The establishment of a portable high sensitivity exhaled thoron activity measurement system.

A portable system, using electrostatic collection, for the measurement of exhaled thoron activity in humans is described, together with details of the basic theory, equipment, calibration procedures, measurement and preliminary use. The portable system built on experience at the Argonne National Laboratory (ANL) to achieve a reduction in measurement time from 30 h to 200 min, and to increase the total efficiency of the system from 50% (at ANL) to 70%. The limit of detection of the system (2sigma above zero) is 0.007 Bq of thoron activity outside the body. The total standard error of this system is 47% for a thorium lung burden of 0.22 Bq. The average background of this scintillation detector was 0.003 counts min(-1).

Recent results from a study of thorium lung burdens and health effects among miners in China.

The purpose of this study was to obtain more information about health effects among the dust-exposed male miners of Bayun Obo Rare-Earth and Iron Mine, China. From 2,390 male miners from the seven dust-generating workshops of the mine, 136 dust-exposed miners were randomly selected for study. Of these, 64 men were from the high-dust-generating workshop and 72 from the lower-dust-generating workshops; the latter group was used as an internal control. Physical measurements and medical examinations were carried out on each of these 136 men. The average measured thorium lung burden for the high-dust-exposure miners was significantly greater than that for the group of lower-exposure miners, and the incidence of severe breathlessness and pneumoconiosis of stage 0(+) was also significantly raised in the high-exposure group relative to the low-exposure group. An epidemiological study of lung cancer mortality among all the miners and staff of this mine was also carried out. This showed significantly raised levels of lung cancer mortality in both exposed miners and unexposed workers when compared with the Chinese population, and the level in exposed miners was significantly higher than that in unexposed men. The general high rate of lung cancer mortality in the workers of the mine is attributed to high levels of cigarette smoking, and the raised rate in the exposed miners relative to the unexposed workers to inhalation of silica- and thorium-bearing dusts and thoron progeny.

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.