Ann. occup. Hyg., Vol. 46, No. 1, pp. 128-129, 2002
© 2002 British Occupational Hygiene Society
Published by Oxford University Press
Letters to the Editor |
Reply
Mr Rogers is correct in pointing out the difficulties encountered in understanding the exposure histories of the members of the Wittenoom cohorts and the inadequacy of the dust monitoring data resulting from the sampling strategies and instruments that were used. Unfortunately this is a common experience when endeavouring to use exposure data collected for compliance with various standards for epidemiological purposes.
In trying to understand the health effects of crocidolite, it has been disappointing that despite the expertise of the industrial hygienist who conducted the 1966 survey and the logistics of going to such a remote town in the Pilbara region of Western Australia, only 38 ‘static’ samples were collected during the visit, and that the only reporting or documentation of the results occurred in a conference in 1968. The Wittenoom workers and township residents are unique in that they were exposed exclusively to crocidolite, and their employment histories have been well documented. Follow-up of the cohorts has been undertaken over the past 25 years throughout Australia and also in Italy. In Australia, assessment of mesothelioma incidence has been complete as a result of mesothelioma registries, cancer registries and pathology records, as well as mortality records accessed in all states since the 1940s. Vital status, cancer incidence and certified causes of death are therefore well established for the cohorts.
In 1983 we endeavoured to make the best use that we could of the available dust measurements in order, at least, to look at internal dose–response relationships, in addition to documenting disease incidences and mortality ratios for the workforce as a whole. In 1991 we carried out similar work on a cohort of residents of the township of Wittenoom who were known not to have worked for the Australian Blue Asbestos Company. Mr Major was of great assistance in helping us understand the relative exposures of the various job categories in relation to those job categories for which sampling had been carried out by him in 1966. We never stated that Mr Major agreed with exposure estimates, as reading of the cited paper clearly indicates (De Klerk et al., 1989). We also engaged the assistance of the mine and mill supervisors, the company management and government mines inspectors to assist in interpolating and extrapolating between jobs, and, with the help of the much-criticized results of the earlier konimeter surveys, to estimate historical exposures. This exercise permitted us to attribute fibre/ml exposures to the various job categories.
We have published a validation of our estimates that shows clear agreement with lung fibre burdens (De Klerk et al., 1996) and, based on the ‘guesstimates’, we have also shown clear dose–response relationships between exposure and all asbestos-related diseases in this cohort. Indeed, during this same period, Mr Rogers used risk estimates based on these exposure estimates in at least two publications (Nevill and Rogers, 1992; Rogers and Nevill, 1995) without questioning their validity.
It is most disappointing that the material collected by Mr Major was apparently available for recounting and reanalysis by him and Mr Rogers until the recent past and then unaccountably disappeared from the National Occupational Health and Safety Commission when Mr Rogers left the Commission, although he had previously stated at the Inhaled Particles Meeting in Cambridge in 1996 that he was in possession of the material.
A. W. MUSK and N. H. DE KLERK
University of Western Australia, Nedlands, WA 6907, Australia
If the exposure estimates are underestimates, then Mr Major and Mr Rogers have missed the opportunity to rectify the problem and contribute to science.
REFERENCES
De Klerk NH, Armstrong BK, Musk AW, Hobbs MST. (1989) Cancer mortality in relation to measures of exposure to crocidolite at Wittenoom Gorge in Western Australia. Br J Ind Med; 46: 529–36.[Medline]
De Klerk NH, Musk AW, Williams VM, Filion PR, Whitaker D, Shilkin KB. (1996) Comparison of measures of exposure to asbestos in former crocidolite workers from Wittenoom Gorge, W. Australia. Am J Ind Med; 30: 579–87.[Medline]
Nevill M, Rogers A. (1992) Inquiry into asbestos issues at Wittenoom, Perth.
Rogers A, Nevill M. (1995) Occupational and environmental mesotheliomas due to crocidolite mining activities in Wittenoom, Western Australia. Scand J Work Environ Health; 21: 259–64.[Web of Science][Medline]
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