Operationally defined associations of arsenic and copper from soil and mine waste in south-west England

Abstract

Arsenic and copper fractionation was studied in contaminated soil and mine waste materials from a mining site in Devon, UK. Ten soil samples with Cu concentrations ranging from 300-6144 mg/kg and As concentrations ranging from 5512-39715 mg/kg were sequentially extracted using the modified method of Tessier et al. (1979) and Wenzel et al. (2001). The Classical Tessier et al. (1979) scheme was shown to be inadequate for studying either Cu or As fractionation as it severely underestimated the Fe-oxide associated fraction. The Modified Tessier et al. (1979) scheme, including the two additional steps specifically targeting Fe-oxides, was shown adequate for both Cu and As fractionation; however the Wenzel et al. (2001) protocol allows the prediction of changes in lability of As in various solid phases as a result of soil remediation or alteration in environmental factors. In agreement with other studies, arsenic was found to be held predominantly in the amorphous Fe-oxide fraction (55%-94%), which can be potentially mobilised with a change in redox conditions. A significant proportion of As can also be remobilised from the soils through the process of anion exchange. Copper presented a different fractionation pattern as it was distributed mainly between the organic/sulfide and the Fe-Mn oxide fractions. Although the total concentrations of Cu in the soils are much lower than As, Cu appears to be solubilised to a much greater extent as indicated by the higher percentage contribution of Cu in the easily mobilisable fractions.