3c: Risk assessment of mercury exposure to fish, birds, and wildlife

Methylmercury contamination of the environment is an important issue globally and birds are useful bioindicators for mercury monitoring programs. We synthesized all of the available data on mercury contamination of birds in western North America. We obtained original data from multiple databases and conducted a literature review to obtain additional mercury concentrations. In total, we compiled 29,219 original bird mercury concentrations from 225 species, and obtained an additional 1,712 mean mercury concentrations, representing 19,998 individuals and 176 species, from 200 publications. To make mercury data comparable across bird tissues, we used published equations of tissue mercury correlations to convert all mercury concentrations into blood-equivalent mercury concentrations (µg/g wet weight [ww]). Blood-equivalent mercury concentrations differed among species, foraging guilds, habitat types, locations, and ecoregions. Piscivores and carnivores exhibited the greatest mercury concentrations, whereas herbivores and granivores exhibited the lowest mercury concentrations. Bird mercury concentrations were greatest in ocean and salt marsh habitats and lowest in terrestrial habitats. Bird mercury concentrations were above toxicity benchmarks in many areas throughout western North America, and multiple hotspots were identified. We also summarized the published toxicity benchmarks established for multiple tissues, and translated them into a common blood-equivalent mercury concentration. Bird health, physiology, behavior, and reproduction were affected across a range of blood-equivalent mercury concentrations, with many documented effects in the range of 1.0 to 3.0 µg/g ww and more severe effects occurring over 3.0 µg/g ww. Overall, 66% of birds sampled in western North American exceeded a blood-equivalent mercury concentration of 0.2 µg/g ww (above background levels), which is the lowest-observed effect level, 28% exceeded 1.0 µg/g ww (moderate risk), 8% exceeded 3.0 µg/g ww (high risk), and 4% exceeded 4.0 µg/g ww (severe risk). Mercury monitoring programs should sample bird tissues that are most-easily translated into tissues with well-developed toxicity benchmarks and that are directly relevant to bird reproduction. These high priority sampling tissues include whole blood, eggs, and juvenile down feathers. Our results indicate that mercury contamination of birds is prevalent in many areas throughout western North America, and large-scale ecological attributes are important factors influencing bird mercury concentrations.

Eggshells are a potential tool for non-lethally sampling contaminant concentrations in bird eggs, yet few studies have examined their utility to represent mercury exposure. We assessed mercury concentrations in eggshell components for 23 bird species and determined whether they correlated with total mercury (THg) in egg contents. Additionally, we designed a multi-experiment analysis to examine how THg is partitioned into eggshell components, specifically the hardened eggshells, the material adhered to the eggshell, and the inner eggshell membrane. THg concentrations in eggshells were much lower than in egg contents, and almost all of the THg within the eggshell was contained within the material adhered to eggshells and the inner eggshell membrane, and specifically not within the calcium-rich hardened eggshells. Despite having very little mercury, THg concentrations in hardened eggshells had the strongest correlation with egg contents among all eggshell components. However, species with the same THg concentrations in eggshells had different THg concentrations in egg contents, indicating that there is no global predictive equation among species for the relationship between eggshell and egg content THg concentrations. Further, for all species, THg concentrations in eggshells decreased with relative embryo age. Although the majority of mercury in eggshells was contained within the inner membrane and material adhered to the eggshell, and not within the hardened eggshell, THg concentrations in hardened eggshells can be used to estimate THg concentrations in egg contents if embryo age and species are addressed.

Mercury is highly toxic to fish and wildlife, and can impair behavior, physiology, survival, and reproduction. Sampling bird blood is a common means for evaluating site-specific exposure risk of mercury to wildlife. However, blood mercury concentrations can change rapidly through time, due to changing environmental factors at a site and changing physiological factors within the birds themselves. We studied seasonal and physiological influences on mercury concentrations in western grebes (Aechmophorus occidentalis) and Clark’s grebes (A. occidentalis) across 29 lakes and reservoirs in California, USA. Additionally, at three of these lakes, we conducted a time series study, in which we repeatedly sampled grebe blood mercury concentrations during the spring, summer, and early fall. Grebe blood mercury concentrations were higher among males (0.61±0.12 µg/g ww) than females (0.52±0.10 µg/g ww), higher in Clark’s grebes (0.58±0.12 µg/g ww) than western grebes (0.51±0.10 µg/g ww), and exhibited a strong seasonal pattern (decreasing by 60% from spring to fall). Further, the relationship between grebe blood mercury concentrations and wing primary feather molt exhibited a shallow U-shaped pattern, where mercury concentrations were highest among birds that had not yet begun molting, decreased approximately 24% between pre-molt and late molt, and rising approximately 19% from late molt to post-molt. Because grebes did not begin molting until mid-summer, lower grebe blood mercury concentrations observed in late summer and early fall were consistent with the onset of primary feather molt. However, because sampling date was a much stronger predictor of grebe mercury concentrations than molt, other seasonally changing environmental factors likely played a larger role than molt in the seasonal variation in grebe mercury concentrations. In the time series study, we found that seasonal trends in grebe mercury concentrations were not consistent among lakes, indicating that lake-specific variation in mercury dynamics influence the overall seasonal decline in grebe blood mercury concentrations. These results highlight the importance of accounting for sampling date, as well as ecological processes that may influence mercury concentrations, when developing monitoring programs to assess site-specific exposure risk of mercury to wildlife.

Polar bears are long-lived marine mammals, which occupy apical trophic positions in Arctic food webs. Accordingly, they are exposed to high levels of dietary mercury (Hg), the majority of which is likely derived from anthropogenic sources. Despite high levels of exposure, recent data indicate that polar bears accumulate relatively low concentrations of total Hg in their brain stems (~0.07 ppm wet weight). Conversely, concentrations of total Hg of 30 ppm wet weight, mainly in the form of inorganic Hg, have been reported for polar bear liver tissues. The accumulation of high concentrations of inorganic Hg in the liver may be a result of demethylation of more toxic methylmercury (MeHg). MeHg demethylation in the liver is often considered a detoxification mechanism and may serve to protect the brain and explain the low total Hg concentrations observed therein. While it is well known that polar bears accumulate elevated inorganic Hg concentrations in liver, it is not well understood how inorganic and MeHg are distributed at the subcellular level. In this context, we measured total Hg and MeHg in the livers of 42 polar bears and explore how these forms of Hg are distributed at the subcellular level. We aim to better asses the risk of Hg exposure in polar bear by applying a subcellular partitioning procedure to separate a subset of livers into putative metal-sensitive fractions (cytosolic enzymes, organelles) and detoxified metal fractions (metallothionein-like proteins and peptides, granule-like structures). Mercury in metal-sensitive fractions has the potential to cause negative health effects. Polar bear livers were subjected to a subcellular partitioning procedure using differential centrifugation, NaOH digestion, and heat denaturation techniques. The resulting fractions were analyzed for total and MeHg by direct mercury analyzer and GC-CVAFS, respectively. Results of this research indicate that inorganic Hg is the predominant form of Hg in polar bear livers (mean = 99%) over a wide range of total Hg concentrations (3.5 to 32 ppm wet weight). The subcellular distributions of non-essential metals, such as Hg, may provide important insight into detoxification/toxicity mechanisms at the subcellular level, and may ultimately allow for better risk assessments.

The Petit-Saut hydroelectric dam was filled in 1994 on the Sinnamary River in French Guiana (Amazonian basin). Since dams construction physicochemical conditions were monitored in the reservoir and in the river downstream to characterize the impact of rain forest flooding and role of hydroelectric reservoir on mercury methylation. Indeed, French Guiana soils contain high level of mercury coming from atmospheric depositions and also from illegal goldmining sites that use elemental mercury for gold extraction.

Previous studies that analyzed monitoring results showed that physicochemical modifications generated by dam construction led to an important production of methylmercury (MeHg) in the anoxic part of the reservoir and in the downstream river.

Sampling was carried out over 22 years and 5500 fish were analyzed (57 species and 7 different diets). And we distinguished 4 different sites: the upstream part of the river defined as reference and the upstream part under the influence of the goldming, the reservoir and the downstream part of the Sinnamary river.

This high level of MeHg newly produced after dams construction impacted fish mercury concentrations. Monitoring of MeHg concentrations in muscle of Hoplias aimara, a piscivorous fish used as mercury sentinel, shows a progressive increase between 1994 and 2007 in the reservoir and downstream river. MeHg concentrations were multiplied by a factor 2 in ten years in the two sites. Levels of mercury contamination analyzed in other fish species characterized by other diets (omnivorous, herbivorous ...) confirmed this trend with contamination 2 to 10 times higher in fish collected in Sinnamary river, according to the diet. In other compartments of the ecosystem the same thing is noticed.

Comparatively to MeHg concentrations measured in H. aimara muscle collected in the main rivers of French Guiana between 2003 and 2006, were significantly lowest than Sinnamary ones.

After 20 years of increase, MeHg in H. aimara muscle seems to point out a decrease in the reservoir and in the downstream river. This decrease is to be compared with the improvement of the physicochemical characteristics of the environment. Indeed decrease of the organic matter concentrations issued from flooded rain forest degradation, lead to an increase of oxygenated water layer in the reservoir. This newly conditions are less propitious to mercury methylation. This tends to show that the influence of the dam on the levels of mercury contamination in organisms might decrease with time and consequently that water quality improves.

Nalcor Energy is currently constructing the Muskrat Falls hydroelectric dam on the Churchill River in Labrador, Canada. Flooding of the reservoir began in late 2016. At the environmental assessment hearings which preceded the project, concerns were raised by the Nunatsiavut Government and the Government of Canada about downstream increases in aquatic methylmercury in Lake Melville, as a result of dam construction. This project began in 2013, to determine the baseline mercury concentrations in the eggs of marine birds breeding in Lake Melville, prior to flooding of the Muskrat Falls reservoir. We collected eggs of ring-billed gulls (Larus delawarensis) and common terns (Sterna hirundo) on islands in western Lake Melville in 2013-15. These eggs were analysed individually for total mercury, and in 2015 for stable carbon and nitrogen isotopes (δ13C and δ15N, respectively). We found no differences in mean egg mercury concentrations among islands or among years for either ring-billed gulls or common terns. The geometric mean of egg mercury concentrations in common tern eggs (0.92 μg/g, dry wt.) was significantly greater than in ring-billed gull eggs (0.77 μg/g), while the variance in mercury concentrations was greater in the gull eggs. In eggs collected in 2015, δ15N was analysed to investigate the trophic patterns of the gulls and terns. Comparing δ15N data (mean ± SD) between ring-billed gull eggs (10.5 ± 1.3‰) and common tern eggs (12.5 ± 0.5‰) indicated that the gulls foraged over a wider trophic range, and on average at a lower trophic level than the terns. Mercury concentrations in the gull eggs were unrelated to either δ13C or δ15N. However, in the common tern eggs, both δ13C and δ15N were negatively associated with mercury concentrations. Current mercury levels in the Lake Melville gull and tern eggs pose little risk to seabird populations. However, the two highest mercury concentrations observed in ring-billed gull eggs were probably associated with adverse effects on reproductive success. This study provides baseline data prior to the flooding of the Muskrat Falls reservoir, which we will use to assess the amount and duration of subsequent mercury increases after flooding.

Environmental stressors can negatively affect avian cognitive abilities, potentially reducing fitness, for example by altering response to predators, display to mates, or memory of locations of food. We expand on current knowledge by investigating the effects of dietary methylmercury on avian cognition. Captive zebra finches (Taeniopygia guttata) were dosed for their entire lives with sub-lethal levels of mercury, at the environmentally-relevant dose of 1.2 parts per million. In our first study we compared the dosed birds to controls of the same age using tests of three cognitive abilities: spatial memory, inhibitory control, and color association. In the spatial memory assay, birds were tested on their ability to learn and remember the location of hidden food in their cage. The inhibitory control assay measured their ability to ignore visible but inaccessible food in favor of a learned behavior that provided the same reward. Lastly, the color association task tested each birds ability to associate a specific color with the presence of hidden food. Dietary methylmercury negatively affected spatial memory ability but not inhibitory control or color association. Our second study focused on three behavioral assays not tied to a specific skill or problem-solving: activity level, neophobia and social dominance. Zebra finches exposed to dietary methylmercury throughout their lives were subordinate to, and more active than, control birds. We found no evidence that mercury exposure influenced our metric of neophobia. Together, these results suggest that mercury selectively harms neurological pathways that control different cognitive abilities in birds, with complex effects on behavior and fitness. Monitoring schemes can use behavioral endpoints for detecting effects of toxicants, and risk assessment should consider the potentially grave impact of cognitive problems caused by contaminant exposure. For example, many birds store their food for later retrieval, live in complex social hierarchies, and migrate using memory of spatial landmarks. Mercury exposure would severely compromise these ecological functions, even if it had no effect on commonly measured endpoints such as nesting success or body condition.

The U.S. National Park Service (NPS) safeguards over 400 special places for the protection of unique natural resources and scenic beauty. As a nation, we have promised to leave national parks in an unimpaired condition so that they will continue to provide services such as decomposition, climate regulation, and biodiversity maintenance, as well as serving the educational, recreational, and spiritual needs of society. Yet in many parks, stresses including those from mercury (Hg) have degraded resources. Research and monitoring efforts across the 84 million acres represented by NPS units include assessments of Hg in insects, fish, birds, snow, and air. Although celebrated as some of the most pristine ecosystems in the U.S., this research provides persuasive evidence that Hg may currently be impacting national park resources, and that Hg reductions are likely needed in order to meet the NPS mission to protect these resources for future generations. Even protected areas such as national parks are subjected to Hg contamination because it is delivered through atmospheric deposition, often after long-range transport. Understanding the risk of Hg contamination in NPS units is a challenge because deposition loads and accumulation in the food web are decoupled; elemental or inorganic Hg must first be converted to methylmercury (MeHg) in order to equate to ecosystem harm. Since 2015, NPS has been operating under an interim guidance for Hg condition that incorporates interpolated concentrations of Hg deposition, based on the Mercury Deposition Network, and predicted concentrations of MeHg in NPS surface waters, based on the U.S. Geological Survey (USGS) Methylmercury Model. While this spatial analysis can be used to determine Hg status in parks, it is a rough estimate of condition. Resource condition assessments are supposed to provide direction to park management for each NPS unit. So, to more accurately calculate Hg condition or status in parks, the NPS worked with USGS to: (1) complete a research synthesis identifying Hg toxicological benchmarks on wildlife, and (2) compile a dataset on Hg levels in biota from NPS units. These data are being used to compare measured Hg concentrations in park wildlife with established thresholds, generating park-specific condition assessments. Where park-specific biological exposure data do not exist, the condition defers to the interim guidance. This novel approach provides better understanding of the Hg issue across our national parks, supports park planning processes, prioritizes research needs, drives policy, and fosters more informed management decisions across our protected landscapes.

We analyzed the study design and data used to model a predictive relationship between blood mercury (Hg) concentrations and reduction in nest success of Carolina wren (Thryothorus ludovicianus) (Jackson et al. 2011), which has been considered for use in assessments of ecological risk and natural resource damages. Our analysis indicated that the study design and data interpretation were insufficient for predicting reduction in nest success at specific blood Hg concentrations. The reference site selection process was not documented, the number of samples was small (i.e., only two and four abandoned nests at reference and contaminated sites, respectively, in the 2010 dataset of 40 nests used in the predictive model), and the mixed use of artificial (box and tube) and natural nests (with natural nests disproportionately used in reference sites in 2010) confounded interpretation. In addition, the 2010 dose-response relationship between blood Hg and reduction in nest success was biased by the exclusion of two predated nests upstream (because blood Hg data was lacking) and inclusion of one parasitized and three predated nests downstream. We used the mathematical model MARK, similar to MCestimate used by Jackson et al., to evaluate statistical models explaining observations. Our modeled results based on analysis of abandoned nests indicated that cavity type was an important covariate, along with location.We also calculated 30-day nest success using Mayfield estimation. For the pooled 2007 to 2009 dataset where all but one cavity was artificial (and therefore cavity type was controlled), 30-day nest success based on abandoned nests was the same at reference and contaminated sites. In 2010, 30-day nest success based on abandoned nests was higher in the reference sites than in the contaminated sites and higher than both in 2007-2009, however the reference sites had twice as many natural cavities as the contaminated sites. While nest success data and mathematical models have potential for assessing contaminant impacts, robust studies require extensive data collection and accounting for multiple factors other than contaminants that impact nest success and, perhaps more importantly, fecundity. Variable results among years indicate the need for multi-year studies. Mathematical models are powerful; however, conclusions are ultimately limited by the quality and quantity of observations. The Jackson et al. predictive relationship between blood Hg and reduction in nest success is compromised by its study design and small dataset, and therefore should not be used for quantitative estimation of risk, injury, or service loss to songbirds.

Onondaga Lake in Syracuse, NY is a 12 km2 lake that has been impacted by a long history of municipal and industrial activity, including two former mercury cell chlor-alkali plants. Since 2004, the lake has experienced significant improvements in water quality following upgrades to the Metropolitan Sewage Treatment Plant that significantly reduced phosphorus and ammonia concentrations in the lake. In addition, in accordance with the Consent Decree for the Onondaga Lake Superfund Site, nitrate addition to the hypoliminion to limit methylmercury release from profundal sediment has occurred annually since 2011, and dredging and capping of contaminated sediment was completed by Honeywell in 2016. Mercury concentrations in prey fish samples have been monitored since 2008 to provide baseline data and to evaluate the effect of the remediation on lower levels of the food chain. Three composite samples of small prey fish by species were collected annually from each of eight locations in the lake and analyzed for total mercury. The locations were selected to represent various sediment management areas with a range of mercury concentrations in sediment. The predominant species were Banded Killifish with occasional collections of Round Goby, Golden Shiner, and Brook Silverside. Alewife were also collected. Under baseline conditions prior to sediment remediation, mercury concentrations in prey fish were approximately 0.31 mg/kg in areas with elevated mercury concentrations in sediment and 0.14 mg/kg in areas on the opposite side of the lake from former discharge points. Following sediment remediation, mercury concentrations in all areas were similar to those observed on the opposite side of the lake under baseline conditions. Reductions in mercury concentrations in prey fish are expected to result in reduced concentrations in upper trophic level fish, although the timing and magnitude are subject to multiple factors including their relative consumption of planktivorous and benthivorous prey fish.

Mercury (Hg) contamination in aquatic ecosystems is known to pose reproductive and health risks to biota. In past studies, we found high levels of Hg exposure in salt marsh obligate bird species, suggesting that high degrees of bioaccumulation and biomagnification occur in these ecosystems. What is currently unknown are the annual trends and variance seen in biota Hg levels. Invertivorous songbirds, such as the above species are now recognized as best indicators of mercury in the salt marsh ecosystems, where methylmercury (MeHg) biomagnifies in the food chain to levels that can adversely affect reproductive success. With changes to Hg emissions regulations, understanding how MeHg bioavailability changes over time in biota is important. To assess annual mercury changes in mercury exposure of salt marsh songbirds, we non-lethally sampled blood and feathers from several species: Nelsons Sparrow in Maine, Saltmarsh Sparrow in Maine, Massachusetts and New York and Seaside Sparrow in New York to detect and assess Hg changes over time in the same study areas. We analyzed over 13 years of blood and feather mercury data collected from saltmarsh-breeding birds across the Northeast, as a result of multiple projects from 2001 to 2016, to quantify magnitude and trends of mercury exposure for these three species of conservation concern. We found that Hg concentrations are significantly different by site, species, and individual age and temporal trends vary by location after time of sampling has been accounted. Many locations show decline in Hg exposure over the study time period while fewer are stable or increasing. As a result of these projects; 1) we identified several hot spots of mercury in the northeast: (2) we evaluated temporal trends in songbird mercury exposure in northeastern salt marshes.

Greenland halibut (Rheinhardtius hippoglossoides) is a circumpolar, Arctic flatfish distributed in both the Atlantic and Pacific Oceans. This species is a cold and deep-water organism, living at depths between 400 and 2000 m and exhibit bathypelagic behavior. Greenland halibut is also an important fishery resource in the Barents Sea and the Norwegian Sea, although the fisheries have been strictly regulated since 1992. In 2006, it was reported that values of mercury in a consignment of this fish were greater than the EU maximum level of 0.5 mg Hg/kg.

Based on risk factors for bioaccumulation of toxic substances, the Greenland halibut was therefore chosen for a comprehensive baseline study to evaluate the food safety status along with cod, saithe, herring and mackerel. The major substances for concern have been mercury along with dioxins and dioxin-like PCBs, which have scientifically based tolerable weekly intake values (TWIs) and also have maximum levels for trade in Europe.

In the baseline study, 1288 Greenland halibut were collected from 27 different positions in the Barents Sea and the Norwegian Sea between 2006 and 2008. Additionally, follow up studies in the Norwegian Sea have been performed for five more years, most recently in 2015. The overall mean of mercury concentration in the baseline study was 0.22 mg Hg/kg wet weight, which is one of the highest recorded mercury concentrations in the North East Atlantic. Furthermore, 99 out of 1288 halibut (7.7 %) showed values greater than the maximum level of 0.5 mg Hg/kg.

Mercury concentrations in this species were size dependent and 44 % of Greenland halibut over 5 kg had concentrations above 0.5 mg Hg/kg while only 2.9 % of those less than 3 kg had concentrations above the EU maximum level. New data analyses and studies have also evaluated the effects of food web dynamics and energy sources on mercury concentrations and bioavailability in this species.

In conclusion, the Greenland halibut is a fish species with relatively high levels of mercury, although the average is below the EU maximum level of 0.5 mg Hg/kg. The size dependent nature of mercury bioaccumulation and spatial variation and integration over time require that Greenland halibut biomonitoring continues to ensure safe consumption of this species by humans.

Marine mammals, such as dolphins, can be exposed to high concentrations of persistent pollutants, including mercury (Hg), due to biomagnification and bioaccumulation. Previous research on marine mammals and other mammalian species indicates that exposure to Hg can negatively impact neurological, hepatic, renal, and immune functions. In cetaceans, skin has been used as a biomonitor of trace element concentrations in the internal tissues of live animals, while liver is the most commonly analyzed tissue for Hg exposure in dead animals. This study aims to evaluate the Hg levels in stranded dolphins from the estuarine and oceanic waters of Virginia, USA and to evaluate the correlations between tissue types. Available tissues were obtained from 128 dolphins that were recovered and necropsied by the Virginia Aquarium Stranding Response Program from 2009-2015. Samples of liver, kidney, muscle, skin, cerebrum, cerebellum, and pons were analyzed for total Hg concentration. Liver samples were found to contain the highest levels of total Hg, followed by the kidney. Concentrations were lower in muscle, skin and brain. Twenty percent of individuals tested had liver concentrations greater than the observed effect level for liver abnormalities seen by Rawson et al. (1993), which suggests that mercury may have impacted liver function in these animals. There was a positive correlation between length and mercury concentration, likely reflecting the bioaccumulation of mercury in older animals. Regressions between tissue types from this study will be presented in order to evaluate the use of skin or liver for estimating concentrations in the other tissue types (kidney, muscle, cerebrum, cerebellum, and pons). Mercury levels in this population will be compared to published studies from Florida, Israel and France in order to evaluate the relative exposure of the different populations. As this is the only study we know of to measure mercury in multiple brain regions of T. truncatus, a comparison of brain tissues will be made and levels will be compared to toxicity thresholds from the literature.

The determination of mercury in fish tissues are of great concern for public health authorities because of the high potential toxicity. Fish absorb Hg easily and accumulate it in their tissues, and is the main route for human contamination. Even at low concentrations, mercury poses a significant risk to the environment and human health because of its neurotoxic characteristics and its intensive biomagnification. The objective of this research was to determine the concentration of total mercury (Hg-T) in different species of fish commercialized in the markets of the Aracaju, Salvador e Macei cities, in the northeast region of Brazil. The fish species were selected according to their availability in the region and were purchased in local markets from May 2014 to April 2016. Some of the species analyzed were: Catfish (Bagre spp), dolphinfish (Coryphaena hippurus), Acoupa weakfish (Cynoscion acoupa and Cynoscion spp), snapperfish (Lutjanus spp), mullet (Mugil spp), sardines (Sardinella brasiliensis), amberjacks (Seriola spp), and tuna fish (Thunnus spp). A portions of fish muscle tissue was removed from the dorsal-lateral area and lyophilized for 48 h and ground in a processor to obtain homogeneous samples. For the total extraction 0.5 g of dry weight sample was digested with the solution (1H2SO4 + 1HNO3) in a cold finger capped herlenmeyer. The extracts were analyzed by cold vapor atomic absorption spectrometry (CVAAS) with a Lumex RA915+. The mean concentrations found in the species ranged from 136 to 72,331 ng g-1. The highest concentrations were found in tuna fish. This fact can be attributed to its piscivorous feeding habit, confirming the bioaccumulation between different trophic chains. The planktivorous species (sardines and mullets) have the lowest concentration. The total mercury levels presented in this study are below of the maximum permitted by Brazilian legislation for fishery products. In Brazil, the legal limit for Hg content in fishery products is of 500 ng g1 for non-carnivorous fish species. The concentrations found were considered high, in general, the levels of total mercury in the target species do not present great risks for consumers based on the maximum tolerable limits.

Mercury (Hg) release to the South River (SR), Virginia, occurred from a former DuPont plant between 1929 and 1950. Legacy Hg in the potentially impacted areas has been the subject of numerous studies over the last four decades. The South River Science Team (SRST), a multi-stakeholder collaborative program, was established in 2001 to investigate the potential impacts to the aquatic and riparian terrestrial systems along the South River and a portion of the South Fork Shenandoah River (SFSR).

As a part of the SRST Program, a foundational modelling framework was developed based on Bayesian Network-Relative Risk Models (BN-RRMs) for evaluating overall risks from multiple stressors (including Hg and pesticides used in agriculture) and environmental factors (e.g., water quality and habitat suitability). The BN-RRMs allow an integration of competing remedial priorities among different stakeholders, involving risk and ecological services. In addition, the models can be iterative for learn and adapt opportunities, which is consistent with the proposed adaptive management approach for the corrective actions. To support the remedial/risk decisions, the BN-RRMs must reflect the remedial approaches and be consistent with the remedial goals. Five contiguous risk regions were defined, including an upstream reference region, within the watershed along approximately 40 miles of the SR and a portion of the SFSR (10 miles upstream and 30 miles downstream of the former DuPont plant). The risk regions were configured to be as consistent as possible with natural breaks based on land use and hydrogeology, the upstream-to-downstream remedial approach and existing short- and long-term monitoring stations. Baseline relative risk scores were calculated for biotic and abiotic endpoints of importance to the stakeholders (e.g., risks to smallmouth bass and public river use). A series of what-if scenarios were also evaluated to predict the outcomes of potential remedial alternatives.

The results of the modelling indicate that: 1) environmental conditions (e.g., water quality and habitat suitability) are important in considering the overall risk, although Hg is the primary chemical stressor, 2) relative risks vary among the risk regions owing to their spatial differences, 3) remedial measures to mitigate potential risk from Hg may achieve varying degrees of overall risk mitigation due to multiple stressors and factors. These results demonstrate that BN-RRMs are a useful tool to: 1) communicate a holistic approach to risk evaluations, 2) integrate stakeholder priorities in making remedial/risk decisions, and 3) apply adaptive management approaches at complex contaminated sites.

Marine and estuarine fish accumulate methylmercury (MeHg) to elevated concentrations, often higher than in freshwater systems. Because MeHg is a potent neurotoxic agent, it is plausible that high tissue concentrations could affect swimming behavior in marine fish which in turn could affect their populations in contaminated waters. We examined sublethal effects of MeHg to a marine forage fish, Sheepshead minnow (Cyprinodon variegatus). Fish were fed a diets comprised of artificial and natural foods (brine shrimp) with varying MeHg concentrations, as high as 4 ppm. The fish were reared on Hg-free and contaminated diets from an age of 5 days until 4 weeks when they reached juvenile stage. Growth rates, swimming activity, response to olfactory cues, and prey-capture ability were tested. Results to date indicate that a MeHg-rich diet has no significant impact on fish swimming activity (swimming speed, acceleration, active time and swimming distance), response to olfactory signals, or prey-capture ability. However, MeHg had a slight impact on the growth rates of these fish.

Patterns in the relative differences in contaminant concentrations between the sexes of mature fish may reveal important behavioral and physiological differences between the sexes. We determined whole-fish total mercury (Hg) concentrations in 23 female summer flounder (Paralichthys dentatus) and 27 male summer flounder from New Jersey coastal waters. To estimate the change in Hg concentration due to release of eggs at spawning, Hg concentration in the somatic tissue and ovaries of 5 of the 23 female summer flounder were also determined. To ascertain whether most of the Hg in the summer flounder was methylmercury (MeHg), whole-fish MeHg concentrations were determined in all 50 summer flounder. Whole-fish Hg concentrations averaged 113 ng/g for females and 111 ng/g for males. Thus, females were 2% higher in Hg concentration than males, on average, but the difference was not statistically significant. Based on Hg determinations in the somatic tissue and ovaries, we predicted that Hg concentration of females would increase by 3.6%, on average, immediately after spawning due to release of eggs. On average, 92% of the Hg in the summer flounder was MeHg. To determine whether the effect of sex on Hg concentration was significantly different from the effect of sex on polychlorinated biphenyl (PCB) concentration, we paired our Hg determinations with PCB determinations from a previous study, and applied regression analysis. Sex significantly interacted with contaminant type (Hg or PCBs), as males were 43% higher in PCB concentration than females, whereas females were 2% higher in Hg concentration than males. Males eliminating Hg from their bodies at a faster rate than females was a likely explanation for this discrepancy between the two contaminant types. Overall, the Hg and PCB concentrations in the summer flounder were relatively low, and therefore our findings also had implications for continued operation of the summer flounder fishery.

Elevated blood and tissue Mercury (Hg) is known to cause adverse effects on songbirds. Recent laboratory studies indicate that Hg impairs foraging behavior, immune system function and flight ability. All of these factors can individually or together affect songbird migration success and survivorship in the field. Here we compared Hg level in tail feathers collecting from five migratory songbird species in two age classes (adult or juvenile), migratory distances (long/short migrating distance or resident) and forage guilds (insectivore, omnivore or granivore) in the fall and spring migration season in the same banding location (Long Point, Ontario, Canada) to assess whether the annual return rate was predicted by tail-feather Hg concentrations, which are conserved over the winter non-breeding season. It was predicted that tail-feather Hg in fall would be higher than in the spring, indicating that the individuals with high Hg burden in the fall migration would have lower fitness and thus lower migratory survivorship. Our results suggest that this prediction is borne out for two long-distance migratory neotropical insectivores. Notably, the spring returning cohort of black- poll warbler had almost half of the Hg concentration of those that departed in the fall. We conclude that higher Hg body burden negatively impacts avian insectivore long-distance migration survivorship.