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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:
from 2007/09/06 to 2007/12/07
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method A.8 (Partition Coefficient)
Version / remarks:
Cited as Directive 84/449/EEC, A.8
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
shake-flask method to: flask method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Key result
Type:
log Pow
Partition coefficient:
-2.99
Temp.:
22 °C
pH:
7
Details on results:
In the definitive test the pH of n-octanol saturated water was 1.7.

The relationship between partition coefficient, dissociation constant and pH was calculated using the following equation:
Pow' = Pow/1+10e(pH-pKa)
where:
Pow' = partition coefficient of ionised form
Pow  = partition coefficient of molecular form
pKa = dissociation constant
pH = aqueous phase pH

Using this equation, the partition coefficient of thioglycolic acid has been determined to be 1.89 at 22°C (+ or - 0.5°C), or logP = 0.276.
At pH 7, the partition coefficient was estimated to be 1.01*10e-3, so logP = -2.99.
Conclusions:
Validity criteria were fulfilled.
The linearity of the detector response with respect to concentration was assessed for the test material over the nominal concentration range of 0 to 50 mg/L. This was satisfactory with a correlation coefficient of >= 0.998 being obtained for both the organic phase analysis matrix and the aqueous phase analysis matrix.
Executive summary:

The partition coefficient of thioglycolic acid was evaluated in a study performed in accordance with OECD testing guideline 107 and GLP requirements.

The partition coefficient of thioglycolic acid has been determined to be 1.89 at 22°C (+ or - 0.5°C) and pH = 1.7, or Kow = 0.276.

The log Kow of thioglycolic acid was estimated to be of -2.99 at pH 7 (Kow = 1.01*10e-3).

Thioglycolic acid is expected not to bioaccumulate in the environment.

Description of key information

A partition coefficient study has been carried out with thioglycolic acid according to OECD 107. The measured partition coefficient for thioglycolic acid is -2.99 at 22°C.

Key value for chemical safety assessment

Log Kow (Log Pow):
-2.99
at the temperature of:
20 °C

Additional information

Based on mercaptoacetic acid Log Kow value obtained in the frame of the OECD test, it can be concluded that bioaccumulation potential of mercaptoacetic acid and salts of it is negligible.

Since the salts of mercaptoacetic acid dissociate in aqueous solution, the log Kow of the free acid is used as surrogate for the salts.