Registration Dossier

Administrative data

Key value for chemical safety assessment

Additional information

Gene mutation (bacterial)

Currently, existing Ames data in the form of a GLP conducted study on mixed xylenols is available. Under this study, mixed xylenols were tested up to 5 mg/plate (maximum recommended dose) and returned a negative result in the absence and presence of metabolic activation (S9). Supporting studies on mixed cresols and also on the individual cresol isomers all confirm in the absence and presence of S9 that these test materials do not increase background gene mutation rates above that of the solvent control. Based on stuctural similiarites it is reasonable to assume that ethylphenols would return the same result.

 

Mammalian gene mutation (in vitro)

A recently conducted gene mutation study on CHL V79 cells targeting the hprt locus returned negative results in the absence and presence of S9 mix, when tested up to cytotoxic concentrations in two independent experiments. In the second experiment a non-dose related increase in mean mutant frequency was observed, however these increases were accompanied by cytotoxicity and were non-reproducible when compared to the first independent experiment.

Several MLA studies targeting thetklocus have been performed on all three cresol isomers and have returned negative results. It is important to note however that no cytotoxicity data were discussed / presented or evidence of precipitate; therefore the limiting factor for the maximum dose level tested was not justified. However, based on structrual similarities with xylenols, cresols along with ethylphenols would be expected to return results comparable to the GLP study performed.

 

Mammalian chromosome aberration (in vitro)

Two GLP mammalian CHO chromosomal aberration studies condcted on mixed xylenols and mixed phenols confirmed increases in chromosomal aberrations in both the absence and presence of S9. In both cases acceptable levels of toxicity were obtained. Similar results were also obtained with with m,o and p cresols, however or note not concurrent measure of cytotoxicity was performed (only conducted in a range-finder experiment). However, based on structrual similarities with xylenols and ethylphenols, cresols would be expected to return results which were comparable when accompanied by concurrent cytotoxicity measures.

 

In vivo bone marrow micronucleus

The mouse bone marrow micronucleus study on 3,5 xylenol conducted confirmed no evidence of micronuclei induction in the bone marrow polychromatic erthyrocytes of mice when tested up to a dose of 1500 mg/kg (maximum tolerated dose - MTD). Despite deaths occuring (1 male and 1 female at the 48 hr sample point), as there were no gender differences, it is deemed acceptable to combine the data (resulting in sufficient numbers of animals/group), thereby confirming both an acceptable assay and a negative result. Further support to justifiy a read-across approach comes from additional mouse bone marrow micronucleus studies on the 2,4 and 2,6 xylenol isomers which also returned negative results when tested up to an MTD.

Other in vivo data providing additional support comes from 2 dominant lethal studies (o and p-cresol) and a mouse bone marrow chromosome aberration study (m-cresol). In the case of the chromosome aberration study, whilst it is pointed out the no bone marrow toxicity was observed at the maximum dose tested (as evidence by no decrease in mitotic index), this clinical signs of toxicity reported would be considered evident of an MTD being achieved.

 

Genetic Toxicology Summary

Under REACH for the registration of above 1000 tons/annum the minimum requirements for the genetic toxicology endpoint are bacterial gene mutation assay, in vitro mammalian gene mutation and chromsome aberration assays and in vivo assay. The available data, irrespective of the endpoint examined, test material used or assay used all return comparable results, which strongly suggestive that these test materials are indistinguishable, and where data is absent from a particular chemical there is strong evidence that read across approach can be taken.

Whilst positive results were obtained in the in vitro mammalian chromosome assay, the negative in vivo data confirms that in the in vitro result is not realised, imply thus that the in vitro positive result was not biologically relevant (possible resulting from a cell culture / in vitro artefact). The overall conclusion from these data confirm under the requirements of this registration the genetic endpoint has been adequately addressed and these chemicals are devoid of genetic potential under the testing protocol used.


Short description of key information:
Gene mutation (bacterial):
Key study: mixed xylenol (Ames). Wagner & Atta-Safoh, 2004. KL.1. Negative-/+S9;
Supporting study: mixed cresols (Ames). Pool & Lin, 1982. KL.2. Negative -/+S9;
Supporting study: m-cresols. MHLW, 2001. KL.1. Negative -/+S9;
Supporting study: o-cresols (Ames). Pepper et al., 1981. KL.1. Negative -/+S9;
Supporting study: o-cresols (Ames). Hawoth et al., 1983. KL.2. Negative -/+S9;
Supporting study: p-cresols (Ames). Hawoth et al., 1983. KL.2. Negative -/+S9;

Mammalian chromosome aberation (in vitro):
Key study: xyelnol (CHO). Gudi, 2004. KL.1. Positive -/+S9;
Supporting study: ethylphenol (CHO). Gudi, 2004. KL.1. Positive -/+S9;
Supporting study: m-cresol (CHO). CMA, 1988. KL.3. Negative -S9; Positive +S9;
Supporing study: o-cresol (CHO). CMA., 1988. KL.3. Positive -/+S9;
Supporting study: p-cresol (CHO). CMA, 1988. KL.3. Positive -/+S9;

Mammalian gene mutation (in vitro):
Key study: xylenol (CHL V79, hprt). Bednarijova, 2010. KL.1. Negative +/-S9;
Supporitng study: m-cresol (MLA, tk). CMA, 1988. KL.3. Negative +/-S9;
Supporting study: o-cresol (MLA, tk). Pepper et al., 1986. KL.2. Negative +/-S9;
Supporting study: p-cresol (MLA, tk). CMA, 1988. KL.2. Negative +/-S9;

Chromsome abberation (in vivo):
Key study: 3,5 xylenol (MMT). Engelhardt, 1998. KL.1. Negative;
Supporting study: 2,4 xylenol (MMT). Engelhardt, 1998. KL.1. Negative;
Supporting study: 2,6 xylenol (MMT). Engelhardt, 1998. KL.1. Negative;
Supporting study: m-cresol (rat chrom abs). CMA, 1988. KL.3. Negative;
Supporting study: o-cresol (DLT). CMA, 1989. KL.1. Negative;
Supporting study: p-cresol (DLT). CMA, 1989. KL.1. Negative;

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification