Mercury Concentrations in Double-Crested Cormorant Chicks Across Canada.

Mercury (Hg) biomagnifies in aquatic food chains and can reach high concentrations in fish-eating birds. Spatial patterns of Hg have been found in freshwater ecosystems across Canada for many taxa, including fish and birds. However, it often is challenging to sample a representative population size of adult birds to monitor concentrations of contaminants over a large spatial scale. Moreover, adult birds can migrate and can show a contaminant profile that may not be representative of local resources. The goals of this study were (1) to determine if there was a spatial pattern of Hg concentrations in piscivorous birds, (2) to develop a model to estimate Hg concentrations in breeding adults using chicks as proxy, and (3) to develop predictive equations among non-lethal tissues that are representative of local resources in adults (blood and growing feathers). Double-crested Cormorant (Phalacrocorax auritus) chick growing feathers were sampled at 19 sites across Canada. Adult tissues (freshly grown feathers and blood) were sampled at five of those locations to establish correlations between age classes and between adult tissues. We found an increase in Hg concentrations with latitude up to 50°N followed by a decrease. There was a decrease in Hg concentrations from west to east, which contradicts previous studies. We found a good correlation of Hg concentrations between adults and chicks and among adult tissues. Our study shows that chicks are representative of adults and can be a suitable proxy for monitoring local mercury concentrations across Canada.

Joint analysis of stressors and ecosystem services to enhance restoration effectiveness.

With increasing pressure placed on natural systems by growing human populations, both scientists and resource managers need a better understanding of the relationships between cumulative stress from human activities and valued ecosystem services. Societies often seek to mitigate threats to these services through large-scale, costly restoration projects, such as the over one billion dollar Great Lakes Restoration Initiative currently underway. To help inform these efforts, we merged high-resolution spatial analyses of environmental stressors with mapping of ecosystem services for all five Great Lakes. Cumulative ecosystem stress is highest in near-shore habitats, but also extends offshore in Lakes Erie, Ontario, and Michigan. Variation in cumulative stress is driven largely by spatial concordance among multiple stressors, indicating the importance of considering all stressors when planning restoration activities. In addition, highly stressed areas reflect numerous different combinations of stressors rather than a single suite of problems, suggesting that a detailed understanding of the stressors needing alleviation could improve restoration planning. We also find that many important areas for fisheries and recreation are subject to high stress, indicating that ecosystem degradation could be threatening key services. Current restoration efforts have targeted high-stress sites almost exclusively, but generally without knowledge of the full range of stressors affecting these locations or differences among sites in service provisioning. Our results demonstrate that joint spatial analysis of stressors and ecosystem services can provide a critical foundation for maximizing social and ecological benefits from restoration investments.

Rating impacts in a multi-stressor world: a quantitative assessment of 50 stressors affecting the Great Lakes.

Ecosystems often experience multiple environmental stressors simultaneously that can differ widely in their pathways and strengths of impact. Differences in the relative impact of environmental stressors can guide restoration and management prioritization, but few studies have empirically assessed a comprehensive suite of stressors acting on a given ecosystem. To fill this gap in the Laurentian Great Lakes, where considerable restoration investments are currently underway, we used expert elicitation via a detailed online survey to develop ratings of the relative impacts of 50 potential stressors. Highlighting the multiplicity of stressors in this system, experts assessed all 50 stressors as having some impact on ecosystem condition, but ratings differed greatly among stressors. Individual stressors related to invasive and nuisance species (e.g., dreissenid mussels and ballast invasion risk) and climate change were assessed as having the greatest potential impacts. These results mark a shift away from the longstanding emphasis on nonpoint phosphorus and persistent bioaccumulative toxic substances in the Great Lakes. Differences in impact ratings among lakes and ecosystem zones were weak, and experts exhibited surprisingly high levels of agreement on the relative impacts of most stressors. Our results provide a basin-wide, quantitative summary of expert opinion on the present-day influence of all major Great Lakes stressors. The resulting ratings can facilitate prioritizing stressors to achieve management objectives in a given location, as well as providing a baseline for future stressor impact assessments in the Great Lakes and elsewhere.

Tracking overwintering areas of fish-eating birds to identify mercury exposure.

Migration patterns are believed to greatly influence concentrations of contaminants in birds due to accumulation in spatially and temporally distinct ecosystems. Two species of fish-eating birds, the Double-crested Cormorant (Phalacrocorax auritus) and the Caspian Tern (Hydroprogne caspia) breeding in Lake Ontario were chosen to measure the impact of overwintering location on mercury concentrations ([Hg]). We characterized (1) overwintering areas using stable isotopes of hydrogen (δ(2)H) and band recoveries, and (2) overwintering habitats by combining information from stable isotopes of sulfur (δ(34)S), carbon (δ(13)C), nitrogen (δ(15)N), and δ(2)H in feathers grown during the winter. Overall, overwintering location had a significant effect on [Hg]. Both species showed high [Hg] in (13)C-rich habitats. In situ production of Hg (e.g., through sulfate reducing bacteria in sediments) and allochthonous import could explain high [Hg] in birds visiting (13)C-rich habitats. Higher [Hg] were found in birds with high δ(2)H, suggesting that Hg is more bioavailable in southern overwintering locations. Hotspot maps informed that higher [Hg] in birds were found at the limit of their southeastern overwintering range. Mercury concentrations in winter feathers were positively related to predicted spatial pattern of [Hg] in fish using the National Descriptive Model of Mercury in Fish (NDMMF) based on bird spatial assignment (using δ(2)H). This study indicates that the overwintering location greatly influences [Hg].

Mercury in little brown bat (Myotis lucifugus) maternity colonies and its correlation with freshwater acidity in Nova Scotia, Canada.

Insectivorous little brown bats are exposed to elevated concentrations of mercury (Hg) through their preference for aquatic-based prey. Here we investigated spatial patterns of total Hg (THg) in fur from 10 little brown bat maternity colonies across Nova Scotia, and assessed relationships with the acidity of nearby lakes and rivers. Total Hg concentrations were measured in fur samples from 149 adult female little brown bats. Values showed significant variation among colonies (mean range 3.76-27.38 µg/g, dry weight), and 48% of individuals had Hg concentrations in excess of the 10 µg/g threshold associated with neurochemical changes in Chiroptera conspecifics (n = 26) from Virginia. Average surface water acidity parameters (pH and acid neutralization capacity) within an 8 km radius of each maternity roost showed strong negative associations with average colony fur THg concentrations. This suggests that freshwater acidity in foraging grounds explains much of the variation in average fur THg concentrations in little brown bat colonies. These findings highlight the significant role that water quality may have on Hg bioaccumulation within terrestrial species that feed on aquatic prey.

Contamination of mercury during the wintering period influences concentrations at breeding sites in two migratory piscivorous birds.

Many aquatic fish-eating birds migrate long distances and are exposed to different mercury concentrations ([Hg]) during their annual cycle. Here we examined the importance of migration on [Hg] in two colonial migratory fish-eating bird species. We determined temporal trends of [Hg] and stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N) during the annual cycle in Double-crested Cormorants (Phalacrocorax auritus) and Caspian Terns (Hydroprogne caspia) breeding in Lake Ontario by a repeated sampling of breast feathers and blood from recaptured individuals. We found an effect of previous winter [Hg], species, sex, and location to explain variations of Hg at breeding sites. This suggests Hg carryover from winter to summer periods and that variations of [Hg] in the summer are partially explained by [Hg] in the winter. Carryover of Hg among seasons and slow changes in [Hg] over time were found especially for individuals in high winter exposure groups, suggesting a slow depuration rate and a fast uptake rate for both species. In contrast, stable isotope values rapidly switched to reach equilibrium at a similar midpoint regardless of winter habitat or diet suggesting minimal carryover of isotopic signatures. The potential of Hg carryover from wintering sites indicates that Hg concentrations in birds at a given time may be influenced by previous exposure from distant locations.

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.

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.

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.

Biomagnification of mercury in aquatic food webs: a worldwide meta-analysis.

The slope of the simple linear regression between log10 transformed mercury (Hg) concentration and stable nitrogen isotope values (δ(15)N), hereafter called trophic magnification slope (TMS), from several trophic levels in a food web can represent the overall degree of Hg biomagnification. We compiled data from 69 studies that determined total Hg (THg) or methyl Hg (MeHg) TMS values in 205 aquatic food webs worldwide. Hg TMS values were compared against physicochemical and biological factors hypothesized to affect Hg biomagnification in aquatic systems. Food webs ranged across 1.7 ± 0.7 (mean ± SD) and 1.8 ± 0.8 trophic levels (calculated using δ(15)N from baseline to top predator) for THg and MeHg, respectively. The average trophic level (based on δ(15)N) of the upper-trophic-level organisms in the food web was 3.7 ± 0.8 and 3.8 ± 0.8 for THg and MeHg food webs, respectively. For MeHg, the mean TMS value was 0.24 ± 0.08 but varied from 0.08 to 0.53 and was, on average, 1.5 times higher than that for THg with a mean of 0.16 ± 0.11 (range: -0.19 to 0.48). Both THg and MeHg TMS values were significantly and positively correlated with latitude. TMS values in freshwater sites increased with dissolved organic carbon and decreased with total phosphorus and atmospheric Hg deposition. Results suggest that Hg biomagnification through food webs is highest in cold and low productivity systems; however, much of the among-system variability in TMS values remains unexplained. We identify critical data gaps and provide recommendations for future studies that would improve our understanding of global Hg biomagnification.

Freshwater fish-consumption relations with total hair mercury and selenium among women in eastern China.

Wild fish from Qiandao Hu, a reservoir in the Zhejiang Province in eastern China, have increased mercury (Hg) concentrations exceeding the World Health Organization's (WHO) recommended guidelines. Due to the importance of freshwater biota in the local cuisine, dietary exposure to increased neurotoxic Hg is a concern in this region. An environmental hair-marker study was undertaken coincident with a cross-sectional epidemiologic study with 50 women age 17-46 years living in a Qiandao Hu fishing village. Diet, occupation, and other possible sources of Hg were recorded by way of questionnaires. Total mercury (THg) and selenium (Se) concentrations were measured in human hair samples and in important market fish species. Fish THg and Se concentrations were increased, with some fish concentrations >200 ng/g THg and 500 ng/g Se (wet weight [ww]). However, the average hair THg was low at 0.76 ± 0.51 µg/g dry weight, lower than the WHO's no observable-adverse effect level (50 µg/g), whereas the average hair Se was 1.0 µg/g. Hair THg concentration was positively associated with the average mass of fish consumed weekly, indicating that fish consumption is the main contributor to hair THg in this geographic area. The age-related hair THg trend was not linear but instead demonstrated a rapid increase in THg before age 25 years, followed by consistent concentrations in all ages after age 25 years. There was a positive correlation (p < 0.001) between molar Se and Hg in the hair samples, suggesting a possible antagonistic relation. This is the first study examining the relation between dietary Hg exposure and hair THg in an eastern China community where freshwater fish, as opposed to marine fish, dominates the cuisine.

Arsenic and mercury contamination and complex aquatic bioindicator responses to historical gold mining and modern watershed stressors in urban Nova Scotia, Canada.

Beginning in the late-1800s, gold mining activities throughout Nova Scotia, eastern Canada, released contaminants, notably geogenic arsenic from milled ore and anthropogenic mercury from amalgamation, to local environments via surface water flows through tailings fields. We investigated recovery from and legacy effects of the tailings field at the Montague Gold District (~1863-1940) on nearby urban lake ecosystems using geochemical measures and zooplankton remains archived in dated sediment cores from an impact (Lake Charles) and a reference (Loon Lake) lake. Sedimentary levels of total arsenic and total mercury were used to assess mining-related inputs. Arsenic concentrations remain elevated at nearly 300 times above sediment guidelines in Lake Charles surface sediments, due to its upward mobilization from enriched sediment intervals and sequestration by iron oxyhydroxides in surficial sediments. Peak mercury concentrations at Lake Charles were eight times above sediment guidelines during the mining period, and since ~1990 have recovered to levels observed before mining began. Legacy mining impacts at Lake Charles and non-mining related environmental changes in the post-1950 sediments at both lakes have thus combined to structure assemblage compositions of primary consumers. At both lakes, assemblages of pelagic-dominated Cladocera differed (p ≤ 0.05) during the mining period compared to periods before and after mining. Taxon richness differed (p ≤ 0.01) only between the pre- and post-mining periods at mining-impacted Lake Charles and reflects long-term declines of substrate-dwelling littoral taxa. Geochemical and biological recovery have not completely occurred at Lake Charles despite the mine district's closure ~80 years ago. Our findings demonstrate that impacts of ore processing and amalgamation from historical gold mining, combined with recent watershed stressors, continue to affect sedimentary arsenic geochemistry and intermediate trophic levels of nearby, downstream aquatic habitats.

Evaluation of a nanoscale zero-valent iron amendment as a potential tool to reduce mobility, toxicity, and bioaccumulation of arsenic and mercury from wetland sediments.

Gold mining in the 1800s has led to the contamination of wetlands with introduced mercury (Hg) and geogenic arsenic (As). In situ risk management tools to reduce mobility and toxicity of Hg and As are needed to support natural restoration of impacted ecosystems. Here, we explored whether a nanoscale zero-valent iron (nZVI) slurry injected into two different contaminated wetland sediments can reduce Hg and As mobility to the overlaying water and toxicity to two aquatic invertebrates, burrowing mayflies (Hexagenia spp.) and Chinese mystery snails (Cipangopaludina chinensis). Total water Hg and As concentrations overlying both contaminated sediments were reduced by at least 75% and 88% respectively when treated with nZVI slurry. In the first sediment, juvenile snail survival increased from 75% in the untreated sediment to 100% in all nZVI treatments. The 2% nZVI treatment level was the only one with surviving mayflies (33%) and growth of juvenile snails. No snails or mayflies survived in the second sediment, regardless of nZVI treatment level. However, snails survived longer in this sediment with 4% and 8% nZVI. To improve reactivity of nZVI without increasing nZVI dose, future studies should investigate matrix-supported nZVI for reducing mobility and toxicity of As and Hg in wetland sediments.

Toward Sustainable Environmental Quality: Priority Research Questions for North America.

Anticipating, identifying, and prioritizing strategic needs represent essential activities by research organizations. Decided benefits emerge when these pursuits engage globally important environment and health goals, including the United Nations Sustainable Development Goals. To this end, horizon scanning efforts can facilitate identification of specific research needs to address grand challenges. We report and discuss 40 priority research questions following engagement of scientists and engineers in North America. These timely questions identify the importance of stimulating innovation and developing new methods, tools, and concepts in environmental chemistry and toxicology to improve assessment and management of chemical contaminants and other diverse environmental stressors. Grand challenges to achieving sustainable management of the environment are becoming increasingly complex and structured by global megatrends, which collectively challenge existing sustainable environmental quality efforts. Transdisciplinary, systems-based approaches will be required to define and avoid adverse biological effects across temporal and spatial gradients. Similarly, coordinated research activities among organizations within and among countries are necessary to address the priority research needs reported here. Acquiring answers to these 40 research questions will not be trivial, but doing so promises to advance sustainable environmental quality in the 21st century. Environ Toxicol Chem 2019;38:1606-1624. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Spatial and temporal trends of mercury concentrations in young-of-the-year spottail shiners (Notropis hudsonius) in the St. Lawrence River at Cornwall, ON.

The St. Lawrence River at Cornwall, Ontario is an "Area of Concern" because of mercury (Hg) biomagnification from bottom sediments. To assess the spatial and temporal distribution of Hg in the food web, young-of-the-year (YOY) spottail shiners (Notropis hudsonius) were collected in August 2005 from five sites along the Cornwall waterfront within a Hg-contaminated zone and two reference zones. The results were compared to analyses made between 1979 and 2000 by the Ontario Ministry of the Environment. Total Hg concentrations in spottail shiners from the contaminated zone were significantly higher than in reference zones, confirming previous observations. Within the contaminated zone, there were significant differences in Hg concentrations among three sites spaced about 500 m apart, consistent with a high degree of site fidelity of YOY fish and suggesting a possible internal source of Hg. Hg concentrations in spottail shiners are decreasing regionally, although year-to-year variability was high, particularly in the contaminated zone. Stable isotope analyses of spottail shiners did not reveal any differences in nitrogen isotope composition among zones that would indicate differences in food-web structure and Hg biomagnification. However, carbon sources at an upstream reference zone were not the same as within the Area of Concern. Differences in carbon isotope composition at two sites within the contaminated zone corresponded to differences in Hg concentrations, consistent with a unique internal source of Hg. The variation in Hg contamination of YOY spottail shiners over fine spatial and temporal scales provide important insights about the potential release of Hg from contaminated sediments and the role of climate in regional trends. Sessile YOY fish provide a precise indicator for demonstrating these differences and for assessing their cause.

Mercury and selenium in the food web of Lake Nahuel Huapi, Patagonia, Argentina.

Despite located far from point sources of Hg pollution, high concentrations were recorded in plankton from the deep oligotrophic Lake Nahuel Huapi, located in North Patagonia. Native and introduced top predator fish with differing feeding habits are a valuable economic resource to the region. Hence, Hg and Se trophic interactions and pathways to these fish were assessed in the food web of this lake at three sites, using stable nitrogen and carbon isotopes. As expected based on the high THg in plankton, mercury did not biomagnify in the food web of Lake Nahuel Huapi, as most of the THg in plankton is in the inorganic form. As was observed in other aquatic systems, Se did not biomagnify either. When trophic pathways to top predator fish were analyzed, they showed that THg biomagnified in the food chains of native fish but biodiluted in the food chains of introduced salmonids. A more benthic diet, typical of native fish, resulted in higher [THg] bioaccumulation than a more pelagic or mixed diet, as in the case of introduced fish. Se:THg molar ratios were higher than 1 in all the fish species, indicating that Se might be offering a natural protection against Hg toxicity.

Halogenated phenolic compounds in wild fish from Canadian Areas of Concern.

Concentrations of halogenated phenolic compounds were measured in the plasma of brown bullhead (Ameiurus nebulosus) from 4 Canadian Areas of Concern (AOCs), to assess exposure to suspected thyroid-disrupting chemicals. Hydroxylated polychlorinated biphenyls (OH-PCBs) were detected in every sample collected in 3 of the AOCs; the detection frequency was lower in samples from the Detroit River AOC. The OH-PCBs most frequently detected were pentachloro, hexachloro, and heptachloro congeners, which are structurally similar to thyroid hormones. Pentachlorophenol (PCP) was detected at highest concentrations (1.8 ng/g) in fish from Prince Edward Bay, the Bay of Quinte Lake reference site, and Hillman Marsh (the Wheatley Harbour reference site), suggesting local sources of contamination. Elevated PCP concentrations were also detected in the plasma of brown bullhead from exposed sites in the Toronto and Region AOC (0.4-0.6 ng/g). Triclosan was consistently detected in the Toronto and Region AOC (0.05-0.9 ng/g), consistent with wastewater emission. Greater concentrations were occasionally detected in the plasma of brown bullhead from the Bay of Quinte AOC. Concentrations of polybrominated diphenyl ethers were highest in the Toronto and Region AOC, and at 2 of the Bay of Quinte AOC exposed sites near Trenton and Belleville. Distribution patterns reflected the properties and usage of the compounds under investigation and the characteristics of each AOC. Environ Toxicol Chem 2017;36:2266-2273. © 2017 SETAC.

Mercury and other trace elements in a pelagic Arctic marine food web (Northwater Polynya, Baffin Bay).

Total mercury (THg), methylmercury (MeHg) and 22 other trace elements were measured in ice algae, three species of zooplankton, mixed zooplankton samples, Arctic cod (Boreogadus saida), ringed seals (Phoca hispida) and eight species of seabirds to examine the trophodynamics of these metals in an Arctic marine food web. All samples were collected in 1998 in the Northwater Polynya (NOW) located between Ellesmere Island and Greenland in Baffin Bay. THg and MeHg were found to biomagnify through the NOW food web, based on significant positive relationships between log THg and log MeHg concentrations vs. delta15N muscle and liver . The slope of these relationships for muscle THg and MeHg concentrations (slope=0.197 and 0.223, respectively) were similar to those reported for other aquatic food webs. The food web behavior of THg and delta15N appears constant, regardless of trophic state (eutrophic vs. oligotrophic), latitude (Arctic vs. tropical) or salinity (marine vs. freshwater) of the ecosystem. Rb in both liver and muscle tissue and Zn in muscle tissue were also found to biomagnify through this food web, although at a rate that is approximately 25% of that of THg. A number of elements (Cd, Pb and Ni in muscle tissue and Cd and Li in seabird liver tissue) were found to decrease trophically through the food web, as indicated by significantly negative relationships with tissue-specific delta15N. A diverse group of metals (Ag, Ba, La, Li, Sb, Sr, U and V) were found to have higher concentrations in zooplankton than seabirds or marine mammals due to bioconcentration from seawater. The remaining metals (As, Co, Cu, Ga, Mn, Mo and Se in muscle tissue) showed no relationship with trophic position, as indicated by delta15N values, although As in liver tissue showed significant biomagnification in the seabird portion of the food web.

Lake and watershed influences on the distribution of elemental contaminants in the Rideau Canal System, a UNESCO world heritage site.

Watershed-specific variables such as sediment particle size distribution, water depth, sedimentation rate, focusing factors, and catchment area to lake area ratio can affect the distribution of trace element contaminants to lakes. The aim of this study was to investigate sources of metals to three headwater lakes and to quantify effects of watershed-specific variables on spatial and temporal trends of trace elements (As, Cd, Co, Cr, Cu, Hg, K, Ni, Pb, Rb, and Zn) in sediments and mercury (Hg) concentrations in fish. Surface sediment and water samples were used to characterize spatial patterns, while sediment cores were collected to portray temporal trends. Historical trends of Hg in northern pike (Esox lucius) were assessed in relation to paleolimnological trends of sediment Hg concentrations. Similarity in timing of sediment peak trace element concentrations for the lakes suggests large-scale, atmospheric sources. The lake with highest catchment area-to-lake area ratio was consistently associated with highest sediment elemental concentrations and displayed significant correlations between increased sediment Hg concentrations and decreased pike tissue concentrations over time. This suggests that catchment area-to-lake area ratio is an important factor influencing the concentration of atmospherically derived contaminants within lake sediments and their transfer through the food web.

Distribution of mercury in archived fur from little brown bats across Atlantic Canada.

Total mercury (Hg) concentrations were measured in archived fur from adult female little brown bats sampled at maternity roosts across Atlantic Canada. Mercury concentrations varied significantly among regions and roosts. Bats from Nova Scotia and Newfoundland had the highest median Hg concentrations (9.67 µg/g and 9.51 µg/g) among regions, and individuals from Kejimkujik National Park had the highest Hg (median: 28.38 µg/g) among roosts. Over one third of individuals sampled had fur Hg concentrations exceeding thresholds associated with neurochemical responses. Within-roost examinations of stable carbon and nitrogen isotopes in fur showed inconsistent associations with Hg concentrations. Therefore, the hypothesis that within-roost variation in Hg is driven by variation in diet is not supported by this data, and it is recommended that key prey items be included in future mercury bioaccumulation studies for bats. The elevated mercury fur concentrations for bats from southern Nova Scotia remains an anomaly of concern even when placed in the larger context of Atlantic Canada.