What Is Asbestos?

Asbestos is a group of naturally occurring fibrous minerals. These minerals, found in soil and rocks in many parts of the world, are made of magnesium, silicon, and other elements. Some asbestos fibers are curly (or "serpentine"). The most common asbestos in industrial use, known as chrysotile, or white asbestos, has curly fibers. Other asbestos fibers are straight and needle-like (or "amphibole"). These include amosite, crocidolite, tremolite, actinolite, and anthophyllite. Asbestos fibers are resistant to heat and many chemicals. As a result, asbestos has been used as an insulating material since ancient times. Since the industrial revolution, asbestos was used to insulate factories, schools, homes, and ships, to make automobile brake and clutch parts, roofing shingles, ceiling and floor tiles, cement, and textiles, and hundreds of other products.

During the first half of the 1900s, growing evidence demonstrated that asbestos is a health hazard causing scarring of the lungs. In the early 1900s, exposure to asbestos dust in the workplace was not controlled. Beginning in England in the 1930s, steps were taken to protect workers in the asbestos industry by installing ventilation and exhaust systems. However, in the huge shipbuilding effort during World War II, large numbers of workers were exposed to high levels of asbestos. As asbestos-related cancers became better recognized in the second half of the twentieth century, additional measures were taken to reduce exposure, and exposure standards were established. In addition to more careful handling, there has been a dramatic decrease in the import and use of asbestos since the mid-1960s, and alternative insulating materials have been developed. As a result, asbestos exposure has dropped dramatically in the United States. However, exposure continues in some other countries. And in this country, there is still a potential for exposure from asbestos that remains in place in older buildings, water pipes, and other settings.

How Are People Exposed to Asbestos?

People are exposed to asbestos mainly through inhaling fibers in the air they breathe. This may occur when mining and processing asbestos, producing asbestos-containing products, or installing asbestos insulation. It may also occur when older asbestos-containing materials begin to break down. In any of these situations, asbestos fibers tend to create a dust composed of tiny particles that can float in the air. In addition, asbestos can enter the body through ingestion. This may occur when people consume contaminated food or liquids (such as water that flows through asbestos cement pipes). It may also occur when people cough up asbestos they have inhaled, then swallow their saliva.

Many people are exposed to very low levels of naturally occurring asbestos in outdoor air as a result of erosion of asbestos-bearing rocks. The potential for such exposure is higher in areas where rocks have higher asbestos content. After the collapse of the World Trade Center in 2001, there was concern about the presence of asbestos in the dust. Recommendations were made for testing and cleaning of residences in Lower Manhattan to minimize any health risks from such exposures.

However, the people with the heaviest exposure were those who worked in asbestos industries, such as shipbuilding and insulating. Many of these people recall working in thick clouds of asbestos dust, day after day.

Family members of asbestos workers are also potentially exposed to higher levels of asbestos because the fibers are carried home on the workers’ clothing, and can then be inhaled by others in the household. Removing asbestos from homes and other buildings can cause some exposure, although modern asbestos abatement workers are trained to use appropriate protective equipment to minimize exposure.

Exposure to asbestos-containing building material is also a concern, particularly in older buildings. If building materials like insulation and ceiling and floor tiles begin to decompose over time, asbestos fibers can be found in indoor air and may pose a threat to human health (EPA). There is no risk to human health if the asbestos is bonded into intact finished products, such as walls and tiles. As long as the material is not damaged or disturbed, for example by drilling or remodeling, there is no way for the fibers to be released into the air and inhaled. Maintenance workers who sweep up and dispose of the asbestos dust or handle damaged asbestos-containing building materials are often exposed to higher levels than other occupants of these buildings.

Asbestos may be detected in the water supply as well as in the air. It may be released into the water through several sources, such as erosion or natural deposits, corrosion from asbestos-cement pipes, and the break down of roofing materials containing asbestos that are then transported into sewers.

Although use of asbestos has declined in many developed countries, its use continues to present a hazard in other parts of the world. More than 70% of the world’s asbestos production is used in Eastern Europe, Latin America, and Asia.

Does Asbestos Cause Cancer?

Lung Cancer

Inhalation of asbestos fibers has been proven to cause lung cancer. The connection between asbestos exposure and lung cancer was noted as early as 1925, and confirmed by many epidemiologic studies of asbestos-exposed workers over the next 70 years. All four main types of commercially used asbestos, chrysotile, amosite, anthophyllite, and mixtures containing crocidolite, are associated with an increased risk of lung cancer. An increase in lung cancer has also been observed after exposure to minerals containing tremolite and actinolite, and to tremolitic material mixed with anthophyllite and small amounts of chrysotile (IARC-Supp 17).

Approximately 1 in 7 people who suffer from asbestosis, a lung disease caused by prolonged high exposure, eventually develops lung cancer. The higher the exposure to asbestos, the higher the risk of lung cancer. Smoking acts together with asbestos to greatly increase the risk of lung cancer.; asbestos workers who smoke face a much higher risk than asbestos workers who do not smoke. Evidence suggests that asbestos-exposed workers who quit smoking can reduce their risk of developing lung cancer by as much as 50% within 5 years of quitting (NCI).

Mesothelioma

Mesothelioma is a rare form of cancer that affects the thin membranes lining the abdomen and chest. Mesothelioma is closely linked with asbestos; most cases of mesothelioma result from direct occupational asbestos exposure.

However, mesotheliomas have been observed not only among workers who are occupationally exposed to crocidolite, amosite, and chrysotile, but also among their family members and people living in the neighborhoods surrounding asbestos factories and mines (IARC). It is estimated that one third of the mesothelioma cases in the United States may be due to non-occupational exposure such as these (IARC). Although scientists know that the risk of developing mesothelioma increases with the amount of asbestos exposure, there is no way to measure exactly the minimum amount of asbestos exposure that can lead to mesothelioma. However, mesothelioma is very rare in the general population of the United States.

Unlike lung cancer, mesothelioma risk is not increased among smokers.

Other Types of Cancer

There is evidence that asbestos also causes other types of cancer, although the evidence is not as strong as for lung cancer and mesothelioma. Cancer of the larynx is one such cancer, although it has been difficult to separate the contributory role of asbestos from the strong effect of smoking. Many studies have also found an increase in stomach and colon cancer among workers in the asbestos industry, although this association is still debated.

What Do Epidemiologic Studies Show?

As explained above, much of the evidence about asbestos-associated cancers comes from epidemiologic studies.

What Do Animal Studies Show?

Tests on several different species, using several different methods of exposure, have confirmed that asbestos causes cancer in animals. Inhalation exposure of asbestos has been tested in rats, intrapleural administration (injection into the chest cavity) in rats and hamsters; intraperitoneal (injection into the abdominal cavity) injection in mice, rats, and hamsters; and ingestion in rats and hamsters (IARC). All commercial forms of asbestos have produced tumors in animals. The size and shape of the asbestos fibers influence the incidence of tumors; smaller fibers – less than 0.5 micrometers (um) in diameter (1 micrometer, or "micron", is 1 millionth of a meter) – seem more hazardous, perhaps because they are more likely to reach the deepest parts of the lungs (IARC).

A series of lifetime feeding studies have been done to determine if oral exposure to asbestos increases the risk of cancer. These studies reported that short-range (98% of fibers are shorter than 10 um) asbestos fibers did not significantly increase the tumor incidence in rats; however, the incidence of benign tumors of the large intestines in male rats increased when the animals were exposed to intermediate-range (65% of fibers are longer than 10 um) asbestos fibers (EPA).

What Do the Expert Agencies Say?

Based on animal and human evidence like the examples above, expert agencies have evaluated the cancer causing nature of asbestos.

The National Toxicology Program evaluates exposures that may be carcinogenic (cause cancer). Exposures that are thought to be carcinogenic are included in the Reports on Carcinogens, published every 2 years. Each exposure is assigned to 1 of 2 categories: "known to be human carcinogens," and "reasonably anticipated to be human carcinogens." The first category includes substances for which human studies (epidemiology studies and/or experimental studies) provide "sufficient evidence" of carcinogenicity in humans. The second category includes substances for which there is limited evidence of carcinogenicity in humans and/or sufficient evidence of carcinogenicity in experimental animals.

Using this scheme, the National Toxicology Program classifies asbestos as a known human carcinogen.

The International Agency for Research on Cancer (IARC also evaluates exposures that may be carcinogenic. IARC classifies exposures into one of four categories:

• Group 1 exposures are those "known to be carcinogenic to humans," usually based on "sufficient" human evidence, but sometimes based on "sufficient" evidence in experimental animals and "strong" human evidence.

• Group 2 exposures are divided into two categories. Group 2A ("probably carcinogenic to humans") has stronger evidence, and Group 2B ("possibly carcinogenic to humans") has weaker evidence.

• Group 3 exposures are not considered classifiable, because available evidence is limited or inadequate.

• Group 4 exposures are "probably not carcinogenic to humans," based on evidence suggesting lack of carcinogenicity in humans and in experimental animals.

IARC rated asbestos a known human carcinogen (Group 1).

The Environmental Protection Agency, through its Integrated Risk Information System, uses a classification scheme very similar to that of IARC. It classifies exposures into 1 of 5 categories:

• (A) Human carcinogen
• (B) Probable human carcinogen
• (C) Possible human carcinogen
• (D) Not classifiable as to human carcinogenicity
• (E) Evidence of noncarcinogenicity for humans

EPA classified asbestos as a human carcinogen.

Does Asbestos Cause Any Other Health Problems?

The major health problem caused by asbestos exposure, aside from cancer, is asbestosis. This is a scarring (or "fibrotic") disease of the lungs that develops when a person breathes high levels of asbestos over time. The principal symptoms of asbestosis are shortness of breath and cough. Asbestosis is a serious disease that can result in disability or death. It is most commonly found among asbestos workers. Asbestos can also result in scar-like tissue in the membranes around the lung, called pleural thickening, skin lesions like warts, and immunological effects.

What Should I Do if I’ve Been Exposed to Asbestos?

If you have been exposed to asbestos, it is important to assess the amount of your exposure. If you were exposed only very briefly, or only at very low levels, your risk of a resulting disease is minimal. However, it you were exposed at high levels, you may be at increased risk of the diseases discussed above. You can protect your health in several ways:

• If you are a smoker, it is essential that you stop smoking.
• Get regular health checkups from a doctor experienced with asbestos-related diseases. People with heavy asbestos exposure often have periodic chest x-rays and lung function tests.
• It may be advisable for you to receive vaccines against flu and pneumonia. Discuss this with your physician.
• Get prompt medical attention for any respiratory illness.

How Can I Avoid Exposure to Asbestos?

You should also avoid any future exposure to asbestos. If there is a possibility of on-the-job exposure, like renovating old buildings for example, then you should use all protective equipment, work practices, and safety procedures designed for working around asbestos (NCI). If you live in an older home, there may be asbestos-containing insulation or other materials. A knowledgeable expert can check your home to determine if there is any asbestos and if it poses any risk of exposure. This may involve testing the air for asbestos levels. You may then decide to have the asbestos removed from your home. You should hire a qualified contractor to perform this job to avoid contaminating your home further or causing any exposure to the workers. You should not attempt do remove asbestos-containing material yourself.

What's the Bottom Line?

Asbestos is well recognized as a carcinogen. It causes lung cancer, mesothelioma, and other cancers. The people at highest risk are those with very heavy exposure, usually over many years on the job. Smoking acts together with asbestos to greatly increase the risk of lung cancer. While asbestos use is much less common now than it was years ago, there is still a potential for exposure in older buildings and products.

Other Resources Addressing Asbestos

Agency for Toxic Substances and Disease Registry (ATSDR). ToxFAQs for Asbestos.
Internet Address: www.atsdr.cdc.gov/tfacts61.html
Telephone: 1-888-422-8737

Environmental Protection Agency (EPA)
Internet Address: www.epa.gov/asbestos/
Telephone: 202-260-2090

International Agency for Research on Cancer (IARC)
Asbestos, Vol 14 at
www-cie.iarc.fr/htdocs/indexes/vol14index.html
Asbestos, Supplement 7, at
www-cie.iarc.fr/htdocs/monographs/suppl7/asbestos.html

National Cancer Institute (NCI). Asbestos Exposure: Questions and Answers
Internet Address: www.cancer.gov/cancertopics/factsheet/Risk/asbestos
Telephone: 1-800-422-6237

National Institutes of Health, National Institute of Environmental Health Sciences, National Toxicology Program. Eleventh report on carcinogens.
Internet Address: ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s016asbe.pdf

Revised: 01/31/2006