A Two-Generation Reproduction Study with Monochlorobenzene Vapor in Rats

Groups of 30 male and 30 female Sprague–Dawley CD rats, designated as the F0 generation, were exposed to vapor of monochlorobenzene (MCB) at target concentrations of 0, 50, 150, or 450 ppm for 10 weeks prior to mating and during mating, gestation, and lactation. The progeny of the F0 generation was designated as the F1 generation and groups of 30 male and 30 female F1 animals were exposed to the same concentrations of MCB as the F0 parents. Exposure of F1 animals was initiated 1 week postweaning and lasted 11 weeks pnor to mating and through mating, gestation, and lactation. All F2 pups were observed through weaning at which time they were killed. Observations made during the study included body weights, food consumption, mating and fertility indices, pup and litter survival indices, and histopathology of selected tissues. No mortality was observed during the course of this study. Body weights and food consumption for all treated groups were comparable to controls during the growth period. Maternal body weight data during gestation and lactation were also comparable between the control and treated groups. Mating and fertility indices for males and females for both generations appeared unaffected by treatment. Pup and litter survival indices for all treated groups were comparable to those of controls. Hepatocellular hypertrophy and renal changes (tubular dilation with eosinophilic material, interstitial nephritis, and foci of regenerative epithelium) were observed among F0 and F1 male rats exposed to 150 and 450 ppm MCB. The incidence of bilateral degeneration of the testicular germinal epithelium was increased among F0 adults in the high-concentration group and this lesion was observed only unilaterally in the mid- and high-concentration group F1 adults. The relationship of these testicular changes to exposure to MCB is unclear because there did not appear to be any increase in intensity and/ or incidence of testicular lesions among F1 adults that had longer exposure. In addition, overall mean mating and fertility indices for all groups were comparable for both generations. In summary, exposure of rats to MCB at levels of 50, 150, or 450 ppm did not have any adverse effects on reproductive performance or fertility of male and female rats.