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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Regarding all available test on toxicity to microorganisms, the most relevant test resulting in the lowest PNEC value is used for assessment.
The sensitivity of activated sludge to p-cresol was determined by a respiration inhibition test according to OECD Guideline 209. The 2h IC50 for respiration inhibion of microorganisms is 440 mg/L.
The effect of p-cresol on Nitrosomonas activity was measured as a nitrification inhibition method comparable to ISO/DIS 9509. The 24 h-IC50 was 27 mg/L.
For respiration, the 49 h-IC50 was 260 mg/L. Nitrification inhibition by p-cresol was also measured by a similar method yielding an EC75 of 16.5 mg/L during a 2 -4 h incubation period. The EC50(48 h) with respect to growth of Tetrahymena pyriformis accounts for 157 mg/L testing p-cresol.
In order to protect the efficiency of sewage treatment plants, inhibition of nitrification is identified to be the most sensitive test system.

Key value for chemical safety assessment

EC50 for microorganisms:
16.5 mg/L

Additional information

Several tests are available to evaluate the toxicity of p-cresol to microorganisms.

The influence of p-cresol on the nitrification process in domestic wastewater is described in an experiment. A purified activated sludge was incubated for 2 to 4 hours to the wastewater (BSB5 = 250 mg/l, 50 to 80 mg NH4-N/l) fortified with different concentrations of p-cresol. The effect on the inhibition of the nitrification was determined by photometric analysis of nitrite and nitrate. An EC75-value of 16.5 mg/l is given for the inhibition of the reaction step of ammonia to nitrite. Nitrification inhibition by p-cresol was also measured by a similar method yielding an IC50 of 27 mg/L during a 2 h incubation period.

The protozoa Tetrahymena pyriformis was exposed to p-cresol for 48 hours using the cell multiplication inhibition test method. An EC50 of 157 mg/l was obtained.

The sensitivity of activated sludge to p-cresol was determined by a respiration inhibition test according to OECD Guideline 209. The 3h IC50 for respiration inhibion of microorganisms is 440 mg/L.