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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:
supporting study
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
results derived from a (Q)SAR model, with limited documentation / justification
Qualifier:
no guideline followed
Principles of method if other than guideline:
The phototransformation of AAPB in air by reaction with OH radicals was calculated using EPIWIN v3.11, AOPWIN v1.91. As the test substance is a complex mixture of C8-, C10-, C12-, C14-, C16, and C18- fatty acids derivates, the half-lives of the individual components were calculated.
GLP compliance:
no
Estimation method (if used):
PHOTOCHEMICAL REACTION WITH OH RADICALS
- Concentration of OH radicals: 500000 molecules/cm³ (24h-day)
- Degradation rate constant:
C8: 42.769E-12 cm³/molecule x s
C10: 45.595E-12 cm³/molecule x s
C12: 48.420E-12 cm³/molecule x s
C14: 51.247E-12 cm³/molecule x s
C16: 54.073E-12 cm³/molecule x s
C18: 56.899E-12 cm³/molecule x s
- Temperature for which rate constant was calculated: 25°C
- Computer programme: EPIWIN, AOPWIN v1.91
Test performance:
The photodegradation AAPB in air was estimated using EPIWIN v3.11, AOPWIN v1.91.
% Degr.:
50
Sampling time:
9 h
Test condition:
25°C/ C8 derivative
% Degr.:
50
Sampling time:
8.4 h
Test condition:
25 °C/ C10 derivative
% Degr.:
50
Sampling time:
8 h
Test condition:
25 °C/ C12 derivative
% Degr.:
50
Sampling time:
7.5 h
Test condition:
25 °C/ C14 derivative
% Degr.:
50
Sampling time:
7.1 h
Test condition:
25 °C/ C16 derivative
% Degr.:
50
Sampling time:
6.8 h
Test condition:
25 °C/ C18 derivative
Based on a OH radical concentration of 500000 molecules/cm³ (24 h-day, average 
hydroxyl concentration) and the estimated atmospheric reaction rate constants 
EPIWIN v3.11, AOPWIN v1.91) the half-lives were calculated for AAPB 
consisting of C8-, C10-, C12-, C14-, C16-, and C18-fatty acids according 
to specification:

C8   k(OH)=42.769E-12 cm³/molecule x s; t1/2=9h
C10  k(OH)=45.595E-12 cm³/molecule x s; t1/2=8.4h
C12  k(OH)=48.420E-12 cm³/molecule x s; t1/2=8h
C14  k(OH)=51.247E-12 cm³/molecule x s; t1/2=7.5h
C16  k(OH)=54.073E-12 cm³/molecule x s; t1/2=7.1h
C18  k(OH)=56.899E-12 cm³/molecule x s; t1/2=6.8h

The results indicate theoretically a rapid photodegradation (t1/2<10 h) of the 
components (C8 -C18 fatty acids) of AAPB. Based on the ionic 
character of the compound and the low vapor pressure the occurrence of gaseous 
AAPB in air is expected to be negligible and therefore this 
degradation pathway is of minor importance.
Validity criteria fulfilled:
not applicable
Conclusions:
Based on a OH radical concentration of 500000 molecules/cm³ (24 h-day, average hydroxyl concentration) and the estimated atmospheric reaction rate constants (EPIWIN, AOPWIN v1.91) the half-lives were calculated for AAPB consisting of C8-, C10-, C12-, C14-, C16-, and C18-fatty acids according to specification:
C8 k(OH)=42.769E-12 cm³/molecule x s; t1/2=9h
C10 k(OH)=45.595E-12 cm³/molecule x s; t1/2=8.4h
C12 k(OH)=48.420E-12 cm³/molecule x s; t1/2=8h
C14 k(OH)=51.247E-12 cm³/molecule x s; t1/2=7.5h
C16 k(OH)=54.073E-12 cm³/molecule x s; t1/2=7.1h
C18 k(OH)=56.899E-12 cm³/molecule x s; t1/2=6.8h
The results indicate theoretically a rapid photodegradation (t1/2<10 h) of the components (C8 -C18 fatty acids) of AAPB. Based on the ionic character of the compound and the low vapor pressure the occurrence of gaseous AAPB in air is expected to be negligible and therefore this degradation pathway is of minor importance.

Description of key information

The phototransformation of AAPB consisting of C8-, C10-, C12-, C14-, C16-, and C18-fatty acids was calculated using EPIWIN v3.11, AOPWIN v1.91. The calculation yielded half-lives ranging from 6.8 h (C18 derivate) to 9 h (C8 derivate).

Key value for chemical safety assessment

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

Additional information

The phototransformation of AAPB consisting of C8-, C10-, C12- , C14- , C16-, and C18-fatty acids was calculated using EPIWIN v3.11, AOPWIN v1.91. Based on a OH radical concentration of 500000 molecules/cm³ (24 h-day, average hydroxyl concentration) and the estimated atmospheric reaction rate constants (C8: 42.769 x 10E-12 cm³/molecule x s; C10: 45.595 x 10E-12 cm³/molecule x s; C12: 48.420 x 10E-12 cm³/molecule x s; C14: 51.247 x 10E-12 cm³/molecule x s; C16: 54.073 x 10E-12 cm³/molecule x s, and C18: 56.899 x 10E-12 cm³/molecule x s) half-lives ranging from 6.8 h (C18 derivate) to 9 h (C8 derivate) were calculated. The results indicate theoretically a rapid photodegradation (t1/2<10 h) of the components (C8 -C18 derivates) of AAPB. Due to the ionic character of the compound and the low vapor pressure, however, the occurrence of gaseous AAPB in air is expected to be negligible and therefore this degradation pathway is only of minor importance.