Unveiling mercury's hidden threat: An integrated methodology for soil mercury risk assessment in Syr Darya River Basin, Central Asia

Abstract

Mercury (Hg) contamination of soil poses a significant threat to ecological and human health. Integrating risk assessment with a comprehensive analysis of the physical and chemical properties of soil enables macroscopic understanding of the potential risks associated with Hg. The integrated risk assessment framework was achieved by applying a projection pursuit clustering (PPC) model that considered ecological and human health risks, soil environmental factors derived from the SHapley Additive Explanation–eXtreme Gradient Boosting (SHAP-XGBoost) model, and exposure risk vulnerability. It was found that the concentrations of Hg in the soils of the Syr Darya River Basin ranged from 3.70 to 40.10 ng/g and Fe2O3, Al2O3, and soil organic carbon (SOC) were important factors in the variation in Hg concentrations. Regions with a high risk of soil Hg were identified using the proposed integrated risk assessment framework, with the geographical distribution concentrated near the cities of Kyzylorda and Kazalinsk. From the perspective of different land use types, shrub soil sampling sites had the largest percentage of high Hg risk values, followed by cropland, bare land, and grassland. These findings confirm that the combined risk values depend not only on Hg concentrations, but also on environmental variables and socioeconomic conditions. Integrated risk assessment of soil Hg is based on machine learning and projection pursuit clustering models, which can provide a novel perspective for potential toxic element pollution evaluation, prevention, and treatment.