Long-term monitoring of thorium inhaled by workers and assessment of thorium lung burden in China

The long-term monitoring of thorium inhaled by workers and assessment of their thorium lung burden has been carried out in China since 1960. Various monitoring methods have been adopted, such as chemical analysis of thorium concentration in urine samples; assessing thorium lung burden by measurement of 212Pb etc. using a whole-body counter; measurement of exhaled thoron using a ZnS detector; or exhaled thoron decay products using an electrostatic collection system. Our experience over more than 20 years has shown that the last named measurement system is the best method for monitoring and assessing the lung burden of thorium (ThO2) inhaled by miners and workers. (author)