PUBLIC HEALTH STATEMENT 

 CHLOROMETHANE CAS#: 74-87-3 

Division of Toxicology December 1998 

__________________________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 

This Public Health Statement is the summary 

chapter from the Toxicological Profile for 

Chloromethane. It is one in a series of Public Health 

Statements about hazardous substances and their 

health effects. A shorter version, the ToxFAQsTM is 

also available. This information is important 

because this substance may harm you. The effects 

of exposure to any hazardous substance depend on 

the dose, the duration, how you are exposed, 

personal traits and habits, and whether other 

chemicals are present. For more information, call 

the ATSDR Information Center at 1-888-422-8737. 

_____________________________________ 

This public health statement tells you about 

chloromethane and the effects of exposure. 

The Environmental Protection Agency (EPA) 

identifies the most serious hazardous waste sites in 

the nation. These sites make up the National 

Priorities List (NPL) and are the sites targeted for 

long-term federal cleanup. Chloromethane has been 

found in at least 172 of the 1,467 current or former 

NPL sites. However, it's unknown how many NPL 

sites have been evaluated for this substance. As 

more sites are evaluated, the sites with 

chloromethane may increase. This is important 

because exposure to this substance may harm you 

and because these sites may be sources of exposure. 

When a substance is released from a large area, 

such as an industrial plant, or from a container, such 

as a drum or bottle, it enters the environment. This 

release does not always lead to exposure. You are 

exposed to a substance only when you come in 

contact with it. You may be exposed by breathing, 

eating, or drinking the substance or by skin contact. 

If you are exposed to chloromethane, many factors 

determine whether you'll be harmed. These factors 

include the dose (how much), the duration (how 

long), and how you come in contact with it. You 

must also consider the other chemicals you're 

exposed to and your age, sex, diet, family traits, 

lifestyle, and state of health. 

 

1.1 WHAT IS CHLOROMETHANE? 

 

Chloromethane (also known as methyl chloride) is a 

clear, colorless gas. It has a faint, sweet odor that is 

noticeable only at levels which may be toxic. It is 

heavier than air and is extremely flammable. 

Chloromethane is produced in industry, but the it 

also occurs naturally, and most of the 

chloromethane that is released to the environment 

(estimated at up to 99%) comes from natural 

sources. Chloromethane is always present in the air 

at very low levels. Most of the naturally occurring 

chloromethane comes from chemical reactions that 

occur in the oceans or from chemical reactions that 

occur when materials like grass, wood, charcoal, 

and coal are burned. It is also released to the air as 

a product of some plants or from rotting wood. 

In the past, chloromethane was widely used as a 

refrigerant, but refrigerators no longer use 

chloromethane because of its toxic effects. It was 

also used as a foam-blowing agent and as a 

pesticide or fumigant. A working refrigerator that is 

more than 30 years old may still contain 

chloromethane, and may be a source of high-level 

exposure. Today, nearly all commercially produced 

chloromethane is used to make other substances, 

mainly silicones (72% of the total chloromethane 

used). Other products that are made from reactions 

involving chloromethane include agricultural 
 PUBLIC HEALTH STATEMENT 

 CHLOROMETHANE CAS#: 74-87-3 

Division of Toxicology December 1998 

__________________________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 

chemicals (8%), methyl cellulose (6%), quaternary 

amines (5%), and butyl rubber (3%). 

Chloromethane is completely used up so that by the 

end of the process there is no or little 

chloromethane left to be released, disposed of, or 

reused. It is, however, found as a pollutant in 

municipal waste streams from treatment plants and 

industrial waste streams as a result of formation or 

incomplete removal. There are also some 

manufacturing processes for vinyl chloride that 

result in chloromethane as an impurity in the vinyl 

chloride end product. 

1.2 WHAT HAPPENS TO 

CHLOROMETHANE WHEN IT ENTERS 

THE ENVIRONMENT? 

Chloromethane has been identified in air, surface 

water, groundwater, soil, and sediment. Most 

releases of chloromethane will be to the air. 

Chloromethane rapidly moves through the air and is 

present at very low concentrations throughout the 

atmosphere. Naturally occurring chloromethane is 

continuously released into the atmosphere from 

oceans, rotting wood, forest fires, and volcanoes. 

When grass, coal, or wood are burned, 

chloromethane is released to the air. The burning of 

grasslands and forests accounts for about 20% 

(ranging from 10 to 40%) of the total 

chloromethane in the air. Releases from the oceans 

account for another 80 to 90%. Chemical 

companies release some chloromethane gas to the 

air during the production of chloromethane or when 

it is used to make other substances, but the amount 

is relatively very small (0.2 to 0.6%) compared to 

natural sources of the total chloromethane in the 

atmosphere. 

Chloromethane breaks down very slowly (months to 

years) in the air. Chloromethane can dissolve in 

water, and small amounts of chloromethane in air 

may go into surface waters or groundwater when it 

rains. Chloromethane can also enter water from 

industrial or municipal waste streams or from water 

that comes in contact with municipal or hazardous 

waste sites. Chemical companies generally treat 

waste water to remove chloromethane. 

Chloromethane is a gas at room temperature, and 

when present in water, most will evaporate rapidly 

to the air. Small amounts of dissolved 

chloromethane may move below the surface of the 

water or be carried to the groundwater. It breaks 

down very slowly (months to years) in plain water, 

but certain kinds of small organisms in water may 

break it down more quickly (days). When 

chloromethane comes in contact with soil it does 

not stick to the soil. Most of the chloromethane in 

soil will move to the air. Some may dissolve in 

water and move down through the soil layers to the 

groundwater or into well water. Chloromethane 

does not concentrate in sediments, or in animals and 

fish in the food chain. 

 

1.3 HOW MIGHT I BE EXPOSED TO 

CHLOROMETHANE? 

Most (99%) of the chloromethane in the 

environment comes from natural sources. 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, human activities, mostly combustion and 

manufacturing, add to the chloromethane in the air, 

resulting in somewhat higher levels, up to 1 ppb. 

Chloromethane exposures in the less than 5 ppb 
 PUBLIC HEALTH STATEMENT 

 CHLOROMETHANE CAS#: 74-87-3 

Division of Toxicology December 1998 

__________________________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 

range are much lower (1,000 to 10,000 times lower) 

than the exposure levels that have been shown to 

have toxic effects. Chloromethane is also present in 

some lakes and streams and has been found in 

drinking water (including well water) at very low 

levels in the parts per billion to part per trillion (ppt) 

range. Chloromethane may be formed to a small 

extent in tap water that has been chlorinated. You 

could be exposed to levels in air higher than the 

background levels if you live near a hazardous 

waste site or an industry that uses chloromethane. 

If chloromethane is present at waste sites, it can 

move through the soil into underground water. We 

have very little information on the levels of 

chloromethane in groundwater. Chloromethane is 

not generally found in food. 

The people most likely to be exposed to increased 

levels of chloromethane in the air are those who 

work in chemical plants where it is made or used. 

Chloromethane is also an impurity in vinyl chloride 

when the vinyl chloride is produced by heating 

another chemical, 1,2-dichloroethane. Exposure to 

chloromethane can occur from this kind of vinyl 

chloride or the disposal of vinyl chloride waste from 

this process. The proper enforcement of workplace 

regulations and the recycling of chloromethane 

during the manufacturing process help prevent 

worker exposures to levels that would be considered 

harmful. In the past (more than 30 years ago), 

chloromethane was also widely used as the 

refrigerant in refrigerators. Some of these old 

refrigerators may still be in use or may be located in 

storage areas. Chloromethane may be released from 

leaks in these refrigerators, leading to potentially 

very high exposures, especially in areas with poor 

ventilation. Liquid contact could also occur 

following a leak in an older refrigerator containing 

chloromethane. Other general population sources 

of chloromethane exposure include cigarette smoke; 

polystyrene insulation; aerosol propellants; home 

burning of wood, grass, coal, or certain plastics; and 

chlorinated swimming pools. The chloromethane in 

the outdoor environment, however, is almost totally 

from natural sources. 

1.4 HOW CAN CHLOROMETHANE ENTER 

AND LEAVE MY BODY? 

Chloromethane can enter your body through your 

lungs, if you breathe it in, or through your digestive 

tract if you drink water containing it. The 

chloromethane that you breathe in or drink rapidly 

enters the bloodstream from the lungs or the 

digestive tract and moves throughout the body to 

organs such as the liver, kidneys, and brain. Very 

little of the chloromethane that enters the body 

remains unchanged. The portion of the 

chloromethane that does not get changed in your 

body leaves in the air you breathe out. The rest is 

changed in your body to other breakdown products 

that mostly leave in the urine. The breakdown 

process takes anywhere from a few hours to a 

couple of days. 

Breathing air that contains chloromethane vapor is 

the most likely way you would be exposed if you 

live near a hazardous waste site. Contact with 

liquid chloromethane is rare, but could occur in an 

industrial accident from a broken metal container. 

Prolonged skin contact with liquid chloromethane is 

unlikely, because it turns into a gas very quickly at 

room temperature. It is not known how much 

chloromethane liquid or gas will enter the body 

through contact with the skin, but the amount is 

probably very low. 
 PUBLIC HEALTH STATEMENT 

 CHLOROMETHANE CAS#: 74-87-3 

Division of Toxicology December 1998 

__________________________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 

1.5 HOW CAN CHLOROMETHANE AFFECT 

MY HEALTH? 

If the levels are high enough (over a million times 

the natural levels in outside air), even brief 

exposures to chloromethane can have serious effects 

on your nervous system, including convulsions, 

coma, and death. Some people have died from 

breathing chloromethane that leaked from 

refrigerators in rooms that had little or no 

ventilation. Most of these cases occurred more than 

30 years ago, but this kind of exposure could still 

happen if you have an old refrigerator that contains 

chloromethane as the refrigerant. Some people who 

were exposed to high levels of chloromethane while 

they were repairing refrigerators did not die, but 

they did have toxic effects like staggering, blurred 

or double vision, dizziness, fatigue, personality 

changes, confusion, tremors, uncoordinated 

movements, nausea, or vomiting. These symptoms 

can last for several months or years. Complete 

recovery has occurred in some cases, but not in 

others. Exposure to chloromethane can also harm 

your liver and kidney, or have an effect on your 

heart rate and blood pressure. If you work in an 

industry that uses chloromethane to make other 

products, you might be exposed to levels that could 

cause symptoms resembling drunkenness and 

impaired ability to perform simple tasks. 

To protect the public from the harmful effects of 

toxic chemicals and to find ways to treat people 

who have been harmed, scientists use many tests. 

One way to see if a chemical will hurt people is to 

learn how the chemical is absorbed, used, and 

released by the body; for some chemicals, animal 

testing may be necessary. Animal testing may also 

be used to identify health effects such as cancer or 

birth defects. Without laboratory animals, scientists 

would lose a basic method to get information 

needed to make wise decisions to protect public 

health. Scientists have the responsibility to treat 

research animals with care and compassion. Laws 

today protect the welfare of research animals, and 

scientists must comply with strict animal care 

guidelines. 

Harmful liver, kidney, and nervous system effects 

have developed after animals breathed air 

containing high levels of chloromethane (one 

million times higher than natural levels). Some of 

these animals died from exposure to high levels of 

chloromethane. Similar effects were seen in 

animals that breathed low levels continuously and 

animals that breathed high levels for shorter periods 

with some breaks from exposure. 

Animals that breathed relatively low test levels of 

chloromethane (but still one hundred thousand to 

one million times higher than background levels 

people are exposed to) over a long period (weeks to 

months) had slower growth and developed brain 

damage. Some male animals were less fertile or 

even sterile or produced sperm that were damaged. 

Females that became pregnant by the exposed males 

lost their developing young. 

Male mice that breathed air containing 

chloromethane (one million ppb) 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 can cause 

sterility, miscarriages, birth defects, or cancer in 

humans. The Department of Health and Human 

Services (DHHS) has not classified chloromethane 

for carcinogenic effects. The International Agency 

for Research on Cancer (IARC) calls chloromethane 
 PUBLIC HEALTH STATEMENT 

 CHLOROMETHANE CAS#: 74-87-3 

Division of Toxicology December 1998 

__________________________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 

a Group 3 compound, which means it cannot be 

determined whether or not it is a carcinogen 

because there is not enough human or animal data. 

The Environmental Protection Agency (EPA) 

considers chloromethane possibly carcinogenic to 

humans (i.e., Group C) based on limited evidence of 

carcinogenicity in animals. 

1.6 HOW CAN CHLOROMETHANE AFFECT 

CHILDREN? 

 

This section discusses potential health effects from 

exposures during the period from conception to 

maturity at 18 years of age in humans. 

Children may be exposed to chloromethane from 

the same sources as adults. These sources include 

outside air, indoor air, and drinking water. 

Exposures are generally well below safe levels. 

The people most heavily exposed to chloromethane 

are workers in chemical plants where it is made or 

used. With proper safeguards to prevent children 

from entering these work areas, children would not 

be expected to have high exposures. Old 

refrigerators that used chloromethane as a 

refrigerant and that are leaking chloromethane, 

however, are a potential source that could result in 

high exposures to children. 

There have been no studies on whether children are 

more or less susceptible than adults to harmful 

health effects from a given amount or 

chloromethane. We do not know if chloromethane 

affects the developing fetus or the development of 

young children. There is no information on 

exposure to high levels of chloromethane in 

children (for example, accidental poisoning), but we 

expect similar effects to those seen in adults 

(including harmful effects on the nervous system 

and kidneys). We do not know if the effects for 

children would be similar to those in adults for 

lower levels or for longer exposures. There have 

been no studies where young animals were exposed 

to chloromethane. Animal studies have shown that 

female adult rats that were exposed to 

chloromethane during pregnancy had young that 

were smaller than normal, with underdeveloped 

bones, and possibly abnormal hearts (although this 

effect remains uncertain). 

We do not know if chloromethane or its breakdown 

products in the body can cross the placenta and 

enter into the developing young. We also do not 

know if chloromethane or its breakdown products 

can enter into a nursing woman's milk. We do 

know that chloromethane is broken down and 

eliminated from the body very quickly in adults. 

Although we expect the breakdown and elimination 

of chloromethane to be the same in children as in 

adults, more studies are needed to answer this 

question and the other questions concerning the 

movement of chloromethane into the fetus or into 

nursing young through breast milk, and what 

amounts might result in harmful effects. 

1.7 HOW CAN FAMILIES REDUCE THE 

RISK OF EXPOSURE TO 

CHLOROMETHANE? 

If your doctor finds that you have been exposed to 

significant amounts of chloromethane, ask your 

doctor if children may also be exposed. When 

necessary your doctor may need to ask your state 

Department of Public Health to investigate. 

Families can reduce the risk of exposure to 

chloromethane by properly disposing of the older 

types of refrigerators that used chloromethane as a 
 PUBLIC HEALTH STATEMENT 

 CHLOROMETHANE CAS#: 74-87-3 

Division of Toxicology December 1998 

__________________________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 

refrigerant. If you live near a chemical plant that 

makes or uses chloromethane, or near a hazardous 

waste site that stores it, you should teach your 

children not to play in or around these sites. If 

family members work in a chemical facility that 

manufactures or uses chloromethane, they should 

become familiar with the safety practices that are 

used to prevent exposure to harmful levels. They 

should also become familiar with their rights to 

obtain information from their employer concerning 

the use of chloromethane and any potential 

exposure they might be subject to at work. 

You should teach your children about the dangers of 

breathing smoke from burning vinyl plastic or 

silicone rubber products, and should properly 

dispose of all such products. Chloromethane (as 

well as other toxic compounds) is released from 

burning polyvinyl chloride. If you are concerned 

that chloromethane may be in your drinking water, 

you can have your water tested and learn about the 

proper water filter to use to remove chloromethane 

(as well as other possible contaminants) from your 

drinking water. If you are concerned that products 

you are using might contain chloromethane, you can 

check the labels for ingredients or contact the 

manufacturer for additional information. 

1.8 IS THERE A MEDICAL TEST TO 

DETERMINE WHETHER I HAVE BEEN 

EXPOSED TO CHLOROMETHANE? 

 

There are no known reliable medical tests to 

determine whether you have been exposed to 

chloromethane. Symptoms resembling drunkenness 

and food poisoning, along with a sweet odor of the 

breath, may alert doctors that a person has been 

exposed to chloromethane. 

1.9 WHAT RECOMMENDATIONS HAS THE 

FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH? 

The federal government develops regulations and 

recommendations (sometimes called advisories or 

guidelines) to protect public health. Regulations 

can be enforced by law. Federal agencies that 

develop regulations for toxic substances include the 

Environmental Protection Agency (EPA), the 

Occupational Safety and Health Administration 

(OSHA), and the Food and Drug Administration 

(FDA). Recommendations provide valuable 

guidelines to protect public health but cannot be 

enforced by law. Federal organizations that develop 

recommendations for toxic substances include the 

Agency for Toxic Substances and Disease Registry 

(ATSDR) and the National Institute for 

Occupational Safety and Health (NIOSH). 

Regulations and recommendations can be expressed 

in not-to-exceed levels in air, water, soil, or food 

that are usually based on levels that affect animals; 

then they are adjusted to help protect people. 

Sometimes these not-to-exceed levels differ among 

federal organizations because of different exposure 

times (an 8-hour workday or a 24-hour day), the use 

of different animal studies, or other factors. 

Recommendations and regulations are also 

periodically updated as more information becomes 

available. For the most current information, check 

with the federal agency or organization that 

provides it. Some regulations and 

recommendations for chloromethane include the 

following: 

To protect workers, OSHA has set a regulation of 

an average permissible exposure limit of 50 parts of 
 PUBLIC HEALTH STATEMENT 

 CHLOROMETHANE CAS#: 74-87-3 

Division of Toxicology December 1998 

__________________________________________________________________________________________

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 

chloromethane per million parts of workroom air 

(50 ppm) during each 8-hour work shift in a 40-

hour workweek. 

1.10 WHERE CAN I GET MORE 

INFORMATION? 

If you have any more questions or concerns, 

please contact your community or state health or 

environmental quality department or: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, Mailstop F-32 

Atlanta, GA 30333 

Information line and technical assistance: 

Phone: 888-422-8737 

FAX: (770)-488-4178 

ATSDR can also tell you the location of 

occupational and environmental health clinics. 

These clinics specialize in recognizing, evaluating, 

and treating illnesses resulting from exposure to 

hazardous substances. 

To order toxicological profiles, contact: 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

Phone: 800-553-6847 or 703-605-6000 

Reference 

Agency for Toxic Substances and Disease Registry 

(ATSDR). 1998. Toxicological profile for 

chloromethane. Atlanta, GA: U.S. Department of 

Health and Human Services, Public Health Service.