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Toxicity to microorganisms

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Description of key information

Under normal use conditions, potassium superoxide is not anticipated to be exposed to the aquatic environment. Exposure to the water is only possible if KO2 is accidentally released. However, when exposed, potassium superoxide reacts rapidly with water to produce potassium hydroxide (KOH), oxygen (O2) and potassium hydrogen peroxide (KHO2), which slowly degrades to KOH, H2O2 (hydrogen peroxide) and O2. Therefore, aquatic toxicity of KO2 could be anticipated to be due, in part, to the degradation product H2O2. KOH further dissociates into potassium and hydroxyl ions which constitute normal ion pool of the medium. On the other hand, hydrogen peroxide is likely to degrade within a short time in aquatic medium due to many alternative and competitive degradation pathways. Especially, in alkaline medium and in the presence of heavy and transition metals it is degraded rapidly and in presence of different microorganisms it is degraded catalytically. As a result, the contribution of toxicity from hydrogen peroxide is likely to be low. Overall, the aquatic toxicity of potassium superoxide is likely to be low and a quantitative estimation of the hazard potential will not be appropriate due to its rapidly changing degradation kinetics.

Key value for chemical safety assessment

Additional information

A study was conducted to determine the toxicity to aquatic microorganisms of the test substance according to OECD Guideline 209, in compliance with GLP. Activated sludge of a predominantly domestic sewage was exposed for 3 h to the test substance at nominal concentrations of 1 to 1000 mg/L. Two controls with no exposure to the test substance and one positive control (3,5-dichlorophenol) were included. After the exposure, the oxygen demand was measured once per minute during a period of 11 minutes. The test substance inhibited the respiration of activated sludge in a concentration dependent manner. However, the effect was reversible with time due to the rapid degradation of the test substance mediated by the biological matrix. The effect of 3,5-DCP on the respiration rate of activated sludge increased with time. The EC50 value for the positive control was 6 mg/L at the 3 h measurement. Under the study conditions, the 3 h EC50 of the substance in an activated sludge of a predominantly domestic sewage was determined to be 466 mg/L (European Chemicals Bureau, 2003).

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