To a certain degree, perhaps it isn’t too surprising that the researchers found microplastics here in the Pyrenees, because in their sampling they came across another important clue: a fine orange dust. This probably blew in from the Sahara, a phenomenon this monitoring station has recorded for over a century. (More incredible still, dust from the Sahara also crosses the Atlantic to fertilize the rainforests of South America.)

“The winds don't make a distinction between the type of the particles,” says marine geologist Michèlle van der Does, who has studied the long-range transport of dust particles, but who wasn’t involved in this new work. “These plastic particles are much bigger than the dust particles we find, although we find these giant dust particles as well. But their density is much lower, so they're also more easily transported over great distances.”

Another consideration is the unique nature of plastic decomposition. As microplastics break apart, theoretically their properties would change. So a single fiber might break into two fibers, creating new pieces with new aerodynamics. As they break down further, microplastics eventually become something even more sinister: the nanoplastic, a piece smaller than a micron, or a millionth of a meter.

These vanishingly small bits of plastic can get just about anywhere, including throughout an organism’s tissues, as researchers found when they introduced nanoplastics to scallops. “What they showed was that within 6 hours these nanoparticles are marching through the animal,” says study coauthor Steve Allen, an environmental pollution scientist at the University of Strathclyde and EcoLab (and spouse of Deonie Allen). “They're in every part of the animal in 6 hours.”

It’s not just the plastic itself that organisms have to worry about. “We do know that these plastics absorb all of the chemicals they pass through in the environment, like pesticides,” Steve Allen says. “We also know they have heavy metals sticking to them. So if these particles pass into your lungs and carry those chemicals in there, we don't know what's going to happen there yet either.”

Even more concerning: Nanoplastics look a lot like the nanoparticles used in medicine to deliver drugs in the human body. “So they can go through the blood-brain barrier potentially in exactly the same way but carrying their toxins,” Deonie Allen says. “And this is really worrying.” To be clear, though, this idea has not been backed up with data.

Researchers have, however, explored another troubling characteristic of plastic in the oceans. “In some ecosystems like coral reefs, plastics work as disease vectors,” says Luiz Rocha, curator of fishes at the California Academy of Sciences, who wasn’t involved in this study. “So a piece of plastic is like a little petri dish for all kinds of bacteria, including pathogens. As they go along the reef, they touch one coral and another coral and they transmit the disease.”

Whether microplastics could act as disease vectors on land is yet another question that demands more research. But it’s important to keep in mind that the microplastic and nanoplastic problem isn’t a land-sea dichotomy. Plastic’s effect on sea creatures has been much more thoroughly studied than its effects on land creatures like us, but there’s also quite a bit of interplay between the two environments.

Take laundry, for instance. Washing clothing like yoga pants and fleeces can release hundreds of thousands of synthetic fibers per wash cycle into the environment. “They don't get completely removed by the filters, they don't get completely removed by the wastewater treatment plants,” says University of Aveiro analytical chemist João Pinto da Costa, who has studied plastics in the environment but who wasn’t involved in this new research. The fibers end up in rivers and seas, but also in sediments, where they dry out and get picked up by the wind. “Also, when you're just putting your clothes up to dry, it's easy to imagine that a lot of fibers will be transported in the wind.”