Soil threshold values of total and available cadmium for vegetable growing based on field data in Guangdong province, South China

BACKGROUND: Human exposure to cadmium (Cd) is largely attributed to consumption of vegetables grown in polluted soils. In China, guidelines set for Cd in soils are uniform for different crops and diverse soil types, but not risk based. A high-density sampling of 711 paired soil and vegetables was carried out across Guangdong, South China. We aimed to model the transfer of Cd from soil to leafy, rootstalk and fruit vegetables, and to set regional guidelines of Cd [total and diethylenetriaminepentaacetic acid (DTPA) -extractable] in soil for vegetable safe production. RESULTS: Both total and DTPA-extractable Cd concentrations in soil were good predictors for Cd in vegetables. The transfer of Cd in soil to vegetables could be estimated by nonlinear models, with better fit when using DTPA-extractable Cd than total Cd in soil. The calculated thresholds of soil total Cd were 2.42, 0.94 and 1.57 mg kg(-1) whereas those of soil DTPA-extractable Cd were 1.08, 0.33 and 0.63 mg kg(-1) for leafy, rootstalk and fruit vegetable fields in Guangdong, respectively, all higher than the national soil Cd threshold. CONCLUSION: Cadmium-contaminated risk for vegetable production in Guangdong province might have been over-estimated according to the Chinese Environmental Quality Standard for Soil.