Hydrogen sulfide (H2S) is a colorless and rotten-egg odoured gas. Some people can smell H2S at very low levels (as 0.5 ppb in air). Most H2S in the air comes from natural sources. It is produced when bacteria break down plant and animal material, often in stagnant waters with low oxygen content such as bogs and swamps.

Hydrogen sulfide (H2S) is a colorless and rotten-egg odoured gas. Some people can smell H2S at very low levels (as 0.5 ppb in air). Most H2S in the air comes from natural sources. It is produced when bacteria break down plant and animal material, often in stagnant waters with low oxygen content such as bogs and swamps.

Volcanoes, hot springs and underwater thermal vents also release H2S. Industrial sources of H2S include petroleum and natural gas extraction and refining, pulp and paper manufacturing, rayon textile production, chemical manufacturing and waste disposal.

Some bacteria change calcium sulfate, the major component of wallboard, into H2S. If construction and demolition debris contain large quantities of wallboard hydrogen sulfide can be formed. Production is greatest when the wallboard is finely crushed and when there is little oxygen, such as the debris is buried and soaked with water.

H2S gas also can be found in groundwater, especially in wells near oil fields wells that penetrate shale or sandstone. It is known as sewer gas, because it is often produced by the decay of waste material.

H2S is extremely toxic, and is corrosive to metals such as iron, zinc, copper, lead and cadmium. It reacts with water to form sulfuric acid that corrodes lead-based paint, concrete, metals and sewer lines.