Influence of sodium selenite on203Hg absorption,distribution, and elimination in male mice exposed to methyl203Hg

To study the effects of long-term selenium supplementation on absorption, distribution, and elimination of methylmercury (MeHg) in mice, three groups of male mice (Balb/c CA) were exposed for 7 wk to 0, 0.6, and 3 ppm sodium selenite in tap water. They were then given a single oral dose of Me²⁰³Hg (2 μmol/kg) by gastric intubation, and elimination of²⁰³Hg was followed by whole-body counting for 49 d at the same Se exposure as previously. Twenty-four hours and 49 d after dosage, 6–7 animals/group were sampled for analysis of²⁰³Hg distribution in the body. Glutathione peroxidase (GSH-PX) activity in blood and selenium levels in the liver were used as measures of selenium status. Gastrointestinal absorption of Me²⁰³Hg was not influenced by the Se status of the animals. Selenium supplementation of MeHg-exposed mice caused an enhanced whole-body elimination of Hg, but selenium-supplemented animals did not have lower Hg levels in the brain and kidney than nonsupplemented animals. The effect of selenium on the accumulation, of Hg in the brain was dose-dependent, a high dose (3 ppm Se) causing a higher initial accumulation of Hg. The intracellular distribution of²⁰³Hg in the liver and kidney was not affected by Se. The results indicate that selenium treatment of MeHg-exposed mice may have a positive effection the health of the animals by decreasing the total body burden of MeHg.     

Spectroscopic characterization of rat kidney Hg,Cu-metallothionein

Absorption, circular dichroism (CD), magnetic circular dichroism (MCD) and emission spectra are reported for rat kidney Hg,Cu-metallothionein isoform 3 isolated following induction of the metallothionein with HgCl2. While the absorption spectrum is featureless, both the CD and MCD spectra show resolved bands that arise from the Cu-thiolate and Hg-thiolate groups. The emission spectrum at 77 K is much more complicated than would be expected for a copper (I)-containing metallothionein. It is suggested the emission only arises from the copper-thiolate groups but that the presence of the mercury results in copper ions in several different environments depending on the nature of the nearest neighbour.     

Modeling Sorption of Cd,Hg and Pb in Soils by the NICA-Donnan Model

Metal adsorption is an important process at the soil-solution interface that controls metal bioavailability and toxicity. In this study, batch adsorption experiments were conducted to investigate the binding of Cd, Hg and Pb in soils collected from around metal smelters in Quebec and Ontario, Canada. It was found that soil organic matter enhanced the retention of Cd, Hg and Pb. Assuming that the surfaces of soil particles behaved similarly to organic matter, we used the Non-Ideal Competitive Adsorption (NICA)-Donnan model to derive the parameters for surface complexation of the three metals. The shape of the Cd, Hg and Pb adsorption isotherms are briefly discussed with respect to the results of the experimental measurements and the model predictions. The average values of the NICA-Donnan model parameters could be used to give reasonable predictions of metal sorption in the soils of this study.     

何首乌块根中砷、镉、汞和铅含量的检测及其富集特性

何首乌是著名传统常用中药,为蓼科(Polygonaceae)植物何首乌(Polygonum multiflorum Thunb.)的块根.生首乌具有解毒、消痈和润肠通便的作用,制首乌则有补肝肾、益精血、乌须发和强筋骨之功效[1].何首乌最早出现于唐代李翱所著的<何首乌传>,<本草图经>及<本草纲目>描述何首乌"叶叶相对",展学峰等认为二者所指为现今的萝摩科(Asclepiadaceae)植物白首乌(Cynanchum bungei Decne.)[2].何首乌野生资源分布于陕西南部、甘肃南部及华东、华中、华南和西南,日本也有分布[3]     

Mono- (Ag, Hg) and di- (Cu, Hg) valent metal ions effects on the activity of jack bean urease. Probing the modes of metal binding to the enzyme

The inhibition of urease by heavy metal ions has been habitually ascribed to the reaction of the ions with enzyme thiol groups, resulting in the formation of mercaptides. To probe the modes of metal binding to the enzyme, in this work the reaction of mono- (Ag, Hg) and di- (Cu, Hg) valent metal ions with jack bean urease was studied. The enzyme was reacted with different concentrations of the metal ions for different periods of times, when its residual activity was assayed and thiol content titrated. The titration carried out with DTNB was done to examine the involvement of urease thiol groups in metal ion binding. The binding was further probed by reactivation of the metal ion-enzyme complexes with DTT, EDTA and dilution. The results are discussed in terms of the HSAB concept. In inhibiting urease the metal ions showed a common feature in that they inhibited the enzyme within a comparable micromolar range, and also in that their inhibition was multisite. By contrast, the main distinguishing feature in their action consisted of the involvement of enzyme thiol groups in the reaction. Hg (2+) and Hg2(2+) inhibition was found thoroughly governed by the reaction with the enzyme thiols, and the complete loss of enzyme activity involved all thiols available in the enzyme under non-denaturating conditions. In contrast, Ag+ and Cu2+ ions for the complete inactivation of the enzyme required 53 and 60% of thiols, respectively. Accordingly, Ag+ and Cu2+ binding to functional groups in urease other than thiols, i.e. N- and O-containing groups, cannot be excluded. Based on the reactivation experiments this seems particularly likely for Cu2+, whose concurrent binding to thiols and other groups might distort the architecture of the active site (the mechanism of which remains to be elucidated) resulting in the observed inhibitory effects.     

Complexation of Hg with phytochelatins is important for plant Hg tolerance

Three-week-old alfalfa (Medicago sativa), barley (Hordeum vulgare) and maize (Zea mays) were exposed for 7 d to 30 μm of mercury (HgCl(2) ) to characterize the Hg speciation in root, with no symptoms of being poisoned. The largest pool (99%) was associated with the particulate fraction, whereas the soluble fraction (SF) accounted for a minor proportion (<1%). Liquid chromatography coupled with electro-spray/time of flight mass spectrometry showed that Hg was bound to an array of phytochelatins (PCs) in root SF, which was particularly varied in alfalfa (eight ligands and five stoichiometries), a species that also accumulated homophytochelatins. Spatial localization of Hg in alfalfa roots by microprobe synchrotron X-ray fluorescence spectroscopy showed that most of the Hg co-localized with sulphur in the vascular cylinder. Extended X-ray Absorption Fine Structure (EXAFS) fingerprint fitting revealed that Hg was bound in vivo to organic-S compounds, i.e. biomolecules containing cysteine. Albeit a minor proportion of total Hg, Hg-PCs complexes in the SF might be important for tolerance to Hg, as was found with Arabidopsis thaliana mutants cad2-1 (with low glutathione content) and cad1-3 (unable to synthesize PCs) in comparison with wild type plants. Interestingly, high-performance liquid chromatography-electrospray ionization-time of flight analysis showed that none of these mutants accumulated Hg-biothiol complexes.     

Kinetics,Isotherms, and Thermodynamics of Hg(II) Biosorption onto Carica papaya

Carica papaya, a novel sorbent, was evaluated for sorption of Hg(II) from synthetic aqueous solutions using various pseudo-second order kinetic models as well as equilibrium sorption models. Batch kinetic and equilibrium experiments were carried out for the sorption of Hg(II) onto C. papaya at pH 6.5 and solid to liquid ratio (s/l) 1.0 g L^?1. The kinetic data were fitted to second order models of Sobkowsk and Czerwinski, Ritchie, Blanchard, Ho and McKay, whereas Langmuir, Freundlich, and Redlich-Peterson models were used for the equilibrium data. A comparative study on both linear and nonlinear regression showed that the Sobkowsk and Czerwinski and Ritchie's second order model were the same. Ho and McKay's pseudo-second order model fitted well to the experimental data when compared with the other second order kinetic expressions. Langmuir isotherm parameters obtained from the four Langmuir linear equations by using linear method were dissimilar, but were the same when nonlinear method was used. Additionally, various thermodynamic parameters, such as ΔG ⁰, ΔH ⁰, and ΔS ⁰, were calculated. The negative values of Gibbs free energy (ΔG ⁰) and ΔH ⁰ confirmed the intrinsic nature of biosorption process and exothermic, respectively. The negative value of ΔS ⁰ showed the decreased randomness at the solid-solution interface during biosorption.     

G-quadruplex DNAzyme-based Hg2+ and cysteine sensors utilizing Hg2+-mediated oligonucleotide switching

A simple and sensitive colorimetric Hg(2+) detection method is reported, based on the Hg(2+)-mediated structural switch of an unlabeled oligonucleotide strand. In the absence of Hg(2+), the oligonucleotide strand forms a stem-loop. A G-rich sequence in the strand is partially caged in the stem-loop structure and cannot fold into a G-quadruplex. In the presence of Hg(2+), T-Hg(2+)-T coordination chemistry leads to the formation of another stem-loop structure and the release of the G-rich sequence. The released sequence folds into a G-quadruplex, which binds hemin to form catalytically active G-quadruplex DNAzymes. This is detected as an absorbance increase in a H(2)O(2)-2,2'-azinobis(3-ethylbenzothiozoline)-6-sulfonic acid (ABTS) reaction system using UV-vis absorption spectroscopy. This simple colorimetric sensor can detect aqueous Hg(2+) at concentrations as low as 9.2 nM with high selectivity. Based on the strong binding interaction between Hg(2+) and the sulfur-containing amino acid cysteine (Cys), and the competition between Cys and a oligonucleotide for Hg(2+), the proposed Hg(2+)-sensing system can be further exploited as a Cys-sensing method. The method has a detection limit for Cys of 19 nM.     

制定我国土壤环境标准(汞、镉、铅和砷)的探讨

本文依据国内外土壤环境质量标准的研究现状,在提出土壤环境标准制定依据和原则的基础上,对Hg、Cd、Pb和As的土壤环境质量标准进行了研究。研究表明,我国土壤环境质量功能分区可包括:(1)自然保护区或“清洁”无污染区;(2)农牧区;(3)森林区;(4)城市区、废物处置区和工矿区。其相应的土壤环境质量标准,汞为0.10、0.20、0.50和1.00mg/kg;镉为0.15、0.30、0.50和1.00mg/kg;铅为30、60、100和300mg/kg;砷为15、20、27和30(砂土区除外)mg/kg,并论证这些标准值在全国应用的可能性。为全国土壤质量的宏观管理与控制污染提供了科学依据。     

Preliminary study of the distribution of the toxic elements As,Cd, and Hg in human hair and tissues by RNAA

In order to study the relationships between trace element concentrations of hair and internal body burdens, a radiochemical NAA technique has been used for determination of the elements As, Cd, and Hg in autopsy samples of liver, kidney-cortex, lung, and hair from 24 male persons who died by accident. High significant positive correlations were observed between the As concentration in hair and in kidney-cortex, and between Cd and Zn concentrations in kidney-cortex. The contents of Cd, both for lung and kidney-cortex, were related to the smoking habits of the subjects.

     

Detailed Assessment of the Kinetics of Hg-Cell Association,Hg Methylation,and Methylmercury Degradation in Several Desulfovibrio Species

The kinetics of inorganic Hg [Hg(II)_i] association, methylation, and methylmercury (MeHg) demethylation were examined for a group of Desulfovibrio species with and without MeHg production capability. We employed a detailed method for assessing MeHg production in cultures, including careful control of medium chemistry, cell density, and growth phase, plus mass balance of Hg(II)_i and MeHg during the assays. We tested the hypothesis that differences in Hg(II)_i sorption and/or uptake rates drive observed differences in methylation rates among Desulfovibrio species. Hg(II)_i associated rapidly and with high affinity to both methylating and nonmethylating species. MeHg production by Hg-methylating strains was rapid, plateauing after ∼3 h. All MeHg produced was rapidly exported. We also tested the idea that all Desulfovibrio species are capable of Hg(II)_i methylation but that rapid demethylation masks its production, but we found this was not the case. Therefore, the underlying reason why MeHg production capability is not universal in the Desulfovibrio is not differences in Hg affinity for cells nor differences in the ability of strains to degrade MeHg. However, Hg methylation rates varied substantially between Hg-methylating Desulfovibrio species even in these controlled experiments and after normalization to cell density. Thus, biological differences may drive cross-species differences in Hg methylation rates. As part of this study, we identified four new Hg methylators (Desulfovibrio aespoeensis, D. alkalitolerans, D. psychrotolerans, and D. sulfodismutans) and four nonmethylating species (Desulfovibrio alcoholivorans, D. tunisiensis, D. carbinoliphilus, and D. piger) in our ongoing effort to generate a library of strains for Hg methylation genomics.     

Dual-rhodamine urea derivative, a novel chemidosimeter for Hg(II) and its application in imaging Hg(II) in living cells

Abstract  The synthesis and spectral properties of a chemidosimeter 1,4-di[2-(6-ethylamino-3-ethylimino-2,7-dimethyl-3H-xanthen-9-yl) benzoic acid (aminomethyl)-3-phenylthiourea] benzene (1) for Hg(II) ions are reported, and it has been demonstrated that 1 can be used as a fluorescent probe for monitoring Hg(II) ions in living cells. Graphical abstract  A highly sensitive fluorescent probe (1) was developed as a fluorescent and colorimetric chemodosimeter in dimethyl sulfoxide/methanol solution with a broad pH range (pH 5–10) and high selectivity toward Hg²⁺ ions but no significant response toward other competitive cations. Furthermore, by means of confocal laser scanning microscopy experiments, it is demonstrated that 1 can be used as a fluorescent probe for monitoring Hg²⁺ in living cells. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Distribution,Speciation and Bioaccumulation of Hg and As in Mariculture Sediments from Dongshan Bay,China

Hg and As are the major hazardous pollutants in marine sediments due to their high toxicity to benthonic organisms. Understanding the spatial distribution, speciation and bioaccumulation of these toxic elements in sediments is therefore of high environmental importance for identifying their potential risks. Sediments and bivalves Paphia undulata were collected from the mariculture area of Dongshan Bay, China, for characterizing geochemistry (by using the European Community Bureau of Reference (BCR) sequential extraction procedure) and bioaccumulation of Hg and As [by calculating the biota sediment accumulation factor (BSAF)]. Both elements in sediments were mostly associated with the residual fraction (69.52–95.06% and 88.22–91.12% of the total concentration, respectively), followed by the oxidizable (bound to sulfides and organic matter) fraction (1.25–25.32% and 3.62–6.00%, respectively). However, Hg presented a higher bioaccumulation than As. Correlation analysis indicated that As in residual fraction and Hg in oxidizable fraction exert positive contributions (R = 0.927, P < 0.01 and R = 0.869, P < 0.05, respectively) on their own bioaccumulation factor. This indicated that P. undulata could adsorb both Hg in organic fraction and As in residual fraction from the sediments. Therefore, we should pay more attention to the potential dissolution and release of metals bound to sediments in the digestive tracts of marine organisms.     

Quantifying Hg within ectomycorrhizal fruiting bodies,from emergence to senescence

Ectomycorrhizal fruiting bodies (basidiomata) collected from forested areas in southwestern New Brunswick were analyzed for total mercury, sulphur, nitrogen, and carbon concentrations (THg, TS, TN, and TC, respectively). This analysis was done for caps and stalks and by development stage (emergent, mature, senescent) across 27 species associated with five classes, eight families, and 13 genera. Across the species, THg correlated positively with TN and TS, thereby implying N as well as S mitigated transfer of Hg from the mycelia into the basidiomata, with THg ranging from 3 to 10?457 ppb. TS, TN, and TC varied from 0.07 to 1, 1 to 11, and 43 to 53 %, respectively. Cap and stalk THg, TS, TN, and TC were also correlated to one another, with mean stalk/cap ratios of 0.59, 0.76, 0.71, and 0.98, respectively. Soil availability indexed by THg, TS, TN, and TC within the forest floor contributed to basidiomatal THg as well. THg, THg/TS, and THg/N varied strongly by species. These variations involved: (i) no growth dilution and no volatilization (Group I), (ii) growth dilution only (Group II), (iii) growth dilution followed by loss during senescence (Group III), and (iv) growth dilution combined with loss from emergence onward (Group IV). Depending on species, TN and TS remained the same or declined from 100 % at emergence to about 80 and 70 % at senescence. Lack of THg decline for the Group I species would be due to HgS encapsulation. Reanalyzing the freeze-dried samples revealed that THg continued to drop during the first year of air-dry storage for the Group II, II, and IV species, but TS, TN, and TC remained stable. The results were quantified by way of best-fitted regression models.     

Avian species differences in the intestinal absorption of xenobiotics (PCB, dieldrin, Hg2+)

Intestinal absorption of a polychlorinated biphenyl, dieldrin, and mercury (from HgCl2) was measured in adult Northern bobwhites, Eastern screech owls, American kestrels, black-crowned night-herons and mallards in vivo by an in situ luminal perfusion technique. bobwhites, screech owls and kestrels absorbed much more of each xenobiotic than black-crowned night-herons and mallards. Mallards absorbed less dieldrin and mercury than black-crowned night-herons. Mercury absorption by kestrels was more than twice that in screech owls and eight times that observed in mallards. Pronounced differences in xenobiotic absorption rates between bobwhites, screech owls and kestrels on the one hand, and black-crowned night-herons and mallards on the other, raise the possibility that absorptive ability may be associated with the phylogenetic classification of birds.     

制定我国土壤环境标准（汞,镉,铅和砷）的探讨

本文依据国内外土壤环境质量标准的研究现状,在提出土壤环境标准制定依据和原则的基础上,对Hg、Cd、Pb和As的土壤环境质量标准进行了研究。研究表明,我国土壤环境质量功能分区可包括:(1)自然保护区或“清洁”无污染区;(2)农牧区;(3)森林区;(4)城市区、废物处置区和工矿区。其相应的土壤环境质量标准,汞为0.10、0.20、0.50和1.00mg/kg;镉为0.15、0.30、0.50和1.00mg/kg;铅为30、60、100和300mg/kg;砷为15、20、27和30(砂土区除外)mg/kg,并论证这些标准值在全国应用的可能性。为全国土壤质量的宏观管理与控制污染提供了科学依据。