Residues of illegal drugs in Europe’s waterways are harming populations of critically endangered European eels, according to new research. Scientists in Italy found that eels placed in cocaine-polluted waters developed muscle damage and other bodily changes that could decrease their ability to migrate and reproduce.
A team of biologists at the University of Naples Federico II and University of Salerno published their findings in the journal Science of the Total Environment.
To learn more about how illicit drugs affect European eels (Anguilla anguilla), the team placed two groups of farm-raised eels in waters containing trace amounts of cocaine – at 20 nanograms per litre, the amount is about equal to that found in certain rivers. After being kept in cocaine-polluted water for 50 consecutive days, the eels were moved to tanks containing drug-free water for either three days or ten days, depending on the group.
During the experiment, the team found that the cocaine-exposed eels appeared hyperactive, but otherwise seemed as healthy as a group of eels placed in drug-free water. However, further analysis following dissection showed that the animals exposed to cocaine experienced a range of negative health effects.
The drug accumulated in the eels’ tissues, including the muscles, brain, gills and skin, among others. The muscles also showed signs of swelling and fibre breakdown, which did not resolve even after the ten-day recovery period.
“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 authors wrote in their study.
These adverse health effects could impact eels’ ability to migrate and reproduce, the study warned. After spending as much as 20 years in fresh or brackish water, European eels migrate across the Atlantic Ocean to spawn in the Sargasso Sea, a section of the Atlantic that lies just east of the Caribbean Sea, not far from the eastern United States.
Successful migration requires “sufficient energy reserves,” in addition to “healthy skeletal muscle and an efficient aerobic metabolism,” according to the study. Cocaine-related damage to the eels’ muscles could therefore limit their ability to reach the Sargasso Sea and reproduce.
“Data show a great presence of illicit drugs and their metabolites in surface waters worldwide,” lead author Anna Capaldo, a research biologist at the University of Naples Federico II, told National Geographic. Concentrations of these substances can be higher in water surrounding densely populated cities, she added, noting that previous studies have identified especially high amounts in the Italian Amo River near Pisa and in the Thames River near London’s Houses of Parliament.
The study’s findings are particularly concerning given the European eel’s status as a critically endangered species. Habitat-loss, pollution, dam construction and over-fishing already pose serious threats to European eels, reports Smithsonian Magazine.
Capaldo told National Geographic that avoidance of illegal drugs and improved wastewater treatment could help alleviate the issue.
Daniel Snow, the director of the University of Nebraska’s Water Sciences Laboratory, who was not involved in this research, told National Geographic that he hoped the research would encourage people to give more consideration to the consequences of drug use, but was not convinced it would be enough to drive behavioural change.
“If that was the solution, then laws would actually stop use. There is no evidence that laws actually do control use,” he said.
Snow added that water treatment was a more viable solution, but would come at a cost: “You can basically treat anything to any degree of purity, it’s just about how much money you want to put into the treatment process.”