Sediment quality Atlantic Ocean watershed: chapter 4

Freshwater reaches of the St. Lawrence River: îles de Contrecoeur National Wildlife Area

Highest butyltins (BTs) concentrations are found in an area with very still water, near île aux Rats, where they reach more than 2000 ng Sn/g, largely exceeding the probable effects threshold for aquatic fauna.

The wharf, located upstream of the archipelago, could be the source of this contamination. The occurrence of butyltins is also observed hinting possibly at a recent contamination due to biocide paints still in use on commercial ships.

Locations where concentrations of butyltins were observed in surface sediments of the îles de contrecoeur.
Spatial distribution of  sediment contamination by BTs in the St. Lawrence river near Contrecoeur

The figure shows the spatial distribution of sediment contamination by BTs in the îles de Contrecoeur in 2008. Approximately ten triangles are distributed on the territory going from highly contaminated in red, contaminated in yellow to not or slightly contaminated in green. It is upstream of the sector near the wharf that we observe the highly contaminated zones while they are slighty or not contaminated downstream.

Locations vary between these following classes: not, or weakly, contaminated, contaminated and highly contaminated. We observe seven zones not, or weakly, contaminated located mainly in the îles, six contaminated zones located along the shoreline and finally, four highly contaminated zones located at the wharf and in the still water zone, near île aux Rats.

Did you know?
Among all BTs concentrations measured in sediments from the freshwater reaches of the St. Lawrence River,  scientists have measured the highest concentrations in the îles de Contrecoeur National Wildlife Area, a protected area since 1981.

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