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In an in vitro gene mutation study, bacterial and mammalian cells were exposed to sodium arsenite in a series of tests:

Bacterial cell gene mutation assays:

- Spot test (WP2, WP6, WP10 and WP44s-NF): 0.01 and 0.1 M

- Treat and plate protocol (WP2 and WP6): 25 mM

- Fluctuation tests (WP2): Experiment 1 (0.4 mM) and Experiment 2 (1 and 2 mM)

- Induction of λ prophage: WP2s (λ): Experiment 1 (10 mM, 20 minutes) and Experiment 2 (1 and 10 mM, 30 minutes)

Chinese hamster lung fibroblasts (V79):

- Ouabain resistant marker: 0.5 µM, 2 days and 5.0 µM, 1 hour

- Thioguanine resistant marker: 20 and 100 µM, 1.5 hours

 

In the E. coli system, Trp+ revertants were not induced by arsenite in spot tests, treat and plate protocols, or fluctuation tests. The mutator effect of a tif-1 strain was partially blocked by arsenite. Arsenite did not cause the induction of lambda prophage. In Chinese hamster cells, arsenite did not induce ouabain-resistant mutants or thioguanine-resistant mutants.

 

Under the test conditions, sodium arsenite is not considered as mutagenic to E. coli or to Chinese hamster cells. 

In an in vitro mammalian cell gene mutation test performed similarly to OECD guideline 476, L5178Y/ TK+/- mouse lymphoma cells were exposed to sodium arsenate at concentrations of 26, 34, 46, 61 and 81 μg/mL in the absence of metabolic activation and the exposure duration was 3 hours.

 

Positive controls (methyl methane sulphonate) induced the appropriate response. No significant increases in mutant frequency were observed following treatment of sodium arsenate in the absence of metabolic activation.

 

Under the test conditions, sodium arsenate is not considered as mutagenic in mouse lymphoma L5178Y cells.

In an in vitro chromosomal aberration assay conducted similarly to OECD Guideline 473, whole blood cultures were incubated for 72 hours and treated with various concentrations (1-10-10 µM) of sodium arsenite for the last 24 hours. Also, mitotic arrest was evaluated in cultures treated for the last 2 hours. Cells were harvested and samples were processed for evaluation of aneuploidogenic and mitotic arrest. Number of chromosomes in 200 metaphases of first and second division cells was scored.

 

Positive controls (colcemid at 10-2 µM) induced the appropriate response. A dose-related effect was observed: highest concentration (10-2 µM sodium arsenite) induces 28.33 and 22.4% hyperploid cells in first and second division respectively and 29% tetraploid cells. Sodium arsenite produced 40.24 and 12.93% of the mitotic arrestant effect at 10-2 µM and 10-10 µM, respectively). A different individual susceptibility effect was observed in both parameters and confirmed with the chromosome aberrations levels induced by arsenic in the same donors.

 

Under the test conditions, sodium arsenite was found to have an aneuploidogenic and a mitotic arrestant effect in cultured human lymphocytes. The authors of the report did not include a comment in their summary of the report, but a positive effect was also observed in terms of an increase in chromosome aberrations.

An in vitro gene mutation assay was conducted with sodium arsenite in the supF gene of pZ189 shuttle vector system in DNA repair proficient GM0637 human fibroblasts to determine whether arsenic alone induces mutation and whether the combination of arsenic and UV irradiation leads to a yield of mutants greater than the sum of the arsenic or UV treatments alone. Sodium arsenite was tested at the concentrations of 1, 2.5 and 5.0 µM in GM 637 human fibroblasts for 72 hours and plasmid was irradiated with 320 J/m2. Poisson distribution followed by student’s t-test was used to assess the effects of sodium arsenite on mutant frequencies.

 

Sodium arsenite alone produced significant increases in the pZ189 mutant frequency at the concentration of 5.0 µM, whereas 1 and 2.5 µM arsenite were not mutagenic. UV irradiation (320 J/m2) increased the yield of mutants 3.5-fold above the background rate. When UV-irradiated plasmid was allowed to replicate in fibroblasts treated with sodium arsenite, the yields of mutations were significantly greater (p < 0.01) than the yield expected and the greatest potentiation of UV-induced mutations (4.9-fold) was observed at 1 µM arsenite. Restriction digest and DNA sequencing analyses indicated that arsenite alone produces large-scale rearrangements, frameshifts and base substitutions. Hotspots for deletions were observed to be associated with a previously reported deletion hotspot involving 5'-CpC and runs of cytosines. Base substitutions observed involved A:T→T:A transversions.

 

Under the test conditions, arsenite alone was found to be mutagenic in human fibroblast cells and potentiated the UV-induced mutations in plasmid DNA.


Short description of key information:
Four reports are included that cover mutagenicity in bacterial cells, mutagenicity in mammalian cells and chromosome aberrations in mammalian cells. The results for bacterial mutagenicity are negative whilst both negative and positive results were reported for mammalian cell mutagenicity. Positive responses were reported for chromosome aberrations in mammalian cells in vitro. In terms of a weight of evidence approach the data are contradictory. Arsenic was negative in bacterial cells and negative in two studies in mammalian cells for mutagenicity, both of which used protocols similar to the OECD 476 guideline. However, in a research-based assay method, positive results were obtained for mutagenicity. In a study using human lymphocyte cells some evidence of clastogenicity and aneuploidy were observed. Therefore, on balance it is concluded that arsenic may be positive for genotoxicity in vitro. No reliable evidence for or against genotoxicity in vivo is available.

Endpoint Conclusion: Adverse effect observed (positive)

Justification for classification or non-classification

Not to be classified because no positive results have been reported in the in vivo study.