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Metals and PFAS concentrations in aquatic environments and fish of the Brooks Range, Alaska

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Fish muscle, sediment, plants and invertebrates were sampled along the Dalton Highway and in three western Brooks Range rivers. Mean total mercury in fish muscle ranged from not detected in slimy sculpin to about 270 µg/kg wet weight in northern pike. Only a few large predators passed the levels at which Alaska advises eating fewer meals, and lead was not detected in most fish.

Key numbers

All values are total mercury (THg), µg/kg wet weight, muscle; means of site means with n fish in parentheses (Table 2, p. 7):

  • Northern pike: Dalton Highway waterbodies 270 (2), Koyukuk River 274 (6), John River 134 (4), Alatna River 204 (10).
  • Arctic grayling: Dalton Highway 32 (29), Koyukuk 140 (1), John 34 (12), Alatna 137 (11), Kobuk 152 (10).
  • Burbot, Dalton Highway: 93 (5). Slimy sculpin: not detected at all sites sampled. Other species: 28 to 109.
  • Highest single fish: northern pike from the Koyukuk River, 990 µg/kg; a large lake trout from Island Lake, 510 µg/kg (p. 11).
  • Arctic grayling were higher in the western rivers (mean 102.75 µg/kg) than at Dalton Highway sites (35.80 µg/kg); pike did not differ (273.33 versus 183.93 µg/kg) (p. 16).
  • Lead was not detected in larger-bodied fish in any river; arsenic was intermittently detected below 130 µg/kg except Kobuk River inconnu, 100 to 14,000 µg/kg (p. 16).
  • Screening levels applied: US FDA “Choices to Avoid” above 460 µg/kg; Alaska Department of Health categories above 200 µg/kg (16 meals a month) to above 1360 µg/kg (“Do Not Eat”) (p. 9).

Methods (brief)

Dorsal muscle without skin, homogenized; THg, total arsenic, copper, zinc and lead by EPA SW-846 6020B and 7471A at a commercial laboratory (p. 9). Non-detects were set to half the minimum detection limit only when averaging mixed groups. Detection limits vary by sample and are listed in the supplement (Table S4).

Limitations: total mercury only (methylmercury not measured; the authors cite earlier work showing over 94% is methylmercury in northern Alaska fish). Group sizes are small and some samples are composites. Wild-caught subsistence fish, not market fish.

Implications

Certification: Adds wet-weight muscle THg for wild northern freshwater species, with species and fish size as the main drivers.

Courses: A clear example of predator and size effects on fish mercury.

App: Supports low mercury estimates for grayling and whitefish and moderate ones for pike.

Microbiome: Not applicable.

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