Effects of dissolved oxygen on kraft pulp mill effluent toxicity

Effects of reduced dissolved oxygen on the toxicity of kraft mill effluent to juvenile coho salmon, Oncorhynchus kisutch , were determined in short-term, constant-flow bioassays conducted in freshwater. Effects of dissolved oxygen on toxicity demonstrated for a wide range of oxygen concentrations, viz ., from 3.4 to approximately 9 mg 1 −1 , at water temperatures of 12 ± 1°C. With each successive lower oxygen level tested, the median survival time of the test fish and the 24-h tl m values were lower. Possible factors influencing observed results are discussed, as is application of results for protection of fish in waters receiving kraft mill wastes.