Respiratory health effects of opencast coalmining: a cross sectional study of current workers.

OBJECTIVE: To identify whether there is evidence of pneumoconiosis and other respiratory health effects associated with exposure to respirable mixed dust and quartz in United Kingdom opencast coalmines.
METHODS: A cross sectional study of current workers (1224 men, 25 women) was carried out at nine large and medium sized opencast sites in England, Scotland, and Wales. To characterise a range of occupational groups within the industry, full shift measurements of personal exposures to respirable dust and quartz were taken. Up to three surveys were carried out at each site, covering all four seasons. For the purposes of comparisons with health indices these groups were further condensed into five broad combined occupational groups. Full sized chest radiographs, respiratory symptoms, occupational history questionnaires, and simple spirometry were used to characterise the respiratory health of the workforce. Logistic or multiple regression techniques were used to examine relations between indices of exposure and respiratory health.
RESULTS: None of the group geometric mean dust concentrations, based on 626 valid dust samples, exceeded 1 mg.m-3, and 99% of all quartz concentrations were below 0.4 mg.m-3, the current maximum exposure limit. The highest quartz concentrations were experienced by the rock drilling team and drivers of bulldozers (used to move earth and stone from layers of coal). There were clear differences in mean respirable dust and quartz concentrations between occupational groups. These were consistent across the different sites, but depended in part on the day of measurement. The variations between sites were not much greater than between days, suggesting that differences between sites were at least partly explained by differences in conditions at the time of the measurements. The prevalence of radiographic small opacities profusion category > or = 1/0, based on the median of three readings, was 4.4%. Five men had category 2 pneumoconiosis and two men (including one of these five) had progressive massive fibrosis category A. From regression analyses, the relative risk of attaining a profusion of category > or = 0/1 was estimated to be doubled for every 10 years worked in the dustiest, preproduction opencast jobs, after allowing for age, smoking, and site effects. Risk was not associated with time worked in any other occupation within the industry, nor with previous employment in underground mining or other dusty jobs. Symptoms of chronic bronchitis were present in 13% of the men. Frequency of chronic bronchitis was influenced by years worked in dusty jobs outside opencast mining, but not by time spent in occupations within the industry. Asthmatic symptoms were reported by 5% of the workforce, close to the mean frequency found in adult men. No positive associations were found between asthma and occupational exposures. Lung function on average was close to predicted value and showed no relation to time worked in opencast occupations.
CONCLUSIONS: Frequency of (mostly mild) chest radiographic abnormalities is associated with working in the dustier, preproduction jobs in the industry. Although some of these mild abnormalities may be non-occupational (due to aging or smoking), the association with exposure indicates a small risk of pneumoconiosis in these men, and the need to monitor and control exposures, particularly in the high risk occupations.