Mercury bioaccumulation and biomagnification in a small Arctic polynya ecosystem

A specific visual-volumetric sensor for mercury ions based on smart hydrogel

On the basis of the "seeing is believing" concept and the existing theory of Hg2+ coordination chemistry, for the first time, we innovatively designed and synthesized a visual-volumetric sensor platform with fluorescein and uracil functionalized polyacrylamide hydrogel. Without the aid of any complicated instruments and power sources, the sensor-enabled quantitative μM-level Hg2+ detection Hg2+ by reading graduation on a pipette with the naked eye. The sensor undergoes volumetric response and shows a wide linear response range to Hg2+ (1.0 × 10-6-5.0 × 10-5 mol L-1) with 2.8 × 10-7 mol L-1 as the detection limit. The highly selective (easily distinguished Hg2+ from other common metal ions), rapid response (∼30 min), and acceptable repeatability (RSD < 5% in all cases) demonstrated that the developed sensor is suitable for onsite practical use for the determination of Hg2+ while being low-cost, simple, and portable. The design principles of the obtained materials and the construction techniques and methods of the sensors described in our study provide a new idea for the research and development of smart materials and a series of visual-volumetric sensors for other analytes.

New insight into biomagnification factor of mercury based on food web structure using stable isotopes of amino acids

Although many attempts have been carried out to elaborate trophic magnification factor (TMF) and biomagnification factor (BMF), such as normalizing the concentration of pollutants and averaging diet sources, the uncertainty of the indexes still need to be improved to assess the bioaccumulation of pollutants. This study first suggests an improved BMF (i.e., BMF') applied to mercury bioaccumulation in freshwater fish from four sites before and after rainfall. The diet source and TP of each fish were identified using nitrogen stable isotope of amino acids (δ15NAAs) combined with bulk carbon stable isotope (δ13C). The BMF' was calculated normalizing with TP and diet contributions derived from MixSIAR. The BMF' values (1.3-27.2 and 1.2-27.8), which are representative of the entire food web, were generally higher than TMF (1.5-13.9 and 1.5-14.5) for both total mercury and methyl mercury, respectively. The BMF' implying actual mercury transfer pathway is more reliable index than relatively underestimated TMF for risk assessment. The ecological approach for BMF calculations provides novel insight into the behavior and trophic transfer of pollutants like mercury.

Mercury accumulation, biomagnification, and relationships to δ13C, δ15N and δ34S of fishes and marine mammals in a coastal Arctic marine food web

Combining mercury and stable isotope data sets of consumers facilitates the quantification of whether contaminant variation in predators is due to diet, habitat use and/or environmental factors. We investigated inter-species variation in total Hg (THg) concentrations, trophic magnification slope between δ15N and THg, and relationships of THg with δ13C and δ34S in 15 fish and four marine mammal species (249 individuals in total) in coastal Arctic waters. Median THg concentration in muscle varied between species ranging from 0.08 ± 0.04 μg g-1 dw in capelin to 3.10 ± 0.80 μg g-1 dw in beluga whales. Both δ15N (r2 = 0.26) and δ34S (r2 = 0.19) best explained variation in log-THg across consumers. Higher THg concentrations occurred in higher trophic level species that consumed more pelagic-associated prey than consumers that rely on the benthic microbial-based food web. Our study illustrates the importance of using a multi-isotopic approach that includes δ34S when investigating trophic Hg dynamics in coastal marine systems.

Mercury bioaccumulation and speciation in coastal invertebrates: Implications for trophic magnification in a marine food web

Studies on mercury bioaccumulation and biomagnification in coastal invertebrates in eastern Canada are limited, but these data are necessary to determine risk of mercury exposure effects in upper trophic level organisms. We quantified methylmercury (MeHg), total mercury (THg), and stable isotopes of δ¹³C and δ¹⁵N in 14 species of invertebrates in the Minas Basin. The overall mean concentration of MeHg (12.78 ± 11.23 ng/g dw) was approximately 10 times below the Canadian guideline for the protection of wildlife consumers like fish and birds of 157.20 ng/g dry weight (dw). Invertebrates at higher trophic positions (δ¹⁵N) had greater THg and particularly MeHg. The Trophic Magnification Factors (TMF) for MeHg and THg (1.59 and 1.21 respectively) were similar to others reported in studies of food webs containing higher trophic level organisms.

Arctic methylmercury cycling

Anthropogenic mercury (Hg) undergoes long-range transport to the Arctic where some of it is transformed into methylmercury (MeHg), potentially leading to high exposure in some Arctic inhabitants and wildlife. The environmental exposure of Hg is determined not just by the amount of Hg entering the Arctic, but also by biogeochemical and ecological processes occurring in the Arctic. These processes affect MeHg uptake in biota by regulating the bioavailability, methylation and demethylation, bioaccumulation and biomagnification of MeHg in Arctic ecosystems. Here, we present a new budget for pools and fluxes of MeHg in the Arctic and review the scientific advances made in the last decade on processes leading to environmental exposure to Hg. Methylation and demethylation are key processes controlling the pool of MeHg available for bioaccumulation. Methylation of Hg occurs in diverse Arctic environments including permafrost, sediments and the ocean water column, and is primarily a process carried out by microorganisms. While microorganisms carrying the hgcAB gene pair (responsible for Hg methylation) have been identified in Arctic soils and thawing permafrost, the formation pathway of MeHg in oxic marine waters remains less clear. Hotspots for methylation of Hg in terrestrial environments include thermokarst wetlands, ponds and lakes. The shallow sub-surface enrichment of MeHg in the Arctic Ocean, in comparison to other marine systems, is a possible explanation for high MeHg concentrations in some Arctic biota. Bioconcentration of aqueous MeHg in bacteria and algae is a critical step in the transfer of Hg to top predators, which may be dampened or enhanced by the presence of organic matter. Variable trophic position has an important influence on MeHg concentrations among populations of top predator species such as ringed seal and polar bears distributed across the circumpolar Arctic. These scientific advances highlight key processes that affect the fate of anthropogenic Hg deposited to Arctic environments.

Mercury biomagnification in benthic, pelagic, and benthopelagic food webs in an Arctic marine ecosystem

Mercury (Hg) is a ubiquitous toxic metal that biomagnifies in food webs, and can reach high concentrations in top predators. Evaluating Hg biomagnification in Arctic marine food webs is critical for understanding Hg dynamics and estimating exposure to understudied fish and wildlife consumed by humans. The majority of studies conducted on Hg biomagnification in the Arctic have focused on pelagic food webs. Benthic and benthopelagic food webs in Arctic marine ecosystems also support many species of subsistence and commercial importance, and data are lacking for these systems. In this study, we investigated food web structure and Hg biomagnification for the benthic, pelagic, and benthopelagic marine food webs of inner Frobisher Bay in Nunavut. Stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N), as well as total (THg) and methyl (MeHg) mercury concentrations were measured in fish, invertebrates, and zooplankton. Biomagnification in each food web was quantified with Trophic Magnification Slopes (TMS) and Trophic Magnification Factors (TMF). The highest TMS and TMF values were exhibited by the benthopelagic food web (TMS = 0.201; TMF = 1.59), followed by the pelagic food web (TMS = 0.183; TMF = 1.52), and lastly the benthic food web (TMS = 0.079; TMF = 1.20), with δ¹⁵N explaining 88%, 79%, and 9% of variation in Hg concentrations, respectively. TMS and TMF values were generally low compared to other Arctic marine food webs. Results from food web structure analyses indicated that the benthic food web had the greatest trophic diversity, trophic redundancy, and largest isotopic niche area of all food webs studied. Greater food web complexity may thus result in reduced MeHg biomagnification, but further study is required. Acquiring Hg and food web structure data is critical for predicting the effects of climate-induced environmental change on Hg dynamics, especially in the context of Arctic marine ecosystems.

Comparison of Pollution Levels, Biomagnification Capacity, and Risk Assessments of Heavy Metals in Nearshore and Offshore Regions of the South China Sea

Seawater and fish were collected from nearshore (Pearl River Estuarine, PRE) and offshore (middle of the South China Sea, MSCS) regions of the South China Sea (SCS) to determine the heavy metals (HMs) pollution status and biomagnification characteristics. Results show that Cu in PRE seawater was moderately contaminated. Overall pollution risk of seawater were PRE (3.32) > MSCS (0.56), whereas that of fish was MSCS (0.88) > PRE (0.42). δ¹³C and δ¹⁵N exhibited distinguished characteristics for PRE and MSCS fish, indicating the diverse energy sources, nitrogen sources, and food web structures of nearshore and offshore regions. Cu was biomagnified whereas Pb and Ni were biodiluted in offshore fish. Hg presented significant biomagnification in both of nearshore and offshore fish. Finally, the target hazard quotient of Hg (1.41) in MSCS fish exceeded the standard limit, which was posed by high Hg concentration and consumption rate of offshore fish.

Drivers of biomagnification of Hg, As and Se in aquatic food webs: A review

Biomagnification of trace elements is increasingly evident in aquatic ecosystems. In this review we investigate the drivers of biomagnification of mercury (Hg), arsenic (As) and selenium (Se) in aquatic food webs. Despite Hg, As and Se biomagnify in food webs, the biomagnification potential of Hg is much higher than that of As and Se. The slope of trophic increase of Hg is consistent between temperate (0.20), tropical (0.22) and Arctic (0.22) ecosystems. Se exerts a mitigating role against Hg toxicity but desired maximum and minimum concentrations are unknown. Environmental (e.g. latitude, temperature and physicochemical characteristics) and ecological factors (e.g. trophic structure composition and food zone) can substantially influence the biomagnification process these metal (oids). Besides the level of bioaccumulated concentration, biomagnification depends on the biology, ecology and physiology of the organisms that play a key role in this process. However, it may be necessary to determine strictly biological, physiological and environmental factors that could modulate the concentrations of As and Se in particular. The information presented here should provide clues for research that include under-researched variables. Finally, we suggest that biomagnification be incorporated into environmental management policies, mainly in risk assessment, monitoring and environmental protection methods.

Exposure to cumulative stressors affects the laying phenology and incubation behaviour of an Arctic-breeding marine bird

Wildlife are exposed to multiple stressors across life-history stages, the effects of which can be amplified as human activity surges globally. In Arctic regions, increasing air and ocean temperatures, more severe weather systems, and exposure to environmental contaminants all represent stressors occurring simultaneously. While Arctic vertebrates, including marine birds, are expected to be at risk of adverse effects from these individual stressors, few studies have researched their combined impacts on breeding behaviour and reproductive success. The interactive effects of environmental conditions and mercury (Hg) contamination on laying phenology and incubation behaviour were examined in female common eiders (Somateria mollissima, mitiq, ᒥᑎᖅ ᐊᒪᐅᓕᒡᔪᐊᖅ) nesting at Canada's largest Arctic breeding colony. Conditions with higher pre-breeding air temperatures were linked to females with higher egg Hg concentrations laying earlier than those with lower Hg values. Furthermore, examination of a total of 190 days of incubation behaviour from 61 eiders across two years revealed a negative relationship between wind speed and the frequency of incubation interruptions. Importantly, exposure to higher air temperatures combined with lower Hg concentrations was significantly correlated with increased incubation interruptions. Although previous research has shown that warmer spring temperatures could afford lower quality females more time to improve body condition to successfully lay, results suggest these females may face stronger cumulative fitness costs during incubation in warmer years, potentially in combination with the effects of Hg on physiological stress and hormone secretion. This study highlights how multiple stressors exposure, driven by human-induced environmental changes, can have a complex influence on reproduction.

Methylmercury in caddisflies and mayflies: Influences of water and sediment chemistry

Quantifying methylmercury (MeHg) concentrations and uptake at the base of the food web is useful for assessing mercury exposure risk to higher trophic level organisms. Higher MeHg concentrations near the base of the food web may result in more MeHg exposure and accumulation in higher trophic organisms. Here, we analyze MeHg in caddisflies, mayflies, lake water, and sediment collected from two temperate lakes and one brook in Kejimkujik National Park, Nova Scotia, Canada. Overall, caddisfly larvae MeHg (15.38-276.96 ng/g; n = 29) was not significantly correlated with water chemistry. Whereas mayfly naiads MeHg (14.28-166.82 ng/g; n = 31) was positively correlated with water MeHg (r_s = 0.43), negatively correlated with pH (r_s = -0.49), and positively correlated with dissolved organic carbon (DOC; r_s = 0.48). Of the mercury in insect tissues, the %MeHg ranged from 56 to 75 % in caddisfly larvae and 38-47 % in mayfly naiads. MeHg bioaccumulation factors (BAF) varied greatly (water to tissue BAFs = 0.145 × 10⁶-1.054 × 10⁶; sediment to tissue BAFs = 0.017 × 10⁶-0.541 × 10⁶). This study highlights the importance of quantifying variations in MeHg bioaccumulation and BAFs of common aquatic insect bioindicators at the base of complex food webs.

Biomagnification and trophic transfer of total mercury and methylmercury in a sub-tropical montane forest food web, southwest China

Little is known about the bioaccumulation and trophic transfer of total mercury (THg) and methylmercury (MeHg) via food webs in terrestrial ecosystems, especially in subtropical forest ecosystems. In the present study, THg and MeHg were determined as well as the carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope composition in samples of soils, plants, invertebrates, and songbird feathers to construct food webs in a remote subtropical montane forest in Mt. Ailao, southwest China and assess the bioaccumulation, biomagnification, and trophic transfer of Hg. Results showed that the trophic levels (TLs) of all consumers ranged from 0.8 to 3.3 and followed the order of songbirds > spiders > omnivorous insects > herbivorous insects > plants, and THg and MeHg exhibited a clear biomagnification up the food chain from plants-herbivorous/omnivorous insects-spiders-songbirds. The lowest MeHg concentration was observed in pine needles ranged from 0.104 to 0.949 ng g^-1 with only a 1.6% ratio of MeHg to THg (MeHg%), while the highest MeHg concentrations ranged from 425 to 5272 ng g^-1 in songbirds with MeHg% values of up to 96%. High values of trophic magnification slope (TMS) for THg (0.22) and MeHg (0.38) were observed in plant-invertebrate-songbird food chain, verifying the significant bioaccumulation of Hg, particularly MeHg, in the remote subtropical forest ecosystem. This study confirmed the production and efficient biomagnification of MeHg in remote subtropical montane forest and the significant bioaccumulation of MeHg in terrestrial top predators.

Fecal Methylmercury Correlates With Gut Microbiota Taxa in Pacific Walruses (Odobenus rosmarus divergens)

OBJECTIVES

Methylmercury metabolism was investigated in Pacific walruses (Odobenus rosmarus divergens) from St. Lawrence Island, Alaska, United States.

METHODS

Total mercury and methylmercury concentrations were measured in fecal samples and paired colon samples (n = 16 walruses). Gut microbiota composition and diversity were determined using 16S rRNA gene sequencing. Associations between fecal and colon mercury and the 24 most prevalent gut microbiota taxa were investigated using linear models.

RESULTS

In fecal samples, the median values for total mercury, methylmercury, and %methylmercury (of total mercury) were 200 ng/g, 4.7 ng/g, and 2.5%, respectively, while in colon samples, the median values for the same parameters were 28 ng/g, 7.8 ng/g, and 26%, respectively. In fecal samples, methylmercury was negatively correlated with one Bacteroides genus, while members of the Oscillospirales order were positively correlated with both methylmercury and %methylmercury (of total mercury). In colon samples, %methylmercury (of total mercury) was negatively correlated with members of two genera, Romboutsia and Paeniclostridium.

CONCLUSIONS

Median %methylmercury (of total mercury) was 10 times higher in the colon compared to the fecal samples, suggesting that methylmercury was able to pass through the colon into systemic circulation. Fecal total mercury and/or methylmercury concentrations in walruses were comparable to some human studies despite differences in seafood consumption rates, suggesting that walruses excreted less mercury. There are no members (at this time) of the Oscillospirales order which are known to contain the genes to methylate mercury, suggesting the source of methylmercury in the gut was from diet and not in vivo methylation.

Mercury biomagnification in an ichthyic food chain of an amazon floodplain lake (Puruzinho Lake): Influence of seasonality and food chain modeling

Mercury (Hg) biomagnification in fish food chains is a relevant subject due to the high fish consumption of the Amazonian population and the high toxicity of this metal. In the Amazon, floodplain lake hydrodynamics change considerably along the four seasons of the hydrological cycle (rising water, high water, falling water and low water), which can influence Hg bioaccumulation in fish. The main aim of this study was to evaluate if Hg biomagnification is influenced by seasonality in a floodplain lake (Puruzinho Lake) in the Brazilian Amazon. Additionally, the influence of food chain modeling on measurement of Hg biomagnification was tested. Hg concentrations and stable isotope signatures (carbon and nitrogen) were estimated in four species, Mylossoma duriventre (herbivorous), Prochilodus nigricans (detritivorous), Cichla pleiozona (piscivorous) and Serrasalmus rhombeus (piscivorous). The "trophic magnification slope" (TMS) of the food chain composed by the four species was calculated and compared among the four seasons. There was no significant seasonal variation in TMS among rising water, high water, falling water and low water seasons (p = 0.08), suggesting that Hg biomagnification does not change seasonally. However, there was significant variation in TMS among different food chain models. Lower TMS was observed in a food chain composed of detritivorous and piscivorous fish (0.20) in comparison with a food chain composed of the four species (0.26). The results indicate food chain modeling influences TMS results.

Methylmercury biomagnification in coastal aquatic food webs from western Patagonia and western Antarctic Peninsula

Mercury (Hg) is a global pollutant of concern because its organic and more toxic form, methylHg (MeHg), bioaccumulates and biomagnifies through aquatic food webs to levels that affect the health of fish and fish consumers, including humans. Although much is known about trophic transfer of MeHg in aquatic food webs at temperate latitudes in the northern hemisphere, it is unclear whether its fate is similar in biota from coastal zones of the southeastern Pacific. To assess this gap, MeHg, total Hg and food web structure (using δ¹³C and δ¹⁵N) were measured in marine macroinvertebrates, fishes, birds, and mammals from Patagonian fjords and the Antarctic Peninsula. Trophic magnification slopes (TMS; log MeHg versus δ¹⁵N) for coastal food webs of Patagonia were high when compared with studies in the northern hemisphere, and significantly higher near freshwater inputs as compared to offshore sites (0.244 vs 0.192). Similarly, in Antarctica, the site closer to glacial inputs had a significantly higher TMS than the one in the Southern Shetland Islands (0.132 vs 0.073). Composition of the food web also had an influence, as the TMS increased when mammals and seabirds were excluded (0.132-0.221) at a coastal site. This study found that both the composition of the food web and the proximity to freshwater outflows are key factors influencing the TMS for MeHg in Patagonian and Antarctic food webs.

Formalin-preserved zooplankton are not reliable for historical reconstructions of methylmercury bioaccumulation

Time-series measurements of methylmercury (MeHg) concentrations in short-lived planktic animals, such as copepods, could allow for an evaluation of mercury (Hg) inputs and transferability to organisms in marine environments. If reliable, MeHg measurements in formalin-preserved marine animals could offer insights into past environmental MeHg levels. In the present study, we examined whether the amount of MeHg changed over time in formalin-preserved copepods for two species, Acartia tonsa, and Temora longicornis. Over a 51 (A. tonsa) and 7 (T. longicornis) week incubation, we found significant changes in MeHg content in both copepods, while the timing of these changes differed between species. Furthermore, we investigated the mechanism behind these temporal changes through a separate incubation experiment of formalin spiked with two levels of organic matter (OM), and stable-isotope-enriched Hg tracers. We found that the methylation of an inorganic ¹⁹⁹Hg tracer was significantly higher in OM-enriched solutions in comparison to a control seawater-formalin solution. Our results suggest that formalin-preserved copepods are not fit for studies of past trends due to ongoing and unpredictable abiotic transformations of Hg in chemically preserved animal tissue.

Arctic cleansing diet: Sex-specific variation in the rapid elimination of contaminants by the world's champion migrant, the Arctic tern

Contamination of Arctic marine environments continues to be a concern for wildlife managers. Because the Arctic is a sink for the long-range transport of persistent organic pollutants (POPs), many studies have detected high concentrations of POPs in various Arctic birds. In this study from high Arctic Canada, we show that male Arctic terns (Sterna paradisaea), which migrate from the Antarctic to the Arctic annually to breed, decline in concentrations of many hepatic POPs through the breeding season. This suggests that local Arctic food webs are less contaminated than regions where terns fed during or migration, despite that the terns appear to feed at a higher trophic level near their colony.

The role of benthic macrofauna in the trophic transfer of mercury in a low-diversity temperate coastal ecosystem (Puck Lagoon, southern Baltic Sea)

Mercury (Hg) is a global pollutant that affects human and ecosystem health. Hg is a serious threat especially for the marine environment, in which it undergoes bioaccumulation and biomagnification, reaching elevated concentrations in fish and other seafood. The research aimed at investigating the trophodynamics of Hg in the basal links of the marine food chain: benthic macrofauna and its main food sources (i.e. suspended and sediment organic matter, micro- and macrophytobenthos). The results showed that both the amount and the origin of organic matter affected the Hg level in particular trophic groups of macrozoobenthos. The intensive inflow of terrestrial material influenced the enrichment of suspended particles and microphytobenthos in Hg, leading to increased Hg concentrations in filter-feeding macrofauna. The input of Hg-rich marine matter transported from the deeper parts of the Gulf of Gdańsk along with the near-bottom currents caused higher Hg levels in deposit feeders. The biomagnification factor (BMF) of Hg through benthic food web was dependent on environmental conditions occurring in the studied areas, in particular, factors favouring the growth and fecundity of macrofauna. Consequently, as a result of biodilution, the trophic transfer of Hg was less effective in a more productive region, despite the elevated Hg concentrations in dietary components of the macrofauna and in the surrounding environment.

Limited effects of changing prey fish communities on food quality for aquatic predators in the eastern Canadian Arctic in terms of essential fatty acids, methylmercury and selenium

We determined concentrations of eicosapentaenoic and docosahexaenoic acids (EPA + DHA), Σomega-3, polyunsaturated fatty acids (ΣPUFA), selenium, methylmercury, and selenium:methylmercury (Se:Hg) ratios in native and northward-redistributing sub-Arctic marine fish and invertebrates from low, mid-, and high Canadian Arctic latitudes. There was no clear latitudinal trend in nutrient or contaminant concentrations. Among species, EPA + DHA concentrations in native Arctic cod (Boreogadus saida) were similar to concentrations in sub-Arctic capelin (Mallotus villosus) and sand lance (Ammodytes spp.) (444-658 mg.100 g^-1), and higher than in most other species. Concentrations of EPA + DHA were related to lipid content, but to a greater extent for higher trophic position species (R² = 0.83) than for species at lower trophic positions (R² = 0.61). Selenium concentrations were higher in sand lance (1.15 ± 0.16 μg g^-1) than in all other species (0.30-0.69 μg g^-1), which was significantly, but weakly, explained by more pelagic feeding in sand lance. Methylmercury concentrations were similar (and Se:Hg ratios were higher) in capelin, sand lance, and Arctic cod (0.01-0.03 μg g^-1 wet weight (ww)) and lower than in other prey (0.12-0.26 μg g^-1 ww), which was significantly explained by the smaller size of these species and more pelagic feeding habits than other fish. These results suggested that a shift in prey fish composition from Arctic cod to capelin and/or sand lance is unlikely to reduce the food quality of the prey available to marine predators at least with respect to concentrations of essential fatty acids, selenium, and Se:Hg ratios.

Mercury and selenium concentrations in Scyphozoan jellyfishes and pyrosomes from Monterey Bay National Marine Sanctuary

Gelatinous zooplankton including jellyfishes, pyrosomes, and salps serve as important prey items for a number of marine species; however, relatively few studies have examined contaminant concentrations in these animals. Scyphozoans (Aurelia sp., Chrysaora colorata, C. fuscescens, and Phacellophora camtschatica) and Thaliaceans (Pyrosoma sp.) were collected from 2009 to 2011 from Monterey Bay National Marine Sanctuary and analyzed for total mercury and selenium concentrations. In general, mercury (0.0001-0.0016 μg/g wet weight) and selenium (0.009-0.304 μg/g wet weight) concentrations of the sampled organisms were low; however, the two Pyrosoma sp. had total mercury and selenium concentrations that were one order of magnitude higher than the Scyphozoans. There was a significant positive relationship between mercury and selenium concentrations in jellyfishes and pyrosomes, suggesting a potential detoxification mechanism in these lower trophic level organisms. This study provides evidence that trophic transfer of mercury and selenium likely occurs through ingestion of gelatinous prey.

Spatial and taxonomic variation of mercury concentration in low trophic level fauna from the Mediterranean Sea

Studies of mercury (Hg) in the Mediterranean Sea have focused on pollution sources, air-sea mercury exchange, abiotic mercury cycling, and seafood. Much less is known about methylmercury (MeHg) concentrations in the lower food web. Zooplankton and small fish were sampled from the neuston layer at both coastal and open sea stations in the Mediterranean Sea during three cruise campaigns undertaken in the fall of 2011 and the summers of 2012 and 2013. Zooplankton and small fish were sorted by morphospecies, and the most abundant taxa (e.g. euphausiids, isopods, hyperiid amphipods) analyzed for methylmercury (MeHg) concentration. Unfiltered water samples were taken during the 2011 and 2012 cruises and analyzed for MeHg concentration. Multiple taxa suggested elevated MeHg concentrations in the Tyrrhenian and Balearic Seas in comparison with more eastern and western stations in the Mediterranean Sea. Spatial variation in zooplankton MeHg concentration is positively correlated with single time point whole water MeHg concentration for euphausiids and mysids and negatively correlated with maximum chlorophyll a concentration for euphausiids, mysids, and "smelt" fish. Taxonomic variation in MeHg concentration appears driven by taxonomic grouping and feeding mode. Euphausiids, due to their abundance, relative larger size, importance as a food source for other fauna, and observed relationship with surface water MeHg are a good candidate biotic group to evaluate for use in monitoring the bioavailability of MeHg for trophic transfer in the Mediterranean and potentially globally.

Do concentrations in eggs and liver tissue tell the same story of temporal trends of mercury in high Arctic seabirds?

Mercury (Hg) remains a key contaminant of concern in Arctic biota, and monitoring of Hg concentrations in seabird tissues will be an effective approach to track the effects of implementing the Minamata Convention. We examined trends in total Hg (THg) in liver and egg tissues of two Arctic seabirds, thick-billed murres (Uria lomvia) and northern fulmars (Fulmarus glacialis), between 1976 and 2013 to assess whether both tissues showed similar patterns of Hg change. Hepatic THg was consistently higher than egg THg, and both species had similar egg THg concentrations, but fulmars had higher hepatic THg than murres. Murre THg concentrations showed more relative variation through time than fulmars. We suggest that egg THg better reflects exposure of birds to THg in local, Arctic prey, whereas liver THg may incorporate longer term, year-round THg exposure. Additional analysis of THg distribution in Arctic seabirds post-laying would help inform interpretation of long-term trends.

The distribution and trends of persistent organic pollutants and mercury in marine mammals from Canada's Eastern Arctic

Arctic contaminant research in the marine environment has focused on organohalogen compounds and mercury mainly because they are bioaccumulative, persistent and toxic. This review summarizes and discusses the patterns and trends of persistent organic pollutants (POPs) and mercury in ringed seals (Pusa hispida) and polar bears (Ursus maritimus) in the Eastern Canadian Arctic relative to the rest of the Canadian Arctic. The review provides explanations for these trends and looks at the implications of climate-related changes on contaminants in these marine mammals in a region that has been reviewed little. Presently, the highest levels of total mercury (THg) and the legacy pesticide HCH in ringed seals and polar bears are found in the Western Canadian Arctic relative to other locations. Whereas, highest levels of some legacy contaminants, including ∑PCBs, PCB 153, ∑DDTs, p,p'-DDE, ∑CHLs, ClBz are found in the east (i.e., Ungava Bay and Labrador) and in the Beaufort Sea relative to other locations. The highest levels of recent contaminants, including PBDEs and PFOS are found at lower latitudes. Feeding ecology (e.g., feeding at a higher trophic position) is shaping the elevated levels of THg and some legacy contaminants in the west compared to the east. Spatial and temporal trends for POPs and THg are underpinned by historical loadings of surface ocean reservoirs including the Western Arctic Ocean and the North Atlantic Ocean. Trends set up by the distribution of water masses across the Canadian Arctic Archipelago are then acted upon locally by on-going atmospheric deposition, which is the dominant contributor for more recent contaminants. Warming and continued decline in sea ice are likely to result in further shifts in food web structure, which are likely to increase contaminant burdens in marine mammals. Monitoring of seawater and a range of trophic levels would provide a better basis to inform communities about contaminants in traditionally harvested foods, allow us to understand the causes of contaminant trends in marine ecosystems, and to track environmental response to source controls instituted under international conventions.

Hepatic trace element concentrations of breeding female common eiders across a latitudinal gradient in the eastern Canadian Arctic

We examined hepatic concentrations of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), manganese (Mn), mercury (Hg), rubidium (Rb), selenium (Se) and zinc (Zn) in 10 breeding female common eiders (Somateria mollissima) from each of three colonies across 20° of latitude. Levels of many elements were elevated in eiders, although generally below levels of toxicological concern. We found significant differences in concentrations of As, Rb, Hg, Mn and Se among colonies, but not in a consistent pattern with latitude, and Hg:Se molar ratios did not vary among colonies. Furthermore, overlap in element concentrations from birds at different colonies meant that we could not reliably differentiate birds from different colonies based on a suite of their hepatic trace element concentrations. We encourage other researchers to assess baseline trace element levels on this important, harvested species, as a means of tracking contamination of nearshore benthic environments in the circumpolar Arctic.

Mercury and persistent organic pollutants in native and invading forage species of the Canadian Arctic: Consequences for food web dynamics

Contaminant dynamics within Arctic marine food webs may be altered through the climate-driven northward invasions of temperate/boreal species. Here, we compare tissue concentrations of total mercury (THg) and legacy and emerging persistent organic pollutants (POPs) in native versus invading forage species sampled from 2012 to 2014 near Arviat, Clyde River, and Resolute Bay, NU, representing, low, mid- and high eastern Canadian Arctic regions, respectively. Concentrations of THg, legacy Σ-polychlorinated biphenyls (ΣPCB) and Σ-organochlorine (ΣOC) pesticides were detected in all forage species, whereas emerging halogenated flame retardants were detected in only a few individuals. Concentrations of major contaminant groups among regions did not vary for Arctic cod (Boreogadus saida), while for sculpin (Cottoidea) there was no clear latitudinal trend. Thus, considering interspecific variation, native sculpin and northern shrimp (Pandalus borealis) had the highest overall concentrations of THg (0.17 ± 0.02 and 0.21 ± 0.01 μg g^-1 wet weight, respectively), ΣPCB (322 ± 35 and 245 ± 25 ng g^-1 lipid weight (lw), respectively), and ΣOC (413 ± 38 and 734 ± 64 ng g^-1 lw, respectively). Comparing the keystone native species, Arctic cod, to its 'replacement' species, capelin (Mallotus villosus) and sandlance (Ammodytes spp.), THg concentrations were higher in Arctic cod compared to capelin (p < 0.001), which was partly explained by differences in fish length. Conversely, capelin and sandlance had higher concentrations of most POPs than Arctic cod (p < 0.02). Neither feeding habitat (based on δ¹³C), trophic position (based on δ¹⁵N), nor fish length significantly explained these differences in POPs between Arctic cod, capelin and sandlance. Higher POPs concentrations, as well as variation in congener/compound patterns, in capelin and sandlance relative to Arctic cod seem, therefore, more likely related to a more "temperate"-type contaminant signature in the invaders. Nevertheless, the relatively small (up to two-fold) magnitude of these differences suggested limited effects of these ecological changes on contaminant uptake by Arctic piscivores.

Hazardous properties and toxicological update of mercury: From fish food to human health safety perspective

The mercury (Hg) poisoning of Minamata Bay of Japan widely activated a global attention to Hg toxicity and its potential consequences to the aquatic ecosystem and human health. This has resulted to an increased need for a dynamic assembly, contextualization, and quantification of both the current state-of-the-art and approaches for understanding the cause-and-effect relationships of Hg exposure. Thus, the objective of this present review is to provide both hazardous toxic properties and toxicological update of Hg, focusing on how it ultimately affects the aquatic biota to potentially produce human health effects. Primarily, we discussed processes that relate to Hg exposure, including immunological aspects and risk assessment, vulnerability, toxicokinetics, and toxicodynamics, using edible fish, swordfish (Xiphias gladius), as a model. In addition, we summarized available information about Hg concentration limits set by different governmental agencies, as recognized by national and international standardization authorities.

Distribution, Bioaccumulation, Trophic Transfer, and Influences of CeO2 Nanoparticles in a Constructed Aquatic Food Web

In view of the final destination of nanomaterials, the water system would be an important sink. However, the environmental behavior of nanomaterials is rather confusing due to the complexity of the real environment. In this study, a freshwater ecosystem, including water, sediment, water lettuce, water silk, Asian clams, snails, water fleas, Japanese medaka, and Yamato shrimp, was constructed to study the distribution, bioaccumulation, and potential impacts of CeO₂ nanoparticles (CeO₂ NPs) via long-term exposure. The results demonstrated most of the CeO₂ NPs deposited in the sediment (88.7%) when the partition approached to the constant 30 days later. The bioaccumulated Ce in six tested biota species was negatively correlated with its trophic level, showing no biomagnification of CeO₂ NPs through this food web. CeO₂ NP exposure induced visual abnormalities in hydrophytes, including chlorophyll loss in water silk and water lettuce, ultrastructural changes in pyrenoids of water silk, and root elongation in water lettuce. The generation of hydroxyl radical (·OH) and cell-wall loosening induced by CeO₂ NP exposure might mediate the root growth in water lettuce. The findings on the environmental behavior of CeO₂ NPs in water system have provided useful information on the risk assessment of nanomaterials.

Diet dichotomy between two migrant seabirds breeding near a high Arctic polynya

High Arctic polynyas are predictable areas of open water, which offer long-distance migrant seabirds a reliable source of food during a period when they have to replenish and accumulate energy for reproduction. Investigating the interaction between species nesting sympatrically in the vicinity of polynyas should provide insights into the role that such oceanographic features play for pre-breeding seabirds. We used stable isotopes (δ13C and δ15N) to compare the diet of two ground-nesting seabirds, Sabine's gull (Xema sabini) and Arctic tern (Sterna paradisaea), nesting on an island adjacent to a recurring polynya in the Canadian high Arctic in 2008 and 2009. We show that, unlike Arctic terns, the diet of Sabine's gulls appears to include a non-negligible amount of terrestrially derived prey during early incubation, and that overall both species segregate their dietary niche during pre-laying and early incubation.

Persistent organic pollutant and mercury concentrations in eggs of ground-nesting marine birds in the Canadian high Arctic

We collected eggs of eight marine bird species from several colony sites in the Canadian high Arctic located at approximately 76°N and analyzed them for concentrations of legacy persistent organic pollutants (POPs) and mercury. We provide the first report on concentrations of POPs in eggs of three Arctic species (Thayer's gull Larus thayeri, Sabine's gull Xema sabini, Ross's Gull Rhodostethia rosea), and we found significant differences in each of the POP profiles among the five species with sufficient data for statistical comparisons (Thayer's gull, black guillemot Cepphus grylle, Sabine's gull, Arctic tern Sterna paradisaea and common eider Somateria mollissima borealis). The Ross's Gull had unexpectedly high POP concentrations relative to the other species examined, although this was based on a single egg, while glaucous gull Larus hyperboreus eggs from our sampling location had very low POPs. Sabine's gulls had the lowest Hg of the eggs studied, consistent with their low trophic position, but concentrations of their legacy POPs were higher than expected. We also noted that total hexachlorocyclohexanes were higher than reported elsewhere in the circumpolar Arctic in three species.

Methylmercury Concentration in Fish and Risk-Benefit Assessment of Fish Intake among Pregnant versus Infertile Women in Taiwan

This study examined methylmercury (MeHg) concentrations in fish, the daily MeHg exposure dose, and the risk-benefit of MeHg, ω-3 polyunsaturated fatty acid (ω-3 PUFA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) related to fish intake among pregnant and infertile women in Taiwan. The measured MeHg concentrations in fish did not exceed the Codex guideline level of 1 mg/kg. Swordfish (0.28 ± 0.23 mg/kg) and tuna (0.14 ± 0.13 mg/kg) had the highest MeHg concentrations. The MeHg concentration in the hair of infertile women (1.82 ± 0.14 mg/kg) was significantly greater than that of pregnant women (1.24 ± 0.18 mg/kg). In addition, 80% of infertile women and 68% of pregnant women had MeHg concentrations in hair that exceeded the USEPA reference dose (1 mg/kg). The MeHg concentrations in hair were significantly and positively correlated with the estimated daily MeHg exposure dose. Based on the risk-benefit evaluation results, this paper recommends consumption of fish species with a low MeHg concentration and high concentrations of DHA + EPA and ω-3 PUFA (e.g., salmon, mackerel, and greater amberjack).

Pan-Arctic concentrations of mercury and stable isotope ratios of carbon (δ(13)C) and nitrogen (δ(15)N) in marine zooplankton

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

C-Phycocyanin as a potential biosensor for heavy metals like Hg2+ in aquatic systems

Fluorescence quenching ability of C-phycocyanin (CPC) as a biosensor for detection of Hg²⁺ in lower concentrations (μM) in aquatic environment.

The skin of Commerson's dolphins (Cephalorhynchus commersonii) as a biomonitor of mercury and selenium in Subantarctic waters

The skin of bycaught Commerson's dolphins was tested for mercury (Hg) and selenium (Se) biomonitoring in Subantarctic environments. The correlation of levels detected in the skin with those found in internal tissues - lung, liver, kidney and muscle - was assessed to evaluate how skin represents internal Hg and Se distribution for monitoring purposes. Mercury in skin had a concentration range of 0.68-3.11 μg g(-1) dry weight (DW), while Se had a higher concentration range of 74.3-124.5 μg g(-1) DW. There was no significant correlation between selenium levels in any of the analyzed tissues. Thus, the skin selenium concentration did not reflect the tissular Se levels and did not provide information for biomonitoring. The lack of correlation is explained by the biological role of Se, provided that each tissue regulates Se levels according to physiological needs. However, the skin Hg level had significant positive correlation with the levels in internal tissues (ANOVA p<0.05), particularly with that of muscle (R(2)=0.79; ANOVA p=0.0008). Thus, this correlation permits the estimation of Hg content in muscle based on the multiplication of skin biopsy levels by a factor of 1.85. Mercury bioindication using skin biopsies is a non-lethal approach that allows screening of a large number of specimens with little disturbance and makes possible an adequate sampling strategy that produces statistically valid results in populations and study areas. The correlation between Hg levels in the skin and internal tissues supports the use of the epidermis of Commerson's dolphins for Hg biomonitoring in the waters of the Subantarctic, which is a poorly studied region regarding Hg levels, sources and processes.

Mercury in the marine environment of the Canadian Arctic: review of recent findings

This review summarizes data and information which have been generated on mercury (Hg) in the marine environment of the Canadian Arctic since the previous Canadian Arctic Contaminants Assessment Report (CACAR) was released in 2003. Much new information has been collected on Hg concentrations in marine water, snow and ice in the Canadian Arctic. The first measurements of methylation rates in Arctic seawater indicate that the water column is an important site for Hg methylation. Arctic marine waters were also found to be a substantial source of gaseous Hg to the atmosphere during the ice-free season. High Hg concentrations have been found in marine snow as a result of deposition following atmospheric mercury depletion events, although much of this Hg is photoreduced and re-emitted back to the atmosphere. The most extensive sampling of marine sediments in the Canadian Arctic was carried out in Hudson Bay where sediment total Hg (THg) concentrations were low compared with other marine regions in the circumpolar Arctic. Mass balance models have been developed to provide quantitative estimates of THg fluxes into and out of the Arctic Ocean and Hudson Bay. Several recent studies on Hg biomagnification have improved our understanding of trophic transfer of Hg through marine food webs. Over the past several decades, Hg concentrations have increased in some marine biota, while other populations showed no temporal change. Marine biota also exhibited considerable geographic variation in Hg concentrations with ringed seals, beluga and polar bears from the Beaufort Sea region having higher Hg concentrations compared with other parts of the Canadian Arctic. The drivers of these variable patterns of Hg bioaccumulation, both regionally and temporally, within the Canadian Arctic remain unclear. Further research is needed to identify the underlying processes including the interplay between biogeochemical and food web processes and climate change.

Biomagnification of mercury in mollusks from coastal areas of the Chinese Bohai Sea

Biomagnification of methylmercury and growth dilution of inorganic mercury were found during the trophic transfer of mercury in different mollusk species.