Cocaine Pollution Seems to Make Salmon Swim Farther Than Usual. Scientists Don’t Know the Long-Term Consequences

The illegal drug’s main byproduct, benzoylecgonine, caused more robust effects than cocaine itself. Wastewater treatment plants often don’t fully process such metabolites, so they are frequently found in bodies of water at higher concentrations than their parent drugs

Sarah Kuta | Daily Correspondent

April 23, 2026

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The world’s waterways are becoming increasingly contaminated with pharmaceuticals and illegal drugs—and the pollutants are seeping into marine animals. Cocaine, specifically, has been found in sharks, shrimp, mussels and eels, but exactly how these human-derived contaminants might be affecting wildlife has remained mysterious.

Now, new research offers a first look at how cocaine can alter the behavior of fish in the wild. Young Atlantic salmon exposed to cocaine’s primary metabolite—the compound created when human bodies break down the drug, which gets excreted into wastewater—swam farther than their sober peers in a Swedish lake, researchers report in a study published April 20 in the journal Current Biology.

The findings affirm the need to “carefully understand and manage all of the diverse chemicals society uses that can end up in our waterways,” Mark Servos, an ecotoxicologist at the University of Waterloo in Canada who was not involved with the research, tells Science’s Erik Stokstad.

The scientists behind the new study visited an Atlantic salmon hatchery in southern Sweden, where they outfitted 105 two-year-old, captive-raised fish with tracking tags and slow-release capsule implants. In one-third of the group, the implants gradually released cocaine into the creatures’ bodies. In another third, the devices released cocaine’s main metabolite, benzoylecgonine. In the final third—the control group—the implants provided no chemical related to the drug.

Then, the juvenile fish entered Vättern, a large lake roughly 150 miles southwest of Stockholm, where their movements were tracked for eight weeks. The benzoylecgonine-exposed salmon swam up to almost twice as far each week compared with sober salmon, the researchers found. Near the end of the study period, the metabolite-exposed fish had wandered up to about 20 miles from the release site, while the control creatures had traveled up to roughly 12 miles.  

Fish that got the cocaine treatment showed a similar pattern, although the effect was weaker and less consistent, study co-authors Marcus Michelangeli, an ecotoxicologist at Griffith University in Australia, and Jack Brand, an ecologist at the Swedish University of Agricultural Sciences, write in the Conversation.

The fact that benzoylecgonine, not cocaine itself, seemed to have the biggest effect on the fish’s behavior was somewhat of a surprise. But this finding could offer a potential path forward for future research.

When humans consume cocaine, our bodies rapidly break it down into metabolites—primarily, benzoylecgonine. These byproducts get excreted and flushed into local wastewater systems. But many wastewater treatment plants are not set up to fully remove these substances, so they end up in rivers, lakes and coastal waters, per the Conversation.

As a result, metabolites like benzoylecgonine typically occur at higher concentrations in the wild than their parent drugs. “If we’re doing risk assessments and not including compounds like these metabolites and derivatives, we may be missing a big chunk of the environmental risk we’re exposing these animals to,” Brand tells the Guardian’s Ian Sample.

This study focused only on behavior, so the researchers don’t know how pollutants might affect salmon’s long-term survival or reproduction. Additionally, the implants probably didn’t exactly replicate how a fish would ingest drugs and metabolites in the water on their own.

But the findings do offer a glimpse into the possible effects of cocaine and benzoylecgonine contamination. If fish are swimming more and traveling longer distances, they might be wasting precious energy they could be expending on more useful tasks, like foraging. They also might be entering new habitats, where they could encounter different predators and foods.

“The rule of thumb in our business is that any alterations to physiology or behavior in fishes should be considered adverse,” James Meador, an environmental toxicologist with the National Oceanic and Atmospheric Administration who was not involved with the research, tells the New York Times’ Annie Roth.

Atlantic salmon are already under pressure from habitat loss, climate change, invasive species, fisheries and other threats, so adding drug contamination to the mix could further jeopardize the species’ chances of survival.

And that’s just salmon. These and other pollutants are likely affecting other animals, too.

“Many aquatic organisms in human-impacted environments are living in a dilute cocktail of biologically active chemicals,” Brand tells Scientific American’s Gennaro Tomma. “We’re only really scratching the surface.”

Sarah Kuta | Read More

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.