Chloromethane is a clear, colorless gas (vapor) that is difficult to smell. It has a faintly sweet, nonirritating odor at high levels in the air. It is a naturally occurring chemical that is made in large amounts in the oceans and is produced by some plants and rotting wood and when such materials as grass, wood, charcoal, and coal burn. Chloromethane is also produced industrially, but most of it is destroyed during use. It is used mainly in the production of other chemicals such as silicones, agricultural chemicals, and butyl rubber. Producers of the chemical supply the chemical to their customers as a liquified gas in metal containers. Chloromethane was used widely in refrigerators in the past, but generally this use has been taken over by newer chemicals such as Freon. Some functioning refrigerators more than about 30 years old may contain chloromethane.

Structural diagram: National Institutes of Health

Fate & Transport

Since chloromethane is continuously released into the atmosphere from oceans and biomass, a very low concentration will always be present. When present in water, chloromethane will evaporate rapidly. Chloromethane will evaporate from the soil surface, but if present in a landfill or waste site, it may move downward and get into well water.

Exposure Pathways

Because chloromethane is made in the oceans by natural processes, it is present in air all over the world. In most areas, the outside air contains less than 1 part of chloromethane in a billion parts of air (ppb). In cities, however, the air may contain up to 3 ppb. It is also present in some lakes and streams and has been found in drinking water (including well water) at very low levels in the ppb range. Chloromethane is also found in tap water that has been chlorinated. If chloromethane is present at waste sites, it may get into underground water as it passes downward through the soil. Very low levels may be present naturally in the soil. There have been no reports that chloromethane is found in food. You could be exposed to levels somewhat higher than the background levels, although probably still very low levels, if you live near a hazardous waste site or a source of industrial release.

The people most likely to be exposed to increased levels of chloromethane in the air are those who work where it is made. Other occupations or industries that present a higher risk of exposure to chloromethane include building contracting, metal industries, transportation, car dealers, and service-station attendants. In the past (more than 30 years ago), chloromethane was widely used in refrigerators, and people may still be exposed to it if these old refrigerators leak the gas into their homes. Other consumer sources of chloromethane include cigarette smoke; polystyrene insulation; aerosol propellents; home burning of wood, grass, coal, or certain plastics; and the use of chlorinated swimming pools.


Chloromethane can enter your body through the lungs if you breathe it in or through the digestive tract if you drink water containing it. Almost all of the chloromethane that you breathe in or drink rapidly enters the bloodstream from the lungs or the digestive tract. Chloromethane can also enter your body through the skin if you come into contact with it, but the amount that enters this way is not known. Breathing air that contains chloromethane vapor is the most likely way you could be exposed if you live near a hazardous waste site. Chloromethane goes rapidly from the lungs into the bloodstream, and then it or its breakdown products go to organs such as the liver, kidneys, and brain. The portion of the chloromethane that does not get changed in your body leaves in the air you breathe out, and the breakdown products of chloromethane formed in the body leave in the urine. These processes take anywhere from a few hours to a couple of days.

Health Effects

If the levels are high enough (over a million times the natural level in outside air), brief exposures to chloromethane can have serious effects on the nervous system, including convulsions, coma, and death. Some people have died from breathing chloromethane that leaked from refrigerators in rooms with little or no ventilation in their homes. Most of these cases occurred more than 30 years ago, but exposure could still happen if you have an old refrigerator that contains chloromethane as the refrigerant. Others exposed to high levels this way or to leaks while they were repairing refrigerators did not die but had effects such as staggering, blurred and double vision, dizziness, fatigue, personality changes, confusion, tremors, uncoordinated movements, nausea, and vomiting. These symptoms can last for several months or more, but complete recovery is possible. Exposure to chloromethane has also had harmful effects on the liver, kidney, heart rate, and blood pressure. If you work in an industry that uses chloromethane to make other products, you might be exposed to chloromethane levels that cause some symptoms that resemble drunkenness and impaired ability to perform simple tasks.

Harmful liver, kidney, and nervous system effects have developed after animals breathed air containing high levels of chloromethane (100,000 times higher than natural levels) for a few hours each day for 1 or more days. Animals have also died from exposure to high levels of chloromethane. When mice breathed the vapors for only several hours per day, they could be exposed to higher levels of chloromethane before developing effects than if they breathed the vapors all day for several days. The same effects occurred in animals when they were exposed to lower levels of chloromethane for longer periods. In long-term exposure experiments, animals that breathed air containing chloromethane grew more slowly than animals that were not exposed. Male rats that breathed air containing chloromethane developed effects in their reproductive organs that made them less fertile or even sterile. They also produced sperm that were damaged, causing female rats that became pregnant by these exposed male rats to lose their fetuses.

Female rats that were exposed to chloromethane during pregnancy had smaller than normal fetuses with underdeveloped bones. Female mice that are exposed during pregnancy may produce fetuses with abnormal hearts, but this issue is controversial. Male mice that breathed air containing chloromethane for 2 years developed tumors in their kidneys, but female mice and male and female rats did not develop tumors. It is not known whether chloromethane could cause sterility, miscarriages, birth defects, or cancer in humans.

Information excerpted from:

Toxicological Profile for Chloromethane December 1990

Agency for Toxic Substances and Disease Registry
U.S. Dept. of Health and Human Services