Trisilicon tetranitride

Endpoint summary

Additional information

Gene Mutations

A key study in Silicon Nitride for gene mutations in mammalian cells was performed according to OECD guideline 476 and in accordance with GLP (Huntingdon Life Sciences, 2012). The test system is based on detection and quantitation of forward mutation at the functionally hemizygous hypoxanthine phosphoribosly transferase (HPRT) locus in Chinese hamster ovary (CHO-K12) cells. Four independent tests, two in the absence of metabolic activaton (S9 mix) and two in the presence of S9 mix are reported. The vehicle for the test substance was sodium chloride (0.9% w/v), in which it formed a dosable suspension at 14 mg/mL. Cytotoxicity was measured as Day1 relative survival. In the absence of S9 mix cells exposed to Silicon Nitride showed Day1 relative survival values of 101 to 21% for test 1 and 94 to 17% for test 2 relative to the vehicle control. Silicon Nitride did not significantly increase the mutant frequency in either test. In the presence of S9 mix the figures were 102 to 43% for test 1 and 103 to 44% for test 2 relative to the control. Silicon Nitride did not significantly increase the mutant frequency in either test. In conclusion, Silicon Nitride did not demonstrate mutagenic potential in the in vitro HPRT cell mutation assay.

Ames Test (Bacterial Reverse Mutation test)

A bacterial reverse mutation (Ames) test was conducted according to OECD guideline 471 and EC method B. 13/14 (ARC Seibersdorf research GmbH, 2005). The test was performed according to the "Direct Plate Incorporation Method". As test system the bacterial strains Salmonella typhimurium TA97a, TA98, TA100, TA102 and TA1535 were used. The test substance was suspended in water and concentrations of 62, 185, 556, 1667 and 5000 ug per plate were tested with and without S-9 mix as an external metabolising system. No toxicity of the test substance to bacteria was observed up to 5000 ug per plate. Silicon Nitride was therefore judged to be non-mutagenic under the conditions of the test.

Another bacterial reverse mutation (Ames) test was conducted (Mitsubishi Chemical Safety Institute Ltd). The test was performed according to the pre-incubation method. As test system the bacterial strains Salmonella Typhimurium TA100, TA1535, TA98, TA1537 and Escherichia coli WP2 uvrA/pKM101 were used. The test substance was suspended in DMSO and concentrations of

313, 625, 1250 and 5000 ug/plate were tested with and without S9 -mix as an external metabolising system. No toxicity of the test substance to bacteria was observed at any tested concentration, therefore Silicon Nitride was judged to be non-mutagenic under the conditions of the test.

Chromosome Aberrations

A chromosomal aberration test of Silicon Nitride was conducted using Chinese hamster cells (CHL/IU) in order to evaluate its cytogenetic effects on cultured cells (Mitsubishi Chemical Safety Institute Ltd). Concentrations for use in the main study were selected based on the results of a cell growth inhibition study. Tests were carried out in the presence and absence of S9 mix. In the test by 24 -hr continuous treatment, the highest concentration was set at 200 ug/mL followed by 5 lower concentrations with a common ratio of 2. The test was repeated at 50, 100, 200, 300, 400 and 500 ug/mL since 50% or greater cell growth inhibition was not observed. The incidence of structural aberrations and polyploid cells was less than 5% after 24 -hr continuous treatment. It was concluded that Silicon Nitride does not induce chromosomal aberrations under the conditions of the test.

Justification for selection of genetic toxicity endpoint

The mammalian cell gene mutation test was conducted to international guidelines and in accordance with GLP.

Short description of key information:

Silicon Nitride did not demonstrate mutagenic potential in an in vitro HPRT cell mutation assay. Silicon Nitride also did not demonstrate mutagenic properties in a bacterial reverse mutation test (Ames test). Silicon Nitride also did not induce chromosomal aberrations in a chromosomal aberrration study.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Silicon Nitride was not a mutagen in one in vitro test with mammalian cells. Two negative results were obtained with bacteria (Ames test). There was also a negative result with a chromosomal aberration test. Therefore Silicon Nitride should not be classfied for mutagenicity.