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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:
other: Scientifically accepted calculation method
Justification for type of information:
1. SOFTWARE
Estimation Programs Interface (EPI) Suite for Microsoft Windows, v4.11 (US EPA, 2012)

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

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
- CC(=O)C=Cc1ccccc1
- See also section 'Test Material'.

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
See attached QMRF.

5. APPLICABILITY DOMAIN
See attached QPRF.

6. ADEQUACY OF THE RESULT
- The model is scientifically valid (see attached QMRF).
- The model estimates the rate constant for the atmospheric, gas-phase reaction between photochemically produced hydroxyl radicals and organic chemicals.  It also estimates the rate constant for the gas-phase reaction between ozone and olefinic/acetylenic compounds. The rate constants estimated by the program are then used to calculate atmospheric half-lives for organic compounds based upon average atmospheric concentrations of hydroxyl radicals and ozone (see also attached QMRF).
- See attached QPRF for reliability assessment.
Guideline:
other: ECHA Guidance R.6
Principles of method if other than guideline:
- Software tool(s) used including version: EPIWIN v4.1
- Model(s) used: AOPWIN v1.92
- Model description: see field 'Justification for non-standard information', 'Attached justification'
- Justification of QSAR prediction: see field 'Justification for type of information', 'Attached justification'
GLP compliance:
no
Remarks:
Not applicable.
Specific details on test material used for the study:
CC(=O)C=Cc1ccccc1
Estimation method (if used):
EPISuite (EPIWIN) v4.1, software AOPWIN v1.92 by US-EPA
Light source:
other: 12 h light day
Details on light source:
The program assumes a 12 h light day with an OH concentration of 1.5E6 OH/cm³.
Details on test conditions:
The program AOPWIN v1.92 estimates the gas-phase reaction rate between hydroxyl radicals and the desired chemical. Additional information is given if it will be important for the chosen compound. Also the atmospheric half-life is automatically calculated.
Reference substance:
no
Remarks:
Not applicable.
Preliminary study:
Not applicable.
Test performance:
Not applicable.
% Degr.:
50
Sampling time:
2.44 h
Test condition:
Cis-isomer; assuming a 12 hr day and 1.5E6 OH/cm³ at 25 °C
% Degr.:
50
Sampling time:
2.16 h
Test condition:
Trans-isomer; assuming a 12 hr day and 1.5E6 OH/cm³ at 25 °C
Results with reference substance:
Not applicable.

Table 1: Results of phototransformation in air for4-phenylbutenone at 25 °C

Parameter

Method

Result

Hydroxyl Radicals

Gas-phase reaction rate

AOPWIN v1.92 calculation

Cis-isomer:

52.695E-12 cm3/molecule-sec

Trans-isomer:

59.535E-12 cm3/molecule-sec

Hydrogen Abstraction

AOPWIN v1.92 calculation

0.102E-12 cm³/molecule-sec

Addition to Aromatic Rings

AOPWIN v1.92 calculation

1.833E-12 cm²/molecule-sec

Addition to Olefinic Bonds

AOPWIN v1.92 calculation

Cis-isomer:

50.76E-12 cm3/molecule-sec

Trans-isomer:

 57.60E-12 cm3/molecule-sec

Atmospheric half-life

AOPWIN v1.92 calculation

(12-hr day; 1.5E6 OH/cm3)

Cis-isomer: 2.44 hours

Trans-isomer: 2.16 hours

Ozone reaction

Overall Ozone Rate Constant

AOPWIN v1.92 calculation

Cis-isomer: 

2.835E-17 cm3/molecule-sec

Trans-isomer:

5.670E-17 cm3/molecule-sec

Half-life

AOPWIN v1,92 calculation (at 7E11 mol/cm³)

Cis-isomer: 9.70 hours

Trans-isomer: 4.85 hours

Nitrate radical reaction

AOPWIN v1.92 calculation

Not important.

Validity criteria fulfilled:
yes
Remarks:
Scientifically accepted calculation method.
Conclusions:
The study report describes a scientifically accepted calculation method for the phototransformation in air using the US-EPA software AOPWIN v1.92.No GLP criteria are applicable for the usage of this tool and the QSAR estimation is easily repeatable.
Executive summary:

The phototransformation in air of the test substance was determined by the computer program AOPWIN v1.92 (EPIWIN software) by US-EPA (Chemservice S.A., 2012). This tool estimates the gas-phase reaction rate for the reaction between the most prevalent atmospheric oxidant (hydroxyl radicals) and a substance. For olefins and acetylenes the gas-phase ozone radical reaction rates are estimated as well. Additional information is given by the program if nitrate radical reaction will be important. The assumed average hydroxyl radical and ozone concentration are automatically used to calculate the atmospheric half-live for the chemical of interest. For 4-phenylbutenone the results differ to a certain extend in some reaction classes depending which isomer is considered (cis- or trans-isomer). The reaction with hydroxyl radicals is splitted into three classes: “Hydrogen Abstraction”, which gives an OH rate constant of 1.010E-11 cm³/molecule-sec, “Addition to Aromatic Rings”, with an OH rate constant of 1.833E-12 cm³/molecule-sec and “Addition to Olefinic Bonds” – resulting in different overall rate constants, depending which isomer is taken into account: for the cis-isomer the OH rate constant is defined as 5.076E-13 cm³/molecule-sec, whereas the trans-isomer gives a value of 5.760E-13 cm³/molecule-sec. The OVERALL OH rate constant for the cis-isomer is predicted as 5.269E-13 cm³/molecule-sec and 5.953E-13 cm³/molecule-sec for the trans-isomer. The half-lives are predicted as 2.44 hours for the cis-isomer and 2.16 hours for the trans-isomer, assuming a 12 hour light day and an OH concentration of 1.5E6/cm³. Furthermore, 4-phenylbutenone will be able to undergo ozone reactions. The cis-isomer possesses an overall ozone rate constant of 2.835E-17 cm³/molecules-sec and a half-life at 7.0E11 mol/cm³ of 9.70 hours, whereby the prediction of the trans-isomer results in an overall ozone rate constant of 5.67E-17 cm³/molecules-sec and a half-life of 4.85 hours. All calculations were performed supposing a surrounding temperature of 25 °C.

Description of key information

Calculation with AOPWIN v1.92 (EPIWIN software by US-EPA): 
Cis-isomer: overall gas-phase reaction constant: 5.27E-13 cm³/molecules-sec, with an half-life of 2.44 days by assuming a 12 h light day with an OH concentration of 1.5E6 OH/cm³ and 25 °C.
Trans-isomer: overall gas-phase reaction constant: 59.5352E-12 cm³/molecules-sec, with an half-life of 2.16 days by assuming a 12 h day with an OH concentration of 1.5E6 OH/cm³ and 25 °C.

Key value for chemical safety assessment

Additional information

The phototransformation in air of the test substance was determined by the computer program AOPWIN v1.92 (EPIWIN v4.1) by US-EPA. This tool estimates the gas-phase reaction rate for the reaction between the most prevalent atmospheric oxidant (hydroxyl radicals) and a substance. For olefins and acetylenes the gas-phase ozone radical reaction rates are estimated as well. Additional information is given by the program if nitrate radical reaction will be important. The assumed average hydroxyl radical and ozone concentration are automatically used to calculate the atmospheric half-life for the chemical of interest. For 4-phenylbutenone the results differ to a certain extend in some reaction classes depending which isomer is considered (cis- or trans-isomer). The reaction with hydroxyl radicals is splitted into three classes: “Hydrogen Abstraction”, which gives an OH rate constant of 1.01E-11 cm³/molecule-sec, “Addition to Aromatic Rings”, with an OH rate constant of 1.83E-12 cm³/molecule-sec and “Addition to Olefinic Bonds” – resulting in different overall rate constants, depending which isomer is taken into account: for the cis-isomer the OH rate constant is defined as 5.08E-13 cm³/molecule-sec, whereas the trans-isomer gives a value of 5.76E-13 cm³/molecule-sec. The OVERALL OH rate constant for the cis-isomer is predicted as 5.27E-13 cm³/molecule-sec and 5.95E-13 cm³/molecule-sec for the trans-isomer. The half-lives are predicted as 2.44 hours for the cis-isomer and 2.16 hours for the trans-isomer, assuming a 12 hour light day and an OH rate of 1.5E6/cm³. Furthermore, 4-phenylbutenone will be able to undergo ozone reactions. The cis-isomer possesses an overall ozone rate constant of 2.83E-17 cm³/molecules-sec and a half-life at 7.0E11 mol/cm³ of 9.70 hours, whereby the prediction of the trans-isomer results in an overall ozone rate constant of 5.67E-17 cm³/molecules-sec and a half-life of 4.85 hours. All calculations were performed supposing a surrounding temperature of 25 °C.