Hydrogen Sulfide H2S
Hydrogen sulfide (H2S) is a poisonous, colorless gas with a characteristic odor of rotten eggs. It naturally
occurs in the gases from volcanoes, sulfur springs, undersea vents, swamps and stagnant bodies of
water and in crude petroleum and natural gas. Additionally, bacteria, fungi, and actinomycetes release
hydrogen sulfide during the decomposition of sulfur-containing proteins and by the direct reduction of
sulfate (SO42-). Hydrogen sulfide is frequently encountered in various industries and may be released to
the environment as a result of their operations. Some of these industries include natural gas production,
municipal sewage pumping and treatment plants, landfilling, swine containment and manure handling,
pulp and paper production, construction in wetlands, asphalt roofing, pelt processing, animal slaughter
facilities, tanneries, petroleum refining, petrochemical synthesis, coke production plants, viscose rayon
manufacture, sulfur production, iron smelting, and food processing.
Humans may be exposed to hydrogen sulfide both from its endogenous production or from exogenous
sources. Most endogenous production apparently results from the metabolism of sulfhydryl-containing
amino acids (e.g., cysteine) by bacteria present in both the intestinal tract and the mouth; however, it is
also produced in the brain and several smooth muscles (e.g., thoracic aorta) by enzymes found in these
tissues. In the brain, hydrogen sulfide produced from reactions catalyzed by the cystathionine β-synthase
enzyme from the desulfhydration of cysteine acts as a neuromodulator. Physiological concentrations of
hydrogen sulfide enhance the N-methyl-D-asparate (NMDA) receptor mediated response and can
facilitate the induction of hippocampal long-term potentiation. Hydrogen sulfide produced in the mouth
is a component of bad breath (halitosis); concentrations between 1 and 100 ppb have been measured in
mouth air. It is generated in the large intestine by the bacterial reduction of inorganic sulfate and sulfite,
and by fermentation of sulfur-containing amino acids. It can compose up to 10% of intestinal gases. In
flatus, hydrogen sulfide concentrations as high as 18 ppm were recorded in individuals on a normal diet.
http://www.atsdr.cdc.gov/toxprofiles/tp114-c2.pdf
Health Factors
NIOSH Immediately Dangerous To Life or Health Concentration (IDLH): 100 ppm
Potential symptoms: Apnea; coma; convulsions; irritated eyes, conjunctivitis pain, lacrimation, photophobia, corneal
vesiculation; respiratory system irritation; dizziness; headaches; fatigue; insomnia; GI disturbances
Health Effects: Acute systemic toxicity (HE4); CNS effects (HE7) Irritation-Eye, (Conjunctivitis), Lungs---Moderate
(HE15)
Affected organs: Respiratory system, eyes
Exposure Limits
OSHA Permissible Exposure Limit (PEL) for General Industry: 29 CFR 1910.1000 Z-2 Table -- Exposures shall not
exceed 20 ppm (ceiling) with the following exception: if no other measurable exposure occurs during the 8-hour work
shift, exposures may exceed 20 ppm, but not more than 50 ppm (peak), for a single time period up to 10 minutes.
OSHA Permissible Exposure Limit (PEL) for Construction Industry: 29 CFR 1926.55 Appendix A -- 10 ppm, 15 mg/m3
TWA
OSHA Permissible Exposure Limit (PEL) for Maritime: 29 CFR 1915.1000 Table Z-Shipyards -- 10 ppm, 15 mg/m3
TWA
American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV): 10 ppm, 14 mg/m3
TWA; 15 ppm, 21 mg/m3 STEL
National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL): 10 ppm, 15
mg/m3 Ceiling (10 Minutes)
http://www.osha.gov/dts/chemicalsampling/data/CH_246800.html