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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
13-14 pregnant rabbits per group; exposure restricted to gestation days (GD) 7-19

Data source

Referenceopen allclose all

Reference Type:
study report
Title:
Unnamed
Year:
1989
Report Date:
1989
Reference Type:
publication
Title:
Inhalation developmental toxicity in rabbits on dimethylacetamide with cover letter
Author:
BASF Corp.
Year:
1989
Bibliographic source:
TSCATS OTS0535030
Reference Type:
publication
Title:
Developmental toxicity of dimethylacetamide in rabbits following inhalation exposure
Author:
Klimisch HJ & Hellwig J
Year:
2000
Bibliographic source:
Human Exp Toxicol 19: 676-683

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Deviations:
yes
Remarks:
13-14 pregnant rabbits per group; exposure restricted to gestation days (GD) 7-19
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
Specific details on test material used for the study:
- Name of test material: dimethylacetamide (DMAC)
- Source: BASF AG
- Purity: 99.9%
- Batch No.: 86/104
No further details available.

Test animals

Species:
rabbit
Strain:
other: Russian
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Dr. Karl Thomae GmbH, Biberach/Riss, Germany
- Mean body weight at initiation: 2.3 kg
- Age at initiation: 23-27 weeks old
- Acclimation period: Prior to artificial insemination
- Housing: Individually
- Certified diet and tap water: ad libitum (water and diet analysed for contaminations, negative results)

ENVIRONMENTAL CONDITIONS:
- Temperature: 20-24 °C
- Humidity: 30-70 %
- Photoperiod: 12 hours dark/12 hours light

Administration / exposure

Route of administration:
inhalation
Type of inhalation exposure (if applicable):
whole body
Vehicle:
air
Details on exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION /EXPOSURE PARAMETERS
The animals were adapted to exposure conditions (air without test substance) at gestation days 1-4.
Vapourisation was performed at a temperature of 50, 60, or 65°C (low, mid, and high dose, respectively) in an evaporator resulting in a mixture with air (50 % relative air humidity, 22 °C; compressed air in high dose group); the vapour-air-mixture was discharged into the exposure chamber (ca. 1.1 m³). There was negative pressure for treatment groups and positive pressure for the control group. Technical parameters of exposure (temperature, pressure, air humidity, air flow) were controlled.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Measurement of total hydrocarbon by GC technique (calibrated); daily intermittend sampling.
Temperature (23.5, 24.7, 24.6, 25.3 °C at 0, 0.2, 0.7, 2 mg/L) and relative air humidity (53 %) were kept constant.
Details on mating procedure:
- Impregnation procedure: Artificial insemination
Duration of treatment / exposure:
Gestation days (GD) 7-19
Frequency of treatment:
Daily for 6 h/day
Duration of test:
GD 29
Doses / concentrationsopen allclose all
Dose / conc.:
0.2 mg/L air (analytical)
Remarks:
± 0.01 mg/l (SD). 0.2 mg/l (nominal concentration).
Dose / conc.:
0.7 mg/L air (analytical)
Remarks:
± 0.01 mg/l (SD). 0.7 mg/l (nominal concentration).
Dose / conc.:
2 mg/L air (analytical)
Remarks:
± 0.06 mg/l (SD). 2.0 mg/l (nominal concentration).
No. of animals per sex per dose:
Initial 15 rabbits per group.
In satellite groups (control and high dose) 5 pregnant rabbits.
Control animals:
yes, concurrent no treatment
Details on study design:
Dose selection rationale: No details

Examinations

Maternal examinations:
CLINICAL SIGNS, MORTALITY:
Clinical signs were recorded daily during, prior and after exposure (mortality).

BODY WEIGHT:
Body weight was measured on GD 3, 7, 10, 13, 16, 19, 21, 24, 27 and 29.
Corrected body weight gain was measured (substracting uterus weight).

GROSS PATHOLOGY:
At termination a necropsy was performed.

OTHER:
In satellite groups (control and high dose; n=5) additional clinical chemistry parameters were assessed (blood sampling at GD 20) and histopathology of the liver was performed; clinical chemistry parameters included alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, inorganic phosphate, calcium, glucose, total protein, bilirubin, triglyceride.
Ovaries and uterine content:
The ovaries and uterine content was examined after termination.
Examinations included:
- Gravid uterus weight
- Number of corpora lutea
- Number of implantations
- Number of resorptions (temporally differenciated), dead and living fetuses
Fetal examinations:
Fetal weight, sex, viability and placental weight were recorded (fetal length was not measured .

Retardations and variations were recorded as well as malformations, based on:
- External examinations
- Soft tissue examinations
- Skeletal examinations (via x-rays)
- Head examinations (12 transversal sections after fixation in Bouin's solution)

Statistics:
WILLIAMS test
FISHER exact test
KRAUTH test
NOVA-DUNNETTS test
Level of significance: p<0.05
Clinical chemistry: KRUSKAL-WALLIS, MANN-WHITNEY U-Tests
Indices:
See results
Historical control data:
Yes

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:
no effects observed
Mortality:
no mortality observed
Description (incidence):
There was one abort in the low dose group on GD 23 (dam sacrificed).
Body weight and weight changes:
no effects observed
Gross pathological findings:
no effects observed

Maternal developmental toxicity

Pre- and post-implantation loss:
no effects observed
Dead fetuses:
no effects observed
Other effects:
effects observed, non-treatment-related
Description (incidence and severity):
There were effects on mean uterus weight (increased at 0.2 mg/l and 0.7 mg/l level) related to the low number of fetuses in the control group (compared to historical controls). Furthermore, placental weight was reduced in treatment groups, but this effects was also related to the reduced number of living fetuses in the control group (see also placental weight/litter).

In each group one rabbit was not pregnant (conception rate 93.3 % in all groups).

Effect levels (maternal animals)

open allclose all
Dose descriptor:
NOAEC
Effect level:
2 mg/L air
Based on:
test mat.
Basis for effect level:
clinical signs
mortality
body weight and weight gain
Dose descriptor:
NOAEC
Effect level:
2 mg/L air
Based on:
test mat.
Basis for effect level:
pre and post implantation loss
dead fetuses

Maternal abnormalities

Abnormalities:
no effects observed

Results (fetuses)

Fetal body weight changes:
effects observed, treatment-related
Description (incidence and severity):
2.0 mg/l: Reduced fetal and placental weights were observed.
0.7 mg/l: Effects on fetal weight in these dose groups were considered not to be of toxicological relevance (low number of fetuses in control group and increased litter weight in treatment groups)
Changes in sex ratio:
no effects observed
Skeletal malformations:
effects observed, non-treatment-related
Description (incidence and severity):
2.0 mg/l: Increased variations (skeletal variations of ribs, sternum and vertebral column; separated origin of the carotids; also increased compared to historical controls) were observed.

0.7 mg/l: Increases in skeletal retardations (not dose related) were within the historical range.
Visceral malformations:
effects observed, treatment-related
Description (incidence and severity):
Increased malformations (not significant but uncommon in historical controls like malformations of the vasculature; increased incidence in defects of the septum) were considered by the authors to be treatment related.

Effect levels (fetuses)

Dose descriptor:
NOAEC
Effect level:
0.7 mg/L air (analytical)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
fetal/pup body weight changes
skeletal malformations
visceral malformations

Fetal abnormalities

Abnormalities:
effects observed, treatment-related
Localisation:
skeletal: rib
other: skeletal: sternum, vertebral column; visceral: vasculature, defects of the septum

Overall developmental toxicity

Developmental effects observed:
yes
Lowest effective dose / conc.:
2 mg/L air (analytical)
Treatment related:
yes
Relation to maternal toxicity:
developmental effects in the absence of maternal toxicity effects
Dose response relationship:
no

Any other information on results incl. tables

Developmental toxicity in rabbits after inhalation exposure to N,N-dimethylacetamide

Data related to main groups

Parameter

Vehicle control

0.2 mg/L

0.7 mg/L

2 mg/L

Pregnant rabbits

14/15

14/15

14/15

14/15

Rabbits with abort

-

1

-

-

Implantations/dam

6.0

6.92

7.50

6.71

Living fetuses/dam

4.71

6.54

6.71

5.57

Dead implants/dam

1.29

0.38

0.79

1.14

% post-implantation loss

23.1

6.0

13.3

17.9

Placental weight m&f (g)

4.94

4.23**

4.22**

4.03**

Placental weight/litter (g)

24.4

27.2

27.3

21.8

Litter weight (g)

206.7

244.3

252.5

197.9

Fetal weight m and f (g)

41.3

37.5*

38.4*

35.9**

% fetuses/litter with soft tissue malformations

6.4

2.1

3.2

13.6

% fetuses/litter with soft tissue variations

48.4

30.4

40.9

85.0*

% fetuses/litter with skeletal variations

9.2

8.0

23.8

61.6**

*: p<0.05; **: p<0.01

Applicant's summary and conclusion

Conclusions:
The NOAEC for developmental effects in rabbits after inhalation exposure was 0.7 mg/L and the LOAEC 2 mg/L; no maternal toxicity was found at dose levels up to 2 mg/L.
Executive summary:

The test substance was investigated for its tertatogenic potential in female rabbits (Chbb) exposed by inhalation for 6 hours/day. Fifteen animals per dose group and control group were used and concentrations were chosen to be 0.2, 0.7, and 2.0 mg/l. Analytically analyzed concentrations were 0.2 ± 0.01, 0.7 ±0.01, and 2.0 ± 0.0.6 mg/l. Two satellite groups, each consisting of five animals, were used for the control group and the highest concentration (2.0 mg/l). Satellite groups were observed for clinical signs, body weight, lethality, different clinical biochemistry parameter, gross pathology, and histopathological investigation of the liver. Maternal animals of the main groups were observed for clinical signs, body weight, lethality, weight of uterus, gross pathology, implants, and corpora lutea. Fetuses were examined for number, weight, sex, weight of placenta, external observations, soft tissue observations including observations of the head, and skeletal observations.

Maternal toxicity was not obseved neither in main groups nor in satellite groups. Observations of fetuses and maternal animals were as follows:

2.0 mg/l:

- significantly reduced weight of fetuses and placenta

- increase in malformations although not statistically significant (primary heart and vessel malformations)

- statistically significant increase in skeletal and visceral variations

0.7 mg/l:

no effects observed

0.2 mg/l:

no effects observed

The highest concentration led to fetal toxicity and a slight teratogenic effect. The NOAEL for maternal animals was >2.0 mg/l (57 -fold higher than the vaild MAK value of 10 ppm) and for fetuses 0.7 mg/l (20 -fold higher than the valid MAK vlaue of 10 ppm).