Use of herbicide linked to Parkinson’s is on the rise in the US

[MUSIC PLAYING] FLORA LICHTMAN: Hey, it’s Flora, and you are listening to Science Friday. Paraquat is a herbicide widely used in agriculture. It’s toxic. It’s been linked to Parkinson’s, and it’s been banned in over 70 countries. But not here. In fact, its use here is on the rise.

One of the plants in the US that processes paraquat is in Wayne County in southeastern Mississippi. And according to a startling piece of reporting from my next guest, the plant is leaking large amounts of paraquat into the air. Here to tell us more is environmental reporter, Delaney Nolan, who reported the story for The Lens and the Mississippi River Basin Ag & Water Desk. Delaney, thanks for being here.

DELANEY NOLAN: Thanks so much for having me. I love Science Friday.

FLORA LICHTMAN: Oh, thanks. Take us to this plant in Mississippi. Where is it? What does it do?

DELANEY NOLAN: Yeah, this is a plant in Waynesboro, Mississippi, which is a small, quite rural town. And at this plant, they formulate and repackage paraquat. So paraquat is this cheap, super toxic, what they call burn-down agent herbicide. So we don’t make paraquat in the United States anymore. Now, it is mostly made in China or the UK, and it’s imported to the US.

FLORA LICHTMAN: Where it’s banned, right?

DELANEY NOLAN: Where it’s banned. It’s banned in China. It’s banned in the UK. It’s banned in EU. It’s banned in Brazil. It’s banned in more than 70 countries because it is, again, so poisonous.

FLORA LICHTMAN: So what is the plant doing exactly?

DELANEY NOLAN: So they take this chemical, paraquat, and they add some other little chemicals and additives, and then they repackage it. They are turning it into a product that then gets distributed and sold to farmers.

FLORA LICHTMAN: So what did you find in terms of emissions?

DELANEY NOLAN: Yeah. So paraquat is not technically considered an air pollutant. So it’s not something like ozone that’s regulated by the federal government and says, hey, if your facility emits over a certain amount of this, you have to get a permit.

Instead, paraquat is a toxic chemical. That means it’s regulated by something called the Toxics Release Inventory, which, basically, is this publicly available database where a little over 600 different toxic chemicals are tracked just to keep people informed. So it’s not saying how much you’re allowed to release, but a community can look up what’s around them and what chemicals are being released in the air.

So I was able to see all the releases of paraquat that have been reported in the last about 10 years. And this facility in Waynesboro, Mississippi is way out above the rest and the amounts that it is emitting. So I’ll give you a little bit of comparison.

If you’re a farmer, and you want to treat an acre of your farm, you’ll use about a pound of paraquat. Other places that handle paraquat, they have released between 1 and 5 pounds of paraquat into the air in the last five years. The Waynesboro facility, in 2024, released 47,000 pounds of paraquat into the air. That is a crazy amount of paraquat that is being released into the air as a fugitive emission.

FLORA LICHTMAN: A fugitive emission. So it’s not coming out of a smokestack. It’s leaking. But why? Why is it leaking so much paraquat?

DELANEY NOLAN: We don’t have more information about that, unfortunately. I reached out to the company, which is called Sipcam Agro, as well as the plant manager, to try to learn a little bit more about why so much of this paraquat is going into the air.

But all we can see is that these are reported as fugitive emissions, which generally means that it’s not a deliberate part of the process that’s coming out of a smokestack, and it’s an estimate as well. So this is probably based on some information they have about the repackaging process. But the actual numbers could be higher or lower.

FLORA LICHTMAN: Is it legal, Delaney?

DELANEY NOLAN: It is legal, yeah. What they’re doing is absolutely legal because, again, this is not an air pollutant that’s regulated by the federal government. They have to report it. And the State, so in this case, the Mississippi Department of Environmental Quality, they have purview to regulate or set maximum thresholds. But generally, States aren’t doing that.

FLORA LICHTMAN: We know paraquat has been linked to Parkinson’s. Are there elevated Parkinson’s rates in this area?

DELANEY NOLAN: There are. And so I want to also give this with a grain of salt, because paraquat exposure can take years to show up as Parkinson’s disease. So I wouldn’t say that the rates that we are seeing of elevated Parkinson’s are necessarily tied to the emissions right now.

Paraquat can also be used in agriculture and forestry. So it could be that people were getting exposed to paraquat from the timber industry long before Sipcam showed up. But that said, yeah, Wayne County has top 7% rates of Parkinson’s mortality for reporting counties in the country.

FLORA LICHTMAN: Thanks for sharing this reporting with us.

DELANEY NOLAN: Thank you so much for listening.

FLORA LICHTMAN: Environmental reporter, Delaney Nolan. She reported the story for The Lens and the Mississippi River Basin Ag & Water Desk.

Up next, what are the risks of paraquat exposure, and how well do we understand the biological link to Parkinson’s? My next guest has studied paraquat exposure for more than 25 years and is here to explain. Dr. Beate Ritz is a professor of epidemiology at UCLA. Welcome to Science Friday.

BEATE RITZ: Thank you for having me.

FLORA LICHTMAN: So take us through it. Biologically, how well understood is this link between paraquat and Parkinson’s? Are we beyond a correlation?

BEATE RITZ: Absolutely, in terms of biologic understanding, we are. But I also think we are very close to, in humans, to what we call a causal association, because you’re not doing human experiments, you’re using observational studies. But from the animal models, the cell models, and everything we chemically about paraquat, I would say, we understand quite well what paraquat does to cells and possibly, also does to these dopamine cells that die in Parkinson’s disease.

FLORA LICHTMAN: What does it do to cells?

BEATE RITZ: Well, it initiates something we call redox cycling. And that is a mechanism that generates a lot of what’s called oxidative stress. Oxidative stress is something that you can compare to rusting of a car, where molecules are rusting, or the membranes of cells are, basically, becoming rancid, like fat becomes rancid when it’s out in oxygen for too long. And that’s the kind of processes that actually happen with paraquat.

But in human and mammalian cells, we also know that paraquat actually impairs something we call the respiratory chain of mitochondria. And there’s a complex I that seems to be specifically attacked and taken out by paraquat.

FLORA LICHTMAN: So paraquat is damaging these cells that we know are the cells that are damaged in Parkinson’s disease, these dopamine neurons, right?

BEATE RITZ: Yes, exactly. But it might not even be just dopamine neurons. It could also be some kind of immune cells that are very reactive in this area of the brain where the dopamine neurons sit. So this oxidative stress could also just be acting on these immune cells that then become kind of angry.

And when they become angry, they harm the neurons. So whether it’s just dopaminergic neurons who are suffering or the whole system in that part of the brain where these neurons live is not really clear yet.

FLORA LICHTMAN: You said that we’re close to causal association in humans. Tell me more.

BEATE RITZ: Yes. I’m a little biased here because I studied paraquat exposure in humans for so long, but I really do think we recently came out with the definitive study in California of more than 800 patients and as many control subjects, where we had really good exposure assessment through the Pesticide Use Report system in California. And we showed, in many ways, with many analyzes, that paraquat exposure at the workplace and homes was related to Parkinson’s very strongly.

FLORA LICHTMAN: Can we quantify the elevation of risk?

BEATE RITZ: Well, that would really also depend on what exposure scale you’re using. But if you’re just wanting something, on average, it’s probably at least a doubling of the risk. But it depends on the lengths of exposure and the intensity of exposure, as well as your individual susceptibility of vulnerability to these agents. Because some humans are actually much more vulnerable to these mechanisms of oxidative stress than others.

FLORA LICHTMAN: We were just talking about this plant in Mississippi that was emitting paraquat into the air. Do the risks of paraquat exposure change if you’re breathing it in?

BEATE RITZ: Actually, breathing it in through your nose, let’s say, is probably extremely dangerous because the cells in the nose have a direct link to the neurons in the olfactory bulb. And that is also where, actually, Parkinson’s often starts. It starts with a loss of smell and probably, a protein aggregation that we call alpha synuclein aggregation, which is the hallmark of Parkinson’s. It’s the proteins that we find in these Lewy bodies that we are seeing in the brain of Parkinson’s patients.

So that is really starting in the olfactory bulb. And from there, it could actually then move on to the dopamine neurons in the midbrain. So the nose is an excess organ directly to the environment.

And through the nose, you can get into the brain. You can get toxins into the brain, basically, avoiding also, what we call the blood-brain barrier, where you have some defense against toxins from the environment. They can’t as easily come from the blood, let’s say into the brain.

FLORA LICHTMAN: And this is what industry says, that the blood-brain barrier is protecting people from–

BEATE RITZ: Exactly.

FLORA LICHTMAN: Vermont is poised to be the first State to ban paraquat, a very recent bill. It’s sitting just waiting for the governor’s signature. I’m curious for you, as someone who’s studied this for so long, what are your thoughts on that?

BEATE RITZ: Well, I think it’s really time that somebody has the courage in the US to do what you just said, which is ban paraquat. Paraquat should have been banned 25, 30 years ago when we basically found that we can give rodents paraquat and see all of the signs and symptoms of Parkinsonism in humans and when we started to understand what the mechanisms are and how toxic paraquat is.

So it is quite amazing that nobody in the US, so far, has banned paraquat.

FLORA LICHTMAN: I think that’s the perfect place to land. Dr. Beate Ritz is a professor of epidemiology at UCLA. This episode was produced by Kathleen Davis, and if you liked the show, let us know. Give us a review– only five stars, please– on your favorite platform of choice. We’ll catch you next time. I’m Flora Lichtman.

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