A chemical formerly manufactured by 3M has been found at elevated levels in nine more metro area lakes, according to a study released Tuesday, and is likely entering the waters through stormwater runoff.
The Minnesota Pollution Control Agency (MPCA) collected 381 fish from 20 lakes and two river reaches last spring and summer. They were analyzed them for PFOS (perfluorooctane sulfonate) and related compounds. 3M manufactured the chemical for decades for use in Scotchgard, firefighting foams and other products before ceasing production in 2002.
The metro lakes study began after the surprise discovery last spring of relatively high levels of PFOS in bluegills from Lake Calhoun in Minneapolis. Scientists couldn’t explain the source of the contamination, because the lake is not near any known areas where 3M manufactured or disposed of the chemical.
The findings of the latest study are mixed, said Paul Hoff, MPCA supervisor of environmental reporting and special studies.
Three lakes in Minneapolis and six in surrounding counties contained fish with PFOS levels “high enough to possibly be of concern,” said Hoff, while 11 other lakes showed little or no trace of the chemical.
The inconsistent results mean that the source of PFOS is probably not from air emissions from 3M’s manufacturing plant in Cottage Grove, he said.
“We’re pretty certain that the higher levels are attributable to something specific in the watershed of those lakes that came in via stormwater runoff,” Hoff said. The PFOS might have entered the system long ago or in more recent months, he said, and may have come from firefighting foam residue, the chrome plating industry or various consumer products ranging from older water- and grease-resistant coatings, lubricants and hydraulic fluids.
Hoff said the next step is to study what drains into the lakes of concern and how PFOS moves through the food chain. It is widely known to accumulate in blood and does not break down in the environment.
State health officials said in a statement that they will evaluate the new MPCA fish data and determine whether additional warnings about fish consumption will be issued. In April, authorities advised anglers to eat no more than one meal per month of bluegills taken from Calhoun and four connecting lakes. They stressed that although the fish contained high levels of PFOS, the chemical was present at extremely low levels in the lakes’ waters and posed no risks for swimmers, boaters and pets.
The lakes with elevated levels of PFOS in fish are: Lake Johanna (Arden Hills), Cedar (Minneapolis), Harriet, Hiawatha, Jane, Keller, Powers, Red Rock and Tanners.
Waters with little or no trace of PFOS are Cedar (Scott County), Centerville, Colby, Green Mountain, Hydes, Independence, Nokomis, Peltier, Upper Prior, Sarah and Silver.
Fish from Lake Minnetonka and Lake Josephine were also tested, but those results are not available yet. Hoff said that lakes were selected for testing based mainly on their popularity for fishing, and that PFOS tends to accumulate in bluegills, crappies and bass more than northern pike and walleye. He said that fish were also collected from lakes around the state last summer as part of mercury studies and that some will be analyzed for PFOS for comparison with urban lakes.
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