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We have developed an in-air particle-induced x-ray emission(PIXE) analysis system that provides elemental distribution images in a region of 3 × 3 cm 2 with a spatial resolution of ∼0.5 mm. We call this system an in-air submilli-PIXE camera. This system consists of a submilli-beam line, beam scanners and a data acquisition system for elemental mapping. We applied the in-air submilli-PIXE camera to phytoremediation research. Phytoremediation is a technology for cleaning metal-contaminated soils using plant physiology. Pteris vittata, which is known as a hyperaccumulator of arsenic, was analyzed by the PIXE camera. Elemental images of laminas were obtained in vivo without sample preparation. The elemental map of the laminas in several centimeters region showed that arsenic was accumulated in the edges of P. vittata fronds and redistributed in the laminas at different growth stages. The submilli-PIXE camera is an effective tool for undertaking phytoremediation research.

Pytoremediation using an arsenic hyperaccumulator, Petris vittata L., has generated an increasing interest worldwide due to both environmentally sound and cost effectiveness. However the mechanism of arsenic accumulation by this fern is not clear at this time. This study examined the uptake of arsenate (As(V)) and arsenite (As(III)) by a hydroponic culture of Pteris vittata using both in-air submilli-PIXE for different parts of the fern and in-air micro-PIXE for the tissue cells. These PIXE analysis systems used 3 MeV proton beams from a 4.5-MV single-ended Dynamitron accelerator at Tohoku University, Japan. The fern took up both arsenate and arsenite from hydroponic solutions which were spiked with 50 mg of arsenic per litter. Final amount of arsenic accumulation in the fern is 1,500 mg per kg (wet weight) of the plant biomass in arsenite treatment and 1,100 mg per kg in arsenate treatment. Arsenic accumulation was not observed at the root parts of the ferns. The in-vivo mapping of elements by submilli-PIXE analyses on the fern laminas showed the arsenic accumulation in the edges of a pinna. The micro-PIXE analyses revealed arsenic maps homogeneously distributed in cells of the lamina, stem and rhizome of the fern. These results indicate that arsenic, both arsenate and arsenite in a contaminated medium are translocated quickly from roots to fronds of Pteris vittata, and distributes homogeneously into tissue cells of the fern laminas.