Diehard contact carriers (as the author of this article) will tell you that the best thing about the lenses is that they are invisible. But that very invisibility, although an asset in the eye, is an environmental liability after the short life of each lens is over. New research presented at the annual American Chemical Society conference on Monday suggests that US users do not really think about where their contact lenses go after they have been removed – and that is a big problem, both on land and in the water.

The conclusions are strict: as a result of the lax way of disposing of one in five of the approximately 45 million contact lens wearers in the United States, thousands of kilos of microplastic enter the environment – not to mention the tons of waste the packaging produces the lenses come in. And even if contact lenses are not flushed through the toilet or fall into the sink, they are not recycled.

"We do not know which fraction (presumably small) users of contact lenses use the recycling of both lenses and packaging," said Rolf Halden, an engineer at Arizona State University. Popular science in an e-mail interview. Contact lenses do not contain instructions for recycling the structurally complicated lenses or the polypropylene blister packs in which they occur. Halden and his co-authors, graduates Charlie Rolsky and Varun Kelkar, say that the best recycling option for these materials would be for the manufacturer to take them back. "The cleaner and more homogeneous the recycling stream is, the easier the recycling process and the higher the value of the export, so we want these blister packs and lenses to go straight back to the manufacturer," Halden said. Popular science.

To get these results, the three conducted an online survey of 400 people who match the demographics of contact lens users across the country with questions about their disposal practices. This survey showed that 15 to 20 percent of American contact users throw their lenses on the toilet or in the sink instead of throwing them in the trash can. To find out what happens to them after their journey through the drain, the researchers tested how contact lenses behaved in wastewater treatment tanks, where all the water goes.

Contact lenses are made of complicated polymers that create a material known as hydrogel. The team discovered that these polymers sink to the bottom of the waste water tanks.

"Given that the contact lenses do not degrade in the treatment plant, they only have two outlets," Halden said earlier today to a panel of journalists in a press conference at the annual meeting of the American Chemical Society. "One is through the waste water, as purified waste water, and the other becomes part of the sewage sludge that is the by-product of the treatment of waste water."

This means that many lenses end up on fields in artificial fertilizer. From there the miniscule fragments can end up almost anywhere, even in the water thanks to run-off. Literally billions of lenses end up in American waste water every year, Halden said. Although each is small, the researchers found that together they add at least 44,000 pounds of contact lens bits. The small packs with which the lenses are delivered add more than 14,000 tons of polypropylene plastic to the impact. The research has not yet been done or published by peer review.

"Disposable contact lenses are more vulnerable than other plastics, especially once they have been dried," Halden said Popular science. "Dry contact lenses easily spread into very small pieces that can reach even more places and are even harder to detect."

That is a lot of waste, especially when compared to the small boxes with contact lens packages that each contact carrier handles itself. And it is part of a much, much bigger problem of & # 39; invisible & # 39; plastic pollution, says Sara-Jeanne Royer. Royer, who was not involved in the current research, is a postdoctoral research assistant at the University of Hawaii who investigates plastic pollution. "There are still so many unknown sources of plastic pollutants," she says. She compares the news about contact lenses with that about microbeads in facial scrubs or microfibers from clothing – just more plastic sources that enter the environment as part of daily tasks.

But contact lenses are a bit different than one of these examples, because they are medical devices. "In the medical field they are very concerned about the chance of infection and infection," says Royer. In other words, nobody wants to risk your gnarly eye bacteria to get someone else's eyeball to land (or anywhere else, for that matter). Because of these concerns, she says: "They do not seem to work very well with recycling." But contact lenses are currently being thrown away like all other waste, not like medical waste.

However, there is the possibility that this product can be recycled in an unusual and useful way. What Halden and his co-authors ask for is a shift in the culture of contact lens manufacturers, but they think that a take-back program in which the manufacturer recycles the lenses and blister packs can make a significant difference. One company, Bausch & Lomb, already has a specific program aimed at daily users of contact lenses.

If you can not send your lenses to a recycling program, Halden says, the best option is to throw them in the rubbish bin. And maybe we're thinking about switching from daily newspaper to monthly, because this particular problem shows that even a small change can make a difference.