Nano mercury selenide as a source of mercury for rice.

Mercury (Hg) is a persistent and toxic metal while mercury selenide (HgSe) is generally considered as the environmental sink of Hg in its biogeochemical cycle. Recent studies found nano-sized HgSe (nano-HgSe) could be transformed by certain bacteria. This raises safety concerns about the application of selenium (Se) to curb Hg contamination in farmlands. Therefore, hydroponic experiments were performed in which rice plants were cultured with different concentrations of nano-HgSe and micro-sized HgSe (micro-HgSe) to explore their bioavailability and toxicity. It was found that both nano-HgSe and micro-HgSe did not affect the germination of rice seeds but affected the growth of rice seedlings. However, nano-HgSe could be more readily absorbed by roots and transferred to the aboveground parts compared to micro-HgSe. The highest Hg and Se levels were found to be 5255.67 ± 2496.14 µg/g and 1743.75 ± 61.87 µg/g, respectively in roots when exposed to 5000 mg/L nano-HgSe. Besides, small portion (1.2%) of methylmercury (MeHg) to total Hg was found accumulated in rice stem when exposed to 100 mg/L nano-HgSe, suggesting that nano-HgSe could be decomposed. Furthermore, nano-HgSe exposure brought oxidative damage to rice with decreased chlorophyll content and GSH-Px activity. In all, nano-HgSe was found to be more absorbable, transportable and methylated in rice plant compared to micro-HgSe. This suggests that although Se application in Hg contaminated farmland is an effective way to reduce the bioavailability of Hg, the risk of the possible remobilization of HgSe should not be neglected. Besides, the finding that nano-HgSe can act as an environmental source of Hg for plants deepens the understanding of biogeochemical cycle of Hg. More works are required to study the factors affecting the formation of nano-HgSe in the environment and the mechanisms of Hg methylation in rice plants after exposure to nano-HgSe.

Understanding the Solution Behavior of Epinephrine in the Presence of Toxic Cations: A Thermodynamic Investigation in Different Experimental Conditions.

The interactions of epinephrine ((R)-(-)-3,4-dihydroxy-α-(methylaminomethyl)benzyl alcohol; Eph-) with different toxic cations (methylmercury(II): CH3Hg+; dimethyltin(IV): (CH3)2Sn2+; dioxouranium(VI): UO22+) were studied in NaClaq at different ionic strengths and at T = 298.15 K (T = 310.15 K for (CH3)2Sn2+). The enthalpy changes for the protonation of epinephrine and its complex formation with UO22+ were also determined using isoperibolic titration calorimetry: HHL = -39 ± 1 kJ mol-1, HH2L = -67 ± 1 kJ mol-1 (overall reaction), HML = -26 ± 4 kJ mol-1, and HM2L2(OH)2 = 39 ± 2 kJ mol-1. The results were that UO22+ complexation by Eph- was an entropy-driven process. The dependence on the ionic strength of protonation and the complex formation constants was modeled using the extended Debye-Hückel, specific ion interaction theory (SIT), and Pitzer approaches. The sequestering ability of adrenaline toward the investigated cations was evaluated using the calculation of pL0.5 parameters. The sequestering ability trend resulted in the following: UO22+ >> (CH3)2Sn2+ > CH3Hg+. For example, at I = 0.15 mol dm-3 and pH = 7.4 (pH = 9.5 for CH3Hg+), pL0.5 = 7.68, 5.64, and 2.40 for UO22+, (CH3)2Sn2+, and CH3Hg+, respectively. Here, the pH is with respect to ionic strength in terms of sequestration.

Limited effects of changing prey fish communities on food quality for aquatic predators in the eastern Canadian Arctic in terms of essential fatty acids, methylmercury and selenium.

We determined concentrations of eicosapentaenoic and docosahexaenoic acids (EPA + DHA), Σomega-3, polyunsaturated fatty acids (ΣPUFA), selenium, methylmercury, and selenium:methylmercury (Se:Hg) ratios in native and northward-redistributing sub-Arctic marine fish and invertebrates from low, mid-, and high Canadian Arctic latitudes. There was no clear latitudinal trend in nutrient or contaminant concentrations. Among species, EPA + DHA concentrations in native Arctic cod (Boreogadus saida) were similar to concentrations in sub-Arctic capelin (Mallotus villosus) and sand lance (Ammodytes spp.) (444-658 mg.100 g-1), and higher than in most other species. Concentrations of EPA + DHA were related to lipid content, but to a greater extent for higher trophic position species (R2 = 0.83) than for species at lower trophic positions (R2 = 0.61). Selenium concentrations were higher in sand lance (1.15 ±â€¯0.16 µg g-1) than in all other species (0.30-0.69 µg g-1), which was significantly, but weakly, explained by more pelagic feeding in sand lance. Methylmercury concentrations were similar (and Se:Hg ratios were higher) in capelin, sand lance, and Arctic cod (0.01-0.03 µg g-1 wet weight (ww)) and lower than in other prey (0.12-0.26 µg g-1 ww), which was significantly explained by the smaller size of these species and more pelagic feeding habits than other fish. These results suggested that a shift in prey fish composition from Arctic cod to capelin and/or sand lance is unlikely to reduce the food quality of the prey available to marine predators at least with respect to concentrations of essential fatty acids, selenium, and Se:Hg ratios.

Low-thermal remediation of mercury-contaminated soil and cultivation of treated soil.

In this study, low-thermal technology was used to treat the mercury contaminated farmland soil from a chemical plant in Guizhou Province, China. A series of field planting experiments were also aimed at determining the content of total and methyl-Hg in crop plants after thermal treatment. The results showed that the mercury concentration in soils was reduced about 70% from 255.74 mg/kg to 80.63 mg/kg when treated at 350 °C for 30 min in engineering-scale experiments, and the treated soil retained most of its original soil. Organic-bound and residual mercury in treated soil were reduced by 64.1 and 56.4% by means of a sequential extraction procedure, respectively. The total and methyl-mercury concentrations in crops decreased significantly, and the degree of soil mercury accumulation to crop roots has been reduced significantly. The total Hg concentrations in potato and corn were lower than the mercury tolerance limits for food in China, and the Hg concentration of radish was close to the limit. The technology provides a more sustainable remediation method for treating mercury-contaminated farmland soil in future engineering applications.

Selenium inhibits sulfate-mediated methylmercury production in rice paddy soil.

There is increasing interest in understanding factors controlling methylmercury (MeHg) production in mercury-contaminated rice paddy soil. Sulfate has been reported to affect MeHg biogeochemistry under anoxic conditions, and recent studies revealed that selenium (Se) could evidently reduce MeHg production in paddy soil. However, the controls of sulfate and Se on net MeHg production in paddy soil under fluctuating redox conditions remain largely unknown. Microcosm experiments were conducted to explore the effects of sulfate and Se on net MeHg production in rice paddy soil. Soil was added with 0-960 mg/kg sulfate, in the presence or absence of 3.0 mg/kg selenium (selenite or selenate), and incubated under anoxic (40 days) or suboxic conditions (5 days), simulating fluctuating redox conditions in rice paddy field. Sulfate addition moderately affected soil MeHg concentrations under anoxic conditions, while reoxidation resulted in evidently higher (18-40%) MeHg levels in sulfate amended soils than the control. The observed changes in net MeHg production were related to dynamics of sulfate and iron. However, Se could inhibit sulfate-mediated MeHg production in the soils: Se addition largely reduced net MeHg production in the soils (23-86%, compared to the control), despite of sulfate addition. Similarly, results of the pot experiments (i.e., rice cultivation in amended soils) indicated that soil MeHg levels were rather comparable in Se-amended soils during rice growth period, irrespective of added sulfate doses. The more important role of Se than sulfate in controlling MeHg production was explained by the formation of HgSe nanoparticles irrespective of the presence of sulfate, confirmed by TEM-EDX and XANES analysis. Our findings regarding the effects of sulfate and Se on net MeHg production in rice paddy soil together with the mechanistic explanation of the processes advance our understanding of MeHg dynamics and risk in soil-rice systems.

Methylmercury Increases and Eicosapentaenoic Acid Decreases the Relative Amounts of Arachidonic Acid-Containing Phospholipids in Mouse Brain.

The membrane phospholipid composition in mammalian brain can be modified either by nutrients such as dietary fatty acids, or by certain toxic substances such as methylmercury (MeHg), leading to various biological and toxic effects. The present study evaluated the effects of eicosapentaenoic acid (EPA) and MeHg on the composition of the two most abundant membrane phospholipid classes, i.e., phosphatidylcholines (PtdCho) and phosphatidylethanolamines (PtdEtn), in mouse brain by using a two-level factorial design. The intact membrane PtdCho and PtdEtn species were analyzed by liquid chromatography-mass spectrometry. The effects of EPA and MeHg on the PtdCho and PtdEtn composition were evaluated by principal component analysis and ANOVA. The results showed that EPA and MeHg had different effects on the composition of membrane PtdCho and PtdEtn species in brain, where EPA showed strongest impact. EPA led to large reductions in the levels of arachidonic acid (ARA)-containing PtdCho and PtdEtn species in brain, while MeHg tended to elevate the levels of ARA-containing PtdCho and PtdEtn species. EPA also significantly increased the levels of PtdCho and PtdEtn species with n-3 fatty acids. Our results indicate that EPA may to some degree counteract the alterations of the PtdCho and PtdEtn pattern induced by MeHg, and thus alleviate the MeHg neurotoxicity in mouse brain through the inhibition of ARA-derived pro-inflammatory factors. These results may assist in the understanding of the interaction between MeHg, EPA and phospholipids, as well as the risk and benefits of a fish diet.

Chemical Detoxification of Organomercurials.

Organomercurials including methylmercury are ubiquitous environmental pollutants and highly toxic to humans. Now it could be shown that N-methylimidazole based thiones/selones having an N-CH2CH2OH substituent are remarkably effective in detoxifying various organomercurials to produce less toxic HgE (E=S, Se) nanoparticles. Compounds lacking the N-CH2CH2OH substituent failed to produce HgE nanoparticles upon treatment with organomercurials, suggesting that this moiety plays a crucial role in the detoxification by facilitating the desulfurization and deselenization processes. This novel way of detoxifying organomercurials may lead to the discovery of new compounds to treat patients suffering from methylmercury poisoning.

High methylmercury production under ferruginous conditions in sediments impacted by sewage treatment plant discharges.

Sewage treatment plants (STPs) are important point sources of mercury (Hg) to the environment. STPs are also significant sources of iron when hydrated ferric oxide (HFO) is used as a dephosphatation agent during water purification. In this study, we combined geochemical and microbiological characterization with Hg speciation and sediment amendments to evaluate the impact of STP's effluents on monomethylmercury (MMHg) production. The highest in-situ Hg methylation was found close to the discharge pipe in subsurface sediments enriched with Hg, organic matter, and iron. There, ferruginous conditions were prevailing with high concentrations of dissolved Fe(2+) and virtually no free sulfide in the porewater. Sediment incubations demonstrated that the high MMHg production close to the discharge was controlled by low demethylation yields. Inhibition of dissimilatory sulfate reduction with molybdate led to increased iron reduction rates and Hg-methylation, suggesting that sulfate-reducing bacteria (SRB) may not have been the main Hg methylators under these conditions. However, Hg methylation in sediments amended with amorphous Fe(III)-oxides was only slightly higher than control conditions. Thus, in addition to iron-reducing bacteria, other non-SRB most likely contributed to Hg methylation. Overall, this study highlights that sediments impacted by STP discharges can become local hot-spots for Hg methylation due to the combined inputs of i) Hg, ii) organic matter, which fuels bacterial activities and iii) iron, which keeps porewater sulfide concentration low and hence Hg bioavailable.

Protolytic cleavage of Hg-C bonds induced by 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone: synthesis and structural characterization of mercury complexes.

Multinuclear ((1)H, (77)Se, and (199)Hg) NMR spectroscopy demonstrates that 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzim(Me)), a structural analogue of the selenoamino acid, selenoneine, binds rapidly and reversibly to the mercury centers of HgX2 (X = Cl, Br, I), while X-ray diffraction studies provide evidence for the existence of adducts of composition [H(sebenzim(Me))]xHgX2 (X = Cl, x = 2, 3, 4; X = I, x = 2) in the solid state. H(sebenzim(Me)) also reacts with methylmercury halides, but the reaction is accompanied by elimination of methane resulting from protolytic cleavage of the Hg-C bond, an observation that is of relevance to the report that selenoneine demethylates CysHgMe, thereby providing a mechanism for mercury detoxification. Interestingly, the structures of [H(sebenzim(Me))]xHgX2 exhibit a variety of different hydrogen bonding patterns resulting from the ability of the N-H groups to form hydrogen bonds with chlorine, iodine, and selenium.

Evaluation of the risk/benefit associated to the consumption of raw and cooked farmed meagre based on the bioaccessibility of selenium, eicosapentaenoic acid and docosahexaenoic acid, total mercury, and methylmercury determined by an in vitro digestion model.

The bioaccessibility of total lipids, EPA, DHA, Se, Hg, and MeHg in raw and cooked meagre (Argyrosomus regius) was studied by using an in vitro digestion method. A risk-benefit assessment of raw and cooked meagre on the basis of the bioaccessibility data was carried out. The bioaccessibility of total lipids was generally high in raw and cooked meagre with exception of grilled fish. For EPA and DHA, bioaccessibility percentages were low never surpassing the 50% in raw, boiled, and grilled meagre. The bioaccessibility percentage of Se was equal or higher than 82% (grilling treatment). Likewise, for Hg and MeHg, high bioaccessibility values were determined with exception of grilled meagre, displaying lower values of 54% and 64%, respectively. The risk-benefit probabilistic assessment brought about a recommendation of a maximum consumption of two weekly meals for boiled or roasted meagre and three weekly meals for grilled meagre.

Chelating agents for the sequestration of mercury(II) and monomethyl mercury(II).

Both mercury(II) and monomethyl mercury(II) poisonings are of great concern for several reasons. As it happens for other metals, chelation therapy is the most indicated treatment for poisoned patients. The efficacy of the therapy and the reduction of side-effects can be sensibly enhanced by an accurate knowledge of all the physiological mechanisms involved in metal uptake, transport within and between various tissues, and (possibly) clearance. All these aspects, however, are strictly dependent on the chemical speciation (i.e., the distribution of the chemical species of a component in a given system) of both the metal and the chelating agent in the systems where they are present. In this light, this review analyzes the state of the art of research performed in this field for mercury(II) and methylmercury(II). After a brief summary of their main sources, the physiological patterns for the treatment of mercury poisoning have also been considered. The binding ability of various chelating agents toward mercury has been then analyzed by modeling the behavior of the main classes of ligands present in biological fluids and/or frequently used in chelation therapy. Their sequestering ability has been successively evaluated by means of a semiempirical parameter already proposed for its objective quantification, and the main characteristics of an efficient chelating agent have been evaluated on this basis.

In-situ subaqueous capping of mercury-contaminated sediments in a fresh-water aquatic system, Part II-evaluation of sorption materials.

The function and longevity of traditional, passive, isolation caps can be augmented through the use of more chemically active capping materials which have higher sorptive capacities, ideally rendering metals non-bioavailable. In the case of Hg, active caps also mitigate the rate and extent of methylation. This research examined low cost, readily available, capping materials for their ability to sequester Hg and MeHg. Furthermore, selected capping materials were evaluated to inhibit the methylation of Hg in an incubation study as well as the capacity of a selected capping material to inhibit translocation of Hg and MeHg with respect to ebullition-facilitated contaminant transport in a column study. Results indicated that bauxite had a better capacity for mercury sorption than the other test materials. However, bauxite as well as soil capping materials did not decrease methylation to a significant extent. Materials with larger surface areas, higher organic matter and acid volatile sulfide (AVS) content displayed a larger partitioning coefficient. In the incubation experiments, the presence of a carbon source (lactate), electron acceptor (sulfate) and the appropriate strains of SRB provided the necessary conditions for Hg methylation to occur. The column study showed effectiveness in sequestering Hg and MeHg and retarding transport to the overlying water column; however, disturbances to the soil capping material resulting from gas ebullition negated its effectiveness.

Simultaneous speciation and preconcentration of ultra trace concentrations of mercury and selenium species in environmental and biological samples by hollow fiber liquid phase microextraction prior to high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry.

Nowadays, hollow fiber membrane extraction techniques are widely used due to the high enrichment factors obtained with many different types of analytes and samples. In this paper, we propose a new analytical method that allows the simultaneous extraction of methylmercury, inorganic mercury and Se(4+) and determination by high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The detection limits obtained are very low (110-230ng/L) with relative standard deviations below 15% for all the analytes and averaged recoveries in fortified samples in the range of 71-99%. The precision of the analytical method is very good which overcomes one of the most important shortcomings of membrane extraction techniques. Several variables were studied to get optimal extraction conditions for the analytes. This method has been validated with real world samples such as water (tap, river and estuarine) and human blood plasma.

Mercury and methylmercury in Korean herbal medicines and functional health foods.

Total mercury (Hg) and methyl mercury (MeHg) were analysed in functional health foods (FHFs) and in Korean herbal medicines (KHMs). A total of 560 samples (FHFs, n = 511; KHMs, n = 49) were collected. The levels of total Hg in 416 samples were lower than the limit of detection. MeHg analysis was conducted in 45 samples and the ranges of MeHg levels in samples were less than the LOD of 38.92 ng g(-1). Weekly intake per body weight (WIPBW) values of total Hg in FHFs and KHMS were 0.89 and 11.77 ng kg(-1) BW, respectively. The margins of exposure (MOEs) of total Hg for FHFs and KHMS were 598,753 and 36,503, respectively. The WIPBW values of MeHg for FHFs and KHMS were 0.22 and 0.01 ng kg(-1) BW, respectively. MOE values of MeHg for FHFs and KHMS were 412,276 and 517,363, respectively.

Influence of nutrient level on methylmercury content in water spinach.

Widely consumed vegetables are often cultivated in sewage waters with high nutrient levels. They can contain high levels of methylmercury (MeHg), because they can form MeHg from inorganic Hg in their young shoots. We determined whether the MeHg uptake and the MeHg formation in the shoots of water spinach (Ipomoea aquatica) were affected by the presence of a high nutrient level in the growth medium. Water spinach shoots were rooted and pretreated in growth medium containing 7% (low) or 70% (high) Hoagland nutrient solution; thereafter, the plants were treated with either 0.02 microM MeHg or 0.2 microM HgCl2 for 3 d. Half the plants were then analyzed for total Hg and MeHg. The remaining plants were transferred to mercury-free medium with low or high nutrient levels and posttreated for 3 days before analysis of total Hg and MeHg in order to measure MeHg formation in the absence of external Hg. The results indicate that nutrient level did not influence MeHg uptake, but that a high nutrient level reduced the distribution of MeHg to the shoots 2.7-fold versus low nutrient level. After treatment with HgCl2, MeHg was found in roots and new shoots but not in old shoots. The MeHg:total-Hg ratio was higher in new shoots than in roots, being 13 times higher at high versus low nutrient levels. Thus, MeHg formation was the same in new shoots independent of inorganic Hg concentration, since the total Hg level decreased at a high nutrient level.

Computational studies of structural, electronic, spectroscopic, and thermodynamic properties of methylmercury-amino acid complexes and their Se analogues.

Quantum chemical calculations have been carried out to study the structural, electronic, spectroscopic, and thermodynamic properties of five methylmercury-amino acid complexes and their selenium analogues. The structural properties of methylmercury-amino acids are very similar to their Se analogues except for those properties that are directly related to the Se atom which has a larger covalent radius. Characteristic stretching frequencies are observed for Hg-S/Se and Hg-C bonds. Electronic properties of both methylmercury-amino acids and their Se analogues are different from each other, with the S complexes showing stronger electrostatic attractions which leads to stronger bonds to mercury. The methylmercury complexes with selenoamino complexes, however, are thermodynamically more favorable (DeltaG of formation from suitable model reactants) than those of the corresponding amino acid complexes. This can be traced to the lower stability of the reactant selenoamino acids. Such different stability and favorability of formation might be responsible for the different physiological activity in biological systems such as the Hg-Se antagonism.

Chemical forms of mercury and selenium in fish following digestion with simulated gastric fluid.

Fish is a major dietary source of potentially neurotoxic methylmercury compounds for humans. It is also a rich source of essential selenium. We have used in situ mercury L(III)-edge and selenium K-edge X-ray absorption spectroscopy to chemically characterize the methylmercury and selenium in both fresh fish and fish digested with simulated gastric fluid. For the mercury, we confirm our earlier finding [ Harris et al. ( 2003 ) Science 301 , 1203 ] that the methylmercury is coordinated by a single thiolate donor, which resembles cysteine, and for the selenium, we find a mixture of organic forms that resemble selenomethionine and an aliphatic selenenyl sulfide such as Cys-S-Se-Cys. We find that local chemical environments of mercury and selenium do not change upon digestion of the fish with simulated gastric fluid. We discuss the toxicological implications for humans consuming fish.

Methylmercury accumulation and fluxes across the intestine of channel catfish, Ictalurus punctatus.

The excised intestines of channel catfish, Ictalurus punctatus, were perfused at 20 or 4 degrees C for 1 h 45 min, with methylmercury (CH(3)HgCl) alone, or in the presence of excess L-cysteine (L-Cys), D-cysteine (D-Cys), L-methionine (L-Met); or with ouabain or probenecid to identify the potential CH(3)Hg(II) uptake pathways in fish intestines. A temperature effect was noted, with CH(3)Hg(II) concentrations in tissues perfused at 20 degrees C being higher than at 4 degrees C, substantiating the idea that mechanisms requiring metabolic energy are involved in CH(3)Hg(II) uptake in fish intestines. The results indicate that, when CH(3)Hg(II) is complexed as the CH(3)Hg-L-Cys complex, it is taken up via an L-neutral amino acid carrier and rapidly transported to the serosal side of the intestine. Methylmercury uptake could be inhibited by probenecid and ouabain, although probenecid had less impact on CH(3)Hg(II) uptake than ouabain. Our results for CH(3)Hg(II) uptake in the presence of D-Cys, L-Met in excess of L-Cys, or with a metal mixture further established that CH(3)Hg(II) uptake across fish intestines occurs via a variety of pathways, including an energy-dependent L-neutral amino acid carrier, and that the route and amount of accumulation were a function of CH(3)Hg(II) speciation in the digestive tract of the fish.