Effect of Calcium and Magnesium Addition on Arsenic Leaching from Paddy Field Soil of Bangladesh

Arsenic (As) that has been accumulated from irrigation groundwater to paddy field soil by sorption has the potential for food contamination by plant uptake and recontamination of the groundwater. This study evaluated the effect of calcium (Ca) and magnesium (Mg) addition on As leaching from paddy field soil collected from the southwest region of Bangladesh. Batch experiments were employed to systematically investigate the role of Ca and Mg addition on the leaching behavior of As under different concentrations of Ca and Mg, pH conditions and anaerobic incubation. Results indicated that As leaching was highly decreased with the increase of Ca and Mg addition, at pH greater than 9.0 and during anaerobic incubation. In contrast, Iron (Fe) leaching was decreased by Ca and Mg addition. Adsorption of Ca and Mg was observed and significant correlation with adsorbed As was obtained in all batches. The probable mechanism was precipitation of As due to the increase in the positive surface charge of the Fe hydroxide solids by Ca and Mg adsorption. This study also indicated that Ca and Mg addition could decrease As leaching even under the presence of phosphorus.