Plan St-Laurent - Pour un développement durable

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Highlights

Publication of a study monitoring changes in contaminants in the St. Lawrence River

To combat pollution in the St. Lawrence, the first step is to establish the type (quality and quantity) of pollutants involved. With that in mind, on October 15, 1998, the St. Lawrence Centre released a study describing the main chemicals present in the river between Cornwall and Québec.

The study, entitled Mass Balance of Chemical Contaminants in the St. Lawrence River and carried out in 1995 and 1996 under the St. Lawrence Plan, focussed on 85 specific substances in six classes: metals, polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine and organophosphorus pesticides, and triazines. The purpose was to determine what enters the river from the Great Lakes and the Ottawa River, and what flows out of it downstream into the estuary and the Gulf.

The situation portrayed by the researchers in the report was fairly encouraging, although it did not minimize how much still needs to be done before the river is entirely free from pollution. With regard to PCB concentrations, the study noted that the St. Lawrence is a relatively pollution-free river when compared with other waterways around the globe. Levels of PCBs were 5 to 10 times lower than the concentrations measured in Lake Ontario during the 1980s. And while PAH levels have not fallen from what they were10 years earlier, the St. Lawrence ranks in the middle compared with other waterways affected by these substances. According to the report, metal concentrations are similar to those found in environments with little or no contamination, and 10 to 100 times below those measured in the most polluted European rivers.

This St. Lawrence Centre study was innovative in a number of ways, including the techniques used to quantify contaminants at trace levels. Several contaminants are toxic at very small concentrations, sometimes equivalent to less than one billionth of a gram, or even less than one thousandth of that concentration, in a litre of water.

News release