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In the key bacterial reverse mutation assay (equivalent to OECD guideline 471), MEK was tested in a non-GLP study at doses of 0, 0.1, 0.5, 2, 16, or 32 µL/plate in the absence of exogenous metabolic activation (Aroclor 1254-induced rat liver S9)and 0, 0.05, 0.1, 0.5, 2, or 16 µL/plate in the presence of exogenous metabolic activation in Salmonella typhimurium strains TA 98, TA 100, TA 1535, TA 1537, and TA 1538 (Haworth, 1984).  The plates were incubated in triplicate; however, an independent repeat experiment was not performed. Dimethyl sulfoxide (DMSO) was used as the vehicle and positive controls were included in all incubations. Cytotoxicity (defined as a moderately to extremely reduced background lawn) was observed in the presence of metabolic activation at a dose of at 32 µL/plate; however, noincrease in the reverse mutation rate was noted at any MEK concentration either in the absence or presence of metabolic activation. Incubation with positive control substances in the absence or presence of metabolic activation resulted in anticipated increases in reverse mutation rates.

In a supportive non-GLP bacterial reverse mutation assay (equivalent to OECD guideline 471), MEK was tested at doses of 0, 31.25, 62.5, 125, 250, 500, 1,000, 2,000, or 4,000 µg/plate both in the absence and presence of exogenous metabolic activation (Aroclor 1254-induced rat liver S9) in S. typhimurium strains TA 98, TA 100, TA 1535, TA 1537, and TA 1538 and Escherichia coli strains WP2 and WP2 uvr A (Priston, 1982).  The plates were incubated in triplicate and an independent repeat experiment was performed. DMSO was used as the vehicle and positive controls were included in all incubations. Cytotoxicity was not observed and no increase in the reverse mutation rate was noted at any MEK concentration either in the absence or presence of metabolic activation. Incubation with positive control substances in the absence or presence of metabolic activation did not always result in anticipated increases in reverse mutation rates; hence this study is considered reliable with restrictions.

In a non-GLP mammalian chromosome aberration test (equivalent to OECD guideline 473), MEK was tested at doses of 0, 250, 500, or 1,000 µg/mL in the absence of exogenous metabolic activation in rat liver (RL4) cells (Priston, 1982).  Incubations at each concentration were done in triplicate; however, an independent repeat experiment was not performed.  Distilled water was used as the vehicle and 7,12-dimethylbenzanthracene was used as the positive control compound. No cytotoxicity was observed and no chromosome damage was noted at any MEK concentration.  Incubations with the positive control compound resulted in anticipated increases in chromatid damage.

In the key mammalian gene mutation assay (equivalent to OECD guideline 476), MEK was tested in a non-GLP study at doses of 0, 0.89, 1.2, 1.6, 2.1, 2.8, 3.8, 5.0, 6.7, 8.9, 12.0, 16, or 21 µL/mL in the absence of exogenous metabolic activation (Aroclor-induced rat liver S9) and at doses of 0, 0.67, 0.89, 1.2, 1.6, 2.1, 2.8, 3.8, 5.0, 6.7, 8.9, 12, or 16 µL/mL in the presence of exogenous metabolic activation in mouse lymphoma L5178Y cells (Rogers-Back, 1984)The experiment was conducted in triplicate; however, an independent repeat experiment was not performed. DMSO was used as the vehicle and ethyl methanesulfonate and 7,12-dimethylbenz[a]anthracene were used as the positive control compounds in the absence and presence of metabolic activation, respectively. No cytotoxicity and no increase in the mutant frequency were observed at any MEK concentration in the absence or presence of metabolic activation. Incubation with positive control substances in the absence or presence of metabolic activation resulted in anticipated increases inthe mutation frequencies.

In a supportive non-GLP mammalian gene mutation assay (equivalent to OECD guideline 476), MEK was tested at doses of 0, 9, 13, or 18 µL/mL in the absence of exogenous metabolic activation (Aroclor-induced rat liver S9) and at doses of 0, 6, 8, or 10 µL/mL in the presence of exogenous metabolic activation in BALB/3T3 Clone A31-1 mouse embryo cells (Putman, 1984)The experiment was conducted in triplicate; however, an independent repeat experiment was not performed. Phosphate buffered saline (PBS) was used as the vehicle and N-methyl-N’-nitro-N-nitrosoguanidine and benzo[a]pyrene were used as the positive control compounds in the absence and presence of metabolic activation, respectively. No cytotoxicity and no increase in the mutant frequency were observed at any MEK concentration in the absence or presence of metabolic activation. Incubation with positive control substances in the absence or presence of metabolic activation resulted in anticipated increases in the mutation frequencies.

In a non-GLP unscheduled DNA synthesis assay (equivalent to OECD guideline 482), MEK was tested at doses of 0, 0.1, 0.5, 1.0, 2.5, or 5.0 µL/mL in primary rat hepatocytes (Curren, 1984).  Incubations at each concentration were done in triplicate; however, an independent repeat experiment was not performed. DMSO and ethanol were used as the vehicles and 2-acetylaminofluorene was used as the positive control compound.  Cytotoxicity was noted at a dose of 5.0 µL/mL; however, no increases in the average nuclear grain count were observed at any MEK concentration.  Incubation with the positive control substance resulted in an anticipated increase in the average nuclear grain count.

In a non-GLP yeast gene mutation assay (equivalent to OECD guideline 480), MEK was tested at doses of 0, 0.01, 0.1, 0.5, 1.0, or 5.0 mg/mL in Saccharomyces cerevisiae both in the presence and absence of exogenous metabolic activation (Aroclor 1254-induced rat liver S9) (Priston, 1982).  Incubations at each concentration were done in quadruplicate and the experiment was performed in at least duplicate. DMSO was used as the vehicle and 4-nitroquinoline-N-oxide and cyclophosphamide were used as the positive control compounds in the absence and presence of metabolic activation, respectively. No cytotoxicity was observed and no increase in the rate of mitotic gene conversion was noted at any MEK concentration in the absence or presence of metabolic activation.  Incubation with the positive control substances resulted in anticipated increases in the rate of mitotic gene conversion.  As the post-treatment incubation period was 3 days as opposed to the recommended 4 to 7 days, this study is considered reliable with restrictions.

In a non-GLP micronucleus assay (equivalent to OECD guideline 474), MEK was administered via intraperitoneal (IP) injection to male and female CD-1 mice at a dose of 1.96 mL/kg body weight (Putman, 1984).  Corn oil was used as the vehicle and triethylenemelamine was administered via the IP route as the positive control compound. Mice were sacrificed at 12, 24, or 48 hours following injection of test article or control (5 mice/sex/time point). Test article-treated mice appeared heavily sedated immediately following dose administration; however, no animals died and no other clinical signs of toxicity were observed. No statistically significant increases in the number of micronucleated polychromatic erythrocytes were noted at any time point. The positive control compound produced anticipated increases in the number of micronucleated polychromatic erythrocytes. The use of only 1 dose level instead of the recommended 3 rendered this study reliable with restrictions.


Short description of key information:
The genetic toxicity of methyl ethyl ketone (MEK) has been assessed in 7 in vitro studies (including 2 bacterial reverse mutation assays, a mammalian chromosome aberration test, and a yeast gene mutation assay) and an in vivo micronucleus assay. Negative results were reported in all the studies.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

The substance does not meet the criteria for classification and labelling for this endpoint, as set out in Regulation (EC) No. 1272/2008.