Mercury at the top of the world: A 31-year record of mercury in Arctic char in the largest High Arctic lake, linked to atmospheric mercury concentrations and climate oscillations.

Lake Hazen, the largest lake north of the Arctic circle, is being impacted by mercury (Hg) pollution and climate change. The lake is inhabited by two morphotypes of land-locked Arctic char (Salvelinus alpinus), a sensitive indicator species for pollution and climatic impacts. The objectives of this study were to describe the trends in Hg concentration over time and to determine the relationship of climate to length-at-age and Hg concentrations in each char morphotype, as well as the relationship to atmospheric Hg measurements at a nearby monitoring station. Results for Hg in char muscle were available from 20 sampling years over the period 1990 to 2021. We found significant declines in Hg concentrations for both morphotypes during the 31-year study period. Increased rain and earlier freeze-up of lake ice during the summer growing season was linked to increased length-at-age in both char morphotypes. For the large morphotype, higher total gaseous Hg in the fall and winter seasons was related to higher concentrations of Hg in char, while increased glacial runoff was related to decreases in char Hg. For the small morphotype char, increased snow and snow accumulation in the fall season were linked to declines in char Hg concentration. The Atlantic Multidecadal Oscillation and Arctic Oscillation were positively related to the large char Hg trend and Arctic Oscillation was positively related to the small char Hg trend. Significant trend relationships between atmospheric Hg and Hg in biota in remote regions are rare and uniquely valuable for evaluation of the effectiveness of the Minamata Convention and related monitoring efforts.

Temporal trends of mercury in Arctic biota: 10 more years of progress in Arctic monitoring.

Temporal trend analysis of (total) mercury (THg) concentrations in Arctic biota were assessed as part of the 2021 Arctic Monitoring and Assessment Programme (AMAP) Mercury Assessment. A mixed model including an evaluation of non-linear trends was applied to 110 time series of THg concentrations from Arctic and Subarctic biota. Temporal trends were calculated for full time series (6-46 years) and evaluated with a particular focus on recent trends over the last 20 years. Three policy-relevant questions were addressed: (1) What time series for THg concentrations in Arctic biota are currently available? (2) Are THg concentrations changing over time in biota from the Arctic? (3) Are there spatial patterns in THg trends in biota from the Arctic? Few geographical patterns of recent trends in THg concentrations were observed; however, those in marine mammals tended to be increasing at more easterly longitudes, and those of seabirds tended to be increasing in the Northeast Atlantic; these should be interpreted with caution as geographic coverage remains variable. Trends of THg in freshwater fish were equally increasing and decreasing or non-significant while those in marine fish and mussels were non-significant or increasing. The statistical power to detect trends was greatly improved compared to the 2011 AMAP Mercury Assessment; 70% of the time series could detect a 5% annual change at the 5% significance level with power ≥ 80%, while in 2011 only 19% met these criteria. Extending existing time series, and availability of new, powerful time series contributed to these improvements, highlighting the need for annual monitoring, particularly given the spatial and temporal information needed to support initiatives such as the Minamata Convention on Mercury. Collecting the same species/tissues across different locations is recommended. Extended time series from Alaska and new data from Russia are also needed to better establish circumarctic patterns of temporal trends.

Laser ablation ICP-MS Co-localization of mercury and immune response in fish.

Mercury (Hg) contamination is a global issue with implications for both ecosystem and human health. In this study, we use a new approach to link Hg exposure to health effects in spotted gar (Lepisosteus oculatus) from Caddo Lake (TX/LA). Previous field studies have reported elevated incidences of macrophage centers in liver, kidney, and spleen of fish with high concentrations of Hg. Macrophage centers are aggregates of specialized white blood cells that form as an immune response to tissue damage, and are considered a general biomarker of contaminant toxicity. We found elevated incidences of macrophage centers in liver of spotted gar and used a new technology for ecotoxicology studies, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), to colocalize aggregates and Hg deposits within the tissue architecture. We conclude that Hg compromises the health of spotted gar in our study and, perhaps, other fish exposed to elevated concentrations of Hg.

Mercury methylation and demethylation potentials in Arctic lake sediments.

Mercury (Hg) transformations in sediments are key factors in the Hg exposure pathway for wildlife and humans yet are poorly characterized in Arctic lakes. As the Arctic is rapidly warming, it is important to understand how the rates of Hg methylation and demethylation (wich determine Hg bioavailability) change with temperature in lake sediments. Methylation and demethylation potentials were determined for littoral sediments (2.5 m water depth) in two deep and two shallow lakes in the Canadian Arctic using Hg stable isotope tracers at incubation temperatures of 4, 8, or 16 °C for 24 h. Compared to sediments from other regions, Hg methylation and demethylation potentials in these sediments are low. The maximum depth of the lake from which sediment was collected exerted a stronger influence over methylation potential than sediment Hg concentration or organic matter content; the shallowest lake had the highest Hg methylation potential. Sediments from the shallowest lake also demonstrated the greatest response to the temperature treatments, with significantly higher methylation potentials in the 8 and 16 °C treatments. Sediments from the deep lakes demonstrated greater demethylation potentials than shallow lakes. The methylmercury to total Hg ratio in sediments supported the measured transformation potentials as the lake with the greatest methylation potential had the highest ratio. This study supports previous works indicating that Hg methylation potential may increase as the Arctic warms, but demethylation potential does not respond to warming to the same degree, indicating that Hg methylation may predominate in warming Arctic sediments.

Effects of Non-native Fish on Lacustrine Food Web Structure and Mercury Biomagnification along a Dissolved Organic Carbon Gradient.

Although the introduction of non-native fish species has been shown to alter trophic ecology in aquatic ecosystems, there has been limited research on how invasive species alter methylmercury (MeHg) biomagnification in lacustrine food webs. We sampled surface water and biota from 8 lakes in Quebec, Canada, spanning a range of dissolved organic carbon (DOC) concentrations (2.9-8.4 mg/L); 4 lakes were inhabited by native brook trout (Salvelinus fontinalis), and the remaining lakes contained brook trout and a non-native fish, Allegheny pearl dace (Margariscus margarita). Periphyton, zooplankton, macroinvertebrates, and fish were analyzed for: 1) stable carbon (δ13 C) and nitrogen (δ15 N) isotope ratios to delineate food webs, and 2) total Hg (THg) or MeHg. Compared with the brook trout from reference lakes, fish from invaded lakes had higher length-standardized THg concentrations as well as a narrower dietary range and elevated trophic level, inferred from unadjusted δ13 C and δ15 N values, respectively. The rate of Hg biomagnification was similar across invaded and reference lakes, implying little effect of the invasive fish on the trophic transfer of MeHg. Despite differences in food web structure due to pearl dace invasion, DOC was the strongest predictor of brook trout THg levels for all lakes, suggesting that underlying environmental factors exerted a stronger influence on brook trout THg concentrations than the presence of a non-native forage fish. Environ Toxicol Chem 2020;39:2196-2207. © 2020 SETAC.

Temporal trends, lake-to-lake variation, and climate effects on Arctic char (Salvelinus alpinus) mercury concentrations from six High Arctic lakes in Nunavut, Canada.

Climate warming and mercury (Hg) are concurrently influencing Arctic ecosystems, altering their functioning and threatening food security. Non-anadromous Arctic char (Salvelinus alpinus) in small lakes were used to biomonitor these two anthropogenic stressors, because this iconic Arctic species is a long-lived top predator in relatively simple food webs, and yet population characteristics vary greatly, reflecting differences between lake systems. Mercury concentrations in six landlocked Arctic char populations on Cornwallis Island, Nunavut have been monitored as early as 1989, providing a novel dataset to examine differences in muscle [Hg] among char populations, temporal trends, and the relationship between climate patterns and Arctic char [Hg]. We found significant lake-to-lake differences in length-adjusted Arctic char muscle [Hg], which varied by up to 9-fold. Arctic char muscle [Hg] was significantly correlated to dissolved and particulate organic carbon concentrations in water; neither watershed area or vegetation cover explained differences. Three lakes exhibited significant temporal declines in length-adjusted [Hg] in Arctic char; the other three lakes had no significant trends. Though precipitation, temperature, wind speed, and sea ice duration were tested, no single climate variable was significantly correlated to length-adjusted [Hg] across populations. However, Arctic char Hg in Resolute Lake exhibited a significant correlation with sea ice duration, which is likely closely linked to lake ice duration, and which may impact Hg processing in lakes. Additionally, Arctic char [Hg] in Amituk Lake was significantly correlated to snow fall, which may be linked to Hg deposition. The lack of consistent temporal trends in neighboring char populations indicates that currently, within lake processes are the strongest drivers of [Hg] in char in the study lakes and potentially in other Arctic lakes, and that the influence of climate change will likely vary from lake to lake.