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Diss Factsheets

Administrative data

Description of key information

In a 90-day inhalation study in Fischer 344 rats, animals were exposed to methyl ethyl ketone (MEK) concentrations at 0 (control), 1254 ppm, 2518 ppm, or 5041 ppm for 6 hours/day, 5 days/week for 89 or 90 consecutive days.  This GLP study was equivalent to OECD Test Guideline 413. Although a NOEC was not determined by study authors, based on the data a NOAEC of 5014 ppm can be considered for subchronic inhalation toxicity given that the effects noted in both sexes at 5014 ppm were limited to non specific effects including decreased body weight and increased absolute liver weights and liver to body weight ratios. Supportive studies for MEK were not located.  Dermal and oral studies have not been conducted. 

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records
Reference
Endpoint:
sub-chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1981
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Well documented, according to accepted guidelines.
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)
Deviations:
no
GLP compliance:
yes
Remarks:
However, GLP statement was not signed
Limit test:
no
Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., Portage, MI
- Age at study initiation: 6 weeks old
- Weight at study initiation: 117-119 g (males) and 93-94 g (females)
- Housing: Individual housing in 8 cubic meter stainless steel and glass chambers
- Diet (e.g. ad libitum): Purina Certified Rodent Chow ad libitum, except during exposure
- Water (e.g. ad libitum): Filtered tap water ad libitum, except during exposure
- Acclimation period: 14-day quarantine period


ENVIRONMENTAL CONDITIONS
- Temperature (°F): approximately 70 ºF
- Humidity (%): approximately 50%
- Photoperiod (hrs dark / hrs light): 12 hours:12 hours
Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
other: unchanged (no vehicle)
Details on inhalation exposure:
The test article was vaporized in a 3-neck, round bottom flask. The test article was metered to the vaporization flask using a FMI Lab Pump. The vapors were swept from the flask by a continuous supply of conditioned, compressed air and entered the chamber through a turret located at the top of the chamber. In the turret, the vapors were mixed with chamber supply air. The metered flow of test article into the vaporization flask and total air through the chamber were adjusted to maintain the target concentration within the chamber. The test article delivery rate and total airflow through the chamber were used in calculating the nominal concentration within the chamber.

Airflow was monitored continuously throughout the exposure by reading the pressure differential from a minihelic pressure gauge and recording the corresponding airflow from a prepared calibration graph showing airflow versus differential pressure. The graph was prepared by plotting various airflow readings from an Autotronic Controls Turbine Flow Meter at different differential pressure readings and drawing a-curve. The negative pressure of each test chamber was maintained at 0.1 inches of water. The control chamber was maintained at a positive pressure of 0.02 inches of water. Negative and positive pressures were measured with minihelic pressure gauges.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
A gas chromatographic chamber monitoring system was employed throughout the study to analyze chamber air samples obtained by both manual and automatic sampling methods. Precision sampling gas syringes were used to obtain the manual samples of the test atmosphere by piercing a self-sealing rubber septum inserted in the two sampling ports on the chamber doors. Samples obtained were injected into the gas chromatograph to determine chamber concentration. Automated chamber monitoring was achieved using a Valco Instruments custom designed, pneumatically operated sampling system. The system operated using a continuous flow through a 16-port multiple stream complex in conjunction with a 10-port gas sampling valve. The 10-port valve was plumbed into the gas chromatograph via the carrier inlet and analytical column. A calibrated sample loop was used to control the injection volume. A digital valve controller determined the frequency of injections and started the analog to digital converter which transferred the gas chromatographic results to the data system. The data system read the position of the sampling valve for sample identification and computed the concentration based on peak areas. Results of all injections were stored in data files and the time-weighted average (TWA) computed for each exposure day. The chamber air monitoring instruments were located in a space physically separated from the inhalation laboratory.

Each test chamber was sampled approximately once/hour. Control chamber and room atmospheres were sampled from one to five times/day. All samples were monitored for hexane and methyl ethyl ketone. A Miran IA infrared analyzer was used as a continuous monitor in all test chamber on a selected basis for distribution studies. A stainless steel bellows pump pulled chamber air through the gas cell and exhausted it back into the chamber. A chart recorder was used to obtain a continuous readout of absorbance. The concentration was determined using a calibration graph.
Duration of treatment / exposure:
89 or 90 consecutive days.
Frequency of treatment:
6 hours/day, 5 days/week (use of non-standard dosing regime was used to simulate the conditions encountered in the workplace).
Remarks:
Doses / Concentrations:
1254 ppm
Basis:
analytical conc.
Remarks:
Doses / Concentrations:
2518 ppm
Basis:
analytical conc.
Remarks:
Doses / Concentrations:
5041 ppm
Basis:
analytical conc.
No. of animals per sex per dose:
15 rats/sex/dose
Control animals:
yes, concurrent no treatment
Positive control:
None used.
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice-daily.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Twice-daily.

BODY WEIGHT: Yes
- Time schedule for examinations: Weekly.

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

OPHTHALMOSCOPIC EXAMINATION: Yes

HAEMATOLOGY: Yes

CLINICAL CHEMISTRY: Yes

URINALYSIS: Yes
- Time schedule for collection of urine: prior to necropsy
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes

OTHER: Five males and five females (Dedicated animals) from each exposure group and the control group were used exclusively for the following special study. The thoracic aorta was cannulated via the left ventricle. Vascular perfusion with lactated Ringer’s solution was immediately followed with 2% glutaraldehyde. Following perfusion, the brain, spinal cord, and right and left sciatic and tibial nerves were removed and placed in glutaraldehyde overnight. The next day they were washed in phosphate buffer. Sections of medulla and the tibial nerve were osmicated and dehydrated. The medulla and sciatic nerve were embedded in Epon, sectioned at 1 micrometer and stained with toluidine blue. The tibial nerve was osmicated, placed in an Epon mixture and then teased on a glass slide to isolate individual nerve fibers. A minimum of fifty nerve fibers/animal were evaluated by light microscopy for evidence of neuropathy. Other tissues were stored in 10% neutral buffered formalin. Specimens from all groups were examined.
Sacrifice and pathology:
GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes
Statistics:
Parametric data such as body weight or food consumption were analyzed using an analysis of variance (ANOVA). Statistically significant differences that were noted were further studied by either Tukey’s (equal populations) or Scheffe’s (unequal populations) Test of Multiple Comparison. Non-Parametric data such as organ weight ratios were analyzed using a Kruskal-Wallis ANOVA and a Test of Multiple Comparison.
Clinical signs:
effects observed, treatment-related
Mortality:
mortality observed, treatment-related
Body weight and weight changes:
effects observed, treatment-related
Food consumption and compound intake (if feeding study):
no effects observed
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
no effects observed
Haematological findings:
effects observed, treatment-related
Clinical biochemistry findings:
effects observed, treatment-related
Urinalysis findings:
no effects observed
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Gross pathological findings:
effects observed, treatment-related
Histopathological findings: non-neoplastic:
not examined
Histopathological findings: neoplastic:
effects observed, treatment-related
Details on results:
CLINICAL SIGNS AND MORTALITY: None of the animals died; however, clinical signs observed included irritation, swelling, or crustiness associated with the animal’s ear tag. Crusty eye was observed in both control (6) and test (4) animals. Crusty muzzle was observed in one test animal as was crusty nose in another. None of the observations noted were considered to be related to test article administration.

BODY WEIGHT AND WEIGHT GAIN: Significant difference between control and test group mean body weight gains was observed in male and female rats of the high-dose group. The high-dose male and female body weights were transiently depressed early in the study, starting at week one, while the low-dose male and mid-dose male and female body weights were elevated as the study progressed.

OPHTHALMOSCOPIC EXAMINATION: None of the abnormalities observed were considered significant since they were distributed in both control and test animals and because these abnormalities are common in Fischer 344 rats of this age.

HAEMATOLOGY: The mean corpuscular hemoglobin in high-dose male and female rats was significantly higher than that of controls. In high-dose female rats, the mean corpuscular hemoglobin concentration was also elevated. This increase in hemoglobin corresponds to a slight but not significant decrease in the number red blood cells. No additional significant differences between test and control animals were observed.

CLINICAL CHEMISTRY: No significant differences between test and control animals were observed in male rats. Glutamic pyruvic transaminase was elevated in mid-dose females. Alkaline phosphatase and glucose were significantly increased in high-dose female rats. The trend, although not statistically significant, was also seen in male rats. The increase in alkaline phosphatase is probably associated with the significant increase in liver weight. The elevation is considered mild. It should be noted that the sodium and potassium values are high for all groups. This was possibly due to a delay (10 days) in running these chemistries because of instrumentation down-time. It is most probable that evaporation occurred in all samples resulting in the high values in all samples. Potassium levels in high-dose females were statistically higher than control values.

URINALYSIS: No statistical differences between test and control animals were observed except for the volume of the urine in male rats which was elevated; however, all values were within the normal range for rats, and the differences were not considered to be related to test article administration.

ORGAN WEIGHTS: In high-dose male rats, the liver weight, liver/body weight ratio, and liver/brain weight ratio were significantly elevated. The kidney/body weight ratio was significantly elevated in the same animals. In female rats a significant dose response was observed in increased liver weight. In high-dose female rats, significantly depressed spleen and brain weights were also observed. The liver/body weight ratio was significantly elevated and the brain/body weight ratio was significantly depressed in high-dose female rats. Also in high-dose female rats, the liver/brain and kidney/brain weight ratios were significantly elevated.

GROSS PATHOLOGY: Most lesions were minor in nature and limited in their frequency of occurrence. None were interpreted as related to the administration of the test article. Only one tissue mass (neoplasm) was observed, and it occurred in a control male. The mesenteric tissue masses seen in 3 animals proved to be accessory spleens. A reddish discoloration of the mandibular lymph nodes was observed in 22 rats and was noted at least in one rat from all four groups. Likewise, 10 to 20 percent of the animals in all four groups exhibited insignificant exudation around the site of the ear tags. A relatively high percentage (20 to 40 percent) of the females (other than in high-dose animals) had cysts of the ovaries. These cysts were one centimeter or less in diameter, thin-walled, and contained clear to reddish fluid. Other lesions were minor and occurred randomly in all groups.

HISTOPATHOLOGY: NEOPLASTIC (if applicable): Histopathologic lesions attributable to the test article administration were not present in any of the rats. A wide variety of histopathologic lesions were observed; however, they were considered to be spontaneous in origin, occurring randomly in a small percentage of the animals from all four groups.
Dose descriptor:
NOAEC
Effect level:
5 041 ppm
Sex:
male/female
Basis for effect level:
other: see 'Remark'
Critical effects observed:
not specified

No changes in neurological function was observed.

Executive summary:

Although a NOEC was not determined by study authors, based on the data a NOAEC of 5014 ppm can be considered for subchronic inhalation toxicity given that the effects noted in both sexes at 5014 ppm were limited to non specific effects including decreased body weight and increased absolute liver weights and liver to body weight ratios.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEC
14 870 mg/m³
Study duration:
subchronic
Experimental exposure time per week (hours/week):
30
Species:
rat

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

In a whole body 90-day inhalation study in Fischer 344 rats, animals were exposed to methyl ethyl ketone (MEK) at concentrations of 0 (control), 1254 ppm, 2518 ppm, or 5041 ppm, equivalent to 0, 3700, 7430 or 14870 mg/m³ for 6 hours/day, 5 days/week for 89 or 90 consecutive days (Cavender, 1981). This GLP study was equivalent to OECD Test Guideline 413. No mortalities were observed during the study. Clinical signs noted (including irritation, swelling, ear tag crustiness, and/or crusty eye in control and treated animals) were not related to the administration of the test article. High-dose (5041 ppm) male and female body weights were transiently depressed starting at week one, while the low-dose male and mid-dose male and female body weights were elevated as the study progressed. There were no test article related changes in ophthalmoscopy and urinalysis. The mean corpuscular haemoglobin (in high-dose males and females) and mean corpuscular haemoglobin concentration (in high-dose females only) were increased compared to controls. The increase in haemoglobin corresponded to a slight (but not significant) decreased in the number of red blood cells. The serum glutamic-pyruvic transaminase (SGPT) activity in the 2500-ppm female rats was elevated while the 5000-ppm female rats exhibited significantly decreased SGPT activity. Potassium levels in high-dose (5041 ppm) females were statistically higher than control values. In high-dose (5041 ppm) male rats, liver weights, liver/body weight ratio, liver/brain weight ratio and kidney/body weight ratios were significantly elevated. In female rats, a significant dose response was observed in increased liver weight. In high-dose (5041 ppm) female rats, the liver/body weight ratio, liver/brain ratio, and kidney/brain weight ratios were significantly elevated while the brain/body weight ratio was significantly depressed. Liver pathology showed no lesions. Significantly depressed spleen and brain weights were also observed. Only minor macroscopic lesions were observed and none were attributed to test article administration. Any neoplastic lesions observed were not related to test article administration. No changes in neurological function were observed. 

Although a NOEC was not determined by study authors, based on the data a NOAEC of 5014 ppm, equivalent to 14870 mg/m³ can be considered for subchronic inhalation toxicity given that the effects noted in both sexes at 5014 ppm were limited to non specific effects including decreased body weight and increased absolute liver weights and liver to body weight ratios.

Based on the same data, the OECD SIAR (OECD, 1997) concluded that the NOAEL is 5000 ppm.

The observed liver enlargement is considered to be an adaptive response and not indicative of systemic toxicity. Kidney lesions in rats have been determined to not be relevant to humans (Swenberg & Lehman-McKeeman, 1999; USEPA, 1991). Research has been conducted on the mechanisms of MIBK carcinogenicity which has provided a more concrete evidence that MIBK-induced kidney and liver tumors occur in rodents by mechanisms that are not relevant to humans (Borghoff et al., 2015; Hughes et al., 2016). Data on the repeated dose toxicity of methyl isobutyl ketone (MIBK) are included in support of the read across of reproductive toxicity.

The chronic toxicity of MIBK has been examined in a study in which male and female F344 rats and B6C3F1 mice were exposed to 0, 450, 900 or 1800 ppm of MIBK by inhalation, 6 hours/day, and 5 days/week for 2 years (Stout et al, 2008). The key target organs were kidneys in the rats and liver in mice. Incidence of chronic progressive nephropathy (CPN) was observed in both male and female rats, with effects in males associated with an increase in renal tumours at the 1800 ppm dose. Treatment related increase in the incidence of hepatocellular tumours were reported in mice at the highest dose group.

Information on the repeated dose toxicity of isopropyl alcohol is provided in support of read across from secondary butanol in other parts of the dossier. The effects of isopropyl alcohol on the rat has been evaluated in a 90-day and a two-year inhalation study. Repeated dose effects observed in both studies were limited to occasional body weight changes, liver weight increases (without pathological changes) and male rat-specific kidney effects. In the 90-day study, transient narcotic effects were observed; they did not persist after exposure and there were no changes in the functional observational battery. The effects observed in studies on isopropyl alcohol are very similar to those observed in studies with MEK.

References

Borghoff SJ, Poet TS, Green S, Davis J, Hughes B, Mensing T, Sarang SS, Lynch AM, Hard GC. 2015. Methyl isobutyl ketone exposure-related increases in specific measures of alpha-2u-globulin (alpha2u) nephropathy in male rats along with in vitro evidence of reversible protein binding. Toxicology 333:1–13.

Hughes BJ, Thomas J, Lynch AM, Borghoff SJ, Green S, Mensing T, Sarang SS, LeBaron MJ. 2016. Methyl isobutyl ketone-induced hepatocellular carcinogenesis in B6C3F1 mice: A constitutive androstane receptor (CAR)-mediated mode of action. Regul Appl Toxicol, (81), 421-429.

OECD, 1997. SIDS Initial Assessment Report For SIAM 6: Methyl ethyl ketone CAS 78-93-3. Paris, France, 9-11 June 1997

Swenberg JA, Lehman-McKeeman LD (1999) alpha 2-Urinary globulin-associated nephropathy as a mechanism of renal tubule cell carcinogenesis in male rats. IARC scientific publications: 95-118.

USEPA (2003b) Toxicological Review of Methyl Isobutyl Ketone (CAS No. 108-10-1): In Support of Summary Information on the Integrated Risk Information System (IRIS). https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0173tr.pdf.

Swenberg JA, Lehman-McKeeman LD (1999) alpha 2-Urinary globulin-associated nephropathy as a mechanism of renal tubule cell carcinogenesis in male rats. IARC scientific publications: 95-118.

USEPA (1991) Alpha2u-globulin: Association with chemically induced renal toxicity and neoplasia in the male rat.

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.