ABSTRACT
The mobility, toxicity and bioavailability of arsenic (As) in environment is mainly dependent on retention efficiency of different soil types that it interacts in aquifer systems. Attenuation potential of a representative soil for As was evaluated in this study in order to understand the control of aquifer soil on As bioavailability around a severely contaminated site (up to ~128 mg/kg) of Rupnagar District, Punjab, India. The soil belongs to an agricultural field with minor As content (~1.2 mg/kg) and is the dominant soil type in this region composed mainly of sand, silt and clay. Commonly encountered geochemical variables like PO4 3−, NO3 − and pH were evaluated. The results indicate that As attenuation by the soil was maximum at pH 6 (1 g/kg) that lowered to ~43% at pH 10 possibly due to soil surface repulsive force. The positive and negative correlation of released PO4 3− and SO4 2− with residual As, respectively at different pH is suggestive of HAsO4 2−-PO4 3− aqueous complexation and likely HAsO4 2−-SO4 2− ion exchange governing the overall attenuation mechanisms. Increasing aqueous PO4 3− and NO3 − concentrations as controls exhibited a slight inverse relation with residual As partly supporting As-PO4 complexation, while NO3 − seems non-responsive. The study suggests that the aquifer soils possess considerable retentive efficiency for As, especially under near-neural pH conditions in presence of dissolved PO4 3− through both ion-exchange and aqueous complexation processes.
