3,5-xylenol

Endpoint summary

Additional information

Bacterial reverse mutation assay:

Currently, existing Ames data in the form of a GLP conducted study [1] on mixed xylenols is available. Under this study, 3,5 -xylenol was present at ~10.7% (active) in the mixture tested up to 5 mg/plate (maximum recommended dose). Consequently, the maximum active concentration of 3,5-xylenol tested was 0.536 mg/plate.

This issue is discussed below, with discussion of supporting published data on other xylenols which can support a read across approach so that a further Ames study is not required.

 

Discussion of available Ames data on 3,5-xylenol and other xylenols

As discussed above, a GLP study conducted by Wagner and Atta-Safuh [1] has been undertaken on mixed xylenols. This mixture contained various xylenols, with the 3,5 isomer being present at 10.7%, resulting in a maximum concentration of 0.536 mg/plate tested. In the absence of toxicity, higher concentrations could have been tolerated in the test system.

Dean et al [2] assessed a variety of industrial chemicals in the Ames assay. Reported in the paper, 3,5-xylenol (3,5 dimethylphenol) was tested in a full complement ofs.typhrium (TA1535; TA1537; TA1538; TA98; TA100), e.coli (WP2; WP2uvrA) and s.cerevisiae (JD1). Concentrations up 2 mg/plate were tested in the absence and presence of S9. 3,5-xylenol was concluded as negative, however no toxicity data were reported.

Florin et al [3] assessed a variety of tobacco smoke constituents using the Ames (spot test) assay. In this paper not only was 3,5-xylenol, but also other isomers including 2,3; 2,4; 2,5; 2,6 and 3,4 were also assessed. All xylenols were tested in the absence and presence of S9, with a full complement of s.typhrium strains (TA98, TA100, TA1535 and TA1537). All the aforementioned xylenols tested were concluded as devoid of any mutagenic activity via the Ames assay. All were tested up to 30 umol/plate (3.7 mg/plate) with toxicity reported for the majority of xylenols in isolated strains. For 3,5-xylenol toxicity was observed with TA98.

Pool and Lin [4] assessed a variety of phenolic compounds and phenolic fractions obtained from smokehouse smoke condensates. 2,4-xylenol was examined up to 5 mg/plate using a full complement ofs.typhriumstrains (TA1535, TA1537, TA1538, TA98, TA100). At this dose toxicity was observed in all strains, with no increase in the revertant rate.

Finally, a study undertaken by Microbiological Associates [4] examined 2,6-xylenol (T1570) using the same strain set as stated above. In this study the 2,6 isomer was tested up to a maximum concentration of 5 mg/plate. Again, no increase in the revertant rate was observed with this isomer.

 

References:

1. Wagner, V.O. and Atta-Safoh, S. (2004). Mixed xylenols: Bacterial reverse mutation assay. Bioreliance Study Number AA89JJ.502.BTL.

2. Dean, B.J., Brooks, T.M., Hodson-Walker, G. And Hutson, D.H. (1985). Genetic toxicology testing of 41 industrial chemicals.Mutation Research,153, 57-77.

3. Florin, I., Rutberg, L., Curvall, M. and Enzell, C.R. (1980). Screening of tobacco smoke constituents for mutagenicity using the Ames test.Toxicology,18, 219-232.

4. Pool, B.L. and Lin, P.Z. (1982). Mutagenicity testing in thesalmonella typhimuriumassay of phenolic compounds and phenolic fractions obtained from smokehouse and smoke condensates.Food Chemical Toxicology,20, 383-391.

5. Curren, R.D. (1980). Activity of T1570 in thesalmonella/microsomal assay for bacterial mutagenicity. Microbiological Associates (MA) notebook number: 1570-102.

Mouse bone marrow micronucleus

The mouse micronucleus study (study no: 26M0613/96445) 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). 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.

Genetic Toxicology Summary

Under REACH for the registration of transported isolated intermediate above 1000 tons/annum the minimum requirements for the genetic toxicology endpoint are bacterial gene mutation assay. Mixed xylenols (with 3,5-xylenol present at ~10%), 2,3; 2,4; 2,5; 2,6; 3,4 and 3,5-xylenol (tested up to toxic concentrations in isolated strains) and 2,4 and 2,6-xylenol (tested up to 5 mg/plate) have been evaluated in numerous separate Ames assay using a full complement of s.typhrium (and in isolated cases with E.coli) strains, both the absence and presence of S9 mix. These data are strongly suggestive that the isomers are indistinguishable in the Ames assay and there is strong evidence that read across in particular from all the isomers discussed be used to provide support for 3,5-xylenol, confirming that up to a maximum recommended concentration (5 mg/plate, in accordance with current regulatory guidelines) there is no evidence of gene mutation in this assay type.

Furthermore, an in vivo mouse bone marrow micronucleus study is also available which confirms that 3,5 xylenol is negative when tested up to a maximum tolerated dose. These data therefore confirm under ther requirements of this registration that genetic endpoint has been addressed and 3,5 xylenol is devoid of genetic potential.

Short description of key information:
Bacterial reverse gene mutation - Wagner 2004 (key study)
Bacterial reverse gene mutation - Dean 1985 - (supporting study)
Bacterial reverse gene mutation - Florin 1980 - (supporting study)
Bacterial reverse gene mutation - Pool 1982 - (supporting study)
Bacterial reverse gene mutation - Curren 1980 - (supporting study)
Mouse micornucleus - Engelhardt 1998

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Genetic toxicology endpoint negative for the requirements needed for a transport isolated intermediate (>1000 tons/yr).