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Environmental fate & pathways

Phototransformation in air

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Reference
Endpoint:
phototransformation in air
Type of information:
(Q)SAR
Adequacy of study:
key 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:
1. SOFTWARE
EpiSuite v4.11, US EPA, 2012

2. MODEL (incl. version number)
AOP v1.92

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
see attachment (Photodegradation_QSAR justification.pdf)

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint: photodegradation via hydroxyl radicals and ozone
- Unambiguous algorithm:
(1) Hydrogen Abstraction
(2) Reaction with specific Nitrogen and Sulfur fragments and reaction with hydroxy (OH) fragments such as alcohols and phenols
(3) Addition to Triple Bonds
(4) Addition to Olefinic Bonds
(5) Addition to Aromatic Rings
(6) Addition to Fused Rings

- Defined domain of applicability:
Currently there is no universally accepted definition of model domain. However, users may wish to consider the possibility that property estimates are less accurate for compounds outside the Molecular Weight range of the training set compounds, and/or that have more instances of a given fragment than the maximum for all training set compounds. It is also possible that a compound may have a functional group(s) or other structural features not represented in the training set, and for which no fragment coefficient was developed. These points should be taken into consideration when interpreting model results.
- Appropriate measures of goodness-of-fit and robustness and predictivity:
Hydroxyl Radical Estimation accuracy (comparing experimental to estimated values)
correlation coefficient (r2) 0.963
standard deviation (sd) 0.218
absolute mean error (me) 0.127
For the 667 AOPWIN estimations, 90% are within a factor of two of the experimental value and 95% are within a factor of three.

Ozone Reaction Rate Estimation Accuracy:
correlation coefficient (r²) 0.88
standard deviation (sd) 0.52
absolute mean error (me) 0.35

5. APPLICABILITY DOMAIN
- Descriptor domain: The components of the substance are within the molecular weight range of the training set compounds, and all fragments are represented in the training set. Thus, it is concluded, that the substance is within the applicability domain.
- Similarity with analogues in the training set: several linear and branched alkanes and alkenes, which are considered to be similar, are present in the training set. Some experimental database structure matches were identified.

6. ADEQUACY OF THE RESULT
The QSAR prediction is valid and of good reliability. Thus, the result is adequate for environmental fate assessment.
Principles of method if other than guideline:
Estimation of the photodegradation of the components by QSAR (EpiSuite v4.11, US EPA, 2012; AOP v1.92)
GLP compliance:
no
Remarks:
not applicable for in silico study
Estimation method (if used):
PHOTOCHEMICAL REACTION WITH OH RADICALS
- Concentration of OH radicals: 1.5E+06/cm³
- Temperature for which rate constant was calculated: 25°C
- Computer programme: Epiwin v4.11, AOPWIN v1.92


Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: C(CCCC)(CC)C
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: CCC(C)C(C)CC
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: CC(CC)C(C)CC
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: CC(CC)=C(C)CC
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: C(CCCCCC)C
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: CCC(C)C(=CC)C
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: CC(=CC)C(C)CC
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: CC(C)CC(C)CC
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: C(C(CC)C)(=C)CC
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Remarks on result:
other: CCC(O)(C)CCCC
Transformation products:
not measured

for details see attachment

Conclusions:
The photodegradation of the constituents of Oxooel LS9 were estimated by QSAR (EpiSuite v4.11, US EPA, 2012; AOP v1.92).
The half life for hydroxyl radical reaction ranged from 1.14 h to 15.49 h. For olefins, additionally reaction with ozone is possible; half lives ranged from 13.75 min to 22.92 h.
Overall, these results indicate fast photodegradation of the constituents.

Description of key information

The photodegradation of the constituents of Oxooel LS9 were estimated by QSAR (EpiSuite v4.11, US EPA, 2012; AOP v1.92).

The half life for hydroxyl radical reaction ranged from 1.14 h to 15.49 h. For olefins, additionally reaction with ozone is possible; half lives ranged from 13.75 min to 22.92 h.

Overall, these results indicate fast photodegradation of the constituents.

Key value for chemical safety assessment

Additional information