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EC number: 235-231-8 | CAS number: 12136-78-6
Three OECD guideline studies were performed to assess the genotoxicity potential of Molybdenum disilicide. The substance resulted not genotoxic in the bacterial reverse gene mutation assay (Ames test), non-mutagenic in an in vitro mammalian cell gene mutation test and not inducing structural chromosomal aberrations in an in vitro mammalian chromosome aberration test.
In conclusion, Molybdenum disilicide is not expected to exert genetic toxicity.
Pre-experiment for toxicity and Main experiments I and II:
Result tables are attched in box "Attached background material"
In a reverse gene mutation assay in bacteria (OECD 471) strains of S. typhimurium (TA98, TA100, TA1535, TA1537, TA102) were exposed to Molybdenum disilicide (≥ 98.57 % purity) in Aqua dest. at concentrations of 31.6, 100, 316, 1000, 2000 and 5000 µg/plate (experiment 1: plate incorporation, experiment 2: pre-incubation) in the presence and absence of mammalian metabolic activation. Molybdenum disilicide was tested up to the limit dose (5.0 mg/plate). The positive controls induced the appropriate responses in the corresponding strains. There was no evidence of induced mutant colonies over background.
This study is classified as acceptable. This study satisfies the requirement for Test Guideline OECD 471 for in vitro mutagenicity (bacterial reverse gene mutation) data.
Experiments I and II:
In the OECD 473 in vitro chromosomal aberration test and under the experimental conditions reported, the test item Molybdenum disilicide did not induce structural chromosomal aberrations in human lymphocyte cells.
In the main experiment precipitation was observed at concentrations 5 mM (withoutmetabolic activations) and 0.50 mM (withmetabolic activation).
No biologically relevant growth inhibition (reduction of relative survival below 70%) was observed after the treatment with the test item in experimentwithoutmetabolic activation (Table3).
In the experimentwithmetabolic activation a biologically relevant growth inhibition (reduction of relative survival below 70%) was observed after the treatment with the test item. The relative survival was 57% for the highest concentration (5 mM) evaluated (Table 3). Additionally, at concentration 0.75 mM the relative survival was 46%, but since the next lower and next higher concentration showed a relative survival above 70%, this effect was considered as an outlier and therefore not relevant.
In the main experimentwithoutandwithmetabolic activation all validity criteria were met. The mutant values of the negative and solvent controls fall within the historical data range of the test facility and the cloning efficiencies of the negative and solvent controls are > 50%.
The positive controls, DMBA (1.0 µg/mL) and EMS (300 µg/mL) showed statistically significant increases in mutant frequency, thereby demonstrating both the sensitivity and validity of the test systems.
Experiment without metabolic activation
In the experimentwithoutmetabolic activationthemutant values of the negative, solvent controls and all mutant values of the test item concentrations found were within the historical control data of the test facilityEurofins Munich(about 8.5 - 40.2 mutants per 106cells).The positive control EMS induced a distinct increase in mutant frequency with 174.6 mutants/106cells (Table4).
The mutant frequencies induced by the test item did not show a biologically relevant increase (Table4). None of the observed mutant frequencies was statistically significantly increased over those of the solvent controls (Table7).
The highest mutant frequency was observed at a concentration of 0.10 mM (39.5 mutants per 106cells) with a relative survival of 71%.
Experiment with metabolic activation
In the experimentwithmetabolic activationthe mutant values of the negative, solvent controls and all mutant values of the test item concentrations found were within the historical control data of the test facilityEurofins Munich(about 9.6 - 44.0 mutants per 106cells).The positive control DMBA induced a distinct increase in mutant frequency with 439.7 mutants/106cells (Table6).
The mutant frequencies induced by the test item did not show a biologically relevant increase (Table6). None of the observed mutant frequencies was statistically significantly increased over those of the negative controls (Table8).
The highest mutant frequency was observed at a concentration of 0.05 mM (39.5 mutants per 106cells) with a relative survival of 102%.
Based on the available data, Molybdenum disilicide does not warrant classification for mutagenicity.
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