Hydrogen sulfide
Hydrogen sulfide is often produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion which is done by sulfate-reducing microorganisms. H 2S also occurs in volcanic gases, natural gas, and in some sources of well water. The human body produces small amounts of H 2S and uses it as a signaling molecule.
Hydrogen sulfide-2