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Adsorption / desorption

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Endpoint:
adsorption / desorption: screening
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
supporting study
Study period:
2019
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Principles of method if other than guideline:
The Koc of the substance was calculated based on the approach presented in Franco and Trapp (2008), where regressions were developed to predict separately the Koc for the neutral and ionic molecule species of organic electrolytes from their log Kow and pKa values.



GLP compliance:
no
Type of method:
other: calculation according to Franco and Trapp (2008)
Computational methods:
The following equation for bases was applied to the substance:

log Koc = log [Fn * 10^(0.37 * log Pn + 1.70) + FIon * 10^(pKa^0.65 * f^0.14)]

where:

Fn = 1 / (1 + 10^(a * (pH - pKa)))
FIon = 1 - Fn
f = Kow / (Kow + 1)

The following input values were used:
a = -1 for bases
pH = 4.5
Pn = Pow value of the test item as determined by Harlan (2015) was 0.916 at pH 12 and 22°C
pKa = predicted dissociation constants for the test item as determined by Harlan (2015) were approximately 9.18, 8.57 and 7.33 using ACD/I-Lab Web Service

Adsorption coefficients were determined for the range of predicted pKa values, resulting in the following log Koc and Koc values:

Log Koc = 2.08 or Koc = 119, for pKa = 9.18
Log Koc = 2.96 or Koc = 919, for pKa = 7.33
Key result
Type:
Koc
Value:
119 L/kg
Remarks on result:
other: pKa = 9.19
Type:
Koc
Value:
919 L/kg
Remarks on result:
other: pKa = 7.33
Conclusions:
The adsorption coefficient of the substance was estimated based on the approach developed by Franco and Trapp (2008). Koc values of 119 and 919 L/kg were calculated for the pKa values of 9.18 and 7.33, respectively.
Endpoint:
adsorption / desorption: screening
Study period:
12-12-2014 to 09-05-2015
Data waiving:
study technically not feasible
Justification for data waiving:
other:

Description of key information

Harlan (2015) concluded that the determination of the adsorption coefficient of the substance was not possible according to 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. A preliminary assessment of the test item indicated that it would be at least partially ionized across the relevant pH range of 5 to 7 (this considered range is slightly different than the pH range of 5.5 -7.5 recommended in the OECD 121 guideline). Therefore, it is anticipated that adsorption to the organic carbon content of soils and sediments will not be the dominant mechanism controlling the mobility of the test item in the environment. Adsorption of cationic species occurs primarily by an ion-exchange mechanism and thus depends on the cation-exchange capacity of the sorbent as well as a variety of other parameters (Boethling, R. S. 1994. Environmental aspects of cationic surfactants. In J. Cross and E. J. and Singer (ed.), Cationic surfactants: Analytical and Biological Evaluation, vol. 53. Marcel Dekker, Inc., New York, USA.). Consequently, the true adsorption coefficient of the test item will be significantly higher than any Koc value determined by the EC C19 / OECD 121 method or via any computer-based Koc estimation software.

In order to account for the specific ion-exchange mechanism regulating the adsorption of cationic species to particulate matter, the adsorption of the substance was calculated based on the approach developed by Franco and Trapp (2008) for the estimation of soil-water partition coefficients for ionizable organic chemicals. In this approach, regressions were developed to predict separately the Koc for the neutral and ionic molecule species of organic electrolytes based on the substance's log Kow and pKa. Koc values of 119 and 919 L/kg were calculated using predicted pKa values of 9.18 and 7.33, respectively. The lowest value was used as a worst case for the chemical safety assessment.

Key value for chemical safety assessment

Koc at 20 °C:
119

Additional information