All scientists have to do is search new waters, it seems, and the mystery of mutated intersex fish grows more disturbing.
Most recently, they’ve found male smallmouth bass carrying eggs in Pennsylvania’s Susquehanna, Delaware, and Ohio river basins, according to a new report by the U.S. Geological Survey. Male fish at every site sampled had immature eggs in their testes, with the highest percentage in the Susquehanna. Previously in the Chesapeake Bay drainage, research revealed evidence of the effects of endocrine-disrupting chemicals in the Potomac.
Vicki Blazer, lead author of the study, said that the pollutants affecting bass, as well as white suckers, “are most likely complex mixtures form both agriculture sources, such as animal wastes, pesticides and herbicides, and human sources from wastewater treatment plan effluent and other sewage discharges.”
"The prevalence and severity of the immature eggs in smallmouth bass corresponded with the percent of agricultural land use in the watershed above the collection sites," the scientist said. "Chemical compounds associated with estrogenic endocrine disruption, in particular estrone, a natural estrogen, were also associated with the extent and severity of these effects in bass."
Meanwhile, a toxicologist with the U.S. Environmental Protect Agency office in Denver reported that her research on fathead minnows is suggesting that “a very potent synthetic female hormone . . . can wipe out fish populations over several generations, and it’s the male fish that are most affected.”
Previously, Kristen Keteles added, studies had shown that male fish below wastewater treatment plants can lose masculine characteristics and become indistinguishable from females when exposed to estrogen and other endocrine disruptors.
“Our new study found that a potent form of female hormone estrogen used in prescription drugs not only causes the males to look female; it also appears to be toxic to male fish and these effects may impact future generations of fish.”
These disturbing discoveries regarding fish, which could portend similar problems for other species, began to emerge in the late 1970s, with anglers fishing wastewater lagoons in Great Britain, according to Whitney Jacobs, a former Conservation Associate at B.A.S.S. who researched the effects of environmental estrogens on male fish while doing graduate work in fisheries at the University of Georgia.
But the first reports of intersex was not documented in scientific literature until 1994 and the first major national assessment of the problem was not published until 2009, she added.
“Widespread occurrence of intersex in black basses (Micropterus spp.) from U.S. rivers, 1995-2004” revealed intersex in 3 percent of fish collected and in 4 of 16 species--- largemouth bass, smallmouth bass, common carp, and channel catfish.
“However, it was most prevalent in largemouth and smallmouth bass,” Jacobs said. “The study also found the greatest incidence of the condition in the southeastern U.S.”
More recently, a 2014 report from scientists at the University of Georgia revealed these mutations aren’t confined to rivers. In “Survey of Intersex Largemouth Bass from Impoundments in Georgia USA,” they said that 48 percent of male largemouth bass collected from 11 reservoirs without direct municipal or agricultural wastewater inputs were intersex. Additionally, they found the condition in nine of the fisheries.
“The high incidence of intersex males in small impoundments demonstrates the condition is not confined to rivers and suggests that factors other than those previously associated with intersex (i.e., municipal wastewater) may be involved,” the researchers concluded.
Scientists hope that future research will reveal those additional factors. Meanwhile, they believe that fish that live downstream of wastewater treatment plants are most at risk, because of chemicals that can’t be filtered out of discharges.
“Humans excrete hormones and medications, which often end up in our rivers and streams from sewage,” said Keteles, adding that flushing medications also contributes to the problem.
“The water is treated, but many hormones and pharmaceuticals are not completely removed by wastewater treatment plants,” she said.
“My team is trying to determine what this means for fish, and ultimately for people, too.”
(This article appeared originally in B.A.S.S. Times.)