Toxicity Profiles

RAGs A Format for Asbestos - CAS Number 1332214

Asbestos is the name that’s used for a group of six different fibrous minerals (amosite, chrysotile, crocidolite, and the fibrous varieties of tremolite, actinolite, and anthophyllite) that occur naturally in soil and rocks in some areas. Asbestos fibers vary in length and may be straight or curled. Chrysotile is the only asbestos in the curled (serpentine) group, whereas the straight (amphibole) group is represented by actinolite, amosite, anthophyllite, crocidolite, and tremolite. Asbestos fibers are chemically inert, or nearly so. They do not evaporate, dissolve, burn, or undergo significant reactions with other chemicals. The essential characteristic of asbestos minerals is their fibrous nature. The gross fibers, which are visible to the naked eye, are actually bundles of much finer fibrils that are submicroscopic in size. Asbestos has been widely used because it is noncombustible and nonconducting and has a relatively high chemical resistance. Asbestos was introduced in the late 1800s to make heat- and acid-resistant fabrics. It is now used in a variety of applications such as in the building industry to strengthen cement and plastics; for heat insulation and sound absorption; in brake shoes and clutch plates; and as asbestos cloths for fire protection, including the cladding of structural steel beams. Asbestos also has valuable filtration properties. In 1991, a U.S. federal court overturned an EPA regulation that banned most uses of asbestos by 1997. Presently, only asbestos-containing products that were not being manufactured, imported, or processed after July 1989, remain subject to the prohibition requirements of the EPA regulation.

Asbestos mainly affects the lungs. Changes in the membrane surrounding the lung are quite common in workers exposed to asbestos. These are also sometimes found in people living in areas with high levels of asbestos in the air, but effects on breathing usually aren’t serious. Breathing very high levels of asbestos may result in a slow buildup of scar-like tissue in the lungs and in the membrane that surrounds the lungs. This disease is called asbestosis, and is usually found in asbestos workers and not in the general public. It has been estimated that cumulative exposures of 17-75 fibers-year/mL would result in fibrotic lung lesions, and cumulative exposures of 3.5-300 fibers-year/mL would cause death in humans. People with asbestosis have shortness of breath, often along with a cough and sometimes heart enlargement. This is a serious disease and can eventually lead to disability or death.

It is known that asbestos causes cancer in people. There are two types of cancer caused by exposure to high levels of asbestos: cancer of the lung tissue itself and mesothelioma, a cancer of the membrane that surrounds the lung and other internal organs. Both of these are usually fatal. These diseases don’t develop immediately, but show up only after many years. Interactions between cigarette smoke and asbestos increase your chances of getting lung cancer. Studies of workers suggest that breathing asbestos can increase the chances of getting cancer in other parts of the body (stomach, intestines, esophagus, pancreas, kidneys), but this is not certain. People who are exposed to lower levels of asbestos may also have an increased risk of developing cancer, but the risks are usually small and are difficult to measure.

Based on EPA guidelines, asbestos was assigned to weight-of-evidence group A, human carcinogen. Based on observations of increased mortality and incidence of lung cancer, mesotheliomas, and gastrointestinal cancer in occupationally exposed workers are consistent across investigators and study populations.

The following is a presentation of the toxicity information associated with Asbestos:

• The Inhalation Unit Risk is 2.3E-04 (fibers/L)-1.
• The Inhalation Risk study target organ is lung.
• The Inhalation Unit Risk study cancer type is lung cancer.
• The Inhalation Unit Risk is based on the U.S. EPA study from 1986.