Abstract
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 (μXRF) combined
with μX-ray absorption near-edge spectroscopy (μXANES). 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. μXAS and
μXRF 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 μXAS techniques is a
powerful analytical technique for the study of As speciation in soil and plant
samples
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