Arsenic mobility and bioavailability in flooded industrially polluted UK soils

There is a paucity of studies focusing on the fate of arsenic (As) in poorly drained peri-urban land or clay-lined landfills. Evidence from rice paddy soils would indicate enhanced mobility and bioavailability of this metalloid in soils with impeded drainage. The fate of As was investigated in two historically contaminated UK soils possessing similar As concentrations, derived from different sources of industrial waste. Test soils differed significantly in Fe, Mn, and P content. Arsenic mobility was measured by soil pore-water sampling under flooded and drained watering regimes. Arsenic bioavailability was measured in terms of uptake by the floating macrophyte Lemna minor and two rice cultivars that differed in As tolerance and radial oxygen diffusion properties. Flooding of one test soil greatly enhanced iron (Fe) and manganese (Mn) content of pore-water, followed by increases in As content and poor growth of rice. No such processes were evident in the other soil. It is argued that testing As-contaminated soils by flooding combined with chemical analyses and plant assays, provides a realistic indication of future risk associated with waterlogged conditions.