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Environmental fate & pathways

Henry's Law constant

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Endpoint:
Henry's law constant
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Please refer to the justification for grouping of substances provided in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
H:
0 Pa m³/mol
Temp.:
20 °C
Remarks on result:
other: calculated from air-water distribution coefficient
H:
0 Pa m³/mol
Temp.:
12 °C
Remarks on result:
other: calculated from air-water distribution coefficient
Conclusions:
The Henry's Law Constant was calculated on the basis of experimental determined air-water distribution data (Kaw) for 12 and 20 °C and was 1.65E-04 and 1.70E-04 Pa m³/mol, for the source substance Dimethylsilanediol (DMSD) respectively. The source substance is the hydrolysis product of the target substance. Since the hydrolysis half life is < 1 h, the results derived for the source substance describe well the fate of the target substance.
Endpoint:
Henry's law constant
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
For principles of method please refer to the field "any other information on material and methods incl. tables".
GLP compliance:
no
H:
0 Pa m³/mol
Temp.:
20 °C
Remarks on result:
other: calculated from air-water distribution coefficient
H:
0 Pa m³/mol
Temp.:
12 °C
Remarks on result:
other: calculated from air-water distribution coefficient

The air-water distribution data are provided in the cross referenced study by Xu 2011. For 25°C the Kaw value was 6.96E-08. The authors indicate that the air-water distribution ratio of the substance is not significantly different when octanol (three phase system) is present or not (binary system). On this basis the Henry constant was calculated for 12 and 20 °C and was 1.65E-04 and 1.70E-04 Pa m³/mol, respectively.

Conclusions:
The Henry's Law Constant was calculated on the basis of experimental determined air-water distribution data (Kaw) for 12 and 20 °C and was 1.65E-04 and 1.70E-04 Pa m³/mol, respectively.
Endpoint:
Henry's law constant
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
For principles of method please refer to the field "any other information on material and methods incl. tables".
GLP compliance:
no
H:
0 Pa m³/mol
Temp.:
20 °C
Remarks on result:
other: calculated from air-water distribution coefficient
H:
0 Pa m³/mol
Temp.:
12 °C
Remarks on result:
other: calculated from air-water distribution coefficient

The air-water distribution data are provided in the cross referenced study by Xu and Kropscott 2012. For 25 °C the Kaw value was 9.33E-08 (log Kaw = -7.03) in a binary (air-water) system. On this basis the Henry constant was calculated for 12 and 20 °C and was 2.21E-04 and 2.27E-04 Pa m³/mol, respectively.

Description of key information

Key value for chemical safety assessment

Henry's law constant (H) (in Pa m³/mol):
0
at the temperature of:
12 °C

Additional information

Volatilisation from water is not relevant for the parent substance dimethoxydimethylsilane due to its very rapid hydrolysis to dimethylsilanediol and methanol in contact with water or soil moisture. Thus the assessment of the volatilization potential is based on the hydrolysis products.

Dimethylsilanediol: 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). Using the dimensionless distribution coefficient air/water, the HLC can be calculated with the following formula: HLC = Kaw*RT, where R is the gas constant (8.314 Pa m3 mol-1 K-1). A log Kaw value of -6.94 at 20 °C was determined for dimethylsilanediol in a reliable study conducted according to generally accepted scientific principles (Xu, 2011). This is equivalent to a dimensional Henry's Law Constant of 1.65E-4 Pa m³/mole at 12 °C.

The HLC can also be estimated from the ratio of the vapour pressure (VP) to the water solubility (WS) including the molecular weight (MW): HLC = (VP*MW)/WS. The calculated HLC value for the hydrolysis product dimethylsilanediol at environmental temperature (5.738E-04 Pa m³/mole at 12°C) is comparable to the experimentally derived value, 1.65E-4 Pa m³/mole, indicating a negligible potential for volatilization from the water phase.

Methanol: For the second hydrolysis product methanol volatilization is assumed to be low (HLC: 0.461 Pa m³/mole at 25 °C and 0.3827 Pa m³/mole at 12 °C; Gaffney et al. 1987 as cited in EPIsuite v4.1).