Heavy metal accumulation and mobility in a soil profile depend on the organic waste type applied

Abstract

PurposeWhile organic waste amendments can initially improve soil physicochemical properties, including nutritional benefits to plants and increased microorganism activity, long-term application of excessive amounts of organic wastes can cause accumulation of heavy metals (HMs). Thus, the current study examined the accumulation of HMs in agricultural soil profiles following organic waste application.Materials and methodsThree common organic sludge, including municipal sewage sludge (MSS), industrial sewage sludge (ISS), and leather sludge (LS), were applied annually to an agricultural soil under field conditions over 7years (1994-2000) at a rate of 25 and 50tha(-1)year(-1). Subsequently, when organic sludge amendments were ceased, the experimental plots were cultivated without any treatments for another 12years (2001-2012) and the changes in HM concentrations along the soil depth profile were monitored together with soil pH, dissolved organic carbon (DOC), and dehydrogenase activity (DHA).Results and discussionSignificant increases in Cu, Pb, and Zn concentrations were observed down to a depth of 80cm in soils treated with ISS and LS, where sludge application also increased the levels of Cd, Cr, Pb, and Zn and their movement down the soil profile. However, with the exception of Cu, no significant changes in HM concentrations were observed following treatment with MSS. At a depth of 80cm, soils which had received 25 and 50tha(-1) LS showed, respectively, 4 and 14 times higher Cr levels than the control soil.ConclusionsOrganic sludge induced changes in soil pH and soil DOC concentration which were the key factors influencing HM movement and accumulation following organic sludge treatment.