1,3-bis(trimethylsilyl)urea

Endpoint summary

Description of key information

Acute oral toxicity (OECD 420, rat, f): LD50 = > 300 < 2000 mg/kg bw

Acute inhalation toxicity (OECD 433, rat, m/f): LC50 > 5.30 mg/L (aerosol)

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

23 Jul - 20 Aug 2019

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 420 (Acute Oral Toxicity - Fixed Dose Method)

Version / remarks:

adopted in 2001

Deviations:

yes

Remarks:

On 3 days the temperature was approx. 20 - 27 °C instead of 19 - 25 °C; the age of the animals was 7 - 12 weeks instead of 8 - 12 weeks

Qualifier:

according to guideline

Guideline:

EU Method B.1 bis (Acute Oral Toxicity - Fixed Dose Procedure)

Version / remarks:

adopted in 2008

GLP compliance:

yes (incl. QA statement)

Remarks:

Hessisches Ministerium für Umwelt, Klimaschutz, Landwirtschaft und Verbraucherschutz, Wiesbaden, Germany

Test type:

fixed dose procedure

Limit test:

no

Specific details on test material used for the study:

Dose calculation was adjusted to purity with a correction factor of 1.03.

Species:

rat

Strain:

Wistar

Remarks:

Han TM

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Envigo RMS B.V., Inc, AD Horst, The Netherlands
- Females nulliparous and non-pregnant: yes
- Age at beginning of treatment: 7 - 12 weeks
- Weight at beginning of treatment: 159.7 - 197.9 g
- Fasting period before study: The animals were fasted over night before treatment, with constant ad libitum access to drinking water.
- Housing: In groups of 5 in Makrolon Type IV cages with wire mesh top and granulated soft wood bedding.
- Diet: certified 2018C Teklad Global 18% protein rodent diet, ad libitum
- Water: tap water, ad libitum
- Acclimation period: at least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2
- Humidity (%): 45 - 65
- Photoperiod (hrs dark / hrs light): 12 / 12

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on oral exposure:

VEHICLE
- Concentration in vehicle: 30 and 200 mg/mL
- Amount of vehicle: 10 mL/kg bw
- Justification for choice of vehicle: The test item was not stable in water due to hydrolysis.

MAXIMUM DOSE VOLUME APPLIED: 10 mL/kg bw

Doses:

Pilot study: 300 and 2000 mg/kg bw
Main study: 300 mg/kg bw

No. of animals per sex per dose:

Pilot study: 1 female per dose
Main study: 4 females

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations: Clinical observations and inspections for morbidity / mortality were performed at least 3 times within the first six hours after application (i.e., 30 minutes and 1 hour, 2 hours and 4 hours after dosing), thereafter at least once daily for 14 days. All surviving animals were observed for 14 days after dosing.
- Frequency of weighing: Body weights were recorded on Day 0 (prior to dosing), Day 7 and 14.
- Necropsy of survivors performed: Yes, gross necropsy was performed on all animals that died or were humanely killed during the study and at the end of the in-life part. Any macroscopic abnormalities were recorded.

Statistics:

No statistical analysis was performed.

Preliminary study:

In the sighting study, two single females each were dosed at 300 and 2000 mg/kg bw/day. The animal dosed at 2000 mg/kg bw/day had to be humanely sacrificed 4 h after application due to moribund condition and unconsciousness. The animals showed clinical signs of toxicity starting 30 minutes after dosing, including decreased activity, ataxia, decreased respiration rate, sunken flanks, piloerection, lethargy, and laboured respiration. At macroscopical examination, a full urinary bladder was observed. Based on these findings, the main study was conducted at 300 mg/kg bw.

Key result

Sex:

female

Dose descriptor:

LD50

Effect level:

> 300 - < 2 000 mg/kg bw

Based on:

test mat.

Mortality:

Pilot study:
300 mg/kg bw: 0/1 females died
2000 mg/kg bw: 1/1 females was sacrificed for humane reasons 4 hours post-dosing.
Main study: No mortality occured during the study period.

Clinical signs:

other: Pilot study: 300 mg/kg bw: 1/1 females showed piloerection, hunched posture, decreased activity and a decreased respiration rate within 4 hours post-administration. The effects were fully reversible by study Day 1. 2000 mg/kg bw: 1/1 females showed decr

Gross pathology:

Pilot study:
300 mg/kg bw: There were no abnormal findings at gross necropsy.
2000 mg/kg bw: The animal sacrificed for humane reasons was found to have a full urinary bladder.

Main study: 3 - 4 red nodules above the thymus were noted in 1/4 females, being indicative of enlarged lymph nodes. The effect was not attributed to treatment. There were no findings in the remaining animals.

Interpretation of results:

other: Acute Oral 4, H302 according to Regulation (EC) No. 1272/2008

Conclusions:

In this acute oral toxicity study in rats a LD50 value between 300 - 2000 mg/kg bw was determined.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

> 300 - < 2 000 mg/kg bw

Quality of whole database:

The available information comprises an adequate and reliable study, and is thus sufficient to fulfil the standard information requirements set out in Annex VII, 8.5, of Regulation (EC) No. 1907/2006.

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

01 Apr - 12 May 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 433 (Acute Inhalation Toxicity: Fixed Concentration Procedure)

Version / remarks:

adopted in 2018

Deviations:

no

GLP compliance:

yes

Test type:

fixed concentration procedure

Limit test:

no

Species:

rat

Strain:

Wistar

Remarks:

RccHan®:WIST

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Envigo RMS Ltd. (UK)
- Age at study initiation: 8 - 12 weeks
- Weight at study initiation: 242 - 295 g (males) and 185 - 191 g (females)
- Fasting period before study: no
- Housing: Individually during the sighting study and in groups of 5 during the main study. The cages were made of a polycarbonate body with a stainless steel mesh lid. Autoclaved softwood bark-free fiber was used as bedding.
- Diet: Teklad 2014C Diet, ad libitum
- Water: potable water from the public water supply, ad libitum
- Acclimation period: at least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 24
- Humidity (%): 40 - 70
- Photoperiod (hrs dark / hrs light): 12 / 12

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose only

Vehicle:

air

Mass median aerodynamic diameter (MMAD):

2 - 2.2 µm

Geometric standard deviation (GSD):

2.25 - 2.64

Remark on MMAD/GSD:

The Mass Median Aerodynamic Diameter (MMAD) ± Geometric Standard Deviation (GSD) was 2.1 ± 2.25 µm at 1 mg/L (sighting study) and 2.0 ± 2.34 µm (sighting study) and 2.2 ± 2.64 µm (main study) at 5 mg/L air, respectively.

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: The exposure apparatus was a Flow through nose-only chamber (ADG Developments Ltd, Hitchin, Hertfordshire, England) with an aluminum alloy construction comprising a base unit, one animal exposure section with 20 exposure ports, and a top section.
- Exposure chamber volume: approximately 30 L
- Method of holding animals in test chamber: plastic nose-only restraint tube
- Source and rate of air (airflow): The aerosol was generated by Wright Dust Feed Mechanism, which produces and maintains test atmospheres containing dust by suspending material scraped from the surface of compressed powder in a stream of dry air. The inlet airflow was 44 L/min.
- Method of particle size determination: The particle size distribution was characterized twice during each exposure period. The aerosol samples were drawn with a flow of 2 L/min. Particle size distribution was determined by cascade impaction using a Marple 290 Series Personal Cascade Impactor (Andersen Instruments, Smyrna, Georgia, USA). Amounts of test item collected were measured gravimetrically. Subsequently the Mass Median Aerodynamic Diameter (MMAD) and the Geometric Standard Deviation (GSD) were derived.
- Treatment of exhaust air: Extract airflow was drawn by in-house vacuum system and filtered locally. The flow was 45 - 46 L/min.
- Mean temperature in air chamber: 19.8 ± 0.65 °C (1 mg/L, sighting study), 19.4 ± 0.22 °C (5 mg/L, sighting study) and 19.7 ± 0.21 °C (5 mg/L, main study).
- Humidity in air chamber: 9.4 ± 0.88% (1 mg/L, sighting study), 14.8 ± 2.42% (5 mg/L, sighting study) and 16.8 ± 1.23% (5 mg/L, main study).

TEST ATMOSPHERE
- Brief description of analytical method and equipment used: Aerosol samples were collected by using a glass microfiber filter held in an open face filter holder. Five samples were collected during each exposure.
- Samples taken from breathing zone: yes

Analytical verification of test atmosphere concentrations:

yes

Remarks:

gravimetric

Duration of exposure:

4 h

Concentrations:

Sighting study:
1.02 ± 0.020 and 5.04 ± 0.283 mg/L air (analytical concentrations)
1.34 and 6.58 mg/L air (nominal concentrations)

Main study:
5.30 ± 0.225 mg/L air (analytical concentration)
6.34 mg/L air (nominal concentration)

No. of animals per sex per dose:

Sighting study: 1 male and 1 female per step (2 steps)
Main study: 5 males

Control animals:

no

Details on study design:

- Duration of observation period following administration: 8 - 10 days (sighting study) and 15 days (main study).
- Frequency of observations: Throughout the study all cages were checked at least twice daily, once in the morning and again towards the end of the normal working day, for dead or moribund animals. The animals were observed for clinical signs prior to dosing, at hourly intervals during exposure, 1 and 2 hours after exposure and as late as possible in the working day of exposure. Thereafter, the animals were inspected visually at least twice daily for evidence of ill-health or reaction to treatment. Any deviation from normal was recorded at the time in respect of nature and severity, date and time of onset, duration and progress of the observed condition, as appropriate. Detailed physical examinations were performed weekly.
- Frequency of weighing: In the sighting study, rats were weighed at least once during the week prior to exposure, on Day 1 (prior to dosing) and on Days 2, 4 and 10. In the main study, rats were weighed at least once during the week prior to exposure, on Day 1 (prior to dosing) and on Days 2, 4, 8 and 15.
- Necropsy of survivors performed: Yes, all main study animals were subjected to a macroscopic examination which consisted of opening the cranial, thoracic and abdominal cavities. The macroscopic appearance of all examined organs was recorded. Tissues were discarded following necropsy. Special attention was paid to the lungs and respiratory tract for signs of irritancy and local toxicity during necropsy observation.

Statistics:

No statistical analysis was performed.

Preliminary study:

In the sighting study, each one male and one females were dosed at 1 mg/L air, corresponding to an analytical concentration of 1.02 ± 0.020 mg/L air. Evident toxicity was not observed therefore a further one male and one female received a single 4-hour nose only exposure of the test item at the target concentration of 5 mg/L, corresponding to an analytical concentration of 5.04 ± 0.283 mg/L air, and observed for seven days. The results of this exposure determined the starting exposure level for the main exposure.

Key result

Sex:

male

Dose descriptor:

LC50

Effect level:

> 5.3 mg/L air (analytical)

Based on:

test mat.

Exp. duration:

4 h

Mortality:

No mortality occurred during the study period.

Clinical signs:

other: Please refer to "Any other information on results incl. tables".

Body weight:

A slight loss in mean body weight was noted in the animals one day following exposure, which was considered to be a consequence of food and water removal during exposure. The finding was considered as normal body weight variation and therefore not attributed to treatment. For details please refer to Table 2 under "Any other information on results incl tables".

Gross pathology:

Necropsy revealed no substance-related findings. 1/5 males was observed to have small testes and epididymides bilaterally. The findings were reported to be occasionally observed in inhalation studies due to the method of restraint and duration of exposure and therefore not attributed to treatment.

Clinical signs:

After dosing, powder in the nose was observed in 4/5 males and an unsteady gait was noted in 5/5 males one hour after exposure. The findings had resolved in 2/5 males within 2 hours after exposure and by study Day 5 in the remaining animals. Decreased activity was seen in 4/5 males, with a flattened posture seen in 3/5 males in Day 1. Both signs resolved in all animals by study Day 2.

Piloerection and hunched posture were noted in 2/5 males 1 and 2 hours after exposure. Salivation was noted in 1/5 animals, which further showed closed bilateral eyes 1 hour after exposure and slow breathing 2 hours after exposure. All signs had resolved by study Day 2.

Clinical signs associated with the dosing procedure included wet fur (1/5) and staining of the nose (1/5) for some animals, these were considered to be a consequence of tube restraint during exposure.

Body weight development:

Table 2: Mean body weights

	Day P19	Day 1	Day 2	Day 4	Day 8	Day 15
Mean	275.2	282	278.8	281.2	288.4	297.8
SD	9.44	10.54	10.28	11.54	14.33	14.18
% control	100.00	102.47	101.31	102.18	104.80	108.21

Interpretation of results:

other: CLP/EU GHS criteria not met, no classification required according to Regulation (EC) No. 1272/2008

Conclusions:

CLP: not classified

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LC50

Value:

> 5.3 mg/L air

Quality of whole database:

The available information comprises an adequate and reliable study, and is thus sufficient to fulfil the standard information requirements set out in Annex VIII, 8.5, of Regulation (EC) No. 1907/2006.

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Acute oral toxicity:

N,N-Bis-(trimethylsilyl)urea was tested for acute oral toxicity according to OECD guideline 420 (fixed dose procedure) and in compliance with GLP (ICCR-Roßdorf GmbH, 2020a). The test item was dissolved in corn oil and administered by oral gavage to female Wistar rats.

A sighting study was performed prior to the main study, in which doses of 300 and 2000 mg/kg bw were administered to one female each. The animal dosed at 2000 mg/kg bw showed systemic effects and had to be sacrificed for humane reason, therefore the main study was conducted at 300 mg/kg bw. In the main study, 4 additional females were administered 300 mg/kg bw at a constant dose volume of 10 mL/kg bw and observed for a time period of 14 days. Mortality, clinical sings of toxicity and individual body weights were recorded. At terminal sacrifice, all animals were subjected to gross necropsy.

No mortality occurred at 300 mg/kg bw. Clinical signs of toxicity comprised decreased activity, hunched posture, piloerection, lethargy and laboured respiration within 24 hours post-dosing. The effects were fully reversible by study Day 2. There were no treatment-related effects on body weight development. At scheduled necropsy, 3 - 4 red nodules above the thymus were noted in 1/4 females, being indicative of enlarged lymph nodes. The effect was not attributed to treatment.

Under the tested conditions, the acute oral LD50 in female rats was established to be within the range of > 300 and < 2000 mg/kg bw.

 

Acute inhalation toxicity:

In an acute inhalation toxicity study according to OECD guideline 433 (fixed concentration procedure) and in compliance with GLP (Covance Laboratories Ltd., 2020a), Wistar rats were exposed to aerosols of the test item by nose-only application. A sighting study with each 1 male and 1 female animal dosed at nominal concentrations of 1 and 5 mg/L air (achieved concentrations of 1.02 and 5.04 mg/L air) was performed to select a suitable concentration for the main inhalation study. The mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) in the sighting study were 2.1 ± 2.25 µm at 1 mg/L and 2.0 ± 2.34 µm at 5 mg/L.

In the main study, a group of 5 male rats was exposed for 4 hours to an aerosol concentration of 5.30 ± 0.225 mg/L air. The MMAD and GSD was 2.2 ± 2.64 µm. During exposure and thereafter, the animals were observed for clinical signs of toxicity and mortality. During a 14-days observation period, the animals were inspected for general health and mortality and individual body weights were recorded on Day 1 (prior to dosing) and on Days 2, 4, 8 and 15. At terminal sacrifice, all animals were subjected to gross macroscopical examination.

No mortality was observed throughout the study. After dosing, powder in the nose was observed in 4/5 males and an unsteady gait was noted in 5/5 males one hour after exposure, which remained up to 5 days after exposure. Decreased activity was seen in 4/5 males, with a flattened posture seen in 3/5 males in Day 1. Both signs resolved in all animals by study Day 2. Piloerection and hunched posture were noted in 2/5 males 1 and 2 hours after exposure. Salivation was noted in 1/5 animals, which further showed closed bilateral eyes 1 hours after exposure and slow breathing 2 hours after exposure. All signs had resolved by study Day 2. Clinical signs associated with the dosing procedure included wet fur in 1/5 animals and staining of the nose in 1/5 animals and were considered to be a consequence of tube restraint during exposure.

A slight loss in mean body weight was noted in the animals one day following exposure, which was considered to be a consequence of food and water removal during exposure. The finding was considered as normal body weight variation and therefore not attributed to treatment.

At necropsy, 1/5 males was observed to have small testes and epididymides bilaterally. The observation was considered to be occasionally observed and not attributed to treatment.

Under the tested conditions, the acute inhalation LC50 in male rats was established to be > 5.30 mg/L air.

 

Justification for classification or non-classification

The available data on acute oral toxicity of the test substance meet the criteria for classification as Acute Tox. 4 (H302) according to Regulation (EC) No. 1272/2008. The available data on acute inhalation toxicity do not meet the criteria for classification according to Regulation (EC) No. 1272/2008, and are therefore conclusive but not sufficient for classification.