page_title: Hydrogen sulfide
section_title: Occurrence
hierarchical_section_title: Hydrogen sulfide / Uses / Occurrence
caption_attribution_description: Deposit from hydrogen sulphide (volcanic rock in Nea Kameni, Santorini, Greece)
context_page_description: Hydrogen sulfide is the chemical compound with the formula H
  ₂S. It is a colorless chalcogen hydride gas with the characteristic foul odor of rotten eggs. It is very poisonous, corrosive, and flammable.
  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.
  Swedish chemist Carl Wilhelm Scheele is credited with having discovered the chemical composition of hydrogen sulfide in 1777.
  The British English spelling of this compound is hydrogen sulphide, but this spelling is not recommended by the International Union of Pure and Applied Chemistry or the Royal Society of Chemistry.
context_section_description: Small amounts of hydrogen sulfide occur in crude petroleum, but natural gas can contain up to 30%. Volcanoes and some hot springs (as well as cold springs) emit some H
  ₂S, where it probably arises via the hydrolysis of sulfide minerals, i.e. MS + H
  ₂O → MO + H
  ₂S. Hydrogen sulfide can be present naturally in well water, often as a result of the action of sulfate-reducing bacteria. Hydrogen sulfide is created by the human body in small doses through bacterial breakdown of proteins containing sulfur in the intestinal tract, therefore it contributes to the characteristic odor of flatulence. It is also produced in the mouth (halitosis).
  A portion of global H
  ₂S emissions are due to human activity. By far the largest industrial source of H
  ₂S is petroleum refineries: The hydrodesulfurization process liberates sulfur from petroleum by the action of hydrogen. The resulting H
  ₂S is converted to elemental sulfur by partial combustion via the Claus process, which is a major source of elemental sulfur. Other anthropogenic sources of hydrogen sulfide include coke ovens, paper mills (using the Kraft process), tanneries and sewerage. H
  ₂S arises from virtually anywhere where elemental sulfur comes in contact with organic material, especially at high temperatures. Depending on environmental conditions, it is responsible for deterioration of material through the action of some sulfur oxidizing microorganisms. It is called biogenic sulfide corrosion.
  In 2011 it was reported that increased concentration of H
  ₂S, possibly due to oil field practices, was observed in the Bakken formation crude and presented challenges such as "health and environmental risks, corrosion of wellbore, added expense with regard to materials handling and pipeline equipment, and additional refinement requirements".
  Besides living near a gas and oil drilling operations, ordinary citizens can be exposed to hydrogen sulfide by being near waste water treatment facilities, landfills and farms with manure storage. Exposure occurs through breathing contaminated air or drinking contaminated water.
  In municipal waste landfill sites, the burial of organic material rapidly leads to the production of anaerobic digestion within the waste mass and, with the humid atmosphere and relatively high temperature that accompanies biodegradation, biogas is produced as soon as the air within the waste mass has been reduced. If there is a source of sulfate bearing material, such as plasterboard or natural gypsum (calcium sulphate dihydrate), under anaerobic conditions sulfate reducing bacteria converts this to hydrogen sulfide. These bacteria cannot survive in air but the moist, warm, anaerobic conditions of buried waste that contains a high source of carbon – in inert landfills, paper and glue used in the fabrication of products such as plasterboard can provide a rich source of carbon – is an excellent environment for the formation of hydrogen sulfide.
  In industrial anaerobic digestion processes, such as waste water treatment or the digestion of organic waste from agriculture, hydrogen sulfide can be formed from the reduction of sulfate and the degradation of amino acids and proteins within organic compounds.  Sulfates are relatively non-inhibitory to methane forming bacteria but can be reduced to H₂S by sulfate reducing bacteria, of which there are several genera.
caption: Deposit of sulfur on a rock, caused by volcanic gas
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