Scientists have exposed European eels to small concentrations of cocaine for 50 days in a row, noting the illicit drug has a negative impact in their natural behaviour.
A study published in the academic journal Science of the Total Environment shows how the small concentrations of illicit drugs that find their way into the aquatic environment through wastewater negatively impact eels’ life cycle.
European eels spend 15 to 20 years in waterways before making the jump into the Atlantic Ocean to spawn in the Sargasso Sea. The study found that cocaine dangerously affects the animal’s natural reproduction cycle.
For starters, cocaine increases their cortisol levels, a stress hormone that induces fat consumption. Higher levels of Cortisol could delay their breeding journey, as eels need to build up fat before their long migration.
Cocaine also increases their dopamine levels, which stops them from reaching sexual maturity. Researchers also found the drug makes their muscles swell and breakdown, which could further complicate their ability to make their breeding trip on time.
“All the main functions of these animals could be altered,” Anna Capaldo, research biologist at the University of Naples Federico II and lead author of the study, told National Geographic.
The paper also notes that all these adverse effects persist even after the scientists removed the eels from their cocaine infused water and placed them in rehabilitation for 10 days.
The study found that there was a significant presence of illicit drugs and their metabolites in surface waters around the globe, with the highest levels found near densely populated cities like London or Pisa – both of which are visited by countless tourists every year.
Eels are commonly farmed for food, but their wild population is considered critically endangered by the International Union for Conservation of Nature – a fact that makes these findings all the more alarming.
While a drastic reduction of drug use is not a viable short-term solution, Capaldo says the problem could be solved with more efficient wastewater treatment – because the thing is, cocaine is just one of the many threats in the water.
In addition to cocaine, waterways around the world commonly contain residue from other illicit drugs, antibiotics, pesticides and heavy metals.
“We don’t know the possible consequences of such combinations of substances, but clearly they could influence the survival and/or the health status of the eels,” Capaldo says.