In Sweden, Atlantic salmon are being exposed to cocaine by researchers, leading to some unexpected findings. Erin McCallum, an aquatic ecology associate professor at the Swedish University of Agricultural Sciences, explained that the study aimed to explore the effects of cocaine and other substances found in water bodies globally, including Canada, on fish behavior.
A recent study published in Current Biology revealed that juvenile Atlantic salmon in Lake Vättern, Sweden, exhibited increased swimming distances after ingesting cocaine or its metabolite, benzoylecgonine. According to McCallum, this behavior could potentially offer more habitat options and food sources for the fish, but it also exposes them to higher risks, such as encountering poor habitats or new predators.
To conduct the study, researchers utilized slow-release chemical implants to administer cocaine or benzoylecgonine to the salmon and monitored their movements over eight weeks. The results showed that fish exposed to benzoylecgonine swam nearly twice the distance per week and dispersed about 12 kilometers farther across the lake. Although the effects were less pronounced, fish exposed to cocaine displayed similar behaviors.
Mark Servos, a biology professor at the University of Waterloo, commended the study for its innovative approach outside the laboratory setting. He emphasized the importance of understanding the potential subtle yet significant changes in wild fish populations due to substances present in water bodies.
McCallum highlighted the issue of drug residues entering waterways through wastewater treatment plants, affecting fish globally. Cocaine, tramadol, and codeine are among the frequently detected drugs in water bodies worldwide. In a separate study, wild sharks off the coast of Rio de Janeiro were found to have cocaine in their muscles and liver.
In Canada, research by Servos and colleagues at the University of Waterloo discovered various substances, including fentanyl and methadone, in small freshwater fish collected downstream of urban wastewater treatment plants. The environmental impact of these compounds remains a relatively unexplored area, with ongoing research necessary to assess their effects on aquatic ecosystems.
While the risks to humans are minimal, the potential effects on fish reproduction remain a concern. Servos emphasized the need for further research to understand the implications of these compounds and evaluate the feasibility of upgrading wastewater treatment facilities to mitigate their environmental impact. More comprehensive monitoring programs are required to assess the effects of drug metabolites on wildlife and the overall pollution impact on ecosystems.
