Dynamics of arsenic in agricultural soils irrigated with arsenic contaminated groundwater in Bangladesh

Arsenic (As) concentrations in the soil layers of 12 rice fields located in fourAs affected areas and two unaffected areas inBangladesh were monitored during 2003. In the unaffected areas, where irrigation water contained little As (b1 μg/L), As concentrations of rice field soils ranged from 1.5 to 3.0 mg/kg and did not vary significantly with either depth or sampling time throughout the irrigation period. In the As affected areas where the irrigation water contained elevated As (79 to 436 μg/L), As concentrations of rice field soils were much higher compared to those in the unaffected areas and varied significantly with both depth and sampling time. For the top 0 to 150 mmof the soil, the As concentration increased significantly at the end of the irrigation season (May–June 2003). About 71% of the As that is applied to the rice fieldwith irrigation water accumulates in the top 0 to 75mmsoil layer by the end of the irrigation season. After the wet season during which the rice fields were inundated with flood/rain water, the As concentrations in the soil layer decreased significantly andwere reduced to levels comparable to those found in soil samples collected at the beginning of the irrigation period. The long-term As accumulation in agricultural soil appears to be counteracted by biogeochemical pathways leading to As removal from soil.