Hydrogen Sulfide

The hydrogen sulfide molecule is the sulfur analog of water, witha central sulful atom in place of the central oxygen atom.

Hydrogen sulfide is a gas at room temperature with an odor that resembles rotten eggs. Natural sources of it include bacterial decomposition of proteins and volcanic eruptions.

Nasal detection of hydrogen sulfide is possible at concentration as low as 0.02 part per million. Despite its easy detection, its presence can be dangerous because it exerts an anesthetic effects on nasal passages, causing the nose to rapidly lose its ability to detect its presence. Hydrogen sulfide is lethal at a concentration of 100 parts per million.

Decomposition of albumin, a sulfur-rich protein present in eggs, produces hydrogen sulfide. The pale green color often found at the interface of the yolk and white portion of a cooked egg is caused by the presence of hydrogen sulfide. Egg yolk is rich in iron-containing proteins, and H2S produced from albumin during cooking reacts with these proteins to form iron sulfide, the source of the green color.

[source: Chemical Principles by H. Stephen Stoker]