Lack of Tremolite in UICC Reference Chrysotile and the Implications for Carcinogenicity

Abstract

In 1935, Lynch and Smith reported that in addition to causing asbestosis, asbestos might also cause lung cancer and soon after Heuper (1942) felt sufficient evidence existed to call asbestos a carcinogen. There is continuing controversy about aspects of asbestos-related disease. Few argue about the carcinogenicity of asbestos; disagreements exist regarding other issues, such as if asbestosis is needed before a lung cancer can be attributed to asbestos (Churg et al., 1984). Some of these controversial issues have been addressed elsewhere by Frank (1994). One area of controversy has been the ability of chrysotile to produce lung cancer and mesothelioma. In spite of much evidence to the contrary, some still hold to the view that chrysotile, as chrysotile, does not cause these. Central to this belief has been what has been called the (Wagner, 1986; McDonald et al., 1989). Certain policy questions may be influenced by the claimed lack of chrysotile's ability to cause disease. One should recall that some have advocated that only certain fibre types, such as tremolite in chrysotile, produce disease, especially cancer (Churg et al., 1984; Wagner, 1986), but other data have shown this to be untenable (Begin et al., 1992; Stayner et al., 1996). There is now evidence by Karjalainen et al. (1994) of the ability even of anthophyllite to produce mesothelioma. Few populations have ever been identified where only chrysotile exposure had taken place, but Mancuso (1988) documented mesotheliomas among such workers in the U.S. Despite evidence to the contrary, some authors (Case, 1991; Dunnigan, 1988; Mossman and Gee, 1989; Mossman et al., 1990) have persisted in putting forth information that is not in keeping with most other scientific evidence. One reason for the erroneous conclusion that chrysotile does not cause mesothelioma may be that tremolite is more readily found in lung tissue than chrysotile (Churg et al., 1984). Although tissue analysis has been useful for some issues, given the differences between amphibole and chrysotile persistence in vivo, concluding that fibres remaining caused disease is fraught with difficulty. A detailed analysis of the issue of the amphibole hypothesis has recently been published by Stayner et al. (1996), with the conclusion that dismissing chrysotile as a cause of mesothelioma and other asbestos-related diseases is inappropriate.