RADIOLOGICAL CHANGES AND FIBRE EXPOSURE IN CHRYSOTILE WORKERS AGED 60-69 YEARS AT THETFORD MINES

Abstract X-ray readings by an international panel were analysed from a sample of 515 chrysotile production workers at Thetford Mines, at or near the end of at least 20 years' employment. At the operative time, their average age was 64.6 yr and their average gross service 42.3 yr. Asbestos exposure originally assessed in millions of dust particles per cubic foot was re-estimated in fibres per ml. The prevalence of small parenchymal opacities, 1/0 or more and 2/1 or more, was directly related to fibre (and dust) concentrations; pleural changes were related to duration of employment but not to measures of concentration. Smokers did not have higher prevalences of radiological changes than non-smokers. Despite factors which may have limited the effects of survivor bias, the true gradients of exposure-response were probably steeper than those observed.