Registration Dossier

Administrative data

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.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1981
Report Date:
1981

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
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

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): Methyl ethyl ketone.
- Physical state: Colorless liquid.
- Purity: At least 99.9%

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals 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

Administration / exposure

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).
Doses / concentrationsopen allclose all
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.

Examinations

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.

Results and discussion

Results of examinations

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.

Effect levels

Dose descriptor:
NOAEC
Effect level:
5 041 ppm
Sex:
male/female
Basis for effect level:
other: see 'Remark'

Target system / organ toxicity

Critical effects observed:
not specified

Any other information on results incl. tables

No changes in neurological function was observed.

Applicant's summary and conclusion

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.