RESUMO
Pot experiments and laboratory analysis methods were used to investigate the form transformation of additional copper and selenium and their bioavailability for pakchoi (Brassica chinensis) in co-contaminated soil. The results showed that Cu mainly existed in residual bound form, while selenium was present mainly in organic bound and residual form in the uncontaminated soil. In the contaminated soil, copper was mainly bounded to hydrated oxides of iron and manganese, while Se was in exchangeable and carbonate forms. After one month of growing season, Cu tended to transfer into organic bound fractions, while Se tended to bind to hydrated oxides of iron and manganese. The I(R) value of Cu decreased with increasing copper and selenium concentrations, while the I(R) value of Se decreased with increasing Se concentration and had nothing to do with the concentration of exogenous Cu for both before planting and after harvesting of pakchoi. The parameters estimated by S curve fitting indicated that suitable amount of Se (< or = 10 mg x kg(-1)) could promote the Cu uptake by pakchoi, and certain amount of Cu (< or = 400 mg x kg(-1)) could promote Se absorption by pakchoi. Both the I(R), values for Cu and Se had similar trends as the Cu, Se concentrations in pakchoi, which meant that the I(R) value could be used to evaluate the bioavailability of heavy metals in soil. Partial correlation analysis showed that Cu and Se in exchangeable and organic bound forms in soil had better bioavailability for pakchoi. Therefore, the I(R) value of elements in soils and the change of elements before planting and after harvesting of pakchoi can be used as indicators for evaluating the bioavailability of heavy metals.
