[Transformation of copper and chromium in co-contaminated soil and its influence on bioavailability for pakchoi (Brassica chinensis)].

Heavy metal fractions in soil play an important role in the bioavailability for plants. A pot experiment was carried out to study the transformation and bioavailability for pakchoi of exogenetic copper and hexavalent chromium in co-contaminated soil. The results showed that one month after tested heavy metals were added into soil, the chromium was present mainly in residual and organic bonded form while copper was mainly bound to hydrated oxides of iron and manganese as well as residual form. Lower concentrations copper (< or = 400 mg x kg(-1)) in soil could promote chromium transform from other forms to exchangeable form while higher concentrations copper (> or = 800 mg x kg(-1)) in soil would inhibit this transformation. Similarly, chromium in low concentrations (< or = 5 mg x kg(-1)) could facility copper transform to residual form while chromium in high concentrations (> or = 20 mg x kg(-1)) would reduce such transformation process. Both added chromium to soil polluted by high concentrations copper and added copper to high chromium content soil could promote the polluted soil reach quasi-equilibrium state. Additionally, adding copper in soil could inhibit chromium uptake of pakchoi by promoting soil OM-Cr transformed into RES-Cr. While adding chromium in soil could reduce copper uptake of pakchoi by stimulating the EXE-Cu transformed into the RES-Cu. Therefore, it is necessary to take into consideration the synthetic effects of copper and chromium when carrying on assessment and phytoremediation to co-contaminated soil.