State officials Friday warned people to limit how often they eat fish caught from Twin Lake in Robbinsdale and Crystal.
The lake has been found to have levels of a man-made perfluorochemical (PFC) in the fish similar to the higher levels previously measured in metro area lakes Calhoun, Elmo and Johanna, the state Health Department announced Friday afternoon.
The PFOS (perfluorooctonate sulfate) levels in these fish place them in the one meal per month consumption category, given no impact from other contaminants, the department said. Special cleaning and cooking precautions used to reduce contaminants such as PCBs that concentrate in fat are not effective with PFOS.
The chemicals were made by Maplewood-based 3M beginning in the 1940s for use in Scotchgard, Teflon and other products that resist heat, oil, stains, grease and water, including nonstick cookware, stain-resistant fabrics and fire-fighting foam. 3M, a leading maker of the chemicals at plants in Minnesota and Alabama, decided to stop production in 2000 and ended all manufacturing by 2002. There are few studies of the health effects of PFCs on people, but studies by 3M of workers exposed to PFCs during manufacturing show no apparent problems.
Twin Lake covers 213 acres and offers anglers crappie, bluegill, northern pike and sunfish.
“Our concern with consuming fish is any long-term exposure to contaminants,” said Patricia McCann, the department’s fish consumption advisory coordinator. “Our advice for how often it is safe to eat fish is set at a level that is protective of human health over many years of continuous fish eating.”
The department is in the process of analyzing the data from this latest round of lake sampling by the Minnesota Pollution Control Agency (MPCA) for PFCs as well as data on additional lakes from the Department of Natural Resources for mercury and polychlorinated biphenols (PCBs). A combined analysis of all the data — covering mercury, PCBs and PFCs — is then compiled and formatted to develop a revised fish consumption advisory.
Wide range of PFOS
The new PFC data are from 15 metro lakes including samples from the Minneapolis chain of lakes.
Since PFCs were first discovered in metro area lakes in 2007, fish from 55 lakes in the metro area have been tested for PFCs.
McCann said there is a wide range in the levels of PFOS detected in these fish and some are undetectable.
“Currently, the pattern of contamination is not understood and we are unable to predict which waters may have higher levels in the fish.” McCann said. “There are many unanswered questions and missing pieces to this puzzle. Unlike mercury and PCBs, we don’t yet understand the relationships between species or between lakes regarding PFCs.
“We have the most information about PFOS levels in bluegill, crappie and smallmouth bass, which account for 90 percent of the samples analyzed for PFCs. Most of the advice based on PFOS for these fish is one meal per week or unrestricted.” “Currently the pattern of contamination is not understood and we are unable to predict which waters may have higher levels in the fish.” McCann said. “There are many unanswered questions and missing pieces to this puzzle.”
Various health effects have been shown in laboratory animals exposed to high doses of PFOS, the PFC that accumulate in fish. Among the effects: decreased HDL, or good, cholesterol and changes in thyroid hormone levels in some animals.
The Associated Press contributed to this report.