Distribution and nature of arsenic along former railway corridors of South Australia.

Elevated concentrations of arsenic (As) have been detected in soils of former railway corridors in South Australia, Australia. Elevated As concentrations resulted from the long-term application of As-based herbicides to control grass growth along former railway corridors. A study of former railway corridors revealed considerable surface (0-10 cm) contamination with As (<20 to >1000 mg As kg-1). The distribution of As in soils was related with particle size fraction and iron (Fe) oxide content. Total As increased markedly with decreasing particle size; sand<<silt<clay, with increasing As concentration generally correlated with increasing Fe concentrations (R2=0.57). A sequential fractionation of soils collected from selected sites showed that As was primarily associated with the amorphous and crystalline Fe and Al oxide materials. Solid phase speciation of As-contaminated soil indicated that arsenate (AsV) was the dominant As species present in the soil. However, in some soils, arsenite (AsIII) composed up to 40% of the total As present. The reasons for the presence of AsIII under alkaline and aerobic conditions are unclear.