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Partition coefficient

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Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
2a/2b: guideline study or comparable to guideline study without detailed documentations and acceptable restrictions. Slow-stirring method is better adapted for for substances with Log Kow > 4 that may form emulsion. Results obtained between 3 different labs are consistent one with each other and with results from HLPC method and calculation method.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 123 (Partition Coefficient (1-Octanol / Water), Slow-Stirring Method)
Deviations:
no
GLP compliance:
not specified
Type of method:
shake-flask method to: flask method
Remarks:
version 1981
Partition coefficient type:
octanol-water
Type:
log Pow
Partition coefficient:
7.137
Temp.:
25 °C
pH:
ca. 7
Type:
log Pow
Partition coefficient:
7.453
Temp.:
25 °C
pH:
ca. 7
Type:
log Pow
Partition coefficient:
7.27
Temp.:
25 °C
pH:
ca. 7
Details on results:
As no data on pH was given in the study, we assume that partition coefficient was determined at a neutral pH, relevant for the environment.

- Lab 1 Log Kow = 7.137 +/- 0.153.

- Lab 2 Log Kow =7.453 +/- 0.061.

These slight differences might be due to less accurate temperature control in the first lab system. Temperature influence the emulsion formation which could result in a higher concentration measured in the aqueous phase and hence lower Log Kow value.

However, stir-flask technique is at least reproducible from one lab to another (variation in no more than 0.3 log unit between labs).

- Log Kow from Ellington and Floyd (1996) is 7.27 +/- 0.04 (n=3)

- These results are consistent with

- results obtained during the ring test for OECD guideline 117 (Log Kow = 7.8 +/- 1.4 (n=16) in Klein et al., 1988) and,

- SPARC computed value (LogKow =7.54 in Ellington and Floyd, 1996).

Conclusions:
Log Kow of DEHP was measured by stir-flask method give consistent results between 2 different lab with Log Kow= 7.137 and 7.453.
Therefore DEHP as to be considered as potentially bioaccumulative.
Executive summary:

In an interlaboratory evaluation, 2 labs compared their results for the obtention of Log Kow value with stir-flask method OEDCD 107 ( 1981). The aim was to test the applicability of this method for measuring Log Kow value greater than 4 or 5 by reducing emulsion formation. Therefore the 2 layers (water and octanol ) were not shaken together but stirred without mixing.

Few years later Ellington and Floyd (1996) followed the same slow stir method for the determination of DEHP octanol water partition coefficient

No precision of which analytical method was applied for the analysis of DEHP content in each phase was precised.

Log Kow obtained were:

- Lab 1: 7.137 +/- 0.153

- Lab 2: 7.453 +/- 0.061

- Ellington and Floyd (1996): 7.27 +/- 0.04 (n=3)

The difference might be due to less accurate temperature control. As temperature influence the emulsion formation which could result in a higher concentration measured in the aqueous phase and hence lower Log Kow value.

However, stir-flask technique is at least reproducible from one lab to another (variation in no more than 0.3 log unit between labs).

These results are consistent with results obtained during the ring test for OECD guideline 117 (Log Kow = 7.8 +/- 1.4 (n=16) in Klein et al., 1988)

and with SPARC computed value (LogKow =7.54 in Ellington and Floyd 1996).

DEHP as to be considered as potentially bioaccumulative.

As slow-stirring method is better adapted for substances that may form emulsion, as results obtained between 3 different labs are consistent one with each other and with results from HLPC method and calculation method this study is considered as reliable with restriction.

Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Version / remarks:
1995
Deviations:
no
GLP compliance:
no
Other quality assurance:
ISO/IEC 17025 (General requirements for the competence of testing and calibration laboratories)
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Key result
Type:
log Pow
Partition coefficient:
ca. 6.07
Temp.:
30 °C
pH:
>= 5 - <= 8
Details on results:
Results:
Mobile phase
[Acetonitrile:water]
Retention time
[min.]
log P
(interpolated)
1:1 53.2 6.22
3:2 27.94 5.91
2:3 - -
Standard deviation: 0.22
Average Partition Coefficient (n-octanol/water): 6.07 ± 0.22
Conclusions:
Average Partition Coefficient (n-octanol/water): 6.07 ± 0.22
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: 2d: Test procedure in accordance with national standard method (US EPA draft ASTM standard) and value consistent with other HPLC determined values from Mc Duffie (1981)
Qualifier:
according to
Guideline:
other: draft ASTM standard
Deviations:
not specified
Qualifier:
equivalent or similar to
Guideline:
other: protocol from Swann et al. 1983
GLP compliance:
not specified
Type of method:
HPLC method
Remarks:
Retention time measurements and calculation of Kow using linear correlation developed with standards of known Kow
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Type:
log Pow
Partition coefficient:
7.94
Temp.:
25 °C
pH:
ca. 7
Details on results:
It appears that the correlation between HPLC retention time and Kow hold from the standards and lower molecular weight phthalic acid esters did not hold for DEHP (high molecular weight). However this result is consistent with other HLPC determined values (Mc Duffie (1981) Log Kow=8.06).
As no data on pH was given in the study, we assume that partition coefficient was determined at a neutral pH, relevant for the environment.
Conclusions:
HPLC determined Log Kow for DEHP is estimated to 7.94. DEHP is therefore considered as potentially bioaccumulative.
Executive summary:

Howards et al. (1985) estimated partition coefficient of DEHP and other phthalic acid esters with an HPLC method according to the ASTM draft standard based on Swann et al. (1983). Retention times are recorded and Kow is calculated using the linear correlation developped with standards of known Kow.

In the test conditions Log Kow for DEHP is estimated to 7.94. DEHP is therefore considered as potentially bioaccumulable.

It appeared that the correlation between HPLC retention time and Kow hold from the standards and lower molecular weight phthalic acid esters did not hold for DEHP (high molecular weight). However this result is consistent with other HLPC determined values (Mc Duffie (1981) Log Kow=8.06).

As test procedure is in accordance with national standard method (US EPA draft ASTM standard) and value is consistent with other HPLC determined values, this study is considered as reliable with restrictions.

Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: 2c: Guideline study without detailed documentations / Comparable to guideline with acceptable restrictions This study is a ring test for establishment of OECD 117 guideline (HPLC method).
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Deviations:
not specified
GLP compliance:
not specified
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Type:
log Pow
Partition coefficient:
7.861
Temp.:
25 °C
pH:
ca. 7
Details on results:
Log Kow= 7.861 +/- 1.329 (n=13)
The scattering of results is caused by extrapolation from lower Log Kow of reference compounds.
Authors showed from the whole experiment that with this method the Log Kow can be obtained within +/- 0.5 unit.
As data were obtained from various laboratories, various temperatures have been applied from 20 up to 40°C. However authors showed that temperature was not a critical experimental parameter.
As no data on pH was given in the study, we assume that partition coefficient was determined at a neutral pH, relevant for the environment.
Conclusions:
In an intercomparison test on HPLC method for determination of Log Kow, DEHP showed an average value of 7.861 +/- 1.329 (n=16, all labs together). The high standard deviation is explained by the fact this value was extrapolated above the values from reference substances.
Executive summary:

Klein et al. 1988, in an intercomparison test on HPLC method for determination of Log Kow, showed an average value of Log Kow for DEHP= 7.861 +/- 1.329 (n=16, all labs together).

The high standard deviation is explained by the fact this value was extrapolated above the values from reference substances, which, in the guideline do not have Log Kow beyond 6.5. The domain of validity is given to be 0 to 6.

Authors showed from the whole experiment that with this method the Log Kow can be obtained within +/- 0.5 unit.

Description of key information

- n-Octanol - Water partition coefficient: Numerous data are reported in the literature. Due to the ability of DEHP to form a colloidal dispersion in water, results from stirring method OECD 107 are not considered as reliable (Leyder, 1983). Only results based on slow-stir methods (similar to OECD 123) or HPLC technique (OECD 117 or similar) are therefore assumed to be useful.

Five measured values are available and considered as reliable and are supported with 2 calculated values and 1 average value from literature review. Therefore a weight of evidence approach based on measured data and supported with estimated ones was applied.

- Octanol-air partition coefficient: One calculated value is available. According to the model based on the 'three solubility approach' and the molar volume of phthalate esters, DEHP show an Log Koa 10.5 at 25°C. This calculated value is estimated to be reliable with accepatble restrictions as the model give caculated values for vapour pressure, Log Kow and  water solubility in accordance with recently measured ones.

- Particle-gas partition coefficient has been estimated from vapor pressure according to relationship reported by Naumova et al (2003) based on 1800 partition coefficients of polycyclic aromatic hydrocarbons considered as reasonably resemble phthalate esters. Log Kp = -0.6. This data is supported by value calculated by Cousins and Mackay, 2000 on basis of 'three solubilities approach' a model validated previously (Log Kp= -1.19) and which sustains the behaviour of DEHP to have more affinity to particles than for air.

Key value for chemical safety assessment

Log Kow (Log Pow):
7.5
at the temperature of:
20 °C

Additional information

A subset of the experimental and calculated data reported in the literature is presented below:

 Method  Log Kow  Flag  Reference
 Slow stir method (OECD 123 draft guideline)  7.137 +/- 0,153  WoE  Brooke et al. (1990)
   7.453 +/- 0,061  WoE  DeBruijn et al. (1989)
   7.27 +/- 0,04  WoE  Ellington and Floyd (1996)
 HPLC method (similar to OECD 117 guideline)  7.94  WoE  Howard et al. (1985)
   7.8 +/- 1,4  WoE  Klein et al. (1988)
 SPARC calculation model (2009 updated with v4.5)  7.54 (7.66)  SS  Ellington and Floyd (1996)
 QSAR model based on solubilities and Le Bas molar volumes  7.73  SS  Cousins and Mackay (2000)
 Literature average validated in previous Risk Assessment Report (2008)  7.5  SS  Staples et al. (1997)

Considering the measured values the average value of DEHP partition coefficient is 7.52.

This value is supported by SPARC calculation model (considered as reliable in R7a guidance document) and the model based on three solubilities developped by Cousins and Mackay (2000). Moreover, these values are in accordance with average value from measured data from literature (Staples et al. 1997). Value wich was recommended and used in the RAR (2008).