Imma Perfetto
Cosmos science journalist
While modern medicine allows us to manage or cure previously untreatable diseases and conditions, pharmaceuticals and their metabolites have untold consequences when they make their way into the environment.
“Pharmaceutical pollutants are an emerging global issue, with over 900 different substances having now been detected in waterways around the world,” says Dr Marcus Michelangeli of Griffith University’s Australian Rivers Institute, whose research explores how wildlife adapts to rapid environmental change.
“Of particular concern are psychoactive substances like antidepressants and pain medications, which can significantly interfere with wildlife brain function and behaviour.”
Michelangeli is co-author of a new study which found that exposing juvenile Atlantic salmon to the common pharmaceutical pollutant clobazam, which is approved for use as anti-anxiety and anti-seizure medication, alters their ability to migrate.
Clobazam exposure increased the number of salmon reaching the end of their river-to-sea migration. It also increased the speed at which they passed through the turbines at 2 hydropower dams along the way.
The researchers suggest this likely happened due to heightened risk-taking behaviour.
“While the increased migration success in salmon exposed to clobazam might seem like a beneficial effect, it is important to realise that any change to the natural behaviour and ecology of a species is expected to have broader negative consequences both for that species and the surrounding wildlife community,” Michelangeli cautions.
According to the researchers, clobazam and other benzodiazepine drugs with the same mechanism of action are commonly detected in wastewater-affected aquatic ecosystems around the world.
“Most previous studies examining the effects of pharmaceutical pollutants on wildlife have been conducted under controlled laboratory conditions, which don’t fully capture the complexities of natural environments,” says Michelangeli.
“This study is unique because it investigates the effects of these contaminants on wildlife directly in the field, allowing us to better understand how exposure impacts wildlife behaviour and migration in a natural context.”
The multi-year field experiments involved 279 juvenile wild Atlantic salmon (Salmo salar) from the River Dal in central Sweden.
Slow-release chemical implants delivered 1 of 4 pharmaceutical treatments: clobazam; tramadol; clobazam-tramadol mixture; or no pharmaceuticals. Tramadol, also a pharmaceutical pollutant, is an opioid used to treat chronic pain.
The researchers tracked the tagged fish across a roughly 28km stretch of the river as they migrated downstream to reach the Baltic Sea. They found no difference in the time taken for the different groups to complete the migration, nor in the overall success at passing through hydropower dams.
A simultaneous lab-based study found the slow-released drugs accumulated in the salmons’ tissues, including the brain, at concentrations previously seen in wild fish. Crucially, neither drug was detected in the tissues of the control fish, indicating that the salmon were free from external contaminations.
Tracking juvenile Atlantic salmon shoaling behaviour. Credit: Marcus Michelangeli
The experiments also revealed that, compared with controls, clobazam-exposed salmon shoals (groups) were less cohesive in the presence of a predator.
The findings suggest that heightened risk-taking behaviour and reduced shoaling cohesion could make clobazam-exposed salmon more vulnerable to predators in the wild.
“Our findings raise important questions about how pharmaceutical pollution alters migration behaviour and survival in the wild,” says Dr Jack Brand, who led the study at the Swedish University of Agricultural Sciences.
“Next, we aim to track fine-scale movements of exposed fish using high-resolution animal tracking tools and miniature biologgers – tiny electronic tags that record physiological data such as stress levels or detect predation events – to determine whether behavioural changes from pharmaceutical pollution influences predation risk.
“Expanding our understanding of how different psychoactive pollutants and their interactions affect migration success will be crucial for predicting the long-term impacts on fish populations.
“This is especially important in an increasingly polluted world, where evidence-based policies are needed to protect vulnerable species and ecosystems.”
The study appears in the journal Science.
