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Under the conditions of this test, 11 % inhibition of respiration rate of the sludge was recorded at 100 mg 1-ETHYL-3-METHYL IMIDAZOLIUM ETHYLSULFATE per litre. Hence, the EC50 of 1-ETHYL-3-METHYL IMIDAZOLIUM ETHYLSULFATE exceeded 100 mg/L.

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The influence of 1-ETHYL-3-METHYL IMIDAZOLIUM ETHYLSULFATE on the respiration rate of activated sludge was investigated after a contact time of 30 minutes. The study procedure was based on OECD Guideline No. 209, adopted April 4, 1984, EEC Directive 67/548 amended November 18, 1987 (87/302), Part C, Publication No. L133, adopted May 30, 1988 and ISO Standard 8192 (1986). 1-ETHYL-3-METHYL IMIDAZOLIUM ETHYLSULFATE was a light yellow viscous liquid with a purity of 99.0% (HPLC). The water solubility of 1-ETHYL-3-METHYL IMIDAZOLIUM ETHYLSULFATE is > 1000 g/L at 20.1 ± 0.5 °C (pH 8.3, NOTOX Project 417206). For the activated sludge respiration inhibition test a stock solution of 0.5 g/L was prepared by adding 508.3 mg test substance to 1000 ml of Milli-RO water (tap water purified by reverse osmosis; Millipore Corp., Bedford, Mass., USA). Thorough mixing (10 minutes) was used to accelerate dissolving and to ensure homogeneity. The pH of the clear and colourless stock solution was 7.7. A concentration of 100 mg/L, corresponding to 100 ml of the prepared stock solution in 500 ml final volume, was tested in duplicate. 11 % inhibition of respiration rate of the sludge was recorded at 100 mg 1-ETHYL-3-METHYL IMIDAZOLIUM ETHYLSULFATE per litre. The duplicate measurement confirmed the result of the first measurement. Therefore, no further testing was needed. Since all criteria for acceptability of the test were met, this study was considered to be valid. In conclusion, under the conditions of this present test, 11 % inhibition of respiration rate of the sludge was recorded at 100 mg 1-ETHYL-3-METHYL IMIDAZOLIUM ETHYLSULFATE per litre. Hence, the EC50 of 1-ETHYL-3-METHYL IMIDAZOLIUM ETHYLSULFATE exceeded 100 mg/L.