Assessment of the Acute Toxicity, Growth Impairment, and Flesh Tainting Potential of a Bleached Kraft Mill Effluent on Rainbow Trout (Salmo gairdneri)

Static and continuous-flow bioassays utilizing juvenile rainbow trout (Salmo gairdneri) were conducted on a northern Ontario bleached kraft mill effluent to assess the range of acute toxicity and related sublethal effects. The acute toxicity of the total mill effluent, as determined by static bioassay procedures, ranged from a 96-h LC50 value of 14–49.0% vol/vol. The results of these bioassays depended on testing methodology and effluent treatment systems employed by the mill when samples were collected. Continuous-flow bioassays conducted on the effluent Produced 96-h LC50 values of 21.8 and 24.8% vol/vol. Growth rate of juvenile rainbow trout (1–2 g) held under continuous-flow conditions for 18 days was significantly reduced at 6% vol/vol effluent concentration (P < 0.05). Flavor of yearling rainbow trout [Formula: see text] exposed to 3% effluent for 48 h was significantly impaired (P < 0.05). This effluent concentration, the lowest level impairing flavor represents approximately 0.12 of the 96-h LC50 derived from continuous-flow bioassays. No significant flavor impairment was detected in fish exposed for 144 h to a 2% effluent concentration Flavor impairment at a 3% vol/vol effluent concentration, the most sensitive sublethal response measured in this study, may also be the most critical response when assessing the economic impact of a kraft mill discharge to a freshwater ecosystem.