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Plain chest radiographs from a one in six random sample of the workforce of the asbestos industry at Wittenoom, Western Australia between 1943 and 1966 have been classified for degree of profusion and pleural thickening by two independent observers according to the 1980 UICC-ILO Classification of Radiographs for the pneumoconioses to clarify the effect of degree of radiological abnormality on survival. A total of 1106 subjects were selected. Each subject's age, cumulative exposure to crocidolite, and time since first exposure were determined from employment records, the results of a survey of airborne concentrations of fibres > 5 mu in length conducted in 1966, and an exposure rating by an industrial hygienist and an ex-manager of the mine and mill at Wittenoom. By the end of 1986 193 subjects had died. Conditional logistic regression was used to model the relative risk of death in five separate case-control analyses in which the outcomes were deaths from: (1) all causes, (2) malignant mesothelioma, (3) lung cancer, (4) asbestosis, and (5) other causes excluding cancer and asbestosis. Up to 20 controls per case were randomly chosen from all men of the same age who were not known to have died before the date of death of the index case. After adjustment for exposure and time since first exposure, there were significant and independent effects of radiographic profusion and pleural thickening on all cause mortality. The effect of profusion was largely a result of the effect on mortality from malignant mesothelioma and asbestosis but not lung cancer. The effect of pleural thickening was greatest on mortality from other causes, mainly ischaemic heart disease. This study has shown that degree of radiographic abnormality has an independent effect on mortality from malignant mesothelioma, asbestosis, and all causes even after allowing for the effects of age, degree of exposure, and time since first exposure.

Respiratory symptoms, spirometry, and transfer factor were measured in 208 non-smoking Western Australian underground goldminers (mean age 32) to identify the presence of respiratory abnormalities resulting from underground work. These subjects were part of a larger group of 771 subjects attending for statutory periodic chest x ray examinations in the industry. They had worked underground for a median of three years. The prevalence odds ratios of bronchitis, dyspnoea, wheeze, and asthma all tended to be related to duration of underground employment, even after adjusting for age, those for wheeze and asthma reaching statistical significance. After adjusting for age and height the duration of employment also had a significant effect on TL/VA but not on FEV1, FVC, or TL. These changes are consistent with the presence of airway narrowing and non-specific lung fibrosis or emphysema in non-smoking underground goldminers.

In 1979 all former workers from the Wittenoom asbestos industry who could be traced to an address were sent a questionnaire to determine smoking history. Occupational exposure to crocidolite was known from employment records. Of 2928 questionnaires sent, satisfactory replies were received from 2400 men and 149 women. Eighty per cent of these had smoked at some time and 50% were still smoking. Since that time 40 cases of lung cancer and 66 cases of compensatable asbestosis have occurred in this cohort. The incidence of both lung cancer and asbestosis was greatest in those subjects with the highest levels of exposure to crocidolite and in ex-smokers. Statistical modelling of the joint effects of these exposures on the incidence of each disease indicated that crocidolite exposure multiplied the rates of lung cancer due to smoking and that smoking has no measurable effect on the rates of asbestosis. There was also some evidence that the incidence rate of lung cancer is falling with time.