Accumulation, speciation, and distribution of metal(loids) in plants: Applications of synchrotron techniques in environmental sciences.

摘要

In the last two decades, synchrotron based techniques have gained popularity and been increasingly used in environmental sciences. The present dissertation has relied significantly in the use of synchrotron based techniques to study the speciation, coordination, and distribution of toxic metal(loids) in plants. This study included three plant species: Parkinsonia florida, Prosopis juliflora, and Zea mays. P. florida is a plant species native to the semi-desert regions of North America. The cultivation characteristics of this shrub/tree suggest that it could be used for phytoremediation purposes in semiarid regions. P. florida plants were tested for their capacity to remove arsenic (As) from As(V) and As(III) treated soils. Plants grown in two soils with different physicochemical properties accumulated detectable amount of As only in roots. Linear combination microXANES data analysis from the roots exposed to As(V) treated soil showed that As was reduced to As(III). Also, a fraction of the reduced As was found coordinating to S in a form consistent with As-Cys3. In addition, As speciation in the rhizosphere of mesquite (P. juliflora) plants was studied using synchrotron techniques. The selected soil for this study was a sandy clay loam spiked with As(III) and As(V). In all cases As was found in soil as As(V) whereas in the roots it was found as As(III)-thiolate species. In plants, S has also been found linked to other toxic elements like cadmium (Cd). The link between S concentration, Cd uptake, and the synthesis of low molecular weight thiols was investigated using ICP/OES and XAS. ICP-OES determinations demonstrated that Cd, like As, was mainly accumulated in the roots of corn plants. XAS analyses demonstrated the link between Cd and sulfur ligands within the plant. The results indicate that Cd inside the corn roots and shoots is bound to sulfur ligands with interatomic distances of 2.51-2.52 A. The results from the present research corroborate the application of synchrotron based state of the art techniques in the study of plant-metal interactions.