Nearly 45 million people in the United States wear contact lenses. These tiny circles aid our vision just like routine eyeglasses but do not last for a long time. Unlike the latter, after a certain period, contact lenses have to be disposed of.

This is where a team of Arizona State University researchers encountered the problem of micro-plastic pollution — the pressing environmental concern scientists have been warning us about.

Contact Lenses in Sewage Sludge Contact lenses recovered from treated sewage sludge could harm the environment. Photo: Charles Rolsky

Normally, one would think micro-plastic pollution occurs mainly due to the disposal of commonly seen consumer product plastics and industrial waste, and contact lenses are too small to drive such a problem. But, if the recent survey conducted by these researchers is to be believed, contact disposal is a major concern.

Nearly 20 percent of contact lens wearers in America or some 9 million people are flushing used lenses down the toilet or drain, as per the study. This, as per initial estimates, would amount to 3.36 billion lenses or 20 metric tons of plastic being washed down the drain every year — in the U.S. alone.

The researchers conducted the survey after noting no other study in the past looked at contact lens disposal from the perspective of pollution. But, that was just one part of the work.

In order to fully determine the real impact of the disposed of lenses, the team had to know what happens when they go down the drain, into wastewater treatment plants.

Understanding how contact lens plastics would react to treatment processes was critical to determine their real-world impact. But, the transparency of the lenses made it difficult for the team to see its behavior directly.

So, the group sourced common polymers used in different contact lenses and exposed them to various microorganisms found in wastewater treatment plants. The work revealed “noticeable changes in the bonds of the contact lenses after long-term treatment with the plant's microbes," Varun Kelkar, a member of the team, said in a statement.

This indicated microbes in treatment facilities affect structural strength of contact lenses, making them weak. As a result of this alteration, they break down extremely small pieces of plastic debris, contributing to the problem of micro-plastic pollution.

From there, the micro-plastics in the wastewater sludge can enter land or water-based ecosystems, harming living beings. Animals, for instance, can mistake them for food and suffer from a range of digestive problems.

More worryingly, as many animals are involved in long food chains, some of these particles might even reach back to humans in the form of their food supply.

"Ultimately, we hope that manufacturers will conduct more research on how the lenses impact aquatic life and how fast the lenses degrade in a marine environment," Rolf Halden, another study author, added.

The team, in fact, thinks manufacturers should mention the exact way of disposing these lenses on their packaging (by placing them with other solid waste) while looking for ways to develop more advanced, easily degradable versions.

The study was presented at the 256th National Meeting & Exposition of the American Chemical Society.