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Egg laying male carp and endocrine disruptors
by Bob Hartzler

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December 20, 1996-- A major issue facing agriculture is the recent allegations that certain classes of pesticides may disrupt the hormonal balance in wildlife and humans. An article in the December 13 issue of Science revealed the complexity of this issue.

The article reported on the disruption of hormonal balance in fish in both the US and Britain. Problems with fish sexual development were first reported by British biologists who found that the testes of carps in a heavily polluted river near London were filled with eggs. The scientists speculated that pollutants in the water were acting like a sex hormone, supporting the theory of endocrine disrupters.

Two new studies have provided insights into the problem of hermaphroditic fish. A study by the USGS found that fish in polluted rivers and streams across the U.S. had abnormal levels of sex hormones compared to fish from cleaner sites. The project director cautioned that 'there's a lot of fuzziness to the data set' and that it is too early to come to definite conclusions about cause and effect relationships.

The second study was conducted in Britain and evaluated the effect of pollutants on rainbow trout kept in cages near sewage outfall pipes. They used a variety of techniques to isolate compounds likely to cause estrogenic effects in fish. Rather than industrial pollutants, they found that three hormones found in women were responsible for the estrogenic effects. The researchers concluded the hormones were excreted in the urine, therefore making their way into the sewage lines.

The author of the article concluded that both sets of results bolster concerns that hormone-like chemicals may be harming ecosystems on a broad scale. He also stated that the fact that natural substances have been fingered in the one study should sound a cautionary note to investigators to avoid jumping to conclusions on the sources of observed problems.

The article demonstrates the complexity of this issue, and it is likely that there will be continued debate on the role of pesticides as endocrine disrupters.

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
http://www.weeds.iastate.edu
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