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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption to solid soil phase is not expected.

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. 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 1-methylimidazole (CAS 616-47-7) (Q)SAR results were used for the estimation of the adsorption potential. 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 the adsorption potential are not provided.




In order to assess the adsorption potential of the substance, the Koc value was estimated using (Q)SAR models.

At environmentally relevant conditions, the substance will primarily exist as a cation in the environment (pKa = 6.95; see IUCLID Ch.4.21). Cations generally adsorb stronger to soils containing organic carbon and clay than their neutral counterparts. Franco & Trapp (2008, 2009, 2010) have developed a method to take this effect into consideration when assessing the adsorption potential. The method is based on the dissociation constant pKa and the log Kow for the uncharged molecule.

The adsorption coefficient was calculated according to Franco & Trapp (2008, 2009, 2010) to correct for the charged molecule at pH 5, 7, and 8. This pH range is representative for 98% of the European soils. The substance is within the model's applicability domain. The Koc values of the Franco & Trapp method give a good indication on the adsorption potential of a substance depending on the pH conditions of soil.

Regarding the charged molecule, at pH 7 the log Koc was estimated to be 2.6 (Koc = 407 L/kg) following the method of Franco & Trapp, 2008, 2009, 2010 (BASF, 2021)and using the estimated pKa of 6.95 (BASF SE, 2021, SRC PhysProp Database; see IUCLID Ch. 4.21) and the calculated log Kow for the uncharged molecule of -0.19 (measured; BASF AG, 1989; No.104547/01). The correction was performed for pH 5, 7, and 8, which represents 98% of the European soils. The value at pH 7 will be used as key value, i.e. for PEC and PNEC calculations.


Since the substance is also present as uncharged molecule in the environment at higher pH (>7) the adsorption potential was furthermore assessed using the MCI and the log Kow method of the KOCWIN v2.00 module of EPI Suite v4.11. The MCI module is more reliable than the log Kow method of KOCWIN v2.00, which estimates a log Koc of 1-methylimidazole of 1.51 (Koc = 32.5) based on the n-octanol/water partition coefficient (log Kow = -0.19; BASF AG, 1989; report no.: 104547/01). The log Kow method resulted in a log Koc of 1.22 (Koc = 16.5). The substance is within the applicability domain of both methods. These estimates are representative for uncharged molecules. 


Based on these findings, the substance is not expected to adsorb to the solid soil phase.