Reactive gaseous mercury is generated from chloralkali factories resulting in extreme concentrations of mercury in hair of workers.
ABSTRACT: Occupational exposure of chloralkali workers to highly concentrated mercury (Hg) vapour has been linked to an increased risk of renal dysfunction and behavioural changes. It is generally believed that these workers are exposed to elemental Hg, which is used in abundance during the production process however, the lack in analytical techniques that would allow for identification of gaseous Hg species poses a challenge, which needs to be addressed in order to reach a consensus. Here, we present the results from simulated exposure studies, which provide sound evidence of higher adsorption rate of HgCl2 than Hg0 and its irreversible bonding on the surface of hair. We found that chloralkali workers were exposed to HgCl2, which accumulated in extremely high concentrations on the hair surface, more than 1,000 times higher than expected from unexposed subjects and was positively correlated with Hg levels in the finger- and toenails.
Project description:Mercury (Hg) is extremely toxic for all living organisms. Hg-tolerant symbiotic rhizobia have the potential to increase legume tolerance, and to our knowledge, the mechanisms underlying Hg tolerance in rhizobia have not been investigated to date. Rhizobial strains of <i>Ensifer medicae</i>, <i>Rhizobium leguminosarum</i> bv. <i>trifolii</i> and <i>Bradyrhizobium canariense</i> previously isolated from severely Hg-contaminated soils showed different levels of Hg tolerance. The ability of the strains to reduce mercury Hg<sup>2+</sup> to Hg<sup>0</sup>, a volatile and less toxic form of mercury, was assessed using a Hg volatilization assay. In general, tolerant strains displayed high mercuric reductase activity, which appeared to be inducible in some strains when grown at a sub-lethal HgCl<sub>2</sub> concentration. A strong correlation between Hg tolerance and mercuric reductase activity was observed for <i>E. medicae</i> strains, whereas this was not the case for the <i>B. canariense</i> strains, suggesting that additional Hg tolerance mechanisms could be playing a role in <i>B. canariense</i>. Transcript abundance from <i>merA</i>, the gene that encodes mercuric reductase, was quantified in tolerant and sensitive <i>E. medicae</i> and <i>R. leguminosarum</i> strains. Tolerant strains presented higher <i>merA</i> expression than sensitive ones, and an increase in transcript abundance was observed for some strains when bacteria were grown in the presence of a sub-lethal HgCl<sub>2</sub> concentration. These results suggest a regulation of mercuric reductase in rhizobia. Expression of <i>merA</i> genes and mercuric reductase activity were confirmed in <i>Medicago truncatula</i> nodules formed by a sensitive or a tolerant <i>E. medicae</i> strain. Transcript accumulation in nodules formed by the tolerant strain increased when Hg stress was applied, while a significant decrease in expression occurred upon stress application in nodules formed by the Hg-sensitive strain. The effect of Hg stress on nitrogen fixation was evaluated, and in our experimental conditions, nitrogenase activity was not affected in nodules formed by the tolerant strain, while a significant decrease in activity was observed in nodules elicited by the Hg-sensitive bacteria. Our results suggest that the combination of tolerant legumes with tolerant rhizobia constitutes a potentially powerful tool in the bioremediation of Hg-contaminated soils.
Project description:Microbial activity is a critical factor controlling methylmercury formation in aquatic environments. Microbial communities were isolated from sediments of two highly mercury-polluted areas of the Tagus Estuary (Barreiro and Cala do Norte) and differentiated according to their dependence on oxygen into three groups: aerobic, anaerobic, and sulphate-reducing microbial communities. Their potential to methylate mercury and demethylate methylmercury was evaluated through incubation with isotope-enriched Hg species (<sup>199</sup>HgCl and CH?<sup>201</sup>HgCl). The results showed that the isolated microbial communities are actively involved in methylation and demethylation processes. The production of CH?<sup>199</sup>Hg was positively correlated with sulphate-reducing microbial communities, methylating up to 0.07% of the added <sup>199</sup>Hg within 48 h of incubation. A high rate of CH?<sup>201</sup>Hg degradation was observed and >20% of CH?<sup>201</sup>Hg was transformed. Mercury removal of inorganic forms was also observed. The results prove the simultaneous occurrence of microbial methylation and demethylation processes and indicate that microorganisms are mainly responsible for methylmercury formation and accumulation in the polluted Tagus Estuary.
Project description:The present study addresses existing data on the affinity and conjugation of sulfhydryl (thiol; -SH) groups of low- and high-molecular-weight biological ligands with mercury (Hg). The consequences of these interactions with special emphasis on pathways of Hg toxicity are highlighted. Cysteine (Cys) is considered the primary target of Hg, and link its sensitivity with thiol groups and cellular damage. <i>In vivo</i>, Hg complexes play a key role in Hg metabolism. Due to the increased affinity of Hg to SH groups in Cys residues, glutathione (GSH) is reactive. The geometry of Hg(II) glutathionates is less understood than that with Cys. Both Cys and GSH Hg-conjugates are important in Hg transport. The binding of Hg to Cys mediates multiple toxic effects of Hg, especially inhibitory effects on enzymes and other proteins that contain free Cys residues. In blood plasma, albumin is the main Hg-binding (Hg<sup>2+</sup>, CH<sub>3</sub>Hg<sup>+</sup>, C<sub>2</sub>H<sub>5</sub>Hg<sup>+</sup>, C<sub>6</sub>H<sub>5</sub>Hg<sup>+</sup>) protein. At the Cys<sub>34</sub> residue, Hg<sup>2+</sup> binds to albumin, whereas other metals likely are bound at the N-terminal site and multi-metal binding sites. In addition to albumin, Hg binds to multiple Cys-containing enzymes (including manganese-superoxide dismutase (Mn-SOD), arginase I, sorbitol dehydrogenase, and ?-aminolevulinate dehydratase, etc.) involved in multiple processes. The affinity of Hg for thiol groups may also underlie the pathways of Hg toxicity. In particular, Hg-SH may contribute to apoptosis modulation by interfering with Akt/CREB, Keap1/Nrf2, NF-?B, and mitochondrial pathways. Mercury-induced oxidative stress may ensue from Cys-Hg binding and inhibition of Mn-SOD (Cys<sub>196</sub>), thioredoxin reductase (TrxR) (Cys<sub>497</sub>) activity, as well as limiting GSH (GS-HgCH<sub>3</sub>) and Trx (Cys<sub>32, 35, 62, 65, 73</sub>) availability. Moreover, Hg-thiol interaction also is crucial in the neurotoxicity of Hg by modulating the cytoskeleton and neuronal receptors, to name a few. However, existing data on the role of Hg-SH binding in the Hg toxicity remains poorly defined. Therefore, more research is needed to understand better the role of Hg-thiol binding in the molecular pathways of Hg toxicology and the critical role of thiols to counteract negative effects of Hg overload.
Project description:The reaction of mercury(II) chloride with bis-(pyridin-3-ylmeth-yl)sulfane (<i>L</i>, C<sub>12</sub>H<sub>12</sub>N<sub>2</sub>S) in methanol afforded the title crystalline coordination polymer <i>catena</i>-poly[[di-chlorido-mercury(II)]-?-bis-(pyridin-3-ylmeth-yl)sulfane-?<sup>2</sup><i>N</i>:<i>N</i>'], [HgCl<sub>2</sub><i>L</i>] <sub><i>n</i></sub> . The asymmetric unit consists of one Hg<sup>II</sup> cation, one <i>L</i> ligand and two chloride anions. Each Hg<sup>II</sup> ion is coordinated by two pyridine N atoms from separate <i>L</i> ligands and two chloride anions. The metal adopts a highly distorted tetra-hedral geometry, with bond angles about the central atom in the range 97.69?(12)-153.86?(7)°. Each <i>L</i> ligand bridges two Hg<sup>II</sup> ions, forming an infinite -(Hg-<i>L</i>) <sub><i>n</i></sub> - zigzag chain along the <i>b</i> axis, with an Hg?Hg separation of 10.3997?(8)?Å. In the crystal, adjacent chains are connected by inter-molecular C-H?Cl hydrogen bonds, together with Hg-Cl?? inter-actions [chloride-to-centroid distance = 3.902?(3)?Å], that form between a chloride anion and the one of the pyridine rings of <i>L</i>, generating a two-dimensional layer extending parallel to (101). These layers are further linked by inter-molecular C-H?? hydrogen bonds, forming a three-dimensional supra-molecular network.
Project description:Small-scale or artisanal mining, using gold-mercury amalgamation to extract gold from ore, is a significant source of exposure for the workers and nearby populations. Few studies on hair mercury (Hg) have been conducted in Africa despite the fact that Africa has several gold deposits. No studies have been conducted in Eritrea that is one of the emerging gold producing countries in Africa. The aim of the study was to assess the Hg concentration in hair samples (n = 120) of a population living in Asmara, capital of Eritrea, and to evaluate the influence of some factors on the Hg levels in hair. Information on age, height, weight, occupation, smoking and fish consumption of participants were collected via questionnaire. Hair Hg concentration was significantly higher among women compared to men (p < 0.001) and among women preparing spicy products in Medeber market compared to those who did other jobs (p = 0.010). These results highlight the need for routine biomonitoring surveys and for health promotion campaigns devoted to local decision makers and workers.
Project description:Of all divalent metals, mercury (Hg<sup>II</sup> ) has the highest affinity for metallothioneins. Hg<sup>II</sup> is considered to be enclosed in the ? and ? domains as tetrahedral ?-type Hg<sub>4</sub> Cys<sub>11-12</sub> and ?-type Hg<sub>3</sub> Cys<sub>9</sub> clusters similar to Cd<sup>II</sup> and Zn<sup>II</sup> . However, neither the four-fold coordination of Hg nor the existence of Hg-Hg atomic pairs have ever been demonstrated, and the Hg<sup>II</sup> partitioning among the two protein domains is unknown. Using high energy-resolution XANES spectroscopy, MP2 geometry optimization, and biochemical analysis, evidence for the coexistence of two-coordinate Hg-thiolate complex and four-coordinate Hg-thiolate cluster with a metacinnabar-type (?-HgS) structure in the ? domain of separate metallothionein molecules from blue mussel under in vivo exposure is provided. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the ? domain, acts as a nucleation center for the polynuclear complex and that the five CXC motifs from this domain serve as the cluster-forming motifs. Oligomerization is driven by metallophilic Hg???Hg interactions. Our results provide clues as to why Hg has higher affinity for the ? than the ? domain. More generally, this work provides a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions.
Project description:The title compound, [HgCl(2)(C(7)H(8)S)](n), was isolated from the reaction of MeSPh with HgCl(2). The Hg(II) atom has a distorted tetra-hedral geometry and is coordinated by one S atom and three Cl atoms. Two of the Cl atoms act as bridging ligands between the Hg atoms, forming a two-dimensional polymeric structure.
Project description:To evaluate the role of atmospheric heterogeneous reactions on the ice nucleation ability of airborne dust particles, we investigated the systematic study of ice nucleation microphysics with a suite of atmospherically relevant metals (10), halides (4), and oxyhalides (2). Within a minute, a kaolin-iron oxide composite (KaFe) showed efficient reactions with aqueous mercury salts. Among the different mercury salts tested, only HgCl<sub>2</sub> reacting with KaFe generated HgKaFe, a highly efficient ice nucleating particle (HEIN). When added to water, HgKaFe caused water to freeze at much warmer temperatures, within a narrow range of -6.6 to -4.7 °C. Using a suite of optical spectroscopy, mass spectrometry, and microscopy techniques, we performed various experiments to decipher the physical and chemical properties of surface and bulk. KaFe was identified as a mixture of different iron oxides, namely, goethite, hematite, magnetite, and ?-Fe<sub>2</sub>O<sub>3</sub>, with kaolin. In HgKaFe, HgCl<sub>2</sub> was reduced to Hg<sub>2</sub>Cl<sub>2</sub> and iron was predominantly in maghemite form. Reduction of Fe<sup>2+</sup> by NaBH<sub>4</sub>, followed by aerial oxidation, helped KaFe to be an exact precursor for the synthesis of HEIN HgKaFe. Kaolin served as a template for synthesizing iron oxide, opposing unwanted aggregation. No other metal or metal halide was found to have more efficient nucleating particles than HgCl<sub>2</sub> with KaFe composite. The chelation of Hg(II) hindered the formation of HEIN. This study is useful for investigating the role of morphology and how inorganic chemical reactions on the surface of dust change morphology and thus ice nucleation activity. The understanding of the fundamentals of what makes a particle to be a good ice nucleating particle is valuable to further understand and predict the amount and types of atmospheric ice nucleating particles.
Project description:The asymmetric unit of the title compound, [Hg(4)Cl(8)(C(5)H(9)NO(2))(2)](n), consists of four HgCl(2) units and two L-proline ligands in the zwitterionic form. In each HgCl(2) unit, the Hg(II) ion is strongly bonded to two Cl atoms, and the Hg(II) ions in two of the HgCl(2) units are chelated by O atoms of two l-proline ligands, with one strong and one weak Hg-O bond. In the crystal structure, HgCl(2) and L-proline units are linked to form an extended chain along the a axis. The chain structure is further stabilized by N-H?Cl hydrogen bonds, and the chains are arranged in layers parallel to the ab plane. The structure of the title compound was originally determined by Ehsan, Malik & Haider [(1996). J. Banglad. Acad. Sci.20, 175] but no three-dimensional coordinates are available.
Project description:Redox conditions and organic matter control marine methylmercury (MeHg) production. The Black Sea is the world's largest and deepest anoxic basin and is thus ideal to study Hg species along the extended redox gradient. Here we present new dissolved Hg and MeHg data from the 2013 GEOTRACES MEDBlack cruise (GN04_leg2) that we integrated into a numerical 1-D model, to track the fate and dynamics of Hg and MeHg. Contrary to a previous study, our new data show highest MeHg concentrations in the permanently anoxic waters. Observed MeHg/Hg percentage (range 9-57%) in the anoxic waters is comparable to other subsurface maxima in oxic open-ocean waters. With the modeling we tested for various Hg methylation and demethylation scenarios along the redox gradient. The results show that Hg methylation must occur in the anoxic waters. The model was then used to simulate the time evolution (1850-2050) of Hg species in the Black Sea. Our findings quantify (1) inputs and outputs of Hg<sub>T</sub> (~31 and ~28 kmol yr<sup>-1</sup>) and MeHg<sub>T</sub> (~5 and ~4 kmol yr<sup>-1</sup>) to the basin, (2) the extent of net demethylation occurring in oxic (~1 kmol yr<sup>-1</sup>) and suboxic water (~6 kmol yr<sup>-1</sup>), (3) and the net Hg methylation in the anoxic waters of the Black Sea (~11 kmol yr<sup>-1</sup>). The model was also used to estimate the amount of anthropogenic Hg (85-93%) in the Black Sea.