Dimethyl ether

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Remarks:

It concerns a non-GLP study but with internal review. Evaluation with respect to developmental effects are well performed. However, the report clearly shows errors when describing clinical signs/behaviour during exposure as evidenced by has conflicting information.

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)

Deviations:

yes

Remarks:

only examined the period of organogenesis; only 1/3 of fetuses were examined for soft tissue alterations (guideline states that 1/2 of fetuses should be examined for soft tissue alterations)

GLP compliance:

no

Remarks:

With signature for internal approval and review.

Test material

Test material information

Constituent 1

Reference substance name:

Dimethyl ether

EC Number:

204-065-8

EC Name:

Dimethyl ether

Cas Number:

115-10-6

Molecular formula:

C2H6O

IUPAC Name:

dimethyl ether

Details on test material:

Purity: 99.9%

Test animals

Species:

rat

Strain:

other: Crl:CD(R)(SD)BR

Details on test animals or test system and environmental conditions:

There were two parts of the study that both involved pregnant nulliparous female rats.
TEST ANIMALS
-Age at study initiation: Not specified
-Weight at study initiation: 150-160 grams (Part 1) or 240-270 grams (Part 2)
-Fasting period before study: None
-Housing: All animals were housed in suspended, wire-mesh, stainless steel cages
-Housing (mating): Co-habitation with mature males of the same strain overnight
-Housing (post-mating): Two females per cage (part 1), individually (part 2)
-Diet: ad libitum (except during exposure)
-Water: ad libitum (except during exposure)
-Acclimation period: Female rats were quarantined for at least one week after arrival

ENVIRONMENTAL CONDITIONS:
-Temperature (ºC): 22-25 (72-77 ºF)
-Humidity (%): 36-70
-Air changes (per hr): Not specified
-Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

inhalation: gas

Type of inhalation exposure (if applicable):

whole body

Vehicle:

air

Remarks on MMAD:

Not applicable as test substance is a gas

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus (Part I): 12-inch diameter cylindrical glass exposure chambers (20 L chambers for test groups and 40 L chambers for controls).
- Exposure apparatus (Part II): Dams were exposed in 750 L glass and stainless steel chambers.

- Method of holding animals in test chamber (Part I): For each exposure, rats were loaded into cylindrical wire mesh baskets (3-5 per basket) which were stacked in the chamber. This allowed the dams free movement in their respective basket.
- Method of holding animals in test chamber (Part II): For each exposure, rats were loaded into 2.0 L compartmentalized stainless steel wire mesh baskets. This allowed the dams free movement in their respective basket.

- Source and rate of air (Part I): Test atmospheres were metered from a stainless steel cylinder, through a flowmeter, and into the exposure chamber. The mixed atmosphere was introduced into the top of the exposure chamber and vented from the bottom.
- Source and rate of air (Part II): Test atmospheres were metered from a stainless steel cylinder, through a flowmeter, and into a mixing flask (500 mL, 3 neck round bottom). At the mixing flask, the test substance was mixed with a 10 L/min air stream prior to entry into the exposure chamber. This mixture was introduced into the top of the exposure chamber where it was further diluted with room air to a total flow of 250 L/min.

- Chamber oxygen concentration (Part I): ≥ 19% during all exposures.
- Chamber oxygen concentration (Part II): 21% during all exposures.

- Chamber temperature (Part I): ≤ 27 ºC for all exposures
- Chamber temperature (Part II): ≤ 27 ºC for all exposures


TEST ATMOSPHERE
- Brief description of analytical method used (Part I): On the fourth exposure day, instrument problems necessitated a switch to a back-up analytical system. For exposures 1 through 4 atmospheric concentrations of the test substance were determined using a Varian Aerograph (Model 600D) gas chromatograph equipped with a flame ionization detector. The column employed was a 6-ft long x 2-mm ID stainless steel tube packed with 10% SE-30 on 60/80 mesh Chromosorb W. For exposures 5 through 11, test substance concentrations were determined using a Hewlett Packard Model 5710A gas chromatograph equipped with a flame ionization detector. The column employed was a 2-ft long x 2-mm ID glass coil packed with 3% OV-17 on 80/100 mesh Supelcoport.
- Brief description of analytical method used (Part II): Atmospheric concentrations of the test substance were determined using a Varian Aerograph (Model 600D) gas chromatograph equipped with a flame ionization detector. The column employed was a 6-ft long x 2-mm ID stainless steel tube packed with 10% SE-30 on 60/80 mesh Chromosorb W.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Method of Analysis: GC
CONCENTRATION VERIFICATION
Conducted at all concentration levels (Part I): 0, 0.5, 2.0, 4.0% (0, 5000, 20000 and 40000 ppm)
Results (Part I): 0, 0.450, 1.95, 3.82%
Conducted on all dose levels (Part II): 0, 0.125, 0.5, 2.0 % (0, 1250, 5000 and 20000 ppm)
Results (Part I): 0, 0.125, 0.501, 2.01 %

Part 1: DME concentrations generated in the exposure chambers were 0, 4500 ± 26, 19500 ± 117, and 38220 ± 458 ppm for the 0, 5000, 20000, and 40000 ppm groups, respectively.
Part 2: DME concentrations generated in the exposure chambers were 0, 1250 ± 50, 5000 ± 230, and 20000 ± 580 ppm for the 0, 1250, 5000, and 20000 ppm groups, respectively.

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: not specified
- Length of cohabitation: overnight
- Proof of pregnancy: detection of spermatozoa in vaginal lavage (referred to as day 1 of gestation)

Duration of treatment / exposure:

Days 6-15 of gestation

Frequency of treatment:

6 hours daily

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0, 4500, 19500, 38220 ppm (part 1)
analytical conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0, 1250, 5000, 20000 ppm (Part 2)
analytical conc.

No. of animals per sex per dose:

Part 1: 14 controls and 7 per concentration group
Part 2: 27 controls and 27 per concentration group

Control animals:

yes, concurrent vehicle

Details on study design:

- Concentration selection rationale: Based on the available information on toxicity.
- Route selection rationale: Most likely route for human exposure.

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: The animals were observed for signs of toxicity and changes in behavior upon arrival, at breeding, and daily from days 6-21 of gestation when the dams were sacrificed

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: The animals were observed for signs of toxicity and changes in behavior upon arrival, at breeding, and daily from days 6-21 of gestation when the dams were sacrificed

BODY WEIGHT: Yes
- Time schedule for examinations: The dams were weighed on the day of arrival, on the day of mating, and several times during gestation.

FOOD CONSUMPTION: Yes
- Time schedule for examinations: During gestation

WATER CONSUMPTION: No

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day # 21
- Organs examined: liver, 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
- Number and positions of all live and dead fetuses: Yes

Fetal examinations:

- Weighed and sexed: Yes: all live and dead per litter
- External examinations: Yes: all live per litter
- Visceral examinations: Yes: one-third per litter, as well as the stunted fetuses and fetuses with external malformations
- Skeletal examinations: Yes: all (live and dead) per litter
- Head examinations: Yes: all fetuses examined for visceral alterations

Statistics:

The litter was considered to be the experimental unit for statistical evaluation. The Fisher's exact probability test was used to determine the statistical significance of the incidence of implantations, resorptions, and of individual alterations if more than 75% ties occurred in the data. The significance of differences between the control and experimental groups for maternal body weight and body weight gain were analyzed by a one-way analysis of variance, by LSD, and by Dunnett's test. For all other analyses of incidence of alterations, the Mann-Whitney U test was used. Jonckheere's test was used to determine whether a significant dose-related response was present. The level of statistical significance selected was p<0.05.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Pregnancy ratios for Part I were 14/14, 7/7, 7/7, and 7/7 for the 0, 5000, 20000, and 40000 ppm groups, respectively. Pregnancy ratios for Part II were 25/27, 24/27, 27/27, and 25/27 for the 0, 1250, 5000, and 20000 ppm groups, respectively.
Dams exposed at the 40000 ppm level gained significantly less weight during the early exposure period than the controls and showed no response to sound. Dams exposed at the 20000 level showed a slight  decrease in response to sound.  The response of the 5000 ppm group was equivocal. 

Effect levels (maternal animals)

Dose descriptor:

NOAEC

Effect level:

5 000 ppm

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

Maternal abnormalities

Abnormalities:

not specified

Results (fetuses)

Details on embryotoxic / teratogenic effects:

A summary of reproductive outcomes are provided in tables 1 and 2. All parameters (except sex ratio) are reported as means/litter.
Embryo-fetal toxicity was evident at the 40000 ppm level, which was expressed as decreased fetal body weight (of borderline statistical significance in the 20000 ppm group) and as an increased incidence of several skeletal variations (partial rib development in the lumbar region and partial or complete doubling of one or more vertebral centra). An increased incidence of one skeletal variation (extra ossification centers in the lumbar area), which was considered exposure related, was present in the 5000 ppm group. In the 1250 ppm group, the only type of variation with an incidence statistically higher than that of the control group was unossified hyoid bones. This statistically significant increase was isolated in that it occurred only in the lowest exposure group tested and therefore was not considered an adverse effect of the test compound.
Only one malformed fetus occurred in the 20000 ppm group; it had an umbilical hernia. No malformed fetuses were detected in the 5000 ppm or control group. In the 1250 ppm group, one fetus had multiple malformations, one had no right carotid artery, one had no innominate artery, and in another litter one fetus had no innominate artery.

Table 3 presents incidence data for the variations discussed above. The results are presented as fetuses/litters.

Effect levels (fetuses)

1

Dose descriptor:

NOAEC

Effect level:

>= 40 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: The test substance was not shown to be teratogenic at any level of exposure in this study

2

Dose descriptor:

NOAEC

Effect level:

20 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Reduced fetal weight at the next higher level tested of 40000 ppm

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Table 1: Part I

Concentration (ppm):	0	5000	20000	40000
Corpora lutea:	15.4	15.9	15.4	16.4
Implantations:	14.9	15.0	15.1	16.0
No. of Resorptions:	1.4	1.0	1.3	1.3
Total No. of Fetuses:	NR	NR	NR	NR
Total No. of Live Fetuses:	189	98	97	103
Mean Fetal Weight (g):	4.0	3.8	3.8	3.6
Sex Ratio:	NR	NR	NR	NR
NR = Not Reported

Table 2: Part II

Concentration (ppm):	0	1250	5000	20000
Corpora lutea:	16.7	16.3	15.2	15.7
Implantations:	14.0	15.3	14.7	14.9
No. of Resorptions:	1.0	1.0	1.0	0.9
Total No. of Fetuses:	13.0	14.3	13.7	14.0
Total No. of Live Fetuses:	13.0	14.3	13.7	14.0
Mean Fetal Weight (g):	3.8	3.7	3.8	3.7
Sex Ratio (% males):	48.5	48.1	50.1	50.5

Table 3

Variation:	0 ppm	1250 ppm	5000 ppm	20000 ppm
Number examined for skeletal exams	325/25	343/24	370/27	350/25
Rib - rudimentary	2/1	3/3	7/4	21/11†
Rib – extra	0	0	4/2	4/2
Rib – thickened	0	0	0	2/1
Rib – wavy	1/1	0	0	0
Rib – extensive wavy	1/1	0	1/1	0
Rib - extra ossification center	19/12	32/15	76/23#	117/23#
Centrum - dumbbelled	12/7	14/6	29/13	37/15#
Centrum - bipartite	5/3	8/6	16/9	13/8
Hyoid – partially ossified	12/7	6/6	9/7	6/6
Hyoid – unossified	2/2	14/8†	5/3	8/5
Hyoid – bipartite	1/1	0	0	0
# = Significantly different from control incidence b y two-tailed Mann-Whitney U test. † = Significantly different from control incidence by Fisher’s exact test.by two-tailed Mann-Whitney U test. † = Significantly different from control incidence by Fisher’s exact test.

Applicant's summary and conclusion

Conclusions:

The test substance was not uniquely toxic to the developing fetus. A reduced fetal weight was observed at 40000 ppm. The NOAEC for teratogenicity was at least 40000 ppm (75370 mg/m3). The study and the conclusions fulfil the quality criteria (validity, reliability, repeatability).

Executive summary:

Groups of pregnant rats were exposed to the test substance by inhalation at concentrations of 0, 5000, 20000 and 40000 ppm (Part I - RF) and 0, 1250, 5000, and 20000 ppm (Part II - full study) from days 6 -15 of gestation. Before sacrifice, data were collected on clinical signs, feed consumption and body weight. On day 21 of gestation, all surviving dams were sacrificed and examined for gross pathologic changes, and their reproductive status was determined. Their fetuses were weighed, sexed, and examined for external, visceral, and skeletal alterations.

Part 1 (RF):

Design: Rats (SD, 150-160 g): 7 females/grp (14 for control); 0, 0.5%, 2.0%, and 4.0% in air; 6 h/d, during GD 6-15 (10 days); sacrifice GD 21.

Observations: behaviour, clinical signs, BW and feed consumption, gross pathology and reproduction status.

Dams exposed to the test substance at the 40000 ppm level showed no response to a sound stimulus during exposure and gained significantly less weight during the early exposure period than did the control dams. In the groups exposed to the lower levels, the only test substance-related effect demonstrated among the dams was a slight decrease in response to sound at 20000 ppm: the response of the 5000 ppm exposure group was described as ‘equivocal’.

Fetuses: weighted, sexed, examined for external, visceral and skeletal alterations.

Results: at 4% no response to sound stimuli and lower increase in BW; other groups were indistinguishable.

No maternal organ changes observed; no differences in liver weight all groups. No effects on reproductive status.

 

Part 2 (Main study):

Design: Rats (SD, 240-270 g): 27 females/grp; 0, 0.125%, 0.5%, and 2.0% in air; 6 h/d, during GD 6-15 (10 days); sacrifice GD 21.

(4% was not selected because the safety precautions in view of explosion risks used in Part I could not be employed in the larger chambers needed for Part II.)

Observations: behaviour, clinical signs, BW and feed consumption, gross pathology and reproduction status.

Fetuses: weighted, sexed, examined for external, visceral and skeletal alterations.

Results: 2% showed slightly decreased response to sound. No difference in BW.

No maternal organ changes observed; no differences in liver weight all groups; no differences in incidence of pregnancy, corpora lutea,

implantations, resorptions, stunted fetuses, or in the number of live fetuses per litter. However at 2% fetal weight was only just significant lower in one specific statistical test (one-tailed Mann-Whitney U test; p = 0.045) (See attached graph: no effects at 2%)

Not teratogenic at any level.

At 0.5% and 2% showed an increased incidence of several skeletal variations. The reports therefore select NOEC of 0.125%.

"The skeletal changes noted were those regarded as being normal variants which signified that the dam was stressed sufficiently to express developmental instability inherent in the species. In comparison to maternal effect levels, DME was not demonstrated to represent a unique hazard to the rat conceptus."

(Separate report in which the investigators of both Haskell and TNO jointly evaluated both PNDT studies from Haskell and TNO concludes that in this study 2.0% is the NOAEC)

Conclusion: NOAEC = 2.0% DME in air