Sediment quality Atlantic Ocean watershed: chapter 2

Lake Saint-François

Lake Saint-François - Stéphane Lorrain, St.Laurent Center

Industrial activities in the Cornwall-Massena region in the last century were a significant source of sediment contamination in Lake Saint-François. However, since the end of the 80's, the contamination from mercury is gradually abating. In 2008, the contamination of sediments from Lake Saint-François by metals was low, except for the North sector where mercury and zinc persist.


Mercury Concentrations in Lake Saint-François Sediments in 2008.
Spatial distribution of sediment contamination by mercury  in Lake Saint-François  

The figure shows the spatial distribution of the concentrations of mercury in the surface sediment of lake Saint-François in 2008. Concentrations vary between 0 and 0.67 micrograms/g. They are highest downstream of Cornwall, in Ontario, and downstream of the lake near Saint-Zotique.

Despite the fact that their concentrations have decreased by approximately 95 % since 1979, PCBs are still occurring in 2008 in sediments from the southern part of Lake Saint-François. Also, scientists detect dioxins and furans everywhere they have analyzed them. Results show relatively high concentrations in the southern part of the lake and upstream of Cornwall.

Starting in the 60’s, tributyltin (TBT) was used, among other uses, as a biocide applied on the hull of ships and small crafts in order to prevent organisms from sticking to submergent surfaces. TBT is included in the class of organotin compounds and is known as being toxic. In Canada, the Prohibition of Certain Toxic Substances Regulations (2012) prohibits the manufacture, use, sale and offer for sale on import of tributyltin (TBT). Despite these regulations, this compound remains widely used in many countries.

Harbour areas and marinas show generally the highest concentrations of TBT. In Lake Saint-François, highest concentrations were found in the sediments near Creg Quay’s marina in Bainsville, in Ontario, and in Valleyfield’s marina.

As for PBDEs, the majority of the highest concentrations is located in the upstream part of the lake and would originate from the Great Lakes.  It is however difficult to determine the impact of TBT and PBDEs on benthic organisms, because, to date in Canada, no quality criterion has been officially adopted in regards to those substances.

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