Ethoxyquin

Endpoint summary

Description of key information

Skin sensitisation in vitro: Data waiving, in vivo studies are available.

Skin sensitisation in vivo: not sensitising; Buehler test, topical induction (100%), topical challenge (50%), guinea pig, m/f (OECD 406, GLP)

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

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Remarks:

Peer-reviewed assessment report (attached in section 13)

Qualifier:

according to guideline

Guideline:

EPA OPP 81-6 (Skin Sensitisation)

Version / remarks:

US EPA FIFRA Guideline §81-6

Deviations:

yes

Remarks:

Purity of the test compound was not determined by the laboratory prior to conduct of the test.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

Deviations:

not applicable

GLP compliance:

yes

Remarks:

self-certified to US EPA regulations at 40 CFR Parts 160 and 792

Type of study:

Buehler test

Justification for non-LLNA method:

Test was conducted for another regulatory purpose, other than and prior to REACH registration.

Species:

guinea pig

Strain:

Hartley

Sex:

male/female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Harlan Sprague Dawley, Inc., Indianapolis, IN, USA

Route:

other: topical

Vehicle:

unchanged (no vehicle)

Day(s)/duration:

Once per week for three weeks for a total of three induction exposures. The duration of the exposures was six hours.

Adequacy of induction:

not specified

No.:

#1

Route:

other: topical

Vehicle:

not specified

Concentration / amount:

50%

Day(s)/duration:

Two weeks after the last induction exposure

Adequacy of challenge:

highest non-irritant concentration

No.:

#2

Route:

other: topical

Vehicle:

not specified

Concentration / amount:

50%

Day(s)/duration:

One week after challenge, test group animals were re-challenged to confirm the initial results.

Adequacy of challenge:

highest non-irritant concentration

No. of animals per dose:

6

Details on study design:

MAIN STUDY
A. INDUCTION EXPOSURE
- No. of exposures / Exposure period / Test groups / Frequency of applications / Duration: A test group was dosed topically for each 6 hours with the undiluted test material once per week for three weeks for a total of three induction exposures.
- Control group: A positive control group of three male and three female guinea pigs was included to demonstrate the reliability of the test system. The positive control group was induced and challenged on a similar regimen as the test group with dinitrochlorobenzene (DNCB) as the positive control material. Two naive control groups of three male and three female guinea pigs each were dosed only at challenge and re-challenge, respectively, in the same manner as the test group and served as irritation controls.
- Concentrations: neat

B. CHALLENGE EXPOSURE
- No. of exposures: 2
- Day(s) of challenge / Exposure period / Test groups: Two weeks after the last induction exposure, test group animals were challenged for detection of sensitisation by topical application of a concentration of the test material that had been proven to be non-irritating before to previously unexposed areas of skin. One week after challenge, test group animals were re-challenged to confirm the initial results. The test material concentrations used for induction challenge and re-challenge dosing were selected based on the results of range-finding experimentation in the primary irritation phase.
- Control group: see above
- Site: previously unexposed areas of skin
- Concentrations: 50%
- Evaluation (hr after challenge): Reactions to challenge and re-challenge dosing were evaluated at approximately 24 and 48 hours after completion of exposure.

OTHER: Body weights and clinical observations were recorded just prior to initiation of dosing and at termination.

Challenge controls:

Two naive control groups of three male and three female guinea pigs each were dosed only at challenge and re-challenge, respectively, in the same manner as the test group and served as irritation controls.

Positive control substance(s):

yes

Remarks:

dinitrochlorobenzene (DNCB)

Positive control results:

Induction phase: For positive control group animals, irritation noted after the first induction dosing with 0.25 % DNCB included five slight (grade 1) erythema reactions and one very slight (grade ±) reaction. Following the second induction, positive control group dermal findings included one severe (grade 3) reaction and five sites with moderate (grade 2) reactions. Eschar was present on five sites following second induction. After the third induction dosing, five animals had slight reactions and one site had a very slight erythema reaction. In addition, eschar was noted on one site following the third induction.
Challenge phase: In the positive control group, there was one slight and five moderate (grade 2) reactions). Eschar was observed for one animal at 24 hours post-dose. By 48 hours, slight and moderate erythema was noted for three animals each. Focal eschar and eschar were present on one site each at 48 hours post-challenge.
Re-challenge phase: Four and five very slight reactions were observed at the 24- and 48-hour observations, respectively, for naïve control II group guinea pigs dosed with 50 % ethoxyquin.

Key result

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

50% ethoxyquin

No. with + reactions:

10

Total no. in group:

12

Clinical observations:

The 50 % concentration of ethoxyquin induced ten very slight (grade ±) reactions at 24 hours for test group animals following challenge dosing.

Remarks on result:

other:

Remarks:

result similar to control

Reading:

1st reading

Hours after challenge:

48

Group:

test chemical

Dose level:

50% ethoxyquin

No. with + reactions:

10

Total no. in group:

12

Clinical observations:

By 48 hours, irritation included nine sites with very slight reactions and one with a slight (grade 1) reaction.

Reading:

rechallenge

Hours after challenge:

24

Group:

test chemical

Dose level:

50% ethoxyquin

No. with + reactions:

12

Total no. in group:

12

Clinical observations:

There were 12 very slight (grade ±) reactions noted for test group animals re-challenged with 50 % ethoxyquin. Focal eschar was noted for one site at both 24 and 48 hours.

Reading:

rechallenge

Hours after challenge:

48

Group:

test chemical

Dose level:

50% ethoxyquin

No. with + reactions:

12

Total no. in group:

12

Clinical observations:

By 48 hours, dermal irritation included 11 very slight reactions and one site with a slight (grade 1) reaction. Focal eschar was noted for one site at both 24 and 48 hours. At 48 hours post-dose, four animals had desquamation.

Findings

General: There were no deaths, clinical findings, or remarkable changes in body weights observed during the study.

 

Primary irritation phase

One very slight (regarded as “grade ±” by the study author) reaction was noted for sites dosed with 50 % ethoxyquin at the 24 and 48 hour observations. The undiluted (100 %) concentrate of ethoxyquin induced one slight (grade 1) and one very slight erythema at the 48-hour scoring. Based on these results, undiluted ethoxyquin was considered to be appropriate for induction and was used in order to maximise the potential for systemic exposure. The 50 % concentration of ethoxyquin in acetone was considered to be the maximal, essentially nonirritating concentration and was therefore appropriate for challenge and re-challenge dosing.

 

Induction phase

Undiluted ethoxyquin induced seven very slight (grade ±) reactions in the test group following both the first and second induction dosings. Six sites had very slight reactions and one site had a slight (grade 1) reaction after the third induction dose. For positive control group animals, irritation noted after the first induction dosing with 0.25 % DNCB included five slight (grade 1) erythema reactions and one very slight (grade ±) reaction. Following the second induction, positive control group dermal findings included one severe (grade 3) reaction and five sites with moderate (grade 2) reactions. Eschar was present on five sites following second induction. After the third induction dosing, five animals had slight reactions and one site had a very slight erythema reaction. In addition, eschar was noted on one site following the third induction.

 

Challenge phase

The 50 % concentration of ethoxyquin induced ten very slight (grade ±) reactions at 24 hours for test group animals following challenge dosing. By 48 hours, irritation included nine sites with very slight reactions and one with a slight (grade 1) reaction. Five very slight reactions were observed at both 24 and 48 hours for naïve control I group animals dosed with 50 % ethoxyquin. In addition, focal eschar was noted for one animal at both 24 and 48 hours. In the positive control group, there was one slight and five moderate (grade 2) reactions). Eschar was observed for one animal at 24 hours post-dose. By 48 hours, slight and moderate erythema was noted for three animals each. Focal eschar and eschar were present on one site each at 48 hours post-challenge.

 

Re-challenge phase

There were 12 very slight (grade ±) reactions noted for test group animals re-challenged with 50 % ethoxyquin. By 48 hours, dermal irritation included 11 very slight reactions and one site with a slight (grade 1) reaction. Focal eschar was noted for one site at both 24 and 48 hours. At 48 hours post-dose, four animals had desquamation. Four and five very slight reactions were observed at the 24- and 48-hour observations, respectively, for naïve control II group guinea pigs dosed with 50 % ethoxyquin.

 

Incidence and severity indices

The “Sensitisation Incidence Index” was calculated to be 1/12 (8 %) for the test group following challenge dosing with ethoxyquin. The Irritation Severity Indices were 0.4 and 0.5 at 24 and 48 hours, respectively, for the test group and 0.4 at both 24 and 48 hours postdosing for the naïve control I group. In contrast, the Sensitisation Incidence Index was calculated to be 6/6 (100 %) for the positive control group following challenge dosing with 0.1 % DNCB. The Irritation Severity Indices were 1.8 and 1.5 at 24 and 48 hours, respectively.

 

Table Skin sensitisation study with ethoxyquin in albino guinea pigs. Incidence of dermal responses at challenge.

Group	Test material	Interval	0	±	1	2	3	No. of animals	Irritation severity index
Test	50% ethoxyquin	24h	2	10	0	0	0	12	0.4
Test	50% ethoxyquin	48h	2	9	1	0	0	12	0.5
Control-I	50% ethoxyquin	24h	1	2	0	0	0	6	0.4
Control-I	50% ethoxyquin	48h	1	2	0	0	0	6	0.4
Positive Control	0.1% DNBC	24h	0	0	1	5	0	6	1.8
Positive Control	0.1% DNBC	48h	0	0	3	3	0	6	1.5

DNCB = dinitrochlorobenzene

Interpretation of results:

GHS criteria not met

Conclusions:

As information was provided via a peer-reviewed assessment report, it can be considered as sufficiently reliable to assess the sensitizing potential of ethoxyquin in guinea pigs. There were no deaths, clinical findings, or remarkable body weight changes.
The positive control material (DNCB) was demonstrated to be an extreme sensitising agent under the conditions of this study based on the Sensitisation Incidence Index of 100 %, thereby demonstrating the reliability of the test system.
Based on a Sensitisation Incidence Index of 8 % (1/12) following both initial challenge and re-challenge dosing with ethoxyquin, the test material may be considered to have a very weak sensitising potential in albino guinea pigs.
As however the irritation response is largely similar to control, this can be also considered as a biological, non-treatment-related variance, so classification as a skin sensitizer is not triggered. For the classification as skin sensitizer Cat. 1B, in the Bühler assay, ≥ 15 % of the animals must be responding at > 20 % topical induction dose. There is no evidence for a response of the animals over control.

Executive summary:

In a modified Buehler method dermal sensitization study (US EPA FIFRA Guideline §81-6, equivalent to OECD 406) with ethoxyquin, six male and six female Hartley albino guinea pigs were tested. Dinitrochlorobenzene servesd as positive control.

There were no deaths, clinical findings, or remarkable changes in body weights observed during the study.

Undiluted ethoxyquin induced seven very slight (grade ±) reactions in the test group following both the first and second induction dosings. Six sites had very slight reactions and one site had a slight (grade 1) reaction after the third induction dose.

The 50 % concentration of ethoxyquin induced ten very slight (grade ±) reactions at 24 hours for test group animals following challenge dosing. By 48 hours, irritation included nine sites with very slight reactions and one with a slight (grade 1) reaction.

There were 12 very slight (grade ±) reactions noted for test group animals re-challenged with 50 % ethoxyquin. By 48 hours, dermal irritation included 11 very slight reactions and one site with a slight (grade 1) reaction. Focal eschar was noted for one site at both 24 and 48 hours.

At 48 hours post-dose, four animals had desquamation.

In this study, ethoxyquin is not a dermal sensitizer.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

In the available OECD 406 study, in the Challenge phase, the 50 % concentration of ethoxyquin induced ten very slight (grade ±) reactions at 24 hours for test group animals following challenge dosing. By 48 hours, irritation included nine sites with very slight reactions and one with a slight (grade 1) reaction. Five very slight reactions were observed at both 24 and 48 hours for naïve control I group animals dosed with 50 % ethoxyquin. In addition, focal eschar was noted for one animal at both 24 and 48 hours. In the positive control group, there was one slight and five moderate (grade 2) reactions). Eschar was observed for one animal at 24 hours post-dose. By 48 hours, slight and moderate erythema was noted for three animals each. Focal eschar and eschar were present on one site each at 48 hours post-challenge.

In the Re-challenge phase, there were 12 very slight (grade ±) reactions noted for test group animals re-challenged with 50 % ethoxyquin. By 48 hours, dermal irritation included 11 very slight reactions and one site with a slight (grade 1) reaction. Focal eschar was noted for one site at both 24 and 48 hours. At 48 hours post-dose, four animals had desquamation. Four and five very slight reactions were observed at the 24- and 48-hour observations, respectively, for naïve control II group guinea pigs dosed with 50 % ethoxyquin.

Based on a Sensitisation Incidence Index of 8 % (1/12) following both initial challenge and re-challenge dosing with ethoxyquin, the test material may be considered to have a very weak sensitising potential in albino guinea pigs.

As however the irritation response is largely similar to control, this can be also considered as a biological, non-treatment-related variance, so classification as a skin sensitizer is not triggered. For the classification as skin sensitizer Cat. 1B, in the Bühler assay, => 15 % of the animals must be responding at > 20 % topical induction dose. There is no evidence for a response of the animals over control.