In Our Streams: Prozac and Pesticides

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Wastewater-treatment plants are pretty good at getting rid of common pollutants like bacteria and heavy metals, but a nationwide survey last year showed that plenty of manmade chemicals still get through. U.S. rivers and streams are tainted with, among other things, pesticides, antibiotics and even common drugs such as aspirin and Prozac, flushed down drains and out into the water supply. The concentrations tend to be very low — less than one part per trillion, in some cases — but nobody can say for sure whether they're low enough to be safe.

So the U.S. Geological Survey (USGS), which did last year's study, is out in the field again this summer. Scientists are pouring nontoxic red dye into streams in Iowa and Colorado to study how water flow disperses pollutants. The next step, says Dana Kolpin, the research hydrologist who is coordinating the project, will be to go back and measure the concentrations of various drugs and industrial chemicals. Some of these substances, he says, may disappear faster than the dye test would predict — perhaps because they degrade quickly or bind to sediments in the stream bottom. Others may disperse more gradually, and those are the ones that treatment-plant operators should concentrate on removing.

Once they have figured out how the dozens of compounds on their list are dispersed, USGS and other scientists will address the question of how dangerous they are to human health — research that should take several more years. "We have no evidence that these chemicals are harmful at these levels," says Kolpin. "But we also have no proof that they aren't."