Butyl chloroformate

Endpoint summary

Additional information

In an Ames test performed in accordance with OECD guideline 471 and GLP the test substance was tested for its mutagenicity. The tester strains Salmonella typhimurium TA 1535, TA 1537, TA 98 and TA 100 were used to examine the mutagenic potential of the test substance up to concentrations of 5000 µg/plate in a preincubation test (BASF 1988). Dimethylcarbamyl chloride (DIMCA), which is structurally related to the test substance and described as Ames positive, was tested in parallel as a positive reference compound to demonstrate the sensitivity of the test procedure chosen. A clear bacteriotoxic effect was observed at doses of about  ≥ 0.005 µL/ plate (without S-9 mix) and from about 0.2 µL - 0.3 µL/plate onward (with S-9 mix). An increase in the number of his+ revertants using the test substance was not observed either without S-9 mix or after the addition of a metabolizing system. With the positive reference compound DIMCA the expected positive reaction was demonstrated both with and without metabolic activation.

In addition a chromosome aberration test is available (OECD 473, GLP) where the test article was assessed for its potential to induce structural chromosome aberrations in V79 cells of the Chinese hamster in vitro in the absence and presence of metabolic activation by S9 mix (BASF 1990). Preparation of chromosomes was done 7 h (300 µg/mL) , 18 h (10, 200 420 µg/mL ) and 28 h (300 ,420 µg/mL) after start of the treatment with the test article. The treatment interval was 4 h. In each experimental group two parallel cultures were used. Per culture 100 metaphases were scored for structural chromosomal aberrations. The test groups treated with the following concentrations were evaluated: Experiment 1: without S9 mix: 7 h: 300 µg/mL; 18 h: 10, 200, 420, µg/mL; 28 h: 300 µg/mL; with S9 mix: 7 h: 300 µg/mL; 18 h: 10, 200, 420 µg/mL; 28 h: 420 µg/mL. Experiment 2: with S9 mix: 28 h: 350, 420 µg/mL. Treatment with 420 µg/mL clearly reduced the plating efficiency of the V79 cells. Also, the mitotic index was reduced after treatment with the highest concentration at each fixation interval in the presence and absence of S9 mix with the exception at interval 18 h (without S9 mix). Higher concentrations of the test article than 420 µg/mL could not be dissolved in the culture medium. In experiment 1, there was a slight, but statistically significant increase in cells with structural aberrations after treatment with the test article at fixation interval 28 h with metabolic activation by S9 mix. However, in the independent experiment 2 this result could not be confirmed. Additional investigations on the cytotoxic potential of the test article in the high concentration range (350, 380, 420 µg/mL) were performed with monolayer mass cultures. They revealed heavy toxic effects (with 420 µg/mL reductions to 27 % survival without S9 mix and 15 % survival with S9 mix) 28 h after treatment with the test article. These findings indicate that there might be an induction of chromosome aberrations by the toxic effects of the test article concentration of 420 µg/mL and not by genotoxic properties per se. The contradictory results of experiment 1 and experiment 2 (with S9 mix) can be explained by the possibility that within the survival range of 26 - 15 % different cell populations (experiment 1 and 2) express toxicity-induced chromosome reactions differently, in the one case leading to a positive result in the other case to a negative result. Possibly, the high toxicity of the test article with this concentration is responsible for the different results obtained in the independent experiments. Appropriate reference mutagens were used as positive controls and showed distinct increases in cells with structural chromosome aberrations. Taking into account the high toxicity at 420 µg/mL and non-reproducibility of the clastogenic effect in experiment 2, it can be concluded that the increased frequency of aberrations in experiment 1 is assumed to be the result of highly toxic influences on the chromosome structure and not of a genotoxic potential of the test article per se.

Short description of key information:
According to the available data, the test substance is not mutagenic in the Ames test (OECD 471, GLP) and does not induce chromosome aberrations in Chinese hamster V79 cells (OECD 473, GLP).

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on the results obtained in the Ames test and chromosome aberration study, classification for genetic toxicity is not warranted in accordance with EU Classification, Labeling and Packaging of Substances and Mixtures (CLP) Regulation No. 1272/2008.