According a recent report from CBS, between 2.25 million and 3 million Americans are flushing their contact lenses down the sink or the toilet.

And that adds up to six to ten metric tons of contact lenses piling up in wastewater plants every year.

When you flush your contact lens down the drain, it doesn’t dissolve. It breaks into smaller and smaller fragments. When those fragments get back into the water supply, they sink to the bottom of ponds or rivers, where bottom-feeding fish mistake them for food. And through these fish, the fragments of your old contact lens can end up on someone’s dinner plate.

So how should you dispose of contact lenses? First, check if your community offers recycling for contact lenses. If recycling isn’t an option, toss them in the garbage.