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Hydrogen sulfide is a highly toxic gas which is immediately lethal in concentrations greater than 2000 ppm. The toxic end-point is due to anoxia to brain and heart tissues which results from its interaction with the celluar enzyme cytochrome oxidase. Inhibition of the enzyme halts oxidative metabolism which is the primary energy source for cells. A second toxic end-point is the irritative effect of hydrogen sulfide on mucous membranes, particularly edema at sub-lethal doses (250 to 500 ppm) in which sufficient exposure occurs before conciousness is lost. Recovered victims of exposure report neurologic symptoms such as headache, fatigue, irritability, vertigo, and loss of libido. Long-term effects are similar to those caused by anoxia due to other toxic agents like CO, and probably are not due to specific H2S effects. H2S is not a cumulative poison. No mutagenic, carcinogenic, reproductive or teratogenic effects have been reported in the literature.
Ammann, H., F. Bradow, D. Fennell, R. Griffin, AND B. Kearney. Health Assessment Document for Hydrogen Sulfide, Review Draft. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/8-86/026A (NTIS PB87117420).