BIOCHEMICAL EFFECTS OF SUBCHRONIC REPEATED EXPOSURES TO LOW AND MODERATE CONCENTRATIONS OF HYDROGEN SULFIDE IN FISCHER 344 RATS

Emissions of hydrogen sulfide (H2S) gas are commonly encountered in sour gas processing operations. In this study, systemic biochemical changes were assessed in Fischer 344 rats after a repeated exposure regime (8 h/ day, 5 days/ wk for 5 wk) to atmospheres containing 0, 1, 10, and 100 ppm (0, 1.4, 14, and 140 mg/ m 3) H2S. Biochemical activities were analyzed in lung, brain, and liver mitochondria for cytochrome oxidase, and in erythrocytes for superoxide dismutase and glutathione peroxidase. Exposure at the lowest concentration (1 ppm) did not cause any significant changes in these biochemical activities; however, rats exposed to increased concentrations of H S 2 (10 and 100 ppm) showed significantly lower activity (p < .05) of cytochrome oxidase in lung mitochondria than the control rats (0 ppm). The cytochrome oxidase activity in brain mitochondria also appeared to be lower in rats exposed to 10 ppm and 100 ppm H2S than in the control rats, but the differences were not statistically significant. In liver mitochondria, the activity of cytochrome oxidase was not affected by these exposures. A small decrease (~8%) in superoxide dismutase activity of erythrocytes was observed in rats exposed to 100 ppm H2S. It is suggested that repeated exposures to even low concentrations of H 2S can reduce the activity of a critical mitochondrial enzyme, cytochrome oxidase, in lungs and possibly other tissues. This reduction in mitochondrial cytochrome oxidase could be an early-stage biochemical event of H2S toxicity in pulmonary tissues.