Chronic Toxicity of a Fluoride Mixture to Freshwater Organisms

Chronic toxicity of a solution, containing 1.5% of Hydrofluozirconic acid and 1.0% of Ammonium bifluoride as the active ingredients, to two freshwater species was investigated in this study. The fathead minnow, Pimephalespromelas, and the water flea, Ceriodaphniadubia, were used as test organisms. Survival, growth and/or reproduction were used as endpoints. The solution had a low pH of 2.5 and was highly toxic to both species. Following 7 days of exposure of fathead fry to the solution, a 7 day LC₅₀ of 2.26% was obtained. A survival NOEC of 1.25% solution and a growth NOEC of 0.625% was obtained. Survival data from the ceriodaphnia toxicity test produced an 8 day LC₅₀ of 3.11%. A survival NOEC of 2.5% and a reproduction NOEC of 0.625% was also determined. Fathead minnow fry were tested again for chronic toxicity after adjusting the pH of the solution from 2.5 to 7.5. The pH adjusted solution yielded a 7 day LC₅₀ of less than 6.25%, the lowest concentration tested. Both survival and growth had a NOEC of less than 6.25%.