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Toxicity to microorganisms

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Description of key information

The inhibition of the degradation activity of activated sludge is not anticipated when introduced in appropriate low concentrations. 
Read across was applied using these results and the EC50 of the test substance was determined to be greater than 1000 mg/L and the EC10 was determined to be 370 mg/L.

Key value for chemical safety assessment

Additional information

A study according to OECD 209 (BASF 2010) was performed to determine the toxic effects of the test substance 2-methylbutan-1-ol (CAS 137-32-6) on the oxygen consumption rate of aerobic micro-organisms (activated sludge) after short-term exposure of 180 min, compared with the blank control. The nominal concentrations of the surrogate test substance were: 0 (control), 62.5 mg/L, 125, 250, 500 and 1000 mg/L. The inoculum was activated sludge from a municipal waste treatment plant. The sludge concentration was 1.5 g/L and a synthetic medium according to the guideline was used. A reference substance (3,5 dichlorophenol) was used as positive control. The EC50 was determined to be greater than 1000 mg/L and the EC10 was determined to be 470 mg/L.

In addition a study according to OECD 209 (BASF 2010) was performed to determine the toxic effects of the surrogate test substance pentanol, branched and linear (CAS 94624-12-1) on the oxygen consumption rate of aerobic micro-organisms (activated sludge) after short-term exposure of 180 min, compared with the blank control. The inoculum was activated sludge from a municipal waste water treatment plant. The sludge concentration was 1.5 g/L. A reference substance (3,5 dichlorophenol) was used as positive control. The EC50 was determined to be greater than 1000 mg/L and the EC10 was determined to be 370 mg/L.

Supplementary a study according to ISO 8192 (Test for Inhibition of Oxygen Consumption by activated sludge) (BASF 1989) was performed to determine the toxicity of the read across substance pentan-1-ol after 180 min of exposure. The EC20 was determined to be greater than 1000 mg/L. No EC10 and EC50 values are given. 

In conclusion, as the EC10 value determined with the read-across substance pentanol, branched and linear (CAS 94624-12-1) was lower than the EC10 value determined in the study with the target substance itself, the smaller value (3h-EC10 = 370 mg/L) was chosen as “key value” and also used for PNEC derivation, reflecting a worst case scenario.