Young Atlantic salmon exposed to cocaine and its breakdown product, benzoylecgonine, swim farther and more widely in the wild, a new study shows. This behavioral change can put them in risky situations, researchers say.
“[T]he effects of illicit drug pollution on aquatic wildlife is not just a laboratory finding — it can measurably alter wildlife behaviour under natural conditions,” study co-author Jack Brand, an ecologist at the Swedish University of Agricultural Sciences, told Mongabay by email.
Researchers are increasingly detecting cocaine and its primary metabolite, benzoylecgonine, in aquatic wildlife, from sharks to freshwater shrimp. However, most studies into the impacts on behavior and brain chemistry in animals have been done in laboratory settings, Brand said. “We wanted to find out whether these effects translate to the real world.”
The researchers selected Lake Vättern in Sweden for their real-world experiment. Young Atlantic salmon (Salmo salar) are released in the lake from a hatchery each year for recreational fishing.
In some of these hatchery-raised 2-year-old salmon, the researchers implanted small devices that slowly released chemicals. One group of 35 fish received implants containing cocaine, another group got benzoylecgonine, while a third, control, group didn’t receive any chemical.
The researchers found that in the exposed fish groups, concentrations of the chemicals per fish averaged about 43 nanograms per gram for cocaine, and 34 ng/g for benzoylecgonine. Previous studies have found up to 107.5 ng/g of cocaine in muscle samples of wild sharks, and nearly 70 ng/g of cocaine in some wild crustaceans.
“These [results] are broadly consistent with what we’d expect for fish living downstream of major urban wastewater outfalls in regions where cocaine use is prominent,” Brand said.
Over an eight-week period, the salmon exposed to cocaine or benzoylecgonine swam farther and more widely than the control group. The effects were strongest in fish exposed to benzoylecgonine, which swam up to 1.9 times farther per week than unexposed fish and dispersed up to 12.3 kilometers (7.6 miles) farther across the lake.
Movement “determines which habitats a fish uses, what food it encounters, what predators it’s exposed to, and how much energy it expends,” Brand said. “Fish that are moving farther and dispersing more widely than they normally would are potentially entering unfamiliar or suboptimal habitats and spending more energy on locomotion; energy that could otherwise go towards growth or building reserves for later life stages.”
The effects of benzoylecgonine are particularly concerning because it’s considered an inactive product in humans, Brand said. “[O]ur findings highlight that metabolites deserve greater attention in environmental risk assessments. Benzoylecgonine is more abundant than cocaine in most waterways and, based on our results, may be more disruptive to fish behaviour.”
Cocaine pollutants reach waterways after they pass through humans, and wastewater treatment plants fail to eliminate them. Brand said the study’s finding “underscores the need for improved wastewater treatment and more comprehensive environmental monitoring” of both parent compounds and their metabolites.
Banner image of young Atlantic salmon, by Jörgen Wiklund via Eurekalert.
This story first appeared on Mongabay
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