The quantitative risks of mesothelioma and lung cancer in relation to asbestos exposure: the Wittenoom data.

The Ontario Royal Commission in 1984, in its chapter entitled 'Criteria for Evaluating Cohort Studies and the Limitations of Asbestos Epidemiology', commented that 'It is therefore no accident that one of the weakest parts of all asbestos epidemiology is the quality of the quantitative exposure data' (Dupre et al., 1984). Such comments are of particular relevance to the cumulative crocidolite exposure levels used by Hodgson and Darnton (2000) in their mesothelioma and lung cancer risk estimates for the cohort of Australian Blue Asbestos workers (commonly known as the Wittenoom cohort). It is important to realize that while Wittenoom is the name of a very remote town in the northwest of the state of Western Australia, the Wittenoom cohort in fact worked over three mining and various milling operations, and lived in two residential areas (Rogers and Nevill, 1995). The Wittenoom Gorge mine and mill, which operated from 1943 to 1958, initially hired some previously exposed miners from the 1937–46 Yampire Gorge crocidolite mine and mill. A new Wittenoom Gorge mill was constructed in 1949, and various modifications and attempts at dust control were made until its closure in 1958. The Colonial Gorge mine and mill commenced operation in the adjacent gorge in 1953, running until 1966, when it was closed for economic reasons. Throughout the 23 years of employment of the 6500 male Wittenoom cohort, various upgrades were made in production and dust control, but overall the three mines and mills were always extremely dusty. In addition, there was considerable general environmental exposure in several residential areas associated with the crocido-lite mining activities. Dust monitoring was conducted by the Mines' Inspectorate using a konimeter to determine compliance with the general particulate (non-fibre) standard of the day. Many hundreds of such measurements were recorded for the early 1950s until 1966. The vast majority of the results were recorded as 1000+ particles per cc, indicating overloading of the koni-meter, and research has found consequently that these data were never suitable for estimating airborne fibre concentrations. The only attempt at fibre level monitoring was made in the Colonial Gorge mine and mill by one of us (G.M.) in 1966 over 12 shifts, when the then modern mill was operating at full capacity. During this time, some 38 'static' samples were collected using two Casella Long Running Thermal Precipita-tors. In addition, three 'clean air' samples were taken ~100 m outside the mill which, when …