A Twenty-year Follow-up Study on Health Effects Following Long-term Exposure to thorium Dusts

A twenty-year follow-up study was carried out a Baiyun Obo Rare-earth Iron Mine in China. This mine has been mined since 1958. Its ore contains 0.04% of ThO2 and 10% of SiO2. Objective: the purpose of this study is to investigate possible health effects in dust-exposed miners following long-term exposure to thorium-containing dusts and thoron progeny. Methods: by using the negative high voltage exhaled thoron progeny measurement system to estimate the miner's thorium lung burden. Results: The highest thorium lung burden among 1158 measurements of 638 miners was 11.11Bq. The incidence of stage O+ pneumoconiosis was increased among dust-exposed miners. An epidemiological study showed that the lung cancer mortality of the dust-exposed miners was significantly (P<0.005) higher than that of the controls. conclusions: It is suggested that the differences results results long-term exposure to thorium-containing dusts (carcinogens are ThO2 and SiO2) and thoron progeny. This is the first evidence in humans of the carcinogenicity after long-term inhalation of thorium-containing dusts and thoron progeny. The total person-years of observation for the dust-exposed miners and the controls were 62712 and 34672 respectively. (Author) 11 refs