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Description of key information

An Activated Sludge Respiration Inhibition test with the source substance showed that the 3-h NOEC is >=100 mg/L. There was no significant inhibitory effect on the respiration rate of activated sludge.

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Executive summary of the study performed with the source substance:

The effect of P-2290 on the respiration rate of activated sludge was assessed by the methods detailed in EC Directive 881302, 'Biodegradation - Activated Sludge Respiration Inhibition test' and OECD Test Guideline 209, 'Activated Sludge, Respiration Inhibition test' adopted 4 April 1984, and the US Environmental Protection Agency (EPA), Toxic Substances Control Act, (TSCA), and the Federal Insecticide, Fungicide, and Rodenticide Act, (FIFRA); Office of Prevention, Pesticides and Toxic Substances, (OPPTS) Method 850.6800, (public draft issued April 1 W6), Modified Activated Sludge, Respiration Inhibition Test for Sparingly Soluble Chemicals. Samples of activated sludge (suspended solids 1.6 g/l), fed with synthetic sewage, were exposed to the test substance at nominal concentrations of 1, 10 and 100 mg/L for three hours. Single mixtures were prepared at 1 and 10 mg/L and the highest level was prepared in triplicate. Their rates of oxygen consumption were determined using an oxygen electrode and compared with those of controls, containing activated sludge and synthetic sewage alone, which were established at the beginning and end of the culture series. The reference inhibitor 3,5 -dichlorophenol (3,5 -DCP) was employed at 3.0, 10.0 and 32.0 mg/l, as a positive control. The specific respiration rate of the control culture established at the end of the test series (24.2 mgO2/g/h) was 98% of the rate of that established at the start (24.6 mg02/g/h). The three-hour 50% effect concentration (EC50) for 3,5 -DCP was calculated to be 9.4 mg/l (95% confidence limits 7.4 - 11.8 mg/l). These results show that the test was valid and that the sample of activated sludge employed was sensitive to inhibition. P-2290 had no biologically significant inhibitory effect on the respiration rate of activated sludge at any of the concentrations employed in the test. The respiration rate of activated sludge was reduced at most by 10% of the mean control value, in one replicate at a nominal concentration of 100 mg/l; no reduction was seen in two further replicates at this level. The EC20, EC50 and EC100 of the test substance could not therefore be calculated but these must be greater than 100 mg/l, the highest level tested.