The Toxicity of Ozone to the Bluegill

Ozone toxicity to bluegill (Lepomis macrochirus) was determined using standard bioassay procedures. In initial work bluegill were exposed to water containing ozone for 24 h; the Lc₅₀ was 0.06 ppm. A second experiment simulated “shock defouling” — the periodic dosing of power plant cooling water with high biocide concentrations to prevent biofouling. The Lc₅₀ for a series of six 30-min exposure periods spaced 8 h apart was 0.32 ppm. A third experiment attempting to determine the effects of sublethal concentrations resulted in the death of 9 of 15 bluegill after 4 weeks of exposure to 0.01 ppm of ozone. No controls died in any experiment. It was concluded that ozone is highly toxic to bluegill. Safe limits for long-term exposure probably lie well below 0.01 ppm. The results of this study and an examination of the literature indicate that ozone is more toxic than chlorine; however ozone is readily removed from treated water while some chlorine compounds are not.