Some Pre-Cooked Seafood May Carry More Chemicals Than Raw Fish, Study Finds

Millions of shoppers grab a ready-to-heat seafood dinner every week, won over by a fish dish that only needs a few minutes in the microwave. A new study from Spain found that shrink-wrapped fillets and frozen shrimp dishes tend to carry more than just omega-3s: a mix of industrial chemicals that can leach from plastic packaging and during cooking. The reassuring part is that the measured amounts stayed below the safety limits that health agencies rely on.

Researchers wanted to know what tags along in convenience seafood, so they looked past the usual focus on raw fish. Published in the journal Analytical and Bioanalytical Chemistry, their work is the first to screen a broad set of “high production volume chemicals,” compounds churned out at more than 500 tons a year, in ready-made seafood meals. These substances turn up in plastic wrap, electronics, perfumes, and flame-resistant coatings.

Every chemical family the team searched for showed up in at least one of the 18 dishes tested, a lineup that spanned squid, salmon, shrimp, sardines, mussels, hake, and cod, some of the most popular seafood in Spain’s Catalonia region. Two benzothiazole compounds, OHBT and NH2BT, were the exceptions, landing either undetectable or too faint to measure. Levels in the cooked meals generally were higher than those found in earlier studies of raw fish and shellfish from the same waters, suggesting that processing and packaging may contribute to contamination rather than the seafood carrying it alone.

Which Industrial Chemicals Turned Up in Pre-Cooked Seafood?

Chemists at Universitat Rovira i Virgili in Tarragona tested for five chemical families. Phthalates, used to make plastics soft and flexible, have been tied to hormone disruption and reproductive concerns. The rest included flame retardants, synthetic fragrances found in soaps and cleaners, and two families used in dyes, disinfectants, and industrial coatings.

Phthalates were the heaviest presence across nearly every meal. Two hake dishes stood out for sky-high di-n-octylphthalate (DnOP) readings, which topped out near 3,969 nanograms per gram and pulled the averages up almost single-handedly. Mussels told a different story, where a flame retardant called TEHP dominated, reaching 2,540 and 2,123 nanograms per gram in the two mussel dishes. A nanogram is a billionth of a gram, so even these peaks represent tiny absolute amounts.

One pattern jumped out. Oily, fat-seeking chemicals like flame retardants and synthetic musks piled up in fattier fish such as salmon and sardines. Phthalates leaned the other way, appearing more in lean fish like cod and hake, a clue pointing to packaging as a likely source rather than buildup inside the fish itself.

How Packaging and Cooking Add to the Chemical Load

Meals fell into three groups based on how they were sold: freshly cooked in bulk, refrigerated in single portions, and frozen. Nearly all sat in some form of plastic. Packaging style and cooking method both seemed to sway which chemicals ended up in the food, though the study could not tie any single packaging type or cooking method to consistently higher or lower levels.

Because the cooked dishes carried more contamination than raw seafood from the same area, something between the boat and the plate appears to add to the load. Earlier work cited in the study backs this up: grilling fish can cause certain phthalate levels to climb, and time spent in plastic during storage or reheating can allow flame retardants to migrate into the food.

Who Eats the Most Pre-Cooked Seafood, and Who’s Most Exposed?

To turn lab readings into real diets, the researchers estimated how much of each chemical each of six groups would consume, based on known eating habits in Catalonia: adult men, adult women, teenage boys, teenage girls, men over 65, and women over 65.

Senior men landed at the top of the exposure list, and not because their food was any dirtier. Older men in this region simply eat more seafood than anyone else studied. The researchers ran the estimates under three scenarios, from cautious to worst-case, and the answer held every time. Even the worst-case scenario for the most exposed group remained below the level that would raise a flag.

For chemicals that might cause cancer, the team used a margin-of-exposure method, comparing human intake against a benchmark dose drawn from animal studies. The gaps came out far wider than the point where European regulators start to worry. Non-cancer risks followed the same pattern, remaining a small fraction of the harmful threshold.

What It Means for Seafood Lovers

In Spain, ready-to-heat seafood has become a grocery staple, accounting for 37% of pre-cooked meal sales between 2022 and 2023, according to figures cited in the study. As shoppers keep reaching for food that heats in minutes, knowing what rides along in the tray matters, even when today’s science calls the risk low.

None of this turns a fish dinner into something to fear. It does suggest that plastic wrapping and factory processing may leave a trace worth watching, which is why the authors call for more work. For now the numbers look manageable, but the long game, years of small daily doses of chemical mixtures, sits outside what this study set out to measure.

Disclaimer: This article summarizes a single peer-reviewed study for general information and is not medical, dietary, or health advice. The findings reflect 18 pre-cooked seafood meals bought in one region of Spain and may not apply elsewhere. The study estimated exposure and risk under specific conditions and did not measure long-term or combined exposure from all foods. Anyone with questions about seafood, chemical exposure, or their own diet should consult a qualified healthcare professional.

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