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Toxicity to microorganisms

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Description of key information

GLP study performed according to OECD 209 guideline:
3h-NOEC = 31.6 mg/L.
3h-EC50 >1000 mg/L.

Key value for chemical safety assessment

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

Additional information

One key study is available to assess the effect of the test item on the respiration of activated sewage sludge, using a 3h static test according to OECD guideline 209 with GLP statement.

The test solutions were prepared as follows:

- two control solutions: activated sludge in dechlorinated water to obtain a final sludge concentration of 1.6 g/L,

- five test item solutions: activated sludge in dechlorinated water (at 1.6 g/L) and test item (to obtain final concentrations of 10, 31.6, 100, 316 and 1000 mg/L),

- three reference item (3,5 -dichlorophenol) solutions: activated sludge in dechlorinated water (at 1.6 g/L) and reference item (to obtain final concentrations of 4, 12 and 36 mg/L).

The oxygen consumption of these solutions was measured for approximately 10 minutes, with a chart recorder, after an aeration of 3 hours. The EC50 (concentration expected to cause 50% inhibition of the respiration rate) of the test item and the reference item was determined considering the oxygen consumption of the controls as 100%.

As the validity criteria were met (the difference between the two controls was below 15% and the EC50 of the reference item was between 5 and 30 mg/L), the test was considered valid.

Inhibitions of the respiration rate at 10, 31.6, 100, 316 and 1000 mg/L were 0%, 0%, 9%, 11% and 21%, respectively, relative to mean of the controls. Hence, a significant inhibition of the respiration rate (> 15% relative to mean of the controls) was noted only at 1000 mg/L.

Under experimental conditions, the 3h-NOEC and the 3h-EC50 of the test item is 31.6 mg/L and >1000 mg/L for activated sludge, respectively.