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EC number: 225-097-9 | CAS number: 4657-00-5
The test item Basic Orange 22 was examined for the ability to induce gene mutations in tester strains of Salmonella typhimurium and Escherichia coli, as measured by reversion of auxotrophic strains to prototrophy. The five tester strains TA1535, TA1537, TA98, TA100 and WP2 uvrA were used. Experiments were performed both in the absence and presence of metabolic activation, using liver S9 fraction from rats pre-treated with phenobarbital and 5,6-benzoflavone.The test item was used as a solution in dimethylsulfoxide (DMSO).
The test item Basic Orange 22 was assayed in the toxicity test at a maximum concentration of 5000 µg/plate and at four lower concentrations spaced at approximately half-log intervals: 1580, 500, 158 and 50.0 µg/plate.
Dose related toxicity, from severe to mild, was observed at all or almost all dose levels with all tester strains both in the absence and presence of S9 metabolic activation. A more pronounced toxic effect was observed with TA100 and TA1537 tester strains, showing severe toxicity at all concentrations tested. Based on these results, it was necessary to perform an additional toxicity test where the dose levels of 50.0, 15.8, 5.00, 1.58 and 0.500 µg/plate were assayed. Dose related toxicity was observed at the three highest dose levels both in the absence and presence of S9 metabolism. No remarkable increase in revertant colonies was noted with any tester strain/activation condition combinations. No precipitation of the test item was observed at the end of the incubation period at any dose level, in the absence or presence of S9 metabolism.
On the basis of toxicity test results, in Main Assay I, using the plate incorporation method,the test item was assayed at the following dose levels:
Tester strain S9 Dose level (µg/plate)
TA1535 and WP2 uvrA ± S9: 200, 100, 50.0, 25.0, 12.5 and 6.25 (µg/plate)
TA98 ± S9: 400, 200, 100, 50.0, 25.0 and 12.5 (µg/plate)
TA1537 ± S9: 16.0, 8.00, 4.00, 2.00, 1.00 and 0.500 (µg/plate)
TA100 - S9: 16.0, 8.00, 4.00, 2.00, 1.00 and 0.500 (µg/plate)
TA100 + S9: 32.0, 16.0, 8.00, 4.00, 2.00, 1.00 and 0.500 (µg/plate)
Toxicity, as indicated by microcolony formation, thinning of the background lawn and/or reduction in revertant colonies was observed at higher concentrations with all tester strains both in the absence and presence of S9 metabolic activation.
As no relevant increase in revertant numbers was observed at any concentration tested,Main Assay II was performed including a pre-incubation step for all treatments.
The concentration-range was slightly modified to take into account the toxicity observed in Main Assay I and the following dose levels were used:
TA1535 ± S9: 80.0, 40.0, 20.0, 10.0, 5.00 and 2.50 µg/plate
TA1537 − S9: 10.0, 5.00, 2.50, 1.25 and 0.625 µg/plate
TA100 + S9: 10.0, 5.00, 2.50, 1.25 and 0.625 µg/plate
TA1537 + S9: 20.0, 10.0, 5.00, 2.50, 1.25 and 0.625 µg/plate
TA100 - S9: 10.0, 5.00, 2.50, 1.25, 0.625 and 0.313 µg/plate
WP2 uvrA ± S9: 160, 80.0, 40.0, 20.0, 10.0 and 5.00 µg/plate
TA98 ± S9: 320, 160, 80.0, 40.0, 20.0 and 10.0 µg/plate
Toxicity was observed at highest dose levels with all tester strains; a more pronounced toxic effect was generally observed in the absence of S9 metabolic activation.
No precipitation of the test item was observed in any experiment, at any dose level in the absence or presence of S9 metabolic activation.
The test item did not induce two-fold increases in the number of revertant colonies in the plate incorporation or pre-incubation assay, at any dose level, in any tester strain, in the absence or presence of S9 metabolism.
It is concluded that the test item Basic Orange 22 does not induce reverse mutation in Salmonella typhimurium or Escherichia coli in the absence or presence of S9 metabolism, under the reported experimental conditions.
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