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Hydrogen Sulfide

Hydrogen Sulfide
Hydrogen sulfide (H2S) is a colorless gas. At low concentrations, it has an obnoxious odor similar to rotten eggs. It is soluble in water. It is produced in nature primarily through the decomposition of organic matter by bacteria. It is a constituent of natural gas, petroleum, sulfur deposits, volcanic gases and sulfur springs.

Hydrogen sulfide (H2S), the gas with the odor of rotten eggs, was formally discovered in 1777, over 239 years ago. For many years, it was considered an environmental pollutant and a health concern only in occupational settings. Recently, however, it was discovered that H2S is produced endogenously and plays critical physiological roles as a gasotransmitter. 

Although at low physiological concentrations it is physiologically beneficial, exposure to high concentrations of H2S is known to cause brain damage, leading to neurodegeneration and long-term neurological sequelae or death. Neurological sequelae include motor, behavioral, and cognitive deficits, which are incapacitating.

The U.S. Occupational Safety and Health Administration (OSHA) has regulations regarding the permissible concentrations of hydrogen sulfide, but they only pertain to healthy adult males in the workplace. These regulations do not apply to residential exposures and do not cover the more sensitive population, which includes the elderly, the very young and those with pre-existing illness.

Exposure can occur from various sources including ambient air near petroleum refineries, sewage treatment plants, sewers (sewer gas) and septic tanks. Sewer gas contains hydrogen sulfide and reduced sulfur compounds, such as methyl and dimethyl sulfide, ethyl and diethyl sulfide. These organo-sulfur compounds add to the toxicity of hydrogen sulfide in sewer gas.

Exposure to hydrogen sulfide occurs primarily by inhalation but can also occur by ingestion (contaminated food) and skin (water and air). Once taken into the body, it is rapidly distributed to various organs, including the central nervous system, lungs, liver, muscle, etc.

The health effects of hydrogen sulfide include acute system toxicity, central nervous system effects, irritation of eyes and lungs, nausea, dizziness, loss of balance, headaches, and shortness of breath. Studies have also shown that hydrogen sulfide affects the myelin sheaths in the brain. 

Here is an excerpt from one of those studies:

We studied ultrastructural and morphometric characteristics of nerve cells and myelinated fibers in the cerebral cortex after chronic exposure to natural gas containing hydrogen sulfide in low concentrations. Radioisotope assay revealed activation of protein synthesis in nerve cells after chronic exposure to natural hydrogen sulfide-containing gas in low concentrations (10 mg/m(3)by H2S) for 2 weeks. After 1 month the ultrastructure of myelinated fibers was characterized by sectorial loosening and demyelination.

Source:  Hooper DG, Shane J, Straus DC, Kilburn KH, et al. Isolation of Sulfur-Reducing and Oxidizing Bacteria Found in Contaminated Drywall. Int J Mol Sci. 2010;11:647-655.  doi:10.3390/ijms11020647. To read this research paper, click here.

Olfactory Accommodation (olfactory paralysis)

The most dangerous aspect of hydrogen sulfide results from olfactory accommodation or olfactory paralysis. This means that the individual can accommodate to the odor and is not able to detect the presence of the chemical after a short period of time. Death can occur.

Hydrogen sulfide

Hydrogen sulfide gas can cause serious health effects including acute system toxicity, central nervous system effects, irrigation of eyes and lungs, nausea, dizziness, loss of balance, headaches, shortness of breath, paralysis, etc.

Additional research papers on this topic include:

Kilburn KH. Effects of Hydrogen Sulfide on Neurobehavioral Function. South Med J. 2003 Jul;96(7):639-646. To read the abstract, click here.

Kilburn KH, Thrasher JD, Gray MR. Low-Level Hydrogen Sulfide and Central Nervous System Dysfunction. Toxicol Ind Health. Published online 26 May 2010. doi:10.1177/0748233710369126. To read the abstract, click here.

Kilburn KH, Warshaw RH. Hydrogen Sulfide and Reduced-Sulfur Gases Adversely Affect Neurophysiological Functions. Toxicol Ind Health. 1995 Mar-Apr;11(2):185-197. To read the abstract, click here.

Legator MS, Singleton CR, Morris DL, Philips DL. Health Effects from Chronic Low-Level Exposure to Hydrogen Sulfide. Arch Environ Health. 2001 Mar-Apr;56(2):123-131. To read the abstract, click here.
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