Exposure to tremolite asbestos and respiratory health in Swedish dolomite workers

Objectives-Deposits of carbonate rock like limestone and dolomite may conta in tremolite asbestos. This study assessed the exposure to tremolite asbest os and the respiratory health of Swedish dolomite workers. Methods-95% of 137 eligible workers at two dolomite producing companies com pleted a self administered questionnaire that included questions on respira tory symptoms and were examined with spirometry as well as chest radiograph y. Total exposure to dust was gravimetrically measured and the tremolite as bestos content of the dust was assessed with polarisation and phase contras t microscopy. Results-Dolomite dust concentrations were moderate (median 2.8 mg/m(3)) and tremolite asbestos concentrations were generally below the limit of detect ion (<0.03 fibres/ml). Somewhat higher values, around 0.1 fibres/ml, were o btained in manual stone sorting and bagging. Respiratory symptoms suggestiv e of chronic bronchitis were more related to smoking than to estimates of i ndividual exposure to dust. The mean vital capacity was 0.21 lower than exp ected after adjustment for sex, age, height, and smoking but the decline in lung function was not associated with current or cumulative exposure to du st in a clear cut way. Two definite cases of pleural plaques and one possib le case of simple pneumoconiosis were noted, but the plaques could not be a ttributed exclusively to exposure to tremolite asbestos. Conclusions-Dolomite mining and milling may indeed entail low levels of exp osure to tremolite asbestos, but this exposure was not a strong determinant of respiratory symptoms, lung function, or pneumoconiosis in exposed Swedi sh workers. This was true also for dolomite dust. The hazards of exposure t o tremolite asbestos may vary across deposits, however, and additional stud ies at other sites of carbonate rock exploitation are warranted.