More than 90 percent of the waters tested for plastics by a team of citizen scientists this summer have turned up positive results, though the source of the pollutants remains unknown.

Skye Borden of Environment Montana and a team of university interns set out in April to test 50 waters across the state for signs of microplastics. By the end of June, samples from 10 sites had been placed under a microscope, and nine of them bore signs of plastic fibers, filaments and film.

“A pretty high percentage of our sites had some form of plastic in them, and we've found a wide variety of plastics,” Borden said. “Most have had fibers or hard plastics, and then another group also had film. It's what you'd get from either plastic bags or wrappers, like wrappers on a cigarette box.”

The plastics would generally pass unnoticed to the human eye if not for the high magnification of a microscope. One sample taken at the Russell Gates Memorial on the Blackfoot River produced a broken fragment of hard plastic, as did a sample from Blackwell Flats on the Kooenai River.

A sample from Big Pine on the Clark Fork River produced 11 plastic fibers, while a sample collected from Kona Bridge produced two fibers, one fragment and one film.

“The three main sources in Montana would be from clothing, like fleece, along with monofilament fishing line,” Borden said. “Bailing twine is also in that fiber category. There have been a lot of hard fragments also, which would be something like bottles or containers, things like that.”

Adventure Scientists launched a pilot study of five sites along the Gallatin River several years ago and found plastic particles in each of them. The effort gave rise to the Gallatin Microplastics Initiative – a wider research effort to study plastics in the watershed and potential solutions.

Borden is applying methods and parameters developed by Mississippi State University in hopes of answering a similar question: How widespread are microplastics across Montana and what might be done to address it?

“We sort of understood that plastic pollution was a problem, and for the past few decades, our approach to solving it was an anti-litter campaign,” she said. “I think that's ingrained into our cultural consciousness at this point, and it doesn't seem to be enough. We need be doing more to limit the flow of plastics into our lives.”

Microplastics derive from a variety of sources, including plastic bottles and bags, clothing, cosmetics and toothpaste. They end up as beads, filaments or granules smaller than a pencil eraser. By 2050, scientists believe, plastics will outweigh all the fish in the ocean, posing great risk to marine life and the food it produces.

But plastics have also made their way inland, turning up in surprising locations. That includes the upper elevations of the French Pyrenees and Montana’s own watersheds. Samples taken in Colorado's Rocky Mountain National Park found plastics in the rain.

“There's a lot of unknowns right now about how microplastics move around the Earth,” Borden said. “Just in the past year, we've found them in places where people are really not expecting to find them. There's a growing recognition that atmospheric deposition plays a pretty huge part in the distribution of microplastics.”

While weather may play a role in distributing microplastics in the rural areas of Montana, human activity may also be at fault, intentional or otherwise. The team has collected and sampled trash at each of the sites where they've also tested the water.

“We've found plastics in some form at every site we've been to,” said Borden. “I'm finding a lot of plastic trash at these sites, but very little of it seems to be intentionally littered.

“There's a lot of corners of bags, small chunks of bailing twine, torn fishing line – things where the person who was using it probably didn't intend for it to get into the environment.”