Why Contact Lenses Can't Be Flushed Down The Toilet

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Why Contact Lenses Can't Be Flushed Down The Toilet
Why Contact Lenses Can't Be Flushed Down The Toilet
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Why contact lenses can't be flushed down the toilet

According to a new study, one in five contact lens wearers flushes their lenses down the sink or toilet rather than throwing them in the trash. This poses a serious potential environmental hazard.

Why contact lenses can't be flushed down the toilet
Why contact lenses can't be flushed down the toilet

Photo: freestockphotos.biz /

According to a new study by the Biodesign Institutes Center for Environmental Health Engineering at Arizona State University, one in five contact lens wearers flushes their lenses down the sink or toilet rather than throwing them in the trash. The paper was presented at the National Meeting and Exposition of the American Chemical Society.

This poses a serious potential environmental hazard. According to the director of the Center and co-author of the project, Dr. Rolf Halden, the problem is that contact lenses are not biodegradable: “These are medical devices - you do not expect them to be super biodegradable. Good for contact lens wearers during use, but not so good when things are released into the environment."

“We found that 15 to 20% of contact lens wearers flushed the lenses down the sink or toilet,” said graduate student Charles Rolsky, a member of the research team, in a report. "That's a fairly large number considering that approximately 45 million people in the US wear contact lenses, which equates to about 1.8-3.36 billion lenses washed out annually, or about 20-23 metric tons of plastic in wastewater per year."

Contact lenses washed down the drain end up in a sewage treatment plant. Denser than water, the lenses sink to the bottom, ultimately posing a threat to aquatic life, especially bottom fish, which can swallow them.

Analyzing what happens to lenses is problematic for several reasons. As you know, contact lenses are transparent, which makes them difficult to observe in the complex environment of a wastewater treatment plant. In addition, the plastics used in lenses differ from other plastic waste (polypropylene, which can be found in everything from car batteries to textiles). Contact lenses are made from a combination of polymethyl methacrylate, silicones and fluoropolymers to create a softer material that allows oxygen to pass through the lens to the eye. Therefore, it is unclear how wastewater treatment affects lenses.

To address this problem, researchers exposed five polymers found in most contact lenses to the anaerobic and aerobic microorganisms present in wastewater treatment plants. They found noticeable changes in the bonds of contact lenses after prolonged treatment - microbes actually altered the surface of contact lenses, weakening the bonds in plastic polymers.

“When plastic loses some of its structural strength, it will physically break down, which … will eventually lead to the formation of microplastics,” says third team member Varun Kelkar.

Aquatic dwellers can mistake indigestible microplastics for food, which negatively affects their digestive system. Some of these animals, as part of a long food chain, end up in human food.

Contact lens packaging currently does not inform customers of their disposal. Corporations should add labels recommending that contact lenses be thrown in the trash, not washed away. Holden noted that several manufacturers have already launched recycling programs to recover plastic from lenses.

“Ultimately, we hope that manufacturers will do more research on how lenses affect aquatic life and how quickly lenses degrade in the marine environment,” concludes Holden.

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