New research from Griffith University, in collaboration with international partners, has found that cocaine pollution in freshwater environments can alter the behavior of wild salmon and other fish, changing how they move in natural ecosystems.
The research examined juvenile Atlantic salmon in Lake Vättern, Sweden, which provided the first field-based evidence that illicit drug contamination can affect wildlife behavior outside laboratory conditions.
The study tracked 105 juvenile Atlantic salmon over an eight-week period using slow-release chemical implants and acoustic telemetry. The researchers divided the fish into three groups: a control group, a group exposed to cocaine, and a group exposed to benzoylecgonine (the main metabolite of cocaine commonly found in wastewater systems). The combination of groups enabled researchers to compare how both the parent drug and its breakdown product influenced movement patterns in a natural environment.
The research results indicated that exposure to benzoylecgonine had the strongest impact on behaviors. Fish exposed to this compound swam up to 1.9 times farther per week than unexposed individuals and dispersed as far as 12.3 kilometers across the lake. Over time, researchers noticed the changes becoming stronger, suggesting long-term exposure and altering the way the salmon moved and lived in their environment.
“Where fish go determines what they eat, what eats them, and how populations are structured,” said study co-author Dr. Marcus Michelangeli, from Griffith University’s Australian Rivers Institute, in a statement. “If pollution is changing these patterns, it has the potential to affect ecosystems in ways we are only beginning to understand.”
How is cocaine entering the water?
The illicit substances primarily enter through wastewater treatment plants, which are not designed to fully remove pharmaceutical and illicit drug residues. While earlier laboratory studies had shown that cocaine could influence animal behavior, the new research shows its outcome and effects on natural environments.
Surprisingly, the metabolite benzoylecgonine produced stronger effects than cocaine itself. This aspect is significant, as researchers noted that when they checked the environment for pollutants, they usually looked for the original chemical (i.e., the “parent compound”). However, that chemical often breaks down other substances (metabolites), which are actually more commonly found in rivers and lakes. This means that these products, when broken down, might affect living things differently than the original chemical.
The researchers emphasized that the recent findings found no evidence that such products affect humans who consume wild fish, and there is currently no risk from doing so, as these compounds degrade over time in the environment, reducing any long-term effects or human exposure.
“The idea of cocaine affecting fish might seem surprising, but the reality is that wildlife is already being exposed to a wide range of human-derived drugs every day,” said Michelangeli. “The unusual part is not the experiment, it’s what’s already happening in our waterways.”
The researchers say the next step will be to examine the widespread behavior across different species, which will help provide better assessments of the broader environmental effects of these chemicals.
The recent study appeared in Current Biology.
Chrissy Newton is a PR professional and the founder of VOCAB Communications. She currently appears on The Discovery Channel and Max and hosts the Rebelliously Curious podcast, which can be found on YouTube and on all audio podcast streaming platforms. Follow her on X: @ChrissyNewton, Instagram: @BeingChrissyNewton, and chrissynewton.com. To contact Chrissy with a story, please email chrissy @ thedebrief.org.