Faecal excretion of thorium by NORM workers

Exposure to thorium-bearing dust in industries handling and processing monazite and other minerals can pose radiological risks to workers. This study aimed to reassess historical faecal bioassay data collected over 10 d from two monazite plant workers using updated biokinetic and dosimetric models. Another objective was to evaluate the feasibility of faecal thorium bioassay for contemporary operations involving naturally occurring radioactive materials (NORM). The retrospective analysis found that the bioassay-derived thorium intakes were significantly higher than those estimated via personal air sampling. The effective dose estimates for the two workers were similar and ranged from 0.95 to 2.40 mSv over the 5-d exposure period, depending on the worker's assumed mode of breathing. The study confirmed that faecal thorium bioassay remains a viable tool for monitoring workers exposed to insoluble thorium dust, but the timing of sample collection, individual physiology, and background dietary intake of NORM must be considered.