Male minnows placed in Duluth sewage effluent not only developed female characteristics but also lost their male behavior traits and were less able to reproduce, new research revealed.
The male fathead minnows lost their aggressive ability to protect nests, fight off rivals and mate with female fish.
The males lost the horns on their heads, their gonads shrank and they began to produce an egg protein found only in healthy females, according to the University of Minnesota study.
The male minnows weren't sterile; they simply didn't have the drive or ability to mate.
"Their aggressive behaviors are severely repressed by exposure to effluent," said Dalma Martinovic, a contract scientist for the Environmental Protection Agency'sMid-Continent Ecology Division laboratory in Duluth. She did the research for the University of Minnesota. "Exposed animals didn't reproduce."
The compounds also affected female fish.
Females "exposed for 14 days never recovered," she said. "They never reproduced again."
It's the first study to look at the reproductive behavior of fish exposed to sewage effluent and not just their fertility or physical condition. But the results echo other studies that found male fish with female egg proteins, caused by estrogen-like compounds in sewage effluent.
Because the minnows were placed in 100 percent effluent from the Western Lake Superior Sanitary District treatment plant, effects in harbors water, where the effluent would be diluted, are unclear.
But the results are renewing concerns over endocrine-disrupting compounds that humans are pumping into the environment, especially through wastewater treatment.
"The effects are subtle, insidious. ... But over the long term, over generations [of minnows], this may be affecting natural selection," said Peter Sorenson, University of Minnesota fisheries scientist. "This has probably been going on for some time. ... We could eventually see a decline in the quality of the gene pool and the ability for fish populations to reproduce and thrive."
Scientists said it's unlikely any danger exists for effects on human reproduction because the levels of compounds found are so low and because drinking water sources are well away from the sewage discharge.
Parts of the research were published recently in the journal Environmental Toxicology and Chemistry and included researchers from the EPA and University of Minnesota.
As startling as the wastewater's impact on fish, however, is where the female-like estrogens in Duluth wastewater apparently are coming from.
New research by scientists at the University of Minnesota Twin Cities shows the estrogen compounds that are probably causing problems in the Duluth minnows come not from people or synthetic human compounds, but from high concentrations of phytoestrogens extracted from trees during the papermaking process at paper mills.
The tree estrogens mimic animal estrogens and biologically affect the fatheads, biologists said.
The levels of the estrogen-like compounds in WLSSD effluent follow flow patterns from paper mills that make up almost half of the plant's inflow.
In the past, it was believed that most endocrine-disrupting estrogens were from birth-control drugs, surfactants in detergents, pesticides or other human sources.
But those compounds aren't getting through the WLSSD treatment plant in levels high enough to cause problems, said Paige Novak, associate professor civil engineering at the University of Minnesota.
"That's the good news," Novak told WLSSD officials and staff at a recent presentation.
Instead, Novak's team of scientists found unusually high levels of genistein, a plant estrogen, in WLSSD wastewater. And Novak said the source probably is paper mill wastewater.
In one test, treated WLSSD effluent contains 83 micrograms per liter of genistein, "10 times higher than the level where we'd expect to see biological effects" on minnows, Novak said.
Scientists are concerned that the same kind of estrogens coming from paper mill wastewater also may be coming from other industries that refine plants. Preliminary research shows high levels in ethanol plant wastewater.
As more ethanol plants come online, that could become a major issue for wastewater treatment plants. That research has not yet been published, however.
Novak said studies are needed to determine if the compounds can be treated by filtration through membranes or through activated carbon or biological control.
Martinovic said the fathead minnow experiment used100 percent treated effluent from the WLSSD plant and that it's unlikely that the effluent, once diluted in the Duluth-Superior harbor of the St. Louis River, would have the same effect.
"I'm concerned [that it may be affecting fish in the river], but I wouldn't pass judgment yet," she said.
The News Tribune first reported in 2001 that minnows were developing female egg proteins when placed in Duluth and Twin Cities sewage effluent. But scientists at the time weren't sure what was causing the problem and hadn't looked at actual mating and reproduction behavior.
Martinovic said re-searchers should look closer at fish in the Duluth-Superior harbor portion of the St. Louis River. "We need to go out there and look," she said.
Sorenson said the issue is woefully under-researched and under-funded.
"We're just about out of money for our part of it, and we haven't even started to look at what's going on out there" in the St. Louis River, he said.
Kurt Soderberg, executive director of the WLSSD, said it's encouraging that the plant's treatment is catching many endocrine-disrupting compounds but that it's not clear how the utility might change to catch more. He also called for more state and federal research, noting that it was a national, even global issue.
"There doesn't appear to be anything that we could or should do differently from our current strategies," Soderberg said. "We will continue to make our facilities available for continued research, we will continue to look for source reduction, like the pharmaceutical collection, and we will challenge our industry and the regulators to determine just how serious a problem this is for long-term effects in the natural environment."