Ten different species of fish in the Great Lakes have been found to have detectable levels of human antidepressants in their brains, including the active ingredients of Prozac, Zoloft and Sarafem.
Use of antidepressants in the US rose by 65% from 1999-2002 and 2011-14. This increase in consumption has also led to an increase in waste, with the antidepressant molecules finding their way into the natural environment.
Many species of fish caught from the Niagara River, had several different antidepressant molecules in their brain tissue, according to a study in the journal Environmental Science & Technology.
"These active ingredients from antidepressants, which are coming out from wastewater treatment plants, are accumulating in fish brains," study author Diana Aga of the University at Buffalo College of Arts and Sciences. "It is a threat to biodiversity, and we should be very concerned.
Fixing outdated sewage treatment plants would help to reduce the scale of the problem, the researchers said.
"These plants are focused on removing nitrogen, phosphorus, and dissolved organic carbon but there are so many other chemicals that are not prioritized that impact our environment," Aga said.
"As a result, wildlife is exposed to all of these chemicals. Fish are receiving this cocktail of drugs 24 hours a day, and we are now finding these drugs in their brains."
The problem is made worse by accidents where untreated sewage ends up in natural waterways. Half a billion gallons of sewage and storm water flowed into local rivers in Buffalo, including the Niagara River, the Investigative Post recently reported.
The effects of these drugs on the fish's biology is not fully understood.
"These drugs could affect fish behaviour. We didn't look at behaviour in our study, but other research teams have shown that antidepressants can affect the feeding behaviour of fish or their survival instincts. Some fish won't acknowledge the presence of predators as much."
The fish who had several different antidepressants in their brains were of particular concern, the researchers said. These chemicals built up over time, reaching concentrations of up to 20 times greater than in the river water itself. Further research will need to be carried out to determine what risk this poses to the fish and the wider ecosystem.