Enhanced Susceptibility of Methylmercury Bioaccumulation into Seston of the Laurentian Great Lakes

Abstract

Mercury concentrations in the Laurentian Great Lakes waters are among the lowest reported in the literature, while game fish concentrations approach consumption advisory limits, particularly in Lakes Superior, Huron, and Michigan, indicating efficient methylmercury transfer from water to game fish. To determine if increased transfer efficiency is evident within the lower food web, we measured (2010−2018) mercury and dissolved organic carbon (DOC) in water, and in size-sieved seston, dietary tracers (carbon and nitrogen isotope ratios), phytoplankton methylmercury bioaccumulation, and methylmercury biomagnification between increasing seston size fractions. We observed consistently low filter-passing methylmercury (<0.010 ng L −1 ) and comparatively variable DOC (1.1 to 3.4 mg L −1 ) concentrations. Methylmercury biomagnification factors between size-sieved seston were similar between lakes. Bioaccumulation factors in phytoplankton were among the highest in the literature (log 5.5 to 6.1), exceeding those in oceans, smaller lakes, and streams, and was influenced by DOC. Higher bioaccumulation rates increase the susceptibility of methylmercury accumulation into the food web. Because mercury is dominantly delivered to the Great Lakes through the atmosphere and the biota therein is highly susceptible to methylmercury uptake, we propose that the Laurentian Great Lakes are excellent sentinels to trace the success of efforts to decrease global mercury emissions (e.g., Minamata Treaty) in the future.

Using Carbon, Nitrogen, and Mercury Isotope Values to Distinguish Mercury Sources to Alaskan Lake Trout

“…For plankton analyses, SRM IAEA 452 (Scallop - Pecten. Maximus ) recoveries were consistently within 10% of reported values, reagent blanks were negligible, and an in-house secondary standard to verify ongoing instrument calibration was within 10% of expected concentration …”

“…Unacidified filter-passing water was collected, refrigerated, and analyzed for dissolved organic carbon (DOC; Tables S2–S3). Details of ancillary water analyses and associated quality control procedures can be found on the U.S. Geological Survey Mercury Research Laboratory (USGS-MRL) website. ,, Seston were collected by vertical tows in the surficial 20 m with a 52 μm Nitex mesh net and subsequently size sieved (Table S4). …”

Plankton population dynamics and methylmercury bioaccumulation in the pelagic food web of mine-impacted surface water reservoirs

“…Under reducing conditions, anaerobic microorganisms convert inorganic Hg into neurotoxic methylmercury (MeHg), which bioaccumulates in aquatic ecosystems (Bigham et al, 2017 ). Methylmercury concentrates in suspended particulate matter (SPM), which serves as the main source of MeHg to the pelagic food web (Ogorek et al, 2021 ). Further accumulating in zooplankton and their predators through dietary intake, MeHg concentrations in fish can exceed aqueous concentrations by 7 orders of magnitude (Ogorek et al, 2021 ).…”

“…Methylmercury concentrates in suspended particulate matter (SPM), which serves as the main source of MeHg to the pelagic food web (Ogorek et al, 2021 ). Further accumulating in zooplankton and their predators through dietary intake, MeHg concentrations in fish can exceed aqueous concentrations by 7 orders of magnitude (Ogorek et al, 2021 ). Ingestion of fish contaminated with MeHg can cause a range of neurological, reproductive, and cardiovascular defects in humans (Hong et al, 2012 ), and behavioral, neurochemical, hormonal, and reproductive changes in mammals, birds, and fish (Scheuhammer et al, 2007 ).…”

“…In this field study, we assessed factors governing the uptake of Hg and MeHg into SPM and zooplankton in four Hg-impaired surface water reservoirs over four seasons from 2019 to 2021. We focused on uptake into the base of the pelagic food web because this is known to be the key step that controls MeHg concentration in fish (Lehnherr, 2014 ; Wu et al, 2019 ; Ogorek et al, 2021 ). Combining water chemistry data, algal and zooplankton taxonomic composition, and stable C and N isotope values of SPM and zooplankton samples, we investigated key differences between the reservoirs that may contribute to discrepancies in Hg and MeHg bioaccumulation.…”