What is asbestos?
Asbestos is a group of minerals that occur naturally as bundles of fibers. These fibers, found in soil and rocks in many parts of the world, are made of silicon, oxygen, and other elements. There are 2 main types of asbestos fibers:
- Serpentine asbestos fibers are curly. The most common asbestos in industrial use, known as chrysotile, or white asbestos, has curly fibers.
- Amphibole asbestos fibers are straight and needle-like. There are several types of amphibole fibers, including amosite, crocidolite, tremolite, actinolite, and anthophyllite.
Amphiboles (particularly crocidolite) are considered to be more likely to cause cancer, but even the more commonly used chrysotile fibers have been linked to cancer.
Asbestos fibers are strong, resistant to heat and to many chemicals, and do not conduct electricity. As a result, asbestos has been used as an insulating material since ancient times. Since the industrial revolution, asbestos has been used to insulate factories, schools, homes, and ships, and to make automobile brake and clutch parts, roofing shingles, ceiling and floor tiles, cement, textiles, and hundreds of other products.
During the first half of the 1900s, growing evidence showed that breathing in asbestos caused 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 20th century, measures were taken to reduce exposure, including establishing exposure standards. 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, it is still used in some products, and there is still a potential for exposure to asbestos in older buildings, water pipes, and other settings. Heavier asbestos use continues in many other countries as well.
How are people exposed to asbestos?
People are exposed to asbestos mainly by inhaling fibers in the air they breathe. This may occur during mining and processing asbestos, making asbestos-containing products, or installing asbestos insulation. It may also occur when older buildings are demolished or renovated, or 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 fibers can be swallowed. This may happen 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, and 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. In some areas, 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.
However, the people with the heaviest exposure are those who worked in asbestos industries, such as shipbuilding and insulation. Many of these people recall working in thick clouds of asbestos dust, day after day.
Family members of asbestos workers can also be exposed to higher levels of asbestos because the fibers can be carried home on the workers' clothing, and can then be inhaled by others in the household.
Exposure to asbestos is also a concern 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 health threat. There is no health risk 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), the fibers are not released into the air. Maintenance workers who sweep up and dispose of the asbestos dust or handle damaged asbestos-containing materials are often exposed to higher levels than other occupants of these buildings. Removing asbestos from homes and other buildings can also cause some exposure, although modern asbestos abatement workers are trained to use appropriate protective equipment to minimize exposure.
Although use of asbestos has declined in many developed countries, its use is still a health hazard in some other parts of the world. Much of the world's asbestos production is used in Eastern Europe, Latin America, and Asia, and its use is on the rise in many of these areas. In 2005, the World Health Organization estimated that 125 million people worldwide were exposed to asbestos at work, despite the known links to cancer and other lung diseases for more than 60 years.
Does asbestos cause cancer?
Evidence from studies in both people and laboratory animals has shown that asbestos can increase the risk for some types of cancer.
When asbestos fibers in the air are inhaled, they may stick to mucus in the throat, trachea (windpipe), or bronchi (large breathing tubes of the lungs) and may be cleared by being coughed up or swallowed. But some fibers may reach the ends of the small airways in the lungs or penetrate into the outer lining of the lung and chest wall (known as the pleura). These fibers may irritate the cells in the lung or pleura and eventually cause lung cancer or mesothelioma.
