Researchers say they have discovered high concentrations of human antidepressants in the brains of fish found in the Niagara River.

A study published in the journal Environmental Science and Technology detected the pharmaceutical drugs in the brain tissue of 10 different species, including bass and walleye.

Researchers from the U.S. and Thailand say the discovery raises serious environmental concerns, since the Niagara River connects two of the Great Lakes, Lake Erie and Lake Ontario.

“These active ingredients from antidepressants, which are coming out from wastewater treatment plants, are accumulating in fish brains,” study co-author Diana Aga, a University at Buffalo chemistry professor, said in a news release.

“It is a threat to biodiversity, and we should be very concerned.”

Researchers say the antidepressant buildup could affect fish behaviour and potentially disrupt the aquatic ecosystem.

Although scientists say the levels of antidepressants found in the fish do not pose a risk to people who eat them, the environmental risks are “real.” 

“Scientists are just beginning to understand what the consequences might be," study co-author Randolph Singh said.

The study looked for a variety of pharmaceutical drugs and chemicals found in personal care products while testing the organs and muscles of the Niagara River fish. The 10 different species tested were: smallmouth bass, largemouth bass, rudd, rock bass, white bass, white perch, walleye, bowfin, steelhead and yellow perch.

Antidepressants or their metabolites, the products of metabolic reactions, were found in the brains of every fish species studied.

The highest concentration was found in a rock bass, which had about 400 nanograms of norsertraline, a metabolite of sertraline, the active ingredient in antidepressant Zoloft, per gram of brain tissue. Metabolites of active ingredients found in drugs Celexa, Prozac and Sarfem were also found in rock bass.

Overall, more than half of the fish brain samples had norsertraline levels of 100 nanograms per gram or higher.

The authors of the study say their research raises questions about the effectiveness of wastewater treatment plants, which they say have not “kept up with the times.”

Aga said wastewater treatment processes focus on removing human excrement and killing disease-causing bacteria. But remnants of antidepressantsfound in urine, as well as many other chemicals in the wastewater, are largely ignored, she said.

“As a result, wildlife is exposed to all of these chemicals. Fish are receiving this cocktail of drugs 24 hours a day,” Aga said.