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Tests on freshwater and marine organisms have shown that o-, m-, and p-cresol can exert toxic effects to aquatic organisms. Comparing results of freshwater and marine studies, cresols tend to be more toxic to marine organisms.

Short-term toxicity

The lowest LC50 values found in short-term toxicity tests on freshwater fish species range between 4.4 mg/L (p-cresol) and 7.6 mg/L (m-cresol).

Also in studies on short-term toxicity to aquatic invertebrates toxic effects of cresols could be observed. EC50 values of 9.6 mg/L and 7.7 mg/L were found on the freshwater species Daphnia pulex and Daphnia magna for o-cresol and p-cresol. In contrast, m-cresol seems to be less toxic to aquatic invertebrates. For m-cresol an EC50 of > 99.5 mg/L was determined on Daphnia pulicaria. The lower toxicity of m-cresol to aquatic invertebrates is supported by findings of marine studies. A critical EC50 of 5 mg/L was found for p-cresol on the marine sea urchin Strongylocentrotus droebachiensis, while testing with m-cresol resulted in a higher EC50 of 30 mg/L.

Reliable results on short-term toxicity of cresols to algae or cyanobacteria are not available.

Comparing short-term results on fish and aquatic invertebrates the most sensitive LC50 was found to be 4.4 mg/L on the fish species Salmo trutta, determined for p-cresol. In general L(E)C50 values on fish and aquatic invertebrates are similar.

 

Long-term toxicity

In a non-guideline study (comparable to OECD 212) long-term toxic effects of o-, m-, and p-cresol to eggs and larvae of the marine fish species Gadus morrhua were tested. p-Cresol was found to be more toxic than o-cresol and m-cresol. NOEC values of 3 mg/L were determined for o- and m-cresol, while the most critical NOEC of 0.3 mg/L was found on p-cresol. The long-term toxic effect of p-cresol also was tested on the freshwater fish species Pimephales promelas in a study similar to OECD 210. After an exposure period of 32 d a NOEC of 1.35 mg/L was found.

Long-term toxicity to aquatic invertebrates was tested with p-cresol. In a study according to a guideline proposal of the German Umweltbundesamt a NOEC of 1 mg/L was determined on Daphnia magna.

Toxicity of cresols to aquatic algae and cyanobacteria was studied by Bringmann and Kuehn (1975, 1976, 1978, 1990). NOEC values of 6.8 mg/L and 13 mg/L were determined for o-cresol and m-cresol on the cyanobacteria Microcystis aeruginosa. p-Cresol was tested on the green algae Desmodesmus subspicatus and resulted in an EC10 of 4.6 mg/L.

Comparing the three trophic levels the most sensitive NOEC-freshwater was found to be 1 mg/L on Daphnia magna and the most sensitive NOEC-marine was found to be 0.3 mg/L on Gadus morrhua. Both results were determined on p-cresol.

 

Toxicity to microorganisms

Numerous studies examining the toxicity of o-, m-, and p-cresol to microorganisms are available.

The sensitivity of activated sludge to m-cresol and p-cresol was determined by respiration inhibition tests according to OECD 209. IC50 values of 462 mg/L and 440 mg/L were found for m-cresol and p-cresol.

Nitrification inhibition of m-cresol and p-cresol was measured in tests comparable to ISO/DIS 9509 resulting in an EC75 of 11.4 mg/L for m-cresol and an EC50 of 27 mg/L for p-cresol. In non-guideline studies on inhibition of nitrification an EC75 of 16.5 mg/L was found for p-cresol and an EC75 of 12.8 mg/L was found for o-cresol.

Cell multiplication inhibition tests on the bacteria Pseudomonas putida and the protozoa Entosiphon sulcatum resulted in the following NOEC values:

 

o-cresol

m-cresol

Pseudomonas putida

NOEC = 33 mg/L

NOEC = 53 mg/L

Entosiphon sulcatum

NOEC = 17 mg/L

NOEC = 31 mg/L

Testing growth inhibition of p-cresol on Tetrahymena pyriformis an EC50 of 157 mg/L was found.

Comparing all data on toxicity to microorganisms, tests on nitrification inhibition resulted to be the most sensitive one. The lowest EC75 of 11.4 mg/L, determined for m-cresol, was used for PNEC calculation.