Redefining soil arsenic standards: Crop-specific bioavailable arsenic thresholds for safer food production

Arsenic (As), a carcinogenic metalloid, threatens human health primarily through dietary exposure. Current soil total As standards often misestimate As risks and misalign with food safety standards, making arable soils key pathways for As entering the food chain. This study proposed soil bioavailable As (BAs) as a more accurate risk indicator to supersede total As. To establish a crop safety-based soil As risk assessment framework, this study integrated field sampling and literature data (100 leafy vegetable-, 182 wheat-, and 66 rice-soil pairs). We developed standardized BAs extraction protocols (0.5 M NH₄H₂PO₄ for dryland soils; 0.43 M HNO₃ for paddy soils); built BAs-based models for predicting As levels in crops (R² > 0.7 for all crops); and derived crop-specific safety thresholds for soil BAs: 17.62 mg/kg for leafy vegetables, 38.99 mg/kg for wheat, and 0.79 mg/kg for rice. Our results revealed that BAs-based thresholds and predictive models significantly outperformed traditional total As standards in assessing soil As contamination risk, with accuracy increasing by 57.4 % for wheat and 74.4 % for rice. This research proposed a novel strategy to predict As accumulation in agricultural products based solely on soil BAs, eliminating the need for measuring additional soil physicochemical properties. Replacing total soil arsenic with crop-specific bioavailable arsenic thresholds represents a critical advancement for science-based precision agriculture in arsenic-endemic regions, striking an optimal balance between analytical efficiency and human health protection.