The fate and bioaccessibility of arsenic in an abandoned smelter site: Distribution, mobility and potential risks

Arsenic (As) contamination in soil is a major environmental concern due to its grave threat to human health and ecosystems. In this paper, 2250 soil samples were collected to assess the speciation, bioaccessibility, and human health risk of As in soils from a legacy nonferrous metal smelter, as well as to simulate the As transport from contaminated soil into groundwater. The results indicated that 3.5% of soil samples exceeded the risk screening value (RSV), with the highest exceedance rate (9.54%) observed at a depth of 1.0 m. The proportion of water-soluble As and surface-adsorbed As (12-49%) exhibited a positive correlation with the total As concentration. The bioaccessibility of As (Bio_As) ranged from 7.77% to 28.11%. Human health risk assessment (HHRA) based on total As concentration indicated unacceptable risk levels (CR > 1 ×10⁻⁶; HQ > 1), whereas risk values based on bioavailable and bioaccessible concentrations were reduced by 58-63%, suggesting a substantial overestimation of actual health risks. EPACMTP model suggested that the predicted As concentrations in groundwater ranged from 1.61 to 7.20 µg/L that are within the standard limit of 0.01 mg/L, indicating a low risk of groundwater contamination by arsenic. Arsenic level was significantly attenuated by 44.35-fold to 110.07-fold during transport from surface soils through the vadose zone. Moreover, the subsequent dispersive transport of arsenic in groundwater was governed by its release kinetics from the soil. This study provides new insights into the fate, transport, and bioaccessibility of arsenic in soils and associated risks, offering a basis for reducing soil and groundwater contamination risks and optimizing remediation strategies.