ORONOCO — The state fish consumption advisory for Lake Zumbro north of Rochester was tightened from unrestricted to once a week because the fish might contain too high a level of a chemical used in nonstick coatings and stain-resistant fabrics, according to a new study.

It was the only lake out of 59 checked to have enough perfluorooctane sulfonates to have the state tighten warning level for the general population, according to the Minnesota Department of Health that did the study along with the U.S. Environmental Protection Agency. The level for pregnant women, women who might become pregnant and children younger than 15 had been once a week.

Lake Zumbro is a manmade reservoir of the Zumbro River downriver of Rochester.

In scientific studies of the family of chemicals called perfluorocarbons that includes PFOs, “animals are given much higher doses than we would ever expect people to consume. At these very high concentrations, in laboratory studies, PFCs cause harmful changes, including cancer, in the liver and other organs. Developmental problems (e.g., delays in growth and maturation) have been seen in the offspring of rats and mice exposed to PFCs while pregnant,” the department says on its website.

The new recommendation says carp, catfish and northern are contaminated by mercury, crappies by PFOs and largemouth bass by both. PFOs were found in all the fish; the department uses the contaminant with the highest level to set its recommendations.

In nearly all the 55 lakes tested outside the Twin Cities, PFO levels were low to undetectable.

Pat McCann, a department environmental health, said Zumbro was chosen because the department already had fish from that lake and because it wanted to select lakes across the state. It was a screening test, meant to see what’s out there. “At this point, we really don’t know where we are going to find it,” she said.

Yet it’s not greatly surprising that the PFOs were found there because the lake is downriver of the Rochester Wastewater Treatment Plant, she said.

Lake Pepin, a natural reservoir of the Mississippi River downriver of the Twin Cities and its wastewater plant, also has fish consumption warnings based on the PFOs, she said.

The warnings are put out not to halt consumption of fish but to help people decide which species, and which size, are best for their health, she said.

Doug Schultz, a health department spokesman, said now that PFOs have been found, the Minnesota Pollution Control Agency will begin looking at where the chemicals come from and what to do about them.