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Aims: The consumption of rice grain produced in mercury (Hg) contaminated soil was identified as a major route of dietary Hg exposure. The aims were 1) to determine the most suitable concentration of Se that can lead to least Hg accumulation in rice grain in real Hg contaminated paddy field in Qingzhen, and 2) to elucidate the possible mechanism of the protection against the phytotoxicity of Hg in rice by Se. Methods: Rice plants were treated with different concentrations (0, 0.01, 0.1, 0.5, 1 and 5 μg/mL) of sodium selenite in a real paddy field in Qingzhen, Guizhou, China. The concentrations of Hg and Se in soil, stream water, rice tissues, and the seed setting rate (SSR) and thousand seed weight (TSW) were checked. The distribution and chemical forms of Hg and Se in rice root were studied by XRF and XAS. Results: Treating the rice plants with 0.5 μg/mL of sodium selenite achieved the lowest Hg accumulation in rice grain while the highest SSR and TSW. In rice root, XRF found decreased Hg uptake, and XAS found Hg-Se complexes were formed. These findings, together with the formation of biological barriers like iron plaque, could explain the decreased accumulation of Hg in rice grain at Se levels below 0.5 μg/mL. Se concentrations over 0.5 μg/mL led to increased Hg accumulation and decreased SSR and TSW, which were ascribed to the significantly increased Se accumulation in rice grain. Conclusions: This field study suggest that treatment with appropriate level of Se (0.5 μg/mL in this study) is an efficient way to reduce Hg accumulation in rice and increase rice yield and quality, thereafter to protect the health of the rice-dependent populations in Hg-contaminated area. [ABSTRACT FROM AUTHOR]

Abstract: Human hair and blood samples from persons living in the town of Wanshan, a mercury mine area in Guizhou Province of China, were collected and the quantitative speciation and structural information of Hg and S in hair samples and of Hg in erythrocyte and serum samples were studied using X-ray absorption spectroscopy. Least-squares fitting of the X-ray absorption near-edge spectra found that inorganic mercury is the major mercury species in hair samples (91.74%), while inorganic and methyl mercury are both about 50% of total mercury in RBC and serum samples, which is in agreement with the data obtained by acidic extraction, fractionation of Hg2+ and CH3Hg+ and quantification by ICP-MS. Curve-fitting analysis revealed that the Hg–S bond length and coordination number in hair were 0.248±0.002nm and 3.10, respectively, while the S–Hg bond length and coordination number in hair were 0.236±0.002nm and 4.05. The Hg–S bond length and coordination number in RBC were 0.251±0.003nm and 4.09, respectively, while they were 0.228±0.002nm and 4.08 in serum, respectively. The techniques for speciation, structural and binding information described in this study will find the potential application in similar studies of other elements. [Copyright &y& Elsevier]

Methylmercury (MeHg) in rice grains grown in Hg-contaminated areas has raised environmental health concerns. Pot experiments found that selenium (Se) could reduce MeHg levels in rice grains. However, relatively high levels of Se (up to 6 mg/kg) were applied in these pot experiments, which may have adverse effects on the soil ecology due to the toxicity of Se. The aims of this work were thus to study 1) the effect of low levels of Se on the accumulation and distribution of Hg, especially MeHg, in rice plants grown in a real Hg-contaminated paddy field and 2) the effect of Se treatment on Se and other nutritional elements (e.g., Cu, Fe, Zn) in grains. A field study amended with different levels of Se was carried out in Hg-contaminated paddy soil in Qingzhen, Guizhou, China. The levels of MeHg and total Hg were studied using cold vapor atomic fluorescence spectrometry (CVAFS) and inductively coupled plasma mass spectrometry (ICP-MS). The distribution and relative quantification of elements in grains were examined by synchrotron radiation X-ray fluorescence analysis (SR-XRF). This field study showed that low levels of Se (0.5 μg/mL, corresponding to 0.15 mg Se/kg soils) could significantly reduce total Hg and MeHg in rice tissues. Se treatment also reduced Hg distribution in the embryo and endosperm and increased the levels of Fe, Cu, Zn and Se in grains and especially embryos. This field study implied that treatment with an appropriate level of Se is an effective approach to not only decrease the level of MeHg but to also increase the levels of nutritional elements such as Fe, Cu, Zn and Se in rice grains, which could bring beneficial effects for rice-dependent residents living in Hg-contaminated areas. • Low level of Se (0.15 mg Se/kg soils) significantly reduced total Hg and MeHg in rice grains. • Selenium treatment reduced Hg distribution in embryo and endosperm of grains. • Selenium treatment increased the levels of Fe, Cu, Zn and Se in grains especially embryos. [ABSTRACT FROM AUTHOR]