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Partition coefficient

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Endpoint:
partition coefficient
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Study period:
August, 2018
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
See attached QMRF and QPRF documents.
Qualifier:
equivalent or similar to
Guideline:
other: Fragment constant calculation method
Version / remarks:
Use of QSAR model is consistent with ECHA "Guidance on information requirements and chemical safety assessment Chapter R.6: QSARs and grouping of chemicals".
Deviations:
not applicable
Principles of method if other than guideline:
See attached QMRF and QPRF documents.
Type of method:
calculation method (fragments)
Partition coefficient type:
octanol-water
Specific details on test material used for the study:
Partition coefficient was predicted based on the weighted average of eight individual constituents of the UVCB substance. These components, along with water, comprise ca. 98% of the quantified constituents and ca. 78% of the total composition.
Key result
Type:
log Pow
Partition coefficient:
ca. 5.6
Remarks on result:
other: Predicted using QSAR model
Details on results:
The range of predicted constituent partition coefficients is 4.92 – 7.94. However, the lowest and highest predicted values are associated with constituents that comprise <1.5% of the typical UVCB composition. Since the partition coefficient is a ratio of the concentrations of the UVCB mixture in octanol and water, the logKow of the mixture can be appropriately predicted by calculating the weighted average of the constituent partition coefficients. The average partition coefficient weighted by each constituent’s typical concentration in the mixture is logKow = 5.6.

The partition coefficient value can be considered to represent the value(s) at an unspecified, probably ambient temperature (ca. 20°C), since no mention is made in the guidelines of the temperature at which the reference substance’s log Pow values were determined. Partition coefficients of the test and reference substances are assumed to vary with temperature in the same way.
Conclusions:
The partition coefficient (logKow) of [ω-hydroxy-C16 (saturated and unsaturated) and C16 (unsaturated)] fatty acids is determined to be 5.6.
Executive summary:

The n-octanol/water partition coefficient of [ω-hydroxy-C16 (saturated and unsaturated) and C16 (unsaturated)] fatty acids was predicted based on measured and estimated logKow values of eight (8) individual UVCB constituents obtained using the ECOSAR (Ecological Structure-Activity Relationship) Class Program version 2.0. These constituents, along with water, comprise more than ca. 98% of the quantified constituents and ca. 78% of the total UVCB composition.

Since the partition coefficient is a ratio of the concentrations of the UVCB mixture in octanol and water, the logKow of the mixture is appropriately predicted by calculating the weighted average of the constituent partition coefficients. The average partition coefficient weighted by each constituent’s typical concentration in the mixture is logKow = 5.6. This value is consistent with the measured partition coefficient of a similar read-across substance (EC/List number 943-164-7).

Endpoint:
partition coefficient
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Study period:
19 December 2016 - 18 April 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
The partition coefficient of a read-across substance (EC/List number 943-164-7) was assessed according to OECD method 117. The read-across substance was produced by the same E. coli fermentation process as [ω-hydroxy-C16 (saturated and unsaturated) and C16 (unsaturated)] fatty acids, but was extracted using a different solvent.
Qualifier:
according to
Guideline:
other: EU Method A.24 Partition Coefficient (n-octanol/water): High Performance Liquid Chromatography (HPLC) Method
Version / remarks:
2016
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Version / remarks:
2004
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 830.7570 (Partition Coefficient, n-octanol / H2O, Estimation by Liquid Chromatography)
Version / remarks:
1996
Deviations:
no
GLP compliance:
yes
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Key result
Type:
log Pow
Partition coefficient:
3.1
Temp.:
20 °C
Remarks on result:
other: Peak 1 (Peak area of 14%). Non-buffered mobile phase
Key result
Type:
log Pow
Partition coefficient:
5.2
Temp.:
20 °C
Remarks on result:
other: Peak 2 (Peak area of 7.9%)
Key result
Type:
log Pow
Partition coefficient:
5.5
Temp.:
20 °C
Remarks on result:
other: Peak 3 (Peak area of 78%)
Details on results:
- Retention times of reference substances used for calibration: see table below
- Details of fitted regression line: log k' = 0.326 x log Pow – 0.830 (r = 0.996, n=14)
- Graph of regression line and chromatograms: see attachment
- Both chromatograms of the test item showed one major peak (78% area) and severall small peaks. The small peaks with peak areas of 14 and 7.9% were also used for logPow calculations.
- Average retention data for test item: see table below
- The value of log Pow obtained from duplicate measurements was within ± 0.1 log units.

Table: Results Partition coefficient n-octanol-water (HPLC method)

Substance

tr,1
[min]

tr,2
[min]

mean tr
(n=2)

log Pow

Pow

Area
%

Formamide (t0)

0.602

0.603

0.603

 

 

 

Benzylalcohol

0.771

0.773

 

1.1

 

 

Bromobenzene

1.551

1.550

 

3.0

 

 

Biphenyl

2.575

2.571

 

4.0

 

 

Dibenzyl

4.278

4.263

 

4.8

 

 

Triphenylamine

7.827

7.784

 

5.7

 

 

4,4’-DDT

11.239

11.167

 

6.5

 

 

Benzo[ghi]perylene

18.096

17.948

 

7.2

 

 

Test item – peak 1

1.496

1.491

1.494

3.1

1.2E03

14

Test item – peak 2

5.128

5.118

5.123

5.2

1.7E05

7.9

Test item – peak 3

6.069

6.060

6.065

5.5

3.0E05

78

Remark: the log Pow values of the reference substances are according to OECD TG 117.

Conclusions:
The log Pow value was determined to be 5.5 based on the peak of the main test item.

Executive summary:

The log Pow of the substance was determined using the HPLC method in a GLP study according to EC A.8, OECD 117 and OPPTS 830.7570. The mobile phase was a gradient with 75/25 (v/v) methanol/water and methanol and the wavelength of detection 210 nm.

Formamide was used as unretained substance. Duplicate injections of unretained substance, reference substances and test item. Both chromatograms of the test item showed one major peak and severall small peaks. The log Pow value for the peaks with areas of 14%, 7.9% and 78% was determined to be 3.1, 5.2 and 5.5, respectively. The log Pow of the UVCB substance is determined to be 5.5 based on the peak of the main test item.

Description of key information

The logKow of the UVCB substance is predicted by calculating the average of the constituent partition coefficients weighted by their typical concentration in the mixture. The weighted average partition coefficient is logKow = 5.6. This value is consistent with the measured partition coefficient of a similar read-across substance (EC/List number 943-164-7).

Key value for chemical safety assessment

Log Kow (Log Pow):
5.6

Additional information