If you're one of the approximately 45 million Americans who wear contact lenses, researchers at Arizona State University have a request based on their new study: Stop flushing them down the sink or toilet. The researchers concluded that disposing of lenses this way—and they estimate that up to 20% of wearers do so—takes a surprisingly large environmental toll. The study, presented at the National Meeting and Exposition of the American Chemical Society, estimates that up to 3.36 billion lenses get flushed per year, and that amounts to about 50,000 pounds of plastic, reports USA Today. The problem is that the lenses don't just dissolve when they reach wastewater treatment plants—they break down into potentially dangerous microplastics that wind up in sewage sludge, and that sludge is routinely applied on land for soil conditioning.
"We know that whatever's in sludge can make its way into runoff from heavy rains, back into surface water and that is a conduit to the oceans," researcher Rolf Halden tells the BBC. "There is the potential of these lenses being taken on quite a journey." One remedy is obvious, notes the Atlantic. The researchers looked at 11 brands and did not find any directions for proper disposal. Users should skip the sink or toilet and instead put their contacts with their solid trash, though one hope for the future is that manufacturers will get better about recycling old lenses. As of now, the researchers say that only one major manufacturer, Bausch + Lomb, is seriously pursuing such an initiative. (This contact lens wearer recently got a bizarre, 28-year-old surprise.)