Are we underestimating exposures from NORM dust?

The inhalation of dust containing naturally occurring radioactive materials (NORM) associated with mining and mineral processing operations may lead to potential long-term health impacts, including cancer and chronic lung disease, due to alpha particle-emitting radionuclides. This study evaluates the effectiveness of air sampling strategies used to estimate radiation doses from NORM exposure, with a focus on the Western Australian minerals industry. The objectives were to review current sampling and analysis protocols, identify factors contributing to over- or underestimation of dose, and propose adjustments to improve intake assessments. A review of research and guidelines applicable to NORM dust exposure was conducted, and the sampling efficiency of the government-recommended 7-hole and IOM sample heads was compared, considering measured dust particle size distributions. Key inhalation-related parameters, including use of similar exposure group (SEG) mean concentrations, worker breathing rates, median dust particle size, and intake-to-dose conversion factors, were analysed to assess their influence on intake calculations. The findings indicate that use of the 7-hole sampler, currently recommended by local guidelines, may underestimate airborne radioactivity concentrations by 2-fold or more, primarily due to reduced sampling efficiency for larger particles. Standard default assumptions for breathing rates and aerosol characteristics used to convert the measured concentrations to intake and dose may further contribute to underestimation. This study recommends updating air sampling methods and dose assessment protocols to better align with workplace-specific exposure conditions and improve worker health protection in NORM industries.