Although the levels of the chemicals that the fish swam in were very low even before the upgrade, the chemicals are endocrine disrupters. They mimic estrogen and may disrupt the endocrine (hormone) system of both animals and humans, said the study's principal investigator, David Norris, PhD, an integrative physiology professor at the University of Colorado at Boulder.
Norris' team reported in 2006 that native male fish in Boulder Creek decreased in numbers with respect to females and numerous intersex fish were found downstream of the wastewater treatment plant. After a technology upgrade to the wastewater treatment plant in 2008, the reproductive disruption in the fish was far less pronounced. However, Norris said the study results should still concern people.
"The fish are a wake-up call," Norris said. "Our bodies and those of the much more sensitive human fetus are being exposed everyday to a variety of chemicals that are capable of altering not only our development and physiology but that of future generations as well."
With other scientists, Norris studied samples of the wastewater effluent, the plant-treated water that enters the stream and becomes another city's drinking water. Grants from the U.S. Environmental Protection Agency (EPA) and the city of Boulder supported this research.
They found other endocrine disrupters, including synthetic and natural reproductive steroids. They believe the chemicals come from natural female hormones and birth control pills excreted via urine and from detergents, cosmetics and other consumer products flushed down toilets and drains. The amount of estrogens in the sampled effluent was enough to explain the effects on the fish "downstream" from the treatment plant—in the river below the plant, according to Norris. The researchers saw no signs of reproductive disruption in fish upstream.
Also, the investigators exposed adult male fathead minnows to wastewater effluent they diluted with water taken from upstream of the plant. After seven days' exposure to this water, the fish had suppressed male sex characteristics and greatly elevated levels of the protein vitellogenin. Female fish make vitellogenin under the influence of estrogens, and male fish produce very little of it, so elevated levels in males indicate estrogen exposure, Norris explained.
After the technology upgrade to the wastewater treatment plant in 2008, the effluent was considerably less estrogenic to the fish. After the treatment plant's upgrade, the minnows exhibited less intense loss of male sex characteristics, an initial analysis found. "It took 28 days to get a significant elevation in vitellogenin and then only in 100 percent effluent," Norris said. "However, these improvements seen in wildlife will not substantially lessen the risk to human health because drinking water is not the major source of estrogenic chemicals for people."
Aaron Lohr | EurekAlert!
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