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Toxicological information

Acute Toxicity: dermal

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Administrative data

acute toxicity: dermal
Type of information:
experimental study
Adequacy of study:
key study
Study period:
10. Oct. 2022-09. Mar. 2023
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
according to guideline
OECD Guideline 402 (Acute Dermal Toxicity: Fixed Dose Procedure)
Version / remarks:
adopted 09 October 2017
GLP compliance:
yes (incl. QA statement)
Test type:
fixed dose procedure
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Test material form:
Specific details on test material used for the study:
Cyclic trimethylolpropane formal (CTF)
chemical name 5-ethyl-1,3-dioxane-5-methanol
CAS number 5187-23-5, EC number 225-967-8
a clear, colourless liquid.
It was received on 21 September 2022 and stored at 15-25°C, under nitrogen, protected from light.

Test animals

Crl:WI(Han) strain
Details on test animals or test system and environmental conditions:
Species Selection
The rat was selected because it is a rodent species recommended by various regulatory authorities. The rat has been found to be the most tractable species for the dosing procedures used in this type of study at this laboratory. The strain of rat was selected as it is widely used for this type of study and a literature base is available for comparative purposes.

Animal Specifications and Acclimatisation
Female (nulliparous, non-pregnant) Crl:WI(Han) strain rats were obtained from Charles River (UK) Ltd., Margate. All animals were given a clinical inspection for ill health on arrival and a sample was weighed.

The condition of the animals was assessed daily throughout the acclimatization period of 14 to 22 days. A clinical inspection was performed prior to study commencement to ensure the animals were suitable for the test procedures. Overtly healthy animals were arbitrarily allocated to the study at least one day before treatment commenced.

Animals were in a body weight range of 184 to 210 g on the day of dosing (Day 1). Based on information from the supplier the rats were approximately 8 to 10 weeks old on Day 1. Individual body weights were within ±20% of the mean weight of any previously dosed animals.


During the acclimatisation period, up to five rats of the same sex were accommodated in cages that conformed to the 'Code of Practice for the Housing and Care of Animals Bred, Supplied or Used for Scientific Purposes' (Home Office, London, 2014). From the day prior to dosing (Day-1), each rat was individually housed in a similar cage. After completion of the Day 3 observations animals allocated to the main study were returned to group housing.

Bedding was provided on a weekly basis to each cage by use of clean European softwood bedding (Datesand Ltd., Manchester, UK). The bedding had been analysed for specific contaminants and the results retained on file.
No contaminants were present in bedding at levels which might have interfered with achieving the objective of the study.


Mains water was provided, ad libitum, via cage-mounted water bottles. The water had been periodically analysed for specific contaminants.
No contaminants were present in water at levels which might have interfered with achieving the objective of the study. Results are retained on file.

5LF2 EU Rodent Diet 14% (LabDiet, St Louis, USA) was freely available to the animals at all times. Each batch of diet had been analysed for specific constituents and contaminants by the manufacturer.
No contaminants were present in diet at levels which might have interfered with achieving the objective of the study. Results are retained on file.

The animal rooms were designed to permit a minimum of 15 air changes per hour.
The temperature and humidity ranges were 19 to 25°C and 40 to 70% respectively.
Daily recordings of maximum and minimum temperature and humidity were made.
Fluorescent lighting was controlled automatically to give a cycle of 12 hours light and 12 hours dark.

In order to enrich both the environment and the welfare of the animals, they were provided with wooden Aspen chew blocks, nesting materials and rodent retreats ( Wooden chew blocks were only provided for animal numbers 460 and 461 from the day of dosing. This deviation from protocol was considered not to have affected the integrity or outcome of the study as the absence of environmental enrichment does not affect the end points of the study). The nesting material was removed from the cages on the day of dosing and returned when the bandages were removed.

Animal Identification
A number written on the tail in indelible ink on the day before dosing individually identified the rats. A colour-coded card on each cage gave information including study number, group number, animal numbers and sex.

In-life Start Date: 11 October 2022
Experimental Completion Date: 16 November 2022

Administration / exposure

Type of coverage:
unchanged (no vehicle)
Details on dermal exposure:
Electric clippers were used to remove all hair from the dorsum on the day before dosing. The dermal test site was an area of at least 10% of the total body surface on the clipped dorsum of the rat.

The test article was spread as uniformly as possible over the dermal test site. A dense gauze patch was placed over the treated skin and retained in place by an elasticated, open-weave, adhesive compression bandage. This was wrapped securely around the torso of the animal.

The dressing was removed approximately 24 hours after application. The dermal test site of each rat was lightly brushed clean of any solid residues and swabbed with water-moistened cotton wool before the animal was returned to the holding cage.

The test article was administered as supplied. The specific gravity was determined (1.106 g/mL) and used to calculate the appropriate dose volume for the required dose level. Individual dose volumes (mL) were calculated from the body weights of the rats on the morning of dosing (Day 1), the selected dose volume and the density of test article.
Duration of exposure:
24 hours
Preliminary test:1000 and 2000 mg/kg
Main Study: 2000 mg/kg
No. of animals per sex per dose:
Preliminary test: one female per dose level
Main Study: 2 females per dose level

In total 4 animals used in this study.
Control animals:
not required
Details on study design:

- Duration of observation period following administration: 14 days

- Frequency of observations and weighing:
Clinical signs were recorded immediately post-dose, at approximately 15 and 30 minutes post-dose, hourly between 1 and 4 hours post-dose (inclusive), twice daily on Days 2, 3 and 4 and once daily from the fifth to last day of the observation period, Day 15*. *On day 15, the actual time was not recorded for the 15-minute post-dosing observation for animal number 458. This deviation from protocol was considered not to have affected the integrity or outcome of the study as sufficient observations were conducted.
All animals were examined at the beginning and end of the working day throughout the acclimatisation and study periods to ensure they were in good health.
Rats were weighed on Day-1 (day before dosing) and on Days 1, 4, 8 and 15.

-Dermal Reactions observation:
The condition of the dermal test site was recorded following removal of the dressing on Day 2, at approximately 24, 48 and 72 hours following removal of the dressing and once daily thereafter for the duration of the study period. Erythema and oedema were scored. See scoring scales in table 1 below.

- Necropsy of survivors performed: yes
Rats were killed on Day 15. Each animal was anaesthetised using isofluorane. Once a suitably deep plane of anaesthesia had been established, the animal was exsanguinated by the severing of major blood vessels. After exsanguination a full macroscopic necropsy was performed and all lesions were recorded.
The necropsy procedure included inspection of external surfaces and orifices, the dermal test site, all viscera and tissue within the abdominal, thoracic and cranial cavities, free-hand sectioning of the liver and kidneys and examination of representative sections of mucosal surfaces of the stomach and intestinal tract.
No tissue preservation or histopathological assessment of tissues was undertaken.
No statistic

Results and discussion

Preliminary study:
The preliminary test was completed using one female per dose level in a sequential manner at dose levels of 1000 and 2000 mg/kg (The second animal was dosed 48 hours after the first animal). No treatment-related effects were seen in the preliminary test. Two animals were treated at 2000 mg/kg in the main study.
Effect levels
Key result
Dose descriptor:
Effect level:
>= 2 000 mg/kg bw
Based on:
test mat.
Remarks on result:
not determinable due to absence of adverse toxic effects
There were no deaths in either the preliminary test or the main study.
Clinical signs:
Body weight:
other body weight observations
All rats in the preliminary test and in the main study gained weight during the first and second weeks of the study. see details in Table 2 below.
Gross pathology:
No macroscopic changes were noted at necropsy of all animals from the preliminary test or the main study.
Other findings:
Dermal Reactions: There were no dermal reactions noted in either the preliminary test or in the main
study. See table 3 below.

Any other information on results incl. tables

Table 2 Individual Body Weights and Weekly Increments (preliminary test + main study).

Dose Level (mg/kg)

Animal Number

Body Weight (g) at:

Increment (g)


Day 1

Day 4

Day 8

Day 15

Day 1 to 8

Day 8 to 15




































Table 3 Dermal Reactions (preliminary test + main study).

Day (time after removal of dressing)Dermal ReactionDose Level: 1000 mg/kgDose Level: 2000 mg/kg
Animal No. 458 Animal No. 459Animal No. 460Animal No. 461
3 (24 hours)Erythema0000
4 (48 hours)Erythema0000
5 (72 hours) Erythema0000
6-15 (daily)Erythema0000

- No other dermal changes apparent.

Applicant's summary and conclusion

Interpretation of results:
GHS criteria not met
The test article, Cyclic trimethylolpropane formal (CTF), was considered to have no significant acute toxic risk in respect of its acute dermal toxicity and did not meet the criteria for classification according to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS, ninth revised edition, 2021).
Executive summary:

This study was conducted to determine the acute dermal toxicity of the test article, Cyclic trimethylolpropane formal (CTF), following a single (24 hour) semi-occluded topical application to the rat. The test article was applied as an undiluted liquid to the clipped dorsum of female
rats (Day 1). The sighting study commenced at a dose level of 1000 mg/kg. As this animal survived a further animal was treated at 2000 mg/kg. As this animal also survived, two further animals were treated at 2000 mg/kg. The treated areas of dorsum were covered by a semi-occlusive dressing for 24 hours. All four animals were killed on Day 15 and subsequently underwent a full necropsy. No animal died and there were no clinical signs of reaction to treatment. No overt dermal changes were noted at the test site. All rats achieved body weight gains during the first and second weeks of the study. No macroscopic changes were apparent at necropsy. The test article was considered to have no significant acute toxic risk in respect of its acute dermal toxicity and did not meet the criteria for classification according to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS, ninth revised edition, 2021).