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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Data waiving:
study technically not feasible
Justification for data waiving:
other:
Justification for type of information:
No determination of the adsorption coefficient was possible by the HPLC estimation method, Method C19 Adsorption Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001. This was since the method was invalid for the test item. The method is not valid for quaternary amines which present a cationic species at all pH values. In addition to the absence of relevant reference items to form a valid calibration, such cationic species have been demonstrated to interact with the HPLC column stationary phase by mechanisms other than partitioning, thus invalidating the estimation of the adsorption coefficient of the test item by comparison to the capacity factors of reference substances of known adsorption coefficient values.
The HPLC column stationary phase required by the guidelines is that of cyanopropyl groups established on a silica backbone. Critically however, this silica backbone contains a number of free silanol groups (Si-OH) which present an anionic charge at a neutral mobile phase pH as required by the method. This presents a significant opportunity for retention of a cationic substance by secondary ionic interactions, as opposed to true partitioning onto the cyanopropyl groups as intended by the method. Potentially more critically though is that overall, the actual concept of an organic carbon normalized adsorption coefficient for a cationic molecule is limited as the organic carbon content of a soil or sludge may not be the critical factor for the mobility of the substance,
hence the absence of correlation between partition coefficient and apparent adsorption coefficient for this chemical class. No alternative estimation method was available for the adsorption coefficient of this test item. For example, KOCWIN v 2.00 (September 2010) © 2000 to 2008 US EPA, the adsorption coefficient estimation module of EPI Suite is not considered valid for cationic substances, with no amines present in the validation data set and an error message obtained if a cationic quaternary amine is entered.

Description of key information

No determination of the adsorption coefficient was possible by theHPLC estimation method, Method C19 Adsorption Coefficient of Commission Regulation(EC) No 440/2008 of 30 May 2008 and Method 121 of the OECD Guidelines for Testing ofChemicals, 22 January 2001. This was since the method was invalid for the test item. The method is not valid for quaternary amines which present a cationic species at all pH values.No alternative estimation method was available for the adsorption coefficient of this test item.

Key value for chemical safety assessment

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