Derivation of regional risk screening values and intervention values for cadmium-contaminated agricultural land in the Guizhou Plateau

Given the complex geology of karst terrain, regional geochemical cadmium (Cd) anomalies, and widespread man-made soil contamination across the Guizhou Plateau, proper decision-making models are needed for soil zonal management to lower risks of exceedances of contaminants, especially Cd, in agricultural produce. We conducted agricultural field investigations (n=240) to characterize distribution of soil Cd and its relationship with soil types and soil properties. Additional 70 typical soils with differing soil types and properties were used in greenhouse experiments to derive reliable Cd soil-vegetable relationships and develop regional soil criteria. A soil type-dependent soil Cd anomaly and a soil pH-dependent Cd distribution in soils were identified, and Carbonati-Udic Argosols had the highest soil Cd (mean 0.92 mg center dot kg(-1)) and relatively higher soil pH. High geochemically reactive Cd fraction in soil, with the superposition of elevated soil acidification, posed serious environmental risks. The bioaccumulation of Cd in Brassica p., a cruciferous crop, was controlled by the Cd (bio)availability in soil, which was strongly affected by soil pH. An extended Freundlich-type model and a polynomial surface model can precisely predict the bioaccumulation of Cd. However, the latter was more suitable for deriving local soil criteria as it was less sensitive to soil pH, thus avoiding overprotection and underprediction at low and high soil pH ranges, respectively. Risk screening values were derived by accounting for model uncertainties and indicated that 93% of agricultural soils were safe for growing vegetables. Our findings can support farmers and policymakers in safe use of Cd-contaminated croplands.