Researchers said the effect on humans from antidepressants in waste water is likely negligible. (R. David Duncan III/Associated Press/The News & Advance)A significant amount of antidepressant medicine exists in Montreal's waste water, affecting fish tissue and brain activity, a study by the University of Montreal's chemistry department has found.

The study says the phenomenon likely occurs in many cities around the world because Montreal has a typical sewage-treatment system.

The controlled study involved brook trout exposed to varying amounts of effluent Montreal water over a three-month period.

Dr. Sébastien Sauvé, who works in the university's chemistry department, said researchers measured a biomarker — a synapse activity in the brain tissue — and there was a clear reduction in that activity from the fish being exposed to waste water.

"We have data that does show that antidepressant drugs do accumulate in fish tissues — there's significantly more in the liver than in the muscle, but there's also more in the brain tissues," Sauvé told The Canadian Press.

"[The brain] is a bit more of a cause for concern because we have a molecule that's known and used for brain alteration functions in humans, so if we do have an accumulation in fish brain, it raises a question of what the impact is on the fish."

Sauvé said the study revealed that ozone treatment reduces the level of antidepressants in the waste water as it leaves the plant. Montreal is experimenting with that kind of treatment.

But the structure of that type of medication makes it difficult to remove its traces, even with a high-tech treatment facility, Sauvé noted. He also said there should be more research into the long-term ecological effects of fish being exposed to antidepressants.

In Montreal, one in four people are believed to consume some type of anti-psychotic or antidepressant drug. It's a number that researchers based on pharmaceutical sale numbers and Health Department estimates of 555 million pills sold in Quebec each year.

No danger to humans

Researchers say if Montrealers drank two litres of tap water a day for 70 years, they would have only had the equivalent of a small fraction of a pill. (CBC)This study's authors, however, want to reassure people that the effect of water-borne antidepressants on humans is likely negligible, given the amounts involved.

Sauvé said the actual amount of the drugs in the ecosystem is quite small, despite the potential impact.

"The amount of antidepressants being released into our [St. Lawrence] river works out to roughly the equivalent of a grain of salt in an Olympic-size swimming pool," Sauvé said.

"That's not enough to affect people, should they be brave enough to go fishing out there," he said. "I'd be more worried about the trace metals. Nevertheless, we are seeing an impact on the river's ecosystem, which should concern cities everywhere."

Eating the fish wouldn't be a huge cause for concern, Sauvé said. Most of the drugs' impact is in the fish liver and brain, but the muscle was largely unaffected in the part people would eat.

"If we do a comparison with the exposure to humans from the traces of those compounds that remain in drinking water, the risk is really minimal," Sauvé said. "If someone was to drink two litres of tap water a day, every day, for 70 years, they would have had the equivalent of ... a small fraction of a pill."

The peer-reviewed study received funding from Health Canada, the St. Lawrence Action Plan and the Canadian Foundation for Innovation. It was published online by Chemosphere on Jan. 5, 2011.