Chrysotile asbestos: enough is enough
Authors: Mark R Cullen
Journal: The Lancet (1998)

In a spate of recent publications, 1 McDonald JC McDonald AD Chrysotile, tremolite and carcinogenicity. Ann Occup Hyg. 1997; 41: 699-705 Crossref PubMed Google Scholar , 2 Liddell FDK McDonald AD McDonald JC The 1891–1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992. Ann Occup Hyg. 1997; 41: 13-36 PubMed Google Scholar , 3 McDonald AD Case BW Churg A et al. Mesothelioma in Quebec chrysotile miners and millers: epidemiology and aetiology. Ann Occup Hyg. 1997; 41: 707-719 Crossref PubMed Google Scholar , 4 Liddell FDK McDonald AD McDonald JC Dust exposure and lung cancer in Quebec chrysotile miners and millers. Ann Occup Hyg. 1998; 4: 7-20 Google Scholar J K McDonald, J C McDonald, F D K Liddell, and their collaborators have added to the now large body of work on the cancer risks associated with exposure to chrysotile asbestos. As with most of their work since 1980, the focus of these new data and analyses is the still unresolved curiosity of differential risks for cancer among different populations exposed to asbestos, especially the apparent gap in mesothelioma risk between the high rates among people exposed to amphibole asbestos fibres, crocidolite and amosite, and the apparently lower rates among those exposed exclusively to chrysotile, the white asbestos still actively produced in Quebec and Zimbabwe. There remains too the mystery of striking differences in risks of lung cancer. These risks are historically quite modest among chrysotile miners and millers, yet almost 50-fold higher among textile millers working with the very same asbestos. 5 Dement JM Harns RL Symons MJ Shy CM Exposures and mortality among chrysotile asbestos workers. Part II: mortality. Am J Indust Med. 1983; 4: 421 Crossref PubMed Scopus (125) Google Scholar , 6 McDonald AD Fry JS Woolley AJ McDonald JC Dust exposure and mortality in an American chrysotile textile plant. Br J Indust Med. 1983; 40: 361 PubMed Google Scholar Other exposure settings typically fall near one or the other end of this disturbingly broad range. Simple unifying theories for lung cancer and mesothelioma risk have been elusive, the more so because chrysotile asbestos found in nature is typically contaminated, to varying degrees, by the amphibole and highly carcinogenic fibre tremolite. 7 Wagner JC Chamberlain M Brown RC et al. Biological effects of tremolite. Br J Cancer. 1982; 45: 352-360 Crossref PubMed Scopus (69) Google Scholar , 8 Amandus HE Wheeler R The morbidity and mortality of vermiculite miners and millers exposed to tremolite—actinolite. Part II: Mortality.,. Am J Indust Med. 1987; 11: 15-26 Crossref PubMed Scopus (102) Google Scholar Hence there remains important scientific debate about the basis for the carcinogenicity of fibrous minerals. In addition, 9 Cullen MR Controversies in asbestos-related lung cancer. Occup Med: State of the Art Revs. 1987; 2: 259-272 PubMed Google Scholar , 10 Smith AH Wright CC Chrysotile asbestos is the main cause of pleural mesothelioma. Am J Indust Med. 1996; 30: 252-266 Crossref PubMed Scopus (121) Google Scholar , 11 McDonald JC Armstrong B Doell D McCaughey WT McDonald AD Sebastien P Mesothelioma and asbestos fiber type: evidence from lung tissue analyses. Cancer. 1989; 63: 1544-1547 Crossref PubMed Scopus (143) Google Scholar public health and regulatory controversy persists on what, if any, appropriate uses chrysotile may have. And there continues to be fuel for increasingly intensified litigious behaviour, at least in North America.