Here's What Happens When You Flush Contact Lenses Down the Toilet (and Why You Shouldn't)

Scientists are hoping your answer isn't "flush them down the toilet" or "toss them into the sink."

That's because a new study finds that discarding contacts lenses in these ways may ultimately end up contributing to microplastic pollution in waterways. Microplastics measure under 0.2 inches (5 millimeters) in length — about the size of a sesame seed or smaller — and can wind up in the ocean and the Great Lakes, posing a potential threat to aquatic life, according to the National Oceanic and Atmospheric Administration.

So, Halden and his team started with a survey of 139 individuals, including both contact lens wearers and non-wearers. They found that "15 to 20 percent of contact lens wearers are flushing contacts down the sink or toilet," lead study author Charlie Rolsky, a doctoral student in biology at the same institution, said in a statement. "This is a pretty large number, considering roughly 45 million people in the U.S. alone wear contact lenses."

Wastewater is also mixed with a variety of bacteria, which are tasked with breaking down biological waste. To better understand how these bacteria affect contact lenses, the researchers soaked five different contact lens materials in mixtures containing these bacteria for varying amounts of time. They found that lenses came out largely intact — though further analysis showed that the bacteria had weakened some of the chemical bonds in the materials, making it easier for the lenses to fragment into smaller pieces. This, ultimately, is what could lead to the formation of microplastics, the researchers said.

TOPICS

Sara is a staff writer for Live Science, covering health. She grew up outside of Philadelphia and studied biology at Hamilton College in upstate New York. When she's not writing, she can be found at the library, checking out a big stack of books.