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Toxicity to terrestrial plants

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Description of key information

There is no study on chronic toxicity towards terrestrial plants available using p-cresol as test substance and a read-across from m-cresol is applied.
The toxicity of m-cresol to lettuce seedlings (Lactuca sativa) was determined according to OECD Guideline 208 in soil. The EC50 was 69 mg/kg soil d.w. after 7 d, 96 mg/kg soil d.w. after 14 d and 50 mg/L solution after 21 d of incubation .
However, in case of only one test result is available, the risk assessment should be performed both on this test result and on the basis of the outcome of the aquatic toxicity data. Therefore the equilibrium partitioning method with the PNEC for aquatic organisms is also taken into account for assessment.

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Additional information

There is no study on chronic toxicity towards terrestrial plants available using p-cresol as test substance.

In order to get a comprehensive data set for p-cresol a read-across from m-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.

Several studies of toxicity of m-cresol towards terrestrial plants were found in the literature. The scope of the terrestrial effects assessment under the adopted REACH regulation is restricted to soil organisms in a narrow sense and does not actually include adverse effects on soil functions that are only indirectly linked to the biota in soils. Some tests were designed assessing the influence of m-cresol on germination and growth on moist filter paper or agar treated with the substance. As no soil was used in the tests standardisation of soil effect data to given soil parameters is not possible. Further, converting the results to an appropriate dimension is not applicable. Therefore the results should not be used for the hazard assessment. Using soil, short-term toxicity of m-cresol to lettuce (Lactuca sativa) was examined. The test compound was incorporated into soil according to OECD-guideline 208. The organic matter of 2 soil types used was given as 1.4 to 1.8 %. Lettuce seed was sown and the weight of the crops (above-ground biomass) was measured after 7 and 14 days. After an exposure period of 14 days, a nominal EC50 of 96 mg/kg soil (dry weight) was obtained. According to TGD (EU 2003), the effect concentration (EC50 96 mg/kg) is corrected for a standard soil with a content of organic matter of 3.4 % resulting in a corrected EC50 of 233 mg/kg. The authors stated that “at the end of the test, the concentrations of most phenols in soil had dropped to a low value ( < 20% of the initial analysed concentrations) ".