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Environmental fate & pathways

Henry's Law constant

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Reference
Endpoint:
Henry's law constant
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
other information
Study period:
2017
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Justification for type of information:
QSAR calculation: detailed information see "any other information on materials and methods" and "any other information on results"
Principles of method if other than guideline:
Estimation Program Interface EPI-Suite version 4.11: HENRYWIN (v3.20). The bond contribution method is used to calculate the volatility of the substance from the aqueous phase.
The Estimation Program Interface was developed by the US Environmental Agency's Office of Pollution Prevention and Toxics, and Syracuse Research Corporation (SRC). © 2000 - 2012 U.S. Environmental Protection Agency for EPI SuiteTM (Published online in November 2012).
GLP compliance:
no
H:
0 Pa m³/mol
Temp.:
25 °C

Validity of the model:

1. Defined Endpoint: Henry's Law Constant

2. Unambinguous algorithm: For phthalic acid the following descriptors were applied:

bond estimation method

 class  bond contribution description  value
Hydrogen 4  Hydrogen to Carbon (aromatic) Bonds  -0.6172
Hydrogen 2  Hydrogen to Oxygen Bonds  6.4635
Fragment 6  Car-Car

 1.5828

Fragment 2  Car-CO   2.4775
Fragment 2  CO-O   0.1429

3. Applicability domain:

With a molecular weight of 166.13 g/mol the substance is within the range of the training set (26.04 - 451.47 g/mole). Regarding the structure, the fragment descriptors used by the program for the estimation are complete.

4a. Statistical characteristics (bond method):

number in dataset: 442

correlation coeff. (r²): 0.977

standard deviation: 0.4

average deviation: 0.249 [all statistical data related to the LWAPC value]

4b. Statistical characteristics (group method):

number in dataset: 318

correlation coeff. (r²): 0.956

standard deviation: 0.397

average deviation: 0.223 [all statistical data related to the LWAPC value]

5. Mechanistic interpretation:

The Henry's law constant is an important factor in determining the environmental fate of chemicals. Indeed, this constant is a fundamental input for fugacity models that estimate the multimedia partitioning of chemicals.

This model is based on the calculation of respective descriptor values, with the help of experimentally derived HLC's for defined groups that comprise a compound. For modelling each compound is then split into its subgroups and the respective values are summed up to yield the HLC.

Adequacy of prediction:

The result for phthalic acid falls within the applicability domain described above and the estimation rules applied for the substance appears appropriate. Therefore the predicted value can be considered reliable yielding a useful result for further assessment.

Conclusions:
The QSAR determination of the Henry's Law Constant for phthalic acid using the model HENRYWIN included in the Estimation Program Interface (EPI) Suite v4.11 revealed a value of 2.21 E-7 Pa*m³/mol at 25°C for the unaffected molecule of the substance as any decomposition (e.g. hydrolysis) of the substance is not taken into account by the program.
Executive summary:

The QSAR determination of the Henry's Law Constant for phthalic acid using the model HENRYWIN included in the Estimation Program Interface (EPI) Suite v4.11 revealed a value of 2.21 E-7 Pa*m³/mol at 25°C for the unaffected molecule of the substance as any decomposition (e.g. hydrolysis) of the substance is not taken into account by the program.

Description of key information

The Henry´s Law Constant was calculated to be 2.21E-7 Pa m³/mole, indicating that phthalic acid is non volatile from water surfaces.

Key value for chemical safety assessment

Henry's law constant (H) (in Pa m³/mol):
0
at the temperature of:
25 °C

Additional information

The Henry’s law constant for phthalic acid is estimated, using the Bond-method of the EPI-Suite software. The HLC is estimated as 2.21 x 10-7 Pa m³/mol, indicating that phthalic acid is non volatile from water surfaces.