Study Finds Benzoylecgonine Increases Dispersal Distance of Atlantic Salmon Smolts in Lake Vättern

A study published in Current Biology in April 2026 examined how cocaine and its metabolite benzoylecgonine affect the movement of Atlantic salmon in Lake Vättern, Sweden. Lead author Jack Brand and colleagues selected 105 two-year-old Atlantic salmon smolts from the Gammelkroppa salmon hatchery. Each fish received a surgically implanted slow-release capsule.

One-third of the salmon received cocaine implants, one-third received benzoylecgonine implants, and one-third served as controls with no drug implants. The implant doses were designed to mimic environmentally realistic exposure levels found in contaminated waterways. All implanted salmon were released into Lake Vättern and tracked for eight weeks using acoustic telemetry tags.

9 times the distance per week compared to control fish. Benzoylecgonine-exposed salmon dispersed up to 20 miles (32 kilometers) from the release site by the end of the experiment, while control salmon dispersed about 12 miles (19 kilometers). Benzoylecgonine-exposed fish traveled roughly 60 percent farther than control fish.

Cocaine-exposed salmon tended to move more than controls but showed a weaker and more variable effect than benzoylecgonine-exposed salmon. Only the benzoylecgonine group showed a clear, statistically robust increase in movement rate and dispersal distance. Benzoylecgonine-exposed salmon distributed themselves more broadly across the lake compared to control and cocaine-exposed groups.

1 grams of benzoylecgonine into waterways every day, according to a 2024 study published in Water Research. That study found average surface-water concentrations of roughly 100 ng/L for cocaine and around 250 ng/L for benzoylecgonine, with some pollution hotspots reaching concentrations in the thousands of ng/L.

Wastewater treatment plants are very rarely successful in fully removing cocaine and benzoylecgonine compounds.

Benzoylecgonine is generally more abundant and persistent than cocaine in local waters. Trace levels of THC, MDMA, methadone and antidepressants have been detected in aquatic ecosystems around the world. Previous studies examined the effects of cocaine on crayfish and eel larvae.

Researchers tested the effects of cocaine and benzoylecgonine on Atlantic salmon (Salmo salar) in Lake Vättern, Sweden.