ABSTRACT
<p><b>OBJECTIVE</b>To investigate the possible effects of long-term exposure to dust containing thorium and thoron progeny on dust-exposed miners.</p><p><b>METHODS</b>A negative, high voltage, exhaled thoron progeny measurement system was used to estimate the miners' thorium lung burden.</p><p><b>RESULTS</b>The highest thorium lung burden of 638 miners was 11.11 Bq. The incidence of stage 0(+) pneumoconiosis was higher among dust-exposed miners. Lung cancer mortality of the dust-exposed miners was significantly higher than that of controls (P < 0.005).</p><p><b>CONCLUSION</b>There is a difference in cancer rates between those who have long-term exposure to dust containing thorium (in which carcinogenic ThO(2) and SiO(2) exist) and thoron progeny and those who have not.</p>