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Toxicity to microorganisms

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Description of key information

The test item was considered not toxic to waste water bacteria (activated sludge) at or below a concentration of 3.2 mg/L, which was considered as the NOEC. The 3 hour EC50 was determined to be 612 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:
612 mg/L
EC10 or NOEC for microorganisms:
3.2 mg/L

Additional information

Charles River Laboratories (2017) is a GLP compliant study following OECD guideline 209 and is therefore considered reliable without restrictions (Klimisch 1). The mean control oxygen uptake rate exceeded 20 mg per 1 g of activated sludge in an hour (26 mg oxygen). The coefficient of variation of oxygen uptake in the control replicates did not exceed 30% at the end of the definitive test (13%). The criteria for acceptability of the test were met, therefore, the study was deemed as valid. A combined range-finding and limit test were conducted with the concentrations 10, 100 and 1000 mg/L.  A control (6 replicates) and an abiotic control (1 replicate) were tested. The pH of the sludge was 7.2 on the day of testing. The combined limit/range-finding test results displayed 10% inhibition of the respiration rate at 10 mg/L, 39% at 100 mg/L and 63% at 1000 mg test item per litre. It was therefore expected that the EC50 was between 100 and 1000 mg/L. For the final test, nominal concentrations of 1.0, 3.2, 10, 32, 100, 320 and 1000 mg/L were used. 5 replicates were used per test group and 6 replicates were used for the control. In conclusion, the study showed that the test item was considered non-toxic to the activated sludge (waste water bacteria) at and above the concentration of 3.2 mg/L (NOEC). The 3 hour EC50 was determined to be 612 mg/L.