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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:
26 November 2003 to 01 December 2003
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
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
Qualifier:
according to guideline
Guideline:
EPA OPPTS 830.7550 (Partition Coefficient, n-octanol / H2O, Shake Flask Method)
Deviations:
no
GLP compliance:
yes
Type of method:
shake-flask method to: flask method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Type:
Pow
Partition coefficient:
14
Temp.:
25 °C
pH:
5
Type:
log Pow
Partition coefficient:
1.2
Temp.:
25 °C
pH:
5
Type:
Pow
Partition coefficient:
14
Temp.:
25 °C
pH:
7
Type:
log Pow
Partition coefficient:
1.1
Temp.:
25 °C
pH:
7
Type:
Pow
Partition coefficient:
13
Temp.:
25 °C
pH:
9
Type:
log Pow
Partition coefficient:
1.1
Temp.:
25 °C
pH:
9
Details on results:
Following centrifugation, the equilibrium concentrations of the test item in either the two clear separated phases were all less than 2483 mg/L i.e. less than 0.01 molar.
The individual log Pow values of all six samples varied between 1.14 to 1.17 for the citrate buffer, 1.12 and 1.15 for the phosphate buffer and 1.10 and 1.16 for the borax buffer solutions. All were found to be within the range of ± 0.3 log units.

Table 1: Results with buffer solution pH 5

Sample number

P1

P2

P3

P4

P5

P6

Amount of test material (mg)

30.3088

29.2121

62.3125

60.2188

14.8553

16.1514

Volume of octanol (mL)

20

20

40

40

10

10

Volume of water (mL)

20

20

20

20

20

20

Concentration of the test material in the octanol phase (mg/L)

1469.220

1423.408

1542.763

1545.409

1423.382

1471.300

1471.972

1401.249

1593.563

1490.749

1422.459

1453.813

Average concentration:

1470.596

1412.329

1568.163

1518.079

1422.921

1462.557

Concentration of the test material in the aqueous phase (mg/L)

103.054

100.832

111.355

106.919

96.386

105.439

102.307

102.122

111.304

106.649

96.465

102.957

Average concentration:

102.681

101.477

111.330

106.784

96.426

104.198

pH of aqueous phase

4.97

4.97

4.97

4.97

4.97

4.98

Average pH of aqueous phase

5.00

Amount of test material in the octanol phase (mg)

29.4119

28.2466

62.7265

60.7232

14.2292

16.6256

Amount of test material in the aqueous phase (mg)

2.0536

2.0295

2.2266

2.1357

19.2850

2.0840

Total amount of test material in the two phases (mg)

31.4655

30.2761

64.9531

62.8589

16.1577

16.7096

Recovery (%)

104

104

104

104

109

103

Pow

14.32

13.92

14.09

14.22

14.76

14.04

Average Pow

14.12

14.16

14.40

Average Pow ± standard deviation

14 ± 0.30

Log Pow

1.2

 

Table 2: Results with buffer solution pH 7

Sample number

P1

P2

P3

P4

P5

P6

Amount of test material (mg)

23.7286

23.4295

29.4115

30.8073

18.9430

18.8433

Volume of octanol (mL)

20

20

40

40

10

10

Volume of water (mL)

20

20

20

20

20

20

Concentration of the test material in the octanol phase (mg/L)

1127.954

1123.905

728.501

764.207

1637.202

1644.009

1155.229

1103.739

726.507

774.955

1658.220

1688.024

Average concentration:

1141.592

1113.822

727.504

769.581

1648.711

1666.017

Concentration of the test material in the aqueous phase (mg/L)

82.254

78.122

53.768

55.310

119.415

127.703

81.653

78.659

54.392

55.124

117.680

124.929

Average concentration:

81.954

78.391

54.080

55.217

118.548

126.316

pH of aqueous phase

6.99

6.99

7.00

7.00

7.00

6.99

Average pH of aqueous phase

7.00

Amount of test material in the octanol phase (mg)

22.8318

22.2764

29.1002

30.7832

16.4871

16.6602

Amount of test material in the aqueous phase (mg)

1.6391

1.5678

1.0816

1.1043

2.3710

2.5263

Total amount of test material in the two phases (mg)

24.4709

23.8442

30.1818

31.8875

18.8581

19.1865

Recovery (%)

103

102

103

104

100

102

Pow

13.93

14.21

13.45

13.94

13.91

13.19

Average Pow

14.07

13.70

13.55

Average Pow ± standard deviation

14 ± 0.38

Log Pow

1.1

 

Table 3: Results with buffer solution pH 9

Sample number

P1

P2

P3

P4

P5

P6

Amount of test material (mg)

29.0127

28.8133

30.1094

31.2061

27.9160

28.2151

Volume of octanol (mL)

20

20

40

40

10

10

Volume of water (mL)

20

20

20

20

20

20

Concentration of the test material in the octanol phase (mg/L)

1427.103

1402.427

747.179

716.648

2324.970

2434.682

1410.997

1395.177

738.297

716.165

2356.201

2413.251

Average concentration:

1419.050

1398.802

742.738

716.407

2340.586

2423.967

Concentration of the test material in the aqueous phase (mg/L)

102.778

97.631

55.312

57.700

175.047

180.058

101.749

96.936

56.789

56.281

177.874

185.136

Average concentration:

102.264

97.284

56.051

56.991

176.461

182.597

pH of aqueous phase

9.04

9.05

9.05

9.04

9.04

9.04

Average pH of aqueous phase

9.00

Amount of test material in the octanol phase (mg)

28.3810

27.9760

29.7095

28.6563

23.4059

24.2397

Amount of test material in the aqueous phase (mg)

2.0456

1.9457

1.1210

1.1398

3.5292

3.6519

Total amount of test material in the two phases (mg)

30.4263

29.9217

30.8305

29.7961

26.9351

27.8916

Recovery (%)

105.0

104.0

102.0

95.5

96.5

98.9

Pow

13.88

14.38

13.25

12.57

13.26

13.27

Average Pow

14.13

12.91

13.27

Average Pow ± standard deviation

13 ± 0.62

Log Pow

1.1

 

Conclusions:
Under the conditions of the test, the partition coefficients of the test material at 25 °C was Pow 14 (± 0.30), 14 (± 0.38) and 13 (± 0.62) for buffer solutions at pH5, pH7 and pH 9 respectively. The respective log Pow values were 1.2, 1.1 and 1.1. The study is considered to be reliable, relevant and adequate for risk assessment and classification and labelling purposes.
Executive summary:

The octanol/water partition coefficient of the test material was determined in accordance with the standardised guidelines OECD 107, EU Method A.8 and EPA OPPTS 830.7550 using the shake flask method. Under the conditions of the test the partition coefficients of the test material at 25 °C were Pow 14 (± 0.30), 14 (± 0.38) and 13 (± 0.62) for buffers solutions at pH 5 (citrate buffer), pH 7 (phosphate buffer) and pH 9 (borate buffer) respectively. The respective log Pow values were 1.2, 1.1 and 1.1.

Description of key information

Log Pow 1.1 (Pow 14), at 25 °C and pH 7, OECD TG 107, Das 2003a

Key value for chemical safety assessment

Log Kow (Log Pow):
1.1
at the temperature of:
25 °C

Additional information

The octanol/water partition coefficient of the test material was determined in two studies in accordance with the standardised guidelines OECD 107, EU Method A.8 and EPA OPPTS 830.7550. In the key study (Das 2003a), using the shake flask method with buffered solutions, the partition coefficients of the test substance at 25 °C were Pow 14 (± 0.30), 14 (± 0.38) and 13 (± 0.62) for buffers solutions at pH 5 (citrate buffer), pH 7 (phosphate buffer) and pH 9 (borate buffer) respectively. The respective log Pow values were 1.2, 1.1 and 1.1. In the supporting study (Das 2003b), the octanol/water partition coefficient was determined to be Pow 8.6 (± 0.14) (log Pow 0.93) at 25 °C, using the same guidelines (non-buffered solutions).

The partition coefficient does not vary greatly between the different testing approaches and overall indicate the same property of the test material. Both studies were reported to a high standard, performed in compliance with GLP and to standardised guidelines. The results from the shake flask method are selected as the key value because there are a direct measurement of the octanol-water partitioning, and the more conservative result. Although, none of the standardised tests for partition coefficient are considered suitable for surface active materials (slow-stirring is considered the most appropriate test), the two studies examine the partition coefficient at different pHs and demonstrate little difference in the partitioning coefficients in each test. Both studies were assigned a reliability score of Klimisch 1 and as such were considered suitable for use as an accurate reflection of the test substance.

The available data are considered to be complete and the result determined, log Pow 1.1 (Pow 14), at 25 °C and pH 7, was taken forward for risk assessment.