Mesitylene

Endpoint summary

Description of key information

It is concluded that 1,3,5-trimethylbenzene is irritating to the skin and eyes of rabbits.  Respiratory irritation (decreased respiratory rate) was observed in mice with 2551 mg/m3 producing a 50 % decrease. No irritation was noted in human studies but these were conducted at much lower doses than the animal studies.

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

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study, GLP status unclear, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

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

Principles of method if other than guideline:

Mesitylene was applied to shaved rabbit skin and erythema and oedema recorded (using Draize criteria) at 1, 24, 48, and 72 hr after removal of the patch. Observations continued thereafter every 2 days until dermal responses had resolved in at least one rabbit.

GLP compliance:

not specified

Species:

rabbit

Strain:

New Zealand White

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Proefstations voor Veeteelt (Merelbeke, Belgium)
- Age at study initiation: 9-24 weeks
- Weight at study initiation: 2.75-5.2 kg
- Housing: individual mesh wire bottom cages
- Conventional Laboratory diet ad libitum
- Tap-water ad libitum
- Acclimation period: At least 7 days
- Normal housing conditions

Type of coverage:

occlusive

Preparation of test site:

shaved

Vehicle:

unchanged (no vehicle)

Controls:

other: area of untreated skin used for comparison

Amount / concentration applied:

0.5 ml

Duration of treatment / exposure:

4 hours, occluded

Observation period:

The animals were examined for signs of erythema and edema formation at 1, 24, 48 and 72 hr after removal of the test patch

Number of animals:

5 or 6 (not specified)

Irritation parameter:

erythema score

Basis:

mean

Time point:

24/48/72 h

Score:

2.33

Remarks on result:

other: time course information not available

Irritation parameter:

edema score

Basis:

mean

Time point:

24/48/72 h

Remarks on result:

not measured/tested

Interpretation of results:

Category 2 (irritant) based on GHS criteria

Conclusions:

Mesitylene caused erythema (overall mean 2.33) when applied to shaved rabbit skin under occlusion for 4 hr.

Executive summary:

The skin irritation potential of mesitylene toward shaved rabbit skin was evaluated according to Annex V of directive 67/548 EEC. The sample (0.5 ml) was applied under occlusion for 4 hr with an area of untreated skin serving as control. The overall mean score for erythema (all animals over a 72 hour period) was 2.33; no oedema was reported. The results indicate that mesitylene is irritating to rabbit skin.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Eye irritation

Link to relevant study records

Reference

Endpoint:

eye irritation: in vivo

Type of information:

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

Remarks:

Read-across to the test material (Shellsol A) is justified by the description of its composition – it is described as being composed of predominantly trimethylbenzenes, of which mesitylene is one.

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, near-guideline study, available as unpublished report, restrictions in design and/or reporting but otherwise adequate for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 405 (Acute Eye Irritation / Corrosion)

GLP compliance:

no

Species:

rabbit

Strain:

New Zealand White

Details on test animals or tissues and environmental conditions:

- Source: Ranch Rabbits, Crawley, Sussex, UK
- Age at study initiation: no data
- Weight at study initiation: no data
- Housing: no data
- Diet (e.g. ad libitum): no data
- Water (e.g. ad libitum): no data
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS: no data

IN-LIFE DATES: no data

Vehicle:

unchanged (no vehicle)

Controls:

no

Amount / concentration applied:

0.2 mL undiluted Shellsol A

Duration of treatment / exposure:

single instillation

Observation period (in vivo):

7 days

Number of animals or in vitro replicates:

2 male and 2 female

Details on study design:

Shellsol A instilled into conjunctival sac of right eye, untreated left eye served as a control. Eye irritation assessed 1,2,3 and 7 days after instillation according to numerical scheme cited in Federal Register (28 (110), 6.6.1963. para 191.12. Test for eye irritation)

Irritation parameter:

cornea opacity score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

0

Reversibility:

fully reversible

Remarks on result:

no indication of irritation

Irritation parameter:

iris score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

0

Reversibility:

fully reversible

Remarks on result:

no indication of irritation

Irritation parameter:

conjunctivae score

Basis:

mean

Time point:

24/48/72 h

Score:

>= 0 - <= 1

Max. score:

2

Reversibility:

fully reversible within: 1 day

Remarks:

after 30 min. highest schore of 2 for two animals

Remarks on result:

probability of weak irritation

Irritation parameter:

chemosis score

Basis:

mean

Time point:

24/48/72 h

Score:

>= 0 - <= 1

Max. score:

2

Reversibility:

fully reversible within: 1 day

Remarks:

after 30 min.: score of 2 for one animal and score of 1 for 3 animals

Irritant / corrosive response data:

Thirty minutes after instillation, slight to moderate conjunctival redness was present in all 4 rabbits and slight to moderate chemosis was present in 3 rabbits. Conjunctival discharge was present in one rabbit at the 30 minute and day 1 reading but did not persist. These conjunctival effects did not persist, no chemosis was seen after 1 day, very slight redness was seen in 2 rabbits at 1 day but all redness had cleared by day 2. There were no corneal or iridial effects.

Other effects:

There was an immediate pain reaction following instillation into the eye.

Eye irritation scores of Shellsol A

Time		Cornea				Iris				Conjunctiva
										Redness				Chemosis
	Animal number	9	10	56	57	9	10	56	57	9	10	56	57	9	10	56	57
after 30 mins		0	0	0	0	0	0	0	0	2	1-2	1	1	2	1	0-1	0
after 1 day		0	0	0	0	0	0	0	0	0-1	0	0-1	0	0	0	0	0
after 2 days		0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
after 3 days		0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
after 7 days		0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0

Interpretation of results:

other: EU GHS: not irritating

Conclusions:

Shellsol A was practically non-irritating to the rabbit eye.

Executive summary:

One drop (0.2 mL) of Shellsol A instilled into the rabbit eye caused an immediate pain reaction but thereafter was practically non-irritating.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Additional information

 Non-human information

Skin

The key study is provided by Jacobs and Martens (1987) where the skin irritation potential of the isomer,1,3,5-trimethylbenzene (mesitylene), was investigated on shaved rabbit skin. A sample (0.5 ml) was applied under occlusion for 4 hr with an area of untreated skin serving as control. The overall mean score for erythema (for all animals over a 72 hour period) was 2.33; no oedema was reported. The results indicate that 1,3,5 trimethylbenzene is irritating to rabbit skin. This study is supported by other data on 1,3,5 trimethylbenzene demonstrating that concentrations in excess of 25% were irritating to rabbit skin (Jacobs et al, 1987). A study on undiluted Shellsol A (a mixture of trimethylbenzenes CAS# 64742-95-6) also showed that this was a moderate skin irritant following a single 24 hour application to abraded and non-abraded occluded rabbit skin.

In conclusion, the data indicate that 1,3,5- trimethylbenzene has the potential to be irritating to skin.

 

 

Eye

1,3,5 -Trimethylbenzene is irritating to the eye. This was concluded by SCOEL (1994) in relation to all the trimethylbenzene isomers, but the only reference available is an IUCLID 4 entry (ESBI, 1990) where the results of a rabbit occular irritation test showed that 1,2,4- trimethylbenzene was irritating to the eyes, but details are lacking and the study cannot be sourced. An earlier study on Shellsol A (a mixture of trimethylbenzenes CAS No. 64742-95-6) showed that one drop instilled into the rabbit eye caused an immediate pain reaction but thereafter was practically non-irritating.

In spite of these apparently conflicting results, and in the absence of reliable information to the contrary, the harmonized EU position (indicating the 1,2,4- trimethylbenzene is irritating to the eye) is adopted for 1,3,5-trimethylbenzene.

 

 

Respiratory tract

Respiratory sensory irritation effects of 1,2,4-trimethylbenzenes in male Balb/C mice were investigated under conditions of acute exposure (Korsak et al, 1997). Male Balb/C mice were exposed to trimethylbenzenes for 6 min. Respiratory sensory irritation was quantified by determination of the decrease in respiratory rate. 1,3,5 -Trimethylbenzene depressed respiration rate and the concentration at which the respiratory rate was decreased to 50% (RD50) was 519 ppm (2551 mg/m3). A 90 day study is also described in the same publication (see Section on Repeat dose Toxicity). Rats were exposed to 1,2,4-trimethylbenzene for 90 days, at concentrations of 25, 100 and 250 ppm. There was no evidence of systemic toxicity at concentrations up to and including 250 ppm (1230 mg/m3. The total number of cell macrophages, polymorphonuclear leukocytes and lymphocytes in the brochiolar lavage (BAL) fluid at all three test concentrations was increased compared with the controls. Total protein lactate dehydrogenase and acid phosphatase activity in BAL were also increased in all exposed groups. These changes are indicative of mild respiratory irritation, however, a concentration-dependency was not seen, and therefore some adaptation may have taken place.

In conclusion, these data indicate that 1,3,5- trimethylbenzene has the potential to be irritating to the respiratory tract.

 

 

Human Information

 

Some information is available on the potential for trimethylbenzenes to cause irritation in humans. In human volunteer toxicokinetics studies on inhaled trimethylbenzenes, subjects were asked to assess (i) Discomfort in eyes: burning, irritation, or running eyes; (ii) discomfort in nose: burning, irritation, or running nose; (iii) discomfort in throat or airways; (iv) headache; (v) fatigue; (vi) nausea; (vii) dizziness; (viii) intoxication; (ix) difficulty in breathing and (x) smell of solvent. No effects were reported at concentrations up to 120 mg/m3 (Jarnberg et al, 1996).

 

Conclusions

The available data from animal studies indicates that 1,3,5 - trimethylbenzene, in common with other trimethylbenzene isomers, is irritating to skin, eyes and respiratory tract. Although no adverse effects were noted in human volunteer studies these were conducted at concentrations at least an order of magnitude lower than those in animal studies. ReferenceFirth MJ (2008). Derivation of a chronic reference dose and reference concentration for trimethylbenzenes and C9 aromatic hydrocarbon solvents. Reg Tox. Phamacol. 52, 248 -256

 

Justification for selection of skin irritation / corrosion endpoint:

The available key and supporting studies indicate that 1,3,5-trimethylbenzene is irritating to the skin

 

Justification for selection of eye irritation endpoint:

Trimethylbenzenes are classified for eye irritation, Category 2, H319, under CLP

 

Effects on skin irritation/corrosion: irritating

 

Effects on eye irritation: irritating

 

Effects on respiratory irritation: irritating

Justification for classification or non-classification

1,3,5 -Trimethylbenzene is currently classified as irritating to the respiratory tract H335 according to Annex VI of Regulation (EC) No 1272/2008.

Under CLP it is proposed that additional classification is warranted : Eye Irritation Category 2, H319 Causes serious eye irritation; STOT-SE Category 3 H335 May cause respiratory irritation and Skin Irritation H315 Causes skin irritation.