Hakai Magazine

Coastal science and societies

steamed clams
Researchers found lower than expected levels of microplastic pollution in shellfish collected off the coast of British Columbia. Photo by Don Paulson/Alamy Stock Photo

Some Plastic Pollution Isn’t Plastic After All

One study finds British Columbia shellfish are surprisingly light on plastic pollution.

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by Nicola Jones

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The sea is awash with microscopic bits of plastic. But a hint of good news is emerging from Vancouver Island, British Columbia, where a recent investigation found that the amount of plastic contamination in shellfish there is just a tiny percentage of what the scientists expected.

For the study, the British Columbia Shellfish Growers’ Association worked with researchers from Fisheries and Oceans Canada (DFO) to investigate how much plastic is inside the province’s clams and oysters. The researchers studied roughly 20 sites—a mix of aquaculture and wild—from around Vancouver Island, and one site from mainland British Columbia. (The research was partly funded by the shellfish industry.)

When the researchers first pried open the oysters and clams and examined them under the microscope, they found that the shellfish were rife with tiny bits of foreign material. But under further investigation, the team found that only about a quarter of this detritus was actually plastic. Much of the rest was natural fibers such as cotton. “That was shocking to me,” says Christopher Pearce, an aquaculture expert with DFO.

Microplastics are tiny bits of plastic, typically smaller than five millimeters across. A 2017 report from the International Union for Conservation of Nature concluded that 1.4 million tonnes of microplastic are dumped into the ocean per year—the equivalent of one plastic grocery bag for every person on the planet each week. The effects of all this pollution isn’t well understood, though these plastics are known to make their way into the food chain.

Pearce says he expected to find hundreds or even thousands of microplastics in each oyster or clam. In the end, he and his colleagues found an average of less than one piece of plastic per shellfish. There was no difference between farmed and wild sites, indicating that aquaculture nets and floats probably aren’t a big source of microplastics—at least at the studied sites.

“It makes me feel better, at least about eating our local shellfish,” says Sarah Dudas, an ecologist at the University of Victoria who worked on the study. But the research also showed the ubiquity of microplastics. “They’re absolutely everywhere. Even in areas that look pristine.”

The new results come on the heels of work by Leah Bendell, an ecotoxicologist at Simon Fraser University in Burnaby, British Columbia. This past May, she reported “alarmingly high” amounts of microplastics in the seafloor sediment in a prime oyster farming region near Denman Island, just off Vancouver Island, prompting calls for further investigation into the region’s shellfish.

The researchers collected a range of tiny microplastic fibers from the shellfish. Photos by Garth Covernton

One of Bendell’s graduate students, Cassandra Murphy, also found high rates of plastic pollution in the region. In her recently completed doctoral thesis investigating British Columbia’s shellfish at sites along Vancouver Island, from Quadra Island to the Puget Sound, Murphy found between six and 650 pieces of microplastic per gram of shellfish—the top end being higher than any previously reported levels. The DFO results work out to less than two particles per gram.

Dudas cannot account for the discrepancy, though it may be due to differences in technique. Murphy’s research, Dudas notes, reports much smaller plastic particles than her team was comfortable identifying using their approach. Bendell notes that the amount of plastic might vary a lot even within short distances; it may be that the specific sites she and Murphy looked at simply had more plastic than the ones investigated by DFO.

But the most striking thing about the DFO research was how little of the contaminant material turned out to be plastic. When the DFO team sent samples to the Vancouver Aquarium for close chemical analysis, only six of the 27 fibers suspected to be microplastics were plastic. The rest turned out to be fibers such as cotton or rayon. “It all just looks like laundry lint under the microscope,” says Dudas.

Pearce suspects other scientists may have mistaken nonplastic contaminants for plastic in their research. “Most certainly, people have been visually identifying things as microplastics that are probably not,” says Pearce.

There are other reasons scientists may be overestimating the extent of plastic pollution as well, he says. Some contaminants may be particles shed from researchers’ clothing. In 2015, for example, a study found that the synthetic particles supposedly found in German beer and honey were likely contaminants from the lab.

Bendell thinks more recent studies are likely more accurate. “People are getting much better at this,” she says. Murphy’s study, in particular, found a lot of plastic microbeads, which are much easier to properly identify than fibers.

Still, even natural fibers might cause problems. Cotton, for example, can carry pesticides, and at least one red dye is known to be carcinogenic. But materials such as plant cellulose—the foundation of rayon—should break down faster than nonbiodegradable plastics, which might make them less damaging.

The DFO team did find genetic evidence that the shellfish seemed stressed by the contamination—plastic or otherwise—which may be having a long-term effect on their health.

All of the researchers agree that more work needs to be done to figure out how to best count the microplastics in our food and what they’re doing to the ecosystem and to consumers. “When you think about how much plastic we’re constantly exposed to …” says Dudas. “We know so little it’s actually quite terrifying.”