Arsenic Fractionation in Paddy Field Soil of Middle and Lower Ganga Plain in Relation to Soil Physico-chemistry

Le résumé fourni par la source

Arsenic (As) pollution in paddy field through geogenically contaminated irrigation water is a big challenge in many countries. Soil physico-chemistry is crucial in As accumulation in soil as well as its release in soil solution. To assess potential toxic effect of As on crops and to humans it is essential to determine the availability of As in soil solution. In this study, fractionation of As was performed in As contaminated paddy field soils from Uttar Pradesh i.e. Middle Ganga Plain (MGP) and West Bengal i.e. Lower Ganga Plain (LGP) and analyzed in relation to soil properties. The percent of total As extracted was 0.87 to 6.5% as water soluble, 0.13 to 4.8% exchangeable, 6.8 to 14% specifically sorbed and 11 to 21% As in amorphous Fe oxide associated. Most of the As (57 to 79 %) was found in crystalline Fe oxide and residual fraction i.e. incorporated in minerals. The concentration of As in soil and its release in different fractions was strongly correlated to the soil properties. Higher clay content, high Fe and Ca and low P and S seems the main factors for accumulation of As in soil of LGP. The primary causes of the high release of As, particularly in water soluble and amorphous Fe oxide associated As, appeared to be high TOC, alkaline pH, and high EC. Conversely, the soils of MGP were more sandy, low in TOC and OM, and have relatively higher available P and S causing a higher release of exchangeable and specifically sorbed As. Although amorphous Fe oxide was the primary As binding fraction in both soils, it would be a substantial source of accessible As in a reducing environment.

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