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Persistent Pollutants

Podcast: California confronts monitoring challenges for microplastics in drinking water

As California gears up to test for microplastics in drinking water, Stereo Chemistry explores efforts to detect the particles and what their presence means for health

by Britt E. Erickson , Kerri Jansen
February 21, 2023


Photo of a hand covered in microplastics with water in the background.
Credit: Shutterstock
Credit: C&EN

Researchers reported finding microplastics in drinking water nearly 5 years ago, prompting California lawmakers to require monitoring of the state’s drinking water for the tiny particles. But in 2018, there were no standard methods for analyzing microplastics. So California regulators reached out to chemists and toxicologists from all sectors to develop those methods. They also sought assistance in developing a health-based limit to help consumers understand what the monitoring results mean for their health. In this episode of Stereo Chemistry, we will hear from some of the scientists leading those groundbreaking efforts.

Subscribe to Stereo Chemistry now on Apple Podcasts, Spotify, or wherever you listen to podcasts.

The following is a transcript of the episode. Interviews have been edited for length and clarity.

Sherri Mason: The real intention behind both of those studies, I’ll be honest, was to make an impact. It was definitely to get people talking and to realize that this issue is not something that’s abstract, that’s out there, that’s in the oceans, distant from them. It’s in your tap water.

Kerri Jansen: That’s Sherri Mason—she goes by Sam. We’re hearing her reflect on work she did nearly 5 years ago analyzing microplastics in tap water and bottled water. Those studies sent a shock wave through the public and beyond. And today, we’re looking at how that work triggered a regulatory and scientific revolution.

This episode is part of our ongoing series about the future of water. I’m your host, Kerri Jansen.

And I’m excited to welcome back C&EN reporter Britt Erickson. Hi, Britt!

Britt Erickson: Hi Kerri!

Kerri: Britt is one of our policy reporters at C&EN. And, Britt, you’ve been covering microplastics basically as long as “microplastics” has been a thing, right?

Britt: I guess so! I think I first covered plastic pollution in the oceans in 2010. But this focus on tiny microplastics, it’s much newer.

Kerri: So, let’s start by defining microplastics. What are we talking about here?

Britt: Well, you’ve probably seen the pictures of plastic trash littering beaches.

Kerri: Sure.

Britt: Well, over time the plastic debris breaks down into smaller and smaller particles. And when those particles are less than 5 mm, we typically call them microplastics.

Kerri: Right. OK.

Britt: And I think it’s really important to understand that microplastics are everywhere. They’re not just in water, they’re in the air, in the soil; they’ve been found in wildlife. And scientists have found microplastics in human blood and lung tissue. There’s no doubt that we are being exposed to them.

Kerri: And today we’re going to focus on microplastics in drinking water specifically. Why is that such a big deal right now?

Britt: That’s largely due to a big policy decision coming out of California. By the end of 2023, California’s government will become the first in the world to require monitoring for microplastics in drinking water. And the state is investigating whether it should set a limit on microplastic levels in drinking water to protect public health. That would be a world first, too.

All of this is happening because of a California law passed in 2018. And that law was triggered by Sam’s study on microplastics in tap water.

Kerri: Wow, OK, well, she did say she wanted to make an impact!

Britt: But here’s the thing: when California passed its law, there were no standard methods for detecting microplastics in water, and there were very few studies on their health effects. How are you supposed to regulate microplastics when you don’t even have a good way to measure them? Basically, the science was not ready for this new policy.

Kerri: In this episode, we’ll trace the research that prompted this groundbreaking policy. Then we’ll hear from chemists and toxicologists about the challenges they’ve overcome and those that lie ahead as they try to help regulators unravel the risks of tiny plastic particles in the water that we drink everyday.

Britt, can you take us back to the beginning. When did microplastics become a household word?

Britt: Well, the story begins with some of the first reports of microplastic pollution in freshwater ecosystems. So Sam, from the tap water study, she is now the director of sustainability at Penn State University in Erie, Pennsylvania.

Sam’s first paper on microplastic pollution came out in 2013. Now, that work showed that colorful plastic microbeads were slipping through water treatment processes and getting into the Great Lakes. It actually led the Food and Drug Administration to ban plastic microbeads in cosmetics and personal care products in 2015. Sam told me she was surprised by how much interest there was in that work.

Sherri Mason: I didn’t realize exactly how much people loved the Great Lakes. I probably should have not been surprised by that. But they love them quite a bit. And so we started kind of making a splash with our work from the very get-go.

Britt: So that’s when consumers really started thinking about potential adverse effects of microplastics. Sam followed up that work with a paper on microplastics in tap water and then bottled water. That was really the first time that anyone had looked at microplastics in those water sources. Research had come out from Germany looking at microplastics in beer. There were some studies from China looking at microplastics in salt. But no one had really taken the next step to look at what’s in our drinking water.

The tap water study was really a community science project, where real normal people collected tap water samples. They gathered 159 samples from 14 countries on 5 continents.

Kerri: Oh, wow.

Britt: Yeah, that’s a lot of samples to detect microplastics in.

Sherri Mason: It was definitely a citizen science kind of campaign. We did collaborate with a organization called Orb Media. So they helped us do that kind of outreach.

Britt: So these people that were collecting the water samples were just everyday people, they’re not specialized scientists. They just collected their tap water, putting a cap on the jar, and shipping it back to the lab.

Kerri: So, the same thing I’d do if I were filling a glass of water to drink.

Britt: Yeah, exactly, that was the idea. And the results showed that more than 80% of the tap water samples contained microplastics.

Kerri: So definitely not an isolated issue.

Britt: Yeah.

Kerri: So you said 80% of samples had microplastics. How many plastic particles were in there? I mean, are we talking like 2 pieces or a hundred? Or thousands?

Britt: They found an average of about 5 pieces of plastic per liter of tap water. So that’s just a couple of plastic particles in a glass of water. You probably wouldn’t even notice them.

But the method they used for this study could only detect particles down to about 100 μm—about the width of a human hair. There’s a good chance there were smaller particles in there, too. In the bottled water, they used a more sensitive method, and they actually found more than 300 particles per liter.

Kerri: That’s so much plastic!

Britt: That does seem like a lot. And I think that’s what caught the attention of California lawmakers.

Kerri: Ok, so at this point, lawmakers think there’s probably microplastics in their tap water, but they don’t have any detail on how much of this stuff is in their water particularly, just based off of Sam’s studies. Or how levels might change over time.

Britt: That’s right. You have to understand exposure before you can determine health risks. They needed some way to get the full picture.

Kerri: OK, and that’s why they passed this law. To kind of force everyone to figure this out, fast.

Britt: Exactly. But remember, in 2018 when California enacted the law, we didn’t really have methods yet for testing for microplastics in drinking water, at least not methods that everyone could agree on.

Scott Coffin: It seemed that every laboratory was using their own proprietary method or something that they had adapted from a previous method published in the literature. And really it was the wild west at that point.

Britt: That’s Scott Coffin from the California State Water Resources Control Board. Scott is a toxicologist and research scientist. The Water Board hired him in 2019 to help get the state’s microplastics monitoring program off the ground.

Scott Coffin: There were no standards for even what type of instrument to use, or what to report. Quality control was largely absent. And so this is really a great opportunity for a governmental organization to come in and bring all the researchers together to agree on the type of standards that should be adopted by the community.

Britt: So as the regulators are scrambling to come up with these new methods, they reached out to chemists and toxicologists from all sectors—government, industry, and academia. They needed a good, harmonized way to detect microplastics in drinking water. Only then could they understand how much of this stuff people were being exposed to.

Kerri: Hang on, though. We monitor all kinds of contaminants in water. Why can’t we just use an existing method? What makes detecting microplastics such a challenge?

Britt: Well microplastics are not just one contaminant. They are a mixture of different polymer types. They have different shapes and sizes. And they are not dissolved. They are solid particles.

It’s hard to get a handle on exactly which polymer it is, whether it’s got metals associated with it. Sometimes they have these plasticizers and different colors.

Kerri: OK, yeah, that’s complicated.

Britt: And that’s why it’s so hard to come up with one method to detect all microplastics. Sam’s team was actually one of the first groups exploring possible analysis methods. They used dyes to help find the tiny particles.

Sherri Mason: In the case of tap water, we used rose bengal, which stains things that are not plastic. So allowing the plastic to be more easily seen. In the case of the bottled water, we decided to use Nile red. It sticks to the plastic and not to other things, and allows them to fluoresce under certain wavelengths of light. So it made it really nice to be able to shut off all the lights in the lab, and then these particles would glow.

Britt: Of course, being able to see the particles is one thing; actually counting them is another.

Sherri Mason: You have these fluorescing particles in the darkness of your lab—it reminded us of like looking at stars in the night sky. And so we reached out to an astronomer, and asked: do y’all have some way of like counting stars in the night sky? He really quickly developed this software he called Galaxy Count that would take those fluorescing particles and count them for us.

Kerri: Ah, that’s cool. Better than counting them all by hand, for sure.

Britt: Yeah. Scientists have been trying out a lot of different approaches.

And remember, these mixtures can be very complex. So researchers are now starting to use more automated methods that can count the particles for you, and identify the polymer type, and send the data to a database automatically. These advanced methods combine microscopy with spectroscopy. Microscopy provides a way to see the particles. Spectroscopy provides information about their chemical makeup.

Kerri: Mm. So there’s all of these new methods now, but it’s still a problem if not everyone is using the same one.

Britt: Right. So California regulators looked at the most popular methods out there and picked their favorite two. They then got labs around the world to test the methods to ensure that they all got the same results for a given sample. Here’s Scott again.


Scott Coffin: The methods that we developed are quite, I would say, quite prescriptive. They have a standard operating protocol that has very specific steps that laboratories should follow. Everything from extraction of the particles, to analysis, and reporting into a database. We want to make sure that there are as few uncertainties as possible with the analysis.

Britt: One of the methods relies on Raman spectroscopy, the other Fourier transform infrared, or FT-IR spectroscopy. Both methods can identify polymer types. FT-IR can detect particles as small as about 50 μm. Raman has the advantage of being able to detect even smaller particles—down to 20 μm—but it’s much more expensive than FT-IR, and it doesn’t work well for certain particles. So it’s not like we can just use one or the other—they’re complementary.

Kerri: Got it. But the older methods had a limit of around 100 μm, and now we can identify particles down to 20 μm.

Britt: Yeah, I was pretty impressed. But then Scott hit me with a plot twist.

Scott Coffin: Incidentally, a lot of water treatment plants are already removing particles down to about 10 microns or so.

Kerri: So the particles that might actually show up in drinking water are still too small for any analysis method to see.

Britt: Right. So that means that when California water providers start up their monitoring later this year, as they are required to do by this 2018 law, they will only have to monitor sources of drinking water, such as rivers and reservoirs. Those sources haven’t been filtered yet, so there might be some data there that we can actually track. They’ll keep that up for at least a couple years.

Scott Coffin: Hopefully in 3 years’ time, these methods that we’re using or additional methods will come online and be able to detect these smaller particles.

Britt: In the future, regulators also want a method that can report the mass of particles, not just the number of particles. Because mass or concentration is typically used in risk assessments. Other labs are working on making methods faster and cheaper. Right now it can take about a week to identify just 2,000 particles, which is obviously an obstacle to more widespread monitoring.

And, look, we’ve been talking about California this whole time, because that’s where this groundbreaking law was passed. But this effort will very likely expand beyond California.

Scott said he hopes California will serve as a model for how the US Environmental Protection Agency and other states can implement microplastic monitoring programs. So there’s been a lot of work since 2018 to standardize methods for detecting microplastics in water. The methods aren’t perfect, but they’re a start.

Kerri: OK, so we have some ways now to start to understand how much of this stuff is actually in our drinking water, even though it sounds like comprehensive data is still a ways off. But even without knowing the exact levels, we do know that we’re ingesting some microplastics. So I guess that brings us to our next big question: Is that bad for us?

Britt: Yeah, that’s an important question. And the answer is, it’s complicated.

Kerri: Coming up next, we’ll explore what scientists have learned about the health risks of microplastics. That’s after a short break.

Mark Feuer DiTusa: Hi, I’m Mark Feuer DiTusa, C&EN’s podcast producer! And I’m here to ask for your help. We here at Stereo Chemistry are looking for new candidates to join us for C&EN’s Bonding Time, our podcast project that pairs up two sensational chemists for an in-depth conversation about their science and . . . whatever else comes to mind.

Leigh Krietsch Boerner (in interview): How do you keep going?

Sarah Reisman: Compartmentalization? [laughter]

Melanie Sanford: Exactly!

Mark (voice over): So who do you want to hear on a future installment of C&EN’s Bonding Time? We want to know! You can reach us on Twitter by tweeting @cenmag, or you can send us an email at Use the subject line “C&EN’s Bonding Time.” Once again, that email address is Now back to the show.

Kerri: Ok, Britt. In the first part of this episode, we heard about science that prompted California to require monitoring for microplastics in drinking water. We also heard about the state’s struggles to standardize methods for that effort, to understand how much of this stuff people are being exposed to. But the big question we haven’t tackled yet is—are microplastics in our drinking water actually harmful to our health?

Britt: Right. Well, that’s a question that a lot of people have, of course! So, let’s go back to 2018, when California passed its monitoring law. One of the requirements of that law is for the state to consider whether to adopt some sort of limit that could help consumers better understand what microplastics in their drinking water means for their health. But in 2018, there weren’t very many studies on the health effects of microplastics.

So the job of developing that limit went to our favorite toxicologist-slash-water regulator, Scott Coffin. And he’s a great fit for that job, because Scott has been interested in the health effects of plastic pollution since 2013, when he led a group of students from around the world on an ecotourism trip to Costa Rica.

Scott Coffin: We had some free time. So I brought the students along the beach with some trash bags. We just went along and picked up debris. And this was a very remote region in Costa Rica that had no nearby towns or cities. So we later talked to some of the local volunteers and learned that the trash that we were finding on the beaches was actually washing up from the ocean.

Britt: When I caught up with Scott last fall, he had just returned from a trip to Australia, where he presented some of California’s microplastics work at the International CleanUp Conference. I wanted to get his perspective on whether California is ready to adopt a limit on microplastics in drinking water to protect public health. The law only says regulators have to consider doing so. Here’s what he told me.

Scott Coffin: We conducted a health effects workshop to provide recommendations to the state on whether we can develop a number using today’s science. And our group reached consensus that we’re not quite there yet, in terms of developing a quantitative limit, but we are pretty close. We identified 29 in vivo animal studies that exposed these animals to polystyrene plastics of certain sizes. And we found fairly consistent levels that cause some type of biological effect. Particularly, four of these studies reported effects on male reproductive systems.

Kerri: Well, that seems pretty clear.

Britt: Not so fast. All those studies used polystyrene beads, which are round, smooth, rigid plastic beads. The stuff you see in the environment is more like fragments, with jagged edges. So polystyrene beads probably don’t tell the whole story. Scott and everyone else I talked to acknowledge that. But for now, that’s the best data they have.

Scott told me that he expects within the next 3 years or so to have enough information to develop a recommended limit that can be used in regulations. But so far, that work is all still based on the beads; it is unlikely to take into consideration all the different potential hazards associated with various types of microplastics and the impurities that attach to them.

Kerri: So, it’s a start.

Britt: Yeah. But I wanted to learn more about how researchers are trying to move beyond those beads. So I talked with Christie Sayes. She’s an environmental scientist and toxicologist at Baylor University in Waco, Texas. She investigates the health impacts of microplastics, using water samples she gets from a variety of sources, including the US EPA.

Christie Sayes: They have a lot of chemicals associated with them, either the plastic itself, which includes the polymer base, the plasticizer, any other hardening agents or solubilization agents that the surfaces may have. But then they also have adsorbed or absorbed environmental contaminants associated with them as well.

Britt: Each of those chemicals in the mixture could have different health effects. So Christie’s lab is trying to tease apart the effects of each component in the mixtures.

Christie Sayes: What our lab has focused on is comparing the microplastic particle that has all of its chemical constituents, such as the pigments and the plasticizers and metals and other additives that may go into the plastic processing part. And we’re testing each one of those individual components separately, individually, to then compare the contributions of the individual constituents or components in a plastic to the actual resultant microplastic at the end.

Britt: They test some microplastic particles collected from the environment, but they also create their own in the lab. They then expose various cell cultures to the particles in vitro using systems that mimic digestion and inhalation.


Christie Sayes: We have a couple of different model systems in our lab, we have a gut on a chip model and a lung on a chip model. We also are developing a brain on the chip model as well.

Britt: The chip part is really just a square plastic dish that can be made either the size of the palm of your hand or just a couple centimeters in either direction. There is a membrane in the middle of the dish that separates the top and bottom.

So, you add cell culture media to the bottom layer. The top layer gets whatever kind of cells line whatever organ you’re talking about. So for the gut model, they use cells that line the intestines. And then they use a gentle vacuum to flow a suspension that contains microplastics through that cell layer.

So they’re trying to get an understanding of what happens when these cells in your gut are exposed to microplastic particles. What they’re seeing is the cells are not really taking them up. Instead, it’s more of a, like a scraping, like they’re causing inflammation because of the jagged edges, but they’re not being taken up because they’re too big.

Kerri: Hmm. Interesting.

Britt: And you don’t get that kind of reaction with the smooth spherical particles, which is why this research is so important.

Kerri: Yeah. So, are other groups also trying to fill in some of these data gaps related to the health effects of microplastics?

Britt: Yeah, the European Union is funding several studies. It’s important to understand that we are just starting to see the health effects work in the scientific literature, and right now there are more questions than answers. Here’s Christie again:

Christie Sayes: We know we’re being exposed to them. We need to then marry that up with, are there effects? And are those effects transient and something that we can get over and simply excrete through our body and not have lasting effects? Or are the effects sustained, and then turn into a chronic condition like chronic inflammation or chronic neuro inflammation that may cause a debilitating condition?

Britt: And it’s not just regulators and scientists who are taking on this issue. Industry groups, also, are putting money into trying to answer some of these questions related to health effects of microplastics. There’s an international coalition of chemical industry groups that’s spending several million dollars every year on microplastics research. Right now, a lot of these efforts are focused on standardizing materials and methods for health studies, which is similar to the work we discussed for standardizing analytical methods.

Kerri: OK, so, with the health data still a few years away, if someone is concerned about their possible exposure—their likely exposure—to microplastics, what do these experts say we can do now to help reduce that exposure?

Britt: Unfortunately there’s not much consumers can do to remove microplastics from their water. Scott told me there is no indication that household filters like a Brita filter are effective at removing microplastics. So without investing a lot of money in something like a reverse osmosis system, there’s not much we can do right now.

But here’s what I think is interesting—yes, there’s a lot more work to be done on microplastics, but the science has advanced really quickly in the last few years. It’s actually quite remarkable considering not many people were talking about microplastics a decade ago.

Kerri: Right. And do you think those advances would have happened as quickly without that law?

Britt: It’s hard to say for sure. I talked with at least one representative from an industry organization who says the law did not change the pace of research, that the work started before the bill and would have continued even without that new policy. But on the other hand, maybe California’s action did push things forward. Scott thinks it did.

Scott Coffin: The legislature understood that unless there is a government agency calling for standardization, for monitoring, for some type of consensus, that might not happen. And I think they were right about that. This bill forced the community to come together. Because we had a deliverable and a deadline and we had a stakeholder that was going to actually use that deliverable. And for scientists, knowing that your work will directly be impactful is the most invigorating and motivating thing.

Kerri: And that’s what we were hearing from Sam, as well, at the beginning of the episode, that idea of having an impact.

Britt: Yeah. And Sam told me she sees outreach as an essential part of that impact, for all scientists.

Sherri Mason: Too many of us, as scientists, we sit in the lab, and we do our work. And we publish in peer-reviewed journal articles that are read by 10 people. And that gets us what we need to continue our jobs, and we take a lot of satisfaction in that. But we have to get our science out into the public to really have that work make an impact.

Britt: I doubt we’d be seeing laws like California’s without researchers like Sam talking to the press and getting the word out about microplastic pollution. And I was curious what that meant to her, to have played such a key role in creating this impact.

Sherri Mason: I decided at a very early age that I wanted to be a chemist, and I decided I wanted to be an environmental chemist, and it was all about trying to have an impact on society. So it’s that little girl in me that when I hear, when I become aware of kind of the impact that my research has had, the little girl in me is just kind of jumping up and down and sitting there like proud super girl, hands on the hips going yeah! So yeah, I love my work. And I love the fact that it’s seen and leading to an awareness and change.

Kerri: This episode of Stereo Chemistry was written by Britt Erickson with audio editing by Mark Feuer DiTusa. Stereo Chemistry’s executive producer is me, Kerri Jansen. Full credits for this episode are in the show notes.

Stereo Chemistry is the official podcast of Chemical & Engineering News. C&EN is an independent news outlet published by the American Chemical Society. Thanks for listening.


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