Male fish are developing feminine characteristics from excess hormones in rivers and lakes, scientists say.
“In the 1990’s, scientists in Britain were starting to find a large number of male fish downstream of sewage treatment plants with eggs or egg proteins in their blood,” Fisheries and Oceans of Canada ecotoxicologist Karen Kidd said. “Basically, these male fish were becoming feminized. It’s because they’re being exposed to either natural or synthetic hormones in sewage plant discharge.”
Birth control pills and laundry detergents are just two of the 75 household compounds that might be causing male fish to develop eggs. Products such as birth control pills, detergents and insecticides contain chemicals mimicking the female hormone estrogen.
Women who use birth control pills release synthetic estrogen in their urine. Laundry wastewater contains a significant amount of estrogen mimics from detergents. Sewage treatment plants can only break down about 80 percent of these estrogen mimics in wastewater. The remainder enters rivers and lakes and interferes with the hormone systems of fish and other aquatic life.
“It’s a big problem,” Minnesota Sea Grant environmental chemist Deb Swackhamer said. “We saw problems in wildlife around the country, in Beluga whales in the St. Lawrence River, in alligators in Florida and in birds in the Great Lakes.”
Scientists are also conducting studies in Great Britain and Canada.
“We don’t know how severe the problem is or how widely these feminized male fish can be found,” Kidd said. “That’s something I think in the next several years we’ll know a lot more about.”
In addition to egg-development, the male fish have lowered sex-drives and sperm-counts as a result of the synthetic estrogen, Swackhamer said.
“It has to do with competitive spawning behavior,” Swackhamer said. “You’ve got one healthy fish and one exposed fish. When you put those two together, the healthy fish always gets the girl.”
Swackhamer said exposed male fish can still reproduce with a female, but only if healthy males are not there to compete. Despite their inability to compete, Swackhamer said fish populations do not seem to be affected by the reproductive problems.
“The wastewater has something in it that is estrogenic enough to cause the vitellogenin [female egg protein] to be in the male fish, but it’s not sufficient enough to cause reproductive effects,” Swackhamer said.
Scientists are conducting studies to determine whether the feminized male fish are affecting entire fish populations.
“What we don’t know is whether or not these feminized males can still continue to successfully reproduce,” Kidd said. “Once we understand the extent of the problem, we can make a more concentrated effort on wastewater treatment to reduce our inputs of it into the environment.”
