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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The organic carbon partition coefficient (Koc) for C.I. Direct Blue 264 was predicted using the QSAR calculation of the Estimation Program Interface (EPI) Suite v4.11. 
The Koc was estimated to be 9.19 L/kg (Log Kow method), and 1E+10 L/kg (MCI method). The results relate to the unaffected molecule of C.I. Direct Blue 264 as any decomposition (e.g. hydrolysis) of a substance is not taken into account by the program.

Key value for chemical safety assessment

Koc at 20 °C:
9.19

Additional information

C.I. Direct Blue 264 is an UVCB substance consisting of phthalocyanine copper complexes. All constituents have copper phthalocyanine as basic structure. They carry further different numbers of two different types of side chains (sulfonic acid and dimethylaminopropyl sulfonamide). A calculation of the Log Koc for an UVCB substance is not feasible. Therefore the Log Koc of all constituents was calculated separately in order to determine the worst case (= highest value, showing the highest potential for adsorption to soil). As a conclusion copper phthalocyanine complexes carrying 0 to 4 dimethylaminopropyl sulfonamide groups as side chains were used in the simulation.

Copper phthalocyanine complexes carrying sulfonic acid side chains were not used, because the respective coefficient for this fragment is 0 and does therefore not contribute to the calculation of the entire molecule.

The copper atom in the center of the molecule was removed for the calculation as the bonding of Cu to a quaternary ammonium is not included in the training and validation set of the program. Displaying the outside margin of the molecule, the side chains are expected to contribute predominantly to a potential adsorption to soil. Thus this approach seems to be justified.

Using the Log Kow method the calculated Log Koc values for phthalocyanine with 0 to 4 dimethylaminopropyl sulfonamide side chains vary between -0.17 and 0.96, which is in good agreement to the calculated Log Kow of <-0.2 predicting a very small adsorption potential for C.I. Direct Blue 264.

The results determined with the MCI method on the other hand revealed values >10 for the Log Koc. Such high adsorption potential is unjustified and not expected due to the calculated Log Kow. As a conclusion the results obtained with the MCI method are not further used in the risk assessment of C.I. Direct Blue 264.

The highest Log Koc value (0.96) determined with the Log Kow method was determined for phthalocyanine with 2 dimethylaminopropyl sulfonamide side chains. The respective structure is not highly complex and the applied rules appear appropriate. One individual uncertainty for the investigated structure is available as the molecular weight of phthalocyanine with 2 dimethylaminopropyl sulfonamide side chains exceeds the range of the training set.

However, since the molecular weight is within the range of the validation set and the calculated result is in good agreement with the determined Log Kow, the calculation of the Log Koc fulfills the requirements for a valid simulation and is further used in the assessment for describing the entire UVCB substance C.I. Direct Blue 264.

[LogKoc: 0.96]