Ammonium undecafluorohexanoate

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption, other

Remarks:

adsorption

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

1. SOFTWARE
ChemProp(TM) Main Module 6.5, Public OSIRIS Edition

2. MODEL (incl. version number)
Franco, Fu & Trapp (Partitioning, soil sorption coefficient, Koc), ionizable substances, acids and bases

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
See “Test material information”

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
See attached information on the model provided by the developer. Further information on the OECD criteria as outlined by the applicant is provided below under "Any other information of materials and methods incl. tables"

5. APPLICABILITY DOMAIN
See attached information and information as provided in "Any other information on results incl. tables".

6. ADEQUACY OF THE RESULT
See assessment of adequacy as outlined in the "Overall remarks, attachments" section.

Qualifier:

according to guideline

Version / remarks:

REACH Guidance on QSARs R.6

Principles of method if other than guideline:

- Software tool(s) used including version: ChemProp v6.5
- Model(s) used: Franco, Fu & Trapp
Full reference and details of the used formulas can be found in:
1. Franco A, Fu W, Trapp S 2009. Influence of soil pH on the sorption of ionizable chemicals: Modeling advances. Environ. Toxicol. Chem. 28: 458-464.
2. Franco A, Trapp S 2008. Estimation of the soil-water partition coefficient normalized to organic carbon for ionizable organic chemicals. Environ. Toxicol. Chem. 27: 1995-2004.
- Model description: see field 'attached justification' and 'any other information on material and methods'
- Justification of QSAR prediction: see field 'Justification for type of information', 'Attached justification' and/or 'overall remarks'

GLP compliance:

no

Type of method:

other: calculation

Media:

soil

Details on test conditions:

BASIS FOR CALCULATION OF Koc:
- Estimation software: ChemProp v6.7, Franco, Fu and Trapp 2009 model for acids OR/AND ChemProp v6.7, Franco and Trapp 2008 model for bases
- Log Kow: 3.12
- pKa: 3.29
- pH: 4, 7 and 9

Type:

log Koc

Value:

1.46 dimensionless

pH:

4

% Org. carbon:

5

Remarks on result:

other: based on eq. 2 (acids)

Type:

Koc

Value:

28.84 L/kg

pH:

4

% Org. carbon:

5

Remarks on result:

other: based on eq. 2 (acids)

Type:

log Koc

Value:

1.57 dimensionless

pH:

7

% Org. carbon:

5

Remarks on result:

other: based on eq. 2 (acids)

Type:

Koc

Value:

37.15 L/kg

pH:

7

% Org. carbon:

5

Remarks on result:

other: based on eq. 2 (acids)

Type:

log Koc

Value:

1.57 dimensionless

pH:

9

% Org. carbon:

5

Remarks on result:

other: based on eq. 2 (acids)

Type:

Koc

Value:

37.15 L/kg

pH:

9

% Org. carbon:

5

Remarks on result:

other: based on eq. 2 (acids)

For detailed information on the results please refer to the attached report.

Description of key information

The potential for adsorption of ammonium undecafluorohexanoate (CAS 21615-47-4) is considered to be low (log Koc < 3).

Additional information

Ammonium undecafluorohexanoate (CAS 21615-47-4) is considered to have a low potential for adsorption. Based on the pKa of 3.29 the anionic form is considered to be the dominant form in environmental media. The hydrophobic/lipophobic nature of the substances does not indicate potential for adsorption to organic matter. This is further supported by (Q)SAR calculations using the model from Franco, Fu & Trapp (acid model) as well as experimental results from perfluorinated acids with C-chain lengths of the fluorinated carbon backbone of C8-C12. The (Q)SAR calculation was performed for the anionic acid form of the substance for pH 4, 7 and 9 (5% organic carbon). Log Koc values of 1.46 - 1.57 indicate a low potential for adsorption to particulate organic matter.

This result from (Q)SAR is in line with the result from an experimental study performed with the dissociation product perfluorohexanoic acid (Kawashima, 2018). This study was performed according to OECD 121 at two different pH levels (pH 2 and pH 7 at 25 °C) to investigate the adsorption of the dissociated and undissociated form of the acid. At pH 2 a log Koc of 4.27 resulted whereas under environmental conditions a low potential for adsorption resulted (log Koc < 1.25).

Further investigations of the adsorption potential are available in a study from Higgins & Luthy, (2006). In this study the adsorption potential of several perfluorinated acids (PFAs: C8-C12) was investigated. Five different sediments were exposed to the different substances for 10 d to allow equilibration between the water and sediment phase. Recoveries ranged from 63 (±3) to 120 (±7)% for triplicate vials, with an overall average mass balance for all samples and all analytes of 96 (±10)% (n=1250). Distribution coefficients were determined via the aqueous loss method: aqueous concentrations were determined for all samples, and the corresponding sediment concentrations calculated. Regression based log Koc values were determined to be 2.11 (C8), 2.50 (C9), 2.92 (C10) and 3.47 (C11), respectively. This result clearly indicates that the CF2 moiety is the determining structural element determining the adsorption of perfluorinated carboxylates. Each CF2 moiety contributes to 0.5 - 0.6 log units to the measured adsorption coefficients. Consequently the log Koc of perfluorohexanoic acid (C6), the anionic acid form of ammonium undecafluorohexanoate, can be derived to be approx. 1.11. Based on the result from (Q)SAR and confirmation from experimental determination it can be assumed that the potential of ammonium undecafluorohexanoate for adsorption is low.

 

Reference

Higgins & Luthy (2006): Sorption of perfluorinated surfactants on sediments. Environ. Sci. Technol., Vol. 40, pp. 7251-7256.