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Environmental fate & pathways

Phototransformation in air

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Reference
Endpoint:
phototransformation in air
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
Principles of method if other than guideline:
The photodegradation has been estimated using EPI Suite ver. 4.10  (US-EPA, 2008)
GLP compliance:
no
Details on test conditions:
Sensitiser (for indirect photolysis): OH
% Degr.:
50
Sampling time:
0.4 d
Test condition:
OH radicals photolysis
% Degr.:
50
Sampling time:
1.01 d
Test condition:
ozone radicals photolysis
DT50:
4.529 h
Test condition:
reaction with OH radicals; standard EPA model (AOPwin)
DT50:
24.179 h
Test condition:
reaction with atmospheric ozone radicals; standard EPA model (AOPwin)
Transformation products:
not specified

AOP Program (v1.92) Results:

===========================

SMILES : O=C(OCCCCCCCC)C(=C)C

CHEM   : 2-Propenoic acid, 2-methyl-, octyl ester

MOL FOR: C12 H22 O2

MOL WT : 198.31

------------------- SUMMARY (AOP v1.92): HYDROXYL RADICALS (25 deg C) --------

Hydrogen Abstraction       =  10.3555 E-12 cm3/molecule-sec

Reaction with N, S and -OH =   0.0000 E-12 cm3/molecule-sec

Addition to Triple Bonds   =   0.0000 E-12 cm3/molecule-sec

Addition to Olefinic Bonds =  17.9900 E-12 cm3/molecule-sec

Addition to Aromatic Rings =   0.0000 E-12 cm3/molecule-sec

Addition to Fused Rings    =   0.0000 E-12 cm3/molecule-sec

  OVERALL OH Rate Constant =  28.3455 E-12 cm3/molecule-sec

  HALF-LIFE =     0.377 Days (12-hr day; 1.5E6 OH/cm3)

  HALF-LIFE =     4.528 Hrs

------------------- SUMMARY (AOP v1.91): OZONE REACTION (25 deg C) -----------

  OVERALL OZONE Rate Constant =     1.137500 E-17 cm3/molecule-sec

  HALF-LIFE =      1.007 Days (at 7E11 mol/cm3)

  HALF-LIFE =     24.179 Hrs

Experimental Database:  NO Structure Matches

Fraction sorbed to airborne particulates (phi):

 4.35E-005 (Junge-Pankow, Mackay avg)

 7.94E-005 (Koa method)

    Note: the sorbed fraction may be resistant to atmospheric oxidation

Half-Lives (hr), (based upon Biowin (Ultimate) and Aopwin):

     Air:      6.587

     Water:    360

     Soil:     720

     Sediment: 3240

       Biowin estimate: 3.199  (weeks       )

  Advection Times (hr):

     Air:      100

     Water:    1000

     Sediment: 5e+004

Conclusions:
Using EPA's standard modelling method, the half-life was determined to be 4.5 h for the reaction with hydroxyl radicals, 24.2 h for the reaction with ozone and 6.6 h combined.
Executive summary:

Using  EPA's standard  modelling method, the half-life was determined to be 4.5 h for the reaction with hydroxyl radicals, 24.2 h for the reaction with ozone and 6.6 h combined.

Description of key information

Model calculation using EpiSuite 4.10 (AOP program v1.92, US-EPA, 2008):

Half-life for reaction with hydroxyl radicals ( 1.5E6 OH/cm³) = 4.5 h

Half-life for reaction with ozone (at 7E11 mol/cm³) =  24.2 h

Combined calculation result = 6.6 h

Key value for chemical safety assessment

Half-life in air:
4.5 h

Additional information

n-octyl methacrylate (n-OMA) does not possess UV-absorbing structures. Therefore, direct photolysis is not expected to occur to any significant degree.

While experimental data with model atmospheres exist for MMA which are broadly consistent with model data, no experimental photodegradation data exist for n-OMA. A model calculation using EpiWin v4.10 AOP v1.92 showed a rate constant for the reaction of n-OMA with hydroxyl radicals in the atmosphere of 28.3455 E-12 cm³/molecule*sec. From this rate constant the half-life for the reaction of OH radicals with the test substance is calculated as 4.5 h.

In conclusion, after evaporation or emission to air, n-octyl methacrylate will be rapidly degraded by photochemical processes.