N-hexane

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1988

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable with restrictions because there was no GLP statement provided, and limited data on methods were reported, but the study seemed to be well-conducted.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1988

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

This study examined the effect of inhalation of n-hexane vapors to fetal development. Groups of 35 pregnant and 10 virgin female mice were exposed to concentrations of 0, 200, 1000, or 5000 ppm of test substance vapors for 20 hrs/day, daily, during gestational days 6 -17. During exposure, females were weighed regularly. At the end of the exposure period, the females were sacrificed, and the uterine contents were examined for parameters including number of live fetuses, number of implantations, and number of resorptions. Fetuses were also examined for malformations.

GLP compliance:

no

Limit test:

yes

Test material

Test material information

Constituent 1

Reference substance name:

N-hexane

EC Number:

203-777-6

EC Name:

N-hexane

Cas Number:

110-54-3

Molecular formula:

C6H14

IUPAC Name:

hexane

Details on test material:

- Name of test material (as cited in study report): n-hexane
- Analytical purity: 99.2%
- Lot/batch No.: H-222
- Storage condition of test material: 65 degree F, stored under a blanket of nitrogen

Test animals

Species:

mouse

Strain:

CD-1

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, Raleigh NC
- Weight at study initiation: 28.7-31.5 g
- Housing: cages
- Diet (e.g. ad libitum): NIH-07 diet, ad libitum
- Water (e.g. ad libitum): ad libitum



ENVIRONMENTAL CONDITIONS
- Temperature (°C): 73 +/- 3 degrees F
- Humidity (%): 50 +/- 15 %
- Air changes (per hr): approx. 15
- Photoperiod (hrs dark / hrs light): 12 hrs light/12 hrs dark

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Battelle-designed chambers, 2.3 m3 stainless steel chambers
- Method of holding animals in test chamber: cages
- Method of conditioning air: Hexane in a 19 l stainless steel reservoir is pumped into delivery tubes to vaporizers at the fresh air inlet to the exposure chambers. The vaporizers are heated to aid in evaporation. Micrometering pumps are used to adjust the concentration.
- System of generating particulates/aerosols:
- Temperature, humidity in air chamber: 73 +/- 3 degree F, 50 +/- 15%
- Air change rate: approx. 15 changes per hour
- Treatment of exhaust air: building exhaust


TEST ATMOSPHERE
- Brief description of analytical method used: Atmosphere was tested using a on-line GC with automatic 8-port sampling valve.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Atmosphere was tested using a on-line GC with automatic 8-port sampling valve.

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 1 male to 1-2 females
- Length of cohabitation: up to five nights
- Proof of pregnancy: vaginal plug referred to as day 0 of pregnancy

Duration of treatment / exposure:

20 hrs/day

Frequency of treatment:

daily

Duration of test:

gestation days 6-17

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 200, 1000, 5000 ppm
Basis:
nominal conc.

No. of animals per sex per dose:

35 pregnant females, 10 virgins per dose

Control animals:

yes, sham-exposed

Examinations

Maternal examinations:

BODY WEIGHT: Yes
- Time schedule for examinations: plug positive females - days 0, 6, 9, 12, and 18
virgin females - 12 day prior to exosure, days 1, 4 and 7, before sacrifice


POST-MORTEM EXAMINATIONS: Yes / No / No data
- Sacrifice on gestation day 20
- Organs examined: nongravid uteri

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: 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: all per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: Yes: half per litter

Statistics:

SAS statistical software, Duncan's multiple range test
Mean body weigths: SAS General Linear Models Procedure with analysis of variance
Dose response: orthogonal trend test

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Mean weight gain for pregnant females in the 5000 ppm group was significantly reduced compared to controls. There was also a significant reduction in gravid uterine weight in the 200 and 5000 ppm groups. A significant reduction in uterine weight to extra-gestational weight gain was seen in the 5000 ppm group as well. Number of implantations per litter was also reduced in the 5000 ppm group, and also the number of live implants per litter. An increase in intrauterine death was significantly greater only in the 200 ppm group. The incidence of late resorptions was significantly increased in the 5000 ppm group.

Effect levels (maternal animals)

1

Key result

Dose descriptor:

NOAEC

Effect level:

1 000 ppm

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

LOAEC

Effect level:

5 000 ppm

Basis for effect level:

other: maternal toxicity

3

Key result

Dose descriptor:

LOAEC

Effect level:

200 ppm

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
Fetal weights of females in the 5000 ppm group were significantly reduced. The only significant increase in malformations as compared to controls, was an exencephalic fetus in the 5000 ppm group, however, as this was only seen in one fetus, and this malformation was also present in the control group, it is not considered treatment related. Rather it is an anomalous result due to the low background incidence of this malformation.

Effect levels (fetuses)

Key result

Dose descriptor:

LOAEC

Effect level:

200 ppm

Basis for effect level:

other: developmental toxicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Significant results of mouse developmental toxicity study

Concentration	0 ppm	200 ppm	1000 ppm	5000 ppm
Mean body weight – gestational day 18 (g)	57.0 ± 5.0	54.8 ± 4.0	55.7 ± 4.9	53.7 ± 4.6
Uterine mean weight (g)	21.4 ± 3.8	19.2 ± 3.4	20.2 ± 3.5	17.8 ± 3.9
Live fetuses/litter	12.0 ± 2.6	10.6 ± 2.2	11.4 ± 2.4	10.2 ± 2.7
Resorptions/litter	0.6 ± 0.7	1.6 ± 1.7	0.8 ± 0.9	1.1 ± 1.2
Late resorptions/litter	0.0 ± 0.2	0.4 ± 0.9	0.4 ± 0.6	0.5 ± 0.8
% live fetuses/litter	95.5 ± 5.6	87.2 ± 12.2	93.5 ± 7.2	89.7 ± 12.4
% resorptions/litter	4.5 ± 5.6	12.8 ± 12.2	6.5 ± 7.2	10.3 ± 12.4
% late resorptions/litter	0.3 ± 1.3	3.4 ± 6.6	2.9 ± 4.6	4.5 ± 6.5
Female fetal weight (g)	1.39 ± 0.10	1.37 ± 0.10	1.35 ± 0.10	1.31 ± 0.11
% exencephaly/litter affected	0 ± 0	0 ± 0	0 ± 0	0.5 ± 2.5

Applicant's summary and conclusion

Conclusions:

The maternal NOAEC was 1000 ppm, and the maternal LOAEC was 5000 ppm based on reduced body weight. The developmental LOAEC was 200 ppm (704 mg/m3) based on increased resorptions and reduced uterine weight. There was no NOAEC for developmental toxicity.

Executive summary:

This study examined the effect of inhalation of n-hexane vapors to fetal development. Groups of 35 pregnant and 10 virgin female mice were exposed to concentrations of 0, 200, 1000, or 5000 ppm of test substance vapors for 20 hrs/day, daily, during gestational days 6 -17. During exposure, females were weighed regularly. At the end of the exposure period, the females were sacrificed, and the uterine contents were examined for parameters including number of live fetuses, number of implantations, and number of resorptions. Fetuses were also examined for malformations. Body weight was significantly reduced in 5000 ppm exposure females. There was significant reduction in gravid uterine weight in the 200 ppm group, there was also an increase in intrauterine death in this group. Fetal weights were also reduced in the 5000 ppm group. No biologically significant increase in malformations was found. The NOAEC for maternal toxicity is 1000 ppm, and the LOAEC is 5000 ppm based on reduced body weight. There was no NOAEC found for developmental toxicity, and the LOAEC is 200 ppm (704 mg/m³) based on reduced fetal weight gain.