Over the last decade, the use of softer plastic contact lenses has grown rapidly with people using daily, weekly or monthly disposables in greater numbers than ever before.
Study co-author Rolf Halden, director of ASU's Center for Environmental Health Engineering, said in a statement that he hopes the new research will compel contact lens manufacturers to label their products with information about how to dispose properly of lenses ― that is, in a trash can and not a toilet bowl.
"When the plastic loses some of its structural strength, it will break down physically".
The ASU research team is presenting their results today at the 256th National Meeting and Exposition of the American Chemical Society (ACS), held in Boston from August 19-23.
Aquatic organisms are known to mistake microplastics for food, introducing the indigestible plastics into long food chains.
"Good for the contact lens wearer during use, not so good when the things get out into the environment".
Lab member Charlie Rolsky, a PhD student, told the conference: 'We began looking into the United States market and conducted a survey of 139 people.
Of an estimated 45 million U.S. contact lens wearers, that's around 9 million right there.
Analyzing what happens to contact lenses and lens fragments once emitted by wastewater-treatment plants has been a challenge for researchers.
Lenses that are flushed away travel through the sanitary sewer system and most end up in wastewater treatment plants, and, being heavier than water, they tend to sink to join the sludge. 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.
Contact lenses frequently contain acrylic, silicones and fluoropolymers.
Once sewage laden with contact lens fragments is pumped onto soil it may seep into the environment in different ways, the researchers say.
Researchers from Arizona State University exposed five polymers that are present in many manufacturers' contact lenses to anaerobic and aerobic micro-organisms found in wastewater treatment plants.
The researchers found that contact lenses are so flexible that they can sometimes slide through the physical barriers meant to filter out nonbiological waste at treatment plants. Thus, pollution from contact lenses has avoided detection until now.
About 45 million people in the USA alone use contact lenses, according to a survey conducted by the researchers, and between 15 percent and 20 percent of those users said they flush their used lenses down the toilet or sink. 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 study researchers'] method of making assumptions and estimations is quite reasonable", she adds. Its main offices are in Washington, D.C., and Columbus, Ohio.