2-(2H-benzotriazol-2-yl)-p-cresol

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

2-(2H-benzotriazol-2-yl) -p-cresol is considered to be not genotoxic in-vitro based on studies on mutagenicity in bacteria and mammalian cells.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

2-(2H-benzotriazol-2-yl) -p-cresol is not carcinogenic as determined by feeding studies in rats and mice.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

2-(2H-benzotriazol-2-yl) -p-cresol is considered to be not mutagenic in bacteria. The key study for mutagenicity in bacteria (Arni 1979) was chosen based on the amount of experimental detail available. It was performed following the design of OECD Guideline 471 (1997) with deviations: S. typhimurium TA 102 or E. coli WP2 uvrA strains are missing and non standard positive control compounds were used for strains in the absence of metabolic activation. Positive control incubations were not performed for all strains in the presence of metabolic activation. The key study pre-dates GLP requirements. Tested concentrations were up to 0.81 mg per plate, which is in the non-toxic precipitating range. The substance was also found to be non mutagenic in Salmonella typhimurium TA1535, TA1537, TA1538, TA98, TA100 (Hacmiya 1982 and Hachitani 1981) and in Salmonella typhimurium TA1538, TA98, TA100 (Jonsen 1980) but test concentrations were only as high as 0.1 mg/plate. No mutagenicity was observed in strain TA 98 at 1.8 mg/plate (Shiozawa 1999). No structural alert for mutagenicity was identified using the QSAR tool DEREK (Ciba 2009).

The test substance was assessed for its potential to induce gene mutations at the hypoxanthine-guanine phosphoribosyl transferase (HPRT) locus in Chinese hamster ovary (CHO) cells in vitro. The GLP-study was performed following OECD No. 476 (2016). Two independent experiments were carried out, both with and without the addition of liver S9 mix from phenobarbital- and ß-naphthoflavone induced rats (exogenous metabolic activation).

Following attachment of the cells for 20 - 24 hours, cells were treated with the test substance for 4 hours in the absence and presence of metabolic activation. Subsequently, cells were cultured for 6 - 8 days and then selected in 6-thioguanine-containing medium for another week. Finally, the colonies of each test group were fixed with methanol, stained with Giemsa and counted.

The vehicle controls gave mutant frequencies within the range expected for the CHO cell line. Both positive control substances, ethyl methanesulfonate (EMS) and 7,12-dimethylbenz[a]-anthracene (DMBA), led to the expected statistically significant increase in the frequencies of forward mutations.

In both experiments in the absence and the presence of metabolic activation no cytotoxicity was observed up to the highest concentrations evaluated for gene mutations.

Based on the results of the present study, the test substance did not cause any biologically relevant increase in the mutant frequencies either without S9 mix or after the addition of a metabolizing system in two experiments performed independently of each other. Thus, under the experimental conditions of this study, the test substance is not mutagenic in the HPRT locus assay under the in vitro conditions in CHO cells in the absence and the presence of metabolic activation.

Regarding genotoxicity in vivo, there are three studies that are of sufficient quality to serve as key study. The chromosome aberration study in Chinese hamster (Strasser 1981) was chosen as key study, as it contains sufficient detail to suggest GLP-like characteristics and follows the procedure of OECD testing guideline 475. Four animals (two females and two males) from each group treated (two doses of 500, 1000 or 2000 mg/kg bw by gavage) and from the negative and from the positive control group each were analysed by reference to the following criteria: Chromatide-type aberrations, chromosome-type aberrations, chromatide gaps and chromosome pulverization. There was no indication of a clastogenic effect. The nucleus anomaly test in Chinese hamster (Langauer 1977) is almost identical in design to the micronucleus test in vivo (OECD 474), specifically, more parameters than micronuclei in erythroblasts recorded and only 1000 bone marrow cells evaluated without giving the actual number of erythroblasts. Each three males and females received two gavage doses of 500, 1000 or 2000 mg/kg bw with a 24h interval. Animals were sacrificed 24h after the second treatment. The following was scored: Single Jolly bodies, fragments of nuclei in erythrocytes, micronuclei in erythroblasts, micronuclei in leucopoietic cells, bizarre forms of nuclei, polyploid cells and necrobiotic cells. An oral dose of cyclophosphamide at 128 mg/kg bw was used as a positive control. Absence of genotoxicity in the micronucleus test performed with doses of 630, 1250, 2500 mg/kg bw was also published in the literature (Hacmiya 1982, Hachitani 1981). No indication of genotoxicity was observed in the dominant lethal study in mice with single doses of 1000 or 3000 mg/kg bw (Fritz 1975a). The study design is sufficiently similar to OECD Guideline 478 (1984) for this study to be adequate. No positive control was used, but published data from that period shows results of positive control substances from studies performed at that laboratory and by the same study directors. The study pre-dates GLP requirements.

Justification for classification or non-classification

The available experimental test data are reliable and suitable for classification purposes under Regulation 1272/2008, Annex I. As a result the substance is not considered to be classified as a mutagen under Regulation (EC) No. 1272/2008.