Ethylbenzene

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Guideline study reported in a publication original report not available. Study well documented and meets generally accepted scientific principles. The publication does not specifically state that this was a GLP study but the inference is that it was carried out under GLP.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Cross-reference 2

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

publication

Title:

Developmental toxicities of ethylbenzene, ortho-, meta-, para-xylene and technical xylene in rats following inhalation exposure

Author:

Saillenfait, A.M., Gallissot, F., Morel, G. and Bonnet, P.

Year:

2003

Bibliographic source:

Food and Chemical Toxicology. 41:415-429.

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Principles of method if other than guideline:

Not applicable

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Ethylbenzene

EC Number:

202-849-4

EC Name:

Ethylbenzene

Cas Number:

100-41-4

Molecular formula:

C8H10

IUPAC Name:

ethylbenzene

Details on test material:

- Name of test material (as cited in study report): Ethylbenzene
- Analytical purity: ≥99.5%

Test animals

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: IFFA CREDO Breeding Laboratories
- Age at study initiation: not specified
- Weight at study initiation: 180-200 g
- Fasting period before study: none
- Housing: individually housed in polycarbonate cages with stainless steel wire lids
- Diet (e.g. ad libitum): food pellets (UAR Alimentation Villemoisson, France), ad libitum except during exposure
- Water (e.g. ad libitum): filtered tap water, ad libitum except during exposure
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): controlled to 21±2 ºC
- Humidity (%): 50 ± 5% relative humidity
- Air changes (per hr): not specified
- Photoperiod (hrs dark / hrs light): 12 hour light/dark cycle

Administration / exposure

Route of administration:

inhalation

Type of inhalation exposure (if applicable):

whole body

Vehicle:

other: air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Exposures were conducted in 200-L glass/stainless steel inhalation chambe
- Method of holding animals in test chamber: not specified
- Source and rate of air: not specified
- Method of conditioning air: not specified
- Temperature, humidity, pressure in air chamber: not specified
- Air flow rate: not specified
- Air change rate: not specified
- Method of particle size determination: not specified
- Treatment of exhaust air: not specified

TEST ATMOSPHERE
- Brief description of analytical method used: Concentrations of ethylbenzene in the inhalation chambers were monitored by a sampling system coupled to a gas chromatograph equipped with a flame ionization detector
- Samples taken from breathing zone: not specified

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Actual mean exposure concentrations achieved in the chambers were 99, 500, 1001 and 1998 ppm of ethylbenzene

Details on mating procedure:

1 male to 2-3 females caged together overnight. The day that vaginal smears were sperm positive was considered to be gestation day (GD) 1.

Duration of treatment / exposure:

Gestation days 6-20

Frequency of treatment:

daily from gestation days 6-20

Duration of test:

Gestation days 6-20

No. of animals per sex per dose:

Group size: 23-26 bred rats/group, 21-25 pregnant/group

Control animals:

yes, concurrent no treatment

Details on study design:

not specified

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Presumed daily although not specifically mentioned

BODY WEIGHT: Yes
- Time schedule for examinations: Bodyweights recorded on GD 0, 6, 13 and 21 and weight changes were calculated for the period GD0-6, 6-13 and 13-21

FOOD CONSUMPTION: Yes
- Time schedule for examinations: Measured for the periods GD 6-13 and 13-21

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 21
- Organs examined: not carried out other than examination of the uterus

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes

Fetal examinations:

- External examinations: Yes: [all per litter]
- Soft tissue examinations: Yes: [half per litter]
- Skeletal examinations: Yes: [half per litter]
- Head examinations: No data

Statistics:

The litter was considered as the basic experimental unit for statistical analyses of the fetal data. The number of corpora lutea, implantation sites and live fetuses, maternal feed consumption, and various body weights were analyzed by one-way analysis of variance (ANOVA), followed by Dunnett's test if differences were found. The percentage of non-live implants, resorptions, and males, and the proportions of fetuses with alterations in each litter were evaluated by the Kruskal-Wallis test followed by the Mann-Whitney test where appropriate. Rates of pregnancy and percentages of litters with any malformations or external, visceral or skeletal variations were analyzed by using Fisher's test. Where applicable, least-squares analysis was carried out. The reported level of statistical significance was P < 0.05.

Indices:

Pregnancy (%), Pre- and post-implantation loss (%)

Historical control data:

None

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
There were no exposure related mortality during the study. Clinical signs of toxicity (ataxia, decreased motor activity) were seen at 2000 ppm with ethyl benzene. Dams exposed to 1000 or 2000 ppm showed significant decreases in maternal body weight throughout exposure and was also reflected in the corrected weight gain. Food consumption was decreased in dams exposed to 1000 and 2000 ppm ethylbenzene over the time periods 6-13, 13-21 and 6-21 days of gestation.

Effect levels (maternal animals)

1

Dose descriptor:

NOAEC

Effect level:

500 ppm

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOAEC

Effect level:

500 ppm

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
The pregnancy percent, number of corpora lutea and number of implantations were comparable between the control and treated dose groups. A non-statistically significant difference in the incidence of non-live implants and resorptions were noted in the 2000 ppm dose group when compared with the control dose group. Litter size was comparable between the treated and control dose groups, while a statistically significant dose-related reduction in fetal weights were noted in the 1000 and 2000 ppm dose groups. The number of viable fetuses and sex ratio were found comparable between the control and treated dose groups. No significant differences in external abnormalities were observed between the control and treated dose groups. Visceral malformations occurred in one or few fetuses from the 100, 1000 and 2000 ppm exposure groups, without a clear dose relationship and no statistical significance. There was an increased number of fetuses with skeletal or any other variations at 1000 and 2000 ppm.

Effect levels (fetuses)

Dose descriptor:

NOAEC

Effect level:

2 000 ppm

Basis for effect level:

other: teratogenicity

Remarks on result:

other: effect type not specified

Remarks:

There was no evidence of teratogencity with ethylbenzene in rats at dose levels up to 2000 ppm exposed via inhalation from gestation day 6-20. There was however evidence of slight developmental toxicity indicated by reductions in foetal body weight and a higher incidence of skeletal variations at 1000 and/or 2000 ppm with ethyl benzene. This was in the presence of maternal toxicity evidenced by clinical signs of toxicity at 2000 ppm and reduced body weight and food consumption at 1000 and 2000 ppm. Based on the results of the study, the NOAEL for teratogenicity was 2000 ppm, the NOAEL for maternal toxicity was 500 ppm and the NOAEL for developmental toxicity of ethyl benzene was 500 ppm.

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

None

Applicant's summary and conclusion

Conclusions:

There was no evidence of teratogencity with ethylbenzene in rats at dose levels up to 2000 ppm exposed via inhalation from gestation day 6-20. There was however evidence of slight developmental toxicity indicated by reductions in foetal body weight and a higher incidence of skeletal variations at 1000 and/or 2000 ppm with ethyl benzene. This was in the presence of maternal toxicity evidenced by clinical signs of toxicity at 2000 ppm and reduced body weight and food consumption at 1000 and 2000 ppm. Based on the results of the study, the NOAEL for teratogenicity was 2000 ppm, the NOAEL for maternal toxicity was 500 ppm and the NOAEL for developmental toxicity of ethyl benzne was 500 ppm.

Executive summary:

In this developmental toxicity study, groups of Sprague-Dawley rats (23-26 bred rats/group; 21-25 pregnant/group) were exposed to ethylbenzene via the inhalation route (whole body) daily from gestation days 6-20 (6 hours/day), at doses of 0, 100, 500, 1000 and 2000 ppm. The study was conducted according to OECD TG 414.

 

Parameters examined were clinical signs of toxicity, body weight and gains, food consumption, examination of uterine content (the uterus was removed and weighed and the number of corpora lutea, implantation sites, resorptions, dead and live fetuses were recorded), fetal examination (live fetuses were weighed, sexed, and examined for external anomalies including those of the oral cavity. Half of the live fetuses were preserved in Bouin's solution and examined for internal soft tissue changes. The other half were fixed in 70% ethanol, eviscerated, and then processed for skeletal staining with Alizarin Red S for subsequent skeletal examination).

 

Gross pathology of the animals were limited to examination of the uterus.

Actual mean exposure concentrations achieved in the chambers were 0, 99, 500, 1001 and 1998 ppm of ethylbenzene.

 

There were no exposure related mortality during the study. Clinical signs of toxicity (ataxia, decreased motor activity) were seen at 2000 ppm with ethyl benzene.

 

Dams exposed to 1000 or 2000 ppm showed significant decreases in maternal body weight throughout exposure and was also reflected in the corrected weight gain.

 

Food consumption was decreased in dams exposed to 1000 and 2000 ppm ethylbenzene over the time periods 6-13, 13-21 and 6-21 days of gestation.

 

The pregnancy percent, number of corpora lutea and number of implantations were comparable between the control and treated dose groups.

 

A non-statistically significant difference in the incidence of non-live implants and resorptions were noted in the 2000 ppm dose group when compared with the control dose group.

 

Litter size was comparable between the treated and control dose groups, while a statistically significant dose-related reduction in fetal weights were noted in the 1000 and 2000 ppm dose groups.

 

The number of viable fetuses and sex ratio were found comparable between the control and treated dose groups.

 

No significant differences in external abnormalities were observed between the control and treated dose groups.

 

Visceral malformations occurred in one or few fetuses from the 100, 1000 and 2000 ppm exposure groups, without a clear dose relationship and no statistical significance.

 

There was an increased number of fetuses with skeletal or any other variations at 1000 and 2000 ppm.

 

In conclusion, there was no evidence of teratogencity with ethylbenzene in rats at dose levels up to 2000 ppm exposed via inhalation from gestation day 6-20. There was however evidence of slight developmental toxicity indicated by reductions in foetal body weight and a higher incidence of skeletal variations at 1000 and/or 2000 ppm with ethyl benzene. This was in the presence of maternal toxicity evidenced by clinical signs of toxicity at 2000 ppm and reduced body weight and food consumption at 1000 and 2000 ppm. Based on the results of the study, the NOAEL for teratogenicity was 2000 ppm, the NOAEL for maternal toxicity was 500 ppm and the NOAEL for developmental toxicity of ethylbenzene was 500 ppm.