Isobutyl vinyl ether

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

In in vitro studies no mutagenic activity was found in bacteria or mammalian cells as well as no clastogenic or aneugenic activity in mammalian cells.

Additional information

Gene mutation in bacteria:

A study was performed to investigate the potential of Isobutylvinylether to induce gene mutations according to the plate incorporation test and the pre-incubation test using the Salmonella typhimurium strains TA 1535, TA 1537, TA 98, TA 100, and the Escherichia coli strain WP2 uvrA (BASF SE, 2018). The assay was performed in two independent experiments both with and without liver microsomal activation. Each concentration, including the controls, was tested in triplicate. The test item was tested at the following concentrations: Pre-Experiment/Experiment I: 3; 10; 33; 100; 333; 1000; 2500; and 5000 μg/plate and experiment II: 33; 100; 333; 1000; 2500; and 5000 μg/plate. No precipitation of the test item occurred up to the highest investigated dose. In experiment I the plates incubated with the test item showed normal background growth up to 5000 μg/plate with and without S9 mix in all strains used. In experiment II reduced background growth was observed in all strains with and without S9 mix, except of strain WP2 uvrA. Toxic effects, evident as a reduction in the number of revertants (below the indication factor of 0.5), were observed in experiment I in strain TA 100 with S9 mix from 2500 to 5000 μg/plate and in experiment II in strain TA 100 from 1000 to 5000 μg/plate without S9 mix and at 1000 and 5000 μg/plate with S9 mix. No substantial increase in revertant colony numbers of any of the five tester strains was observed following treatment with Isobutylvinylether at any dose level, neither in the presence nor absence of metabolic activation (S9 mix). There was also no tendency of higher mutation rates with increasing concentrations in the range below the generally acknowledged border of biological relevance. Appropriate reference mutagens, used as positive controls, induced a distinct increase in revertant colonies and thus, showed the sensitivity of the test system and the activity of the metabolic activation system. In conclusion, the test item did not induce gene mutations by base pair changes or frameshifts in the genome of the strains used. Therefore, Isobutylvinylether is considered to be non-mutagenic in this Salmonella typhimurium and Escherichia coli reverse mutation assay.

In a supporting study comparable to OECD TG471 with acceptable restrictions (non-GLP; only 4 strains tested; E. coli WP2 or S. typhimurium TA102 strain missing, however, no oxidizing or cross linking activity expected) S. typhimurium TA98, TA100, TA1535, or TA1537 were exposed to 0, 20, 100, 500, 2500, 5000 µg/plate with and without S9 -mix in 1) the standard plate test and 2) in the preincubation test (triplicate plates; vehicle control, pos. control). No increase in the number of revertants was found at dose levels including the recommended limit dose of 5 mg/plate. A bacteriotoxic effect was seen only in the preincubation test with S9-mix from 500 or 2500 µg/plate onward (all tester strains) and without S9-mix at a dose of 5000 µg/plate (only in TA1535). Positive control substances caused increases in the number of revertants as expected, indicating proper test conditions. Data on historical controls were not available, however, vehicle controls were within the range of literature values.

Conclusion: No mutagenicity was seen in S. typhimurium TA98, TA100, TA1535, TA1537 in the presence and absence of metabolic activation at dose levels up to the recommended limit dose (5 mg/plate).

Gene mutation in mammalian cells:

Isobutylvinylether was assessed for its potential to induce gene mutations at the hypoxanthine-guaninephosphoribosyltransferase (HPRT) locus in Chinese hamster ovary (CHO) cells in vitro (BASF SE, 2018). In this study, in the absence and the presence of metabolic activation no relevant cytotoxicity (relative survival below 20%) was observed up to the highest evaluated concentration (800 µg/mL; lowest precipitating concentration) evaluated for gene mutations. The vehicle controls gave mutant frequencies within the range expected for the CHO cell line. Both positive control substances led to the expected statistically significant increase in the frequencies of forward mutations. The test substance did not cause any biologically relevant increase in the mutant frequencies either without S9 mix or after the addition of a metabolizing system. Thus, Isobutylvinylether is not mutagenic in the HPRT locus assay under in vitro conditions in CHO cells in the absence and the presence of metabolic activation.

In a further HPRT assay (BASF 1993, GLP Guideline study according to OECD TG476), Chinese hamster Ovary (CHO) cells were exposed with and without metabolic activation (MA) to 0, 0.01; 0.05; 0.10; 0.50; 1; 5; 10 mg/mL in 2 independent experiments. Negative control, vehicle (DMSO) control and positive control were valid. Cytotoxic effects (reduced cloning efficiencies) were seen at >= 5 mg/mL with and without MA. No mutagenicity was reported in the 1st experiment. In the 2nd trial, statistically significant increases in mutant frequencies were detcted without MA at 0.50 mg/mL and with MA at 0.01, 0.05 and 5 .0 mg/mL; the increases were not considered to be biologically significant because none of the other criteria for a positive response were met and because the statistical significances were mainly due to the unusually low, but within the historical range lying mutation rates of the respective controls.

Chromosome aberration:

In a mammalian cell chromosome aberration assay (according to OECD TG473) V79 cells were treated with 0, 1250, 2500, 5000 µg/mL in the presence and absence of a metabolic activation system (MA). The exposure period was 4 h with MA and 18 without MA. Samples were harvested at 18 h (low, intermediate and top dose) and 28 h (top dose only) after the beginning of a 4 -hour treatment (with MA) or of a 18 -hour treatment (without MA). Concurrent negative controls, vehicle controls and positive controls were valid. No cytotoxic effects were seen even at the high dose level (recommended limit dose). The test substance did not lead to an increase of structural chromosomal aberrations incl. and excl. gaps either with or without MA. The significant increase in aberration at a sampling time of 28 h is of no biological relevance; the observed values are within the range of the historical control data for this sampling time. An increase in the number of cells containing numerical chromosomal aberrations was not demonstrated.

Conclusion: The test substance showed neither chromosome damaging (clastogenic) effects nor an aneugenic activity in V79 cells in vitro.

Short description of key information:
In in vitro studies no mutagenic activity was found in bacteria or mammalian cells as well as no clastogenic or aneugenic activity in mammalian cells.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Classification is not warranted according to the criteria of EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.