Swedish study finds cocaine residues alter movement patterns of salmon
-
Erik Winnfors Wannberg
Share article:
Cocaine breakdown products can alter the behaviour of salmon, showing that illegal drugs are also an environmental problem. Researchers are now calling for more effective wastewater treatment. Cocaine residues affected the behaviour and movement patterns of young salmon in Vättern, Sweden’s second largest lake. Exposed fish swam up to 1.9 times further per week and moved up to 12.3 kilometers further across the lake. This is shown by a new study from the Swedish University of Agricultural Sciences (SLU).
Researchers at SLU have investigated how cocaine pollution affects the behaviour and movements of aquatic animals. The study, published in the journal Current Biology , shows that cocaine-related substances alter both the movement patterns and dispersal of young Atlantic salmon in the wild. “Cocaine and other illegal drug pollution is a growing environmental problem worldwide. Many substances are excreted after use and pass through wastewater treatment plants that are not designed to completely remove them,” says Jack Brand, researcher at SLU and the study’s first author, in a press release.
Substances that change animal behaviour
Cocaine and its breakdown products are now regularly detected in lakes, rivers and coastal waters around the world. They have also been found in aquatic animals. “These substances are particularly problematic because they affect the brain even at low concentrations. This gives them great potential to change animal behaviour,” says Michael Bertram, associate professor at SLU, in the press release.
Global problem
When reading the study, it is easy to see that the problem is extensive. According to the authors, 292 million people worldwide use illegal substances (2022). A large part of the chemical compounds in drugs are excreted from the body and then end up in the aquatic environment. This is because wastewater treatment plants (WWTP’s) are not adapted to capture the chemicals.
First real-life study
Unlike most previous studies, which have been conducted under simplified laboratory conditions that do not capture the complexity of real-world environments, this study was conducted in a natural ecosystem. The researchers exposed young salmon to diluted, environmentally relevant concentrations of cocaine and its main metabolite benzoylecgonine and followed their movements in Lake Vättern. “We found that benzoylecgonine, which is the main breakdown product of cocaine and is often found in aquatic environments, had particularly strong effects. Exposed fish were more active, swam up to 1.9 times further per week and spread up to 12.3 kilometers further across the lake compared to control fish. Interestingly, the metabolite had a greater effect than cocaine itself,” says Jack Brand.
Ecological effects of cocaine residues
In humans, cocaine is rapidly broken down into benzoylecgonine, which often remains in the body longer and occurs in higher concentrations in the environment. “Our results suggest that risk assessments that focus solely on cocaine may underestimate the ecological effects of its breakdown products”, says Tomas Brodin, professor at SLU. Because movement is crucial to how animals use habitats, find food, avoid predators, and maintain populations, even small changes can have significant consequences.
Improved wastewater treatment is necessary
“If pollution changes how animals move, it can ultimately affect habitat use, predator-prey relationships, and even how populations are linked to each other,” says Jack Brand. The researchers emphasize that the problem requires several measures, including improved wastewater treatment, increased monitoring of both drugs and their degradation products in the environment, and updated risk assessments. “Our study shows that drugs are not only a societal problem, but also a concrete environmental challenge,” concludes Michael Bertram.
This article was published first by the Swedish platform for water professionals cirkulation.se
