Mercury Compounds Research Articles

Prospects for Fungal Bioremediation of Acidic Radioactive Waste Sites: Characterization and Genome Sequence of Rhodotorula taiwanensis MD1149.

Highly concentrated radionuclide waste produced during the Cold War era is stored at US Department of Energy (DOE) production sites. This radioactive waste was often highly acidic and mixed with heavy metals, and has been leaking into the environment since the 1950s. Because of the danger and expense of cleanup of such radioactive sites by physicochemical processes, in situ bioremediation methods are being developed for cleanup of contaminated ground and groundwater. To date, the most developed microbial treatment proposed for high-level radioactive sites employs the radiation-resistant bacterium Deinococcus radiodurans. However, the use of Deinococcus spp. and other bacteria is limited by their sensitivity to low pH. We report the characterization of 27 diverse environmental yeasts for their resistance to ionizing radiation (chronic and acute), heavy metals, pH minima, temperature maxima and optima, and their ability to form biofilms. Remarkably, many yeasts are extremely resistant to ionizing radiation and heavy metals. They also excrete carboxylic acids and are exceptionally tolerant to low pH. A special focus is placed on Rhodotorula taiwanensis MD1149, which was the most resistant to acid and gamma radiation. MD1149 is capable of growing under 66 Gy/h at pH 2.3 and in the presence of high concentrations of mercury and chromium compounds, and forming biofilms under high-level chronic radiation and low pH. We present the whole genome sequence and annotation of R. taiwanensis strain MD1149, with a comparison to other Rhodotorula species. This survey elevates yeasts to the frontier of biology's most radiation-resistant representatives, presenting a strong rationale for a role of fungi in bioremediation of acidic radioactive waste sites.

Mercury as a Global Pollutant and Mercury Exposure Assessment and Health Effects

Mercury and its compounds are classified into three main groups: metallic mercury (Hg0), inorganic mercury (Hg2+), and organic mercury (methyl mercury: CH3Hg+, etc.). Metallic mercury is the only metal that is liquid at ambient temperature and normal pressure, which readily forms an amalgam with other metals. Therefore, mercury has long been used for refining various metals, and mercury amalgam has been used for dental treatment. Mercury has also been used in measuring instruments such as thermometers, barometers and blood pressure monitors, as well as electric appliances such as lighting equipment and dry batteries. Large amounts of metallic mercury are still used in other countries as a catalyst in the production of caustic soda by electrolysis. In addition, mercury compounds have been used in various chemicals such as mercurochrome, agricultural chemicals, and mildew-proofing agents. However, the use of mercury has also caused health problems for people. Minamata disease in Japan is a typical example. Also, since mercury is highly volatile, it is discharged as a product of industrial activities or derived from volcanoes, and it has been concluded on the basis of the findings of the United Nations Environment Program (UNEP) that it is circulating globally. Therefore, with the aim of establishing an internationally legally binding treaty for the regulation of mercury use to reduce risk, an intergovernmental negotiating committee was established in 2009. Japan actively contributed to this negotiation owing to its experience with Minamata disease, which led to the Convention on the regulation of mercury use being discharged as the "Minamata Convention on Mercury" and the treaty came into force on August 16, 2017. In this review, we introduce 1) the Global Mercury Assessment by UNEP; 2) mercury kinetics, exposure assessment and toxicity of different chemical forms; 3) large-scale epidemics of methylmercury poisoning; 4) methylmercury exposure assessment and health survey in whale-eating populations; 5) elemental mercury exposure assessment and health survey of mercury mine workers in China.

Comprehensive Analysis of BIRC Family Gene Expression Changes by Mercury Compounds and Arsenic Exposure in Neuroblastoma, Kidney, and Hepatic Cells

Comprehensive Analysis of BIRC Family Gene Expression Changes by Mercury Compounds and Arsenic Exposure in Neuroblastoma, Kidney, and Hepatic Cells

Review—Electrochemical Sensors and Biosensors for Determination of Mercury Ions

Due to its toxicity, mercury determination is of great importance in human health and pollution monitoring. The mercury compounds can be released into our environment in several ways. Therefore, so many analytical procedures have been developed for detection of mercury. In this review, the analytical methods used for determination of mercury ions have been reported highlighting the electrochemical methods and in particular electrochemical biosensors. The electrochemical biosensors for determination of mercury were categorized into three groups including DNA-based, enzyme-based and whole-cell based biosensors and the mechanisms of the function of each group were described. The advantages and challenges of each class of biosensors are discussed in this review.

Localization and Accumulated Concentration Changes of Mercury Compound in Reproductive Organs of Female Mice with Time

Localization and Accumulated Concentration Changes of Mercury Compound in Reproductive Organs of Female Mice with Time

Lithobates catesbeianus (American Bullfrog) oocytes: a novel heterologous expression system for aquaporins.

ABSTRACTXenopus laevis oocytes are a valuable tool for investigating the function of membrane proteins. However, regulations around the world, specifically in Brazil, render the import of Xenopus laevis frogs impractical, and, in some cases, impossible. Here, as an alternative, we evaluate the usefulness of the North American aquatic bullfrog Lithobates catesebeianus, which is commercially available in Brazil, for the heterologous expression of aquaporin (AQP) proteins. We have developed a method that combines a brief collagenase treatment and mechanical defolliculation for isolating individual oocytes from Lithobates ovaries. We find that they have a similar size, shape, and appearance to Xenopus oocytes and can tolerate and survive following injections with cRNA or water. Furthermore, surface biotinylation, western blot analysis, and measurements of osmotic water permeability (Pf) show that Lithobates oocytes can express AQPs to the plasma membrane and significantly increase the Pf of the oocytes. In fact, the Pf values are similar to historical values gathered from Xenopus oocytes. Due to the presence of a mercury sensitive cysteine (Cys or C) in the throat of the water channel, the Pf of oocytes expressing human (h) AQP1, hAQP1FLAG [FLAG, short protein tag (DYKDDDDK) added to the N-terminus of AQP1], hAQP8, and rat (r) AQP9 was inhibited with the mercurial compound p-chloromercuribenzene sulfonate (pCMBS), whereas AQPs lacking this Cys – hAQP1C189S mutant [residue Cys 189 was replaced by a serine (Ser or S)] and hAQP7 – were mercury insensitive. Contrary to previous studies with Xenopus oocytes, rAQP3 was also found to be insensitive to mercury, which is consistent with the mercury-sensitive Cys (Cys 11) being located intracellularly. Thus, we consider Lithobates oocytes to be a readily accessible system for the functional expression and study of membrane proteins for international researchers who do not currently have access to Xenopus oocytes.

Two frequency ultrasound in preparation of the samples of natural brines to determine mercury by “cold vapor” absorption

Using of two-frequency ultrasound (US) in preparation of the samples of brines to determine Mercury by “cold vapor” absorption was studied. At this process US was used for: to destruct organic Mercury compounds, to carry out the process of Mercury extraction by ditizone in Carbon tetrachloride solution and to destruction and homohenization of Mercury extracts. It was found out by experiment that: to destruct organic Mercury compounds, also to destruct and homohenizate Mercury extracts using of simultaneous action of US of high and low frequencies is optimal. Comparison of the results, obtained with use of US of high (0.9-5.0 МHz)and low (18-100 kHz) frequencies show us that the best results were obtained with use of US of high (1.5-2.5 МHz) frequency. Change of frequency of low frequency US from 18 up to 100 kHz does not make the significant influence on the value of Mercury extraction at destruction of organic Mercury compounds. At this process intensity of low frequency US should be 1.5-2.5 W/cm2, of high frequency-2.5-3.0 W/cm2. The dependence between the degree of Mercury extraction and contain of fulvic acids (FA) in brines was determined. It was shown that for brines with contains of FA up to 10 mg/kg, the degree of Mercury extraction is 95-98%, for brines with contains of FA 10-20 mg/kg, the degree of Mercury extraction is 90-95%, and for brines with contains of FA above 20 mg/кg, the degree of Mercury extraction less than 90%. At using the standard methodic to determine Mercury in brines with contains of FA above 30 mg/kg, the degree of Mercury extraction less than 80%. At the destruction of Mercury extracts (Mercury (ІІ) dithizonates in Carbon tetrachloride) the maximal possible value of Mercury extraction was observed at simultaneous action of US of two frequencies- 18-100 kHz and intensity 1.5-2.5 W/cm2 , of frequency- 1.0-2.5 МHz and intensity 2.5-3.0 W/cm2 during 15-30 s. At Mercury extraction under US action the maximal possible value of Mercury extraction was observed at frequency- 500-800 kHz and intensity 0.3-0.5 W/cm2 during 1-3 min. The methodic to determine Mercury in natural brines with low end 0.0005 mkg/l was developed. The standard deviation of the obtained results is 0.06-0.09, according to standard methodic Sr ≥0.12. Simplification of reproducibility of the obtained results let us to control the tendency of fluctuations of Mercury content in natural brines as a result of anthropogenic pollution also as a result to using brines from various sources from various depth of the well.

Mercury in sediments of harbor areas of the Baltic Sea: compilation of data and comparison of legislation in the individual countries

Mercury is a very toxic chemical element and presents a very high level of chemical and biological activity. Long-term emissions of this element into the environment created a global pool of mercury, as a result of mercury forms has been constantly mobilised, deposited and re-mobilised up till now. The continued releases increase the overall values of the global mercury cycle in the air, water, sediments/soil as well as flora and fauna. Port sediments, which containing large deposits of mercury compounds may constitute a potential threat to the marine environment. Moreover harbour basins, which are mainly located in the estuary areas, can be exposed on the pollutants collected by the river flowing through the whole basin area. Furthermore, some contamination can be also supplied to the harbour areas as a result of cargo handling, ship traffic, the discharge of industrial and municipal wastewater etc. These contamination are largely deposited in the benthic sediments. This study summarizes results of mercury concentration in the sediments collected from the marine ports of the Baltic Sea (31 ports). Additionally, it references them to the existing legislation of the individual countries. These data came from the various sources: scientific articles, data submitted by different ports, port-related organisations within the framework of the project SMOCS [35], as well as own research..It has been found differences between each country's legal system. These are related to the different limit values used for the contamination assessment of mercury in port sediments. Another issue is an application of different analytical methodologies in environmental survey. The common analytical methodolody for the determination of mercury compounds together with defined similar limit values for the polluted sediments seems to be extremly important issue in terms of planning as well as managing Baltic Sea port’s sediments

Mercury in grain size fractions of aggregates and extractive waste from hard coal mining

Abstract Hard coal production is closely linked to the generation of significant quantities of extractive waste that require further use, in practice recognized as waste or as a raw material. It is therefore important to seek further or improve existing methods of waste material management. Studies conducted in earlier works have shown that it is possible to obtain a low-sulfur grain size fraction (grain class) so that it can be used in excavations requiring reclamation by filling. The purpose of the research presented in this paper is to determine the mercury content in hard coal mining by-products. The presence of mercury in the waste material is known and documented in the literature. However, the level of the content of this element in aggregates or wastes is important. This paper presents the problem of determining the minimum size of rock fractions meeting the specified limits for mercury content above which the material can be considered as safe are used to fill post-mining excavations. The total mercury content was determined using the classical atomic absorption method for all the collected and isolated samples (Altec AMA-254 analyzer). The total mercury content of the samples in the analytical state (Hga) was determined. Laboratory research included waste material directly from production (mining and processing of rock) from the one of the hard coal mine USCB. Coal sludge (silt) (after dewatering on filter presses) and 13 aggregates samples were analyzed, and then separated into 15 grain size fractions. The mercury determination method used in the study allowed its content in the range of 0.0568 to 0.0787 mg/kg, on an average mean of 0.0649 mg/kg (average moisture of the samples - 4.3%). On the other hand, the total mercury content of all the fractions extracted from 13 samples of aggregates showed a high variability in the content of this element, with a noticeabletendency of decreasing mercury content along with the increase in grain size. The average values of the total mercury content decrease from 0.4030 mg/kg for the finest fraction (0-6 mm) to 0.0291 mg/kg for the thickest fraction (120-200 mm) (aggregate sample moisture at approximately 1%). In general, it can be stated that the analyzed samples of coal sludge and grain fractions of aggregates meet the criteria for inert mining waste with respect to the mercury content. Based on the studies conducted, it can be concluded that due to the presence of mercury there is no need to discard fine fractions from aggregates. However, the removal of waste rock material less than 8 mm significantly increases the quality of the material. The obtained results and the statistical analysis clearly indicate a strong correlation between the occurrence of mercury and total sulfur in the material (R2 linear coefficient of determination at 0.9151), where no weathering has yet occurred. In the case of weathering, however, there is no correlation between the occurrence of mercury and sulfur, which may be due to the differences in the processes that govern the transformation and migration of mercury and sulfur compounds.

Cysteine and histidine residues are involved in Escherichia coli Tn21 MerE methylmercury transport.

Bacterial resistance to mercury compounds (mercurials) is mediated by proteins encoded by mercury resistance (mer) operons. Six merE variants with site‐directed mutations were constructed to investigate the roles of the cysteine and histidine residues in MerE protein during mercurial transport. By comparison of mercurial uptake by the cell with intact and/or variant MerE, we showed that the cysteine pair in the first transmembrane domain was critical for the transport of both Hg(II) and CH 3Hg(I). Also, the histidine residue located near to the cysteine pair was critical for Hg(II) transport, whereas the histidine residue located on the periplasmic side was critical for CH 3Hg(I) transport. Thus, enhanced mercurial uptake mediated by MerE may be a promising strategy for the design of new biomass for use in the bioremediation of mercurials in the environment.

Organomercury complexes bearing (thioxothiazolidin-5-yl)methyl moiety by intramolecular heteromercuration reaction of diallyldithiocarbamate

Reaction of diallyldithiocarbamate and mercury chloride in different mole ratios afforded two different organomercury complexes: ((3-allyl-2-thioxothiazolidin-5-yl)methyl)mercury(II) chloride and N,N-diallyl-dithiocarbamat(3-allyl-2-thioxothiazolidin-5-yl)methyl)mercury(II) represented as complex 1 and 2 respectively. The complexes were characterized by microanalysis, spectroscopic (IR, 1H and 13C NMR) techniques and their structures were elucidated by X-ray crystallography. Formation of both complexes occurred by intramolecular solvomercuration reactions via the allylic double bond. This reaction pathway was favoured by the properties of the reactants used: mercury chloride and an alkenamine derivative. The dithiocarbamate moeiety acted as a highly nucleophilic neighbouring group, and induced heterocyclization process by anchimeric assistance leading to formation of thiazol, a five-membered ring in both complexes. The structure of complex 1 presents a mercury compound in which the positive charge of the Hg2+ atom is balanced by dithiocarbamato and chloride anions acting as monodentate ligands, while in complex 2 the Hg atom is coordinated to three dithiocarbamate ligands and a ring closure occurred with one of the S atoms forming a thiazole ring.

Non-rigid coordination behavior of the ambidentate phosphinoyldithioformate ligands, [S2CP(O)R2]-, (R = Ph, CH2Ph) in organometallic Lead(IV) and Mercury(II) compounds

A series of phosphinoyldithioformate compounds were synthesized from metathesis reactions of K[R2P(O)CS2], and R'nPbCl4-n and R’HgCl. The compounds isolated were characterized using infrared, UV and multinuclear NMR (1H, 13C, and 31P) spectroscopy. Structural diversity of these compounds is revealed through analysis of the infrared and NMR spectroscopy, where variable temperature 31P NMR spectroscopy data of 6 reveals non-rigid coordination behavior and an equilibrium of aniso bonded S,S 4-membered ring, and S,O bonded 5-membered ring bonding modes in [MeHg{S2CP(O)(Ph)2}], (6–6′). The crystal structure of 6′ shows the mercury atom in a T-shape geometry with S,O-bidentate coordinated ligand although room temperature NMR indicated the coordination to the mercury in 6 is non rigid in solution. Variable temperature 31P NMR spectroscopy yielded an average value of ΔG#6-6´ = 45.7 ± 1.7 kJ mol−1 for the temperature range of 190 K–283 K. The crystal structure of [Ph2Pb{S2CP(O)(Ph)2}2(H2O)], 1, reveals the lead atom in an unusual seven coordinate geometry with two S,O-bidentate coordinated ligands and axial phenyl groups. The seventh ligand is a water molecule bonded to lead forming a pentagonal plane.

Mercury in soils of the agro-industrial zone of Zima city (Irkutsk oblast)

Data on mercury concentrations in soils of the agro-industrial zone of Zima city in Irkutsk oblast are discussed. It is shown that mercury concentrations in the plow horizon of studied soils exceed background values. The distribution pattern of mercury in soils of the investigated area is characterized. The revealed mercury anomalies are allocated to the industrial zone of the Sayanskkhimprom plant. The combined analysis of data on mercury concentrations in the plow and subplow horizons and on the chemical composition of snow indicates that mercury enters the soil mainly with atmospheric precipitation and is present there in the adsorbed form. The correlation analysis indicates that the local thermal power station plays a significant role as the source of mercury emission to the atmosphere. Close relationships between mercury concentrations and concentrations of mobile forms of elements attest to the presence of mobile organomineral mercury compounds in the studied soils.

ON THE ROLE OF BIOMONITORING IN THE ASSESSMENT OF THE HEALTH OF THE POPULATION EXPOSED TO MERCURY

When examining the population exposed to organic and inorganic compounds of mercury, a comprehensive approach is proposed, including chemical monitoring of environmental objects, biological monitoring, clinical examination of persons exposed to mercury, identification of high-risk groups.

Hair mercury (Hg) levels, fish consumption and semen parameters among men attending a fertility center.

General population exposure to methylmercury (MeHg), the most common organic mercury compound found in the environment, occurs primarily through the consumption of contaminated fish and shellfish. Due to limited studies and lack of consideration of effect modification by fish consumption, it remains uncertain if exposure to mercury affects semen parameters. Thus, we investigated whether hair Hg levels, a biomarker of mercury exposure, were associated with semen parameters among men attending an academic fertility center, and whether this relationship was modified by intake of fish. This analysis included 129 men contributing 243 semen samples who were enrolled in the Environment and Reproductive Health (EARTH) Study between 2005 and 2013, and had data of hair Hg, intake of fish and semen parameters available. Hair Hg levels were assessed using a direct mercury analyzer. Intake of fish was collected using a validated food frequency questionnaire. Semen parameters were analyzed following WHO 2010 evaluation criteria. Generalized linear mixed models with random intercepts accounting for within-man correlations across semen samples were used to evaluate the association of hair Hg levels and semen parameters adjusting for age, BMI, smoking status, abstinence time and alcohol intake. Effect modification by total fish intake (≤1.68 vs. >1.68 servings/week) was tested. The median hair Hg levels of the men was 0.72ppm and ranged from 0.03 to 8.01ppm; almost 30% of the men had hair Hg levels >1ppm. Hair Hg levels were positively related with sperm concentration, total sperm count, and progressive motility, after adjusting for potential confounders and became attenuated after further adjustment for fish intake. Specifically, men in the highest quartile of hair mercury levels had 50%, 46% and 31% higher sperm concentration, total sperm count and progressive motility, respectively, compared to men in the lowest quartile. These associations were stronger among men whose fish intake was above the study population median. Semen volume and normal morphology were unrelated to hair Hg levels. These results confirmed exposure to MeHg through fish intake and showed the important role of diet when exploring the associations between heavy metals and semen parameters among men of couples seeking fertility care. Further research is needed to clarify the complex relationship between fish intake and Hg, and potential effects on male reproductive health, specifically, semen parameters.

Quantitation Method for Polyfunctional Thiols in Hops (Humulus lupulus L.) and Beer Using Specific Extraction of Thiols and Gas Chromatography-Tandem Mass Spectrometry.

A method for the quantitation of six polyfunctional thiols, 4-methyl-4-sulfanylpentan-2-one (4MSP), 3-sulfanyl-4-methylpentan-1-ol (3S4MP), 3-sulfanyl-4-methylpentyl acetate (3S4MPA), 3-sulfanyl-3-methylbutan-1-ol (3S3MB), 3-sulfanylhexan-1-ol (3SH), and 3-sulfanylhexyl acetate (3SHA), in hops and beer without organic mercury compounds was developed. The method employed specific extraction of thiols using a silver ion solid phase extraction (SPE) cartridge and gas chromatography-tandem mass spectrometry (GC-MS/MS). For all thiols analyzed, good linearity was achieved by adding thioglycerol as an analyte protectant. Recoveries for both hops (74-100%) and beer (79-113%) were acceptable, and the repeatability for both was also good (relative standard deviations of 2.8-8.4%). The limits of detection for the six polyfunctional thiols were below their odor thresholds in beer. The method was applied to quantitation of hops and beer flavored with thiol-containing hop varieties. Due to their detected levels and level variations in different beers, 4MSP and 3S4MP are thought to be important polyfunctional thiols for the characteristic flavor of hop varieties.

Cleavage of Hg-C Bonds of Organomercurials Induced by ImOHSe via Two Distinct Pathways.

We show that the N-methylimidazole-based selone ImOHSe having an N-CH2CH2OH substituent has the remarkable ability to degrade methylmercury by two distinct pathways. Under basic conditions, ImOHSe converts MeHgCl into biologically inert HgSe nanoparticles and Me2Hg via the formation of an unstable intermediate (MeHg)2Se (pathway I). However, under neutral conditions, in the absence of any base, ImOHSe facilitates the cleavage of the Hg-C bond of MeHgCl at room temperature (23 °C), leading to the formation of a stable cleaved product, the tetracoordinated mononuclear mercury compound (ImOHSe)2HgCl2 and Me2Hg (pathway II). The initial rate of Hg-C bond cleavage of MeHgCl induced by ImOHSe is almost 2-fold higher than the initial rate observed by ImMeSe. Moreover, we show that ImYSe (Y = OH, Me) has an excellent ability to dealkylate Me2Hg at room temperature. Under acidic conditions, in the presence of excess ImYSe, the volatile and toxic Me2Hg further decomposes to the tetracoordinated mononuclear mercury compound [(ImYSe)4Hg]2+. In addition, the treatment of ImOHSe with MeHgCys or MeHgSG in phosphate buffer (pH 8.5) afforded water-soluble Hg(SeS) nanoparticles via unusual ligand exchange reactions, whereas its derivative ImOMeSe or ImMeSe, lacking the N-CH2CH2OH substituent, failed to produce Hg(SeS) nanoparticles under identical reaction conditions.

The Impact of the Major Baltic Inflow of December 2014 on the Mercury Species Distribution in the Baltic Sea.

The Baltic Sea is a marginal sea characterized by stagnation periods of several years. Oxygen consumption in its deep waters leads to the buildup of sulfide from sulfate reduction. Some of the microorganisms responsible for these processes also transform reactive ionic mercury to neurotoxic methylmercury. Episodic inflows of oxygenated saline water from the North Sea temporally re-establish oxic life in deep waters of the Baltic Sea. Thus, this sea is an especially important region to better understand mercury species distributions in connection with variable redox conditions. Mercury species were measured on three Baltic Sea campaigns, during the preinflow, ongoing inflow, and subsiding inflow of water, respectively, to the central basin. The inflowing water caused the removal of total mercury by 600 nmol m-2 and of methylmercury by 214 nmol m-2 in the Gotland Deep, probably via attachment of the mercury compounds to sinking particles. It appears likely that the consequences of the oxygenation of Baltic Sea deep waters, which are the coprecipitation of mercury species and the resettlement of the oxic deep waters, could lead to the enhanced transfer of accumulated mercury and methylmercury to the planktonic food chain and finally to fish.

Activation of the Hg–C Bond of Methylmercury by [S2]-Donor Ligands

Here we report that [S2]-donor ligands BmmOH, BmmMe, and BmeMe bind rapidly and reversibly to the mercury centers of organomercurials, RHgX, and facilitate the cleavage of Hg-C bonds of RHgX to produce stable tetracoordinated Hg(II) complexes and R2Hg. Significantly, the rate of cleavage of Hg-C bonds depends critically on the X group of RHgX (X = BF4-, Cl-, I-) and the [S2]-donor ligands used to induce the Hg-C bonds. For instance, the initial rate of cleavage of the Hg-C bond of MeHgI induced by BmeMe is almost 2-fold higher than the initial rate obtained by BmmOH or BmmMe, indicating that the spacer between the two imidazole rings of [S2]-donor ligands plays a significant role here in the cleavage of Hg-C bonds. Surprisingly, we noticed that the initial rate of cleavage of the Hg-C bond of MeHgI induced by BmeMe (or BmmMe) is almost 10-fold and 100-fold faster than the cleavage of Hg-C bonds of MeHgCl and [MeHg]BF4 respectively, under identical reaction conditions, suggesting that the Hg-C bond of [MeHg]BF4 is highly inert at room temperature (21 °C). We also show here that the nature of the final stable cleaved products, i.e. Hg(II) complexes, depends on the X group of RHgX and the [S2]-donor ligands. For instance, the reaction of BmmMe with MeHgCl (1:1 molar ratio) afforded the formation of the 16-membered metallacyclic dinuclear mercury compound (BmmMe)2Hg2Cl4, in which the two Cl atoms are located inside the ring, whereas due to the large size of the I atom, a similar reaction with MeHgI yielded polymeric [(BmmMe)2HgI2]m·(MeHgI)n. However, the treatment of BmmMe with ionic [RHg]BF4 led to the formation of the tetrathione-coordinated mononuclear mercury compound [(BmmMe)2Hg](BF4)2, where BF4- serves as a counteranion.

Mercury bioavailability, transformations, and effects on freshwater biofilms.

Mercury (Hg) compounds represent an important risk to aquatic ecosystems because of their persistence, bioaccumulation, and biomagnification potential. In the present review, we critically examine state-of-the-art studies on the interactions of Hg compounds with freshwater biofilms, with an emphasis on Hg accumulation, transformations, and effects. Freshwater biofilms contain both primary producers (e.g., algae) and decomposers (e.g., bacteria and fungi), which contribute to both aquatic food webs and the microbial loop. Hence they play a central role in shallow water and streams, and also contribute to Hg trophic transfer through their consumption. Both inorganic and methylated mercury compounds accumulate in biofilms, which could transform them mainly by methylation, demethylation, and reduction. Accumulated Hg compounds could induce diverse metabolic and physiological perturbations in the microorganisms embedded in the biofilm matrix and affect their community composition. The bioavailability of Hg compounds, their transformations, and their effects depend on their concentrations and speciation, ambient water characteristics, biofilm matrix composition, and microorganism-specific characteristics. The basic processes governing the interactions of Hg compounds with biofilm constituents are understudied. The development of novel conceptual and methodological approaches allowing an understanding of the chemo- and biodynamic aspects is necessary to improve the knowledge on Hg cycling in shallow water as well as to enable improved use of freshwater biofilms as potential indicators of water quality and to support better informed risk assessment. Environ Toxicol Chem 2017;36:3194-3205. © 2017 SETAC.