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Asbestos-related cancer and the amphibole hypothesis - Stayner and colleagues respond.

Stayner-LT; Dankovic-DA; Lemen-RA
Am J Publ Health 1997 Apr; 87(4):688
We thank Dr Wagner for his comments regarding our paper. We do not believe our article misrepresented the evidence for an association between mesothelioma and asbestos exposure. We agree with Dr Wagner's main point, which is that the incidence of mesothelioma is greater in epidemiologic studies of workers exposed to crocidolite than either chrysotile or amosite, and recognized this fact in our paper. Interpretation of these epidemiologic findings is hampered by the lack of control for potential differences in exposure levels and fiber dimensions. Nonetheless, ample evidence suggests that exposure to chrysotile is a risk factor for mesothelioma. As we reviewed in our paper, numerous cases of mesothelioma have been reported in several studies of workers exposed to chrysotile. In fact, Dr Wagner recognized in his early papers that there were cases of mesothelioma in South Africa and Britain whose only known exposure was to chrysotile asbestos. Toxicologic studies, some of which were conducted by Dr Wagner, also demonstrate an increase in mesotheliomas among animals exposed to chrysotile. Dr Wagner suggests mesotheliomas occur in chrysotile-exposed workers only when there is tremolite contamination. While this statement is technically correct, it is virtually uninformative. Contamination by small percentages (<1%) of tremolite has been present in all of the reported epidemiologic studies of chrysotile- exposed workers. Unfortunately, studies of workers exposed to pure chrysotile have yet to be reported. In addition, this issue may be viewed as academic since workers are exposed to a mixture of fiber types and to commercial chrysotile containing tremolite. A key point of our paper is that irrespective of mesothelioma, exposure to chrysotile asbestos should be viewed as a significant carcinogenic hazard. There is no serious disagreement in the scientific community that chrysotile asbestos exposure is causally associated with lung cancer and appears to be as potent a lung carcinogen as crocidolite or other forms of asbestos. The excess of lung cancer is generally far larger than the excess of mesothelioma in most epidemiologic studies of asbestos-exposed workers, a fact recognized in a recent review by Dr Wagner. Dr Wagner suggested that our paper and the accompanying editorial may have "confused readers." We hope that this letter will help to clarify any remaining confusion about exposure to chrysotile asbestos. Such exposure should be regarded as a serious potential public health hazard.
Asbestos-dust; Asbestos-fibers; Asbestosis; Occupational-exposure; Occupational-hazards; Exposure-assessment; Workplace-studies
Leslie T. Stayner, PhD, National Institute for Occupational Safety and Health, Robert A. Taft Laboratories, 4676 Columbia Pkwy-Mailstop C15, Cincinnati, OH 45226-1998
12001-28-4; 12001-29-5; 12172-73-5
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American Journal of Public Health