2,4-diethyl-9H-thioxanthen-9-one

Endpoint summary

Description of key information

- Skin irritation / corrosion: not irritating [based on the results of a reliable OECD 404 study of the related substance 2-Isopropylthioxanthone (CAS 5495-84-1, EC 226-827-9)];

- Eye irritation: not irritating [based on results of a reliable OECD 405 study of the related substance 2-Isopropylthioxanthone (CAS 5495-84-1, EC 226-827-9)];

- Respiratory irritation: The conclusion of not irritant to the respiratory tract is based on the absence of significant irritating effects on other membranes, specifically the eye.

Key value for chemical safety assessment

Skin irritation / corrosion

Link to relevant study records

Reference

Endpoint:

skin irritation: in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

04 June 1998 to 12 June 1998

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 404 (Acute Dermal Irritation / Corrosion)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.4 (Acute Toxicity: Dermal Irritation / Corrosion)

Deviations:

no

GLP compliance:

yes

Species:

rabbit

Strain:

New Zealand White

Remarks:

Crl:NZW/KbI.BR

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 11 to 14 weeks old
- Weight at study initiation: 2.05 to 2.41 kg
- Housing: Rabbits were housed in floor-pens, each accommodating one animal throughout the acclimatisation and experimental phases of the study. Each pen had a minimum floor area of 0.6 square metres. The partitions between pens were constructed of slotted laminate board 1.0 m high. Wood chips were provided as floor litter. Each batch of wood chips was analysed for specific contaminants.
- Diet: Ad libitum
- Water: Ad libitum
- Acclimation period: 8 to 13 days

ENVIRONMENTAL CONDITIONS
- Temperature: 16 to 22 °C
- Humidity: 40 to 80 % (expected range)
- Air changes: 10 air changes per hour
- Photoperiod: The room was illuminated by fluorescent strip-lights for twelve hours daily.

Type of coverage:

semiocclusive

Preparation of test site:

clipped

Vehicle:

unchanged (no vehicle)

Controls:

no

Amount / concentration applied:

TEST MATERIAL
- Amount applied: 500 mg

Duration of treatment / exposure:

4 hours

Observation period:

3 days

Number of animals:

3

Details on study design:

TEST SITE
- Area of exposure: 30 x 20 mm area on the clipped dorsum
- Type of wrap if used: After moistening with approximately 0.1 mL of water, the dose was spread uniformly over the designated area and then each site was covered by a dense gauze patch (30 x 20 mm) on Day 1. This in turn was covered by a larger gauze patch (40 x 40 mm) and an open weave elasticated adhesive bandage which was wrapped firmly around the torso to secure the applied dose and patch in the correct position. The dressing was considered to be semi-occlusive.

REMOVAL OF TEST SUBSTANCE
- The test patch was removed after four hours and the treated skin was lightly brushed clean of any solid residues and swabbed with moist cotton wool. The location of the test site was marked on the dorsum with indelible ink after completion of the cleansing process.

OBSERVATION TIME POINTS
- The condition of the treated skin of the sentinel was assessed for a period of at least three days to ensure the test material did not cause severe dermal changes. Subsequently, two further rabbits were subjected to a single, four hour, semi-occluded topical application of 500 mg of test material to moistened skin.
- Clinical signs: A detailed account of any clinical signs of ill health or systemic toxicity was maintained.
- Body weights: Each rabbit was weighed on the day before dosing (Day -1).
- Dermal reactions: The conditions of the dermal test sites were recorded immediately after removal of the patches and dressings from the sentinel animal. The condition of all dermal test sites was recorded approximately one hour, 24. 48 and 72 hours after removal of the patch and dressing. Inflammatory skin reactions were graded according to the following scheme:

Erythema and eschar:
- No erythema = 0
- Very slight erythema = 1
- Well-defined erythema = 2
- Moderate erythema = 3
- Severe erythema (beet redness) or eschar preventing reading of erythema = 4

Oedema:
- No oedema = 0
- Very slight oedema (barely perceptible) = 1
- Slight oedema (edges of area well-defined by definite raising) = 2
- Moderate oedema (edges raised approximately 1 mm) = 3
- Severe oedema (raised >1 mm and extending beyond area of exposure) = 4

TERMINAL PROCEDURES
- All rabbits were killed by intravenous injection of an overdose of sodium pentobarbitone, following confirmation that the condition of the dermal test sites was normal, on Day 4. No tissue preservation or histopathological assessment of tissues was undertaken.

Irritation parameter:

erythema score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

4

Remarks on result:

no indication of irritation

Irritation parameter:

edema score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

4

Remarks on result:

no indication of irritation

Irritant / corrosive response data:

Dermal responses
- No dermal change or response to treatment was observed in any animal throughout the observation period.

Other effects:

Clinical signs
- There were no signs of toxicity or ill health in any rabbit during the observation period.

Interpretation of results:

other: Not classified in accordance with EU criteria

Conclusions:

Under the conditions of this study the test material 2-Isopropylthioxanthone (CAS 5495-84-1, EC 226-827-9) was determined to be non-irritating to the skin.

Executive summary:

A study was performed to investigate the potential of the test material 2-Isopropylthioxanthone (CAS 5495-84-1, EC 226-827-9) to cause dermal irritation in accordance with the standardised guidelines OECD 404 and EU Test Method B.4 under GLP conditions.

The test article (500 mg) was applied to a 30 x 20 mm area on the clipped and moistened dorsum of each of three New Zealand White rabbits on Day 1. The treated area of skin was covered by a semi-occlusive bandage for four hours. Dermal reactions to treatment were assessed for up to three days after removal of the dressings.

No dermal changes were observed following a single semi-occluded application of the test material to intact rabbit skin for four hours.

Under the conditions of this study the test material 2-Isopropylthioxanthone (CAS 5495-84-1, EC 226-827-9) was determined to be non-irritating to the skin.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Link to relevant study records

Reference

Endpoint:

eye irritation: in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

09 June 1998 to 15 June 1998

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 405 (Acute Eye Irritation / Corrosion)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.5 (Acute Toxicity: Eye Irritation / Corrosion)

Deviations:

no

GLP compliance:

yes

Species:

rabbit

Strain:

New Zealand White

Details on test animals or tissues and environmental conditions:

TEST ANIMALS
- Age at study initiation: 11 to 14 weeks old
- Weight at study initiation: 2.25 to 2.51 kg
- Housing: Rabbits were housed in floor-pens, each accommodating one animal throughout the acclimatisation and experimental phases of the study. Each pen had a minimum floor area of 0.6 square metres. The partitions between pens were constructed of slotted laminate board 1.0 m high. Wood chips were provided as floor litter. Each batch of wood chips was analysed for specific contaminants.
- Diet: Ad libitum
- Water: Ad libitum
- Acclimation period: 10 to 13 days
- Both eyes of each rabbit were examined for indications of corneal, iridial or conjunctival damage or irritation. After initial visual examination, one drop of 2 % aqueous fluorescein solution was instilled into both lower conjunctival sacs, allowed to disperse for thirty seconds and removed from the eyes by irrigation with approximately 10 mL water for irrigation jetted gently from a syringe. The corneal surface was illuminated with an ultraviolet source and inspected for areas of absorption of the fluorescing dye that would indicate epithelial damage. Only rabbits with eyes free from damage or irritation were accepted onto study.

ENVIRONMENTAL CONDITIONS
- Temperature: 16 to 22 °C
- Humidity: 40 to 80 % (expected range)
- Air changes: 10 air changes per hour
- Photoperiod: The room was illuminated by fluorescent strip-lights for twelve hours daily.

Vehicle:

unchanged (no vehicle)

Controls:

yes, concurrent no treatment

Amount / concentration applied:

TEST MATERIAL
- Amount applied: Approximately 55 mg (the weight equivalent to 0.1 mL)

Duration of treatment / exposure:

After instillation the eyelids were held closed for a few seconds to prevent loss of the dose.

Observation period (in vivo):

3 days

Number of animals or in vitro replicates:

3 animals

Details on study design:

EXPERIMENTAL PROCEDURE
- Before the first animal could be dosed the pH of the test material was checked. A 25 % m/v dispersion in purified water had a pH of 5.0. Since this was within the acceptable range of pH 2.0 to 11.5, the study continued.
- One dose consisting of approximately 55 mg (the weight equivalent to 0.1 mL) of powdered test material, dispensed from a spatula, was instilled into the left conjunctival sac of a single New Zealand White rabbit (the "sentinel"). The lower eyelid was gently prised away from the eyeball to create a receptacle for the dose. After instillation the eyelids were held closed for a few seconds to prevent loss of the dose. The right eye remained untreated and served as a control to the treated eye. The day of dosing was designated as Day 1. The condition of the treated eye of the sentinel was assessed for a period of at least three days to ensure the test material did not cause ocular damage.
- Subsequently, approximately 55 mg of test article, as supplied, was similarly instilled into the left conjunctival sac of each of two further rabbits.


EXPERIMENTAL OBSERVATIONS
- Clinical signs: A detailed account of any clinical signs of ill health was maintained.
- Body weights: Each rabbit was weighed on the day before dosing (Day -1).
- Ocular response: The "initial sting" response was assessed and recorded immediately after instillation of the test material. The response was graded according to the following scheme:
No response = 0 = None
A few blinks only, normal within two minutes = 1 = Practically none
Rabbit blinks and attempts to open eye but reflex closes it = 2 = Slight
Rabbit keeps eye shut and puts pressure on it, may rub eye = 3 = Moderate
Rabbit holds eye tightly shut, may struggle or squeal = 4 = Marked

- Ocular changes were assessed and recorded immediately, half an hour, one and four hours after treatment on Day 1 and 24, 48 and 72 hours after dosing. Ocular changes were graded according to the following scheme:
- Cornea- degree of opacity
No ulceration or opacity = 0
Scattered or diffuse areas of opacity other than slight dulling of normal lustre, details of iris clearly visible = 1
Easily discernible translucent area, details of iris slightly obscured = 2
Nacreous area, no details of iris visible but size of pupil barely discernible = 3
Opaque cornea, iris not discernible through opacity = 4

- Cornea- area of corneal opacity
Total area of opacity amounts to < 25 % of corneal area = 1
Area of opacity amounts to 25 to < 50 % of corneal area = 2
Area of opacity amounts to 50 to < 75 % of corneal area = 3
Area of opacity amounts to 75 % or more of corneal area = 4

- Iris
No reaction = 0
Markedly deepened rugae, congestion, swelling, moderate circumcorneal hyperaemia or injection, any of these or any combination thereof: iris still reacting to light = 1
No iridial reflex to light, haemorrhage or gross destruction (any or all of these) = 2

- Conjunctivae - redness
Blood vessels normal = 0
Some blood vessels definitely hyperaemic (injected) = 1
Diffuse, crimson colour, individual vessels not easily discernible = 2
Diffuse beefy red appearance = 3
This refers to the most severe readting of palpebral and bulbar conjunctivae as compared to the right control eye.

- Conjunctivae - chemosis
No swelling = 0
Any swelling above normal = 1
Obvious swelling with partial eversion of lids = 2
Swelling with lids about half-closed = 3
Swelling with lids more than half-closed = 4
Assessment includes the nictitating membrane.

- Conjunctivae - discharge
No discharge = 0
Any discharge greater than normal, not including the small amount normally present in the inner canthus = 1
Discharge with moistening of eyelids and hairs just adjacent to the eye = 2
Discharge with moistening of eyelids and hair for a considerable area around the eye = 3

- The treated eyes were examined visually and, where appropriate, with the aid of a device to illuminate the eye.
- At examinations carried out 24 hours after treatment 2 % aqueous fluorescein solution was applied to the cornea and then washed out with water for irrigation or purified water. The corneal surface was then illuminated by an ultraviolet source and inspected for areas of epithelial disruption highlighted by absorption of the fluorescing dye.

TERMINAL PROCEDURES
- All rabbits were killed by intravenous injection of an overdose of sodium pentobarbitone, following confirmation that the condition of the treated eyes was normal on Day 4. No tissue preservation or histopathological assessment of tissues was undertaken.

Irritation parameter:

cornea opacity score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

4

Irritation parameter:

iris score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

2

Irritation parameter:

conjunctivae score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

3

Irritation parameter:

chemosis score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

4

Other effects:

OCULAR RESPONSE
- Instillation of the test material caused no initial sting response.
- A single instillation of the test material caused some injection of the blood vessels of the conjunctivae in two rabbits on Day 1. A small amount of discharge was noted following treatment of one rabbit one half hour after dosing only. There were no other reactions to treatment and the absence of absorption of applied fluorescein dye showed that there was no damage to the epithelium. All reactions had resolved by Day 2.

CLINICAL SIGNS
- No observations were noted for any rabbits during the course of the study.
- One rabbit voided soft faeces on Day 2 but was normal by Day 3. This finding was not considered to be indicative of systemic toxicity or ill health.

Table 1: Group mean values for ocular reactions

Time of observation (h)	Ocular reaction
	Corneal opacity	Iris	Conjunctival redness	Chemosis
1	0.0	0.0	0.7	0.0
4	0.0	0.0	0.7	0.0
24	0.0	0.0	0.0	0.0
48	0.0	0.0	0.0	0.0
72	0.0	0.0	0.0	0.0
Mean of 24, 48 and 72 hour scores	0.0	0.0	0.0	0.0

 

Interpretation of results:

other: Not classified in accordance with EU criteria

Conclusions:

Under the conditions of the study, the test material 2-Isopropylthioxanthone (CAS 5495-84-1, EC 226-827-9) has been determined to be not irritating.

Executive summary:

A study was conducted to investigate the potential of the test material 2-Isopropylthioxanthone (CAS 5495-84-1, EC 226-827-9) to cause eye irritation in accordance with the standardised guidelines OECD 405 and EU Test Method B.5 under GLP conditions.

The test material (nominally 55 mg: weight equivalent to 0.1 mL) was instilled into one conjunctival sac of each of three New Zealand White rabbits on Day 1. Ocular reactions were assessed for up to three days after treatment.

Ocular instillation of the test material provoked no initial sting reaction.

A single instillation of the test material caused some injection of the blood vessels of the conjunctivae in two rabbits on Day 1. A small amount of discharge was noted following treatment of one rabbit one half hour after dosing only. There were no other reactions to treatment. All reactions had resolved by Day 2.

Under the conditions of the study, the test material 2-Isopropylthioxanthone (CAS 5495-84-1, EC 226-827-9) has been determined to be not irritating.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

No skin and eye corrosion/irritation studies are available for the registration substance 2,4-diethyl-9H-thioxanthen-9-one ("DETX", CAS 82799-44-8, EC 280-041-0) itself.

Reliable data of the structurally related substance 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9) are used to address the endpoint, which is considered entirely appropriate for the assessment of the skin and eye corrosion/irritation potential of DETX.

The only difference between the source substance ITX and the target substance DETX can be reduced to slightly differing substituents: ITX possesses one isopropyl group, whereas DETX two ethyl groups.

Skin Irritation in vivo

A study was performed to investigate the potential of the closely related test material ITX to cause dermal irritation in accordance with the standardised guidelines OECD 404 and EU Test Method B.4 under GLP conditions. The study was awarded a reliability score of 2 in accordance with the criteria set forth by Klimisch et al. (1997).

The test article (500 mg) was applied to a 30 x 20 mm area on the clipped and moistened dorsum of each of three New Zealand White rabbits on Day 1. The treated area of skin was covered by a semi-occlusive bandage for four hours. Dermal reactions to treatment were assessed for up to three days after removal of the dressings.

No dermal changes to erythema or oedema were observed following a single semi-occluded application of the test material to intact rabbit skin for four hours.

Under the conditions of this study the test material 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9) was determined to be non-irritating to the skin.

In a supporting study, the potential of the test material ITX to cause dermal irritation was investigated in accordance with the standardised guidelines OECD 404 and EU Test Method B.4. The study was awarded a reliability score of 2 in accordance with the criteria set forth by Klimisch et al. (1997).

Approximately 24 hours prior to application of the test material, hair was removed with electric clippers from the dorso-lumbar region of each rabbit exposing an area of skin approximately 10 cm square. A 0.5 g amount of test material was applied under a 2.5 cm square gauze pad, moistened with 0.5 mL distilled water, pad to one intact skin site on each animal. Each treatment site was occluded with an elastic adhesive dressing for a four hour period. The animals were not restrained during the exposure period and were returned to their cages. At the end of the exposure period, the semi-occlusive dressing and gauze pad were removed and the treatment site was washed using water to remove any residual test material.

Examination of the treated skin was made on Day 1 (i.e. approximately 30 minutes after removal of the patches) and on Days 2, 3 and 4. There was no response to treatment in any of the animals throughout the observation period.

Under the conditions of this study the test material 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9) was determined to be non-irritating to the skin.

Eye Irritation in vivo

A study was conducted to investigate the potential of the test material ITX to cause eye irritation in accordance with the standardised guidelines OECD 405 and EU Test Method B.5 under GLP conditions. The study was awarded a reliability score of 2 in accordance with the criteria set forth by Klimisch et al. (1997).

The test material (nominally 55 mg: weight equivalent to 0.1 mL) was instilled into one conjunctival sac of each of three New Zealand White rabbits on Day 1. Ocular reactions were assessed for up to three days after treatment.

Ocular instillation of the test material provoked no initial sting reaction. A single instillation of the test material caused some injection of the blood vessels of the conjunctivae in two rabbits on Day 1.

A small amount of discharge was noted following treatment of one rabbit one half hour after dosing only. There were no other reactions to treatment. All reactions had resolved by Day 2.

Under the conditions of the study, the test material 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9) has been determined to be not irritating.

In a supporting study the potential of the test material ITX to cause irritation to the eye was investigated in accordance with the standardised guidelines OECD 405 and EU Method B5. The study was awarded a reliability score of 2 in accordance with the criteria set forth by Klimisch et al. (1997).

Three male New Zealand White rabbits were treated with the test material, the eyes of each animal were examined prior to instillation of the test material to ensure that there was no pre-existing corneal damage or conjunctival inflammation. A 60 mg amount of test material, the weight occupying a volume of 0.1 mL, was placed into the lower everted lid of one eye of each animal. The eyelids were then gently held together for one second before releasing. The contralateral eye remained untreated and served as a control. Examination of the eyes was made after 1 hour and 1, 2, 3, 4 and 7 days after instillation. Observation of the eyes was aided by the use of a handheld torch.

None of the animals gave a "positive" response. No corneal damage or iridial inflammation was observed in any of the animals. Mild conjunctival irritation was seen in all three animals. The eyes were normal two or three days after instillation.

Under the conditions of the study, the test material 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9) has been determined to be not irritating.

Justification for classification or non-classification

Based on the results for 2-Isopropylthioxanthone (CAS 5495-84-1, EC 226-827-9), the structurally related registration substance 2,4-diethyl-9H-thioxanthen-9-one (CAS 82799-44-8, EC 280-041-0) does not meet the CLP classification criteria with respect to irritation or corrosion to the skin and eye, as set out in Regulation (EC) No. 1272/2008.