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Metro Area Lakes Contaminated by PFOs

by 5m Editor
26 February 2009, at 12:00am

US - Twin Lake in Hennepin County (Robbinsdale-Crystal) has been found to have levels of a perfluorochemical (PFC) in the fish similar to the higher levels previously measured in lakes Calhoun, Elmo and Johanna. The PFOS (perfluorooctonate sulfate) levels in these fish place them in the one meal per month consumption category, given no impact from other contaminants.

"Our concern with consuming fish is any long-term exposure to contaminants," said Patricia McCann, fish consumption advisory coordinator for the Minnesota Department of Health (MDH). "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 advisory is updated annually to reflect new fish contaminant data.

MDH is in the process of analyzing the fish tissue 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 (DNR) for mercury and polychlorinated biphenols (PCBs). A combined analysis of all of the data – mercury, PCBs and PFCs – is then compiled and formatted to develop a revised fish consumption advisory. MDH expects to receive additional PFC data from MPCA that will be incorporated into the new advisory as well. The updated advisory will be ready by the opening of fishing season.

The new PFC data are from 15 metro lakes including samples from the Minneapolis chain of lakes. The data is from an ongoing effort by MPCA and other agencies to investigate the extent of and sources of PFC contamination.

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."

Most health experts recommend eating fish two times per week. "People should choose to eat fish that can be eaten that often," McCann said, "but it's okay to include a meal of fish from the once-per-month category, too. Spacing out meals of fish over time is the way to keep exposure to a safe level."

Fish are a good low-fat source of protein and contain many vitamins and minerals. Eating fish may help protect adults against cardiovascular disease. Pregnant women and women who may become pregnant should also eat fish because eating fish promotes eye and brain development in fetuses.

Scientists' understanding of mercury and PCBs in fish throughout the state and about species and waters allows MDH to provide Statewide Safe Eating Guidelines as part of its fish consumption advisory program, McCann said. For example, we know that walleye, northern and bass are the species with the highest levels of mercury and we know that Lake Superior and the major river systems have PCB levels of concern, whereas the inland lakes do not. The guidelines can be found on the MDH Web site at http://www.health.state.mn.us/divs/eh/fish/index.html.

MDH also provides site-specific advice for eating fish from a lake or river where the contaminants have been measured. Site-specific advice can also be found on the MDH Web site at http://www.health.state.mn.us/divs/eh/fish/index.html as well as the DNR's Lakefinder at http://www.dnr.state.mn.us/lakefind/index.html.

A variety of health effects occur in laboratory animals exposed to high doses of PFOS, the PFC that accumulates in fish. The most sensitive effects (i.e., effects observed at the lowest dose causing adverse effects) are decreased high-density lipoprotein (HDL or good cholesterol) and changes in thyroid hormone levels in some animals. Special cleaning and cooking precautions used to reduce contaminants like PCBs that concentrate in fat are not effective with PFOS.

PFCs are a group of manmade chemicals that have been used for decades to make products that resist heat, oil, stains, grease and water.

5m Editor