Why You Shouldn’t Flush Your Contacts Down The Drain

4:53 minutes

a close up of two pieces of ripped contact lenses that are covered in grime
Contact lenses recovered from treated sewage sludge could harm the environment. Credit: Charles Rolsky

Since they came on the market in 1995, people have been wearing daily, single-use contact lenses to see clearly. Unlike their reusable counterparts that are changed out weekly or even monthly, these lenses don’t need to be cleaned and stored at the end of the day. Instead, you open a fresh, sterile pair of contacts every day. While these contacts are better for the health of your eyes, it also means throwing out little pieces of plastics every day—and some of these contact lenses are infiltrating our waterways.

[The world’s oceans are overflowing with plastics pollution.]

Research from Arizona State University estimates that 20 to 23 metric tons of contact lenses end up in waterways each year. Charles Rolsky, a Ph.D. student in the Biodesign Center for Environmental Health Engineering at Arizona State University,  joins Ira Flatow to discuss how contacts are polluting our water.

Editor’s note: This article was updated on August 24, 2018 to replace the metric ton estimate previously cited by EurekAlert (6 to 10 metric tons) with measurements from Arizona State University (20 to 23 metric tons). 

Segment Guests

Charles Rolsky

Charles Rolsky is a PhD student in the Biodesign Center for Environmental Health Engineering at Arizona State University in Tempe, Arizona.

Segment Transcript

IRA FLATOW: Now it’s time to play Good Thing, Bad Thing.


Because every story has a flipside. We’re going to talk about contact lenses. They’ve become more convenient, you know, because the single use kind came on the market that made it very easy for people, made it very convenient to use. But when you open a new pair of contact lenses every morning– maybe you do that– do you throw out that little piece of plastic every night? And then, you know, you rush to flush the plastic lens down the drain– maybe the toilet, maybe the sink. Well, it turns out that those plastic lenses are clogging our waterways. Here to tell us more about that is Charles Rolsky, a PhD student at Arizona State University. Welcome to Science Friday.

CHARLES ROLSKY: Thank you so much for having me. I’m a huge fan of the show.

IRA FLATOW: Oh that’s great to have you on here. So tell us about it. So the good thing about this, of course, is that they are single use, they’re better for your eyes, right, because it maybe keeps out some infections that reusing a contact lens might have. That’s the good news.

CHARLES ROLSKY: Sure. Yeah, good news is maybe less time exposed to your contact lens holder, or less time in your eye, maybe you kind of reduce the chances of something bad happening. We can see that is a good thing.

IRA FLATOW: OK. So then the bad thing is, we’ve got so many of these being flushed down the toilet or the sink.

CHARLES ROLSKY: Yeah, the bad news is people kind of– maybe they lose track of them. I don’t wear them because it grosses me out to touch my eye, but I think you can accidentally or sometimes intentionally flush them down the sink or toilet. And then from there, they have a pretty incredible journey.

IRA FLATOW: [LAUGHS] That’s interesting. I see the movie. How many contact wearers and lenses are we talking about? What’s the bulk of this?

CHARLES ROLSKY: So we’re talking about roughly 45 million people in the United States wearing contact lenses every year. And an increasing proportion of them are switching to daily disposable just because they’re easy. There’s– a lot less health risks, and there’s also incentives with buying in bulk. So we’re definitely seeing a trend of those increasing.

IRA FLATOW: Do they know what percentage of people who wear the disposables are actually getting rid of them down the drain?

CHARLES ROLSKY: So we did a survey here at ASU and we found that around 20% of those wearing contact lenses are actually flushing them down the sink or toilet.

IRA FLATOW: 15% to 20% then. I guess if you would– how many millions of people? That’s a lot of contact lenses.

CHARLES ROLSKY: Yeah, it ends up being thousands of kilograms ending up as waste every year, especially because they’re going through and interacting with wastewater treatment plants, which was also part of our study.

IRA FLATOW: Well, tell us what happens when they get there, to the treatment plant.

CHARLES ROLSKY: Well, so what happens is they encounter a couple of different degradative atmospheres or environments. They have a nice little tango with a lot of microorganisms, which we’ve shown to the microorganisms to break the contacts down a little bit. But ultimately, they persist. And the physicality of the treatment process can also turn to contact lenses into smaller pieces which we lovingly refer to as microplastics. And from there, they end up in biosolids, which is the treated biological matter. And it can either be burned, or applied on land, or sent to a landfill. So it ends up being a pretty fascinating journey for these little plastic pieces.

IRA FLATOW: So how did you know that the lens weren’t actually being filtered out of this sewage waste system?

CHARLES ROLSKY: To answer this in a non-disgusting way, we checked the filters at multiple stages of the treatment process. And then we actually looked through the biosolids at the end of the biotreatment process, or the water treatment process. And going through a lot of organic material was fun, but we ended up finding some contact lens fragments. And so this material was going to be trucked out to either be applied on land, or sent to a landfill, or burned.

IRA FLATOW: I have to ask what the disgusting way of describing this would be in a family-oriented–

CHARLES ROLSKY: So we lovingly say– yeah, we say a biological material. But if you can imagine, the majority of the stuff that comes out of your house is flushed. So I think your imagination can then ride with that one.

IRA FLATOW: So where do these bits of plastic end up after they leave the sewage plant?

CHARLES ROLSKY: So if it’s land applied, it can be sent to any type of agricultural area where they’re looking to enrich the soil. If it’s sent to an incinerator, then it’s going to be burned. And then it can also be sent to a landfill site. And the danger here is that microplastics are known to absorb contaminants at pretty high concentrations. So they basically act as a vehicle for some of these nasty pollutants. So if you’re burning it, it could end up in the atmosphere. If it’s being applied, you know, this is agriculture, it’s also got runoff. It’s basically acting as a vehicle to deliver some of these nasty things.

IRA FLATOW: So let’s put a Warning label on it and say, you know, maybe people will stop.

CHARLES ROLSKY: Absolutely. Yeah, we’ve found that none of the contact lens boxes that we looked through had any type of disposal strategy suggested. So I think that if these manufacturers were to sort of put a small label on their saying to throw them with the solid waste, it would be good.

IRA FLATOW: Well, thank you, Charles, for taking time to be with us today.

CHARLES ROLSKY: Thank you so much.

IRA FLATOW: Charles Rolsky, PhD student at Arizona State University.

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