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Traces of pharmaceutical drugs are finding their way into waterways around the world. A new study in the journal Science suggests that this kind of pollution can mess with salmon migration in somewhat surprising ways. NPR's Jonathan Lambert has more.
JONATHAN LAMBERT, BYLINE: Drugs that act on our minds often target parts of the brain shared by many species. That means that if they get into the environment, these drugs can potentially influence the behavior of lots of other animals. Jack Brand is a biologist at the Swedish University of Agricultural Sciences.
JACK BRAND: For the last 10 to 15 years, we've sort of known that pharmaceuticals that are in the environment can affect animal behavior under laboratory conditions.
LAMBERT: That can be dangerous. For example, lab fish exposed to a common class of anxiety medications called benzodiazepines became more antisocial and less fearful. Such changes are worrisome to Brand, but just how worrisome isn't yet clear.
BRAND: Does that actually translate to effects in the wild? Do these affect fish or other organisms in their natural environment, and can that affect population-level responses?
LAMBERT: Scientists have detected over 900 different pharmaceutical ingredients in aquatic ecosystems worldwide. Assessing the real-world effects of these drugs on complex behaviors like migration is pretty tricky.
BRAND: We can't, you know, dump a bunch of pharmaceuticals into the river.
LAMBERT: So instead, Brand and his colleagues implanted slow-release pharmaceuticals into 279 hatchery-raised Atlantic salmon.
BRAND: Which then releases a slow, controlled dose of a certain pharmaceutical of interest to the fish as it completes its migratory journey.
LAMBERT: One of the pharmaceuticals they tested was the benzodiazepine clobazam. Special trackers helped the team monitor both exposed and nonexposed fish as they swam from release sites across multiple dams to eventually reach the Baltic Sea. They found that the anxiety medication altered their migratory success, but not necessarily how they thought it would.
BRAND: More clobazam-exposed fish eventually migrated through the river and reached the Baltic Sea than unexposed fish.
LAMBERT: The success of drugged fish might have to do with crossing dams, which can be harrowing. To get past those dams, salmon have to navigate turbines, which can be lethal. The team found that drugged fish traversed those dams two to three times faster than nondrugged fish.
BRAND: And so we suspect that these fish that are exposed to clobazam are more risk-prone, more solitary, and therefore just sort of beelining it through the dams rather than waiting around for their salmon friends.
LAMBERT: Does that mean that it's good to give salmon benzos? Probably not, says Brand.
BRAND: Any departure from natural behavior is likely to have potential broad, negative consequences for the population.
LAMBERT: For example, subsequent lab experiments found that clobazam made salmon less likely to school with other fish. That could make them more vulnerable to getting picked off by a predator. Karen Kidd is an ecotoxicologist at McMaster University. She says that the biggest takeaway is that these drugs really can alter behavior in the wild.
KAREN KIDD: They've done something that no one else has done.
LAMBERT: Still, she has questions.
KIDD: What we don't know is what happened to the salmon once they got to the Baltic. Like, did they have better survival or worse survival?
LAMBERT: Kidd also wonders how anxiety medication interacts with all the pain meds, antibiotics and other drugs polluting natural waters. But she says we don't have to wait for all the answers to do something. Improving wastewater treatment or designing drugs that break down more easily could help ensure that drugs are only affecting their intended targets - us.
Jonathan Lambert, NPR News.
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