Important deficits of lung function in three modern colliery populations: relations with dust exposure

To determine whether dust-related “clinically important” deficits of lung function still occur in British coal miners we have analyzed the relationship between lifetime cumulative exposure to respirable dust and risk of defined functional deficits in a population of miners who were examined between 1981 and 1986. The study group consisted of a sample of men who had worked at any one of three collieries (South Wales, Yorkshire, and North East England) between 1970, when new dust standards were introduced, and date of medical survey. There were 1,671 men studied, including men who had left the collieries. “Clinically important” deficits of FEV1 from predicted values derived in this population were defined by comparisons with questionnaire data on exercise tolerance limited by breathlessness. The mean FEV1 of men in the South Wales colliery, for example, who said they had to stop for breath when walking at their own pace on level ground was 942 ml less than the predicted value for nonsmokers after taking age and stature into account. Individual cumulative exposures to respirable dust were calculated from a long-term program of measurements of dust concentrations and occupational records commencing in 1953. In the three colliery populations, 24, 24, and 12% in South Wales, Yorkshire, and the North East, respectively, had FEV1 deficits that were at least as severe as the average deficit associated with the severe grade of exertional dyspnea described above. In all collieries deficits were more common in smokers than in nonsmokers, and more common in men who had left the industry than in men still within it. Dust concentrations and exposures experienced by the men in the study populations fell progressively during the 1970s from previous levels. They were notably higher in the S. Wales colliery than in the other two, particularly in the early period before the end of the 1960s. Concentrations and exposures were lowest in the colliery in the North East. Age and lifetime cumulative dust exposure were more highly correlated than in previous studies, particularly in the Yorkshire colliery. In the Yorkshire and North East collieries deficits could not be shown to be associated with exposure to respirable dust; but in the South Wales colliery risks of functional deficits were obviously dust-related. Estimates of the frequency of the above deficit for nonsmokers were 3.5% for zero dust exposure and 20% for an exposure of 400 ghnm−3 (a high exposure). Corresponding figures for smokers were 10.5 and 45%, respectively; 10% of men in S. Wales with this deficit had progressive massive fibrosis. Reexamination of data from earlier studies confirmed adverse effects of dust on lung function in miners at all three collieries. The possible reasons for not being able now to demonstrate such relationships at two of them include beneficial effects on miners’ health of improved dust control since 1970 and confounding between dust exposure and age. We suggest that future decisions on dust control limits should take into account estimated relations between dust exposure and functional deficits, including those attributable to pneumoconiosis.