Distribution of different inorganic forms of arsenic in selected arsenic affected soils of the Bengal Delta Basin

Inorganic soil arsenic (As) fractions from three representative arsenic affected surface soils of West Bengal, collected from Ambikanagar, Chakla, Iajpur (Block-Deganga, District-North 24-Parganas) as well as the control site at Gayespur (Block-Chakdah; District-Nadia), were fractionated into different soil arsenic pools by following the sequential extraction methodology. These soils were also subjected to extraction of As by using several individual extracts in order to adjudge their efficacy in extracting soil arsenic fractions. The findings suggested that the inorganic fractions of soil arsenic were in the order of Ws-As < Al-As < Ca-As < Fe-As. The Fe-As contributed 44.7% to 74.7% towards arsenic sequential sum. Soils of Iajpur had the highest sum of As fractions followed by those from Ambikanagar and Chakla. As regards the individual extractants used, the efficacy of the latter in extracting soil arsenic fell in the order, (NH4)(2)CO3 = CH3COONH4 < Na2CO3 < NaHO3 < NaOH = NH4F < HCl + H2SO4 < KH2PO4 < HCl < H2SO4. Among these extractants used, 0.5 N H2SO4 (pH 0.9) proved superior to others in releasing acidic and alkaline cation-bound arsenic in soils, whereas the 0.1 N NaOH (pH 13.0) also showed promise in releasing arsenic bound by the sesquioxides of the given soils, in agreement with the findings from the sequential extraction scheme followed in these soils. A careful perusal of these results suggested that iron components played dominant role in facilitating accumulation of arsenic in these soils.