Assessment of arsenic availability to roots in contaminated Tuscany soils by a diffusion gradient in thin films (DGT) method and uptake by Pteris vittata and Agrostis capillaris

P>A laboratory study was conducted to evaluate the availability of arsenic (As) to roots in nine soils from five fields in Tuscany (Italy). Concentrations of As in soils range from 200 to 1200 mg kg(-1) as a result of human activities and natural deposition. In a first stage, potentially root-available As and the risk of crop uptake were estimated using the diffusion gradient in thin films (DGT) technique. In a second stage, a glasshouse experiment was performed to compare As depletion in the rhizosphere by the hyperaccumulator Pteris vittata (ladder brake), and by the test plant Agrostis capillaris (colonial bentgrass). In this stage, DGT results were supported by a sequential extraction procedure. The main objectives were to study the root availability of As in old, contaminated soils and the modification of the available pool size over time. The phytoextraction efficiency of Pteris vittata as applied to this case study was also investigated. In all samples, concentrations of total and potentially root-available As in soil solution were small compared with total As in soil (approximately 0.0003-0.03%, corresponding to 3.5-350 mu g l(-1), respectively). There was also little re-supply of As from the solid phase to the soil solution. In the rhizosphere, despite uptake by Pteris and Agrostis, total and root available As in solution were sustained over time. It appeared that plants induced a re-supply of As from the solid phase. Despite the uptake and translocation of As by Pteris (50.7 mg kg(-1) and 6.6 mg As kg(-1) in fronds and roots, respectively) together with plant biomass (17.2 g per plant), the success of phytoextraction appears unlikely. The results obtained demonstrated the sensitivity of DGT to root-induced changes in soil and the suitability of the technique as an easy-to-use tool to predict assimilation by plants.