Influence of Flue Gas Desulphurization Ash on Phytotoxicity and Bioavailability of Zinc in Zn-Contaminated Soils.

Phytotoxicity of Zn due to metal accumulation in soils can be remediated by stabilization techniques using alkaline residuals such as flue gas desulphurization (FGD) ash. The FGD can immobilize Zn bioavailability by inducing various sorption processes such as surface precipitation, adsorption to mineral surfaces, and ion exchange. Sewage sludges from different wastewater treatment plants were applied annually from 1977 to 1986 to a Metea sandy loam soil (loamy, mixed, mesic Typic Hapludalfs) at four Zn loadings (0, 1.43, 2.67, and 11.3 Mg ha^-1) and four replicates. Treatment 2 that received the highest Zn loading caused Zn phytotoxicity and reduced dry matter yields of crops grown between 1985 and 2007. In 2007, we initiated a study to evaluate the suitability of FGD as an amendment to stabilize and reduce Zn phytoavailability, and remediate the phytotoxicity. A portion of each replicate plot was treated with 16.8 Mg ha^-1 of FGD, and soybean (Glycine max L.) was grown to maturity in 2007. The added FGD increased soil pH of all the treatments. Yield of soybean grown on Zn impacted plots treated with FGD was improved and was not different from yields observed in control and other treatments at P = 0.05. Similarly, Zn concentrations in the diagnostic soybean leaf from  Treatment 2 were reduced by FGD treatment. In 2007, as in previously-grown crops, the lowest grain yield and highest Zn concentrations were observed in Treatment 2 plots that were not amended with FGD. The FGD treatment also decreased concentrations of Ni, Pb, and Cr in diagnostic tissues of soybean grown in Treatment 2 plots. The study indicated that FGD can be used to stabilize and reduce Zn phytoavailability and phytotoxicity.