N,N-dimethylacetamide

Developmental toxicity / teratogenicity

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

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1989

Report date:

1989

Reference 2

Reference Type:

publication

Title:

Inhalation developmental toxicity in rabbits on dimethylacetamide with cover letter

Author:

BASF Corp.

Year:

1989

Bibliographic source:

TSCATS OTS0535030

Reference 3

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

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

Test material information

Constituent 1

Reference substance name:

N,N-dimethylacetamide

EC Number:

204-826-4

EC Name:

N,N-dimethylacetamide

Cas Number:

127-19-5

Molecular formula:

C4H9NO

IUPAC Name:

N,N-dimethylacetamide

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 or test system 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 / concentrations

Doses / concentrations 1

Dose / conc.:

0.2 mg/L air (analytical)

Remarks:

± 0.01 mg/l (SD). 0.2 mg/l (nominal concentration).

Doses / concentrations 2

Dose / conc.:

0.7 mg/L air (analytical)

Remarks:

± 0.01 mg/l (SD). 0.7 mg/l (nominal concentration).

Doses / concentrations 3

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)

1

Dose descriptor:

NOAEC

Effect level:

2 mg/L air

Based on:

test mat.

Basis for effect level:

body weight and weight gain

clinical signs

mortality

2

Dose descriptor:

NOAEC

Effect level:

2 mg/L air

Based on:

test mat.

Basis for effect level:

dead fetuses

pre and post implantation loss

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: Increased skeletal variations, e.g. sternebrae fused and accessory ribs, both outside historical range, but no statistically significant increase in total skeletal variations. 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:

0.2 mg/L air (analytical)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: increased skeletal variations

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.:

700 mg/m³ 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 teratogenic potential in female Humalayan rabbits exposed by inhalation (study report of BG Chemie, 1989; published by Klimish and Hellwig, 2000). Fifteen animals per dose group and control group were used and exposed to 0.2, 0.7, and 2.0 mg/l (equivalent to 0, 57, 200 or 570 ppm) for 6 hours/day from GD7-19 and sacrified at GD29. Two satellite groups exposed to 0 or 2.0 mg/L with 5 animals per group were observed for clinical signs, lethality and body weight until GD20 and clinical chemistry, gross pathology and histopathological investigation of the liver were performed. 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.

Fetotoxic effects were caused at a concentration of 0.7 mg/L (increased skeletal variations, e.g. fused sternebrae and accessory ribs), but there was no statistically significant increase in total skeletal variations. At 2.0 mg/L fetotoxic effects (e.g., significantly decreased fetal and placental weights, increase in soft tissue and skeletal variations) and also signs of a weak teratogenic effect expressed as a marginal, statistically not significant increase in soft tissue malformations (regarding the heart and great vessels) were observed. No compound-related effects were observed in the fetuses after exposure to 0.2 mg/l.
Thus, the highest concentration tested under these conditions (2.0 mg/1) was found to be a no-observable-adverse-effectlevel (NOAEL) for the maternal Himalayan rabbit, whereas 0.2 mg/L was defined as the NOAEL for the developing organism.