1,3-dimethylurea

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: full guideline and GLP study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1993

Report date:

1993

Reference 2

Reference Type:

secondary source

Title:

No information

Author:

OECD SIDS

Year:

2005

Bibliographic source:

cited in OECD SIDS 1,3-Dimethylurea (CAS: 96-31-1)

Reference 3

Reference Type:

secondary source

Title:

Initial Submission: Letter from BASF Corporation submitting preliminary results of a Prenatal Toxicity Study with N,N´-Dimethylurea

Author:

TSCATS

Year:

1993

Bibliographic source:

EPA/OTS; Doc #88-930000161

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes (incl. QA statement)

Remarks:

testing laboratory

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

1,3-dimethylurea

EC Number:

202-498-7

EC Name:

1,3-dimethylurea

Cas Number:

96-31-1

Molecular formula:

C3H8N2O

IUPAC Name:

1,3-dimethylurea

Details on test material:

- Name of test substance: N,N'-Dimethylurea
- Test substance No.: 90/88
- CAS No.: 96-31- 1
- Abbreviation used in the laboratory: DMH
- Aggregate state/color: solid/white
- Storage conditions: Room temperature
- Degree of purity: > 96%
- Safety precautions: The usual precautions for handling chemicals.

Test animals

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Karl Thomae, Biberach/Germany
- Age at study initiation: 75-84 days
- Mean weight at study initiation: 232 g
- Housing: singly
- Diet (e.g. ad libitum): standard Kliba 343 diet ad libitum.
- Water (e.g. ad libitum): water ad libitum.
- Acclimation period: at least 5 days

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

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Remarks:

doubly distilled

Details on exposure:

The test substance was administered as aqueous solution to 21-23 pregnant rats per group by gavage in the morning; a control group was dosed with doubly distilled water.
A standard dose volume of 10 ml/kg bw was used. The calculation of the volume adminsitered was based on the individual body weight determined at the beginning of the administration period (day 6 p.c.). Each day, the test substance solutions were freshly prepared shortly before the administration.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analytical determinations of the purity and the homogeneity of the test substance itself were carried out in the analytical laboratories of BASF AG before the beginning of the study (method : chromatography HPLC).
A reanalysis of the test substance for verification of its stability was carried out after the termination of the study.
Analytical verifications of the stability of the test substance solutions over a period of 10 days ( maximum) were carried out before the beginning of the study.
Furthermore, samples of the test substance solutions were sent to the analytical laboratories of BASF AG twice during the study period for verification
of the concentrations. The test substance solutions were analyzed by HPLC.

Details on mating procedure:

25 females/group were mated from about 16:00 hours to about 7:30 hours on the following day. If sperm was detected microscopically in the vaginal smear in the morning, the animals were considered to be fertilized. This day was designated "day 0".

Duration of treatment / exposure:

gestation day 6 to 15

Frequency of treatment:

daily

Doses / concentrations

Remarks:

Doses / Concentrations:
0; 30; 100; 200 mg/kg
Basis:
actual ingested

No. of animals per sex per dose:

20

Control animals:

yes, concurrent vehicle

Details on study design:

Sex: female
Duration of test: until day 20 post coitum

Examinations

Maternal examinations:

The animals were examined for clinical symptoms at least once a day.
Food consumption and body weights were recorded regularly throughout the study period. All animals were weighed on days 0,1,3,6,8,10,13,15,17,and 20 p.c. The state of health of the animals was checked at least once each day.
ORGANS/PARAMETERS EXAMINED AT NECROPSY (MACROSCOPIC AND MICROSCOPIC): on day 20 p.c., all surviving females were sacrificed and assessed by gross pathology. In additon, the following was recorded:
- weight of unopened uterus
- number of corpora lutea
- number and distribution of implantation sites, classified as live fetuses, dead implantations (early resorptions, late resorptions, dead fetuses).
The corrected body weight gain was calculated (terminal body weight on day 20 p.c. minus weight of the unopened uterus minus body weight on day 6 p.c.), as were conception rate, and pre- and postimplantation losses.
The fetuses were dissected from the uterus, sexed, weighed and further investigated for any external, soft tissue and/or skeletal findings. Furthermore, the viability of the fetuses and the condition of the placentae, the umbiical cords, the fetal membranes and fluids were examined.
Individual placental weights were recorded. Half of the fetuses per dam were placed in ethyl alcohol and the others were placed in Bouin´s solution for fixation and further evaluation. Soft tissue examination was performed according to the method described by Barrow and Taylor (J. Morph. 127, 291-306, 1969), skeletal examinations were made under a stereo-microscope after staining according to Dawson's method (Stain Technol 1, 123, 1926).

Statistics:

Dunnett`s t-test for body weight, body weight change, corrected body weight gain, weight of the uterus, weight of fetuses, weight of placentae, corpora lutea, implantations, pre-and postimplantation losses, resorptions, live fetuses.
Fisher´s Exact Test for conception rate, mortality of dams, all fetal findings. Significance levels set at p < 0.05 and p < 0.01.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Details on maternal toxic effects:
200 mg/kg bw/day: clear signs of maternal toxicity were observed as distinctly reduced food consumption of the dams during the treatment period (days 6-15 p.c.; -34%), markedly lower mean body weights of the dams in comparison to the controls, negative mean weight gains on day 6-10 p.c., and diminished corrected mean body weight gains (-37%).
Piloerection on 11 dams during the treatment period about 2-7 hours after the test substance administration.
100 mg/kg bw/day: overt signs of maternal toxicity in form of reduced food consumption during the whole treatment period (days 6-15 p.c.; -21%), lower mean body weights, distinctly impaired mean weight gains on day 6-10 p.c. (-66%), as well as diminished corrected mean body weight gains (-26%). There were no clincal signs of toxicity.
30 mg/kg bw/day: no substance-induced findings on dams.

Effect levels (maternal animals)

Dose descriptor:

NOAEL

Effect level:

30 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Details on embryotoxic / teratogenic effects:
200 mg/kg bw/day: embryo-/fetotoxicity was observed in this group in form of reduced mean placental weights (-13%) and fetal body weights (-8%). The malformations rate was not increased. However, the numbers of fetuses with one soft tissue variation (hydroureter) and with indications of delayed ossification (incomplete ossification or reduced size of sterneba(e)) were increased.
100 mg/kg bw/day: Increased incidence of one fetal soft tissue variation (hydroureter). No teratogenic effects were recorded.
30 mg/kg bw/day: no substance-induced findings on fetuses.

External malformations were recorded for one control fetus (cleft palate) and for one high dose fetus (brachygnathia, cleft palate and aglossia). These or very similar malformations were also present in the historical laboratory control data at a low frequency and were therefore assessed as being of spontaneous origin. Soft tissue examinations revealed malformations of the heart (dilatation of both or one ventricle(s), dextrocardia, septal defects) in all groups except the low dose without dose relationship.
Furthermore, hydrocephaly was found in one low dose fetus, while a unilobular lung occurred in one intermediate and one high dose fetus each. Due to the fact that no statistically significant differences were found between the groups, and no dose-relationship existed, and/or because several of the aforementioned effects (i.e. dextrocardia, hydrocephaly and dilatation of heart ventricles) were also present in the historical laboratory control data at a low incidence, these malformations were regarded as being of spontaneous nature by the authors.
In all groups two soft tissue variations occurred (dilated renal pelvis and hydroureter), attaining statistical significance in the 100 and 200 mg/kg bw/day groups. If compared with the historical control data it is obvious that the increased occurrence of dilated renal pelvis was a sponstaneous effect and not related to treatment with the substance. All relevant values (fetal incidence 27 and 35% in 100 and 200 mg/kg bw/day groups, respectively; litter incidence 80% or 91%) were within the range of biological variation (fetal incidence 7.1 - 66.9%, litter incidence 36.4 - 100%) and the concurrent control values were rather low (fetal incidence 16%, litter incidence 52%). The increase in hydroureters, however, was induced by the test substance with incidences clearly outside the historical control ranges (8.2; 9.4; 19; 27% in control; 30; 100; 200 mg/kg bw/day groups, respectively).

Effect levels (fetuses)

1

Dose descriptor:

NOAEL

Effect level:

30 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: fetotoxicity

2

Dose descriptor:

NOAEL

Effect level:

100 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: embryotoxicity

3

Dose descriptor:

NOAEL

Effect level:

200 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified