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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)
Remarks:
Estimated by calculation
Adequacy of study:
key study
Study period:
no data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Qualifier:
no guideline available
Principles of method if other than guideline:
Calculated using structure-reactivity relationships and linear free-energy relationships.
GLP compliance:
no
Estimation method (if used):
PHOTOCHEMICAL REACTION WITH OH RADICALS
- Concentration of OH radicals: 1,000,000 molecule/cm³
- Degradation rate constant: 4.6E-11 cm³/(molecule*sec)
DT50:
8.5 h
Test condition:
OH concentration = 500000 molecules/cm³, rate constant = 4.6E-11 cm³/molecule*s

Developed structure-reactivity relationships between reaction rate constant and ionization potential for classes of compounds.

Reaction products expected were CO, CO2,and dicarbonyls, which undergo further rapid reaction.

Validity criteria fulfilled:
not applicable
Conclusions:
Half life: 8.5 hours
Executive summary:

A calculation assuming a sensitizer-concentration (OH-radical) of 1,000,000 molecules/cm³ and a rate constant of 4.3E-11 cm³/molecule*sec predicted a half-life in the atmosphere of 4.5 hours (Grosjean and Williams, 1991, cited in OECD SIDS 2004). Taking into account a regular OH concentration of 500,000 molecules/cm³ the half-life increases to 8.5 hours.

Description of key information

After evaporation or exposure to the air, the substance will be rapidly degraded by photochemical processes.

Key value for chemical safety assessment

Additional information

A calculation assuming a sensitizer-concentration (OH-radical) of 1,000,000 molecules/cm³ and a rate constant of 4.3E-11 cm³/molecule*sec predicted a half-life in the atmosphere of 4.5 hours (Grosjean and Williams, 1991, cited in OECD SIDS 2004). Taking into account a regular OH concentration of 500,000 molecules/cm³ the half-life increases to 8.5 hours. Nevertheless, photodegradation is not supposed to be an important fate path in the atmosphere as the substance would hydrolyse rapidly with the atmospheric water forming maleic acid.