Synthetic fibers that make up much of modern clothing are making their way into the stomachs of razor clams and oysters, according to a new study from researchers at Portland State University.

The vast majority of razor clams and oysters that were collected along the Oregon Coast tested positive for microplastics, the researchers found. The results of the study, conducted by Britta Baechler, a student in the university’s Earth, environment and society program, and Elise Granek, a professor of environmental science and management, were published in the journal Limnology and Oceanography Letters.

The shellfish in question were plucked from 15 sites, from Clatsop in the north to Gold Beach near the California border, in both the spring and summer of 2017. Of the roughly 300 shellfish analyzed, all but two contained at least some microplastics, Granek said in a statement.

“Whether it was a fairly urban site or a rural site, estuary or open-coast beach, both species had microplastics,” she said. “Although we think of the Oregon Coast as a much more pristine coastline compared to California, Puget Sound or the Eastern Seaboard, when we are talking about microplastics, we’re still seeing that human footprint on even our more pristine coastline.”

Granek and Baechler found an average of 11 pieces of microplastic in each specimen, with the foreign materials primarily consisting of microfibers, which can be cast off of synthetic textiles — yoga pants, fleece and other active wear — as they go through washing machine cycles.

“These microfilaments can be shed from clothing, up to 700,000 per load of laundry,” Baechler said. “Those particles then travel out through grey water into wastewater and to the coast.”

Experts have also said that derelict fishing gear could be a potential source of contamination. The fishing industry and oyster framers have often been scapegoated in the past for microplastic pollution, but Granek said there was no clear scientific consensus on the source of the fibers.

“It’s not because people aren’t managing our fisheries well or are being unclean in their practices,” she said. “We’re all using plastics on a daily basis. We are all the source of contamination in our seafood.”

Granek also noted that microplastics are nearly ubiquitous in our modern environment and that their potential effects on human health are not well understood.

“Microplastics are not just in our seafood,” she said. “We know that they are in our beer, in our salt, in our drinking water.”

The impact of microplastics on shellfish health is another area where further research is needed. Some studies have shown that the presence of these foreign microfibers could impede growth or reproduction in shellfish.

“If reproduction or growth is impaired, that could really affect not just individual clams or oysters, but possibly local populations of these organisms as well,” Baechler said.