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...
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