What Radioactive Animals Teach Us About Nuclear Fallout

IRA FLATOW: This is Science Friday. I’m Ira Flatow. When I say “radioactive wildlife,” I’ll bet your brain goes to Chernobyl’s wolves, which, believe it or not, despite the odds, are still thriving at the site of the nuclear disaster. Or maybe you’ve heard of the rat snakes in Fukushima that pick up radioactive contamination as they slither around.

Well, let’s add two more to that list of radioactive critters– turtles and wild boar. Yes, the hairy pigs. They’re the subjects of two new studies that looked at radioactivity in wildlife and mapped out where it came from. Joining me are Dr. Cyler Conrad, Archeologist at Pacific Northwest National Lab in Richland, Washington, who worked on the turtle study, and Dr. Georg Steinhauser, Professor of Applied Radiochemistry at the Vienna University of Technology in Vienna, Austria, who looked at boar. Welcome to Science Friday.

GEORG STEINHAUSER: Hello.

CYLER CONRAD: Thank you for having us.

IRA FLATOW: Nice to have you. OK, then. Let’s start with your study about wild boars. Why choose them?

GEORG STEINHAUSER: Because they’re famous, actually. So ever since Chernobyl, they’ve been studied quite intensely in Europe. So we’re not talking about Chernobyl, or the vicinity of Chernobyl. We’re talking about Central Europe– so Germany, Austria, Switzerland. these countries.

And they have been known to be radioactive. So they are known to accumulate radioactive cesium. But what is even more interesting than just the sole accumulation– basically, they violate the law of physical decay, because they keep more radioactive than they should be, from a physical perspective.

So the half-life of cesium 137 is 30 years. And when we look at wild hog meat, or their flesh, It keeps radioactive at levels that should no longer be allowed, should not be permitted by the half-life. So they keep more and more radioactive than they should be, and we don’t observe the half-life that we should observe. So that’s fascinating.

IRA FLATOW: Why is that?

GEORG STEINHAUSER: Well, we tried to find it out. And we’re still not fully there, but we have now published a paper that kind of sheds some light on onto the whole story. We looked into the isotopic composition of that cesium. So until now, basically, or until, like, two weeks ago, everybody only looked at the cesium 137. And that’s, of course, a very prominent fission product– radioactive.

And now we added another isotope that has not been observed previously in that system, and that’s the cesium 135. And with those two, we can establish an isotopic fingerprint, and it can tell us, where does the cesium come from? Until a few years ago, everybody thought, well, it must be all Chernobyl– or basically, almost everything must be from Chernobyl, because that’s the prime source of radioactivity in Europe.

But it turned out in our study that we found the fingerprint of nuclear weapons fallout. And that is very prominent, actually, in wild hogs. So they keep their radioactivity from 60 years ago.

IRA FLATOW: Wow. You must have been surprised by that.

GEORG STEINHAUSER: Oh, yeah. Basically, very much. We were very much surprised. Actually, when my PhD student first came to me and told me the results of his first measurements, he had a sad face– a frowny face, basically– and said, something went wrong. The analysis wasn’t correct.

Because it looked like the result must be off, and the analysis must be wrong. But in fact, the fingerprint was so, so much dominated by the nuclear weapons fallout, the analysis was correct. But just– our view of the world wasn’t there yet.

IRA FLATOW: That is really fascinating. Why is it just the boars that are radioactive, and not the other animals?

GEORG STEINHAUSER: We can only speculate about that. But I think it is because they are the only animals that get their food sources from underground, especially in winter, when it’s cold. When food on the surface is scarce, then they have to dig. And so they dig down to find those truffles– not our human truffles, but these deer truffles.

And they are known to be hyper-accumulators of radioactive cesium. And since the cesium moves very slowly through soil, it migrates very, very slowly– only tiny fractions of an inch per year– the Chernobyl cesium has not arrived there yet. So these mushrooms, they still accumulate the old cesium from the 1960s. And the 1986 Chernobyl cesium has not even arrived there, at least not at its full extent.

IRA FLATOW: That’s amazing. So what does this tell you, then, about how radioactive materials move around the world?

GEORG STEINHAUSER: Well, nature doesn’t forget, right? So once a radionuclide has been released into the environment, of course, in many environmental compartments, we lose sight of this radioactivity after a while. So we’re no longer worried about our apples, or plums, or whatever vegetables being contaminated from Chernobyl, because the radioactivity, or those radioactive atoms, those ions, they’re immobilized in soil. They are washed out.

So they just move elsewhere. And our vegetables and our apple trees can no longer take them up. But that doesn’t mean that the cesium is gone. It’s just elsewhere. And we found this elsewhere– it’s all in the wild boar.

IRA FLATOW: That’s amazing. Cyler, let’s move to your study about uranium in turtle shells. Why turtles?

CYLER CONRAD: Yeah. That’s something that we were really interested in, because we wanted to understand ways in which we could establish long-term records of contamination, essentially, over the 20th century, when all of these activities were occurring, especially above-ground nuclear testing. And we wanted to find a way to measure those records accurately, in real time, when those events occurred. And so you can imagine that something like a tree ring– that is a really useful environmental kind of sink, because it’s able to capture different information within the rings, and you can backtrack and essentially establish these chronological records through time.

But essentially, radionuclides, like uranium– it migrates within tree ring layers. And so you might see uranium signals from nuclear events that are occurring prior to when they should have. And you can think of 1945 as, essentially, the onset of this. And in some studies, we know that uranium moves between tree rings. And so it’s not entirely a useful type of sample to look at these long-term records over time.

But we know that turtles– and I mean turtles, and tortoises, and sea turtles– they grow that colorful material on the back of their shells. It’s called scute keratin, and it’s a tissue that’s quite similar to human fingernails, for example. And they grow that material in sequential layers over time.

And so we were able to find turtles that inhabited areas where past nuclear testing occurred, or other types of nuclear activity, and then sequentially analyzed and picked up signals– very, very small signals– of nuclear activities in the landscape from these turtle shells. it was really quite remarkable. We think of them as walking tree rings, as an example.

IRA FLATOW: Turtle rings.

CYLER CONRAD: Yeah.

IRA FLATOW: So how do you know where to go look for the rings on the turtles? Do you have special places you look for?

CYLER CONRAD: Yeah. Different turtles grow that scute keratin in different ways, and we spent a lot of time with each of the different types of turtles that we were studying, actually working out the growth characteristics of that shell scute keratin to understand, OK. We know that we have a layer that was formed at this time, and so we can sample that layer and get a picture to, essentially, this calendar year. And so we spent a lot of time working out, essentially, the mechanics and the growth characteristics of keratin for different turtles from these different locations where nuclear events occurred.

IRA FLATOW: Hm. How does the uranium end up in the turtles in the first place?

CYLER CONRAD: Ah, yeah. It’s a really interesting process. And as Georg was just mentioning, I think there’s a fun connection here between what wild boar are experiencing, and also how turtles are experiencing this out in the environment, where we know that sediments, for example, are trapping these radionuclides, are trapping these elements in isotopes. They’re being accumulated and retained within different organisms– plants and animals– in different ways. But because turtles are on the ground, they’re digging their burrows, they’re breathing in the dust of some of these environments, there seems to be a very clear mechanism in the routing of this contamination into their tissues, which is then deposited in that scute keratin on their shells from things like sediments and soils, and then also the plants that they’re consuming that are growing and living within those same sediments and soils.

IRA FLATOW: This is really interesting. You know, I want to know if there could be some very old turtles still around, maybe 100 years old, with radiation from the first nuclear tests.

CYLER CONRAD: Mm-hmm. Yep. It’s quite possible. And we’re really interested in trying to find those types of samples, you know? We’re still studying lots of different turtles, and tortoises, and sea turtles out there. But you know, Galapagos tortoises, for example, or sea turtles that have a very long-lived life– it is quite possible that they might be picking up these signals or might have picked up these signals in real-time, when they experienced those events sort of on this global scale.

And we focused our work on museum specimens. And that helped us find really special and unique turtles from, say, the Oak Ridge Reservation that was collected in 1962, but had a sequence back to 1955. You know, it’s really quite remarkable. And I think there’s still a lot to learn.

I think we’ve established that we can measure these very small quantities of elements and isotopes within turtle shell, and now this really opens up a much larger question of, OK, how many different turtles are picking this up from what types of environments? And how far back does that record go in time? And really, that leads us to being able to establish and reconstruct really specific localized and regional records of contamination, either through fallout or through other types of waste in the environment. We can pick up those records in these turtles.

IRA FLATOW: What surprised you about your findings with turtles? You said, oh, my goodness. I never expected that.

CYLER CONRAD: Yeah. We were surprised in many ways. In one way, we were surprised that we were able to actually do this, because there had been a lot of previous research on turtles, especially sort of measuring the radioactivity in turtles, as an entire animal. So we were really surprised that, say, you take a green sea turtle from Enewetak in the Republic of the Marshall Islands.

You know, it’s collected 20 years after testing ends, and yet the analysis of its shell scute keratin is picking up a very distinct uranium isotopic ratio that is telling us something about the testing that occurred roughly 20 years prior to when that turtle died and was collected. So we were really surprised at the specific isotopes that were still present in these shells, even though they’re in such small quantities, that they were able to accurately tell us something about that nuclear event in the landscape. And it was very closely tied, and really, it retained that information, and was able to tell that story about what we’ve known about these nuclear legacies throughout the world.

IRA FLATOW: Georg, a study from a few years ago found that snakes around Fukushima carry radiation in their bodies. And of course, Chernobyl’s wolves are a famous example. How is your study similar or different from those?

GEORG STEINHAUSER: I don’t want to bore you with my boar study too much, so if there’s so many–

IRA FLATOW: You got that in. You had to get that out.

[LAUGHTER]

You’re on the right show for a pun like that.

GEORG STEINHAUSER: If there’s so many interesting animals out there. So actually, I would like to add fish, at some point, to this collection. So I love fishing. So that would be interesting.

So of course, our study is in line with all those previous studies that shows the accumulation of a radioactive material in some organism. What we can add now is, like, a different dimension. By using this isotopic fingerprint, the ratio of the two isotopes that we have studied– the cesium 135 and the 137– we can now expand our knowledge, and we can show mixing effects. And we can also show the buildup of the accumulation.

So that is kind of, like, a snowball effect. And some animals are more sensitive, in a way, than others, and they are more prone to accumulation. And the boar are certainly one of those, certainly.

IRA FLATOW: This is Science Friday from WNYC Studios. We’re talking about how scientists can study radiation through wildlife. Let’s look at the big picture. What do studies like this tell us about the environmental and health effects of nuclear weapons, Georg?

GEORG STEINHAUSER: Well, it doesn’t come as a surprise that the fallout from nuclear weapons explosions from the 1950s and 60s– that it started to become worrisome, in a way. It’s not a surprise that President Kennedy and Nikita Khrushchev negotiated the Partial Test Ban Treaty that was opened for signature in 1963 that banned all atmospheric nuclear explosions. And that was, in my understanding, pretty much an emergency brake, because the northern hemisphere got contaminated pretty severely with the nuclear weapons fallout.

So I don’t know the numbers for the cesium. But for plutonium, I think the number is– when you go into your backyard, and you grab a handful of dirt, you’re also holding one billion atoms of plutonium in your hands. That is a result from the fallout in the 1950s.

IRA FLATOW: Everybody’s?

GEORG STEINHAUSER: Everybody’s backyard on the whole northern hemisphere. It could not be too remote from anywhere, everywhere. It’s global fallout. So–

IRA FLATOW: That is a– that’s a sobering image I’m having.

GEORG STEINHAUSER: Yeah. Well, that’s the onset of the Anthropocene. That’s when humankind started to shape nature as a whole.

IRA FLATOW: Wow. Cyler, the US has a long nuclear legacy. What can studies like yours tell us about this?

CYLER CONRAD: Yeah. Our work studying these turtles has really– you know, it’s highlighted to us the ability to use certain types of animals in the environment to reconstruct something about these events in the environment. Something– and I think Georg is speaking to this, too– the capability today, the sensitivity of our instrumentation, in order to be able to even measure these isotopes and understand the mixing and the routing of those isotopes in the environment– that really allows us, now, to take a step back and really look back in time, try and find some of these animals or other organisms that are growing these sequential tissues, similar to a tree ring, or like Georg mentioned, a lake sediment core, even an ice core, something like that, and being able to actually measure those radionuclides from human events and understand, OK, this is what a specific record looks like from this location.

And I think for turtles and tortoises and sea turtles, there’s something even more broadly relevant and important about their ability to retain this type of environmental information in their tissue in a sequential way. And that is really important because as we need to find ways to study and understand, say, regional and localized effects of climate change, for example, there’s a lot of isotopic and elemental information that’s embedded within those sequential scute layers. And I think that if we focus our research back onto the environment and trying to understand these animals and organisms, we can really reconstruct something about our human past and that anthropogenic impact in the environment, on those landscapes, and help better understand how we can, essentially, mitigate and prepare for the future.

IRA FLATOW: Fascinating stuff. Gentlemen, I want to thank you for taking time to be with us today.

CYLER CONRAD: Thank you so much.

GEORG STEINHAUSER: Sure. Thank you so much.

CYLER CONRAD: You’re welcome. Dr. Cyler Conrad, Archeologist at Pacific Northwest National Lab in Richland, Washington. Dr. Georg Steinhauser, Professor of Applied Radiochemistry at the Vienna University of Technology in Austria.

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