A follow-up study on the relationship between thorium lung burden and health effects on miners (1982-91)

Abstract

The results of an investigation (1982-91) on the natural thorium lung burden and its health effects on miners in the Baiyan Obo mine are reported. An electrostatic collection system was used to measure the exhaled thoron activity. Measurements of exhaled thoron activity were carried out on 588 miners (985 measurements) who had inhaled thorium-containing dusts. Exhaled thoron activity was also determined on 124 persons (124 measurements), who had not inhaled thorium-containing dusts. The average thorium lung burdens of the 588 miners and the 124 controls were 0.85 Bq and 0.15 Bq, respectively. Of the 588 miners, 7 had a thorium lung burden higher than 3.7 Bq, 5 had a thorium lung burden higher than 4.44 Bq and 1 miner had the highest thorium lung burden of 5.56 Bq. In about 20% of these miners the thorium lung burden was 0.74 Bq. There was no definite increase in the incidence of lung cancers in more than 2000 miners who had inhaled thorium dusts and thoron daughters in the period 1958-90. Of the miners who had inhaled thorium dusts, there was a significant increase in the incidence of respiratory symptoms, lung function disorders and pneumoconiosis stage 0+ and stage 1. Based on the results of animal experiments and the low percentage of thorium in the dust, the authors suggest that disorders of the respiratory tract were due mainly to other chemical components in the dust, such as SiO2 and other chemical elements. The role of thorium is negligible. The average air thorium dust concentrations in the main workshops and the average thorium lung burden of the thorium dust-inhaling miners were lower by a factor of 20 and 3 respectively in 1991 compared with 1983.