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Toxicity to microorganisms

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Description of key information

In an Activated Sludge Respiration Inhibition Test, the EC50 of the test item was determined to be > 1000.0 mg/L. The EC10 of the test item was determined to be 630.0 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L
EC10 or NOEC for microorganisms:
630 mg/L

Additional information

To assess the effects of the test item on the oxygen consumption of municipal activated sludge, an Activated Sludge Respiration Inhibition Test according to OECD guideline 209 and EU Method C.11 was conducted in compliance with GLP principles. Activated sludge from a municipal wastewater treatment plant was exposed for 3 hours to nominal concentrations of 1000, 500, 250, 125 and 62.5 mg/L of the test item (based on the test item without correction of purity and blank controls; 3 replicates for each concentration). The test item was weighed in the required amounts for the test concentrations directly to the test vessels. A blank control (with 6 replicates) and a positive control with the reference substance 3,5-dichlorophenol (with 2 replicates for each concentration; 100, 10, 1 mg/L) was performed in parallel. The initial sludge concentration in the test vessels was 1.5 g/L dw. The consumption rate (mg O2/L*x minutes) of each test concentration and the blank controls were determined after 3 hours of exposure. The oxygen consumption was measured over a period of 8 -10 minutes. 6 to 6.3 minutes from the plotted track within a linear range of the graph was used for the determination of the respiration rate. The consumption rates (mg O2/L*h) were used to calculate the inhibition effects at particular test concentrations compared to the mean consumption rate of all controls. In result, the 3-h EC10 was determined to be 630 mg/L; the 3-h EC20, EC50 and EC80 was determined to be >1000 mg/L. The coefficient of variation of the six replicates of blank control was 7.7 % O2 consumption. Furthermore, the 3-h EC50 of 3,5-dichlorophenol was 3.8 mg/L and the mean oxygen uptake of the blank controls was 23 mg/g*h. In conclusion, the test conformed to all validity criteria and is valid.