1. Occurrence and Significance
Sulfide is often present in groundwater and sediment. It is produced by decomposition of organic matter and bacterial reduction of sulfate. It is sometimes found in industrial or municipal wastewater. Hydrogen sulfide escaping into the air from sulfide-containing wastewater causes odor nuisances. The threshold odor concentration of H2S in clean water is between 0.025 and 0.25 μg/L. Gaseous H2S is very toxic and has claimed the lives of numerous workers. At levels toxic to humans, it interferes with the olfactory system, giving a false sense of the safe absence of H2S. It attacks metals directly, and indirectly has caused serious corrosion of concrete sewers because it is oxidized biologically in the presence of oxygen to H2SO4 on the pipe wall. Dissolved H2S is toxic to fish and other aquatic organisms.