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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:
other: Model Atmospheric Oxidation Program for Microsoft Windows (AOPWIN version 1.92a) has been used.
Justification for type of information:
QSAR prediction: migrated from IUCLID 5.6
Qualifier:
no guideline followed
Principles of method if other than guideline:
The Atmospheric Oxidation Program for Microsoft Windows (AOPWIN) estimates the rate constant for the atmospheric, gas-phase reaction between photochemically produced hydroxyl radicals and organic chemicals.
GLP compliance:
no
Light source:
not specified
Reference substance:
yes
Remarks:
OTNE: 1-(1,2,3,4,5,6,7,8octahydro-2,3,8,8-tetramethyl-2-naphthalenyl)ethanone CAS 54464-57-2 and HHCB: (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethycyclopenta-[γ-2-benzopyran) CAS 1222-05-5
DT50:
7.3 h
Test condition:
OH radical, 12h daylight average and a OH radical concentration of 1.5E6 molecule/cm3
DT50:
5.5 h
Test condition:
OH radical, 12h daylight average and a OH radical concentration of 2.0E6 molecule/cm3
Transformation products:
no

Table 1 shows the estimated and measured half-life times of OTNE and HHCB and the estimated half-life time of AHTN. The estimations are based on the calculations by the The Atmospheric Oxidation Program for Microsoft Windows (AOPWIN) module in the "The Estimations Programs Interface for Windows" (EPI Suite version 4.0). The OH radical concentration was 2.0·106 molecules/cm3 instead of the default 1.5·106molecules/cm3 , since the former value is used in another article to calculate the half-life times of HHCB and OTNE in table 1. The differences between the estimated and measured values are within a factor of 2 and are therefore in good agreement.

The output of the AOPWIN calculations are attached.

Table 1 Half-life times of OTNE, HHCB and AHTN in hours with a OH radical 12 -hour day light average concentration of 2.0·106molecules/cm3.

Estimated
Substance Literature AOPWIN
OTNE 1.0 0.75
HHCB 3.7 2.6
AHTN 5.5
Validity criteria fulfilled:
yes
Remarks:
The molecular weight is within the domain. No specific fragments are present in AHTN that could give rise large errors.
Conclusions:
The estimated half-life time of AHTN is 5.5 h.
Executive summary:

The half-life time of AHTN was estimated using the AOPWIN module (version 1.92) in the EPIO suite (version 4.0). The structurally related substances HHCB (Cas 1222 -05 -5) and OTNE (CAS 54464 -57 -2) were used as references, since their values do not appear in the training set of AOPWIN and their experimental values were actually determined in a study. The estimated and experimental values were in good agreement within a factor of 2. The estimated half-life time of AHTN of is 5.5 hours.

Description of key information

The phototransformation in air was assessed on the basis of read across of 4 fragrance molecules, of which one is very close structurally related (HHCB), and the result from the EPIWIN Aopwin model for the test item.

Key value for chemical safety assessment

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

Additional information

The EU Risk Assessment Report (2008) reported rate constants for gas phase reactions of OH radicals of related fragrance molecules, including HHCB: (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethycyclopenta-[γ-2-benzopyran) CAS 1222-05-5. HHCB and AHTN have the same molecular weight. The main body of AHTN is tetralin and that of HHCB is indane, which is structurally related. The carbon ring of the tetralin and indane are similarly substituted by 6 methyl groups. The main difference is the way in which the benzyl group has been substituted by other groups. HHCB has another 5 -member carbon ring attached to the benzene in which an oxygen is incorporated as in an ether. For gas phase reactions involving OH radicals, it is believed that the structures are sufficiently similar to apply read-across. The experimental results show that the estimated rate constants for this reaction are within a factor of 1.5 from the estimated values for these fragrance substances with short half lives. This implies that the estimated rate constant for AHTN is expected to be similar and relatively accurate as well. The estimated rate constant for the gas-phase reaction with OH radicals k = 1.7.10-11cm3molecule-1s-1. Assuming a daylight period of 12 h and 1.5.106OH cm-3, the estimated atmospheric half-life is 7.3 hours or 0.6 d (Syracuse estimation). These data suggest that the atmospheric lifetime of the test item is sufficiently short that it will not undergo long-range transport to any significant extent.

Source: EU Risk Assessment AHTN, European Chemicals Bureau, May 2008

The EU Risk Assessment Report referenced to Aschmann et. al., Environ. Sci. Technol. 2001 (35), p. 3595-3600 (2001).