Metals are unavailable to plants when fixed within relatively inert mineral matrices in soil. The success of phytoremediation may be limited by restricted bioavailability of metals in such nonlabile forms. We conducted a pot trial with EDTA added at rates of 0,0.1,1.0,5.0, and 10 mmol kg{sup}(-1), to soil historically contaminated with sewage sludge to increase the availability of metals to a test crop, Indian Mustard (Brassica juncea). The soil was found to have large total concentrations (mg kg{sup}(-1)) of Cd (59.3), Cu (664), Pb (605), Ni (489), and Zn (1780); the EDTA-extractable metal contents (mg kg-1) were Cd (36.2), Cu (483), Pb (302), Ni (372), and Zn (1280). Isotopic dilution of 109{sup left}Cd was used to measure labile Cd both (i) chemically (the E value: 28.3 mg Cd kg{sup}(-1)) and (ii) biologically (the L value). Comparison of E and L values was then used to determine whether nonlabile Cd was mobilized by the chelate treatment. Addition of EDTA increased plant uptake of Cd, Zn, Pb, Ni, and Cu from sludge-amended soil but did not facilitate access to the nonlabile pool of Cd in the soil; E values and L values were similar across the range of EDTA applications. Thus it was apparent that the small EDTA concentrations applied in phytoremediation to increase metal solubility are probably insufficient to mobilize fixed forms of Cd.
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