Minnesota Researchers Track Hormone-Disrupted Fish
DULUTH, Minn. -- Researchers have found that male fathead minnows placed in treated sewage water here have developed female characteristics -- a sign of hormone-disrupting chemicals.
It' s an indication that something external is fooling the hormone system of male fish, the University of Minnesota scientists and other researchers said.
Another sign is that male walleyes tracked in the Mississippi River have been found to be sterile, apparently from estrogen-like compounds from a sewage plant that disrupted their hormone systems.
Researchers are certain it' s a compound that mimics female estrogen, but how widespread the problem is among wild fish or whether fish populations may be at risk because males can' t reproduce is unclear.
So far, there' s no indication that humans are at risk from whatever compounds are causing the problems, often called endocrine disrupters, scientists said.
" This could have some very real ecological ramifications, and potential human health concerns. It' s a big maybe now, however, because we just don' t know yet, " said Peter Sorenson, a University of Minnesota fisheries professor. " But when you have male fish in Minnesota becoming feminized, it' s something that needs a serious look."
Scientists found female egg protein, called vitellogenin, in male Mississippi River walleyes in a study reported in 1998. That ongoing study near a Twin Cities sewage plant appears to show those male walleyes have become sterile. Researchers during the 2000 and 2001 spawning seasons found no sperm in those walleyes.
" That' s an indication that this is not just an issue for a specific fish, but that this has some ecological impacts, that it may be affecting the population, " said Deb Swackhamer, a University of Minnesota environmental chemist.
University of Minnesota professor Ira Adelman, a fisheries biologist heading the walleye study, said the river walleyes near the Twin Cities sewage plant have " sky-high" female egg protein levels caused by exposure to estrogenic compounds found in the sewage effluent.
But because of other possible factors, such as water temperatures, Adelman said he' s not ready to blame estrogens for their sterility.
In addition to the University of Minnesota, the Minnesota Sea Grant program, the Environmental Protection Agency' s Mid-Continent Ecology lab in Duluth and UMD' s Natural Resources Research Institute in Duluth are either studying or funding research on the issue.
The Western Lake Superior Sanitary District in Duluth and the Twin Cities sewage authority also are trying to develop a plan to stop it, either at the treatment plant or at the problem' s source upstream in the sewage system.
The research has produced more questions than answers.
In Duluth, for example, female egg protein was found this year in male laboratory minnows placed in effluent from the Western Lake Superior Sanitary District. But it' s not yet clear if those low levels of female egg proteins affected the minnow' s ability to reproduce.
Researchers also aren't sure why fish in the Twin Cities seem more severely affected by the estrogen exposure than laboratory fish.
Goldfish and minnows placed in Twin Cities sewage effluent developed female egg proteins, according to a study to be published within weeks, but they haven' t shown reproductive problems as serious as those of the wild walleye.
Scientists are trying to determine, from nearly 1, 000 possibilities, which estrogens or estrogen-mimicking compounds are causing Minnesota male fish to feminize.
The compounds are " turning on switches" in the male fish that would never be turned on by its own hormones, scientists say. The resulting changes can' t be reversed. The fish don' t go back to being healthy males, even if they swim elsewhere.
In addition to natural estrogens that all female animals -- including humans -- produce, possible suspects include compounds in detergents, plasticizers (like those in plastic packing peanuts) and insecticides.
The banned insecticide DDT, for example, mimics estrogen.
The sources of the compounds could be paper mills, livestock feed lots, farms, industrial waste and city sewage, Swackhamer said. Another recent study found male carp in several rivers across Minnesota with female egg proteins -- some below sewage plants but some well upstream, confusing scientists more.
Research by Swackhamer and others has all but ruled out human estrogen as the problem in the Minnesota waters.
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