2-methylbutane

Endpoint summary

Description of key information

Skin Sensitisation

2-methylbutane was not a dermal sensitizer in a Guinea-Pig Maximization test (OECD TG 406).

 

Respiratory Sensitisation

no data

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Reference 1

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991-07-23 to 1991-09-04

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable without restrictions because it is in compliance with the OECD principles of GLPs.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

Deviations:

yes

Remarks:

Information regarding the nature of the test material was not provided, but was noted to be the responsibility of the Sponsor. This deviation was not expected to affect the study results.

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method B.6 (Skin Sensitisation)

Deviations:

yes

Remarks:

Information regarding the nature of the test material was not provided, but was noted to be the responsibility of the Sponsor. This deviation was not expected to affect the study results.

GLP compliance:

yes

Type of study:

other: Not specified, but similar to the Guinea-pig Maximization test method, using Draize dermal scores and Freunds Complete Adjuvant (FCA)

Justification for non-LLNA method:

Acceptable study that followed sound scientific principles.

Species:

guinea pig

Strain:

Hartley

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Hazleton Research Products, Inc., Denver, Pennsylvania
- Age at study initiation: approximately 6 weeks
- Weight at study initiation: 313 to 416 g
- Housing: individual, suspended stainless steel caging, indirect bedding
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): not reported
- Acclimation period: 15 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): maintained 18 to 22°C
- Humidity (%): maintained 40 to 70%
- Air changes (per hr): not reported
- Photoperiod (hrs dark / hrs light): 12 hours dark and 12 hours light

IN-LIFE DATES: From: 1991-07-23 to 1991-09-04

Route:

other: intradermal at day 0 and epicutaneous, occlusive at day 7

Vehicle:

other: ethanol and reverse osmosis water

Concentration / amount:

Nominal: 5.0% at first induction, 100% at second induction, and 1.0% at challenge
Actual: 4.14% at first induction and 0.717% at challenge

Route:

epicutaneous, occlusive

Vehicle:

other: ethanol and reverse osmosis water

Concentration / amount:

Nominal: 5.0% at first induction, 100% at second induction, and 1.0% at challenge
Actual: 4.14% at first induction and 0.717% at challenge

No. of animals per dose:

20; only 10 control animals used for challenge exposure

Details on study design:

MAIN STUDY
A. INDUCTION EXPOSURE
Day 0
- Exposure: intradermal
- Application: three pairs of injections
- Dose: 0.1 mL
- Test groups: exposed to FCA and test material
- Site 1: along spinal cord, near first thoracic vertebra; FCA/water
- Site 2: along spinal cord, near first thoracic vertebra; 5.0% test material in carrier
- Site 3: along spinal cord, caudal from first thoracic vertebra; 5.0% test material in FCA/water
- Control group: exposed to FCA and carrier
- Site 1: along spinal cord, near first thoracic vertebra; FCA/water
- Site 2: along spinal cord, near first thoracic vertebra; 100% carrier
- Site 3: along spinal cord, caudal from first thoracic vertebra; 5.0% carrier in FCA/water

Day 7
- Exposure: occlusive topical application
- Duration: 48 hours
- Dose: 0.5 mL
- Test groups: exposed to 100% test material
- Control group: exposed to 100% carrier
- Site: injected area on the dorsal surface

B. CHALLENGE EXPOSURE
Day 21
- Exposure: occlusive topical application
- Duration: 24 hours
- Dose: 0.4 mL
- Test groups: exposed to 1.0% test material in carrier on right flank, 100% carrier on left flank
- Control group: exposed to 1.0% test material in carrier on right flank, 100% carrier on left flank (10 animals only)
- Site: right and left flanks in the abdominal region
- Evaluation (hr after challenge): 24 and 48 hours after removal of challenge patches

Challenge controls:

Control group responses were used to distinguish true sensitization from local irritation produced by a single exposure to the same concentration of test material. Test material was applied to the left flank of all treated and ten of the control group animals, while carrier alone was applied to the right flank of all treated and the same ten control group animals.

Positive control substance(s):

yes

Remarks:

1 chloro-2,4-dinitrobenzene (DNCB)

Positive control results:

The positive control material (DNCB) elicited reactions from all 20 animals both at 24 and 48 hours after removal of the challenge patch. Based on these results, the animals and methods used are capable of detecting the sensitisation potential of the test material.

Reading:

1st reading

Hours after challenge:

24

Group:

negative control

Dose level:

1.0% test material (0.4 mL)

No. with + reactions:

0

Total no. in group:

10

Clinical observations:

No abnormal clinical observations were noted

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: negative control. Dose level: 1.0% test material (0.4 mL). No with. + reactions: 0.0. Total no. in groups: 10.0. Clinical observations: No abnormal clinical observations were noted.

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

1.0% test material (0.4 mL)

No. with + reactions:

0

Total no. in group:

20

Clinical observations:

No abnormal clinical observations were noted

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: test group. Dose level: 1.0% test material (0.4 mL). No with. + reactions: 0.0. Total no. in groups: 20.0. Clinical observations: No abnormal clinical observations were noted.

Reading:

1st reading

Hours after challenge:

24

Group:

positive control

Dose level:

0.1% DNCB (0.4 mL)

No. with + reactions:

15

Total no. in group:

15

Clinical observations:

-

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: positive control. Dose level: 0.1% DNCB (0.4 mL). No with. + reactions: 15.0. Total no. in groups: 15.0. Clinical observations: -.

Reading:

2nd reading

Hours after challenge:

48

Group:

negative control

Dose level:

1.0% test material (0.4 mL)

No. with + reactions:

0

Total no. in group:

10

Clinical observations:

No abnormal clinical observations were noted

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: negative control. Dose level: 1.0% test material (0.4 mL). No with. + reactions: 0.0. Total no. in groups: 10.0. Clinical observations: No abnormal clinical observations were noted.

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

1.0% test material (0.4 mL)

No. with + reactions:

0

Total no. in group:

20

Clinical observations:

No abnormal clinical observations were noted

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: test group. Dose level: 1.0% test material (0.4 mL). No with. + reactions: 0.0. Total no. in groups: 20.0. Clinical observations: No abnormal clinical observations were noted.

Reading:

2nd reading

Hours after challenge:

48

Group:

positive control

Dose level:

0.1% DNCB (0.4 mL)

No. with + reactions:

10

Total no. in group:

15

Clinical observations:

-

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: positive control. Dose level: 0.1% DNCB (0.4 mL). No with. + reactions: 10.0. Total no. in groups: 15.0. Clinical observations: -.

All animals survived to study termination and displayed a weight gain from their day 0 values. No abnormal clinical inlife observations were noted for any animals during the study. One control group animal displayed very slight erythema 24 hours following patch removal for the ethanol dose site. No other signs of dermal irritation were noted for either dose group on days 23 and 24. Based on the lack of signs of dermal irritation during the challenge phase of this study, isopentane shows no sensitization potential.

Interpretation of results:

other: Not sensitising

Conclusions:

2-methylbutane was considered non-irritating.

Executive summary:

In this skin sensitisation study with isopentane young adult Hartley albino guinea pigs (20 females per dose) were tested using the Guinea Pig Maximization Test method. Guinea pigs were exposed to the test material via induction twice to allow for development of sensitisation, then challenged and compared to the control group and examined for signs of dermal irritation.

There was no evidence of dermal irritation or sensitisation in this study. 2 -methylbutane is not a dermal sensitizer. This study is classified with a Klimisch score of 1, reliable without restrictions, because it is in compliance with the OECD principles of GLP and because it is similar to OECD Guideline 406 and EU Method B.6.

Reference 2

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable without restriction because it is in compliance with the OCED principles of GLPs.

Justification for type of information:

A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across: supporting information

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

GLP compliance:

yes

Type of study:

not specified

Justification for non-LLNA method:

Acceptable study that followed sound scientific principles.

Species:

guinea pig

Strain:

Hartley

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Hazleton Research Products, Inc., Denver, Pennsylvania
- Age at study initiation: Approximately 6 weeks
- Weight at study initiation: 324 to 409 grams
- Housing: Individual (during test period) in suspended stainless steel cages
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 15 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18.33 to 21.67°C
- Humidity (%): 40 to 70%
- Photoperiod (hrs dark / hrs light): 12 hours dark and 12 hours light

IN-LIFE DATES: From: 1991-07-21 To: 1991-09-04

Route:

intradermal and epicutaneous

Vehicle:

other: Freund's Complete Adjuvant (FCA)

Concentration / amount:

Induction Phase: 5% n-pentane in ethanol (Site 2); 5% n-pentane in FCA/Water (Site 3)
Challenge Phase: 1% n-pentane in ethanol

Route:

epicutaneous, occlusive

Vehicle:

other: Freund's Complete Adjuvant (FCA)

Concentration / amount:

Induction Phase: 5% n-pentane in ethanol (Site 2); 5% n-pentane in FCA/Water (Site 3)
Challenge Phase: 1% n-pentane in ethanol

No. of animals per dose:

20

Details on study design:

MAIN STUDY
A. INDUCTION EXPOSURE
- No. of exposures: 6
- Test groups: FCA/Water; n-pentane in ethanol; n-pentane in FCA/Water
- Control group: FCA/Water; Ethanol; 5% Reverse Osmosis Water in FCA/Water
- Site: Mid-dorsal region, near the scapula
- Duration: 0 to 7 days
- Concentrations: same throughout

B. CHALLENGE EXPOSURE
- No. of exposures: 1
- Day(s) of challenge: 21
- Exposure period: 24 hours
- Test groups: n-pentane
- Control group: Ethanol
- Site: L Flank - n-pentane; R Flank - Carrier (ethanol)
- Concentrations: 1.0% n-pentane in ethanol
- Evaluation (hr after challenge): 24, 48

Challenge controls:

0.4 mL of carrier - ethanol (100% ) was administered topically to guinea pigs in the treatment and irritation control groups

Positive control substance(s):

yes

Remarks:

1-chloro-2,4-dinitrobenzene (DNCB)

Positive control results:

not reported

Reading:

1st reading

Hours after challenge:

24

Group:

negative control

Dose level:

100% ethanol (0.4 mL)

No. with + reactions:

0

Total no. in group:

20

Clinical observations:

No clinical signs observed

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: negative control. Dose level: 100% ethanol (0.4 mL). No with. + reactions: 0.0. Total no. in groups: 20.0. Clinical observations: No clinical signs observed.

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

1% in ethanol

No. with + reactions:

0

Total no. in group:

20

Clinical observations:

No treatment-related clinical signs observed

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: test group. Dose level: 1% in ethanol. No with. + reactions: 0.0. Total no. in groups: 20.0. Clinical observations: No treatment-related clinical signs observed.

Reading:

1st reading

Hours after challenge:

24

Group:

positive control

Dose level:

0.1% DNCB in acetone

No. with + reactions:

15

Total no. in group:

15

Clinical observations:

slight to severe erythema and edema were observed at 24 and 48 hours post challenge

Remarks on result:

other: see Remark

Remarks:

Reading: 1st reading. . Hours after challenge: 24.0. Group: positive control. Dose level: 0.1% DNCB in acetone. No with. + reactions: 15.0. Total no. in groups: 15.0. Clinical observations: slight to severe erythema and edema were observed at 24 and 48 hours post challenge.

Table 1. Incidence of Challenge in Guinea Pig - Ethanol
Dermal Observation	Dermal Score
	No. of animals	0	1	2	3	4
Irritation Control Group
24 hr erythema	10	10	0	0	0	0
24 hr edema	10	10	0	0	0	0
48 hr erythema	10	10	0	0	0	0
48 hr edema	10	10	0	0	0	0
Treatment Group
24 hr erythema	20	20	0	0	0	0
24 hr edema	20	20	0	0	0	0
48 hr erythema	20	20	0	0	0	0
48 hr edema	20	20	0	0	0	0

Table 2. Incidence of Challenge in Guinea Pig – MRD-91-962
Dermal Observation	Dermal Score
	No. of animals	0	1	2	3	4
Irritation Control Group
24 hr erythema	10	10	0	0	0	0
24 hr edema	10	10	0	0	0	0
48 hr erythema	10	10	0	0	0	0
48 hr edema	10	10	0	0	0	0
Treatment Group
24 hr erythema	20	20	0	0	0	0
24 hr edema	20	20	0	0	0	0
48 hr erythema	20	20	0	0	0	0
48 hr edema	20	20	0	0	0	0

Table 3. Incidence of Challenge in Guinea Pig – DNCB (Positive Control)
Dermal Observation	Dermal Score
	No. of animals	0	1	2	3	4
Irritation Control Group - Acetone
24 hr erythema	15	15	0	0	0	0
24 hr edema	15	15	0	0	0	0
48 hr erythema	15	15	0	0	0	0
48 hr edema	15	15	0	0	0	0
Treatment Group – 0.1% DNCB in Acetone
24 hr erythema	15	0	0	9	6	0
24 hr edema	15	6	5	4	0	0
48 hr erythema	15	0	3	7	0	5
48 hr edema	15	5	3	7	0	0

Interpretation of results:

other: Not sensitising

Conclusions:

n-Pentane showed no irritation or sensitization potential after intradermal and topical application in Guinea pigs (experimental days one and seven), followed by occluded dermal challenge on day 21. n-Pentane is not a dermal sensitiser.

Executive summary:

A dermal sensitisation study was conducted in guinea pigs (20 females/dose; 15 females for positive control) using n-pentane.

Induction Phase: An area near the scapula in the mid-dorsal region of all animals was clipped on the day prior to intradermal injection of tbe test material and/or carrier. 6 intradermal injections (0.1 mL each) were administered to 3 different sites as follows: Site 1: FCA/water to treated and control groups; Site 2: 5.0% n-pentane in carrier (ethanol) to the treated group, 100% ethanol to the control group; Site 3: 5.0% n-pentane in FCA/Water to the treated group, 5.0% carrier (reverse osmosis water) in FCA/Water to the control group. On day 7 following injection, 0.5 mL of a mild to moderately irritating dose of n-pentane was administered topically over the previously injected areas and covered with occlusive wrapping. Control animals received topical carrier applications instead.

Challenge Phase: 21 days post induction phase, 0.1 mL of n-pentane (1.0% in ethanol) was applied topically to the left flank of both treated and control irritation groups. 0.4 mL of the carrier (ethanol) was applied to the right flank. All applications were kept secure under occlusive wrapping for 24 hours and animals observed for dermal effects for 48 hours.

Sensitization was evaluated by comparing the reactions of treated animals with the reactions of control animals that received a single epidermal exposure to the test material. Control responses were used to distinguish true sensitization from local irritation produced by the same concentration of test material.

All animals survived to study termination and displayed a weight gain from their day 0 values. Abnormal clinical observations during scheduled intervals were limited to one treated group animal that was emaciated and had a small amount of stool. Another animal exhibited slight emaciation and poor food consumption. Clinical signs observed in these two animals were considered to be correlated to the stress of the wrapping procedure and not treatment-related. No signs of dermal irritation were observed at any dose in either patch group. DNCB elicited positive reactions from all tested animals 24 and 48 hours after removal of the patch challenge.

Based on the lack of signs dermal irritation observed in the study, n-pentane is not considered a dermal sensitiser. This study was given a Klimisch score of 1 and classified as reliable without restriction because it is in compliance with the OCED principles of GLPs.

Reference 3

Endpoint:

skin sensitisation: in vitro

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

an in vitro skin sensitisation study does not need to be conducted because adequate data from an in vivo skin sensitisation study are available

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

Key skin sensitisation data is available for 2-methylbutane. This information is supported by data available for structural analogue, pentane, and presented in the dossier. This data is read across to 2-methylbutane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

Skin Sensitisation

 

2-methylbutane

 

In a key skin sensitisation study (Exxon Biomedical Sciences Inc., 1991) with isopentane, young adult Hartley albino guinea pigs (20 females per dose) were tested using the Guinea Pig Maximization Test method. Guinea pigs were exposed to the test material via induction twice to allow for development of sensitisation, then challenged and compared to the control group and examined for signs of dermal irritation.

 

There was no evidence of dermal irritation or sensitisation in this study. 2 -methylbutane is not a dermal sensitizer. This study is classified with a Klimisch score of 1, reliable without restrictions, because it is in compliance with the OECD principles of GLP and because it is similar to OECD Guideline 406 and EU Method B.6.

Pentane

For n-pentane, a study (Exxon Biomedical Sciences, Inc., 1991) was conducted using guinea pigs (20 females/dose; 15 females for positive control; Trimmer, 1991). For the induction phase, six intradermal injections (0.1 mL each) were administered to three different sites as follows: Site 1: FCA/water to treated and control groups; Site 2: 5.0% n-pentane in carrier (ethanol) to the treated group, 100% ethanol to the control group; Site 3: 5.0% n-pentane in FCA/Water to the treated group, 5.0% carrier (reverse osmosis water) in FCA/Water to the control group. On day 7 following injection, 0.5 mL of a mild to moderately irritating dose of n-pentane was administered topically over the previously injected areas and covered with occlusive wrapping. Control animals received topical carrier applications instead. The challenge phase was conducted 21 days post induction phase. n-Pentane (0.1 mL of n-pentane; 1.0% in ethanol) was applied topically to the left flank of both treated and control irritation groups. All animals survived to study termination and displayed a weight gain from their day 0 values. Abnormal clinical observations during scheduled intervals were limited to one treated group animal that was emaciated and had a small amount of stool. Another animal exhibited slight emaciation and poor food consumption. Clinical signs observed in these two animals were considered to be correlated to the stress of the wrapping procedure and not treatment-related. No signs of dermal irritation were observed at any dose in either patch group. DNCB elicited positive reactions from all tested animals 24 and 48 hours after removal of the patch challenge. Based on the lack of signs dermal irritation observed in the study, n-pentane was not considered a dermal sensitiser. 

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

There are no reports of respiratory sensitization from 2-methylbutane in laboratory animals or humans. However, skin sensitization studies utilizing 2-methylbutane and structural analogue pentane found no indication of skin sensitization in guinea pigs. With these observations, it is presumed that 2-methylbutane will not be a respiratory sensitizing agent.

Justification for classification or non-classification

Based on available substance specific and read across data, 2-methylbutane does not meet the criteria for classification as a skin or respiratory sensitizer under the new Regulation (EC) 1272/2008 on classification, labeling and packaging of substances and mixtures (CLP).