m-cresol

Endpoint summary

Additional information

Short-term toxicity:

A large number of acute toxicity tests on several species are available for m-cresol. The most sensitive fish species in acute toxicity tests belong to the salmonids. In a static tests on the toxicity of m-cresol the highest toxicity is a 96h LC50 value of 7.6 mg/L with Salvelinus fontinalis.

The acute toxicity of m-cresol to Daphnia pulicaria was determined in a flow-through immobilisation test after an exposure period of 48 h. Based on measured concentrations a 48h-EC50 > 99.5 mg/l was determined.

The toxicity of m-cresol to the freshly fertilized eggs of the marine sea urchin Strongylocentrotus droebachiensis was determined by a static test. For m-cresol the EC50 (96 h) is 30 mg/L.

Long-term toxicity:

There are no reliable data on chronic toxicity towards fish and aquatic invertebrates available using m-cresol as test substance. In order to get a comprehensive data set for m-cresol a read-across from p-cresol is applied, in accordance with the following justification:

Data from substances who’s physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity may be used in a read-across approach in order to avoid unnecessary animal testing. It can be stated that the 3 cresols act as a prime example of substances that are suitable for read-across. Cresols are isomers and, thus ideally fulfill the recommended criteria of structural similarity. In its chemical structure, a cresol molecule has a methyl group substituted onto the benzene ring of a phenol molecule, by different arrangement of the -CH3 groups are three structural isomers possible. (ortho-cresol, meta-cresol and para-cresol). Of particular importance to environmental effects are the values for partition coefficient (log Kow), vapour pressure, water solubility and dissociation constant. The values of the isomers are very close together, resulting in the same environmental fate and behaviour. Further, with regard to the bioderadation behavior, all 3 cresols are readily biodegradable. Concerning aquatic toxicity of the cresols on aquatic species, a large number of experimental results from tests with fish, invertebrates and algae are available, indicating a similar toxicity of all isomers, with p-cresol being slightly more toxic in acute tests: Based on the similarities in the results mentioned above the read-across approach is therefore scientifically justified.

Studies resulting in the most sensitive NOEC are used for read-across.

The most reliable chronic toxicity value was obtained in a long-term toxicity of p-cresol to aquatic invertebrates. The study was conducted under Semi-Static Reproduction according to the preliminary guideline proposal of the German Umweltbundesamt from1984. After 21 days of exposure a NOEC of 1 mg/l was determined

Chronic toxicity of p-cresol to fish was tested with Pimephales promelas in an Early-Life Stage Toxicity Test equivalent to OECD Guideline 210. The 32d NOEC is 1.35 mg/L.

Toxicity to aquatic algae and cyanobacteria:

The toxicity of m-cresol to the blue-green algae Microcystis aeruginosa (Cyanaophyceae) was determined in a cell multiplication inhibition test according to the guideline DEV L9. The relevant 8d-NOEC (EC3) for growth rate is 13 mg/L.

Toxicity to microorganisms:

The sensitivity of activated sludge to m-cresol was determined by a respiration inhibition test according to OECD Guideline 209. The 3h IC50 for respiration inhibion of microorganisms is 462 mg/L. In a non-guideline study the effect of m-cresol on activated sludge was determined by a respiration inhibition test. An 49 h-IC50 of 440 mg/L was obtained. Nitrification inhibition by m-cresol was measured by a method similar to ISO/DIS 9509 yielding an EC75 of 11.4 mg/L during a 2-4 h incubation period. In a cell multiplication inhibition test conducted with Entosiphon sulcatum a 72h-NOEC of 31 mg/l is determined. For Pseudomonas putida a NOEC of 53 mg/l was obtained in a cell multiplication inhibition test during 16 hours of exposure.