Plastic pollution is filtering up into the fish that we eat

As an agrarian civilization, almost all of what humans eat is farmed — with the notable exception of seafood. Aside from some farmed fish, most seafood we consume is still caught in the wild. Yet while it might seem that there is something more pure and traditional about consuming "wild" food as opposed to farmed food, the seafood that we eat soaks in a sea contaminated by plastic — and it turns out that a lot of that pollution may be making its way into our bodies via seafood. 

Indeed, when it comes to plastics, consumers of seafood may be eating so much of the pernicious pollution that they are regularly chowing down on the equivalents of soda bottles and credit cards. Yet you will never hear a literal "crunch," and the reason for this is simple, unsettling and disgusting: The plastic in your seafood is "microplastic," a term for any plastic particle that is less than 5 mm in length.

Though you can neither feel or taste it (usually), the odds are high that it is in your seafood. The most recent example of this came from a 2022 study in the scientific journal Marine Pollution Bulletin. It found that three out of four commercial fish species from Australia and New Zealand contained microplastics in their edible flesh. On average there were 2.5 microplastic particles for each fish.

Nor is this the only study to discover microplastics in the seafood we eat.

"The presence of microplastics in commercial seafood is well-documented on a global scale for finfish as well as shellfish like mussels, clams, oysters, and shrimp," Dr. Britta Baechler, Associate Director of Ocean Plastics Research at Ocean Conservancy, told Salon by email. Baechler cited a recent review study that found that 60% of fish examined globally contained microplastics; it also found that carnivorous fish tend to contain more microplastics than omnivores. "This is particularly notable considering that many commercially important fish species are carnivorous," Baechler added.

Baechler explained that animals which eat through filter-feeding, including bivalves such as oysters and claims, are vulnerable to contaminants in large part because they pump massive quantities of water through their bodies every day. That is how filter-feeders extract their food.

"Microfibers – threadlike plastics frequently shed from clothing and textiles – are the most common form of microplastics ingested by marine fish, crustaceans, and bivalves in most studies to date," Baechler told Salon.

John Hocevar, a marine biologist and director of Greenpeace's oceans campaign, emphasized the pervasiveness of microplastics when explaining how they contaminate seafood. Because microplastics are prevalent in soil, they get sucked into plants through their roots. They enter the water itself, while the smallest particles can become airborne. When they rain back down, they enter the oceans.

"According to the UN, there are over 50 trillion microplastics in the ocean," more than the number of stars in the Milky Way, Hocevar proclaimed. "Due to the sheer quantity of microplastics in the ocean, it would be difficult to find any marine animal without plastic particles in its gut or tissues." 

Of the seafood most likely to contain microplastics, Hocevar listed bivalves like oysters as well as those which have high concentrations of sediment, like sea cucumbers. But animals higher on the trophic pyramid — meaning those that are larger and carnivorous, typically — are also a risk. 

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"Microplastics and the chemicals associated with them are also likely to bioaccumulate in top level predators such as tuna and sharks," Hocevar explained. "A 2022 study found hundreds of microplastics in a single can of tuna."

If these statistics on microplastics in seafood seem piecemeal — a little bit of data on one region here, some figures on a can of tuna over there — that is because the fishing industry is de-regulated to the point of chaos. It is virtually impossible to obtain a comprehensive picture of the scope of plastic contamination in seafood — or, for that matter, to even accurately assess which types of commonly eaten foods are most contaminated. The individual quirks involved in how we prepare our seafood dishes further complicate potential assessments.

"It's impossible to say which species have more microplastics because it depends so much on where and how they are harvested, as well as what you are eating," Baechler told Salon. "Typically, people eat a whole oyster, not a whole fish, for example."

Despite the extensive documentation on microplastics in seafood, Baechler says there are still gaps in knowledge. "For example, there haven't been any studies on microplastic concentrations in Alaska pollock, which is one of the biggest U.S. fisheries by weight, nor are there any studies on microplastics in commercially fished U.S. shrimp, which is another major U.S. fishery," Baechler says.

The law isn't doing much better than science at catching up with the problem. Dr. Anja Brandon, Associate Director of U.S. Plastics Policy at Ocean Conservancy, has a PhD in environmental engineering and co-authored both state and federal legislation regulating plastics in recent years (including the federal Break Free From Plastic Pollution Act of 2021 and California's Plastic Pollution Prevention and Packaging Producer Responsibility Act). Brandon acknowledged to Salon that even though "we have laws on the books that are meant to regulate pollution from these types of manufacturing facilities," the tragic reality is that "microplastics, especially pre-production pellets (sometimes called 'nurdles'), are getting away scot-free because they have not been specifically classified or labeled as a pollutant."

Bluntly put, "current law allows plastics producers and shippers to discharge trillions of small pre-production plastic pellets directly into waters with little to no repercussions."

While there are no repercussions for the polluters, the same likely will not be the case for the people who eat the plastic-filled seafood. As Baechler noted with alarm, one recent study in the journal Environmental Science & Technology found that children ingest roughly 550 microplastics every day — and adults ingest roughly 880 per day — just by breathing and eating eight common foods and beverages including fish, mollusks, water (tap and bottled) and milk.

"Whether or not microplastics impact human health is a relatively new field of study, but what we know so far is troubling," Baechler wrote to Salon. "Plastics and microplastics contain many harmful additives and tend to collect additional contaminants from their surroundings." Baechler noted that microplastic ingestation has been correlated with irritable bowel syndrome, while plastic-associated chemicals such as BPA "show correlations with chronic illnesses such as cardiovascular disease and type 2 diabetes."

"A recent paper showed microplastics impact human cell function in a lab setting, and suggested that at current exposure levels, humans may already be experiencing toxic effects from microplastics including allergic responses, cell damage and cell death," Baechler added.