Non-occupational exposure to chrysotile asbestos and the risk of lung cancer
Reviewers: Kenneth Blank, MD
Source: The New England Journal of Medicine, May 28, 1998 Vol 338, No. 22, p.1565
Asbestos is a mineral fiber, which has many forms. Chrysotile, which is mined primarily in Quebec Canada, is the most common asbestos found in the United States. Asbestos has long been known as a human carcinogen. Lung, pleural, laryngeal and gastrointestinal cancer have all been associated with asbestos exposure. The risk of developing cancer from asbestos is related to both the amount of exposure and the length of time since exposure (cancer from asbestos exposure typically takes decades to develop). In addition to cancer, asbestos also causes a potentially lethal inflammatory disease of the lungs, appropriately called asbestosis. Based on the evidence linking asbestos to cancer and lung disease, the Environmental Protection Agency (EPA) declared asbestos a carcinogen and new use of asbestos in the United States has virtually ended.
Following the EPA's regulations heavy asbestos exposure has virtually subsided in the United States and attention has now been turned towards determining the risk of cancer from lower doses of asbestos. Asbestos remains in schools, homes and commercial buildings across the country. Asbestos in these structures is not a public health hazard unless it is disturbed and gains access to the air, where it can be inhaled. The current standard of practice is to visually inspect asbestos in schools, as long as the asbestos is in place and undisturbed, do nothing.
Materials and Methods
However, debate continues regarding the risk posed to the general population by low levels of asbestos. In the May 28, 1998 issue of the New England Journal of Medicine, Camus and colleagues attempt to estimate the risk of non-occupational exposure to asbestos. Women in provinces of Quebec where asbestos is mined were compared to women in other parts of Canada in regard to the risk of dying from lung cancer. In addition, this risk was compared to the risk of lung cancer based on the EPA's risk assessment model. Men were excluded to prevent accidentally including asbestos miners who would be sure to have very high exposure.
The authors calculated a standardized mortality ratio of 1.0 due to lung cancer in the women in the mining towns compared to women in non-mining areas, which means that there was no excess risk of dying from lung cancer. In contrast the EPA risk model predicted a relative risk of death due to lung cancer of 2.1 given the level of asbestos in the mining towns.
Discussion and ConclusionsA variety of explanations can be offered to account for the discrepancy between the EPA's model and the author's calculations. These explanations include:
- The overestimation of the women's past asbestos exposure;
- the fact that the EPA's model is based on amphibole asbestos not chrysotile asbestos which the women were exposed too;
- the fact that the EPA model is based on exposure to small asbestos fibers not the large ones that these women were likely exposed too.
Asbestos sales to developing nations remain strong and properly estimating the health risk of low levels of asbestos is critical. In a sharply worded editorial accompanying the article, Philip J. Landrigan of the Mount Sinai School of Medicine in New York argues that given the myriad of explanations accounting for the discrepancy, the current regulatory standards for asbestos should remain in place. Furthermore, he cautions against concluding that asbestos can be used without risk in developing nations.