Leaching of macronutrients and metals from undisturbed soils treated with metal-spiked sewage sludge. 3. Distribution of residual metals

Abstract

Sewage sludge is increasingly been applied to land in New Zealand in an attempt to recycle the valuable plant nutrients such material contains. However, there are concerns regarding the environmental fate of heavy metals contained in the sludge. This study examines the soil profile distributions of metals (Cd, Cr, Cu, Ni, Pb, Zn) in large undisturbed soil lysimeters treated with metal-spiked sewage sludge, following 3 years of drainage leachate monitoring. For 3 forest soils that had all received surface applications of sludge, analytical results demonstrated considerable transport of metals from the sludge into the underlying litter and mineral soil layers. Determination of individual metal/Cr ratios revealed considerable differential mobility between metals, with Cd, Ni, and Zn being most mobile, and Cu and Pb being only slightly more mobile than Cr. Total metal analysis was relatively insensitive in detecting metal movement down the soil profile compared with determination of extractable metals (EDTA or Ca(NO3)2 extraction). Maximum depths of metal penetration varied between metals, but were similar for all 3 forest soils, averaging 0.15, 0.20, 0.25, 0.35, and 0.45 m for Pb, Cu, Cd, Ni, and Zn, respectively. In contrast to the forest soils, when sludge was incorporated into the top 0.10 m of 2 pasture soils, little movement of metals could be detected below the layer of incorporation. However, even in these soils, the determination of metal/Cr ratios indicated that some differential movement of metals had taken place. For the forest soils, the results indicate considerable potential for the long-term and sustained leaching of metals by normal convective and diffusive transport processes. This would appear to be of less concern where sludge has been incorporated into the pasture soils. These results clearly have implications for selection of the most appropriate soils and conditions for sludge application to the land.

Chemical Changes and Heavy Metal Partitioning in an Oxisol Cultivated with Maize (Zea mays, L.) after 5 Years Disposal of a Domestic and an Industrial Sewage Sludge

“…The different concentrations of the analyzed metals at 20-40 cm deep (Table 3) possibly reflect a certain mobility of these elements, which was also observed by many other authors (Tiller 1989;Giusquiani et al 1992;Mbila et al 2001;McLaren et al 2005;Toribio & Romanya 2006;Antoniadis 2008). In support of this hypothesis, the organic carbon content is influenced by the doses of sewage sludge at depth (Table 2), indicating a possible mobility of organic complexes accountable for the mobilization of metals at depth (Strobel 2001;Tipping 2002;Tan 2003).…”

Cadmium in plants on polluted soils: Effects of soil factors, hyperaccumulation, and amendments

“…More Cd leached out of the forest soils than the pasture soils, and this was expected from the acidic forest soils. Sludge was surface applied to the forest soils and incorporated in the top 10 cm in the pasture soils (McLaren et al, 2005). After three years, there was little movement of Cd below the level of incorporation in the pasture soils, while in the three forest soils the metal penetrated to 0.25 m from the top.…”

Heavy Metals in Contaminated Soils: A Review of Sources, Chemistry, Risks and Best Available Strategies for Remediation

“…Heavy metals most commonly found in biosolids are Pb, Ni, Cd, Cr, Cu, and Zn, and the metal concentrations are governed by the nature and the intensity of the industrial activity, as well as the type of process employed during the biosolids treatment [31]. Under certain conditions, metals added to soils in applications of biosolids can be leached downwards through the soil profile and can have the potential to contaminate groundwater [32]. Recent studies on some New Zealand soils treated with biosolids have shown increased concentrations of Cd, Ni, and Zn in drainage leachates [33,34].…”