Urea

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

No standard studies are available. It is considered extremely unlikely that occupational, primary or secondary exposure to urea will result in any effects on fertility as the levels of exposure will be insignificant compared to those present in the body as a result of protein catabolism.

No indications for adverse effects on the reproductive organs were derived from the repeated dose toxicity or carcinogenicity studies in various species after oral (rats, mice), dermal (rats) and subcutaneous route (dogs).

Finally, a supporting study demonstrated that raising concentrations of crude protein (CP) in pasture in spring by the frequent application of urea fertiliser did not affect ovarian follicular dynamics, luteal function, onset of oestrus and reproductive performance of dairy cows under farming conditions.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Large quantities of urea are formed naturally in the human body as a consequence of normal protein catabolism. Urea is shown to be essentially without toxicity in the available studies and no effects (organ weight, gross pathology, histopathology) were observed on the reproductive organs of rats and mice exposed to urea at very high dietary levels for 12 months (Fleischman et al, 1980). The level of any primary, occupational or secondary exposure to urea is likely to be insignificant compared to the quantities (20-50 g/day) produced by normal metabolism and present at high concentrations in the blood. It is therefore considered that urea is very unlikely to be a reproductive toxin and testing cannot be justified scientifically.

No indications for adverse effects on the reproductive organs were derived from the repeated dose toxicity or carcinogenicity studies in various species. The oral repeated dose toxicity & carcinogenicity studies (12 -month studies in F-344 rats and C57BL/6 mice) with urea in the diet at concentrations of 4500, 9000 or 45000 did not reveal any treatment-related effects on the reproductive organs. Using default conversion factors, the highest dose level of 45000 ppm in the diet corresponded to approximately 2250 mg/kg bw/d in the rat and 6750 mg/kg bw/d in the mouse (Fleischman et al., 1980). The 4 -week  and 25 -week dermal toxicity studies at 10, 20 and 40% urea concentrations in Wistar rats also did not reveal any treatment related effects in the reproductive organs (Sato et al, 1977). Finally, the studies in unilaterally nephrectomised dogs injected subcutaneously with 10% urea solution (3000-4000 mg/kg bw) every 8 hours over a period of 45 days also indicated that urea was of very low toxicity following repeated administration (Balestri et al, 1971).

A supporting study was available to assess if raising concentrations of crude protein (CP) in pasture in spring by the frequent application of urea fertiliser would affect ovarian follicular dynamics, luteal function, onset of oestrus and reproductive performance of dairy cows under farming conditions in New Zealand (Ordóñez et al., 2007). Spring-calved dairy cows were grazed for 101 days in paddocks that were either not fertilised (Control; n=20) during the course of the study, or were fertilised with 40–50 kg nitrogen (N)/ha every 4–6 weeks (High-N; n=20). Similar generous pasture allowances were offered to both groups. Concentrations of CP in pasture, urea in serum and progesterone in milk were measured. Ovarian follicular and luteal dynamics were determined using ultrasonography. Oestrous behaviour and the number, time and outcome of inseminations were also recorded. Mean concentrations of CP in pasture and urea in serum was higher in the High-N than the Control group (25.2 vs 21.6 and 8.3 vs 5.4 mmol/L for CP and urea, respectively; p<0.001). Intervals between calving and first oestrus, first insemination and conception, the time of first emergence of a dominant follicle, milk progesterone concentration, and the diameter of the corpus luteum (CL) in the first luteal phase did not differ significantly between groups. The interval from calving to first ovulation tended (p=0.10) to be lower and the diameter of the dominant follicle of the oestrous cycle at which cows conceived was greater (p=0.02) in Control than High-N cows. In conclusion, the use of large amounts of urea fertiliser during spring and the consequent increases in concentrations of CP in pasture and urea in serum did not negatively affect any of the parameters of reproductive performance of pasture-fed dairy cows that were assessed in this study.

Effects on developmental toxicity

Description of key information

In a key prenatal developmental toxicity study, urea was administered orally to female pregnant rats by gavage at dose levels of 100, 300 or 1000 mg/kg bw/day from the 6th to 20th day of pregnancy. In the dams, there were no item-related effects on the maternal and reproductive parameters. In the fetuses, there was also no test item-related influence on the prenatal fetal development and no malformations nor variations were noted during the macroscopic, skeletal and soft tissue examinations. In conclusion, the NOAEL was above 1000 mg Urea/kg bw/day for maternal developmental and foetal toxicity as well as for teratogenicity. It is considered extremely unlikely that occupational, primary or secondary exposure to urea will result in developmental toxicity as the levels of exposure will be insignificant compared to those present in the maternal and foetal circulation as a result of protein catabolism.

Link to relevant study records

Reference

Reference 1

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016

Reliability:

1 (reliable without restriction)

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.31 (Prenatal Developmental Toxicity Study)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: 100116B3 obtained from Borealis Agrolinz Melamine GmbH
- Expiration date of the lot/batch: January 10, 2017
- Purity test date: 11 July 2016

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: At +10°C to +25°C, dry and protected from light.
- Stability under test conditions: expiry date covered till January 10, 2017
- Solubility and stability of the test substance in the solvent/vehicle: stability is tested in the study
- Reactivity of the test substance with the solvent/vehicle of the cell culture medium: no

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing: no
- Preliminary purification step (if any): no
- Final dilution of a dissolved solid, stock liquid or gel: dilution of solid in tap water
- Final preparation of a solid: dilution in tap water

FORM AS APPLIED IN THE TEST (if different from that of starting material): dilution in tap water.

Species:

rat

Strain:

other: CD® / Crl:CD(SD)

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Research Models and Services, Germany GmbH, Sandhofer Weg 7, 97633 Sulzfeld, Germany
- Age at day 0 of pregnancy: 59 days
- Weight at day 0 of pregnancy: 199.8 - 251.0 g
- Fasting period before study: Not applicable.
- Housing: Except during the mating period, the dams were kept singly in MAKROLON cages (type III plus) with a basal surface of approx. 39 cm x 23 cm and a height of approx. 18 cm. Granulated textured wood released for animal bedding (Granulat A2, J. Brandenburg, 49424 Goldenstedt/Arkeburg, Germany) was used as bedding material in the cages. The cages were cleaned and changed once a week. The animals received one piece of wood (certified for animal use) to gnaw on once weekly at change of the cages. Octagon-shaped red-tinted huts (polycarbonate) were placed in the cages to offer the animals a resting and hiding place.
- Diet (e.g. ad libitum): Commercial diet ssniff® R/Z V1324 (ssniff Spezialdiäten GmbH, 59494 Soest, Germany served as food. This food was offered daily ad libitum.
- Water (e.g. ad libitum): Drinking water (in drinking bottles) was offered ad libitum.
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22°C ± 3°C (maximum range)
- Humidity (%):55% ± 15% (maximum range)
- Air changes (per hr): between fifteen to twenty air changes per hour
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From (Start of mating) August 15, 2016 To: September 08, 2016

Route of administration:

oral: gavage

Vehicle:

other: tap water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The test item formulations were freshly prepared every day.
The test item was dissolved in the vehicle to the appropriate concentration and was administered orally at a constant volume (5 mL/kg bw/day ) once daily from the 6th to the 20th day of gestation.
The amount of the test item was daily adjusted to the current body weight of the animal. The control animals received the vehicle at the same administration volume daily in the same way.
The male rats for mating remained untreated.

VEHICLE
- Justification for use and choice of vehicle (if other than water): tap water

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

For the analysis of the test item-vehicle formulations, samples of approximately 4 mL were taken (divided into 2 aliquots of 2 mL) at the following times and stored at -20°C or colder until analysis at LPT.
1) At start of dosing:
Analysis of stability and concentration:
Immediately after preparation of the formulations as well as after 8 and 24 hours storage of the test item preparations at room temperature.
3 samples/dose level group; groups 2 - 4
Number of samples: 3 x 3 = 9
Sampling date: August 23, 2016

2) At the end of the dosing period (at a time when the majority of animals was dosed):
Analysis of concentration:
During treatment with the test item always before administration to the last animal of the dose level group.
1 sample/dose level group; groups 2 – 4
Number of samples: 1 x 3 = 3
Sampling date: September 07, 2016

Sum of all samples: 12

The samples were labelled with the study number, species, type of sample, aliquot number, concentration, sampling time and date.
The analytical method (HPLC-UV) was validated by LPT. The following parameters were determined:
- Linearity
- Accuracy
- Precision
- Sensitivity
- Specifity
- Stability.
The investigation of the validation parameters (see above) indicated that the method employed is suitable for the determination of Urea in test item formulations.
The results of the test item formulation analysis are as follows:
-Concentration and stability before administration to the last animal on test day 6: 101.0% - 105.8% of nominal concentration
-Concentration before administration to the last animal on test day 21: 102.4% - 103.6% of nominal concentration.

The measured actual concentrations of the test item in the test item vehicle mixtures were between 102.4% and 105.8% of the nominal concentrations, indicating correctly prepared formulations.

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 1/1
- Length of cohabitation: 1 male and 1 female animal were placed together in one cage during the dark period. Each morning a vaginal smear was taken to check for the presence of sperm.
- Further matings after two unsuccessful attempts: yes. If findings were negative (no sperm in vaginal smear), mating was repeated with the same partner. This procedure was repeated until enough pregnant dams were available for all groups. Rats which did not become pregnant were excluded from the analysis of the results and replaced by other animals. A post-mortem negative staining according to SALEWSKI was carried out in the replaced animals in order to confirm the non-pregnancy status.
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: sperm in vaginal smear referred to as day 0 of pregnancy

Duration of treatment / exposure:

Day 6 to 20 of gestation

Frequency of treatment:

once daily

Duration of test:

22 days:
- 5 adaptation days
- 1 mating day
- 15 administration days from gestation days 6 to 20
- Laparotomy on gestation day 21

Dose / conc.:

0 mg/kg bw/day (actual dose received)

Remarks:

based on test item

Dose / conc.:

100 mg/kg bw/day (actual dose received)

Remarks:

based on test item

Dose / conc.:

300 mg/kg bw/day (actual dose received)

Remarks:

based on test item

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

Remarks:

based on test item

No. of animals per sex per dose:

25 pregnant females per group
20 litters per dose group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale in rats from literature:
Urea was shown to be of low toxicity following chronic administration to the rat. In a 12-month carcinogenicity screening assay, F344 rats (50/sex/group) were exposed to urea in the diet at concentrations of 4500, 9000 or 45000 ppm for 12 months. Five animals/sex/group were sacrificed at the end of the 365-day exposure for histopathology; interim deaths were similarly investigated. All remaining animals were sacrificed after the 4-month recovery period and investigated histopathologically. There were no signs of toxicity. Survival and body weights were unaffected by treatment. Gross and microscopic pathology did not reveal any treatment-related effects. No effects were observed at the highest dose level (4.5% in the diet). It is therefore concluded, based on the results of this study, that urea is of very low chronic toxicity (Fleischman et al., 1980).
Limited information on urea was available from an older non-guideline study in rats. Female rats (6/group) were gavaged with urea at doses equivalent to 500 mg/kg b.w./day during gestation for 14 days. Pups were necropsied at 48 hours after delivery and assessed for teratogenicity and renal effects. No hypertrophy or other kidney changes were detected in the pups, nor were there any teratogenic effects noted. Pup weight at birth was slightly lower in the treated group (5.15 g) compared to controls (5.93 g), but pups from treated dams gained more weight over the study period (Seipelt et al., 1969).
References:
-Fleischman, R.W., Baker, J.R., Hagopian, M., Wade, G.G., Hayden, D.W., Smith, E.R., Weisburger, J.H. and Weisburger, E.K.: Carcinogenesis bioassay of acetamide, hexanamide, adipamide, urea and P-tolylurea in mice and rats. Journal of Environmental Pathology and Toxicology 3(5-6): 149-70, 1980.
-Seipelt, H., Zoellner, K., Hilgenfeld, E. and Grossmann, H.: Studies on kidneys of newborn rats after chronic urea administration to the mother. Zeitschrift fur Urologie und Nephrologie 62(8): 623-7, 1969.
Based on the outcome of these two studies, it was decided to test up to the highest dose of 1000 mg/kg bw (limit dose) in a dose range finding study for a prenatal developmental toxicity. The results of this dose-range-finding study (LPT study no. 33779) showed a slightly reduced body weight for the dams of the high dose group (1000 mg/kg bw), but no changes were noted in behaviour or external appearance and no noteworthy differences in food consumption were noted. Reproduction data per group and per dam and fetal/placental weights did not show any differences between groups.
Together with the fact that no external malformations or variations were noted for the fetuses, dose levels of 100, 300 or 1000 mg Urea/kg bw/day were selected in agreement with the Sponsor for the present main study (LPT study no. 33780).

- Rationale for animal assignment (if not random):
Four (4) groups of pregnant rats were established, each obtained from matings which were carried out on a daily basis. Vaginal lavages were taken each morning. Day 0 of pregnancy was the day on which sperm was found in the vaginal lavage. When positive, the animals were assigned to the test groups by mating day using a Provantis®-generated randomization based on the body weight of the animals.

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily (for any signs of behavioural changes, reaction to treatment, or illness.)
Immediately after administration, any signs of illness or reaction to treatment were recorded. In case of changes, the animals were observed until the symptoms disappeared.
In addition, animals were checked regularly throughout the working day from 7.00 a.m. to 3.45 p.m.
On Saturdays and Sundays, the animals were checked regularly starting from 7.00 a.m. to 11.00 a.m. with a final check performed at approximately 3.30 p.m.
Dated and signed records of appearance, change and disappearance of clinical signs were maintained on clinical history sheets for individual animals.
Further checks were made early in the morning and again in the afternoon of each working day to look for dead or moribund animals. This allowed post mortem examinations to be carried out during the working period of that day. On Saturdays and Sundays, a similar procedure was followed except that the final check was carried out at approximately midday.
Animals showing signs of abortion or premature delivery would have been sacrificed on the same day. Fetuses obtained this way were examined for abnormal development, whenever possible. No abortion occurred in the study.

DETAILED CLINICAL OBSERVATIONS: No
- Time schedule: /

BODY WEIGHT: Yes
- Time schedule for examinations:
The weight of each rat was recorded on day 0 of gestation (the day of detection of a positive mating sign), followed by daily weightings - always at the same time of the day.
The body weight gain was calculated in intervals (i.e. day 0-3, 3-6, 6-9, 9-12, 12-15, 15-18 and 18-21), for the whole study (gestation day 0 - 21) and for the period after the start of dosing (gestation day 6 to gestation day 21). Furthermore the carcass weight and the net weight change from day 6 are given.
Carcass weight = Terminal body weight - uterine weight
Net weight change from day 6 = Carcass weight - body weight on day 6
These measurements were also used for calculating the daily amount of test item to be administered.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
The quantity of food consumed by each rat was recorded daily. Food intake per rat (g/rat/day) was calculated using the total amount of food given to and left by each rat in each group on completion of a treatment day.
The relative food consumption (g/kg bw/day) was calculated using the following formula:
Daily food consumption [g/kg bw/day]= Total food intake in g /Body weight in kg
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No; not applicable (gavage)

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No
- Time schedule for examinations: Daily monitoring by visual appraisal of the drinking water bottles was maintained throughout the study. Dehydration of the animals was avoided.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 21 (CO2 narcosis)
- Organs examined: ovaries, uterus, internal organs and placenta.
The ovaries and the uteri of the dams were removed; the gravid uteri (in toto) were weighed. In order to check for possible drug effects, a dissection with macroscopic examination of the internal organs and placentae of the dams was carried out on the day of sacrifice or on the day on which the animals were found dead. In case of macroscopical findings, the affected maternal tissues were preserved in 7% buffered formalin for possible future histopathological examinations.

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
- Other: live/dead fetuses; sex ratio of fetuses; macroscopic inspection of the placentae for example for focal indurations or abnormal appearance; placentae weights and fetuses weights

Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: No

Statistics:

The statistical evaluation of the parametrical values was done by Provantis using the following settings:
Homogeneity of variances and normality of distribution were tested using the BARTLETT’s and SHAPIRO-WILKS test. In case of heterogeneity and/or non-normality of distribution, stepwise transformation of the values into logarithmic or rank values was performed prior to ANOVA. If the ANOVA yielded a significant effect (p ≤ 0.05), intergroup comparisons with the control group were made by the DUNNETT’s test (p ≤ 0.01 and p ≤ 0.05).

The statistical evaluation of non-parametrical values was done using the FISHER or Chi2 test:
FISHERs exact test, n < 100; (p ≤ 0.05 and p ≤ 0.01)
or
Chi2 test, n ≤ 0.01 (p ≤ 0.05 and p ≤ 0.01)

The respective calculations for the FISHER and Chi2 test were performed using Provantis (maternal macroscopic findings at necropsy or findings during the external or internal macroscopic examination of the fetuses) or an internal computer program (e.g. findings during the fetal skeletal or soft tissue examination).
Note:
The statistical evaluation of the pre- and post-implantation index (per group) using the number of corpora lutea, implantation sites and/ or fetuses per group was done using StatXact 4.0.1 software.

Indices:

Group indices:
Pre-implantation loss [%] = [Corpora lutea (per group) - Implantations (per group)/ Corpora lutea (per group)]x 100
Post-implantation loss [%] = [Implantations (per group) - living fetuses (per group)/ Implantations (per group)] x 100

Mean indices per litter:
Pre-implantation loss [%] = sum of pre-implantation losses per litter in a group [%]/ number of litters in a group
Post-implantation loss [%] = sum of post-implantation losses per litter in a group [%]/ number of litters in a group

Historical control data:

Summarized results of the 59 last embryotoxicity studies in Sprague-Dawley rats (Charles River Deutschland GmbH) performed at CRO in the years 2000 to July 2015

Clinical signs:

no effects observed

Description (incidence and severity):

No changes in behaviour, the external appearance and the faeces were noted in the control group and in the treatment groups.

Mortality:

no mortality observed

Description (incidence):

No premature death was noted in the control group and in the test item-treated groups.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No test item-related changes in body weight in comparison to the control group were noted for the dams of the treatment groups.
The values of body weight gain showed no differences between the control group and the test item-treated groups for the period after the start of treatment (gestation days 6 to 21).
A marginal but statistically significant difference (at p ≤ 0.05) compared to the control was noted for the body weight gain of the high dose group between gestation days 0 to 3. This finding is considered to be incidental due to its occurrence before start of the treatment period on gestation day 6.
No test item-related differences for the absolute body weight gain and the net body weight gain (without gravid uterus) between the control group and the dams of the treatment groups were noted between gestation day 6 and gestation day 21.
The marginally decreased net body weight gain (without gravid uterus) in comparison to the control (statistically not significant) noted for the dams of the intermediate dose group (minus 15.3%) and the high dose group (minus 18.5%) is within the range of normal variability and not considered to be test item-related or adverse.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

No test item-related differences in food consumption were noted between the dams of the control group and the dams treated with 100, 300 or 1000 mg Urea/kg bw/day.
An incidental increase in relative food consumption was noted for the low dose group on gestation days 3 to 4, before start of the treatment period on gestation day 6, being statistically significant (at p ≤ 0.01) compared to the control.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

no effects observed

Description (incidence and severity):

No test item-related changes in drinking water consumption were noted between the dams of the control group and the dams of the treatment groups by visual appraisal.

Ophthalmological findings:

no effects observed

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Description (incidence and severity):

No test item-related differences were noted between the gravid uterus weight and carcass weight of the control dams and the dams of the treatment groups.
The placental weights showed no test item-related differences between the control group and the treatment groups.
At 300 mg Urea/kg bw/day, a slight but statistically significant decrease (at p ≤ 0.05) was noted for the mean placental weights (mean: 0.49 g) compared to the incidentally high control values (mean: 0.55 g). This finding is considered as not test item-related as the values were within the range of LPT background data (0.48 - 0.53 g). Above all, no corresponding findings were noted for the high dose group (1000 mg Urea/kg bw/day).

Gross pathological findings:

no effects observed

Description (incidence and severity):

Macroscopic inspection of the internal organs and tissues of the dams during laparotomy revealed no test item-related changes in the dams of the control and the dams of the treatment groups.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Description (incidence and severity):

In case of macroscopical findings, the affected maternal tissues were preserved in 7% buffered formalin for possible future histopathological examinations. Macroscopic inspection of the internal organs and tissues of the dams during laparotomy revealed no test item-related changes in the dams of the control and the dams of the treatment groups.

Histopathological findings: neoplastic:

not examined

Number of abortions:

no effects observed

Description (incidence and severity):

No abortion occurred in the study.

Pre- and post-implantation loss:

no effects observed

Description (incidence and severity):

No test item-related influence on the reproductive parameters (number of implantation sites, fetuses, resorptions and the index of post-implantation) were noted between the dams of the control group and the dams of the treatment groups.
No dams with total implantation loss were seen in the control and treatment groups.

Total litter losses by resorption:

no effects observed

Description (incidence and severity):

No test item-related influence on the reproductive parameters (number of implantation sites, fetuses, resorptions and the index of post-implantation) were noted between the dams of the control group and the dams of the treatment groups.

Early or late resorptions:

no effects observed

Description (incidence and severity):

No test item-related influence on the reproductive parameters (number of implantation sites, fetuses, resorptions and the index of post-implantation) were noted between the dams of the control group and the dams of the treatment groups.

Dead fetuses:

no effects observed

Description (incidence and severity):

No abortion occurred in the study and there were no dams without viable fetuses in the control and treatment groups.

Changes in pregnancy duration:

not examined

Description (incidence and severity):

Migrated Data from removed field(s)
Field "Effects on pregnancy duration" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsMaternalAnimals.MaternalDevelopmentalToxicity.EffectsOnPregnancyDuration): not examined
Field "Description (incidence and severity)" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsMaternalAnimals.MaternalDevelopmentalToxicity.DescriptionIncidenceAndSeverityEffectsOnPregnancyDuration): OECD 414. There were no dams with early delivery observed in the control and treatment groups.

Changes in number of pregnant:

effects observed, non-treatment-related

Description (incidence and severity):

One animal in the 100 mg/kg group was not pregant; no other non-pregancies were observed.

Key result

Dose descriptor:

NOAEL

Remarks:

maternal toxicity

Effect level:

> 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Basis for effect level:

other:

Remarks on result:

not determinable due to absence of adverse toxic effects

Fetal body weight changes:

no effects observed

Description (incidence and severity):

The fetal weights showed no test item-related differences between the control group and the treatment groups.
Fetuses were considered as runts if their weight was less than 70% of the mean litter weight. No runts were noted at 100, 300 or 1000 mg Urea/kg bw/day.
One runt was noted in the control group (no. 13-13). This incidence is within the normal range of variation.

Migrated Data from removed field(s)
Field "Fetal/pup body weight changes" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsFetuses.FetalPupBodyWeightChanges): no effects observed
Field "Description (incidence and severity)" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsFetuses.DescriptionIncidenceAndSeverityFetalPupBodyWeightChanges): The fetal weights showed no test item-related differences between the control group and the treatment groups.
Fetuses were considered as runts if their weight was less than 70% of the mean litter weight. No runts were noted at 100, 300 or 1000 mg Urea/kg bw/day.
One runt was noted in the control group (no. 13-13). This incidence is within the normal range of variation.

Reduction in number of live offspring:

no effects observed

Description (incidence and severity):

No dead fetus was noted in the control group and in the test item treated groups (100, 300 or 1000 mg Urea/kg bw/day).

Changes in sex ratio:

no effects observed

Description (incidence and severity):

No test item-related differences between the ratio of male and female fetuses (range: 0.90 - 1.12) were noted between the control group and the treatment groups.

Changes in litter size and weights:

no effects observed

Changes in postnatal survival:

not examined

Description (incidence and severity):

Not applicable to OECD 414 study design.

External malformations:

no effects observed

Description (incidence and severity):

No macroscopically visible external alterations (malformations or variations) were noted for the fetuses of the treatment groups (100, 300 or 1000 mg Urea/kg bw/day) during the macroscopic inspection at laparotomy.

Skeletal malformations:

no effects observed

Description (incidence and severity):

No skeletal malformations were noted for the fetuses of the control group and the test item-treated groups (100, 300 or 1000 mg Urea/kg bw/day) during the skeletal examination according to DAWSON.

Visceral malformations:

effects observed, non-treatment-related

Description (incidence and severity):

No malformations were noted for the fetuses of the control group and the fetuses of the treatment groups (100, 300 or 1000 mg Urea/kg bw/day) during the soft tissue examination according to WILSON.
During the examination of the organs and tissues according to WILSON variations were noted for the cerebrum ((subdural) haemorrhage), the cerebral ventricle (dilatation of the 4th ventricle), the kidneys (uni- or bilateral dilatation of the renal pelvis, reduced in size or malpositioned) and the liver (haemorrhagic focus/foci).
No test item-related differences in the incidences of the observed variations were noted between the control group and the treatment groups.
The slightly but significantly increased incidence of total soft tissue variations (at p ≤ 0.05 compared to the control) noted for the intermediate dose group (300 mg Urea/kg bw/day) is considered to be not test item-related as no dose-response relationship was noted and the incidence was within the range of LPT background data.

Description (incidence and severity):

The macroscopic inspection of the organs and tissues for gross alterations at laparotomy revealed no malformations or variations for the fetuses of the control group and the fetuses of the treatment groups (100, 300 or 1000 mg Urea/kg bw/day).
Skeletal variations were noted for the ribs (wavy) and the sternebrae (bipartite, misaligned to a slight degree or misshapen).
No test item-related increase in the incidence of the observed skeletal variations in comparison to the control group was noted for the fetuses of the treatment groups (100, 300 or 1000 mg Urea/kg bw/day).
Retardations (delayed ossifications) were related to the skull (incomplete ossification of frontal, parietal and/or interparietal areas), the hyoid (unossified), the sternum (sternebra(e) incompletely ossified, reduced in size or unossified), the thoracic vertebral bodies (bipartite or dumbbell-shaped), the sacral vertebral bodies (unossified), the caudal vertebral bodies (no or only one body ossified), the os pubis and the os ischii (in-completely ossified or unossified) and the metacarpalia and metatarsalia (absence of ossification in metacarpalia 2 to 5 and metatarsalia 2 to 5).
No test item-related increase in the incidence of skeletal retardations at 100, 300 or 1000 mg Urea/kg bw/day was noted during skeletal examination according to DAWSON.
A thoracic cavity filled with blood was noted for one fetus each of the control group and the low dose level group and two fetuses of the high dose group. These observations are a preparation induced artefact and not considered as test item-related.

Details on embryotoxic / teratogenic effects:

Laparotomy revealed no dead fetuses or runts at any tested dose level (100, 300 or 1000 mg Urea/kg bw/day).
No malformations were noted during external / internal macroscopic inspection at laparotomy, skeletal examination (according to DAWSON) or soft tissue examination (according to WILSON).
No test-item related variations were noted in the fetuses during external / internal macroscopic inspection at laparotomy or soft tissue examination (according to WILSON) at any tested dose level. Skeletal examination (according to DAWSON) revealed no test item-related variations or retardations.
All further prenatal changes noted are without any biological relevance.

Key result

Dose descriptor:

NOAEL

Effect level:

> 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other:

Remarks on result:

not determinable due to absence of adverse toxic effects

Key result

Developmental effects observed:

no

Table1. Reproductive data of the dams

Parameter		Group 1 Control (n=20)	Group 2 100 mg/kg (n=20)	Group 3 300 mg/kg (n=20)	Group 4 1000 mg/kg (n=20)
Corpora lutea	total mean per dam	294 14.7	292 14.6	287 14.4	291 14.6
Implantation sites	total mean per dam	285 14.3	290 14.5	281 14.1	289 14.5
Resorptions	total mean per dam	14 0.7	10 0.5	5 0.3	18 0.9
Early resorptions	total mean per dam	13 0.7	9 0.5	3 0.2	17 0.9
Late resorptions	total mean per dam	1 0.1	1 0.1	2 0.1	1 0.1
Live fetuses	total mean per dam	271 13.6	280 14.0	276 13.8	271 13.6
Dead fetuses	total	0	0	0	0
Pre-implantation loss [%]	per group ##1 mean per dam	3.1 2.9	0.7 0.6	2.1 2.0	0.7 0.9
Post-implantation loss [%]	per group ##2 mean per dam	4.9 5.1	3.4 3.3	1.8 1.6	6.2 6.2

Statistical analyses were performed for the mean values per dam using an ANOVA/DUNNETT test.

##1: The statistical comparison of the pre-implantation loss per group was done by comparing the values of implantation sites/corpora lutea of the test group with the ratio of implantation sites/corpora lutea of the control group using the Chi²test (*/**: p ≤ 0.05/p ≤ 0.01).

##2: The statistical comparison of the post-implantation loss per group was done by comparing the values of live fetuses/implantation sites of the test group with the ratio of fetuses/implantation sites of the control group using the Chi²test (*/**: p ≤ 0.05/p ≤ 0.01).

Conclusions:

In this prenatal developmental toxicity study, the test item Urea was administered orally to female rats at dose levels of 100, 300 or 1000 mg/kg bw/day from the 6th to 20th day of pregnancy.
Under the present test conditions, the no-observed-adverse-effect level (NOAEL) was above 1000 mg Urea/kg bw/day for the dams.
The no-observed-adverse-effect level (NOAEL) for the fetal organism was also above 1000 mg Urea/kg bw/day.
No test item-related malformation was noted at any of the test item treated groups. There was no test item-related increase in the incidence of fetal external / internal, skeletal or soft tissue variations or skeletal retardations at any tested dose level.
In conclusion, no embryotoxic properties of the test item were noted during external / internal, skeletal and soft tissue examination up to the highest tested dose of 1000 mg Urea/kg bw/day by oral administration. Under the conditions of the study, Urea did not show any teratogenic potential.

Executive summary:

In this prenatal developmental toxicity study, the test item Urea was administered orally to female  pregnant CD® / Crl:CD(SD) rats by gavage at dose levels of 100, 300 or 1000 mg/kg bw/day from the 6th to 20th day of pregnancy. Tap water was used as vehicle and the administration volume was 5 mL/kg bw/day. The measured actual concentrations of the test item in the test item vehicle mixtures were between 101.0% and 105.8% of the nominal concentrations, indicating correctly prepared formulations. On gestation day 21, the dams were laparotomised and examined for implantation sites, resorptions in the uterus and for the condition of the fetuses.On gestation day 21, the dams were laparotomised and examined for implantation sites, resorptions in the uterus and for the condition of the fetuses.

Examination of the dams:

No premature death was noted in the control group and in the treatment groups. No changes were noted in behaviour, the external appearance or the faeces.

No test item-related differences in body weight, body weight gain and food consumption were noted between the control group and the treatment groups.

The visual appraisal of the drinking water consumption revealed no test item-related influence at any tested dose level.

No test item-related changes were noted during the macroscopic inspection nor for the gravid uterus or carcass weights of the dams at necropsy.

No test item-related influence was noted on the reproductive parameters (number of implantation sites, resorptions and fetuses).

Examination of the fetuses:

No dead fetuses were noted in any of the test groups. No test item-related influence was detected on the prenatal fetal development with respect to the number of resorptions, number of live fetuses, fetal and placental weights, the values calculated for the post-implantation loss and the sex distribution of fetuses.

No malformations nor variations were noted during the macroscopic examinations at laparotomy (external inspection and inspection of the organs and tissues for gross lesions), the skeletal examination according to DAWSON and the soft tissue examination according to WILSON.

Conclusions
The no-observed-adverse-effect level (NOAEL) was above 1000 mg Urea/kg bw/day for the dams.

The no-observed-adverse-effect level (NOAEL) for the fetal organism was also above 1000 mg Urea/kg bw/day.

No embryotoxic properties of the test item were noted during external / internal, skeletal and soft tissue examination up to the highest tested dose of 1000 mg Urea/kg bw/day by oral administration. Under the conditions of the study, Urea did not show any teratogenic potential.

Reference 2

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Remarks:

Dose range finding study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method B.31 (Prenatal Developmental Toxicity Study)

Deviations:

no

Principles of method if other than guideline:

As the study is a dose range finding study, only 3 females/group were used and 2 litters/group were evaluated. For evaluation of malformations and variations, only external examenination took place.

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: 100116B3 obtained from Borealis Agrolinz Melamine GmbH
- Expiration date of the lot/batch: January 10, 2017
- Purity test date: 11 July 2016

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: At +10°C to +25°C, dry and protected from light.
- Stability under test conditions: expiry date covered till January 10, 2017
- Solubility and stability of the test substance in the solvent/vehicle: stability is tested in the OECD 414 study.
- Reactivity of the test substance with the solvent/vehicle of the cell culture medium: no.

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing: no
- Preliminary purification step (if any): no
- Final dilution of a dissolved solid, stock liquid or gel: dilution of solid in tap water.
- Final preparation of a solid: dilution in tap water.

FORM AS APPLIED IN THE TEST (if different from that of starting material): dilution in tap water.

Species:

rat

Strain:

other: CD® / Crl:CD(SD)

Route of administration:

oral: gavage

Vehicle:

other: tap water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The test item formulations were freshly prepared every day.
The test item was dissolved in the vehicle to the appropriate concentration and was administered orally at a constant volume (5 mL/kg bw/day ) once daily from the 6th to the 20th day of gestation.
The amount of the test item was daily adjusted to the current body weight of the animal. The control animals received the vehicle at the same administration volume daily in the same way.
The male rats for mating remained untreated.

VEHICLE
- Justification for use and choice of vehicle (if other than water): tap water

Analytical verification of doses or concentrations:

yes

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 1/1
- Length of cohabitation: The mating procedure was repeated until sufficient pregnant rats were available for all groups.
- Further matings after two unsuccessful attempts: yes. If findings were negative (no sperm in vaginal smear), mating was repeated with the same partner, until sufficient pregnant rats were available for all groups.
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: sperm in vaginal smear referred to as day 0 of pregnancy

Duration of treatment / exposure:

from gestation days 6 to 20

Frequency of treatment:

once daily

Duration of test:

23 days:
-6 adaptation days
-1 mating day
-15 administration days from gestation days 6 to 20
- Laparotomy on gestation day 21

Dose / conc.:

0 mg/kg bw/day (actual dose received)

Remarks:

based on test item100% nominal

Dose / conc.:

100 mg/kg bw/day (actual dose received)

Remarks:

based on test item 100% nominal

Dose / conc.:

300 mg/kg bw/day (actual dose received)

Remarks:

based on test item 100% nominal

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

Remarks:

based on test item 100% nominal

No. of animals per sex per dose:

3

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale in rats from literature:
Urea was shown to be of low toxicity following chronic administration to the rat. In a 12-month carcinogenicity screening assay, F344 rats (50/sex/group) were exposed to urea in the diet at concentrations of 4500, 9000 or 45000 ppm for 12 months. Five ani-mals/sex/group were sacrificed at the end of the 365-day exposure for histopathology; interim deaths were similarly investigated. All remaining animals were sacrificed after the 4-month recovery period and investigated histopathologically. There were no signs of toxicity. Survival and body weights were unaffected by treatment. Gross and microscopic pathology did not reveal any treatment-related effects. No effects were observed at the highest dose level (4.5% in the diet). It is therefore concluded, based on the results of this study, that urea is of very low chronic toxicity (Fleischman et al., 1980).
Limited information on urea was available from an older non-guideline study in rats. Female rats (6/group) were gavaged with urea at doses equivalent to 500 mg/kg b.w./day during gestation for 14 days. Pups were necropsied at 48 hours after delivery and assessed for teratogenicity and renal effects. No hypertrophy or other kidney changes were detected in the pups, nor were there any teratogenic effects noted. Pup weight at birth was slightly lower in the treated group (5.15 g) compared to controls (5.93 g), but pups from treated dams gained more weight over the study period (Seipelt et al., 1969).
Based on these two studies, it is proposed to test up to highest dose of 1000 mg/kg b.w. (limit dose) in the dose-range-finding study.
References:
-Fleischman, R.W., Baker, J.R., Hagopian, M., Wade, G.G., Hayden, D.W., Smith, E.R., Weisburger, J.H. and Weisburger, E.K.: Carcinogenesis bioassay of acetamide, hexanamide, adipamide, urea and P-tolylurea in mice and rats. Journal of Environmental Pathology and Toxicology 3(5-6): 149-70, 1980.
-Seipelt, H., Zoellner, K., Hilgenfeld, E. and Grossmann, H.: Studies on kidneys of newborn rats after chronic urea administration to the mother. Zeitschrift fur Urologie und Nephrologie 62(8): 623-7, 1969.

- Rationale for animal assignment (if not random):
Four (4) groups of pregnant rats were established, each obtained from matings which were carried out on a daily basis. Vaginal lavages were taken each morning. Day 0 of pregnancy was the day on which sperm was found in the vaginal lavage. When positive, the animals were assigned to the test groups by mating day using a Provantis®-generated randomization based on the body weight of the animals.

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily (for any signs of behavioural changes, reaction to treatment, or illness.)
Immediately after administration, any signs of illness or reaction to treatment were recorded. In case of changes, the animals were observed until the symptoms disappeared.
In addition, animals were checked regularly throughout the working day from 7.00 a.m. to 3.45 p.m.
On Saturdays and Sundays, the animals were checked regularly starting from 7.00 a.m. to 11.00 a.m. with a final check performed at approximately 3.30 p.m.
Dated and signed records of appearance, change and disappearance of clinical signs were maintained on clinical history sheets for individual animals.
Further checks were made early in the morning and again in the afternoon of each working day to look for dead or moribund animals. This allowed post mortem examinations to be carried out during the working period of that day. On Saturdays and Sundays, a similar procedure was followed except that the final check was carried out at approximately midday.
Animals showing signs of abortion or premature delivery would have been sacrificed on the same day. Fetuses obtained this way were examined for abnormal development, whenever possible. No abortion occurred in the study.

DETAILED CLINICAL OBSERVATIONS: No
- Time schedule: /

BODY WEIGHT: Yes
- Time schedule for examinations:
The weight of each rat was recorded on day 0 of gestation (the day of detection of a positive mating sign), followed by daily weightings - always at the same time of the day.
The body weight gain was calculated in intervals (i.e. day 0-3, 3-6, 6-9, 9-12, 12-15, 15-18 and 18-21), for the whole study (gestation day 0 - 21) and for the period after the start of dosing (gestation day 6 to gestation day 21). Furthermore the carcass weight and the net weight change from day 6 are given.
Carcass weight = Terminal body weight - uterine weight
Net weight change from day 6 = Carcass weight - body weight on day 6
These measurements were also used for calculating the daily amount of test item to be administered.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
The quantity of food consumed by each rat was recorded daily. Food intake per rat (g/rat/day) was calculated using the total amount of food given to and left by each rat in each group on completion of a treatment day.
The relative food consumption (g/kg bw/day) was calculated using the following formula:
Daily food consumption [g/kg bw/day]= Total food intake in g x 1000/Body weight in g
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No; not applicable (gavage)

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No
- Time schedule for examinations: Daily monitoring by visual appraisal of the drinking water bottles was maintained throughout the study. Dehydration of the animals was avoided.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 21 (CO2 narcosis)
- Organs examined: ovaries, uterus, internal organs and placenta.
The ovaries and the uteri of the dams were removed and the uteri (in toto) were weighed. Uteri without fetuses were examined for possible implantation sites according to SALEWSKI to confirm their pregnancy status.
In order to check for possible drug effects, a dissection with macroscopic examination of the internal organs and placentae of the dams was carried out on the day of scheduled laparotomy or on the day on which the animals were found dead. In case of macroscopical findings, the affected maternal tissues were preserved in 7% buffered formalin for possible future histopathological examinations.

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
- Other: live/dead fetuses; sex ratio of fetuses

Fetal examinations:

2 litter per group were examined:
- External examinations: Yes: all per litter
- Soft tissue examinations: No
- Skeletal examinations: No
- Head examinations: No

Statistics:

The statistical evaluation of body weight and food consumption of the dams was done by Provantis using the following settings:
Homogeneity of variances and normality of distribution were tested using the BARTLETT’s and SHAPIRO-WILKS test. In case of heterogeneity and/or non-normality of distribution, stepwise transformation of the values into logarithmic or rank values was performed prior to ANOVA. If the ANOVA yielded a significant effect (p ≤ 0.05), intergroup comparisons with the control group were made by the DUNNETT’s test (p ≤ 0.01 and p ≤ 0.05).
Significantly different data are indicated in the summary tables of the result sections of the report.
No statistical analysis was conducted for data obtained at laparotomy as only 2 litters/group were evaluated.

Indices:

Group indices:
Pre-implantation loss [%] = [Corpora lutea (per group) - Implantations (per group)/ Corpora lutea (per group)]x 100
Post-implantation loss [%] = [Implantations (per group) - living fetuses (per group)/ Implantations (per group)] x 100

Mean indices per litter:
Pre-implantation loss [%] = sum of pre-implantation losses per litter in a group [%]/ number of litters in a group
Post-implantation loss [%] = sum of post-implantation losses per litter in a group [%]/ number of litters in a group

Clinical signs:

no effects observed

Description (incidence and severity):

No changes in behaviour, the external appearance and the faeces were noted in the control group and in the treatment groups.

Mortality:

no mortality observed

Description (incidence):

No premature death was noted in the control group and in the treatment groups.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No test item-related changes in body weight in comparison to the control group were noted for the dams of the treatment groups. However, after the start of dosing a slight reduction in body weight (statistically not significant) was noted for the dams of the high dose group (at maximum 6.1% below the value of the control group on gestation day 7). After gestation day 7 the body weight of the high dosed dams recovered and no noteworthy differences in body weight between the high dosed dams and the control group were noted during the further course of the study.
The values of body weight gain showed no differences between the control group and the test item-treated groups for the period after the start of treatment (gestation days 6 to 21). Only for the whole study period a marginally reduced body weight gain (statistically not significant) was noted for the dams of the intermediate and the high dose group, which was not considered as test item-related or adverse.
No test item-related changes between the control group and the treatment groups were noted for the absolute body weight gain and the net body weight gain (without gravid uterus) for the period after the start of treatment between gestation day 6 and gestation day 21.

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

No test item-related differences in food consumption were noted between the dams of the control group and the dams treated with 100, 300 or 1000 mg Urea/kg bw/day.
Statistically significant differences in food consumption which were considered as not test item-related are an increase in maternal food consumption in the 100 and 1000 mg dose group on gestation days18-19 (p ≤0.05). The slight difference in comparison to the control is without biological relevance.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

no effects observed

Description (incidence and severity):

No test item-related changes in the consumption of drinking water was noted for the dams treated with 100, 300 or 1000 mg Urea/kg bw/day by visual appraisal.

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

No test item-related changes in the gravid uterus weight and the carcass weight (terminal body weight minus gravid uterine weight) were noted between the dams of the control group and the dams of the treatment groups.

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Macroscopic inspection of the internal organs and tissues of the dams during laparotomy revealed no test item-related changes in the dams of the control and the dams of the treatment groups.
However, a dilatation of the renal pelvis was noted for dam no. 11 of the high dose group. This singular observation was not considered as test item-related.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Number of abortions:

no effects observed

Description (incidence and severity):

No test item-related differences for the reproductive parameters (numbers of implantation sites, resorptions, live fetuses as well as pre- and post-implantation loss) were noted between the dams of the control group and the dams treated with 100, 300 or 1000 mg Urea/kg bw/day.

Pre- and post-implantation loss:

no effects observed

Description (incidence and severity):

No test item-related differences for the reproductive parameters (numbers of implantation sites, resorptions, live fetuses as well as pre- and post-implantation loss) were noted between the dams of the control group and the dams treated with 100, 300 or 1000 mg Urea/kg bw/day.

Total litter losses by resorption:

no effects observed

Description (incidence and severity):

No test item-related differences for the reproductive parameters (numbers of implantation sites, resorptions, live fetuses as well as pre- and post-implantation loss) were noted between the dams of the control group and the dams treated with 100, 300 or 1000 mg Urea/kg bw/day.

Early or late resorptions:

no effects observed

Description (incidence and severity):

No test item-related differences for the reproductive parameters (numbers of implantation sites, resorptions, live fetuses as well as pre- and post-implantation loss) were noted between the dams of the control group and the dams treated with 100, 300 or 1000 mg Urea/kg bw/day.

Dead fetuses:

no effects observed

Description (incidence and severity):

No dead fetus was noted in the control group and in the treatment groups.

Changes in pregnancy duration:

not examined

Description (incidence and severity):

Migrated Data from removed field(s)
Field "Effects on pregnancy duration" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsMaternalAnimals.MaternalDevelopmentalToxicity.EffectsOnPregnancyDuration): not examined

Changes in number of pregnant:

not examined

Dose descriptor:

NOAEL

Effect level:

> 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Remarks:

100% nominal

Remarks on result:

not determinable due to absence of adverse toxic effects

Fetal body weight changes:

no effects observed

Description (incidence and severity):

No test item-related differences for the placental and fetal weights were noted between the control group and the treatment groups (100, 300 or 1000 mg Urea/kg bw/day).
Migrated Data from removed field(s)
Field "Fetal/pup body weight changes" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsFetuses.FetalPupBodyWeightChanges): no effects observed
Field "Description (incidence and severity)" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsFetuses.DescriptionIncidenceAndSeverityFetalPupBodyWeightChanges): No runt was noted in the control group or in the treatment groups (100, 300 or 1000 mg Urea/kg bw/day). Fetuses were considered as runts if their weight was less than 70% of the mean litter weight.

Reduction in number of live offspring:

no effects observed

Description (incidence and severity):

No dead fetuses were noted in the litters of the dams of the control group and in the litters of the dams treated with 100, 300 or 1000 mg Urea/kg bw/day.

Changes in sex ratio:

no effects observed

Description (incidence and severity):

No test item-related influence on the ratio of live male fetuses to live female fetuses were noted for all treatment groups.
The sex ratios of the pups (male / female) were 1.00 in the control group, 1.67 in the low dose group, 3.17 in the intermediate dose group and 1.00 in the high dose group. The increased numbers of male fetuses in the intermediate dose group is considered to be spontaneous and within the variability of the small number of fetuses examined per group.

Changes in litter size and weights:

no effects observed

Changes in postnatal survival:

not examined

External malformations:

no effects observed

Description (incidence and severity):

No macroscopically visible malformations or variations were noted for the fetuses of the control group or the treatment groups (100, 300 or 1000 mg Urea/kg bw/day) during the external examination of the fetuses at laparotomy.

Skeletal malformations:

not examined

Visceral malformations:

not examined

Dose descriptor:

NOAEL

Effect level:

> 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Remarks:

100% nominal

Sex:

male/female

Conclusions:

In this dose-range-finding study for a prenatal developmental toxicity study, the test item Urea was administered orally to female rats at dose levels of 100, 300 or 1000 mg/kg bw/day from the 6th to 20th day of pregnancy. Under the present test conditions, the no-observed-adverse-effect level (NOAEL) was above 1000 mg Urea/kg bw /day for the dams.
The no-observed-adverse-effect level (NOAEL) for the fetal organism was also above 1000 mg Urea/kg bw/day.
The external inspection at laparotomy revealed no malformations or variations.
Based on the data obtained in this dose-range-finding study, the following dose levels are suggested for LPT Study No . 33780 (Prenatal developmental toxicity study in rats):
0, 100 mg, 300 mg and 1000 mg Urea/kg bw/day, p.o.

Executive summary:

Urea was administered once daily by oral gavage from gestation day 6 until gestation day 20 to 4 groups of pregnant CD® / Crl:CD(SD) rats, consisting of 3 animals per group, at dose levels of 0, 100, 300 and 1000 mg/kg bw/day. Mature female CD® / Crl:CD(SD) rats were used for this experiment. On gestation day 21, the dams were laparotomised and examined for implantation sites, resorptions in the uterus and for the condition of the fetuses. 2 litters per dose group were examined.

Examination of the dams:

No premature deaths were noted in the control group and in the treatment groups (100, 300 or 1000 mg Urea/kg bw/day).

No changes in behaviour, the external appearance or the faeces were noted. No test item-related differences in body weight, body weight gain and food consumption were noted between the control group and the treatment groups. The visual appraisal of the drinking water consumption revealed no test item-related influence at any tested dose level.

No test item-related changes were noted during the macroscopic examination at necropsy nor gravid uterus weight and carcass weight.

Examination of the fetuses:

No test item-related influence was detected on the prenatal fetal development with respect to the number of resorptions, number of live fetuses, fetal and placental weights, the values calculated for the post-implantation loss and the sex distribution of fetuses. Laparotomy revealed no dead fetuses or runts in the test item groups or the control group.

No test item-related malformations nor variation were noted at the external inspection of the fetuses.

Conclusion

Under the present test conditions, the no-observed-adverse-effect level (NOAEL) was above 1000 mg Urea/kg bw /day for the dams.

The no-observed-adverse-effect level (NOAEL) for the fetal organism was also above 1000 mg Urea/kg bw/day.

No dead fetuses and no test item-related resorptions were noted. The external inspection at laparotomy revealed no malformations or variations.

Based on the data obtained in this dose-range-finding study, the following dose levels are suggested for LPT Study No . 33780 (Prenatal developmental toxicity study in rats): 0, 100, 300 and 1000 mg Urea/kg bw/day, p.o.

Reference 3

Endpoint:

developmental toxicity

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

See attachment

Species:

rabbit

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

reliable

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

In a key prenatal developmental toxicity study (Hansen, 2017), the test item Urea was administered orally to female pregnant CD® / Crl:CD(SD) rats by gavage at dose levels of 100, 300 or 1000 mg/kg bw/day from the 6th to 20th day of pregnancy. The measured actual concentrations of the test item in the test item vehicle mixtures were between 101.0% and 105.8% of the nominal concentrations. On gestation day 21, the dams were laparotomised and examined for implantation sites, resorptions in the uterus and for the condition of the fetuses. In the dams, no premature death, nor changes in behaviour, body weight (gain) and food/water consumption were noted between the control group and the treatment groups. No test item-related changes were noted during the macroscopic inspection nor for the gravid uterus or carcass weights of the dams at necropsy. No test item-related influence was noted on the reproductive parameters (number of implantation sites, resorptions and fetuses). In the fetuses, no test item-related influence on the prenatal fetal development with respect to the number of resorptions, number of live fetuses, fetal and placental weights, the values calculated for the post-implantation loss and the sex distribution of fetuses. No malformations nor variations were noted during the macroscopic, skeletal and soft tissue examinations. Under the conditions of the study, Urea did not show any teratogenic potential. In conclusion, the NOAEL was above 1000 mg Urea/kg bw/day for maternal developmental and foetal toxicity as well as for teratogenicity.

In a supporting dose range finding study (Hansen, 2016), urea was administered once daily by oral gavage from gestation day 6 until gestation day 20 to 4 groups of pregnant CD® / Crl:CD(SD) rats, consisting of 3 animals per group, at dose levels of 0, 100, 300 and 1000 mg/kg bw/day. On gestation day 21, the dams were laparotomised and examined for implantation sites, resorptions in the uterus and for the condition of the fetuses. Two litters per dose group were examined. In the dams, no premature death, no changes in behavior, body weight (gain) and food/water consumption were noted between the control group and the treatment groups. No test item-related changes were noted during the macroscopic examination at necropsy nor gravid uterus weight and carcass weight. In the fetuses, no test item-related effects were observed. Laparotomy revealed no dead fetuses, runts, malformations or variations at external examination. The dose levels for the main study were selected as 0, 100, 300 and 1000 mg Urea/kg bw/day, p.o.

A study of limited design also did not indicate any teratogenicity or effects on renal development in the rat (Seipelt et al, 1969), however slightly lower pup weights were seen at the dose level of 500 mg/kg bw/d in this study. The findings were observed in a small group of 6 animals and were overruled by the key developmental toxicity study; the dose of 500 mg/kg bw can be considered as NOAEL from a conservative viewpoint. Finally, a screening assay in chick eggs is considered to be of limited value (Mora et al, 1991).

Large quantities of urea are formed naturally in the human body as a consequence of normal protein catabolism. Urea is shown to be essentially without toxicity in the available studies. The level of any primary, occupational or secondary exposure to urea is likely to be insignificant compared to the quantities (20-50 g/day) produced by normal metabolism and present at high concentrations in the maternal and foetal circulation.

A developmental toxicity study in a second non-rodent species is waived based on a weight-of-evidence approach providing scientific reasons. Urea is endogenous in humans and animals, and is eliminated mainly via the kidney. Urea was negative for developmental and foetal toxicity in the rat developmental toxicity study up to the limit dose, and it is not expected to result in developmental and foetal toxicity in other species. Uraemia, which is a high blood concentration of urea either due to physiological or pathological conditions, is not tolerated very well by all species. Rabbits are different from other species in various viewpoints towards urea gastro-intestinal tolerance and systemic elimination. Uraemia in rabbits can become problematic due to gastro-intestinal (especially caecum) impactation of high urea or ammonium concentrations, leading to increased pH and dysbiosis at the caecum and diarrhea. In addition, once systemically absorbed, rabbits are characterised by a lack of kidney urea concentration, leading to dehydration and bad condition due to the osmotic activity of urea. These specific rabbit issues may complicate toxicological testing, especially in pregnant female rabbits in developmental toxicity studies which are more susceptible to stress. Therefore the rabbit is not considered appropriate to be used as a second species for developmental toxicity testing. The same applies to guinea-pigs. For animal welfare reasons, higher animal species are not considered.

Justification for classification or non-classification

Developmental toxicity testing in rats dosed orally up to 1000 mg/kg bw did not result in adverse effects. There are no studies in animals showing clear evidence of reproductive effects. The results of the available studies do not trigger classification according to Directive 67/548/EEC.