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Long-term toxicity to fish

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Description of key information

No data on chronic toxicity to fish are available for m-cresol and therefore, a read-across from p-cresol is applied.
The 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. This toxicity study is classified as acceptable and satisfies the guideline requirements for the chronic fish study.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish
Effect concentration:
1.35 mg/L

Additional information

Concerning long-term toxicity to fish there are only non-reliable data available. A read-across approach from p-cresol is applied to get a comprehensive data set for m-cresol, based on the following justification:

Justification for the read-across approach:

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.

The most reliable chronic toxicity value was obtained in an Early-Life Stage Toxicity Test with Pimephales promelas. Usually, in long-term test the test species Oncorhynchus mykiss should be used

, as salmonids showed the lowest effect values in acute fish studies. It is expected that Oncorhynchus mykiss and Pimephales promelas will show similar effects in a FELS test. A review of the 20 relevant data for acute fish tests for m-cresol showed that LC50 values are in the same order of mangnitude for both species and it is therefore not predictable which of the species would show the lowest effect values in chronic tests. Pimephales promelas is also one of the recommended species in OECD guideline 210.

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