Toward an assessment of the global inventory of present-day mercury releases to freshwater environments

Aquatic ecosystems are an essential component of the biogeochemical cycle of mercury (Hg), as inorganic Hg can be converted to toxic methylmercury (MeHg) in these environments and reemissions of elemental Hg rival anthropogenic Hg releases on a global scale. Quantification of effluent Hg releases to aquatic systems globally has focused on discharges to the global oceans, rather than contributions to freshwater systems that affect local exposures and risks associated with MeHg. Here we produce a first-estimate of sector-specific, spatially resolved global aquatic Hg discharges to freshwater systems. We compare our release estimates to atmospheric sources that have been quantified elsewhere. By analyzing available quantitative and qualitative information, we estimate that present-day global Hg releases to freshwater environments (rivers and lakes) associated with anthropogenic activities have a lower bound of ~1000 Mg· a−1. Artisanal and small-scale gold mining (ASGM) represents the single largest source, followed by disposal of mercury-containing products and domestic waste water, metal production, and releases from industrial installations such as chlor-alkali plants and oil refineries. In addition to these direct anthropogenic inputs, diffuse inputs from land management activities and remobilization of Hg previously accumulated in terrestrial ecosystems are likely comparable in magnitude. Aquatic discharges of Hg are greatly understudied and further constraining associated data gaps is crucial for reducing the uncertainties in the global biogeochemical Hg budget

Seabird Transfer of Nutrients and Trace Elements from the North Water Polynya to Land during the Mid-Holocene Warm Period, Carey Islands, Northwest Greenland + Supplementary Appendix Figure S1 (See Article Tools)

Seabird guano from large nesting colonies is known to increase trace metal levels in adjacent terrestrial environments today, when global oceans are contaminated with Hg, Cd, and other metals. But the effect of seabird guano in the pre-industrial period has rarely been studied. We used stable C and N isotopic and trace element analyses of a peat core that represents ca. 2000 years of organic matter accumulation to examine the effect on trace elements and nutrients of a seabird colony that existed in northern Baffin Bay during the Holocene Thermal Maximum (ca. 8000–5000 yr BP). Although C and N concentrations were typical of those in other peats, isotopic data identified marine organic matter as the main source of N and a minor source of C in the peat and showed that the unknown seabird was a fish-eating species that was summer-resident for the 2000 yr period. Concentrations of Cd, Br, Sr, and Zn in peat were up to an order of magnitude higher than in ombrotrophic (air-fed) bogs elsewhere, whereas Hg and Cu concentrations were similar to those in other peats, suggesting relatively low levels of Hg and Cu in the guano. This surprising result for Hg contrasts with studies on modern seabirds, in which guano markedly increased environmental Hg concentrations. It could be a consequence of Hg concentrations in Arctic marine food webs in the pre-industrial period that were an order of magnitude lower than those of today.On sait aujourd’hui que le guano d’oiseaux marins provenant des grandes colonies nicheuses fait augmenter les teneurs en métaux-traces dans les milieux terrestres adjacents et que tous les océans sont contaminés au Hg, au Cd et autres métaux. Toutefois, l’effet du guano d’oiseaux marins dans la période préindustrielle a rarement fait l’objet d’études. Nous avons utilisé des isotopes stables de carbone d’azote et des analyses d’oligoéléments d’une carotte de tourbe, qui représente environ 2000 ans d’accumulation de matières organiques, pour examiner l’effet de la présence d’une colonie d’oiseaux marins qui a existé dans le nord de la baie de Baffin pendant le maximum thermique de l’Holocène (environ 8000 à 5000 ans BP) sur les oligoéléments et les nutriments. Même si les concentrations de C et de N étaient semblables à celles se trouvant dans d’autres tourbes, les données isotopiques ont démontré que la principale source de N, et une source mineure de C, provenaient de matières organiques marines, indiquant ainsi que les oiseaux marins inconnus étaient des espèces piscivores qui y ont résidé l’été pendant 2000 ans. Les concentrations de Cd, Br, Sr et Zn dans la tourbe étaient d’un ordre de grandeur supérieur à celles des tourbières ombrotrophes (alimentées par l’air) d’ailleurs, tandis que les concentrations de Hg et de Cu étaient semblables à celles d’autres tourbes, ce qui laisse sous-entendre des niveaux relativement bas de Hg et Cu dans le guano. Ce résultat concernant le Hg est surprenant, car il est contraire aux études modernes sur les oiseaux marins démontrant que le guano a considérablement augmenté les concentrations de Hg dans l’environnement. Cette augmentation pourrait être attribuable aux concentrations de Hg dans les réseaux alimentaires marins de l’Arctique lors de la période préindustrielle, d’un ordre de grandeur inférieur aux concentrations d’aujourd’hui

High mercury accumulation in deep-ocean hadal sediments

Ocean sediments are the largest sink for mercury (Hg) sequestration and hence an important part of the global Hg cycle(1). Yet accepted global average Hg flux data for deep-ocean sediments (> 200 m depth) are not based on measurements on sediments but are inferred from sinking particulates(2). Mercury fluxes have never been reported from the deepest zone, the hadal (> 6 km depth). Here we report the first measurements of Hg fluxes from two hadal trenches (Atacama and Kermadec) and adjacent abyssal areas (2-6 km). Mercury concentrations of up to 400 ng g(-1) were the highest recorded in marine sediments remote from anthropogenic or hydrothermal sources. The two trench systems differed significantly in Hg concentrations and fluxes, but hadal and abyssal areas within each system did not. The relatively low recent mean flux at Kermadec was 6-15 times higher than the inferred deep-ocean average(1,3), while the median flux across all cores was 22-56 times higher. Thus, some hadal and abyssal sediments are Hg accumulation hot-spots. The hadal zone comprises only similar to 1% of the deep-ocean area, yet a preliminary estimate based on sediment Hg and particulate organic carbon (POC) fluxes suggests total hadal Hg accumulation may be 12-30% of the estimate for the entire deep-ocean. The few abyssal data show equally high Hg fluxes near trench systems. These results highlight a need for further research into deep-ocean Hg fluxes to better constrain global Hg models

Volcanic mercury and mutagenesis in land plants during the end-Triassic mass extinction

During the past 600 million years of Earth history, four of five major extinction events were synchronous with volcanism in large igneous provinces. Despite improved temporal frameworks for these events, the mechanisms causing extinctions remain unclear. Volcanic emissions of greenhouse gases, SO2, and halocarbons are generally considered as major factors in the biotic crises, resulting in global warming, acid deposition, and ozone layer depletion. Here, we show that pulsed elevated concentrations of mercury in marine and terrestrial sediments across the Triassic-Jurassic boundary in southern Scandinavia and northern Germany correlate with intense volcanic activity in the Central Atlantic Magmatic Province. The increased levels of mercury-the most genotoxic element on Earth-also correlate with high occurrences of abnormal fern spores, indicating severe environmental stress and genetic disturbance in the parent plants. We conclude that this offers compelling evidence that emissions of toxic volcanogenic substances contributed to the end-Triassic biotic crisis

Volcanic mercury and mutagenesis in land plants during the end-Triassic mass extinction

During the past 600 million years of Earth history, four of five major extinction events were synchronous with volcanism in large igneous provinces. Despite improved temporal frameworks for these events, the mechanisms causing extinctions remain unclear. Volcanic emissions of greenhouse gases, SO2, and halocarbons are generally considered as major factors in the biotic crises, resulting in global warming, acid deposition, and ozone layer depletion. Here, we show that pulsed elevated concentrations of mercury in marine and terrestrial sediments across the Triassic-Jurassic boundary in southern Scandinavia and northern Germany correlate with intense volcanic activity in the Central Atlantic Magmatic Province. The increased levels of mercury-the most genotoxic element on Earth-also correlate with high occurrences of abnormal fern spores, indicating severe environmental stress and genetic disturbance in the parent plants. We conclude that this offers compelling evidence that emissions of toxic volcanogenic substances contributed to the end-Triassic biotic crisis

Climate change and mercury in the Arctic : Abiotic interactions

Dramatic environmental shifts are occuring throughout the Arctic from climate change, with consequences for the cycling of mercury (Hg). This review summarizes the latest science on how climate change is influencing Hg transport and biogeochemical cycling in Arctic terrestrial, freshwater and marine ecosystems. As environmental changes in the Arctic continue to accelerate, a clearer picture is emerging of the profound shifts in the climate and cryosphere, and their connections to Hg cycling. Modeling results suggest climate influences seasonal and interannual variability of atmospheric Hg deposition. The clearest evidence of current climate change effects is for Hg transport from terrestrial catchments, where widespread permafrost thaw, glacier melt and coastal erosion are increasing the export of Hg to downstream environments. Recent estimates suggest Arctic permafrost is a large global reservoir of Hg, which is vulnerable to degradation with climate warming, although the fate of permafrost soil Hg is unclear. The increasing development of thermokarst features, the formation and expansion of thaw lakes, and increased soil erosion in terrestrial landscapes are increasing river transport of particulate-bound Hg and altering conditions for aquatic Hg transformations. Greater organic matter transport may also be influencing the downstream transport and fate of Hg. More severe and frequent wildfires within the Arctic and across boreal regions may be contributing to the atmospheric pool of Hg. Climate change influences on Hg biogeochemical cycling remain poorly understood. Seasonal evasion and retention of inorganic Hg may be altered by reduced sea-ice cover and higher chloride content in snow. Experimental evidence indicates warmer temperatures enhance methylmercury production in ocean and lake sediments as well as in tundra soils. Improved geographic coverage of measurements and modeling approaches are needed to better evaluate net effects of climate change and long-term implications for Hg contamination in the Arctic. Highlights • Current evidence indicates climate change is influencing Hg cycling in the Arctic. • Permafrost thaw, glacier melt, and coastal erosion are increasing Hg export. • Arctic permafrost is a global Hg reservoir, vulnerable to degradation and release. • Experiments show warmer temperatures increase MeHg in Arctic sediments and soils. • Net effects of climate change on Arctic Hg contamination remain poorly resolved

The fate of mercury in Arctic terrestrial and aquatic ecosystems, a review

International audienceThis review is the result of a series of multidisciplinary meetings organised by the Arctic Monitoring and Assessment Programme as part of their 2011 Assessment 'Mercury in the Arctic'. This paper presents the state-of-the-art knowledge on the environmental fate of mercury following its entry into the Arctic by oceanic, atmospheric and terrestrial pathways. Our focus is on the movement, transformation and bioaccumulation of Hg in aquatic (marine and fresh water) and terrestrial ecosystems. The processes most relevant to biological Hg uptake and the potential risk associated with Hg exposure in wildlife are emphasised. We present discussions of the chemical transformations of newly deposited or transported Hg in marine, fresh water and terrestrial environments and of the movement of Hg from air, soil and water environmental compartments into food webs. Methylation, a key process controlling the fate of Hg in most ecosystems, and the role of trophic processes in controlling Hg in higher order animals are also included. Case studies on Eastern Beaufort Sea beluga (Delphinapterus leucas) and landlocked Arctic char (Salvelinus alpinus) are presented as examples of the relationship between ecosystem trophic processes and biologic Hg levels. We examine whether atmospheric mercury depletion events (AMDEs) contribute to increased Hg levels in Arctic biota and provide information on the links between organic carbon and Hg speciation, dynamics and bioavailability. Long-term sequestration of Hg into non-biological archives is also addressed. The review concludes by identifying major knowledge gaps in our understanding, including: (1) the rates of Hg entry into marine and terrestrial ecosystems and the rates of inorganic and MeHg uptake by Arctic microbial and algal communities; (2) the bioavailable fraction of AMDE-related Hg and its rate of accumulation by biota and (3) the fresh water and marine MeHg cycle in the Arctic, especially the marine MeHg cycle