This report examines mercury concentrations in the marine environment of the Restigouche River, near a mercury cell chloralkali plant operated by Pioneer Chemicals Canada Inc. (PCI) in Dalhousie, New Brunswick. The PCI plant is a known point source of mercury in the area, but the extent of marine contamination in the Baie des Chaleurs as a result of those discharges has not been recently evaluated.

Marine sediments (five transects), mussel tissue (six locations) and effluent samples (four locations) were obtained in the vicinity of the PCI plant and analyzed for total mercury. Mussel tissues were also analyzed for condition index, metallothioneins and zinc in the digestive gland and gonad as well as gonad vitellin-like proteins and digestive gland lipid peroxidation. Results indicated that the area of the Restigouche River around the PCI plant had elevated concentrations of mercury in sediment and mussel tissue compared with local background concentrations. Mercury concentrations in sediments decreased with distance from the chlor-alkali plant. Concentrations in sediments ranged from 0.03 mg/kg at a distance of 4.6 km to 1.96 mg/kg at a distance of 20 m from the shoreline at the plant. Nine sites had mercury concentrations exceeding the CCME Interim Sediment Quality Guideline (0.13 mg/kg), the furthest of which was 1090 m from PCI. Mercury concentrations in water discharges from four of the five observed outfalls ranged from 0.84 to 4.32 µg/L. Mercury concentrations in mussel tissue ranged from 0.02 mg/kg at a distance 4.6 km from the plant to 1.40 mg/kg directly in front of the plant. Condition index and zinc concentrations in mussels close to the plant were correlated with mercury levels; however, some abnormal biomarker results were found at locations far from the plant as well, indicating other sources of contaminants.

Further studies are recommended to define the area of contamination near the PCI plant, as well as to determine the potential impact of other sources of mercury in the area. The environmental risk of the mercury contamination should also be more clearly established.

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