They may look tiny and harmless, but with billions being flushed each year, they're having a bigger environmental impact than you may realize.
Contact lenses have improved quality of life for many people, allowing them to see the world more clearly without having to deal with glasses. Forty-five million Americans wear them, and an estimated 5 to 15 percent of Europeans. Along with this convenience, however, goes a significant amount of waste, generated by the plastic packaging, foil tops, and the lenses themselves.
Researchers from Arizona State University decided to quantify the U.S.-based waste, since there has been no previous study done on what happens to contact lenses at the end of their useful life. The team began by surveying contact lens users and was surprised to find that 15 to 20 percent dispose of old lenses down the drain or toilet. As study co-author Charles Rolsky said,
“This is a pretty large number [that amounts] to 1.8–3.36 billion lenses flushed per year, or about 20–23 metric tons of wastewater-borne plastics annually."
When flushed or washed down the drain, lenses enter the wastewater stream and end up at wastewater treatment plants. They become incorporated into sewage sludge that is spread on fields to fertilize the soil. The quantities are significant: for every two pounds of sludge, a pair of contact lenses can typically be found. In co-author Rolf Halden's words, it creates "a pathway of macro- and microplastics from lenses to enter terrestrial ecosystems where potential adverse impacts are poorly understood."
The researchers experimented with the various types of plastics used to make contact lenses, exposing them to the anaerobic and aerobic microorganisms that are found in biological wastewater-treatment plants to determine their effect. From an ASU press release,
"The team concluded that microbes in the wastewater-treatment facility actually altered the surface of the contact lenses, weakening the bonds in the plastic polymers and promoting their disintegration into microplastics."
Microplastics are a tremendous source of pollution, the extent of which is only starting to be grasped. They enter lakes, rivers, and oceans, where they are ingested by marine wildlife and enter a long food chain. This can cause chemical leaching, a false sense of satiety, and malnutrition, as well as be passed on to any humans who eat contaminated fish or crustaceans. Microplastics also contribute to the swirling gyres of plastic debris in the world's oceans.
Is there a solution? Until researchers are able to come up with a contact lens that is "inert during use but labile and degradable when escaping into the environment," or until every optometrist and contact lens dispenser adopts a recycling program like the one recently launched by Bausch & Lomb together with TerraCycle, the best thing is to dispose of contact lenses with other solid waste. The ASU team wants manufacturers to include proper disposal information on its packaging as a reminder to users that where they put their old lenses does have an impact on the planet.