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St. Louis River Mercury Study



SUBJECT: GLNPO Project completion:  St. Louis River Mercury Study

USEPA's Great Lakes National Program Office (GLNPO) announces the
completion of its portion of this grant to the Fond du Lac Tribe
(GLNPO funding $70,000).

SUMMARY:

The St. Louis River, the largest U.S. tributary to Lake Superior, has
been identified by the IJC as an Area of Concern, in part due to the
presence of toxic contaminants in fish tissue and negative impacts on
the benthic community.  Mercury (Hg) levels in walleye are elevated
at various locations along the lower St. Louis River, with the
highest values occuring near and within six small reservoirs.  As a
result of past industrial practices and discharges, the sediments
have accumulated contaminants, including Hg, behind the reservoir
dams.

A preliminary survey of Hg concentrations as a function of depth in
cores from three reservoirs showed a significant peak in Hg levels
in some strata.  Results of a study on mercury in fish along the
lower St. Louis River have demonstrated the likelihood that sediments
in the lower river reservoirs may influence mercury residues in fish.

This project was a follow up to a preliminary sediment survey of the
lower St. Louis River reservoirs.  The goal was to conduct a more
detailed study to assess sediment mercury contamination and its
importance in bioaccumulation, resuspension, and transport.
Investigations consisted of two components: 1) a mercury-in-sediment
cores survey; and 2) a mercury-in-benthos survey that included
measuring mercury in the corresponding surface sediments.

keywords: St. Louis River Area of Concern, contaminated water and
sediments, mercury

ENVIRONMENTAL RESULTS AND PRODUCTS:

Two of the three highest mercury concentrations were from Scanlon
Reservoir, while elevated concentrations were also observed in
Thompson Reservoir, Knife Falls Reservoir, and Forbay Reservoir.
The most widespread contamination appears to be in Thompson
Reservoir where 5 of the 10 highest concentrations were found.

The information on mercury contamination in these reservoirs has been
very useful in showing the need for mitigating those areas where high
levels of this contaminant are at or near the surface.  Current
research to develop practical mercury mitigation technology is using
some of the knowledge gained in this study.  A project report,
"Assessment of Mercury Contamination in the Sediments of Six
Reservoirs on the Lower St. Louis River, Minnesota", has been
published and is available.

REFERENCE INFORMATION:

For additional information, please contact GLNPO project officer
Callie Bolattino (312-353-3490; bolattino.callie@epamail.epa.gov),
referencing Fiscal Year 1993 grant number GL995478-01-0.

Information on additional GLNPO projects is available via links
to GLNPO's Internet home page:  http://www.epa.gov/glnpo/