Importance of sorption versus fixation reactions in decreasing metal bioavailability for in situ remediation

Abstract

An increasing number of studies are being conducted to evaluate the potential of different materials as amendments for in situ remediation of soils and aquatic systems polluted with inorganic contaminants such as heavy metals and phosphorus. Isotopic dilution techniques can provide an insight into changes in the partitioning of contaminants between labile and non-labile pools following incorporation of remediation materials. However, it is unclear whether movement of contaminants from isotopically- exchangeable to non-isotopically exchangeable pools (fixation) has a significant role to play in the reduction of bioavailability, compared simply to the decrease in solution contaminant concentration (sorption) which is induced following amendment addition. In this study, different remediation treatments were applied to a range of soils industrially contaminated with metals including Cd and Zn. Plants were grown in the different treatments and solution metal concentrations and isotopically-exchangeable pools assessed. The contribution to the decrease in metal bioavailability of sorption versus fixation reactions, and hence the utility of isotopic tehniques for screening prospective remediation treatments, was determined by comparing the relative changes in plant metal concentration, soil solution metal concentration and isotopically-exchangeable Cd and Zn induced by the amendments.