U.S. Geological Survey scientist Jeff Writer said even small amounts of the chemicals are cause for concern.

"It's complicated and these compounds we produce tend to show up -- they don't just go away," Writer said. "So, I think the focus is to really start thinking about our role in producing compounds that persist and what potential problems that might have."

Writer said additional studies are planned to learn more about long term effects on fish. The Minnesota Pollution Control Agency and St. Cloud State University were partners in the research