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Toxicity to microorganisms

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Description of key information

The effect of the substance on the respiration rate of activated sludge was investigated in a test in accordance with OECD TG 209 and GLP. Samples of activated sludge (suspended solids 1.6 g/l), fed with synthetic sewage, were exposed for three hours to dilutions of the test substance. Two tests were conducted, the first of which comprised a preliminary range finding test at nominal concentrations of 10, 100 and 1000 mg/l (in triplicate). In the second (definitive) test, the substance was employed at nominal concentrations of 3.3, 10 (in triplicate) and 30 mg/l. The results of the preliminary test indicated that inhibition of respiration rates in the mixtures containing the test substance at nominal concentrations of 100 and 1000 mg/l were similar and the EC50 could not be determined. Therefore, the definitive test conducted aimed to define the three-hour NOEC which was considered as the highest tested concentration less than the calculated 20% effect concentration (EC20). The specific respiration rates of control cultures established at the end of the two-test series (27.3 and 26.8 mgO2/g/h) were 100% and 98% of the rates of those established at the start (27.3 and 27.3 mgO2/g/h). The EC20 was calculated from the results of the definitive test to be 29.8 mg/l (95% confidence limits, 24.7 – 35.3 mg/l) and the NOEC from this investigation, based on nominal concentrations, was considered as 10 mg/l.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
10 mg/L

Additional information