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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 limited documentation / justification
Qualifier:
no guideline followed
Principles of method if other than guideline:
EpiWin v4.11 SRC AOP v1.92 calculation
GLP compliance:
no
Specific details on test material used for the study:
CALCULATION INPUT:
SMILES : CC(=C)C(=O)OC(C)(C)C
LogKow (experimental) = 2.54
Estimation method (if used):
PHOTOCHEMICAL REACTION WITH OH RADICALS
- Concentration of OH radicals: 500000 molecules/cm3
- Degradation rate constant: 18.6278 E-12 cm3/molecules*s
- Computer programme: SRC AOP v.192
DT50:
20.67 h
Test condition:
The test item is within the applicability domaine of the model

AOP Program (v1.92) Results:
===========================
SMILES : CC(=C)C(=O)OC(C)(C)C
CHEM : tert-butyl methacrylat
MOL FOR: C8 H14 O2
MOL WT : 142.20
------------------- SUMMARY (AOP v1.92): HYDROXYL RADICALS (25 deg C) --------
Hydrogen Abstraction = 0.6378 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 = 18.6278 E-12 cm3/molecule-sec
HALF-LIFE = 1.723 Days (12-hr day; 0.5E6 OH/cm3)
HALF-LIFE = 20.671 Hrs

Conclusions:
According to Q(SAR) data using SRC AOP v1.92, tert-butyl methacrylate will be rapidly degraded by photochemical processes after exposure to the air reacting with the photochemically produced hydroxyl radicals and with ozone (calculated half-life for a 24-hour day and 0.5E06 OH/cm3: 20.67 hours; for a 24-hour day and 7E11 O3/cm3: 1 day).

Description of key information

After evaporation or exposure to the air, tert-butyl methacrylate will be rapidly degraded by photochemical processes.
Calculated half-life for a 24-hr day and 0.5E+06 OH/cm3: 20.67 hr

Key value for chemical safety assessment

Half-life in air:
20.67 h
Degradation rate constant with OH radicals:
0 cm³ molecule-1 s-1

Additional information

There are no experimental data on photodegradation of tert-butyl methacrylate. According to Q(SAR) data using SRC AOP v1.92, tert-butyl methacrylate will be rapidly degraded by photochemical processes after exposure to the air reacting with the photochemically produced hydroxyl radicals and with ozone (calculated half-life for a 24-hour day and 0.5E06 OH/cm3: 20.67 hours; for a 24-hour day and 7E11 O3/cm3: 1 day) (BASF SE, 2009). Since tert-butyl methacrylate shows a Henry's Law constant of 281 Pa*m3/mol at 25 °C, rapid evaporation from the water surface can be expected.

 

Therefore, photodegradation may play a considerable role under environmental conditions.