The Clara cell: an electron microscopy examination of the terminal bronchioles of rats and monkeys following inhalation of hexachlorocyclopentadiene.

The effects of inhalation of hexachlorocyclopentadiene (Hex) up to 14 wk on the terminal bronchioles of rats and monkeys was examined by electronic microscopy. Exposed rats elicited a concentration-related increase in the incidence of electron-lucent inclusions in the bronchiolar Clara cells when compared to controls. The inclusions in the high-concentration (0.2 ppm) group were round and more abundant than the rod-shaped inclusions observed in the intermediate (0.05 ppm) and low-concentration (0.01 ppm) exposure group. No ultrastructural changes were observed that could be attributed to the inhalation of Hex vapor in exposed monkeys. The origin and significance of these inclusions is discussed in light of the literature.

Effects of inhalation exposure to hexachlorocyclopentadiene on rats and monkeys.

Hexachlorocyclopentadiene (Hex or C-56) is a highly reactive intermediate used in the production of some insecticides, flame retardants, and resins. The present study was conducted to evaluate the inhalation toxicity of high-purity Hex (97.7%) in rats and monkeys to provide information on the potential hazards of accidental exposure of workers to Hex vapors. Acute, range-finding (14-d), and subchronic (90-d) inhalation studies were conducted with Sprague-Dawley rats and subchronic (90-d) inhalation studies were conducted with cynomolgus monkeys. Both acute and range-finding studies with rats showed a steep dose-response curve, and male rats were more sensitive than females. In the range-finding study with rats the threshold of toxicity for Hex was 0.11-0.5 ppm. Histopathologic examination on rats in the 0.5 ppm group revealed lesions in the olfactory and bronchiolar epithelium and inflammatory exudate in the lumens of the respiratory tract; these changes were consistent with observed impaired respiratory function, confirming the lung as the main target organ. Recovery and regression of lung lesions in rats were noted 2-3 wk after termination of exposure. In the 90-d study, inhalation of Hex vapors at concentrations up to 0.2 ppm for 6 h/d, 5 d/wk, produced no detectable physical or clinical effect and no remarkable gross or histological alterations in rats or monkeys.

Dominant lethal studies with technical chlordane, HCS-3260, and heptachlor: heptachlor epoxide.

Male albino mice in groups of eight were each given single doses, either by gavage or by intraperitoneal injection, of either technical chlordane (50 or 100 mg/kg), HCS-3260 (50 or 100 mg/kg), or heptachlor:heptachlor epoxide (25:75) (7.5 or 15 mg/kg). The males were subsequently mated with three untreated females for six consecutive weeks. No dominant lethal changes among females that had mated with the treated males were produced.