Melnyk et al. 2021 — Total mercury in anadromous fish, Penobscot River, Maine
This US EPA/ATSDR study measured total mercury concentrations in six species of anadromous fish (and roe) returning to the Penobscot River in Maine after dam removal restored fish passage. Samples were collected during two consecutive spawning seasons (2017 and 2018). The study compared mercury levels against EPA reference doses to assess risks for Penobscot Indian Nation members who consume these fish at traditional subsistence rates. All species except sea lamprey were within current consumption advisories at 40 g/day; sea lamprey consistently exceeded HQ > 1 and a recommendation was issued to avoid consumption. Wildlife risk for mink, otter, and eagle was also assessed.
Key numbers
Total mercury concentrations (µg/kg wet weight), combined means by species:
- Alewife (Alosa pseudoharengus): 90.8 µg/kg
- American shad (Alosa sapidissima): 72 µg/kg fillet; 8.62 µg/kg roe
- Blueback herring (Alosa aestivalis): 51.5 µg/kg
- Rainbow smelt (Osmerus mordax): 120 µg/kg
- Striped bass (Morone saxatilis): 166 µg/kg
- Sea lamprey (Petromyzon marinus): 628 µg/kg
Full range: 4 µg/kg ww (roe) to 1040 µg/kg ww (sea lamprey).
Human health evaluation at 40 g/day consumption (tribal advisory rate):
- Alewife, American shad, blueback herring, roe, rainbow smelt: HQ < 1 (safe at advisory rate)
- Striped bass 2017: two composites had HQ > 1 (confidence interval spanned 1)
- Sea lamprey: consistently HQ > 1 both years; not safe at any ingestion rate
Wildlife values exceeded:
- Mink (threshold 70 µg/kg): rainbow smelt, striped bass, sea lamprey
- Otter (threshold 100 µg/kg): striped bass, sea lamprey
- Eagle (threshold 160 µg/kg): sea lamprey
Mercury assumed 100% as methylmercury for conservative worst-case; RfD for MeHg = 0.1 µg/kg BW/day (EPA IRIS).
Methods (brief)
Fish collected during upstream spawning migration at Milford Dam fish lift, Penobscot River, ME (2017–2018). Tissue composited from 3–10 individual fish per composite, n=75 composites total. Total mercury by Direct Mercury Analyzer–80 (DMA-80) using thermal decomposition and amalgamation with atomic absorption spectrophotometry (US EPA SW-846 Method 7473). LOD = 0.013 ng/kg. Recovery >90%, RPD <5%. Moisture and lipid content also determined. Survey package methods in R used for clustered composite design. This is a US EPA Office of Research and Development manuscript published in Sci Total Environ 2021 (CC BY).
Implications
Certification: Provides US EPA-measured tHg baseline for anadromous fish species. Sea lamprey far exceeds safe consumption threshold; striped bass at moderate risk at high consumption rates. Values here are for recently dam-removed, restored river — not from heavily industrially impacted systems, providing a useful baseline for relatively “clean” river fish mercury. Resident fish from same river were previously found at 290–708 µg/kg, substantially higher.
Courses: Excellent illustration of mercury accumulation in fish, trophic-level effects (sea lamprey as a parasitic species at trophic level 4 concentrated mercury ~4-fold vs lower-level species), and culturally sensitive risk assessment for tribal subsistence fishing communities.
App: Anadromous fish category. Note that tHg was reported and assumed to be 100% methylmercury (MeHg) for the risk calculation. The wiki treats tHg and MeHg as non-substitutable; the conservative assumption here is noted. Actual MeHg fraction in fish is typically 90–100% of tHg.
Microbiome: Not addressed.