Hydrogen Sulfide in the Air and Body: Dangers and Functions
The Significance of Hydrogen Sulfide
Hydrogen sulfide, or H2S, is a flammable, explosive, and toxic gas in the environment. It's known for its rotten egg smell and is sometimes called sour gas or stink damp. The gas is very dangerous for humans at high concentrations. In low concentrations, however, it's a normal component in our bodies, where it actually has benefits.
H2S is released from decomposing organic matter, geothermal activity, and industry. It's widespread in the atmosphere but is more concentrated in some environments than in others. It's a potential problem in the oil and gas industries.
Hydrogen sulfide in the atmosphere can make breathing difficult and damage the nervous system. The more concentrated the H2S, the more pronounced its effects. It can be deadly at high concentrations.
Despite its dangers in the environment, the hydrogen sulfide that is normally present in our bodies has some useful functions. It acts as a signaling molecule in the nervous system and probably in the circulatory system as well. Recent research suggests that low levels of the chemical may have other important health benefits in humans. Once scientists have learned more about the action of H2S in the body, it may be possible to use the chemical to treat certain health problems.
It's important to remember that hydrogen sulfide is potentially very dangerous. The functions of the endogenous chemical (hydrogen sulfide that's made in very low concentrations inside our body) and the possible health benefits of low concentrations of the chemical are described in this article for general interest only.
Sources and Location of the Chemical
Hydrogen sulfide in the environment comes from both natural and industrial sources. Bacteria produce the chemical when they decompose material that was once living, such as dead bodies and animal or human wastes. The chemical may also be released from sulfur springs and volcanic eruptions.
H2S is common in places with a large quantity of decaying organic matter and a low concentration of oxygen. It's heavier than air and tends to collect in low lying areas, including underground sewers, animal manure pits, swamps, and salt marshes.
Industries in which people may be exposed to hydrogen sulfide include oil refineries, pulp and paper mills, mines, solid waste landfills, wastewater treatment plants, and tanneries. Workers at commercial companies that handle manure may also be exposed to the chemical.
Hydrogen sulfide is also present in the gas expelled from our intestine. The chemical produces smelly flatulence if it's sufficiently concentrated. It's produced when gut bacteria break down protein.
How Can the Chemical Be Detected?
H2S is an invisible gas. It often has a rotten egg smell at lower concentrations and a sickly sweet smell at higher concentrations. After an initial odor there may be no smell at all, however. This is because the gas can deaden a person's sense of smell after they have been exposed to a high concentration for a short time or a low concentration for a long time. The smell may also be masked by the odor of other chemicals.
Some people can detect the presence of H2S at lower concentrations than other people. Fortunately, hydrogen sulfide detectors can monitor the air in potentially dangerous areas so that everyone is aware of the presence of the chemical.
Possible Symptoms of Hydrogen Sulfide Poisoning
Hydrogen sulfide enters the lungs and is easily absorbed into the bloodstream. Very little is absorbed through the skin. H2S can cause severe skin irritations, however.
The symptoms produced by hydrogen sulfide poisoning depend on the concentration of the chemical and the length of the exposure. Exposure to a moderately low concentration of the chemical may cause the following symptoms:
- eye, nose, and throat irritation
- stomach upset
- difficulty breathing due to irritation of the lungs
Anyone experiencing some of these symptoms should visit a doctor, especially if the symptoms have no known cause, are severe, or last for a long time.
As the exposure increases, a person may experience confusion, fatigue, and a condition called pulmonary edema. In this condition fluid collects in the air sacs of the lungs, making breathing very difficult. It's essential that medical aid is obtained in this situation. Exposure to a high concentration of hydrogen sulfide may cause these additional symptoms:
- low blood pressure
- muscle cramps
- lack of muscle coordination
- inability to reason
- loss of consciousness
Loss of consciousness followed by death may be very rapid in an area with a high concentration of hydrogen sulfide.
Endogenous Hydrogen Sulfide in the Nervous System
Nerves transmit electrical messages, or nerve impulses, in order to control the processes that take place in our bodies. A nerve impulse is passed from one neuron (nerve cell) to the next. There is a tiny gap between successive neurons.
When a nerve impulse reaches the end of a neuron, tiny vesicles (sacs) in the neuron release a chemical called a neurotransmitter. Neurotransmitter molecules travel across the gap between neurons, join to receptors on the membrane of the second neuron, and (often) trigger the start of a new nerve impulse. The region where one neuron ends and another begins is called a synapse.
Some gases act as neurotransmitters. These include nitric oxide, carbon monoxide, and hydrogen sulfide. Carbon monoxide is another gas that is dangerous in the atmosphere but helpful in the low concentrations found in the body. The gaseous neurotransmitters aren't stored in vesicles like most other neurotransmitters and they don't work in the same way. They do influence the transmission of the nerve impulse at the synapse, however. The mechanisms by which they do this are still being studied. The chemicals are often referred to as gasotransmitters.
Functions in the Circulatory System
In mice, the lining of the blood vessels produces hydrogen sulfide. The chemical relaxes the muscles in the walls of the vessels, causing the blood vessels to expand. Researchers have discovered that hydrogen sulfide is also produced by the human cardiovascular system and causes blood vessels to expand. Its mechanisms of action are still being investigated, however. The chemical seems to have a similar function to nitric oxide, another gas that expands blood vessels.
It has been suggested—but not yet proved—that the beneficial effects of garlic on blood vessels and blood pressure are due in part to the production of hydrogen sulfide after garlic is eaten.
A very low and safe concentration of hydrogen sulfide may one day be used as a medicine. The chemical can't be used for this purpose yet, however.
Possible Anti-Aging Benefits
Hydrogen sulfide may have anti-aging benefits. University scientists from China suggest that it slows aging in several ways. They say that "the evidence is mounting" that the chemical activates an enzyme called SIRT1 (also called sirtuin-1 and sirtuin deacetylase 1). This enzyme is thought to influence lifespan by a variety of methods.
The scientists also say that H2S interacts with a gene known as klotho, which codes for a protein of the same name and is involved in anti-aging processes. In addition, research suggests that H2S reduces inflammation and is an antioxidant.
Alzheimer's and Parkinson's Disease
Researchers have noticed that the normal level of hydrogen sulfide in the brain is significantly reduced in people with Alzheimer's disease. They have also noticed that rats suffering from a disorder similar to Parkinson's disease have low levels of H2S in their brains.
Both diseases involve problems with protein folding and a condition called ER stress. Protein molecules have a complex structure that includes folds in a specific shape. The ER (endoplasmic reticulum) is involved in the correct folding of proteins. If ER stress exists and many proteins fold incorrectly, health problems may develop. Hydrogen sulfide appears to be helpful in this situation. It may also be beneficial in other ways.
When the rats with a condition resembling Parkinson's disease were given an appropriate concentration of the chemical, their movement problems disappeared. Though the discovery is exciting, results in rats (or mice) don't always apply to humans. As in the other potential medical uses of hydrogen sulfide, many questions need to be answered and more research is needed.
The term "suspended animation" as used in biology means the slowing of life processes without stopping them or ending life. A worm called Caenorhabditis elegans, or C. elegans, readily enters a state of suspended animation when exposed to hydrogen sulfide in the correct concentration. Its rapid movements slow and then stop. Once the H2S is removed from the air, the worm returns to its active state, apparently unharmed. C. elegans is a popular animal in anti-aging studies.
Scientists have suggested that a state of suspended animation induced by hydrogen sulfide could be useful in humans. It might be helpful in certain disease conditions and during long-distance space travel, for example. Much more research is required in relation to the feasability of these ideas, however.
Hydrogen sulfide is a very interesting chemical. It can be dangerous and deadly in the environment or helpful as a normal component of our bodies. Hopefully researchers will soon learn how to use the chemical to benefit our lives.
- Hydrogen Sulfide from the Occupational Health and Safety Administration, United States Department of Labor
- A Hydrogen Sulfide Management PDF from the CDC (Centers for Disease Control and Prevention)
- Hydrogen Sulfide in Farts from New Scientist
- H2S in the Nervous System from Boston University
- Role of Hydrogen Sulfide in Cardiovascular Homeostasis from Frontiers in Pharmacology
- Hydrogen Sulfide in Human Health from The Globe And Mail newspaper
- Hydrogen sulfide: The next anti-aging agent? from the Medical Xpress news service
- H2S and Alzheimer's disease from the ScienceDaily new service
- Suspended animation in C. elegans from Popular Mechanics
- Possible medical benefits of suspended animation from the U.S. National Library of Medicine
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.
© 2013 Linda Crampton