2,3-epoxybutane

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: basic data given, comparable to guideline/standards

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

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

1,2-epoxybutane

EC Number:

203-438-2

EC Name:

1,2-epoxybutane

Cas Number:

106-88-7

Molecular formula:

C4H8O

IUPAC Name:

2-ethyloxirane

Details on test material:

1,2-epoxybutane

Test animals

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

A group of 380 young, adult female Wistar rats (4-5 weeks old, 100-125 g on receipt) was purchased from Hilltop Lab Animals, Inc. , Scottdale, PA, for the experiment with each agent. The rats were acclimated in the laboratory for a minimum of 10 days before initiation of experiments; in the butylene oxide experiment, they were kept for about a month before use. Males (8 weeks old, 300-324 g) of the same strain were purchased at the start of the study. Males which did not inseminate a female were culled and replaced for each subsequent experiment.
The animals were housed in stainless steel cages before, during, and after inhalation exposure. Caging of experimental females was individual within the exposure chamber except during the mating period. Cage assignment was not random and the locations were not rotated. At the completion of each daily exposure, the generator was disconnected, the chambers were flushed with fresh air for at least one-half hour, and the chamber doors were opened.
Wayne Lab-Blox was provided ad libitum, except during the daily exposure period when the food was removed. Water was supplied by an automatic watering system which was disconnected and drained prior to initiation of each exposure. Food consumption was recorded for a 2-day period prior to inhalation exposure, twice weekly during the pre-gestational exposure period, and at 2-day intervals throughout the gestational exposures. The survival, appearance, and behavior of the parental females during the experimental period were noted. There were no variations in diet or light cycle and there was no use of pesticides, medications, or other extraneous chemicals during the experimental period. Humidity was not controlled.
Each female rat was uniquely identified by consecutively numbered ear tags, which provided coding as well as identification. A computer file was created of the weights and identification numbers of the females and a randomization program was used to assign the animals randomly by weight to the three pregestational treatment groups. The rats were also coded as to pregestation exposure group by subcutaneously injecting india ink in the forepaw: filtered air-no mark, low concentration-left, high concentration right. A similar rnarking of the hindpaw was done after assignment to gestational exposure groups. This procedure, which obviated errors in recording of group assigment, permitted the person who killed the rats to be aware of exposure history. Since the uterus was removed and examined by other prosectors, however, treatment group was not known during evaluations.
On the Friday prior to initiation of exposure, the animals were placed in the exposure chamber and the food in each housing uni t was weighed to allow calculation of the pre-exposure food consumption. In the butylene oxide experiment, the females were individually weighed again prior to placement in the exposure chambers. The female rats were weighed at least twice weekly during pregestation exposure and on days 1, 7, 14, and 21 of gestation.

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

other: room air

Details on mating procedure:

Pregestational exposures ordinarily began on a Monday and were continued for 7 hours per day, 5 days a week, for 3 weeks. The females were transferred to a standard rack united and caged with males (2:1). Vaginal lavages were performed the following mornings and examined for the presence of sperm. Sperm-positive females were randomly assigned to gestational exposure groups. Gestational exposures were started on the day on which sperm were detected which was denoted as day 1 of gestation (d.g. 1). Mating and initiation of gestational exposures continued for 7 - 9 days, until about 36 sperm-positive rats were assigned to each experimental group. Gestational exposures were performed 8 hours per day, 7 days per week, through d.g. 19. All exposed mated rats were sacrificed at d.g. 21.
Based upon the combination of pregestational and gestational exposures, 1 control and 6 experimental groups were formed. These groups will be identified by the pregestational and gestational exposure in the presentation of results:
Air-air (control) - 3-week pregestational exposure to filtered air followed by exposure to filtered air during days 1 - 19 of gestation. Air-low - 3-week pregestational exposure to filtered air followed by low level exposure during days 1-19 of gestation. Air-high - 3-week pregestational exposure to filtered air followed by high level exposure during days 1-19 of gestation. Low-air - 3-week pregestational low level exposure followed by exposure to
filtered air during days 1-19 of gestation. Low-low - 3-week pregestational low level exposure followed by low level exposure during days 1-19 of gestation. High-air - 3-week pregestational high level exposure followed by exposure to filtered air during days 1-19 of gestation. High-high - 3-week pregestational high level exposure followed by high level exposure during days 1-19 of gestation.

Duration of treatment / exposure:

day 1 - 19 of gestation, additionally groups with pregestational exposure of 21 days

Frequency of treatment:

7 hours/day, 5 days/week

Duration of test:

until day 21 (cesarian section)

Doses / concentrations

Remarks:

Doses / Concentrations:
250, 1000 ppm (0.75, 3.0 mg/l)
Basis:
nominal conc.

No. of animals per sex per dose:

total: 380

Control animals:

yes

Details on study design:

The animals were sacrificed by introduction of carbon dioxide into an euthanisa chamber. Necropsy were performed on all animals; liver, lung, and kidneys were weighed. Internal abnormalities of the pregnant and non-pregnant animals were also recorded. Samples of the ovaries, uterus, liver, lungs with trachea, and kidneys were perserved in 10% neutral buffered formalin. Histopathological examination was performed on tissues from 25% of the pregnant animals, selected at random. The residual tissues and the tissues from the remaining 75% of the animals and from the non-pregnant animals have been preserved for possible future examination.

Examinations

Maternal examinations:

The uterus, with ovaries attached, was removed from each animal immediately upon sacrifice and the total number of implantation sites was counted. The ovaries were removed and identified as right or left , the Corpora lutea were counted, and the ovaries were fixed in NBF for histologic examination. The uterus was opened and counts of living and dead fetuses and of resorptions were made. The resorptions were classified as to the stage of gestation at which death appeared to have occurred. The fetuses were removed from the surrounding membranes in serial order and the amniotic fluid was observed for any abnormalities in color. Concurrently, the placentas were removed, weighed and examined; abnormal placentas were fixed in 10% NBF for histological examination.

Fetal examinations:

The living and recently dead fetuses were blotted on a moist surface, weighed, the crown-rump length measured, and the sex was determined. Each fetus was examined under an illuminated magnifier for gross external abnormalities and assigned, by coin-toss, into one of two groups for more detailed teratologic examination. In one group, the heads were removed and fixed in Bouin's fluid for subsequent examination of serial thin razor blade sections by the method of Wilson (1965).
These fetuses were examined for internal abnormalities by Staples' modification of Wilson's method (Staples, 1974; Wilson, 1965). Slightly more than one-half on the fetuses were examined in this manner since the lab. established a requirement that a minimum of 2 fetuses per horn and 4 fetuses per litter would be examined, except when precluded by the presence of fewer fetuses. The fetuses of the second group were eviscerated and together with the decapitated carcasses, were fixed in alcohol and prepared for evaluation of skeletal abnormalities by the Staples and Schnell (1964) modification of the method of Dawson (1926). The cleared Alizarin Red S stained skeletons were examined under low power magnification, following a defined checklist to ensure observation and recording of defects.

Statistics:

Fisher's Exact Probability Test was used on the maternal and fetal data; Bonferronni's method was used to adjust for the problem associated with multiple comparisons against a control group. In all instances, differences from the control group at probability levels of 0.05 or less were accepted as statistically significant.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Details on maternal toxic effects:
No mortality without pregestational exposure (0/38). High pregestational exposure caused one death (1/42). However, this death was not regarded as substance-related (the surviving animals showed no signs of servere toxicity; no further details are given in the report). Pregestational exposure to 1000 ppm of butylene oxide produced a slight, but statistically significant, reduction in the body weight of the rats relative to the controls at most time periods. The differences were transient and were not statistically significant at the end of the pregestation exposure. By 7 days of gestational exposure, the rats exposed at the high levels were significantly lighter than the controls, and remained lighter throughout the study. No remarkable changes in food consumption were produced by pregestational or gestational exposure of rats. The exposure did not affect liver weights. The exposure did not have a major effect on lung weight. No statistically significant differences in placental weight were detected. Apparently normal corpora lutea were noted in the sections of ovary from each rat.
The exposure led to a slightly reduced percentage of sperm-positive rats which were pregnant (36/37, 33/37, 28/35, 33/42, 38/44, 33/40, 31/39 for air-air, air-low, air-high, low air, low-low, high-air and high-high respectively) although no clear dose relationship was seen and the decrease was not statistically significant.

Effect levels (maternal animals)

Dose descriptor:

NOAEC

Effect level:

> 1 000 ppm

Basis for effect level:

other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Details on embryotoxic / teratogenic effects:
The exposure had no statistically significant effect on either the weight or length of the fetuses in rats. Statistically significant differences in the sex ratios were not observed. Pregestational and/or gestational exposure did not have statistically significant effects on any of the measures of reproductive success. Alterations of the nature or incidence of morphologic changes related to exposure were not noted.

Effect levels (fetuses)

Dose descriptor:

NOAEC

Effect level:

> 1 000 ppm

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

There was little indication of maternal toxicity of butylene oxide in the rat other than relatively trivial effects on weight gain and a few organ weights.