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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:
key study
Study period:
2016
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:
Accepted calculation method
Reference:
Composition 0
Principles of method if other than guideline:
Estimation Program Interface EPI-Suite version 4.1: 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 - 2011 U.S. Environmental Protection Agency for EPI SuiteTM (Published online in January 2011).
GLP compliance:
no
Test material information:
Composition 1
Key result
H:
0 Pa m³/mol
Temp.:
25 °C
Remarks on result:
other: Bond estimation method

Validity of the model:

1. Defined Endpoint:Henry's Law Constant

2. Unambinguous algorithm:For Norandrostendione the following descriptors were applied:

Bond estimation method:

 class  bond contribution description  value
 Hydrogen  23 Hydrogen to Carbon (aliphatic) Bonds -2.7526
Hydrogen  1 Hydrogen to Carbon (olefinic) Bonds  -0.1005
 Hydrogen  1 Hydrogen to Carbon (acetylinic) Bonds  0.0040
 Hydrogen 1 Hydrogen to Oxygen Bonds  3.2318
 Fragment  16 C-C  1.8609
 Fragment  2 C-Cd  0.1269
 Fragment  1 C-CO  1.7057
 Fragment  1 C-O 1.0855 
 Fragment  1 C-Ct   0.5375
 Fragment   1 Cd-CO  1.9260
 Fragment   1 C#C 0.0000 
 Fragment   1 Cd=Cd  0.0000

*the maximum number of instances of this bond occurring in any single compound of the training set is exceeded

Group estimation method:

For some fragments of the substance needed for the group estimation method there are no descriptor values available. As a consequence the descriptors are incomplete for the substance and this method cannot be used for the calculation of the HLC.

3. Applicability domain:With a molecular weight of 272.39 g/mole 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. But as indicated in the table above some bonds occur more often in the structure of the substance than found in any single substance of the training set.

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.

5. Adequacy of prediction:

The result for Norethisterone falls within the applicability domain described above and the estimation rules applied for the substance appear appropriate. But an individual uncertainty for the investigated substance is available as some bonds occur more often in the structure of the substance than found in any single substance of the training set. But as the substance has a low vapour pressure (<0.001 Pa at 25°C) non-volatility of the substance from water is expected. Therefore the present calculated value can be used as a worst case regarding volatility of the substance from water.

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 revealed a value of 0.0000587 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 Henry's Law Constant (HLC) was predicted using the QSAR calculation of the Estimation Program Interface (EPI) Suite v 4.1. The HLC was estimated to be 0.0000587 Pa*m³/mol. The result relates to 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 QSAR determination of the Henry's Law Constant revealed a value of 5.87*10-05Pa*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.

Key value for chemical safety assessment

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

Additional information