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Additional information

Three studies have been conducted to evaluate the potential for genetic toxicity. Two in vitro assays, Bacterial Reverse Mutation Assay and a Chromosome Aberration sudy, have been performed. An in vivo Mouse Micronucleus Assay has also been conducted.

 

In the Bacterial Reverse Mutation Assay, the test substancewas tested in theSalmonella typhimuriumreverse mutation assay with four histidine-requiring strains of Salmonella typhimurium (TA1535, TA1537, TA100 and TA98) and in the Escherichia coli reverse mutation assay with a tryptophan-requiring strain of Escherichia coli WP2uvrA in two independent experiments. The test substance was tested up to concentrations of 5000 µg/plate in the absence and presence of S9-mix.

 

The test substance did not induce a dose-related, two-fold increase in the number of revertant (His+) colonies in each of the four tester strains (TA1535, TA1537, TA98 and TA100) and in the number of revertant (Trp+) colonies in tester strain WP2uvrA both in the absence and presence of S9-metabolic activation. These results were confirmed in an independently repeated experiment.

 

Based on the results of this study it is concluded that the test substance is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.

 

In the Chromosome Aberration study, the test substance was tested with and without activation in Chinese Hamster Ovary cells. In the initial assay, concentrations of 33.9. 48.4, 69.1, 98.7, 141, 202, 288, 412, 588, 840, 1200, 1720, 2450, 3500, and 5000 micrograms/mL were tested with and without activation. Cultures treated with 840, 1200 2450 and 5000 micrograms/mL were analyzed for chromosomal aberrations. No significant increases in cells with chromosomal aberrations were observed at any of these concentrations.

 

In the confirmatory assay, cultures were treated for 6 hours with activation and 17.5 and 41.6 hours without activation. Concentrations of 78.5, 157, 313, 625, 875, 1250, 1500, 2000, 2500, 3750 and 50000 micorgrams/mL were tested without activation. Concentrations of 625, 1250, 2500, 3750 and 5000 micrograms/mL were tested with metabolic activation. 

 

An increase in cells with chromosomal aberrations was seen at the highest concentration in the assay with metabolic activation. A statistically significant increase was not observed at the same concentration in the initial assay and the response was only at the high dose in the confirmatory assay. Since the test article is known to readily hydrolyze, the conditions of the assay may have influenced the study results and the biological relevance of the single high dose result is uncertain.

 

The test substance was considered negative for inducing chromosomal aberrations in Chinese Hamster Ovary cells with and without activation, except at a single high dose with metabolic activation where an equivocal response was observed.

 

In the in vivo Mouse Micronucleus Study, bone marrow from treated animals was harvested at 24 and 48 hours. The treatment group animals were dosed at 2000 mg/kg in 10ml/kg dose. Bone marrow from positive and negative control groups were also harvested at 24 and 48 hours. 

 

No increase in the mean frequency of micronucleated polychromatic erythrocytes was observed in the polychromatic erythrocytes of the treated animals. The positive and negative controls responded within historical limits. Treated animals showed no decrease in the ratio of polychromatic to normochromatic erythroxytes compated to vehicle controls. 

 

The test substance was not clastogenic in the micronucleus test under the conditions of this test.


Endpoint Conclusion:

Justification for classification or non-classification