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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Activated sludge, OECD 209, Respiration Inhibition Test: NOEC(3h): 320 mg/L 

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
320 mg/L

Additional information

The toxicity towards aquatic microorganisms was investigated according to the conditions of OECD Guideline 209 (Clarke, 2012). Activated sludge, collected at an aeration tank of a predominantly domestic sewage treatment plant (STP) was used as inoculum. Synthetic sewage was used as respiration substrate. The used test water was deionised reverse osmosis water containing less than 1 mg/L Dissolved Organic Carbon (DOC). Based on the findings in the range-finding test and review, the definitive test was conducted with test concentrations of 100, 320 and 1000 mg/L to obtain a No Observed Effect Concentration (NOEC). 3,5-dichlorophenol was used as reference, resulting in an EC50(3h) value of 11 mg/L with 95 % confidence limit range of 8.6 - 14 mg/L. The pH was measured before and after the exposure time of 3 hours. The oxygen consumption was determined after 30 min contact time and at termination of the test. In some instances, the initial and final dissolved oxygen concentrations were below those recommended in the guideline (7 mg O2/L and 2 mg O2/L, respectively). No adverse effects on the test results are given in that cases, since the oxygen consumption rate as determined over the linear portion of the oxygen consumption trace. No statistically significantly toxic effects were shown at the test concentrations of 100 and 320 mg/L. Effects were observed at 1000 mg/L, concluding that the NOEC is determined as 320 mg/L after 3 h exposure.