Complexation of copper in the effluent of a sewage treatment plant and an estimate of its influence on toxicity to coho salmon

Measurements by cupric ion electrode of the complexing capacity of the effluent from a sewage treatment plant (STPE) averaged 0.300 mg 1^?1. Of the complexed Cu 67% was due to compounds of 10,000 MW. Organic compounds removable by activated carbon composed 88% of the total organic carbon and were responsible for 87% of the complexation. Complexation of Cu²⁺ by STPE diminishes the toxicity from total Cu to juvenile coho salmon; the LC₅₀ was 0.164 mg 1^?1 for river water vs 0.286 mg 1^?1 for 40% STPE. The LC₅₀ of Cu²⁺ was approximately the same (0.017 vs 0.022 mg 1^?1) in both matrices; this species thus appears to play a toxic role. The mean survival time in diluted STPE with added Cu was inversely proportional to the Cu²⁺ concentration.