Cornwall (UK) has suffered extensive arsenic contamination due to the historic mining and processing of mineral ores. Standard procedures for contaminated land risk assessment (DEFRA and Environment Agency, 2002a) are probably unworkable in Cornwall, with a very large number of sites classified as contaminated by arsenic. Methods of measuring the speciation and mobility of arsenic are essential for effective and rapid risk assessments of arsenic contamination.
Three clusters of lysimeters were installed in three different areas of an arsenic-contaminated Cornish site. A novel phosphoric acid microwave extraction technique was applied to the soils removed from the lysimeter holes; HPLC-HG-AFS analysis showed the majority of solid-phase arsenic to be arsenate (AsV). Pore waters obtained from the lysimeters showed variable, relatively low levels of arsenite (AsIII) and arsenate (AsV) to be present (<1–129 μg l–1). Less toxic arsenate predominated in most pore waters, with the presence of minor amounts of arsenite suggesting heterogeneous redox conditions. Pore-water arsenic concentrations were strongly positively related to solid-phase arsenate concentrations.
The use of techniques that assess the speciation of arsenic both in the solid and aqueous phases of a soil provides important information about the mobility of arsenic. The methodology presented in this paper may offer a novel basis for risk assessments of other contaminated sites.