Tiny amounts of a common anti-anxiety medication — which ends up in wastewater after patients pass it into their urine — significantly alters fish behaviour, according to a new study. The drug makes timid fish bold, antisocial and voracious, researchers have found. Oxazepam belongs to the class of drugs called benzodiazepines, the most widely prescribed anxiety drugs, and is thought to be highly stable in aquatic environments. It acts by enhancing neuron signals that damp down the brain's activity, helping patients to relax.
An article in Science this week now places the drug on a growing list of pharmaceutical products that escape wastewater treatment unscathed and may be affecting freshwater communities1. A chemical found in contraceptive pills, known as 17-β-estradiol, and the antidepressant drug fluoxetine (Prozac) have been shown to alter behaviour in the fathead minnow (Pimephales promelas), and the popular anti-inflammatory drug ibuprofen reduces courtship behaviour in male zebrafish (Danio rerio). Taken together, the evidence suggests that tests of possible pollutants must go beyond merely cataloguing fatal or highly toxic doses, says Todd Royer, an ecologist at Indiana University in Bloomington. “This study really highlights the importance of non-lethal effects,” he says. Even if a drug doesn't kill or cause acute toxicity, it could be altering “community structure and other ecosystem processes”, he explains.