Eels getting high in UK’s cocaine-polluted rivers

The presence of cocaine and other recreational drugs in British rivers is putting at further risk an already critically endangered species of eel, a new study has found.

Traces of cocaine frequently make their way into Britain’s waters after passing through users’ bodies, and may be causing serious health problems for fish including eels, according to researchers at Italy’s University of Naples Federico II.

The European eel spends its life living in waterways across Europe, migrating to the ocean to breed and then die, says ScienceAlert. The young then make their way from the ocean back inland again, repeating the cycle.

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Toxic pollution, overfishing, parasites, climate change and hydroelectric dams have endangered the eel’s habitat and migration cycles in recent decades, and cocaine and its metabolites is now believed to pose another major threat, reports the science news site.

In a recent study, researchers took 150 farm-raised European eels and divided them into several different tanks. Some of the tanks contained small amounts of cocaine - 20 nanograms per liter, about the same concentration as that found in some UK rivers - while others were filled with plain tap water.

The eels exposed to the cocaine appeared hyperactive but otherwise in the same general health as drug-free eels. However, according to National Geographic’s Joshua Rapp Learn, the researchers found that cocaine had accumulated in the drugged eels’ muscles, brains, gills, skin and other tissue. Their muscles were swollen, and even showed signs of fibre breakdown.

European eels spend up to 20 years in fresh waters, then undertake a vast migration across the Atlantic to spawn in the Sargasso Sea east of the Caribbean, says Smithsonian magazine.

“Our results suggest that cocaine, at environmental concentrations, could compromise both the sustained swimming, ensured by the slow red muscle, and the burst swimming, ensured by the fast, white muscle,” warn the authors of the report, published in the journal Science of the Total Environment.

“This study shows that even low environmental concentrations of cocaine cause severe damage to the morphology and physiology of the skeletal muscle of the silver eel, confirming the harmful impact of cocaine in the environment that potentially affects the survival of this species,” the report continues.

According to the US National Center for Biotechnology Information, the rivers with the highest concentration of cocaine are the River Thames in London and the Arno River in Tuscany, Italy.