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Physical & Chemical properties

Partition coefficient

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Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Guideline:
other: Three Phase Equilibrium Method
Principles of method if other than guideline:
Principle of test
The objective was to derermine the distribution of Dimethylsilanediol (DMSD) in air, water, octanol systems and the dependence of these distributions from temperature. Therefore a three phase system (air, octanol, water) was used. The Kaw, Kow and Koa were determined.

Short description of test conditions
A 100 mL borosilicate glass syringe was used in which a three phase system of air, octanol and water was established for the experiments. The experiment was conducted in an incubator in which the temperature was controlled.

Parameters analysed / observed
The distribution/concentration of the substance between the three phases was measured via reversed phase HPLC/RAM, Normal phase HPLC/RAM and LSC Analysis.
GLP compliance:
no
Type of method:
HPLC method
Remarks:
with liquid scintillation counting (LSC)
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Key result
Partition coefficient:
ca. 6.82
Temp.:
25 °C
Remarks on result:
other: log Koa; extrapolated from log Koa at four temperatures, plotted against the 1/T
Key result
Partition coefficient:
6.58
Temp.:
20.2 °C
Remarks on result:
other: log Koa ± 0.34; Temperature ± 0.3 °C
Key result
Partition coefficient:
ca. -7.16
Temp.:
25 °C
Remarks on result:
other: log Kaw; extrapolated from log Kaw at four temperatures, plotted against the 1/T
Key result
Partition coefficient:
-6.94
Temp.:
20.2 °C
Remarks on result:
other: log Kaw ± 0.33; Temperature ± 0.3 °C
Key result
Type:
log Pow
Partition coefficient:
ca. -0.36
Temp.:
25 °C
Remarks on result:
other: Extrapolated from log Kow at four temperatures, plotted against the 1/T
Key result
Type:
log Pow
Partition coefficient:
-0.38
Temp.:
20.2
Remarks on result:
other: log Pow ± 0.4; Temperature ± 0.3 °C

Results


The reversed phase HPLC chromatogram of DMSD-containing water showed small fraction (2 -5%) of dimer diol in the three phase equilibrium.


Normal phase HPLC chromatograms of the 1 -octanol from the three-phase equilibrium clearly indicated the existence of dimer diol, trimer diol and up to 6 compounds with shorter retention times than DMSD, especially for 35°C.


In previeous study equilibrium was found to be reached within 2 h if the equilibration started from DMSD containing water at 20°C (Xu and Kropscott, 2011). The shortest time for all experiments was close to 20 h but no obvious deviation from their corresponding average values was observed.


Overall, the values of log Kaw, log Koa and log Kow were relatively constant over time at each temperature.


The measured partition coefficients were, obtained from a three-phase equilibrium state.


 


When the average values of three partition coefficients at four temperatures were plotted against the reciprocal of the equilibrium temperature, three linear correlations were obtained as follows:


 


log Kaw= -19.70 + 3739.5/T R2= 0.974 (n = 4)


log Koa= 21.34 - 4328.9/T R2= 0.980 (n = 4)


log Kow= 1.67 - 604.2/T R2= 0.988 (n = 4)


 


Based on these equations the partition coefficients for 25°C were:


log Kaw = -7.16,


log Koa = 6.82,


log Kow = -0.36


 


Measured values of partition coefficients in the current study are consistent with the log Kaw value measured at 35°C using a syringe system containing water/air phases only (Xu and Kropscott 2011).


 


Reference


Xu, S. and Kropscott, B. 2011. A Method for Determining Environmental Partition Coefficients of Dimethylsilanediol under Various Conditions.

Conclusions:
The study determined the distribution of Dimethylsilanediol (DMSD) in a three phase system (air, water, octanol). The partition coefficients for 25°C were log Kaw = -7.16, log Koa = 6.82 and log Kow = -0.36 in the three phase system.
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
Principle of test:
The objective was to determine the distribution of volatile methyl siloxanes such as Dimethylsilanediol (DMSD) in air, water, octanol systems. Therefore a three phase system (air, octanol, water) was used. The Kaw, Kow and Koa were determined.

Short description of test conditions:
A 100 mL borosilicate glass syringe was used in which a three phase system of air, octanol and water was established. The experiments were conducted in an incubator at constant temperature.

Parameters analysed / observed:
The distribution/concentration of the substance between the three phases was measured via reversed phase HPLC/RAM, Normal phase HPLC/RAM and LSC Analysis.
GLP compliance:
no
Type of method:
other: Distribution of DMSD in a three phase system octanol - air - water system
Partition coefficient type:
other: air - octanol - water
Type:
log Pow
Partition coefficient:
-0.41
Temp.:
20 °C
Remarks on result:
other: pH assumed to be neutral

Table 1: Experimental Results for Room Temperature Partition Measurements Based on Three Phase Equilibration for DMSD.

 

No of replicates

average temperature

average concentration [mg/L]

log Kaw

log Koa

log Kow

δ

 

 

octanol

air

water

 

 

 

 

12

20.1

29

1.0E-05

70

-6.84 ±0.34

6.4 ±0.31

-0.41 ±0.1

0.03

 

δ = log Kow - log Kaw - log Koa

The minimum equilibrium time for dimethylsilanediol (DMSD) was between 2 and 20 h depending on whether the equilibrium was started with 14C-DMSD-containing water and DMSD-free 1-octanol phase or DMSD-free water (10 mL) and 14C-DMSD-containing 1-octanol (0.4 mL), respectively.

Using those equilibrium times, the average concentrations of DMSD in the three phases and subsequently the three partition coefficients (Kaw, Koa, Kow) of the three phase system were calculated.

The results show that the measured partition coefficients were obtained from the equilibrium states, not the steady states.

Conclusions:
The study determined the distribution of Dimethylsilanediol (DMSD) in a three phase system (air, water, octanol).  
A log Kaw = -6.84 ±0.34, log Koa = 6.41 ±0.31 and log Kow =  -0.41 ±0.1 were determined for the three phase system.
Endpoint:
partition coefficient
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Study period:
2022
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
See attached QMRF/QPRF
Principles of method if other than guideline:
The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details).

The model is the publicly available KOWWIN v1.68 program (USEPA 2011). KOWWIN is part of EPI Suite v4.1 and may be downloaded from http://www.epa.gov/oppt/exposure/pubs/episuite.htm. The model is based on fragment values. That is, the chemical structure is broken down into its constituent functional groups, and the contribution of each group toward the overall partition coefficient is calculated. The constants used within KOWWIN have been derived by SRC from a wide range of organic chemicals. The authors of this QMRF have carried out additional validation and found the method to be applicable organosilicon compounds, excluding di- and tri-alkoxysilanes.

USEPA 2011. KOWWIN v. 1.68, US EPA. 2011. Estimation Programs Interface Suite™ for Microsoft® Windows, v 4.10. United States Environmental Protection Agency, Washington, DC, USA. Available at http://www.epa.gov/oppt/exposure/pubs/episuite.htm.
GLP compliance:
no
Partition coefficient type:
octanol-water
Type:
log Pow
Partition coefficient:
-0.38
Temp.:
20 °C

Estimated value, no data available for temperature and pH

Conclusions:
A Log Kow of -0.4 was obtained for the hydrolysis product using an appropriate calculation method. The result is considered to be reliable.

Description of key information

Log Kow = -0.38 at 20.2°C (octanol/water/air three-phase equilibrium method)

Key value for chemical safety assessment

Log Kow (Log Pow):
-0.38
at the temperature of:
20.2 °C

Additional information

The key study is supported by a Log Kow of -0.4 at pH 7 and 20°C, calculated using a valid QSAR method. An additional study provided a Log Kow value of -0.41, determined by the distribution in a three phase system (no guideline given).