Cyclohexane

Endpoint summary

Description of key information

Cyclohexane is considered to be a skin irritant based on results from animal experiments.   It is slightly irritating to the eyes in animal experiments but not to an extent that would require classification.  

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:

weight of evidence

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:

Cyclohexane 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
- Diet: Conventional Laboratory diet ad libitum
- Water: Tap-water ad libitum
- Acclimatisation period: At least 7 days
- Normal housing conditions

Type of coverage:

occlusive

Preparation of test site:

shaved

Vehicle:

unchanged (no vehicle)

Controls:

no

Amount / concentration applied:

0.5 mL

Duration of treatment / exposure:

4 hours, occluded

Observation period:

Animals examined for signs of erythema and oedema 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

Remarks:

for all animals, all timepoints

Time point:

24/48/72 h

Score:

1.93

Remarks on result:

other: time course information not available

Irritation parameter:

erythema score

Basis:

mean

Remarks:

maximum erythema score (Smax)

Time point:

other: 119 h (time of Smax)

Score:

2.56

Irritation parameter:

edema score

Basis:

mean

Remarks:

for all animals, all timepoints

Time point:

24/48/72 h

Score:

0

Interpretation of results:

not irritating

Conclusions:

Cyclohexane caused erythema (overall mean 1.93) when applied to shaved rabbit skin under occlusion for 4 hr. The magnitude of the response was below the threshold for classification.

Executive summary:

The skin irritation potential of cyclohexane 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 all times points) was 1.93; no oedema was reported. The results indicate that cyclohexane is not irritating to rabbit skin.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Eye irritation

Link to relevant study records

Reference

Endpoint:

eye irritation, other

Remarks:

In Vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP status unknown, 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)

Deviations:

yes

Remarks:

Deviation did not impact the scientific validity of the study.

GLP compliance:

not specified

Species:

rabbit

Strain:

not specified

Details on test animals or tissues and environmental conditions:

Not reported

Vehicle:

not specified

Controls:

no

Amount / concentration applied:

Not reported

Duration of treatment / exposure:

Not reported

Observation period (in vivo):

7 days

Number of animals or in vitro replicates:

6

Irritation parameter:

overall irritation score

Remarks:

cornea

Basis:

mean

Time point:

other: 1 h

Score:

2

Reversibility:

fully reversible within: 24 h

Irritation parameter:

overall irritation score

Remarks:

iris

Basis:

mean

Time point:

other: 1 h

Score:

0.8

Reversibility:

fully reversible within: 24 h

Irritation parameter:

overall irritation score

Remarks:

conjunctivae

Basis:

mean

Time point:

other: 1 h

Score:

2

Reversibility:

fully reversible within: 24 h

Irritation parameter:

overall irritation score

Basis:

other: total (cornea, iris and conjuctivae)

Time point:

other: 1 h

Score:

3.7

Reversibility:

fully reversible within: 24 h

The report states that corneal opacity (involving up to 25% of the cornea) was noted in one rabbit and iritis in another 1 hr post-instillation however the rapid reversibility of these responses (both fully resolved by 24 hr) suggests possible over-interpretation. Conjunctival redness was also noted in 5 rabbits with conjunctival chemosis in one, however responses again cleared within 24 hours.

Interpretation of results:

slightly irritating

Conclusions:

Slight eye irritation effects were present 1 hour after instillation but had resolved within 24 hours.

Executive summary:

Slight eye irritation effects were present 1 hour after instillation but had resolved within 24 hours.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Additional information

Skin

Non-human information

There are two skin irritation studies using rabbits reported (HLA, 1982e; Jacobs and Martens, 1987), both performed in accordance with EEC Directive 83/467/EEC. The first study, conducted under a semi-occlusive dressing, gave a primary irritation score of zero 24 h and 72 h. The second study, under a semi-occlusive dressing, gave a mean erythema score of 1.93 calculated over the 24 h and 72 h post-application period. In this study the erythematous reaction reached maximum severity at 5 days post-application with a gradual increase in dermal reaction for a further 144 h observation time. Overall, it was concluded (RAR, 2004) that the irritation reactions were significant and still present at the end of the study.

In addition, a 14 -day repeated dermal application study in rabbits on uncovered skin has been reported (Treon et al., 1943a). An initial erythematous response, gradually progressing to skin hardening, fissuring and bleeding with continued application was reported (RAR, 2004), with healing of the lesions within one week once application of cyclohexane had ceased.

Human information

Very little information has been reported on the irritation effects of cyclohexane in humans. No eye irritation was reported in a human volunteer study (Lammers et al, 2009) where the maximum exposure concentration was 250 ppm (860 mg/m³).

The following information was cited in the RAR (2004) from an UK HSE review of cyclohexane. Application of undiluted liquid cyclohexane to human skin for 1 hour produced erythema and weal formation.

Eye

Non-human information

Washed and unwashed primary eye irritation studies in rabbits are available (HLA, 1982f; 1982g). In the unwashed study, at one hour post instillation, corneal opacity, involving up to 25% of the cornea, was noted in one rabbit and iritis was noted in another rabbit. Conjunctival redness was noted in five rabbits with conjunctival chemosis in one rabbit. All ocular lesions had cleared within 24 hours and no conjunctival discharge was noted in any of the six animals.

Human information

Very little information has been reported on the irritation effects of cyclohexane in humans. In a TNO study (Lammers et al, 2009), human volunteers exposed to 250 ppm (860 mg/m³) of cyclohexane complained of irritation of the eyes more frequently than those treated with 25 ppm (86 mg/m³).

Respiratory tract

Non-human information

Acute inhalation exposure to cyclohexane at a nominal concentration of 32, 880 mg/m³ of air did not appear to produce upper airway irritation in mice (Phillips Petroleum Company, 1982i). In this study, cyclohexane (vapour) was administered to 2 groups of 4 cd-1 male mice for 2 periods of 1 minute separated by 10 minutes. The only effect noted was a slight decrease (11.2% and 5.8%) in the respiratory rate of only one animal (out of four) in the two experiments. This animal also exhibited very slight respiratory pauses which may have been due to upper airway irritation.

Human information

A human study (Lammers et al, 2009) on volunteers reported slight signs of irritation of the throat noted more frequently at 250 ppm (860 mg/m³) than at 25 ppm (86 mg/m³). These findings which could be treatment related were 'subjective' and complaints irritation of the eyes and throat more frequent after exposure to 250 ppm

 

Justification for selection of skin irritation / corrosion endpoint:
Liquid cyclohexane is moderately irritating to rabbit skin, and may also cause defatting.

Justification for selection of eye irritation endpoint:
Liquid cyclohexane is slightly irritating to rabbit eye, but not to an extent that would lead to classification.

Effects on skin irritation/corrosion: moderately irritating

Justification for classification or non-classification

In relation to skin irritation, although the animal studies gave results slight below the limits of classification, the RAR (2004) concluded that it had been demonstrated that the irritant properties of cyclohexane were delayed and persisted until the end of observation period (16 days).

Since defatting properties are also expected, it was concluded that cyclohexane be classified under CLP as Category 2 H315.

Liquid cyclohexane is slightly irritant to the eyes in animal  experiments, but not to the extent which warrants any classification.  Although cyclohexane vapour exhibited slight respiratory irritant properties in mice, these effects were slight and insufficient to warrant classification.

There is no evidence of any significant eye or respiratory tract irritation in humans which would warrant classification