© 2006 American Thoracic Society
Residential Proximity to Naturally Occurring Asbestos: Health Risk or Ecologic Fallacy?From the Authors:We agree with Dr. Brodkin and colleagues, and discussed in our article that the absence of lifetime residential history is a limitation of the study (1). In a separate analysis, not reported, we have shown an absence of differential movement of former asbestos union members from the San Francisco Bay Area to California counties with more naturally occurring asbestos (NOA). This suggests that confounding due to prior occupational exposure does not explain our findings. Direct measurement of individual asbestos exposure is an interesting idea but one that would be impossible with this study design and resources. As we noted, a prospective case-control study of incident mesotheliomas with complete lifetime residential and occupational histories would help address these issues. Recent work by the EPA in California has shown that significantly increased airborne exposure to asbestos fibers can occur with activities such as running and playing baseball on unpaved fields with NOA (2). Additional work is needed to characterize behavioral, demographic, geologic, and meteorological factors associated with increased asbestos fiber exposure from NOA. The more important question is how these findings should be interpreted and used by scientists and public health officials. Asbestos and mesothelioma is one of the most well-established and specific associations of any known occupational carcinogen. Studies around the world have demonstrated an association of NOA and mesothelioma, both from household uses such as whitewash and from residential proximity to NOA (3, 4). These studies suggest that there is no threshold level for risk of mesothelioma from asbestos. Important questions remaining, then, are whether the association with NOA occurs in this country and whether efforts to reduce human exposure to NOA are appropriate in view of the scientific uncertainties. Our data support recognition of the association, and we believe best public health practice principles support actions to reduce those exposures of greatest risk, such as exposures from quarries with amphibole asbestos located near residential areas. As Sir Richard Doll noted, "The best sort of experiment is an experiment in prevention.... Proof in the strict logical sense may not have been obtained but does that matter if the disease has disappeared?" (5)
University of California at Davis, Davis, California FOOTNOTES Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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