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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.

The early life environment has widespread consequences for later health and disease. To prevent the disease in later life, the assessment of fetal environment is very important. In Japan, birthweight has fallen rapidly during recent two decades. The reduction of birthweight represents reduced fetal nutrition. Deciduous tooth enamel contains pre- and postnatal enamel and its chemical composition reflects the status of metabolism of trace elements during formation period. Deciduous tooth enamel is considered to be a suitable indicator of trace elements exposure in utero. We applied micro-PIXE analysis to investigate the trace elemental content in deciduous tooth enamel. Two deciduous canines from one healthy Japanese boy were used for this study. The enamel section including pre-and postnatal enamel was prepared for micro-PIXE analysis. Five trace elements (Na, Mg, Cl, Zn, and Sr) were detected in the scanning area of tooth. The distribution profiles of 5 elements were obtained as X-ray maps. The distribution profiles of zinc and chlorine were specific, and showed higher concentration in surface enamel. No elements showed different profiles of X-ray maps between pre-and postnatal enamel in this sample. The results of this study suggested that micro-PIXE analysis would be able to estimate the trace elements in prenatal and postnatal enamel, respectively.

Pteris vittata is a fern reported to be an arsenic hyper-accumulator. To develop the practical application of the fern to a phytoremediation technique, it is necessary to explicate the effective accumulation mechanism. In this study, the arsenic distribution and the elemental correlation in the cellular level were examined in the fronds supplied with arsenate and arsenite separately via xylem vessel using an in-air micro-PIXE system at Tohoku University. The difference in transportation rate between arsenate and arsenite as well as the translocation of elements necessary for plant metabolism was revealed in different tissues of the fronds accumulating arsenic in high concentration. Hence, the in-air micro-PIXE analysis is an effective measure for undertaking phytoremediation research of hyper-accumulator plants.

Naturally shed deciduous teeth are potentially useful as a biomarker of environmental exposure. To assess the prenatal environment of child, we tried to present the neonatal line on the elemental maps and investigate the trace elements in pre- and post-natally formed tooth enamel using micro-PIXE. Generally, the neonatal line is observed more clearly in the tooth from child who has some difficulties at birth. In this study, five deciduous teeth from five children with developmental disorders were used for analysis. Seven trace elements (Na, Mg, Si, Cl, Fe, Zn, and Sr) were detected in enamel of all five teeth. The line, it was thought neonatal line, was observed on the elemental map of Ca and P in the tooth from the child with serious birth complications. In order to compare the elemental concentration between pre- and post-natal enamel, concentration variation of elements were projected along the line perpendicular to the neonatal line. Lower Ca concentration in prenatal enamel was observed. By tracing the location of neonatal line on the other elemental maps, the concentrations of detected trace elements were compared in the same way. The differences of concentration of these trace elements between pre- and post-natal enamel were not clear because of much statistic variation. We could determine the trace elemental profiles and concentrations around the neonatal line in the enamel from the child with serious birth complications.

A lot of radiocesium had been deposited onto pastures and grasslands following Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. More radiocesium was accumulated in root-mat horizon than in both above ground plant bodies and mineral soils. In this study, factors causing higher radiocesium concentrations in root-mat horizon were evaluated by the addition of stable cesium solution and particle-induced X-ray emission (PIXE) analysis. Results suggest that adsorption onto root surfaces played a significant role in Cs accumulation in root-mat horizon. Furthermore, absorption of Cs was key to its long-term preservation. The adsorption of Cs by clay minerals also contributed to its retention. A slow water infiltration rate may also affect the enrichment of radiocesium in root-mat horizon. Based on these results, it is concluded that both biotic and abiotic factors contributed to the effective retention of radiocesium in root-mat horizons following the FDNPP accident.

The amount of contaminated soil with radioactive cesium (Cs) is more than 22 million cubic meters as a result of the Fukushima Daiichi nuclear power plant accident. In order to save the cost for keeping the soil covered, it is necessary to reduce its volume. To seek methods of efficient volume reduction, we investigated the cross-sections of contaminated soil particles using autoradiography (ARG), SEM, particle-induced X-ray emission (PIXE) analysis. The results of ARG showed that the radioactive Cs atoms were distributed on the surface of contaminated soil particle. PIXE analysis showed that K, Fe and Ti were distributed also on the surface of contaminated soil particle. Therefore, it is considered that the radioactive Cs contamination correlated with the distribution of K, Fe, and Ti. Moreover, the result suggests that it is possible to reduce the volume of contaminated soil by peeling off the radioactive Cs contaminated surface of soil.

Japan Atomic Energy Agency (JAEA) has been conducting research and development of MA(III) recovery from high level liquid waste (HLLW) by extraction chromatography technology for reduction in amount and environmental impact of radioactive waste. The behavior of adsorbed cations inside the adsorbent packed in a column is necessary to be evaluated for improvement of the adsorbent or flow-sheet to achieve targeted MA(III) recovery performance. In this paper, micro-PIXE analysis was carried out on the particles sampled from various positions of the column to reveal the behavior of cations inside the packed column with CMPO/SiO₂-P adsorbent using RE(III) as simulated elements of MA(III). Simple experiment and data analysis were shown to be effective to reveal inside of the column, and formation and transportation of the adsorption bands were observed for some cations which are extractable by the CMPO extractant. Some part of Zr(IV) and Mo(VI) were found to remain inside the column without distinct transportation even after the elution operation. Those results will contribute to design more practical MA(III) recovery flow-sheet.

The Zr and Mo removal from HLLW is the current issue for repeated usage of the CMPO/SiO₂-P-packed column. The adsorbability of the 2-mm-sized HDEHP/SiO₂-P adsorbent, which was prepared by fabricating a SiO₂ particle from the vibration cutting method and adapting a new polymerization method, was evaluated by the batch-wise adsorption experiment. In spite of the impregnation ratio of the HDEHP extractant, the extraction of Zr and Mo ions from the simulated HLLW was achieved but lanthanide ions e.g., Nd and Gd were also extracted as a minor component. Such unusual adsorption behavior of lanthanide ions could be only provided by accurate, sensitive and reliable micro-PIXE analysis.