Regional environmental risk thresholds for cadmium in Chinese agricultural soils: Integrating zonal soil types and...

Scientific soil environmental quality standards are critical for preventing "over-protection" and "under-protection" of soil ecosystems, and for supporting soil quality and risk assessments. To account for pedogenic processes and spatial heterogeneity in regional soil development, we classified China's agricultural soils into nine zones with distinct soil types and pedogenic properties. Sixty soil samples from diverse ecoregions were analyzed for Cd toxicity using pot experiments and literature-derived datasets. Species sensitivity distribution (SSD) modeling was used to derive region-specific HC₅ thresholds (the concentration that protects 95 % of species), revealing significant variability in Cd bioconcentration factors (BCFs: 0.09-1.62) across soil types and crops. Effect concentrations (EC_x) for ecological indicators also differed markedly among soils with contrasting physicochemical properties. To account for the changed bioavailability of Cd due to aging processes in real field conditions, toxicity data were corrected using aging factors (AFs). SSD-derived HC₅ values varied 0.14-0.72 mg·kg^-1 across nine subzones, with regression models linking HC₅ to soil properties. Comparative analysis with China's Soil Environmental Quality Standard (GB 15618) highlighted the inadequacy of a uniform national criterion, demonstrating the necessity of region-specific standards. This work provides empirical evidence and methodological frameworks to optimize soil environmental quality regulations across China's agro-ecological zones.