6-amino-1,3-dimethyluracil

Endpoint summary

Description of key information

Acute toxicity oral: Wistar rat m/f, 5/sex, oral: gavage, 5000 mg/kg in 0.5% aqueous carboxymethyl cellulose, similar to OECD 401: LD50 > 5000 mg/kg, LD0 ≥ 5000 mg/kg, no abnormalities noted

Acute toxicity dermal: Wistar rat m/f, 5/sex, 2000 mg/kg in water, semi-occlusive, 24h exposure, OECD 402, GLP: LD50 > 2000 mg/kg, LD0 ≥ 2000 mg/kg, no abnormalities noted

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

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 401 (Acute Oral Toxicity)

Deviations:

no

GLP compliance:

no

Test type:

standard acute method

Limit test:

yes

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Dr. K. Thomae GmbH
- Weight at study initiation: mean body weight: female: 180 g, male: 181 g (5000mg/kg)
- Fasting period before study: about 16 hours before administration
- Housing: 5 rats per cage
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: at least one week


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

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Details on oral exposure:

VEHICLE
0.5% aqueous carboxymethyl cellulose
- Concentration in vehicle: 50 g test substance per 100 ml
- Justification for choice of vehicle: Aqueous formulation corresponds to the physiological medium


MAXIMUM DOSE VOLUME APPLIED: 10 ml

Doses:

200mg/kg bw; 2000mg/kg bw; 5000 mg/kg bw

No. of animals per sex per dose:

5000mg/kg bw: 5 female rats, 5 male rats

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days (5000 mg/kg bw)
- Frequency of observations: daily
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight, histopathology

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 5 000 mg/kg bw

Mortality:

5000 mg/kg bw: 0/10

Clinical signs:

other: no abnormality detected

Gross pathology:

no abnormalities detected

Interpretation of results:

practically nontoxic

Remarks:

Migrated information Criteria used for interpretation of results: EU

Executive summary:

Acute oral toxicity was analyzed in a study performed in large part equivalent to method described in OECD guideline 401. Five male and female Wistar rats received doses of 5000 mg/kg bw by gavage. Since no mortality was noted during the 14-day observation period, the LD50 was found to be >5000 mg/kg bw. Due to the observed LD50 in a study performed equivalent to OECD guideline, no classification according EU and GHS criteria is required according Directive 67/548/EC or EU GHS criteria (Regulation (EC) N° 1907/2006)

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

discriminating dose

Value:

5 000 mg/kg bw

Quality of whole database:

There is a sufficiently reliable oral toxicity study similar to OECD 401 on the registered substance available, the tonnage-driven data requirements are fully met, so the database is of high quality.

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

acute toxicity: inhalation

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because exposure of humans via inhalation is not likely taking into account the vapour pressure of the substance and/or the possibility of exposure to aerosols, particles or droplets of an inhalable size

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
According to REACH Annex VIII column 2, 8.5.2. Testing by the inhalation route is appropriate if exposure of humans via inhalation is likely taking into account the vapour pressure of the substance and/or the possibility of exposure to aerosols, particles or droplets of an inhalable size.
The substance melts at 299°C, the boiling point could not be determined with the most sensitive method, i.e. vapour pressure measurement by effusion method, weight loss, according to OECD Guideline for the Testing of Chemicals 104. It could not be determined because the vapour pressure is too low. The vapour pressure itself was determined as very low, i.e. 1 * 10exp(-7) hPa at 25°C (calculated using the Modified Watson Correlation, OECD 104, GLP). So, the exposure to 1,3-dimethyl-4-aminouracil via inhalation of vapour can be disregarded as no vapour will be formed during handling. Also, the substance is a solid, so the formation of inhalable droplets or aerosols can furthermore be excluded.
The particles of 1,3-Dimethyl-4-aminouracil form various size agglomerates. The measurement of the single particles was not possible. The amount of test item with a particle size below 250 µm was only about 2 %. This amount is too small and not relevant for the particle size distribution. The main agglomerate size was found in the range of 250 µm to 2000 µm. 50 % of the test item agglomerates exceeded 500 µm. 0.00% were < 75µm. According to ECHA’s guidance on data requirements Chapter R.7c, In humans, particles with aerodynamic diameters below 100 μm have the potential to be inhaled. Particles with aerodynamic diameters below 50 μm may reach the thoracic region and those below 15 μm the alveolar region of the respiratory tract. As obvious, only less than 2% of the particles in general have the potential to be inhaled, and none of the particles have the potential to reach the part of the lung in which no ciliary clearance occurs. Also, direct dust exposure is excluded during handling, hence not fulfilling the above-mentioned criteria for the necessity of testing.
Furthermore, testing is scientifically not necessary and would not reveal any additional information which cannot be derived from other available acute toxicity data, so that testing can be omitted due to animal welfare:
According to ECHA’s guidance, Moderate log P values (between -1 and 4) are favourable for absorption directly across the respiratory tract epithelium by passive diffusion. The log Pow of the test item 1,3-dimethyl-4-aminouracil was determined to be -0.4 at 20°C and pH 6.2-6.9 (flask method, OECD 107). Hence, this value may indicate a certain potential for absorption. With a water solubility of 5.46 g/L at 20°C, absorption here can also not be excluded, in case any particle reaches the respiratory tract. Further, there are no signs of toxicity obvious via the oral or dermal route.
There is no study available (and required) for the acute inhalation toxicity of 1,3-dimethyl-4-aminouracil; however, there are LD50 values via other application routes available:
Oral: LD50 > 5000 mg/kg, LD0 ≥ 5000 mg/kg (similar to OECD 401)
Dermal LD50 > 2000 mg/kg, LD0 ≥ 2000 mg/kg (OECD 402, GLP)
The obtained values are consistent and can be hence considered as reliable, and may be so used for further considerations:
According to OECD guideline 403 (Acute inhalation toxicity), the concentration of respirable particles for limit testing is 5 mg/L over 4 h. Taking into account for rats a standard respiratory volume of 0.2 l/min and average body weight of 250 g (Guidance on information and requirements and chemical safety assessment, chapter R.8: Characterisation of dose [concentration]-response for human health, Version 2.1, November 2012, ECHA, http://echa.europa.eu/web/guest/guidance-documents/guidance-on-information-requirements-and-chemical-safety-assessment), a total respiratory volume of 48 litre over 4 h can be assumed. This would result in a total dose of 240 mg per rat, which is equivalent to 960 mg/kg bw.
Assuming in a worst-case scenario that this total dose will be absorbed to 100%, and assuming furthermore that the orally applied amount is only absorbed to 50%, this dose would correspond to an oral dose of 1920 mg/kg bw. This value is below the relevant determined LD50 and even LD0 via the oral and dermal route, i.e. 2000 mg/kg bw. Hence, it can be reasonably assumed that an additional acute toxicity test via the inhalation route would reveal an LC50inhalation >5 mg/l, most likely even a LC0inhalation ≥5 mg/l. This is supported by the reasonably assumable hindered absorption via the inhalatory route compared to the oral one due to the particle size and tendency of the particles to form agglomerates.
Furthermore, during the investigation of the acute dermal toxicity, no alterations of the skin were detected, and 1,3-dimethyl-4-aminouracil is neither a skin nor eye irritant nor a dermal sensitizer. So it can be additionally concluded, that no local effects during inhalation toxicity testing are likely occur and need to be regarded.
In consequence, the available oral and dermal acute toxicity studies are sufficient to cover this endpoint, no acute toxicity testing via inhalation route needs to be performed and can consequently be waived due to animal welfare.

Endpoint conclusion

Endpoint conclusion:

no study available

Acute toxicity: via dermal route

Link to relevant study records

Reference

Endpoint:

acute toxicity: dermal

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2002-03-01 - 2002-05-13

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 402 (Acute Dermal Toxicity)

Version / remarks:

OECD Guidelines for Testing of Chemicals, Section 4, Number 402 "Acute Dermal Toxicity", adopted February 24, 1987.

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.3 (Acute Toxicity (Dermal))

Version / remarks:

Directive 92/69/EEC, B.3. "Acute Toxicity-Dermal", July 31, 1992

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

standard acute method

Limit test:

yes

Specific details on test material used for the study:

- Storage condition of test material: at room temperature, (range of 20 ± 3 °C), away from direct sunlight
- Stability under test conditions: Stable under storage conditions
- Stability of test item in vehicle: 90 days in PEG 300 at room temperature

- Final dilution of a dissolved solid, stock liquid or gel: The dose formulation was made shortly before administration.
The test item was weighed into a tared glass beaker on a suitable precision balance and the vehicle added (weight:volume). The formulations were prepared using a magnetic stirrer.
Homogeneity of the test item in the vehicle was maintained during administration using a magnetic stirrer.

Species:

rat

Strain:

other: HanBrl: Wist (SPF)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: RCC Ltd, Biotechnology & Animal Breeding Division CH-4414 Füllinsdorf/Switzerland
- Number of animals per group: 5 males and 5 females
- Age at study initiation: Males: 8 weeks, Females: 10 weeks
- Housing: During acclimatization in groups of five in Makrolon type-4 cages with standard softwood bedding. During treatment and observation individually in Makrolon type-3 cages with standard softwood bedding ("Lignocel", Schill AG, CH-4132 Muttenz).
- Diet (e.g. ad libitum): Pelleted standard Kliba 3433 rat/mouse maintenance diet, batch no. 119/01 (Provimi Kliba AG, CH-4303 Kaiseraugst/ Switzerland) ad libitum.
- Water (e.g. ad libitum): Community tap-water, from Füllinsdorf ad libitum.
- Acclimation period: Under laboratory conditions for 1 week, after health examination. Only animals without any visible signs of illness were used for the study.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3°C
- Humidity (%): 30-70%
- Air changes (per hr): 10-15 air changes per hour
- Photoperiod (hrs dark / hrs light): 12 hours fluorescent light/12 hours dark, music during the light period.

Type of coverage:

semiocclusive

Vehicle:

water

Remarks:

Purified water (deionised water which was processed and treated by the PURELAB Option-R unit. This latter links four purification technologies: reverse osmosis, adsorption, ion-exchange and photo oxidation)

Details on dermal exposure:

TEST SITE
- Area of exposure: the backs of the animals, an area of approximately 10 % of the total body surface
- Type of wrap if used: a semi-occlusive dressing was wrapped around the abdomen and fixed with an elastic adhesive bandage.

REMOVAL OF TEST SUBSTANCE
- Washing (if done): the skin was flushed with lukewarm tap water and dried with disposable paper towels
- Time after start of exposure: 24 hours after the application

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): the test item was applied at a dose of 2000 mg/kg body weight
Application volume/kg body weight: 4ml

VEHICLE
- Amount(s) applied (volume or weight with unit): test item formulated ad 4 ml /kg bw
- Concentration (if solution): 50%

Duration of exposure:

24 hours

Doses:

2000 mg/kg body weight

No. of animals per sex per dose:

5 males and 5 females

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: Mortality / Viability: Daily during acclimatization and twice daily during days 1-15. Body weights on test days 1 (prior to administration), 8 and 15. Clinical signs daily during acclimatization and at approximately 1, 2, 3 and 5 hours after administration on test day 1. Once daily during days 2-15. All abnormalities were recorded.
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight

Statistics:

No statistical analysis was used.

Key result

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 2 000 mg/kg bw

Based on:

test mat.

Key result

Sex:

male/female

Dose descriptor:

LD0

Effect level:

>= 2 000 mg/kg bw

Based on:

test mat.

Remarks on result:

not determinable due to absence of adverse toxic effects

Remarks:

No deaths occurred during the study. No systemic or local signs of toxicity were observed during the study period.

Mortality:

The animals survived the experiment.

Clinical signs:

other: Following single administration of the test item at a dose of 2000 mg/kg b.w. no clinical signs were observed during the observation period.

Gross pathology:

No macroscopic findings were observed at necropsy.

Interpretation of results:

GHS criteria not met

Remarks:

EU implementation

Conclusions:

The study was conducted according to OECD 402 under GLP without deficiencies. Hence, the study can be considered as sufficiently reliable to assess the acute dermal toxicity of the test item to rats.
The median lethal dose of 1,3-DIMETHYL-4-AMINOURACIL after single dermal administration to rats of both sexes, observed over a period of 14 days is:
LD50 (rat): greater than 2000 mg/kg body weight
This is greater than the limit dose for classification as acute toxic Cat. 4 (2000 mg/kg) according to Regulation 1272/2008, hence, the substance does not need to be classified as acutely toxic via the dermal route.

Executive summary:

One group of five male and five female HanBrl: Wist (SPF) rats was treated with 1.3-DIMETHYL-4-AMINOURACIL (CD 19-0456) by dermal application at a dosage of 2000 mg/kg. The test item was diluted in vehicle (purified water) at a concentration of 0.5 g/ml and administered at a volume dosage of 4 ml/kg. The animals were examined daily during the acclimatization period and mortality, viability and clinical signs were recorded. All animals were examined for clinical signs at approximately 1, 2, 3 and 5 hours after treatment on day 1 and once daily during test days 2-15. Mortality/viability was recorded twice daily during test days 1-15. Body weights were recorded on day 1 (prior to administration) and on days 8 and 15. All animals were necropsied and examined macroscopically.

No deaths occurred during the study.

No clinical signs were observed during the observation period.

The body weight of the animals was within the range commonly recorded for this strain and age.

No macroscopic findings were observed at necropsy.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

discriminating dose

Value:

2 000 mg/kg bw

Quality of whole database:

There is a reliable dermal toxicity study according to OECD 402 on the registered substance available, the tonnage-driven data requirements are fully met, so the database is of high quality.

Justification for classification or non-classification

According to Regulation 1272/2008, the cut-off value for classification as acutely toxic (Cat. 4) is 2000 mg/kg in both dermal and oral acute toxicity studies. The following values are available:

LD50 > 5000 mg/kg, LD0 ≥ 5000 mg/kg (acute oral toxicity, no abnormalities noted)

LD50 > 2000 mg/kg, LD0 ≥ 2000 mg/kg (acute dermal toxicity, no abnormalities noted)

Further, in an acute inhalation study, based on those results and toxicokinetic data, no LC50 values below the limit dose of5 mg/L over 4 h are reasonable to be expected.

Hence, 1,3-dimethyl-4-aminouracil does not need to be classified as acutely toxic according to Regulation 1272/2008, irrespective of the route of application.