A recent study conducted in Sweden has revealed an unusual scenario where Atlantic salmon are being exposed to cocaine by researchers, causing them to exhibit abnormal behavior. Erin McCallum, an aquatic ecology associate professor at the Swedish University of Agricultural Sciences, acknowledged the unconventional nature of the study but emphasized the importance of understanding the impact of substances like cocaine on aquatic life, given their presence in water bodies globally.
The study, recently published in Current Biology, involved juvenile Atlantic salmon in Lake Vättern being exposed to cocaine and its metabolite, benzoylecgonine. The results showed that the fish exposed to benzoylecgonine displayed increased swimming distances, suggesting potential changes in their habitat exploration patterns and exposure to risks such as encountering predators.
To induce the drug’s effects on the salmon, researchers utilized slow-release chemical implants containing either cocaine or benzoylecgonine. Over an eight-week period, the fish exposed to benzoylecgonine exhibited significantly enhanced swimming capabilities, covering a distance of over 12 kilometers more than their sober counterparts. The effects of cocaine exposure were also observed but were comparatively weaker and less consistent.
Mark Servos, a biology professor at the University of Waterloo, commended the study for its innovative approach in studying the real-world effects of drug exposure on wildlife. He emphasized the importance of understanding the subtle yet potentially significant changes that these substances could induce in wild fish populations.
McCallum highlighted the issue of drug residues entering waterways through human waste and wastewater treatment plant effluents, affecting aquatic organisms globally. She referenced a 2025 study that identified the presence of various drugs, including cocaine, tramadol, and codeine, in water bodies worldwide. Additionally, a 2024 report from Brazil documented the presence of cocaine in wild sharks off the coast of Rio de Janeiro.
The study underlines the need for further research to comprehensively assess the impact of drug residues and their metabolites on aquatic ecosystems. McCallum emphasized the importance of considering these metabolites, often overlooked in environmental monitoring programs, as potential contributors to the observed effects on wildlife.
While the risks to humans from these drug residues are minimal, the impact on fish reproduction and overall ecosystem health remains a concern. Servos stressed the need for continued research to better understand the implications of these compounds and evaluate potential mitigation strategies, such as enhanced wastewater treatment processes, despite the associated costs. The ongoing investigation aims to shed light on the broader implications of drug pollution in aquatic environments and advocate for proactive measures to safeguard wildlife populations.