US EPA 1999 — Mercury Update: Impact on Fish Advisories
This EPA Office of Water fact sheet (September 1999) summarizes total-mercury and methylmercury concentrations measured in US freshwater fish, the resulting state-level fish consumption advisories, and recommended monthly meal limits keyed to fish-tissue mercury. As of December 1998 mercury was the basis for 1,931 advisories in 40 states (an 8% one-year increase and 115% increase from 899 advisories in 1993). The fact sheet describes biomagnification factors, expected MeHg fraction of total Hg in fish, and gives a structured methylmercury risk-based consumption-limit table that has been widely adopted by state fish-advisory programs.
Key numbers
US National Contaminant Biomonitoring Program (NCBP), 315 composite whole-fish samples from 109 stations (1984–85): mercury maximum 0.37 ppm, geometric mean 0.10 ppm, 85th percentile 0.17 ppm wet weight. Mean tissue concentration of 0.12 ± 0.08 ppm in predatory species (trout, walleye, largemouth bass) was significantly higher than the mean of 0.08 ± 0.06 ppm in bottom feeders (carp, white sucker, channel catfish) (p. 2).
EPA National Study of Chemical Residues in Fish (NSCRF, 1987): mercury detected at 92% of 374 sites; fish-tissue maximum 1.77 ppm, arithmetic mean 0.26 ppm, median 0.17 ppm wet weight (p. 2).
Table 1 — Mean mercury concentrations in freshwater fish (ppm wet weight, Bahnick et al. 1994):
- Bottom feeders: Carp 0.11; White sucker 0.11; Channel catfish 0.09
- Predator fish: Largemouth bass 0.46; Smallmouth bass 0.34; Walleye 0.52; Brown trout 0.14
Table 2 — Mean and minimum-maximum ranges for Northeast US fish species (ppm wet weight, NESCAUM 1998): Largemouth bass mean 0.51 (range 0–8.94); Smallmouth bass 0.53 (0.08–5.0); Yellow perch 0.40 (0–3.15); Eastern chain pickerel 0.63 (0–2.81); Lake trout 0.32 (0–2.70); Walleye 0.77 (0.10–2.04); Brown bullhead 0.20 (0–1.10); Brook trout 0.26 (0–0.98). One largemouth bass sample contained 8.94 ppm; one smallmouth bass 5 ppm.
Marine fish mercury: Atlantic shark mean MeHg 0.88 µg/g wet weight across nine species; Northwest Atlantic bluefin tuna mean muscle Hg 3.41 µg/g dry weight (p. 2).
Bioconcentration / biomagnification: bioconcentration factor for MeHg in fish ~3 × 10^6; MeHg in predator fish ~7 million times higher than dissolved MeHg in surrounding water. Total Hg in apex predators (pike, shark, swordfish) ~10,000–100,000× higher than inorganic Hg in surrounding waters (p. 2).
MeHg fraction of total Hg in adult fish: 90–100% (p. 1, “Sources of Mercury in the Environment”).
Table 3 — EPA risk-based monthly fish-consumption limits for MeHg (assuming consumer body weight 72 kg, 8-oz meal size 0.227 kg, MeHg RfD 1×10^-4 mg/kg/day):
- 16 meals/month: tissue >0.03–0.06 ppm
- 12 meals/month: >0.06–0.08 ppm
- 8 meals/month: >0.08–0.12 ppm
- 4 meals/month: >0.12–0.24 ppm
- 3 meals/month: >0.24–0.32 ppm
- 2 meals/month: >0.32–0.48 ppm
- 1 meal/month: >0.48–0.97 ppm
- 0.5 meals/month: >0.97–1.9 ppm
- None (<0.5/month): >1.9 ppm
Advisory growth: mercury-based advisories rose from 899 in 1993 to 1,931 in 1998 (+115%). Number of states with advisories rose from 27 (1993) to 40 (1998). Top states by advisory count (1998): Minnesota 821, Wisconsin 402, Indiana 126, Florida 97, Georgia 80, Massachusetts 58, Michigan 53, New Jersey 30, New Mexico 26, South Carolina 24, Montana 22. Ten states issued statewide freshwater advisories; five Gulf Coast states issued statewide coastal-marine advisories.
EPA interim RfD for MeHg = 1×10^-4 mg/kg-day (cited from EPA IRIS, 1999c). Estimated lethal dose for acute MeHg exposure: 10–60 mg/kg. Estimated body half-life of MeHg in humans: 44–80 days.
Methods (brief)
Fact-sheet synthesis (not primary analysis); cites US EPA NSCRF (1987), US FWS NCBP (1984–85), Bahnick et al. 1994, NESCAUM 1998, and EPA 1997 Mercury Study Report to Congress. EPA position stated explicitly: in absence of speciated analysis, total Hg should be measured and the conservative assumption applied that all mercury in fish is present as MeHg. Concentrations reported on wet-weight basis except as noted; the bluefin tuna value cited from another source is reported on dry weight. Fact sheet does not report LOD/LOQ values. Sample numbers reflect site counts and composite-sample counts rather than individual fish.
Implications for wiki use
This source is a US fish-advisory framework anchor rather than a primary analytical study. It contributes freshwater-fish and seafood mercury occurrence context from cited national programs and state advisories, and it documents EPA’s conservative convention of treating fish-tissue total Hg as MeHg when speciation is unavailable.
For product routing, this source is strongest for fresh fish and freshwater fish, especially high-trophic recreational and subsistence-caught species. Its marine values for shark and bluefin tuna are useful as predatory-fish context, but the page should not be treated as a finished-product canned-fish or infant-food study.
For regulation pages, the source explicitly cites the EPA IRIS methylmercury RfD used to build fish-consumption advisory bands. The table is source-side advisory context, not a wiki-created threshold.
Wiki pages this source may touch
- mercury-methyl
- mercury-total
- fish
- freshwater-fish
- shark
- seafood
- fresh-fish
- fish-freshwater
- seafood
- epa-iris-methylmercury-rfd
Verification notes
- The manual-fetch PDF is a scanned EPA copy with no embedded text; values were checked against the rendered PDF pages and the public EPA PDF landing file.
- No DOI is assigned to this EPA fact sheet.
Page history
The five most recent substantive edits to this page. 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.