Canadian aquatic physiology researcher Laura McDonnell quit eating fish, but not for the usual environmental reason like protecting endangered stock or because of the taste. She’s too aware of fraud and plastic pollution to put herself at risk.

At The Walrus, McDonnell explains how mislabeled fish makes it onto our dinner plates, and how mislabeling a mackerel for a tuna, say, can have health consequences. She doesn’t dislike fish or want to quit it, but there are just too many players in the supply chain to identify the culprits in frauds. Worse yet are the pollutants: with the staggering amount of microplastic now floating in the Earth’s aquatic systems, she doesn’t believe there is any natural body of water pure enough to produce a safe, edible fish, so she quit. Even to a diehard fish-eater like me, who eats canned saury for breakfast and sardines for lunch, she makes a convincing case.

As much as I love fish, I can’t pretend that they’re wise animals with refined palates. Researchers have found that when given the choice between natural and microplastic food items, fish tend to choose the plastic. For most aquatic animals, finding food while avoiding predators is a struggle, so being picky or discerning is not evolutionarily beneficial; most species grab their desired snack quickly and head right back to their hiding place. As a result, aquatic animals often ingest floating bits of plastic, either by confusing colourful microplastics for something else, or by ingesting plastic-contaminated prey. Filter-feeding animals such as clams, oysters, and mussels obtain their nutrients by sucking in water, trapping small floating particles within in it, and then spitting the water back out. Mussels are so efficient at this process that they’ve been used to clear up polluted waterways. Unfortunately, much of what they trap these days is plastic: a recent study estimated that the average European could ingest about 11,000 microplastics per year just by including mussels and oysters in their diet.

Due to bioaccumulation (when a substance’s concentration increases in an animal over time) and biomagnification (when a substance’s concentration increases as it moves up the food chain), the concentration of microplastics in larger, older, and predatory fish such as tuna is likely to be higher than in smaller species or younger individuals. So what happens to other top predators—humans—who eat a seafood-rich diet during their lifetime? Even though current research shows we do not absorb most plastics, it’s possible that a small amount (about 1 percent) can still accumulate in our bodies over time.

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