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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
Study period:
2010
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Use of validated QSAR, which is described extensively in peer-reveiwed literature. The substance falls within the application domain.
Justification for type of information:
QSAR prediction: migrated from IUCLID 5.6
Reason / purpose:
reference to same study
Principles of method if other than guideline:
The second-order rate constant for reaction with photochemically-generated hydroxyl radical (indirect photolysis) was estimated using U.S. EPA AOPWIN software v1.92a (June 2008). The associated atmospheric half-life was calculated from an assumed average hydroxyl radical concentration of 500,000 molecules/cm3 and 24 hr. day (ECHA recommended values). Estimates were made for the lowest and highest molecular weight homologues of the UVCB substance. The homologue giving the longest predicted half-life is used in environmental exposure calculations in the chemical safety assessment.
GLP compliance:
no
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
not applicable
Estimation method (if used):
U.S. EPA AOPWIN software v1.92a (June 2008).
Light source:
other: sunlight irradience producing default tropospheric hydroxyl radical concentration of 500,000 molecules/cm3
Details on light source:
not applicable
Details on test conditions:
Half-lives calculated from estimated second-order rate constant, default hydroxyl radical concentration of 500,000 molecules/cm3, and 24-hr. photoday.
Reference substance:
no
Preliminary study:
not applicable
DT50:
>= 2.5 - <= 11.9 h
Test condition:
Estimated half-life for indirect photolysis with hydroxyl radical (500,000 molecules/cm3)
Results with reference substance:
not applicable

 

NLP #

 

Substance Abbreviation

 

 

SMILES

 

MW (g/mole)

Hydroxyl Radical Second-order Rate Constant (cm3/molecule*sec)

Estimated

Half-life

(days)*

EstimatedHalf-life (hrs.)*

4

TMP + PO

 

 

CC(O)COCC(CO)(CC)CO

192.3

3.2E-11

0.50

11.9

OC(C)COC(C)COC(C)COCC(CC)(COCC(C)OCC(C)O)COCC(C)OCC(C)O

540.7

1.6E-10

0.10

2.5

OC(C)COCC(COCC(C)O)(CC)COCC(C)O

308.4

6.9E-11

0.23

5.6

*Estimated half-life based on hydroxyl radical concentration of 500,000 molecules/cm3and 24 hr. day

The lowest-molecular weight homologues of the UVCB substance are expected to have the longest half-lives in the atmosphere. This is due to relative low molecular weigth compared to the highest molecular weight homologue; and the mode of degradation is expected to be the same for all homologues. The estimated half-life for the lowest-molecular weight homologue is used to represent the atmospheric half-life for all components of the UVCB substance in the chemical safety assessment.

Conclusions:
Estimated half-lives for the components of this UVCB substance range from 2.5 to 11.9 hours, based on a default hydroxyl radical concentration of 500,000 molecules/cm3. The longest estimated half-life, associated with the lowest-molecular weight homologue, is used to represent the atmospheric half-life of all homologous components of the UVCB substance in the chemical safety assessment.

Description of key information

Estimated half-lives for the components of this UVCB substance range from 2.5 to 11.9 hours.

Key value for chemical safety assessment

Half-life in air:
11.9 h

Additional information

Estimated second-order rate constants for reaction of hydroxyl radical with lowest and highest-molecular weight homologues of the UVCB substance range from 3.2E-11 to 1.6E-10 cm3/molecule*sec. Corresponding half-lives range from 2.5 to 11.9 hours, based on a default hydroxyl radical concentration of 500,000 molecules/cm3. The longest estimated half-life, associated with the lowest-molecular weight homologue, is used to represent the atmospheric half-life of all homologous components of the UVCB substance in the chemical safety assessment.