Pollution such as pharmaceutical residues is an emerging problem and we need more knowledge about how it affects wildlife. The study, published in the journal Science, is the most comprehensive to date on how pharmaceutical pollution can affect the behaviour of animals in the wild.
The researchers fitted 279 juvenile salmon with implants that medicated the fish with levels of pharmaceuticals equivalent to those frequently detected in the environment. One of the drugs was the anti-anxiety and sedative medication clobazam. Using animal-tracking transmitters, the researchers were able to follow the salmon during their 28-kilometer migration from the River Dal, Sweden, to the Baltic Sea.
To reach the sea, the salmon had to pass two hydropower dams. Normally, salmon often stop and hesitate when they reach these barriers, but the medicated salmon behaved differently.
– Salmon exposed to clobazam passed the hydropower dams faster than the unexposed fish. It also meant that more of the medicated salmon eventually reached the Baltic Sea. In follow-up laboratory experiments, we could see that salmon exposed to clobazam became more antisocial and risk-prone. This is one explanation for why they chose to swim quickly past the obstacle themselves instead of waiting for others, says Jack Brand, Researcher at SLU in Umeå and lead author of the study.
Drugs can change the migration process
Even though exposed fish were more successful in reaching the Baltic Sea, it is not a positive outcome overall. Any change to the natural behaviour and ecology of a species is expected to have wide-ranging impacts not only for that species but on the surrounding wildlife community.
The International Union for Conservation of Nature (IUCN) has classified Atlantic salmon as endangered in parts of Europe.
– Migration to the sea is a vital life-history event for young salmon. They feed and grow in open water before returning to rivers to spawn. Our results show that exposure to common drug residues can alter this process, with potential impacts for the persistence of populations. The long-term consequences are not clear and will require further research, says Michael Bertram, Assistant Professor at SLU in Umeå and the study’s senior author.
Pharmaceutical residues end up in aquatic ecosystems during production, use, and disposal. Almost 1000 different substances have been detected in lakes, rivers, and oceans worldwide. The scientists describe this as a rapidly increasing threat to wildlife and ecosystems globally.
– Psychoactive medications are of particular concern due to their ability to influence brain function and alter the behaviour of wildlife, says Michael Bertram.
Advanced wastewater treatment methods have been successful in reducing pharmaceutical contamination but almost no countries have the necessary infrastructure or have not yet implemented it.
– There are several potential solutions to address the issue of pharmaceutical pollution, including strengthening regulatory measures and upgrading wastewater treatment technology, says Tomas Brodin, Professor at SLU in Umeå.
