Methyl mercaptan, also known as methanethiol, is a colorless gas with a smell like rotten cabbage. It is a natural substance found in the blood, brain, and other tissues of humans and other animals, and it is released from animal feces. It occurs naturally in certain foods such as some nuts (filberts) and cheese (Beaufort).
Methyl mercaptan is released from decaying organic matter in marshes and is present in the natural gas of certain regions of the United States, in coal tar, and in some crude oils. Methyl mercaptan is manufactured for use in pesticides, as a jet fuel additive, in the plastics industry, and in making methionine, a nutrient that is added to poultry feed. Methyl mercaptan is also released as a decay product of wood in pulp mills.
We know very little about what happens to methyl mercaptan after it is released to the environment. Because it is a gas, most of it probably goes into the air. Sunlight can break it down into other substances. If methyl mercaptan is released to soil, it probably then goes into the air or is carried through the soil by rain or any other water that contacts it.
Exposure to methyl mercaptan
Methyl mercaptan is always present in your body and in your urine and feces. It can also be present in the breath of persons with liver damage. You can be exposed to methyl mercaptan in the air if you live near a natural source of this gas, such as a marsh, an underground gas pocket, or a dump site that releases it. We have no information on the levels of methyl mercaptan that come from these sources.
Methyl mercaptan has not been found in drinking water, so you would probably not be exposed to it in this way. Methyl mercaptan is a natural part of certain foods, such as nuts and cheeses. It has also been approved for use as a food additive. Because of its unpleasant smell, very little can be added to food. You could be exposed to small amounts of methyl mercaptan by eating foods that contain it. However, we have no information on the levels of methyl mercaptan in food.
You can be exposed to methyl mercaptan if you work at a wood-pulp mill or sewage treatment plant or if you work in a factory that uses it to make other products such as jet fuel, pesticides, or poultry feed. Measurements of methyl mercaptan in the air inside these mills were lower than 4 ppm (4 parts of methyl mercaptan per million parts of air). Methyl mercaptan has been found in the environmental air at 4 ppb (4 parts of methyl mercaptan per billion parts of air).
Levels of methyl mercaptan in soil are probably very low. Even at hazardous waste sites, the levels were about 83 ppb.
Pathways for methyl mercaptan in the body
Methyl mercaptan can enter your body when you breathe in air or eat food that contains this chemical. We do not know if methyl mercaptan can enter your body through the skin or what happens to it after it enters your body, Studies in rats suggested it leaves the body quickly. After methyl mercaptan reaches the blood, it is either breathed out unchanged or is broken down to other substances (within one hour). These substances may be breathed out from the lungs or leave the body with the urine within a few hours.
Health effects of methyl mercaptan
We have very little information on the health effects of exposure to methyl mercaptan. A worker exposed to very high levels (exact amount unknown) of this compound for several days when he opened and emptied tanks of methyl mercaptan went into a coma (became unconscious), developed anemia (a blood disorder) and internal bleeding. He died within a month after this incident.
We do not know whether long-term exposure of humans to low levels of methyl mercaptan can result in harmful health effects such as cancer, birth defects, or problems with reproduction.
Methyl mercaptan can be smelled and recognized in Air when it is there at a level of about 1.6 ppb (1.6 parts of methyl mercaptan per billion parts of air). It can be smelled when it is present in water at a level far lower than 1 ppb.
Medical tests for exposure to methyl mercaptan
Methyl mercaptan is always present in your body. There is a test that can be used to find out if it is present in your blood at levels that are higher than normal, which may happen if you are exposed to high levels of this substance. This test requires special equipment and is not usually available in a doctor's office. It can be done in a special laboratory. However, this test cannot be used to find out how much methyl mercaptan you were exposed to or to predict whether harmful health effects will occur.
Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Agency for Toxic Substances and Disease Registry. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Agency for Toxic Substances and Disease Registry should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.