Subchronic inhalation toxicity of benzene in rats and mice.

A subchronic inhalation toxicity study of benzene was conducted in CD-1 mice and Sprague-Dawley rats. Four groups of animals consisting of 150 mice and 50 rats/sex each were exposed to concentrations of 1, 10, 30, and 300 ppm benzene vapor, 6 hours/day, 5 days/week, for 13 weeks. Additional groups of mice and rats, of equal size, were exposed under similar conditions to filtered air and served as control groups. Thirty mice and 10 rats/sex in each group were sacrificed after 7, 14, 28, 56, and 91 days of treatment. Criteria used to evaluate exposure-related effects included behavior, body weights, organ weights, clinical pathology, gross pathology, and histopathology. Fifty animals per sex of each species were exposed concurrently for cytogenetic studies. In addition, blood serum was obtained for immunological assays. The results of these two studies will be reported separately. No consistent exposure-related trends were seen in the clinical observations and body weight data. Exposure-related clinical pathology changes were seen in the high-level (300 ppm) animals of both species. In the mice, these changes included decreases in hematocrit, total hemoglobin, erythrocyte count, leukocyte count, platelet count, myeloid/erythroid ratios, and percentage of lymphocytes. Mean cell volume, mean cell hemoglobin, glycerol lysis time, and the incidence and severity of red cell morphologic changes were increased in the mice. In the rats, decreased lymphocyte counts and a relative increase in neutrophil percentages were the only exposure-related clinical pathology alterations. Histopathologic changes were present in the thymus, bone marrow, lymph nodes, spleen, ovaries, and testes of mice exposed to 300 ppm and in most cases the incidence and severity of the lesions were greater in the males. These changes in the testes and ovaries at 300 ppm were also seen at lower concentrations, but they were of doubtful biological significance. In rats, the only exposure-related lesion consisted of slightly decreased femoral marrow cellularity in the animals exposed to 300 ppm.

Subchronic inhalation toxicity of morpholine in rats.

The inhalation toxicity of 25-, 100-, and 250-ppm morpholine was investigated by 6 hr/day, 5 day/week exposures to Sprague-Dawley rats for 13 weeks. Irritant effects of morpholine exposures were evident mostly in the high exposure group; a reddish discharge was observed around the nose and mouth in the 250-ppm group rats after the first week; salivation was also observed. Ten rats/sex/dose level were sacrificed after 7 weeks. The high-level (250-ppm) exposure resulted in focal erosion and focal squamous metaplasia of the maxilloturbinates; effects were observed in 6/10 male rats and 2/10 female rats. There was also a sporadic increase of secretions in the Harderian gland sections. Almost all high-level rats sacrificed after 13 weeks demonstrated comparable effects; the lesions, which were increased in incidence and severity, involved the nasal septum and anterior nasal cavities in addition to the nasoturbinates and maxilloturbinates. Lesions of chronic murine pneumonia were increased in severity in the 250-ppm group. The only compound-related histomorphologic alterations observed in the 100-ppm group consisted of focal necrosis and necrotic cell debris in the nasal cavity of two female rats at terminal sacrifice. No exposure related effects were observed in the 25-ppm group. No significant compound-related effects on body weight, clinical chemistry, hematology, or organ weight data were observed.

Subchronic inhalation toxicity of 1,3-dichloropropene/1,2-dichloropropane (D-D) in mice and rats.

Groups of 28 male and 28 female CD-1 mice and Fischer 344 rats were exposed to a mixture of 1,3-Dichloropropene and 1,2-Dichloropropane (D-D) vapors. Exposure concentrations were 0, 5 (4.7), 15 (14.4), or 50 (53.7) ppm, 6 h/d, 5 d/wk for 6 or 12 wk. The following parameters were evaluated: pharmacotoxic signs, body weights, hematology (HGB, HCT, RBC, WBC, and diff. leukocyte count), serum chemistry (BUN, GLU, ALB, GPT, and ALP), urinalysis, gross pathology, histopathology, organ weights, and organ weight/body weight ratios of brain, heart, liver, kidneys, testes or ovaries, and adrenals. The only exposure-related clinical effects observed were increased mean liver/body weight ratios of male rats and mean kidney/body weight ratios of female rats at the 50 ppm exposure level. Slight to moderate diffuse hepatocytic enlargement in 12 of 21 of the 50-ppm male mice after 12 wk exposure was the only compound-related histopathologic change present.

Effects of aging on the induction of angiosarcoma.

Adult, Sprague-Dawley albino rats of four different ages (6, 18, 32 and 52 weeks) were exposed to 940 ppm vinyl chloride by inhalation for 24 weeks, 5 days/week, 7 hr/day. In each age group, there were 110 to 128 males and the same number of females. The similarly housed control group, which was not exposed to vinyl chloride, consisted of the same number of males and females in each age group. All animals that died spontaneously, or were sacrificed moribund, or were killed at scheduled times (3, 6 and 9 months after initial exposure) were autopsied. All organs were examined grossly, and several tissues from each animal were examined microscopically. The older the rats were when they were first exposed, the greater the incidence of angiosarcomas. The incidences of angiosarcomas in the four age groups (from youngest to oldest) in the exposed males in the nonscheduled sacrifice groups were: 0/37 (0%); 0/44 (0%); 3/45 (6.7%); and 13/55 (24%). Similarly, for the females, these incidences were: 2/38 (5.3%); 7/47 (15%); 23/49 (47%); and 11/54 (20%). Most of the angiosarcomas were highly anaplastic, primary tumors in the livers that metastasized to the lungs. Only one angiosarcoma was seen in all the control rats; that occurred in subcutaneous tissue. This study demonstrated that older adult animals and females are more susceptible to the angiosarcoma-inducing effects of vinyl chloride than young adult animals and males, respectively.

Toxicity of low concentration long-term exposure to an airborne mixture of nitrous oxide and halothane.

To evaluate experimentally the questions of reproductive, teratological, cytogenetic, and tumorigenic sequelae of long-term exposures to escape levels of halothane plus nitrous oxide (N2O), male and female rats were exposed either to air, to 1 ppm halothane plus 50 ppm N2O, or to 10 ppm halothane plus 500 ppm N2O for 7 hr/day, 5 days/wk for appropriate periods of time. In one experiment, young adult female rats were exposed for 60 days, then mated and reexposed either staring with Day 1 or Day 6 of gestation until Day 15. The former were permitted to deliver naturally while the latter were delivered by C-section on Day 20. The young adult males used in breeding were also exposed for 60 days prior to mating and then for a total of 52 weeks thereafter. At termination, bone marrow cell and spermatogonial metaphase preparations were made and assessed for cytogenetic abnormalities. The mated females were evaluated for ovulation, pre- and post-implantation loss, fetal growth, fetal abnormalities, and early post-natal development, as appropriate. In a parallel experiment, 50 male and 50 female weanling rats in each group were exposed for 104 weeks to the same levels and then evaluated for tumor development with emphasis on the reticuloendothelial system. The results indicated a significant reduction in ovulation and implantation efficiency from exposure to the higher levels and slightly retarded fetal development at both levels. No teratological or abortifacient effects were noted. No tumorogenic effects were observed. However, cytogenetic damage to both bone marrow and spermatogonial cells was seen at both levels.

Chronic exposure to low concentrations of halothane-nitrous oxide: lack of carcinogenic effect in the rat.

The effects of prolonged exposure to low-concentration combinations of halothane and nitrous oxide on tumor incidence, especially with regard to the reticuloendothelial system, were studied. Three groups of 50 male and 50 female Fischer 344 rats each were studied. For seven hours/day, five days/week, for 104 weeks, Group I was exposed to filtered air (control); Group II, to halothane, 1 ppm, and nitrous oxide (N2O), 50 ppm; Group III, to halothane, 10 ppm, and N2O, 500 ppm. No evidence of exposure-related effects on body weight, appearance, behavior, survival, or hematologic findings was found. Histologic evaluation of the reticuloendothelial system and of other major organs revealed neither enhancement of the spontaneous tumor rate nor any unusual neoplasm. Thus, this study did not lend support to the hypothesis that these anesthetic agents in low concentrations are responsible for the reportedly higher than average incidence of reticuloendothelial malignancies in operating room personnel.

Chronic, inhalation exposure of rats, rabbits, and monkeys to 1,2,4-trichlorobenzene.

Three groups composed of rats, rabbits, and monkeys were exposed for 26 weeks to 1,2,4-trichlorobenzene (-TCB), and one group of each species was used as a control group. The nominal exposure concentrations of 1,2,4-TCB were 25.0, 50.0, and 100.0 ppm. Pulmonary function and operant behavior tests in monkeys, ophthalmoscopic examinations in rabbits and monkeys, and measurement of body weights and hematologic and serum biochemical determinations in all species were conducted before and during the exposure period. At termination of 1, 3, and 6 months of exposure, microscopic examination of selected rat tissues was performed. Microscopic changes were seen in the parenchymal of livers and kidneys from all groups of rats exposed to 1,2,4-TCB when sacrificed after 4 and 13 weeks of exposure, but no exposure-related abnormalities or other effects were seen after 26 weeks of exposure in any species.

Repeated topical applications of 1,2,4-trichlorobenzene. Effects on rabbit ears.

In a study to evaluate its acnegenic potential, increasing concentrations of 1,2,4-trichlorobenzene were applied topically to the ventral surface of the rabbit ear three times weekly for 13 weeks. Additional groups of rabbits received similar treatment with petroleum ether (solvent controls), received no treatment (negative controls), and received four once-weekly treatments with hexachlorodiphenyloxide, a known chloracnegenic agent (positive controls). Skin response to 1,2,4-trichlorobenzene was characterized grossly by dermal irritation directly related to the concentration of test material; there were the associated histologic changes of acanthosis and hyperkeratosis; there was no primary follicular involvement characteristic of acneform dermatitis. Dermal responses to hexachlorodiphenyloxide consisted of gross follicular enlargement, with waxy excretion on pressure, and severe scaling. The affected ear appeared thickened up to three times normal size and histologic sections showed primary follicular involvement characterized by marked thickening of the sheath and marked distention of the follicles with keratin, with resultant comedone formation, typical of chloracne.