WASHINGTON -- Two studies by researchers at Michigan State University's (MSU) Institute of Environmental Toxicology point to human estrogens, not industrial compounds, as the cause of estrogenic activity in fish exposed to wastewater treatment plant effluent.
The researchers sampled water from Lake Mead, Nevada and the Las Vegas Wash, a river that receives large amounts of treated sewage and empties into Lake Mead. U.S. Geological Survey scientists previously had found high levels of vitellogenin in male fish at these sites, an indicator of estrogenic activity since vitellogenin is a protein normally found only in female fish. The study concluded that natural estrogens, such as from humans and animals, and pharmaceutical estrogens were the likely cause of this estrogenic activity.
The MSU researchers found that the low environmental levels of nonylphenol did not produce estrogenic activity. Industrial compounds such as nonylphenol, which can exhibit weak estrogenic characteristics in laboratory tests, have been suggested as the cause of estrogenic activity in the environment.
In a similar study of Michigan sites, the MSU researchers again found that the human estrogens in wastewater and river water produced an estrogenic response while the environmental levels of nonylphenol did not.
The researchers suggest that the efficiency of biological wastewater treatment has an impact on whether estrogenically active substances occur in the discharge: in other words, better treatment leads to cleaner effluent. In addition, the researchers note that male fish exposed to effluent in the U.S. are less likely to produce vitellogenin than those exposed to effluents in the U.K., which could be related to the lower U.S. human population density and the likelihood that effluent constitutes a higher proportion of the water in U.K. rivers.
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