Hydrogen sulfide, a compound of hydrogen and sulfur, is a corrosive, flammable and highly toxic gas with a characteristic rotten-egg odor. It is produced naturally by decaying organic matter, particularly in low oxygen conditions, and it is emitted from sewage sludge, liquid manure, sulfur hot springs and natural gas. It is used in several industries, including for the production of some organic compounds and food processing, and is a by-product of various industrial processes including oil refining, mining, and pulp and paper processing.