Toxic chemicals and their impacts in the St. Lawrence Estuary and Saguenay Fjord,Quebec, Canada: from a chemical to an ecosystem-based risk manage

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The St. Lawrence Estuary (SLE) and Saguenay Fjord (SF), Quebec, Canada, have received world-wide attention in the early 1980s when high concentrations of contaminants and high prevalence of lesions including neoplasia, hermaphrodism and infection by opportunistic agents were reported in beluga whales (Delphinapterus leucas). Both persistent organic pollutants (POPs) such as PCBs mainly originating from the upstream industrialized sectors of the Great Lakes and the upper St. Lawrence River, and local contamination by polycyclic aromatic hydrocarbons (PAHs) and mercury have been incriminated. The release of these chemicals has been successfully reduced through environmental regulations and restoration of contaminated areas. Since 1970s, declines in mercury, PAHs and PCBs have been observed in sediments and in biota. However, organisms remain exposed to complex mixtures of contaminants including regulated persistent compounds remaining in the ecosystem and newer compounds which also have the potential of causing deleterious effects. Interactions between toxic chemicals and other environmental stressors may increase the risk of deleterious impacts. New concerns include: chronic inputs of tributyltin from ship transportation associated with reproductive/immune disturbances, interaction between nutritional condition and POPs, increasing concentrations of brominated flame retardants in beluga tissues and inputs of agricultural chemicals and nutrients from SLE tributaries. Several fish populations historically used as preys by the beluga are declining as a consequence of multiple anthropogenic factors. Moreover hypoxic area in the bottom of the SLE is increasing and could act as an additional stressor. An ecosystem-based approach is being developed to pursue the protection the SLE/SF ecosystems facing multiple stressors and variable environmental conditions.