When fish swim in waters tainted with antidepressant drugs, they become anxious, anti-social and sometimes even homicidal.
New research has found that the pharmaceuticals, which are frequently showing up in U.S. streams, can alter genes responsible for building fish brains and controlling their behavior.
Antidepressants are the most commonly prescribed medications in the United States; about 250 million prescriptions are filled every year. And they also are the highest-documented drugs contaminating waterways, which has experts worried about fish. Traces of the drugs typically get into streams when people excrete them, then sewage treatment plants discharge the effluent.
Exposure to fluoxetine, known by the trade name Prozac, had a bizarre effect on male fathead minnows, according to new, unpublished research by scientists at the University of Wisconsin-Milwaukee.
Male minnows exposed to a small dose of the drug in laboratories ignored females. They spent more time under a tile, so their reproduction decreased and they took more time capturing prey, according to Rebecca Klaper, a professor of freshwater sciences who spoke about her findings at a Society of Environmental Toxicology and Chemistry conference last fall. Klaper said the doses of Prozac added to the fishes’ water were “very low concentrations,” 1 part per billion, which is found in some wastewater discharged into streams.
When the dose was increased, but still at levels found in some wastewater, females produced fewer eggs and males became aggressive, killing females in some cases, Klaper said at the conference.
The drugs seem to cause these behavioral problems by scrambling how genes in the fish brains are expressed, or turned on and off. The minnows were exposed when they were a couple of months old and still developing.
There appeared to be architectural changes to the young minnows’ brains, Klaper said at the toxicology conference. Growth of the axons, which are long nerve fibers that transmit information to the body, was disrupted.
The new findings build on Klaper’s previous research, which tested minnows with the gene changes to see how well they avoided predators. They swam longer distances and made more directional changes, which suggests that the drugs induced anxiety.
The drugs used in the study were among the most common in sewage: Prozac, Effexor and Tegretol. The researchers tested each drug alone and in combination.
“At high doses we expect brain changes,” Klaper said. “But we saw the gene expression changes and then behavioral changes at doses that we consider environmentally relevant.”
However, there is too little evidence to know whether pharmaceuticals are having any impacts on fish populations in the wild, said Bryan Brooks, an environmental science professor at Baylor University who has extensively studied pharmaceuticals in streams and fish.
Any changes in reproduction, eating and avoiding prey can have devastating impacts for fish populations, Klaper said.
The most vulnerable fish populations are those downstream of sewage treatment plants, where prescription drugs consistently show up in higher levels than in other waterways. It’s only within the past decade that technology has allowed plants to test for the chemicals in their wastewater and in waters downstream, though most still don’t, said Steve Carr, supervisor of the chemistry research group at the Los Angeles County Sanitation Districts.
One of the antidepressants tested in the fish – Tegretol – comes into the treatment plants and goes out at near constant levels, said Eric Nelson, a senior chemist with the Los Angeles County Sanitation Districts.