Effects of sludge on heavy metals release from peppermint-planted soils during time as assessed by DGT technique

Abstract

ABSTRACT The desorption kinetics of Cd, Pb, and Zn was investigated as a function of sewage sludge amount (0, 10, and 30 g kg−1), incubation time length (30 and 120 days) and plant cultivation (Mentha pipertia L.) using diffusive gradient in thin-film (DGT) technique. Kinetic parameters result of studied metals suggested that an increase in desorption rate constant (K−1), distribution coefficient (Kd), and resupply (R) values as well as a decrease in response time (Tc) over time in planted soils treated with 30 g kg−1 sewage sludge, which then resulted in a significant increase in plant metals concentrations. In 10 g kg−1 sewage sludge treated soils, a reverse trend was observed for the parameters over time (except for Kd values of Cd). Statistical analyses showed that Zn and Pb desorption rates were more influenced by dissolved organic carbon (DOC) compared to pH. For Cd, there was a significant agreement between K−1 and clay content. It is concluded that unlike Zn and Pb, the decreased R value of Cd that was reflected by the increased Tc and the reduced K−1 after extended incubation period may be the main factor limiting the Cd availability.