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This story was originally published by Atlas Obscura. It appears here as part of the Climate Desk collaboration.

On a recent sticky summer afternoon in Manhattan, a team of scientists took to the Hudson River to trawl for trash. There weren’t any mangled bags, plastic bottles, or other waterlogged debris bobbing on the water’s gray-green surface, but that’s not what the researchers were looking for, anyway—I tagged along as they piled into a boat to skim a fine-mesh net across the top of the water and ensnare the teeny pieces that only come into clear view beneath a microscope.

Microplastics, which are shards measuring less than 5 millimeters in diameter, can take many forms—they might be pellets, foams, films, lines, or nurdles (the goofy name for plastics made to be melted down into other plastics)—but they’re all pretty hard to spot with the naked eye. Increasingly, researchers are concluding that many waterways are host to a slurry of itty-bitty plastic pieces. Baseline data for microplastics in the Hudson River is pretty sparse, though, and mitigation tactics are still somewhat foggy. The surest way to track microplastics’ sprawl and scope is to collect samples over time. So, we cruised up and down the watery corridor between the New York City and New Jersey skylines at a speed of around five knots, on a mission to scoop them up.

At Pier 40, near Greenwich Village, they measured the water temperature and coordinates, then looked to flags flapping on the shore to see which way the wind was blowing. Since irascible weather and choppy water could affect their collection results, they estimated conditions on the water using the Beaufort scale, where 0 is a mirror-calm day, and 12 indicates hurricane-force winds. This was a 1, said Carrie Roble, the director of science and stewardship at Hudson River Park, and the project’s leader. “A pretty chill day,” she said, and as good as any for collecting nearly invisible trash from the park’s estuarine sanctuary.

We headed south, where the Statue of Liberty towered in the distance; jet skiers bounced past, shooting north, and white sailboats clustered farther afield. All the while, Emma Samstein, a high-school volunteer, sat with a foot on the net, to keep it from splashing up out of the water. (This is a free alternative to rigging up weights, and it’s also “a good thigh workout,” Samstein said.) The goal was to keep the net steady—since plastics float to the surface—without adding turbulence, which could cause them to disperse. As the boat puttered along, water and shards of plastic flowed into the net, which billowed alongside the vessel like a windsock. The trapped debris dropped into a plastic collection cup affixed to the bottom of the net. The irony of using plastic to find plastic, in a crusade against plastic, was not lost on anyone involved.

Humans shed plastic waste all over the world, and nearly no portion of the planet’s waters is free of our fingerprints. Very few places are devoid of microplastics—certainly not the oceans, but not rivers, not lakes, and not sediments, either, the University of Toronto ecologists Chelsea Rochman and Kennedy Bucci recently pointed out in an article for The Conversation. Most infamous, perhaps, is the detritus swirling around the soupy Great Pacific Garbage Patch, where wind and waves churn microplastics into a long-simmering stew. But plastics—and microplastics in particular—have made their way pretty much everywhere.

“What is clear is that our plastic ‘footprint’ extends even to the ends of the Earth, to areas we may hope and expect to be pristine.”

This April, a team of Japanese researchers analyzing photos and videos from more than 5,000 dives conducted between 1983 and 2014 found widespread evidence of single-use plastic products in the deepest parts of the ocean, more than a thousand kilometers (621 miles) from shore. These were even wedged into the depths of the Mariana Trench, some 10,898 meters (35,756 feet) below the water’s surface. This finding indicated “a clear link between daily human activities and remote environments where no direct human activities occur,” the researchers wrote in a paper, poetically titled “Human footprint in the abyss,” in the journal Marine Policy. In June, researchers from Greenpeace and the University of Exeter released the results of a plastic-sleuthing journey around the Antarctic Peninsula, where they detected microplastics—including polyester, propylene, and acetate foam—in all eight of the surface-water samples they studied. The scientists weren’t able to tell whether these had sloughed off nearby, from fishing boats or nets, or whether they had been carried long distances on the current. “What is clear is that our plastic ‘footprint’ extends even to the ends of the Earth, to areas we may hope and expect to be pristine,” said research scientist David Santillo in a statement.

In the last 10 or 15 years, researchers have mostly been asking where microplastics are. “Now that it’s established that they’re pretty much anywhere you look—in water, in air—we’re trying to move into, where do they come from, how do they move around, where do they end up?” says Julie Dimitrijevic, a graduate student at Simon Fraser University who studies microplastics and blue mussels. “We understand that we are putting microplastics in the water, whether through mismanaged waste, or through our wastewater treatment plants,” but have a murkier understanding of the specific load, Dimitrijevic adds. (Miscalculations are also possible, Dimitrijevic says, when a suspected microplastic isn’t submitted to spectroscopic analysis.)

Though microplastics are all around us, we’re still not quite sure just how harmful they are. Previous research has found that these little menaces tend to work their way up the food chain—one species ingests them, and then another gobbles up that plastic-eater, and so on. In addition to potentially screwing with marine creatures’ endocrine systems and metabolisms, microplastics could also make their way into human bellies. Scientists in the ecotoxicology research group at Simon Fraser University in Burnaby, British Columbia, recently detected microplastics (mainly microbeads, fibers, and fragments) at all of the locations they sampled in Lambert Channel and Baynes Sound, which sit within the heart of British Columbia’s major oyster-growing region. “It would be be prudent to assess the degree to which oysters from this region are ingesting microplastics,” the team wrote in a recent report in PLOS One.

Some studies have offered projections about how many microplastics a human might consume via the seafood that they eat, but that’s a bit of a moving target, too, because various species interact with microplastics in different ways, Dimitrijevic says—the number of microplastics you might guzzle from an oyster wouldn’t necessarily hold steady for a mussel or a clam. Overall, “the exact nature and scale of the threats that microplastics pose to marine ecosystems have not yet been fully determined,” the Greenpeace team noted in its report. To come closer to understanding it, many researchers are calling for more data—and in New York City, that means putting boats out in the water, and eyeballs up to microscopes.

Between June and October, Roble and crew sample a handful of sites spanning the Hudson River Park’s estuarine sanctuary. (They spend 15 minutes at each location, and when they’re covering a small distance, the crew steers the boat in circles to run down the clock.) Each of the locations presents different challenges—which also means they’re ripe to reveal different types of data.

At Pier 26, downtown, Roble gestured toward shore to point out a pipe opening up into an inlet. There, soft plastic whales and inflatable dolphins enclose an area where kayakers can paddle. This is also a discharge point for combined sewer overflows. When the sewer system is especially taxed—say, after a deluge—more water pours out of its mouth.

As a changing climate promises a wetter world, researchers are eager to learn more about the relationship between rain and the volume of plastics entering waterways. Roble has noticed a difference between wetter and drier years, even over the two years that the team has been sampling. In 2016, the samples averaged 188,657 pieces of microplastic per square kilometer; in 2017, the average was half that—99,692 pieces—and Roble attributes this difference to a drier year. “There’s a correlation between rain, wet weather events, and the abundance of microplastics in the system,” she said. It’s not necessarily that there were fewer pieces of plastic to enter the system, but rather that there was less rain to flood the waterways with them.

Reducing the number of microplastics sullying the waterways might involve changes both upstream and downstream, from companies to governments to consumers, Roble said. It would entail reminding residents, during downpours, to hold off on long showers, running dishwashers, or other behaviors that contribute to overloading systems. It would involve companies pledging to remove microbeads from their face wash or other beauty products (and replacing them with biodegradable alternatives). It would require city-wide efforts, such as reducing single-use items like straws—which degrade into microplastics—and doubling down on green infrastructure that would capture and slowly release stormwater instead of sending it barreling straight into the waterways. “We want to find solutions that fit the scale of the problem,” Roble said.

“We want to find solutions that fit the scale of the problem.”

That sounded frustrating, I thought, because the problem is somewhat intractable. Tallying microplastics, let alone halting them in their tracks, struck me as a Sisyphean task. Even when more data about microplastics does come into clear view, there will still be nanoplastics to contend with. These are generally accepted to be particles smaller than one micron, Dimitrijevic says. (A human hair and a single leaf of paper are both significantly thicker.) How do you grapple with a problem that’s everywhere, and invisible, and so difficult to wrangle or keep hold of? “Doing these projects, yeah, I don’t anticipate that it’s going to be an uplifting discovery or finding,” Roble told me, up on the dock. But she thinks that data and education are a place to start.

Each time the 15 minutes are up, Roble’s team hauls the net out of the water. It looks brown; it has snagged plastics, but other things, too, and the team spritzes it down with a water-filled squirt bottle to dislodge whatever has caught. They rinse everything down into the plastic jar, and then transfer the contents into a glass mason jar labeled with the site location and date.

Back on shore, each sample will spend 24 hours drying out in a sieve, and will then sit in wet peroxide to dissolve any organic material that has held on. Then, the team will slide the samples under a dissecting microscope and sort the plastics by hand, using tweezers to isolate one piece at a time and logging each as a nurdle, pellet, or whatever it turns out to be. Sometimes, it’s hard to tell, even with the help of 30x magnification. The group showed me a photo of a green object that I was certain was a leaf—it was green, vaguely oval, and it even appeared to be lined with veins. “Fakeout,” Roble said. Since plastics and organic materials can look really similar, the team also uses hot probes to see whether something smokes (suggesting it’s organic material) or melts (indicating that it’s plastic). In the corner of the photo, I noticed two little wisps: melted plastic.

On the boat, in between trawls, I held one of the mason jars up to the sun and swirled the water inside. To my eye, it contained an entire world: smears of sand; squishy little jellyfish that looked like globs of clear hair gel; fingernail-sized isopods with scrambling legs; a tangle of rippling brown rockweed. So many signs that the opaque waterway is teeming with life. Then, one of the scientists pointed to a just-visible microplastic bobbing on the surface of the sample—a little chunk of porous-looking foam.

It’s easy to forget what what happens outside our field of vision. City dwellers who don’t discover the water up close may tend to “only think of it on a surface level,” Roble said. “You can’t see below the surface, you can’t see that there’s 70 species of fish, you can’t see that the ecosystem is pretty dynamic.” It’s easy to forget the threats to that ecosystem, too, in the form of a little problem that keeps on mounting.