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Toxicological information

Repeated dose toxicity: inhalation

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Administrative data

Endpoint:
sub-chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP compliant guideline study, no restrictions, fully adequate for assessment.

Data source

Referenceopen allclose all

Reference Type:
study report
Title:
Unnamed
Year:
1989
Report Date:
1989
Reference Type:
publication
Title:
Evaluation of 13-week inhalation toxicity study on methyl t-butyl ether (MTBE) in Fischer 344 rats.
Author:
Lington AW, Dodd DE, Ridlon SA, Douglas JF, Kneiss JJ & Andrews LS
Year:
1997
Bibliographic source:
Journal of Applied Toxicology, 17
Reference Type:
publication
Title:
Neurotoxicological evaluation of methyl tertiary-butyl ether in rats.
Author:
Daughtrey WC, Gill MW, Pritts IM, Douglas JF, Kneiss JJ & Andrews LS
Year:
1997
Bibliographic source:
Journal of Applied Toxicology, 17 Suppl 1, S57-64

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
EPA OTS 798.2450 (90-Day Inhalation Toxicity)
Qualifier:
according to
Guideline:
other: EPA OTS 798.6050 (functional observation battery testing)
Qualifier:
according to
Guideline:
other: EPA OTS 798.6200 (motor activity)
Qualifier:
according to
Guideline:
other: EPA OTS 798.6400 (neuropathology)
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): MTBE
- Physical state: clear colourless liquid
- Analytical purity: >99 %
- Lot/batch No.: BRRC batch nr: 51-270 A&B, 51-382 A&B, 51-424 A&B, and 51-464 A&B

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Chrales River Breeding Laboratories
- Age at study initiation: 35 days
- Housing: individually
- Diet: ad libitum
- Water: ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22+- 3
- Humidity (%): 30-70
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
other: unchanged (no vehicle)
Details on inhalation exposure:
All exposures were conducted in 4.3 m3 stainless-steel and glass inhalation chambers. Airflow in each chamber was approximately 1000 L/min (14 air changes per hour). For the generation of atmospheres, liquid MTBE was metered from a piston pump into a heated glass evaporator. The tempearture was maintained at the lowest level sufficient to vapourize liquid. The resulting vapour was carried into the chamber by a countercurrent air stream that entered the bottom of the evaporator.

TEST ATMOSPHERE
- Brief description of analytical method used: by gas chromatography
- Samples taken from breathing zone: yes
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
once ervery 20 minutes during each 6 hour exposure by gas chromatography
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
5 days/week, 6 hours/day
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
800, 4000 and 8000 ppm
Basis:
other: target concentration
Remarks:
Doses / Concentrations:
797 (23), 3920 (129) and 8043 (194) ppm (SD between brackets)
Basis:
analytical conc.
No. of animals per sex per dose:
25/sex/dose in the general study of which 10/sex/dose in neurotoxicity study
Control animals:
yes

Examinations

Observations and examinations performed and frequency:
All animals were individually observed daily for signs of toxic effects. Observation of the eyes before and after 13 weeks of exposure. Body w eights were obtained before exposure (day 0), weekly during exposure and preceding sacrifice. Individual food consumption was determined weekly for the first 6 weeks of the exposure regimen. Hematological and serum chemistry analyses were performed prior to initiation (five of each sex) and at the 5th and 13th weeks of exposure (ten of each sex per dose). The measured blood chemistry and haematological parameters included those listed in the OECD guideline 413.
Additionally, aldosterone, corticosterone, and adrenocorticotropic hormone levels were measured at week 13.
Sacrifice and pathology:
The necropsy and histological examination (gross macroscopy and histology) included the organs listed in OECD guideline 413.
Other examinations:
Neurotoxicity assay included functional observation battery (FOB), measures of motor activity 20 hours after last exposure at an examination of neuropathological signs. Nervous system was evaluated microscopically in the 10 animals that were in the neurotoxicity evaluation. Various sections of the brain, spinal cord and ganglia were included in the examination.

Kidney sections from five male rats in each treatment group and five female rats of the control and high dose animals were stained for the presence of α2u-globulin the proximal tubule using a monoclonal antibody. From these same animals, a similar set of slides was prepared as for the α2u-re-evaluation. For this, an additional set of slides for the ten remaining rats was prepared. The immunohistochemical staining was conducted in Swenberg’s laboratory at the University of North Carolina. After staining, the slides were sent back to Bushy Run Research Center, where they where analysed by Fowler and Chun. To identify nonspecificprotein accumulation in the epithelial cells of the proximal tubules, Fowler and Martin analysed the slides, which had been stained using Mallory’s Heidenhain staining method.
Statistics:
Results form the control group were compared with the treatment groups by use of analysis of variance: ANOVA, Barlett's homogeneity of variance and Duncan's multiple range tests.The latter test was used to delineate which exposure groups differed from the control when F from the ANOVA was significant. If Bartlett's test indicated heterogeneous variances, all groups were compared by an ANOVA for unequal variances, followed if necessary by a t-test. The fiducial limit of 0.05 (two-tailed) was used as the critical level of significance for all comparisons.

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 specified
Water consumption and compound intake (if drinking water study):
no effects observed
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):
no effects observed
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
no effects observed
Details on results:
No animals died. The only treatment related clinical finding was ataxia in the 8000 ppm group. Body weights were significantly lower at the highest concentration along the test period in male and female rats; differences to control at the end of the study were –6% and –3%, respectively. The mid-dose group animals had decreased body weights only during the five first weeks of the dosing. At the end of dosing, relative and absolute liver and kidney weights were significantly increased in low, mid and high dose in males (liver: 8%, 20% and 39%; kidney: 5%, 12%, 20%) and in the mid and high dose females (liver: 13% and 15%; kidney: 12%, 10%). In addition, male and female adrenal weight showed an increasing trend with the dose. Both sexes had a statistically significantly increased relative adrenal weight at the two highest doses. The weight increase was probably related to stress, since also the blood corticosterone levels were higher than in controls. Males and females had a depressed absolute brain weight and length in the 8000 ppm group, although not statistically significantly. Haematological parameters expressed only slight, no more than 5% difference to the control values, with statistical seen significance only in the two highest doses. Namely, the changes for males were a 2-4% reduction in red blood cell count, a 2-5% increase in mean corpuscular volume (MCV), 2-3% increase in mean corpuscular haemoglobin concentration (MCHC). There was also an increase in the number of reticulocytes and leukopenia (mostly lymphopenia). These were statistically significant in either mid or high dose group. The high-dose females had increased haematocrit and segmented neutrophil count at study termination. In serum chemistry, significant effects were seen mostly in high-dose males who manifested slight increases in levels of calcium, phosphorus, albumin and total protein.
Both, the high and medium dose males, had a significant decrease in their liver transaminases (SGOT, SGPT). Males and females of the 8000 ppm group had a significantly elevated blood corticosterone level, both more than 3.5 times the control level. aldosterone level in female medium and high dose rats also showed a 36% and 57% increase to control rats, although this change was not considered statistically significant. The only significant findings at necropsy were concentration-related weight (relative to body weight) increases in adrenals, liver and kidneys at 4000 and 8000 ppm, males being more affected than females. Microscopically, again, only the high dose males had higher incidences of lymphoid hyperplasia in the lymph nodes, moderate haemosiderosis of the spleen and large hyaline droplets of the kidney. Peripheral and central nervous system did not have any treatment-related alterations. The 4,000 ppm males demonstrated a weak hyaline droplet response. Fowler and Martin (1994) found a greater amount of protein accumulated in the kidneys of male rats but they were not able to show an increase in droplet size or protein distribution with the dose. The immunohistochemical analysis of the kidney slides, showed the presence of α2u-globulin in the protein droplets found in tubules. However, they found neither exposure-response relationship, nor α2upositive proteinaceous casts at the junction of the proximal tubules and the thin limb of Henle. FOB parameters showed few differences to control, such as decreased hind-limb grip in midconcentration males and decrease in latency to rotate, which in their inconsistency were not considered indicative of nervous system dysfunction. Although some variation from control was seen in the motor activity of high dose males (-) and mid-dose females (+) on day 55, neither consistency nor dose relation could be found to give these symptoms a biological significance.

Effect levels

Dose descriptor:
NOAEC
Effect level:
800 ppm
Sex:
male/female
Basis for effect level:
other: mild toxicity at the next higher concentration: organ enlargement (liver, kidney, adrenals) and at the highest concentration, male rats displayed mild lesions in the lymph nodes, spleen and kidney

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion