They come out of your fleece every time you do a load of laundry.

Microfibers, which are tiny threads of polyester, nylon, acrylic and other synthetic textiles, were first discovered by ecologist Mark Browne in 2011. Researchers have been finding them in waterways around the world ever since.

Texas is no exception. In 2015, researchers at Baylor University sampled sunfish in the Brazos River and found that 45 percent had microplastics in their guts. Baylor Ph.D. candidate Colleen Peters was the lead author of the study and said the team was surprised to find that 96 percent of the plastics in the sunfish were microfibers.

Microfibers are close cousins to microbeads, the tiny particles put in beauty products to give them a "scrubbing" effect. The beads are subject to the Microbead-Free Waters Act of 2015, which banned production and sale of microbeads.

But scientists are learning that a new type of microplastic, microfibers, could pose an even bigger threat than microbeads.

Microplastics (tiny pieces of plastic less than 5mm in size) are considered toxic because they contribute to plastics pollution in rivers, lakes and oceans around the world. The plastics can poison fish and move up the food chain.

The team at Baylor wanted to find out what kind of plastics they were dealing with in their local waterway. "We looked at the Brazos River, which runs right through Waco, and we noticed that after every storm event there were massive flows of plastic and trash that enter into the river," Peters said. That trash was made up of mostly Styrofoam, old cups and plastic bags.

"We were expecting to see something, but we were not expecting to see the majority of particles recovered to be microfibers."

To date, most studies have been conducted in marine waterways. Their study adds to the growing body of knowledge about microplastics in freshwater. More recently, the team sampled fish downstream in the Gulf of Mexico, in and around the mouth of the Brazos channel. They are expecting similar results from the study, which is being prepared for publication.

The effects of this on humans could be two-fold. Chelsea Rochman, an assistant professor who studies microplastics at the University of Toronto, bought fish for human consumption at markets in Indonesia and California in 2015 and found that at least a quarter of fish from both markets contained man-made litter in their guts. The litter was almost entirely made up of microfibers.

In this July 2013 photo provided by State University of New York at Fredonia, Sherri Mason, right, a New York environmental scientist who led a research team studying microplastics in the Great Lakes, examines a trawling device used to collect plastic "microbeads" from the water's surface with University of Buffalo student Shayne McKay on Lake Ontario. Illinois environmentalists expecting a battle with business over a call for a ban on the tiny bits of plastic used in personal care products, found the industry quickly collaborated. With similar bans pending in at least three other large states, the extinction of microbeads, now showing up inside fish that are caught for human consumption, is happening in an unusually short amount of time. (AP Photo/SUNY-Fredonia) (AP)

Rochman said that fibers can harm fish by blocking their digestive tracts or by absorbing, and then leaching harmful chemicals into other organs.

Sherri Mason, chemistry professor at the State University of New York at Fredonia, said that microfibers are an even bigger concern than microbeads because they can't be as easily excreted.

And even though humans are unlikely to eat a fish's guts, Mason said we're still at risk because as fibers linger in fish, they can potentially leach toxins into other parts of its body - parts that we do eat.

Back in Texas, Peters' team is focused on understanding why fish are ingesting plastics in the first place. Rather than focusing on toxicity, they want to know whether fish with varying diets and feeding habits ingest different types or amounts of plastic.

This is an important step because of the number of fibers entering our water each time we do laundry. Patagonia, a leader in sustainable apparel, has been on top of the microfiber story since it first surfaced. Last year, they commissioned a study which was conducted by students at the University of California-Santa Barbara and found that on average, each time a fleece is laundered, about 81,000 microfibers are released. Anywhere from 6,500 to 28,000 can make it past the wastewater treatment plant and into the water.

Unlike microbeads, microfibers are not an additive - they are simply part of our clothing - which means they'll be much harder to regulate.

Like many other researchers, Peters thinks that the ban on microbeads is an important, but small, step.

Although they raise the public's awareness about microplastics in general, she said we're starting to learn that microbeads are a small part of a much bigger problem.

Tina Knezevic worked for Environment Canada and the Canadian Environmental Assessment Agency, and worked throughout 2014 and 2015 for the International Union for Conservation of Nature in Brussels, Belgium. She's currently a fellow in global journalism at the Munk School of Global Affairs in Toronto.