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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:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Qualifier:
no guideline followed
Principles of method if other than guideline:
Calculation using AOPWIN v1.92
GLP compliance:
no
Specific details on test material used for the study:
- Substance name (as in EPISuite CAS inventory): Propanal, 2-methyl-
- SMILES: O=CC(C)C
Estimation method (if used):
PHOTOCHEMICAL REACTION WITH OH RADICALS:
- Computer programme: SRC AopWin v1.92;
- Concentration of OH radicals: 5E+05 molecules/cm³ (northern hemisphere);
- Time frame: 24-hour day;
- Degradation rate constant: 23.2757 E-12 cm³/molecule·s;
- Temperature for which rate constant was calculated: 25°C.
Key result
DT50:
16.543 h
Test condition:
half-life calculated for the following conditions: sensitizer for indirect photolysis: OH; 0.5E+06 OH/cm³, 24h day; substance presumably within applicability domain

SUMMARY (AOP v1.92):

HYDROXYL RADICALS (25 °C):

Hydrogen Abstraction

23.2757 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

0.0000 E-12 cm3/molecule-sec

Overall OH Rate Constant

23.2757 E-12 cm3/molecule-sec

Half-life

0.689 Days

Half-life

16.543 Hrs

Executive summary:

QPRF:AOPWIN

1.

Substance

See “Test material identity”

2.

General information

 

2.1

Date of QPRF

See “Data Source (Reference)”

2.2

QPRF author and contact details

See “Data Source (Reference)”

3.

Prediction

3.1

Endpoint
(OECD Principle 1)

Endpoint

Phototransformation in air

Dependent variable

Hydroxyl reaction rate constant (cm3/molecule*sec)

3.2

 

Model or submodel name

AOPWIN

Model version

1.92

Reference to QMRF

QMRF: Estimation of Atmospheric Degradation Using AOPWIN v1.92 (EPI Suite v4.11): Hydroxyl Radical Reaction

Predicted value (model result)

See “Results and discussion”

Input for prediction

- Chemical structure via CAS number or SMILES

Descriptor values

- Structure fragments

3.3

Algorithm
(OECD Principle 2)

Domain (On-Line AOPWIN User’s Guide):

As the complete training sets for AOPWIN's estimation methodology are not available, describing a precise estimation domain for this methodology is not possible. There is no information on the number of instances of fragments in the training dataset.

If the substance is a member of one of the following chemical classes, the substance is probably within the applicability domain of the model (based on information by other authors, e.g. Posthumus and Slooff, 2001):

alkanes, haloalkanes, alkenes, haloalkenes, polyenes, terpenes, alkynes, aldehydes, ketones, alcohols, glycols, ethers, esters, epoxides, thiols, thioethers, aliphatic amines, hydrazines, nitrites, nitrates, nitriles, P-containing organics, aromatic compounds (alkylbenzenes, halobenzenes, phenols, PAHs, styrene, methoxybenzene, aniline, nitrobenzene, biphenyl, dibenzofurans, dibenzodioxins)

Fulfilled

The substance is not within the applicability domain of the model if it is a perhalogenated alkane.

Not Fulfilled

Substance is a secondary, tertiary and heterocyclic amine. Estimated values highly uncertain.

Not Fulfilled

3.4

The uncertainty of the prediction
(OECD principle 4)

- n = 667

- correlation coefficient r2= 0.963

- standard deviation = 0.218

- absolute mean error = 0.127

- 90% of the estimated rate constants within a factor of two of the experimental data

- 95% of the estimated rate constants within a factor of three of the experimental data

3.5

The chemical mechanisms according to the model underpinning the predicted result
(OECD principle 5)

Reaction rate constants for hydroxyl radicals are the summation of the following mechanisms:

(1) Hydrogen abstraction

(2) Reaction with specific nitrogen and sulphur fragments and reaction with hydroxyl (OH) fragments such as alcohols and phenols

(3) Addition to triple bonds

(4) Addition to olefinic bonds

(5) Addition to aromatic rings

(6) Addition to fused rings

The model works according to the group contribution method which uses fragments and the corresponding reaction values to estimate the reaction rate constant of a given substance.

References

- R Posthumus and W Slooff (2001). Implementation of QSARs in ecotoxicological risk assessments. RIVM report 601516 003. Online: http://rivm.openrepository.com/rivm/bitstream/10029/9559/1/601516003.pdf

- US EPA (2012). On-Line AOPWIN User’s Guide.

Description of key information

The half-life after reaction with hydroxyl radicals is estimated to be ca. 16.5 hours by means of QSAR (EPISuite module AOPWIN (v1.92)). A 24 -h averaged hydroxyl radicals concentration of 5E+05 OH /cm³ was used in the estimation.

With a half-life of < 2 days, after evaporation or exposure to the air compartment, the product will be rapidly degraded by photochemical processes. As the cut-off time for reaching the stratosphere is 2 days, the substance is considered not to have potential for reaching the stratosphere and/or long-range atmospheric transport.

Key value for chemical safety assessment

Additional information

QSAR-disclaimer:

In Article 13 of Regulation (EC) No 1907/2006, it is laid down that information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI (of the same Regulation) are met.

According to Annex XI of Regulation (EC) No 1907/2006 (Q)SAR results can be used if (1) the scientific validity of the (Q)SAR model has been established, (2) the substance falls within the applicability domain of the (Q)SAR model, (3) the results are adequate for the purpose of classification and labeling and/or risk assessment and (4) adequate and reliable documentation of the applied method is provided.

For the assessment of isobutyraldehyde (Q)SAR results were used for phototransformation in air (hydroxyl radical reaction).The criteria listed in Annex XI of Regulation (EC) No 1907/2006 are considered to be adequately fulfilled and therefore the endpoint(s) sufficiently covered and suitable for risk assessment.