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Scrambled Sexual Signals

Hormones and chemicals that mimic hormones are getting into our waterways and can impact fish.

Some male fish in local waters are getting mixed signals from their own bodies, which are interfering with their sex life. According to Sea Grant researcher Deb Swackhamer, professor with the University of Minnesota's School of Public Health, everyday sorts of chemicals that get into waterways may affect the environment, and can scramble the hormonal signals that rule fish development and reproduction.

She and her research team of Peter Sorensen, Ira Adelman, Randy Lehr, and Heiko Schoenfuss from the University of Minnesota are studying endocrine-disrupting chemicals and their impact on fish in the Duluth-Superior Harbor and in the Mississippi River near St. Paul, MN. Endocrine disrupters are a class of chemicals that can interfere with the hormone system of animals, which regulates many important processes in the body. These chemicals can get into the environment through effluent from sewage systems, paper mills, feed lots, and through industrial waste.

The researchers are studying a subset of disrupters called environmental estrogens, which mimic the actions of estrogen (a female hormone) and can affect the reproductive cycle and sexual development. Environmental estrogens include the hormone estrogen itself (which many animals, including humans, release naturally), synthetic hormones such as those found in birth control pills, and industrial products such as detergents, plasticizers (such as those found in packaging peanuts), and insecticides.

"Hormones are a switch to a process," explained Swackhamer during a public presentation about her research at the Great Lakes Aquarium this spring. "If you think of your body as a coffee maker, hormones turn on the switch. The problem with environmental estrogens is that they don't know how or when to turn the switch off. They can cause abnormal responses in organisms or can block responses. Hormones control development and reproduction, so environmental estrogens can interfere with these processes."

The most visible reports of problems caused by endocrine disrupters in the United States include alligators in Lake Apopka, Florida, which showed population declines because males were feminized and unable to reproduce due to a pesticide spill. Beluga whales in the St. Lawrence River are showing similar effects. Scientists in Great Britain are also conducting studies on fish. When levels of environmental estrogens in effluent are compared between Great Britain and the U.S., levels are lower here.

"The good news is our sewage treatment plants are doing a good job of removing environmental estrogens," said Swackhamer. "The bad news is the low levels still seem to affect fish."

Swackhamer and her team, which also includes graduate students Dalma Martinovic, and Jim Levitt, are farther along in their study of the Mississippi River than of the Duluth-Superior Harbor. They are:

  • testing the effluent from sewage treatment plants and surrounding waters for environmental estrogens,
  • looking at fish from the river and harbor to assess effects of effluent exposure on reproduction,
  • testing fish allowed to breed in the lab to see if they suffer reproductive problems when exposed to effluent, and
  • looking for the presence of vitellogenin in male fish, an egg yolk protein normally found only in females.

The researchers found that male carp and walleye taken near the sewage treatment plant on the Mississippi had significantly higher vitellogenin than fish from a reference site. Male walleye were especially susceptible, showing a decrease in gonad size, and a total lack of sperm.

However, the research team has just completed a lab study which demonstrates that while goldfish exposed to sewage effluent for a 10-week period experience lower sperm production and behavioral changes, it's not enough to cause reproductive failure.

"This suggests the effects of environmental estrogens in effluent are subtle," said Swackhamer. "But even subtle effects in the lab may have an impact on wild fish, where reproductive opportunities are limited and competition is severe." The researchers are currently exploring the importance of these effects.

In the Duluth-Superior Harbor, the team found environmental estrogens in the effluent from the Western Lake Superior Sanitary District. They exposed laboratory minnows to the effluent and found that the males had vitellogenin in their blood. The researchers are currently assessing the minnows' ability to reproduce. This summer they will be collecting data on wild fish from the harbor.

Swackhamer's was one of several projects funded last year through a National Sea Grant initiative and the Environmental Services Division of the Metropolitan Council of Minnesota, and the University of Minnesota Water Resources Center. The findings are expected to assist resource managers in meeting the congressional mandates of the 1996 Safe Drinking Water Act and the 1996 Food Quality Protection Act to develop strategies for screening endocrine-disrupting chemicals.

For more information about her research, contact Swackhamer at: (612) 626-0435 or dswack@tc.umn.edu.


By Marie Zhuikov
August 2001

Return to August 2001 Seiche



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