LUNG-CANCER MORTALITY AND AIRWAYS OBSTRUCTION AMONG METAL MINERS EXPOSED TO SILICA AND LOW-LEVELS OF RADON DAUGHTERS

Starting from a cross-sectional survey in 1973, the mortality of two c ohorts of Sardinian metal miners was followed through December 31, 198 8. In mine A, the quartz concentration in respirable dust ranged betwe en 0.2% and 2.0% and the exposure to radon daughters averaged 0.13 wor king level (WL), with the highest estimated cumulative exposure around 80-120 WLM. In mine B, the silica content was much higher (6.529%), b ut exposure to radon daughters was significantly lower than in mine A. More than 98% of the overall work force in 1973 (1,741 miners) entere d the cohort, providing 25,842.5 person-years. Smoking, occupational h istory, chest radiographs, and lung function tests were available for the cohort members at admission. Mortality for all causes was slightly lower than expected. A significant excess for nonmalignant chronic re spiratory diseases was noticed in both mines. Twenty-four subjects die d of lung cancer, 17 from mine A (SMR: 128; 95% confidence interval [C I]: 75-205) and 7 from mine B (SMR: 85; 95% CI: 34-175). The SMR for l ung cancer was highest among the underground workers from mine A (SMR: 148; 95% CI: 74-265), with a significant upward trend by duration of employment in underground jobs. Mine B underground miners showed lung cancer SMRs close to 100 without a significant trend by duration of em ployment. Among underground miners with spirometric airways obstructio n in 1973, those from mine A showed the highest risk (SMR: 316; 95% CI : 116-687). The relationship did not change after adjusting for age an d smoking. Based on the present findings, crystalline silica per se do es not appear to affect lung cancer mortality. A slight association be tween lung cancer mortality and exposure to radon daughters, though wi thin relatively low levels, may be considered for underground miners f rom mine A. Impaired pulmonary function may be an independent predicto r of lung cancer and an important risk factor enhancing the residence time of inhaled carcinogens, i.e., alpha particles or PAHs, by impairi ng their bronchial and alveolar clearance. (C) 1994 Wiley-Liss, Inc.