Contact lenses may appear harmlessly soft and small, but a big chunk of American users are improperly disposing their used lenses and adding to the planet's microplastic problem, Arizona State University researchers found.

In a survey of 409 wearers, about 1 in 5 responded that they flushed their used lenses down the toilet or sink instead of throwing them in the trash, according to a new study presented at the American Chemical Society's National Meeting and Exposition.