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Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2008.11.26-2008.12.22
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method A.8 (Partition Coefficient)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
The Department of Health of the Government of the United Kingdom
Type of method:
shake-flask method to: flask method
Partition coefficient type:
octanol-water
Analytical method:
gas chromatography
Type:
Pow
Partition coefficient:
ca. 2.2
Temp.:
22 °C
pH:
ca. 2.9
Type:
log Pow
Partition coefficient:
ca. 0.343
Temp.:
22 °C
pH:
ca. 2.9
Type:
Pow
Partition coefficient:
ca. 0.005
Temp.:
22 °C
pH:
ca. 7
Type:
log Pow
Partition coefficient:
ca. -2.32
Temp.:
22 °C
pH:
ca. 7
Details on results:
The partition coefficient determined for each sample is shown in Table 1. Mean partition coefficient has been reported: 2.20, log10Pow=0.343. The test material has a predicted dissociation constant of 4.34±0.1. Testing was performed at pH=2.9±0.1 to obtain the test material in its non-ionised form.
Partition coefficient at environmentally relevant pH (pH=7) was calculated using Equation 1. The test material has a corrected coefficient of 4.81×10-3, log10P’ow=-2.32 at pH=7.

Table 1:

sample number

n-octanol/water volume ratio

partition coefficient

log10Pow

mean partition coefficient

1

1:2

2.04

0.310

2.28

2

2.53

0.403

3

1:1

1.98

0.297

2.07

4

2.16

0.335

5

2:1

2.39

0.378

2.26

6

2.13

0.327

 

Equation 1:

P’ow=Pow/(1+10(pH-pKa))

Where: P’ow= corrected partition coefficient, Pow= estimated partition coefficient, pKa = 4.34, pH = 7.

Executive summary:

The octanol-water partition coefficient has been determined to be Pow=2.20, log Pow=0.343 at pH=2.9±0.1 and 22°C (study performed at pH=2.9±0.1), and Pow=0.00481, log Pow=-2.32 at pH=7 and 22°C (value calculated), by using the shake-flask method, according to Method A8 Partition Coefficient of Council Regulation (EC) No 440/2008 of 30 May 2008 and Method 107 of the OECD Guidelines for Testing of Chemicals, 27 July 1995.

Description of key information

Octanol-water partition coefficient: Pow=2.20, log Pow=0.343 at pH=2.9±0.1 and 22°C (study performed at pH=2.9±0.1), and Pow=0.00481, log Pow=-2.32 at pH=7 and 22°C (value calculated)

Key value for chemical safety assessment

Log Kow (Log Pow):
-2.3
at the temperature of:
22 °C

Additional information

The study performed in experimental laboratory (Fox, 2009, Harlan), dedicated to estimate the partition coefficient of the test material 3-mercaptopropionic acid, has been chosen as a key study. The octanol-water partition coefficient has been determined to be Pow=2.20, log Pow=0.343 at pH=2.9±0.1 and 22°C (study performed at pH=2.9±0.1), and Pow=0.00481, log Pow=-2.32 at pH=7 and 22°C (value calculated), by using the shake-flask method, according to Method A8 Partition Coefficient of Council Regulation (EC) No 440/2008 of 30 May 2008 and Method 107 of the OECD Guidelines for Testing of Chemicals, 27 July 1995.

The other two reported studies (Hansch et al., 1995 and Leo, 1995) are supporting studies. They reported the following values of log Pow: 0.09 and 0.43, respectively. The information given there is not complete (no information about temperature and pH) but qualitatively supports the key study (log Pow<3).