Atmospheric thorium pollution and inhalation exposure in the largest rare earth mining and smelting area in China.

Exposure to radionuclide thorium (Th) has generated widespread public concerns, mainly because of its radiological effects on human health. Activity levels of airborne 232Th in total suspended particulate (TSP) were measured in the vicinity of the largest rare earth mine in China in August 2012 and March 2013. The mean activity concentrations of 232Th in TSP ranged from 820μBqm-3 in a mining area in August 2012 to 39,720μBqm-3 in a smelting area in March 2013, much higher than the world reference of 0.5μBqm-3. Multistatistical analysis and Kohonen's self-organizing maps suggested that 232Th in TSP was mainly derived from rare earth mining and smelting practices. In addition, personal inhalation exposures to 232Th associated with respirable particulate (PM10) were also measured among local dwellers via personal monitoring. The mean dose values for different age groups in the smelting and mining areas ranged from 97.86 to 417μSvyear-1 and from 101.03 to 430.83μSvyear-1, respectively. These results indicate that people living in the study areas are exposed to high levels of widespread 232Th.