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1. Diet shifts drive mercury bioaccumulation and distribution in tissues of the longnose lancetfish (Alepisaurus ferox)

   https://doi.org/10.1016/j.marpolbul.2025.117590  

   Chen, Rachel S; Paulson, Erik T; Schartup, Amina T; Choy, C Anela (April 2025, Marine Pollution Bulletin)

   Monitoring the impacts of global efforts to reduce mercury (Hg) emissions is limited by the collection of biological samples at appropriate spatiotemporal scales. This is especially true in the deep sea, a vast region with food webs that cycle bioaccumulative methylmercury (MeHg). Within a species, understanding the distribution of Hg across tissue types can reveal how Hg accumulates in the body and inform how useful a species is for biomonitoring geographic regions or vertical habitats of the ocean. We focus on a globally distributed deep-sea fish, the longnose lancetfish (Alepisaurus ferox, n = 69 individuals), and measure total mercury (THg) and MeHg concentrations in 10 tissue types (brain, caudal white muscle, dorsal white muscle, gallbladder, gill filament, gonad, heart, intestine, liver, and stomach lining). Across all tissue types, THg and MeHg concentrations were higher in large lancetfish (≥1.8 kg) than small lancetfish (<1.8 kg), but concentrations were relatively stable within size classes. THg levels were highest in liver, intestine, and heart, followed by caudal white muscle, dorsal white muscle, stomach lining, and gill filament, then by gonad and gallbladder. We describe how ontogenetic diet shifts explain Hg bioaccumulation in pelagic predators inhabiting similar waters to lancetfish. We hypothesize that diet shifts to deeper-dwelling prey and fishes drive increases in THg and MeHg concentrations in large lancetfish. We propose lancetfish as a strong candidate for monitoring spatiotemporal variability of Hg in the deep pelagic – they are commonly captured in global fisheries and may reflect Hg sources in two distinct vertical habitats of the ocean. 

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2. Mercury stocks in discontinuous permafrost and their mobilization by river migration in the Yukon River Basin

   https://doi.org/10.1088/1748-9326/ad536e  

   Smith, M_Isabel; Ke, Yutian; Geyman, Emily_C; Reahl, Jocelyn_N; Douglas, Madison_M; Seelen, Emily_A; Magyar, John_S; Dunne, Kieran_B_J; Mutter, Edda_A; Fischer, Woodward_W; et al (August 2024, Environmental Research Letters)

   Abstract Rapid warming in the Arctic threatens to destabilize mercury (Hg) deposits contained within soils in permafrost regions. Yet current estimates of the amount of Hg in permafrost vary by ∼4 times. Moreover, how Hg will be released to the environment as permafrost thaws remains poorly known, despite threats to water quality, human health, and the environment. Here we present new measurements of total mercury (THg) contents in discontinuous permafrost in the Yukon River Basin in Alaska. We collected riverbank and floodplain sediments from exposed banks and bars near the villages of Huslia and Beaver. Median THg contents were 49⁺¹³/₋₂₁ng THg g sediment⁻¹and 39⁺¹⁶/₋₁₈ng THg g sediment⁻¹for Huslia and Beaver, respectively (uncertainties as 15th and 85th percentiles). Corresponding THg:organic carbon ratios were 5.4^+2.0/_−2.4Gg THg Pg C⁻¹and 4.2^+2.4/_−2.9Gg THg Pg C⁻¹. To constrain floodplain THg stocks, we combined measured THg contents with floodplain stratigraphy. Trends of THg increasing with smaller sediment size and calculated stocks in the upper 1 m and 3 m are similar to those suggested for this region by prior pan-Arctic studies. We combined THg stocks and river migration rates derived from remote sensing to estimate particulate THg erosional and depositional fluxes as river channels migrate across the floodplain. Results show similar fluxes within uncertainty into the river from erosion at both sites (95⁺¹²/₋₄₇kg THg yr⁻¹and 26⁺¹⁵⁴/₋₁₃kg THg yr⁻¹at Huslia and Beaver, respectively), but different fluxes out of the river via deposition in aggrading bars (60⁺⁴⁰/₋₂₉kg THg yr⁻¹and 10^+5.3/_−1.7kg THg yr⁻¹). Thus, a significant amount of THg is liberated from permafrost during bank erosion, while a variable but generally lesser portion is subsequently redeposited by migrating rivers. 

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3. Low mercury concentrations in a Greenland glacial fjord attributed to oceanic sources

   https://doi.org/10.1038/s43247-024-01474-9  

   Lindeman, M_R; Straneo, F.; Adams, H_M; Nelson, M_J_S; Schartup, A_T (June 2024, Communications Earth & Environment)

   Abstract As the role of the Greenland Ice Sheet in the Arctic mercury (Hg) budget draws scrutiny, it is crucial to understand mercury cycling in glacial fjords, which control exchanges with the ocean. We present full water column measurements of total mercury (THg) and methylmercury (MeHg) in Sermilik Fjord, a large fjord in southeast Greenland fed by multiple marine-terminating glaciers, whose circulation and water mass transformations have been extensively studied. We show that THg (0.23-1.1 pM) and MeHg (0.02-0.17 pM) concentrations are similar to those in nearby coastal waters, while the exported glacially-modified waters are relatively depleted in inorganic mercury (Hg(II)), suggesting that inflowing ocean waters from the continental shelf are the dominant source of mercury species to the fjord. We propose that sediments initially suspended in glacier meltwaters scavenge particle-reactive Hg(II) and are subsequently buried, making the fjord a net sink of oceanic mercury. 

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4. Mercury source changes and food web shifts alter contamination signatures of predatory fish from Lake Michigan

   https://doi.org/10.1073/pnas.1907484116  

   Lepak, Ryan F.; Hoffman, Joel C.; Janssen, Sarah E.; Krabbenhoft, David P.; Ogorek, Jacob M.; DeWild, John F.; Tate, Michael T.; Babiarz, Christopher L.; Yin, Runsheng; Murphy, Elizabeth W.; et al (November 2019, Proceedings of the National Academy of Sciences)

   To understand the impact reduced mercury (Hg) loading and invasive species have had on methylmercury bioaccumulation in predator fish of Lake Michigan, we reconstructed bioaccumulation trends from a fish archive (1978 to 2012). By measuring fish Hg stable isotope ratios, we related temporal changes in Hg concentrations to varying Hg sources. Additionally, dietary tracers were necessary to identify food web influences. Through combined Hg, C, and N stable isotopic analyses, we were able to differentiate between a shift in Hg sources to fish and periods when energetic transitions (from dreissenid mussels) led to the assimilation of contrasting Hg pools (2000 to present). In the late 1980s, lake trout δ 202 Hg increased (0.4‰) from regulatory reductions in regional Hg emissions. After 2000, C and N isotopes ratios revealed altered food web pathways, resulting in a benthic energetic shift and changes to Hg bioaccumulation. Continued increases in δ 202 Hg indicate fish are responding to several United States mercury emission mitigation strategies that were initiated circa 1990 and continued through the 2011 promulgation of the Mercury and Air Toxics Standards rule. Unlike archives of sediments, this fish archive tracks Hg sources susceptible to bioaccumulation in Great Lakes fisheries. Analysis reveals that trends in fish Hg concentrations can be substantially affected by shifts in trophic structure and dietary preferences initiated by invasive species in the Great Lakes. This does not diminish the benefits of declining emissions over this period, as fish Hg concentrations would have been higher without these actions. 

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5. Evaluating methods for determining mercury concentrations in ancient marine fish and mammal bones as an approach to assessing millennial-scale fluctuations in marine ecosystems

   https://doi.org/10.3389/fevo.2023.1251282  

   Avery, Julie P.; Castellini, J. Margaret; Misarti, Nicole; Keenan, Mary; Gastaldi, Angela; Funk, Caroline; O’Hara, Todd M.; Rea, Lorrie D. (October 2023, Frontiers in Ecology and Evolution)

   Parducci, Laura (Ed.)

   Millennial-scale datasets of heavy metals in biota are difficult to obtain but are important for determining patterns and underlying drivers of toxicant concentrations. This is particularly important to better discriminate contemporary natural and anthropogenic sources. Globally mercury is a contaminant of concern. Post-industrial increases in mercury in arctic biota have been documented and monitoring of Steller sea lions (Eumetopias jubatus) in the Aleutian Islands, Alaska, has revealed a high proportion of pups with fur mercury concentrations above thresholds of concern in some regions. As bone is a tissue that is well preserved in archeological middens, it may prove useful for developing long-term mercury data sets under appropriate conditions. The goal of this study was to evaluate methodologies for measuring mercury concentration in Steller sea lion bone using a direct mercury analyzer, considering sample preparation methods and variability among bone tissue types (e.g., compact versus spongy bone). Finally, we directly compare sensitivity and precision of two different direct mercury analyzer models. Based on the methods presented here, direct mercury analysis using the Nippon MA-3000 can quantify small (ppb) quantities of Hg accurately and precisely in 20 to 60mg of bone with minimal specimen processing. The described method is efficient, relatively inexpensive, and requires minimal bone, conserving rare and valuable specimens. Hydrogen peroxide cleaning and collagen extraction were not required, and may be detrimental for optimal Hg quantification in bone. Further, while homogenization of distinct compact and spongy bone did not impact concentration determination, variance of technical replicates was lower improving quantitation precision. Most importantly, significant differences between compact and spongy bone exist within some individual specimen; however, the difference is not consistent and may indicate differential Hg exposure windows influenced by turnover rate of bone types. We conclude bone provides a natural archive for mercury ecosystem dynamics over millennial time scales in regions where appropriate samples are available. Compact bone has lower and less variable [THg] simplifying analysis and interpretation of data; however, the more dynamic concentrations observed in spongy bone should not be dismissed as invaluable due to their variability in [THg]. Comparisons of [THg] between bone type within individual may provide insight into more acute changes in mercury exposure within an individual’s lifetime. 

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