Here's Why You Should Never Flush Your Contact Lenses Down The Toilet

Scientists have issued a stern warning to contact lens users: If you flush used lenses down the toilet or sink, you risk clogging our already polluted waterways and oceans with even more plastic trash.

Wastewater treatment facilities in the U.S. simply don’t do a good enough job of filtering out the tons of contact lenses that are disposed of through the sewer system, according to new research presented Sunday at the American Chemical Society’s meeting in Boston.

The researchers found that contact lenses are so flexible that they can sometimes slide through the physical barriers meant to filter out nonbiological waste at treatment plants. The study’s authors, all of whom are from Arizona State University, told The New York Times that they interviewed workers at waste treatment facilities who confirmed seeing lenses floating in wastewater.

The researchers also tested how lenses fared when treated with microorganisms that are used at wastewater treatment facilities to break down biological waste.

The results were troubling.

The lenses were not broken down completely and instead showed signs of structural damage, said study co-author Varun Kelkar. That left them vulnerable to getting splintered into smaller fragments that could be released into waterways ― which could cause lasting harm to the fish and other organisms, as well as to the humans who may eventually eat those creatures.

“We found that there were noticeable changes in the bonds of the contact lenses after long-term treatment with the plant’s microbes,” Kelkar said in a statement. “When the plastic loses some of its structural strength, it will break down physically. This leads to smaller plastic particles which would ultimately lead to the formation of microplastics.”

Microplastics are a major source of water pollution globally. Up to 51 trillion microplastic particles, weighing as much as 236,000 metric tons, could be floating in the world’s oceans, according to a 2015 study. Marine organisms are known to consume these tiny plastic fragments, and recent studies have shown microplastic contamination in fish and shellfish are ending up on people’s dinner plates.

The new research suggests that contact lenses could be exacerbating this microplastics problem.

About 45 million people in the U.S. alone use contact lenses, according to a survey conducted by the researchers, and between 15 percent and 20 percent of those users said they flush their used lenses down the toilet or sink. Between 1.8 billion and 3.3 billion lenses are flushed each year in the United States, researchers estimated. That amounts to “about 20 to 23 metric tons of wastewater-borne plastics annually,” said Charles Rolsky, the study’s lead author, according to a post on ASU’s website.

The microplastics formed by contact lenses could also be making a mark on land.

“Sewage sludge is an abundant material routinely applied on land for sludge disposal and soil conditioning, thereby creating a pathway of macro- and microplastics from lenses to enter terrestrial ecosystems where potential adverse impacts are poorly understood,” the researchers wrote in the ASU post.

Study co-author Rolf Halden, director of ASU’s Center for Environmental Health Engineering, said in a statement that he hopes the new research will compel contact lens manufacturers to label their products with information about how to dispose properly of lenses ― that is, in a trash can and not a toilet bowl.

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This article originally appeared on HuffPost.