Heavy metal accumulation and mobility in a soil profile depend on the organic waste type applied
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While 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 methods
Three 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 7 years (1994–2000) at a rate of 25 and 50 t ha−1 year−1. Subsequently, when organic sludge amendments were ceased, the experimental plots were cultivated without any treatments for another 12 years (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 discussion
Significant increases in Cu, Pb, and Zn concentrations were observed down to a depth of 80 cm 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 80 cm, soils which had received 25 and 50 t ha−1 LS showed, respectively, 4 and 14 times higher Cr levels than the control soil.
Organic sludge induced changes in soil pH and soil DOC concentration which were the key factors influencing HM movement and accumulation following organic sludge treatment.
KeywordsIndustrial sewage sludge Leather sludge Long-term application Municipal sewage sludge Organic waste Soil heavy metals
This study was carried out with the support of “Research Program for Agricultural Science & Technology Development (Project No. PJ01332103)”, National Academy of Agricultural Science, Rural Development Administration, Republic of Korea. Dr. Gary Owens gratefully acknowledges the financial support of the Australian Research Council Future Fellowship Scheme (grant number FT120100799) for funding his salary.
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