Think Out Loud

Oregon State University scientists find tiny tire particles can harm aquatic life

By Sheraz Sadiq (OPB)
March 9, 2022 2 p.m. Updated: March 14, 2022 10:05 p.m.

Broadcast: Wednesday, March 9

Scientists at Oregon State University found that micro and nano-sized plastic particles from tires harm the growth and development of aquatic species such as mysid shrimp.

Scientists at Oregon State University found that micro and nano-sized plastic particles from tires harm the growth and development of aquatic species such as mysid shrimp.

John Dickens


Most of the rubber found in a car’s tire today is synthetic, made from plastic. And when tire tread wears down from driving, tiny plastic particles are shed into the environment. They present a growing source of pollution in waterways. So scientists at Oregon State University wanted to see if tiny bits of tire plastic, which are too small to even be seen by the naked eye, affect the health of animals like fish and shrimp that are found in coastal and freshwater ecosystems. We’re joined by Stacey Harper, a professor of environmental and molecular toxicology and environmental engineering, and Susanne Brander, an assistant professor in the fisheries, wildlife and conservation sciences department.

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Note: The following transcript was computer generated and edited by a volunteer.

Dave Miller: This is Think Out Loud on OPB, I’m Dave Miller. Every time we drive down a road we leave something behind – actually a lot of things, because our tires are constantly shedding tiny tiny plastic particles along with chemicals that are also embedded in the synthetic rubber. Those chemicals and those particles, micro and nano plastics often end up in the water in streams and rivers and oceans. They also end up in organisms that live in that water. So scientists at Oregon State University set out to learn how coastal and freshwater ecosystems are being affected. They published their findings recently in two scientific journals. They join us now to talk about what they learned. Stacey Harper is a Professor of Environmental and Molecular Toxicology and Environmental Engineering at OSU. Susanne Brander is an Assistant Professor in the Fisheries Wildlife and Conservation Sciences Department and part of the Coastal Oregon Marine Experiment Station at OSU. Welcome to you both.

Stacey Harper/Susanne Brander: Thank you. Thank you so much for having us today.

Dave Miller: Susanne Brander first. Can you give us a sense for the scale of this issue? How much microplastic or even smaller bits, nanoplastic is coming off of tires in the US every year?

Susanne Brander: Sure. As far as the statistics on that, I don’t have that off hand but we know that about 30% of the tire tread erodes from your typical tire and studies that have been conducted off the coast of South Carolina and also more recently in the San Francisco Bay are finding that tire particles are one of the biggest contributors to micro-plastic pollution. So really something that’s just arrived on the horizon in some ways in terms of us knowing more about it, so really concerning.

Miller: How small are the bits of plastic that we’re talking about here?

Brander: I’ll let Stacey take that one.

Stacey Harper: We’re dealing with the smaller end of microplastics. Microplastics go over a wide range, up to 300 microns. We’re dealing with the much smaller particles below five millimeters, so think about a grain of sand or a grain of salt, and then below that where you can no longer see the particles with the naked eye. And that would be in the nano scale.

Miller: And we’re talking about plastic even though we’re talking about tires because a lot of what’s in tires right now is actually synthetic, it’s actually plastic as opposed to natural rubber from rubber trees?

Harper: That’s a really good question. Tires are composed of a really complex mixture of synthetic polymers. So mostly synthetic rubber with a mixture of natural rubbers and then sometimes polyester and nylon fibers, as well as a lot of different chemical additives. It’s really a truly complex mixture that’s wearing from the tires and most tires are no longer made primarily of natural rubber any longer, so really would be considered a micro-plastic or a nano-plastic if small enough.

Miller: Stacey Harper, so there are these micro or nano plastics and then also chemicals that are embedded in these tires that also leach out?


Harper: Yes, that’s correct. So the chemicals- and we’ve known for a little bit some of the chemicals that cause some of the fish kills that we’ve seen in the salmon in the Pacific Northwest. So we’ve identified that. But ours is really the first investigation trying to look at the effects of the tire particles themselves, including that nano-sized fraction of particles that are invisible to the naked eye.

Miller: Stacey Harper. Can you describe the setup of these experiments physically, how you went about setting up these inquiries?

Harper: Yes. So for us, we were hoping to kind of mimic what is commercially available for all of the plastic studies that we do, and the tires are no different. So we went and purchased a standard, never been driven, standard passenger car tire, and milled it down using a cryo-mill. We cut it into small little bits and then stuck it in a chamber that we could then flash freeze, and there are some metal balls in there where we could just smash them up until they were reduced to basically a powder and then we have some separation techniques where we can separate out the size that’s kind of in that micro-sized range and the nano-size range and do our experiments from there. Then my lab focuses on freshwater organisms, whereas Susanne does some of the aquatic organisms that live in estuaries and marine systems.

Miller: Susanne, let’s start with the saltier version of this experiment. You looked at two different saltwater animals if I’m not mistaken, a kind of fish and a kind of shrimp, both of which can be found near the Oregon coast. Can you give us first the sort of the high level sense for your findings?

Brander: Sure. And just to clarify, we used a larval fish species that is used as a model across North America for measurement of responses to different pollutants. And so it’s found off the coast of California but not off the coast of Oregon and then the species of invertebrate we used, which is a micro-shrimp, is also commonly used across North America for such studies, and there are species of micro-shrimp found along the Oregon coast. But we looked at early life stages of these organisms, so the fish hatched out into tire particle exposures and the micro-shrimp were about seven days old. So only a few millimeters long each. We really wanted to get at that sensitive window when organisms are likely going to be more responsive to exposures. And we looked at both growth and behavior. We found that particles had an impact on growth just over a short time window of exposure just over a few days, and that the presence of particles also changed the way both organisms behaved in the water.

Miller: In what ways was their behavior changed?

Brander: That’s a really good question. So we use a system called Noldus EthoVision. And it’s basically a chamber that uses a computer to continuously record behavioral responses during an experiment. We’re able to measure things like distance, where in the chamber that the animals are swimming in, where they’re sort of spending the most time. We’re also able to measure subtle changes like their turn angle, how quickly they can turn and what angle that turn is at as well as something called meandering, which is basically just measuring you know how random their movements are. And all of these things in the wild can add up to increased susceptibility to predation or can also add up to increased difficulty in obtaining food. So there is really an ecologically relevant way to measure pollutant impacts.

Miller: And you were able to find these variations in either size or behavior after just a couple of days of exposure to the tiny bits of plastic?

Brander: That’s right. In the fish, we saw that both the micro- and nano-sized fractions impacted their growth. And as you increase the concentration, you saw a concomitant decrease in growth. And similarly with micro-shrimp we also saw a decrease in growth although they were somewhat less sensitive to the nanoparticles, but that may have been because they are relatively older and a bit larger in size compared to the fish species that we used. But we saw impacts on both.

Miller: Did you see impacts at concentrations of these particles that have been found in the wild?

Brander: That’s a really excellent question, and yes, we did, in some cases. We tried to match the mass of the particles we were using to mass concentrations that have been measured off the coast of South Carolina, off the coast of California, even, and some studies from Europe. And so our concentrations, if you weighed the amount of particles matched in some cases what is detected in the environment, what we don’t know and what Stacey alluded to earlier is at these smaller size fractions. We don’t necessarily know how many individual particles are out there, but predictions say that it’s likely that these particles are breaking down into smaller and smaller fragments.

Miller: So Stacey Harper, let’s turn to the freshwater piece of this. You looked at embryonic zebrafish and a kind of plankton. What did you find?

Harper: Let me start with the plankton because that was a simpler study where we take the- they’re called daphnia. And they’re a typical eco-tox model that’s been used for years. And we do the exposures for just two days. And we record things like immobility and then mortality. And what we found with the daphnia responses was all of the exposures whether they were particles in the nano- or micro- fraction and the leachate led to mortality in the daphniads. The microtire particles had higher toxicity than the nano-fractions for these guys, but most of the toxicity could be attributed to the leachate and not particle specific effects, which is different than what we see in the zebrafish, although the presence of the nano-tire particles themselves did enhance the toxicity that we see from the leachate. So we’re able to separate those out and tease apart whether it’s the chemicals that are in the leachate that are leaching from the tire particles or if it’s the particles themselves. So for the zebrafish, what we do is a  96 or a 120 hour or five day exposure. And again, like Susanne’s system, we start with these early embryos that are basically just a ball of cells that are kind of undifferentiated when we start to experiment. And then over five days you have a fully functional little fish swimming around and we can look for a bunch of different morphological malformations and then a couple of behavioral endpoints that we look for in the zebrafish. What we found was that all of the exposures impacted spontaneous movement, which is the first behavior that we recognize in the zebrafish embryos. It’s like a tail flicking that they do naturally at about 24 hours development. Since that’s impacted, that makes us think that it’s either something neurological or potentially muscular impacts on the system. The micro fraction was the only one that delayed the development of the zebrafish, which you can imagine could be detrimental to the fish in the long run if they’re stuck in their enclosed case they might be more food than if they were released. The nano-tire particles was the only one that was lethal, and that was not what we found in the leachate. So this is where we kind of diverge. We also saw some physical malformations, like a curved or bent axis, so the spine of the organism was curved. We noted hatching delays. And then for the leachate itself we saw some unusual ones that were related to like facial malformations, the jaw and the snout and the eyes were malformed. Those were some of the main findings. But I guess the big take home point here is that we’re seeing differences between the leachate which are the chemicals from these tire particles, the micro-fraction and the nano-fraction. So now we know that size and chemical composition are going to play a role in toxicity.

Miller: These chemicals and these bits of plastic are everywhere. They’re in tons of organisms. They are in human bodies as well. How much do we know about the effects on humans? We can’t you can’t put us in the same chambers with these little bits of plastics and do the same controlled experiments. Yet they’re ubiquitous. I mean we are being exposed to them so, but how much do we know and how much can we know about what these chemicals or particles are doing to us?

Harper: Sure, and that’s an excellent question. There is of course a lot less research that’s been done on humans at this point in comparison to aquatic organisms because really the issue of plastic pollution was first discovered and acknowledged in our oceans and now is moving into more freshwater research as well. But in terms of humans, there have been a number of cell line studies done and studies done in a known model such as mice and rodents and indications are that they experience some of the same types of stresses that we see in aquatic organisms. And so at the cellular level we see things like oxidative stress. So the presence of particles can cause the production of something called reactive oxygen species, which can cause damage inside cells, can also cause damage to tissues. We see indications in rodent models that reproduction may be affected at higher concentrations, that there may be influences on the endocrine system and so, but the jury is kind of still out on a lot of those studies and more research is currently being conducted. There’s a big effort in Europe for example, to conduct more research in terms of human health concerns, but we’re absolutely exposed, we know, that all of us contain microplastics, of a variety of types from food, from air, from water. So I think it’s something we’re going to be hearing a lot more about in the coming years.

Miller: Susanne Brander and Stacey Harper, thanks very much.

Brander / Harper: Thank you so much.

Miller: Susanne Brander is an Assistant Professor in the Fisheries Wildlife and Conservation Sciences Department and part of the Coastal Oregon Marine Experiment Station at Oregon State University, Stacey Harper is a Professor of Environmental and Molecular Toxicology there.  Tomorrow on the show, when Mira Jacob’s son was six years old, he started asking more and more complex questions about what it meant to be biracial in America. Jacob found that answering those questions led to some interesting and difficult conversations, which she eventually turned into a graphic memoir. It’s called Good Talk, We’ll talk about it tomorrow in front of an audience at Portland’s Lincoln High School. Thanks very much for tuning in. I’m Dave Miller, we’ll be back tomorrow.

Narrator: Think Out Loud is supported by Steve and Jan Oliver, the Rose E. Tucker Charitable Trust and Michael and Kristin Kern.