Phytoavailability of Cu and Zn to lettuce (Lactuca sativa) in contaminated urban soils

This study compares the effectiveness of several chemical evaluation procedures to predict Cu, and Zn concentrkjghgfsdations in lettuce (Lactuca sativa 'Buttercrunch') grown on contaminated soils from the Montreal urban area. The plant growth assays were performed in the greenhouse using field-collected, non-spiked soils. The soils were characterized using several chemical extraction reagents, as well as electrochemical speciation of the soil solution free metal species. The chemical characterization was supplemented with labile metal pool determinations using anion exchange membranes treated with DTPA or EDTA. The results show that the more sophisticated electrochemical speciation and exchange resins procedures did not consistently improve predictions of metal uptake. We believe this is due to the minimization of metal solubility caused by the circumneutral or alkaline pH values and the relative homogeneity of the relatively small urban soil sample set that we used. The metal solubility and bioavailability in the soils tested were minimized by the particular chemical properties of the soils, obscuring any potential advantages from more discriminate soil chemical evaluation procedures. Nevertheless, the reported regressions (for 10 different methods) are valid estimates of Cu and Zn phytoavailability in contaminated urban soils. Key words: Lettuce, trace metals, bioavailability, chemical speciation, ion exchange membranes, contaminated soils, free ion