In 2003, scientists were startled to discover that some of the male fish in the Potomac River were found to be producing immature eggs in their testes. The fish, dubbed "intersex fish," have also been found in other parts of the country since the initial discovery.
But the U.S. Geological Surveys found last year that the "intersex fish" in the Potomac River and its tributaries are developing female sexual traits at a frequency much higher than scientists have ever seen before, and faster than in any of the other places where the phenomenon has been found. According to fish pathologist Vicki Blazer, nearly all of the male smallmouth bass caught in last year’s survey of Potomac tributaries were the abnormal fish. Smallmouth bass appear to be more susceptible to intersex development than largemouth bass. In the Potomac River itself, 7 of 13 largemouth bass exhibited female characteristics, including three that were actually producing eggs.
The Potomac River and its tributaries provide drinking water for millions of people, so the rapid rise in frequency of these abnormalities is causing concern among many people that the pollutants in the river are becoming more severe and toxic. Scientists say that although it isn’t clear what is causing the male fish to develop female characteristics, it is likely a combination of pollutants.
Some pesticides and chemicals are believed to stimulate the production of estrogen, and estrogen from human waste and birth control pills can end up in the waterways after making its way there via sewage treatment plants. Blazer, who coordinated the study, said that researchers are still studying the results of the survey and are awaiting data that will help them determine the quality of the water at the time the fish were caught. However, preliminary data from the water samples that were taken from the river show a variety of chemical pollutants.
Blazer cautioned that although scientists were surprised by the high frequency of intersex fish, the sample size of the study was relatively small, with only about 10 male and 10 female fish taken from each of eight locations in Maryland, Virginia, and the District of Columbia. The female fish did not exhibit any unusual sex traits, although all the fish—both male and female—had lesions and showed signs of other pollution-related illness. Researchers were reluctant to take many fish from the waters because of conservation concerns, according to Blazer.
The Environmental Protection Agency does not issue guidelines to water treatment plants to test for allowable levels of estrogenic compounds, although the agency has been studying the issue of "endocrine disruptors" since 1996. The water authority for the Potomac River basin, which draws from both the Potomac and the Occoquan rivers and services approximately 1.5 million people, is currently working with the USGS and other scientific agencies to develop methods for eliminating potentially harmful compounds in water during water treatment processes.
Jeanne Bailey, a spokeswoman for Fairfax Water, said that the findings of so many intersex fish are of concern to the water authority. The treatments used by Fairfax Water, which include activated charcoal and ozone, have proven to reduce levels of estrogenic compounds in treated water. Bailey said that people should not draw conclusions of doom and gloom in terms of the USGS findings indicating potential problems with human health. "Fish are a great indicator of the health of our waters," she said. "But they are not a great indicator of what may translate to humans."
But the U.S. Geological Surveys found last year that the "intersex fish" in the Potomac River and its tributaries are developing female sexual traits at a frequency much higher than scientists have ever seen before, and faster than in any of the other places where the phenomenon has been found. According to fish pathologist Vicki Blazer, nearly all of the male smallmouth bass caught in last year’s survey of Potomac tributaries were the abnormal fish. Smallmouth bass appear to be more susceptible to intersex development than largemouth bass. In the Potomac River itself, 7 of 13 largemouth bass exhibited female characteristics, including three that were actually producing eggs.
The Potomac River and its tributaries provide drinking water for millions of people, so the rapid rise in frequency of these abnormalities is causing concern among many people that the pollutants in the river are becoming more severe and toxic. Scientists say that although it isn’t clear what is causing the male fish to develop female characteristics, it is likely a combination of pollutants.
Some pesticides and chemicals are believed to stimulate the production of estrogen, and estrogen from human waste and birth control pills can end up in the waterways after making its way there via sewage treatment plants. Blazer, who coordinated the study, said that researchers are still studying the results of the survey and are awaiting data that will help them determine the quality of the water at the time the fish were caught. However, preliminary data from the water samples that were taken from the river show a variety of chemical pollutants.
Blazer cautioned that although scientists were surprised by the high frequency of intersex fish, the sample size of the study was relatively small, with only about 10 male and 10 female fish taken from each of eight locations in Maryland, Virginia, and the District of Columbia. The female fish did not exhibit any unusual sex traits, although all the fish—both male and female—had lesions and showed signs of other pollution-related illness. Researchers were reluctant to take many fish from the waters because of conservation concerns, according to Blazer.
The Environmental Protection Agency does not issue guidelines to water treatment plants to test for allowable levels of estrogenic compounds, although the agency has been studying the issue of "endocrine disruptors" since 1996. The water authority for the Potomac River basin, which draws from both the Potomac and the Occoquan rivers and services approximately 1.5 million people, is currently working with the USGS and other scientific agencies to develop methods for eliminating potentially harmful compounds in water during water treatment processes.
Jeanne Bailey, a spokeswoman for Fairfax Water, said that the findings of so many intersex fish are of concern to the water authority. The treatments used by Fairfax Water, which include activated charcoal and ozone, have proven to reduce levels of estrogenic compounds in treated water. Bailey said that people should not draw conclusions of doom and gloom in terms of the USGS findings indicating potential problems with human health. "Fish are a great indicator of the health of our waters," she said. "But they are not a great indicator of what may translate to humans."
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