Distribution of different inorganic fractions of arsenic in some soils of West Bengal

Sequential extraction techniques were adopted to separate out different inorganic As fractions from four representative surface soils collected from Gotera and Ghentugachhi (Block-Chakdah, District-Nadia), Gayeshpur (Block-Kalyani, District-Nadia) and Baruipur (Block - Ramnagar, District-South 24 Parganas). The study revealed that the inorganic fractions were in the order: Fe-As > Ca-As > Al-As > Ws-As. The Fe-As contributed 33.5 to 63.1 per cent of the sequential sum. Soils of Ghentugachhi had the highest sum of As fractions followed by the soils of Gotera, Baruipur and Gayeshpur. Arsenic extracted by different extractants showed that the metal was relatively higher in the soils of high As contaminated zone. The amount of extracted As decreased sharply from surface to subsurface and subsoils in all the profiles examined. The effectiveness of the extractants increased with increasing pH of the extractants, and was in the order of NH₄NO₃ < distilled water < NH₄OAc < NaHCO₃, (NH₄)₂CO₃ < NaOH. Sequential extraction was superior and effective in removing As compared to single extractants and the study also revealed that 0.5 M NaHCO₃ may be used as a suitable extractant for As in neutral to slightly alkaline soils.