Arsenic speciation of sediments from the Thames Estuary, London, UK

Arsenic is generally present in the environment as arsenate (AsV) and to a lesser degree as arsenite (AsIII), or the methylated compounds monomethylarsonate (MA) and dimethylarsinate (DMA)1,2, whilst Ellwood et al (2003)3 reported the presence of arsenosugars (As-sugars) in lake sediments. Measurement of individual arsenic (As) species provides valuable information on the varied toxicity of inorganic and organic forms of As. AsIII is considered the most toxic and mobile of As species in soil and sediment. Information regarding the chemical forms (species) of As is useful to understand possible mobilisation from sediment into aqueous phase, since soil and sediments cannot be isolated from geochemical cycles4. The aim of this work was to determine total and measurable arsenic species in the mobilisable fraction of 36 sediment cores from the Thames estuary using a phosphoric/ ascorbic acid extraction, followed by HPLC-ICP-MS analysis5.