Residue from antidepressants leaves the body and ends up in our waterways. Sauvé said his study indicates the problem of antidepressants contaminating marine animals is probably global. Most treatment plants are not equipped to deal with pharmaceuticals. Montreal’s sewage treatment plant treats only solids and does not remove chemicals. “The chemical structure of antidepressants makes them extremely difficult to remove from sewage, even with the most sophisticate systems available,” Sauvé said. Montreal is experimenting with ozone treatment, which, according to the study, reduces the level of antidepressants in the effluent leaving the plant, but does not eliminate them. The research team found eight kinds of anti-depressants in the fish. The highest concentrations came from Prozac.