Exposure to Low Levels of Asbestos from Rocks Can Cause Malignant Mesothelioma

Malignant Mesothelioma Risk

Californians who live close to naturally occurring asbestos sources and who are exposed to low levels of the mineral are at increased risk for developing malignant mesothelioma, a serious cancer of the membrane covering the lung, according to a new study published in the second issue of the October 2005 American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.

Marc B. Schenker, M.D., M.P.H., of the Division of Environmental and Occupational Health, at the University of California, Davis, along with four associates, investigated 2,908 malignant mesothelioma cases reported over a 10-year period (1988 to 1997). Over 50 percent of the men and 58 percent of the women, all of whom were listed in the California Cancer Registry, either had no or low occupational exposure to asbestos.

"People who lived closer to an asbestos source had a greater chance of having mesothelioma, and the chance decreased steadily as the distance increased," said Dr. Schenker.

According to the article, the odds of developing mesothelioma decreased 6.3 percent for every 10 kilometers farther from the asbestos source.

The authors explained that a major strength of the study was the very large number of mesothelioma cases used to assess the potentially weak association between exposure to naturally occurring asbestos and mesothelioma incidence.

"Epidemiological studies have confirmed that occupational exposure to asbestos causes mesothelioma," said Dr. Schenker. "However, almost all population-based studies have found that many mesothelioma cases had no known occupational exposure to asbestos."

Considered rare, mesothelioma usually takes from 30 to 40 years after exposure to develop.