Hg Loading Research Articles

Experimental evidence for recovery of mercury-contaminated fish populations

Anthropogenic releases of mercury (Hg)1–3 are a human health issue4 because the potent toxicant methylmercury (MeHg), formed primarily by microbial methylation of inorganic Hg in aquatic ecosystems, bioaccumulates to high concentrations in fish consumed by humans5,6. Predicting the efficacy of Hg pollution controls on fish MeHg concentrations is complex because many factors influence the production and bioaccumulation of MeHg7–9. Here we conducted a 15-year whole-ecosystem, single-factor experiment to determine the magnitude and timing of reductions in fish MeHg concentrations following reductions in Hg additions to a boreal lake and its watershed. During the seven-year addition phase, we applied enriched Hg isotopes to increase local Hg wet deposition rates fivefold. The Hg isotopes became increasingly incorporated into the food web as MeHg, predominantly from additions to the lake because most of those in the watershed remained there. Thereafter, isotopic additions were stopped, resulting in an approximately 100% reduction in Hg loading to the lake. The concentration of labelled MeHg quickly decreased by up to 91% in lower trophic level organisms, initiating rapid decreases of 38–76% of MeHg concentration in large-bodied fish populations in eight years. Although Hg loading from watersheds may not decline in step with lowering deposition rates, this experiment clearly demonstrates that any reduction in Hg loadings to lakes, whether from direct deposition or runoff, will have immediate benefits to fish consumers.

Inorganic and methylated mercury dynamics in estuarine water of a salt marsh in Massachusetts, USA

Salt marsh estuaries serve as sources and sinks for nutrients and elements to and from estuarine water, which enhances and alleviates watershed fluxes to the coastal ocean. We assessed sources and sinks of mercury in the intertidal Plum Island Sound estuary in Massachusetts, the largest salt marsh estuary of New England, using 25-km spatial water sampling transects. Across all seasons, dissolved (FHg) and total (THg) mercury concentrations in estuarine water were highest and strongly enhanced in upper marshes (1.31 ± 0.20 ng L−1 and 6.56 ± 3.70 ng L−1, respectively), compared to riverine Hg concentrations (0.86 ± 0.17 ng L−1 and 0.88 ± 0.34 ng L−1, respectively). Mercury concentrations declined from upper to lower marshes and were lowest in ocean water (0.38 ± 0.10 ng L−1 and 0.56 ± 0.25 ng L−1, respectively). Conservative mixing models using river and ocean water as endmembers indicated that internal estuarine Hg sources strongly enhanced estuarine water Hg concentrations. For FHg, internal estuarine Hg contributions were estimated at 26 g yr−1 which enhanced Hg loads from riverine sources to the ocean by 44%. For THg, internal sources amounted to 251 g yr−1 and exceeded riverine sources six-fold. Proposed sources for internal estuarine mercury contributions include atmospheric deposition to the large estuarine surface area and sediment re-mobilization, although sediment Hg concentrations were low (average 23 ± 2 μg kg−1) typical of uncontaminated sediments. Soil mercury concentrations under vegetation, however, were ten times higher (average 200 ± 225 μg kg−1) than in intertidal sediments suggesting that high soil Hg accumulation might drive lateral export of Hg to the ocean. Spatial transects of methylated Hg (MeHg) showed no concentration enhancements in estuarine water and no indication of internal MeHg sources or formation. Initial mass balance considerations suggest that atmospheric deposition may either be in similar magnitude, or possibly exceed lateral tidal export which would be consistent with strong Hg accumulation observed in salt marsh soils sequestering Hg from current and past atmospheric deposition.

Aortic Stiffness Hysteresis in Isolated Mouse Aortic Segments Is Intensified by Contractile Stimuli, Attenuated by Age, and Reversed by Elastin Degradation

Aim: Cyclic stretch of vascular tissue at any given pressure reveals greater dimensions during unloading than during loading, which determines the cardiac beat-by-beat hysteresis loop on the pressure-diameter/volume relationship. The present study did not focus on hysteresis during a single stretch cycle but investigated whether aortic stiffness determined during continuous stretch at different pressures also displayed hysteresis phenomena.Methods: Aortic segments from C57Bl6 mice were mounted in the Rodent Oscillatory Set-up for Arterial Compliance (ROTSAC), where they were subjected to high frequency (10 Hz) cyclic stretch at alternating loads equivalent to a constant theoretical pulse pressure of 40 mm Hg. Diastolic and systolic diameter, compliance, and the Peterson elastic modulus (Ep), as a measure of aortic stiffness, was determined starting at cyclic stretch between alternating loads corresponding to 40 and 80 mm Hg, at each gradual load increase equivalent to 20 mm Hg, up to loads equivalent to pressures of 220 and 260 mm Hg (loading direction) and then repeated in the downward direction (unloading direction). This was performed in baseline conditions and following contraction by α1 adrenergic stimulation with phenylephrine or by depolarization with high extracellular K+ in aortas of young (5 months), aged (26 months) mice, and in segments treated with elastase.Results: In baseline conditions, diastolic/systolic diameters and compliance for a pulse pressure of 40 mm Hg were larger at any given pressure upon unloading (decreasing pressure) than loading (increasing pressure) of the aortic segments. The pressure-aortic stiffness (Ep) relationship was similar in the loading and unloading directions, and aortic hysteresis was absent. On the other hand, hysteresis was evident after activation of the VSMCs with the α1 adrenergic agonist phenylephrine and with depolarization by high extracellular K+, especially after inhibition of basal NO release with L-NAME. Aortic stiffness was significantly smaller in the unloading than in the loading direction. In comparison with young mice, old-mouse aortic segments also displayed contraction-dependent aortic hysteresis, but hysteresis was shifted to a lower pressure range. Elastase-treated segments showed higher stiffness upon unloading over nearly the whole pressure range.Conclusions: Mouse aortic segments display pressure- and contraction-dependent diameter, compliance, and stiffness hysteresis phenomena, which are modulated by age and VSMC-extracellular matrix interactions. This may have implications for aortic biomechanics in pathophysiological conditions and aging.

Impact of Athabasca oil sands operations on mercury levels in air and deposition

Abstract. Oil sands upgrading facilities in the Athabasca oil sands region (AOSR) in Alberta, Canada, have been reporting mercury (Hg) emissions to public government databases (National Pollutant Release Inventory (NPRI)) since the year 2000, yet the relative contribution of these emissions to ambient Hg deposition remains unknown. The impact of oil sands emissions (OSE) on Hg levels in and around the AOSR, relative to contributions from global (anthropogenic, geogenic and legacy) emissions and regional biomass burning emissions (BBE), was assessed using a global 3D-process-based Hg model, GEM-MACH-Hg, from 2012 to 2015. In addition, the relative importance of year-to-year changes in Hg emissions from the above sources and meteorological conditions to inter-annual variations in Hg deposition was examined. Surface air concentrations of Hg species and annual snowpack Hg loadings simulated by the model were found comparable to measured levels in the AOSR, suggesting consistency between reported Hg emissions from oil sands activities and Hg levels in the region. As a result of global-scale transport and the long lifetime of gaseous elemental Hg (Hg(0)), surface air concentrations of Hg(0) in the AOSR reflected the background Hg(0) levels in Canada. By comparison, average air concentrations of total oxidized Hg (efficiently deposited Hg species) in the AOSR were elevated up to 60 % within 50 km of the oil sands Hg emission sources. Hg emissions from wildfire events led to episodes of high ambient Hg(0) concentrations and deposition enrichments in northern Alberta, including the AOSR, during the burning season. Hg deposition fluxes in the AOSR were within the range of the deposition fluxes measured for the entire province of Alberta. On a broad spatial scale, contribution from imported Hg from global sources dominated the annual background Hg deposition in the AOSR, with present-day global anthropogenic emissions contributing to 40 % (< 1 % from Canada excluding OSE) and geogenic and legacy emissions contributing to 60 % of the background Hg deposition. In contrast, oil sands Hg emissions were responsible for significant enhancements in Hg deposition in the immediate vicinity of oil sands Hg emission sources, which were ∼ 10 times larger in winter than summer (250 %–350 % in winter and ∼ 35 % in summer within 10 km of OSE, 2012–2013). The spatial extent of the influence of oil sands emissions on Hg deposition was also greater in winter relative to summer (∼ 100 km vs. 30 km from Hg-emitting facilities). In addition, inter-annual changes in meteorological conditions and oil sands emissions also led to significantly higher inter-annual variations in wintertime Hg deposition compared to summer. In 2015, within 10 km of major oil sands sources, relative to 2012, Hg deposition declined by 46 % in winter but 22 % annually, due to a larger OSE-led reduction in wintertime deposition. Inter-annual variations in meteorological conditions were found to both exacerbate and diminish the impacts of OSE on Hg deposition in the AOSR, which can confound the interpretation of trends in short-term environmental Hg monitoring data. Hg runoff in spring flood, comprising the majority of annual Hg runoff, is mainly derived from seasonal snowpack Hg loadings and mobilization of Hg deposited in surface soils, both of which are sensitive to Hg emissions from oil sands developments in the proximity of sources. Model results suggest that sustained efforts to reduce anthropogenic Hg emissions from both global and oil sands sources are required to reduce Hg deposition in the AOSR.

Mercury vertical and horizontal concentrations in agricultural soils of a historically contaminated site: Role of soil properties, chemical loading, and cultivated plant species in driving its mobility

The long term vertical and horizontal mobility of mercury (Hg) in soils of agricultural areas of a historically contaminated Italian National Relevance Site (SIN Brescia-Caffaro) was investigated. The contamination resulted from the continuous discharge of Hg in irrigation waters by an industrial plant (Caffaro S.p.A), equipped with a mercury-cell chlor-alkali process. The contamination levels with depth ranged from about 20 mg/kg dry weight (d.w.) of soil in the top (plow) layer to less than 0.1 mg/kg d.w. at 1 m depth. The concentrations varied also spatially, up to one order of magnitude within the same field and showing a decreasing trend from the Hg source (i.e., irrigation ditches). The concentration profiles and gradients measured were explained considering Hg loading, soil properties, such as the texture, organic carbon content, pH and cation exchange capacity. A Selective Sequential Extraction (SSE) was also applied on soil samples from an ad hoc greenhouse experiment to investigate the role of different plant species in influencing Hg speciation in soils. Although most of the extracted Hg was included in scarcely mobile or immobile forms, some plant species (i.e., alfalfa) showed to importantly increase the soluble and exchangeable fractions with respect to the unplanted control soils, thus affecting mobility and potential bioavailability of Hg.

Mercury stable isotopes reveal the sources and transformations of atmospheric Hg in the high Arctic

The Arctic plays a critical role in the global Hg cycle as both a sink of Hg and, in response to rapid global warming, an emerging source of Hg due to release from permafrost and glaciers. Human activities have led to significant mercury (Hg) contamination in the Arctic over many decades, potentially impacting the health of Arctic ecosystems and indigenous people. Thus, it is crucial to understand the sources and transformations of Hg in the Arctic in order to predict how Hg behaves as emissions and the global climate change. Here we examine Hg stable isotopes in atmospheric particulate Hg (PHg), gaseous elemental Hg (GEM) and surface snow in the high Arctic (Alert, Canada) during polar spring from 2011 to 2015, in order to trace the sources of atmospheric Hg and its fate in Arctic surface environment. Isotope signatures of GEM (δ202Hg = 0.67 ± 0.24‰, Δ199Hg = −0.23 ± 0.04‰, Δ200Hg = −0.06 ± 0.04‰, 2SD) are similar to the average Northern Hemisphere background, suggesting that GEM in the high Arctic atmosphere is well mixed with those from lower latitudes. Surprisingly, the isotope composition of PHg has negative Δ199Hg, which is similar to GEM but distinct from the positive Δ199Hg typically observed for oxidized Hg species elsewhere. Furthermore, Hg in surface snow shows more negative MIF than PHg, indicating post-depositional loss of Hg via photoreduction. We suggest that PHg is primarily sourced from in situ oxidation of GEM and subsequent scavenging by particles, and thus inherited the isotope composition of GEM when the oxidation is near-complete. The photoreduction re-emission of Hg from snow is strongly affected by Hg speciation, but the overall extent of re-emission (20 ± 31%) is lower than previous estimations for other locations, suggesting potentially a greater loading of Hg to Arctic ecosystem via snowmelt.

Effects of Mercury Contamination on The Physiology of Purple Martins ( Progne subis )

Purple Martins (Progne subis) are insectivorous birds that spend their breeding season in North America before migrating to South America, where they molt. Many individuals migrate to the Amazon basin, a region of high mercury (Hg) contamination, which raises the possibility that observed declines in Purple Martins could be linked to mercury exposure. Hg is a toxic heavy metal; exposure to and bioaccumulation of Hg can result in numerous and systemic negative health outcomes, including disruption of hormones like Corticosterone (B) and triiodothyronine (T3). Both play important roles in metabolic regulation in migratory birds. Feathers, tissues that accumulate Hg and hormones during growth and can thus be used as a proxy to assess a bird's Hg load and endocrine profile. The objective of this study is to assess interrelationships among total Hg (THg), B and T3 concentrations in feathers grown in the Amazon and reproductive (productivity) and body condition (mass, fat score) endpoints. We assayed tail feathers from 80 Purple Martins from their breeding grounds in Florida, Virginia, and Wisconsin. The concentration of THg in Purple Martins’ feathers ranged from 1.103 ug/g dw to 8.740 ug/g dw, which is above the level at which physiological impacts have been observed in studies of other avian species. Hg concentration did not significantly differ by sampling locations or correlate with either B, T3 or nest productivity. However, THg concentration negatively correlated with both mass and fat score. Both B and T3 concentrations were significantly higher in Florida than in the other two states, but neither showed correlations with biometric data or nest productivity. Furthermore, B concentrations in three birds from Florida were much higher than the basal range and may indicate a high stress condition during feather-growth in South America. Taken together, our findings suggest that concentrations of THg in Purple Martins’ feathers are high enough to be a cause of concern. The results show that THg concentration negatively impacts the ability of Purple Martins to accumulate fat, which can present a deleterious effect for a migratory bird. This result also indicates carryover effects of Hg contamination at the wintering grounds to the summer breeding grounds, where fat score was measured. The impact on fat accumulation, however, did not appear to be caused by Hg disruption of T3 or B at the time of feather-growth. Nevertheless, endocrine disruption by Hg could still have happened at a later moment. These physiological impacts suggest a possible mechanism by which high THg exposure in the nonbreeding grounds could negatively impact purple martins and have contributed to observed population declines over the last several decade.

APPLICATION OF COUPLED HEC-HMS AND US EPA WASP FOR TRANSPORT MODELLING OF MERCURY IN THE MINING-IMPACTED AMBALANGA RIVER

This study provides a simulation of mercury (Hg) transport in water and sediments in the mining-impacted Ambalanga River located in Upper Agno Subbasin in the Philippines. The Hydrologic Engineering Center - Hydrologic Modeling System (HEC-HMS) and Water Quality Analysis Simulation Program (WASP) of the US Environmental Protection Agency (EPA) were coupled to handle both hydrologic modelling and total Hg transport processes, respectively, for 12 months in the year 2014. Watershed delineation from Digital Elevation Model, rainfall and streamflow data from the local weather bureau, and dam operational data were used to develop the hydrological model. The calibrated HEC-HMS model satisfactorily simulated the flow in the river and its tributaries, which is then used as an input to the Hg transport model. The Ambalanga subbasin was conceptually divided into 29 segments in WASP to represent the water column and the surface benthic sediment. Time-variable sediment and Hg load were applied to the upstream of Ambalanga River. Total Hg concentration in water and sediments at five sampling locations along the Ambalanga River and two sampling locations along the Upper Agno River were measured in 2014-2015, in addition to the Hg monitoring data from the local environmental bureau. The gathered data were used to validate the WASP model, and results show that it was able to reasonably simulate the Hg fate and transport. Simulation results showed a downward trend in Hg concentration in surface water and sediments from upstream to downstream, while Hg in sediments was observed to stabilize over time. The model was further utilized to come up with exceedance curves of Hg in water and sediments as a result of the river’s response to different Hg loading from the known point sources. The exceedance curves derived from the model were used to determine the maximum permissible Hg loading to the river and identify pollution load reduction measures for river rehabilitation.

Distribution and bioavailability of mercury in the surface sediments of the Baltic Sea

The study aimed to determine the level of mercury (Hg) and its labile and stable forms in the surface sediments of the Baltic Sea. The work considers the impact of current and historical sources of Hg on sediment pollution, together with the influence of different environmental parameters, including water inflows from the North Sea. Surface sediments (top 5 cm) were collected in 2016–2017 at 91 stations located in different areas of the Baltic Sea, including Belt Sea, Arkona Basin, Bornholm Basin, Gdańsk Basin, West Gotland Basin, East Gotland Basin, and the Bothnian Sea. Besides, the particulate matter suspended in the surface and near-bottom water was also collected. The analysis of total Hg concentration and individual Hg forms in collected samples was carried out using a 5-step thermodesorption method. This method allows for the identification of three labile and thus biologically available, fractions of Hg, which are mercury halides, organic Hg, mercury oxide and sulphate. Two stable fractions, mercury sulphide and residual Hg, were also determined. The highest Hg concentrations, reaching 341 ng g−1, were measured in the highly industrialised Kiel Bay, which was additionally a munition dumping site during and after World War II. High Hg level, ranging from 228 to 255 ng g−1, was also recorded in the surface sediments of the Arkona Basin, which was a result of the cumulative effect of several factors, such as deposition of Hg-rich riverine matter, favourable hydrodynamic conditions and military activities in the past. The relatively elevated Hg concentrations, varying from 60 to 264 ng g−1, were found in the Gdańsk Basin, a region under strong anthropopressure and dominated by soft sediments. The sum of labile Hg in sediments was high and averaged 67% (with the domination of organic Hg compounds), which means that a large part of Hg can be released to the water column. It was found that the water inflows from the North Sea intensify the remobilisation of Hg and its transformation into bioavailable labile forms. As a consequence, the load of Hg introduced into the trophic chain can increase. Despite the significant reduction of Hg emission into the Baltic in the last decades, surface sediments can be an important secondary Hg source in the marine ecosystem. This is especially dangerous in the case of the western Baltic Sea.

Significant mercury efflux from a Karst region in Southwest China - Results from mass balance studies in two catchments

Karst regions have long been recognised as landscapes of ecological vulnerability, however the mass balance and fate of mercury (Hg) in karst regions have not been well documented. This study focused on the largest contiguous karst area in China and investigated Hg mass balance in two catchments, one with high geological Hg (Huilong) and the other representative of regional background Hg (Chenqi). The mass balance of Hg was calculated separately for the two catchments by considering Hg in throughfall, open field precipitation, total suspended particulate matter (TSP), litterfall, fertilizer, crop harvesting, air-surface Hg0 exchange, surface runoff and underground runoff. Results show that litterfall Hg deposition is the largest loading (from atmosphere) of Hg in both catchments, accounting for 61.5% and 38.5% of the total Hg input at Huilong and Chenqi, respectively. Air-surface Hg0 exchange is the largest efflux, accounting for 71.7% and 44.6% of the total Hg output from Huilong and Chenqi, respectively. Because both catchments are subject to farm and forest land use, cultivation plays an important role in shaping Hg fate. Mercury loading through fertilizer was ranked as the second largest input (28.5%) in Chenqi catchment and Hg efflux through crop harvest was ranked as the second largest output pathway in both Huilong (27.0%) and Chenqi (52.9%). The net Hg fluxes from the catchments are estimated to be 1498 ± 1504 μg m−2 yr−1 and 4.8 ± 98.2 μg m−2 yr−1. The significantly greater magnitude of net Hg source in Huilong is attributed to higher air-surface Hg0 exchange. The output/input ratio of Hg in this study was much greater than has been reported for other forest or agricultural ecosystems and indicates that the karst region of Southwest China is a significant source of atmospheric Hg. The results of this study should be considered in the development of pollution control policies which seek to conserve fragile karst ecosystems characterised by high geological background of Hg.

Effect of organic matter concentration and characteristics on mercury mobilization and methylmercury production at an abandoned mine site.

Thousands of abandoned mines throughout the western region of North America contain elevated total-mercury (THg) concentrations. Mercury is mobilized from these sites primarily due to erosion of particulate-bound Hg (THg-P). Organic matter-based soil amendments can promote vegetation growth on mine tailings, reducing erosion and subsequent loading of THg-P into downstream waterbodies. However, the introduction of a labile carbon source may stimulate microbial activity that can produce methylmercury (MeHg)-the more toxic and bioaccumulative form of Hg. Our objectives were to investigate how additions of different organic matter substrates impact Hg mobilization and methylation using a combination of field observations and controlled experiments. Field measurements of water, sediment, and porewater were collected downstream of the site and multi-year monitoring (and load calculations) were conducted at a downstream gaging station. MeHg production was assessed using stable isotope methylation assays and mesocosm experiments that were conducted using different types of organic carbon soil amendments mixed with materials from the mine site. The results showed that >80% of the THg mobilized from the mine was bound to particles and that >90% of the annual Hg loading occurred during the period of elevated discharge during spring snowmelt. Methylation rates varied between different types of soil amendments and were correlated with the components of excitation emission matrices (EEMs) associated with humic acid fractions of organic matter. The mesocosm experiments showed that under anoxic conditions carbon amendments to tailings could significantly increase porewater MeHg concentrations (up to 13±3ng/L). In addition, the carbon amendments significantly increased THg partitioning into porewater. Overall, these results indicate that soil amendment applications to reduce surface erosion at abandoned mine sites could be effective at reducing particulate Hg mobilization to downstream waterbodies; however, some types of carbon amendments can significantly increase Hg methylation as well as increase the mobilization of dissolved THg from the site.

Environmental challenges from the increasing medical waste since SARS outbreak.

Medical waste is a special class of hazardous pollutants. Improper treatment would cause secondary environmental pollution, especially when responding to public health emergencies. However, there are relatively few researches on the generation of medical waste, and there is a lack of basic understanding of its spatial-temporal heterogeneity. The outbreak of SARS in 2002 is a turning point in China’s medical system reform. We estimated the production of medical waste and pollutants on a provincial scale in China from 2002 to 2018, using the data of medical statistics. Moreover, we forecasted the trend of medical waste in China until 2030, using a combination of environmental pressure model (STIRPAT) and time series model (ARIMA). We found that with the development of China’s medical system and economy (such as the increase in personal income and popularization of universal health care), the number of seeking medical treatment rapidly increase led to explosive growth in medical waste (∼240%) and pollutants (∼260%), and large hospitals are the major sources. By 2030, the production of medical waste would still increase by more than 50% compared with 2018 even there is no the pandemic due to the huge population. The production of medical waste in the eastern region was higher than that in the west under the influence of higher population and GDP, while the per capita medical waste was only affected by household consumption level which had no regional characteristic. Additionally, Hg loads from medical waste are more than twice as high as that from discharged wastewater in some regions, which are facing great control pressures. In the future, when planning for medical waste disposal, policymakers shall increase the disposal facilities based on population and promote mobile treatment equipment to improve efficiency, increase the number of beds in medical institutions rather than building more hospitals, and strengthen basic research on the environmental impact.

Major volcanic eruptions linked to the Late Ordovician mass extinction: Evidence from mercury enrichment and Hg isotopes

Abstract The Late Ordovician mass extinction (LOME) was the second most severe Phanerozoic biodiversity crisis. While environmental deterioration and oceanographic changes associated with the Hirnantian glaciation have been frequently invoked as potential extinction drivers, recent evidence for a large igneous province eruption at that time has challenged this prevailing view. As such, the triggering and killing mechanisms of the LOME remain debated. Here we report mercury (Hg) concentrations, isotopic compositions, Hg/total sulfur (Hg/TS), and Hg/total organic carbon (Hg/TOC) in Late Ordovician limestone/black shale alternations from two successions in South China and Laurentia that straddled the paleoequator. Our results, in both areas, show multiple Hg enrichments before and during the LOME, suggesting a global, or at least a widespread increase in environmental Hg loading. The initial Hg enrichments occur in the mid-upper Katian units and are followed by additional Hg anomalies in the lower Hirnantian strata that coincide temporally with the first pulse of the LOME. Extremely high levels of Hg, Hg/TS, and Hg/TOC, with maximum values of 737 ng g−1, 633 ng g−1 Hg/wt% TS, and 167 ng g−1 Hg/wt% TOC, respectively, represent ~3–13 × background values, indicating increased Hg input to the ocean. The absence of mass-independent fractionation of Hg isotopes in the Hg-enriched intervals suggests a volcanic source for the observed Hg anomalies. The temporal coincidence of Hg anomalies with the extinction horizon in both continents suggests that extensive and widespread volcanism may have had global climatic and ecological impact, and was a primary trigger for prolonged and synergetic deterioration of Late Ordovician environment such as climate changes, ocean acidification, and anoxia, causing the LOME.

Impact of Old and Recent Gold Mining Sites on Mercury Fluxes in Suspended Particulate Matter, Water and Sediment in French Guiana

In 2006 the use of mercury (Hg) was banned for gold mining in French Guiana. However, mining of old placers could mobilize Hg accumulated in soils and sediment. This study aimed to measure the current impact of a mining concession (Boulanger site) on the Hg load in the watershed. Turbidity, Total Mercury (THg), and Monomethylmercury (MMHg) were measured in water, suspended particulate matter (SPM), river sediment and sediments from old tailing ponds along a river section of 30 km up and downstream from a mining concession in French Guiana during a dry and a rainy season. Total dissolved Hg (THgD) concentrations varied little from up- to down-stream but were all higher (fourfold on average) during the rainy season (3.2 to 4.4 ng L−1), than during the dry season and consistent with previous data known for the Amazonian area. Dissolved MMHg (MMHgD) represented up to 30% of THgD during the dry season, which is higher than previous results (typically around 2%). Mercury concentrations in sediments were highest in the vicinity of areas affected by old (before 2006) rather than new gold mining practices. Even though Hg was banned in 2006, present gold mining practices still release natural Hg and Hg inherited from older mining practices into the watershed.

Mercury screening in highly consumed sharpnose sharks (Rhizoprionodon lalandii and R. porosus) caught artisanally in southeastern Brazil

Sharpnose sharks Rhizoprionodon lalandii and R. porosus are frequently captured in fishing activities in Brazil and are significantly consumed by humans, especially in southeastern Brazil. Both species lack population data and suffer intense fishing pressures and habitat degradation, consequently hindering adequate management and conservation actions. In this context, this study aimed to assess mercury (Hg) contamination in R. lalandii, and R. porosus sampled off the coast of Rio de Janeiro, addressing both animal health and public health risks. Sharks were obtained from two artisanal fishing colonies in southeastern Brazil (Copacabana and Recreio dos Bandeirantes), located on the coastal zone adjacent to Guanabara Bay, one of the most important, productive, and contaminated estuaries in Brazil, and a further three artisanal fishing colonies from the Região dos Lagos area (Saquarema, Cabo Frio and Rio das Ostras). Hg concentrations in liver, muscle, and brain in R. lalandii (n = 24) and R. porosus (n = 20) specimens were determined by inductively coupled plasma mass spectrometry. A gravid female measuring 112 cm from Copacabana is the first record for an individual of this size for R. lalandii. No correlation between length and muscle Hg concentrations was observed, and no differences between Hg concentrations for muscle or liver were found between male and female juveniles from either Cabo Frio or Rio das Ostras. No differences in Hg loads were observed herein for both assessed species. Low Hg bioaccumulation in juveniles and nongravid female muscle tissue was noted compared to significantly higher Hg concentrations in gravid females. Hg was detected in all embryos, indicating potential maternal offloading. As Hg thresholds for sharks in particular have not yet been established, whether the Hg concentrations detected in brain pose neurotoxic risks for these animals is not known. Public health concerns concerning adult R. lalandii consumption from Copacabana, however, are significant.

Mercury concentrations and associations with dissolved organic matter are modified by water residence time in eastern Canadian lakes along a 30° latitudinal gradient

AbstractSurface water mercury (Hg) and dissolved organic carbon (DOC) concentrations and their ratios, which play a critical role in food chain bioaccumulation of Hg, were examined in lakes from southern boreal, sub‐Arctic taiga, Arctic tundra and polar desert landscapes of eastern and northern Canada. The study sites investigated span a 30° latitudinal gradient representing differences in climate, ecosystem productivity, and atmospheric mercury deposition. Lakes were selected to obtain a range of simple morphometrics such as area, depth, volume and catchment area, with corresponding differences in water residence times (WRT), ranging from 0.1 to 7.5 years. Total mercury (THg) and mono‐methylmercury (MMHg) concentrations correlated positively but weakly with DOC in lake surface waters along the climate gradient, consistent with lower ecosystem and organic matter productivity at higher latitudes. Specific UV absorbance, an indicator of terrestrial organic matter sources, was found to explain some residual variability in THg not explained by DOC. Concentrations of THg and MMHg and their ratios with DOC, particularly the MMHg : DOC ratio as well as %MMHg, were best explained by inverse associations with WRT. These relationships were apparent both within and between regions along the latitudinal gradient, suggesting a net‐negative effect of in‐lake processing on THg and MMHg concentrations associated with longer WRTs. Since the water MMHg : DOC ratio was previously shown to explain foodweb MMHg in the same study lakes, our results suggest that smaller lakes with shorter residence times are more susceptible to MMHg exposure even at low levels of inorganic Hg loading or MMHg production.

Mercury Uptake Affects the Development of Larus fuscus Chicks.

Current emission and mobilization rates of mercury (Hg) in the environment pose extensive threats to both wildlife and human health. Assessing the exposure risk and effects of Hg contamination in model species such as seabirds is essential to understand Hg risks at the population and ecosystem levels. The lesser black-backed gull (Larus fuscus), a generalist seabird species, is an excellent model species because it forages in both marine and terrestrial habitats, which in turn differ in their Hg exposure risk. To identify possible deleterious effects of Hg exposure on developing L. fuscus chicks, a dietary experiment was carried out and chicks were provided a marine, terrestrial, or mixed diet. The effects of embryonic and dietary Hg exposure on chick body condition and physiological state were assessed at different developmental stages until fledging age (30 d). Overall physiological condition was lower in chicks fed a predominantly marine diet, which coincided with higher Hg loads in blood and primary feathers. However, no effect of dietary uptake of Hg was observed on body condition or in terms of genotoxic damage. Body condition and genotoxic damage correlated instead with Hg exposure during embryonic development, which seems to indicate that embryonic exposure to Hg may result in carry-over effects on later chick development. Environ Toxicol Chem 2020;39:2008-2017. © 2020 SETAC.

Traceable Determination of Atmospheric Mercury Using Iodinated Activated Carbon Traps

Traceable determination of atmospheric mercury (Hg) represents a major analytical problem due to low environmental concentrations. Although Hg pre-concentration on activated carbon (AC) traps is a simple method for sample collection, Hg determination is difficult due to a complex matrix that cannot be easily digested using wet chemistry. Two approaches for Hg loading on iodinated AC, the purging of elemental mercury (Hg0) and the spiking a solution of standard reference material (SRM), were used to test whether spiking SRM solution on AC can be used for the traceable determination of atmospheric mercury collected as Hg0. Mercury on AC was determined using atomic absorption spectrometry after sample combustion. The detector’s response for both loading methods was identical in a wide concentration range, indicating that the spiking of SRM on AC can, indeed, be used for the calibration of analytical systems used for the determination of atmospheric mercury. This was confirmed by the determination of Hg in a real atmospheric sample collected on an iodinated AC trap and using an SRM spiking calibration. Different ACs were compared regarding their ability to quantitatively capture Hg while having the lowest breakthrough. Use of a specific impregnating solution probably converted Hg on AC to Millon’s iodide, as estimated from the fractionation thermogram.

The impact of lime additions on mercury dynamics in stream chemistry and macroinvertebrates: a comparison of watershed and direct stream addition management strategies.

Acid deposition has declined across eastern North America and northern Europe due to reduced emissions of sulfur and nitrogen oxides. Ecosystem recovery has been slow with limited improvement in surface water chemistry. Delayed recovery has encouraged acid-neutralization strategies to accelerate recovery of impaired biological communities. Lime application has been shown to increase pH and dissolved organic carbon (DOC), which could also drive increased mobilization of mercury (Hg) to surface waters. A four-year study was conducted within Honnedaga Lake's watershed in the Adirondack region of New York to compare the effects of watershed and direct channel lime additions on Hg in stream water and macroinvertebrates. All treatments sharply increased stream pH and DOC concentrations, but large differences in the duration of impacts were apparent. The watershed treatment resulted in multi-year increases in concentrations and loads of total Hg (150%; 390%), DOC (190%; 350%) and nutrients, whereas total Hg and DOC increased for short periods (72-96 h) after channel treatments. No response of Hg in macroinvertebrates was evident following the watershed treatment, but a potential short-term and spatially constrained increase occurred after the channel treatment. Our observations indicate that both treatment approaches mobilize Hg, but that direct channel liming mobilizes considerably less than watershed liming over any period longer than a few days. During the final study year, increased methyl Hg concentrations were observed across reference and treated streams, which may reflect an extended dry period, highlighting that climate variation may also affect Hg dynamics.

Late Ordovician mass extinction caused by volcanism, warming, and anoxia, not cooling and glaciation: REPLY

The Ordovician saw major diversification in marine life abruptly terminated by the Late Ordovician mass extinction (LOME). Around 85% of species were eliminated in two pulses 1 m.y. apart. The first pulse, in the basal Hirnantian, has been linked to cooling and Gondwanan glaciation. The second pulse, later in the Hirnantian, is attributed to warming and anoxia. Previously reported mercury (Hg) spikes in Nevada (USA), South China, and Poland implicate an unknown large igneous province (LIP) in the crisis, but the timing of Hg loading has led to different interpretations of the LIP-extinction scenario in which volcanism causes cooling, warming, or both. We report close correspondence between Hg, Mo, and U anomalies, declines in enrichment factors of productivity proxies, and the two LOME pulses at the Ordovician-Silurian boundary stratotype (Dob's Linn, Scotland). These support an extinction scenario in which volcanogenic greenhouse gases caused warming around the Katian-Hirnantian boundary that led to expansion of a preexisting deepwater oxygen minimum zone, productivity collapse, and the first LOME pulse. Renewed volcanism in the Hirnantian stimulated further warming and anoxia and the second LOME pulse. Rather than being the odd-one-out of the "Big Five" extinctions with origins in cooling, the LOME is similar to the others in being caused by volcanism, warming, and anoxia.