The risk of mesothelioma from exposure to chrysotile asbestos.

PURPOSE OF REVIEW This review assesses the risk of developing diffuse malignant mesothelioma of the pleura from exposures to chrysotile fibers and contrasts it with the known risk of amphibole asbestos. RECENT FINDINGS Although a rare cancer, the mortality rates of pleural mesothelioma continue to be significantly elevated because of past occupational exposures to airborne asbestos fibers. New analyses of occupational epidemiologic studies for highly exposed workers show a substantially lower potency and suggest an empiric threshold for chrysotile compared with amphibole asbestos. Important kinetic and pathological differences between chrysotile and amphiboles have been substantiated that support chrysotile's impotency in causing pleural mesothelioma. SUMMARY Excess risk of pleural mesothelioma from past exposures to asbestos, as evidenced by a trend of high incidence rates during the last half century, appears to be the result of nonchrysotile asbestiform fibers. Although scientific efforts and legal arguments continue, the risk of pleural mesothelioma in human populations is probably negligible for exposures to airborne chrysotile asbestos that is not known to be contaminated by amphibole. This distinction for asbestos fiber types is pivotal for understanding hazards and characterizing risks of continued use of natural chrysotile asbestos today and also new nanofibers.