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Contaminants & Science
Mercury, microplastics, PCBs — real concerns, real evidence. Here is what the science actually shows, without the fear or the dismissal.
Note: This page summarizes publicly available evidence and FDA/EPA guidance. It is not medical advice. Pregnant women, nursing mothers, and young children should follow current FDA advisory guidelines on fish consumption. For all other adults, regular consumption of low-contaminant fish is consistently associated with positive health outcomes in large-scale studies.
The Contaminants, One at a Time
Mercury released by coal combustion and industrial discharge bioaccumulates through the food chain. Long-lived, high-trophic predators concentrate it most. It is a neurotoxin with dose-dependent effects.
Higher concern species
- • Swordfish
- • King mackerel
- • Tilefish (Gulf of Mexico)
- • Shark
- • Bigeye tuna
Lower concern species
- • Salmon
- • Pollock
- • Catfish
- • Sardines
- • Shrimp
- • Tilapia
- • Pacific cod
What the evidence supports
The FDA/EPA advise pregnant women and young children to avoid high-mercury species and limit albacore tuna to 6 oz/week. For the general population, the omega-3 benefit of low-mercury fish clearly outweighs the mercury risk at typical consumption levels. The problem is specific species eaten frequently, not seafood in general.
PCBs (polychlorinated biphenyls) are industrial chemicals banned in 1979 but still present in aquatic sediments. They accumulate in fat tissue. Long-lived, high-fat fish from contaminated watersheds carry the highest loads.
Higher concern species
- • Farmed Atlantic salmon (historical — improving)
- • Striped bass (Great Lakes)
- • Bluefish
Lower concern species
- • Alaska salmon
- • Pacific halibut
- • Shrimp
- • Tilapia
- • Most open-ocean fish
What the evidence supports
PCB levels in most commercially sold fish are well below regulatory action levels. Wild Alaska salmon tested consistently low. The primary practical guidance: trim fat from fish (where PCBs concentrate) when eating high-fat species from known-contaminated areas. Open-ocean wild fish are generally safer than freshwater or near-shore farmed fish from legacy contamination zones.
Plastics degrade into particles smaller than 5mm that marine organisms ingest. Research is ongoing. Current evidence on human health effects from dietary microplastic ingestion is limited — plausible concern, not established harm.
Higher concern species
- • Bivalves (oysters, mussels, clams) — whole-body consumption
- • Small fish eaten whole (sardines, anchovies)
Lower concern species
- • Fish fillets — microplastics concentrate in digestive organs, not muscle tissue
What the evidence supports
The science on microplastics in seafood is early-stage. Human health effects from current dietary exposure are not established by current evidence. Bivalve consumers ingest the highest loads because the whole organism is eaten. For fish fillets, microplastics in the gut are removed with cleaning. The precautionary argument favors reduced plastic in the environment; the evidence for individual dietary risk is not yet sufficient for species-specific avoidance recommendations.
Some aquaculture operations use antibiotics, pesticides (for sea lice), and antifoulants. Residues are regulated by the FDA in imported seafood; enforcement has been inconsistent on imports from some countries.
Higher concern species
- • Imported farmed shrimp (some sourcing regions)
- • Farmed tilapia (some import sources)
- • Farmed salmon (varies by country)
Lower concern species
- • U.S. domestic aquaculture — more regulated
- • Certified organic aquaculture
- • RAS (recirculating) operations
What the evidence supports
Buy U.S.-raised farmed fish when possible, or look for ASC or equivalent certified products. Wild-caught fish have no aquaculture input exposure. The resistance concern (antibiotic-resistant bacteria) is the more serious long-term issue, not direct toxicity from residues.
Practical Rules
Vary your species. Eating the same fish weekly concentrates any single contaminant.
Pregnant women and young children: follow FDA guidance on mercury-high species. For everyone else, eat 2–3 servings of low-mercury fish per week.
Trim fat from high-fat species if you are eating fish from contaminated freshwater areas.
For bivalves: buy from certified, regularly tested harvest areas. Closures exist for a reason.
Wild Alaska seafood — salmon, halibut, cod, sablefish — consistently tests at very low contaminant levels.
The nutrition benefit of regular seafood consumption (omega-3s, protein, micronutrients) is well-established and substantially outweighs contamination risk for most species at normal consumption.
The Bigger Picture
The scientific consensus is clear: eating two to three servings of low-mercury fish per week is associated with measurable reductions in cardiovascular disease, improved cognitive outcomes, and better overall health. The omega-3 fatty acids in seafood have no equivalent substitute in a typical diet. Avoiding fish entirely because of contaminant concern is a decision that trades a documented benefit for a poorly quantified risk. The strategy is not avoidance — it is informed selection.