When the MPCA discovered PFOS in Lake Calhoun's bluegills the agency wondered if it was an isolated incident or if it represented more widespread PFC contamination. Agency staff quickly expanded their fish sampling - adding 30 lakes to their testing program. They also sampled more fish species including black crappies, largemouth bass and where they could find them, northern pike.
Paul Hoff, who supervises the unit that conducted the sampling, says the new findings have answered that initial question and they have raised others.
"I think what we can say here is the answer is that Calhoun is not alone in having some elevated levels of PFOS. But it's not also typical. We found a range of concentrations out of these first 10 lakes," he said
For example fish from three lakes - Bald Eagle, White Bear and Square Lake - had such low levels of PFOS that they didn't trigger a consumption advisory. But the black crappies and large mouth bass sampled from Lake Elmo far exceeded the levels of PFOS found in Lake Calhoun bluegills.
In the case of Lake Elmo, Hoff says it's located near 3M's former disposal site in Oakdale. 3M was the sole manufacturer of PFOS until 2002. The company stopped making the compound after discovering that it had distributed widely throughout the environment.
The Ramsey County lakes covered by the advisory are Como, Phalen, Gervais, Gervais Mill Pond, Round, Keller, Kohlman and Spoon. Besides Lake Elmo, the Washington County lakes affected are Olson, Ravine and Demontreville.
Hoff says most of these other lakes are not near known disposal sites. He says since PFOS was used in more than a dozen stain and water resistant products, it's likely that the chemical is still being used in manufacturing, commercial applications and agriculture.
"We do think that storm water conveyance systems, storm sewers and runoff in the surrounding watershed have something to do it. But a lot depends on the land use and what sort of activity takes place within those watersheds," he says.
But Hoff says he's not ready to rule anything out, including the possibility that the chemical has drifted down to the lakes from atmospheric emissions. People should not stop eating fish from metro lakes because of these latest tests, according to Pat McCann, with the Minnesota Department of Health. McCann says the guidelines are based on the assumption that people consume fish over a lifetime. Because PFOS affects different parts of the body than other chemicals like mercury, there is no evidence that it is more harmful in combination with those chemicals, she says.
"For example PFOS, it has an effect on the hormone levels, thyroid hormone levels or on cholesterol. Whereas mercury is a nervous system toxin, it affects your nervous system. And so those two chemicals react very differently in your body and they don't affect the same systems. So you wouldn't think that they would act in an additive kind of way."
The fish consumption advisories for the 12 east metro lakes range from one meal per week to one meal per month depending on the lake and the fish species. In general the advisory recommends only one meal a week for bluegills, black crappies and other sunfish and one meal per month for large mouth bass. But the guidelines are more restrictive for Lake Elmo where the PFOS concentrations are higher.