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ANALYSIS OF SEDIMENT CORES FROM CLAY LAKE BY MECP IN 2017: CHARACTERIZATION OF MERCURY, DIOXINS AND FURANS

Deposition of lake sediment occurs over time and can yield information on past environmental conditions; contaminants such as mercury, dioxins and furans are associated with sediment and because sediments are continuously deposited, analysis of sediment cores can provide a record of when contaminants were released and at what levels.

Clay Lake is the first major lake downstream of the Dryden Mill and where contaminants discharged into the Wabigoon River would accumulate. Knowledge of historically released contaminants such as mercury, dioxins and furans need to be considered before carrying out specific remediation programs in the English and Wabigoon Rivers.

CORES FROM THE EAST BASIN OF CLAY LAKE WERE SLICED INTO SECTIONS AND ANALYZED FOR:

  • Dioxins/furans

  • Total mercury (THg)    

  • Radiochemistry to determine the age of sediments                                                                                                                     

SUMMARY - CORE ANALYSIS OF DIOXINS/FURANS AND MERCURY:

  • Dioxin/furan levels increase in the late 1950s when bleached pulp was first produced and decline in the late 1960s – when elemental chlorine (a major source of dioxins/furans in bleaching) was no longer used.

  • Further decline of dioxin/furan levels in the 1990s is likely due to effect of industry regulations restricting release of dioxins/furans in effluent.

  • Recovery is taking place; however, levels in surface (recent) sediments are still higher than those measured in the deepest (oldest) sediments, which represent conditions before the mill started producing bleached pulp (recent young of year Yellow Perch data indicate dioxins/furans are bioavailable[1] from Clay Lake.

  • Increase in mercury in the early 1960s can be related to the building of the Chlor-alkali plant.

  • Decline of mercury in the 1970s can be related to the time when control measures for mercury discharge were implemented.

 

[1] Ability of a substance to be absorbed by the body through oral intake.

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Indications are that Clay Lake is recovering but not fully recovered to background levels of dioxins/furans and mercury. For an in-depth look at the results of this investigation

[1] Ability of a substance to be absorbed by the body through oral intake.

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