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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption to the solid soil phase is expected. 
The adsorption potential of the compound is dependant on the environmental pH values. The compound has a pKa value of 9.42. At pH values 4 and 7 the compound is entirely present in its positively charged form. At pH 9, 73% are present in its positively charged form whereas 27% are present in its neutral form.

Key value for chemical safety assessment

Additional information

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. Furthermore according to Article 25 of the same Regulation testing on vertebrate animals shall be undertaken only as a last resort.

 

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 the compound (Q)SAR results were used for adsorption/desorption. 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.

 

Therefore, further experimental studies on adsorption/desorption are not provided.

To assess the adsorption/desorption potential of the compound two QSAR methodologies both integrated in the EPISuite v4.11 were used. According to the MCI method (molecular connectivity index) the logKoc of the uncharged molecule was estimated to be 7.7368. Based on the claculated logKow of 6.86 (Kowwin) the logKoc was estimated to be 4.6104. Both estimations were conducted with KOCWIN v2.00 for the uncharged molecule.

However, the calculated pKa of 9.42 (SPARC v4.6, 2012) indicates that the molecule will primarily exist in its positively charged form under environmental conditions (pH 4 to 9). In general, positively charged cations adsorb stronger to sediment and soils containing organic carbon and clay than their neutral counterparts. Therefore, the log Koc was corrected according to the method of Franco and Trapp (2008).

SMILES Input parameter Corrected Koc (logKoc)
logKow pKa pH 4 pH 7 pH 9
CCCCCCCCCCCC(=O)OC1CC(NC(C1)(C)C)(C)C 6.86 9.42 19800 (4.30) 19790 (4.30) 19107 (4.28)

According to these results, adsorption to the solid soil phase is expected.

Franco F, Trapp S. 2008. Estimation of the soil-water partition coefficient normalized to organic carbon for ionizable organic chemicals. Environmental Toxicology and Chemistry, Vol 27, No. 10. pp. 1995 -2004