complex mixture from biological origin

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Justification for type of information:

Justification for using the calculation method
According to Echa guidance R7a (2017), p78:
Guidance on regulatory compliant Kow determination for surfactants:
In many cases a calculated Kow value based on the octanol and water solubilities will be the first choice for surfactants. It is also useful to compare a calculated with a measured value. For the calculation approaches, one needs to consider the pH of the system (which determines the ionisation of the surfactant – see Section R.7.1.17). None of the experimental methods is very well suited for determining the Kow of surface active substances. The shake flask method is the least suitable experimental method for surfactants. HPLC methodology may fail due to secondary interactions, and is sensitive to fluctuations of ionic strength. The slow stirring method in theory is the best, but still not demonstrated to be perfect. If using slow stirring, one needs to demonstrate a consistent result when starting with the surfactant in either phase, not just in the octanol. A working approach for surfactants might be the comparison of measured solubilities in octanol and water. However, it would then be prudent to take the critical micelle concentration in water (cmc) as a solubility limit, in order to avoid the artefact of unrealistically low Kow values.

The calculation of log Kow from solubilities in water (determined via cmc) and octanol in many cases is the first choice for its derivation.

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Calculation from critical micelle concentration and solubility in octanol as described in ECHA guidance R7a (2017).

GLP compliance:

no

Type of method:

estimation method (solubility ratio)

Partition coefficient type:

octanol-water

Analytical method:

other: calculation from critical micelle concentration and solubility in octanol

Key result

Type:

log Pow

Partition coefficient:

2.84

Remarks on result:

not measured/tested

Remarks:

worst case assumption

Details on results:

For details on the calculation, please see section "any other information on results incl. tables".

Calculation

Water solubility from cmc determination: 0,072 g/L

Octanol solubility: 4.8 g/L

Kow = Coctanol / Cwater

max. Kow = Coctanol / min. Cwater = 4.8 g/L / 0.072 g/L = 66.7;  logKow = 1.8

Error estimation

The result of octanol solubility is reported to be not precise as a mixed phase was formed. Assuming a “real” octanol solubility being one order of magnitude higher (50 g/L), the following maximung logKow would result:

Maximum C(Octanol)/C(Wasser) = 50 g/L / 0.072 g/L  = 694; logKow = 2.84

Conclusions:

The estimated logKow calculated from cmc and solubility in octanol is 1.8. As a worst case, the logKow was calculated to be 2.84.

Executive summary:

In this calculation, the logKow of Sophorolipids: fermentation products of glucose and fatty acids, C18 (unsaturated), glycerol esters with yeast Candida, partially hydrolysed was determined. The calculation of logKow from solubilities in water (determined via cmc) and octanol in many cases is the first choice for its derivation. As Sophorolipid is a surfactant (surface tension < 40 mN/m) with acid/base active functional groups, the results from logKow determination via the HPLC method are questionable. Additional interactions between Sophorolipid charged groups and polar groups of the HPLC-column are expected that are not adequately considered by the reference compounds used at the pH of the mobile phase. This makes the result from HPLC logKow determination doubtful. Furthermore, ECHA guidance R7a (2017), p78, recommends to take the critical micelle concentration in water (cmc) as a solubility limit, in order to avoid the artefact of unrealistically low Kow values. The calculations lead to the following values:

Estimated calculated logKow = 1.8.

Worst case logKow = 2.84.

Description of key information

Calculated from cmc and solubility in n-octanol as a worst case assumption. Supported by in silico predition.

Key value for chemical safety assessment

Log Kow (Log Pow):

2.8

Additional information

The calculation of logKow from solubilities in water (determined via cmc) and octanol in many cases is the first choice for its derivation. As Sophorolipid is a surfactant (surface tension < 40 mN/m) with acid/base active functional groups, the results from logKow determination via HPLC method are questionable. Additional interactions between Sophorolipid charged groups and polar groups of the HPLC-column are expected that are not adequately considered by the reference compounds used at the pH of the mobile phase. This makes the result from HPLC logKow determination doubtful.

ECHA guidance R7a (2017), p78, recommends to take the critical micelle concentration in water (cmc) as a solubility limit, in order to avoid the artefact of unrealistically low Kow values. The calculations based on water solubility (CMC) and solubility in octanol lead to the following values:

Estimated calculated logKow = 1.8

Worst case logKow = 2.84

This value is in the same range as the KOWWIN prediction (log Kow 2.80) for the main species of the test item, which is the non-acetylated, oleic linear sophorolipid.