Cross‐basin comparison of mercury bioaccumulation in Lake Huron lake trout emphasizes ecological characteristics

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This study collected multiple age classes of lake trout from Lake Huron's Main Basin, Georgian Bay, and North Channel regions to compare and contrast top predator polychlorinated biphenyl (PCB) bioaccumulation patterns in separate compartments of the same ecosystem. Sum PCB concentrations were highest for Main Basin (260 ± 24.9 ng g(-1) wet wt) fish, followed by Georgian Bay (74.6 ± 16.2 ng g(-1) ) and North Channel (42.0 ± 3.3 ng g(-1)) fish. Discriminant functions analysis of lake trout PCB profiles and stable carbon (δ(13)C) and nitrogen (δ(15)N) isotope values clearly distinguished fish by location, indicating high degrees of basin fidelity throughout their lifetimes in addition to highly contrasting PCB bioaccumulation profiles. These unique profiles were not attributable to significant differences in lake trout lipid contents (p = 0.856) or trophic position (δ(15)N; p = 0.334), with rainbow smelt representing the primary prey across the basins. Furthermore, significant differences were observed among the basins for the relationships between PCB biomagnification factors and hydrophobicity. An empirical model for predicting PCB biomagnification in Lake Huron lake trout indicated that basin-specific population growth rates and prey abundances were significant for explaining these contrasting patterns of PCB bioaccumulation. The results of the present study are fundamental for understanding the role of ecology in legacy persistent organic pollutant (POP) bioaccumulation. Specifically, ecosystem characteristics such as prey abundances, foraging ecology, and ultimately consumer growth can regulate the variability of legacy POP bioaccumulation as observed within and among a wide range of freshwater ecosystems.

Section: Discussionsupporting

confidence: 89%

Section: Discussionsupporting

confidence: 78%

Section: Discussionsupporting

confidence: 52%

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Contrasting PCB bioaccumulation patterns among Lake Huron lake trout reflect basin‐specific ecology

Paterson

Ryder

Drouillard

et al. 2015

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“…The PCB bioaccumulation patterns we have demonstrated in Lake Huron fish also demonstrate the utility of lake trout as a biomonitor in that basin-specific congener profiles evident in this top predator are conserved among lower trophic level species for which bottom-up processes regulate pollutant exposure. Furthermore, our results and those of Abma et al (2015), Paterson et al (2016), andMcLeod et al (2019) support continued monitoring programs that emphasize the importance of basin-specific management strategies for quantifying and understanding the roles of multiple stressors on pollutant bioaccumulation and biomagnification in Great Lakes ecosystems. Specifically, although the transfer of energy and pollutants in Lake Huron's Main Basin, Georgian Bay, and North Channel food webs are facilitated by predator-prey interactions among the same species and similar hierarchical trophic structures, it is potentially differences in the strengths of such interactions within lower trophic levels that regulate energy flow and PCB bioaccumulation patterns in these food webs (Bartley et al 2019).…”

Section: Discussionsupporting

confidence: 69%

“…However, the extent to which such ecological restructuring has occurred in the food webs from each of Lake Huron's 3 basins remains unknown. Recent studies have demonstrated contrasting responses among Lake Huron lake trout with respect to mercury (Hg) and polychlorinated biphenyl (PCB) bioaccumulation in fish collected from each of the lake's 3 basins (Abma et al 2015;Paterson et al 2016). These include a general concentration gradient for Hg and total PCB concentrations with Main Basin > Georgian Bay > North Channel fish and unique PCB congener profiles for fish depending on the basin of collection (Abma et al 2015;Paterson et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Basin‐Specific Pollutant Bioaccumulation Patterns Define Lake Huron Forage Fish

Paterson

Pierdomenico

Haffner

2020

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The Lake Huron ecosystem is unique among the Laurentian Great Lakes (USA/Canada) in that its surface area encompasses 3 distinct basins. This ecosystem recently experienced significant ecological restructuring characterized by changes in primary production, species dominance and abundances, and top predator energy dynamics. However, much of the evidence for this restructuring has been largely derived from biomonitoring data obtained from long‐term sampling of the lake's Main Basin. We examined polychlorinated biphenyl (PCB) concentrations and the stable isotopes of carbon (δ13C) and nitrogen (δ15N) in rainbow smelt (Osmerus mordax), bloater (Coregonus hoyi), and round goby (Neogobius melanostomus) to determine spatial variability in these environmental markers as indicators of the ubiquity of trophic restructuring throughout Lake Huron. Stable isotopes indicated that North Channel fish occupied trophic positions between 0.5 and 1.0 lower relative to Main Basin and Georgian Bay conspecifics, respectively. Sum PCB concentrations for 41 congeners were highest for fish from the Main Basin (27.5 ± 3.0 ng g−1 wet wt) and Georgian Bay (26.3 ± 3.4 ng g−1 wet wt) relative to North Channel (13.6 ± 1.2 ng g−1 wet wt) fish. Discriminant functions analysis demonstrated basin‐specific PCB congener profiles with individual species also having distinct profiles dependent on their basin of collection. These bioaccumulation patterns among Lake Huron forage fish mirror those reported for lake trout in this lake and indicate that the degree of food‐web ecological restructuring in Lake Huron is not equivalent across the basins. Specifically, basin‐specific PCB congener profiles demonstrated that differences among Lake Huron secondary and top predator consumer species are likely dictated by cross‐basin differences in zooplankton community ecology and trophodynamics that can regulate the efficiencies of prey energy transfer and PCB congener bioaccumulation patterns in aquatic food webs. Environ Toxicol Chem 2020;39:1712–1723. © 2020 SETAC

Critical perspectives on mercury toxicity reference values for protection of fish

Fuchsman

Henning

Sorensen

et al. 2016

Environmental management decisions at mercury-contaminated sediment sites are predicated on the understanding of risks to various receptors, including fish. Toxicity reference values (TRVs) for interpreting risks to fish have been developed to assess mercury concentrations in fish or fish prey. These TRVs were systematically evaluated based on several lines of evidence. First, their conceptual basis and specific derivation were evaluated, including a close review of underlying toxicity studies. Second, case studies were reviewed to investigate whether TRVs are predictive of effects on fish populations in the field. Third, TRVs were compared with available information regarding preindustrial and present-day background concentrations of mercury in fish. The findings show that existing TRVs are highly uncertain, because they were developed using limited data from studies not designed for TRV derivation. Although field studies also entail uncertainty, several case studies indicate no evidence of adverse effects despite mercury exposures that exceed the available TRVs. Some TRVs also fall within the range of background mercury concentrations in predatory or prey fish. Lack of information on the selenium status of mercury-exposed fish is a critical confounding factor, and the form of methylmercury used in toxicity testing may also contribute to differences between TRV-based predictions and field observations of mercury effects on fish. On balance, the available information indicates that several of the TRVs reviewed are lower than necessary to protect fish populations. The 20% effect concentration from a previously published dose-response analysis appears closer to an effect threshold, based on available laboratory data. Additional research is needed to provide a stronger basis to establish dose-response relationships for mercury effects on fish.