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Environmental fate & pathways

Phototransformation in air

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Endpoint:
phototransformation in air
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
2014
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Justification for type of information:
QSAR prediction
Principles of method if other than guideline:
Estimation Program Interface EPI-Suite version 4.11: AOPWIN (v1.92) for the estimation of the atmospheric half-lives for organic compounds based upon average atmospheric concentrations of hydroxyl radicals and ozone.
The Estimation Program Interface was developed by the US Environmental Agency's Office of Pollution Prevention and Toxics, and Syracuse Research Corporation (SRC). © 2000 - 2012 U.S. Environmental Protection Agency for EPI SuiteTM (Published online in November 2012).
GLP compliance:
no
Estimation method (if used):
PHOTOCHEMICAL REACTION WITH OH RADICALS
- sensitiser for indirect photolysis: OH radicals
- Concentration of OH radicals: 0.5 E6 OH/cm³, 24 h/d
% Degr.:
50
DT50:
9.4 h
Test condition:
OH radical reaction

1) Defined Endpoint: Rate constant for the atmospheric, gas-phase reaction between photochemically produced hydroxyl radicals and organic chemicals at 25 °C.

2) Unambiguous algorithm: The molecule is separated into distinct fragments. The reaction rate constant for hydroxyl radicals are the summation of the following mechanisms:

Hydrogen Abstraction = 2.2097 E-12 cm³/molecule-sec

Reaction with N, S and -OH = 0.2800 E-12 cm³/molecule-sec

Addition to Triple Bonds = 0.0000 E-12 cm³/molecule-sec

Addition to Olefinic Bonds = 0.0000 E-12 cm³/molecule-sec

**Addition to Aromatic Rings = 38.3681 E-12 cm³/molecule-sec

Addition to Fused Rings = 0.0000 E-12 cm³/molecule-sec

** Designates Estimation(s) Using ASSUMED Value(s)

As depending on the structure of the substance, OH-radicals generally react by one or more of the above mentioned pathways, the result of 40.9 E-12 cm³/molecule-sec for each mechanism indicate that these mechanisms are not relevant for the substance of interest. An "assumed value" is applied, showing that a structure fragment that has not been assigned a numeric value by the developer of the estimation methods used by AOPWIN or derived explicitly from experimental values.

OH Addition to Aromatic Rings Calculation:

Es+ = sipso+(-CL) + sp+(-CL) + sm+(-CL) + sp+(-CL) + sm+(-C(=O)- **) + sp+(-C(=O)- **) + = 1.336

Es+ = sp+(-CL) + sipso+(-CL) + sp+(-CL) + sm+(-CL) + sp+(-C(=O)- **) + sm+(-C(=O)- **) + = 1.336

Es+ = sm+(-CL) + sp+(-CL) + sipso+(-CL) + sp+(-CL) + sm+(-C(=O)- **) + sp+(-C(=O)- **) + = 1.336

Es+ = sp+(-CL) + sm+(-CL) + sp+(-CL) + sipso+(-CL) + sp+(-C(=O)- **) + sm+(-C(=O)- **) + = 1.336

Es+ = sm+(-CL) + sp+(-CL) + sm+(-CL) + sp+(-CL) + sipso+(-C(=O)- **) + sp+(-C(=O)- **) + = 1.336

Es+ = sp+(-CL) + sm+(-CL) + sp+(-CL) + sm+(-CL) + sp+(-C(=O)- **) + sipso+(-C(=O)- **) + = 1.336

Most negative Es+ = 1.336

Log Kar = -11.71 - 1.34(Es+) cm³/molecule-sec

Ring #1 Kar = 0.0316 E-12 cm³/molecule-sec

TOTAL Kar = 0.0316 E-12 cm³/molecule-sec

Note: The bimolecular rate constant karom is expressed as Kar by the program.

The single results for OH addition shows that for the fragment –C(=O)- an assumed value of 0.75 is applied. This value is found in the list of all fragment and reaction values, provided by the program.

3) Applicability domain:

Currently there is no universally accepted definition of model domain.

Due to the fragment-based approach of AOPWIN, estimation is adequate as the fragments present in the molecule are available in the list of all fragment and reaction values provided by the program.

4) Statistical characteristics:

The correlation includes 667 compounds; most experimental values containing a "less than" sign (<) were excluded.

correlation coefficient (r²) 0.963; standard deviation (sd in log units) 0.218; absolute mean error (me) 0.127

5) Mechanistic interpretation:

The reaction values and fragments for the reaction with OH-radicals used as descriptors reflect the most important mechanisms of indirect phototransformation processes possible in the troposphere.

Adequacy of prediction:

The estimation rules applied for the substance appears appropriate.

The predicted result for 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol can be considered reliable yielding a useful result for further assessment.

Validity criteria fulfilled:
not applicable
Conclusions:
The calculated half-life of 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol by photodegradation in air was 9.4 hours with an Overall OH rate constant of 40.9E-12 cm³/molecule-sec.The estimation rules applied for the substance appears appropriate.
The predicted result for 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol can be considered reliable yielding a useful result for further assessment.
Executive summary:

The indirect photodegradation in air was calculated with the Estimation Program Interface EPI-Suite version 4.11.The estimated half-life of 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol was 9.4 hours with an Overall OH rate constant of 40.9E-12 cm³/molecule-sec.

The estimation rules applied for the substance appears appropriate.

The predicted result for 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol can be considered reliable yielding a useful result for further assessment.

The calculated value refers to the unaffected molecule. Any decomposition (e.g. hydrolysis) of the substance is not taken into account by the program.

Endpoint:
phototransformation in air
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Study period:
2009
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The estimation was conducted with the AOP Programm (v.1.92) which is implemented in EPI Suite v.3.20. The calculation method in the program is accepted.
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Method: Calculation with AOP (v.1.92)
GLP compliance:
no
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material: not applicable
Estimation method (if used):
Photochemical reaction with OH radicals
- Concentration of OH radicals: 0.5 E+06 OH/cm³
- Degradation rate constant: 40.8578 E-12 cm³/molecule*sec
- other: 24-h day
Details on light source:
not applicable
Details on test conditions:
Sensitiser (for indirect photolysis): OH
Sensitiser concentration: 500000 molecule/cm³

Preliminary study:
not applicable
Test performance:
no remarks
DT50:
9.42 h
DT50:
0.39 d
Test condition:
24-hr day
Transformation products:
no
Results with reference substance:
not applicable

no remarks

Validity criteria fulfilled:
not applicable
Conclusions:
The half-life of photodegradation in air is calculated to be ca. 9.424 hours (corresponding to 0.393 days).
Executive summary:

The degradation of DBMC in air by reaction with OH-radicals was estimated with the AOP programme (v1.92). Based on a 24 -h day with an OH radical concentration of 0.5 E06 OH/cm³ the overall OH rate constant was calculated to be 40.8578 E-12 cm³/molecule*sec, leading to a half-life of approx. 9.424 hours (equivalent to 0.393 days).

Reference: Lanxess, 2009

Description of key information

The calculated half-life of 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol by photodegradation in air was 9.4 hours with an Overall OH rate constant of 40.9E-12 cm³/molecule-sec. The estimation rules applied for the substance appears appropriate.
The predicted result for 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol can be considered reliable yielding a useful result for further assessment.

Key value for chemical safety assessment

Half-life in air:
0.39 d
Degradation rate constant with OH radicals:
40.9 cm³ molecule-1 s-1

Additional information

The half-life in air was calculated to be 9.4 h for a 24-hour day.