Health officials warned Thursday that no fish caught in Lake Elmo should be eaten because they carry unsafe concentrations of a chemical that most likely came from an old 3M dump — the first time the state has issued such a blanket consumption advisory for a Minnesota lake.

Officials also said that largemouth bass from Lake Harriet in Minneapolis are unsafe for everyone — not just high-risk groups — because of contamination with the same kind of toxin, a perfluorinated chemical (PFC) from another industrial source. And they added new guidance on restrictions for consumption of similarly contaminated fish from five other metro-area lakes and the Mississippi River.

Previously, fish-consumption advisories for about 1,400 lakes and streams statewide have been aimed primarily at pregnant women, children and other groups highly susceptible to contaminants that build up in the tissue of game fish. Almost all of those advisories are related to mercury, PFCs made by 3M or another class of toxic chemicals called PCBs.

On Thursday, officials from the Minnesota Department of Health said that recent studies of fish tissue from the lakes targeted by the advisory and from the Mississippi found PFC concentrations above the levels now considered safe.

Assistant Health Commissioner Paul Allwood said that the advisories are based on long-term exposure, not from eating just one or two fish. "We recognize that some people may like to eat the fish they catch from these lakes, but this recommendation is prudent based on the available information," he said.

The new consumption advisories vary by location and species of fish. Lake Harriet, Lake of the Isles and Bde Maka Ska (formerly Lake Calhoun) in Minneapolis were contaminated with PFCs from the nearby Douglas Corp. plating facility, which was addressed starting in 2010. PFC levels in those lakes have been declining, officials said.

Health officials said the source of contamination in Lake Johanna and Twin Lake in the east metro area has not been confirmed. PFCs in the Mississippi River between the Ford Dam and the lock and dam at Hastings likely came from a disposal site near 3M's Chemolite plant in Cottage Grove.

And Lake Elmo, a deep and clear recreational lake with a boat ramp and fishing dock, was likely contaminated from surface runoff and a plume of groundwater from the former 3M disposal site in Oakdale.

The lake is home to a wide variety of popular game fish, including northern pike, trout, bluegill and crappies, according to the state Department of Natural Resources.

While Minnesota's game-fishing season doesn't open until May 12, pan fish may be taken now. On Thursday evening, no one was fishing at the Lake Elmo Park Reserve, largely because its fishing pier was removed in the fall and won't be replaced until later this month.

The danger of PFCs

PFCs were one of the world's most widely used chemicals because they repel oil and water and make things slippery. In addition to their use in industrial processes, they were the basis of many consumer products such as Gore-Tex, Teflon and Scotchgard, as well as in the firefighting foam used at military and fire-training sites.

3M and other manufacturers agreed to stop making them a decade ago. Earlier this year, Minnesota Attorney General Lori Swanson settled a long-standing lawsuit against 3M for damages to natural resources in the east metro area. The company agreed to pay $850 million to help pay for systems to clean drinking water, and for mitigation of what could be decadeslong damage to groundwater, lakes, streams and the Mississippi.

The company still faces dozens of other lawsuits elsewhere across the country.

Many are driven by the health concerns that have grown in recent years based on new scientific studies that show exposure to PFCs carries risks for high cholesterol, reduced liver function, increased thyroid hormone levels and weakened immune response. Studies also show they can increase the risk of some cancers.

As a result, in the past two years the U.S. Environmental Protection Agency, Minnesota and several other states have drastically lowered the concentrations considered safe for drinking water.

As part of that review, last month the Health Department lowered the concentrations of PFCs in fish considered safe for eating from 800 to 200 parts per billion. That led to the new fish consumption advice released Thursday.

Jim Kelly, the Health Department's environmental health manager, said that this summer the agency will undertake similar studies of fish in other east metro lakes and streams. In general, he said, concentrations of PFCs in ground and surface waters have been declining. But the lowered health risk limits mean even more lakes could be added to the advisory list.

The likely source of the elevated levels of PFCs in Lake Elmo is surface and groundwater contaminated by the former 3M disposal site. The state's recent $850 million settlement with 3M will allow for further investigation that may eventually help reduce the contamination.

Staff writer Pat Pheifer contributed to this report. Josephine Marcotty • 612-673-7394