You take a medication and, after experiencing its benefits, probably don’t think about it further. That may be dangerously myopic from an environmental perspective, according to a report at the recent 2008 AAAS meeting by Dr. Karen Kidd from the University of New Brunswick. Municipal wastewater is “swimming” with all the things we flush down our sewers, including medications and other drugs that pass relatively unaltered through the body. One collection of such aquatically stable compounds includes synthetic estrogens, chemicals that are most commonly found in birth control pills, but which are also produced as byproducts by pulp mills. When estrogen-mimicking compounds enter the water supply, they can wreak havoc on fish living in it. In a seven year study at a northern Ontario lake, Dr. Kidd and colleagues added synthetic estrogens to the water in concentrations similar to those in municipal waste (parts per trillion). What they observed was shocking. Male fish became feminized and began producing female egg proteins. In the females, however, sexual maturation and egg production were retarded. The effects of these exposures to fish in the lake over the period of the study led to near extinction of a minnow population and significant declines in numbers of larger fish. The size of the fish appeared to be inversely related to the effect – smallest fish were most susceptible, probably because they tend to have shorter reproductive cycles, thus experiencing problems more quickly. There is an up side to the report, however, and it is that removing estrogens from the water can essentially reverse the problems, if action is taken quickly enough.