Nano- and Microplastics Found in Tuna and Mahi-Mahi Across Three Oceans

Tuna and mahi-mahi spend their lives in the open ocean, far from most sources of pollution. A new study finds that even there, tiny plastic particles have made their way into their muscle tissue. Researchers led by Texas A&M University measured nano- and microplastics in two ocean predators, dolphinfish (also known as mahi-mahi) and yellowfin tuna, across the Atlantic, Pacific and Indian Oceans, and found them in both species in every ocean basin they examined.

The open-access paper, “Ocean predators as indicators of nano- and microplastic prevalence in pelagic food webs,” was published on October 6, 2026 in Scientific Reports (DOI: 10.1038/s41598-026-72552-5). The corresponding author is Jay R. Rooker of Texas A&M University's Department of Marine Biology in Galveston, with co-authors from more than a dozen institutions in the U.S., Europe, Brazil, Australia, Taiwan, Turkey and Panama, including NOAA's Southwest Fisheries Science Center.

What the team did

• They analysed muscle tissue from dolphinfish (Coryphaena hippurus) and yellowfin tuna (Thunnus albacares) collected across three ocean basins.
• They used pyrolysis gas chromatography tandem mass spectrometry with a lipid correction. This method measures plastic by mass and polymer type, which lets it pick up particles too small to count under a microscope, including nanoplastics.

What they found

• Five plastics made up about 99%. Polycarbonate, polyethylene, polypropylene, polyvinyl chloride (PVC) and nylon-66 accounted for roughly 99% of the total nano- and microplastic concentration in both species.
• Polyethylene led. Polyethylene, one of the most common plastics in packaging, was the dominant polymer in both species, followed by nylon-66, polypropylene and PVC.
• Tuna often carried less. Body burdens were often markedly lower in yellowfin tuna than in dolphinfish from the same region or ocean basin.
• Higher on the food chain didn't mean more plastic. The researchers found no relationship between plastic load and trophic position (where a fish sits in the food web) for either species. Yellowfin tuna sat higher in the food web than dolphinfish in nearly all regions, yet had lower concentrations.
• Location left a signature. Polymer mix and concentration varied from place to place, which the authors say means a fish's plastic “signature” may mark its recent or longer-term exposure history.

The authors' conclusion: nano- and microplastics are pervasive in the muscle tissue of higher-order predators in open-ocean ecosystems across all three ocean basins.

The caveats

This study measured plastic in fish tissue. It did not test drinking water, did not measure how much plastic people take in by eating fish, and makes no human-health finding. The abstract reports patterns between species and regions rather than a single safe or unsafe level.

What it means for readers

Plastic particles turn up across the water cycle, from rivers and lakes to the open sea, and now in the muscle of fast-moving ocean predators. Studies like this one help scientists map where those particles travel and how they move through food webs. It's also a reminder to look at the method behind each headline: this team measured plastic by mass, which can capture nanoplastics that particle-counting methods miss.

A note on scope: this post summarises a peer-reviewed study. It is not medical or dietary advice, and WaterVO was not involved in the research.

Sources

• Rooker, J.R.; Kaiser, K.; Wells, R.J.D.; Zapp Sluis, M.; Gahn, M.B.; et al. “Ocean predators as indicators of nano- and microplastic prevalence in pelagic food webs.” Scientific Reports, published October 6, 2026. DOI: 10.1038/s41598-026-72552-5 · Article page

Photo: yellowfin tuna in the Gulf Stream, NOAA OAR/National Undersea Research Program (public domain).

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