24, 48, 72, and 96 hours. There was no corneal damage in rabbits that underwent washing, but minor damage was observed in the no-wash group. The cornea returned to normal within 3 days. Occasional circumcorneal injection was seen in some rabbits, but all effects on the iris disappeared by posttreatment day 4. Conjunctival responses occurred in all treated rabbits and generally involved varying degrees of redness, chemosis, and discharge. The eyes of the rabbits in the 30-second wash group returned to normal within 24 hours, but the 5-minute wash group was not normal until day 3, and the no-wash group did not return to normal until day 7. The investigators concluded that 1,3,5-trichlorobenzene produced mild transitory eye irritation.

Histological examination of the eyes from rabbits administered technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin in doses of up to 450 mg/kg, 5 days/week for 4 weeks showed no significant treatment-related alterations (Rao et al. 1982).

Body Weight Effects. Application of 0.2 mL of a 100% solution of technical-grade 1,2,4-trichlorobenzene (97 mg/kg) to the ear of rabbits 3 times/week for 13 weeks did not affect body weight (Powers et al. 1975). Application of technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin of rabbits in doses of up to 450 mg/kg, 5 days/week for 4 weeks did not significantly affect body weight (Rao et al. 1982).

3.2.3.3. Immunological and Lymphoreticular Effects

No histological alterations were reported in the spleen from rabbits administered 0.2 mL of a 100% solution of technical-grade 1,2,4-trichlorobenzene (97 mg/kg) to the ear 3 times/week for 13 weeks (Powers et al. 1975). Similar results were reported for the spleen, thymus, and lymph nodes from rabbits following application of technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin in doses of up to 450 mg/kg, 5 days/week for 4 weeks (Rao et al. 1982).

Tests for skin sensitization conducted with 1,2,4-trichlorobenzene or 1,3,5-trichlorobenzene in guinea pigs were negative (Brown et al. 1969; E.I. DuPont 1971; Jorgenson et al. 1976).

3.2.3.4. Neurological Effects

Microscopic examination of the brain, spinal cord, and peripheral nerve from rabbits applied technical-grade 1,2,4-trichlorobenzene onto a shaved area of the back skin in doses of up to 450 mg/kg, 5 days/week for 4 weeks showed no significant treatment-related alterations (Rao et al. 1982).

3.2.3.5. Reproductive Effects

Application of technical-grade 1,2,4-trichlorobenzene to a shaved area of the back skin of male and female rabbits in doses of up to 450 mg/kg, 5 days/week for 4 weeks did not induce gross or microscopic alterations in the reproductive organs (Rao et al. 1982).

3.2.3.6. Developmental Effects

No studies were located that assessed developmental effects in humans or animals following dermal exposure to trichlorobenzenes.

3.2.3.7. Cancer

A 2-year cancer study was conducted with 1,2,4-trichlorobenzene in mice (Yamamoto et al. 1982). Groups of Slc:ddY mice (75/sex/group) were painted with 0.03 mL of a 30 or 60% solution of 1,2,4-trichlorobenzene 2 times/week for 104 weeks. There was high mortality both in the treated and control groups, beginning on week 30. At week 83, <10% of treated females and <15% of treated males survived. The main causes of death were respiratory infections, amyloidosis, and tumors. Histological alterations in tissues appeared more prevalent in the high-dose group, but the number of mice examined was not indicated. Tumors developed in the lungs, kidneys, stomach, urinary bladder, mammary gland, and skin in both treated and control groups. There was no indication of the time to first tumor appearance or whether the tumors were all found in different animals or were multiple tumors in the same animal.

Skin tumors were classified as squamous cell carcinoma, papilloma, and fibroma. This study is inadequate for assessing the potential carcinogenicity of 1,2,4-trichlorobenzene following dermal exposure.

3.4.1.1. Inhalation Exposure

Quantitative data on the absorption of trichlorobenzenes following inhalation exposure are not available for animals. However, indirect evidence that 1,2,4-trichlorobenzene is absorbed through inhalation can be inferred from minor liver effects in rats following inhalation exposure (Kociba et al. 1981).

3.4.1.2. Oral Exposure

Evidence from elimination studies in animals indicate that trichlorobenzene isomers are rapidly and extensively absorbed through the gastrointestinal tract in animals.

1,2,3-Trichlorobenzene. Radiolabeled 1,2,3-trichlorobenzene has been detected in both the urine and feces of rats following oral exposure. Specifically, 92% of administered radioactivity was eliminated through the urine and feces within 24 hours of administration of a single 10 mg/kg gavage dose of ¹⁴C-labeled 1,2,3-trichlorobenzene to male Sprague-Dawley rats (Chu et al. 1987). Overall excretion increased to 95% at 48 hours post ingestion. The percentage of the administered radioactivity in urine alone accounted for 56 and 59% of the total ingested dose at 24 and 48 hours, respectively. Therefore, assuming that none of the radioactivity excreted in the feces was absorbed, at least 59% of the administered dose was absorbed. These results are also consistent with as much as 95% of the administered dose may have been absorbed if all radiolabeled material excreted in the feces had first been absorbed and excreted through the biliary system.

1,2,4-Trichlorobenzene. Within 7 days after receiving a dose of 50 mg/kg of ¹⁴C-labeled 1,2,4-trichlorobenzene, male Wistar rats excreted 66 and 17% of the radioactivity in urine and feces, respectively, suggesting that at least 66% of the administered dose was absorbed (Tanaka et al. 1986). Radioactivity in expired air accounted for 2.1% of the absorbed dose. Excretion in all three excreta reached a peak on day 3, indicating rapid absorption and elimination. Measurements of biliary excretion for 4 days in bile-cannulated rats showed that radioactivity in bile accounted for 45% of the administered dose (Tanaka et al. 1986). Bakke et al. (1992) reported that >60% of a 21 mg/kg dose of ¹⁴C-1,2,4-trichlorobenzene was excreted in bile, while 21% was excreted in the urine of bile-cannulated male Sprague-Dawley rats within 24 hours. Findings from this study indicate an 81% absorption rate following oral exposure to 1,2,4-trichlorobenzene. In control non-cannulated rats, 70 and 9% of the radioactivity was excreted within 24 hours in urine and feces, respectively (Bakke et al. 1992). Following 7 consecutive days of oral dosing of male Sprague-Dawley rats with 181.5 mg/kg/day ¹⁴C-1,2,4-trichlorobenzene, radioactivity in urine was still detectable 21 days after the first oral administration; total radioactivity detected in urine accounted for approximately 72% of the administered dose (Smith and Carlson 1980). Radioactivity in the feces was not detectable past day 15 and accounted for only 4% of the administered dose. Thus, between 72 and 76% of the administered dose was absorbed in this study.

¹⁴C-Labeled material was excreted by both monkeys and rats following oral exposure to a 10 mg/kg dose of ¹⁴C-labeled 1,2,4-trichlorobenzene. By 24 hours after dosing, female Rhesus monkeys had excreted about 40% of the administered radioactivity in the urine and <1% in the feces. Male albino rats, however, excreted 84% of the administered radioactivity in the urine and 11% in the feces by 24 hours. With intravenous administration of 10 mg/kg ¹⁴C-labeled 1,2,4-trichlorobenzene, monkeys eliminated about 22% of the administered radioactivity in urine within 24 hours (none was detected in feces), whereas radioactivity in 24-hour urine and feces in rats accounted for 78 and 7% of the administered dose, respectively (Lingg et al. 1982). These data suggest that differences in elimination rates between rats and monkeys may be due to species differences in metabolic rate or elimination rate, rather than absorption rate.

1,3,5-Trichlorobenzene. The excretion of radioactivity derived from 1,3,5-trichlorobenzene in both the urine and feces of rats has also been monitored following oral exposure. Within 24 hours of a single 10 mg/kg dose of ¹⁴C-labeled 1,3,5-trichlorobenzene to male Sprague-Dawley rats, 82% of radioactivity was eliminated through the urine and feces (Chu et al. 1987). Overall excretion increased to 89% at 48 hours post ingestion. The percentage of administered radioactivity in urine accounted for 47 and 50% at 24 and 48 hours, respectively. Thus, assuming that none of the radioactivity excreted in the feces was absorbed, at least 50% of the administered dose was absorbed. These results are also consistent with as much as 89% of the administered dose may have been absorbed if all radiolabeled material excreted in the feces had first been absorbed and excreted through the biliary system.

3.4.1.3. Dermal Exposure

No quantitative data were located on the absorption of trichlorobenzenes following dermal exposure of animals. Theoretical predictive models based on chemical and physical properties, however, have indicated that 1,2,4-trichlorobenzene has a significant potential for dermal absorption (Fiserova-Bergerova et al. 1990). Specifically, the findings of this study suggest that dermal exposure to 1,2,4-trichlorobenzene is expected to raise the biological levels of this isomer 30% above those occurring during inhalation exposure to threshold limit values. 1,2,4-Trichlorobenzene absorption can also be inferred from evidence of systemic toxicity in animals following dermal exposure (Brown et al. 1969; Yamamoto et al. 1978).

3.4.2.1. Inhalation Exposure

No data on the distribution of trichlorobenzenes following inhalation exposure were located for animals.

3.4.2.2. Oral Exposure

Trichlorobenzene isomers are readily distributed throughout bodily tissues in animals. However, the level of distribution and length of retention vary between isomers. Several studies have been conducted with ¹⁴C-labeled trichlorobenzenes. It should be noted that generally in these studies no distinction can be made between parent compound, metabolites, and recycled carbon incorporated into body macromolecules.

1,2,3-Trichlorobenzene. Radioactivity was present in the blood and tissues of male Sprague-Dawley rats 0.5 hours following gavage administration of 10 mg/kg ¹⁴C-labeled 1,2,3-trichlorobenzene (Chu et al. 1987). Tissue concentrations peaked at 24 hours with very high concentrations appearing in the gastrointestinal tract (2,180 ppb), liver (277 ppb), fat (1,920 ppb), kidney (399 ppb), and bladder (284 ppb). Seven days after dosing, radioactivity in the brain, muscle, testes, and seminal vesicles were no longer detectible. Radioactivity was nearly undetectable in the liver, fat, and skin by 56 days after dosing (Chu et al. 1987). Chu et al. (1987) reported gas chromatography (GC) data that indicated that most of the radioactivity in skin, liver, and fat was the parent compound, whereas that in muscle and kidney was predominantly more polar metabolites.

1,2,4-Trichlorobenzene. Radioactivity was found in the blood and tissues of male Sprague-Dawley rats 0.5 hours after oral dosing with 10 mg/kg ¹⁴C-labeled 1,2,4-trichlorobenzene (Chu et al. 1987). Levels peaked around 4 hours and declined thereafter. High concentrations remained present in the bladder (1,280 ppb), kidney (1,160 ppb), fat (4,260 ppb), skin (243 ppb), liver (680 ppb), and adrenal glands (850 ppb) at 24 hours. Seven days after dosing, radioactivity was no longer detectable in the brain, spleen, muscle, testes, seminal vesicles, epididymis, or prostate. Most tissues showed levels of radioactivity barely distinguishable from background levels 28 days after dosing (<10 ppb except adrenals with 40 ppb) (Chu et al. 1987). Sprague-Dawley rats given a daily oral dose of 181.5 mg/kg ¹⁴C-labeled 1,2,4-trichlorobenzene for 7 consecutive days showed the highest initial concentration of radioactivity in the adrenal glands (Smith and Carlson 1980). This level declined rapidly and no radioactivity could be detected 11 days after dosing. Abdominal fat had the highest concentrations on day 1 (2,033 dpm/g) and maintained detectable concentrations (~20% of day 1 level) through the remainder of the 16-day observation period. The liver also maintained detectable concentrations (1,075 dpm/g on day 1 and 317 dpm/g on day 19) throughout the entire observation period (Smith and Carlson 1980). High levels of radioactivity were found in adipose tissue and skin (81 and 15% of administered dose, respectively) 12 hours following administration of a single 50 mg/kg oral dose of ¹⁴C-labeled 1,2,4-trichlorobenzene to male Wistar rats. Radioactivity was also detectable in muscle and intestine at this time (~8 and 5% of administered dose). By 168 days after dosing, radioactivity was virtually undetectable in all examined tissues (Tanaka et al. 1986).

1,3,5-Trichlorobenzene. An early study by Parke and Williams (1960) indicated a wide distribution of 1,3,5-trichlorobenzene following a 500 mg/kg dose in rabbits. Specifically, 13% of the administered dose was detected in the feces, 23% in the gut, 5% in the pelt, 5% in the depot fat, and 22% in the carcass 8 days after administration. A later study revealed radioactivity in the blood and tissues 0.5 hours after oral dosing of male Sprague-Dawley rats with 10 mg/kg of ¹⁴C-labeled 1,3,5-trichlorobenzene (Chu et al. 1987). As with the other isomers, levels of radioactivity peaked at 1 day after administration. The peak concentrations in tissues with the highest concentrations showed the following order: fat (8,960 ppb) > gastrointestinal tract > salivary gland > adrenal ≈ bladder > liver > kidney > pancreas > epididymis > prostate > skin > lung > seminal vesicle (410 ppb). Peak tissue concentrations were generally higher following administration of 1,3,5-trichlorobenzene compared with 1,2,3- and 1,2,4-trichlorobenzene (Chu et al. 1987). Chu et al. (1987) reported GC data that indicated that most of the radioactivity in skin, liver, and fat was the parent compound, whereas that in muscle and kidney was predominantly more polar metabolites. Côté et al. (1988) found an accumulation of trichlorobenzene isomers in the fat and liver of rats, indicating that 1,3,5-trichlorobenzene accumulated at a higher level in these tissues than 1,2,4- and 1,2,3-trichlorobenzene when presented at 1,000 ppm in food for 13 weeks. The levels of isomer in the fat (15.5–76 ppm in males; 7.8–49 ppm in females) were one order of magnitude higher than those found in the liver (1.4–4.3 ppm in males; 0.73–1.9 ppm in females).

Trichlorobenzenes have been identified in human breast milk; therefore, infants may also be potentially exposed through breast feeding (see Section 6.6, Exposures of Children).

3.4.2.3. Dermal Exposure

Quantitative data on the distribution of trichlorobenzenes following dermal exposure were not located for humans or animals.

3.4.4.1. Inhalation Exposure

No data were found on the elimination and excretion of trichlorobenzenes following inhalation exposure in animals.

3.4.4.2. Oral Exposure

All three isomers of trichlorobenzene have been shown to be rapidly and efficiently eliminated following oral exposure, principally via metabolites in the urine in rabbits (Jondorf et al. 1955) and rats (Bakke et al. 1992; Chu et al. 1987), although enterohepatic biliary circulation has been demonstrated in bile-cannulated rats (Bakke et al. 1992).

1,2,3-Trichlorobenzene. Jondorf et al. (1955) illustrated the rapid elimination of 1,2,3-trichlorobenzene in Chinchilla rabbits administered a 500 mg/kg oral dose. Five days after dosing, 78% of the administered dose had been excreted as trichlorophenols and 62% as oxygen conjugates in urine, with no trace of the isomer found in feces. In rats, 92% of ¹⁴C-labeled 1,2,3-trichlorobenzene was eliminated through the urine and feces within 24 hours of a single 10 mg/kg gavage dose (Chu et al. 1987). Overall excretion increased to 95% at 48 hours post ingestion. The percentage of the radiolabeled 1,2,3-isomer in urine alone accounted for 56 and 59% at 24 and 48 hours, respectively. Data for radioactivity in tissues measured at 0.5, 1, 2, and 4 hours and 1, 2, 7, 14, 28, and 56 days after dose administration were fit to a two-compartment elimination model; estimated half-lives were 9.2 and 145 hours for the first and second compartments, respectively.

1,2,4-Trichlorobenzene. Chinchilla rabbits excreted 42% of a single 500 mg/kg oral dose of 1,2,4-trichlorobenzene as trichlorophenols 5 days after administration (Jondorf et al. 1955). This same study also noted that 38% of the administered dose was excreted in the urine as oxygen conjugates during the same time frame. A later study in rats dosed with 50 mg/kg ¹⁴C-labeled 1,2,4-trichlorobenzene revealed 66 and 17% excretion of radioactivity in urine and feces, respectively, 7 days post administration (Tanaka et al. 1986). Radioactivity in expired air consisted of 2.1% of the absorbed dose. Excretion in all three excreta reached a peak on day 3. Biliary excretion accounted for 45% of the radioactivity. The authors considered the enterohepatic circulation of trichlorobenzene metabolites in the body as a possible explanation for the difference in biliary and fecal excretion rates. Bakke et al. (1992) reported that >60% of a 21 mg/kg dose of ¹⁴C-1,2,4-trichlorobenzene was excreted in bile, while 21% was excreted in the urine of bile-cannulated Sprague-Dawley rats within 24 hours. In control rats without bile cannulation, 70 and 9% of the administered radioactivity was excreted within 24 hours in the urine and feces, respectively (Bakke et al. 1992).

Following a longer period of exposure, 181.5 mg/kg/day of ¹⁴C-labeled 1,2,4-trichlorobenzene for 7 consecutive days, Smith and Carlson (1980) found that the urinary and fecal excretion of the isomer-derived radioactivity in Sprague-Dawley rats peaked during the first 3 days of dosing and declined rapidly thereafter. Radioactivity in the feces was not detectable past day 15 and accounted for only 4% of the administered dose. Urinary excretion, however, displayed detectable radioactivity 21 days after the first oral administration. Radioactivity in the urine accounted for approximately 72% of the administered dose.

Showing variations between species, Lingg et al. (1982) measured excretion rates in both monkeys and rats given a 10 mg/kg oral dose of ¹⁴C-labeled 1,2,4-trichlorobenzene. By 24 hours after dosing, monkeys had excreted 40% of the administered dose in the urine. Less than 1% was found in the feces. Rats excreted 84% of the oral dose via the urine by 24 hours; 11% was found in feces. Following intravenous administration of 10 mg/kg ¹⁴C-labeled 1,2,4-trichlorobenzene, monkeys eliminated about 22% of the administered radioactivity in urine and none in the feces 24 hours after exposure. Rats, on the other hand, excreted 78 and 7% of the administered dose in urine and feces at 24 hours, respectively. Regardless of the route of exposure, rats excreted radioactivity at a rate roughly 2–3 times faster than monkeys following administration of ¹⁴C-labeled 1,2,4-trichlorobenzene.

1,3,5-Trichlorobenzene. In Chinchilla rabbits dosed with a single 500 mg/kg dose by gavage, 9% of the administered dose was excreted as trichlorophenols in the urine during the 5 days after dosing (Jondorf et al. 1955), while 23% was excreted as oxygen conjugates. A follow-up study indicated that only 4 and 14% of a 500 mg/kg dose were eliminated as phenols 8 and 9 days after dosing, respectively (Parke and Williams 1960). A much higher level of excretion, 82% of ¹⁴C-labeled 1,3,5-trichlorobenzene, was found in the urine and feces of Sprague-Dawley rats within 24 hours of a single 10-mg/kg gavage dose (Chu et al. 1987). Overall excretion increased to 89% at 48 hours post ingestion. The percentage of the radiolabeled 1,3,5-isomer in urine alone accounted for 47 and 50% at 24 and 48 hours, respectively. Data for radioactivity in tissues measured at 1, 2, 7, 14, 28, and 56 days after dose administration were fit to a two-compartment elimination model; estimated half-lives were 8 and 67.5 hours for the first and second compartments, respectively (Chu et al. 1987).

3.4.4.3. Dermal Exposure

No data on the elimination and excretion of trichlorobenzenes following dermal exposure were located for animals.