Phytoavailability and phytovariety codetermine the bioaccumulation risk of heavy metal from soils, focusing on Cd-contaminated vegetable farms around the Pearl River Delta, China

Five random vegetable farms were selected to investigate the bioaccumulation risk of heavy metals (HMs) by different type of vegetables around the Pearl River Delta (PRD), China. The concentration order of four major HMs in the surface soil samples was Cd<Cu<Pb<Zn, with only Cd concentrations (1.4-1.8mgkg^-1) significantly higher than the permissible limit (≤0.3mgkg^-1) for agricultural soils. Soil DTPA-extractable (phytoavailable) Cd concentrations differed markedly amongst the five farms, and varied within 0.017-0.17mgkg^-1. Meanwhile, 28.0% of vegetable samples collected from these five farms were contaminated with Cd according to the permissible limit (≤0.05mgkg^-1), and 71.4% of these polluted samples belonged to stem/leaf vegetables. The average bioaccumulation factors of Cd from cultivated soil to stem/leaf vegetables and melon/fruit/bean vegetables varied within 0.021-0.050 and 0.005-0.020 (soil total Cd basis), and 0.50-2.01 and 0.13-0.53 (soil DTPA-extractable Cd basis), respectively. Redundancy analysis (RDA) showed that DTPA-extractable Cd, which negatively but significantly correlated (P<0.05) to soil pH, was the key factor in influencing vegetable Cd accumulation, notably stem/leaf vegetables. The results show that Cd was the primary metal of risk in vegetable farms around the PRD region, and stem/leaf vegetables posed about 2.2 times higher health risks associated with exposure to Cd than melon/fruit/bean vegetables.