Derivation of screening benchmarks for dietary methylmercury exposure for the common loon (Gavia immer): rationale for use in ecological risk assessment

Elevated Heavy Metal(loid) Blood and Feather Concentrations in Wetland Birds from Different Trophic Levels Indicate Exposure to Environmental Pollutants

The research assessed the exposure to total mercury (THg), lead (Pb), and arsenic (As) in Colombian wetland species of different trophic levels Platalea ajaja, Dendrocygna autumnalis and Nannopterum brasilianus. The results show high THg blood levels in P. ajaja (811.00 ± 349.60 µg L-1) and N. brasilianus (209.50 ± 27.92 µg L-1) with P. ajaja possibly exhibiting adverse effects. Blood Pb concentration was high in D. autumnalis (212.00 ± 208.10 µg L-1) and above the threshold for adverse effects, suggesting subclinical poisoning. Levels of blood As were below the assumed threshold for detrimental effect (20 μg L-1). The mean concentration of feather THg was below the assumed natural background levels (5 µg g-1) for all three species. Feather Pb levels exceeded the levels for assumed threshold effects in all sampled N. brasilianus (7.40 ± 0.51 µg g-1). Results for feather As concentration were below the threshold for adverse impacts in all species, although a positive correlation between As and THg concentrations was detected in P. ajaja feathers. The overall results could help understand how metal(loid)s biomagnify through trophic levels and how wetland species may serve as environmental indicators. By exploring the interactions of metal(loid)s within different matrices and body, this study offers insights into the dynamics of contaminant accumulation and distribution in the environment. This concept can be applied to wetlands worldwide, where bird species can serve as indicators of ecosystem health and the presence of contaminants such as heavy metals and metalloids.

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

An important provision of the Minamata Convention on Mercury is to monitor and evaluate the effectiveness of the adopted measures and its implementation. Here, we describe for the first time currently available biotic mercury (Hg) data on a global scale to improve the understanding of global efforts to reduce the impact of Hg pollution on people and the environment. Data from the peer-reviewed literature were compiled in the Global Biotic Mercury Synthesis (GBMS) database (>550,000 data points). These data provide a foundation for establishing a biomonitoring framework needed to track Hg concentrations in biota globally. We describe Hg exposure in the taxa identified by the Minamata Convention: fish, sea turtles, birds, and marine mammals. Based on the GBMS database, Hg concentrations are presented at relevant geographic scales for continents and oceanic basins. We identify some effective regional templates for monitoring methylmercury (MeHg) availability in the environment, but overall illustrate that there is a general lack of regional biomonitoring initiatives around the world, especially in Africa, Australia, Indo-Pacific, Middle East, and South Atlantic and Pacific Oceans. Temporal trend data for Hg in biota are generally limited. Ecologically sensitive sites (where biota have above average MeHg tissue concentrations) have been identified throughout the world. Efforts to model and quantify ecosystem sensitivity locally, regionally, and globally could help establish effective and efficient biomonitoring programs. We present a framework for a global Hg biomonitoring network that includes a three-step continental and oceanic approach to integrate existing biomonitoring efforts and prioritize filling regional data gaps linked with key Hg sources. We describe a standardized approach that builds on an evidence-based evaluation to assess the Minamata Convention's progress to reduce the impact of global Hg pollution on people and the environment.

The global challenge of reducing mercury contamination from artisanal and small-scale gold mining (ASGM): evaluating solutions using generic theories of change

Mercury contamination from artisanal and small-scale gold mining (ASGM) currently accounts for 37% of the global total, often affecting tropical regions where regulations, if they exist, are often poorly enforced. Ingestion by people and other animals damages the nervous, reproductive, and cognitive systems. Despite the efforts of many organizations and governments to curb mercury releases from ASGM, it is increasing globally. There are many possible interventions, all with significant complexity and cost. Therefore, we recommend taking an established systematic approach to articulate the current situation and construct theories of change (ToC) for different possible interventions for any government or organization trying to solve this problem. Here we present a high-level situation analysis and generic ToC to support a more coordinated approach that explicitly builds upon previous experience to identify organization- and situation-appropriate engagement on this issue. We then illustrate the use of these generic models to construct a specific ToC with a policy-focused entry point. This includes interventions through (1) engagement with the global Minamata Convention on Mercury; (2) support for existing national laws and policies connected to ASGM and mercury contamination; and (3) engagement of indigenous people and local communities with governments to meet the governments' legal obligations. By methodically articulating assumptions about interventions, connections among actions, and desired outcomes, it is possible to create a more effective approach that will encourage more coordination and cooperation among governments and other practitioners to maximize their investments and support broad environmental and socio-political outcomes necessary to address this pernicious problem.

Methylmercury Effects on Birds: A Review, Meta-Analysis, and Development of Toxicity Reference Values for Injury Assessment Based on Tissue Residues and Diet

Birds are used as bioindicators of environmental mercury (Hg) contamination, and toxicity reference values are needed for injury assessments. We conducted a comprehensive review, summarized data from 168 studies, performed a series of Bayesian hierarchical meta-analyses, and developed new toxicity reference values for the effects of methylmercury (MeHg) on birds using a benchmark dose analysis framework. Lethal and sublethal effects of MeHg on birds were categorized into nine biologically relevant endpoint categories and three age classes. Effective Hg concentrations where there was a 10% reduction (EC10) in the production of juvenile offspring (0.55 µg/g wet wt adult blood-equivalent Hg concentrations, 80% credible interval: [0.33, 0.85]), histology endpoints (0.49 [0.15, 0.96] and 0.61 [0.09, 2.48]), and biochemical markers (0.77 [<0.25, 2.12] and 0.57 [0.35, 0.92]) were substantially lower than those for survival (2.97 [2.10, 4.73] and 5.24 [3.30, 9.55]) and behavior (6.23 [1.84, >13.42] and 3.11 [2.10, 4.64]) of juveniles and adults, respectively. Within the egg age class, survival was the most sensitive endpoint (EC10 = 2.02 µg/g wet wt adult blood-equivalent Hg concentrations [1.39, 2.94] or 1.17 µg/g fresh wet wt egg-equivalent Hg concentrations [0.80, 1.70]). Body morphology was not particularly sensitive to Hg. We developed toxicity reference values using a combined survival and reproduction endpoints category for juveniles, because juveniles were more sensitive to Hg toxicity than eggs or adults. Adult blood-equivalent Hg concentrations (µg/g wet wt) and egg-equivalent Hg concentrations (µg/g fresh wet wt) caused low injury to birds (EC1) at 0.09 [0.04, 0.17] and 0.04 [0.01, 0.08], moderate injury (EC5) at 0.6 [0.37, 0.84] and 0.3 [0.17, 0.44], high injury (EC10) at 1.3 [0.94, 1.89] and 0.7 [0.49, 1.02], and severe injury (EC20) at 3.2 [2.24, 4.78] and 1.8 [1.28, 2.79], respectively. Maternal dietary Hg (µg/g dry wt) caused low injury to juveniles at 0.16 [0.05, 0.38], moderate injury at 0.6 [0.29, 1.03], high injury at 1.1 [0.63, 1.87], and severe injury at 2.4 [1.42, 4.13]. We found few substantial differences in Hg toxicity among avian taxonomic orders, including for controlled laboratory studies that injected Hg into eggs. Our results can be used to quantify injury to birds caused by Hg pollution. Environ Toxicol Chem 2024;43:1195-1241. Published 2024. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Investigating effects of climate-induced changes in water temperature and diet on mercury concentrations in an Arctic freshwater forage fish

The amount of mercury (Hg) in Arctic lake food webs is, and will continue to be, affected by rapid, ongoing climate change. At warmer temperatures, fish require more energy to sustain growth; changes in their metabolic rates and consuming prey with potentially higher Hg concentrations could result in increased Hg accumulation. To examine the potential implications of climate warming on forage fish Hg accumulation in Arctic lakes, we quantified growth and Hg accumulation in Ninespine Stickleback Pungitius pungitius under different temperature and diet scenarios using bioenergetics models. Four scenarios were considered that examined the role of climate, diet, climate × diet, and climate × diet × elevated prey Hg. As expected, annual fish growth increased with warmer temperatures, but growth rates and Hg accumulation were largely diet dependent. Compared to current growth rates of 0.3 g⋅y^-1, fish growth increased at least 200% for fish consuming energy-dense benthic prey and decreased at least 40% for fish consuming pelagic prey. Compared to baseline levels, the Hg burden per kilocalorie of Ninespine Stickleback declined up to 43% with benthic consumption - indicating strong somatic growth dilution - but no more than 4% with pelagic consumption; elevated prey Hg concentrations led to moderate Hg declines in benthic-foraging fish and Hg increases in pelagic-foraging fish. Bioenergetics models demonstrated the complex interaction of water temperature, growth, prey proportions, and prey Hg concentrations that respond to climate change. Further work is needed to resolve mechanisms and rates linking climate change to Hg availability and uptake in Arctic freshwater systems.

Ventral feathers contained the highest mercury level in brown booby (Sula leucogaster), a pantropical seabird species

Seabirds are extensively used as environmental biomonitors and feathers are among the most analyzed matrices because they are one of the main excretory pathways to detoxify the bird's body of environmental contaminants. Still, there is a variation in contamination level between the different feathers of seabird species, driven by diet and physiology, such as molt strategy and feather formation sequence. We measured total mercury (THg) concentration in different types of feathers (wing, tail, ventral and dorsal) of the same individual in adults and juveniles of brown boobies (Sula leucogaster) from the northern coast of Rio de Janeiro state, Brazil. Brown booby had higher mean THg concentration (μg.g^-1 d. w.) in ventral (adults: 6.46 ± 1.19, 4.79 to 8.34; juveniles: 4.23 ± 0.60, 3.07 to 5.07) and wing (adults: 5.85 ± 1.10, 4.66 to 8.32; juveniles: 3.86 ± 0.54, 3.23 to 4.63), compared to dorsal (adults: 4.52 ± 1.33, 3.01 to 6.44; juveniles: 3.51 ± 0.19, 3.29 to 3.8) and tail feathers (adults: 2.94 ± 0.45, 2.32 to 3.46; juveniles: 2.8 ± 0.23, 2.45 to 3.08). This difference may be explained because feathers grow in a specific sequence during molts leading to different THg concentrations in each type of feather. Additionally, juveniles had significantly lower concentrations of THg than adults in all feather types, which may be explained by the shorter life span, leading to less time to bioaccumulate Hg in their body. It is essential to choose carefully which feather type is more suitable to be used as a biomonitor of THg contamination in a particular species. For brown boobies, we suggest the use of ventral feathers, which represent the highest Hg concentration, are easy to sample and do not impair the seabird's flight ability, although more studies are needed to replicate these results in other tropical seabirds species.

Mercury accumulation in muscle and liver tissue and human health risk assessment of two resident freshwater fish species in Flanders (Belgium): a multilocation approach

Detrimental effects of chemical pollution-primarily caused by human activities-on aquatic ecosystems have increasingly gained attention. Because of its hydrophobic qualities, mercury is prone to easily bioaccumulate and biomagnify through the food chain, decreasing biodiversity and eventually also affecting humans. In the present study, accumulated mercury concentrations were measured in muscle and liver tissue of perch (Perca fluviatilis) and European eel (Anguilla anguilla) collected at 26 sampling locations in Flemish (Belgian) waterbodies, allowing a comparison of these species within a variety of environmental situations. Furthermore, effects of size and weight have been assessed, expected to influence accumulation and storage of pollutants. Mercury concentrations in perch ranged up to 1.7 μg g^-1 dw (median: 0.29 μg g^-1 dw) in muscle and from 0.02 to 0.77 μg g^-1 dw (median: 0.11 μg g^-1 dw) in liver tissue. For eel, these concentrations were between 0.07 and 1.3 μg g^-1 dw (median: 0.39 μg g^-1 dw) and between 0.08 and 1.4 μg g^-1 dw (median: 0.55 μg g^-1 dw) respectively. We found a correlation of accumulated mercury with length in perch, independent of location. Furthermore, a significant difference in accumulated mercury concentrations between the targeted species was measured, with the highest mean concentrations per dry weight in eel liver and muscle tissue. In perch, higher concentrations were found in muscle compared to liver tissue, while in eel, liver tissue showed the highest concentrations. These findings were further considered with concentrations corrected for lipid content, excluding the fat compartment, which is known to a hold negligible portion of the total and methyl mercury concentrations. This confirmed our previous conclusions, except for mercury concentrations in eel. Here there was no longer a significant difference between muscle and liver concentrations. Finally, health risk analyses revealed that only frequent consumption of local eel (> 71 g day^-1) could pose risks to humans.

Mercury in birds (aquatic and scavenger) from the Western Amazon

In the Amazon rainforest, methylmercury (MeHg) is easily biomagnified and bio-accumulated in the aquatic food chain. This unique biome has been studied for occupational and environmental issues related to human health and contamination through fish consumption; however, wildlife studies have not yet addressed fish-eating birds. Different species of birds categorized by foraging strategies and life-stages were studied in the Madeira River Basin (Western Amazon rainforest). Feather and tissue (muscle, liver, kidneys, lungs, heart, brain, and blood) samples were collected opportunistically from six bird species feeding on fish and aquatic fauna and a scavenger (a saprophagous species) during the low-water season (July 2017). All collected samples were analyzed for total Hg (THg); methyl-Hg (MeHg) was determined only in feathers. The mean THg concentrations in feathers (dw) were as follows: Ardea cocoi (4.05 μg g^-1, n = 51) > Egretta thulla (3.94 μg g^-1, n = 5) > Ardea alba (3.80 μg g^-1, n = 61) > Anhinga anhinga (3.69 μg g^-1, n = 8) > Nannopterum brasilianus (3.07 μg g^-1, n = 10). The scavenger Coragyps atratus showed mean THg in feathers (9.93 μg g^-1, n = 30) to be significantly higher than in fish-eating birds. Across species, THg levels in feathers correlated significantly with THg_muscle (p = 0.022) and THg_brain (p = 0.002). THg concentrations varied in tissues (feather > liver > kidneys > lungs > heart > muscle > blood > brain). The Hg_brain:Hg_feather, Hg_brain:Hg_muscle, and Hg_brain:Hg_blood ratios were 0.031, 0.503 and 0.516, respectively. The mean [MeHg:THg] ratio in feathers from aquatic birds varied between species from 14 to 74% with a mean of 38%. Scavenger birds that forage in the terrestrial Amazonian environments concentrate more THg than species that forage in the aquatic environment. None of the aquatic species showed THg concentration in internal organs that were above threshold for risk of Hg toxicity; additionally, they are not listed in the categories of threat by the International Union for Conservation of Nature (IUCN).

Bioaccumulation of mercury is equal between sexes but different by age in seabird (Sula leucogaster) population from southeast coast of Brazil

Since several seabird species have sexual size dimorphism, in which one sex is larger than the other, and may consume bigger prey, this size difference may affect the contamination concentration in the seabird's tissues depending on their sex and age. In this study, mercury contamination was investigated in brown booby (Sula leucogaster) adults and juveniles during their breeding season at the Santana Archipelago, on the southeast coast of Brazil. Two hypotheses were evaluated: 1. As females consume larger prey than males due to the reverse sexual dimorphism, higher total mercury (THg) and methylmercury (MeHg) concentrations are expected in females tissues than in males; 2. Adult seabirds have more time to accumulate mercury than juveniles, so it is expected that adults will show higher THg and MeHg concentrations than juveniles in their feathers, but none in blood since the last indicates the exposure of short time (30-60 days), as it is a constantly synthesized tissue. Feathers and blood were sampled from 20 individuals of each group (males, females and juveniles). Also, 10 eggs of the brown booby and muscle tissue samples of their main prey were collected, from February to October 2018. Females and males had similar THg concentrations in the tissues with no statistical differences between sexes. Thus, the sexual size dimorphism did not influence mercury concentrations among the tissues and both genders can be used as a biomonitor. Brown booby juveniles had low THg and MeHg concentrations compared to adults due to a shorter time of exposure for mercury to bioaccumulate in their tissues. This is the first study, to the best of our knowledge, analyzing methylmercury in feathers, blood and eggs of a tropical seabird, which can be a useful baseline for future studies on the effects of contaminants on this species in tropical regions.

Mercury Accumulation and Elimination in Different Tissues of Zebrafish (Danio rerio) Exposed to a Mercury-Supplemented Diet

In this study, we evaluated the bioaccumulation of mercury in zebrafish (Danio rerio) exposed to mercury-contaminated food for 21 days and the depuration of mercury for a subsequent post-exposure period of 28 days. Four tissues (muscle, liver, gills, and skin) were analyzed for mercury content. Overall, data indicated that Hg accumulation in the liver is faster than in other tissues. Furthermore, the liver is the tissue with the highest accumulation rate per day (0.021 µg Hg g−1 day−1), followed by muscle, skin, and gills. Conversely, the Hg depuration rates in different tissues showed the following order: gills > skin > muscle > liver. The bioaccumulation factor values of liver and muscle increased linearly during the uptake period. The ratios between mercury concentration in liver and muscle during the experiment also increased during the uptake period and remained higher than 1 during the elimination period, suggesting that Danio rerio needed more than 4 weeks of depuration. Finally, the distribution of Hg in the water column during the accumulation period is Hg particulate > Hg dissolved, and during the depuration period it is the opposite, mercury particulate < mercury dissolved. In conclusion, this study contributes to a better understanding of the differences in Hg dynamics during the accumulation and depuration stages in a model fish, also emphasizing the alterations on Hg available in the water column.

Chronological Trends and Mercury Bioaccumulation in an Aquatic Semiarid Ecosystem under a Global Climate Change Scenario in the Northeastern Coast of Brazil

Simple Summary

Managing aquatic systems is becoming increasingly complex due to human impacts, multiple and competing water needs and climate variability. Considering the Hg concentration present in the top layers of sediment (~20 cm around 30 to 40 years) with the outer layers in the tree cores tree rings cores and in the sediment’s cores from Pacoti estuary and the Ceará estuary, overall data indicate an increase in mercury in recent years. A positive and significant correlation (p < 0.05) was revealed between Hg trends in sediments and Hg trends in annular tree rings. This shared Hg pattern reflects local environmental conditions. The results of this work reinforce the indicators previously described in the semiarid NE region of Brazil, showing that global climate change and some anthropogenic factors are key drivers to Hg exposure and biomagnification for wildlife and humans. Possible climate-induced shifts in these aquatic systems highlight the need for accurate and regionally specific metrics of change in the past in response to climate and for improved understanding of response to climate factors. These processes are inducing a greater mobilization of bioavailable Hg, which could allow an acceleration of the biogeochemical transformation of Hg.

Abstract

Due to global warming, in the northeastern semiarid coastal regions of Brazil, regional and global drivers are responsible for decreasing continental runoff and increasing estuarine water residence time, which promotes a greater mobilization of bioavailable mercury (Hg) and allows increasing fluxes and/or bioavailability of this toxic trace element and an acceleration of biogeochemical transformation of Hg. In this work, an application of dendrochemistry analysis (annular tree rings analysis) was developed for the reconstruction of the historical pattern of mercury contamination in a contaminated area, quantifying chronological Hg contamination trends in a tropical semiarid ecosystem (Ceará River Estuary, northeastern coast of Brazil) through registration of mercury concentration on growth rings in specimens of Rhizophora mangle L. and using the assessment in sediments as a support for the comparison of profiles of contamination. The comparison with sediments from the same place lends credibility to this type of analysis, as well as the relationship to the historical profile of contamination in the region, when compared with local data about industries and ecological situation of sampling sites. In order to evaluate the consequences of the described increase in Hg bioavailability and bioaccumulation in aquatic biota, and to assess the biological significance of Hg concentrations in sediments to fish and wildlife, muscle and liver from a bioindicator fish species, S. testudineus, were also analyzed. The results of this work reinforce the indicators previously described in the semiarid NE region of Brazil, which showed that global climate change and some anthropogenic factors are key drivers of Hg exposure and biomagnification for wildlife and humans. Considering the Hg concentration present in the top layers of sediment (~20 cm around 15 to 20 years) with the outer layers in the tree ring cores and in the sediment’s cores from Pacoti estuary and the Ceará estuary, overall the data indicate an increase in mercury in recent years in the Hg surface sediments, especially associated with the fine sediment fraction, mainly due to the increased capacity of small particles to adsorb Hg. There was revealed a positive and significant correlation (p < 0.05) between Hg trends in sediments and Hg trends in annular tree rings. This shared Hg pattern reflects local environmental conditions. The Hg concentration values in S. testudineus from both study areas are not restrictive to human consumption, being below the legislated European limit for Hg in foodstuffs. The results from S. testudineus muscles analysis suggest a significant and linear increase in Hg burden with increasing fish length, indicating that the specimens are accumulating Hg as they grow. The results from both rivers show an increase in BSAF with fish growth. The [Hg] liver/[Hg] muscles ratio >1, which indicates that the S. testudineus from both study areas are experiencing an increase in Hg bioavailability. Possible climate-induced shifts in these aquatic systems processes are inducing a greater mobilization of bioavailable Hg, which could allow an acceleration of the biogeochemical transformation of Hg.

Spatial and temporal trends in mercury levels in the down of black stork chicks in central Europe

Piscivorous avian species may be affected by mercury (Hg) which tends to accumulate in aquatic environments and biomagnifies across the food webs. One of such species is the black stork, whose population increase recently slowed down due to unknown reasons. At the same time Hg contamination and its effects were almost unaudited for this species, so it may have exerted deleterious effects on the population and an evaluation is necessary. This is the first study of this species concerning Hg contamination. Thus, Hg concentrations were investigated in the down of black stork chicks (N = 90) from breeding locations in central and southern Poland (Europe) between 2015 and 2017. As well as Hg levels, morphometric parameters and age were evaluated. Mean Hg concentrations reached 0.7 μg/g d.w. and differed significantly between years, from the lowest value noted in 2017 (mean 0.5 μg/g), through 2016 (0.7 μg/g), to the highest one in 2015 (0.9 μg/g), and between nest locations where higher Hg levels were generally found in northern parts of the study area. Hg concentrations were also unrelated to morphometric parameters. Contrarily, morphometric parameters revealed high correlations between themselves, which was confirmed by the cluster analysis (revealing only two clusters) and principal component analysis (the first PC explained 96.8% of the variance). Hg levels in the down of black storks were rather low with the fluctuation between years and nest locations probably caused by parental exposure during wintering, migration, pre-breeding season and recent exposure through food provided by parents. Such low Hg concentrations seemed not to affect the population from the region studied.

Mercury in the fish of New York's Great Lakes: A quarter century of near stability

We collected 849 fish of 16 species from New York portions of Lake Erie, Lake Ontario and the intervening Niagara River and its tributary Cayuga Creek, and analyzed fillets from individual fish for total mercury. Concentrations ranged from 0.029 to 1.090 ppm wet weight, with 92% below the EPA tissue residue criterion of 0.3 ppm, and thus not posing an undue risk from human consumption. We compared these 2010-2017 results to historical data spanning 40 years to assess temporal changes. The temporal pattern was generally consistent among water bodies and species: Mercury concentrations differed little between the most recent collections and fish taken from 1999-2008 and 1988-1996, while concentrations in all three of these periods were generally lower than in 1970. Smallmouth Bass from Lake Ontario were an exception with a continued decline, likely due to diet change following the introduction of exotic prey. Overall, though, fish tissue mercury concentrations from these large water bodies, which integrate regional influences, appear to have changed little in the last quarter century. We also report a consistent spatial pattern for multiple species having lower mercury concentrations in Lake Erie than in Lake Ontario over the period of record.

A synthesis of patterns of environmental mercury inputs, exposure and effects in New York State

Mercury (Hg) pollution is an environmental problem that adversely affects human and ecosystem health at local, regional, and global scales-including within New York State. More than two-thirds of the Hg currently released to the environment originates, either directly or indirectly, from human activities. Since the early 1800s, global atmospheric Hg concentrations have increased by three- to eight-fold over natural levels. In the U.S., atmospheric emissions and point-source releases to waterways increased following industrialization into the mid-1980s. Since then, water discharges have largely been curtailed. As a result, Hg emissions, atmospheric concentrations, and deposition over the past few decades have declined across the eastern U.S. Despite these decreases, Hg pollution persists. To inform policy efforts and to advance public understanding, the New York State Energy Research and Development Authority (NYSERDA) sponsored a scientific synthesis of information on Hg in New York State. This effort includes 23 papers focused on Hg in atmospheric deposition, water, fish, and wildlife published in Ecotoxicology. New York State experiences Hg contamination largely due to atmospheric deposition. Some landscapes are inherently sensitive to Hg inputs driven by the transport of inorganic Hg to zones of methylation, the conversion of inorganic Hg to methylmercury, and the bioaccumulation and biomagnification along food webs. Mercury concentrations exceed human and ecological risk thresholds in many areas of New York State, particularly the Adirondacks, Catskills, and parts of Long Island. Mercury concentrations in some biota have declined in the Eastern Great Lakes Lowlands and the Northeastern Highlands over the last four decades, concurrent with decreases in water releases and air emissions from regional and U.S. sources. However, widespread changes have not occurred in other ecoregions of New York State. While the timing and magnitude of the response of Hg levels in biota varies, policies expected to further diminish Hg emissions should continue to decrease Hg concentrations in food webs, yielding benefits to the fish, wildlife, and people of New York State. Anticipated improvements in the Hg status of aquatic ecosystems are likely to be greatest for inland surface waters and should be roughly proportional to declines in atmospheric Hg deposition. Efforts that advance recovery from Hg pollution in recent years have yielded significant progress, but Hg remains a pollutant of concern. Indeed, due to this extensive compilation of Hg observations in biota, it appears that the extent and intensity of the contamination on the New York landscape and waterscape is greater than previously recognized. Understanding the extent of Hg contamination and recovery following decreases in atmospheric Hg deposition will require further study, underscoring the need to continue existing monitoring efforts.

Bald eagle mercury exposure varies with region and site elevation in New York, USA

Freshwater fish in several regions of New York State (NYS) are known to contain concentrations of mercury (Hg) associated with negative health effects in wildlife and humans. We collected blood and breast feathers from bald eagle (Haliaeetus leucocephalus) nestlings throughout NYS, with an emphasis on the Catskill region to determine their exposure to Hg. We assessed whether habitat type (lake or river), region (Delaware-Catskill region vs. rest of NY) or sample site elevation influenced Hg concentrations in bald eagle breast feathers using ANCOVA. The model was significant and accounted for 41% of the variability in log₁₀ breast feather Hg concentrations. Mercury concentrations in nestling breast feathers were significantly greater in the Delaware-Catskill Region (geometric mean: 14.5 µg/g dw) than in the rest of NY (7.4 µg/g, dw), and greater at nests located at higher elevations. Habitat type (river vs. lake) did not have a significant influence on breast feather Hg concentrations. Geometric mean blood Hg concentrations were significantly greater in Catskill nestlings (0.78 µg/g ww) than in those from the rest of NY (0.32 µg/g). Mercury concentrations in nestling breast feathers and especially blood samples from the Delaware-Catskill region were generally greater than those reported for most populations sampled elsewhere, including areas associated with significant Hg pollution problems. Bald eagles can serve as valuable Hg bioindicators in aquatic ecosystems of NYS, particularly given their broad statewide distribution and their tendency to nest across all major watersheds and different habitat types.

Mercury in fish from streams and rivers in New York State: Spatial patterns, temporal changes, and environmental drivers

Mercury (Hg) concentrations in freshwater fish across the state of New York frequently exceed guidelines considered harmful to humans and wildlife, but statewide distribution and temporal changes are not well known for the state's streams and rivers. We analyzed existing data to describe recent spatial patterns, identify key environmental drivers, and assess temporal changes. Size classes within sportfishes and prey fishes formed 'functional taxa' (FT), and standardized scores were generated from 2007-2016 data for 218 sites. Muscle Hg in ≥1 sportfish FT exceeded human-health guidelines of 50 ng/g (sensitive populations) and 300 ng/g (general population, GP) at 93 and 56% of sites, respectively, but exceeded 1000 ng/g (a state threshold) at only 10% of sites. Whole-body Hg in ≥1 prey fish FT exceeded wildlife thresholds of 40 ng/g and 100 ng/g at 91 and 51% of sites, respectively. Environmental drivers of recent spatial patterns include extent of forest cover and storage, the latter an indicator of wetlands. Standardized Hg scores increased with increasing atmospheric Hg deposition and storage across rural 'upland' regions of New York. However, scores were not related to atmospheric deposition in more-developed 'lowland' regions due to the limited methylation potential of urban landscapes. Comparisons of 2010-2015 sportfish Hg concentrations with those of 1998 and 2000-2005 showed inconsistent temporal changes both among and within eight sites examined. Some recent stream and river fish Hg spatial patterns differed from those of lake-based studies, highlighting the importance of New York's flowing waters to future Hg monitoring and risk assessment.

A National-Scale Assessment of Mercury Bioaccumulation in United States National Parks Using Dragonfly Larvae As Biosentinels through a Citizen-Science Framework

We conducted a national-scale assessment of mercury (Hg) bioaccumulation in aquatic ecosystems, using dragonfly larvae as biosentinels, by developing a citizen-science network to facilitate biological sampling. Implementing a carefully designed sampling methodology for citizen scientists, we developed an effective framework for a landscape-level inquiry that might otherwise be resource limited. We assessed the variation in dragonfly Hg concentrations across >450 sites spanning 100 United States National Park Service units and examined intrinsic and extrinsic factors associated with the variation in Hg concentrations. Mercury concentrations ranged between 10.4 and 1411 ng/g dry weight across sites and varied among habitat types. Dragonfly total Hg (THg) concentrations were up to 1.8-fold higher in lotic habitats than in lentic habitats and 37% higher in waterbodies with abundant wetlands along their margins than those without wetlands. Mercury concentrations in dragonflies differed among families but were correlated (r² > 0.80) with each other, enabling adjustment to a consistent family to facilitate spatial comparisons among sampling units. Dragonfly THg concentrations were positively correlated with THg concentrations in both fish and amphibians from the same locations, indicating that dragonfly larvae are effective indicators of Hg bioavailability in aquatic food webs. We used these relationships to develop an integrated impairment index of Hg risk to aquatic ecosytems and found that 12% of site-years exceeded high or severe benchmarks of fish, wildlife, or human health risk. Collectively, this continental-scale study demonstrates the utility of dragonfly larvae for estimating the potential mercury risk to fish and wildlife in aquatic ecosystems and provides a framework for engaging citizen science as a component of landscape Hg monitoring programs.

Mercury bioaccumulation in freshwater fishes of the Chesapeake Bay watershed

Chemical contaminants are a threat to the Chesapeake Bay watershed, with mercury (Hg) among the most prevalent causes of impairment. Despite this, large-scale patterns of Hg concentrations, and the potential risks to fish, wildlife, and humans across the watershed, are poorly understood. We compiled fish Hg data from state monitoring programs and recent research efforts to address this knowledge gap and provide a comprehensive assessment of fish Hg concentrations in the watershed's freshwater habitats. The resulting dataset consisted of nearly 8000 total Hg (THg) concentrations from 600 locations. Across the watershed, fish THg concentrations spanned a 44-fold range, with mean concentrations varying by 2.6- and 8.8-fold among major sub-watersheds and individual 8-digit hydrological units, respectively. Although, mean THg concentrations tended to be moderate, fish frequently exceeded benchmarks for potential adverse health effects, with 45, 48, and 36% of all samples exceeding benchmarks for human, avian piscivore, and fish risk, respectively. Importantly, the percentage of fish exceeding these benchmarks was not uniform among species or locations. The variation in fish THg concentrations among species and sites highlights the roles of waterbody, landscape, and ecological processes in shaping broad patterns in Hg risk across the watershed. We outline an integrated Hg monitoring program that could identify key factors influencing Hg concentrations across the watershed and facilitate the implementation of management strategies to mitigate the risks posed by Hg.

Feather mercury increases with feeding at higher trophic levels in two species of migrant raptors, Merlin (Falco columbarius) and Sharp-shinned Hawk (Accipiter striatus)

Mercury (Hg) is a toxic heavy metal that, when methylated to form methylmercury (MeHg), bioaccumulates in exposed animals and biomagnifies through food webs. The purpose of this study was to assess Hg concentrations in raptors migrating through the upper midwestern USA. From 2009 to 2012, 966 raptors of 11 species were captured at Hawk Ridge, Duluth, Minnesota, USA. Breast feathers were sampled to determine the concentration of total Hg. Mean Hg concentrations ranged from 0.11 to 3.46 μg g-1 fresh weight across species and were generally higher in raptors that feed on birds in comparison with those that feed on mammals. To evaluate the effect of dietary sources on Hg biomagnification, carbon and nitrogen stable isotope ratios were measured in feathers of the 2 species with the highest Hg concentrations, Merlin (Falco columbarius) and Sharp-shinned Hawk (Accipiter striatus). Measured δ 13C values were similar in both species and indicated a primarily terrestrial-derived diet, whereas δ 15N values suggested that individual Merlin and Sharp-shinned Hawk feeding at higher trophic levels accumulated higher concentrations of Hg. The risk to birds associated with measured levels of feather Hg was evaluated by calculating blood-equivalent values using an established algorithm. Predicted blood values were then compared to heuristic risk categories synthesized across avian orders. This analysis suggested that while some Merlin and Sharp-shinned Hawk were at moderate risk to adverse effects of MeHg, most of the sampled birds were at negligible or low risk.

Blood mercury levels in mute swans (Cygnus olor) are not related to sex, but are related to age, with no blood parameter implications

Concentrations of mercury (Hg) were examined in the blood of mute swans from rural breeding sites and urban wintering areas in southern parts of Poland, Europe. The birds were classified into three age groups: cygnets, juveniles and adults. To investigate the potential impact of Hg on birds, hematocrit (Ht), reduced glutathione (GSH) levels and morphometric measurements were taken. Using morphometric parameters, we stated that all mute swans sampled were in good condition. The mercury concentrations found were rather low and differed between birds from industrialized wintering areas and rural breeding areas (means 7 ng/mL and 2 ng/mL, respectively). We found no difference in Hg concentrations between the sexes, but concentrations varied significantly between age groups (cygnets 2 ng/mL, juveniles 7 ng/mL and adults 6 ng/mL). A similar trend was observed for hematocrit levels. GSH levels did not differ between any of the groups studied. We found no significant relationship between blood parameters (Ht, GSH) in relation to Hg concentrations. We conclude that the Hg concentrations in blood may be influenced by industrialization, season and age, but generally low concentration such as those found by us do not affect Ht and GSH levels.

Mercury bioaccumulation in stream food webs of the Finger Lakes in central New York State, USA

Studies of mercury (Hg) bioaccumulation in streams draining both forested and agricultural watersheds are not common. Sixteen streams were sampled in the Finger Lakes region in central New York State with a mean agricultural land cover of 48%. Stream fish (Blacknose Dace, Rhinichthys atratulus, an invertivore; and Creek Chub, Semotilus atromaculatus, an omnivore) were collected and analyzed for total Hg (THg), and macroinvertebrates and periphyton were collected and analyzed for methylmercury (MeHg) determination. The effect of water chemistry, land cover, and macroinvertebrate MeHg was assessed as predictors of fish Hg concentrations. Blacknose Dace had significantly higher THg concentrations compared to Creek Chub (229 ng/g vs. 195 ng/g dry weight, respectively), and predatory and omnivorous macroinvertebrates (i.e., Perlidae and Cambaridae) were found to have significantly higher MeHg concentrations compared to other functional feeding groups. Mixed effects models identified macroinvertebrate MeHg concentrations as predictors of stream fish THg concentrations. Partition modeling found fish total length and total suspended solids predicted Blacknose Dace with 'High' vs 'Low' Hg (≥ or < 90 ng/g wet weight, respectively). Overall, stream fish THg concentrations observed were not of concern, unlike other regions in New York State such as the Adirondack Mountains, but a significant proportion of Blacknose Dace (22 - 73%) and Creek Chub (5 - 69%) would be considered a risk to a range of sensitive consumers.

Patterns of mercury and selenium exposure in minnesota common loons

Common loons (Gavia immer) are at risk of elevated dietary mercury (Hg) exposure in portions of their breeding range. To assess the level of risk among loons in Minnesota (USA), we investigated loon blood Hg concentrations in breeding lakes across Minnesota. Loon blood Hg concentrations were regressed on predicted Hg concentrations in standardized 12-cm whole-organism yellow perch (Perca flavescens), based on fish Hg records from Minnesota lakes, using the US Geological Survey National Descriptive Model for Mercury in Fish. A linear model, incorporating common loon sex, age, body mass, and log-transformed standardized perch Hg concentration representative of each study lake, was associated with 83% of the variability in observed common loon blood Hg concentrations. Loon blood Hg concentration was positively related to standardized perch Hg concentrations; juvenile loons had lower blood Hg concentrations than adult females, and blood Hg concentrations of juveniles increased with body mass. Blood Hg concentrations of all adult common loons and associated standardized prey Hg for all loon capture lakes included in the study were well below proposed thresholds for adverse effects on loon behavior, physiology, survival, and reproductive success. The fish Hg modeling approach provided insights into spatial patterns of dietary Hg exposure risk to common loons across Minnesota. We also determined that loon blood selenium (Se) concentrations were positively correlated with Hg concentration. Average common loon blood Se concentrations exceeded the published provisional threshold. Environ Toxicol Chem 2019;38:524-532. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Mercury concentrations in bald eagles across an impacted watershed in Maine, USA

Mercury (Hg) exposure was evaluated in bald eagles (Haliaeetus leucocephalus) in the lower Penobscot River watershed (PRW) in Maine to assess whether Hg discharges from a chlor-alkali plant (HoltraChem) influenced Hg concentrations in nestling tissues. Mean Hg concentrations in nestling blood and breast feathers sampled in marine and estuarine areas potentially contaminated with Hg from HoltraChem (the potential Hg impact zone) were significantly greater than those from reference sites spanning the Maine coast. To place Hg exposure in the potential Hg impact zone into a broader context, Hg exposure in bald eagle nestlings from four habitat types in the PRW was assessed. Mercury concentrations varied significantly across habitat types within the PRW, generally following the pattern: marine=estuarine<freshwater river<lake. While findings suggest that Hg inputs from HoltraChem elevated Hg concentrations in eagles in the potential Hg impact zone, those Hg concentrations were still significantly lower than those of nestlings raised in freshwater river and lake habitats in the PRW and elsewhere in Maine not contaminated by HoltraChem. Breast feathers had 31% higher statistical power to detect Hg differences among habitat types compared to nestling blood, demonstrating their higher value in biomonitoring efforts. Nestling tissue Hg concentrations in the PRW were within the range of reported Hg values for bald eagles, but were generally higher than most population comparisons within habitats. Mercury concentrations in lake-nesting bald eagles in the PRW were impacted primarily by inputs from atmospheric deposition, and Hg exposure in nestlings associated with this habitat type in the PRW often had similar or higher Hg exposure than those associated with point sources elsewhere. Mercury concentrations in bald eagle nestlings and a small sample of adults in our study commonly exceeded levels associated with adverse health effects in other bird species.

Modulators of mercury risk to wildlife and humans in the context of rapid global change

Environmental mercury (Hg) contamination is an urgent global health threat. The complexity of Hg in the environment can hinder accurate determination of ecological and human health risks, particularly within the context of the rapid global changes that are altering many ecological processes, socioeconomic patterns, and other factors like infectious disease incidence, which can affect Hg exposures and health outcomes. However, the success of global Hg-reduction efforts depends on accurate assessments of their effectiveness in reducing health risks. In this paper, we examine the role that key extrinsic and intrinsic drivers play on several aspects of Hg risk to humans and organisms in the environment. We do so within three key domains of ecological and human health risk. First, we examine how extrinsic global change drivers influence pathways of Hg bioaccumulation and biomagnification through food webs. Next, we describe how extrinsic socioeconomic drivers at a global scale, and intrinsic individual-level drivers, influence human Hg exposure. Finally, we address how the adverse health effects of Hg in humans and wildlife are modulated by a range of extrinsic and intrinsic drivers within the context of rapid global change. Incorporating components of these three domains into research and monitoring will facilitate a more holistic understanding of how ecological and societal drivers interact to influence Hg health risks.

Mercury correlates with altered corticosterone but not testosterone or estradiol concentrations in common loons

We investigated the relation between environmental mercury exposure and corticosterone concentrations in free-living adult common loons (Gavia immer). We determined blood and feather mercury concentrations and compared them to testosterone, estradiol, and stress-induced plasma corticosterone concentrations. Although neither testosterone nor estradiol correlated with Hg levels, there was a robust positive relation between blood Hg and stress-induced corticosterone concentrations in males, but not in females. The lack of an effect in females may have been due to overall less contamination in females. There were no significant correlations between feather Hg and stress-induced corticosterone in either sex. To help determine whether Hg had a causal effect on corticosterone, we investigated the impact of experimental Hg intake on the corticosterone stress response in captive juvenile loons. Juveniles were subjected to three different feeding regimes: 0, 0.4 and 1.2μg Hg (as MeHgCL)/g wet weight (ww) fish. We then measured baseline and 30min post-solitary confinement stressor corticosterone concentrations. The Hg fed chicks exhibited a decreased ability to mount a stress response. From these data, we conclude that Hg contamination does appear to alter the corticosterone response to stress, but not in a consistent predictable pattern. Regardless of the direction of change, however, exposure to mercury contamination and the resulting impact on the corticosterone stress response in common loons may substantially impact health, fitness and survival.

Selenium: Mercury Molar Ratios in Freshwater Fish in the Columbia River Basin: Potential Applications for Specific Fish Consumption Advisories

Fish provide a valuable source of beneficial nutrients and are an excellent source of low fat protein. However, fish are also the primary source of methylmercury exposure in humans. Selenium often co-occurs with mercury and there is some evidence that selenium can protect against mercury toxicity yet States issue fish consumption advisories based solely on the risks that methylmercury pose to human health. Recently, it has been suggested the selenium: mercury molar ratio be considered in risk management. In order for agencies to utilize the ratio to set consumption guidelines, it is important to evaluate the variability in selenium and mercury in different fish species. We examined 10 different freshwater fish species found within the Columbia River Basin in order to determine the inter- and intra-specific variability in the selenium: mercury molar ratios and the selenium health benefit values. We found significant variation in selenium: mercury molar ratios. The mean molar ratios for each species were all above 1:1, ranging from 3.42:1 in Walleye to 27.2:1 in Chinook salmon. There was a positive correlation between both mercury and selenium with length for each fish species apart from yellow perch and rainbow trout. All species had health benefit values greater than 2. We observed considerable variability in selenium: mercury molar ratios within fish species collected in the Columbia River Basin. Although incorporating selenium: mercury molar ratios into fish consumption holds the potential for refining advisories and assessing the risk of methylmercury exposure, the current understanding of how these ratios apply is insufficient, and further understanding of drivers of variability in the ratios is needed.

Toxicity reference values for methylmercury effects on avian reproduction: Critical review and analysis

Effects of mercury (Hg) on birds have been studied extensively and with increasing frequency in recent years. The authors conducted a comprehensive review of methylmercury (MeHg) effects on bird reproduction, evaluating laboratory and field studies in which observed effects could be attributed primarily to Hg. The review focuses on exposures via diet and maternal transfer in which observed effects (or lack thereof) were reported relative to Hg concentrations in diet, eggs, or adult blood. Applicable data were identified for 23 species. From this data set, the authors identified ranges of toxicity reference values suitable for risk-assessment applications. Typical ranges of Hg effect thresholds are approximately 0.2 mg/kg to >1.4 mg/kg in diet, 0.05 mg/kg/d to 0.5 mg/kg/d on a dose basis, 0.6 mg/kg to 2.7 mg/kg in eggs, and 2.1 mg/kg to >6.7 mg/kg in parental blood (all concentrations on a wet wt basis). For Hg in avian blood, the review represents the first broad compilation of relevant toxicity data. For dietary exposures, the current data support TRVs that are greater than older, commonly used TRVs. The older diet-based TRVs incorporate conservative assumptions and uncertainty factors that are no longer justified, although they generally were appropriate when originally derived, because of past data limitations. The egg-based TRVs identified from the review are more similar to other previously derived TRVs but have been updated to incorporate new information from recent studies. While important research needs remain, a key recommendation is that species not yet tested for MeHg toxicity should be evaluated using toxicity data from tested species with similar body weights. Environ Toxicol Chem 2017;36:294-319. © 2016 SETAC.

Environmental Origins of Methylmercury Accumulated in Subarctic Estuarine Fish Indicated by Mercury Stable Isotopes

Methylmercury (MeHg) exposure can cause adverse reproductive and neurodevelopmental health effects. Estuarine fish may be exposed to MeHg produced in rivers and their watersheds, benthic sediment, and the marine water column, but the relative importance of each source is poorly understood. We measured stable isotopes of mercury (δ²⁰²Hg, Δ¹⁹⁹Hg, and Δ²⁰¹Hg), carbon (δ¹³C), and nitrogen (δ¹⁵N) in fish with contrasting habitats from a large subarctic coastal ecosystem to better understand MeHg exposure sources. We identify two distinct food chains exposed to predominantly freshwater and marine MeHg sources but do not find evidence for a benthic marine MeHg signature. This is consistent with our previous research showing benthic sediment is a net sink for MeHg in the estuary. Marine fish display lower and less variable Δ¹⁹⁹Hg values (0.78‰ to 1.77‰) than freshwater fish (0.72‰ to 3.14‰) and higher δ²⁰²Hg values (marine: 0.1‰ to 0.57‰; freshwater: -0.76‰ to 0.15‰). We observe a shift in the Hg isotopic composition of juvenile and adult rainbow smelt (Osmerus mordax) when they transition between the freshwater and marine environment as their dominant foraging territory. The Hg isotopic composition of Atlantic salmon (Salmo salar) indicates they receive most of their MeHg from the marine environment despite a similar or longer duration spent in freshwater regions. We conclude that stable Hg isotopes effectively track fish MeHg exposure sources across different ontogenic stages.

Spatial and temporal patterns of mercury concentrations in freshwater fish across the Western United States and Canada

Methylmercury contamination of fish is a global threat to environmental health. Mercury (Hg) monitoring programs are valuable for generating data that can be compiled for spatially broad syntheses to identify emergent ecosystem properties that influence fish Hg bioaccumulation. Fish total Hg (THg) concentrations were evaluated across the Western United States (US) and Canada, a region defined by extreme gradients in habitat structure and water management. A database was compiled with THg concentrations in 96,310 fish that comprised 206 species from 4262 locations, and used to evaluate the spatial distribution of fish THg across the region and effects of species, foraging guilds, habitats, and ecoregions. Areas of elevated THg exposure were identified by developing a relativized estimate of fish mercury concentrations at a watershed scale that accounted for the variability associated with fish species, fish size, and site effects. THg concentrations in fish muscle ranged between 0.001 and 28.4 (μg/g wet weight (ww)) with a geometric mean of 0.17. Overall, 30% of individual fish samples and 17% of means by location exceeded the 0.30μg/g ww US EPA fish tissue criterion. Fish THg concentrations differed among habitat types, with riverine habitats consistently higher than lacustrine habitats. Importantly, fish THg concentrations were not correlated with sediment THg concentrations at a watershed scale, but were weakly correlated with sediment MeHg concentrations, suggesting that factors influencing MeHg production may be more important than inorganic Hg loading for determining fish MeHg exposure. There was large heterogeneity in fish THg concentrations across the landscape; THg concentrations were generally higher in semi-arid and arid regions such as the Great Basin and Desert Southwest, than in temperate forests. Results suggest that fish mercury exposure is widespread throughout Western US and Canada, and that species, habitat type, and region play an important role in influencing ecological risk of mercury in aquatic ecosystems.

Mercury risk to avian piscivores across western United States and Canada

The widespread distribution of mercury (Hg) threatens wildlife health, particularly piscivorous birds. Western North America is a diverse region that provides critical habitat to many piscivorous bird species, and also has a well-documented history of mercury contamination from legacy mining and atmospheric deposition. The diversity of landscapes in the west limits the distribution of avian piscivore species, complicating broad comparisons across the region. Mercury risk to avian piscivores was evaluated across the western United States and Canada using a suite of avian piscivore species representing a variety of foraging strategies that together occur broadly across the region. Prey fish Hg concentrations were size-adjusted to the preferred size class of the diet for each avian piscivore (Bald Eagle=36cm, Osprey=30cm, Common and Yellow-billed Loon=15cm, Western and Clark's Grebe=6cm, and Belted Kingfisher=5cm) across each species breeding range. Using a combination of field and lab-based studies on Hg effect in a variety of species, wet weight blood estimates were grouped into five relative risk categories including: background (<0.5μg/g), low (0.5-1μg/g), moderate (1-2μg/g), high (2-3μg/g), and extra high (>3μg/g). These risk categories were used to estimate potential mercury risk to avian piscivores across the west at a 1degree-by-1degree grid cell resolution. Avian piscivores foraging on larger-sized fish generally were at a higher relative risk to Hg. Habitats with a relatively high risk included wetland complexes (e.g., prairie pothole in Saskatchewan), river deltas (e.g., San Francisco Bay, Puget Sound, Columbia River), and arid lands (Great Basin and central Arizona). These results indicate that more intensive avian piscivore sampling is needed across Western North America to generate a more robust assessment of exposure risk.

Avian mercury exposure and toxicological risk across western North America: A synthesis

Methylmercury contamination of the environment is an important issue globally, and birds are useful bioindicators for mercury monitoring programs. The available data on mercury contamination of birds in western North America were synthesized. Original data from multiple databases were obtained and a literature review was conducted to obtain additional mercury concentrations. In total, 29219 original bird mercury concentrations from 225 species were compiled, and an additional 1712 mean mercury concentrations, representing 19998 individuals and 176 species, from 200 publications were obtained. To make mercury data comparable across bird tissues, published equations of tissue mercury correlations were used to convert all mercury concentrations into blood-equivalent mercury concentrations. 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. Additionally, published toxicity benchmarks established in multiple tissues were summarized and translated into a common blood-equivalent mercury concentration. Overall, 66% of birds sampled in western North American exceeded a blood-equivalent mercury concentration of 0.2 μg/g wet weight (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, such as adult blood and eggs, that are most-easily translated into tissues with well-developed toxicity benchmarks and that are directly relevant to bird reproduction. 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.

Major correlates of mercury in small fish and common loons (Gavia immer) across four large study areas in Canada

We investigated mercury (Hg) concentrations in small fish (mainly yellow perch, Perca flavescens; ∼60% of fish collected) and in blood of common loons (Gavia immer) that prey upon them during the breeding season on lakes in 4 large, widely separated study areas in Canada (>13 lakes per study area; total number of lakes = 93). Although surface sediments from lakes near a base metal smelter in Flin Flon, Manitoba had the highest Hg concentrations, perch and other small fish and blood of common loon chicks sampled from these same lakes had low Hg concentrations similar to those from uncontaminated reference lakes. Multiple regression modeling with AIC analysis indicated that lake pH was by far the most important single factor influencing perch Hg concentrations in lakes across the four study areas (R(2) = 0.29). The best model was a three-variable model (pH + alkalinity + sediment Se; Wi = 0.61, R(2) = 0.85). A single-variable model (fish Hg) best explained among-lake variability in loon chick blood Hg (Wi = 0.17; R(2) = 0.53). From a toxicological risk perspective, all lakes posing a potential Hg health risk for perch and possibly other small pelagic fish species (where mean fish muscle Hg concentrations exceeded 2.4 μg/g dry wt.), and for breeding common loons (where mean fish muscle Hg concentrations exceeded 0.8 μg/g dry wt., and loon chick blood Hg exceeded 1.4 μg/g dry wt.) had pH < 6.7 and were located in eastern Canada.

Accumulation properties of inorganic mercury and organic mercury in the red-crowned crane Grus japonensis in east Hokkaido, Japan

The red-crowned (Japanese) crane Grus japonensis is native to east Hokkaido, Japan, in contrast to the East Asia mainland. Previously, we reported that red-crowned cranes in Hokkaido were highly contaminated with mercury in the 1990s and that the contamination rapidly decreased to a moderate level in the 2000s. In the present study, we determined levels of organic mercury (O-Hg) in the liver and kidney of cranes in east Hokkaido in comparison with levels of total mercury (T-Hg). T-Hg levels in the kidneys were higher than those in the livers in adults but not in subadults and juveniles; however, the reverse was the case for O-Hg even for adults. The ratio of O-Hg to T-Hg in both the liver and kidney decreased as T-Hg increased in the three developmental stages. While the ratios of O-Hg to T-Hg in the liver and kidney of adults were significantly lower than those of juveniles, the ratios were similar for adults and juveniles in a lower range of T-Hg. The ratio of selenium (Se) to T-Hg decreased as T-Hg increased in both the liver and kidney, irrespective of stages. Mercury burdens in feathers were about 59% and 67% of the total body burdens for juveniles and adults, respectively. Furthermore, ratios of carbon and nitrogen stable isotopes to T-Hg varied greatly, with no relation to mercury level in the liver. The results suggest slow accumulation of inorganic mercury in the kidney of red-crowned cranes in east Hokkaido, Japan.

Estimating Mercury Exposure of Piscivorous Birds and Sport Fish Using Prey Fish Monitoring

Methylmercury is a global pollutant of aquatic ecosystems, and monitoring programs need tools to predict mercury exposure of wildlife. We developed equations to estimate methylmercury exposure of piscivorous birds and sport fish using mercury concentrations in prey fish. We collected original data on western grebes (Aechmophorus occidentalis) and Clark's grebes (Aechmophorus clarkii) and summarized the published literature to generate predictive equations specific to grebes and a general equation for piscivorous birds. We measured mercury concentrations in 354 grebes (blood averaged 1.06 ± 0.08 μg/g ww), 101 grebe eggs, 230 sport fish (predominantly largemouth bass and rainbow trout), and 505 prey fish (14 species) at 25 lakes throughout California. Mercury concentrations in grebe blood, grebe eggs, and sport fish were strongly related to mercury concentrations in prey fish among lakes. Each 1.0 μg/g dw (∼0.24 μg/g ww) increase in prey fish resulted in an increase in mercury concentrations of 103% in grebe blood, 92% in grebe eggs, and 116% in sport fish. We also found strong correlations between mercury concentrations in grebes and sport fish among lakes. Our results indicate that prey fish monitoring can be used to estimate mercury exposure of piscivorous birds and sport fish when wildlife cannot be directly sampled.

Mercury in Forage Fish from Mexico and Central America: Implications for Fish-Eating Birds

Mercury (Hg) is a global contaminant of aquatic food chains. Aquatic birds, such as the osprey (Pandion haliaetus), with migratory populations breeding in Canada and the northern United States and wintering in the Central and South America, can be exposed to mercury on both the breeding and wintering ranges. We examined Hg levels in 14 fish taxa from 24 osprey wintering sites identified from satellite telemetry. Our main goal was to determine whether fish species that feature in the diet of overwintering and resident fish-eating birds reached toxicity thresholds for Hg. Mean Hg levels in fish whole carcasses ranged from a high of 0.18 µg g(-1) (wet weight) in Scomberomorus sierra to a low of 0.009 µg g(-1) in Catostomidae. Average Hg levels were within published toxicity threshold values in forage fish for only two sites in Mexico (Puerto Vallarta and San Blas Estuary), and all were marine species, such as mackerel (Scomberomorus sierra), sea catfish (Ariopus spp.), and sardinas species (Centropomus spp.). Except for one sample from Nicaragua, sea catfish from Puerto Morazan, none of the fish from sites in Central America had Hg levels which exceeded the thresholds. Nonmetric multidimensional scaling revealed geographical differences in Hg levels with significant pairwise differences between sites along the Pacific Ocean (Mexico) versus the Bay of Campeche, partly due to differences in species composition of sampled fish (and species distributions). Hg increased with trophic level, as assessed by nitrogen stable isotope ratios (δ(15)N but not δ(13)C), in freshwater and marine, but not estuarine, environments. Hg concentrations in forage fish do not account for the elevated Hg reported for many osprey populations on the breeding grounds, thus primary sources of contamination appear to be in the north.

Interactive effects of climate change with nutrients, mercury, and freshwater acidification on key taxa in the North Atlantic Landscape Conservation Cooperative region

The North Atlantic Landscape Conservation Cooperative LCC (NA LCC) is a public-private partnership that provides information to support conservation decisions that may be affected by global climate change (GCC) and other threats. The NA LCC region extends from southeast Virginia to the Canadian Maritime Provinces. Within this region, the US National Climate Assessment documented increases in air temperature, total precipitation, frequency of heavy precipitation events, and rising sea level, and predicted more drastic changes. Here, we synthesize literature on the effects of GCC interacting with selected contaminant, nutrient, and environmental processes to adversely affect natural resources within this region. Using a case study approach, we focused on 3 stressors with sufficient NA LCC region-specific information for an informed discussion. We describe GCC interactions with a contaminant (Hg) and 2 complex environmental phenomena-freshwater acidification and eutrophication. We also prepared taxa case studies on GCC- and GCC-contaminant/nutrient/process effects on amphibians and freshwater mussels. Several avian species of high conservation concern have blood Hg concentrations that have been associated with reduced nesting success. Freshwater acidification has adversely affected terrestrial and aquatic ecosystems in the Adirondacks and other areas of the region that are slowly recovering due to decreased emissions of N and sulfur oxides. Eutrophication in many estuaries within the region is projected to increase from greater storm runoff and less denitrification in riparian wetlands. Estuarine hypoxia may be exacerbated by increased stratification. Elevated water temperature favors algal species that produce harmful algal blooms (HABs). In several of the region's estuaries, HABs have been associated with bird die-offs. In the NA LCC region, amphibian populations appear to be declining. Some species may be adversely affected by GCC through higher temperatures and more frequent droughts. GCC may affect freshwater mussel populations via altered stream temperatures and increased sediment loading during heavy storms. Freshwater mussels are sensitive to un-ionized ammonia that more toxic at higher temperatures. We recommend studying the interactive effects of GCC on generation and bioavailability of methylmercury and how GCC-driven shifts in bird species distributions will affect avian exposure to methylmercury. Research is needed on how decreases in acid deposition concurrent with GCC will alter the structure and function of sensitive watersheds and surface waters. Studies are needed to determine how GCC will affect HABs and avian disease, and how more severe and extensive hypoxia will affect fish and shellfish populations. Regarding amphibians, we suggest research on 1) thermal tolerance and moisture requirements of species of concern, 2) effects of multiple stressors (temperature, desiccation, contaminants, nutrients), and 3) approaches to mitigate impacts of increased temperature and seasonal drought. We recommend studies to assess which mussel species and populations are vulnerable and which are resilient to rising stream temperatures, hydrological shifts, and ionic pollutants, all of which are influenced by GCC.

Experimental dosing of wetlands with coagulants removes mercury from surface water and decreases mercury bioaccumulation in fish

Mercury pollution is widespread globally, and strategies for managing mercury contamination in aquatic environments are necessary. We tested whether coagulation with metal-based salts could remove mercury from wetland surface waters and decrease mercury bioaccumulation in fish. In a complete randomized block design, we constructed nine experimental wetlands in California's Sacramento-San Joaquin Delta, stocked them with mosquitofish (Gambusia affinis), and then continuously applied agricultural drainage water that was either untreated (control), or treated with polyaluminum chloride or ferric sulfate coagulants. Total mercury and methylmercury concentrations in surface waters were decreased by 62% and 63% in polyaluminum chloride treated wetlands and 50% and 76% in ferric sulfate treated wetlands compared to control wetlands. Specifically, following coagulation, mercury was transferred from the filtered fraction of water into the particulate fraction of water which then settled within the wetland. Mosquitofish mercury concentrations were decreased by 35% in ferric sulfate treated wetlands compared to control wetlands. There was no reduction in mosquitofish mercury concentrations within the polyaluminum chloride treated wetlands, which may have been caused by production of bioavailable methylmercury within those wetlands. Coagulation may be an effective management strategy for reducing mercury contamination within wetlands, but further studies should explore potential effects on wetland ecosystems.

Mercury in streams at Grand Portage National Monument (Minnesota, USA): assessment of ecosystem sensitivity and ecological risk

Mercury (Hg) in water, sediment, soils, seston, and biota were quantified for three streams in the Grand Portage National Monument (GRPO) in far northeastern Minnesota to assess ecosystem contamination and the potential for harmful exposure of piscivorous fish, wildlife, and humans to methylmercury (MeHg). Concentrations of total Hg in water, sediment, and soil were typical of those in forest ecosystems within the region, whereas MeHg concentrations and percent MeHg in these ecosystem components were markedly higher than values reported elsewhere in the western Great Lakes Region. Soils and sediment were Hg-enriched, containing approximately 4-fold more total Hg per unit of organic matter. We hypothesized that localized Hg enrichment was due in part to anthropogenic pollution associated with historic fur-trading activity. Bottom-up forcing of bioaccumulation was evidenced by MeHg concentrations in larval dragonflies, which were near the maxima for dragonflies sampled concurrently from five other national park units in the region. Despite its semi-remote location, GRPO is a Hg-sensitive landscape in which MeHg is produced and bioaccumulated in aquatic food webs to concentrations that pose ecological risks to MeHg-sensitive piscivores, including predatory fish, belted kingfisher, and mink.

Dietary mercury exposure to endangered California Clapper Rails in San Francisco Bay

California Clapper Rails (Rallus longirostris obsoletus) are an endangered waterbird that forage in tidal-marsh habitats that pose risks from mercury exposure. We analyzed total mercury (Hg) in six macro-invertebrate and one fish species representing Clapper Rail diets from four tidal-marshes in San Francisco Bay, California. Mercury concentrations among individual taxa ranged from lowest at Colma Creek (mean range: 0.09-0.2 μg/g dw) to highest at Cogswell (0.2-0.7), Laumeister (0.2-0.9) and Arrowhead Marshes (0.3-1.9). These spatial patterns for Hg matched patterns reported previously in Clapper Rail blood from the same four marshes. Over 25% of eastern mudsnails (Ilyanassa obsolete) and staghorn sculpin (Leptocottus armatus) exceeded dietary Hg concentrations (ww) often associated with avian reproductive impairment. Our results indicate that Hg concentrations vary considerably among tidal-marshes and diet taxa, and Hg concentrations of prey may provide an appropriate proxy for relative exposure risk for Clapper Rails.

A positive correlation between mercury and oxidative stress-related gene expression (GPX3 and GSTM3) is measured in female Double-crested Cormorant blood

Mercury (Hg) is a widespread contaminant that has been shown to induce a wide range of adverse health effects in birds including reproductive, physiological and neurological impairments. Here we explored the relationship between blood total Hg concentrations ([THg]) and oxidative stress gene induction in the aquatic piscivorous Double-crested Cormorants (Phalacrocorax auritus) using a non-lethal technique, i.e., blood gene expression analysis. P. auritus blood was sampled at five sites across the Great Lakes basin, Ontario, Canada and was analyzed for [THg]. To assess cellular stress, the expression of glutathione peroxidases 1 and 3 (GPX1, GPX3), superoxide dismutase 1 (SOD1), heat-shock protein 70 kd-8 (HSP70-8) and glutathione S-transferase µ3 (GSTM3) were measured in whole blood samples using real-time RT-PCR. Results showed a significantly positive correlation between female blood [THg] and both GPX3 and GSTM3 expression. Different levels of oxidative stress experienced by males and females during the breeding season may be influencing the differential oxidative stress responses to blood [THg] observed in this study. Overall, these results suggest that Hg may lead to oxidative stress as some of the cellular stress-related genes were altered in the blood of female P. auritus and that blood gene expression analysis is a successful approach to assess bird health condition.

Temporal variation in fish mercury concentrations within lakes from the western Aleutian Archipelago, Alaska

We assessed temporal variation in mercury (Hg) concentrations of threespine stickleback (Gasterosteus aculeatus) from Agattu Island, Aleutian Archipelago, Alaska. Total Hg concentrations in whole-bodied stickleback were measured at two-week intervals from two sites in each of two lakes from June 1 to August 10, 2011 during the time period when lakes were ice-free. Across all sites and sampling events, stickleback Hg concentrations ranged from 0.37–1.07 µg/g dry weight (dw), with a mean (± SE) of 0.55±0.01 µg/g dw. Mean fish Hg concentrations declined by 9% during the study period, from 0.57±0.01 µg/g dw in early June to 0.52±0.01 µg/g dw in mid-August. Mean fish Hg concentrations were 6% higher in Loon Lake (0.56±0.01 µg/g dw) than in Lake 696 (0.53±0.01 µg/g dw), and 4% higher in males (0.56±0.01 µg/g dw) than in females (0.54±0.01 µg/g dw). Loon Lake was distinguished from Lake 696 by the presence of piscivorous waterbirds during the breeding season. Mercury concentrations in stickleback from Agattu Island were higher than would be expected for an area without known point sources of Hg pollution, and high enough to be of concern to the health of piscivorous wildlife.

Accumulation and hazard assessment of mercury to waterbirds at Lake Chapala, Mexico

Lake Chapala is the largest tropical lake in Mexico. The objectives of this study were to determine bioaccumulation of Hg in fish and to evaluate the potential impacts of Hg in the diet of aquatic birds, particularly the American white pelican (AWPE), in Lake Chapala. Hg concentrations in three fish species ranged from 0.021 to 0.568 μg/g wet weight. Mercury in fish was positively and significantly correlated with total fish length (R2=0.44, P<0.05). The δ15N values in fish were significantly correlated with Hg concentrations in Chapala and the San Antonio Reservoir (R2=0.69, P<0.001 and R2=0.40, P<0.001, respectively). However, Hg concentrations in bird feathers were not significantly different between years, among locations, or among species. Hg concentrations in fish from Lake Chapala were within values reported in many parts of the world. The Hg (mean range of 2.75 to 4.54 μg/g dw) and δD (mean range of -62‰ to -11‰) values in bird feathers suggested a wide pattern of exposure for highly migratory AWPE and egrets, although birds with lower δD values in feathers appeared to have greater concentrations of Hg than those with higher δD values. Contaminant exposure in aquatic birds in Chapala during the breeding season should be monitored next to better determine the potential effects of Hg on resident aquatic birds.

Mercury reduces avian reproductive success and imposes selection: an experimental study with adult- or lifetime-exposure in zebra finch

Mercury is a global pollutant that biomagnifies in food webs, placing wildlife at risk of reduced reproductive fitness and survival. Songbirds are the most diverse branch of the avian evolutionary tree; many are suffering persistent and serious population declines and we know that songbirds are frequently exposed to mercury pollution. Our objective was to determine the effects of environmentally relevant doses of mercury on reproductive success of songbirds exposed throughout their lives or only as adults. The two modes of exposure simulated philopatric species versus dispersive species, and are particularly relevant because of the heightened mercury-sensitivity of developing nervous systems. We performed a dosing study with dietary methylmercury in a model songbird species, the zebra finch (Taeniopygia guttata), at doses from 0.3 – 2.4 parts per million. Birds were exposed to mercury either as adults only or throughout their lives. All doses of mercury reduced reproductive success, with the lowest dose reducing the number of independent offspring produced in one year by 16% and the highest dose, representing approximately half the lethal dose for this species, causing a 50% reduction. While mercury did not affect clutch size or survivorship, it had the most consistent effect on the proportion of chicks that fledged from the nest, regardless of mode of exposure. Among birds exposed as adults, mercury caused a steep increase in the latency to re-nest after loss of a clutch. Birds exposed for their entire lifetimes, which were necessarily the offspring of dosed parents, had up to 50% lower reproductive success than adult-exposed birds at low doses of methylmercury, but increased reproductive success at high doses, suggesting selection for mercury tolerance at the highest level of exposure. Our results indicate that mercury levels in prey items at contaminated sites pose a significant threat to populations of songbirds through reduced reproductive success.

Using sparse dose-response data for wildlife risk assessment

Hazard quotients based on a point-estimate comparison of exposure to a toxicity reference value (TRV) are commonly used to characterize risks for wildlife. Quotients may be appropriate for screening-level assessments but should be avoided in detailed assessments, because they provide little insight regarding the likely magnitude of effects and associated uncertainty. To better characterize risks to wildlife and support more informed decision making, practitioners should make full use of available dose-response data. First, relevant studies should be compiled and data extracted. Data extractions are not trivial--practitioners must evaluate the potential use of each study or its components, extract numerous variables, and in some cases, calculate variables of interest. Second, plots should be used to thoroughly explore the data, especially in the range of doses relevant to a given risk assessment. Plots should be used to understand variation in dose-response among studies, species, and other factors. Finally, quantitative dose-response models should be considered if they are likely to provide an improved basis for decision making. The most common dose-response models are simple models for data from a particular study for a particular species, using generalized linear models or other models appropriate for a given endpoint. Although simple models work well in some instances, they generally do not reflect the full breadth of information in a dose-response data set, because they apply only for particular studies, species, and endpoints. More advanced models are available that explicitly account for variation among studies and species, or that standardize multiple endpoints to a common response variable. Application of these models may be useful in some cases when data are abundant, but there are challenges to implementing and interpreting such models when data are sparse.

Spatial patterns of methylmercury risks to common loons and piscivorous fish in Canada

Deposition of inorganic mercury (Hg) from the atmosphere remains the principle source of Hg contamination for most aquatic ecosystems. Inorganic Hg is readily converted to toxic methylmercury (MeHg) that bioaccumulates in aquatic food webs and may pose a risk to piscivorous fish and wildlife. We conducted a screening-level risk assessment to evaluate the extent of risk to top aquatic piscivores: the common loon (Gavia immer), walleye (Sander vitreus), and northern pike (Esox lucius). Risk quotients (RQs) were calculated on the basis of a dietary Hg exposure indicator (HgPREY) modeled from over 230,000 observations of fish Hg concentrations at over 1900 locations across Canada and dietary Hg exposure screening benchmarks derived specifically for this assessment. HgPREY exceeded benchmark thresholds related to impaired productivity and behavior in adult loons at 10% and 36% of sites, respectively, and exceeded benchmark thresholds for impaired reproduction and health in fishes at 82% and 73% of sites, respectively. The ecozones of southeastern Canada characterized by extensive forest cover, elevated Hg deposition, and poorly buffered soils had the greatest proportion of RQs > 1.0. Results of this assessment suggest that common loons and piscivorous fishes would likely benefit from reductions in Hg deposition, especially in southeastern Canada.

Effects of methylmercury on epigenetic markers in three model species: mink, chicken and yellow perch

We previously reported that methylmercury (MeHg) exposure is associated with DNA hypomethylation in the brain stem of male polar bears. Here, we conveniently use archived tissues obtained from controlled laboratory exposure studies to look for evidence that MeHg can disrupt DNA methylation across taxa. Brain (cerebrum) tissues from MeHg-exposed mink (Neovison vison), chicken (Gallus gallus) and yellow perch (Perca flavescens) were analyzed for total Hg levels and global DNA methylation. Tissues from chicken and mink, but not perch, were also analyzed for DNA methyltransferase (DNMT) activity. In mink we observed significant reductions in global DNA methylation in an environmentally-relevant dietary exposure group (1 ppm MeHg), but not in a higher group (2 ppm MeHg). DNMT activity was significantly reduced in all treatment groups. In chicken or yellow perch, no statistically significant effects of MeHg were observed. Dose-dependent trends were observed in the chicken data but the direction of the change was not consistent between the two endpoints. Our results suggest that MeHg can be epigenetically active in that it has the capacity to affect DNA methylation in mammals. The variability in results across species may suggest inter-taxa differences in epigenetic responses to MeHg, or may be related to differences among the exposure scenarios used as animals were exposed to MeHg through different routes (dietary, egg injection), for different periods of time (19-89 days) and at different life stages (embryonic, juvenile, adult).