Presence of illicit drugs such as cocaine in rivers and lakes, even as little as a few nanograms per litre, causes hyperactivity and severe muscle damage in freshwater eels. The study published in Science of the Total Environment says that this damage could not be reversed even after keeping them in cocaine-free water for 10 days post-exposure.
In the study by researchers from the University of Naples Federico II in Italy, adult male European eels were kept for one month in tanks with 20 nanograms of cocaine per litre. “Eel is an endangered species, included in the Red list of IUCN; moreover, it is an edible species, so
these studies can be informative from a human point of view. Moreover, it is considered an ideal
bio monitor of environmental contamination; indeed, because of its high fat content, it is able to
accumulate contaminants in its tissues,” explains Dr. Anna Capaldo, lead author of the study in an email to The Hindu .
Both the red and white fibres in the muscles of the eels showed evidence of injury-like swelling and breakdown. They also examined other protein markers in their bodies to understand the general health and found that though the health status of the cocaine group was same as the other groups, they appeared hyperactive, with accelerated swimming.
Silver Stage
The report says that the skeletal muscle damage could also hinder the reproductive migration of this species. “Eels transform then from yellow eel into silver eel, in the so-called ‘silvering’ process. In this process the eel “prepares for departure” with the increase in eye size, the regression of the alimentary tract, some proliferation of gonads for example; moreover the body colour becomes silver. The silver stage precedes the spawning migration to the Sargasso sea, 6000 km away from Europe. The silver stage is the last observable stage before the start of the reproductive migration,” explains Dr. Capaldo. This means that the skeletal muscles also act as sufficient energy reserve during migration and their damage could adversely affect the reproduction and survival of the species.
As these eels are edible species, more studies are being carried out to understand if this can affect humans as well.
Only a small percentage of the drugs and antibiotics used by humans are taken up by the body, and most of it is excreted out. “Any polluted river could contain not only cocaine, but also....morphine, pesticides, heavy metals, phenols, antibiotics and so on. All these substances can interact with each other, and the resulting effects are unpredictable. So, the damages that the wild eels [or any marine life form] could experience depend on the type of contamination of the watercourse that is related to the surrounding human activities,” adds Dr.Capaldo.
