Some 45 million Americans wear contact lenses. Of them, 15 million wear daily disposables -- soft plastic discs that are worn once and thrown away.
Now, a trio of researchers has done a first study on what happens to these lenses after they leave our eyes. And the results aren't great.
"We found that 15 to 20 percent of contact wearers are flushing the lenses down the sink or toilet," Charlie Rolsky, a Ph.D. student and the study's lead researcher, told Live Science. "This is a pretty large number, considering roughly 45 million people in the U.S. alone wear contact lenses." Rolsky and his co-authors presented the results Sunday at the annual meeting of the American Chemistry Society.
By their estimates, between six and 10 metric tons of plastic lenses are ending up in U.S. wastewater plants every year, adding to the problem of in oceans, lakes and even .
Contacts flushed down the drain don't biodegrade but instead fragment, sometimes ending up in surface water, the researchers found. They interviewed workers at municipal sewage plants who confirmed they had seen lenses in wastewater, the researchers told The New York Times.
The researchers also tested what happened to contacts in liquids of varying densities, finding that they always sink to the bottom. That's especially dangerous for bottom-feeding fish, who mistake the lenses for food. Eventually, some of these mashed-up and remixed contact particles "find their way to the human food supply," they found.
Rolsky and his co-authors hope that after reading their study, contact-lens makers will "take note and at minimum, provide a label on the packaging describing how to properly dispose of contact lenses, which is by placing them with other solid waste."
The American Optometric Association recommends that patients recycle their contact lenses (and contact cases, boxes and solution) if they live in an area that allows for it. "The regular garbage is the second option. Down the sink drain or toilet is never recommended and is discouraged due to the impact on our environment," the organization said in a statement.
Of course, it's not easy to know what's recyclable and what isn't (and some items that were recycled no longer are, as towns find themselves having to.)
Bausch & Lomb has a recycling program for its Biotrue line, which took in 1.9 million contacts last year, according its recycling partner, Terracycle. The eco-conscious could also consider glasses, which last longer than contacts, tend to cost less over time and come with a .