Asbestos: facts and fiction.

Asbestos: Facts and Fiction I appreciate the opportunity to address the omissions, inaccuracies, and innuendos in the position paper by David P. Rall, "Media and Science: Harmless Dioxin, Benign CFCs, and Good Asbestos" (EHP 102:10). Unfortunately, Rail not only misinterprets the conclusions of our 1990 Science article by Mossman et al. (1) but he fails to mention the database, scientific panel reports, and working groups which have supported our views. Our 1990 article reported on recent papers in the peer-reviewed literature and two international symposia, one at the International Agency for Research on Cancer (2) and the other at Harvard University (3), all concluding that chrysotile fibers are less active than amphibole types (crocidolite, amosite, tremolite) of asbestos in the causation of mesothelioma in man. In his summary of the [ARC meeting, Sir Richard Doll, an eminent epidemiologist, concluded "there is the difference between the effects of chrysotile and amphiboles, which is so great in relation to mesothelioma that it is possible to argue that chrysotile does not cause mesothelioma at all" (2). This observation has been supported by numerous peer-reviewed papers and working groups subsequently (4-6). Rall's statement that "countervailing human data on the carcinogenic effects of chrysotile asbestos (including large numbers of mesotheliomas among Canadians)" exist is reminiscent of a similar claim by Nicholson et al. (7) in which his exaggerated numbers were correctly put into perspective by the epidemiologists studying the Canadian workers (8). His. unreferenced conclusion that mesotheliomas are "largely from chrysotile exposure" in insulation workers and family members who were exposed to "low doses" ignores the fact that these individuals encountered mixed exposures to chrysotile and amphiboles at much higher concentrations than levels of asbestos (predominantly chrysotile) occurring in homes and public buildings today. Moreover, Rall does not acknowledge the significant content of amphibole fibers in the lungs of these workers (9) as well as recent studies showing a correlation between the lung burden of tremolite, but not chrysotile, in the lungs of Canadian miners with mesothelioma (10). In stating that "a threshold of effect has never been found" for asbestos, Rall stands behind the outdated "one fiber can kill" theory of carcinogenesis. However, Rall fails to mention data supporting a threshold for chrysotile in lung cancer (11, asbestosis (12), and mesothelioma (13) as well as a panel report from the Health Effects Institute-Asbestos Research (HEI-AR) detailing animal and in vitro dose-response studies exhibiting noobserved adverse effect levels (NOAELs) for asbestos (14). Our recent work documents a dose-dependent increase in asbestos-induced proto-oncogene activation in mesothelial cells with no induction at lowest concentrations of fibers tested and an enhanced potency of crocidolite asbestos in comparison to chrysotile (15). The emerging database indicating: 1) extremely low concentrations of airborne asbestos fibers in public buildings, schools, and outdoor air as compared to past levels giving rise to disease; 2) minuscule risks from asbestos at levels in indoor and outdoor air today when contrasted with other voluntary and involuntary risks in modern society; and 3) protracted, higher airborne concentrations of fibers after improperly performed asbestos removal operations, led us and other (14,16-18) to question the often unmerited and financially devastating consequences of asbestos abatement from schools and public buildings as well as possible dangers to asbestos-removal workers. As quoted in a recent council report from the American Medical Association (16):