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Environmental fate & pathways

Phototransformation in air

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Endpoint:
phototransformation in air
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Principles of method if other than guideline:
Calculated with AOP Program v1.92 of EPI-Suite Software. The Atmospheric Oxidation Program (AOPWIN) estimates the rate constant for the atmospheric, gas-phase reaction between photochemically produced hydroxyl radicals and organic chemicals. The rate constants are then used to calculate atmospheric half-lives for organic compounds based upon average atmospheric concentrations of hydroxyl radicals and ozone.
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
Sampling time:
8.84 h
Test condition:
calculation

rate constant of 4.56 *10-11cm3/(molecule*sec)

Validity criteria fulfilled:
not applicable
Conclusions:
In the atmosphere a half-life of 8.44 hours for TBBS due to reaction with photochemically produced hydroxyl radicals is estimated by AOPWIN v1.92 with a rate constant of 4.56 *10-11cm3/(molecule*sec), considering an OH-concentration of 500,000 radicals/cm³ as a 24-h average. The estimated half-life in air of MBS is much shorter than 48 hours and hence no potential for long-range transport of TBBS in air is expected.
Executive summary:

In the atmosphere a half-life of 8.44 hours for TBBS due to reaction with photochemically produced hydroxyl radicals is estimated by AOPWIN v1.92 with a rate constant of 4.56 *10-11cm3/(molecule*sec), considering an OH-concentration of 500,000 radicals/cm³ as a 24-h average. The estimated half-life in air of MBS is much shorter than 48 hours and hence no potential for long-range transport of TBBS in air is expected.

Endpoint:
phototransformation in air
Type of information:
(Q)SAR
Adequacy of study:
key study
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
Sampling time:
8.4 h

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 = 0.5018 E-12 cm³/molecule-sec

Reaction with N, S and -OH = 0.0000 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 = 0.0000 E-12 cm³/molecule-sec

**Addition to Fused Rings = 45.1292 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 0.0000 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 cm³molecule-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 N-tert-butylbenzothiazole-2-sulphenamide can be considered reliable yielding a useful result for further assessment.

Validity criteria fulfilled:
not applicable
Conclusions:
The calculated half-life of N-tert-butylbenzothiazole-2-sulphenamide by photodegradation in air was 8.4 hours with an Overall OH rate constant of 45.6E-12 cm³/molecule-sec.The estimation rules applied for the substance appears appropriate.
The predicted result for N-tert-butylbenzothiazole-2-sulphenamide 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 N-tert-butylbenzothiazole-2-sulphenamide was 8.4 hours with an Overall OH rate constant of 45.6E-12 cm³/molecule-sec.

The estimation rules applied for the substance appears appropriate.

The predicted result for N-tert-butylbenzothiazole-2-sulphenamide 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 N-tert-butylbenzothiazole-2 -sulphenamide is not taken into account by the program.

Description of key information

The calculated half-life of TBBS by photodegradation in air was 8.4 hours with an Overall OH rate constant of 45.6E-12 cm³/molecule-sec.The estimation rules applied for the substance appears appropriate.
The predicted result for TBBS can be considered reliable yielding a useful result for further assessment.
The estimated half-life in air of TBBS is much shorter than 48 hours and hence no potential for long-range transport of TBBS in air is expected.

Key value for chemical safety assessment

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

Additional information