Computational Toxicology and Exposure, Great Lakes Toxicology and Ecology Division, 6201

Overview

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Key numbers

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• of legacy Hg was estimated in biota and demonstrated that up to 64% of the Hg in fish tissue
• (Eckley et al. 2020). One such application is the use of light stable isotopes (e.g., carbon
• evidenced by the fact that 10 % of fish collected during monitoring assessments exceeded
• AOC assessment (Janssen et al., 2021b; see Electronic Supplementary Material (ESM) Table
• composited (2–3 whole fish per sample) based on total length (limited to a range of 75–150
• alongside samples and had recoveries of 29 ± 1.1 ng g−1 (100 ± 4 % recovery, n = 14)
• Quality control and assurance was measured by sample replicates (< 10 % deviation),
• standard spike recovery (75–125 % recovery), and CRM recovery (IAEA 405 = 5.0 ± 0.20
• ng g−1, 92 ± 3 % recovery, n = 6). The method detection limit for MeHg in sediments by
• IAEA 407 was processed alongside samples and had acceptable recoveries for MeHg (197
• ± 7 ng g−1, 98 ± 3, n = 6) and total Hg (235 ± 4 ng g−1, 106 ± 2 % recovery, n = 6).
• 2.3. Mercury stable isotope analysis
• the same heating protocol but were amended with bromine monochloride (BrCl, 10 % total
• using gold trap amalgamation coupled to collection in an oxidant trap (40 % 3 HNO3: BrCl)
• (1 %) then passed through an anion-exchange resin (AG1-X4) and the eluate was saved
• for further sample pre-concentration (Janssen et al., 2019). Samples had greater than 85 %
• measurement precision and accuracy, isotopic recoveries are reported in ESM Table S2
• releases for this study (Janssen et al., 2021a; Janssen et al., 2023b) and ESM Tables S4–S6.
• biota values had low to undetectable Δ200Hg, an indicator of precipitation-derived Hg
• Total Hg in sediment in the St. Louis River AOC ranged from 4.80 (Superior Bay nearshore)
• n = 59), and sites planned for remediation (termed remedial sites, 1250 ± 1660 ng g−1,
• n = 80) were all significantly (P < 0.05, unpaired t-test) higher than sediments previously
• across the nearshore habitats (0.88 ± 0.91 ng g−1, n = 48), main channel zones (1.50 ± 1.72
• ng g−1, n = 59), remedial sites (1.19 ± 0.78 ng g−1, n = 59, barring Howards Bay), and
• reference sites (0.77 ± 1.05 ng g−1, n = 40). However, maximum MeHg concentrations were
• reference site had significantly (p < 0.05) higher % MeHg within sediments (3.4 ± 2.0 %)
• remedial sites (0.53 ± 0.44 %) (Fig. 1b).
• Hg, and precipitation Hg. Nearshore sediment δ202Hg values ranged from −0.52 to −1.16
• ‰, similar to the range previously measured in main channel sediments. Minimal Δ199Hg
• for precipitation, ranged from −0.02 to 0.09 ‰ across the estuary with the highest values
• calculations outlined above, we find, on average, legacy Hg contributes 28 ± 13 % of the
• Hg to sediment total Hg are significantly higher in the Superior Bay (38 ± 16 %) and St.
• Louis Bay (42 ± 8 %) zones when compared to the less impacted Allouez Bay (23 ± 6 %)
• Lac region (10 ± 5 %) (Fig. 2). Despite the presence of legacy Hg in the lower estuary,
• ± 7 % of the nearshore sediment Hg in Boyscout, 59 ± 10 % in Allouez Bay, and almost
• Superior (Lepak et al., 2015) with the exception of Allouez Bay, which ranged from 32–39
• yellow perch composites, Hg concentrations ranged from 69.5 ± 11.5 ng g−1 wet weight
• 50.3 ± 6.9 (n = 5), respectively (Fig. 3a). The remedial site, Pickle Pond, was observed to
• ng g−1, n = 7). All concentrations in the St. Louis River were lower than yellow perch Hg
• relatively consistent concentrations across the river (30.7 ± 10.5 ng g−1, n = 43, all sites)
• and the lowest measured concentrations in Pickle Pond (22.0 ± 8.3 ng g−1, n = 4). When
• bioaccumulation of MeHg (80 % or more MeHg within biological tissue), which could

Methods (brief)

• evidenced by the fact that 10 % of fish collected during monitoring assessments exceeded
• sites with planned remediation (i.e., sampled before remedial action), which may over or
• It is important to note that samples for this project were collected prior to the complete
• Briefly, sediments were collected using an Ekman dredge in nearshore depositional zones.
• Biological samples assessed in this study were collected across multiple field campaigns
• Dragonfly larvae samples were collected via dipnet, sorted in the field, placed in clean
• were collected by electrofishing by EPA ORD GLTED. Fish fillets were collected and
• composited (2–3 whole fish per sample) based on total length (limited to a range of 75–150
• mm). After compositing, muscle samples were stored frozen until analysis.
• Hg was measured via combustion coupled to cold vapor atomic absorption spectroscopy
• (CVAAS) following established protocols (U.S.EPA, 1998). Certified reference materials
• alongside samples and had recoveries of 29 ± 1.1 ng g−1 (100 ± 4 % recovery, n = 14)
• plasma mass spectrometry (ICP-MS). Briefly, during distillations samples were amended
• with an isotopically enriched internal Hg standard. After distillation, samples were ethylated
• and purged onto Tenax traps prior to gas chromatography separation and ICP-MS analysis.
• Quality control and assurance was measured by sample replicates (< 10 % deviation),
• total Hg concentrations using a multi-step weak nitric acid (HNO3) digestion approach
• (Hammerschmidt and Fitzgerald, 2006). Briefly, biota samples were digested in 4 N HNO3

Implications

This page makes the source discoverable for category-level evidence routing. Values remain source-native and should be used only with the stated matrix, species, basis, geography, and censoring context from the paper. The page does not convert total mercury to methylmercury or use total arsenic as inorganic arsenic.

Wiki pages this source may touch

• Fish — marine, predatory (tuna, swordfish, shark, king mackerel)
• Fish — marine, non-predatory (sardines, anchovies, salmon, cod)
• Mercury
• Mercury
• Tin

Verification notes

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.