Properties and Health Effects

Summary
Hydrogen sulfide occurs naturally and is also produced by human activities. Just a few breaths of air containing high levels of hydrogen sulfide can cause death. Lower, longer-term exposure can cause eye irritation, headache, and fatigue.

What is hydrogen sulfide?
Hydrogen sulfide is a flammable, colorless gas that smells like rotten eggs. People usually can smell hydrogen sulfide at low concentrations in air ranging from 0.0005 to 0.3 parts per million (ppm). Hydrogen sulfide occurs naturally in crude petroleum, natural gas, volcanic gases, and hot springs. It can also result from bacterial breakdown of organic matter. It is also produced by human and animal wastes. Bacteria found in your mouth and digestive tract produce hydrogen sulfide during the digestion of food containing vegetable or animal proteins. Hydrogen sulfide can also form from industrial activities, such as food processing, coke ovens, paper mills, tanneries, and petroleum refineries. It is used primarily in the production of sulfur and sulfuric acid.

What happens to hydrogen sulfide when it enters the environment?
Hydrogen sulfide can be released into air, water, and soil at places where it is produced or used. It is released primarily as a gas and spreads in the air. It can remain in the air from 1 to 42 days, depending on the season. In air, it can change into sulfur dioxide and sulfates. Levels in water are very low because it readily evaporates. In soil, hydrogen sulfide will be consumed by bacteria and changed to sulfur.

How might I be exposed to hydrogen sulfide?
You might be exposed to hydrogen sulfide from breathing contaminated air or drinking contaminated water. People living near a wastewater treatment plant, a gas and oil drilling operation, a farm with manure storage or livestock confinement facilities, or a landfill may be exposed to higher levels of this chemical. You can be exposed at work if you work in rayon textiles, petroleum and natural gas drilling and refining, or wastewater treatment industries. Workers on farms with manure storage pits or landfills can be exposed to higher levels of hydrogen sulfide. A small amount of hydrogen sulfide is produced by bacteria in your mouth and digestive tract.

How can hydrogen sulfide affect my health?
Studies in humans suggest that the respiratory tract and nervous system are the most sensitive targets of hydrogen sulfide toxicity. Exposure to low concentrations of hydrogen sulfide may cause irritation to the eyes, nose, or throat. It may also cause difficulty in breathing for some asthmatics. Respiratory distress or arrest has been observed in people exposed to very high concentrations of hydrogen sulfide. Exposure to low concentrations of hydrogen sulfide may cause headaches, poor memory, tiredness, and balance problems. Brief exposures to high concentrations of hydrogen sulfide can cause loss of consciousness. In most cases, the person appears to regain consciousness without any other effects. However, in some individuals, there may be permanent or long-term effects such as headaches, poor attention span, poor memory, and poor motor function.

How likely is hydrogen sulfide to cause cancer?
Hydrogen sulfide has not been shown to cause cancer in humans, and its possible ability to cause cancer in
animals has not been studied thoroughly. The U.S. Department of Health and Human Services (DHHS) and the International Agency for Research on Cancer (IARC) have not classified hydrogen sulfide as to its carcinogenicity. The U.S. EPA has determined that data for hydrogen sulfide are inadequate for carcinogenic assessments.

How can hydrogen sulfide affect children?
There is very little information on possible health problems in children who have been exposed to hydrogen sulfide. Exposed children probably will experience effects similar to those experienced by exposed adults. Whether children are more sensitive to hydrogen sulfide exposure than adults is not known. It is not known whether hydrogen sulfide causes birth defects in people. The results of studies in animals suggest that exposure to low concentrations of hydrogen sulfide during pregnancy does not cause birth defects.

How can families reduce the risk of exposure to hydrogen sulfide?
Hydrogen sulfide is part of the natural environment; the general population will have some exposure to hydrogen sulfide. Families can be exposed to more hydrogen sulfide than the general population if they live near natural or industrial sources of hydrogen sulfide, such as hot springs, manure holding tanks, or pulp and paper mills. However, their exposure levels are unlikely to approach those that sicken people exposed at work. Families can reduce their exposure to hydrogen sulfide by avoiding areas that are sources of hydrogen sulfide. For example, individuals of families that live on farms can avoid manure storage areas where high concentrations of hydrogen sulfide may be found.

Is there a medical test to show whether I’ve been exposed to hydrogen sulfide?
Hydrogen sulfide and its breakdown products (metabolites) can be measured in blood and urine. However, the detection of hydrogen sulfide or its metabolites cannot predict the kind of health effects that might develop from that exposure. Because hydrogen sulfide and its metabolites leave the body fairly rapidly, the tests need to be conducted soon after exposure.

Has the federal government made recommendations to protect human health?
The Occupational Safety and Health Administration (OSHA) set an acceptable ceiling limit of 20 ppm for hydrogen sulfide in workplace air. The ceiling limit is a 15-minute timeweighted average that cannot be exceeded at any time during the working day. The National Institute for Occupational Safety and Health (NIOSH) recommends a 10-minute ceiling limit of 10 ppm. NIOSH also determined that 100 ppm is immediately dangerous to life or health of workers.

References
This information is taken from the 2014 Toxicological Profile for Hydrogen Sulfide and Carbonyl Sulfide (Draft for Public Comment) produced by the Agency for Toxic Substances and Disease Registry, Public Health Service, U.S. Department of Health and Human Services in Atlanta, GA.