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You’ve probably heard by now about how microfibers from your synthetic clothes—like yoga pants and stretchy socks—slough off when you do the laundry and wind up in the environment because wastewater treatment plants can’t screen them all out. Everywhere scientists look, from the deep sea to coastal waters to the surface of the Atlantic, they find these tiny fibers, which are less than 5 millimeters long. All along, the hope among scientists and environmentalists has been that organic fibers, like the cotton from your jeans, might not be as persistent in the environment as plastic ones, and would dissolve over time.
Sorry, but not so fast. Writing today in the journal Environmental Science and Technology Letters, researchers at the University of Toronto report how they found oodles of blue denim fibers in sediment samples from the remote Arctic Ocean in Canada’s north, far from human activity. “It does suggest that they ended up there through long-range transport processes. Whether they’re oceanic or atmospheric—we don’t know exactly,” says University of Toronto environmental scientist Sam Athey, co-lead author on the paper. It could well be both: Previously researchers have shown how deep-sea currents transport microfibers vast distances, and how the wind blows the particles from the cities of Europe up into the Arctic.
These blue jean fibers are technically known as “anthropogenically modified cellulose.” (Cellulose is the organic compound that makes up plants like cotton.) “They’re called ‘natural’ textile fibers,” says Athey. “I’m doing air quotes around ‘natural’ because they contain these chemical additives. They also pick up chemicals from the environment, when you’re wearing your clothes, when they’re in the closet.”
All small denim fibers are microfibers, but not all microfibers are denim fibers—that larger class includes synthetic fibers like polyester, too. And of course, these particular fibers are dyed blue with indigo. This chemical makeup gives the fibers a unique signature, which Athey and her colleagues can exploit to distinguish them from other particles in the sediment, using a technique called Raman spectroscopy that measures how light interacts with the chemical bonds in a material. The scientists also eyeballed the fibers with good-old microscopy to make sure a strand of anthropogenically modified cellulose isn’t in fact a strand of polyester or nylon. If you take a look at the picture below, you’ll notice that the blue jean fiber has a twist that betrays it as cotton, not a bit of synthetic fabric, which is smoother and more uniform.
The researchers looked at sediment samples from several habitats, including in the deep-sea Arctic, shallow suburban lakes around Toronto, and the Huron and Ontario Great Lakes. The mean number of microfibers they found per kilogram of dry sediment in each group was, respectively, 1,930, 2,490, and 780. Of those microfibers in general, 22 to 51 percent were anthropogenically modified cellulose, and of that, 41 to 57 percent were indigo denim microfibers. In other words, that’s a lot of denim in the environment. “I think what’s interesting is that a majority of these fibers that we were finding were these anthropogenic cellulose fibers, even in the deep ocean sediments,” says Athey. “And that shows that they are sufficiently persistent to accumulate in these remote regions.”
To be sure that they were characterizing the denim fibers correctly, the scientists ran a separate experiment in the lab, washing three different kinds of blue denim made from 99 or 100 percent cotton: used jeans, new regular jeans, and new mildly distressed jeans. (That meant no more than three holes and some fraying.) They captured their washing machine’s effluent and counted up the fibers.
In accordance with similar studies from other groups, they found that the new jeans shed more fibers than used jeans—which makes sense, as old jeans have long shed all the loose fibers left over from the manufacturing process. But weirdly, they didn’t find a significant difference between the regular new jeans and the mildly distressed new jeans, which you might assume would shed more, given the fraying. “If you have an extremely distressed pair of jeans, they might release a bit more,” says Athey. “But then it could also be the type of material.” Past studies have looked at more synthetic clothes, which probably shed differently than pure cotton. Regardless, Athey and her colleagues landed on a startling figure: A single pair of jeans may release 56,000 microfibers per wash.
The researchers also collected effluent from two wastewater treatment plants, which filter out some, but not all, microfibers before pumping the water into Lake Ontario. (Treatment plants elsewhere pump their effluent out to sea instead.) This landed them at an even more startling figure: Those two plants alone could be unloading a billion indigo denim microfibers per day into the lake. That’s in keeping with the country’s washing habits, as about half of the Canadian population wears jeans almost every day and the average Canadian washes their jeans after just two wears.
Wastewater plants actually do a decent job of sequestering microfibers in the solid “sludge” of human waste, which is turned into “biosolid,” which farmers often use as fertilizer. Unfortunately, packing the microfibers into fertilizer may well be giving them another pathway to get into the sea. As the fertilizer dries on the fields, the wind might pick up the blue jean fibers, and any number of synthetic ones, and deposit them in the ocean for scientists to later find in the sediment. Studies have already shown that microfibers can fly hundreds if not thousands of miles, landing in formerly pristine habitats like the Arctic.
Overall, the problem is that wastewater facilities weren’t designed to capture all these microfibers. They’re catching between 83 and 99 percent of them, but even letting a few percent through is a veritable torrent, given their volume. “The thing is, there’s so many people on the planet—there’s just too many of us,” says University of Toronto environmental scientist Miriam Diamond, coauthor on the paper. “And I think what’s astonishing is how many of us wear jeans. It’s not an indictment of jeans—I want to be really clear that we’re not coming down on jeans. It’s just a really potent example of human impact.”
Once they escape into the environment, these fibers and their fellow microplastics can travel just about anywhere. Earlier this year, a separate team of researchers discovered that ocean currents are transporting microplastics into deep-sea “hotspots.” When the current slows, the particles fall out en masse. The scientists sampled a single square meter of seafloor under the Mediterranean Sea and found 1.9 million pieces of tiny plastic—and that sediment sample was just 5 centimeters thick.
Finding so many denim fibers in the Arctic—around 2,000 microfibers per dry kilogram of sediment, 20 percent of which were indigo denim—jibes with scientists’ evolving understanding of how currents are moving material around the world, with the far north turning into a kind of dumping ground. “What’s really revealing here, and others have hinted at this in the literature, is that the Arctic is an ‘end node’ for subsurface currents,” says Marcus Eriksen, who studies ocean plastic and directs the 5 Gyres Institute, but who wasn’t involved in this research. “What you have is the deep-water conveyor belt, which takes neutrally buoyant debris around the world, ending in the Arctic. Now we’re finding really high sediment loads of microplastics in Arctic sediments.”
This is particularly problematic because in the far north, there’s not nearly as much organic debris to dilute the pollution as there is in temperate zones. “In the Arctic, there’s very little material that falls out of the water column and accumulates as sediment,” says Diamond. “That has implications, right?” Because there’s less sediment, there’s less biological activity—not so many seafloor critters scurrying around processing organic material. “If you don’t have a lot of food around, you eat what’s available. You can’t be fussy,” she says. “So that really points to the next next line of inquiry.” That is: How might denim fibers be incorporated into the deep-sea Arctic food web?
While they didn’t investigate Arctic animals, the University of Toronto researchers did collect rainbow smelt from the Great Lakes. They found 65 percent had microfibers in their guts, as many as 63 fibers per individual. But weirdly, they found only a single indigo denim fiber in the smelt, even though they’d collected the fish specimens near their sediment samples, which contained over 700 microfibers per dry kilogram. Why they found this discrepancy, the researchers can’t say, but it may have something to do with the smelt’s lifestyle. “We’ve more hypothesized in the paper that maybe it had to do with a feeding strategy, this kind of thing,” says Athey. “But we didn’t actually investigate that question specifically in our work.”
“While we certainly need more research to fully understand the effects, we also have ample evidence right now to act,” says Nicholas Mallos, senior director of the Ocean Conservancy’s Trash Free Seas Program, who studies microplastics but wasn’t involved in this new research. We know, for instance, that special filters attached to washing machines can stop 90 percent of microfibers from flowing out to wastewater treatment plants. Those need to be standard on every new washing machine sold, starting right now. “Regardless of whether something synthetic or fibrous,” Mallos adds, “we know there are effective mitigation techniques out there available now that can help stem this pollution pathway into wastewater and ultimately into the marine environment.”
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