Salmon doped against their will: when cocaine travels upriver

We've heard of cities that never sleep. Now, meet fish that never stop swimming. In Lake Vättern, Sweden, Atlantic salmon exposed to cocaine in the water move significantly more than their counterparts, according to a study conducted by Griffith University in Australia and the Swedish University of Agricultural Sciences, published Monday, April 20. A scientific discovery, yes, but also a warning about what's circulating in our rivers, far from our eyes.

Specifically, researchers tracked salmon in their natural environment after a period of exposure to substances related to cocaine. Approximately one hundred individuals were sampled and then exposed to either cocaine or benzoylecgonine, a metabolite produced by the body after consumption. The result: over the course of a week, the fish exposed to cocaine swam 1,9 times farther than the others. The group exposed to the metabolite also showed increased activity, covering an additional 12,3 kilometers during the observed period.

This numerical detail may seem anecdotal, but it isn't. When an animal changes its behavior, it's rarely to please the statistics. The authors are interested here in movement, a key marker: moving more means expending more energy, taking other risks, and changing hunting or escape patterns. In short, the animal's entire equilibrium can be subtly disrupted.

The invisible pollution of wastewater

The Invisible Pollution of Wastewater: Scientists link these observations to a broader phenomenon: the contamination of waterways by drug and pharmaceutical residues, originating primarily from wastewater. "Any abnormal change in animal behavior is concerning," said Marcus Michelangeli, co-author of the study, quoted by the Australian Broadcasting Corporation (ABC). He points to a disturbing reality: rising concentrations of illicit narcotics and pharmaceuticals in rivers, as if our waste were ultimately creating its own uncontrolled pharmacopoeia.

Behind these overactive salmon lies a very concrete mechanism: what we consume, what we excrete, what we throw away, and then what wastewater treatment plants don't always retain. Professor Michael Bertram, from the Swedish University of Agricultural Sciences, calls for strengthening wastewater treatment and monitoring. He insists that these substances pose a full-fledged environmental problem, not just a social or public health issue.

Europe is already scrutinizing its wastewater as a barometer of human habits. In Belgium, a study published in March reported the presence of cocaine throughout the country and an increase in ketamine use. A less comfortable prospect remains: if our rivers become indicators of drug use, they also serve as a breeding ground for wildlife, and the question is no longer just what we tolerate in the streets, but what we allow to end up in the water.