A strange thing is happening to male smallmouth and largemouth bass swimming in waterways in parts of the Northeast: They are increasingly showing up with characteristics of the opposite sex. 
 
 In a survey of 19 national wildlife preserves, researchers from the US Geological Survey (USGS) and the US Fish and Wildlife Service found this month that a whopping 85 percent of smallmouth bass and 27 percent of male largemouth bass were intersex. 
 
 "What we're finding is the presence of immature eggs in the gonads of the male fish," said Luke Iwanowicz, a USGS research biologist. "This has basically been an indication of exposure of estrogens such as compounds that enforce the female physiology." 
 
 Iwanowicz is the lead author of a paper on the phenomenon, which has been published in Ecotoxicology and Environmental Safety. 
 
 Fish are often used as indicators of aquatic health, and in this case, are being used to showcase the increasing threat of endocrine disrupting chemicals (EDCs), which are being dumped into our rivers, streams, swamps, and lakes. Among the main culprits are hormones in livestock manure and herbicides and pesticides found in runoff. Trace amounts of pharmaceuticals, like birth control pills, are also showing up in waterways after being discharged from wastewater treatment plants. 
 
 "Estrogens are hormone signaling molecules that work in low concentrations," Iwanowicz said of the chemicals, which are found mostly in the organs of the fish, rather than the flesh that people eat. 
 
 "The low concentrations of these hormones can have potentially profound effects," he said. "We are looking at fish but, of course, there is that concern that, if this stuff is in the water, it can be affecting other wildlife." 
 
 He added, "We're not sure how it works into the human dimension but it's kind of worth considering." 
 
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 In conducting the study, Iwanowicz and his colleagues did not conduct a chemical analysis on the water so they could not say for sure what was to blame for the intersex fish. But the findings suggest that EDCs were the most likely the culprit. 
 
 The problem of intersex fish has been documented over the past two decades in nearly 40 fish species worldwide. Scientists believe their prevalence is more widespread than previously thought and could be starting to take a toll on some populations, either by reducing a fish's ability to reproduce or weakening its immune system and making them more vulnerable to disease. 
 
 "Estrogenic exposure is a problem throughout the developed world and there are many instances in which fish population health was degraded through the presence of estrogenic compounds," said Heiko L. Schoenfuss, director of the Aquatic Toxicology Laboratory at St. Cloud State University in Minnesota. 
 
 "Although estrogens by themselves seldom reach environmental concentrations that would result in the collapse of a fish population, they are an important and potent environmental stressor that may impeded the recovery of aquatic ecosystems that have experienced other sources of disturbances," he said. 
 
 A 2009 study by the USGS examined 16 fish species from 1995 to 2004 and found a third of all male smallmouth bass and a fifth of all male largemouth bass were intersex. Intersex fish were found in a third of all sites examined from the Apalachicola, Colorado, Columbia, Mobile, Mississippi, Pee Dee, Rio Grande, Savannah, and Yukon River basins. 
 
 John Arway, executive director of the Pennsylvania Fish and Boat Commission, said the most recent findings reflect what has been found in the state's waters. A USGS study last year found intersex fish in Pennsylvania's Susquehanna, Delaware, and Ohio River basins. Four of the wildlife refuges in the latest study are at least partly located in the state. 
 
 "Obviously we're concerned not only about the Susquehanna, but the other waters that either drain into or drain out of those national wildlife refuges," Arway said. 
 
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 Arway said his agency, along with the US Environmental Protection Agency, found that until 2005 there were no reports of disease among smallmouth bass on the Susquehanna River. Since then, sampling in some sites has revealed disease rates of up to 70 percent. 
 
 "One of the things found was that EDCs and herbicides were the likely and probable causes for the effects we are seeing with our bass on the Susquehanna," he said, adding that there has been increased incidences of sores and lesions on the fish, as well as cancerous tumors. 
 
 "[W]e are seeing the population of fishable bass declining on the Susquehanna," he said. "That is not to say EDCs are the only stressor that are effecting these young fish but we are starting to narrow down the causes and EDCs are the likely cause that is infecting and killing these young fish." 
 
 Combating the problem won't be easy, since estrogen is so widespread — all living things produce it, after all — and its effects are often felt at very low concentrations. Fixes like upgrades to treatment plants, would be costly and limiting the use of herbicides and pesticides or controlling runoff from farms faces opposition from the agricultural industry. 
 
 "We need to start acting on some of the chemicals we know cause these effects and not worry about those we can't control like a lot of the antibiotics," Arway said. "We need to trace those concentrations back up the tributaries, find out the major sources of where these chemicals are being applied and then work with the applicators — whether it's the farmers or the lawn care companies — to try to get them to adhere to the label restrictions." 
 
 Follow Michael Casey on Twitter: @Mcasey1 
 
 Image via Flickr ||||| Eighty five percent of male smallmouth bass and 27 percent of male largemouth bass tested in waters in or near 19 National Wildlife Refuges in the Northeast U.S. were intersex, according to a new study by U.S. Geological Survey and U.S. Fish and Wildlife Service researchers. Intersex is when one sex develops characteristics of the opposite sex. It is tied to the exposure of fish to endocrine-disrupting chemicals that can affect the reproductive system and cause the development of characteristics of the opposite sex, such as immature eggs in the testes of male fish. Intersex is a global issue, as wild-caught fish affected by endocrine-disrupting chemicals have been found in locations across the world. Estrogenic endocrine-disrupting chemicals are derived from a variety of sources, from natural estrogens to synthetic pharmaceuticals and agrochemicals that enter the waterways. Examples include some types of birth control pills, natural sex hormones in livestock manures, herbicides and pesticides. “It is not clear what the specific cause of intersex is in these fish,” said Luke Iwanowicz, a USGS research biologist and lead author of the paper. “This study was designed to identify locations that may warrant further investigation. Chemical analyses of fish or water samples at collection sites were not conducted, so we cannot attribute the observation of intersex to specific, known estrogenic endocrine—disrupting chemicals.” This prevalence of intersex fish in this study is much higher than that found in a similar USGS study that evaluated intersex in black basses in nine river basins in the United States. That study did not include river basins in the Northeast. "The results of this new study show the extent of endocrine disrupting chemicals on refuge lands using bass as an indicator for exposures that may affect fish and other aquatic species," said Fred Pinkney, a USFWS contaminants biologist and study coauthor. "To help address this issue, the U.S. Fish and Wildlife Service encourages management actions that reduce runoff into streams, ponds and lakes -- both on and off of refuge lands.” The journal article, Evidence of estrogenic endocrine disruption in smallmouth and largemouth bass inhabiting Northeast U.S. National Wildlife Refuge waters: a reconnaissance study,” by L.R. Iwanowicz, V.S. Blazer, A.E. Pinkney, C.P. Guy, A.M. Major, K. Munney, S. Mierzykowski, S. Lingenfelser, A. Secord, K. Patnode, T.J. Kubiak, C. Stern, C.M. Hahn, D.D. Iwanowicz, H.L. Walsh, and A. Sperry is available online in Ecotoxicology and Environmental Safety. ||||| Scientists are trying to figure out why male fish in the Potomac River are growing immature eggs in their system. Some believe the deformity has to do with agriculture and industrial run-off that finds its way to the river. (Ricky Carioti/The Washington Post) 
 
 For male smallmouth bass, sex change is increasingly not an option. In the chemical-laced Chesapeake Bay watershed and in rivers up through New England, it comes with the territory. 
 
 Based on the latest U.S. Geological Survey on intersex fish, 85 percent of male smallmouth bass in waters in and around national wildlife refuges in the Northeast have developed "characteristics of the opposite sex." That's in addition to 90 percent of the species in some West Virginia waters and 50 percent to 100 percent in the southern stretch of the Potomac River. All of the affected fish had eggs where their testes should be, according to previous studies. 
 
 [One of Europe’s oldest trees is changing its sex] 
 
 Why this is happening remains a mystery, says the lead author of a new study, despite the problem being detected more than a decade ago. “It is not clear what the specific cause of intersex is in these fish,” said Luke Iwanowicz, a USGS research biologist. “This study was designed to identify locations that may warrant further investigation." 
 
 The strongest suspicion focuses on what is poured down the drains of homes, businesses and farms every day. Scientists are worried that prescription drugs such as birth control and mood-control pharmaceuticals, flushed down toilets, and chemical pesticides such as atrazine, washed off farms by rain, have turned creeks, streams and rivers into chemical soups that disrupt the endocrines of marine life. 
 
 [How birth control pills are also altering the sex lives of fish] 
 
 These substances throw off functions that regulate hormones and the reproductive system, said USGS biologist Vicki Blazer, a co-author of the latest study and lead author of numerous earlier reports. At one polluted site Blazer examined in the Susquehanna River near Hershey, Pa., two years ago, 100 percent of the male smallmouth bass sampled had eggs. 
 
 The surprising thing found in the most recent survey, Iwanowicz said, is that the bass are being sexually transformed in more pristine waters at national wildlife refuges managed by the U.S. Fish and Wildlife Service. The agency's 560 refuges -- 71 in the Northeast -- provide a sanctuary for 1,000 fish species, 700 bird species and about 200 species of mammals. 
 
 Smallmouth bass are "like the canary in the coal mine," Iwanowicz said. "In the case of this specific study, we’re getting a better handle on how widespread [the problem] is. We’re seeing this signal at national wildlife refuges, … evidence that in areas that are managed for animal health, stuff is going on behind the scenes." 
 
 
 
 A magnification of a cross-section view of a smallmouth bass' testes that shows immature eggs, which are round circles on the monitor. (Ricky Carioti/The Washington Post) 
 
 Among the 19 refuges included in the study were Blackwater and Patuxent in Maryland, Mason Neck and Rappahannock River Valley in Virginia, Great Swamp in New Jersey, Cherry Valley in Pennsylvania and Moosehorn in Maine. 
 
 "These effects have been observed in other organisms, including mammals," said Don Tillitt, another co-author who is a research toxicologist at the USGS Columbia Environmental Research Center in Missouri. "The mechanism occurs in the epi-genome, around the genome. Not the genes, but how those genes are expressed." 
 
 A USGS study released in March found that male fish exposed to a synthetic hormone called 17a-ethinylestradiol, or EE2, produced offspring that struggled to fertilize eggs. And their grandchildren suffered a 30 percent decrease in their fertilization rate. 
 
 [Here's how the chemical industry blocks science that could determine why fish are changing sex] 
 
 The problem extends well beyond the Chesapeake Bay region that includes the District, Virginia, Maryland, Delaware, West Virginia, New York and Pennsylvania. The USGS, which found intersex bass in the Columbia, Colorado and Mississippi river basins in 2009, calls it a "global issue" given changes that have been identified in locations worldwide. 
 
 The previous study also determined that the chemical BPA, used widely in plastics, had a similar effect on the small Japanese medaka fish. Marine scientists track the medaka because it reproduces so quickly that researchers can see results of subsequent generations faster than slow-reproducing species such as smallmouth bass. 
 
 Intersex changes in male fish have been recorded in 37 species so far, though scientists have yet to identify a single chemical responsible for the transformation. 
 
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– Male bass are experiencing unwanted sex changes, apparently thanks to the "chemical soups" that pass for waterways in the Northeast. The Washington Post reports 85% of male smallmouth bass surveyed in the region have "characteristics of the opposite sex"—specifically eggs where their testes should be. The same is true of 27% of area largemouth bass, Vice adds. For a recently published study, researchers tested bass near 19 wildlife refuges in the Northeast, according to a US Geological Survey press release. Researchers didn't do a chemical analysis of the water where the intersex fish were found, so they can't be sure specifically what is causing the sex changes. But they suspect the problem is things that get dumped down drains and into US waters. Researchers believe the likely culprits are birth control pills, pesticides, hormones in livestock manure, and other chemical-heavy products, according to the press release. Vice reports those products contain estrogen, which can produce dramatic effects even at very low levels. But this isn't just a problem in the Northeast. Up to 90% of male smallmouth bass in parts of West Virginia are intersex, and increasing sex changes have been noted in nearly 40 fish species around the world going back 20 years, according to the Post. Study author Luke Iwanowicz calls these fish "the canary in the coal mine." "We are looking at fish but, of course, there is that concern that, if this stuff is in the water, it can be affecting other wildlife," he tells Vice. (A hermaphrodite cat got gender assignment surgery this year.)