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

This study compares the effectiveness of several chemical evaluation proced ures to predict Cu, and Zn concentrations in lettuce (Lactuca sativa 'Butte rcrunch') grown on contaminated soils from the Montreal urban area. The pla nt growth assays were performed in the greenhouse using field-collected non -spiked soils. The soils were characterized using several chemical extracti on reagents, as well as electrochemical speciation of the soil solution fre e 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 spec iation and exchange resins procedures did not consistently improve predicti ons of metal uptake. We believe this is due to the minimization of metal so lubility caused by the circumneutral or alkaline pH values and the relative homogeneity of the relatively small urban soil sample set that we used. Th e metal solubility and bioavailability in the soils tested were minimized b y the particular chemical properties of the soils, obscuring any potential advantages from more discriminate soil chemical evaluation procedures. Neve rtheless, the reported regressions (for 10 different methods) are valid est imates of Cu and Zn phytoavailability in contaminated urban soils.