2,6-dichlorobenzoxazole

Endpoint summary

Additional information

In the key study (Klimisch 1), 2,6-Dichlorobenzoxazol was tested for mutagenicity in two standard plate incorporation tests and in one preincubation test (each in the absence and in the presence of a metabolizing system) under GLP and according to OECD TG 471 (adopted 1997). In the main plate incorporation test, the substance was tested in bacteria strains TA 100, TA 1535, TA 1537 and TA 98 of S. thyphimurium and with E. Coli WP2uvrA at concentrations of50, 160, 500, 1600 and 5000μg/plate.Because of toxicity in the main plate incorporation test dose levels of 1.6, 5, 16, 50, 160 and 500 μg/plate(S. typhimurium tester strains) and dose levels of 5, 16, 50, 160, 500 and 1600μg/plate

(E. Coli WP2 uvrA) were chosen for the second plate incorporation test and the main preincubation test. For the repeat preincubation test dose levels from 1.6 to 500μg/plate were chosen in the absence of metabolic activation with the tester strain WP2 uvrA.Control plates without mutagen showed that the number of spontaneous revertant colonies was within the laboratory’s historical control range. All the positive controls showed the expected increase in the number of revertant colonies. There was no evidence of induced mutant colonies over background. In conclusion it can be stated that 2,6-Dichlorobenzoxazol is not mutagenic in this bacterial mutation test at any dose level either in the absence or presence of an exogenous metabolic activation system.

In an supporting standard Ames test (Klimisch 2) performed according to the former OECD TG 471 (adopted 1983) and under GLP 2,6-dichlorobenzoxazol was tested for mutagenicity in S. typhimurium strains TA 1535, TA 1537, TA 1538, TA 98 and TA 100 at six dose levels, in triplicate, both with and without metabolic activation. All positive control chemicals produced marked increases in the number of revertant colonies, both with and without metabolic activation and the activity of the S9 fraction was found to be satisfactory. The solvent (dimethylformamide) control plates gave counts of revertant colonies within the normal range. 2,6-Dichlorobenzoxazol caused a reduction in the growth of the bacterial lawn with all of the strains of salmonella tested both with and without metabolic activation. The most sensitive strains to the toxicity of 2,6-Dichlorobenzoxazol were TA 1535 and TA 1537 beginning at 500 µg/plate. 2,6-Dichlorobenzoxazol was, therefore, tested up to its toxic limit. A statistically significant increase in the number of revertant colonies wasrecorded in two of the three assays with and without S9. However, in one experiment with S9 the induction was below factor two, demonstrating that the statistical significance was not biologically signifcant. In all other cases, where the number of revertants was statistically signifcantly increased, the increase was below factor 3. Due to the lack of information about historical control data, a final conclusion about the biological relevance of the statistically significant increase cannot be drawn. Additionally, the TA 1538 strain is not listed as a tester strain in the current OECD TG. Therefore this observed effect can be regarded as ambigous.

In summary, 2,6 -Dichlorobenzoxazol was not mutagenic in all tester strains specified in the current OECD test guideline 471 with and without metabolic activation in both studies.

Short description of key information:
2,6 -Dichlorobenzoxazol was not mutagenic in tester strains specified in the current OECD test guideline 471 with and without metabolic activation in two Ames tests.

Endpoint Conclusion: No adverse effect observed (negative)