Comparative acute toxicity of potassium permanganate to nontarget aquatic organisms

Potassium permanganate (KMnO4) is used worldwide in freshwater pond aquaculture for treatment and prevention of waterborne external parasitic, bacterial, and fungal diseases. Nevertheless, KMnO4 has not been approved by the U.S. Food and Drug Administration, and insufficient information exists to allow evaluation of the environmental risk of KMnO4 exposures. Limited data exist concerning KMnO4 toxicity to nontarget species in systems receiving aquaculture effluent from treated ponds. The goal of this research is to generate effects data for use in developing an ecological risk assessment of KMnO4. Toxicity tests were used to compare the relative sensitivities of five standard aquatic test species to KMnO4. Acute toxicity test results using synthetic moderately hard water show static 96-h mean median lethal concentration (LC50) values +/- standard deviation (SD) of 0.058 +/- 0.006 mg/L for Ceriodaphnia dubia, 0.053 +/- 0.009 mg/L for Daphnia magna, 2.13 +/- 0.07 mg/L for Pimephales promelas, 4.74 +/- 1.05 mg/L for Hyalella azteca, and 4.43 +/- 0.79 mg/L for Chironomus tentans. Most of these values are below the recommended KMnO4 treatment rate of at least 2.0 mg/L or 2.5 times the water's potassium permanganate demand (PPD; an estimation of the available reducing agents in the exposure water), suggesting significant environmental risk. However, repeating these laboratory tests using pond water resulted in significantly reduced toxicity, with static 96-h mean LC50 values (+/-SD) of 2.39 +/- 0.36 mg/L for C. dubia, 1.98 +/- 0.12 mg/L for D. magna, 11.22 +/- 1.07 mg/L for P. promelas, 13.55 +/- 2.24 mg/L for H. azteca, and 12.30 +/- 2.83 mg/L for C. tentans. The PPD of synthetic moderately hard water was 0.329 +/- 0.114 mg/L; however, pond water PPD was 5.357 +/- 0.967 mg/L. The effective disease-treating dose based on 2.5 times the PPD would thus be 0.823 and 13.392 mg KMnO4/L, respectively, exceeding the LC50 for most of these nontarget organisms, even in pond water, immediately after treatment.