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Diss Factsheets

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:
supporting study
Study period:
Not applicable
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Qualifier:
no guideline followed
Principles of method if other than guideline:
An estimation of the atmospheric oxidization rate of the test substance was performed using the Atkinson method using the 'Atmospheric Oxidation Program'.
GLP compliance:
no
Remarks:
Not applicable
DT50:
1 d
Remarks on result:
other: OH- radical concentration = 0.5E+06 OH/cm3; 24 hr light/day
DT50:
0.661 d
Remarks on result:
other: OH- radical concentration = 1.5E+06 OH/cm3; 12 hr light/day
Reaction with:
OH radicals
Remarks on result:
other: 1.618E-11 cm3/mol/sec
Transformation products:
no
Remarks:
M2

PHOTOTRANSFORMATION IN AIR RESULTS


The overall bimolecular rate constant determined for OH radicals for the reaction of the test substance with photochemically produced OH radicals was 1.618E-11 cm3/molecule/sec. Addition to aromatic rings was considered the significant contributor to the overall atmospheric degradation pathway. For the EU scenario, the DT50 was determined to be ~1 days (OH- radical concentration = 0.5E+06 OH/cm3; 24 hr light/day).


 


Table 1. Summary of the OH radical rate parameter and DT50 values conducted under USA and EU regulatory scenarios for the phototransformation of the test substance in the atmosphere.






























 



US Scenario



EU Scenario



OH concentration (106 radicals/cm3)



1.5



0.5



Time frame (hours per day)



12



24



OH rate constant (cm3/molecule/sec)



1.618E-11 



DT50 (days)



0.66



~1



 

Validity criteria fulfilled:
not applicable
Conclusions:

The half-life (Atkinson method) of the test substance in the atmosphere by hydroxyl radical oxidation was estimated to be approximately 1 day assuming the OH radical concentration was 0.5E+06 OH radicals/cm3 and the OH time frame was 24 hours/day. The half-life (Atkinson method) of the test substance in the atmosphere by hydroxyl radical oxidation was estimated to be 0.661 days assuming the OH radical concentration was 1.5E+06 OH radicals/cm3 and the OH time frame was 12 hours/day.
Executive summary:

The rate of photolytic degradation of the test substance in the atmosphere was estimated in the Atmospheric Oxidation Program using the Atkinson method. The overall OH rate constant was calculated to be 1.618E-11 cm3/molecule/sec. The half-life of the test substance in the atmosphere by hydroxyl radical oxidation was estimated to be approximately 1 day assuming the OH radical concentration was 0.5E+06 OH radicals/cm3 and the OH time frame was 24 hours/day. The half-life was estimated to be 0.661 day assuming the OH radical concentration was 1.5E+06 OH radicals/cm3 and the OH time frame was 12 hours/day.

Description of key information

Estimated half-life (Atkinson method) = 0.661 day, hydroxyl radical oxidation, 1.5E+06 OH radicals/cm3 and 12 hours/day timeframe, Glänzel 1996.


Estimated half-life (Atkinson method) = 1 day, hydroxyl radical oxidation, 0.5E+06 OH radicals/cm3 and 24 hours/day timeframe, Glänzel 1996.


Half-life in air = 1 day is used in further risk assessment as the OH radical concentration and timeframe follow the recommendations in EU TGD (2003).

Key value for chemical safety assessment

Half-life in air:
1 d

Additional information

One study is available for this endpoint. The rate of photolytic degradation of the test substance in the atmosphere was estimated in the Atmospheric Oxidation Program using the Atkinson method. The overall OH rate constant was calculated to be 1.618E-11 cm3/molecule/sec. The half-life of the test substance in the atmosphere by hydroxyl radical oxidation was estimated to be approximately 1 day assuming the OH radical concentration was 0.5E+06 OH radicals/cm3 and the OH timeframe was 24 hours/day. The half-life was estimated to be 0.661 day assuming the OH radical concentration was 1.5E+06 OH radicals/cm3 and the OH timeframe was 12 hours/day. Half-life of 1 day is used in further risk assessment as the OH radical concentration and timeframe follow the recommendations in the EU TGD (2003).