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Mercury (Hg), a neurotoxicant released primarily by anthropogenic activity, is present in all the world’s oceans, estuaries, and freshwater bodies (Giang, 2013). In addition to its toxicity to marine biota, Hg bioaccumulates within fish and other seafoods, presenting a threat to human health since fish remain important sources of protein for people across the world (Giang, 2013). Despite improvements in Hg pollution control, levels in commonly consumed marine fish such as bluefin tuna often exceed human health guidelines causing recommendations to limit fish consumption (Giang, 2013). Organic forms of Hg, such as monomethylmercury (MMHg), are more toxic than other forms and are the main causes of concern for human and ecosystem health. Various forms of Hg can transform into MMHg overtime and in certain environments. Elemental mercury (Hg(0)) can transform into different chemical species before becoming MMHg while divalent mercury (Hg(II)) can transform into MMHg through biotic methylation in the water column and sediments under specific chemical and physical conditions (Ming et al., 2019).The U.S. Environmental Protection Agency (EPA) manages approximately 98 ocean dredged material disposal sites (ODMDS) around the country’s federal waters. Disposal sites are used for the disposal of nontoxic sediments that are routinely removed to maintain navigational depths in ports, harbors, and marinas, as well as to support national maritime commerce, commercial fisheries, and recreation (EPA, n.d.). The U.S. Army Corps of Engineers (USACE) is planning to dredge federal channel segments in Newport Bay in Newport Beach, California. Based on sediment samples collected and analyzed for ocean disposal testing, the USACE project sediments were found to be high in Hg contamination (Anchor QEA, LLC., 2020). However, despite the high Hg levels, toxicity tests indicated suitability for ocean disposal at EPA’s LA-3 ODMDS located offshore of Newport Bay (Anchor QEA, LLC., 2020). The current Hg levels at the LA-3 disposal site are low to non-detect, and the effects of disposing of sediments loaded with Hg from the Federal channel in Newport Bay are unknown (Battelle and DAMOSVision, 2015). To address this issue, a literature review of Hg biogeochemical cycling and Hg-methylation was conducted to assist in the understanding of Hg speciation and transport. A policy review was also completed to assess the policies relevant to sediment dredging in California and ocean dumping in federal waters. Related to the policies in place, manuals utilized by USACE and EPA for testing and analysis purposes were reviewed to determine additional sediment and water column tests to minimize the potential risk of Hg contamination in the marine environment. Through the compilation of information, testing and analysis recommendations in addition to current testing were made for the dredge and disposal site locations.

Studies in boreal regions concerning the bioaccumulative neurotoxin methylmercury (MeHg) in natural wetlands and experimental reservoirs have shown that these waterbodies contribute to high MeHg levels in underlying sediments, inundated vegetation, and aquatic organisms. Beaver ponds are natural reservoirs that are ubiquitous in the Canadian boreal region and have been reported to increase downstream MeHg concentrations. However, the reported impacts of beaver ponds on stream MeHg vary widely across a limited number of studies, and factors influencing this variation are not well understood. To quantify the effect of beaver ponds on stream mercury concentrations, water samples were taken upstream and downstream of 10 in-channel beaver impoundments in northwestern Ontario, Canada. The downstream:upstream MeHg concentration ratios were related to pond and landscape characteristics to examine potential factors that play a role in determining the effect of beaver ponds on stream MeHg concentrations. Overall, MeHg concentrations were 1.6 times greater downstream of the beaver ponds, though this increase was not consistent; downstream concentrations up to 12 times greater and up to 5 times less were also observed. Landscape characteristics that can be readily obtained from existing spatial datasets or quantified using remote sensing techniques emerged as better predictors of downstream:upstream MeHg concentrations than site-specific stream chemistry parameters or pond characteristics that are more difficult to ascertain, with drier landscapes indicative of lower background MeHg export being more likely to exhibit greater increases in MeHg downstream of a beaver pond. These results suggest that the effects of beaver ponds on surface water MeHg concentrations are generally small but highly variable, and that the magnitude of the pond’s influence on stream MeHg are lessened in landscapes already conducive to higher MeHg concentrations.

Mercury (Hg) is a toxic contaminant of global concern and the impact on Arctic ecosystems, particularly in seabirds, is critical due to large-scale Hg transport towards polar regions and its biomagnification in marine trophic systems. While the adverse effects of Hg on reproductive processes in seabirds are established, the understanding of Hg maternal transfer pathways and their control on Hg reproductive toxicity is limited. The combination of Hg compounds speciation (inorganic mercury and monomethylmercury MMHg) and Hg stable isotope composition in the different egg compartments (yolk, albumen, membrane, and shell) before embryo development was investigated to provide information on (i) Hg maternal transfer mechanisms, (ii) influence of egg biochemical composition on Hg organotropism and (iii) proxies of inputs of Hg contamination. Eggs of three seabird species (the common eider, the black-legged kittiwake and the little auk) collected within the same breeding period (summer 2020) in East Greenland were investigated. For all seabirds, albumen and membrane, the most protein-rich compartments, were the most contaminated (from 1.2 to 2.7 μg g−1 for albumen and from 0.3 to 0.7 μg g−1 for membrane). In these two compartments, more than 82% of the total Hg amount was in the form of MMHg. Additionally, mass-dependent fractionation values (δ 202Hg) were higher in albumen and membrane in the three species. This result was mainly due the organotropism of MMHg as influenced by the biochemical properties and chemical binding affinity of these proteinous compartments. Among the different egg compartments, individuals and species, mass-independent fractionation values were comparable (mean ± sd were 0.99 ± 0.11‰, 0.78 ± 0.11‰, 0.03 ± 0.05‰, 0.04 ± 0.10‰ for Δ199Hg, Δ201Hg, Δ200Hg and Δ204Hg, respectively). We conclude that initial MMHg accumulated in the three species originated from Arctic environmental reservoirs exhibiting similar and low photodemethylation extent. This result suggests a unique major source of MMHg in those ecosystems, potentially influenced by sea ice cover. [Display omitted] • Protein-rich egg compartments exhibited highest Hg contamination, mostly as MMHg. • MDF values likely reflected Hg organotropism for protein-rich compartments. • Odd-isotopes MIF indicated a single origin of MMHg contamination among seabirds. • Egg membranes/shells are non-invasive indicators of the source of Hg contamination. [ABSTRACT FROM AUTHOR]

In shallow aquatic environments, sediment is a significant source of monomethylmercury (MMHg) for surface water (SW). High-altitude aquatic ecosystems are characterized by extreme hydro-climatic constraints (e.g., low oxygen and high UV radiation). We studied, during two seasons, the diel cycles of MMHg in SW and sediment porewaters (PW) of Lake Uru Uru (3686 m a.s.l, Bolivia) contaminated by urban and mining activities. Our results show that diel changes in SW MMHg concentrations (up to 1.8 ng L−1) overwhelm seasonal ones, with higher MMHg accumulation during the night-time and the dry season. The calculation of MMHg diffusive fluxes demonstrates that the sediment compartment was the primary source of MMHg to the SW. Most MMHg efflux occurred during the dry season (35.7 ± 17.4 ng m−2 day−1), when the lake was relatively shallow, more eutrophicated, and with the redoxcline located above the sediment–water interface (SWI). Changes in MMHg accumulation in the PWs were attributed to diel redox oscillations around the SWI driving both the bacterial sulfate reduction and bio-methylation. Finally, we highlight that although MMHg loading from the PW to the SW is large, MMHg photodegradation and demethylation by microorganisms control the net MMHg accumulation in the water column. [ABSTRACT FROM AUTHOR]

Photodegradation is an important pathway for monomethylmercury (MeHg) degradation in aquatic ecosystems. In this process, dissolved organic matter (DOM) plays an essential role. However, little information is available regarding the photo-transformation of MeHg in shallow aquatic environments, where a significant portion of MeHg is associated with soil suspensions. In this study, 14 soils sampled from different sites in China were used to simulate these conditions. Our results clearly demonstrated that soil organic matter (SOM) was the most important factor controlling the MeHg photodegradation in suspension. Degradation in this heterogeneous aqueous system was shown to be mediated by the 1O 2 produced by organic matter on the surface of the soil particles rather than by DOM. This was confirmed by the strong correlation between the kinetics rate constant of MeHg degradation and steady state concentrations of 1O 2 (R 2 = 0.81). Our results propose a new pathway of MeHg induced by sediment soils under sunlight irradiation. Identification of this pathway may improve the estimates of potential ecological risk of Hg in shallow field ecosystems. Image 1 • MeHg can be photo-degraded with simulated sunlight when soil particles are existed in natural shallow. • Soil organic matter rather than dissolved organic matter plays a dominant role in MeHg photodegradation. • Singlet oxygen is dominating active species for MeHg photodegradation on the surface of soil particles. [ABSTRACT FROM AUTHOR]

In shallow aquatic environments, sediment is a significant source of monomethylmercury (MMHg) for surface water (SW). High-altitude aquatic ecosystems are characterized by extreme hydro-climatic constraints (e.g., low oxygen and high UV radiation). We studied, during two seasons, the diel cycles of MMHg in SW and sediment porewaters (PW) of Lake Uru Uru (3686 m a.s.l, Bolivia) contaminated by urban and mining activities. Our results show that diel changes in SW MMHg concentrations (up to 1.8 ng L−1) overwhelm seasonal ones, with higher MMHg accumulation during the night-time and the dry season. The calculation of MMHg diffusive fluxes demonstrates that the sediment compartment was the primary source of MMHg to the SW. Most MMHg efflux occurred during the dry season (35.7 ± 17.4 ng m−2 day−1), when the lake was relatively shallow, more eutrophicated, and with the redoxcline located above the sediment–water interface (SWI). Changes in MMHg accumulation in the PWs were attributed to diel redox oscillations around the SWI driving both the bacterial sulfate reduction and bio-methylation. Finally, we highlight that although MMHg loading from the PW to the SW is large, MMHg photodegradation and demethylation by microorganisms control the net MMHg accumulation in the water column.

Monomethylmercury (MMHg) is a potent neurotoxicant that can be bioaccumulated and biomagnified through trophic levels. Human populations whose diets contain MMHg are at risk of MMHg toxicity. The gut microbiota was identified as a potential factor causing variation in MMHg absorption and body burden. However, little is known about the role of gut microbiota on Hg transformations. We conducted a series of in vitro experiments to study the effects of dietary nutrient change on Hg metabolism and the human gut microbiota using anoxic fecal slurry incubations. We used stable Hg isotope tracers to track MMHg production and degradation and characterized the microbiota using high throughput sequencing of the 16S rRNA gene. We show that the magnitude of MMHg degradation is individual dependent and rapidly responds to changes in nutrient amendments, leading to complete degradation of the MMHg present. Although the mechanism involved remains unknown, it does not appear to involve the well-known mer operon. Our data are the first to show a nutrient dependency on the ability of the simulated human gut microbiota to demethylate MMHg. This work provides much-needed insights into individual variations in Hg absorption and potential toxicity. [ABSTRACT FROM AUTHOR]

Hybrid nanocomposites based on Fe 3 O 4 magnetic nanoparticles (MNPs) coated with different types of carbon nanotubes (CNTs) have been studied for the first time as sorbent materials for magnetic solid phase extraction (MSPE) for mercury speciation analysis. Monomethylmercury (MMHg) was the target mercury species in water samples and the adsorption and desorption processes were optimized based on this species. Single-walled CNT-MNP showed higher adsorption capacity than double-walled or multi-walled CNTs. Then, the magnetic sorbent was retrieved with an external magnet and MMHg was selectively desorbed from it with dichloromethane (DCM) in two steps with vortex agitation. Inorganic mercury was removed during the desorption stage. The rapid adsorption and desorption equilibrium, the magnetic separation of the sorbent, and the simple and fast synthesis of CNT-MNPs without any additional modification of the CNTs simplified and shortened the extraction procedure. The extract was submitted to derivatization of the mercury species by ethylation (with an optional nitrogen stream evaporation of the organic phase) and injection into a gas chromatograph coupled to an atomic fluorescence detector (GC-pyro-AFS). The overall procedure provides the preconcentration of MMHg up to 150 times and the removal of inorganic mercury at the same time. The procedural limits of detection (LOD) and quantification (LOQ) were 5.4 and 17.9 pg mL −1 , respectively. Moreover, magnetic nanocomposites can be reused at least 7 times without losing their efficiency. The methodology was validated in tap, dam and river water samples to evaluate the performance under real conditions with recoveries from 79% to 97% of spiked MMHg. [ABSTRACT FROM AUTHOR]

Recent investigations revealed that monomethylmercury (MMHg) can be absorbed and accumulated by plants, i.e. rice crops, thus becoming an important route of human exposure to MMHg through diet. The increasing concern about this fact makes that appropriate analytical methods for Hg speciation in these samples are urgently required. Therefore, the aim of this work has been the development of a fast and sensitive method which enables the simultaneous determination of MMHg and inorganic Hg in rice and aquatic plants. The proposed methodology is based on the extraction of Hg species by closed-vessel microwave heating, subsequent derivatization by ethylation and analysis by gas chromatography coupled to atomic fluorescence detection via pyrolysis (GC-pyro-AFS). A careful optimization of the extraction, using both acid (6 N HNO 3 ) and alkaline (tetramethylammonium hydroxide, TMAH) extractants, and derivatization conditions has been carried out. Spiked and unspiked aquatic plants ( Typha domingensis ) and CRMs certified for Total-Hg (BCR-60, BCR-482 and NCS ZC73027, corresponding to aquatic plant, lichen and rice, respectively) have been used. Under the final optimized conditions the simultaneous determination of MMHg and inorganic Hg can be carried out in less than 40 min with no tedious clean-up steps. Quantitative recoveries (from 92% to 101%) were obtained in aquatic plants ( Typha domingensis ) and CRMs spiked with known concentrations of MMHg. For unspiked BCR-60 and BCR-482, no statistically significant differences ( p =0.05) were found in Total-Hg concentrations between those obtained by the sum of species and the certified values for both acid and alkaline extraction. For the analysis of low Hg polluted samples, an additional preconcentration step by evaporation under nitrogen stream was required but adequate blanks were only obtained for acid extraction. Detection limits in the low ng/g range (0.7–1.0 ng/g) were consequently achieved for both Hg species in the case of acid extraction and the analysis of NCS ZC73027 gave satisfactory results without statistically significant differences between the found and certified values ( p = 0.05). [ABSTRACT FROM AUTHOR]

Mercury (Hg) may originate from both anthropogenic and natural sources. The measurement of spatial and temporal variations of Hg isotope ratios in sediments may enable source identification and tracking of environmental processes. In this study we establish the distribution of mercury concentrations and mercury isotope ratios in surface sediments of three transects along the continental shelf and slope in Campos Basin-RJ-Brazil. The shelf showed on average lower total Hg concentrations (9.2 ± 5.3 ng g −1 ) than the slope (24.6 ± 8.8 ng g −1 ). MMHg average concentrations of shelf 0.15 ± 0.12 ng g −1 and slope 0.13 ± 0.06 ng g −1 were not significantly different. Distinct differences in Hg isotope ratio signatures were observed, suggesting that the two regions were impacted by different sources of Hg. The shelf showed more negative δ 202 Hg and Δ 199 Hg values ranging from −0.59 to −2.19‰ and from −0.76 to 0.08‰, respectively. In contrast, the slope exhibited δ 202 Hg values from −0.29 to −1.82‰ and Δ 199 Hg values from −0.23 to 0.09‰. Mercury found on the shelf, especially along the “D” and “I” transects, is depleted in heavy isotopes resulting in more negative δ 202 Hg compared to the slope. Isotope ratios observed in the “D” and “I” shelf region are similar to Hg ratios commonly associated with plants and vegetation and very comparable to those detected in the estuary and adjoining mangrove forest, which suggests that Hg exported from rivers may be the dominating source of Hg in near coastal regions along the northern part of the shelf. [ABSTRACT FROM AUTHOR]

We investigated monomethylmercury (MMHg) concentrations in 448 samples of four common fish species (barbel steed, largemouth bass, leopard mandarin, and bluegill) and the trophic states of 14 artificial reservoirs in South Korea in order to understand how trophic states of reserviors affect MMHg concentrations in fish. The trophic state index (TSI) of each reservoir was determined using empirical equations based on the monthly chlorophyll-a, total phosphorus, and Secchi depth, collected over a three-year period. The length-normalized MMHg concentrations in fish showed a negative correlation with the TSI based on chlorophyll-a (r 2 = 0.90) and total phosphorus (r 2 = 0.75) that may be a result of particle dilution of MMHg in surface waters. This study revealed that MMHg accumulation in fish was better correlated with TSI than MMHg in water, therefore, we suggest that the measurement of TSI based on chlorophyll-a and total phosphorus is an effective way to predict MMHg bioaccumulation across diverse reservoirs. [ABSTRACT FROM AUTHOR]

An inter-laboratory study was conducted to compare results from different analytical methods for monomethylmercury (MeHg) concentrations in 17 soil and sediment samples. The samples were collected from mercury-contaminated areas, including Minamata Bay and Kagoshima Bay in Japan, the Idrija mercury mine in Slovenia, and an artisanal small-scale gold mining area in Indonesia. The Hg in these samples comes from several different sources: industrial waste from an acetaldehyde production facility, volcanic activity, Hg mining activity, and artisanal and small-scale gold mining activity (ASGM). MeHg concentrations in all the samples were measured in four separate laboratories, using three different determination methods: Kagoshima University (Japan), using high-performance liquid chromatography–chemiluminescence detection (HPLC-CL); National Institute for Minamata Disease (Japan), using gas chromatography–electron capture detection; and Metropolitan Council Environmental Services (USA) and Jozef Stefan Institute (Slovenia), both using alkylation-gas chromatography–atomic fluorescence spectrometry detection. The methods gave comparable MeHg results for most of the samples tested, but for some samples, the results exhibited significant variability depending on the method used. The HPLC-CL method performed poorly when applied to samples with elevated sulfur concentrations, producing MeHg concentrations that were much lower than those from the other methods. Additional analytical work demonstrated the elimination of this sulfur interference when the method was modified to bind sulfur prior to the analytical step by using Hg 2+ as a masking agent. These results demonstrate the value of laboratory intercomparison exercises in contributing to the improvement of analytical methods. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coastal and freshwater seafood exhibit distinct isotopic values of C, N and MMHg. • MMHg contents in aquatic organisms are positively correlated to trophic levels. • Coastal fish and shellfish have different pools for MMHg absorption. • MMHg in vivo demethylation in seafood is confirmed by specific-Hg isotope. • High trophic level seafood undergone much more in vivo demethylation of MMHg. Human exposure to monomethylmercury (MMHg) through seafood consumption is a global concern. This study investigates the potential sources and processes of MMHg in seafood of coastal and freshwater areas through combing of δ13C, δ15N, and specific Hg (including MMHg and inorganic Hg (IHg)) isotopes. The results showed that δ13C and δ15N values exhibit different patterns in coastal and freshwater species. Δ199Hg MMHg /δ202Hg MMHg values suggested that coastal and freshwater seafood undergo similar aqueous MMHg photodegradation processes. The Δ199Hg MMHg values could distinguish that, coastal fish absorb MMHg from water column whereas coastal shellfish absorb MMHg mainly from sediment. The positive values of Δ199Hg IHg in seafood could reflect in vivo MMHg demethylation and IHg reabsorption. Positive correlation between δ15N and Δ199Hg IHg indicated that aquatic organisms in various trophic levels may have different MMHg demethylation efficiency. We proposed that combining of multiple isotopes can provide overall profiles on aquatic MMHg biogeochemical cycle and bioaccumulation. [ABSTRACT FROM AUTHOR]

Zooplankton play a central role in marine food webs, dictating the quantity and quality of energy available to upper trophic levels. They act as “keystone” species in transfer of mercury (Hg) up through the marine food chain. Here, we present the first Pan-Arctic overview of total and monomethylmercury concentrations (THg and MMHg) and stable isotope ratios of carbon (δ 13 C) and nitrogen (δ 15 N) in selected zooplankton species by assembling data collected between 1998 and 2012 from six arctic regions (Laptev Sea, Chukchi Sea, southeastern Beaufort Sea, Canadian Arctic Archipelago, Hudson Bay and northern Baffin Bay). MMHg concentrations in Calanus spp., Themisto spp. and Paraeuchaeta spp. were found to increase with higher δ 15 N and lower δ 13 C. The southern Beaufort Sea exhibited both the highest THg and MMHg concentrations. Biomagnification of MMHg between Calanus spp. and two of its known predators, Themisto spp. and Paraeuchaeta spp., was greatest in the southern Beaufort Sea. Our results show large geographical variations in Hg concentrations and isotopic signatures for individual species related to regional ecosystem features, such as varying water masses and freshwater inputs, and highlight the increased exposure to Hg in the marine food chain of the southern Beaufort Sea. [ABSTRACT FROM AUTHOR]

The aim of this study was to identify how hydrologic factors (e.g., rainfall, maximum depth, reservoir and catchment area, and water residence time) and water chemistry factors (e.g., conductivity, pH, suspended particulate matter, chlorophyll-a, dissolved organic carbon, and sulfate) interact to affect the spatial variance in monomethylmercury (MMHg) concentration in nine artificial reservoirs. We hypothesized that the MMHg concentration of reservoir water would be higher in eutrophic than in oligotrophic reservoirs because increased dissolved organic matter and sulfate in eutrophic reservoirs can promote in situ production of MMHg. Multiple tools, including Pearson correlation, a self-organizing map, and principal component analysis, were applied in the statistical modeling of Hg species. The results showed that rainfall amount and hydraulic residence time best explained the variance of dissolved Hg and dissolved MMHg in reservoir water. High precipitation events and residence time may mobilize Hg and MMHg in the catchment and reservoir sediment, respectively. On the contrary, algal biomass was a key predictor of the variance of the percentage fraction of unfiltered MMHg over unfiltered Hg (%MMHg). The creation of suboxic conditions and the supply of sulfate subsequent to the algal decomposition seemed to support enhanced %MMHg in the bloom reservoirs. Thus, the nutrient supply should be carefully managed to limit increases in the %MMHg/Hg of temperate reservoirs. [ABSTRACT FROM AUTHOR]

The methylation of mercury (Hg) is of great concern as methylmercury (MeHg), the most toxic species, is produced. This study examined the possibilities of tert-butyl compounds (tert-butyl alcohol (TBA) and tert-butyl hydroperoxide (TBH)) and other alcohols serving as methyl donors for Hg photo-methylation under light irradiation. The yield of MeHg varied among the methyl donors, and it was also significantly influenced by salinity and pH. MeHg could be generated in the presence of TBH under visible light irradiation. The hydroxyl radical ( OH) was found to promote MeHg production at low levels, but degrade MeHg in excess. The photo-production of MeHg was tentatively proposed via the complexation of Hg and methyl donors, the formation of an intermediate ( O(Hg)C(CH 3 ) 3 ), and the intramolecular methyl transfer from methyl donors to Hg. This study implicates photoreactions between Hg and organic pollutants in understanding the fate and transformation of Hg in the aquatic environment. [ABSTRACT FROM AUTHOR]

Photo-reduction of mercury (Hg) is an important mechanism for removal of both Hg 2+ species and monomethylmercury (MMHg) from surface waters. Large mass independent fractionation (MIF) signatures of Hg isotopes preserved in natural samples are thought to reflect MIF produced during aqueous photo-reduction by the magnetic isotope effect (MIE). Recently, Hg MIF signatures in natural samples are being used to quantify photochemical reduction in aquatic systems. However, the fractionation factors used are from laboratory experiments that did not investigate many of the environmental parameters that may affect MIF during photo-reduction. In this study, the effects of different regions of the solar spectrum on the expression of MIF caused by the MIE during Hg 2+ and MMHg photo-reduction were investigated to assess how the type of radiation affects the extent and signature of MIF. Photo-reduction in the presence of DOM was carried out through exposure to the full natural solar spectrum unfiltered, with the ultraviolet B (UVB; 290–320 nm) portion removed and with both the UVB and the ultraviolet A (UVA; 320–400 nm) removed. There is a clear relationship between the expression and magnitude of MIF and the energy of incident radiation for both Hg 2+ and MMHg photo-reduction. The experiments indicate that MIF produced during photo-reduction of Hg 2+ is significantly influenced by both UVB and UVA radiation. For MMHg photodemethylation, however, UVB radiation is mostly responsible for the MIF with minor contributions from UVA. Overall, there is a lack of correlation between the observed MIF and total photo-reduction in the experiments conducted in this study, which indicates that indirect and other non-MIF producing pathways of photo-reduction are the dominant pathways by which Hg species are being photo-reduced. Extrapolating these experimental results to natural systems is difficult as the experiments were not performed at realistic Hg/DOM ratios and the distribution of ligands that Hg is bound to in the experiments likely differs from natural systems. However, the strong relationship between MIF and energy of incident radiation in this study supports Hg MIF signatures as promising tools for helping to quantify photochemical cycling of mercury, but this study also highlights the need to understand the link between MIF and total photo-reduction before this tool can be fully utilized. [ABSTRACT FROM AUTHOR]

We provide the mercury (Hg) and monomethylmercury (MMHg) levels of the plume water, sulfide ore, sediment, and mollusks located at the hydrothermal vent fields of the southern Tonga Arc, where active volcanism and intense seismic activity occur frequently. Our objectives were: (1) to address the potential release of Hg from hydrothermal fluids and (2) to examine the distribution of Hg and MMHg levels in hydrothermal mollusks (mussels and snails) harboring chemotrophic bacteria. While high concentrations of Hg in the sediment and Hg, As, and Sb in the sulfide ore indicates that their source is likely hydrothermal fluids, the MMHg concentration in the sediment was orders of magnitude lower than the Hg (<0.001%). It suggests that Hg methylation may have not been favorable in the vent field sediment. In addition, Hg concentrations in the mollusks were much higher (10–100 times) than in other hydrothermal vent environments, indicating that organisms located at the Tonga Arc are exposed to exceedingly high Hg levels. While Hg concentration was higher in the gills and digestive glands than in the mantles and residues of snails and mussels, the MMHg concentrations in the gills and digestive glands were orders of magnitude lower (0.004–0.04%) than Hg concentrations. In summary, our results suggest that the release of Hg from the hydrothermal vent fields of the Tonga Arc and subsequent bioaccumulation are substantial, but not for MMHg. [ABSTRACT FROM AUTHOR]

This paper proposes a Fenton-like reaction activated by nanoscale zero-valent iron (nZVI) for aqueous monomethylmercury (MMHg) decomposition. Reacting 10 μg L−1 MMHg with 280 mg L−1 nZVI removed 70% of the aqueous MMHg within 1 min, and its main product was aqueous Hg(II). Within 1 − 5 min, the aqueous Hg(II) decreased while the aqueous, solid, and gas-phase Hg(0) increased with 92% MMHg removal. Then, a secondary Hg(II) reduction to solid Hg(0) was prevalent within 30 − 60 min, with 98% MMHg removal. Diverse-shaped magnetite crystals were observed on the surface of nZVI in 2 h, suggesting that Fe(II) oxidation on magnetite can be a source of electrons for secondary Hg(II) reduction. When FeCl 2 and H 2 O 2 were added to the MMHg solution without nZVI, 99% of the MMHg changed to Hg(II) within 1 min. The reactive oxygen species (ROS) produced by the Fenton-like reaction accounted for the rapid demethylation but not for the further reduction of Hg(II) to Hg(0). The results suggest a three-step pathway of MMHg decomposition by nZVI: (1) rapid MMHg demethylation by ROS; (2) rapid Hg(II) reduction by Fe(0); and (3) slow Hg(II) reduction by magnetite on the nZVI surface. [Display omitted] • The reaction of MMHg with nZVI removed 98% of aqueous MMHg within 1 h. • MMHg was rapidly removed through the oxidative demethylation by ROS. • Rapid removal by ROS was followed by the slow reduction by magnetite. • Quenching of 1O 2 resulted in 96% decrease in MMHg removal rate constant. [ABSTRACT FROM AUTHOR]

This investigation examines how extracellular polymeric substances (EPSs) and environmental factors influence the bioaccumulation of monomethylmercury (MMeHg) using a culture of Microcystis aeruginosa, which dominates eutrophic reservoir populations. The identified EPSs were classified as carbohydrates and proteins. Evaluation of the bioaccumulation of MMeHg in cells by multiple regression analysis reveals that the concentration of EPSs in filtrate, the initial concentration of MMeHg in media, and the age of the culture significantly affected the amount of accumulation of MMeHg. Based on the composition profiles, the concentrations of soluble carbohydrates were significantly higher in the cells with bioaccumulated MMeHg than in the control ones. Preliminary results based on SEM-map investigations suggest that most of the MMeHg accumulated in the cytoplasm (intracellular). Additionally, the effective concentrations (EC50) of MMeHg that inhibit the growth of M. aeruginosa were 5.1 to 7.8 μg/L in the logarithmic phase and 2.5 to 4.6 μg/L in the stationary phase. [ABSTRACT FROM AUTHOR]

Highlights: [•] Reverse phase columns were evaluated for the separation of 15 MMHg-thiol complexes. [•] Phenyl and mixed-mode columns performed better than C18 columns. [•] Detection limits were in the low nmolL−1 range. [•] Four complexes were monitored over time in a phytoplankton culture. [Copyright &y& Elsevier]

Abstract: To better understand the methylation and demethylation of mercury (Hg) in the atmosphere, monomethyl mercury (MMHg) concentrations in wet deposition samples collected in the Minamata Bay area from September, 2009 to August, 2010 were determined. The concentrations of total Hg (dissolved Hg + particulate Hg) and dissolved reactive Hg were also measured. The volume-weighted mean concentrations of dissolved MMHg and total Hg were 0.061 and 5.9 ng L−1, respectively. Almost 90% of total Hg was in the dissolved phase and dissolved reactive Hg was the dominant Hg species in the wet deposition. The wet deposition fluxes of total Hg and reactive Hg increased in the rainy season (summer and fall), while the concentrations and wet deposition fluxes of MMHg were higher in winter and spring than in summer. Factors affecting this seasonal variation of MMHg were also considered. The MMHg in wet depositions may be decomposed by the increased levels of UV radiation in summer months, although MMHg can also be emitted from anthropogenic and biogenic sources and/or produced by photochemical reactions. Long-range transport from the Asian continent may also contribute to the seasonal variation of the wet MMHg deposition flux. [Copyright &y& Elsevier]

An estimated 215,000 tonnes of mercury (Hg) have been emitted to the atmosphere from anthropogenic sources since the nineteenth century, igniting widespread environmental monitoring owing to its toxicity. The environmental fate of Hg is strongly determined by catchment characteristics, especially soil organic matter. In this study, concentrations and pools of Hg were determined for lakes and soils in upland peat-dominated catchments in Ireland to assess controls of aquatic Hg and soil response to changes in emissions. Headwater lakes in upland coastal regions were surveyed for water chemistry and total Hg (THg) during spring 2008. In addition, a sub-set of lakes ( n = 5) were repeatedly sampled during 2009–2011, and their surface soils collected for Hg analysis, including a short (30 cm) peat core to assess temporal Hg fluxes using radiometric 210Pb dating. Peat cores indicated a significant decrease in Hg deposition since the 1980s, in broad agreement with other ‘background’ regions. Total Hg was correlated with total organic carbon (TOC) in the survey and intensive study lakes (r = 0.70 and 0.45), indicative of the strong affinity of Hg to organic matter. At the intensive lakes, monomethylmercury (MMHg) made up 3.3 % of mean THg and exhibited a positive correlation with total SO 42− (r = 0.55). Further, both THg and MMHg were significantly correlated with conductivity (r = 0.48 and 0.54, respectively) potentially owing to marine inputs, and negatively correlated with pH (r = −0.59 and −0.56 respectively). Significant differences in THg (and MMHg) were observed between the five lakes, the highest concentrations (4.45 and 0.16 ng L −1, respectively) tended to be associated with TOC in lakes and occurred at sites in the northwest, characterized by higher levels of soil organic matter (peat) and soil moisture relative to the other sites. In contrast, surface soil pools of THg ranged between 13.6 and 20.8 μg m −2 across study sites and did not vary significantly, but were typical of global background regions. Nonetheless, the organic rich soils that dominate Ireland are a natural sink for THg, and peat harvesting for energy production may release long-term stores of Hg from deeper soil layers. [ABSTRACT FROM AUTHOR]

Abstract: As a consequence of over 500 years of mining and smelting activities (1490–1995), and of its natural geological occurrence, the soil in the Idrija region is highly contaminated with Hg. In order to assess the present situation regarding the Hg levels in local food samples, concentrations of total mercury (THg) and monomethyl mercury (MeHg) were determined in selected vegetables, mushrooms and fish from the Idrija Hg mine area. Hg levels in the foodstuffs analysed were not very high but were elevated compared to the levels in food from non-contaminated areas. The study showed that THg accumulates in mushrooms (X=5680ng/g dry weight, Min=346ng/g dry weight, Max=17,100 dry weight) and chicory (X=1950ng/g dry weight, Min=86ng/g dry weight, Max=17,100ng/g dry weight). In addition, Se and Cd concentrations were determined by ICP-MS in those vegetable and mushroom species in which the highest Hg levels were found. The levels of Cd and Se were below the threshold levels. Based on data from previous studies, we can conclude that the levels of Hg in food have not diminished significantly during the past 15 years after closure of the Hg mine. Special attention should be given to vegetables such as chicory, representing a local seasonal vegetable eaten frequently. [Copyright &y& Elsevier]

Highlights: [•] Mono- (MMHg) and dimethylmercury (DMHg) were sampled from large volumes of air. [•] Tenax®TA, Carbotrap®B, Bond Elut ENV were evaluated for MMHg collection and storage. [•] Bond Elut ENV allows simultaneous collection of DMHg and MMHg from large air volumes. [•] Bond Elut ENV is most suitable for MMHg determination using purge-and-trap methods. [•] Lowering adsorbents temperature to 4°C significantly improved collection efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Photo-degradation (PD) of monomethylmercury (MMHg) is recognized as the most important process in mercury cycling that maintains MMHg at low concentration in water systems. Chloride ion (Cl−) is present widely in ecosystems and it may have an effect on MMHg PD. In this investigation, MMHg PD with various Cl− concentrations under different light radiation intensity and wavelength were performed in a quartz cylinder reactor. Various light radiations were obtained from xenon and ultraviolet (UV) bulbs. The results showed that the first order reaction coefficient decreased (1.35–0.37h−1) with Cl− concentrations, and increased (0.14–0.76h−1) with UV-B radiation intensity. The wavelength mediated PD rates varied from 0.29h−1 to 0.96h−1. The peak emission of Hg0 was excited by UV-B radiation and Hg0 flux of the reactions without Cl− (94.06ng) was higher than that with Cl− by 1–4 times. All the results suggest that Cl− could block MMHg PD and subsequently influence the end products from PD. The wavelength and light intensity have a significant effect on MMHg PD and Hg0 emission. Calculation of MMHg species (%) at initial and terminal time with various Cl− concentrations show that MMHg species changed by Cl− complexation and thus result in different PD mechanisms and pathways. [Copyright &y& Elsevier]

This study investigated the toxicity and bioaccumulation of monomethylmercury (MMHg) using two freshwater cyanobacteria— Oscillatoria tenuisa and Microcystis aeruginosa—that were isolated from a eutrophic reservoir. Tested concentrations were 1, 10, 50, and 250 μg L−1 of MMHg. The MMHg uptake depended on the phases of growth, period of exposure, and initial concentration of MMHg to which the cyanobacteria were exposed. The growth rate during the logarithmic phase was 0.17 day−1 for O. tenuisa, and 0.05 day−1 for M. aeruginosa in 250 μg L−1 of MMHg. These rates were a factor of 3.5–6 lower than that in the original medium without exposure to MMHg. The accumulation of MMHg by cyanobacteria increased rapidly within 4 weeks from the initial value of 1.2 × 10−4 – 1.6 × 10−4 ng cell−1 on sampling day 2 in the lag phase to 0.92 × 10−3 – 7.5 × 10−2 ng cell−1 on sampling day 28 during the stationary phase. The uptake rate of MMHg in the logarithmic phase cultures greatly exceeded that in the stationary cultures. The accumulation of MMHg by cyanobacteria depended on extracellular organic matter (EOM). Linear correlation analysis indicated a significant and negative correlation between the amount of bioaccumulation of MMHg in cyanobacterial cells and EOM concentration in suspension. Additionally, the effective concentrations (EC) of MMHg for inhibiting the growth of the two cyanobacterial species at 96 h (96 h EC50) were determined to be 340 μg L−1 for M. aeruginosa and 568 μg L−1 for O. tenuisa. The no observed effect concentrations (NOEC) for the two species were 64 μg L−1 and 115 μg L−1, respectively. Preliminary results that were based on SEM-map studies suggest that most of the MMHg accumulated in the cytoplasm (intercellular) of M. aeruginosa. [ABSTRACT FROM AUTHOR]

We examined Hg biogeochemistry in Baihua Reservoir, a system affected by industrial wastewater containing mercury (Hg). As expected, we found high levels of total Hg (THg, 664–7421 ng g−1) and monomethylmercury (MMHg, 3–21 ng g−1) in the surface sediments (0–10 cm). In the water column, both THg and MMHg showed strong vertical variations with higher concentrations in the anoxic layer (>4m) than in the oxic layer (0–4 m), which was most pronounced for the dissolved MMHg (p < 0.001). However, mercury levels in biota samples (mostly cyprinid fish) were one order of magnitude lower than common regulatory values (i.e. 0.3–0.5 mg kg−1) for human consumption. We identified three main reasons to explain the low fish Hg bioaccumulation: disconnection of the aquatic food web from the high MMHg zone, simple food web structures, and biodilution effect at the base of the food chain in this eutrophic reservoir. [Copyright &y& Elsevier]

Abstract: The effect of bacterial growth phase is an aspect of mercury (Hg) methylation that previous studies have not investigated in detail. Here we consider the effect of growth phase (mid-log, late-log and late stationary phase) on Hg methylation by the known methylator Desulfovibrio desulfuricans ND132. We tested the addition of Hg alone (chloride-complex), Hg with Suwannee River natural organic matter (SRNOM) (unequilibrated), and Hg equilibrated with SRNOM on monomethylmercury (MMHg) production by ND132 over a growth curve in pyruvate–fumarate media. This NOM did not affect MMHg production even under very low Hg:SRNOM ratios, where Hg binding is predicted to be dominated by high energy sites. Adding Hg or Hg–NOM to growing cultures 24h before sampling (late addition) resulted in ~2× greater net fraction of Hg methylated than for comparably aged cultures exposed to Hg from the initial culture inoculation (early addition). Mid- and late-log phase cultures produced similar amounts of MMHg, but late stationary phase cultures (both under early and late Hg addition conditions) produced up to ~3× more MMHg, indicating the potential importance of growth phase in studies of MMHg production. [Copyright &y& Elsevier]

The effect of dredged sediment reuse on the production and bioconcentration of monomethylmercury (MMHg) was investigated by examining sediments and ragworms found in dredge material banks and surrounding sites in the Venice Lagoon, Italy. Total Hg concentrations in the surface 20 cm of sediments were higher in the banks than in the surrounding sites, but MMHg concentrations were similar, which suggests reduced MMHg production in the banks. Monomethylmercury content in ragworms was significantly lower ( p < 0.05) in the banks than in the surrounding sites. In pore water, concentrations of both sulfate and Fe decreased with depth in the upper 20 cm of the dredge banks. In contrast, sulfate concentrations were constant with depth and large amounts of dissolved Fe occurred in the upper 20 cm of sediments of surrounding sites. Continuous sulfate reduction and possible precipitation of iron sulfide may decrease the production and bioconcentration of MMHg in the dredge material banks compared to the surrounding sites. Overall, the production of MMHg in sediments and its bioconcentration in benthic organisms were connected to the process of sediment diagenesis of organic matter through the control of pore water and sediment geochemistry involving iron and sulfur. [ABSTRACT FROM AUTHOR]

Abstract: In order to evaluate the role of hypoxic conditions of overlying water in the benthic flux and speciation of Hg, we analyzed sediment cores from hypoxic or oxic sites downstream from a sewage outfall in the Damyang Riverine Wetland, Korea. Each core was analyzed for total Hg (THg), monomethylmercury (MMHg), and elemental Hg (Hg0) from sediment, and for THg and MMHg from pore water. Hypoxic conditions of the overlying water near the sewage outfall were associated with a peak production of Hg0, but the lowest production of MMHg, in the upper 2cm sediments. The benthic fluxes of THg and MMHg were estimated at 130–2109ngm−2 day−1 and −12 to 260ngm−2 day−1, respectively. The order of MMHg flux from sediment to overlying water at each site did not follow the order of MMHg concentration in sediment, but was highest in hypoxic water conditions. The results suggest that maintaining oxic conditions in wetland water is important for decreasing the transfer of MMHg from sediment into overlying water. [Copyright &y& Elsevier]

Abstract: Sediment cores were collected from two shallow sites in the Venice Lagoon, Italy, in order to study the lability of organic matter and the methylation rate of inorganic Hg(II). Measurements were made of concentrations of total Hg and monomethylmercury (MMHg), Hg(II) methylation rates, concentrations of total organic carbon and total nitrogen in the sediments, and dissolved sulfate, sulfide, and alkalinity in sedimentary pore waters. A positive linear relationship was detected between the specific Hg(II) methylation rate constant and the fraction of total Hg comprised of MMHg (%MMHg/Hg), indicating that short-term Hg(II) methylation rate reflects a long-term accumulation of MMHg in sediment. In addition, the %MMHg/Hg and specific Hg(II) methylation rate constant in sediment increased with decreasing ratios of total organic carbon to total nitrogen (C/N), whereas concentrations of dissolved sulfate, sulfide, and alkalinity in pore water remained constant. This result suggests that the Hg(II) methylation rate was affected by lability of organic matter. In particular, surface sediments, which contained large fractions of fresh algal organic material (C/N=5.8–7.8), showed higher Hg(II) methylation rates than did deeper sediments (C/N>10). Our results indicate that the C/N ratio can be used as a proxy for the lability of organic matter that influences Hg(II) methylation rate in sulfate-rich marine sediments. [ABSTRACT FROM AUTHOR]

Surface sediments and sediment cores were collected in a mercury (Hg)-contaminated lagoon, namely Largo do Laranjo - Ria de Aveiro, Portugal and analysed in order to establish the monomethylmercury (MeHg) behaviour in this kind of environment. In surface sediments, this compound was only detected in one place (13.2 ng g-1 (dry weight)). In this site, it was determined one of the lowest redox potentials (22 mV), indicative of oxic/anoxic conditions, which favours Hg methylation by enhancing the sulphate-reducing bacteria activity. However, the MeHg percentage obtained was low, namely less than 0.1% of the total Hg. This is probably due to Hg deposition with organic matter and iron oxyhydroxides, decreasing Hg availability to methylation. At the deeper layers, MeHg was also determined, reaching 46.4 ng g-1 (dry weight) and representing less than 0.1% of the total Hg. The higher MeHg percentages were observed near the surface, where Hg seems to be faster methylated as a result of the lower sulphide concencentrations that render bioavailable the inorganic Hg. At depth the low MeHg percentages obtained are due to the formation of HgS and to the adsorption of Hg to iron monosulphides. [ABSTRACT FROM AUTHOR]

Abstract: A method for mercury speciation analysis on cell lines of the human central nervous system has been developed in order to study the intracellular mercury uptake and the distribution of mercury species. Glioblastoma (U373) and neuroblastoma (B103) human cell lines were exposed to different levels of monomethylmercury (MMHg). Mercury species were simultaneously extracted with tetramethylammonium hydroxide (TMAH) using a closed-vessel microwave system. The analysis was performed by ethylation and injection into a CGC-pyro-AFS system. An excellent procedural detection limit of 0.008 µM for MMHg was achieved. Recovery studies of cell extracts spiked with MMHg were done to check the reliability of the method and in all cases satisfactory recoveries (90–108%) were obtained. Remarkable differences between MMHg levels inside both human glioblastoma and neuroblastoma cell lines were found in initial experiments, which seem to be related to different genotoxic effects. [Copyright &y& Elsevier]

The potential for marsh plants to be vectors in the transport of mercury species was studied in the natural, mature, tidal China Camp salt marsh on San Pablo Bay. The fluxes of organic matter, mercury (THg), and monomethylmercury (MeHg) were studied in natural stands of Spartina Jbliosa and Salicornia virginica. Seasonal fluxes from the sediment into aboveground biomass of live plants and subsequent transfer into the dead plant community by mortality were measured. Loss of THg and MeHg from the dead plant community through fragmentation, leaching, and excretion were calculated and were similar to net uptake. Seasonal data were added up to calculate annual mass balances. In S. foliosa, annual net production was 1,757 g DW m-2, and the annual net uptakes in the aboveground biomass were 305 μig THg m-2 and 5.720 μg MeHg m-2. In S. virginica, annual net production was 2,117 g DW m-2, and the annual net uptakes in aboveground biomass were 99.120 jig THg m-2 and 1.990 μtg MeHg m-2. Of both plant species studied, S. foliosa had a slightly lower production rate but greater mercury species uptake and loss rates than S. virginica, and, consequently, it is to be expected that S. foliosa matter may affect the local and possibly the regional food web relatively more than S. virginica. However, the actual effects of the input of mercury-species-containing plant-derived particulate matter into the food webs would depend on trophic level, food preference, seasonal cycle of the consumer, total sediment surface area vegetated, location of the vegetation in the marsh landscape, and estuary bay landscape. Since the levels of mercury species in dead plant material greatly exceed those in live plant material (on a dry weight basis), detritivores would ingest greater mercury species concentrations than herbivores, and consumers of S. foliosa would ingest more than consumers of S. virginica. The greatest THg and MeHg losses of both plant species due to mortality and to fragmentation-leaching-excretion occurred in late spring and early autumn, which corresponds to peak MeHg levels observed in sediments of coastal systems of previous studies, suggesting enhanced THg-MeHg export from the marsh to the nearshore sediment. [ABSTRACT FROM AUTHOR]

Abstract: Optimum conditions for headspace solid-phase microextraction (HS-SPME) in the analysis of monomethylmercury (MeHg) have been determined. Sodium tetra(n-)propylborate (NaBPr4) is used as derivatization reagent to promote volatility. A simple aluminium bar was used to cool the SPME fiber to about 2°C during the equilibration phase just before extraction. HS-SPME was performed using different fibers. The 100μm polydimethylsiloxane (PDMS) and 65μm polydimethylsiloxane-divinylbenzene (PDMS-DVB) fibers showed the best results. Although the extraction efficiency for MeHg derivative of the polydimethylsiloxane-Carboxen (PDMS-CAR) fiber is similar to the other fibers, desorption of MeHg derivative from a PDMS-CAR fiber is poor. Factors affecting the HS-SPME process such as adsorption and desorption times, ionic strength (salting-out) and extraction temperature have been evaluated and optimized thoroughly. The highest extraction efficiency for the PDMS fiber was obtained by extraction at a low temperature (2°C) immediately after equilibration at 30°C. With the PDMS-DVB and PDMS-CAR fiber improvement of extraction efficiency at lower temperatures is negligible. Repeated extraction out of the same vial revealed that about 30% of MeHg derivative is extracted from the headspace with a PDMS fiber at 2°C and about 70% with a PDMS-DVB fiber. Repeated extraction with two different fiber coatings showed that the PDMS-CAR fiber also extracts about 70% but that the desorption is incomplete. Attempts to improve the desorption failed due to degradation of the MeHg derivate at high injection temperatures. The limit of detection (3σ) was 16pg/L MeHg. The relative standard deviation (n =8) for 100pg/L of MeHg was found to be 5%. Linearity of the HS-SPME-GC-atomic emission detection method was established over at least two orders of magnitude in the range 0–2000pg/L. Recovery of a surface water sample spiked at 2ng/L was 85%. The suitability of the procedure was demonstrated by analysis of a surface water sample that showed a concentration of 100pg/L MeHg. The optimized method can be used with standard commercial equipment without further adaptations. [Copyright &y& Elsevier]

Monomethylmercury (CH3Hg+) is both the most ecologically significant and the least well characterized species of mercury in environmental settings. Our understanding of the environmental speciation behavior of this compound is limited both as the result of lesser available laboratory data (when compared to inorganic mercury) as well as the uncertainties associated with our understanding of the properties of environmental ligands. A careful examination and synthesis of data reported in the technical literature led to the following findings: (1) a 25°C, zero ionic strength bicarbonate ion complexation constant estimate is remarkably close to an earlier reported value at 0.4M: CH3Hg+ + HCO3- ...CH3HgHCO3, log10K = 2.6 (+0.22, 1 SD), (2) three 25°C zero ionic strength reaction constants reported by DeRobertis et al. (1998) were confirmed to within ~ +0.1 log10K units: CH3Hg+ +OH-...CH3HgOH, log10K = 9.47; 2CH3Hg+ +H2O...(CH3Hg)2OH+ +H+, log10K = -2.15; CH3Hg+ +Cl-...CH3HgCl, log10K = 5.45, (3) "best estimate" literature complexation constants corrected to zero ionic strength include: CH3Hg+ +F-...CH3HgF, log10K = 1.75 (20°C corr. Schwartzenbach and Schellenberg, 1965); CH3Hg+ +Br -...CH3HgBr, log10K = 6.87 (20°C corr. Schwartzenbach and Schellenberg, 1965); CH3Hg+ +l -...CH3Hgl, log10K = 8.85 (20°C corr. Schwartzenbach and Schellenberg, 1965); and CH3Hg+ +SO4 ²_...CH3HgSO4-, log10K = 2.64 (25°C, DeRobertis et al., 1998), (4) literature reported values for simulating monomethylmercury complexation with the carbonate ion may be too low: CH3Hg+ +CO3 ²-...CH3HgCO3-, log10K = 6.1 (Rabenstein et al., 1976; Erni, 1981), and (5) "best estimate" constants for simulating methyl mercury complexation with reduced environmental sulfur species include: CH3Hg+ +S² -...CH3HgS-, log10K = 21.1; CH3Hg+ +SH-...CH3HgSH, log10K = 14.5 (H+ +SH-..H2S, log10K = 6.88; Dyrssen and Wedborg, 1991); CH3Hg+ +RS-...CH3HgSR, log10K = 16.5 (H+ +RS-..RSH, log10K = 9.96; Qian et al., 2002); and CH3Hg+ +CH3HgS¹ -..(CH3Hg)2S, log10K = 16.32 (Schwartzenbach and Schellenberg, 1965; Rabenstein et al., 1978; and Erni, 1981). [ABSTRACT FROM AUTHOR]

The sequestering capacity of synthetic and naturally occurring polycarboxylate ligands towards monomethylmercury( II) was evaluated by stability quantitative data on the interaction of CH3Hg+ with different molecular weight synthetic polyacrylates (2 and 20 kDa average M.wt) and alginate (70-100 kDa) extracted from brown algae Macrocystis pyrifera. The influence of ionic medium was evaluated by measurements on the CH3Hg+-polyacrylate systems in NaNO3 medium at different ionic strengths (0.10, 0.25, 0.50 and 0.75 mol -1), and a Debye-Hückel type equation was used for the dependence of complex formation constants on ionic strength. Measurements on the CH3Hg+-alginate system were carried out at l=0.10 mol L-1 in NaNO3 medium. By using the stability data, the sequestering capacity of both ligands towards monomethylmercury(II) was determined at different pH values. Results obtained show that the binding ability of polyacrylic ligands (PAA) is stronger than the alginate (AA), following the trend PAA (20 kDa) > PAA (2 kDa) > AA. [ABSTRACT FROM AUTHOR]

Surface sediments (0–2cm) were collected at 40 sites along the Tagus Estuary in July and December 2004. The sediments were analysed for total mercury, monomethylmercury (MMHg) and interpretative parameters (e.g. redox potential, pH, Corg). No significant differences in total Hg, pH, Al, Fe, Mn and Corg were found between sediments collected in the two periods, but MMHg concentrations were higher in July. On average sediments were warmer and more reducing in summer. On the basis of these results, an increase of 7kg of MMHg (+37%) in surface sediments of the Tagus Estuary was estimated. Presumably higher temperatures in summer promote the increase of microbial activity and higher methylation rates. The alterations observed in this study point to the potential importance of seasonal changes in MMHg production at surface sediments with eventual changes in the MMHg uptake by benthic invertebrates and other organisms in the food web. [Copyright &y& Elsevier]

Fifty four samples of surface sediments (1-cm of thickness) and a gravity core of 154-cm long were collected in the Vigo Ria, NW of Iberian Peninsula. In the laboratory the sediments were oven dried at 40°C, desegregated, homogenised and analyzed for total Hg, monomethylmercury (MMHg), Al, and particulate organic carbon (POC). Mercury in sediments varied within a broad range: 0.09 to 8.9 nmol g−1 the higher concentrations being found in the shipyards and docks areas of Vigo port (southern–middle Ria zone). No correlation was found between Hg and POC. The good exponential correlation between total Hg and Al levels suggests that Hg is closely associated with the fine fraction of sediments. Monomethylmercury concentrations in surface sediments ranged between <1.4 (DL) and 8.5 pmol g−1 being the spatial distribution similar to that observed for total Hg. The lack of correlations MMHg–Al and MMHg–POC suggests that in situ processes of methylation/demethylation are responsible for MMHg distribution rather than the sediment characteristics. Additionally, these processes appear mercury-dependent only for Hg concentrations above 2.5 nmol g−1. On the basis of these results it was estimated that 155 kg of Hg (0.1% MMHg) are present in the surface sediments of Vigo Ria, being 61% of anthropogenic origin. [ABSTRACT FROM AUTHOR]

Abstract: An analytical methodology for monomethylmercury (MMHg) determination in aquatic plant tissues with low detection limit (346pgg−1) is proposed. It consists of acid digestion (HBr/CuSO4), cleanup step with a Na2S solution, pre-concentration procedure using a dithizone solution in toluene and quantification by GC–ECD. The performance of the methodology has been tested by determining the MMHg concentrations in the certified reference material Fucus Sea Plant Homogenate—IAEA-140/TM (CRM) and in leaves, stems and roots of the salt marsh plants Sarcocornia fruticosa and Halimione portulacoides. The results obtained for CRM were not statistically different (α =0.056) from the certified value and repeatability was lower than 2.5% for the plant samples analyzed. This coefficient of variation was similar to those obtained in the externally quality control using within-batch and between-batch (<1.4%). [Copyright &y& Elsevier]

Bioaccumulation factors (BAFs) for inorganic mercury in earthworms are usually < 1; however, factors up to ∼10 have been reported. Little information is available concerning the bioaccumulation of organic mercury in earthworms from actual contaminated soils and thus there has been uncertainty in the risk characterization phase of ecological risk assessments of mercury-contaminated sites. This study was initiated to determine the rate of uptake and bioaccumulation of total mercury (T-Hg) and monomethylmercury (MMHg) in Eisenia fetida from soils which have been contaminated with mercury for approximately 30 years. The study consisted of a 28-day uptake phase in three mercury-contaminated soils and one soil with background concentrations of mercury followed by a 14-day depuration phase in background soil only. Total mercury concentrations in the study soils ranged from 85 to 11,542 μg kg−1 dry weight soil; MMHg concentrations ranged from 1.12 to 7.35 μg kg−1 dry weight soil. Time to 90% steady states for T-Hg ranged from 36 to 42 days. A steady state did not occur for any of the MMHg exposures during the 42-day study; estimated time to 90% steady state varied from 97 to 192 days. BAFs for T-Hg ranged from 0.6 to 3.3. BAFs for MMHg ranged from 175 to 249. The BAFs for T-Hg and MMHg were larger in earthworms exposed to the lower contaminated soils and smaller in the higher mercury-contaminated soils. The absolute concentrations of T-Hg and MMHg bioaccumulated in E. fetida, however, were higher in the earthworms exposed to the higher mercury soils and lower in the less mercury-contaminated soils. [ABSTRACT FROM AUTHOR]

Abstract: Sodium tetra(n-propyl)borate (NaBPr4) was introduced as derivatization reagent to extend the possibility for determining ethyl-mercury compounds. This study investigated the artifact formation of methyl- and ethyl-mercury compounds during NaBPr4 derivatization, together with the influence of this artifact on organomercury analysis in environmental samples. The artifact methyl- and ethyl-mercury compounds during NaBPr4 derivatization were evident and depended strongly on the amount of Hg(II) present in the solution for derivatization. Some unidentified organomercury compounds were found when the amount of Hg(II) in the derivatization solution was over 1μg. The amounts of NaBPr4 and acetate buffer and the presence of organometallic compounds other than organomercury showed little influence on the artifact effect. The artifact monoethylmercury encompasses 0.99–2.9% of the amount of Hg(II) present and interferes strongly with the monoethylmercury analysis. The formation rate of artifact monomethylmercury is much lower and ca. 0.03–0.28% of the Hg(II) present. The artifact affects remarkably the monomethylmercury analysis for solid samples when these have a low ratio of monomethylmercury-to-total Hg concentrations (≤0.003) and the recovery of Hg from the samples is high. Mathematical correction seems to be difficult due to the low reproducibility of this artifact effect. Formation of artifact organomercury compounds caused during NaBPr4 derivatization may lead to false Hg speciation and overestimate concentrations of organomercury compounds. [Copyright &y& Elsevier]