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Fish Contaminant Study

In 2000, Fond du Lac participated in a study with the Minnesota Department of Health and the Grand Portage Band, to collect fish from Reservation waters and analyze them for mercury, PCBs, and toxaphene (a powerful agricultural pesticide which has shown up in Great Lakes fish). We collected species of fish favored by band members (channel catfish, walleye, northern pike, and smallmouth bass) from the St. Louis River, and included those species in the study, plus panfish such as bluegills and crappies from seven of the Reservation lakes. The results of the analyses showed that mercury was the only contaminant of concern (of those we measured) for fish from Fond du Lac waters, and we developed consumption guidelines that describe how much, what size, and what species of fish band members can safely consume. These guidelines were intended to encourage band members to eat fish frequently, as they are a healthy source of protein and other nutrients. The advice simply directs people towards smaller fish (walleye, northerns and catfish) and those species of fish (sunfish, crappies) that tend to have lower levels of mercury in them. We plan to resample fish from Reservation waters in the next two years, in order to track any trends in fish mercury levels.


As our base water quality program was established, we looked for opportunities to study other related issues. Mercury is of particular concern in this region, because of the abundance of wetlands, the underlying geology, and water chemistry, all of which lead to a high rate of mercury conversion to its bioavailable form, methylmercury. In this form, mercury is taken up by the aquatic food chain, and its concentration magnifies with each link; predatory fish such as walleye, northern pike, and bass at the top of the food chain tend to have high levels of mercury in their tissue. Fish-eating birds, wildlife, and humans are then exposed to potentially unhealthy levels of mercury as they consume contaminated fish. Mercury is a powerful neurotoxin (toxic to nervous systems); young children who are growing and developing, and women who are nursing babies or may become pregnant are especially at risk from its effects. There are new studies indicating that mercury exposure can lead to increased risk of cardiac disease, as well. Mercury is released to the environment from both natural and man-made sources, but the biggest sources today are from coal-burning power plants and mining. During combustion and ore processing, mercury enters the atmosphere and is transported many miles; it is deposited back on land and water by precipitation.