Flushed contact lenses add to burden of plastic waste

IMAGE Contact lenses recovered from treated sewage sludge could harm the environment.  view more  Credit Charles Rolsky

IMAGE Contact lenses recovered from treated sewage sludge could harm the environment. view more Credit Charles Rolsky

The inspiration for this work first began from personal experience. "But I started to wonder, has anyone done research on what happens to these plastic lenses after their useful lifespan is over?"

A new report reveals that a shocking amount of contact lens users - almost 20 percent - dispose of those little plastic circles in a terribly irresponsible way, by flushing them down the toilet or the drain of the sink.

They found 15-20% of US users simply flick these fiddly lenses down the drain via the bathroom sink or toilet. Halden, Rolsky and a third member of the team, Varun Kelkar, are at the Biodesign Institute's Center for Environmental Health Engineering at Arizona State University (ASU).

Earlier research on the individual waste from an average person's disposable contact lenses in the United Kingdom looked more broadly at the environmental footprint of contacts and compared it to waste from soda cans, suggesting that the lens-related waste is relatively small, per person-roughly equivalent to the disposal of 15 cans of Coca Cola per year.

The calculation of how many lenses end up in our wastewater plants and habitat hinged on a variety of data sources. This $2.7 billion US market has made contact lenses more comfortable and disposable.

The next part of the research was to figure out what happens to those lenses.

To understand how lenses break down in sewage, Rolsky and his colleagues placed the corrective lenses in wastewater treatment tanks filled with hungry microorganisms. Further, the plastics used in contact lenses are different from other plastic waste, such as polypropylene, which can be found in everything from vehicle batteries to textiles.

They are often made with a combination of poly (methylmethacrylate), silicones and fluoropolymers to create a softer material that allows oxygen to pass through the lens to the eye.

These differences make processing contact lenses in wastewater plants a challenge.

Every year, about 45 million Americans rely on contact lenses to see the world more clearly. They also learned that the microbes treatment plants count on to reduce the amount of organic matter did not change the molecular makeup of the polymers found in many contact lenses.

"The plastics may have the capacity of soaking up contaminants, and so the plastic shards. they'll likely be loaded with toxic chemicals, like heavy metals, PCBs [polychlorinated biphenyls] and other things", Halden said.

Mr Kelkar said: '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".

Aquatic organisms are known to mistake microplastics for food, introducing the indigestible plastics into long food chains.

The American Chemical Society research presented Sunday in Boston found 20 percent of 400 contact lens users flush old contact lenses down the toilet or in the sink.

Dr Halden added: 'Ultimately, we hope manufacturers will conduct more research on how the lenses impact aquatic life and how fast the lenses degrade in a marine environment'.