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Fish Contaminant Study
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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.
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Mercury
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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.
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