Rhizosphere and flooding regime as key factors for the mobilisation of arsenic and potentially harmful metals in basic, mining-polluted salt marsh soils

The occurrence of mining areas in the vicinities of salt marshes may affect their ecological functions and facilitate the transfer of pollutants into the food chain. The mobilisation of metals in salt marsh soils is controlled by abiotic (pH, redox potential) and biotic (influence of rhizosphere) factors. The effect of the rhizosphere of two plant species (Sarcocornia fruticosa and Phragmites australis) and different flooding regimes on potentially harmful metals and As mobilisation from salt marsh soil polluted by mining activities were investigated (total concentrations: 536mgkg-1 As, 37mgkg-1 Cd, 6746mgkg-1 Pb, 15,320mgkg-1 Zn). The results show that the changes in redox conditions (from 300mV to -100mV) and pH after flooding and rewetting periods may mobilise the contaminant elements into soil solution (e.g., 100¿gL-1 Cd, 30¿gL-1 Pb, 7mgL-1 Zn), where they are available for plants or may be leached from the soil. Drying periods generated peaks of concentrations in the soil solution (up to 120¿gL-1 Cd and 50¿gL-1 Pb). The risk assessment of As and metal-polluted salt marshes should take into account flood dynamics in order to prevent metal(loid) mobilisation. © 2010 Elsevier Ltd.