A 20-year follow-up study on the effects of long-term exposure to thorium dust.

Objective: To investigate the possible effects of long-term exposure to dust containing thorium and thoron progeny on dust-exposed miners.

Methods: A negative, high voltage, exhaled thoron progeny measurement system was used to estimate the miners' thorium lung burden.

Results: 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).

Conclusion: 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.