Choline chloride

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption, other

Remarks:

calculation of logKoc for ionized molecule

Type of information:

calculation (if not (Q)SAR)

Remarks:

estimated by calculation

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Scientifically acceptable calculation method

Justification for type of information:

1. SOFTWARE
not applicable (please see below)

2. MODEL (incl. version number)
For ionisable chemicals it is possible to apply the equations proposed by Franco and Trapp as explained in the RIVM report “Identification and preliminary analysis of update needs for EUSES2”

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
[Cl-].C[N+](C)(C)CCO, See also section 'Test Material'.

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint: Adsorption / desorption of ionizable substances
- Unambiguous algorithm: yes, 1 equation for acids and 1 equation for bases have been developed to calculate the Koc for ionizable substances using the partition coefficient and the (pH and the) pKa value.
- Defined domain of applicability: ionizable substances (either acids or bases)
- Appropriate measures of goodness-of-fit and robustness and predictivity: please refer to original publication Franco and Trapp, 2008
- Mechanistic interpretation: please refer to original publication Franco, A., 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.

5. APPLICABILITY DOMAIN
- Descriptor domain: ionizable substances (either acids or bases) with a logKow <= 3

6. ADEQUACY OF THE RESULT
Calculation method determining the Koc for charged molecules based on log Kow (uncharged molecule) and pKa. This value can be used in the derivation of the PNEC sediment freshwater / PNEC sediment marine water and PNEC soil with the equilibrium partitioning method.

Principles of method if other than guideline:

Calculation method determining the Koc for charged molecules based on log Kow (uncharged molecule) and pKa.
Input parameters:
1. The substance is a base.
2. log Pow (for uncharged molecule) = -3.77
3. pKa = 10.6 (calculation of pKa of Choline (CAS 62-49-7), as best approximation for choline chloride (CAS 67-48-1)

GLP compliance:

no

Type of method:

other: calculation of pH corrected log Koc for ionized molecule

Media:

soil

Specific details on test material used for the study:

[Cl-].C[N+](C)(C)CCO

Radiolabelling:

no

Remarks:

not relevant (Calculation)

Test temperature:

25 °C

Type:

Koc

Value:

37.6 L/kg

pH:

8

Temp.:

25 °C

Type:

log Koc

Value:

1.6 dimensionless

pH:

8

Temp.:

25 °C

Type:

Koc

Value:

37.7 L/kg

pH:

7

Temp.:

25 °C

Type:

log Koc

Value:

1.6 dimensionless

pH:

7

Temp.:

25 °C

Type:

Koc

Value:

37.7

pH:

5

Temp.:

25 °C

Type:

log Koc

Value:

1.6 dimensionless

pH:

5

Temp.:

25 °C

Details on results (HPLC method):

not relevant for calculations

The data refer to the charged molecule.

Validity criteria fulfilled:

yes

Conclusions:

Choline chloride is the salt of a base. At pH 5 and 7 Koc = 37.7 and at pH 8 Koc = 37.6 L/kg; at pH 5-8 logKoc = 1.6.

Executive summary:

Choline chloride is the salt of a base. Therefore, Koc values can be calculated at different pH according to the calculation approach of Franco and Trapp. The Koc value at 25°C was nearly the same for the range of pH 5 - 8. This indicates that surrounding pH will not have a great influence on adsorption coefficients of choline chloride. At pH 5 and 7 Koc = 37.7 and at pH 8 Koc = 37.6 L/kg; at pH 5-8 logKoc = 1.6.

Description of key information

Calculation according to Franco and Trapp (2008): Koc = 37.7 (logKoc = 1.6) at pH 7 and 25 °C

Key value for chemical safety assessment

Koc at 20 °C:

37.7

Additional information

The organic-normalized sorption coefficient for soil (soil adsorption, Koc) of Choline hydroxide was determined with the computer program from US-EPA (EPIWIN software KOCWIN v2.01; calculated by Chemservice S.A., 2018c, updated 2022). The EPIWIN software KOCWIN v2.01 was used to attest a significant number for soil adsorption. Two different models are used by the QSAR program for this estimation: the Sabljic molecular connectivity (MCI) method as well as with the traditional method which is based on logPow. For the substance Choline chloride the traditional method gives a Koc of 0.0585 L/kg, whereby the MCI method reveals a value of 1.438 L/kg as result. Generally, the MCI method is taken more seriously into account due to the fact, that it includes improved correction factors.

However, due to the fact that Choline chloride is a Quaternary Ammonium Compound (QAC), the adsorption will depend on the cation-exchange capacity of the sorbent and a variety of other parameters. The training set of the KOCWIN software does not include any QACs, therefore, the estimation is outside the prediction domain of the program.

 

As such, a different model was employed. At environmentally relevant conditions, choline chloride will be present in ionized form (pKa= 10.6 at 25 °C calculated for choline (CAS 62-49-7) as best approximation for choline chloride (CAS 67-48-1), see IUCLID Ch 4.21). Therefore, the adsorption coefficient was calculated according to Franco & Trapp (2008, 2009, 2010), a calculation suitable for ionized molecules, to correct for the charged molecule at pH 5, 7, and 8. This pH range is representative for 98 % of the European soils. The model is not yet validated; in addition, the applicability domain is not clearly defined. Nevertheless, 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 logKow for the uncharged molecule. The Koc value at 25 °C was nearly the same for the range of pH 5 - 8. The resulting Koc at pH 7 is 37.7 L/kg (log Koc: 1.6).

 

Furthermore, the OECD SIDS Report for Choline Chloride (2005) covers the result of a QSAR prediction in order to determine the Koc of the substance. The prediction itself was performed with SRC PCKOWIN v1.66 by BASF AG (2003). No details about the input are available, however, the unpublished data is considered as reliable with restrictions (Klimisch 2) and is regarded as critical study for the SIDS endpoint. As result, a Koc of 2.34 with a corresponding logKoc of 0.37 is reported. This information is regarded as supporting information to confirm that the test substance possess only a low soil adsorption potential.