tert-butyl methyl ether

Toxicity to reproduction

Administrative data

Endpoint:

two-generation reproductive toxicity

Remarks:

based on test type (migrated information)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP compliant near-guideline study, minor restrictions, fully adequate for assessment.

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1991

Reference 2

Reference Type:

publication

Title:

Two-generation reproductive toxicity study of methyl tertiary-butyl ether (MTBE) in rats.

Author:

Bevan C, Neeper-Bradley TL, Tyl RW, Fisher LC, Panson RD, Kneiss JJ & Andrews LS

Year:

1997

Bibliographic source:

Journal of Applied Toxicology, 17 Suppl 1, S13-9.

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

No specific guideline was reported. However, the study was generally well conducted.

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

tert-butyl methyl ether

EC Number:

216-653-1

EC Name:

tert-butyl methyl ether

Cas Number:

1634-04-4

Molecular formula:

C5H12O

IUPAC Name:

2-methoxy-2-methylpropane

Details on test material:

- Name of test material (as cited in study report): MTBE
- Physical state: liquid
- Analytical purity: at least 99% (determined by gas chromatography)

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories
- Age at study initiation: 6 weeks
- Housing: individually
- Diet: ad libitum
- Water: ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°F): 66-77
- Humidity (%): 40-70
- Air changes (per hr): 14
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on 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.

Details on mating procedure:

During the mating period, one male was co-housed with one female selected randomly within the the same treatment group for a maximum of 7 days. After 7 days, the females of those pairs that were not confirmed as having mated were placed with males of other unmated pairs within the same treatment group for the reaminder of the 21-day mating period. Mating was confirmed by observation of the a copulatory plug or by the presence of sperm in a vaginal rinse. The day on which mating was confirmed was designated as the female's day 0 of gestation.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

once every 25 minutes during each 6 hours exposure using a Perkin-Elmer gas chromatograph equipped with a flame ionization detector

Duration of treatment / exposure:

10 weeks before mating until delivery of the F1-litter for males;
10 weeks before mating, during 21 day mating period, gestation and lactation starting day 5 and until the day of sacrifice, which followed the weaning of the offspring for females.

Frequency of treatment:

6 hours/day, 5 days/week

Details on study schedule:

The exposure started when the rats were about 6-weeks-old and lasted for 10 weeks before mating. Exposure of the females continued through the 21-day mating period, gestation and lactation starting day 5 and until the day of sacrifice, which followed the weaning of the offspring. Male exposure continued until the delivery of F1-litter. The new parents were randomly selected from the F1-litter at weaning on postnatal day 28, which was also the day they started receiving exposure. The exposure procedure was the same as it was for the P-animals.

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
400, 3000 and 8000 ppm
Basis:
other: target concentration

Doses / concentrations 2

Remarks:

Doses / Concentrations:
402 (8), 3019 (56) and 8007 (137) ppm (SD between brackets)
Basis:
analytical conc.

No. of animals per sex per dose:

25

Control animals:

yes

Examinations

Parental animals: Observations and examinations:

Viability was observed twice a day, detailed clinical examinations were performed once daily and body weights were recorded weekly; female body weights were recorded before mating, during gestation and in the post-natal days until weaning. Food consumption was recorded weekly and for females at every 3-4 days on gestation.

Litter observations:

Litters were examined twice daily. On post-natal days (PND) 0, 1, 4, 7, 14, 21 and 28, litters were counted, weighed and sexed and checked for abnormalities. On PND 4, the size of each litter was reduced by random selection to yield as nearly as possible four male and four female pups per litter. Culled pups were euthanized and given an external examination (including an examination for cleft palate). Abnormal pups were given a gross post-mortem examination.

Postmortem examinations (parental animals):

All adult F0 and F1 animals used for mating went through a post-mortem examination (gross necropsy). Pituitary, testes, epididymis, prostate and seminal vesicles and vagina, uterus, ovaries and respiratory tract were examined microscopically from all parent animals of the control and high dose groups as well as tissues with gross lesions.
Livers from F1-animals were weighed and those of the control and high dose group were studied microscopically.

Postmortem examinations (offspring):

On PND 4, culled pups were euthanized and given an external examination (including an examination for cleft palate).
Abnormal pups were given a gross post-mortem examination.

Statistics:

The unit of comparison was the male, the female (during the pre-mating exposure period), the pregnant female or the litter. Results of quantitative continuous variables were intercompared for the three treatment groups and one control group by use of Levene's test for equal variances, analysis of variance (ANOVA) and t-tests. Non-paramteric data were statistically evaluated using the Kruskal-Wallis test followed by the Mann-Whitney U test for pairwise comparisons when appropriate. Frequency data were compared using the Fisher's exact test.

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

effects observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

no effects observed

Other effects:

effects observed, treatment-related

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

Details on results (P0)

Toxic effects seen in parent F0 animals
Hypoactivity and lack of startle reflex were observed in the parental rats at 3000 and 8000 ppm. Parental animals at 8000 ppm were also ataxic. The 8000 ppm dose group males had a significantly reduced body weight throughout the 10-week pre-mating period. In the beginning of mating, the reduction in male bodyweight was almost 14%. There was also a significant reduction in the bodyweight gain in that group during the first 7 weeks. In the first three pre-mating weeks, male food consumption was reduced on average by 11%. Female body weights did not differ from controls in the pre-mating period but the body weight gain was significantly increased in the 8000 ppm group in the post-natal days 21-28. The overall difference in lactation-period weight gain was more than two-fold (p<0.05).
The reproduction data, such as pregnancy rates, gestation days and mating and fertility indices showed no meaningful differences to control.

Toxic effects seen in parent F1 animals
Hypoactivity and lack of startle reflex were observed in the parental rats at 3000 and 8000 ppm. Parental animals at 8000 ppm were also ataxic. In the adult animals, the highest dose group of F1-males had about 15% less weight gain (p<0.01) during the first two weeks, accompanied by a reduced absolute body weight throughout the pre-mating period. Although no decrease in weight gain was noted with the either male or female rats in the 3000 ppm group, they still had significantly reduced body weight in the first 3-4 pre-mating weeks. Similarly to the parent animals, no differences were noted in female body weights during the gestation period. However, the high-dose group had a significantly increased (4-fold) body weight during the post-natal days 14-21 and the lactation period. Nevertheless, the food consumption was significantly (p<0.01) reduced by approximately 10% during the postnatal days 7-14 in these females. Gross examination at necropsy revealed statistically significantly increased relative liver weights in both sexes of the F1-animals at high dose and in males at 3000 ppm. However, no treatment related histopathological changes were noted.
Pregnancy incidence, mating and fertility and gestation indices were within the control values.

Effect levels (P0)

1

Dose descriptor:

NOAEC

Remarks:

parental toxicity

Effect level:

400 ppm

Sex:

male/female

Basis for effect level:

other: Based on general toxicity signs (reduced bodyweight, hypoactivity, blepharospasms) at 3000 and 8000 ppm in parental animals.

Remarks on result:

other: Generation: P and F1 (migrated information)

2

Dose descriptor:

NOAEC

Remarks:

effects on fertility

Effect level:

8 000 ppm

Sex:

male/female

Basis for effect level:

other: No significant changes in the reproduction parameters

Remarks on result:

other: Generation: P and F1 (migrated information)

Results: F1 generation

General toxicity (F1)

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Sexual maturation:

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings:

no effects observed

Details on results (F1)

The developmental toxicity seen in F1 litter
There was a statistically significant (p<0.01) increase of dead pups in the 8000 ppm group. This followed from the death of an entire litter of 16 pups.However, there was no significant change in the survival index of the F1 generation. The high dose group male and female offspring body weights were significantly lower than the controls during the post-natal days 14-28. The female offspring of the 3000 ppm group had significantly lower body weights also on day 14. In general, when compared to controls, no significant differences were evident in the number of pups stillborn relative to live ones, judging by the survival indices on days 4, 7, 14, 21, 28 or the lactation index.

Developmental effects F2-animals
As in the F1-offspring, the F2-pups also had a significantly increased incidence of dead pups on post-natal day 4 in the high dose group. Again, in a manner similar to F1-pups, the F2-offspring had no significant difference in the survival indices when compared to controls. Male body weights of the 3000 and 8000 ppm dose groups were statistically significantly (p<0.05) reduced when compared to control group. Weight loss was seen in males of the 8000 ppm group during the post-natal days 7-28 and in the males of the 3000 ppm group during days 14-28.

Effect levels (F1)

Dose descriptor:

NOAEC

Remarks:

developmental toxicity

Effect level:

400 ppm

Basis for effect level:

other:

Remarks on result:

other: The F2 generation of pups at 3000 and 8000 ppm also exhibited lowered body weights from postnatal days 14-28 and 7-28, respectively. Body weight gains in both the F1 and F2 litters were also reduced for the corresponding time intervals.

Overall reproductive toxicity

Reproductive effects observed:

not specified