Registration Dossier

Diss Factsheets

Ecotoxicological information

Long-term toxicity to fish

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

For o-cresol no reliable data on chronic fish toxicity are available. 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 31d NOEC is 1.35 mg/L.

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 no reliable data available for o-cresol. The SIDS document on o-Cresol (OECD undated) has proposed to perform a fish early life stage test with Oncorrhynchus mykiss. This proposal was given at that time as PNECs were only "based on QSARs for long-term effects on fish" and as "a risk to the aquatic ecosystem has to be assumed". A read-across approach from p-cresol is applied to get a comprehensive data set for o-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 aromatic 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. The OECD SIDS report recommends using Oncorhynchus mykiss as test species, as salmonids showed the lowest effect values in acute fish studies. It is expected however 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 o-cresol showed that LC50 values are in the range of 6.2 to 41 mg/L, among them 3 results with Oncorhynchus mykiss in the range of 7 to 13 mg/L and 5 results with Pimephales promelas, in the range of 12.6 to 18.2 mg/L. These results are in the same order of mangnitude 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.

The OECD SIDS document for o-cresol has presented QSAR data for 30- and 60 -day FELS test with Oncorrhynchus mykiss: 30d-NOEC=1.8 mg/L, 60d-NOEC=0.12 mg/L. It is generally accepted that QSARs for long-term tests should be for orientation only. In OECD 210, the typical duration of a FELS test with Oncorrhynchus mykiss is 60 days. For pimephales promelas the recommended test period is 28 days which is in good consistency with the test from Barron and Adelman (31 days). Also the outcome of this test (31d-NOEC=1.35 mg/L is in agreement with the QSAR prediction of 0.12 - 1.8 mg/L.

Categories Display