2,6-Octadienal, 3,7-dimethyl-, acid-isomerized

Endpoint summary

Additional information

Absorption

No studies are available that address the absorption of the test substance via the oral, dermal or inhalation route. In general, some preliminary predictions can be made from the substance’s physico-chemical properties. However, it has to be kept in mind that Citrylal is a UVCB substance, consisting of many different chemical constituents. As each of these constituents has different physico-chemical properties, it is impossible to determine an overall toxicokinetic profile for the substance. Instead, the physicochemical properties of the main constituents have been taken into account. Most of the physchem tests performed in the framework of the REACH registration dossier do not provide individual results for the constituents of the UVCB. Therefore, the toxicokinetics assessment is mainly based on QSAR estimations on individual constituents (Episuite).

Oral absorption

Oral absorption can occur along the entire length of the gastro-intestinal tract. For most substances, absorption occurs through passive diffusion. A number of physico-chemical factors determine the extent to which a substance may be absorbed by the oral route. Generally, smaller molecules are more easily absorbed. Furthermore, substances need to be sufficiently water soluble in order to readily dissolve into the gastrointestinal fluids. A moderate log Kow furthermore favors the uptake via passive diffusion. Nevertheless, substances that are more lipophilic might still be absorbed after micellular solubilization.

According to Nielsen et al. (2010), oral absorption is likely for a substance if it has the following properties:

- a molecular weight < 500

- a log Kow between 0 and 4

- water soluble

The constituents of citrylal are assessed in the below table. 

Name	CAS	MW	Log Kow	WS (mg/L)	Oral absorption
p-cymene	99-87-6	134.22	4.0	28	Moderate
ethanol	64-17-5	46.07	-0.14	7.9E5	Moderate
4-isopropenyltoluene	1195-32-0	132.21	3.99	35.29	Moderate
terpinoline	586-62-9	136.24	4.88	9.5	Low
p-mentha-1,5,8-triene	21195-59-5	134.22	4.61	2.96	Low
geranial	141-27-5	152.24	3.45	1340	High
1,5-p-menthadien-8-ol	1686-20-0	152.24	3.12	523	High
p-cymenyl ethyl ether	68279-51-6	178.28	3.68	40.07	Moderate
alpha-terpineole	99-86-5	136.24	4.75	5.92	Low

 

 

Dermal absorption

Like for oral absorption, physico-chemical factors also determine the extent to which a substance may be absorbed by the dermal route. In order for a substance to cross the stratum corneum, the substance should be sufficiently lipophilic (= sufficient solubility in fat). On the other hand, partitioning from the stratum corneum into the epidermis requires sufficient hydrophilicity (= sufficient solubility in water). Hence, the likelyhood of dermal absorption is determined by the substance's log Kow and water solubility values.

According to Nielsen et al. (2010), dermal absorption is likely for a substance if it has the following properties:

- a vapour pressure < 100 Pa

- a log Kow between 1 and 4

- a water solubility in the range of 1 - 100 mg/L (moderate absorption), or 100 - 10000 mg/L (high absorption).

The constituents of citrylal are assessed in the below table.

Name	CAS	VP (Pa)	Log Kow	WS (mg/L)	Dermal absorption
p-cymene	99-87-6	152	4.0	28	High*
ethanol	64-17-5	7910	-0.14	7.9E5	Low*
4-isopropenyltoluene	1195-32-0	99.4	3.99	35.29	Moderate
terpinoline	586-62-9	133	4.88	9.5	Low*
p-mentha-1,5,8-triene	21195-59-5	273	4.61	2.96	Low*
geranial	141-27-5	12.2	3.45	1340	High
1,5-p-menthadien-8-ol	1686-20-0	3.51	3.12	523	High
p-cymenyl ethyl ether	68279-51-6	10.2	3.68	40.07	Moderate
alpha-terpineole	99-86-5	222	4.75	5.92	Low*

* Dermal absorption is furthermore mitigated by the tendency of the substance to evaporate from 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) gives the following criteria:

- Highly volatile substances are considered those substances that have a vapour pressure exceeding 25000 Pa (or boiling point < 50°C), whereas a vapour pressure < 500 Pa (or boiling point > 150C°) indicates a low volatility.

- Log Kow > 0 indicates the potential for direct absorption across the respiratory tract epithelum. Substances with a log Kow value between 0 and 4 are sufficiently lipophilic to allow crossing the alveolar and capillary membranes, and hence are likely to be absorbed as well.

- A sufficient water solubility increases the potential for inhalation absorption. Nevertheless, very hydrophilic substances may be retained within the mucus, and transported out of the respiratory tract by clearance mechanisms.

 

The constituents of citrylal are assessed in the below table.

Name	CAS	VP (Pa)	Log Kow	WS (mg/L)	Inhalation absorption
p-cymene	99-87-6	152	4.0	28	High*
ethanol	64-17-5	7910	-0.14	7.9E5	Very high#
4-isopropenyltoluene	1195-32-0	99.4	3.99	35.29	High*
terpinoline	586-62-9	133	4.88	9.5	Low*
p-mentha-1,5,8-triene	21195-59-5	273	4.61	2.96	Low*
geranial	141-27-5	12.2	3.45	1340	High*
1,5-p-menthadien-8-ol	1686-20-0	3.51	3.12	523	High*
p-cymenyl ethyl ether	68279-51-6	10.2	3.68	40.07	Moderate*
alpha-terpineole	99-86-5	222	4.75	5.92	Low*

* Inhalation absorption is furthermore mitigated by the low tendency of the substance to evaporate.

# The physicochemical parameters would suggest that the substance is too hydrophilic to cross the alveolar and capillary membranes. However, as ethanol as a very low molecular weight it can be absorbed through aqueous pores.

 

Metabolism and Excretion

No information on the metabolism and excretion of the test item is available.

 

References:

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