Washington (AFP) – Contact lenses that are flushed through the toilet or placed in sink drains contribute greatly to microplastic pollution in the oceans, researchers warn Monday.
The amount of plastic waste made by lenses and their packaging in the United States alone is equivalent to 400 million toothbrushes a year, said researchers at Arizona State University who described their findings at the national meeting and the American Chemical Society exhibition in Boston.
"These are important polluters," researcher Rolf Halden of the Center for Environmental Health Engineering of ASU's Biodesign Institute told reporters.
"Every year, billions of lenses end up in American wastewater and they contribute at least 20,000 kilos per contact lens per year."
Halden, who had been in touch for most of his adult life and started the investigation after wondering what happened to all those discarded plastic lenses, calculated that packaging adds about 29 million pounds (13 million kilograms) of polypropylene to the waste of contacts.
Approximately 45 million people in the United States only wear contact lenses, which carry at least 13 billion lenses each year.
A survey among US wearers of contact lenses "found that 15 to 20 percent of the contact lens wearers wash the lenses through the sink or toilet," said researcher Charlie Rolsky, a PhD student at ASU.
And what happens to those lenses?
Researchers followed them to wastewater treatment plants, where they discovered that the lenses fall apart but do not degrade.
The plastic particles either flow into the ocean or become part of sewage sludge, which is often used as fertilizer on land. Runoff then returns these contaminants to the oceans.
Small fish and plankton can confuse microplastics for food.
These indigestible plastics then pass through the food chain and into the human food supply.
Researchers said they hope that their study will be a warning for manufacturers of contact lenses and encourage users to throw them away properly with other solid waste.
Halden said that many people do not realize that rinsing contact lenses is dangerous for the environment.
The scientific team found only one manufacturer of contact lenses, whose packaging advised people how to dispose properly.
"Do not put those lenses in waste water, put them in solid waste or recycle them," said Halden.