Cyclohexylbenzene

Endpoint summary

Description of key information

No experimental data are available for the toxicokinetic assessment of cyclohexylbenzene. A preliminary assessment of toxicokinetic behaviour is carried out based on the substance's physico-chemical properties. Absorption following oral administration will depend on whether micellular solubilisation occurs for cyclohexylbenzene. Dermal absorption is expected to be low due to the high lipophilicity of the substance. Absorption via the inhalation route is likely, but the risk of inhalation exposure is mitigated by the low vapour pressure of cyclohexylbenzene.

Additional information

No studies are available that address the toxicokinetic behaviour of the test substance. Nevertheless, preliminary predictions of the extent to which a substance absorbs following uptake via the oral, dermal or inhalation route can be made from its physico-chemical properties.

Absorption

 

Oral absorption

 

Oral absorption can occur along the entire length of the gastro-intestinal tract. (Nielsen et al., 2010). The molecular weight of cyclohexylbenzene is less than 200, which favours the absorption process. Nevertheless, the substance’s high log Kow (5.6) indicates that passive diffusion through membranes might be hampered. In stead, absorption through micellular solubilisation might be relevant.

 

Dermal absorption

 

A number of physico-chemical factors determine the extent to which a substance may be absorbed by the dermal route.

 

Dermal absorption is likely for substance with the following properties (Nielsen et al., 2010):

·     A vapour pressure below 100 Pa

·     A Log Kow value between 1 and 4

·     Water solubility:

-     1 - 100 mg/L = low to moderate absorption

-     100-10000 mg/L = high absorption

 

Cyclohexylbenzene has a vapour pressure of 25 Pa, a log Kow of 5.6 and a water solubility of 7 mg/L. Based on these physicochemical properties, the dermal absorption of the substance can be considered to be low. In order for a substance to be absorbed, it needs to penetrate through the stratum corneum to reach the epidermis. The relatively high lipophilicity of cyclohexylbenzene, as demonstrated by its high log Kow value, will enable the uptake into the stratum corneum. However, the rate of transfer between the stratum corneum and the epidermis will be slow and will limit absorption across the skin.

Inhalation absorption

 

The main physicochemical parameters determining the extent to which a liquid substance may be absorbed by the inhalation route are the vapour pressure, the log Kow and the water solubility (Nielsen et al., 2010).

 

Highly volatile substances are considered those substances that have a vapour pressure exceeding 25000 Pa, whereas a vapour pressure of less than 500 Pa indicates a low volatility.

 

Log Kow values above 0 indicate the potential absorption directly across the respiratory tract epithelium.

 

Very hydrophilic substances may be retained within the mucus or for low molecular weight substances (MW < 200), could be absorbed through aqueous pores. Very low water solubility (≤1 mg/L) indicates a potential for accumulation in the lung tissue.

 

Based on the physicochemical properties of cyclohexylbenzene (VP 25 Pa, log Kow 5.6 and WS 7 mg/L), it can be concluded that absorption of the substance through the respiratory tract epithelium is likely. However, based on the low vapour pressure it can be concluded that the substance has a low tendency to be evaporated, thus mitigating the likeliness of exposure via the inhalation route.

Metabolism and excretion

 

No information is available on the metabolism and excretion of cyclohexylbenzene.

 

References:

 

Nielsen, E., Ostergaard, G., Larsen, J.C. (2010). Toxicological Risk Assessment of Chemicals; A Practical Guide. Published by: Informa Healthcare. ISBN-13: 9780849372650.