Fish in Texas are absorbing antidepressant drugs from wastewater, according to a new study. The chemicals can apparently alter brain activity in the fish, but a general sense of well-being isn't the likely payoff, the researchers say. Instead, the findings raise the depressing possibility that such chemicals could disrupt the behavior of aquatic organisms and wreak havoc on ecosystems.
Not everything flushed down the toilet is filtered out at sewage-treatment plants. Last year the U.S. Geological Survey released data showing that 80% of 139 streams sampled in 30 states contained traces of hormones, steroids, and other drugs. To find out whether fish in the Trinity River Basin north of Dallas are affected by the widely prescribed antidepressants Prozac and Zoloft, ecologist Bryan Brooks of Baylor University in Waco, Texas, and his colleagues tested samples of three common fish in Pecan Creek. Like more than 300 other streams in the south-central region of the country, the creek waters are made up largely of wastewater that is legally regulated and discharged from a reclamation plant, Brooks notes. In the brains and livers of the fish, the researchers found concentrations as high as 30 parts per billion of the active ingredients and breakdown products of the drugs. Residues in fish muscle that humans might ingest were far lower, however.
Back in the lab, Brooks and his group exposed menaka fish to varying levels of fluoxetine, the active ingredient in Prozac. Analysis of their brain tissue revealed that fish exposed to near environmentally realistic concentrations of fluoxetine had markedly changed levels of the critical brain chemicals dopamine and norepinephrine. "What this actually means for fish behavior and survival, we don't know yet," Brooks says, "but these neurotransmitters are involved in everything from appetite to reproduction." He will present his findings at a meeting of the Society of Environmental Toxicology and Chemistry next week.
These changes in brain chemistry after short exposure in the lab make it likely that longer exposure in the wild is also having an impact, says Marsha Black, an aquatic toxicologist at the University of Georgia, Athens. Also, the presence of several antidepressants in an aquatic environment could multiply the effects, she says. Black's own studies have shown delayed sexual maturity and losses of balance while swimming in mosquito fish exposed to moderate levels of fluoxetine.