Registration Dossier
Registration Dossier
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EC number: 203-372-4 | CAS number: 106-20-7
Adsorption / desorption
Administrative data
Link to relevant study record(s)
Description of key information
Adsorption to solid soil phase is to be expected.
Key value for chemical safety assessment
- Koc at 20 °C:
- 316 227
Additional information
The log Koc was determined to be 5.5 pH 7.0 following the OECD guideline 121 (BASF SE, 2013; study no. 11L00538). At pH 9 no reliable Koc could be determined as the retention time on the HPLC system was larger than for the reference substances (log Koc > 5.63). As 98% of the European soils have a pH within a range of 5 to 8, the value determined at pH 9 is not relevant for the assessment of the substance's environmental fate.
The pKa of 10.59 (calculated; BASF SE, 2020) indicates that the molecule will exist primarily as a cation in the environment. 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 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. The method is based on the dissociation constant pKa and the log Kow for the uncharged molecule. The substance is within the applicability domain of the model. Under environmental conditions (pH from 5 to 8) the test substance is almost completely present in its charged form (as calculated by the formula ionised = 100/(1+10(pKa - pH)): 100% at pH 5 to 8).
Regarding the charged
molecule, at pH 7 the log Koc was estimated to be 4.64 (Koc = 43254
L/kg) following the method of Franco & Trapp (2008, 2009, 2010) and
using the pKa of 10.59 and the measured log Kow for the uncharged
molecule of 6.56. The correction was performed for pH 5, 7 and 8, which
represents 98% of the European soils.
According to REACH Guidance document R7a (v4.1, Oct. 2015), the environmentally relevant pH range normally varies between 5.5 and 7.5 for agricultural soils and sewage treatment plants (R.7.1.17.1: Comment 21, p. 149). Therefore, an additional calculation with Simple Treat v4.0 (an exposure and emission model developed to estimate chemical emission from sewage treatment plants and exposure in surface water) was performed using a log Koc of 5.5, which was determined at pH 7.5 (OECD 121; BASF SE, 2013; study no. 11L00538). At this pH level 82.4% of the substance will adsorb to sludge, (while about 6.4% will distribute into water and 0.00005% into air) without primary sedimentation. If primary sedimentation is included, the substance is predicted to adsorb to 92.2% to sludge at pH 7 (3.2% into water; 0.00002% into air).
Based on the available experimental and calculated data, adsorption of the substance to the solid soil phase is to be expected.
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