Physiographical variability in arsenic dynamics in Bangladeshi soils

Rice plants grown on soils with elevated arsenic have been shown to have increased arsenic content in their grains. To gain a better understanding of the likelihood of high grain arsenic in rice grown in different soils, it is important to understand the factors affecting the bioavailability and mobility of arsenic. Paddy soils from six different physiographic regions of Bangladesh were collected, and diffusive gradients in thin-films (DGT) were used to assess the porewater and solid phase arsenic. While significant differences were identified in total soil arsenic (1.4–9.8 mg/kg), porewater arsenic (AsCsol) (5.6–64.7 µg/l), labile arsenic (AsCDGT) (6.3–77.6 µg/l), and solid phase pool of arsenic (AsKd) (52–1057 l/kg), importantly arsenic resupply capacity was not different between the physiographic regions. All soils had a high ratio of DGT to porewater arsenic (~1), this in conjunction with the porewater arsenic values and the high AsKd values suggesting a large solid phase pool of arsenic capable of contributing towards the resupply/ transport of the labile pool of arsenic in the soil porewater. This indicates that there is less difference in soil arsenic availability than might be predicted based solely on total soil arsenic content between the physiographic regions.