Nearby natural asbestos
Nearby natural asbestos deposits increase mesothelioma risk.(Pulmonary Medicine)
Mesothelioma is significantly more likely to occur in people who live near deposits of naturally occurring asbestos, Marc Schenker, M.D., and his colleagues reported.
The largest epidemiologic study of mesothelioma and naturally occurring asbestos to date concluded that the risk of mesothelioma decreased by more than 6% for every 10 km the subject lived away from the nearest asbestos deposit, said Dr. Schenker and his associates at the University of California, Davis.
"This study supports the hypothesis that [naturally occurring asbestos] causes mesothelioma," Dr. Schenker said during a teleconference sponsored by the university. "It's the first to demonstrate this with a population-based approach, and I would hope that now this discussion can move forward to how to reduce the risk of this preventable form of cancer."
The investigators matched 2,907 mesothelioma cases (2,354 in males) with the same number of pancreatic cancer cases, all of which occurred in California from 1988-1997. They then compared the place of residence at time of diagnosis with the nearest asbestos deposits.
After controlling for age, sex, race, and occupational exposure, there was a 6.3% decrease in the odds of the case being a mesothelioma for every 10 km the subject lived away from an asbestos deposit.
The study also concluded that mesothelioma was strongly associated with occupation in men. Men who were boiler-makers, insulators, plumbers, pipefitters, steamfitters, sheet metal workers, electricians, and painters had a high probability of asbestos exposure.
Although the study establishes a strong link between the cancer and environmental exposure, the absolute risk of mesothelioma remains low, Dr. Schenker said. El Dorado Hills, Calif., which received federal assistance to clean up a naturally occurring asbestos deposit last year, has a population of 32,000, and a mesothelioma case rate of 2 per year.
"The total number of cases in the country is about the same as cancers that occur due to environmental tobacco smoke," Dr. Schenker said.
California has large amounts of asbestos-containing rock, occurring mostly in the Sierra Nevada, Coast Range, and Klamath Mountains in the north and central regions of the state. Many of these areas are experiencing heavy residential growth, which will eventually reflect the presence of the dangerous mineral, Dr. Schenker said.
"The cases we see now are related to exposures 20 or more years ago. I've seen estimates that in the foothills, the population is expected to triple, so exposures today will be reflected in another 20 years. I'm hopeful those cancers will be prevented if we take action now."
Responses need to be "logical, realistic, and affordable," he said. "For instance, when a school is located on [an asbestos] seam, we would want to address that. Ideally, for instance, we wouldn't want to even put a school in that location."
More studies, including deposit mapping and modeling of airborne exposure, are necessary to mount a comprehensive response. Dr. Schenker said. "We should institute public health education efforts through changes in engineering and legislation."
California is not the only area with asbestos deposits. The Environmental Protection Agency (EPA) has also identified 324 such sites in the Eastern United States. When undisturbed, these mineral deposits are not a threat to health. Covering exposed areas with grass or other vegetation, and paving dirt roads, will significantly reduce the risk that the particles will become airborne, the EPA said.
For more information on naturally occurring asbestos, visit the following web site: www.epa.gov/asbestos/clean.htm.
BY MICHELE G. SULLIVAN
Mid-Atlantic Bureau