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Toxicity to microorganisms

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Description of key information

In a 3 h activated sludge respiration inhibition study conducted according to OECD guideline 209 and GLP, the EL50 and NOEL for microorganisms in activated sludge exposed to PEMP product were determined to be 780 mg/L and 100 mg/L, respectively. The study was reliable without restrictions.

Key value for chemical safety assessment

EC50 for microorganisms:
780 mg/L
EC10 or NOEC for microorganisms:
100 mg/L

Additional information

In a 3 h activated sludge respiration inhibition study conducted according to OECD guideline 209 and GLP, microorganisms in activated sludge were exposed to PEMP product at loading rates of 3.2, 10, 32, 100, 320 and 1000 mg/L.

No statistically significant inhibition of the respiration rate of the sludge was recorded at or below a loading rate of 100 mg PEMP product per litre, with mean inhibition values of -6%, 3%, -6% and 0% at 3.2, 10, 32 and 100 mg/L. At higher loading rates the inhibitory effect of PEMP product on aerobic waste water (activated sludge) bacteria increased with increasing loading rate, ranging from an average of 40% inhibition of the respiration rate at 320 mg/L to 51% at 1000 mg/L. The EL50 and NOEL were 780 mg/L and 100 mg/L, respectively.


There was no oxygen uptake from abiotic processes and the result at 1000 mg/L with a nitrification inhibitor showed that the heterotrophic inhibition of the respiration rate was not comparable to the total inhibition. Based on the results of the total and heterotrophic inhibition, nitrification inhibition was calculated to be 149%.