Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2006
Publication Date: 2/5/2007
Citation: Antioniadis, V., Tsadilas, C.D., Ashworth, D.J. 2007. Monometal and competitive adsorption of heavy metals by sewage sludge-amended soils. Chemosphere. 68:489-494.
Interpretive Summary: Sewage sludge is an important source of organic matter and nutrient for agricultural soils. Application of sludge to land also alleviates the need for finding an alternative disposal route. However, sewage sludge also contains a number of heavy metals which can cause toxicity at elevated concentrations and may reduce soil fertility over time. Since most of these metals are bound to the sludge organic matter, their availability and toxicity may be low unless the organic matter is decomposed and the metals released. The partitioning coefficient (or Kd value) of three heavy metals, zinc, nickel and cadmium, between the solid and liquid phases of sludge-amended soils. As organic matter was decomposed over time, cadmium Kd value decreased, indicating an increased affinity for the liquid soil phase and a greater availability (i.e increased potential for mobility to surface water and plant/microbial toxicity). The potential for long-term release of metals should be considered in the risk assessment associated with sewage sludge addition to soils, particularly in climates where degradation of organic matter is likely to be enhanced.
Technical Abstract: Sewage sludge-amended soils may alter their ability to adsorb heavy metals over time, due to the decomposition of sludge-borne organic matter. Thus, we studied Cd, Ni, and Zn adsorption by a sewage sludge-amended soil (Typic Xerofluvent) before and after one-year incubation in both monometal and competitive systems. In the monometal system, the order of decreasing sorption was Zn > Cd > Ni. Competition significantly reduced metal Kd, especially that of Cd which decreased by nearly 50%. Over the course of the incubation there was a 31% reduction of soil organic matter content. At the same time, in competitive systems Cd Kd significantly decreased, while Zn Kd significantly increased, and Ni Kd remained unaffected. This study shows that sewage sludge-amended soils may change in their ability to sorb heavy metals over time at high metal concentrations. The data suggest that Cd is likely to be of most environmental significance in such soils, since it exhibited decreased sorption under competitive conditions and as the organic matter content of the soil was reduced. The potential for long-term release of metals should be considered in the risk assessment associated with sewage sludge addition to soils, particularly in climates where degradation of organic matter is likely to be enhanced.