Trihexyl phosphate

Endpoint summary

Description of key information

Skin sensitisation (OECD 406): not sensitising

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

12 Mar - 14 Apr 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

Version / remarks:

adopted in 1992

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Slovenska Narodna Akreditacna Sluzba, Bratislava, Slovenska Republika

Type of study:

guinea pig maximisation test

Justification for non-LLNA method:

As the test substance is likely to have surfactant properties, the default LLNA study (OECD 429) is not recommended in this case.

Species:

guinea pig

Strain:

Dunkin-Hartley

Remarks:

albino

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Velaz, Czech Republic
- Females nulliparous and non-pregnant: yes
- Age at study initiation: about 10 weeks old
- Weight at study initiation: 462 – 517 g
- Housing: up to 5 animals per cage in plastic cages suspended on stainless steel racks with Lignocel S3/4 bedding (Lufa-ITL GmbH, Germany)
- Diet: laboratory food ssniff (Spezialdiäten GmbH, Germany), offered in recommended doses each day approximately at the same time (analyses were performed)
- Water: tap water (containing 0.05% ascorbic acid), ad libitum (analyses were performed)
- Acclimation period: 5 days
- Indication of any skin lesions: no

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 0.3
- Humidity (%): 58.8 ± 2.2
- Photoperiod (hrs dark / hrs light): 12/12

Route:

intradermal

Vehicle:

other: ethanol

Concentration / amount:

2%

Day(s)/duration:

Day 0 / single injection

Adequacy of induction:

other: highest concentration that did not cause destructive concentration of the skin after 24 h

Route:

epicutaneous, occlusive

Vehicle:

other: ethanol

Concentration / amount:

10%

Day(s)/duration:

Day 7 / 48 h

Adequacy of induction:

other: minimal irritating concentration

No.:

#1

Route:

epicutaneous, occlusive

Vehicle:

other: ethanol

Concentration / amount:

2%

Day(s)/duration:

Day 21 (treated group) and 22 (control group) / 24 h

Adequacy of challenge:

highest non-irritant concentration

No. of animals per dose:

Range finding test: 3 females

Main test:
Test group: 20 females
Negative control group: 10 females

Positive control group: 5 females

Details on study design:

RANGE FINDING TESTS:
Three females were pre-treated intradermally with an injection of 0.1 mL of FCA mixed 1:1 with vehicle (ethanol) 24 h before the induction phase.
These animals were used to assess the primary irritation tests after intradermal injection and after topical application. One animal was treated intradermally with 6 different test substance concentrations (initially 10, 25 and 50% on the right side of the animal; on the next day 1, 2 and 8% on the left side of the animal) and two animals were treated topically (4 different test substance concentrations each: 25, 50, 75 and 100% on one animal and the next day 2, 5, 10 and 15% on the second animal). Observations of the skin for the primary irritancy were scored after 24 h according to the Draize et al. scale. At a test substance concentration of 1%, the intradermal injection caused very slight erythema (grade 1) and no edema, well-defined erythema (grade 2) and very slight oedema (grade 1) were observed at concentrations of 2% or more. After topical application no edema was observed at any concentration, while very slight erythema (grade 1) was observed at 5% and well-defined erythema (grade 2) at 10% or more. According to the results of the range finding study, the following dose levels were selected for the main study:
Induction / intradermal injection: 2%
Induction / epicutaneous application: 10%
Challenge / epicutaneous application: 2%

MAIN STUDY
A. INDUCTION EXPOSURE
- No. of exposures: 2 (intradermal and epicutaneous)
- Exposure period: single injection (intradermal) and 48 h (epicutaneous)

- Test groups:
Intradermal (three pairs of injections; 0.1 mL/site):
Injection 1: Freund's Complete Adjuvant (FCA) 1:1 with water
Injection 2: 2% test substance formulated in vehicle
Injection 3: 2% test substance formulated in a 1:1 mixture FCA/water

Epicutaneous:
The test substance (in the minimal irritating concentration, 10%) was spread over 2 x 4 cm piece of gauze to saturation. The patch was secured with an occlusive dressing for 48 h.

- Control group:
Intradermal (three pairs of injections, 0.1 mL/site):
Injection 1: FCA 1:1 with water
Injection 2: undiluted vehicle
Injection 3: 50% w/v formulation of the vehicle in a 1:1 mixture FCA/water

Epicutaneous:
The vehicle was applied in the same manner as the test item in the treated group and held in contact by an occlusive dressing for 48 h.

- Site: shoulder region
- Frequency of applications: once (intradermal induction on Day 0 and epicutaneous application on Day 7)
- Concentrations: 2% (intradermal) and 10% (epicutaneous)

B. CHALLENGE EXPOSURE
- No. of exposures: 1
- Day of challenge: 21 (treated group), 22 (control group)
- Exposure period: 24 h
- Test groups: test substance and vehicle
- Control group: test substance and vehicle
- Site: flanks, previously unexposed area
- Concentrations: 2% of test substance (epicutaneous application)
- Evaluation: 24 and 48 h after removing the patches

OTHER:
The animals were inspected daily during the study for clinical symptoms. Individual weights of animals were determined shortly before the test substance was applied and at the end of the study.

Challenge controls:

the control group is actually a challenge control

Positive control substance(s):

yes

Remarks:

α-hexylcinnamaldehyde (in concurrent study, reliability check)

Positive control results:

The reliability of experimental technique used was performed with five animals, using α-hexylcinnamaldehyde (positive control) as a part of the study.
The same procedure as on treated and control animals were used. A pilot study was not performed due to the fact that the used substance (α-hexylcinnamaldehyde) is well known. The applied concentrations were chosen based on literature and previous studies.
Induction / Intradermal injection: 0.3%
Induction / epicutaneous application: 100% (undiluted)
Challenge / epicutaneous application: 100% (undiluted)
Well defined erythema (grade 2) was seen 24 h after removal of the patches in 2/5 animals of the positive control group, and slight erythema (grade 1) for the remaining 3/5 animals. This result represents skin sensitization reaction in 100% of tested animals. Slight erythema (grade 1) was still visible 48 h after removal of the patches in 4/5 animals. Edema was not observed in any of the animals. Thus the reliability of the experimental technique could be shown.

Reading:

1st reading

Hours after challenge:

24

Group:

negative control

Dose level:

intradermal induction: 0%; challenge: 2%

No. with + reactions:

0

Total no. in group:

10

Remarks on result:

no indication of skin sensitisation

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

intradermal induction: 2% challenge: 2%

No. with + reactions:

5

Total no. in group:

20

Reading:

1st reading

Hours after challenge:

24

Group:

positive control

Dose level:

intradermal induction: 0.3%, challenge: 100%

No. with + reactions:

5

Total no. in group:

5

Remarks on result:

positive indication of skin sensitisation

Reading:

2nd reading

Hours after challenge:

48

Group:

negative control

Dose level:

intradermal induction: 0% challenge: 2%

No. with + reactions:

0

Total no. in group:

10

Remarks on result:

no indication of skin sensitisation

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

intradermal induction: 2% challenge: 2%

No. with + reactions:

2

Total no. in group:

20

Reading:

2nd reading

Hours after challenge:

48

Group:

positive control

Dose level:

intradermal induction: 0.3%, challenge: 100%

No. with + reactions:

4

Total no. in group:

5

Remarks on result:

positive indication of skin sensitisation

Table 3: Skin reaction in Range finding study

Animal No.	Test substance concentration (%)	Erythema	Edema	Route
1	50	2	1	intradermal injection
	25	2	1
	10	2	1
	8	2	1
	2	2	1
	1	1	0
2	100	2	0	epicutaneous application
	75	2	0
	50	2	0
	25	2	0
3	15	2	0	epicutaneous application
	10	2	0
	5	1	0
	2	0	0

Table 4: Skin response after challenge (treated with 2% of the test substance) and body weight change

Animal No.	Group	Reaction scores				Body weight change/ gain (g)**
		24 h*		48 h*
		Erythema	Edema	Erythema	Edema
1	Control group	0	0	0	0	36
2		0	0	0	0	52
3		0	0	0	0	36
4		0	0	0	0	86
5		0	0	0	0	54
6		0	0	0	0	46
7		0	0	0	0	62
8		0	0	0	0	76
9		0	0	0	0	90
10		0	0	0	0	48
11	Treatment group	0	0	0	0	66
12		0	0	0	0	38
13		0	0	0	0	30
14		0	0	0	0	64
15		0	0	0	0	74
16		0	0	0	0	68
17		1	0	1	0	38
18		0	0	0	0	72
19		0	0	0	0	10
20		0	0	0	0	62
21		1	0	0	0	70
22		1	0	0	0	46
23		0	0	0	0	38
24		1	0	1	0	32
25		0	0	0	0	56
26		0	0	0	0	54
27		0	0	0	0	70
28		1	0	0	0	84
29		0	0	0	0	6
30		0	0	0	0	42

* = time after removal of the patches

** =  before test substance application and at end of the study

Table 5: Skin response and body weight change after treatment with undiluted α-hexylcinnamaldehyde (positive control)

Animal No.	Reaction scores				Body weight change/ gain (g)**
	24 h*		48 h*
	Erythema	Edema	Erythema	Edema
1	1	0	1	0	18
2	1	0	0	0	48
3	2	0	1	0	48
4	1	0	1	0	60
5	2	0	1	0	32

* = time after removal of the patches

** = before test substance application and at end of the study

No clinical signs and no deaths in any of the groups were observed. The body weights of all animals were increasing during the study.

Interpretation of results:

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

Conclusions:

In this guinea pig maximisation test (GPMT) 25% of the animals revealed a positive response after challenge at an intradermal induction concentration of 2%. Thus, the substance is not considered a skin sensitiser according to Regulation (EC) No. 1272/2008.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

Skin sensitisation

A Guinea pig maximisation test (GPMT) was performed with the test substance under GLP conditions and according to OECD guideline 406 (Hameln, 2018). Based on the results of a range finding study with three female Dunkin-Hartley albino guinea pigs, 20 test and 10 control guinea pigs were induced intradermally with 2% test substance (in ethanol) with and without Freund's complete adjuvant (FCA) or the vehicle with and without FCA. On Day 7, a 48-hour epicutaneous induction treatment with 10% of the test substance was performed under occlusive conditions. On Day 21/22, the challenge treatment was performed by epicutaneous application of the test substance at 2% (to the flank) to all animals for 24 h, under occlusive conditions. Skin reactions were evaluated 24 and 48 h after removal of the challenge patches. During the study, no test substance-related clinical signs and no effects on body weight gain were observed in the control or test group. No edema or erythema was observed in the control group, while the test group animals showed slight erythema (5/20 animals) 24 h after removal of the patches. This result represents skin sensitization reaction in 25% tested animals. Very slight erythema was still visible in 2/20 animals 48 h after removal of the patches (no new erythema). No edema was observed at any reading time point. The results of the reliability check were positive, confirming the reliability of the assay.

Based on the results, the test substance had no sensitising effect in guinea pigs under the experimental conditions.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

The available data on skin sensitisation do not meet the classification criteria according to Regulation (EC) 1272/2008, and are therefore conclusive but not sufficient for classification.