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The case of mercury | Aromatic hydrocarbons | Organochlorinated compounds | Beluga contamination

Aromatic hydrocarbons

Since the 40's, aluminium smelters contributed largely to the economic boom of the Saguenay-Lac-Saint-Jean region. Even today, they still drive the economy. During aluminium production, polynuclear aromatic hydrocarbons (PAHs) are emitted from the stacks in the black smoke. PAHs are also produced by the combustion of coal, petroleum, wood, tobacco and paper. The smelters with Söderberg electrolytic cells produced about 2 kilograms of PAHs per ton of aluminium. During the 35 or 40 years that these pots were operated, thousand of tons of PAHs were carried by the wind over long distances and ended up in the Saguenay River watershed.

In the 60's, they began installing scrubbers in the aluminum plants. Particles laden with PAHs were removed to improve air quality in the smelting sectors and to reduce stack emissions. The scrubbers were regularly cleaned and the scrubbing water was released in the Saguenay River for a few years. The Saguenay River flows fast and the water loaded with PAH particles rapidly reached the Fjord. Regional industrial and urban activities thus contributed to producing and depositing hundred of tons of PAHs in the Fjord between 1946 and 1976.

The environmental awareness period began in 1972. Wastewater effluents gradually decreased and they ceased dumping raw sewage water directly into the river to channel them to settling ponds. When a cross section of the sediment layer is sampled and analyzed for total PAH, we first find very weak levels for the pre-industrial period before 1940. After, we may observe a rapid and major PAH increase in the sediments. From 1972 onwards, the PAH level decreases following the installation of new technology scrubbers and the application of environmental laws. Only from 1981 onwards did the Fjord influents really reach the pollution levels considered as less harmful to the environment. The Fjord sediment current levels still remain much higher than before the pre-industrial period and generally above 2 ppm.

Only a few bivalve organisms can significantly bio-accumulate PAHs. They constantly filter suspended particles but cannot metabolise the PAH. This leads to accumulation of these substances in their tissue. On the other hand, fishes and mammals can metabolise (digest and absorb) the contaminated particles such as benzo(a)pyrene, the most studied PAH that is emitted in large amounts in plant smoke and in domestic wood stoves.

Analyzed fish

Scientists demonstrated the proliferation of tumours in certain fish exposed to PAH contaminated sediments. However, it is still impossible to establish a direct link between the presence of the PAH in the Saguenay River and the health of the marine mammals living at the mouth of the Fjord. Certain diseases discovered in dead belugas found along the Saint-Lawrence River shores could well be linked to the presence of the PAH in their food, but there are major obstacles in establishing scientific proof via a link of causes and effect. Indeed, it is impossible to realize experiments directly on the belugas. Scientists must resort to working with land mammals that provide results that are not necessarily comparable to those on belugas.

Researchers

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