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Administrative data

Endpoint:
sub-chronic toxicity: inhalation
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
1981
Reliability:
1 (reliable without restriction)

Data source

Referenceopen allclose all

Reference Type:
publication
Title:
A 90-Day Vapour Inhalation Toxicity Study of Methyl Ethyl Ketone
Author:
Cavender FL, Casey HW, Salem H, Swenberg JA, Gralla EJ
Year:
1983
Bibliographic source:
Fund. Appl. Toxicol. 3, 264-270
Reference Type:
publication
Title:
Unnamed
Year:
1983
Report date:
1981

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)
GLP compliance:
yes
Limit test:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
Butanone
EC Number:
201-159-0
EC Name:
Butanone
Cas Number:
78-93-3
Molecular formula:
C4H8O
IUPAC Name:
butan-2-one
Details on test material:
- Name of test material: methyl ethyl ketone (MEK) ; test article code number 8/80-146
- recieved from: Exxon Chemical Company
- identification: colorless liquid

Test animals

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
- Housing: individually
- Diet (ad libitum except during exposure): Purina Certified Rodent Chow 5002
- Water (ad libitum except during exposure): filtered tap water
- Acclimation period: 14-day quarantine period

ENVIRONMENTAL CONDITIONS
- Temperature (°C): monitored continuously [approximately 21°C]
- Humidity (%): monitored continuously [approximately 50%]
- Photoperiod (hrs dark / hrs light): 12

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
air
Details on inhalation exposure:
The test substance was vaporized in a 3-neck, round bottom flask. The test substance was metered to the vaporization flask using a Lab Pump. The vapours 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 vapours 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 substance 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 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 a 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 pressure gauges.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
A gas chromatographie ehamber monitoring system was employed throughout the study to analyze chamber air samples obtained by both manual and automatic sampling methods.
Duration of treatment / exposure:
- 89 or 90 consecutive calender days or a total of 64 or 65 exposure days
Frequency of treatment:
- 6 hours per day
- 5 days per week
Doses / concentrations
Remarks:
Doses / Concentrations:
0, 1250, 2500 or 5000 ppm
Basis:
nominal conc.
No. of animals per sex per dose:
- 15 males and 15 females per dose
Control animals:
yes
Details on study design:
Animals were housed and exposed in 8 cubic meter stainless steel and glass chambers. Ten 10 male and 10 female animals from each group were considered as Principals and were destined for clinical pathology and histopathology, while the remaining 5 male and 5 female rats per group were designated as Dedicated, destined solely for special neuropathologic studies.

Examinations

Observations and examinations performed and frequency:
Each animal
CAGE SIDE OBSERVATIONS:
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS:
- Time schedule: weekly at weightings

BODY WEIGHT:
- Time schedule for examinations: weekly

FOOD CONSUMPTION:
- Food consumption for each animal determined: weekly

OPHTHALMOSCOPIC EXAMINATION:
- Time schedule for examinations: during quarantine and just before necropsy
- Dose groups that were examined: each animal

HAEMATOLOGY:
- Principal animals were anaesthetized with sodium pentobarbital and blood samples collected from the abdominal aorta at necropsy through a ventral incision. Before injectlon the sodium pentobarbital was diluted 1:1.5 with saline in order to offset evaporation from the viscera after the animal was opened and to prevent shock. A 10 ml syringe equipped with a 22 gauge needle was used to puncture the aorta and collect approximately 7 ml of untreated blood. The following hematologic parameters were measured on whole blood sampIes treated with EDTA anti-coagulant: erythrocyte count, hemoglobin, hematocrit, total and differential leukocyte counts, platelet count, prothrombin time (using brain thromboplastin), mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration. In addition, the following serum chemistry parameters were measured: calcium, potassium, sodium, chloride, phosphorus, glutamic-pyruvic transaminase, glutamic-oxaloacetic transaminase, gamma-glutamyl transpeptidase, alkaline phosphatase, glucose, urea nitrogen, total bilirubin, and total protein.

CLINICAL CHEMISTRY: Yes (cf. HAEMATOLOGY)
- Time schedule for collection of blood: At necropsy
- Animals fasted: Yes, 12 hours prior to necropsy
- How many animals: 10 (principal animals)

URINALYSIS: Yes
- Urine sampies were collected from the Principal animals housed in metabolic cages during a 12-hour fast prior to necropsy
- Parameters examinded: volume, appearance, occult blood, specific gravity, protein, pH, ketone and glucose

NEUROBEHAVIOURAL EXAMINATION:
- Time schedule for examinations: during quarantine and just before necropsy
- Dose groups that were examined: each animal
- Battery of functions tested: assessment of posture, gait, tone and symmetry of the facial muscles and an examination of pupillary, palpebral, extensor thrust, and erossed-extensor thrust reflexes
Sacrifice and pathology:
All animals were subjected to necropsy at the termination of the study. The following tissues and organs were examined and all abnormal findings recorded: all external surfaces, orifices and organs; cranial cavity; carcass; external and cut surfaces of the brain; spinal cord; thoracic, pelvic and abdominal cavities and their viscera; cervical tissues and organs.
The following organs from Principal animals were carefully dissected and trimmed to remove fat and other contiguous tissue and weighed: brain, kidney, spleen, liver, and testes. In addition, the following tissues were collected and examined microscopically: brain (cerebellum, cerebrum [2 levels], medulla, optic nerve), spinal cord (cervical, thoracic & lumbar-two sections each), peripheral nerves (sciatic and anterior tibia), eyes, pituitary, thyroid, parathyroid, salivary glands (submaxillary), heart, lung, spleen, liver, pancreas, adrenals, lymph nodes (mesenteric and mandibular), kidneys, bladder, lachrymal glands, ovaries, uterus, oviducts, vagina, cervix, stomach, small intestine (duodenum, jejunum, ileum), large intestine (large & small colon & caecum), skeletal muscle (thigh), skin, mammary glands - males & females, bone (femur), bone marrow - smear & section, aorta, ear canal with zymbal gland, nasal turbinates (4 levels), trachea, testes, epididymis, oesophagus, thymus, prostate, seminal vesicle, any gross lesions(s). The tissues, organs, and identification tag from the Principal animals were placed in individually labelIed containers' containing 10% buffered formalin and slowly agitated. The lung was infused with a volume of 10 % formalin equal to approximately 75 % of the total lung capacity. After 12 but prior to 48 hours, the tissues were placed in fresh fixative. Tissues were trimmed to a thickness no greater than 0.4 cm for processing. Parenchymal organs were trimmed to allow the maximum possible surface area for microscopic examination. Lymph nodes were bisected (preferably through the hilus). Hollow organs were trimmed and blocked to allow sectioning through the mucosa and serosa. The fixed tissues were embedded and approximately 5 micrometer sections were cut, mounted, and stained with hematoxylin/eosin. All wet tissues, tissue blocks, and slides were identified with the study number and the individual animal number.
Other examinations:
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, 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.
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 ratlos were analyzed using a Kruskal-Walllis ANOVA and a Test of Multiple Comparison.

Results and discussion

Effect levels

open allclose all
Dose descriptor:
NOAEC
Effect level:
5 000 ppm (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: non-adverse effects (transiently decreased body weight gain, changes in organ weights, urine volume) at 5000 ppm
Dose descriptor:
LOEC
Effect level:
5 000 ppm (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: see above

Target system / organ toxicity

Critical effects observed:
not specified

Any other information on results incl. tables

No animals died during the study. Exposure to the low and intermediate concentrations of methyl ethyl ketone had no effect on mean body weight relative to control, although females in the intermediate group exhibited significantly higher body weights during weeks 12 and 13. Transient, statistically significant depressions of mean body weight gains were observed in male (week 1 through 5 and weeks 11 and 12) and female rats (weeks 1 and 2) exposed to the highest concentration of methyl ethyl ketone. No effects were found in the amount of food consumed, tests for neurological function, ophthalmologic observations or hematologic or serum chemistry parameters which were attributed to test article administration. At necropsy, increases in liver weight were noted in 1200 ppm and 2500 ppm females. Increases in liver weight, liver weight/body weight ratios and liver weight/brain weight ratios were observed in both 5000 ppm male and 5000 ppm female rats. In the former kidney weight/body weight ratios also were elevated. Spleen and brain weight, and brain weight/body weight ratios were depressed while kidney weight/brain weight ratios were elevated in 5000 ppm female rats. Urine volumes in 5000 ppm male rats were higher than control values. All of these findings were statistically significant. Mean corpuscular hemoglobin values in both 5000 ppm male and female rats were elevated. Serum glutamic-pyruvic transaminase activity in 2500 ppm female rats was elevated while 5000 ppm females exhibited significantly decreased SGPT activity. In addition, alkaline phosphatase, potassium and glucose values for 5000 ppm female rats were increased relative to controls. While some of these changes are statistically significant, they were considered as incidental findings, without toxicological significance.

Special neurological and routine pathological studies did not reveal any lesions that could be attributed to test article exposure. Lesions were present in rats from all groups that were of a type and a severity that is normally expected in rats of this age.

Applicant's summary and conclusion

Executive summary:

In a subchronic inhalation toxicity study (CIIT, 1983) with the structural analogue methyl ethyl ketone (MEK) groups of 15 male and 15 female Fisher 344 rats were exposed to 0, 1250, 2500 or 5000 ppm MEK vapors 6 hours a day, 5 days a week for a duration of 90 consecutive days. 5 male and 5 female rats per dose group were designated for special neuropathological examinations. Transient, statistically significant depressions of mean body weight gains were observed in male and female rats exposed to the highest concentration of methyl ethyl ketone. No effects were found in the amount of food consumed, tests for neurological function, ophthalmologic observations or hematologic or serum chemistry parameters which were attributed to test article administration. At necropsy, slight but statisitically significant increases in absolute liver weight were noted in 1200 ppm and 2500 ppm females. Increases in liver weight, liver weight/body weight ratios and liver weight/brain weight ratios were observed in both 5000 ppm male and 5000 ppm female rats. In the former kidney weight/body weight ratios also were elevated. Spleen and brain weight, and brain weight/body weight ratios were depressed while kidney weight/brain weight ratios were elevated in 5000 ppm female rats. Urine volumes in 5000 ppm male rats were higher than control values. All of the findings at 5000 ppm were statistically significant. Neuropathological and routine histopathological studies including examination of reproductive organs did not reveal any lesions that could be attributed to MEK exposure. The depressed body weight gain represents an non-adverse effect, as it was transient. Due to the lack of any other corroborative findings, the effects on organ weights and urine volume seen at 5000 ppm are considered as non-adverse effects. Thus, a NOAEC of 5000 ppm (corresponding to 14.7 g/m³) is derived.