Bioaccessibility and Health Risk Assessment of Inhalable Heavy Metals in Soil from the Bayan Obo Mining Area, Northern China

Soil contamination caused by mining activities may pose potential risks to human lungs. This study investigated the pollution levels and inhalable bioaccessibility of selected metal elements in the soils of Bayan Obo, a representative mining city, and Baotou, an industrial city in China. The human health risks of metal elements were also evaluated. The results indicated that La, Ce, and Eu exhibited the highest levels of enrichment, with significant spatial variations. The inhalable bioaccessibility of the metals followed the order: As>Mn>Ni>Pb≈Zn>Cu>Cr>La>Ce>Eu. Health risk assessment results indicated that evaluating human health risks based on total metal concentrations rather than bioaccessible concentrations could not only overestimate the risk of soil metals but, more critically, lead to misidentification of high-risk pollutants. The measured inhalable bioaccessibility data revealed that both non-carcinogenic and carcinogenic risks for children and adults were below safety thresholds, with Mn and As being the primary contributors to non-carcinogenic and carcinogenic risks, respectively.