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Minisymposium 8

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Silica related health effects


J. C. McDonald.National Heart and Lung Institute, Imperial College London, London, UK

Epidemiological evidence will be reviewed for and against the evaluation, made in 1996 by an IARC Working Group, that crystalline silica in the form of quartz or cristobalite from occupational sources is carcinogenic to humans (Group 1). The Working Group had considerable difficulty in reaching this decision, did not do so unanimously, and might not have done so at all, had it not been emphasised that it was concerned with hazard identification, not risk. Of the many studies examined by the Working Group, 10 were identified as providing the least confounded evidence of risk: five including one of registered silicotics were considered positive, and five others negative or equivocal. Since 1997, there has been comparatively little further epidemiological evidence on the lung cancer issue, apart from two somewhat overlapping studies of North American industrial sand workers. Significant relationships between exposure and mortality from lung cancer and silicosis were found in both these studies and, in one, after allowance for smoking. The latter of these two studies, and another of British pottery workers (included among the five considered positive the IARC Working Group), have been recently updated, with results awaiting publication. Since 1977, however, there have been a small number of attempts to relate the scanty available data on exposure–response relationships …

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