Health Effects of Hydrogen Sulfide: Dangers and Benefits
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 at high concentrations. It's also found in our bodies, however, where it actually has health 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, hydrogen sulfide is a normal component of our bodies, where it's present in a very low concentration. 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 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 health problems.
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.
Hydrogen Sulfide Awareness
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
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.
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.
Structure of a Synapse
Functions of 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 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 which 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, but they do influence the transmission of the nerve impulse and also affect other processes in the nervous system.
Although hydrogen sulfide can be deadly, in tiny quantitites inside our body it can be very useful.
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.
Possible Health Benefits of Hydrogen Sulfide
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. This enzyme is thought to influence lifespan. The scientists also say that H2S interacts with a gene known as "klotho", which is involved in anti-aging processes. In addition, research suggests that H2S reduces inflammation and is an antioxidant.
Researchers have noticed that the normal level of hydrogen sulfide in the brain is greatly 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. When the affected rats in one experiment were given the chemical, their movement problems disappeared.
Suspended Animation in a Worm
Hydrogen Sulfide and Suspended Animation
A worm called Caenorhabditis elegans, or C. elegans, enters a state of suspended animation when exposed to hydrogen sulfide. 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.
Mice also enter a state resembling suspended animation when they are exposed to H2S. In one experiment, the gas caused the breathing rate of mice to drop from 120 breaths per minute to less than 10 breaths per minute. Their metabolic rate decreased by 90% and their core temperature fell from 37 degrees Celsius to around 11 degrees Celsius. After six hours of exposure to hydrogen sulfide the mice were exposed to normal air. Their body conditions returned to normal and tests showed that no apparent harm was done.
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.
Hydrogen sulfide is a very interesting chemical. It can be dangerous and deadly in the environment or helpful in 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
- Cardioprotective Effects of H2S from PNAS (Proceedings of the National Academy of Sciences of the United States of America)
- H2S in the Nervous System from Boston University
- Hydrogen Sulfide in Human Health from The Globe And Mail newspaper
- American Society for Microbiology. (2013, January 29). Hydrogen sulfide: The next anti-aging agent?. ScienceDaily. Retrieved July 31, 2017 from www.sciencedaily.com/releases/2013/01/130129121945.htm
- Suspended Animation in Mice from the BBC
© 2013 Linda Crampton