A groundbreaking international study reveals how common pharmaceutical pollutants alter the natural migration behavior of Atlantic salmon (Salmo salar), raising serious environmental concerns.
Published in the prestigious journal Science, the research—led by the Swedish University of Agricultural Sciences—provides the most comprehensive field-based evidence to date of how drug residues in freshwater systems affect fish migration. The study, titled “Pharmaceutical pollution influences river-to-sea migration in Atlantic salmon”, sheds new light on the ecological risks posed by environmental levels of human medications, particularly psychoactive substances.
Clobazam Alters Natural Behavior of Migrating Salmon
The research focused on clobazam, a widely used medication for treating anxiety and sleep disorders. Surprisingly, juvenile Atlantic salmon exposed to environmentally relevant concentrations of clobazam showed enhanced river-to-sea migration success in Sweden’s River Dal, reaching the Baltic Sea faster and more efficiently—especially when passing through man-made obstacles like hydropower dams.
However, experts warn that this behavioral shift, while seemingly beneficial, could have long-term ecological consequences.
“Any alteration to natural behavior can disrupt delicate ecological balances,” said Dr. Marcus Michelangeli, co-author and ecotoxicologist from Griffith University’s Australian Rivers Institute. “Increased migration success might sound positive, but these changes in brain function and risk-taking behavior can lead to broader impacts across the aquatic ecosystem.”
Real-World Field Study Highlights Complex Environmental Impact
Unlike many past experiments conducted under lab conditions, this study was performed directly in natural river systems. Researchers implanted slow-release pharmaceutical devices and tracking transmitters into juvenile salmon to monitor their behavior and migration in real time.
They also tested tramadol, an opioid painkiller frequently found in polluted waterways. The study revealed that both drugs altered fish behavior, including shoaling dynamics—a key aspect of group movement and predator avoidance in fish populations.
Growing Threat of Pharmaceutical Pollution in Aquatic Environments
Dr. Michelangeli emphasized that pharmaceutical pollution is an emerging global environmental threat, with more than 900 different pharmaceuticals detected in water bodies worldwide.
“Psychoactive drugs such as antidepressants, anti-anxiety medications, and painkillers are particularly concerning because they interfere with the neurological systems of aquatic wildlife,” he noted.
He added that standard wastewater treatment plants are often unable to filter out these contaminants, leading to widespread, chronic exposure for freshwater organisms.
Potential Solutions: Green Chemistry and Advanced Wastewater Treatment
Despite the concerning findings, there is hope for mitigation. The research highlights the importance of green chemistry innovations—designing drugs that biodegrade quickly and pose minimal harm after use. Additionally, advanced wastewater treatment technologies are showing promise in reducing pharmaceutical residues before they reach rivers and streams.
Conservation Implications for Endangered Species
The study is particularly timely as Atlantic salmon populations face increasing threats from overfishing, climate change, and habitat fragmentation. The potential for pharmaceutical contaminants to further disrupt key life-cycle events—like migration—adds another layer of urgency for conservationists and policymakers.
Conclusion: A Call to Action
This study underscores the need for holistic environmental risk assessments that include real-world exposure scenarios. It calls for stricter regulation of pharmaceutical disposal, more investment in green technology, and global awareness of how our everyday medications can have unintended ecological consequences.
Reference:
Jack A. Brand et al. (2025). Pharmaceutical pollution influences river-to-sea migration in Atlantic salmon (Salmo salar). Science. DOI: 10.1126/science.adp7174
Provided by: Griffith University