THE EFFECT OF ARSENIC SPECIATION ON ARSENIC UPTAKE AND FATE IN THE PRESENCE OF THE HYPER-ACCUMULATING SPECIES PTERIS CRETICA

Understanding arsenic uptake mechanisms employed by the arsenic hyper-accumulator Pteris cretica is important to optimize its arsenic accumulation capability to further improve the treatment process for small-scale or point of use applications in the developing world.Since most of the approaches for arsenic control using Phytoremediation as a treatment technology that have been conducted using arsenate as arsenic source[26], the present study was carried using arsenite to determine the role of speciation in arsenic uptake by the hyper-accumulator Pteris cretica.It was determined that trivalent arsenic oxidation plays an important role on the overall arsenic uptake. When trivalent arsenic was added to the aerated solution, only about 50% of the initial arsenite concentration was oxidized to arsenate regardless the exposure time. On the other hand, in the presence of Pteris ferns, arsenite is completely oxidized as it is being removed from the solution. In order to further elucidate the fate of arsenite in the presence of plant roots, experiments were conducted with Boston fern (Nephorlepis exaltata) a non hyper-accumulating fern that is sensitive to arsenic [35]. It was observed that the total concentration of arsenic in solution remains constant but arsenite is converted to arsenate.Given that these plant species do not have the ability to oxidize arsenite [24], our hypothesis is that the microbial community of the rhizosphere is responsible for arsenite oxidation as a symbiotic relationship with the plant, which has never been evaluated by other groups working with this technology. Studies in the presence of non-accumulating Boston fern were conducted to evaluate this hypothesis by adding an antibiotic cocktail to the arsenic solution together in an effort to suppress microbiological activity in the rhizosphere and a reduction in arsenite oxidation rates was observed. These results provide evidence of a symbiotic relationship between arsenic oxidizing microorganisms and arsenic hyper-accumulating plants, and suggest that the oxidation step is crucial on the arsenic uptake process when arsenic is present as arsenite