A benzodiazepine seeping into waterways is causing young Atlantic salmon to behave strangely, with fish in the wild migrating more rapidly and taking more risks on their journey from river to ocean. It even seems to be messing with their social dynamics.
An international team of researchers from institutions including Australia’s Griffith University, led by the Swedish University of Agricultural Sciences, has found that the “benzo” clobazam – often prescribed for anxiety and sleep disorders, as well as for controlling seizures – in particular is affecting the salmon. It’s the largest study of its kind, and sheds new light on the impact of pharmaceutical contamination on marine life.
“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 behavior and migration in a natural context,” said Dr Marcus Michelangeli from Griffith University’s Australian Rivers Institute. “While the increased migration success in salmon exposed to clobazam might seem like a beneficial effect, it is important to realize that any change to the natural behavior and ecology of a species is expected to have broader negative consequences both for that species and the surrounding wildlife community.”
The team used slow-release drug implants and tracking transmitters to see how clobazam and another common pharmaceutical pollutant – the opioid tramadol – affected juvenile Atlantic salmon (Salmo salar) in the crucial stage of their life cycle, navigating waterways to make it to the Baltic Sea.
Michael Bertram
Homing in on clobazam as a result of observations in the wild, the researchers then conducted an additional lab study and could see how the drug appeared to impact the species’ shoaling behavior. Shoaling, as opposed to schooling, is a social behavior that could affect breeding and cohesion among groups of fish. While this maybe doesn’t sound like a big deal, the species as a whole has gone from Least Concern on the IUCN Red List – the “bible” for tracking wildlife numbers – to Near Threatened. In some areas they’re endangered, and populations of these freshwater fish in areas like Maine and in the UK have rapidly declined over the last decade.
And their populations have become increasingly fragmented, which means changes in social behavior and making more risky moves are big red flags for a dwindling species.
While benzos are generally seen as sedatives in humans, clobazam-drugged salmon actually navigated their migration route much more rapidly, speeding through two hydropower dams that regularly pose challenges on the important journey. There can be a number of ways this impacts a species – prematurely reaching open waters, fish being less careful about being picked off by predators en route to the sea – that are not fully known.
“Pharmaceutical pollutants are an emerging global issue, with over 900 different substances having now been detected in waterways around the world,” Michelangeli said. “Of particular concern are psychoactive substances like antidepressants and pain medications, which can significantly interfere with wildlife brain function and behavior.
“When you consider realistic exposure scenarios where entire ecosystems are exposed – encompassing multiple species and a diversity of contaminants – the potential consequences become even more complex,” he added.
And, yes, there is evidence that these pharmaceutical contaminants can affect humans who eat drug-affected fish, however, long-term health impacts are not yet fully understood. Generally speaking, low levels of pollutants aren’t going to have any immediate, obvious effect, but there remains a lack of research in the area.
The scientists call for pharmaceutical companies to improve medicine biodegradability, as well as better wastewater treatment to limit what we’re pumping back into the wild.
“Advanced wastewater treatment methods are becoming more effective at reducing pharmaceutical contamination, and there is promising potential in green chemistry approaches,” Michelangeli said.“By designing drugs that break down more rapidly or become less harmful after use, we can significantly mitigate the environmental impact of pharmaceutical pollution in the future.”
The study was published in the journal Science.
Source: Griffith University