Mobility of Copper, Zinc and Lead in a Multi-Element Contaminated Soil Profile Assessed Using a Column Leaching Study.

Leaching potential assessment of metals is needed for beneficial use of contaminated soil for the production of perennial bioenergy crops. A soil column experiment was carried out to investigate the effects of adding a source of carbon (C) to a contaminated soil on the mobility of Cu, Zn and Pb. Soils were sampled on a contaminated site beside a former incinerator (Levis, QC, Canada). Soils were incubated in 108 columns (9 soils x 4 replicates X 3 treatments). Treatments consisted of a control and two different sources of C: hog manure and Switchgrass (Panicum virgatum L) residues, that were applied at the surface of the soil columns at an equivalent rate of 1.3 t C ha^-1. Soil columns were incubated at room temperature for 60 days and were watered weekly with deionized water for a total of 224 mm, which is equivalent to the mean annual rainfall (May to October) where the soils were sampled. Leachates were collected after each leaching event (total of eight) and analyzed for pH, EC, dissolved organic carbon (DOC), Cu, Zn and Pb concentrations. At the end of the experiment, each soil column was divided into 0-5, 5-15 and 15-25 cm depth increments. Soil samples were air-dried and ground before analysis. Results show that the total concentration of all three metals tended to be higher in the hog manure treatments than in the control and the residue treatments. Moreover, hog manure favored the mobility of Zn but not Cu and Pb, for which the results were more variable. Analysis of the leachates will complement and help confirming these results based on soil analysis.