Could Prozac muscle out mussels?

New research raises the possibility that antidepressant drugs may be depressing wild-mussel populations.

Freshwater mussel communities are declining in U.S. waters for reasons that remain poorly understood. Scientists at North Carolina State University in Raleigh wondered about a possible antidepressant link after another research team showed that pregnant zebra mussels, if they're exposed to extra serotonin, release nonviable larvae. Serotonin is the brain chemical boosted by antidepressant drugs such as fluoxetine, the active ingredient in Prozac.

Sewage-treatment plants fail to completely remove fluoxetine and most other drugs, which then can pollute U.S. waters (SN: 6/17/00, p. 388).

To test the vulnerability of wild mussels to these drugs, the North Carolina researchers collected pregnant females of the native--U.S, species Elliptio complanata. Working with Rebecca Heltsley of the National Institute of Standards and Technology in Charleston, S.C., the scientists exposed the mussels to various concentrations of fluoxetine in the lab. All mussels released their larvae within a day.

Moms exposed to 300 micrograms per liter or more of the drug--much higher concentrations than are observed in the wild--released few young that survived. Adult-female mussels incubated at concentrations closer to those found in U.S. waters produced mostly viable young.

The findings don't necessarily mean that U.S. waters are safe for the shellfish, Heltsley says. Mussels and other animals in the wild are exposed to pollutants for long periods, whereas the experiment was brief, she points out. Moreover, she adds, wild mussels may encounter more than one serotonin-enhancing pollutant, and the various drugs' effects could be additive.--J.R.