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Long-term toxicity to aquatic invertebrates

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Description of key information

No data on chronic toxicity towards aquatic invertebrates are available for o-cresol and therefore, a read-across from p-cresol is applied. The long-term toxicity of p-cresol to aquatic invertebrates was determined in a semi-static test according to the preliminary guideline proposal of the German Umweltbundesamt from1984. After 21 days of exposure a NOEC of 1 mg/l was determined.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
1 mg/L

Additional information

There is no study on chronic toxicity towards aquatic invertebrates available using o-cresol as test substance.

In order to get a comprehensive data set for o-cresol a read-across from p-cresol is applied, in accordance with 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 study resulting in the most sensitive NOEC ist used for read-across.

The OECD SIDS document for o-cresol had presented QSAR data for a 21 -day chronic daphnia test with: 21d-NOEC=1 - 1.5 mg/L. Although QSARs for long-term tests should be used for orientation only, it is validated by the outcome of this test (Kuehn 1988, 21d-NOEC=1 mg/L) which is in agreement with the QSAR prediction of 1 - 1.5 mg/L.

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