State Key Laboratory of Environmental Geochemistry Institute of Geochemistry, Chinese Academy of Sciences. June 16, 2014

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1 Institute of Geochemistry, Chinese Academy of Sciences Antagonistic effect of selenium on mercury accumulation in rice plants (Oryza sativa L.) June 16, 214

2 1 Rice MeHg HgT / g kg g -1Rice THg 8 2 MeHg / g kg O. sativa O. sativa National limit for Hg: 2 µg/kg Z. mays Z. mays N. tabacum B.cam.campestris B. oleracea N. tabacum B.campestris B. oleracea MeHg concentrations in rice: µg/kg Qiu et al., J. Agric. Food Chem., 28 1

3 there appears to be a certain threshold value for Se for it to exert its antagonistic effect against Hg bioaccumulation in the rice plant. Zhang, H., et al. (212). Environ. Sci. & Technol. 46, pp

4 Existing knowledge indicates that the involvement of Se in the environment can influence and restrict Hg s migration biogeochemical exposure bioavailability toxicological consequences Antagonism of Hg and Se The existence of a protective effect of Se against Hg toxicity has been recognized for nearly half a century, since Parizek & Ostadalova

5 Se in Soil inhibits Hg Uptake and Translocation in Rice Plant Se in so oil THgingrain grain Translocation Factors of Hg were decreased with increasing Se Levels in soil from root zones * Translocation Factors (TFs) = Concentration in aboveground parts/concentration in root or soil ***Note: these samples were selected from sites with highest levels of both of Se and Hg in soils. Zhang, H., et al. (212). Environ. Sci. & Technol. 46, pp

6 Correlations between THg in grain and Se in root and grain Se in ro oot Se in gr rain THg in grain THg in grain 5

7 Selenium supplementation experiment Na 2 SeO 3 added Harvested 6

8 IHg (mg/kg) Grain Added Se (mg/kg soil) IHg MeHg IHg MeHg Soil Reduction of IHg in 18 grain ranged from 31% to 82%; 12 6 MeH Hg ( g/kg) Reduction of MeHg in grain ranged from 25% to 74% IHg (mg/kg) Me Hg ( g/kg) Grain MeHg (ng/g) r=.82, p< Added Se (mg/kg soil) Soil MeHg (ng/g) 7

9 BAFs s, MeHg BAF Fs, IHg IHg MeHg % MeHg BAFs, Se Se BAFs ranged between.5 and % MeHg ( g/kg) Se R 2 = Added Se (mg/kg soil) Selenium also accumulated in grain 8

10 6 5 Control Soil Soil adde Se F1-DDW Hg Co onc./ngl F1 F2 F3 F4 F5 F6 F7 F2-.1 M CH 3 COOH+.1 M HCl F3-1M KOH (fulic acid) F4-1M KOH(humic acid) F5-12M HNO 3 (elemental form) 5 4 Hg species F1 F2 F3 F4 F5 F6 F7 F6-Aqua regia (sulfur form) F7-HCl+HF(residual) Hg co onc./ngl F4 F5 F6 G1 G2 G3 G4 G5 G6 G7 G8 Experiment Group 9

11 Eh-pH diagram of Se in soils (Mayland et al., 1989) Proton Dissociation Equilibria SOIL H 2 SeO 4 Se (+IV): Selenite H 2 SeO 3 pk 1-3. pk HSeO 4 HSeO 3 pk pk SeO 4-2 SeO 3-2 Se (+VI): Selenate Se (): Ground state Grassland Se (-II): Selenides H 2 Se HSe Paddy Field pk 1 pk 2 H -2 2 Se HSe Se pe+ph >15: Selenate pe+ph = : Selenite pe+ph: <7.5: Selenide Redox Equilibria Hg(II) + HSe(I) () = HgSe(s) + H + (1) MeHg(I) + HSe(I) = HgSe(s) + CH 4 (2) 1

12 Still unclear What is the mechanism of selenium antagonistic effects on mercury in rice plant? Can the Se-treatment method be used for remediation of mercury contamination? How to evaluate the health risk on both selenium and mercury? 11