It's one of nature's healthiest wild foods, the backbone of a major industry in the Pacific Northwest and deeply embedded in the diets and cultures of Indigenous people in the region.
But it, too, has been altered by the world's ubiquitous plastic pollution.
Scientists in Oregon have now found microplastics - particles smaller than 5 millimeters from the degradation of plastic in the environment - in salmon and several other iconic Pacific Northwest fish and seafood species.
They include chinook salmon, Pacific lamprey, black rockfish, lingcod, Pacific herring and pink shrimp.
The tiny particles were lodged in the edible tissue of those species, meaning that humans are, no doubt, consuming the microplastics when they eat them, according to a study by Portland State University.
The study is yet another milestone in a fast-growing body of research that shows microplastics are present in soil, water, air and most of our foods as well as in animal and human bodies - although their potential to harm human health remains unclear.
"It was surprising to see microplastics in these large fin fish, especially those that don't come close inshore. And to see these concentrations in them reinforces this idea that there's nowhere that's immune from plastic pollution," said Elise Granek, an ecologist and professor of environmental science and management at Portland State and one of the study's authors.
MIMIC CONSUMERS
Granek got interested in microplastics because she had been studying pharmaceuticals leaking from wastewater treatment plants into waterways and the Pacific Ocean and their effect on the growth and reproduction of marine organisms.
A decade ago, researchers were just realizing that plastic accumulating in oceans across the globe - including in the Pacific Ocean garbage patch - was breaking apart, posing a threat to fin fish, shellfish and mammals. To prevent more plastics from entering waterways, the U.S. passed a ban on microbeads, tiny plastic particles intentionally designed for use in cosmetics.
Granek's team wanted to test how pervasive microbeads were in marine organisms before the ban went into effect and after, so they collected razor clams and Pacific oysters at 15 sites on beaches and in estuaries on the Oregon coast.
"We were pretty shocked," Granek said. "All but two of the 280 sampled individuals had microplastics in them. But over 99% of the microplastics we found were fibers. Only 0.2% of the contamination was microbeads, so clearly they were not the major source of microplastics entering our shellfish."
Armed with that knowledge, Granek wanted to understand if microplastics also were present in fish living farther offshore where there's less human influence than on beaches where they had earlier sampled the shellfish.
She keyed in on fish and seafood that are an important food source for people in Oregon - as well as for larger fish and mammals like seals that also eat them.
Granek's team collected some of the fish and seafood after it was freshly caught on National Oceanic and Atmospheric Administration research vessels. The lamprey came from samples collected by the Oregon Department of Fish and Wildlife.
But for pink shrimp, black rockfish and lingcod, Granek also sought products that had been through a processing facility and shipped in plastic, to better mimic what consumers might encounter when they buy them.
The fish were rinsed - again, to mimic what human consumers would do - and then researchers cut out pieces of filet to mimic what people would be eating. The pink shrimp and herring were gutted and used whole.
Unlike previous studies on fish, researchers weren't looking at the animals' gut, but rather at its edible meat.
All samples were digested in a base of potassium hydroxide, which breaks down the tissue but not the plastic. The gooey soup that remained was filtered and researchers could look at the microplastics that remained under the microscope.
To identify the type of plastic, Granek teamed up with collaborators at Oregon State University who used an infrared spectrometer to analyze the unique infrared absorption patterns of the plastic chemicals.
FIBERS, FRAGMENTS, FILMS
The study found 1,806 particles of microplastics across 180 of 182 individual fish and seafood samples, collected mostly in 2021 and 2022.
Fibers - which are typically shed by fleece vests and other garments when they're laundered - were the most abundant type of microplastics found, followed by fragments and films. Films include cigarette inserts and plastic wraps while fragments are larger plastic pieces broken down from items such as plastic shovels or a plastic water bottle.
While fibers typically come from fabrics made of polyester and polypropylene - including the PET recycled water bottles that many high-end fleeces tout as sustainable - cellulose blends such as rayon that are made from plants also are in the fiber category because the threads are highly modified with chemical additives.
"Most of what we're seeing is probably from laundered garments and sheets and towels and that sort of thing," Granek said.
The good news: the concentration of microplastics in the edible tissue of the chinook salmon was low - the lowest of all the organisms sampled for the study, followed by black rockfish and lingcod.
Pink shrimp contained by far the most microplastics, with the record number of tiny particles - 36 - found on a single pink shrimp weighing .17 ounces. That's likely because shrimp, which eat really small organisms like zooplankton, feed in areas where microplastics tend to accumulate and may mistake the plastic pieces for food, Granek said.
The study adds evidence to what other researchers have also observed: that microplastics move from the gut to other tissues, organs and muscles.
In humans, microplastics have recently been found in virtually every organ, including in the lungs, human heart tissue, placentas and testes. They've even crossed the blood-brain barrier into the brain itself.
Granek said scientists still don't know the mechanism through which microplastics move within the body of humans or fish. Fibers, in particular, may be able to pass through the gut wall and other tissue because of their narrow dimensions, she said.
HEALTH IMPACTS UNCLEAR
Scientists still don't know, though, whether microplastics can harm us.
A few studies have come out in recent years highlighting the potential correlation or connection between high concentrations of microplastics and health challenges, including inflammatory gut diseases, heart attacks and infertility - but research is still in its infancy, with studies sparse and existing ones yet to be replicated.
"We have next to no evidence of health effects linked to microplastics in the human body," said Linda Kahn, an assistant professor at New York University' School of Medicine.
Still, it's highly concerning that microplastics have been found in nearly every human organ and tissue and have the ability to travel, said Kahn, who studies the impact of chemical exposure on humans.
"They are foreign particles," she said, "and anytime you have a foreign particle in your body, you will have an inflammatory response."
Inflammation can cause an excess buildup of harmful molecules called free radicals that can damage tissue, cell membranes or DNA, Kahn said.
The size and shape of the microplastics - whether they're sharp-edged or rounded, for example - could also lead to different impacts or movement in the body, she said.
Another concern is the chemicals added to plastics to give them flexibility, color, hardness, smoothness and other properties. Scientists already know some of those additives, such as the manufactured chemicals called PFAS that are common in plastic food packaging, have adverse health effects. Other chemicals might be more bound to the microplastic particles so won't circulate as much throughout the body or cause as much damage.
Microplastics also often have microbes living on their surface, Kahn said. So while the plastic itself could be harmless, the microbial colonies could be harmful, she said.
A major challenge, said Kahn, is that science currently lacks a multi-dimensional measure of microplastics, which would tell researchers not just that they exist, but also their size, shape, chemical add-ins and microbes.
Contamination of samples is also a common problem because everything - from the air to the scientists' clothes to the cup in which a sample is collected - already contains the tiny particles.
DON'T STOP EATING FISH
Before you decide to be overly cautious and cut fish or shellfish out of your diet, Granek says: Don't.
Fish is good for humans, loaded with beneficial Omega-3 fatty acids and vitamin D, she said. And microplastics have been found in virtually every food we eat, including beef, chicken and pork, sea salt, honey, craft beer and tea bags.
Not to mention, they're in the air we breathe, the water we drink and the soil we walk on - so people would have to stop eating, breathing or drinking water if they wanted to eliminate them.
"Microplastics are everywhere, so we're not saying that people should stop eating fish or shellfish. They're a really important food source, really high in nutritional value and important to Oregon's economy," Granek said.
"What we are trying to highlight is that if we put plastics out into the environment," she said, "they are going to end up back on our plates."
The best solution? Policies that reduce the production and use of plastics across the world, said Susanne Brander, an ecotoxicologist at Oregon State University and a co-author of the study.
A global approach is key because plastic made in one country often ends up in another, Brander said.
Negotiations over a global plastics treaty have been ongoing since 2022, with the goal of a production cap on plastic and limits on some of the chemical additives. But the negotiations have stalled and it's unclear whether a treaty will materialize, given the re-election of Donald Trump and the increase in plastics production.
"We feel like we have enough scientific evidence to say, we need to limit our production, we need to limit the impacts of plastics and the microplastics that fragment off of them, because it is harming not just the health of wildlife, but it's likely that it's harming our health too," Brander said.
But there are things people can do on other fronts.
Because scientists believe the laundering and drying of clothing may be a significant source of microplastics - especially fibers - laundry and dryer machine filters might be able to stem the flow.
Granek said her team is testing washing machine filters and dryer vent filters in households at the coast to see which are most effective and whether they're reducing the concentration of microplastics coming into local wastewater treatment plants.
A new bill proposed this session would require that all new washing machines sold in Oregon by 2030 have either an internal or external microfiber filter. A similar phase-in of filters has also been proposed in Australia.
Another bill proposes to update Oregon's "Sustainable Shopping Initiative," which in 2019 phased out plastic film grocery bags. The new bill would phase out thicker "recyclable" plastic bags at checkout as well as single-use plastic toiletries at hotels.
Less plastic in the environment would mean, of course, fewer microplastics, Granek said.