Don't throw your contact lenses down the drain

BOSTON, Massachusetts — A new study on contact lenses is proving to be eye-opening.

The study, released Sunday, says many users dispose of their old lenses by flushing them, instead of placing them in trash cans.

Those lenses later end up contributing to pollution in oceans, lakes and rivers.

That's because lenses don't break down completely in sewer systems.  They're also transparent, which makes tracking what happens to them difficult.  They're also made of a material that is not routinely screened for in environmental monitoring studies.

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Roughly 45 million people in the U.S. use about 14-billion contact lenses every year. According to the study, 15-20% of contact lens wearers are flushing their own lenses down the drain. That's about 1.8-3.36 billion lenses flushed per year.

That results in an estimated 50 thousand pounds winding up in sinks and toilets, adding about 20-23 metric tons of wastewater-borne plastics annually.

The study was presented by Arizona State University researchers at a conference in Boston on Sunday.

CNN contributed to this story.

Cox Media Group