Corbis

In the laundry, synthetic clothing sheds microscopic plastic fibers. Corbis

THE GIST

- While synthetic fabrics are washed they shed bits of plastic that can end up in the oceans.

- Manufacturers are not required to test fabrics for their environmental impact.

- More than 65 percent of plastic in the ocean is in bits that are less than a millimeter thick.

Scientists have found an unexpected source for the rising load of tiny plastic bits in the oceans: Washing machines.

When you wash fleece jackets, polypro running shirts and other synthetic fabrics, a new study found, miniscule threads of plastic seep through filters and escape into the environment. Marine microplastics can penetrate the cells of even the tiniest organisms, raising all sorts of health concerns for both sea creatures and the people that eat them.

SCIENCE CHANNEL: Top 10 Weird Sea Creatures

And while washing machines are far from the only source of tiny plastic pieces in the oceans, the study suggests that there might be a need for a new generation of clothing made from natural fibers or synthetic versions that hold together for a longer time, said Mark Browne, an ecologist at University College Dublin.

For now, textile companies are not required to test their products for durability or plastic-shedding potential.

"We've been contacting industry representatives to try to find out that information so that consumers can make a choice, but no one has come forward and I find that disheartening," said Browne, lead author of the new study.

"Consumers have the power when they go into a store to ask whether clothing has been tested for its impact on the environment," he added. "If more and more consumers started doing that, it would then put pressure on the people who actually produce clothes to do something about it."

Pictures of turtles caught in fishing lines or sea birds tangled in soda rings have long drawn attention to the problem of large pieces of floating plastic. But more than 65 percent of plastic debris in the sea is smaller than one millimeter in diameter, Browne said. And scientists have become increasingly concerned about what kind of harm those tiny bits might be causing.

Studies of artificial joints and plastic-based drug delivery devices in people have shown that small pieces of plastic can infiltrate joints and even enter the circulatory systems. Experiments on mussels, among other animals, have shown similar effects in even these simple creatures. And when cells take up plastic, they seem to have trouble functioning as they should.

To gauge the extent of the microplastic problem, Browne and colleagues collected and tested sediment samples from 18 shorelines on six continents. Microplastics were not just ubiquitous, the team reported in Environmental Science & Technology. Concentrations were also highest in the most densely populated countries. Places that produce the most waste, in other words, suffer the most from their waste.

"The plastic you throw away," Browne said, "could end up on your dinner plate."

THE DISCOVERNATOR: Amazing Facts Served Up Hot

Inside the discharge from sewage treatment plants, the researchers then analyzed plastic particles to figure out where they were coming from. Results revealed polyester, acrylic and other plastics that looked just like the materials used in synthetic clothing. In a single wash cycle, follow-up experiments showed, a fleece garment could shed more than 1,900 fibers.

"It seems obvious in hindsight that fibers are leaving clothes in washing machines and ending up in the waste stream, but it hadn't been considered as a source up until this point," said Kara Lavender Law, a research oceanographer at the Sea Education Association in Woods Hole, Mass. "This is eye opening."

Although the health and environmental effects of microplastics have yet to be fully studied, these particles are potentially concerning for a variety of reasons, Law said. In addition to their own potential toxicity, bits of plastic tend to absorb pollutants in the water.

"This isn't just an ocean problem," Law said. "We live in a world full of plastic."