Document MMvVVwQdzNg8YXxKx4QOd6mLM

ST0I999I2 DOW CHEMICAL U.S.A. PLAINTIFF'S EXHIBIT 1603 Building September 4, 1979 midland. Michigan awao To: R. R. Cook - 1603 Building R. J. Moolenaar - 1702 Building From: G. G. Bond - U.S. Medical, Epidemiology, 1603 Bldg. RELATIVE HEALTH EFFECTS OF CROCIDOLITE AND CHRYSOTILE Summary Evidence that crocidolite poses a greater health risk than chrysotile comes principally from epidemiologic studies. These studies suffer from methodologic problems which make extrapolation of relative risk associated with exposure to the various asbestos forms tenuous at best. In addition, experimental animal studies suggest that asbestos may be acting solely as a vehicle for transporting cocarcinogens (trace metals and benzpyrene) into the lung. If this hypothesis for induction of asbestos cancer is valid for humans, then it is suggested that chryso tile would probably be the most potent cocarcinogen of the various forms of asbestos. Clearly then, the literature appears somewhat equivocal on the issue of relative risk associated with chrysotile and crocidolite, and each form of asbestos should be considered as a potential health risk. Epidemiologic Studies There have been several epidemiologic studies1-4 which suggest that chrysotile is the least dangerous form of asbestos with respect to adverse health effects. The evidence, however, appears rather weak and there are numerous methodologic problems associated with these studies which should preclude extrapolation of such a hypothesis. In a 1971 report, titled Airborne Asbestos^ and prepared for the National Research Council, the panel of experts on asbestos concluded: All epidemiologic studies that appear to indicate dif ferences in pathogenicity among types of asbestos are flawed by their lack of quantitative data on cumulative exposures,fiber characteristics, and the presence of cofactors. The different types, therefore, cannot be graded as to relative risk with respect to either asbestosis or neoplasia. AN OPERATING UNIT OP THE DOW CHEMICAL COMPANY 2- - September 4, 1979 Although the N.R.C. statements predate the studies by Enterline et al and Weiss\ the same laws cited in the statements apply to these two studies as weil. In the former study^ the authors could not determine smoking habits, admitted that exposure to mixtures of asbestos types probably occurred, and were only able to "roughly" classify dust levels needed for calculation of cumulative exposures. In the latter study^, no exposure Information of a quantitative nature was available, and the author also did not attempt to characterize smoking habits. Experimental Animal Studies The authors of the N.I.O.S.H. criteria document: Occupational Exposure to Asbestos6 indicate that both chrysotile and crocidolite were found to be markedly toxic to guinea pig macrophages in vitro. The authors argue that animal studies suggest a possible hypothesis for the induction of asbestos cancers; trace metals play an active co-carcinogenic role along with the exogenously derived carcinogen benzpyrene, while asbestos plays a passive role as a metal carrier. It is further argued that if this hypothesis was valid then chrysotile should be the most potent cocarcin ogen of the various forms of asbestos. This would be due to its rela tively high adsorption rate for benzpyrene and due to the intimate asso ciation of large amounts of nickel, chromium, manganese, and iron with certain forms of chrysotile. Conclusion Until better epidemiologic studies are done (i.e., studies of asbestos miners where type of fiber can be ascertained with greater certainty), it is difficult to argue convincingly that crocidolite poses a greater health hazard than does chrysotile. G. G. Bond, M.P.H. Epidemiologist - H&ES ST0I999I3 REFERENCES 1. Braun D. C., T. D. Truan. 1958. An epidemiological study of lung cancer In asbestos miners. AHA Archives Ind. Health 17:634. 2. McDonald J.C., M.R. Becklake, G.W. Gibbs, et al. 1971. Mortality in the chrysotile asbestos mines and mills of Quebec. Arch Environ Health 22:677. 3. Enterline P.E., V. Henderson. 1973. Type of asbestos and respiratory cancer in the asbestos Industry. Arch Environ Health 27:312. 4. Weiss, W. 1977. Mortality of a cohort exposed to chrysotile asbestos. J.O.M. 19(11):737. 5. Airborne Asbestos - 1971. Committee on Biologic Effects of Atmos pheric Pollutants of the Division of Medical Sciences, National Research Council. N.A.S. PB 198-581, U.S. Department of Commerce.6 6. Criteria for a recommended standard: Occupational exposure to asbestos. 1972. N.I.O.S.H. HSM 72-10267. ST0I999I4