Arsenic Localization and Speciation in the Root-Soil Interface of the Desert Plant Prosopis juliflora-velutina

The bioavailability and mobility of arsenic (As) in soils depends on several factors such as pH, organic matter content, speciation, and the concentration of oxides and clay minerals, among others. Plants modify As bioavailability in the rhizosphere; thus, the biogeochemical processes of As in vegetated and non-vegetated soils are different. Changes in As speciation induced by the rhizosphere can be monitored using micro-focused synchrotron-based X-ray fluorescence (mu ARF) combined with mu X-ray absorption near-edge spectroscopy (mu XANES). This research investigated As speciation in the rhizosphere of mesquite (Prosopis juliflora-velutina) plants grown in a sandy clay loam treated with As(III) and As(V) at 40 mg kg(-1) Rhizosphere soil and freeze-dried root tissues of one-month-old plants were analyzed by bulk XAS. Bulk XAS results showed that As(V) was the predominant species in the soil (rhizosphere and non-vegetated), whereas As(III) was dominant in the root tissues from both As(V) and As(III) treated plants. mu XAS and mu XRF studies of thin sections from resin embedded soil cores revealed the As(III) S interactions in root tissues and a predominant As Fe interaction in the soil. This research demonstrated that the combination of bulk XAS and mu XAS techniques is a powerful analytical technique for the study of As speciation in soil and plant samples