Copper mobility in soils as affected by sewage sludge and low molecular weight organic acids

Copper is an essential micronutrient, but at increased concentrations, it quickly becomes toxic to plants, and remediation is needed. Because the land disposal of copper containing sewage sludge is increasing each year, there is a need to evaluate the mobility of copper in soil as affected by sewage sludge and low molecular weight organic acids (citric acid and oxalic acid). Copper mobility was studied in a Marvyn soil (fine-loamy, siliceous, subactive, thermic, Typic Kanhapludult) without or with 1 of 2 sewage sludges from the Birmingham, Alabama area. A total of 5 column experiments were performed. The columns were leached with solutions containing potassium sulfate (10 j2 M/L) to maintain proper ionic strength, in addition to different combinations of copper, oxalic acid, and citric acid. The Cu 2+ concentration in all applied solutions was 1000 mg Cu 2+ per kg of solution. In the column experiments containing sewage sludge, the effluent copper concentration did not reach the influent concentration. In the column experiments without sewage sludge, the influent copper concentrations were easily reached in the effluent, independent of the addition of oxalic or citric acid. A batch equilibrium study showed that both sewage sludges could adsorb more than 50,000 mg of copper per kilogram of sewage sludge, compared with 1250 mg of copper per kilogram of Marvyn soil. This amount is so high that sewage sludges could possibly be used for copper detoxification in mine tailings or farm lands where copper pollution is a potential problem for vegetation. (Soil Science 2006;171:29‐38)