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

Organochlorinated compounds

Organochlorinated compounds constitute another family of well-known toxic products such as DDT, PCBs, dioxins and furans. DDT is a very powerful insecticide that was used in agriculture during the 50s and 60s. In the Lac-Saint-Jean region, where agriculture is a major activity, DDT does not seem to have been used much because little DDT or its degradation products DDE and DDD can be found in the sediments of the lake and the Saguenay River. Consequently, few DDT residues can be found in the Fjord sediments.

Polychlorinated biphenyls (PCBs) are another important group of pollutants consisting of organochlorinated compounds. They are produced by the reaction of chlorine with the biphenyl molecule at high temperature. There are 208 PCB reaction combinations possible. During the 60's, producers discovered that PCBs gave yellowish oil with rather exceptional lubricating and thermal properties. Before knowing they were hazardous, they were widely used in industry and elsewhere, such as for insulation in electrical transformers. Even though their production has been forbidden since 1975, they remained very widely used in industry and they may still be found everywhere on earth, especially in developing countries where standards are less strict or simply impossible to apply.

Dioxins and furans are not produced by industry for use like PCBs or DDT are. They are pollutants produced by pulp and paper plants that use chlorine as a bleaching agent and are also produced by some synthesis processes in the chemical industry. There is no direct source of these compounds in the Saguenay River. However, atmospheric and global fallout did not spare the region. Organochlorinated compounds have molecules that can escape from the ground and water, evaporate to the atmosphere and may be carried over long distances by the wind.

Can the contamination level in the Saguenay River sediments be compared with that found in the Saint-Lawrence River estuary? No, the sediments of the estuary are generally not as highly contaminated as in the Saguenay River. However, a significant amount of organochlorinated compounds and aromatic hydrocarbons is carried by the Saint-Lawrence River and is deposited farther in the marine estuary.

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