Chapter 1: What recent study highlights the effects of cocaine on salmon?
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You're listening to Shortwave from NPR. Maybe you've heard of the movie Cocaine Bear, which came out in 2023. It features a black bear going on a murderous rampage after eating 75 pounds of cocaine.
Chapter 2: How do illicit drugs like cocaine impact fish behavior?
Oh my God, he's gonna die. And I couldn't help but think about it when I read a recent study asking whether sort of trace amounts of these really potent neuroactive drugs that are in our environment can actually affect the movement and behavior of fish in the wild.
That's Jack Brand, an aquatic ecologist at the Swedish University of Agricultural Sciences. And to answer that question, Jack and his team gave a bunch of salmon cocaine. For science. Now, researchers know that prescription drugs pollute aquatic environments when people use the bathroom. Past studies have shown even anti-anxiety drugs can change how fish act.
Fish become, as you'd expect on anti-anxiety drugs, sort of more relaxed. And that's not very good for a small fish.
A chill pill is not ideal when you have a lot of predators to worry about. Beyond that, drugs people use can change how fish forage, how they mate and reproduce. And Jack says these drugs are everywhere.
Chapter 3: What methodology did researchers use to study salmon exposure to cocaine?
But scientists are just starting to understand the consequences for wildlife.
It's definitely present in sort of most ecosystems on Earth now, unfortunately, these sorts of issues of chemical pollution and pharmaceutical pollution. But we're only sort of really starting to scratch the surface into understanding the potential consequences of that.
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Chapter 4: What were the unexpected findings regarding cocaine's metabolite in fish?
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Okay, Jack, we're talking about your like recent study where you exposed salmon to cocaine. First, can you explain how you did that?
So basically what we did is we wanted to get fish of all the same age, genetic background, life history, and so that we could be sure that any changes in movement was caused by that drug administration, not some other confounding effect. And so what we did was we took 105 fish from a hatchery, who were usually reared to be stocked into the lake, and we divided them up into three groups.
One group received a slow-release implant containing cocaine, Another received a slow release implant containing its main metabolite, which basically is the breakdown product of cocaine in humans' bodies, which then gets excreted into the wastewater. And one was a control group, so they received no drug.
Chapter 5: How does increased movement affect salmon's energy expenditure?
And to do that, we basically sedate the fish and perform a sort of minor surgery. We make a small little incision on the underside of the fish and slowly inject the implant. And then we also implanted an acoustic tracker. So this is just sort of a small little black pinging tag, which emits a unique sound.
And then in the lake, we placed a number of underwater microphones or what are called hydrophones. And these can pick up, you know, when a fish passes by those microphones. So we know where a fish was and when. That's so cool.
So you want to study both cocaine and this byproduct.
So basically what happens when people take cocaine is that their bodies partly break it down into this byproduct.
Chapter 6: What long-term questions remain after the salmon study?
Not all the cocaine and this byproduct are absorbed into your body. And what happens is it ends up being excreted when people go to the toilet. And so you have both cocaine and this byproduct being excreted. And then this enters wastewater. And then subsequently, because our wastewater treatment plants aren't really designed to remove these substances, ends up in our aquatic environment.
And you wanted to look at like not just cocaine, but also this byproduct because they're both in there.
That's right. And often the byproduct, this metabolite, is present at higher concentrations than cocaine itself. But largely in mammals, this chemical is thought to be more or less, you know, although it's a little bit complicated, more or less biologically inert, so not very biologically active. Hmm.
Chapter 7: What are the implications of drug pollution in aquatic environments?
And so we wanted to see whether that was also true in fish. But I think one of the interesting parts of our study was we found that the metabolite actually had a greater effect on fish behavior than cocaine, which was not something that we expected.
And we think this is important because, you know, typically when people are doing environmental risk assessments for these types of compounds, they're mainly focusing on the parent compound, so that's cocaine itself, and not really, you know, accounting for these byproducts.
And so here we sort of showed that some of these byproducts may be having actually even greater effects than we originally thought.
That's fascinating. Okay, and when you're talking to people, how do you explain why this work matters?
The reason that we're often concerned about these chemicals is because they target receptors in people's brains that are also present in a wide variety of wildlife species. And so they're what we call evolutionarily conserved, meaning that the same biological systems that these drugs target in you are also present in fish and a wide variety of other vertebrates.
And so that's what makes us particularly concerned about these sort of really potent neuroactive chemicals and how susceptible sort of the vertebrate tree of life may be to the effects of these chemicals on their nervous systems and their behavior.
Okay, so you found...
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Chapter 8: How can wastewater treatment methods be improved to reduce chemical pollution?
salmon exposed to cocaine and this byproduct, this main metabolite, swam further than other salmon. Like, what does swimming distance tell you about salmon behavior or their life?
Yeah, so we basically found that they were moving around twice as far towards the end of the study. And basically, you know, this is a massive increase in energy expenditure. animal behavior is, is fairly finely tuned and, and to exert more energy, that energy has to come from somewhere.
Um, and so at this stage, we don't know if, if they're increasing their foraging behavior to compensate for this, or if their condition just slowly deteriorates over time. Um, and they, you know, becoming worse and worse health over time. We don't know. Um, But definitely there has to be a trade off there. There has to be a trade off in the energy they're consuming as well.
Which can also then have flow on effects for, you know, if they need to eat more, perhaps they're putting themselves more at risk to predators because they're not hiding or they're moving into new areas. They're altering food webs and predator prey interactions and things like that.
Now that you've done this experiment in salmon, what questions do you still want to answer?
Many, many. So one of them that interests me is we don't really know the mechanism that's driving this change. So we don't really understand what it is about this metabolite that's actually causing these increased movement rates in the wild and these fish.
Another thing is I'd like to understand, like I said, our study was only relatively short, a couple of months, but what the long-term consequences of this are, we don't know. And of course, ours is a pretty controlled situation. You know, we deliberately expose a particular group of fish to a particular quantity of a chemical.
But in reality, what happens is there's sort of dilute cocktails of these drugs in the environment. There are many different types of chemicals that affect all different levels of the ecosystem, you know, predators, prey, etc. How that all interacts is very, very difficult to to disentangle.
And I think of these chemicals as sort of this invisible agent of global change is because people can't really see them. And so they don't get the sort of recognition that I think they likely deserve. And I think they're probably having far wider impacts on our wildlife than people are actually aware. And so I think it's really great to sort of raise the issue of this in the public domain.
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