Consumers are becoming more aware of the environmental damage caused by microplastics, which can be found in toothpaste, cosmetics and other personal care products. Now there’s a new source to consider from contact lenses, which – when flushed into wastewater systems – break down into minute pieces of plastic pollution.
That’s according to researchers in the United States who presented their novel findings Sunday at the American Chemical Society conference in Boston, Massachusetts. Through interviews with disposable contact lens users, the team from Arizona State University determined that at least one in six of them are flushing or rinsing their lenses away and into U.S. waterways.
“We found that 15 to 20 percent of contact wearers are flushing the lenses down the sink or toilet,” said Charles Rolsky, a Ph.D. student who presented the work based on 13 different brands of lenses. “This is a pretty large number, considering roughly 45 million people in the U.S. alone wear contact lenses.”
The research team estimates that 20 to 23 metric tons of plastic lenses end up in wastewater each year in the U.S., where disposable contact lenses, sometimes worn for a single day, are a USD$2.7 billion industry. Globally that number soars to $7.5 billion, suggesting far more “invisible” planetary plastic.
Ironically, contact lenses make it easier for others to see but harder for scientists to find, precisely because they’re clear and so small. They’re more dense than water, so they’re likely to sink to the bottom in wastewater plants and waterways, where a pair of contact lenses typically can be found in every kilo of wastewater sludge.
The lens plastic is different from other plastic waste too. “Contact lenses are frequently made with a combination of poly(methylmethacrylate),” or PMMA, Rolsky said. It’s commonly used in windows and signage, but combined with silicones and fluoropolymers in contact lenses to make them softer and allow oxygen to pass through to the eye.
In the wastewater treatment plants, that plastics combination is broken down by anaerobic and aerobic microorganisms, according to the researchers, who replicated the chemical processes in the lab.
“There were noticeable changes in the bonds of the contact lenses after long-term treatment with the plant’s microbes,” said Varun Kelkar, another member of the research team at the ASU Biodesign Institute’s Center for Environmental Health Engineering. “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.”
Those microplastics then enter the food chain and pose a threat to aquatic life, much as tons of tiny plastics added to pharmaceuticals, detergents and other consumer products do in the U.S., European Union and elsewhere. They also pick up and absorb pollution more readily, making them even more toxic.
“These (aquatic) animals are part of a long food chain,” the scientists warn. “Some eventually find their way to the human food supply, which could lead to unwanted human exposures to plastic contaminants and pollutants that stick to the surfaces of the plastics.”
The ASU team wants manufacturers to, at a minimum, make sure packaging instructions call for proper disposal of contact lenses while they pursue better biodegradable options. In the meantime, they’re asking the rest of us to avoid flushing or rinsing used lenses into the wastewater system – and for now, that means throwing them in the trash.