Cyclohexane

Specific investigations: other studies

Administrative data

Endpoint:

behavioural effects

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

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other: GLP (no data), non-guideline human and animal experimental studies available as unpublished reports, no restrictions, fully adequate for assessment.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2009

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The effects on behaviour and toxicokinetics following inhalation cyclohexane were assessed in human volunteers and rats.

GLP compliance:

not specified

Type of method:

in vivo

Endpoint addressed:

basic toxicokinetics

Test material

Test material information

Constituent 1

Reference substance name:

Cyclohexane

EC Number:

203-806-2

EC Name:

Cyclohexane

Cas Number:

110-82-7

Molecular formula:

C6H12

IUPAC Name:

cyclohexane

Details on test material:

- Name of test material (as cited in study report): Cyclohexane
- Physical state: liquid
- Supplier: E. Merck Nederland B.V, Amsterdam, The Nederlands or J.T. Baker Nederland, Deventer, The Nederlands
- Analytical purity: >99%

Test animals

Species:

other: Rat and Human

Strain:

other: WAG/RijCR/BR (rat)

Sex:

male

Details on test animals or test system and environmental conditions:

RATS
- Source: Charles River Wiga, Sulzfeld, Germany
- Age at study initiation: 9-14 weeks
- Weight at study initiation: approx. 200 - 250 g
- Housing: Suspended stainless steel wire mesh cages
- Diet: ad libitum (except during exposure)
- Water: tap water ad libitum (except during exposure)

- ENVIRONMENTAL CONDITIONS
- Temperature: 20-25°C
- Humidity: 40-70%
- Photoperiod: 12 hrs dark / 12 hrs light

HUMAN
- Sex: male
- Age: 22, 23 and 27 yrs
- Height: 174.6 – 190.2 cm
- Weight: 64 – 93.2 kg

Administration / exposure

Route of administration:

inhalation

Vehicle:

other: air

Details on exposure:

Rat – determination of cyclohexane uptake: Whole body exposure. Target concentrations: 0.1, 0.6, 4 and 24 g/m3. A test to determine uptake onto fur used 3 dead animals exposed for 6 hrs to a target concentration of 6000 mg/m3.
Rat – kinetic study: brain and blood cyclohexane concentration was measured following exposure to 0, 1.4, 8 and 28 g/m3; (0, 400, 2300 and 8000 ppm respectively), for 2,4 or 8 hrs.

Human – kinetic study: Volunteers were exposed for 4 hrs to a target concentration of 875 mg/m3 (250 ppm)

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Rat studies – frequent monitoring by GC-FID
Human studies – continuous monitoring by IR absorption

Duration of treatment / exposure:

Rat: 8 hr/day for 1, or 3 consecutive days.
Human: 4 hrs

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0, 100, 600, 4000 and 24000 mg/m3
Basis:
other: Rat: whole body exposures - target concentrations

Doses / concentrations 2

Remarks:

Doses / Concentrations:
6000 mg/m3
Basis:
other: Rat: uptake onto fur (dead animals) - target concentration

Doses / concentrations 3

Remarks:

Doses / Concentrations:
0, 1400, 8000, and 28000 mg/m3
Basis:
other: Rat: whole body exposures - target concentration

Doses / concentrations 4

Remarks:

Doses / Concentrations:
875 mg/m3 (250 ppm)
Basis:
other: Human: 4 hr - target concentration

No. of animals per sex per dose:

Rat: 3/group (uptake study); 3 or 4/group (kinetic study)
Human: 3 males

Control animals:

other: rats -exposed to air only

Details on study design:

The experimental time-concentration curves from the uptake study in rats were compared with a PbPk model simulation of cyclohexane uptake to obtain values of the kinetic parameters. The model consisted of 5 compartments: liver, slowly perfused tissue, rapidly perfused tissue, fat and brain. In addition, a lung compartment for gas exchange was also included. Physiological parameters incorporated into the model were taken from the literature and the solubility of cyclohexane in different tissues was derived from partition coefficients measured in a previously reported study (Leenheers, L. H. 2000. Determination of liquid/air partition coefficients of n-nonane, n-decane, 1,2,4-trimethylbenzene and cyclohexane.TNO report V96.638).

Examinations

Examinations:

Rat: Uptake study – no in-life measurements taken
Rat: Kinetic study: Blood and brain samples were collected at termination and concentrations of cyclohexane were determined using gas chromatographic techniques.
Human: Venous blood samples were collected prior to, during and following exposure. Exhaled alveolar air samples were collected prior to and following exposure. Concentrations of cyclohexane in blood and exhaled alveolar air determined using gas chromatographic techniques.

Results and discussion

Details on results:

Rat: The values obtained for the toxicokinetic parameters by fitting the model to the experimental data were 5.4 mg/kg body weight/h for Vmax and 0.13 mg/L for Km. Cyclohexane concentrations in blood and brain showed no evidence of induced metabolism after 8 hrs or 3x 8 hr exposures.
Human: Inhaled cyclohexane was rapidly taken up, mean blood concentrations after 2 hr exposure were 570 ng/mL rising to 643ng/mL at the end of the exposure period. Following exposure, blood concentrations of cyclohexane decreased rapidly falling to 151.5ng/mL after 1hr and 68 ng/mL after 2 hr; blood concentrations were near or below the LOQ (15 ng/mL) at all later timepoints.
Mean concentrations of cyclohexane in exhaled alveolar air measured after the end of the exposure period were initially 240ug/L; they decreased by approximately 50% within 20 min, were 9.33ug/L after approximately 9 hr and were below the LOQ (1ug/L) after 3 days.

Applicant's summary and conclusion

Conclusions:

In rats, the toxicokinetic parameters for uptake of cyclohexane by inhalation were 5.4 mg/kg body weight/h for Vmax and 0.13 mg/L for Km.
Concentrations in both blood and brain were similar after 3 repeated 8 hr exposures to those measured after a single 8 hr exposure. Concentrations of cyclohexane in brain during exposure were approximately 10x those in blood.
In human volunteers inhaled cyclohexane was rapidly taken up, mean blood concentrations increased to 696 ng/mL by the end of the exposure period. Following exposure, blood concentrations of cyclohexane decreased rapidly. Mean concentrations of cyclohexane in exhaled alveolar air measured after the end of the exposure period were 240 ug/L; they decreased rapidly and were below the LOQ after 3 days.