Distribution and trends of mercury in aquatic and terrestrial biota of New York, USA: a synthesis of 50 years of research and monitoring.

Mercury (Hg) inputs have particularly impacted the northeastern United States due to its proximity to anthropogenic emissions sources and abundant habitats that efficiently convert inorganic Hg into methylmercury. Intensive research and monitoring efforts over the past 50 years in New York State, USA, have informed the assessment of the extent and impacts of Hg exposure on fishes and wildlife. By synthesizing Hg data statewide, this study quantified temporal trends of Hg exposure, spatiotemporal patterns of risk, the role that habitat and Hg deposition play in producing spatial patterns of Hg exposure in fish and other wildlife, and the effectiveness of current monitoring approaches in describing Hg trends. Most temporal trends were stable, but we found significant declines in Hg exposure over time in some long-sampled fish. The Adirondack Mountains and Long Island showed the greatest number of aquatic and terrestrial species with elevated Hg concentrations, reflecting an unequal distribution of exposure risk to fauna across the state. Persistent hotspots were detected for aquatic species in central New York and the Adirondack Mountains. Elevated Hg concentrations were associated with open water, forests, and rural, developed habitats for aquatic species, and open water and forested habitats for terrestrial species. Areas of consistently elevated Hg were found in areas driven by atmospheric and local Hg inputs, and habitat played a significant role in translating those inputs into biotic exposure. Continued long-term monitoring will be important in evaluating how these patterns continue to change in the face of changing land cover, climate, and Hg emissions.

Tracking Fish Lifetime Exposure to Mercury Using Eye Lenses.

Mercury (Hg) uptake in fish is affected by diet, growth, and environmental factors such as primary productivity or oxygen regimes. Traditionally, fish Hg exposure is assessed using muscle tissue or whole fish, reflecting both loss and uptake processes that result in Hg bioaccumulation over entire lifetimes. Tracking changes in Hg exposure of an individual fish chronologically throughout its lifetime can provide novel insights into the processes that affect Hg bioaccumulation. Here we use eye lenses to determine Hg uptake at an annual scale for individual fish. We assess the widely distributed benthic round goby (Neogobius melanostomus) from the Baltic Sea, Lake Erie, and the St. Lawrence River. We aged layers of the eye lens using proportional relationships between otolith length at age and eye lens radius for each individual fish. Mercury concentrations were quantified using laser ablation inductively coupled plasma mass spectrometry. The eye lens Hg content revealed that Hg exposure increased with age in Lake Erie and the Baltic Sea but decreased with age in the St. Lawrence River, a trend not detected using muscle tissues. This novel methodology for measuring Hg concentration over time with eye lens chronology holds promise for quantifying how global change processes like increasing hypoxia affect the exposure of fish to Hg.

Mercury Exposure in Two Fish Trophic Guilds from Protected and ASGM-Impacted Reservoirs in Zimbabwe and Possible Risks to Human Health.

Despite a surge in mercury (Hg) pollution from artisanal and small-scale gold mining (ASGM) in Zimbabwe's drainage basins, little is known about Hg trophodynamics in the country's major reservoirs. We analyzed fish tissues for total mercury (THg) and stable isotopes of nitrogen and carbon (δ15N and δ13C) to compare patterns of biomagnification between two trophic guilds from a protected reservoir (Chivero) and an ASGM-impacted reservoir (Mazowe) and assessed consequences for human and fish health. Mean dry weight THg concentrations were significantly higher for both piscivorous and herbivorous fishes from Mazowe reservoir compared to fishes from similar feeding guilds in Chivero. Trophic magnification slopes (TMS), inferred from linear regressions between log10[THg] and δ15N, revealed significant Hg biomagnification in Mazowe (TMS = 0.28; p < 0.05) and no evidence for Hg biomagnification in Chivero (TMS = - 0.005; p > 0.05). In Mazowe's piscivorous fishes, 32% had wet weight THg concentrations that surpassed 0.2 µg/g ww, a threshold for susceptible human populations and biochemical and gene expression alterations in fish. In addition, 17% of Mazowe's piscivorous fishes surpassed the UNEP THg toxicity threshold for human consumption (0.5 µg/g ww). To reduce exposure to Hg toxicity in humans, the maximum fish consumption for piscivorous species from Mazowe reservoir should not exceed 431 g/week for both adult male and female consumers. Our findings demonstrate the importance of creating freshwater-protected areas to prevent direct Hg contamination of aquatic ecosystems and the need for health agencies to provide fish consumption advisories to vulnerable communities.

Is Mixtures' Additivity Supported by Empirical Data? A Case Study of Developmental Toxicity of PFOS and 6:2 FTS in Wildtype Zebrafish Embryos.

Per- and polyfluoroalkyl substances (PFASs) are a major priority for many federal and state regulatory agencies charged with monitoring levels of emerging contaminants in environmental media and setting health-protective benchmarks to guide risk assessments. While screening levels and toxicity reference values have been developed for numerous individual PFAS compounds, there remain important data gaps regarding the mode of action for toxicity of PFAS mixtures. The present study aims to contribute whole-mixture toxicity data and advance the methods for evaluating mixtures of two key components of aqueous film-forming foams: perfluorooctanesulfonic acid (PFOS), and 6:2 fluorotelomer sulfonic acid (6:2 FTS). Wildtype (AB) zebrafish embryos were exposed to PFOS and 6:2 FTS, both as individual components and as binary mixtures, from 2 to 122 h post-fertilization. Five treatment levels were selected to encompass environmentally relevant exposure levels. Experimental endpoints consisted of mortality, hatching, and developmental endpoints, including swim bladder inflation, yolk sac area, and larval body length. Results from dose-response analysis indicate that the assumption of additivity using conventional points of departure (e.g., NOAEL, LOAEL) is not supported for critical effect endpoints with these PFAS mixtures, and that the interactions vary as a function of the dose range. Alternative methods for quantifying relative potency are proposed, and recommendations for additional investigations are provided to further advance assessments of the toxicity of PFAS mixtures to aquatic organisms.

Emergent Freshwater Insects Serve as Subsidies of Methylmercury and Beneficial Fatty Acids for Riparian Predators Across an Agricultural Gradient.

Aquatic-to-terrestrial subsidies have the potential to provide riparian consumers with benefits in terms of physiologically important organic compounds like omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs). However, they also have a "dark side" in the form of exposure to toxicants such as mercury. Human land use intensity may also determine whether subsidies provide benefits or come at a cost for riparian predators. We sampled insects as well as Eastern Phoebe (Sayornis phoebe) chicks in 2015-2016 within the southern Finger Lakes region to understand how food quality, in terms of n-3 LCPUFAs and methylmercury (MeHg), of emergent freshwater insects compared with that of terrestrial insects and how land use affected the quality of prey, predator diet composition, and MeHg exposure. Across the landscape, freshwater insects had a significantly higher percentage of the n-3 LCPUFA eicosapentaenoic acid (EPA) compared to terrestrial insects and contained significantly more MeHg than terrestrial insects did. In spite of differences in MeHg concentrations between aquatic and terrestrial insects, chick MeHg concentrations were not related to diet composition. Instead, chick MeHg concentrations increased with several metrics of human land use intensity, including percent agriculture. Our findings suggest that freshwater subsidies provide predators with both risks and benefits, but that predator MeHg exposure can vary with human land use intensity.

Mercury Concentrations in Big Brown Bats (Eptesicus fuscus) of the Finger Lakes Region, New York.

The northeastern United States receives elevated mercury (Hg) deposition from United States and global emissions, making it critical to understand the fate of Hg in watersheds with a variety of aquatic habitats and land use types, such as the Finger Lakes region of New York State. Bats are valuable and important organisms to study chronic Hg exposure, because they are at risk of sublethal effects from elevated Hg exposure. The objectives of this study were to: (1) determine total Hg (THg) and methylmercury (MeHg) concentrations in big brown bats (Eptesicus fuscus) of the Finger Lakes region; (2) assess whether morphometric, temporal, or spatial factors predict bat Hg concentrations; and (3) investigate the role of trophic position and diet represented by stable isotopes of carbon and nitrogen in explaining variations in bat Hg concentrations. We found comparable THg and MeHg concentrations to previous studies (THg range 1-45 ppm, MeHg range 0.5-38 ppm) in big brown bat fur collected throughout the Finger Lakes region. On average, MeHg made up 81% of THg in bat fur. Fifteen percent of our samples showed higher THg than a proposed toxicity threshold of 10 ppm. Together, dominant land cover and % wetland cover explained bat THg in the Finger Lakes. Trophic position (i.e., δ15N) was strongest in predicting bat THg in forests but was a weaker predictor of Hg bioaccumulation in bats from agricultural and urban areas. The range of Hg concentrations found in this study warrants further examination into the potential toxicological impacts of Hg to wildlife and the role of land use in Hg exposure to terrestrial organisms of the Finger Lakes.

Mercury concentrations in fish and invertebrates of the Finger Lakes in central New York, USA.

Deleterious health effects in humans and wildlife are associated with the consumption of fish contaminated by mercury (Hg). This study was conducted to assess Hg concentrations in biota of the Finger Lakes (New York, USA), a region where fisheries are important for the economy but where no assessment of the drivers of food web Hg dynamics exists to date. Additionally, this region is of interest for the study of Hg bioaccumulation because of the importance of agricultural land cover, which can affect lake trophic status and thus the bioavailability of methyl Hg (MeHg). The study objectives were to (1) assess if fish Hg concentrations were of concern to humans and wildlife, (2) determine if differences in biota Hg concentrations exist among lakes, and (3) assess models developed for New York State as predictors of present day Finger Lakes fish Hg concentrations. Exploratory analyses were also conducted to assess predictors of fish Hg concentrations using lower trophic level MeHg concentrations, water quality, and lake and land cover characteristics. Fish concentrations were above the EPA criterion (300 ng/g wet weight, ww) in 24% of fish, but only Walleye (Sander vitreus) from Owasco Lake exceeded New York State Department of Health consumption guidelines (1000 ng/g ww). The threshold indicating biological changes within fish (500 ng/g ww) was exceeded in 11% of the individuals sampled. Significant differences were found among lakes for all fish species except Largemouth Bass (Micropterus salmoides). Notably, Lake Trout (Salvelinus namaycush) had significantly lower Hg concentrations in Cayuga Lake compared to other Finger Lakes. This trend was not mirrored in the lower food web, as benthic invertebrates had higher MeHg concentrations in Cayuga Lake. Using models developed for New York State in 2003-2005, observed concentrations in 90% of fish were different (±200 ng/g ww) than expected. Findings from this study suggest Hg dynamics in the Finger Lakes require consideration of fish age, growth rates, and food web structure to accurately predict fish Hg concentrations among lakes.

Reconstructing avian mercury concentrations through time using museum specimens from New York State.

We examined how variation in MeHg concentrations through time is reflected in birds, a taxon commonly used as a biological indicator of ecosystem health. Using museum specimens collected from 1880 to 2016, we measured feather MeHg concentrations in six species of birds that breed in New York State and have distinct dietary and habitat preferences. We predicted that MeHg concentrations in feathers would mirror Hg emission patterns in New York State and increase through time until 1980 then decrease thereafter in response to increased regulation of anthropogenic Hg emissions. We found that MeHg concentrations increased with δ15N, and that MeHg feather concentrations for some individuals from four of the six species examined exceeded concentrations known to cause negative sublethal effects in birds. In contrast to our prediction, MeHg concentrations in feathers did not parallel global or local Hg emissions through time and varied by species, even after controlling for possible changes in diet and habitat. MeHg concentrations varied substantially within species and individual specimens, suggesting that high within-individual variation in feather MeHg concentrations caused by spatiotemporal variation in molt, environmental Hg exposure, or mobility decoupling Hg uptake from breeding sites, may obscure trends in MeHg through time. Our study provides a unique assessment of feather MeHg in six species not typically analyzed using this retrospective approach.

Effect of eutrophication on mercury, selenium, and essential fatty acids in bighead carp (Hypophthalmichthys nobilis) from reservoirs of eastern China.

Analyses of the risks and benefits of consuming fish assess the content of beneficial fatty acids found in fish relative to harmful pollutants such as methylmercury (MeHg). Quantifying the effect of eutrophication on mercury (Hg), selenium (Se) and essential fatty acids (EFAs) in fish is necessary to determine how measures of risk vary with productivity. Total Hg and MeHg, Se and fatty acids, including the EFA eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), were analyzed in Bighead Carp (Hypophthalmichthys nobilis) dorsal muscle tissue from seven subtropical reservoirs of eastern China. Individual elements and fatty acids, as well as derived measures of risk (Se:Hg and hazard quotient, HQ(EFA)) were regressed against indicators of eutrophication, including total phosphorous (TP), chlorophyll-a (chl-a) and phytoplankton species composition. We found low MeHg concentrations (range=0.018-0.13 µg/g ww) and Se concentrations (range=0.12-0.28 µg/g ww), and Se:Hg molar ratios that were well above 1.0, indicating a low risk of Hg toxicity. Bighead Carp had a high content of total polyunsaturated fatty acids (∑PUFAs=44.2-53.6%), which included both EPA (6.9-12.5%) and DHA (16.1-23.2%). However, fish had significantly lower Se:Hg molar ratios in reservoirs with high TP, and lower EPA content with increasing plankton density (i.e. higher chl-a). Phytoplankton species composition predicted Se concentrations, but not Hg concentrations or EFA content. Overall, Hg concentrations in Bighead Carp were very low relative to consumption guidelines, and Se concentrations were adequate to confer protective benefits against MeHg toxicity. Our findings suggest that changes to plankton species composition and density with eutrophication may result in fish of lower nutritional value and thus increase risks to fish consumers by changing the availability of Se and EPA relative to MeHg.

Mercury biomagnification in subtropical reservoir fishes of eastern China.

Little is known about mercury (Hg) biomagnification in the subtropics, aquatic systems with high species diversity resulting in complex food webs. High atmospheric Hg emissions and ubiquitous reservoir fisheries may lead to elevated Hg bioaccumulation in Chinese freshwater fishes. However, stocking practices using fast-growing species can result in low fish total Hg (THg) concentrations. Here, we describe Hg transfer within the fish food web of a large subtropical reservoir, Qiandao Hu (Xin'anjiang reservoir) situated in eastern China. We measured food web Hg biomagnification and THg concentrations in 33 species of stocked and wild fishes. Mercury concentrations in most fishes were low, though we also found high Hg concentrations in wild top predators. The food web structure, assessed using stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N), demonstrated a high degree of omnivory and a long food chain. THg concentrations were highly correlated with fish δ(15)N values. The regression of log10THg against δ(15)N revealed the overall Hg biomagnification rate was low. This study shows that where long food chains exist in subtropical reservoirs, elevated Hg accumulation in top predators can occur despite a low Hg biomagnification rate.

Ebullition rates and mercury concentrations in St. Lawrence river sediments and a benthic invertebrate.

Ebullition, the release of gas from anaerobic decomposition in sediments, was recorded in a mercury-contaminated depositional zone (Zone 1) of the St. Lawrence River Area of Concern in Cornwall, Ontario, Canada. The aim of the present study was to test if this disturbance affected the bioavailability of total mercury (THg) and methylmercury (MeHg) in surficial sediments to a benthic invertebrate (Echinogammarus ischnus). Ebullition rates ranged from <1 to 2,800 ml/m(2) daily, with methane gas comprising 29 to 84% of the total. No direct effects of ebullition were found on either abiotic (sediment or pore water THg or MeHg concentrations) or biotic (amphipod THg or MeHg concentrations) variables measured. Instead, amphipod MeHg concentrations were best predicted by pore water THg and MeHg concentrations, organic matter of surficial sediments, and water depth and location. Trend surface analyses demonstrated that a shallow, southwestern part of Zone 1 was most contaminated with pore water mercury, which decreased in a gradient toward the northeast. Further study is needed to determine if the amount of sediment resuspended by ebullition affects the spatial distribution of mercury.