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Ninety-six-hour static bioassays, with daily toxicant replenishment, were performed on Atlantic salmon (Salmo salar) parr to test for the acute toxicity of spent sulphite liquor (SSL). The LC50 of two batches of fresh SSL varied from 2000 to 2400 ppm, while the LC50 of SSL which had been previously oxidized for 5 days was 2750 ppm. Test fish responded differently to oxidized than to fresh SSL. Caution is urged in the application of 96-hr bioassay results on sulphite pulp mill wastes to field situations.

The 96-hr LC50 of copper to Atlantic salmon parr in water taken from the Exploits River, Newfoundland, is about 125 μg/liter at a total hardness of 8–10 mg/liter CaCO3 and a total alkalinity of 4 mg/liter. However, the addition of spent sulphite liquor from a pulp mill allowed fish to survive more than 180 μg/liter Cu. Considering the variety of organic compounds which have now been shown to chelate dissolved copper, it is likely that a simple model for the prediction of copper toxicity in waters receiving mine effluent will prove impossible.