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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:
10 Dec 2018 to 13 Dec 2018
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)
Version / remarks:
1995
Qualifier:
according to guideline
Guideline:
EPA OPPTS 830.7550 (Partition Coefficient, n-octanol / H2O, Shake Flask Method)
Version / remarks:
1996
GLP compliance:
yes
Type of method:
flask method
Partition coefficient type:
octanol-water
Analytical method:
other: Liquid scintillation counting (LSC)
Key result
Type:
log Pow
Partition coefficient:
2.16
Temp.:
25 °C
pH:
8
Details on results:
Partition coefficients (Pow) were calculated from the measured concentrations of the test substance in each phase for each of six samples. Overall mean n-octanol/water partition coefficient and overall mean of the logarithm (base 10) of the n-octanol/water partition coefficient were calculated for each of the six samples. The mean Pow values for the test substance at n-octanol/water solvent ratios of 1:4, 1:2 and 1:1 were determined to be 148, 168, and 118, respectively. The corresponding mean log Pow values were 2.17, 2.22, and 2.07, respectively. The overall mean log Pow was 2.16 ± 0.077 (n = 6, CV = 3.6%). The results are tabulated in 'Any other information on results incl. tables'.

Feasibility trial

The feasibility trial at a 1:1 n-octanol/water volume ratio yielded a mean partition coefficient estimate of 110 (log Pow = 2.04). Based on this result, it was concluded that n-octanol to water volumes ratios of 1:4, 1:2 and 1:1 would be appropriate for the definitive test.

Stock and pH confirmation

The secondary stock solution of the test substance in acetone used to fortify the partition samples had a mean measured activity (from five replicate aliquots analyzed by LSC) of 30.7732 µCi/mL, which correspronds to a mean measured concentration of 314 µg/mL. For the feasibility trial, mean mass balance recovery was 110%. For the definitive test, the measured pH of the aqueous buffer solution (saturated with n-octanol) and the measured pH of the aqueous phase from a partition sample were within ± 0.1 of the target nominal pH of 8. Prior to the definitive test, the measured pH of the aqueous buffer solution (saturated with n-octanol) was 8.08, and the measured pH value of the aqueous phase from a selected definitive test partition sample was 8.05.

Mass balance determination

For each pH test condition, the total mass recovered based on 14C was calculated for each of the six definitive test vessels. A calculated mass balance was obtained for the test substance in all vessels. The overall mean percent recovery for ZDBC for the six vessels was 113 ± 6.2.

Table: Measured concentrations and partition coefficient results

Sample (1)

Solvent ratio (2)

Measured Concentration (M)

Pow

Mean Pow

Log Pow

Mean log Pow

1A

1:4

1.35E-05

147

148

2.17

2.17

1B

9.21E-08

2A

1:2

1.42E-05

149

2.17

2B

9.48E-08

3A

1:2

1.48E-05

181

168

2.26

2.22

3B

8.21E-08

4A

1:2

1.43E-05

155

2.19

4B

9.21E-08

5A

1:1

1.05E-05

107

118

2.03

2.07

5B

9.80E-08

6A

1:1

1.05E-5

130

2.11

6B

8.14E-08

Overall mean

145

 

2.16

 

Standard Deviation

25

 

0.077

 

CV (%)

17

 

3.6

 

(1) The sample identification suffix “A” = n-octanol phase and “B” = aqueous phase of a given test vessel.

(2) Expressed as the volume ratio of n-octanol to water.

Conclusions:
The n-octanol/water partition coefficient (Pow) of the test substance at 25 ºC at a pH of 8, expressed as the logarithm (log10 Pow) was determined to be 2.16 ± 0.077.

Description of key information

The Log Pow of the test substance was determined to be 2.16 at 25 °C and pH 8 in a OECD TG 107 study using a radiolabelled test item.

Key value for chemical safety assessment

Log Kow (Log Pow):
2.16
at the temperature of:
25 °C

Additional information

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