Three weeks after professional fishermen extracted more than 26,000 pounds of invasive carp from Lake Winona and transported them for sale on the East Coast food markets, the Minnesota Pollution Control Agency announced it had found a "forever chemical" in fish taken from the lake — a chemical that has been linked to cancer.

“I was not aware of this at all but I appreciate you letting me know,” Tony Havranek, a fishing logistics manager for fish broker FisH2O, who was arranging for the sale of the carp. “You operate on the assumption that Minnesota and Wisconsin lakes are safe. Mercury is what we think of. ... This PFOS issue is a really new thing.”

PFOS stands for perfluorooctane sulfonate, a useful chemical that repels stains and water and has been used in many different consumer and industrial products, including carpet, waterproof yet breathable clothing, nonstick cookware and some kinds of firefighting foam. It is called a "forever chemical" because it does not break down in the environment.

More critically, it belongs to a class of compounds that has been linked to cancer and has been labeled an "urgent public health and environmental threat" by the U.S. Environmental Protection Agency.

PFOS was detected in sunfish caught this summer by the DNR, and the Department of Health has issued a fish consumption advisory for sunfish found in Winona. It advises men and boys over age 15 and women not planning to become pregnant to limit consumption of Lake Winona sunfish to one meal a week. It doesn't indicate whether any level of sunfish from Lake Winona is safe for children under 15, pregnant women or women planning to become pregnant.

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The primary U.S. manufacturer of PFOS, 3M, voluntarily stopped making it by 2002, and eight other companies agreed to stop making a related chemical by 2015, according to the EPA.

However, existing stocks remain, and some U.S. manufacturers have not agreed to stop making them, the agency says. They can also be imported from countries where they are still used in manufacturing.

Havranek says his company generally tests fish for mercury and PCBs, chemicals also common in U.S. fish, but not for PFOS. He said he wanted to learn more about the state's testing procedure before deciding what to do with the fish. The fish went to holding ponds in Erie, Michigan, and he said he wasn't sure if they had already gone to market.

“I think the first thing is understanding the data and see if there is a reason to not utilize these fish," he said. "And if that’s the case, it's coming up with Plan B. Is it fertilizer or is it going to be landfill?”

Jim Kelly, who manages the Minnesota Department of Health programs that include the fish consumption advisory, said it was difficult without further testing to determine whether people should limit their consumption of carp from Lake Winona. As it is being sold in other states, he said that will likely be up to the health departments in those states.

Kelly said he didn't want to unduly alarm people about eating seafood, as long as they follow state guidelines.

“Fish is a really healthy source of protein," he said. "There are things in fish that are helpful in the developing brain of the young child. ... It’s a healthy source of protein.”