Propane-1-thiol

Endpoint summary

Description of key information

There are no skin sensitisation data for 1-propanethiol (CAS 107-03-9), therefore data were read-across from the structurally analogous substances isopropyl mercaptan (IPM; 2-propanethiol; CAS 75-33-2) and n-butyl mercaptan (NBM; 1-butanethiol; CAS 109-79-5). 1-Propanethiol (NPM), 1-butanethiol (NBM) and 2-propanethiol (IPM) all contain a thiol (-SH) functional group attached to an aliphatic carbon chain.

Isopropyl mercaptan (2-propanethiol; CAS 75-33-2) gave a positive result in the murine local lymph node assay, indicative of skin sensitisation properties. According to the EC3 of 75%, isopropyl mercaptan (2-propanethiol; CAS 75-33-2) should be considered as a weak sensitizer (CiToxLab, 2013). The study was conducted according to the appropriate OECD Test Guideline 429 and in compliance with GLP.

N-butyl mercaptan (1-butanethiol; CAS 109-79-5) gave a positive result in the murine Local Lymph Node Assay, indicative of skin sensitisation properties (CiToxLAB, 2011). The study was conducted according to an appropriate OECD Test Guideline 429 and in compliance with GLP.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Reference 1

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

02 October 2012 - 15 February 2013

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.42 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of study:

mouse local lymph node assay (LLNA)

Species:

mouse

Strain:

CBA

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: breeder: Janvier, Le Genest-Saint-Isle, France.
- Age/Weight at study initiation: on the beginning of the treatment period, the animals of the preliminary test were approximately 12 weeks old and had a mean body weight of 21.4 g (range: 20.3 g to 23.4 g), the animals of the first main test were approximately 8 weeks old and had a mean body weight of 20.2 g (range: 18.2 g to 22.3 g) and the animals of the second main test were approximately 8 weeks old and had a mean body weight of 18.3 g (range: 17.6 g to 19.4 g).
- Fasting period before study: no
- Housing: polycarbonate cages
- Diet: SSNIFF R/M-H pelleted diet (free access)
- Water: tap water filtered with a 0.22 µm filter (free access)
- Acclimation period: 6 days before the beginning of the study.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2°C
- Humidity (%): 50 ± 20%
- Air changes (per hr): approximately 12 cycles/hour of filtered, non-recycled air
- Photoperiod (hrs dark / hrs light): 12 h/12 h

IN-LIFE DATES: 10 October 2012 to 11 February 2013

Vehicle:

acetone/olive oil (4:1 v/v)

Concentration:

The maximum concentration tested in the both main tests was selected according to the criteria specified in the OECD Guidelines and on the basis of the data that was obtained in the preliminary test:
- the vehicle should be selected on the basis of producing a homogeneous preparation suitable for application of the test item,
- the concentrations were selected from the concentration series 100% (when test item can be sampled by a pipette), 50%, 25%, 10%, 5%, 2.5%, 1%, 0.5%, etc.,
- the maximum concentration of the test item was selected to avoid overt systemic toxicity and excessive local skin irritation the latter being defined by an ≥ 25% increase of the ear thickness.

No. of animals per dose:

Number:
- preliminary test: 4 nulliparous and non pregnant females,
- main tests:
- first main test: 28 nulliparous and non pregnant females,
- second main test: 20 nulliparous and non pregnant females.

Details on study design:

RANGE FINDING TESTS:
The maximum concentration tested in the both main tests was selected according to the criteria specified in the OECD Guidelines and on the basis of the data that was obtained in the preliminary test:
- the vehicle should be selected on the basis of producing a homogeneous preparation suitable for application of the test item,
- the concentrations were selected from the concentration series 100% (when test item can be sampled by a pipette), 50%, 25%, 10%, 5%, 2.5%, 1%, 0.5%, etc.,
- the maximum concentration of the test item was selected to avoid overt systemic toxicity and excessive local skin irritation the latter being defined by an ≥ 25% increase of the ear thickness.

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method: murine Local Lymph Node Assay
- Criteria used to consider a positive response: stimulation Index SI >= 3 and dose-relationship; additional consideration of ear thickness

TREATMENT PREPARATION AND ADMINISTRATION:
- Treatment preparation: The test item was prepared at the chosen concentrations in the vehicle.
The positive control was dissolved in AOO at the concentration of 25% (v/v).
- Administration:
On days 1, 2 and 3, a dose-volume of 25 µL of the control or dosage form preparations was applied to the dorsal surface of both ears, using an adjustable pipette fitted with a plastic tip.
In order to avoid licking and to ensure an optimized application of the test materials, the animals were placed under light isoflurane anesthezia during the administration.
No massage was performed but the tip was used to spread the preparation over the application sites. No rinsing was performed between each application.

Positive control substance(s):

other: α-hexyl cinnamaldehyde (HCA)

Positive control results:

The threshold positive value of 3 for the SI was reached in the positive control group (see the table below).

Parameter:

SI

Value:

2.26

Test group / Remarks:

50%

Parameter:

SI

Value:

2.82

Test group / Remarks:

75% group

Parameter:

SI

Value:

12.16

Test group / Remarks:

100% group

Parameter:

EC3

Value:

>= 75

Parameter:

other: disintegrations per minute (DPM)

Remarks on result:

other: see Remark

Remarks:

First assay: DPM per node: Group 3, Vehicle: 377.50 Group 4, 2.5%: 242.25 Group 5, 5%: 188.63 Group 6, 10%: 194.13 Group 7, 25%: 279.25 Group 8, 50%: 230.13 Group 9, HCA: 2665.00 Seconde assay: DPM per node: Group 10, Vehicle: 184.25 Group 11, 50%:: 415.88 Group 12, 75%: 519.13 Group 13, 100%: 2240.13 Group 14, HCA: 1065.50

STIMULATION INDEXES

First main test

 

Treatment	Concentration (%)	Irritation level	Stimulation Index (SI)
Test item	2.5	I	0.64
Test item	5	I	0.50
Test item	10	I	0.51
Test item	25	I	0.74
Test item	50	I	0.61
HCA	25	-	7.06

-: not recorded.

I: non-irritant (increase in ear thickness < 10%).

Second main test

 

Treatment	Concentration (%)	Irritation level	Stimulation Index (SI)
Test item	50	I	2.26
Test item	75	I	2.82
Test item	100	I	12.16
HCA	25	-	5.78

-: not recorded.

I: non-irritant (increase in ear thickness < 10%).

 

Interpretation of results:

Category 1B (indication of skin sensitising potential) based on GHS criteria

Conclusions:

Isopropyl mercaptan gave a positive result in the murine Local Lymph Node Assay, indicative of skin sensitization properties.
According to the EC3 of 75%, isopropyl mercaptan should be considered as a weak sensitizer.

According to the criteria of CLP Regulation, the test item should be classified as skin sensitizer (category 1 and sub-category 1B) and assigned the signal word “warning” and the hazard statement “H317: May cause an allergic skin reaction”.

Executive summary:

Local Lymph Node Assay (LLNA) (Gerbeix, 2013). This study was conducted in compliance with the principles of Good Laboratory Practice. To assess the irritant potential of propane-2-thiol (through ear thickness measurement), a preliminary test was first performed in order to define the propane-2-thiol concentrations to be used in the main test. Two groups of two female mice received propane-2-thiol, by topical route to the dorsal surface of both ears (one concentration per ear) on days 1, 2 and 3 at the concentrations of 5, 10, 25 or 50% under a dose-volume of 25 µL. From day 1 to day 3 then on day 6, the thickness of both ears of each animal was measured and the local reactions were recorded. Each animal was observed at least once a day for mortality and clinical signs. Body weight was recorded once during the acclimation period, and then on days 1 and 6. On completion of the observation period, the animals were sacrificed then discarded without macroscopicpost-mortemexamination. In the first main test, five groups of four female mice received propane-2-thiol by topical route to the dorsal surface of both ears on days 1, 2 and 3 at concentrations of 2.5, 5, 10, 25 or 50% under a dose‑volume of 25 µL. In the second main test, three groups of four female mice received propane-2-thiol by topical route to the dorsal surface of both ears on days 1, 2 and 3 at concentrations of 50, 75 or 100% under a dose‑volume of 25 µL. In both tests, one negative control group of four females received the vehicle (Acetone/Olive Oil (4/1; v/v)) under the same experimental conditions. Additionally, one positive control group of four females received the positive control,α‑hexylcinnamaldehyde (HCA), at 25% in a mixture acetone/olive oil (4/1; v/v) under the same experimental conditions. For each main test, from day 1 to day 3 then on day 6, the thickness of the left ear of each animal was measured, except in animals of the positive control groups, and the local reactions were recorded. Each animal was observed at least once a day for mortality and clinical signs. Body weight was recorded once during the acclimation period, and then on days 1 and 6. After 2 days of resting, on day 6, the animals received a single intravenous injection of tritiated methyl thymidine (³H-TdR). Approximately 5 hours later, the animals were sacrificed and the auricular lymph nodes were excised. The proliferation of lymphocytes in the lymph node draining the application site was measured by incorporation of³H-TdR. The results were expressed as disintegrations per minute (dpm) per group and as dpm/node. The obtained values were used to calculate Stimulation Indices (SI). No unscheduled deaths and no clinical signs indicative of systemic toxicity were observed during the observation period of both main tests. Body weight of animals was unaffected by propane-2-thiol treatment. No local reactions were observed in any animals of both main tests. No notable increase in ear thickness was observed at any tested concentrations. The SI of the positive control of both main tests was > 3; these main tests were therefore considered valid. No notable lymphoproliferation was noted with propane-2-thiol at any tested concentrations in the first main test. In the second main test, a dose-related increase in the SI was recorded at concentrations ≥ 50%, and the threshold positive value of 3 was exceeded at the concentration of 100%. In the absence of local irritation, the significant lymphoproliferative responses observed were attributed to delayed contact hypersensitivity. Based on the results of the second main test, the EC₃value is equal to 75.5%.

Propane-2-thiol gave a positive result in the murine Local Lymph Node Assay, indicative of skin sensitization properties. According to the EC₃value obtained, propane-2-thiol should be considered as a weak sensitizer.

 

First main test
Treatment	Concentration (%)	Irritation level	Stimulation Index (SI)
Test item	2.5	I	0.64
Test item	5	I	0.50
Test item	10	I	0.51
Test item	25	I	0.74
Test item	50	I	0.61
HCA	25	-	7.06
Second main test
Test item	50	I	2.26
Test item	75	I	2.82
Test item	100	I	12.16
HCA	25	-	5.78

-: not recorded.

I: non-irritant (increase in ear thickness < 10%).

Reference 2

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

15 September to 10 October 2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of study:

mouse local lymph node assay (LLNA)

Species:

mouse

Strain:

other: CBA/J

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Janvier (France)
- Age at study initiation: 8 weeks
- Weight at study initiation: 19.6 to 22.4 g
- Housing: 2 or 4 in polycarbonate cages (Techniplast 1145T) and then individually in disposable crystal polystyrene cages
- Diet (ad libitum): SSNIFF R/M-H pelleted maintenance diet (SSNIFF Spezialdiaten, Germany)
- Water (ad libitum): facility tap water
- Acclimation period: 11 or 13 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 to 24
- Humidity (%): 30 to 70
- Air changes (per hr): approximately 12
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES:
From: 28 September 2011
To: 10 October 2011

Vehicle:

acetone/olive oil (4:1 v/v)

Concentration:

10, 25, 50 or 100% preliminary test
5, 10 25, 50 or 100% main test

No. of animals per dose:

2 females preliminary test
4 females main test

Details on study design:

RANGE FINDING TESTS:
- Compound solubility: solution obtained at 50% concentration of test substance.
- Irritation: no local reaction noted
- Ear thickness response: no increase in ear thickness noted

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method: LLNA
- Criteria used to consider a positive response: SI >= 3 together with dose-response relationship

TREATMENT PREPARATION AND ADMINISTRATION:
The test item was administered as a solution in the vehicle. The test item was mixed by vortex with the required quantity of vehicle. The test item concentrations were expressed in % (v/v). The positive control was prepared at the concentration of 25% (v/v) a mixture of Acetone/Olive Oil (4/1; v/v) (AOO). Dosage forms preparations were prepared extemporaneously on the day of each administration. The dosage forms were be stored at room temperature and delivered to the study room in stoppered plastic tubes.

On days 1, 2 and 3, a dose-volume of 25 μL of the appropriate dosage form preparation was applied to the dorsal surface of one or both ears, using an adjustable pipette fitted with a plastic tip. In order to avoid licking, to ensure an optimized application of the test materials and to facilitate ear thickness measurement, the animals were placed under light isoflurane anaesthesia during the administration. No massage was performed but the tip was used to spread the preparation over the application site. No rinsing was performed.

Positive control substance(s):

hexyl cinnamic aldehyde (CAS No 101-86-0)

Statistics:

The EC3 value (theoretical concentration resulting in a SI value of 3) was determined by linear interpolation of points on the dose-response curve, immediately above and below the 3-fold threshold. The equation used for calculation of EC3 was:

EC3 = c + [(3 - d)/(b - d)] x (a - c)

Where a = the lowest concentration giving Stimulation Index > 3; b = the actual Stimulation Index caused by a; c = the highest concentration failing to produce a Stimulation Index of 3; d = the actual Stimulation Index caused by c.

Group means and Standard deviations calculated where appropriate.

Positive control results:

Group Mean Stimulation Index = 3.97 (experiment was considered valid)
Group Mean dpm = 12822

Parameter:

SI

Value:

5.38

Test group / Remarks:

50% group

Parameter:

SI

Value:

14.4

Test group / Remarks:

100% group

Parameter:

SI

Remarks on result:

other: At 5%, 10% and 25% concentrations of nBM the Stimulation Index was less than 3.

Parameter:

EC3

Value:

30

Parameter:

other: disintegrations per minute (DPM)

Remarks on result:

other: see table

Mortality

There were no unscheduled deaths during the study.

Clinical Signs

There were no remarkable clinical signs noted during the study.

Body weight

There was no effect on body weight.

Ear thickness measurement and local reactions

No local reactions or notable increase in ear thickness were noted in the preliminary test at any concentration.

In the main test, in all females at 100% concentration dryness of the skin on day 6 was recorded and erythema was also noted for one female. All females at 100% concentration also showed an increase in ear thickness between days 1 and 6 (mean value 15.15%).

Interpretation of results:

Category 1 (skin sensitising) based on GHS criteria

Conclusions:

N-butylmercaptan was found to be sensitising in a mouse local lymph node assay, resulting in a Stimulation Index of greater than 3 at concentrations of 50% and above (5.38 and 14.40 at substance concentrations of 50% and 100% respectively). The EC3 value was calculated to be 30%.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

There are no skin sensitisation data for 1-propanethiol (CAS 107-03-9), therefore data were read-across from the structurally analogous substances isopropyl mercaptan (IPM; 2-propanethiol; CAS 75-33-2) and n-butyl mercaptan (NBM; 1-butanethiol; CAS 109-79-5). 1-Propanethiol (NPM), 1-butanethiol (NBM) and 2-propanethiol (IPM) all contain a thiol (-SH) functional group attached to an aliphatic carbon chain. See attachment to Section 13 for justification for read-across.

The local lymph node assay (LLNA) (CiToxLab, 2013) with isopropyl mercaptan (2-propanethiol; CAS 75-33-2) was conducted in compliance with the principles of Good Laboratory Practice. No unscheduled deaths and no clinical signs indicative of systemic toxicity were observed during the observation period of both main tests. Body weight of animals was unaffected by propane-2-thiol treatment. No local reactions were observed in any animals of both main tests. No notable increase in ear thickness was observed at any tested concentrations. The SI of the positive control of both main tests was > 3; these main tests were therefore considered valid. No notable lymphoproliferation was noted with propane-2-thiol at any tested concentrations in the first main test. In the second main test, a dose-related increase in the SI was recorded at concentrations ≥ 50%, and the threshold positive value of 3 was exceeded at the concentration of 100%. In the absence of local irritation, the significant lymphoproliferative responses observed were attributed to delayed contact hypersensitivity. Based on the results of the second main test, the EC₃value is equal to 75.5%. Propane-2-thiol gave a positive result in the murine Local Lymph Node Assay, indicative of skin sensitization properties. According to the EC₃value obtained, 2-propanethiol should be considered as a weak sensitizer.

The mouse local lymph node assay with n-butyl mercaptan (1-butanethiol; CAS 109-79-5) was conducted according to OECD Test Guideline 429 (CiToxLAB, 2011) and in compliance with GLP. The stimulation index (SI) was greater than 3 at concentrations of 50% and above (5.38 and 14.40 at substance concentrations of 50% and 100% respectively). Therefore n-butyl mercaptan was considered to be sensitising. The EC3 value (estimated test substance concentration that will give an SI of 3) was calculated to be 30%.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the available read-across information for isopropyl mercaptan (2-propanethiol; CAS 75-33-2) and n-butyl mercaptan (1-butanethiol; CAS 109-79-5), the registered substance, 1-propanethiol, should be classified as skin sensitizer category 1B “H317: May cause an allergic skin reaction” according to Regulation (EC) No 1272/2008.