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Direct observations: clinical cases, poisoning incidents and other

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direct observations: clinical cases, poisoning incidents and other
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP (no data), non-guideline human and animal experimental studies available as unpublished reports, no restrictions, fully adequate for assessment.
Reason / purpose:
reference to same study

Data source

Reference Type:

Materials and methods

Study type:
study with volunteers
Endpoint addressed:
acute toxicity: inhalation
eye irritation
respiratory irritation
Test guideline
no guideline followed
GLP compliance:
not specified

Test material

Details on test material:
- Name of test material (as cited in study report): Cyclohexane
- Supplier: E. Merck Nederland B.V
- Analytical purity: >99%


Type of population:
not specified
- Sex: male
- Number of subjects exposed: 12
- Age: 20-40 years
- Weight: 66-95 kg
Ethical approval:
confirmed and informed consent free of coercion received
Route of exposure:
Reason of exposure:
Exposure assessment:
Details on exposure:
Target concentrations: 4 hr exposure to 86 mg/m3 (25 ppm) or 860 mg/m3 (250 ppm) in 2 test sessions 7 days apart. [860 mg/m3 = the current 8 hour TWA limit value in the Netherlands]. 86 mg/m3 was selected as a reference in an effort to control for the odour associated with cyclohexane.
Atmosphere generation: Total evaporation at an elevated temperature with a constant flow of cyclohexane in a constant flow of air.
Analysis: Continuously monitored by infrared absorption at 3.49 um using a path length of 3.75 m. The Miran was calibrated at the start of each exposure week using Tedlar bags filled with 44.1 litres of dry compressed air in which 50.0 µL of liquid cyclohexane was injected. Similarly, two 25 ppm bags, two 200 ppm bags and one 300 ppm bag were prepared and used to construct a calibration curve giving 2 at 86 mg/m3, 2 at 690 mg/m3 and one at 1035 mg/m3. The values recorded at the 15-minute intervals were converted to concentration and then averaged for each session.
-Assessments of learning and memory, attention, mood and affect and perceptual coding and performance tests: Behavioural testing was done 90 min before exposure, 45 and 165 min after the start of exposure and 90 min after the 4 hr exposure period.
-Simple reaction time test: at 15 and 135 minutes after the start of exposure.
-Vocabulary test: pre-experimental, in order to obtain an estimate of general verbal ability (used as a demographic parameter and not as an outcome parameter).
-Cognitive functioning: assessed using selected tests from the Neurobehavioral Evaluation System, with additional tests used to examine cognitive function in more detail. The tests include the following:- Mood states questionnaire; Finger-tapping test; Hand-eye coordination test; Simple reaction time test; Switching attention test; Colour word vigilance test; Symbol-digit substitution test; Pattern comparison test; Verbal memory test; Spatial memory span test; Digit memory span test backwards; Pattern memory test.

Results and discussion

Clinical signs:
At inhalation exposures up to 250 ppm cyclohexane there were no significant effects on any of the measured neurobehavioural parameters. At the end of the exposure period, there was no correlation between cognitive performance and blood concentrations of cyclohexane.
Results of examinations:
There were no clear treatment related effects at either dose. Some volunteers reported an increase in headache and dry throat, however there was no eye or respiratory tract irritation apparent. Headache was not reported prior to the first exposure, but was reported by 3 individuals prior to the second exposure, which took place 7 days later. The subjects exposed to 860 mg/m3 cyclohexane were more likely to have been aware that they were being exposed to the higher concentration.
There were no treatment-related effects on mood and affect, psychomotor skills, perceptual coding, attention or learning and memory. A single, statistically significant but implausible reduction in semantic cluster ratio was reported, but is considered not to affect the overall conclusion.
The NOAEC was 250 ppm (860 mg/m3).

Any other information on results incl. tables

Subjective measures: prior to and following exposure, subjects completed short questionnaires. More volunteers in the high-exposure group reported headache and dry throat than those exposed to the lower concentration. There were no consistent reports of eye or respiratory irritation.

Applicant's summary and conclusion

The NOAEC was concluded to be 250 ppm (the highest dose tested).
Executive summary:

There was no evidence of any treatment related effects in human volunteers at 86 mg/m3 or 860 mg/m3. Based on the subjective self-reporting, there was no eye or respiratory tract irritation; some volunteers reported an increase in headache and dry throat. Mood and affect, psychomotor skills, perceptual coding, attention, or learning and memory, were unaffected by treatment.