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Dan Gunderson, MPR News 90.3 FM, Published February 21 2013

Traces of chemicals in Minnesota lakes could harm fish

Tiny amounts of chemicals in Minnesota lakes might be having a big effect on some fish populations, according to two new studies by Minnesota researchers.

From the time they hatch, baby fathead minnows have limited chances of survival. Odds are good that they will be eaten by larger fish. But when exposed to drugs, their chances of surviving are worse, said Heiko Schoenfuss, a professor of toxicology at St. Cloud State University.

Graduate student Daniel Rearick, who works with Schoenfuss, exposed fathead minnows to pharmaceuticals and estrogen at the same levels documented in Minnesota lakes and compared them with other fish that were not exposed.

“What he found, which is really quite striking, is that fish that were exposed were slower to respond, swam away more slowly than their control counterparts, and as a result of that were more likely be eaten by a predator,” Schoenfuss said.

The researchers marked the fish so they could tell them apart. The graduate student then put all the fish into a tank with a predator, a sunfish.

Their results indicate a lower survival rate for the fathead minnows exposed to chemicals. That’s an important finding because fathead minnows are a big source of food for predatory sport fish like walleye.

The chemicals could have the same effect on other species, said Schoenfuss, who is coordinating his research with U.S. Geological Survey scientist Richard Kiesling.

Kiesling, who has been examining how exposure to endocrine-disrupting chemicals affects fish reproduction, studied fathead minnows and bluegills. He found exposed fish spawned later and produced fewer eggs than fish not exposed to the chemicals.

Add that conclusion to the finding that exposed young fish are more likely to be eaten, and the impact is significant, Kiesling said.

“In an environment where there’s such heavy predation, those small differences might be enough make a different in population level responses,” he said.

In other words, it could cause fish populations to drop dramatically.

That’s what happened a few years ago, when Canadian researchers exposed an entire lake to endocrine-disrupting chemicals. The fathead minnow population crashed.

The Canadian scientists weren’t sure what caused it. But the two new Minnesota studies might help explain why. If fish produce fewer young, and those young are more likely to be eaten, the population will shrink.

Although researchers have several puzzle pieces that appear like they fit together, they still haven’t been snapped into place.

Scientists have known for some time that exposure to endocrine-disrupting chemicals causes adult male fish to develop more pronounced feminine characteristics. Other scientific studies have found exposure to traces of the chemicals can cause fish to become more aggressive.

Monitoring shows such compounds are common in Minnesota rivers and lakes, most likely coming from wastewater treatment plants along rivers or septic systems near lakes.

Schoenfuss, the St. Cloud professor, said the latest studies show Minnesota lakes are at risk from pharmaceutical and estrogen compounds.

“Even these very minute concentrations of compounds can have a pretty profound effect on aquatic environments,” he said. “So just because a lake looks nice and there’s still fish in there doesn’t necessarily mean this lake is not susceptible to the effects of endocrine disruption.”

How big is the risk? Kiesling, a hydrologist and water quality specialist, is trying to answer that question. He’s studying Minnesota lakes, trying to determine how much chemical bluegills absorb and how it affects spawning behavior.

But Kiesling said he believes scientists now have a critical mass of research and there’s enough scientific evidence to consider action to protect lakes.