2d: Mercury fate in aquatic and terrestrial food webs

In North America, larval dragonflies are increasingly used as biosentinels for monitoring mercury (Hg) contamination in freshwater food webs. For practical reasons, field studies and monitoring programs alike often do not identify larval dragonflies below the taxonomic level of family. Several studies, however, have recognized that differences in Hg concentration among coincidently collected families do occur and may be associated with distinct family-level behavioral habits or guilds (e.g., burrowers vs. climbers). Understanding the consistency of these differences among guilds across habitats and water bodies will be important to the refinement of protocols using larval dragonflies as biosentinels. Apart from the implications for monitoring Hg, these guild differences generate basic questions about the intersection of environmental toxicology, behavioral ecology, and phylogeny. Two separate field studies conducted in the north-central states of Wisconsin and Michigan (USA) have shown consistent differences in total mercury (THg) concentration between two intraguild (burrower) families of late-instar larval dragonflies: the spiketails (Family Cordulegastridae) and the clubtails (Family Gomphidae). Across 5 of 6 water bodies, 3 streams and 3 lakes, THg concentration in spiketail larvae was significantly greater than in coincidently collected clubtail larvae. Furthermore, spiketail THg concentration was often greater than all other co-occurring larvae belonging to non-burrowing guilds (i.e., sprawlers and climbers). Mean (± SE) THg concentration across water bodies ranged from 170.9 ± 10.0 – 497.8 ± 136.2 ng/g dwt. and from 67.0 ± 2.1 – 165.0 ± 18.2 ng/g dwt. for spiketails and clubtails, respectively. In the 5 water bodies with significant differences, spiketail THg concentrations were between 189% and 558% greater than their clubtail counterparts. An explanation for these differences likely includes voltinism; in the north-central US, spiketails are merovoltine, spending 3 to 4 years as larvae, while clubtails are typically bivotline, spending 2 years as larvae. However, other factors including the amount of body setae (surface area), differences in burrowing behavior, and the significance of their phylogenetic relationship are explored.

In the Amazon, contamination by mercury (Hg) can be derived from: gold mining activities; Soil remobilization processes; and global Hg cycle. In aquatic ecosystems, Hg finds favorable conditions for organification and becomes methylmercury (MeHg), considered the most toxic chemical form of Hg, having the potential to bio-accumulate and/or biomagnify along the food chain. The red dolphin (Inia sp.), an aquatic mammal that inhabits the Amazonian rivers, can be considered a sentinel species of this environmental contaminant. The objective of this work was to evaluate the average level of total Hg (THg) and MeHg in Amazonian dolphins will be compared with the results of THg and MeHg in fish of the region collected along the Madeira river (Rondônia, Brazil). Without causing damage to the animal a simple biopsy was performed for the removal of small pieces of its fatty tissue and soon after, these were returned to the river. The THg and MeHg determinations were performed by cold vapor atomic absorption spectrophotometry and by gas chromatography coupled to atomic fluorescence spectrometry, respectively. The results of THg (n=19) and MeHg (n=65) in red dolphins presented an average of 0.9408 ± 1.0515 mg/kg and 0.6904± 0.5546 mg/kg, respectively. Average THg concentration in fish muscle tissue (n=320) was of 0.3665 ± 0.4858 mg/kg and for non-carnivores 0.3648 ± 0.4857 mg / kg. The results show the dynamics of mercury, where the bulk is in the form of methylmercury (HgT: MeHg ratio of 61%). Carnivorous fish presented higher results than non-carnivorous fish and, consequently, because the porpoises have a diet almost exclusively food in fish and because they are food web tops, showed higher concentrations of HgT and MeHg than carnivorous fish, Result already expected due to biomagnification and bioaccumulation of this contaminant along the trophic chain of resident organisms of the Amazon region.

Mercury is rarely measured in fish from tropical river estuaries but local people rely on these for food. In tropical regions, mangrove forests provide an important nursery for juvenile fish and are used as a habitat by a variety of other aquatic and terrestrial animals. In French Guiana and neighboring countries, there are several factors that could contribute to elevated methylmercury concentrations [MeHg] in estuarine fish: 1). the soils in the Amazon are naturally enriched with Hg; 2). streams and rivers in some areas have been a subject to Hg pollution from small scale artisanal gold mining; 3). A reservoir, Petit Saut, created at time of hydroelectric dam installation upstream Sinnamary River, sources MeHg for downstream. We therefore asked whether fish in the lower part of the estuary have elevated [MeHg] and whether their consumption would pose health hazard to people. During the dry season in October 2015, we have sampled fish by gill net in the mouth of the Sinnamary River Estuary (SRE; 5.45°N 53.01°E), where salinity ranges from ~2 to 32 and where the evolving marine mangrove (Avicenia sp.) forest hugs the river bank. Two catfish species Hexanematichthys proops and Aspistor quadriscutis dominated the 2-day catch (n=28 and 43, respectively) with total lengths ranging from 42 to 67 and 41 to 53 cm, respectively. Other adult fish species e.g. Hexanematichthys couma, Sciades herzbergii, S. passany, Macrodon ancylodon, Cathorops spixii, C. arenatus, Lobotes surinamensis, Pellona flavipinnis, Centropomus undecimalis, C. mexicanus, C. ensiferus, Pseudochenipterus nodosus, Cynoscion acoupa, as well as their juveniles, shrimp and crabs (Uca maraocani) were also collected to establish mercury concentrations in the food web of this ecosystem. Overall, the mean total [Hg] in the muscle tissue were ~ 2-fold higher in H. proops (mean= 0.42; range: 0.17 – 1.34 mg kg-1 wet wt.) in comparison to A. quadriscutis (mean= 0.18; range: 0.03 – 0.47 mg kg-1 wet wt.). The average % MeHg was ~50 for both catfish species. [MeHg] in the other large fish fell within the range of values observed for the above-mentioned catfish. Among all analyzed fish, none exceeded the MeHg safety levels in France (i.e. 0.5 mg kg-1 wet wt.). We therefore conclude that despite a risk of elevated MeHg in fish of SRE, observed [MeHg] were low and catfish of size comparable to that in this study are safe to eat.

A major key to understand the Hg contamination of aquatic biota is the exposure of toxic and organic forms (i.e. methylmercury, MeHg) of mercury (Hg) at the base of the food web, and transfer through consumer trophic levels. While data series of historical Hg concentrations in top consumers of aquatic food webs (e.g. fish, birds) are increasing in peer-review literature, long-term high resolution datasets of Hg in biota from lower food web compartments are scarce. In the present study we tested the hypothesis that long-term changes in MeHg in biota relate to water chemistry and are indirectly linked to climate and deposition change.

We have, through access to historically archived samples, analysed MeHg in samples of littoral macro-invertebrates from two Norwegian boreal lakes, Breidtjern (59.60 N, 11.40 E) and Langtjern (60.37 N, 9.73 E). Breidtjern and Langtjern are both humic lakes with relatively similar water chemistry (data from 2016): total organic carbon concentrations between 10 and 15 mg/L; pH approximately 5.0; total Hg concentrations between 2.5 and 6.5 ng/L; and MeHg concentrations between 0.02 and 0.2 ng/L. The historical samples we analysed date back to 1976 and 1978 for the two lakes, respectively, with samples collected with a frequency of between every second and every fifth year, and yearly after the millennium. We also sampled present-day invertebrates from the two lakes and quantified transfer of aqueous MeHg to the invertebrates (as bio-concentration factors, BCFs). The historical invertebrates are primary and secondary consumers, taxonomically described and fixed in ethanol. Literature suggests that ethanol affects lipid content and therefore stable isotopes, but not MeHg which is primarily associated with proteins. The possible effects from sample storage over time in ethanol solutions were tested by quantifying leakage of MeHg from present-day invertebrates stored over 500 days.

Our study will show if and how records of archived invertebrate samples can be used to untangle historical time-trends of Hg concentrations in boreal lakes. We will, in combination with explanatory variables, highlight the changes in Hg concentrations that can be found with time in these lakes. Included explanatory variables, water chemistry, hydrology, and precipitation, will be used in a statistical analysis of MeHg in primary consumers, similar to an earlier analysis of DOC time series.

Turtles are often used as biomonitors in aquatic ecosystems as they are long-lived top predators making them highly susceptible to both bioaccumulation and biomagnification of mercury. The purpose of this study was to determine mercury exposure in three species of turtles, the red-eared slider (Trachemys scripta), the common snapping turtle (Chelydra serpentina), and the alligator snapping turtle (Macrochelys temminckii), in aquatic ecosystems across western Tennessee. All three species of turtles were trapped at twelve different sites from March to July 2016. Toenails were taken from the back feet of each captured turtle and analyzed for total mercury using a Nippon MA-3000 Direct Mercury Analyzer. Mercury exposure varied significantly among species: alligator snappers (5.26ppm)>common snappers (4.49ppm)>red-eared sliders (1.09ppm). Mercury concentrations in both alligator and common snapping turtle toenails exceeded the EPA recommended consumption level for freshwater fish (0.3 ppm). This is of particular cause for concern from a human health perspective as common snapping turtles are still harvested for human consumption in this region. Mercury concentrations in turtle toenails are a strong predictor of soft tissue and organ concentrations suggesting consumption of common snapping turtles from this region may pose a human health risk.

Vernal pools in Northeast US forests provide critical habitat for numerous invertebrate and amphibian species. However, vernal pools have also been shown to be potential “hotspots” for accumulation and methylation of mercury (Hg). Under the right conditions, the MeHg produced within the pool can bioaccumulate in the vernal pool organisms, which can subsequently become a vector for MeHg transport into the surrounding terrestrial ecosystem. During the spring of 2015, 20 vernal pools in Vermont were sampled for common invertebrates using funnel traps or hand collection. The pools ranged from Rockingham, VT north to Walden, VT, all east of the Green Mountain range, and were influenced by a variety of forest types and land uses. Invertebrate samples were analyzed for MeHg or total Hg concentration, as well as δ13C and δ15N. There was large variation in MeHg concentration across all of the pools. Caddisfly larvae (MeHg range: 6 – 189 ppb DW; 14 pools) and mosquito larvae (MeHg range: 4 – 243 ppb DW; 8 pools) were generally lower than fairy shrimp (MeHg range: 71 – 283 ppb DW; 7 pools) or predatory beetles (Acilius sp. THg range: 51 – 613 ppb DW; 10 pools, Dytiscus sp. THg range: 131 – 342 ppb DW; 6 pools). δ15N of predatory beetles was generally higher than that of fairy shrimp, caddisfly, or mosquito larvae, as expected. Relationships between pool and landscape characteristics and Hg bioaccumulation in resident invertebrates will be discussed.

Plankton and lower trophic level nekton are critical conduits for the transfer of methylmercury (MeHg) in marine food webs, yet little is known about the variation in MeHg concentrations between species and across sites in these lower trophic fauna. Zooplankton were sampled from the neuston layer at both coastal and open sea stations in the Mediterranean Sea during cruise campaigns undertaken in the fall of 2011 and the summers of 2012 and 2013. Horse mackerel and two species of squid were obtained opportunistically during the same cruises. Zooplankton were separated by morphospecies, and the most abundant taxa analyzed for methylmercury (MeHg) concentration. Squid and fish samples were analyzed for total Hg (THg). Data will be presented for euphausiids, mysids, and myctophids, all important prey items for fish, marine mammals, and birds, as well as for the mackerel and squid. Euphausiid MeHg concentration ranged from 22 226 ppb DW with spatial variation between sites. Myctophid MeHg tissue concentrations were similar, ranging from 22-297 ppb DW across all sites, while mysid concentrations were slightly lower (range: 6 204 ppb DW). The data suggest elevated MeHg concentration in the Tyrhennian and Balearic seas in comparison with more eastern and western stations. Horse mackerel had higher muscle tissue concentrations (range across sites: 344 - 1510 ppb DW) on average than flying squid (range: 49 448 ppb DW), with some individuals exceeding the EPA 300 ppb WW tissue criterion. Euphausiids, due to their abundance, larger size, and importance as a food source for other fauna may be a good species to use for MeHg monitoring in marine systems such as the Mediterranean Sea.

The presence of mercury of anthropogenic and natural origin in the aquatic ecosystems of the Amazon represents an exposure factor for neurotoxic, teratogenic and chronic noncommunicable diseases. In the Amazon region, contamination by organic and inorganic mercury can be attributed mainly to high fish consumption and to the practice of goldmining, respectively. The methylmercury levels in humans can be considered an endemic condition in Amazon, mostly in traditional populations such as the riverines and Indigenous , by the expressive daily consumption of fish, as well as cassava flour, chestnut and sometimes meat. However, changes in the livelihoods of these populations, due to political, economic and social factors, have been influencing the human health and the environment, due to the insertion and possible exclusion of risk factors and protective factors, respectively. According to the World Health Organization, diabetes mellitus, metabolic syndrome, overweight and obesity, cardiovascular diseases, cancers and lung diseases, referred as chronic noncommunicable diseases, are the main causes of death related to increasing expectation of life. The mercury contamination can be causally associated with hyperglycemia by direct effect on pancreatic beta cells, with the pathogenesis of the metabolic syndrome, endocrine disorders, inflammatory diseases and the carcinogenic potential by oxidative stress. Metallic mercury compromises the lungs and kidneys, indirectly reflecting blood pressure, by inhalation. Hypertension can also be caused by methylmercury contamination, not only by renal impairment, but also mainly by the activation of the renin angiotensin system. Overweight and obesity are risk factors for cardiovascular events and may be correlated with systemic levels of methylmercury because of it lipophilic potential. These diseases represent a public health problem and affect the quality of life, life expectancy, treatment and hospitalization expenses, labor capacity and regional development. In this context, the epidemiological transition and nutritional transition should be evaluated as important covariates for understanding the effects of exposure to methylmercury on the health of the traditional populations in Amazon. Studies on the relationship between mercury and chronic noncommunicable diseases are extremely important and not enough explored in Amazonian risk populations. The present study aims to evaluate the possible relationship between methylmercury contamination and chronic noncommunicable diseases potentially related to this exposure factor in a riverine population of the Brazilian Amazon. The potential explanatory variables such as lifestyle habits, body-mass index, socioeconomic factors, hypercholesterolemia, selenium and n-3 fatty acid consumption were evaluated.

As a global leader in the export of forest products, Canadian forest managers are tasked with balancing exploitation of one of the countrys most cherished natural resources with maintaining a high standard of forest ecosystem integrity. Despite environmental protection guidelines for forest management, legacies of ecosystem degradation persist, many of which are specific to aquatic environments. One example includes the accelerated input of atmospherically-deposited or weathered contaminants like mercury (Hg) into forest streams via terrestrial erosion following forest harvest operations. In aquatic environments, Hg is transformed by anaerobic bacteria at the sediment-water interface to methylmercury (MeHg), a neurotoxicant with high potential for bioaccumulation and biomagnification in aquatic food webs. In response to concerns for sustaining ecosystem integrity in the face of resource development, this study examines the impact of selection-based harvesting of northern hardwood stands in the Batchawana River watershed on the northeastern shore of Lake Superior in Ontario on bioaccumulation of MeHg in forest stream food webs. The study area consists of four catchments, each with three sampling sites of increasing stream order, that have been subject to either very little harvest (<15% area harvested) or substantial harvest (>60% area harvested) in the last 10 years. Bioaccumulation of methylmercury in northern hardwood stream food webs is assessed by measuring its concentration in stream water and in late instars of the larvae of ubiquitous filter-feeding caddisflies (Hydropsychidae) at all sites within these catchments. Other metrics of the impact of forest management on aquatic ecosystem health include water quality, leaf litter decomposition and associated macroinvertebrates, and fine sediment deposition. Ultimately, this study will look for evidence of whether or not bioaccumulation of MeHg and other impacts to stream health are spatially cumulative downstream of forestry activities, an analysis that has received relatively little attention despite its requirement under Canadian environmental assessment legislation. A comprehensive and predictive understanding of the spatially cumulative effects associated with forest management is critical to maintaining healthy future forests and provisioning of their aquatic ecosystem services.

Although more chemicals are reaching Antarctica, the link between those xenobiotics and specially mercury (Hg) exposure and its effects on Antarctic food web is still poorly understood. Antarctic organisms have long life cycles, tendency to gigantism and slow metabolic rates (due to low temperatures), being more inclined to accumulate and magnify Hg in its organic form methylmercury though the food web in comparison with species of lower latitudes. Due to the new global environmental problems, the study of Hg behavior in the Antarctic is urgent.

In order to identify the interaction of Antarctic species and Hg, a systematic study of the existing literature on the concentrations of these compounds in different organisms was conducted. The organisms considered were zooplankton, crustaceans, benthonic fauna, fish, seabirds and marine mammals. Some databases such as Direct, Springer, Scopus and Web of Science were used. Selection criteria corresponded to the levels of total Hg on the basis of dry weight (d.w.). Subsequently, this information was summarized in tables. Maps of the distribution of total Hg levels in different Antarctic locations were also considered, as well as Hg temporal distribution (80´s, 90´s and current time).

During the 80´s, Hg average levels in crustaceans are ˂ 0.1 μg/g, in seabirds 0.2 μg/g, while in marine mammals are 2.4 μg/g. During the 90´s, Hg levels in crustaceans are 0.025 μg/g and in marine mammals 5.03 μg/g. More recently (between 2000-2016), Hg levels in zooplankton are 0.07 μg/g, in crustaceans 17.67 μg/g, in benthonic organisms 0.18 μg/g, in fish 0.36 μg/g, in seabirds 0.81 μg/g, and in marine mammals are 0. 2μg/g. According to metal distribution in Antarctic locations, the Hg levels are: Admiralty Bay ˃ Antarctic Peninsula ˃ Southern Ocean ˃ Newfoundland Bay ˃ Ross Sea ˃ Bird Island ˃ King George Island ˃ Windmill Island ˃ Antarctic Scotia Sea.

Mercury concentrations have been increasing over the years. More studies are needed in order to correlate reported levels with δ15N isotopes at different trophic levels. Likewise, more studies are needed in different Antarctic locations.

Acknowledgement W. Espejo Thanks CONICYT-Chile for Phd studies. Thanks also are given to project INACH RG 09-14, T12-13 and INACH T31-11, project 214.074.051-1.0 and 216.153.025-1.0 of the Research Division of the Universidad de Concepción-Chile.

The diets of terrestrial consumers can be subsidized by energy and nutrients transported from aquatic ecosystems to terrestrial food webs by emergent aquatic insects. The cross-system transport of energy and nutrients by insects can have a dark side because emergent aquatic insects also transport toxic contaminants such as methyl mercury (MeHg) to terrestrial ecosystems when they emerge. Although many ecological factors influence insect emergence and the cross-system transport of energy and nutrients by insects, the ecological factors regulating insect-mediated MeHg flux have been little studied. In this presentation, we overview our mesocosm and pond experiments examining ecological factors regulating the transport of MeHg out of aquatic ecosystems by emergent insects. We calculate insect-mediated MeHg flux as the product of the MeHg concentrations and biomass of emergent insects. Ecological factors can impact insect-mediated MeHg flux either by affecting MeHg concentrations in emergent insects or by altering the biomass of emergent insects. We overview the effects of four ecological factors on aquatic insect-mediated MeHg flux: 1) predation and community structure, 2) nutrient limitation and productivity, 3) drying disturbance and pond permanence and 4) phenology of insect emergence.

We surveyed mercury (Hg) concentrations in 10 species of bats collected at wind farms in the central United States and found contamination in all species. Mercury contamination in fur was highly variable both within and between species (range 1.08-10.52 μg/g). Despite the distance between sites (up to 1200 km), only 2 of the 5 species sampled at multiple locations had concentrations of Hg that differed between sites. The Hg concentrations observed in this study all fell within the previously reported ranges for bats collected from the northeastern United States and Canada, although many of the bats we sampled had lower maximum Hg concentrations. Juvenile bats had lower concentrations of Hg in fur than adult bats, and we found no significant effect of sex on Hg concentrations in fur. For a subset of 2 species, we also measured Hg concertation in muscle tissue; concentrations were much higher in fur than in muscle and Hg concentration in the 2 tissue types was weakly correlated. Abundant wind farms and ongoing post-construction fatality surveys offer an underutilized opportunity to obtain tissue samples that can be used to assess Hg contamination in bats.

Because of its extreme toxicity and its widespread presence in aquatic food webs, methyl mercury (MeHg) poses a threat to human health. The primary pathway of MeHg into humans is through the consumption of MeHg-contaminated fish. Methyl mercury contamination of water bodies and their food webs vary across the landscape, and many ecological factors have been found to be correlated with MeHg contamination of fish. In this study, we examined the relationship between average MeHg concentrations in five fisheries length categories (stock, quality, preferred, memorable and trophy) of bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides) and average Hg deposition in 14 ecoregions located within all or part of six states in the south central U.S. We focused on bluegill and largemouth bass because they are widely distributed and economically important species of freshwater game fish. The National Descriptive Model of Mercury in Fish was utilized to estimate concentrations of MeHg in bluegill and largemouth bass. Mercury deposition was estimated using wet Hg deposition data from the Mercury Deposition Network adjusted for the presence of coniferous forests. Average MeHg concentrations of bluegill and largemouth bass increased with Hg deposition and fish length category. Only large length categories of bluegill in ecoregions with high levels of Hg deposition had average concentrations of total MeHg above 300 ng/g ww, the threshold concentration of MeHg recommended by the U.S. Environmental Protection Agency for the issuance of fish consumption advisories. The three largest length categories of largemouth bass had MeHg concentrations above 300 ng/g ww in all ecoregions. In ecoregions with high Hg deposition, the largest length category of bass (63 cm TL) had MeHg concentrations over four times greater than 300 ng/g ww. Our study suggests that in the south central U.S., atmospheric Hg deposition adjusted for the presence of coniferous forests sets the potential for MeHg contamination of fish, and that fish species and fish length category determine the observed levels of MeHg contamination. Over 90% of the ecoregion-level variance of MeHg concentrations in bluegill and largemouth bass was accounted for by Hg deposition adjusted for conifers, fish species and fish length category.

Two year round forage fish that reside in South Carolina salt marshes are mummichogs (Fundulus heteroclitus) and Atlantic silversides (Menidia menidia). Mummichogs target prey associated with Spartina alterniflora, from the sediment and within the water column while Atlantic silversides feed on zooplankton in the water column. This study quantified and compared levels of total and methyl mercury in mummichogs and Atlantic silversides from Dunn Sound, SC. Sample collection occurred in February, April, July, and October 2014, and an additional sample event occurred in April 2015 to obtain an annual comparison. Also, gut contents were quantified and compared to determine if there was a potential dietary impact on the concentrations of total and methyl mercury within these fish.

Atlantic silversides had significantly higher whole body total (p < 0.01, Two-Way ANOVA, Tukey) and methyl mercury (p < 0.01, Kruskal Wallace, Dunns Test) concentrations when compared to mummichogs for all of the sampling events. There was no significant difference between total (p = 0.0683, Two-Way ANOVA, Tukey) and methyl (p = 0.1005, Kruskal Wallace) mercury concentrations in the fish when comparing each sampling event. Although percent methylmercury in Atlantic silversides and mummichogs changed significantly by event (p < 0.01, Kruskal Wallace, Dunns Test) there was no significant difference between the species (p < 0.3553, Kruskal Wallace). This suggests that both species of fish assimilate mercury at the same rate.

When comparing April 2014 to April 2015, there was no significant difference in the total mercury concentrations between these fish (p=0.3553, Two way ANOVA). For both species, the concentration of methylmercury was significantly higher in April 2015 relative to April 2014 (p<0.01, Two- way ANOVA, Tukeys Test), however for both years Atlantic silversides had significantly higher methylmercury concentrations relative to mummichogs (p<0.01, Two- way ANOVA, Tukeys Test). There was no significant difference between the percent methylmercury of both species (p=2919, Kruskal Wallace) but April 2015 had significantly greater percentages methylmercury than April 2014 (p<0.01, Kruskal Wallace, Dunns Test).

The quarterly percent gut contents by weight (%W) and number (%N) of Atlantic silversides were significantly different relative to mummichogs (p < 0.01, PERMANOVA). Atlantic silversides consumed greater numbers of crustaceans whereas mummichogs preyed on a variety of organisms within the food web. Differences in the mercury concentrations of these two fish may impact the bioaccumulation and biomagnification of mercury within the salt marsh food web.

Recently, in lakes of Aquitaine region, analysis conducted by ANSES (French Agency for Food, Environmental and Occupational Health and Safety) revealed total mercury concentrations (HgT) exceeding the International Marketing Level in muscle of zander (Sander lucioperca), a carnivorous fish, in 2 lakes (Carcans- Hourtin and Lacanau). A ban on consumption of this species was thus decided. Following this, a multidisciplinary research project was launched in order to better understand the biogeochemical cycle of mercury on these lakes and the origin of mercury.

This study focused on the four largest lakes of Aquitaine (Hourtin-Carcans, Lacanau, Cazaux-Sanguinet, Parentis-Biscarrosse), emblematic environments of the region, closely related to tourism. Each of these hydrosystems has its own characteristics (trophic levels, physicochemical factors, different anthropic pressure between the lakes ...). Their response to a contamination pressure and the evolution over time of this contamination will therefore be potentially different. This integrative study considers all the aquatic compartments: water, sediment, and different level of the trophic chain (phytoplancton, periphyton, macrophytes, mollusks, crustaceans and fishes).

The objectives of the first part of this project were: (1) to measure Hg concentrations in different compartments at one season (for fish: age assessed), (2) to study the structure of these food webs using nitrogen and carbon stable isotope analysis, (3) to check the mercury biomagnification along food webs and to identify a possible entry point of this pollutant in food webs.

The results indicate that carnivorous species like pike (Esox Lucius), zander (Sander lucioperca) and perch (Perca fluviatilis) may exceed the International Marketing Level depending on their size. A biomagnification of Hg along food webs was observed for lakes. A north-south mercury contamination gradient could also be highlighted: Hourtin-Carcans > Lacanau > Cazaux- Sanguinet > Parentis-Biscarosse. Several explanations concerning the origin of this gradient are now available but need to be further studied. This study provides information on the transfer of Hg in the lake ecosystems of south western France and makes it possible to evaluate the risk associated with the presence of Hg in aquatic food webs.

Mercury (Hg) is a global pollutant of concern with impacts on public health and ecosystem quality. First Nations communities whose lives are heavily dependent on traditional foods are particularly susceptible to mercury exposure given that their traditional foods are known to be contaminated with mercury. Most studies have focused on mercury contamination in seafood consumed by First Nations communities, while relatively few studies have investigated other food types. Further, it is assumed that 100% of ingested Hg is bioavailable (reaches the systemic circulation) though new studies suggest that this may be less than 100%. The objective of this study is to characterize in vitro total mercury (THg) bioaccessibility from muscle tissue of four food items consumed by members of the Bigstone Cree Nation (Alberta, Canada).

The food items of concern (grouse, hare, fish, and duck) were collected through a participatory research activity. The THg levels in these samples ranged from 0.02 ppm to 0.34 ppm. Next, we will assess THg bioaccessibility using an in-vitro model of human digestion; bioaccessible THg will be measured in the soluble fraction of the digests. The expected results of this work are an increased understanding of THg bioaccessibility from a range of foods not previously studied, and ultimately improved abilities to assess exposure-related risks.

Since the industrial revolution, atmospheric mercury (Hg) concentrations have been increased by anthropogenic emissions. The Hg concentrations are higher in the Northern Hemisphere than the Southern Hemisphere because of a large extent of the industrial activities in the north. According to a global Hg model, the emitted Hg is likely transported and deposited within the same hemisphere. The deposited Hg can be converted to methylated form of Hg, which is neurotoxic and bioaccumulative in aquatic food webs. Pelagic fishes in the Northern Hemisphere are expected to contain more Hg than those in the Southern Hemisphere. The distribution of such an information has, however, been poorly obtained. In this study, total Hg (THg) and methyl-Hg (MeHg) concentrations in muscle of flying fishes from western Pacific and eastern Indian Oceans from 30º N to 41º S in latitude were measured. These samples can be used to evaluate the hemispheric and latitudinal Hg variations. The THg concentrations of the Northern Hemisphere flying fishes ranged from 30 to 450 ppb (d.w.), whereas the range in the Southern Hemisphere was between 50 and 530 ppb (d.w.). More than 90 % of Hg in most of the flying fishes were MeHg. There was no significant difference in THg concentrations between the Northern and Southern Hemispheres. Variations in THg concentrations of biota are often explained by different body length. Nevertheless, body lengths of the flying fishes in this study were poorly correlated. Positive correlations were observed between the THg concentrations of the flying fishes and latitude in the both Northern (r = 0.42, N = 19) and Southern (r = 0.61, N = 8) Hemispheres. The MeHg concentrations in the flying fishes were also positively correlated with the latitudes. It has been documented that MeHg concentrations of freshwater fishes are increased as wet atmospheric Hg deposition becomes greater. Therefore, the variations in Hg concentrations of the flying fishes likely reflect the magnitude of atmospheric Hg deposition. A global Hg model showed that Hg deposition fluxes were relatively large from 30º to 50º latitude in both hemispheres because of the global atmospheric circulation pattern and the distribution of industrialize areas within those latitudes. This study indicates that atmospheric Hg deposition is directly linked to the Hg levels in marine organisms.

Atlantic silverside (Menidia menidia) is an annual forage fish species whose populations reside in coastal embayments along the Atlantic Ocean. They substantially contribute to the diet of other predatory fish and are therefore a stepping-stone in the trophic transfer of contaminants to the higher trophic levels. Atlantic silversides also serve as a model for planktivorous marine fish in studies of contaminant bioaccumulation, including total mercury (THg) and methylmercury (MeHg). We therefore investigated the spatial and seasonal variability of THg and MeHg in the pelagic food webs of five Long Island Sound (LIS) embayments. Seawater, the suspended particles, copepods, and fish were collected in May, June, July, and September of 2016 from these embayments from Norwalk Harbor in the Western part of LIS to Mumford Cove in the East. Suspended in seawater particles were collected via 20 μm and 3 μm pore size filter membranes to capture the particle pool most relevant to copepod diet (i.e. 3-20 μm). Female copepods of the same species and of similar size were “hand-picked” under the dissecting microscope to limit data variability. Presently no data is available on intersex and interspecies MeHg concentration differences in LIS copepods. Adult fish but not the juveniles were separated based on sex. Muscle tissue was dissected from the adults but for the juvenile fish head and fins were cut off and the abdomen was used for the analysis. Our results show an increase of MeHg concentrations in the silversides from both Mumford Cove or Norwalk Harbor from May to July, but MeHg concentrations in fish from the intermediate locations remained similar during that period. Overall, adult female silverside had MeHg concentrations of 0.34 ± 0.14 (mean ± SD) µg/g dry weight that were 18% higher than males. MeHg concentrations in 2-3 month old silverside juveniles were 0.13 ± 0.05 µg/g dry weight. MeHg concentrations in the copepods were highest in Mumford Cove and decreased towards the Western Sound. Highest MeHg concentrations in copepods from Mumford Cove were found during May and June and declined by 50% in July. The east-west gradient of MeHg concentrations in copepods was steepest in May and least pronounced in July. Insufficient copepods were found in September, likely due the bloom of their predators, gelatinous zooplankton. We will present the bioaccumulation and trophic transfer trends in studied LIS embayments during the spring and summer of 2016.

Mercury is one of the pollutants most resistant to degradation and its bioaccumulation can be highly harmful to aquatic biota, transposing trophic chain levels and reaching top food chain predatory mammals. The Taiamã Ecological Station is a Federal / ICMBIO reserve. The jaguars of Taiamã have as preferential diet the fish and alligator, already evaluated in other studies as bioindicators of mercurial contamination in the Pantanal of Mato Grosso, Brazil. The objective of this study was to evaluate the concentrations of total mercury in jaguar (Panthera onca), using a non - invasive method of barbed wire and adhesive tape and collection of hairs samples obtained in collar / ICMBIO / CENAP. For the composite samples, seven sample points were monitored for six months with a Trap camera, with the objective of individualizing them. A total of 15 samples were collected, of which 13 were individual and 02 were composites (03 and 04 individuals per sample). For the quantification of the concentrations of total mercury was used atomic absorption spectrophotometer, Perkin Elmer (FIMS - system). The average concentration of mercury (μg.Kg) was 4,265,448 (2,130,531 min and 7,259,444 max). There was no significant difference in the concentrations of total mercury between the sexes (T test = 1,571, df = 10.8, p = 0.143), although the females presented the highest concentrations, which surely can cause over the years to Biodiversity. Age also did not explain the variations in concentrations (R2 = 0.1603, p = 0.1753). However, there was a significant negative difference between the concentrations of total mercury and the animals' weight (R2 = 0.3516; p = 0.03269). Thus, lighter animals had the highest concentrations of mercury in the body, suggesting that a mercury demethylation mechanism may be occurring over the life of these animals or individual factors of metal absorption in the body. The results are unprecedented and demonstrate bioaccumulation through trophic chain levels, reaching the largest predatory cat in the Pantanal, Mato Grosso, Brazil through its diet almost exclusively of fish and alligators.

The Amazon region is considereda region with natural mercury (Hg) in soils.However, since the 1980s, tons of Hg were released from the gold mining activity. This fact raises ecological concerns, due this chemical element undergobiomagnification along the trophic chain, reaching the human beings. Thus, fish as the main vectors of methylmercury (MeHg) for human population in the Amazon, demand studies that understand the Hg dynamics in its organisms. The aim of this study was to evaluate the organotropism of Hg in fish tissues (muscle, liver, gills and brain) of the carnivorous species Cichlamonoculus and Pseudoplatystomafasciatum, sampled in Puruzinho lake (Madeira river, Amazon state).These species are consideredas chain top organisms due shows carnivorous food habit. In addition,such species are widely consumed by the riverine population. Fish samples were obtained by fishing net from August 2014 to July 2015. A chemical solubilization (HNO3: H2SO4) was performed for the total mercury determination (THg), followed by oxidation (KMnO4at 5%) and a pre-reduction (NH2OH.HCl at 12%) for further quantification in a cold vapor atomic absorption spectrophotometer.Extraction of methylmercury (MeHg)was carried out through a basic solubilization (KOH at 25%) keeping the sample in an oven at 70°C for 6 hours. Subsequently, aliquots of fish tissue samples were transferred into the vials and buffered with 2M of NaC2H3O2. The samples were ethylated by the addition of NaBEt4 and measured with ultra-pure water for further determination in a gas chromatograph coupled atomic fluorescence spectrophotometer. The analytical quality control was done using certified reference muscle samples (DORM-2 - dogfish).The mean of THg concentrations inP. fasciatum followed the order Liver >Muscle>Brain>Gills, showing a similar order for MeHg in C. monoculus. The order of concentration for THg was Liver>Muscle>Brain>Gills. For the concentrations of MeHg the species followed the same pattern as the first.Percentage of ratio (MeHg/HgT) of the species P. fasciatum was Gills>Brain>Muscle>Liver, and for C. monoculus was Gills>Muscle>Brain>Liver. The highest concentrations of HgT are present in the muscle and liver of the species P. fasciatum and C. monoculus respectively, and thus the highest organotropic ratio of HgT in these species due to their carnivorous food habit.

In 2006, the Committee on the Status of Endangered Species in Canada (COSEWIC) assessed most Lake Sturgeon (Acipenser fulvescens) populations in Manitoba as endangered, although they have yet to be formally listed under the Federal Species at Risk Act (SARA). Currently, commercial and recreational harvest is entirely prohibited, but varying degrees of subsistence harvest persists throughout much of the province. For many First Nation communities in Manitoba, Lake Sturgeon is an important traditional food source and is generally considered an essential and integral part of their distinct cultural identity. Community members occasionally consume large quantities of sturgeon and concerns have been expressed about the associated health risk from mercury exposure. Sturgeon are long-lived, regularly feed on large invertebrates and fish, and thus may accumulate mercury at substantial rates over several decades. However, relatively little is known about mercury concentrations in Lake Sturgeon in Manitoba (and elsewhere in North America). Over the past decade, incidental sturgeon mortalities from several environmental monitoring programs and other environmental assessments in Manitoba have been sampled and analyzed for total mercury (THg) in the axial musculature, substantially expanding the existing data base. Here, we summarize THg concentrations for almost 300 Lake Sturgeon collected from 10 river reaches located within five river systems (four regulated, one unregulated) throughout Manitoba. Mercury concentrations in sturgeon measuring between 97 and 1390 mm fork length and age O+ to 51 years ranged from 0.01 ppm to 0.67 ppm. Mean and median concentrations were 0.12 ppm and 0.09 ppm, respectively, and mean and median lengths were 684 mm and 664 mm, respectively. Except for those from the Saskatchewan River, sturgeon from all other rivers showed a significant relationship between THg and fish length. The slope of the THg-length regression significantly differed between some sturgeon populations, indicating differences in their rate of mercury bioaccumulation. The few available fish from the unregulated Hayes River had the steepest slope of all populations. Thirty (12%) sturgeon exceeded a mercury concentration of 0.2 ppm, which is generally considered the limit for unrestricted fish consumption for subsistence purposes by health organizations. These 30 sturgeon had a mean length of 1053 mm, indicating that subsistence harvest should avoid larger fish to reduce dietary mercury exposure.

This study evaluated the effect of growth of different tissue compartments on the bioaccumulation of mercury (Hg) and polychlorinated biphenyls (PCBs) in silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) from the Three Gorges Reservoir (TGR), China. It was observed that although Hg increased with fish age and size in both species, there was little evidence of PCB concentrations being related to fish size. To investigate this anomalous pattern of bioaccumulation, model simulations were developed and revealed that the growth rate coefficient (kg) of storage tissue compartments exceeded whole body elimination coefficients (ktot) of each contaminant. The kg of lipids also exceeded the kgof protein when expressed on a per unit tissue basis. Using the actual tissue specific kgand calibrated Cd(PCB or Hg concentration in diet), a general bioaccumulation model was able to accurately predict bioaccumulation of PCB and Hg in these two species and major inflection points of chemical accumulation. This study concludes that kgis a dominant process regulating the bioaccumulation of Hg and PCB in silver and bighead carp populations of the TGR. Furthermore, the wider fluctuation in kgof lipid than kg of protein can lead to higher variability in the PCB bioaccumulation rate compared to Hg.

Artisanal and small-scale gold mining (ASGM) in the Madre de Dios region of Peru is causing widespread environmental damage. As global market prices of gold increase, the rainforest is rapidly being cleared for alluvial mining. More than 100,000 acres of protected rainforest have been destroyed by illegal mining over the past decade. As hillsides are washed away, miners use elemental mercury to recover gold in a rudimentary amalgamation process, which is likely driving significant mercury contamination downstream.

The objective of this study is to assess the level of environmental contamination of recent ASGM activities in Madre de Dios. We will monitor sites in the Tambopata and Heath Rivers. Tambopata River receives inputs from the mining-impacted Malinowski River. The Heath River watershed remains undisturbed. Both rivers are in the Tambopata National Reserve and have similar watershed characteristics, such that under normal conditions they would be expected to have similar water quality and ecological conditions.

Samples will be collected at four sites during the rainy season (January-March) and dry season (July-September) in 2017. Sampling sites are in the Tambopata River (one each upstream and downstream of the Malinowski River tributary), one in the Malinowski River, and one in the Heath River. We will quantify the concentrations of mercury (total and methyl mercury) in fine-grained riverbed sediments and in four sentinel fish species (Donsello, Boca chico, Chambira, and Paco). Ancillary physical and chemical parameters (temperature, turbidity, pH, dissolved oxygen, and nitrate) will be measured in-situ. Results from the rainy season will be presented and discussed. We expect to identify distinct patterns between the two river ecosystems and to use the Heath Rivers data as a baseline for future monitoring.

As part of the U.S. Geological Survey (USGS) Regional Stream Quality Assessment studies; the California Stream Quality Assessment (CSQA) evaluated mercury in water, sediment, and fish at 85 stream sites in the coastal chaparral ecological region during spring 2017. The study region spans ~520 km from Santa Barbara in the south to Santa Rosa area in the north and is home to roughly 8 million people as well as is a major agricultural setting that provides much of the nations produce. There are numerous potential sources for mercury (Hg) and other trace elements in the CSQA region, such as selenium that may impact mercury occurrence and bioaccumulation. Sources for Hg include industrial wastewater, municipal wastewater, urban storm runoff, natural geothermal sources, mercury mines, gold mines, and direct atmospheric deposition. The number of mercury mines in the upstream watersheds of the sampling sites ranges from 0 to as many as 50 mines. Many of the watersheds within this region have total maximum daily load limit (TMDLs) management plans in place for mercury. CSQA sampling included weekly water chemistry for six weeks culminating in sampling of bed sediment and full ecological surveys at each site. Fish tissue samples were collected at most sites for analysis of total mercury in composite samples of insectivorous forage fish. Opportunistically game fish were collected and analyzed for total mercury in the fillet tissue. Carbon and nitrogen isotopes were used to evaluate tropic position of the fish. Mercury isotopes were assessed in bed sediment and fish tissue at selected sites to evaluate potential sources of mercury. In addition, water quality information was collected (e.g., dissolved organic carbon, sulfate) that might help to explain mercury methylation in the streams and concentrations of Hg in fish. These results will aid in better understanding the conditions of these streams within this region and assist future management of these streams and downstream waterbodies.

The Dragonfly Mercury Project engages citizen scientists in monitoring mercury contamination in National Parks across the US. The scientist team at the University of Maine, US Geological Survey, and National Park Service (NPS) enlist park staff or community partners, who lead teams of citizen scientists in the collection of dragonfly larvae. Dragonflies are analyzed for mercury, a global pollutant that affects resources the NPS is charged with protecting. The results provide individual parks and NPS data regarding the distribution of mercury at broad spatial scales. Our goals for citizen scientist engagement are to: (1) provide an opportunity for biodiversity discovery; (2) connect people to parks; and (3) provide a vehicle for education and outreach regarding mercury. After field sampling, each park lead completes a short phone survey to provide structured feedback about citizen scientist outcomes. Since 2013, we have conducted a consistent survey covering >100 sampling expeditions across 60 national parks, involving >2,500 citizen scientists who typically contribute ~4 hours each to the project. Preliminary results indicate that deep engagement in the biodiversity discovery objective was an overwhelmingly important aspect of the project, with several participants citing getting kids outdoors as a highlight of the program. At Acadia National Park, expanded sampling plans allowed for multiple citizen science expeditions, with over 660 participants (from middle school students to families to retirees) during 2013-2016. We will discuss our development of key messages for each citizen group type and outline challenges of working with the various citizen groups.

Methylmercury (MeHg) is produced in numerous aquatic ecosystems. Some systems have the potential to easily transfer and biomagnify into both aquatic and terrestrial food webs. While bioaccumulation processes within higher trophic levels have been well documented, processes controlling methylation of inorganic mercury (Hg) and initial steps of accumulation of MeHg into the food web are not as well understood. We have been studying mercury cycling in stream ecosystems at the Smithsonian Environmental Research Center (SERC) which is located on the Coastal Plain on the western shore of the Chesapeake Bay. One part of this research is focused on the transfer of MeHg and Hg to the food web of two first order streams with different watershed histories, one which has been forested for the past 80 years and one that until recently supported agriculture. Production of MeHg in the riparian zone occurs in both streams, but stream and shallow groundwater concentration are much higher in the forested stream. By measuring concentrations of MeHg in sediment, stream pore water, and benthic macroinvertebrates of the two stream ecosystems, we are attempting to identify benthic macroinvertebrate taxa to serve as bioindicators in MeHg risk assessment. Initial examination of macroinvertebrate species diversity and abundance indicates an anticipated difference between the two watersheds, but with some commonality to explore our question. This difference is likely driven by the differing hydrology between the forested and the agriculturally impacted watershed. MeHg and Hg analysis is currently underway and the results will be presented.

A recent study that assessed the mercury (Hg) and selenium (Se) concentrations in >14,000 ocean and freshwater fish has found the overwhelming majority of ocean fish contain far more Se than Hg, and are therefore more likely to prevent than cause Hg toxicity. In contrast, the Hg contents of freshwater fish are inversely related to environmental Se availability, introducing great variability in the risks associated with their consumption. For this reason, the effects of methylmercury (MeHg) exposures from fresh water fish consumption require a better informed approach to risk assessments than those previously available. In all vertebrate tissues, MeHg initially binds to thiols, but since substrate thiols are directly acted upon by certain selenoenzymes, these species become suicide substrates that actively deliver MeHg into the active sites of Se-dependent enzymes in the proper orientation to accomplish its transfer from the substrate thiol to the enzyme selenol. These MeHg-Se conjugates degrade to form mercury selenide (HgSe), an insoluble, biologically unavailable form that cannot be absorbed during digestion. This retires Hg from the biogeochemical cycle, and diminishes the amount available in tissues of predators or human consumers. Because the soils of many North American watersheds are Se-rich, fresh water fish from most regions contain far more Se than MeHg. However, fish from certain regions of North American and many other regions of the world have poor Se availability, either due to low abundance in the geological parent rock material, or due to poor Se bioavailability due to low pH of the watersheds soil or waters. Poor Se availability in freshwater bodies was found to greatly increase MeHg bioaccumulation in Lepomis machrochiris (bluegill), Sander vitreus (walleye), Ictalurus punctatus (channel catfish), Esox Lucius (northern pike), and Micropterus salmoides (largemouth bass). In the absence of sufficient Se, freshwater fish bioaccumulate more MeHg than fish from Se-rich watersheds, and their poor Se contents greatly increase the risks associated with these MeHg exposures. Therefore, these aspects of MeHg associated risks urgently require further study, especially in regions of the world which are known to be Se-poor. The risks associated with eating fish from such watersheds will need to be established on a case by case basis. In summary, MeHg risks cannot be accurately evaluated using outdated methods that only consider MeHg exposures. The Se-Health Benefit Values (HBV) is intended to enable rapid identification of areas at accentuated risk and will more accurately establish MeHg-exposure related health hazards.

Zooplankton are an important vector of methylmercury (MeHg) to aquatic food webs and can be used to assess the role of morphological, land cover, and water quality parameters on MeHg availability. The Finger Lakes (New York, USA) are a series of glacially formed lakes with land cover dominated by agriculture that are experiencing increasing eutrophication. The objective of this study was to evaluate the association of lake productivity, frequency of anoxia, and dissolved organic carbon concentrations with temporal trends in zooplankton MeHg concentrations. Lakes were selected with contrasting land use, watershed size, and depths. We surveyed bulk zooplankton (153 m mesh size) weekly from Honeoye Lake and Seneca Lake in May September 2016. Honeoye Lake is a shallow (max depth 9 m), polymictic lake that undergoes frequent anoxia over the summer while Seneca Lake is a deep (max depth of 198 m), monomictic lake that remains oxygenated in the hypolimnion. We hypothesized that Honeoye Lake will have higher MeHg concentrations in zooplankton due to the frequent anoxic events which can lead to higher MeHg production, and the greater catchment area to surface area ratio (CA:SA) which can increase Hg transport from the watershed. In a preliminary subset of samples, MeHg concentrations were low in both lakes (range = 2 21 ng/g dry weight (dw); mean 10 ng/g dw) compared to bulk zooplankton of a similar size class from other regional watershed systems including Lake Champlain and the Adirondacks. Zooplankton data collected monthly (May-September) in 2015 from a previous study of five Finger Lakes showed significant differences among lakes in May, July, and September. Within lakes, trends varied, but lakes with larger CA:SA (e.g., Honeoye Lake) had significantly higher MeHg concentrations in May. Dissolved organic carbon was not a significant predictor of zooplankton MeHg concentrations with the monthly samples collected in 2015. Analyses of the 2016 zooplankton samples continue and we hypothesize that changes in zooplankton MeHg concentrations on a finer temporal scale will reveal higher MeHg concentrations in Honeoye Lake compared to Seneca Lake.

Although methylmercury (MeHg) can be higher in freshwater than estuarine or marine sediments, it is not known whether MeHg in biota also follows this trend. The objective of this research was to determine if MeHg concentrations in fish and invertebrates decrease along gradients of increasing marine influence in estuaries, as measured by salinity. Fourspine stickleback (Apeltes quadracus), as well as invertebrates (snails, amphipods and chironomids), were collected from each of ten sites along the Saint John River estuary in 2015 and 2016. Sediments and water were also collected in 2016. Total mercury (THg; used as a proxy for MeHg in fish) was measured in whole stickleback and MeHg was measured in pooled invertebrates as well as sediments and water. Stable sulfur (δ34S) (measure of marine influence), carbon (δ 13C) (measures of food sources) and nitrogen isotope (δ 15N) (measure of trophic position) values were also measured, as these help explain variability in MeHg and THg in animals. Analysis of variance tests were used to check for among-site differences in THg in fish and generalized linear models were used to determine which factors predict THg in stickleback and which factors (salinity, dissolved oxygen, length (fish only) and stable isotope values) predict MeHg in invertebrates. Salinity and dissolved oxygen of the sites ranged from 0.1 ppt to 8.1 ppt and from 5.9 to 12.2 mg/L, respectively. Concentrations of THg in stickleback were 109.4 to 1,134.1 µg/kg dry weight (dw) across sites. MeHg ranged from 10.1 to 145.1 µg/kg dw in amphipods, from 22.1 to 613.0 µg/kg dw in snails and from 23.4 – 101.0 µg/kg dw in chironomids across sites. Though there were significant among site differences in THg in fish, these differences seemed to be unrelated to salinity. For stickleback in 2015, mean THg was best predicted by mean length and δ34S. MeHg in both amphipods and snails were significantly predicted by d15N. Although several factors affect the accumulation of MeHg in the tissues of biota, these preliminary results do not suggest salinity was a main influence, although δ34S, another measure of marine influence, explained some variability of THg in 2015 fish. Analyses of samples and data from 2016 is ongoing.

Fish-tissue mercury (Hg) concentrations exceed human health advisory levels and wildlife guidelines in water bodies throughout the northeastern United States. Mercury concentrations in small, mid-trophic level invertivorous fishes and in predatory game fishes of this regions streams were assessed during the summer of 2016 as part of the Northeast Stream Quality Assessment (NESQA), a multi-stressor study conducted by the USGS National Water-Quality Program. The objectives of the fish mercury investigation were to document stream-fish Hg concentrations throughout the region and to describe the environmental factors associated with observed spatial patterns across the region. Streams were located in urban, agricultural, and forested watersheds, and represented a variety of potential mercury sourcess. Total mercury (THg), assumed to be primarily methylmercury (MeHg), was analyzed in fish tissue collected from 91 streams. Small-bodied, mid-trophic, invertivorous fishes were collected from nearly every site, and game fish samples were collected from 54 of the sites. Fish tissue from 23 of the sites was also analyzed for THg isotopes to evaluate Hg sources. The most commonly-collected mid-trophic level fishes were Blacknose Dace (Rhinichthys atratulus, 61 sites), Longnose Dace (R. cataractae, 22 sites), and Creek Chub (Semotilus atromaculatus, 22 sites). These samples consisted of single-species composites of whole specimens. The most commonly-collected game fish samples were salmonids (collected from 26 sites) and centrarchids (mainly Micropterus and Lepomis species; collected from 21 sites). Multiple mid-trophic level species and game fish species were collected at many sites, to facilitate spatial comparisons across the region. Fish and periphyton samples also were analyzed for nitrogen stable isotopes (δ15N) to provide estimates of base-adjusted trophic position (i.e. by adjusting fish δ15N for differences among sites in base nitrogen signature). Fish Hg concentrations will be compared with human-health and wildlife-health guideline levels, and will be analyzed in relation to stream physical data (such as stage, temperature), water quality data (including pH and concentrations of dissolved organic carbon, sulfate, THg and MeHg), bed sediment THg, landscape characteristics, and food web characteristics (based on periphyton, macroinvertebrate, and fish community sampling data) to document factors affecting mercury bioaccumulation in stream-resident fish across the Northeastern United States.

Fish mercury (Hg) concentrations are positively correlated to atmospheric deposition. While North American and global deposition of Hg has declined in recent decades fish Hg concentrations in Boreal Shield lakes of Ontario, Canada, have not shown a similar decline and may even be rising in some areas. At a landscape scale, much of the observed variability in fish Hg concentrations is among waterbodies suggesting ecosystem-level effects on methylmercury production. There is also considerable variation among trophic guilds of fishes within waterbodies, with piscivores usually having the highest Hg concentrations. Variation in Hg concentrations may also be substantial among species within a trophic guild, though the reasons for this have not been closely investigated. We are examining the relative roles of food web position and growth rate in accounting for interspecific variation in mercury concentration of four co-habiting native piscivore species (walleye, northern pike, lake trout and burbot) in 34 Boreal Shield lakes of Ontario. Preliminary results have shown that variation among lakes may be higher than variation among species and much of the interspecific variation in mercury concentrations among boreal piscivores may be accounted for by subtle differences in food web position. Hg and stable isotope data analyses are ongoing, linear models relating total mercury concentration [THg] to carbon source (inferred from 13C), trophic position (inferred from 15N) and growth rate in a standard size of fish (1 kg) will be compared using Akaikes Information Criterion (AIC).

Methylmercury (MeHg) bioaccumulates in food webs. The length of microbial food webs differs between heterotrophic and autotrophic dominated systems. This difference in length could affect the level of MeHg bioaccumulation between the water column and zooplankton communities. Biogeochemical models often have a reduced pelagic microbial food web with simplified carbon and nutrient turnover. To quantify the uptake and trophic transfer of MeHg through the bottom of the food web we use the Baltsem model, a biogeochemical model that has been expanded to include a microbial food web. The model thus includes a detailed scheme for carbon and nutrient cycling in the water column and through three types of phytoplankton (cyanobacteria, diatoms and flagellates), bacteria, heterotroph nanoflagellates, ciliates and mesozooplankton. We recently updated the model to include biogeochemical Hg cycling in the water column and uptake into phytoplankton. Here we add uptake by bacteria as well as trophic transfer of MeHg through both the autotrophic and heterotrophic food web up to mesozooplankton. To validate the model we collected different size classes of seston in the Baltic Sea. The microbial communities in the samples were determined as well as the MeHg content. With the updated model we simulate differences in trophic MeHg transfer between the autotroph and heterotroph food webs. We discuss results from the model simulations with a focus on the impact of variability in autotroph/heterotroph driven food webs for MeHg bioaccumulation.

In ultraoligotrophic lakes of Andean-Patagonia, the aquatic biota generally bears high total mercury (Hg) levels. In these systems, inorganic Hg (Hg2+) makes up to ~93% of the Hg pool. The microplanktonic fraction (20-200 m) of these lakes is dominated by autotrophic dinoflagellates, (Gymnodinium spp.) and mixotrophic ciliates (Ophrydium naumanni and Stentor araucanus). These organisms may potentially incorporate Hg passively from the dissolved phase and, in the case of the mixotrophic ciliates, also through consumption of picoplanktonic organisms, transferring this metal to higher trophic levels. In this investigation we analyzed the passive and active incorporation of Hg2+ by three basal planktonic organisms of contrasting sizes (increasing size: Gymnodinium spp.

Mercury contamination within aquatic ecosystems is of particular concern in the Adirondack Park of New York State due to elevated levels of mercury deposition from global and regional atmospheric sources and watershed characteristics that drive biophysical interactions that mobilize and transform mercury altering its bioavailability. Short-term internal biological forces impact mercury bioaccumulation as fish communities and populations change due to species introductions and lake management practices causing alterations in food web structure and energy transfer. Utilizing archived samples and historical data, total mercury concentrations, diet and age data were evaluated for lake trout, the native top-predator, and smallmouth bass, an introduced top-predator removed annually for over 15 years from Little Moose Lake in the Adirondacks. Mercury concentrations in lake trout have increased over time while smallmouth bass mercury concentrations decreased significantly over the same interval and so changes in mercury deposition are likely not the main driver for these observations. Diets for both species also changed over time with lake trout consuming higher trophic level prey containing higher levels of mercury. The annual bass removal could result in shifts in many different trophic transfer mechanisms that may have influenced the observations in temporal mercury trends in the two top-predator species. The knowledge gained from this in-depth study will allow better evaluation and monitoring of spatial patterns and temporal trends in sportfish mercury concentrations in the context of food web changes to protect human health and the environment.

The average biomagnification of methylmercury (MeHg) through aquatic food webs is quantified as the slope of log MeHg versus stable nitrogen isotopes (delta15N; a measure of relative trophic position). However, these slopes can vary significantly among ecosystems for reasons that are not well understood. In biota, MeHg is stored in proteins, in particular it is bound to the sulphur-containing amino acid cysteine. Our hypothesis was that cysteine content is a better and more consistent predictor of MeHg transfer through lake food webs than delta15N. In 2013, food web taxa (benthic invertebrates, zooplankton, and fish) were collected from six lakes within Kejimkujik National Park, Nova Scotia, Canada, a biological MeHg hotspot. MeHg concentrations and delta15N were measured and compared to protein-bound cysteine (measured as cysteic acid using ultra performance liquid chromatography) in composite invertebrate samples and fish muscle. Cysteine content (nmol per mg tissue) had a strong positive correlation with delta15N (Pearson correlation, r = 0.86; p < 0.001). In addition, log MeHg (mg/kg dw) was significantly and positively related to log cysteine (nmol per mg total protein) (r2 = 0.74-0.90; p < 0.001) within food webs across all lakes; no among-system differences in these slopes were observed (ANCOVA interaction term, p = 0.2134). For these same systems, relationships between MeHg and delta15N resulted in a better goodness of fit (r2 = 0.90-0.95; p < 0.001) and similar slopes (ANCOVA interaction term, p = 0.5059). These results suggest that while cysteine content was a significant predictor of MeHg in aquatic food webs, delta15N explained more of the among-taxa variability within each system.

Bioaccumulation of mercury in fishes is often a complex process influenced by numerous biogeochemical, ecological, and physiological factors at various hierarchical levels. Habitat-specific foraging, including specialization on either littoral or pelagic resources, can be a particularly important ecological process influencing fish tissue mercury concentrations. However, the mechanisms underlying habitat-specific differences in mercury bioaccumulation are poorly understood. In particular, the degree to which differences in mercury bioaccumulation among habitats are due to trophic processes occurring within habitat-specific food webs as compared to variable production of bioavailable methylmercury in different habitats is unclear. To differentiate between these two sources of variation, we measured total mercury and methylmercury concentrations in threespine stickleback fish (Gasterosteus aculeatus) and primary consumers from both littoral (grazing snails) and pelagic (filter-feeding mussels) food webs in seven lakes where the proportion of the lake that was composed of littoral habitat ranged from 10% to 99%. Preliminary results indicate that in all seven lakes methylmercury concentrations of primary consumers were significantly (2- to 4-fold) higher in pelagic taxa than in littoral taxa. However, MeHg concentrations in primary consumers from both habitats displayed nearly identical positive correlations with the proportion of littoral area within lakes. In contrast, we found an inverse-quadratic (U-shaped) relationship between stickleback mercury concentrations and the proportion of littoral area within a lake; concentrations were higher in lakes with proportionally low or high littoral area compared to lakes with nearly equal proportions of the two habitats. Higher mercury concentrations in stickleback from lakes with high relative littoral areas may be due to higher mercury concentrations in the primary consumers at the base of these lakes food webs. However, lakes with low relative littoral area also had low mercury concentrations in primary consumers, suggesting that the elevated concentrations in the stickleback from these lakes are likely due to trophic processes occurring within the food webs. Together these data highlight the importance of considering both trophic and biogeochemical processes when evaluating habitat-specific sources of variation in mercury bioaccumulation.

The consumption of fish is the major exposure route of potentially toxic mercury (Hg) as well as physiologically highly required long-chain polyunsaturated fatty acids (PUFA) to humans. There are considerable differences in Hg and PUFA concentrations of freshwater fish in Sweden and China, with generally lower methyl mercury (MeHg) concentrations in fish from China than Sweden, although aqueous MeHg concentrations are very similar. Such inconsistence encouraged us to explore Hg, MeHg, and PUFA patterns in lake food webs to better understand the contrasts between the freshwater ecosystems of Sweden and China, as well as the large variation within each country. To do this we measured Hg and MeHg concentrations in surface water, plankton, benthic invertebrates, and fishes sampled from 7 freshwater lakes in Sweden and 6 reservoirs in China. Stable carbon (d13C) and nitrogen (d15N) isotope ratios, and PUFA concentrations were measured in aquatic biota. We also included MeHg concentrations and PUFA profiles in different plankton size groups: seston (<25 µm in Sweden), microplankton (64-112 µm in China; 25-100 µm in Sweden), mesozooplankton (112-500 µm in China; 100-500 µm in Sweden) and macrozooplankton (>500 µm in Sweden).

Our preliminary results indicate: 1. Chinese fish muscle samples were rich in the omega-6 PUFA linoleic acid (LIN), whereas Swedish fish samples were rich in the omega-3 PUFA docosahexaenoic acid (DHA); 2. PUFA appear to be effective biomarkers indicative of different food sources in different locations. For example, gamma-linoleic acid (GLA) characteristic of blue-green algae, is significantly higher in Chinese fish muscle samples. 3. MeHg and MeHg/THg were significantly lower in Swedish zooplankton samples, but significantly higher MeHg and MeHg/THg in fish samples as compared to the samples from China; 4. There was a statistically significant negative correlation between MeHg and PUFA, monounsaturated fatty acids (MUFA), saturated fatty acids (SAFA), and terrestrial fatty acids in fish samples from oligotrophic lakes in Sweden. The same trend was not observed in samples from eutrophic lakes in China.

Overall, these data begin reveal the complexity of how food web structures influence regional and global differences in the bioaccumulation of Hg.