Fish are becoming fearless, gluttonous and asocial due to pharmaceutical waste, according to a new study that links these behavioral changes to something as seemingly harmless as a person flushing a toilet.
That is because many drugs are excreted from our bodies intact, such that the potent medicine residues wind up in wastewater where they can affect fish.
Fish exposed to human drugs may not seem like an ecological disaster, but it can be, according to the paper published in the latest issue of the journal Science.
For example, "Fish eat zooplanktons that in turn eat algae," co-author Michael Jonsson told Discovery News. "If the feeding rate of zooplankton increases because the fish become more efficient in feeding ... you get an increased amount of algae. This may lead to oxygen depletion of the aquatic system and a higher risk of algal blooms."
Johnsson and his colleagues at Umeå University focused on how perch behave when they are exposed to the anxiety-moderating drug Oxazepam. It's a commonly prescribed drug, and they found traces of it in wild perch during a routine environmental screening at the River Fyris, Sweden.
Residues of this drug and others are often found downstream from sewage treatment plants that fail to remove or make inactive the pharmaceutical waste.
"Fish bioconcentrate the drugs through their gills," co-author Jerker Fick told Discovery News. "You could say that fish are in equilibrium with the water concentration."
In addition to eating more quickly, the Oxazepam-exposed fish became braver and less social. They left their schools to look for food on their own, a behavior that can be risky, since school formation is a key defense against being eaten by a predator.
Waste from Oxazepam isn't the only problem.
"Fish, being vertebrates, often have the same drug receptors as humans," co-author Jonatan Klamander said. "It is possible that many different kinds of human pharmaceuticals, or other chemical compounds for that matter, also have an effect on fish."
Other marine life could be affected as well, though the researchers point out that species in deeper water may be somewhat protected, since wastewater concentrations would be lower.
"It is a very elegant and convincing study, demonstrating that low concentrations of a pharmaceutical, found in the environment, can seriously affect the behavior of a wild fish," said Joakim Larsson, an associate professor in the University of Gothenburg's Institute of Biomedicine.
Neither Larsson, who was not involved with the project, or the study's authors suggest banning or even switching out certain drugs, since that could hurt the people who need them.
"The main solution to deal with environmental exposure and effects of pharmaceuticals is to require and install more efficient sewage treatment (systems)," Larsson said. "There are, of course, costs involved with that, but more advanced treatment could help society to remove many potentially harmful contaminants in one go."