Every year, Americans flush 2.6 to 2.9 billion contact lenses down the drain according to research from Arizona State University. There's been a lot of research done on single-use plastics such as straws, silverware and plastic bags but no one has yet looked at how these everyday medical devices may contribute to pollution in our soil and waterways.
The calculation of how many lenses end up in our waste water, plants and habitat hinge on a variety of data sources. The CDC states that about 45 million Americans wear contact lenses. By using data from the major contact lens manufacturers about the various types of contacts purchased (daily, biweekly, monthly) the ASU researchers were able to calculate that Americans wear a total of 13.2 to 14.7 billion lenses a year. Next the researchers surveyed more than 400 contact lens users about how they dispose of the products, finding that 21 percent discard their lenses down the toilet or sink. Those cumulative numbers helped them arrive at their estimate of more than 2.5 billion lenses residing within our sewage in a given year. Once sewage laden with contact lens fragments is pumped into soil it may seep into the environment in different ways. Rain could wash lenses into rivers and oceans where they would float like tiny, tentacle-less jellyfish. Or they could sit in soil, desiccating in the sun. The latter scenario in not harmless either. Once these lenses dry they become incredibly brittle and will very likely shatter into very small particles. Then these micro-plastics can persist in the environment and they can be consumed by animals, birds or insects and make their way into the food chain.
Although contact lens pollution is a concern, it is dwarfed by the 8 million metric tons of larger plastic that clogs our oceans every year. There's an easy way to prevent contact lenses from becoming pollutants say the ASU researchers and that is by throwing them in the solid waste compartment of the house- the garbage can is preferable to the sink or the toilet.
(Excepted from Scientific American 8/2018)