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Physical & Chemical properties

Surface tension

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Reference
Endpoint:
surface tension
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
1. HYPOTHESIS FOR THE CATEGORY APPROACH
The hypothesis is that the category members have similar structures and properties (lack of significant surface activity), which are consistent across the category (Scenario 6 in the RAAF). The consistency of this property across the category is discussed in the endpoint summary.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Please refer to the test material identity information within each endpoint study record and in the endpoint summary. The source chemicals and the target chemical are linear aliphatic alcohols which are members of the long chain linear aliphatic alcohol Category.

The long chain linear aliphatic alcohol Category has at its centre an homologous series of increasing carbon chain length alcohols. The category members are structurally very similar. They are all primary aliphatic alcohols with no other functional groups. The category members are linear or contain a single short-chain side-branch at the 2-position in the alkyl chain, which does not significantly affect the properties (‘essentially linear’). The category members have saturated alkyl chains or contain a small proportion of naturally-occurring unsaturation(s) which does not significantly affect the properties. The branched and unsaturated structures are considered to have such similar properties that their inclusion in the category is well justified.
Impurities: Linear and/or ‘essentially linear’ long chain aliphatic alcohols of other chain lengths may be present. These are not expected to contribute significantly to the properties in respect of this endpoint due to consistent properties (see point 3).
There are no impurities present at or above 1% which are not category members or which would affect the properties of the substance.

3. CATEGORY JUSTIFICATION
The category members are structurally very similar (see point 2) and are biochemically very similar. The metabolic synthesis and degradation pathways are well established. This Category is associated with a consistency and predictability in the physicochemical, environmental, and toxicological property data across its members.

The consistency of observations in this property across the range of chain lengths covered by this Category is described in the Endpoint Summary and in the Category Report attached in Section 13.

In this registration, the information requirement is fulfilled based on read-across from undecan-1-ol which is the most similar source substance based on chain length and physicochemical properties.

4. DATA MATRIX
A data matrix for the C6-24 alcohols Category is attached in Section 13.
Reason / purpose:
read-across source
GLP compliance:
no
Type of method:
plate method
Surface tension:
31.8 mN/m
Temp.:
22.5 °C
Conc.:
6.4 mg/L
Remarks on result:
other: Results were converted to mg/L by the authors of this summary using the water solubility of 1-undecanol = 8 mg/L.

Description of key information

The surface tension of dodecan-1-ol is not available therefore a reliable value is read across from a close structural analogue. A value of 31.8 mN/m at 22.5°C and ca. 90% saturated aqueous solution is estimated by read-across from undecan-1-ol.  

n-Aliphatic alcohols consist of a lipophilic alkyl chain combined with a hydroxyl head group which is mildly hydrophilic. A preliminary assessment by calculated Hydrophilic Lipophilic Balance suggests that no surface tension lowering property would be expected on the basis of structure alone.

Key value for chemical safety assessment

Surface tension:
31.8

Additional information

A preliminary assessment by calculated Hydrophilic Lipophilic Balance suggests that no surface tension lowering property would be expected on the basis of structure alone.

The main purpose of determining surface tension is to assess whether a substance is a surfactant and not able to have a log Kow done. The structural analogue n-octanol, which is considerably more soluble in water than dodecan-1-ol, is regularly used with water in the classic two-phase partitioning experiment (e.g. OECD Guideline 107). Octanol and all alcohols do phase separate which suggests that emulsification is not so strong as to create issues with measurement of partitioning or other fate or effects studies.

The Category hypothesis is that the long chain linear aliphatic alcohol family has at its centre an homologous series of increasing carbon chain length, which is associated with a consistency and predictability in the property data across the group, for the physicochemical, environmental, and toxicological property data sets. Predictivity of the surface activity behaviour of dodecan-1-ol based on undecan-1-ol is considered to be reasonable.

Discussion of trends in the Category of C6-24 linear and essentially-linear aliphatic alcohols:

Chemical derivatives of many of the alcohols in this group are products which have commercial uses relating to their properties as surface active agents. The alcohols themselves are not surface active. Whilst the preliminary assessment by Hydrophilic Lipophilic Balance (HLB) suggests that the shortest chain members of the Category (C6 - C8) could be water/oil emulsifiers, this should not be over-interpreted. They are co-surfactants used to modify the properties of other surfactants.

 

Above C8 there is no alert based on HLB for any surface tension lowering property.