Mercury levels in herring gulls and fish: 42 years of spatio-temporal trends in the Great Lakes

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.

Spatial distribution and speciation of mercury in a recovering deepwater redfish (Sebastes mentella) population from St. Lawrence Estuary and Gulf, Canada

Mercury (Hg) pollution poses a significant threat to the environment, particularly in the form of methylmercury (MeHg). However, little is known about the distribution and influencing factors of Hg in deep-sea (>200m) fish, which is crucial for assessing potential health risks to fish and humans. In Canada, the deepwater redfish (Sebastes mentella) has been designated as an endangered species. After a 25-year fishing moratorium, the redfish population in the St. Lawrence Estuary and Gulf is recovering, and resuming of commercial fishing and human consumption are expected. This study aimed to investigate the distribution of MeHg and total Hg (THg) in the muscle of redfish, as well as the factors influencing its distribution, and to assess the potential human health risks associated with redfish consumption. The redfish samples (n = 123) were collected by Fisheries and Oceans Canada in 2019. The concentrations of THg and MeHg in redfish muscle were determined to be 93.3 ± 183 ng/g (mean ± SD, wet weight) and 78.2 ± 149 ng/g, respectively. Large redfish (>30 cm) accumulated 20 to 30 times more Hg than small redfish (17-30 cm). Small redfish from the Estuary-Western Gulf had higher levels of MeHg and THg than those from the Laurentian Channel and the Northeast Gulf, but the Hg availability to redfish among the three areas were similar. Significant predictors of MeHg concentrations in redfish muscle were determined to be fish length, muscle moisture, δ15N, and N%. MeHg consumption by the general population with an average fish consumption rate is not anticipated to have adverse effects. This study establishes a baseline for future Hg monitoring in the deep water environments in this region. Further research is required to elucidate the cause-effect relationships between various environmental/biological parameters and Hg accumulation in deep-sea biota.

Spatiotemporal changes in largemouth bass mercury concentrations from Connecticut waterbodies, 1995-2021

We evaluated spatiotemporal changes in the mean and variation in largemouth bass (Micropterus salmoides) mercury concentrations over three discrete time periods (1995, 2005-2006, and 2019-2021) across 56 Connecticut waterbodies. We detected largemouth bass raw mercury concentrations that exceeded the US Environmental Protection Agency (USEPA) Fish Tissue Residue Criterion (≥ 0.30 µg g^-1 ww) in 75.1%, 63.3%, and 47.7% of all fish sampled during 1995, 2005-2006, and 2019-2021, respectively. Total length (TL)-adjusted largemouth bass mercury concentrations declined across all ecoregions in Connecticut between subsequent sampling periods but increased between 2005-2006 and 2019-2021 in the Northwest Hills/Uplands ecoregion. The coefficient of variation (CV) of largemouth bass TL-adjusted mercury concentrations increased through time, increasing from 25.78% during 1995 to 36.47% during 2019-2021. The probability of a largemouth bass having a raw mercury concentration > 0.30 µg g^-1 ww increased with total length (TL), but the TL with a 50% probability varied across ecoregions and periods. The variation in largemouth bass mercury concentrations highlights the roles that changes to individual behaviors, food web structure, lake properties, and legacy mercury may play in shaping broad patterns and trends in mercury consumption risks.

Mercury in the Polish part of the Baltic Sea: A response to decreased atmospheric deposition and changing environment

Our review of the literature showed that since the beginning of the socio-economic transformation in Poland in the 1990s, the downward trend in Hg emissions and its deposition in the southern Baltic Sea was followed by a simultaneous decrease in Hg levels in water and marine plants and animals. Hg concentrations in the biota lowered to values that pose no or low risk to wildlife and seafood consumers. However, in the first decade of the current century, a divergence between these two trends became apparent and Hg concentrations in fish, herring and cod, began to rise. Therefore, increasing emission-independent anthropogenic pressures, which affect Hg uptake and trophodynamics, remobilization of land-based and marine legacy Hg deposits, as well as the structure of the food web, can undermine the chances of reducing both the Hg pool in the marine environment and human Hg exposure from fish.

Using Fish as a Sentinel in Risk Management of Contaminated Sediments

Sediments polluted by historical emissions from anthropogenic point sources are common in industrialized parts of the world and pose a potential threat to the function of aquatic ecosystems. Gradient studies using fish as a bioindicator are an option to assess the ecological impact of locally polluted areas. This study investigates the remaining effects of historical emissions on sediments outside ten Swedish pulp and paper mills using perch (Perca fluviatilis). The aim has been to obtain a general picture of the impact area of local deposits of cellulose fiber-rich sediments containing elevated levels of trace metals, e.g., Hg, and organochlorines, e.g., dioxins. In addition to analyzing contaminant levels in muscle and liver tissue, morphological measures in the fish that constitute biomarkers for health and reproductivity were measured. Another aim was to augment existing historical data sets to observe possible signs of environmental recovery. Overall, the results indicate only a minor elevation in contaminant levels and a minor impact on the fish health status in the polluted areas, which in several cases is an improvement from historical conditions. However, exceptions exist. Differences in the ecosystems' responses to pollution loads are primarily explained by abiotic factors such as water turnover rate, bottom dynamic conditions, and water chemistry. Weaknesses in the sampling methodology and processing of data were identified. After minor modifications, the applied survey strategy has the potential to be a management tool for decision-makers working on the remediation of contaminated areas.

An assessment of temporal trends in mercury concentrations in fish

The importance of fish consumption as the primary pathway of human exposure to mercury and the establishment of fish consumption advisories to protect human health have led to large fish tissue monitoring programs worldwide. Data on fish tissue mercury concentrations collected by state, tribal, and provincial governments via contaminant monitoring programs have been compiled into large data bases by the U.S. Environmental Protection Agency's Great Lakes National Monitoring Program Office (GLNPO), the Ontario Ministry of the Environment's Fish Contaminants Monitoring and Surveillance Program (FMSP), and many others. These data have been used by a wide range of governmental and academic investigators worldwide to examine long-term and recent trends in fish tissue mercury concentrations. The largest component of the trend literature is for North American freshwater species important in recreational fisheries. This review of temporal trends in fish tissue mercury concentrations focused on published results from freshwater fisheries of North America as well as marine fisheries worldwide. Trends in fish tissue mercury concentrations in North American lakes with marked overall decreases were reported over the period 1972-2016. These trends are consistent with reported mercury emission declines as well as trends in wet deposition across the U.S. and Canada. More recently, a leveling-off in the rate of decreases or increases in fish tissue mercury concentrations has been reported. Increased emissions of mercury from global sources beginning between 1990 and 1995, despite a decrease in North American emissions, have been advanced as an explanation for the observed changes in fish tissue trends. In addition to increased atmospheric deposition, the other factors identified to explain the observed mercury increases in the affected fish species include a systematic shift in the food-web structure with the introduction of non-native species, creating a new or expanding role for sediments as a net source for mercury. The influences of climate change have also been identified as contributing factors, including considerations such as increases in temperature (resulting in metabolic changes and higher uptake rates of methylmercury), increased rainfall intensity and runoff (hydrologic export of organic matter carrying Hg^II from watersheds to surface water), and water level fluctuations that alter either the methylation of mercury or the mobilization of monomethylmercury. The primary source of mercury exposure in the human diet in North America is from the commercial fish and seafood market which is dominated (>90%) by marine species. However, very little information is available on mercury trends in marine fisheries. Most of the data used in the published marine trend studies are assembled from earlier reports. The data collection efforts are generally intermittent, and the spatial and fish-size distribution of the target species vary widely. As a result, convincing evidence for the existence of fish tissue mercury trends in marine fish is generally lacking. However, there is some evidence from sampling of large, long-lived commercially-important fish showing both lower mercury concentrations in the North Atlantic in response to reduced anthropogenic mercury emission rates in North America and increases in fish tissue mercury concentrations over time in the North Pacific in response to increased mercury loading.

Toxicogenomic Assessment of Complex Chemical Signatures in Double-Crested Cormorant Embryos from Variably Contaminated Great Lakes Sites

Using omics approaches to monitor complex environmental mixtures is challenging. Previously, we evaluated in vitro transcriptomic effects of complex organic extracts derived from avian eggs. However, there is a lack of studies using wild species that are naturally exposed to contaminant mixtures. Here, we examined polychlorinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE) residues and gene expression in embryonic liver tissue of double-crested cormorants (Phalacrocorax auritus) collected from six variably contaminated colonies. Colonies near industrialized areas were distinguished from less contaminated sites based on their PCB and PBDE concentrations. The most variably expressed genes between sites were involved in pathways including, xenobiotic metabolism (e.g., Cyp1a4), lipid/bile acid homeostasis (e.g., Lbfabp), and oxidative stress (e.g., Mt4). Hierarchical clustering, based on relative gene expression, revealed a grouping pattern similar to chemical residue concentrations. Further, partial least squares regression analysis was used to estimate chemical concentrations from transcriptomics data. PCB 155 and BDE 47 showed the highest slopes (0.77 and 0.69, respectively) fitted by linear regression of measured and estimated chemical concentrations. The application of transcriptomics to a wild avian species, naturally exposed to complex chemical mixtures and other stressors, represents a promising means to distinguish and prioritize variably contaminated sites.

How closely do mercury trends in fish and other aquatic wildlife track those in the atmosphere? - Implications for evaluating the effectiveness of the Minamata Convention

The Minamata Convention to reduce anthropogenic mercury (Hg) emissions entered into force in 2017, and attention is now focused on how to best monitor its effectiveness at reducing Hg exposure to humans. A key question is how closely Hg concentrations in the human food chain, especially in fish and other aquatic wildlife, will track the changes in atmospheric Hg that are expected to occur following anthropogenic emission reductions. We investigated this question by evaluating several regional groups of case studies where Hg concentrations in aquatic biota have been monitored continuously or intermittently for several decades. Our analysis shows that in most cases Hg time trends in biota did not agree with concurrent Hg trends in atmospheric deposition or concentrations, and the divergence between the two trends has become more apparent over the past two decades. An over-arching general explanation for these results is that the impact of changing atmospheric inputs on biotic Hg is masked by two factors: 1) The aquatic environment contains a large inventory of legacy emitted Hg that remains available for bio-uptake leading to a substantial lag in biotic response time to a change in external inputs; and 2) Biotic Hg trends reflect the dominant effects of changes in multi-causal, local and regional processes (e.g., aquatic or terrestrial biogeochemical processes, feeding ecology, climate) that control the speciation, bioavailability, and bio-uptake of both present-day and legacy emitted Hg. Globally, climate change has become the most prevalent contributor to the divergence. A wide range of biotic Hg outcomes can thus be expected as anthropogenic atmospheric Hg emissions decline, depending on how these processes operate on specific regions and specific organisms. Therefore, evaluating the effectiveness of the Minamata Convention will require biomonitoring of multiple species that represent different trophic and ecological niches in multiple regions of the world.

A rapid method of preparing complex organohalogen extracts from avian eggs: Applications to in vitro toxicogenomics screening

Double-crested cormorants are piscivorous birds that breed in variably contaminated colonies across the Laurentian Great Lakes of North America. Collection and preparation of environmentally relevant extracts from eggs that contain variable concentrations of organohalogen contaminants represents a minimally invasive approach to characterize potential effects of exposure using in vitro bioassays. In the present study, a rapid, efficient lipid freeze-filtration extraction method was used to prepare extracts from double-crested cormorant eggs collected from 5 breeding colonies that had variable organohalogen contaminant burdens. Extracts, solubilized in dimethyl sulfoxide, were administered to chicken embryonic hepatocytes (CEHs) to determine effects on cell viability, 7-ethoxyresorufin-O-deethylase (EROD) activity, and messenger RNA expression using a chicken ToxChip polymerase chain reaction (PCR) array. The EROD median effect concentration (EC50) values were lower for extracts with greater organohalogen contaminant burdens and thus permitted an initial ranking of colonies based on the efficacy of eliciting an aryl hydrocarbon receptor-mediated response. The ToxChip PCR array data provided a more exhaustive, pathway-based evaluation of extract effects; variability in the transcriptomic profiles was associated with organohalogen contaminant burdens. For example, extracts from Mud Island (Detroit River, MI, USA) had among the highest organohalogen contaminant burdens and elicited a greater biochemical (EROD EC50 = 0.005) and transcriptomic response (22/43 genes altered on the array) in CEHs compared with the least contaminated site, which was Mandarte Island (BC, Canada; EROD EC50 = 0.172; 8/43 genes altered). Avian eggs represent a useful biomonitoring tool for determining complex mixture effects, and the combination of a rapid extraction method, an in vitro bioassay, and targeted endpoint evaluation (biochemical and transcriptomic) shows great promise as an environmental effects monitoring approach. Environ Toxicol Chem 2019;38:811-819. © 2019 Crown in the right of Canada. Published by Wiley Periodicals Inc. on behalf of SETAC.

The relationship between mercury exposure and epigenetic alterations regarding human health, risk assessment and diagnostic strategies

BACKGROUND

Exposure to the environmental toxicants poses a serious threat to human health. The extent of exposure and the development of diseases are interrelated with each other. Chronic exposure to mercury (Hg) increases the risk of developing serious human disorders from embryo to adulthood.

OBJECTIVES

The purpose of this review is to highlight the most common human disorders induced by Hg exposure on the basis of epigenetic mechanisms. A growing body of evidence shows that Hg exposure leads to alterations in the epigenetic markers.

METHODS

We performed an organized search of the available literature using PubMed, Google Scholar, Medline, Reaxys, EMBASE and Scopus databases. All the relevant citations, including research and review articles in English were evaluated. The search terms included mercury, Hg, epigenetics, epigenetic alterations, DNA methylation, histone modifications, microRNAs (miRNAs), and risk assessment.

RESULTS

Data on human toxicity due to Hg exposure shows broad variations in terms of chemical nature, doses, and the rate of exposure. Hg consumption either via foods or environmental sources may create deleterious health effects on various physiological systems at least partially through an epigenetic mechanism.

CONCLUSION

Hg exposure could trigger epigenetic alterations, hence leading to various human disorders including reduced newborn cerebellum size, adverse behavioral outcomes, atherosclerosis and myocardial infarction. Similarly, in adults, occupational Hg exposure has been associated with an increased risk of autoimmunity. It has been revealed that miRNAs in the woman's cervix are a novel responder to maternal Hg exposure during pregnancy. Hg-induced epigenetic alterations analysis of kidney tissues showed a significant interruption in renal function. DNA methylation and histone post-translation modifications are predominant types of Hg epigenetic alterations.

Pseudomonas Diversity Within Urban Freshwaters

Freshwater lakes are home to bacterial communities with 1000s of interdependent species. Numerous high-throughput 16S rRNA gene sequence surveys have provided insight into the microbial taxa found within these waters. Prior surveys of Lake Michigan waters have identified bacterial species common to freshwater lakes as well as species likely introduced from the urban environment. We cultured bacterial isolates from samples taken from the Chicago nearshore waters of Lake Michigan in an effort to look more closely at the genetic diversity of species found there within. The most abundant genus detected was Pseudomonas, whose presence in freshwaters is often attributed to storm water or runoff. Whole genome sequencing was conducted for 15 Lake Michigan Pseudomonas strains, representative of eight species and three isolates that could not be resolved with named species. These genomes were examined specifically for genes encoding functionality which may be advantageous in their urban environment. Antibiotic resistance, amidst other known virulence factors and defense mechanisms, were identified in the genome annotations and verified in the lab. We also tested the Lake Michigan Pseudomonas strains for siderophore production and resistance to the heavy metals mercury and copper. As the study presented here shows, a variety of pseudomonads have inhabited the urban coastal waters of Lake Michigan.

Mercury Concentrations in Sentinel Fish Exposed to Contaminated Sediments Under a Natural Recovery Strategy Within the St. Lawrence River Area of Concern at Cornwall, Ontario, Canada

Legacy mercury (Hg) sediment deposits are a long-term issue within the St. Lawrence River (Cornwall) area of concern with three depositional areas along the Cornwall, ON waterfront containing sediments that exceed the Ontario Sediment Quality Guidelines for Hg. Assessing the bioavailability of these Hg-contaminated sediments plays a crucial role in evaluating the effectiveness of the Cornwall Sediment Strategy based on a natural recovery approach. We collected specimens of fallfish (Semotilus corporalis), round goby (Neogobius melanostomus), and yellow perch (Perca flavescens) to assess spatial and temporal trends of Hg concentrations in various areas along the Cornwall waterfront, including zones of contaminated sediments and non-contaminated reference sites. This study revealed that (1) Hg concentrations in fish collected from the contaminated zones remain greater than those of fish from non-impacted locations, indicating that natural recovery is not yet achieved, (2) total Hg concentrations in yellow perch collected in 2016 were greater than those obtained during a previous assessment, indicating a reversal of the previously observed long-term declines, and (3) total Hg concentrations in yellow perch collected at the outlet of Gray's Creek compared with yellow perch from contaminated zones, suggesting other important inputs of Hg to the ecosystem than the legacy contaminated sediments.

Spatiotemporal Variations in Mercury Bioaccumulation at Fine and Broad Scales for Two Freshwater Sport Fishes

Bioaccumulation of mercury in sport fish is a complex process that varies in space and time. Both large-scale climatic as well as fine-scale environmental factors are drivers of these space-time variations. In this study, we avail a long-running monitoring program from Ontario, Canada to better understand spatiotemporal variations in fish mercury bioaccumulation at two distinct scales. Focusing on two common large-bodied sport fishes (Walleye and Northern Pike), the data were analyzed at fine- and broad-scales, where fine-scale implies variations in bioaccumulation at waterbody- and year-level and broad-scale captures variations across 3 latitudinal zones (~5° each) and eight time periods (~5-year each). A series of linear mixed-effects models (LMEMs) were employed to capture the spatial, temporal and spatiotemporal variations in mercury bioaccumulation. Fine-scale models were overall better fit than broad-scale models suggesting environmental factors operating at the waterbody-level and annual climatic conditions matter most. Moreover, for both scales, the space time interaction explained most of the variation. The random slopes from the best-fitting broad-scale model were used to define a bioaccumulation index that captures trends within a climate change context. The broad-scale trends suggests of multiple and potentially conflicting climate-driven mechanisms. Interestingly, broad-scale temporal trends showed contrasting bioaccumulation patterns—increasing in Northern Pike and decreasing in Walleye, thus suggesting species-specific ecological differences also matter. Overall, by taking a scale-specific approach, the study highlights the overwhelming influence of fine-scale variations and their interactions on mercury bioaccumulation; while at broad-scale the mercury bioaccumulation trends are summarized within a climate change context.

A Bayesian assessment of polychlorinated biphenyl contamination of fish communities in the Laurentian Great Lakes

Polychlorinated biphenyl (PCB) contamination has historically posed constraints on the recreational and commercial fishing industry in the Great Lakes. Empirical evidence suggests that PCB contamination represents a greater health risk from fish consumption than other legacy contaminants. The present study attempts a rigorous assessment of the spatio-temporal PCB trends in multiple species across the Canadian waters of the Great Lakes. We applied a Bayesian modelling framework, whereby we initially used dynamic linear models to delineate PCB levels and rates of change, while accounting for the role of fish length and lipid content as covariates. We then implemented Bayesian hierarchical modelling to evaluate the temporal PCB trends during the dreissenid pre- and post-invasion periods, as well as the variability among and within the water bodies of the Great Lakes system. Our analysis indicates that Lake Ontario is characterized by the highest PCB levels among nearly all of the fish species examined. Historically contaminated local areas, designated as Areas of Concern, and embayments receiving riverine inputs displayed higher concentrations within each of the water bodies examined. The general temporal trend across the Great Lakes was that the high PCB concentrations during the early 1970s followed a declining trajectory throughout the late 1980s/early 1990s, likely as a result of the reductions in industrial emissions and other management actions. Nonetheless, after the late 1990s/early 2000s, our analysis provided evidence of a decline in the rate at which PCB concentrations in fish were dropping, accompanied by a gradual establishment of species-specific, steady-state concentrations, around which there is considerable year-to-year variability. The overall trends indicate that reduced contaminant emissions have brought about distinct beneficial changes in fish PCB concentrations, but past historical contamination along with other external or internal stressors (e.g., invasive species, climate change) continue to modulate the current levels, thereby posing potential risks to humans through fish consumption.

Legacy of legacies: Chlorinated naphthalenes in Lake Trout, Walleye, Herring Gull eggs and sediments from the Laurentian Great Lakes indicate possible resuspension during contaminated sediment remediation

Polychlorinated naphthalenes (PCNs) are legacy contaminants, produced primarily as flame retardants and dielectrics until phased-out in Europe and North America in the 1970s. Spatial and temporal trends (1979-2013) of PCN concentrations were studied in whole fish and herring gull eggs throughout the Great Lakes and St. Lawrence River, whereas sediments were analyzed for 2011-2013 only. For both fish and gull eggs, concentrations of PCNs were highest in western Lake Erie (7660 & 3020pg/gww respectively), and declined downstream to St. Lawrence River (range: 34-2370pg/gww). For sediments, concentrations were highest in suspended sediments from the Detroit River (264,000pg/g), and were lower in surficial sediments downstream to the St. Lawrence River (range=440-19,300pg/g). PCNs declined at all sites from ~1980 to 1995, but in Lake Erie concentrations of PCNs increased in gulls fish from 1995 until 2005. The resurgence in PCNs in biota corresponded to the timing of remedial dredging of sediment highly contaminated with PCNs in the Detroit River, whose effects appear to manifest themselves downstream to Lake Ontario. Congener profiles of PCNs differed between Lake Erie and Lake Ontario until post-dredging, where PCN profiles of fish in both lakes became increasingly more similar. PCNs in gull eggs were mostly hepta-PCNs, whereas fish had higher concentrations of lower chlorinated PCNs. Patterns of PCNs in gulls and fish appear to be influenced by differences in not only routes of exposure and differential metabolic ability, but also resuspension of PCN contaminated sediments.

Determinants of mercury contamination in viperine snakes, Natrix maura, in Western Europe

The effects of Hg contamination are presumably widespread across the components of aquatic ecosystems, but investigations have been mainly focused on freshwater fish, because this biota represents a major source of Hg for human populations. Yet, the possible bioaccumulation of Hg on other freshwater meso- and apex-predators (e.g., amphibians, reptiles) has been largely overlooked, especially in Western Europe. In this study, the determinants of Hg concentrations were assessed for the viperine snake (Natrix maura) across 6 populations (>130 individuals sampled in 2016 and 2017) in France and Spain. Specifically, body size, sex, and diet were compared with Hg concentrations measured in ventral scales. Overall, N. maura accumulated Hg in their scales. Sex did not seem to influence Hg concentrations in this species. Significant differences in Hg concentrations were observed between study sites, and these differences were likely to be mediated by site-specific diet. Frog-eating individuals were characterized not only by lower mean values of Hg (0.194±0.018μg·g^-1 versus 0.386±0.032μg·g^-1 for piscivorous individuals), but also by weaker slopes of the body size-Hg relationship as compared to fish-eating snakes, suggesting strong differences in accumulation rates due to food resources. Importantly, the highest slope of the body size-Hg relationship and the highest values of Hg were found in individuals foraging on trout raised by a fish farm, suggesting that fish farming may contribute to Hg contamination in inland freshwater systems. Finally, our results are compared with data on Hg concentrations in other species of aquatic snakes, in order to provide a comparative point for future studies.

Substituted Diphenylamine Antioxidants and Benzotriazole UV Stabilizers in Aquatic Organisms in the Great Lakes of North America: Terrestrial Exposure and Biodilution

Substituted diphenylamine antioxidants (SDPAs) and benzotriazole UV stabilizers (BZT-UVs) are industrial additives of emerging environmental concern. However, the bioaccumulation, biomagnification, and spatial distribution of these contaminants in the Great Lakes of North America are unknown. The present study addresses these knowledge gaps by reporting SDPAs and BZT-UVs in herring gull (Larus argentatus) eggs, lake trout (Salvelinus namaycush), and their food web in the Great Lakes for the first time. Herring gull eggs showed much higher detection frequency and concentrations of target SDPAs and 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV328) than that of the whole body fish homogenate. For herring gull eggs, the samples from upper Great Lakes contained significantly greater levels of SDPAs than those eggs from lower lakes, possibly due to the differences in terrestrial food in diet. Interestingly, the predominant SDPAs in herring gull eggs were dinonyl- (C9C9) and monononyl-diphenylamine (C9) which were previously shown to be less bioaccumulative than other SDPAs in fish. In contrast, dioctyl-diphenylamine (C8C8) was the major SDPA in lake trout, and biodilution of C8C8 was observed in a Lake Superior lake trout food web. Such variations in herring gull eggs and fish indicate the differences in accumulation and elimination pathways of SDPAs and BZT-UVs and require further elucidation of these mechanisms.

Mercury Temporal Trends in Top Predator Fish of the Laurentian Great Lakes from 2004 to 2015: Are Concentrations Still Decreasing?

Mercury (Hg) concentration trends in top predator fish (lake trout and walleye) of the Great Lakes (GL) from 2004 to 2015 were determined by Kendall-Theil robust regression with a cluster-based age normalization method to control for the effect of changes in lake trophic status. When data from the GLs (except Lake Erie) are combined, a significant decreasing trend in the lake trout Hg concentrations was found between 2004 and 2015 with an annual decrease of 4.1% per year, consistent with the decline in regional atmospheric Hg emissions and water Hg concentrations. However, a breakpoint was detected with a significant decreasing slope (-8.1% per year) before the breakpoint (2010), and no trend after the breakpoint. When the lakes are examined individually, Lakes Superior and Huron, which are dominated by atmospheric Hg inputs and are more likely than the lower lakes to respond to declining emissions from areas surrounding the GL, have significant decreasing trends with rates between 5.2 and 7.8% per year from 2004 to 2015. These declining trends appear to be driven by decreasing regional atmospheric Hg emissions although they may be partly counterbalanced by other factors, including increasing local emissions, food web changes, eutrophication, and responses to global climate change. Lakes Michigan, Erie and Ontario may have been more impacted by these other factors and their trends changed from decreasing to non-decreasing or increasing in recent years.