Physical, Chemical, and Biological Factors that Contribute to the Variability of Mercury Concentrations in Largemouth Bass Micropterus salmoides from Missouri Reservoirs

Large-bodied predatory sportfish from Missouri reservoirs can contain elevated methylmercury concentrations that are of concern to the health of consumers. The concentration of total mercury (tHg) in the muscle (which > 95% is in the methylated-Hg form) of harvestable-sized largemouth bass (Micropterus salmoides; LMB) was examined to determine which factors contributed to the variability of tHg concentration in sportfish populations among Missouri reservoirs. Mean tHg concentrations in LMB from each reservoir were compared to physical and chemical characteristics of the reservoir and to biological attributes of each LMB population. Low concentrations of tHg (70-170 ng/g wet weight) in LMB from large reservoirs (surface area ≥ 35,680 acres) were likely related to the dilution of chemical Hg forms with water volume and depth. The highest tHg concentrations in LMB (268-542 ng/g) were from reservoirs with low particulate inorganic material (< 1.5 mg/L) and chlorophyll a concentrations (< 14.6 μg/L), and from LMB populations with a low proportion of large fish (proportional size distribution of LMB > 12 inches was < 33%). These relationships suggest that resource competition among LMB likely contributed to tHg bioaccumulation in reservoirs < 930 acres. Small reservoirs located in northern Missouri also may have greater methylation potential due to warmer water temperatures and anoxic conditions, but more data are needed to confirm these interactions. Fish consumption advisories for reservoirs with large surface area and volume could be reduced from one fish meal per month to one per week. To improve Missouri fisheries and protect consumers, management strategies to limit methylation and improve fish growth should be considered to reduce methylmercury bioaccumulation in small- and medium-sized reservoirs.

Mercury and selenium concentrations in fishes of the Upper Colorado River Basin, southwestern United States: A retrospective assessment

Mercury (Hg) and selenium (Se) are contaminants of concern for fish in the Upper Colorado River Basin (UCRB). We explored Hg and Se in fish tissues (2,324 individuals) collected over 50 years (1962-2011) from the UCRB. Samples include native and non-native fish collected from lotic waterbodies spanning 7 major tributaries to the Colorado River. There was little variation of total mercury (THg) in fish assemblages basin-wide and only 13% (272/1959) of individual fish samples exceeded the fish health benchmark (0.27 μg THg/g ww). Most THg exceedances were observed in the White-Yampa tributary whereas the San Juan had the lowest mean THg concentration. Risks associated with THg are species specific with exceedances dominated by Colorado Pikeminnow (mean = 0.38 and standard error ± 0.08 μg THg/g ww) and Roundtail Chub (0.24 ± 0.06 μg THg/g ww). For Se, 48% (827/1720) of all individuals exceeded the fish health benchmark (5.1 μg Se/g dw). The Gunnison river had the most individual exceedances of the Se benchmark (74%) whereas the Dirty Devil had the fewest. We identified that species of management concern accumulate THg and Se to levels above risk thresholds and that fishes of the White-Yampa (THg) and Gunnison (Se) rivers are at the greatest risk in the UCRB.

Nanoparticle-based 'turn-on' scattering and post-sample fluorescence for ultrasensitive detection of water pollution in wider window

Ultrasensitive detection of heavy metal ions in available water around us is a great challenge for scientists since long time. We developed an optical technique that combines Rayleigh scattering of UV light (365 nm) and post-sample fluorescence detection from colloidal silver (Ag) nanoparticles (NPs) having a surface plasmon resonance (SPR) band at 420 nm. The efficacy of the technique is tested by the detection of several model toxic ions, including mercury, lead, and methylmercury in aqueous media. The light scattering from the Hg-included/inflated Ag NPs at 395 nm was observed to saturate the light sensor even with ppm-order concentrations of Hg ions in the water sample. However, the pollutant is not detected at lower concentrations at this wavelength. Instead, the fluorescence of a high-pass filter (cut-off at 400 nm) at 520 nm is applied to detect pollutant concentrations of up to several hundreds of ppm in the water sample. We also detected lead and methylmercury as model pollutants in aqueous media and validated the efficacy of our strategy. Finally, we report the development of a working prototype based on the strategy developed for efficient detection of pollutants in drinking/agricultural water.

Mercury accumulation in freshwater and marine fish from the wild and from aquaculture ponds

We analysed the total mercury (Hg) accumulation in bodies and gut contents of 13 species of marine wild fish, 7 species of wild freshwater fish and 4 species of farmed fish. In addition, metal concentrations were recorded in water, sediment, fish prey and fodder materials, to track the dynamics of bio-accumulation. Cultured freshwater fish were collected at four Austrian farms and compared with samples obtained from markets. Wild marine fish were collected at Santa Croce bank, in Italy (Mediterranean Sea). Metal accumulation varied with sampling site, species, and age (or weight) of fish. Wild marine fish exhibited higher levels than wild freshwater fish, which in turn had higher Hg levels than cultured freshwater fish. Mercury increased according to trophic levels of consumers. Total Hg contents in muscle of cultured and wild freshwater fish sampled in 2006-2008 did not exceed legal nutritional limits. Similarly, in market samples of trout and carp collected in 2019, we found low or undetectable concentrations of total Hg in muscle tissue. In contrast, some marine fish (both market samples and some species from coastal waters) exceeded the legal limits. Environmental contamination, food webs and biological factors are the main causes of Hg accumulation in fish. Our results reflect the actual differences between specific European sites and should not be generalized. However, they support the generally increasing demand for monitoring mercury pollution in view of its impact on human health and its value as an indicator of ecosystem contamination.

Mercury in Populations of River Dolphins of the Amazon and Orinoco Basins

In the Amazon and Orinoco basins, mercury has been released from artisanal and industrial gold mining since the Colonial time, as well as a result of deforestation and burning of primary forest, that release natural deposits of methyl mercury, affecting the local aquatic vertebrate fauna. This study reports the presence of mercury in river dolphins' genera Inia and Sotalia. Mercury concentrations were analysed in muscle tissue samples collected from 46 individuals at the Arauca and Orinoco Rivers (Colombia), the Amazon River (Colombia), a tributary of the Itenez River (Bolivia) and from the Tapajos River (Brazil). Ranges of total mercury (Hg) concentration in muscle tissue of the four different taxa sampled were: I. geoffrensis humboldtiana 0.003-3.99 mg kg^-1 ww (n = 21, M_e = 0.4), I. g. geoffrensis 0.1-2.6 mg kg^-1 ww (n = 15, M_e = 0.55), I. boliviensis 0.03-0.4 mg kg^-1 ww (n = 8, M_e = 0.1) and S. fluviatilis 0.1-0.87 mg kg^-1 ww (n = 2, M_e = 0.5). The highest Hg concentration in our study was obtained at the Orinoco basin, recorded from a juvenile male of I. g. humboldtiana (3.99 mg kg^-1 ww). At the Amazon basin, higher concentrations of mercury were recorded in the Tapajos River (Brazil) from an adult male of I. g. geoffrensis (2.6 mg kg^-1 ww) and the Amazon River from an adult female of S. fluviatilis (0.87 mg kg^-1 ww). Our data support the presence of total Hg in river dolphins distributed across the evaluated basins, evidencing the role of these cetaceans as sentinel species and bioindicators of the presence of this heavy metal in natural aquatic environments.

Dissolved organic matter reduces the effectiveness of sorbents for mercury removal

Mercury (Hg) contamination of soils and sediments impacts numerous environments worldwide and constitutes a challenging remediation problem. In this study, we evaluate the impact of dissolved organic matter (DOM) on the effectiveness of eight sorbent materials considered for Hg remediation in soils and sediments. The materials include both engineered and unmodified materials based on carbon, clays, mesoporous silica and a copper alloy. Initially, we investigated the kinetics of Hg(II) complexation with DOM for a series of Hg:DOM ratios. Steady-state Hg-DOM complexation occurred within 48 to 120 h, taking longer time at higher Hg:DOC (dissolved organic carbon) molar ratios. In subsequent equilibrium experiments, Hg(II) was equilibrated with DOM at a defined Hg:DOC molar ratio (2.4 · 10^-6) for 170 h and used in batch experiments to determine the effect of DOM on Hg partition coefficients and sorption isotherms by comparing Hg(II) and Hg-DOM. Hg sorption capacities of all sorbents were severely limited in the presence of DOM as a competing ligand. Thiol-SAMMS®, SediMite™ and pine biochar were most effective in reducing Hg concentrations. While pine biochar and lignin-derived carbon processed at high temperatures released negligible amounts of anions into solution, leaching of sulfate and chloride was observed for most engineered sorbent materials. Sulfate may stimulate microbial communities harboring sulfate reducing bacteria, which are considered one of the primary drivers of microbial mercury methylation in the environment. The results highlight potential challenges arising from the application of sorbents for Hg remediation in the field.

Preliminary investigation of polymer-based in situ passive samplers for mercury and methylmercury

Development of an in situ passive sampler for mercury (Hg), and its toxic form, methylmercury (MeHg), using simple polymer films, was explored for the potential to make an efficient and environmentally relevant monitoring tool for this widespread aquatic pollutant. The sulfur-containing polymers polysulfone (PS), and polyphenylene sulfide (PPS), were found to accumulate both MeHg and inorganic Hg (iHg), whereas polyethylene (PE) sorbed iHg but not MeHg, and polyoxymethylene (POM) and polyethersulfone (PES) films had low affinity for both Hg species. Uptake rates of Hg species into polymers were linear over two weeks, and dissolved organic matter at natural levels had no effect on partitioning of MeHg or iHg to the polymers. Sorption of MeHg to PS and PPS from three estuarine sediments correlated with uptake into diffusive gel-type samplers over time, and in PPS, with accumulation by the estuarine amphipod, Leptocheirus plumulosus. These polymers had lower MeHg adsorption rates, but are simpler to assemble, than diffusive gel-type samplers. Higher contaminant concentrations in polymer and gel-type samplers corresponded with porewater concentrations across sediments, suggesting they sample the dissolved MeHg pool, whereas MeHg levels in amphipods were more elevated with higher bulk sediment MeHg, which may reflect feeding strategy. While polymers with higher affinity for MeHg and iHg are needed for some environmental applications, this work suggests a simple sampling approach has potential for time-integrated, environmentally-meaningful MeHg monitoring in contaminated sediments.

The AQUA-MER databases and aqueous speciation server: A web resource for multiscale modeling of mercury speciation

To assess the chemical reactivity, toxicity, and mobility of pollutants in the environment, knowledge of their species distributions is critical. Because their direct measurement is often infeasible, speciation modeling is widely adopted. Mercury (Hg) is a representative pollutant for which study of its speciation benefits from modeling. However, Hg speciation modeling is often hindered by a lack of reliable thermodynamic constants. Although computational chemistry (e.g., density functional theory [DFT]) can generate these constants, methods for directly coupling DFT and speciation modeling are not available. Here, we combine computational chemistry and continuum-scale modeling with curated online databases to ameliorate the problem of unreliable inputs to Hg speciation modeling. Our AQUA-MER databases and web server (https://aquamer.ornl.gov) provides direct speciation results by combining web-based interfaces to a speciation calculator, databases of thermodynamic constants, and a computational chemistry toolkit to estimate missing constants. Although Hg is presented as a concrete use case, AQUA-MER can also be readily applied to other elements. © 2019 Wiley Periodicals, Inc.

Using blood and feathers to investigate large-scale Hg contamination in Arctic seabirds: A review

Mercury (Hg), because of its deleterious effects on wildlife and its high concentrations in polar regions, has been widely studied in the Arctic. This provided important information regarding food web contamination, spatial and temporal trends of Hg in ecosystems or risk assessments for wildlife and Humans. Among the Arctic biota, seabirds have been among the most studied species due to their sensitivity to this toxicant, their role as bioindicators of the contamination status of their environment, and their consumption by Arctic communities. However, most studies that investigated Hg in Arctic seabirds focused on measurements in internal organs or in eggs, while few investigations have been performed on blood and feathers, despite the relevant and complementary information they provide. Here, we first provide a detailed overview of the specific information blood and feathers can bring when investigating Hg contamination of Arctic seabirds, including new knowledge on the poorly studied non-breeding period. Second, we perform a comprehensive review of the use of blood and feathers as non-lethal tissues to study Hg in Arctic seabirds. This review demonstrates important interspecific variations in Hg blood concentrations according to seabird trophic status, with seaducks generally presenting the lowest Hg concentrations while auks have the highest ones. However, all the observed Hg concentrations are below the admitted toxicity thresholds. Hg concentrations in feathers follow similar trends and gulls appear to be the most contaminated species, likely as a consequence of contrasting migratory and overwintering strategies. This review also confirms strong spatial variations with higher concentrations found in the Canadian Arctic and Pacific waters than in Greenland and the European Arctic. It also identifies some major understudied areas such as West Greenland, Aleutian Islands and Russia. Finally, we provide a thorough review of the current knowledge regarding molting patterns in Arctic seabirds, which is an essential information to interpret Hg concentrations measured in feathers. Overall, our results point out the importance of blood and feathers in seabird ecotoxicological assessments and highlight the need for large scale international collaborations and research programs.

Distribution of dissolved gaseous mercury (DGM) and its controlling factors in the Yellow Sea and Bohai Sea

Elemental mercury (Hg⁰) is the major form of mercury (Hg) emitted into the environment via anthropogenic activities, resulting in the distribution of Hg worldwide via atmospheric transport. Hg⁰ in oceans plays an important role in global Hg cycling, mainly by affecting the oceanic-atmospheric exchange of Hg. Due to the large amounts of Hg that are released into Chinese coastal seas from rivers and other sources, Chinese coastal seas are thought to be important sources of Hg in open oceans and in the atmosphere. There have been some studies on the distribution of dissolved gaseous mercury (DGM) in Chinses coastal seas and their controlling factors. However, most of these studies were focused on the surface seawater. There is still a lack of comprehensive study on the DGM through the entire water column in Chinese coastal seas. In this study, two cruises were conducted in August 2017 and in December 2017 to January 2018 to identify the distribution of DGM and its controlling factors in the Yellow Sea (YS) and the Bohai Sea (BS). The concentrations of DGM were higher in summer (167.5 ± 121.4 pg/L) than in winter (41.5 ± 25.5 pg/L), reflecting a significant seasonal variation in DGM. DGM concentrations in the BS and the YS were higher than in open oceans and lower than in some coastal regions. DGM concentrations were generally highest in the BS, followed by the northern YS and the southern YS in summer, whereas the reverse trend was observed in winter. DGM in seawater presented a complicated spatial distribution pattern, with high DGM concentration areas present both nearshore and offshore areas. This result indicates that both terrestrial input and in situ production may play important roles in controlling the DGM distribution. Correlation and multiple regression analyses suggested that temperature (T) and wind speed may be important factors affecting the seasonal variation in DGM in the YS and the BS, and reactive Hg (RHg), dissolved Hg (DHg), dissolved oxygen (DO) and suspended particulate matter (SPM) play important roles in controlling the spatial distribution of DGM.

A prophylactic multi-strain probiotic treatment to reduce the absorption of toxic elements: In-vitro study and biomonitoring of breast milk and infant stools

Potential exposure to toxic elements initially occurs during gestation and after birth via breast milk, which is the principal source of nutrients for infants during the first months of life. In this study, we evaluated whether maternal oral supplementation with a multi-strain probiotic product can protect infants from exposure to arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) via breast milk. In-vitro studies of the bacterial strains present in this probiotic product showed a high bacterial tolerance for As, Cd, Hg, and Pb, and good binding capacity for Cd, Hg, and Pb (72%, 81%, and 64%, respectively) within 1 h of contact. We evaluated concentrations (5 mg L^-1 for Cd and Pb, and 2 mg L^-1 for Hg) that largely exceeded the provisional tolerable weekly intake of these toxic elements via food or water applicable for human consumption. Changes in the levels of these elements in breast milk and newborn stools were evaluated in the control (orally supplemented with placebo) and experimental (orally supplemented with probiotic) groups at birth (t0), 15 days (t15), and 30 days (t30) after delivery. Elemental analysis of breast milk did not show significant differences between the control and experimental groups at different stages of lactation; however, stool samples obtained from newborns of mothers supplemented with the probiotic product showed that Cd levels were significantly reduced (by 26%) at t15 compared with the levels of the controls. Our data did not show an association between concentration of toxic elements in breast milk and that in newborn stools. Indeed, the concentration of Cd, Hg, and Pb in breast milk decreased during the lactation period, whereas the levels of these elements in newborn stools were stable over time. Although our in-vitro data indicate that the consortium of these probiotic strains can absorb toxic compounds, this study was limited by its small sample size and potential uncontrolled confounding effects, such as maternal diet and lifestyle. Therefore, we could not confirm whether prophylactic use of this probiotic product can reduce the absorption of toxic elements. The risk assessment in the studied population evidenced a margin of exposure (MOE) of 1, or between 1 and 10 for Pb, and lower than 50 for As. This poses a potential risk for breastfed infants, indicating that interventions aimed to avoid breastfeeding-related health risks remain a major challenge in public health.

Physio-chemical effects of freshwaters on the dissolution of elementary mercury

Elemental mercury (Hg⁰) is widely used by Artisanal and small-scale gold miners (ASGMs) to extract gold from ore. Due to the unavailability of appropriate waste disposal facilities, Hg⁰-rich amalgamation tailings are often discharged into nearby aquatic systems where the Hg⁰ droplets settle in bottom sediment and sediment-water interfaces. Hg⁰ dissolution and following biogeochemical transformations to methylmercury (MeHg) have been concerned owing to its potential risk to human health and the ecosystem. For reliable estimates of Hg exposure to human bodies using pollutant environmental fate and transport models, knowledge of the Hg⁰ dissolution rate is important. However, only limited literature is available. Therefore, it was investigated in this study. Dissolution tests in a 'dark chamber' revealed that an increase in medium pH resulted in a decrease in the dissolution rate, whereas, a large Hg⁰ droplet surface area (SA) and high Reynolds number (Re) resulted in a faster dissolution. A multivariate first order dissolution model of the form:kˆ=-7.9×10^-5[pH]+7.0×10^-4[logRe]+7.9×10^-4[SA]-2.5×10^-3 was proposed (adjusted R² = 0.99). The Breusch-Pagan and White heteroscedasticity tests revealed that the model residuals are homoscedastic (p-value = 0.05) at the 5% significance level. Parameter sensitivity analysis suggests that slow mercury dissolution from the Hg⁰ droplets to aquatic systems might mask emerging environmental risk of mercury. Even after mercury usage in ASGM is banned, mercury dissolution and following contamination will continue for about 40 years or longer owing to previously discharged Hg⁰ droplets.

Occurrence, Distribution and Risk Assessment of Mercury in Multimedia of Soil-Dust-Plants in Shanghai, China

The urban environment is a complex ecosystem influenced by strong human disturbances in multi-environmental media, so it is necessary to analyze urban environmental pollutants through the comprehensive analysis of different media. Soil, road dust, foliar dust, and camphor leaves from 32 sample sites in Shanghai were collected for the analysis of mercury contamination in soil–road dust–leaves–foliar dust systems. Mercury concentrations in surface soils in Shanghai were the highest, followed by road dust, foliar dust, and leaves, successively. The spatial distribution of mercury in the four environmental media presented different distribution patterns. Except for the significant correlation between mercury concentrations in road dust and mercury concentrations in leaves (r = 0.56, p < 0.001), there was no significant correlation between the other groups in the four media. Besides this, there was no significant correlation between mercury concentrations and land types. The LUR (Land use regression) model was used to assess the impact of urbanization factors on mercury distribution in the environment. The results showed that soil mercury was affected by factories and residential areas. Foliar dust mercury was affected by road density and power plants. Leaf mercury was affected by power plants and road dust mercury was affected by public service areas. The highest average HI (Hazard index) value of mercury in Shanghai was found in road dust, followed by surface soil and foliar dust. The HI values for children were much higher than those for adults. However, the HI values of mercury exposure in all sampling sites were less than one, suggesting a lower health risk level. The microscopic mechanism of mercury in different environmental media was suggested to be studied further in order to learn the quantitative effects of urbanization factors on mercury concentrations.

Temporal trends, lake-to-lake variation, and climate effects on Arctic char (Salvelinus alpinus) mercury concentrations from six High Arctic lakes in Nunavut, Canada

Climate warming and mercury (Hg) are concurrently influencing Arctic ecosystems, altering their functioning and threatening food security. Non-anadromous Arctic char (Salvelinus alpinus) in small lakes were used to biomonitor these two anthropogenic stressors, because this iconic Arctic species is a long-lived top predator in relatively simple food webs, and yet population characteristics vary greatly, reflecting differences between lake systems. Mercury concentrations in six landlocked Arctic char populations on Cornwallis Island, Nunavut have been monitored as early as 1989, providing a novel dataset to examine differences in muscle [Hg] among char populations, temporal trends, and the relationship between climate patterns and Arctic char [Hg]. We found significant lake-to-lake differences in length-adjusted Arctic char muscle [Hg], which varied by up to 9-fold. Arctic char muscle [Hg] was significantly correlated to dissolved and particulate organic carbon concentrations in water; neither watershed area or vegetation cover explained differences. Three lakes exhibited significant temporal declines in length-adjusted [Hg] in Arctic char; the other three lakes had no significant trends. Though precipitation, temperature, wind speed, and sea ice duration were tested, no single climate variable was significantly correlated to length-adjusted [Hg] across populations. However, Arctic char Hg in Resolute Lake exhibited a significant correlation with sea ice duration, which is likely closely linked to lake ice duration, and which may impact Hg processing in lakes. Additionally, Arctic char [Hg] in Amituk Lake was significantly correlated to snow fall, which may be linked to Hg deposition. The lack of consistent temporal trends in neighboring char populations indicates that currently, within lake processes are the strongest drivers of [Hg] in char in the study lakes and potentially in other Arctic lakes, and that the influence of climate change will likely vary from lake to lake.

Concentration of mercury, cadmium, and lead in breast milk from Norwegian mothers: Association with dietary habits, amalgam and other factors

Mercury (Hg), cadmium (Cd), and lead (Pb) are of great concern for food safety and infants are especially sensitive to exposure to the maternal body burden. We quantified these elements in breast milk from Norwegian mothers and determined their association with dietary habits, maternal amalgam fillings, and smoking. Breast milk (n = 300) from the Norwegian Human Milk Study (HUMIS) was analyzed using triple quadrupole inductively coupled plasma mass spectrometry, after an acidic decomposition using microwave technique. We used multiple linear regression to examine predictors of Hg and Cd in breast milk, and logistic regression to test predictors of Pb above the quantification limit. The median breast milk concentrations (minimum - maximum) were 0.20 μg Hg/kg (<0.058-0.89), 0.057 μg Cd/kg (0.017-1.2), and <0.67 μg Pb/kg (<0.2-7.5). Cadmium showed no significant relation with any exposure variable investigated. Lead was associated with intake of liver and kidneys from game. For Hg concentration in breast milk, number of amalgam fillings and high fish consumption were significant predictors (p < 0.001). We detected a significant association (p < 0.01) between Hg in breast milk and maternal consumption of Atlantic halibut, lean fish, mussels and scallops and lifetime consumption of crab. Seafood intake alone explained 10% of variance, while together with amalgam explained 46% of variance in Hg concentration in breast milk. Our findings emphasize the importance of following consumer advice with respect to fish and seafood and points to amalgam as an important source for Hg exposure.

Historical records of mercury deposition in dated sediment cores reveal the impacts of the legacy and present-day human activities in Todos os Santos Bay, Northeast Brazil

We determined depth profiles of total mercury (T-Hg) in six ²¹⁰Pb-dated sediment cores from Todos os Santos Bay to reconstruct the history of anthropogenic Hg accumulation. We also assessed superficial sediments samples from five estuaries. T-Hg concentrations (5-3500 μg kg^-1) presented a large spatial and temporal variability. T-Hg concentrations in Ribeira Bay increased up to 200-fold along time, whereas the fluxes of T-Hg are substantially higher (up to 10,000 fold) than present-day wet deposition for industrialized areas. Sedimentary records indicate that a chlor-alkali plant has been the main source of Hg pollution until the present, although the T-Hg records suggest that harbor, shrimp farming, and oil refinery activities, besides Hg atmospheric depositions, are important across the bay. Sediments in the Ribeira Bay act as an important Hg sink. If sediments are eroded or disturbed, they may release Hg, thus posing a serious risk to wildlife and ecosystem health. CAPSULE: Sedimentary cores provide data on preindustrial levels and also anthropogenic fluxes of Hg for the appraisal of the magnitude, processes and potential risks of the contamination.

Factors influencing methylmercury contamination of black bass from California reservoirs

Understanding how mercury (Hg) accumulates in the aquatic food web requires information on the factors driving methylmercury (MeHg) contamination. This paper employs data on MeHg in muscle tissue of three black bass species (Largemouth Bass, Spotted Bass, and Smallmouth Bass) sampled from 21 reservoirs in California. During a two-year period, reservoirs were sampled for total Hg in sediment, total Hg and MeHg in water, chlorophyll a, organic carbon, sulfate, dissolved oxygen, pH, conductivity, and temperature. These data, combined with land-use statistics and reservoir morphometry, were used to investigate relationships to size-normalized black bass MeHg concentrations. Significant correlations to black bass MeHg were observed for total Hg in sediment, total Hg and MeHg in surface water, and forested area. A multivariate statistical model predicted Largemouth Bass MeHg as a function of total Hg in sediment, MeHg in surface water, specific conductivity, total Hg in soils, and forested area. Comparison to historical reservoir sediment data suggested there has been no significant decline in sediment total Hg at five northern California reservoirs during the past 20 years. Overall, total Hg in sediment was indicated as the most influential factor associated with black bass MeHg contamination. The results of this study improve understanding of how MeHg varies in California reservoirs and the factors that correlate with fish MeHg contamination.

Bio-oxidation of elemental mercury during growth of mercury resistant yeasts in simulated hydrosphere

Transformation of metallic mercury (Hg°) to mercuric ion (Hg²⁺) in hydrosphere is the entrance of mercury cycle in water environments and leads to toxicological impact of serious global concern. Two yeast strains of Yarrowia (Idd1 and Idd2) isolated from Hg-contaminated sediments were studied for their mediating role in Hg° dissolution and oxidation. Growth of the Yarrowia cells in Hg-free liquid medium, incubated for 5 d in closed air-tight systems containing Hg°, produced extracellular polymeric substances (EPS). Approximately 230 (±5.7) ng and 120 (±6.8) ng of the dissolved Hg° were oxidized to Hg²⁺ by the cultures of Idd1 and Idd2, respectively, 5 day post-inoculation. Transmission electron microscopy (TEM) and X-ray energy dispersive spectrophotometry (XEDS) analysis of the EPS and cell mass revealed the presence of extracellular Hg nanoparticles, presumably HgS, as an indication of EPS-Hg complexation that is useful for Hg° dissolution and its eventual oxidation to Hg²⁺ by the cells. Fourier transmission infra-red (FTIR) analyses of the EPS and cell-mass during Hg-oxidation revealed that amine and carbonyl groups were used by EPS for Hg complexation. Our findings provided information about mediatory role played by Yarrowia (Idd1 and Idd2) in hydrosphere in biogeochemical cycling of Hg.

Measurements and Distribution of Atmospheric Particulate-Bound Mercury: A Review

Atmospheric particulate-bound mercury (PBM) plays an important role in the geochemical cycling of mercury (Hg). This study reviewed research progress of the PBM, including the possible emission and deposition pathways, measurement methods and the global distribution. The primary PBM sources are anthropogenic sources, but natural sources could be also a considerable contributor, for instance, chemical transport and dust in the arid and desert area. Different filter methods, such as quartz fibre filters, have been applied to the PBM measurement, and PBM can also be real-time monitored automatically. Generally, the average PBM concentrations were higher in the Northern Hemisphere than in the Southern Hemisphere. However, the PBM level of Antarctica is quite high. PBM concentrations were higher in the urban areas than in the remote areas, and there was a high PBM level in the developing countries. Moreover, high PBM concentrations were observed in the range 20°-60° of northern latitude.

NRXN1 Deletion and Exposure to Methylmercury Increase Astrocyte Differentiation by Different Notch-Dependent Transcriptional Mechanisms

Controversial evidence points to a possible involvement of methylmercury (MeHg) in the etiopathogenesis of autism spectrum disorders (ASD). In the present study, we used human neuroepithelial stem cells from healthy donors and from an autistic patient bearing a bi-allelic deletion in the gene encoding for NRXN1 to evaluate whether MeHg would induce cellular changes comparable to those seen in cells derived from the ASD patient. In healthy cells, a subcytotoxic concentration of MeHg enhanced astroglial differentiation similarly to what observed in the diseased cells (N1), as shown by the number of GFAP positive cells and immunofluorescence signal intensity. In both healthy MeHg-treated and N1 untreated cells, aberrations in Notch pathway activity seemed to play a critical role in promoting the differentiation toward glia. Accordingly, treatment with the established Notch inhibitor DAPT reversed the altered differentiation. Although our data are not conclusive since only one of the genes involved in ASD is considered, the results provide novel evidence suggesting that developmental exposure to MeHg, even at subcytotoxic concentrations, induces alterations in astroglial differentiation similar to those observed in ASD.

Molecular characteristics of sedimentary organic matter in controlling mercury (Hg) and elemental mercury (Hg0) distribution in tropical estuarine sediments

Sedimentary organic matter (SOM) plays an important role in hosting and reducing Hg^II in marine/estuarine sediment. This study provides a better understanding on the influence of nature of SOM, in regulating sedimentary mercury (Hg) and elemental mercury (Hg⁰) distribution, and speciation in the Zuari and Mandovi Estuaries that are representative of monsoon fed tropical estuaries, located in the central west coast of India. Salinity of the overlying water column controlled the physical and chemical characteristics of SOM in the estuarine systems. The high molecular weight (MW) SOM dominated at the mid and upstream (low salinity region) of the estuaries, whereas, the low MW SOM prevailed at the downstream (high salinity region). Sediment Hg showed more affinity towards the SOM of high MW. Increasing MW of SOM increased total sedimentary Hg_T in both the estuaries. SOM with low MW in the estuarine sediment displayed a negative relationship with the sediment Hg concentration. Distribution of Hg⁰ concentration in the estuarine sediment suggests that reduction of Hg^II in presence low MW SOM was a dominant process. It was also found that distribution and speciation of Hg⁰ in the estuarine sediment depends on the quantity, quality of the SOM, and the total sediment Hg loading. This study demonstrated that the competition between Hg-SOM complexation and Hg^II reduction by SOM controls Hg^II/Hg⁰ distribution in tropical estuarine sediment systems.

New insights into the chemical forms of extremely high methylmercury in songbird feathers from a contaminated site

The chemical forms of mercury (Hg), particularly methylmercury (MeHg), in songbird feathers from an abandoned mining region were analyzed via X-ray absorption near-edge structure analysis (XANES). In feathers, proportions of MeHg as total mercury (75.6-100%) quantified by the XANES were directly comparable to the chemical extraction values (74.1-95.9%). Most of MeHg were bound with cysteine (Cys) and reduced glutathione (GSH), whereas inorganic mercury (IHg) was mainly bound with GSH. These results were consistent with those found in fish muscles and human hairs of both fish consumers and occupational Hg exposure populations. Our study suggested that chemical forms and speciation of Hg were highly dependent on the exposure sources and food consumption, respectively. Bird feathers were able to selectively accumulate MeHg due to their special binding ways. However, detailed mechanisms of Hg accumulation in bird feathers remain to be further elucidated.

Dynamics of mercury content in adult sichel (Pelecus cultratus L.) tissues from the Baltic Sea before and during spawning

This study compares the content of mercury in the muscles, liver, kidneys, gonads and gills of male and female individuals of sichel (Pelecus cultratus). Moreover, the trend of changes of mercury concentration before (March) and during (May) the spawning season was examined. Sichel brooders were caught in the Vistula Lagoon during commercial fishing. The mercury content in tissues was determined by atomic absorption using a Milestone DMA-80. The tests revealed a statistically higher mercury concentration in muscles, liver and gonads in male vs. female fish. Moreover, significantly higher mercury concentration was found in male and female fish caught during the spawning season (May) than in those caught before this season (March). Moreover, testes (0.011 ± 0.007 mg kg^-1 w/w) were found to contain 12 times, and ovaries (0.004 ± 0.001 mg kg^-1 w/w) - approx. 19 times less mercury than the muscular tissue of those same fish. This may suggest the existence of a protective barrier, defending future offspring against the transfer of toxic mercury from the parent body to gonads and gametes.

Nutrients mediate the effects of temperature on methylmercury concentrations in freshwater zooplankton

Methylmercury (MeHg) bioaccumulation in freshwater aquatic systems is impacted by anthropogenic stressors, including climate change and nutrient enrichment. The goal of this study was to determine how warmer water temperatures and excess nutrients would alter zooplankton communities and phytoplankton concentrations, and whether those changes would in turn increase or decrease MeHg concentrations in freshwater zooplankton. To test this, we employed a 2 × 2 factorial experimental design with nutrient and temperature treatments. Mesocosms were filled with ambient water and plankton from Cottage Grove Reservoir, Oregon, U.S.A., a waterbody that has experienced decades of elevated MeHg concentrations and corresponding fish consumption advisories due to run-off from Black Butte Mine tailings, located within the watershed. Treatment combinations of warmer temperature (increased by 0.7 °C), nutrient addition (a single pulse of 10× ambient concentrations of nitrogen and phosphorous), control, and a combination of temperature and nutrients were applied to mesocosms. The individual treatments altered phytoplankton densities and community structure, but alone the effects on MeHg concentrations were muted. Importantly, we found a significant interactive effect of nutrients and temperature: the nutrient addition appeared to buffer against increased MeHg concentrations associated with elevated temperature. However, there was variability in this response, which seems to be related to the abundance of Daphnia and edible phytoplankton. Nutrients at low temperature were associated with marginal increases (1.1×) in zooplankton MeHg. Our findings suggest that global change drivers that influence community composition and ecosystem energetics of both zooplankton and phytoplankton can alter MeHg pathways through food webs.

A Portable Setup for the Voltammetric Determination of Total Mercury in Fish with Solid and Nanostructured Gold Electrodes

A simple procedure for field fish sample pretreatment was developed. This treatment in combination with square wave anodic stripping voltammetry (SW-ASV) with solid gold electrodes (SGE) and gold nanoparticle-modified glassy carbon electrodes (AuNPs-GCE) was applied for the determination of total mercury content. A certified reference material (CRM, Tuna Fish BCR 463), ten freeze-dried samples of canned tuna and two fresh fish samples were analysed both with a bench-top voltammetric analyser after microwave digestion and with a portable potentiostat after mild eating using a small commercial food warmer. The results obtained by the two SW-ASV approaches and by a Direct Mercury Analyser (DMA), the official method for mercury determination, were in very good agreement. In particular, (i) the results obtained with in field procedure are consistent with those obtained with the conventional microwave digestion; (ii) the presence of gold nanoparticles on the active electrode surface permits an improvement of the analytical performance in comparison to the SGE: the Limit of Quantification (LOQ) for mercury in fish-matrix was 0.1 μg L-1 (Hg cell concentration), corresponding to 0.06 mg kg-1 wet fish, which is a performance comparable to that of DMA. The pretreatment proposed in this study is very easy and applicable to fresh fish; in combination with a portable potentiostat, it proved to be an interesting procedure for on-site mercury determination.

Mercury leads to features of polycystic ovary syndrome in rats

Mercury (Hg) is a heavy metal and Hg exposure is associated with various neural, immune, and cardiovascular abnormalities. However, few studies have evaluated Hg's toxicologic effect on reproductive and metabolic functions. In this study, we assessed whether Hg exposure results in reproductive and metabolic abnormalities. Hg was administered to adult female Wistar rats, mimicking the Hg levels found in exposed human blood, and their reproductive and metabolic function was assessed. Rats exposed to Hg displayed abnormal estrous cyclicity and ovarian follicular development, with a reduction in ovarian antral follicles and an increase in atretic and cystic ovarian follicles. Uterine atrophy with the presence of inflammatory cells was observed in Hg-exposed rats. The presence of abnormal ovarian fat accumulation, as well as increased ovarian lipid drops accumulation, was observed in Hg-exposed rats. Ovarian oxidative stress was also present in the Hg-exposed rats. High fasting glucose levels, glucose, and insulin intolerance were observed in Hg-exposed rats. Thus, these data suggest that Hg exposure led to abnormal reproductive and metabolic features similar to those found in the polycystic ovary syndrome (PCOS) rat models.

Sorption kinetics of isotopically labelled divalent mercury (196Hg2+) in soil

Understanding the sorption kinetics of Hg²⁺ is the key to predicting its reactivity in soils which is indispensable for environmental risk assessment. The temporal change in the solubility of ¹⁹⁶Hg²⁺ spikes (6 mg kg^-1) added to a range of soils with different properties was investigated and modelled. The sorption of ¹⁹⁶Hg²⁺ displayed a biphasic pattern with a rapid initial (short-term) phase followed by a slower (time-dependent) one. The overall reaction rate constants ranged from 0.003 to 4.9 h^-1 and were significantly correlated (r = 0.94) to soil organic carbon (SOC). Elovich and Spherical Diffusion expressions compellingly fitted the observed ¹⁹⁶Hg²⁺ sorption kinetics highlighting their flexibility to describe reactions occurring over multiple phases and wide timeframes. A parameterized Elovich model from soil variables indicated that the short-term sorption is solely controlled by SOC while the time-dependent sorption appeared independent of SOC and decreased at higher pH values and Al(OH)₃ and MnO₂ concentrations. This is consistent with a rapid chemical reaction of Hg²⁺ with soil organic matter (SOM) which is followed by a noticeably slower phase likely occurring through physical pathways e.g. pore diffusion of Hg²⁺ into spherical soil aggregates and progressive incorporation of soluble organic-Hg into solid phase. The model lines predicted that in soils with >4% SOC, Hg²⁺ is removed from soil solution over seconds to minutes; however, in soils with <2% SOC and higher pH values, Hg²⁺ may remain soluble for months and beyond with a considerable associated risk of re-emission or migration to the surrounding environments.

Iron Sulfide Minerals as Potential Active Capping Materials for Mercury-Contaminated Sediment Remediation: A Minireview

Several innovative approaches have been proposed in recent years to remediate contaminated sediment to reduce human health and environmental risk. One of the challenges of sediment remediation stems from its unfeasible high cost, especially when ex situ strategies are selected. Therefore, in situ methods such as active capping have been emerging as possible options for solving sediment problems. Active capping methods have been extensively tested in field-scale sediment remediation for organic pollutants (e.g., PCBs, PAHs, DDT) contamination with good sequestration efficiency; however, these methods have not been widely tested for control of heavy metal pollutants, such as mercury (Hg). In this review, the potentials of using iron sulfide minerals to sequestrate Hg were discussed. Iron sulfide minerals are common in the natural environment and have shown good effectiveness in sequestrating Hg by adsorption or precipitation. Iron sulfides can also be synthesized in a laboratory and modified to enhance their sequestration ability for Hg. Some of the potential advantages of iron sulfides are pointed out here. Additional tests to understand the possibility of applying iron sulfides as active caps to remediate complicated environment systems should be conducted.

Extenuation of in utero toxic effects of MeHg in the developing neurons by Fisetin via modulating the expression of synaptic transmission and plasticity regulators in hippocampus of the rat offspring

The neurotoxic environmental contaminant, methylmercury (MeHg), has shown to have detrimental effects on the developing brain when exposed during gestation. We have shown in our earlier studies that gestational administration of 3,3',4',7-Tetrahydroxyflavone or Fisetin reduces the toxic effects of MeHg in the developing rat brain. The current study has pivoted to study the mechanism behind the mitigating action of Fisetin against prenatal MeHg exposure induced neurotoxicity. Negligible data is available about the toxicity targets of MeHg in the developing brain. Studies have exhibited that MeHg exposure cause toxic effects on synaptic transmission and plasticity in the offspring brain. Hence, we aimed to study the effect of Fisetin on MeHg induced alterations in the expressions of regulatory genes and proteins involved in synaptic plasticity and transmission. Pregnant rats were grouped according to the type of oral administration as, (i) Control, (ii) MeHg (1.5 mg/kg b. w.), (iii) MeHg + Fisetin (30 mg/kg b. w.) and (iv) Fisetin (30 mg/kg b. w). Maternal administration of Fisetin prevented MeHg exposure induced downregulation of neurogranin (Nrgn), dendrin (Ddn), Syntaxin 1 A (Stx1a), Lin-7 homolog A (Lin7a), Complexin-2 (Cplx2) and Exocyst complex component 8 (Exoc8) genes in the offspring rat. Fisetin also prevented MeHg exposure induced downregulation of brain derived neurotrophic factor (BDNF), Glial-cell derived neurotrophic factor (GDNF) protein expressions and hampered reactive astrogliosis in the hippocampus of F₁ generation rats. Hence, through this study, we conclude that Fisetin modulates the expression of regulatory genes and proteins involved in synaptic transmission and plasticity and extenuates MeHg neurotoxicity in the developing rat brain.

Mercury Sorption and Desorption on Organo-Mineral Particulates as a Source for Microbial Methylation

In natural freshwater and sediments, mercuric mercury (Hg(II)) is largely associated with particulate minerals and organics, but it remains unclear under what conditions particulates may become a sink or a source for Hg(II) and whether the particulate-bound Hg(II) is bioavailable for microbial uptake and methylation. In this study, we investigated Hg(II) sorption-desorption characteristics on three organo-coated hematite particulates and a Hg-contaminated natural sediment and evaluated the potential of particulate-bound Hg(II) for microbial methylation. Mercury rapidly sorbed onto particulates, especially the cysteine-coated hematite and sediment, with little desorption observed (0.1-4%). However, the presence of Hg-binding ligands, such as low-molecular-weight thiols and humic acids, resulted in up to 60% of Hg(II) desorption from the Hg-laden hematite particulates but <6% from the sediment. Importantly, the particulate-bound Hg(II) was bioavailable for uptake and methylation by a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 under anaerobic incubations, and the methylation rate was 4-10 times higher than the desorption rate of Hg(II). These observations suggest direct contacts and interactions between bacterial cells and the particulate-bound Hg(II), resulting in rapid exchange or uptake of Hg(II) by the bacteria. The results highlight the importance of Hg(II) partitioning at particulate-water interfaces and the role of particulates as a significant source of Hg(II) for methylation in the environment.

Methylmercury and total mercury content in soft tissues of two bird species wintering in the Baltic Sea near Gdansk, Poland

Of the various forms of Hg occurring in nature, (mono) methylmercury (MeHg) is an especially toxic form and practically all forms of Hg can be converted into MeHg as a result of natural processes. Total mercury (THg) and MeHg were determined in tissues of two piscivorous birds: razorbill Alca torda and black-throated loon Gavia arctica to provide baseline data on current mercury concentrations for liver, kidneys and pectoral muscle mercury concentrations of birds which winter on the south Baltic Sea coast. Intra and inter-specific comparisons were carried out. The study is conducted between winter and autumn and the distributions of mercury in tissues were compared with data in other studies. The following paper contains discussion of the results based on the statistical analysis and ecology aspect. The highest average Hg content was in the liver (loon ≈ 3.86 mg kg^-1 dw; razorbill ≈ 1.57 mg kg^-1 dw), then in the kidneys (loon ≈ 3.14 mg kg^-1 dw; razorbill ≈ 1.53 mg kg^-1 dw) and the lowest concentrations were in pectoral muscles (loon ≈ 1.97 mg kg^-1 dw; razorbill ≈ 0.67 mg kg^-1 dw).

Microbial generation of elemental mercury from dissolved methylmercury in seawater

Elemental mercury (Hg⁰) formation from other mercury species in seawater results from photoreduction and microbial activity, leading to possible evasion from seawater to overlying air. Microbial conversion of monomethylmercury (MeHg) to Hg0 in seawater remains unquantified. A rapid radioassay method was developed using gamma-emitting ²⁰³Hg as a tracer to evaluate Hg⁰ production from Hg(II) and MeHg in the low pM range. Bacterioplankton assemblages in Atlantic surface seawater and Long Island Sound water were found to rapidly produce Hg⁰, with production rate constants being directly related to bacterial biomass and independent of dissolved Hg(II) and MeHg concentrations. About 32% of Hg(II) and 19% of MeHg were converted to Hg⁰ in 4 d in Atlantic surface seawater containing low bacterial biomass, and in Long Island Sound water with higher bacterial biomass, 54% of Hg(II) and 8% of MeHg were transformed to Hg⁰. Decreasing temperatures from 24°C to 4°C reduced Hg⁰ production rates cell^-1 from Hg(II) 3.3 times as much as from a MeHg source. Because Hg⁰ production rates were linearly related to microbial biomass and temperature, and microbial mercuric reductase was detected in our field samples, we inferred that microbial metabolic activities and enzymatic reactions primarily govern Hg⁰ formation in subsurface waters where light penetration is diminished.

Ultra-trace determination of total mercury in Italian bottled waters

Mercury (Hg) is a widespread, highly toxic persistent pollutant with adverse health effects on humans. So far, concentrations below the method detection limit have always been reported by studies on the concentration of mercury in bottled water when determined using instrumental analytical methods. These are often very expensive and are unaffordable for many laboratories. In this work, a less expensive method based on cold vapour atomic fluorescence spectrometry has been employed to determine total mercury (Hg_T) concentrations in bottled natural mineral waters. In all, 255 waters representing 164 different typologies were analysed. They came from 136 springs located in 18 Italian regions. In all samples, Hg_T concentrations were found in the range of sub-nanogram to a few nanograms per litre, well below the National and European regulatory limit (1 μg L^-1). Differences in Hg_T concentrations were related not only to the environmental characteristics of the springs but also to the extent and impact of human activities. Higher concentrations were found in waters coming from regions with former mining and/or natural thermal and volcanic activity. These data allowed us to estimate the mercury intake by population (adults, children and toddlers) from drinkable mineral waters consumption. The mean mercury daily intake was found to be remarkably lower, not only than the provisional tolerable value (1 μg L^-1 according to European and Italian legislation) but also than the estimated provisional tolerable weekly intake (PTWI) value (4 μg kg^-1 body weight) recommended by the Joint FAO/WHO Expert Committee on Food Additives (JECFA).

Quantifying the impacts of artisanal gold mining on a tropical river system using mercury isotopes

In some locations, artisanal and small-scale gold-mining (ASGM) represents a significant source of anthropogenic Hg to freshwater environments. The Hg released from ASGM can contaminate aquatic fauna and pose health risks to downstream populations. Total Hg (THg) concentrations, speciation, and isotopic compositions were analyzed in water, suspended particulate matter, soil, and bottom sediment samples from pristine areas and in places of active and legacy gold mining along the Oyapock River (French Guiana) and its tributaries. Mass-independent fractionation (MIF) of even Hg isotopes in top soils (Δ²⁰⁰Hg = -0.06 ± 0.02‰, n = 10) implied the uptake of gaseous Hg(0) by plants, rather than wet deposition, as the primary Hg source. Odd isotope MIF was lower in deep soils (Δ¹⁹⁹Hg = -0.75 ± 0.03‰, n = 7) than in top soils (Δ¹⁹⁹Hg = -0.55 ± 0.15‰, n = 3). This variation could be attributed to differences between the isotopic signatures of modern and pre-industrial atmospheric Hg. Combining a Hg-isotope binary mixing model with a multiple linear regression based on physico-chemical parameters measured in the sediment samples, we determined that active mined creek sediments are contaminated by ASGM activities, with up to 78% of THg being anthropogenic. Of this anthropogenic Hg, more than half (66-74%) originates from liquid Hg(0) that is released during ASGM. The remaining anthropogenic Hg comes from the ASGM-driven erosion of Hg-rich soils into the river. The isotope signatures of anthropogenic Hg in bottom sediments were no longer traceable in formerly mined rivers and creeks.

Molecular evidence for novel mercury methylating microorganisms in sulfate-impacted lakes

Methylmercury (MeHg) is a bioaccumulative neurotoxin that is produced by certain anaerobic microorganisms, but the abundance and importance of different methylating populations in the environment is not well understood. We combined mercury geochemistry, hgcA gene cloning, rRNA methods, and metagenomics to compare microbial communities associated with MeHg production in two sulfate-impacted lakes on Minnesota's Mesabi Iron Range. The two lakes represent regional endmembers among sulfate-impacted sites in terms of their dissolved sulfide concentrations and MeHg production potential. rRNA amplicon sequencing indicates that sediments and anoxic bottom waters from both lakes contained diverse communities with multiple clades of sulfate reducing Deltaproteobacteria and Clostridia. In hgcA gene clone libraries, however, hgcA sequences were from taxa associated with methanogenesis and iron reduction in addition to sulfate reduction, and the most abundant clones were from unknown groups. We therefore applied metagenomics to identify the unknown populations in the lakes with the capability to methylate mercury, and reconstructed 27 genomic bins with hgcA. Some of the most abundant potential methylating populations were from phyla that are not typically associated with MeHg production, including a relative of the Aminicenantes (formerly candidate phylum OP8) and members of the Kiritimatiellaeota (PVC superphylum) and Spirochaetes that, together, were more than 50% of the potential methylators in some samples. These populations do not have genes for sulfate reduction, and likely degrade organic compounds by fermentation or other anaerobic processes. Our results indicate that previously unrecognized populations with hgcAB are abundant and may be important for MeHg production in some freshwater ecosystems.

Mercury Stable Isotope Fractionation during Abiotic Dark Oxidation in the Presence of Thiols and Natural Organic Matter

Mercury (Hg) stable isotope fractionation has been widely used to trace Hg sources and transformations in the environment, although many important fractionation processes remain unknown. Here, we describe Hg isotope fractionation during the abiotic dark oxidation of dissolved elemental Hg(0) in the presence of thiol compounds and natural humic acid. We observe equilibrium mass-dependent fractionation (MDF) with enrichment of heavier isotopes in the oxidized Hg(II) and a small negative mass-independent fractionation (MIF) owing to nuclear volume effects. The measured enrichment factors for MDF and MIF (ε²⁰²Hg and E¹⁹⁹Hg) ranged from 1.10‰ to 1.56‰ and from -0.16‰ to -0.18‰, respectively, and agreed well with theoretically predicted values for equilibrium fractionation between Hg(0) and thiol-bound Hg(II). We suggest that the observed equilibrium fractionation was likely controlled by isotope exchange between Hg(0) and Hg(II) following the production of the Hg(II)-thiol complex. However, significantly attenuated isotope fractionation was observed during the initial stage of Hg(0) oxidation by humic acid and attributed to the kinetic isotope effect (KIE). This research provides additional experimental constraints on interpreting Hg isotope signatures with important implications for the use of Hg isotope fractionation as a tracer of the Hg biogeochemical cycle.

The influence of global climate change on the environmental fate of anthropogenic pollution released from the permafrost: Part I. Case study of Antarctica

This article presents a review of information related to the influence of potential permafrost degradation on the environmental fate of chemical species which are released and stored, classified as potential influence in future Antarctic environment. Considering all data regarding climate change prediction, this topic may prove important issue for the future state of the Antarctic environment. A detailed survey on soil and permafrost data permitted the assumption that this medium may constitute a sink for organic and inorganic pollution (especially for persistent organic pollution, POPs, and heavy metals). The analysis of the environmental fate and potential consequences of the presence of pollutants for the existence of the Antarctic fauna leads to a conclusion that they may cause numerous negative effects (e.g. Endocrine disruptions, DNA damage, cancerogenicity). In the case of temperature increase and enhanced remobilisation processes, this effect may be even stronger, and may disturb natural balance in the environment. Therefore, regular research on the environmental fate of pollution is required, especially in terms of processes of remobilisation from the permafrost reserves.

Analysis of 11 trace elements in flight feathers of Italian Sparrows in southern Italy: A study of bioaccumulation through age classes, variability in three years of sampling, and relations with body condition

Trace elements have been acknowledged as one of the subtlest environmental hazards in all compartments of the total environment. Enhanced by activities in the anthroposphere, they accumulate in the atmosphere, lithosphere, and hydrosphere. Eventually, trace elements can bioaccumulate or biomagnifiy in the biosphere, with harmful effects on animals occupying higher trophic levels, including humans. Accordingly, there is great interest in assessing and monitoring trace element concentrations in the biosphere, and birds, especially passerines, have been commonly chosen as biomonitors. In this study, the concentration of 11 trace elements was measured (i.e. aluminum, chromium, manganese, iron, nickel, copper, zinc, arsenic, cadmium, barium, and lead) in flight feathers of Italian Sparrows, a common bird species hitherto not analysed in this respect. Samples were collected in an agricultural area in southern Italy, where a mosaic of natural environments, urbanized areas and industrial facilities can be found. Linear mixed modelling was applied to the analysis of flight feathers in juveniles, juvenile birds moulting to adulthood, and adults in three sampling years on 184 birds. Results are timely as they add new data to the scarce available information on Ba and As in bird feathers and showed clear bioaccumulation patterns from juveniles to adults for As, Cr, and Cd. Moreover, the modelling approach showed that the concentration of elements such as As, Cd and Cr can be variable across the years and that some elements, notably Cd and Ba, were inversely correlated with body mass and wing length, respectively, suggesting potential negative effects on bird health. Finally, when modelling bird body condition and trace elements, results showed that Cd and Ba negatively affect birds regardless of age or sampling year. Thus, the Italian Sparrow could be considered as a valuable biomonitor for trace elements in the total environment, especially for Cd and Ba.

A Model of Mercury Distribution in Tuna from the Western and Central Pacific Ocean: Influence of Physiology, Ecology and Environmental Factors

Information on ocean scale drivers of methylmercury levels and variability in tuna is scarce, yet crucial in the context of anthropogenic mercury (Hg) inputs and potential threats to human health. Here we assess Hg concentrations in three commercial tuna species (bigeye, yellowfin, and albacore, n = 1000) from the Western and Central Pacific Ocean (WCPO). Models were developed to map regional Hg variance and understand the main drivers. Mercury concentrations are enriched in southern latitudes (10°S-20°S) relative to the equator (0°-10°S) for each species, with bigeye exhibiting the strongest spatial gradients. Fish size is the primary factor explaining Hg variance but physical oceanography also contributes, with higher Hg concentrations in regions exhibiting deeper thermoclines. Tuna trophic position and oceanic primary productivity were of weaker importance. Predictive models perform well in the Central Equatorial Pacific and Hawaii, but underestimate Hg concentrations in the Eastern Pacific. A literature review from the global ocean indicates that size tends to govern tuna Hg concentrations, however regional information on vertical habitats, methylmercury production, and/or Hg inputs are needed to understand Hg distribution at a broader scale. Finally, this study establishes a geographical context of Hg levels to weigh the risks and benefits of tuna consumption in the WCPO.

Tailings ponds of the Athabasca Oil Sands Region, Alberta, Canada, are likely not significant sources of total mercury and methylmercury to nearby ground and surface waters

Tailings ponds created during industrial bitumen extraction from the Athabasca Oil Sands Region (AOSR), Alberta, Canada, have been shown to contain numerous contaminants, such as polycyclic aromatic compounds and naphthenic acids, and to slowly leak into adjacent ground and surface waters. Despite elevated concentrations of total mercury (THg) in nearby Athabasca River waters downstream of the AOSR developments, to date there are no published studies of THg or methylmercury (MeHg; a potent neurotoxin) in the AOSR tailings ponds. Here we present concentrations of THg and MeHg, as well as various water chemistry parameters, within four AOSR tailings ponds. Concentrations of SO₄^2-, NH₃, Na, and Cl were elevated in tailings ponds relative to nearby freshwaters. Surface water concentrations of THg (filtered: 0.15-0.57 ng/L) and MeHg (unfiltered: <0.02-0.53 ng/L; filtered: <0.02-0.32 ng/L), though, were generally low in the tailings ponds, with the highest concentrations observed in the oldest pond. In the mature fine tailings that settle out in the ponds, concentrations of THg (37.0-197 ng/g) and MeHg (0.10-0.52 ng/g) were also low, with the highest concentrations again in the oldest pond. We calculated that if all the dissolved THg and MeHg potentially leaking annually from the tailings ponds entered the nearby Athabasca River, river THg and MeHg concentrations would increase by only 0.01% and 0.03%, respectively. Overall, these ponds are likely not significant sources of THg or MeHg to nearby ground and surface waters, although due to the potential for Hg methylation to occur in the ponds themselves, other tailings ponds in the AOSR should be monitored to ensure that concentrations of MeHg in them are also low.

Microbial Mercury Methylation in Aquatic Environments: A Critical Review of Published Field and Laboratory Studies

Methylmercury (MeHg) is an environmental contaminant of concern because it biomagnifies in aquatic food webs and poses a health hazard to aquatic biota, piscivorous wildlife and humans. The dominant source of MeHg to freshwater systems is the methylation of inorganic Hg (IHg) by anaerobic microorganisms; and it is widely agreed that in situ rates of Hg methylation depend on two general factors: the activity of Hg methylators and their uptake of IHg. A large body of research has focused on the biogeochemical processes that regulate these two factors in nature; and studies conducted within the past ten years have made substantial progress in identifying the genetic basis for intracellular methylation and defining the processes that govern the cellular uptake of IHg. Current evidence indicates that all Hg methylating anaerobes possess the gene pair hgcAB that encodes proteins essential for Hg methylation. These genes are found in a large variety of anaerobes, including iron reducers and methanogens; but sulfate reduction is the metabolic process most often reported to show strong links to MeHg production. The uptake of Hg substrate prior to methylation may occur by passive or active transport, or by a combination of both. Competitive inhibition of Hg uptake by Zn speaks in favor of active transport and suggests that essential metal transporters are involved. Shortly after its formation, MeHg is typically released from cells, but the efflux mechanisms are unknown. Although methylation facilitates Hg depuration from the cell, evidence suggests that the hgcAB genes are not induced or favored by Hg contamination. Instead, high MeHg production can be linked to high Hg bioavailability as a result of the formation of Hg(SH)₂, HgS nanoparticles, and Hg-thiol complexes. It is also possible that sulfidic conditions require strong essential metal uptake systems that inadvertently bring Hg into the cytoplasm of Hg methylating microbes. In comparison with freshwaters, Hg methylation in open ocean waters appears less restricted to anoxic environments. It does seem to occur mainly in oxygen deficient zones (ODZs), and possibly within anaerobic microzones of settling organic matter, but MeHg (CH₃Hg⁺) and Me₂Hg ((CH₃)₂Hg) have been shown to form also in surface water samples from the euphotic zone. Future studies may disclose whether several different pathways lead to Hg methylation in marine waters and explain why Me₂Hg is a significant Hg species in oceans but seemingly not in most freshwaters.

Bioavailability of mercury in power plant wastewater and ambient river samples: Evidence that the regulation of total mercury is not appropriate

Mercury (Hg) is a neurotoxin that can cause debilitating effects to human and environmental receptors under high exposure conditions. For industrial and municipal point sources that discharge Hg, wastewater limitations on total Hg (THg) concentrations or loads are typical. While this regulatory practice provides simplicity for regulated industry and water resource agencies (i.e., for analytical detection and reporting purposes), it ignores the important considerations of speciation and bioavailability. In this study, water samples were collected from multiple power plant wastewater, simulated mixing zone, and ambient river locations (N = 10 to 20) and were analyzed for bioavailable Hg forms (methylmercury and acid-labile Hg, or BHg), THg, and dissolved Hg. The median concentration of THg in wastewater, mixing zone, and ambient river samples was 7.1, 5.3, and 2.3 ng/L, respectively. The percentages of THg as BHg (median values) were 18.7%, 29.3%, and 8.5% for wastewater, mixing zone, and ambient river samples. The percentages of methylmercury (MeHg) as THg were not statistically different between paired ambient and mixing zone samples (P > 0.05); this result indicates that wastewater did not increase the MeHg fraction when mixed with ambient water. Multiple regression analysis indicated that variation in THg for combined wastewater and mixing zone samples could be adequately explained by pooled water quality parameters (total suspended solids, total dissolved solids, sulfate, total organic carbon, pH, specific conductivity; r²  = 0.51; P < 0.05); however, no significant regression relationships were apparent for the percentage of BHg. These results, at least for the wastewater samples evaluated, indicate that regulating THg is likely overly conservative, and mechanisms to regulate the bioavailable forms of Hg are needed. If Hg fish tissue monitoring data indicate that concentrations are less than consumption thresholds, metal translator methodologies or bioavailability-based criterion techniques (as currently used for non-Hg trace elements) should be allowed for Hg. Integr Environ Assess Manag 2019;15:142-147. © 2018 SETAC.

Fatty fish, hair mercury and cognitive function in Norwegian preschool children: Results from the randomized controlled trial FINS-KIDS

BACKGROUND

The toxic effects of prenatal methylmercury (MeHg) include neurological abnormalities and developmental delay of which infants and children are particular susceptible. Studies on the effects of low and moderate exposure show conflicting results. Seafood is the main dietary source of MeHg, but also contributes with nutrients regarded as beneficial for development.

OBJECTIVES

To measure the change in total hair mercury concentration (THHg) after an intervention of lunch meals with fatty fish or meat in Norwegian preschool children, and to examine the associations between THHg and cognitive function.

METHODS

Children (n = 232) 4-6 years old were randomized to lunch meals with fatty fish (n = 114) or meat (n = 118) three times a week for 16 weeks. THHg was determined using a Direct Mercury Analyzer, and cognitive function was assessed by the Wechsler Preschool and Primary Intelligence Scale-III (WPPSI-III) pre- and post-intervention. Linear mixed effect models were used to analyze changes in THHg and WPPSI-III scores.

RESULTS

The mean (SD) THHg pre-intervention was 0.373 (0.204) mg kg^-1. Children in the fish group had an increase in THHg (change 0.162, 95% CI 0.111, 0.213 mg kg^-1), whereas children in the meat group had decreased THHg (-0.053, 95% CI -0.103, -0.002 mg kg^-1). There were no notable associations between THHg and the WPPSI-III raw scores at baseline or after 16 weeks of the fish/meat intervention.

CONCLUSIONS

Lunch meals including fatty fish led to a significant increase in THHg, but the values remain below the point of departures used for risk assessment by the EFSA, WHO and US-EPA. We observed no associations between THHg and cognitive function.

Protein and lipid growth rates regulate bioaccumulation of PCBs and Hg in Bighead Carp (Hypophthalmichthys nobilis) and Silver Carp (Hypophthalmichthys molitrix) from the Three Gorges Reservoir, China

This study evaluated the effect of growth of different tissue compartments on the bioaccumulation of mercury (Hg) and polychlorinated biphenyls (PCBs) in Silver Carp (Hypophthalmichthys molitrix) and Bighead Carp (Hypophthalmichthys nobilis) from the Three Gorges Reservoir (TGR), China. A non-steady state bioenergetics/toxicokinetic model was developed to simulate PCB and Hg concentrations in these two species and compared with field data. Simulations using constant whole body growth rate and constant tissue to whole body weight ratios were contrasted against simulations adopting age specific whole body and tissue/age specific growth rates for their goodness of fit to field data. The simulations using age/tissue specific growth rates demonstrated better fit to field data for PCBs compared to the constant growth rate models (22% improved R²), while both models explained similar variation in Hg concentration data. Both species demonstrated higher growth rates of lipids (on a daily basis) relative to whole body and protein contributing to higher growth dilution of PCBs compared to Hg. Although stable isotope data indicated some degree of diet and/or habitat shift, simulations assuming a constant diet concentration explained between 36 and 40% of the variation in fish concentrations for both contaminants and fish species. This study demonstrates that differences in the bioaccumulation rate of PCBs and Hg by Asian carp can be partially explained by differences in the growth rates of key tissue storage compartments associated with each contaminant. These differences in chemical-specific growth dilution subsequently contribute to differences in chemical retention and bioaccumulation patterns of Hg and PCBs by fish.

Assessment of exposure to metals, As and Se in water and sediment of a freshwater reservoir and their bioaccumulation in fish species of different feeding and habitat preferences

The concentrations of metals (Ag, Al, Ba, B, Be, Bi, Cd, Co, Cr, Cu, Fe, Ga, Hg, Li, Mn, Mo, Ni, Pb, Rb, Sr, Tl, U, V, Zn), As and Se were analyzed in water and sediments from three sites of Río Tercero Reservoir (Córdoba, Argentina) during the wet and the dry season. The dynamics of metals in six fish species (Hoplias malabaricus, Oligosarcus jenynsii, Rhamdia quelen, Bryconamericus iheringii, Astyanax fasciatus and Odontesthes bonariensis) from the reservoir were investigated to discover the possible differential influence of habitat and diet on metal accumulation in the fish. In the abiotic matrix, the highest heavy metal concentrations were observed in sediment. The concentrations of Al, Cu and Pb in water exceeded the limits considered as hazardous for aquatic life. Potential ecological risk analysis of metal concentrations in sediment indicated a low ecological risk in Río Tercero Reservoir in all sampling periods. The enrichment factor indicated that Cu, Pb, Zn and Hg come from anthropogenic sources. Among five different organs, the highest metal levels were found in gills and intestine. Rhamdia quelen and Oligosarcus jenynsii were the species with the highest values of metal accumulation in the whole body. Our study showed that the accumulation pattern of these multi-elements in the different fish species did not respond to diet or habitat, but seemed to be related to the detoxification mechanisms and the metabolism of each organism.