What may sound like the beginning of a bad 1980s horror film is actually a modern sign of humanity’s impact on the environment: eels in drug-polluted waters are high on cocaine.

            Earth’s waterways contain trace amounts of a variety of drugs, ranging from prescriptions and over-the-counter medications to controlled substances. While much is known about the sociological and physiological impact of illegal drugs on humans, there is a significant gap in knowledge regarding the impact of drug-laced waterways on other creatures. Nonetheless, efforts are currently being made to address the question.

In research published in Science of the Total Environment, lead author Anna Capaldo and her colleagues studied the impact of trace levels of cocaine found in waterways on the European eel (Anguilla anguilla). The European eel is on the IUCN’s Red List as a ‘critically endangered’ species in the wild, so a greater understanding of the influence of drug pollution in water may be key to aiding in the future conservation of the species.

            In the experiment, Capaldo and her colleagues allowed 150 adult male European eels to acclimate in laboratory tanks for a month before being separated into smaller treatment groups of ten. Eels in experimental groups were exposed to daily doses of cocaine at a concentration of twenty nanograms per liter for fifty days, comparable to the average level of cocaine that would be found in their native waterways. At the end of the exposure trials, two groups were put through a post-exposure recovery trial, where they were placed in tanks containing only tap water. After the experimental trials were reproduced in triplicate, the eels were euthanized to analyze their blood and skeletal muscle tissues, with the goal of ultimately assessing the presence of abnormalities such as muscle protein expression, damage, and apoptosis, as well as general morphology.

            During the trials, the only observational difference between the cocaine-exposed and non-exposed groups was hyperactivity of the drug-exposed eels; however, the post-experimental dissections and analyses revealed devastating physiological results. The eels that were treated with cocaine had accumulations of the drug in their muscles, brains, and gills. Researchers also found a breakdown and swelling of muscle tissues, along with increased levels of cortisol and dopamine, which would impair the buildup of fat stores and stunt sexual maturity. Given that the eel is reliant on making a 6,000-kilometer migration to mating grounds, an impaired muscular system, reduced body fat, and increased adolescence could be fatal for the already endangered teleosts.

            The European eel is critically endangered in the wild due to habitat destruction, overfishing, and pollution, and this novel research regarding drug pollution highlights the distinctly anthropogenic effect on the species. Environmental cocaine concentrations could be mitigated with more efficient systems for wastewater treatment, especially around cities, where the levels can reach an even greater level than the one used for this experiment. While the impact of drug usage is much more often relayed in the context of human health (for obvious reasons), it is important to remember to refocus our scope of understanding and analyze the toll our actions have on the world and creatures around us.

Reference:

Capaldo, A., Gay, F., Lapretti, M., Paolella, G., Martucciello, S., Lionetti, L., Caputo, I., and Laforgia, V. 2018. Effects of environmental cocaine concentrations on the skeletal muscle of the European eel (Anguilla Anguilla). Science of the Total Environment 640:862-873.