Evaluation of the pulmonary inhalation toxicity of diborane

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This study aimed to clarify the subacute pulmonary and testicular toxicity of diborane (B_2H_6, CAS : 19287-45-7) in rats. Male Wister rats were exposed for 8 weeks to 0.11 ppm pr 0.96 ppm of diborane for 6 hours/day, 5days/week. The control group wes exposed to filtered air. Bronchoalveolar lavage fluid (BALF), hematological, biochemical and histopathological examinations were conducted. Sperm counts and spermatic morphological changes were examined in epididymides, and histopathological examination was carried out in testes. BALF examinations revealed that the percentage of neutrophils increased in a dose-dependent manner and that of macrophages decreased in rats exposed to 0.96 ppm. Quantities of total and individual phospholipids in BALF increased in rats exposed to 0.96ppm. The proportion of phosphatidylglycerol plus sphingomyelin decreased, and phosphatidylethanolamine and phosphatidylinositol increased in rats exposed to 0.96 ppm. LDH increased in rats exposed to 0.96 ppm, and ALP showed a dose-dependent increase. In serum, alpha _1-antitrypsin and superoxide dismutase (SOD) activities increased in rats exposed to 0.11 or 0.96 ppm. These changes showed dose-dependent effects on the lung in rats exposed to diborane, possbly indicating that the hyperenergia of type II cells with proliferation and/or hypertrophy without histopathological changes occurred even in rats exposed to 0.11 ppm. Testicular examinations revealed no particular findings. The TLV-TWA of diborane (0.1ppm)(ACGIH 1991) seems to be high and possibly unsafe, considering that the no-observed-effect level over 8 weeks for rat lung was under 0.11 ppm. The current occupational exposure limit of 0.1 ppm TLV-TWA recommended by ACGIH (1991) seems to be too prevent the effects of diborane on workers who may be repeatedly exposed to diborane. It is necessary to manage the working environment carefully in order to avoid exposure to diborane.