WASHINGTON — Most streams that flow near cities and towns are laced with drugs that escape from sewage treatment plants or pharmaceutical factories. Although often occurring at concentrations of a few parts per trillion, these compounds can nevertheless hurt aquatic life, turning male fish into female fish with hormones or giving them the munchies with antianxiety medication. Now comes the first study that shows an effect of drugs on the base of the food web-the nutritious microbial slime that covers the streambed. Experts caution, however, that the work is preliminary.
There's a long list of chemicals that go down the drain, pass through sewage treatment plants, and end up in streams: antibiotics, caffeine, and ingredients in soaps and shampoos, to name just a few. Emma Rosi-Marshall, a stream ecosystem ecologist at the Cary Institute of Ecosystem Studies in Millbrook, New York, and colleagues in Illinois and Indiana, were curious about the impact of common chemicals on photosynthesis and respiration, which are fundamental to the life of an entire ecosystem. Measuring these processes is "like taking the pulse of a stream," Rosi-Marshall says.
The team examined biofilms, which are agglomerations of bacteria, algae, fungi, and organic matter that coat rocks on streambeds. Biofilms matter in part because fish, snails, and insects nibble at them for nourishment. But no one had looked at the impact of pharmaceuticals on the ecological functions of this slippery stuff. The researchers adapted a technique used to study the impact of excess nutrients on stream ecosystems: They took 30-ml cups filled with agar and added one kind of pharmaceutical, then covered them with a filter on which the biofilms could grow. A relatively constant dose of the drug diffused out of the cups, which they placed in three different streams for 18 days. Control cups did not have drugs.