(CNN) Tiny plastic particles are polluting our oceans, where they can stay for centuries, harming sea life and making their way into the human food chain.
These microplastics -- fragments of plastic smaller than 5mm -- are often the result of bigger chunks being worn down by the elements. But a surprisingly large amount comes from people simply washing their clothes.
According to Dutch campaign group Plastic Soup Foundation, with every 11 pound (5 kg) load of laundry, between 600,000 and 17 million clothes fibers are released (other research gives a number closer to the smaller of those figures) -- up to 1.3 grams in weight.
Read: Microplastic pollution is all around us
That may not sound like much, but when you multiply it by every household wash, it adds up. It is estimated that around half a million metric tonnes of microfibers enters our oceans this way every year.
Although microplastics can be dangerous to some marine life, the health risk to humans is still relatively unknown.
Wastewater treatment plants catch some of these fibers, trapping them among a semi-solid gunk known as sewage sludge. But in many countries this sludge is spread on fields as a fertilizer. From here, the fibers may run off into streams, or be carried away by the wind as the fertilizer dries out.
Around two thirds of our clothing consists of synthetic materials, or a mix of natural and synthetic, says Plastic Soup. Our fleece jackets, gym clothes, pyjamas and summer dresses are often made of materials including acrylic, polyester, nylon and poly-cotton blends, which don't break down like natural fabrics.
One solution -- to stop making clothes from plastic fibers -- would need major changes from the fashion industry. But there may be a simpler alternative.
Slovenia-based startup PlanetCare is one of a handful of companies that have products designed to catch fibers shed in the washing machine, before they flow into the water system.
"Our approach is based on the fact that it is better to stop pollution at the source, which is the washing machine," says PlanetCare's chief scientist, Andrej Kržan. "At that point we have fibers not mixed with organic matter and other things, but in a relatively clean stream of water.
"Once you get fibers in the environment, I cant imagine any way to get them back."
The company has created a filter that attaches to the outside of the washing machine or a nearby wall. One end of the filter attaches to the washing machine's outlet pipe, and the other end attaches to a pipe that flows to the drain.
Kržan says it catches around 90% of shed fibers, from over 5mm in size, down to 50 microns -- about the width of a human hair.
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The filters contain a cartridge which PlanetCare recommends should be changed monthly. Users send the cartridges back to PlanetCare, which cleans them and returns them to the customer. The company offers a subscription service for around $11 a month, for which customers get a filter with seven months' worth of cartridges.
As for the fate of the collected microfibers, Kržan says that once PlanetCare has collected enough, it plans for them to be used as a backing material in car upholstery.
Founded in 2017, the company says it has sold 400 filters so far, but aims to reach more people by partnering with washing machine producers. Currently, washing machine manufacturers are not required to have microfiber filters, but Kržan says PlanetCare is in talks with manufacturers and is hopeful that they will eventually integrate its filters into their products.
It's not the only company to have developed a microfiber filter for washing machines. Canadian Environmental Enhancements has a device called Lint LUV-R. Xeros Technologies has a product called XFiltra, and Filtrol is another product in the same area.
A different approach, used by Cora Ball and Guppyfriend is to catch fibers inside the washing machine drum.
Professor Richard Lampitt, of the National Oceanography Centre, in the UK, told CNN that microfiber filters in washing machines can be part of the solution to plastic pollution. He suggests that education and commercial pressures can help increase their uptake.
At this week's Sustainable Brands Oceans conference, in Portugal, Planet Care will announce that it is partnering with GreenEarth Cleaning -- which provides eco-friendly technology to dry cleaners -- to equip 20 Californian laundries with a bigger version of its filter, suitable for commercial use.
They plan to launch at laundries in other U.S. states in 2020.