Cyclohexane, 5-isocyanato-1-(isocyanatomethyl)-1,3,3-trimethyl-, homopolymer, 3,5-dimethyl-1H-pyrazole-blocked

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

A bacterial reverse mutation test (Ames test) was conducted according to OECD TG 471 to investigate the potential of the test substance to induce gene mutations. The assay was performed in two independent experiments, the initial plate incorporation and the subsequent preincubation test, both with and without S9 mix and the following tester strains: Salmonella typhimurium TA 1535, TA 100, TA 1537, TA 98, and TA 102. The doses employed were up to 5000 µg/plate in the plate incubation trial and up to 3200 µg/tube in the preincubation assessment.

Doses up to and including 800 µg per plate did not cause any bacteriotoxic effects. Total bacteria counts remained unchanged and no inhibition of growth was observed. Higher doses had a strain-specific bacteriotoxic effect. Substance precipitation occurred at 500 µg/plate and above. Therefore, the test was no longer interpretable at 3200 µg/plate or tube and above.

Evidence of mutagenic activity of the test substance was not seen. No biologically relevant increase in mutant counts in comparison with the solvent controls was observed. The positive controls increased mutant counts to well over those of the solvent controls, and thus demonstrated the system's sensitivity and the activity of the S9 mix.

 

A study according to OECD TG 476 was further conducted in order to investigate the potential of the substance to induce gene mutations at the HPRT locus in mammalian cells. For that purpose, V79 cells were exposed to the test item for 4 hours with and without metabolic activation in the first experiment and for 4 hours with and for 24 hours without metabolic activation in the second experiment. The maximum concentration of the pre-experiment (2666.7 μg/mL) was based on the solubility properties of the test item in the vehicle (DMSO). The concentration range of the main experiments was limited by precipitation of the test item in aqueous medium.

No substantial and reproducible dose dependent increase of the mutation frequency was observed in both main experiments. Appropriate reference mutagens, used as positive controls, induced a distinct increase in mutant colonies and thus, showed the sensitivity of the test system and the activity of the metabolic activation system.

In conclusion, it can be stated that under the experimental conditions reported the test item did not induce gene mutations at the HPRT locus in mammalian cells.

 

The substance was also examined for mutagenic activity (chromsome breakage and misdistribution of chromosomes) in the in vitro micronucleus test using Chinese Hamster V79 cells in accordance to OECD Guideline 487. Two independent assays were performed in this study, the first assay conducted with a treatment time of 4 hours, without and with a metabolizing system (S9 mix), the second assay with a treatment time of 24 hours (continuous treatment) without S9 mix and with a treatment time of 4 hours with S9 mix. The highest concentration applied in this study (4000 µg/mL) was chosen with regard to the solubility of the test item and with respect to the current OECD guideline 487.

In Experiment I in the absence of S9 mix no cytotoxicity was observed at the highest concentrations. In Experiment II in the absence of S9 mix moderate cytotoxicity was observed at the highest concentration. In the presence of S9 mix no cytotoxicity was observed up to the highest evaluated concentrations.

In both independent experiments no biologically relevant increase in the number of micronucleated cells was observed after treatment with the test item. However, in Experiment II in the presence of S9 mix one single statistically significant increase in micronucleated cells (0.75 %) was observed after treatment with 41.0 µg/mL. Since this value is clearly within the range of the laboratory historical solvent control data (0.05 – 1.70 % micronucleated cells), the finding is regarded as biologically irrelevant.

Therefore, the test item is considered to be non-mutagenic in the in vitro micronucleus test, when tested up to precipitating concentrations.

 

Overall, no genotoxic potential is concluded for the substance by taking into account the three available in vitro genotoxicity assays.

Justification for classification or non-classification

According to Regulation (EC) No 1272/2008, Annex I, no classification is warranted for genetic toxicity.