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Toxicity to microorganisms

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Description of key information

A study according to EU Method C.11, OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test) and OPPTS 850.680 was carried out. The purpose of the 3-hour test was to evaluate the influence of the test item on the activity of the activated sludge by measuring the respiration rate under defined conditions. The respiration rates (total, heterotrophic and nitrification oxygen uptake rates) of samples of activated sludge fed with synthetic sewage were measured in an enclosed cell containing an oxygen electrode after a contact time of 3 hours. 
This preliminary test was used to estimate the range of concentrations of the test item needed in a possible definite test for determining the inhibition of oxygen consumption. The test item was investigated in this study at the nominal concentrations of 10, 100 and 1000 mg/L. Defined amounts of the test item were added directly into the test vessels. One vessel was prepared and investigated at the test item concentrations of 10 and 100 mg/L, and triplicates at the highest examined concentration of 1000 mg/L.
Based on measured oxygen consumption values and calculated specific respiration rates it can be stated that the 3-hour EC10 and EC50 values of the test item are greater than 1000 mg/L. The NOEC was determined to be 1000 mg/L.
The specific respiration rates measured at the highest test item concentration of 1000 mg/L were compared with the blank control values using 2 Sample t-Test (α=0.05). No statistical significant differences were observed in the comparison with the blank control values.
In conclusion, this preliminary test demonstrated the absence of inhibition of oxygen consumption by the test substance up to and including the limit concentration of 1000 mg/L, therefore a definite test was considered unnecessary.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information