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Environmental fate & pathways

Henry's Law constant

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Reference
Endpoint:
Henry's law constant
Type of information:
(Q)SAR
Adequacy of study:
supporting study
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 Bond Contribution Method within the publicly available HenryWin v 3.20 program (USEPA 2011). The Henry’s Law Constant (HLC) is calculated based on chemical structure, as the sum of the bond contribution values for each chemical bond in the molecule. The bond contribution values were determined based on least-square regression analysis of measured HLCs for organic compounds. The authors of the QMRF have carried out additional validation and found the method to be applicable to organosilicon compounds.

USEPA 2011. HenryWin v. 3.20, US EPA. Estimation Programs Interface Suite™ (EPI Suite) for Microsoft® Windows, v 4.10. United States Environmental Protection Agency, Washington, DC, USA (2011). Available at http://www.epa.gov/tsca-screening-tools/download-epi-suitetm-estimation-program-interface-v411.
H:
0 dimensionless
Temp.:
25 °C
Atm. press.:
1 013 hPa
H:
0 Pa m³/mol
Temp.:
25 °C
Atm. press.:
1 013 hPa
Conclusions:
A Henry's Law Constant value of 1.1E-4 Pa-m3/mol at 25°C was obtained for the silanol hydrolysis product using a validated QSAR estimation method. The result is considered to be reliable.

Description of key information

Henry's Law Constant:

Calculated HLC for the parent substance: not relevant due to rapid hydrolysis in contact with water

Calculated HLC for silanol hydrolysis product at 25°C: 1.1E-4 Pa m3/mol

HLC for methanol: 0.461 Pa m3/mol at 25°C

Key value for chemical safety assessment

Additional information

The transfer of a substance from the water phase to the gas phase can be estimated by means of the Henry’s Law Constant (HLC). No measured value for this parameter is available.

 

Volatilisation from water is not relevant for the parent substance due to its rapid hydrolysis in contact with water.

 

For the silanol hydrolysis product, 3-chloropropyl(methyl)silanediol, the predicted water solubility limit cannot be validated accurately due to condensation phenomena. The HLC can be estimated using the established Bond method from HENRYWIN v. 3.20 within the EPIWeb suite v4.11. This method derives the Henry's Law Constant directly from the structure, as the sum of the bond contribution values for each chemical bond in the molecule. The bond contribution values were determined based on least-square regression analysis of measured HLCs for organic compounds.

 

The calculated HLC value for the silanol hydrolysis product at 25°C is very low, 1.1E-4 Pa m3mol-1 (HenryWin v 3.20).

 

Methanol has a reported HLC value of 0.461 Pa m3/mol at 25°C (OECD 2004).