Heavy Metal Index

Fish

3 min read

Fish

Stub page. Contamination profile populates on dedicated mercury and arsenic ingest waves. Fish is the dominant dietary source of methylmercury exposure for most populations (EPA Fish Advice).

Why this commodity accumulates heavy metals

Fish accumulate methylmercury through aquatic-food-web biomagnification: inorganic mercury in water is methylated by sulfate-reducing bacteria in sediment, taken up by plankton, and biomagnified through each trophic step. Predator species at the top of marine food webs (swordfish, shark, king mackerel, tilefish, bigeye tuna, marlin) carry methylmercury concentrations 1 to 2 orders of magnitude above small-pelagic species (sardines, anchovies, herring) and farmed or short-lived freshwater species (salmon, tilapia, trout). See mercury for the methylmercury toxicology, the JECFA 61st PTWI of 1.6 µg/kg b.w./week, and the Faroe Islands and Seychelles cohort literature on developmental neurotoxicity (synthesized in mercury).

Cadmium and lead in fish are commodity-secondary concerns; bivalve molluscs (covered separately at bivalve-molluscs) are the dominant marine-food Cd source (EFSA Cd 2009).

Multi-metal coverage and dedicated subpages

Fish-as-a-commodity is broad enough that future ingest waves will likely produce species-specific pages (tuna, salmon, swordfish) rather than a single fish page treating all species uniformly. The current page is a placeholder that satisfies the wikilink graph and orients consumers toward the dominant concern (methylmercury).

Collado-Lopez et al. 2025 reports fish/fish-mix baby foods as a priority review-level group for arsenic and mercury, with median As 0.165 mg/kg and median Hg 0.016 mg/kg among detected items. This signal should guide retrieval of the underlying primary studies before any fish-containing baby-food p90 is calculated. collado-lopez2025-heavy-metals-baby-food-formula

Regulatory limits that apply

  • jecfa-methylmercury-ptwi — JECFA provisional tolerable weekly intake of 1.6 µg methylmercury/kg b.w./week.
  • efsa-methylmercury-twi — EFSA tolerable weekly intake of 1.3 µg methylmercury/kg b.w./week.
  • EPA Fish Advice — FDA/EPA joint advice for women who might become pregnant, women who are pregnant or breastfeeding, and young children.
  • eu2023-contaminants-maximum-levels and eu-2023-915-cadmium — EU fish maximum levels are species- and tissue-specific. General muscle meat of fish is 0.30 mg/kg (300 ug/kg) Pb, 0.050 mg/kg (50 ug/kg) Cd, and 0.50 mg/kg (500 ug/kg) Hg; listed lower-mercury fish are 0.30 mg/kg (300 ug/kg) Hg, and listed higher-mercury fish including tuna, shark, swordfish, marlin, halibut, pike, and sturgeon are 1.0 mg/kg (1000 ug/kg) Hg.

Sources