Solute Interactions in Soils in Relation to Bioavailability and Remediation of the Environment

Abstract

Unlike organic contaminants, most metals do not undergo microbial or chemical degradation and the total concentration of these metals in soils persists for a long time after their introduction (Adriano, 2003). With greater public awareness of the implications of contaminated soils on human and animal health there has been increasing interest amongst the scientific community in the development of technologies to remediate contaminated sites. For diffuse distribution of metals (e.g. fertilizer-derived Cd input in pasture soils), remediation options generally include amelioration of soils to minimize the metal bioavailability. Bioavailability can be minimized through chemical and biological immobilisation of metals using a range of inorganic compounds, such as lime and phosphate (P) compounds (e.g. apatite rocks), and organic compounds, such as 'exceptional quality' biosolid (Figure 1; Bolan and Duraisamy, 2003). Reducing metal availability and maximizing plant growth through inactivation may also prove to be an effective method of in situ soil remediation on industrial, urban, smelting, and mining sites. The more localised metal contamination found in urban environments (e.g. Cr contamination in timber treatment plants) is remediated by metal mobilization processes that include bioremediation (including phytoremediation) and chemical washing. Removal of metals through phytoremediation techniques and the subsequent recovery of the metals (i.e. phytomining) or their safe disposal are attracting research and commercial interests. However, when it is not possible to remove the metals from the contaminated sites by phytoremediation, other viable options, such as in-situ immobilisation should be considered as an integral part of risk management.