Never wash contact lenses down the drain!

They may look tiny and harmless, but with billions being flushed each year, they’re having a bigger environmental impact than you may realize.

Contact lenses have improved quality of life for many people, allowing them to see the world more clearly without having to deal with glasses. Forty-five million Americans wear them, and an estimated 5 to 15 percent of Europeans. Along with this convenience, however, goes a significant amount of waste, generated by the plastic packaging, foil tops, and the lenses themselves.

Researchers from Arizona State University decided to quantify the U.S.-based waste, since there has been no previous study done on what happens to contact lenses at the end of their useful life. The team began by surveying contact lens users and was surprised to find that 15 to 20 percent dispose of old lenses down the drain or toilet. As study co-author Charles Rolsky said,

“This is a pretty large number [that amounts] to 1.8–3.36 billion lenses flushed per year, or about 20–23 metric tons of wastewater-borne plastics annually.”

When flushed or washed down the drain, lenses enter the wastewater stream and end up at wastewater treatment plants. They become incorporated into sewage sludge that is spread on fields to fertilize the soil. The quantities are significant: for every two pounds of sludge, a pair of contact lenses can typically be found. In co-author Rolf Halden’s words, it creates “a pathway of macro- and microplastics from lenses to enter terrestrial ecosystems where potential adverse impacts are poorly understood.”

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