Potassium 1,1,2,2,3,3,4,4,4-nonafluorobutane-1-sulphonate

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption, other

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2000-12-11 to 2001-01-09

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Study was performed on the free acid form of PFBS. The pH values were within the range 5.96 to 7.77 as specified by OECD TG 106, adsorption and desorption testing on the acid is equivalent to testing on the potassium salt.

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

GLP compliance:

yes

Type of method:

batch equilibrium method

Specific details on test material used for the study:

Perfluorobutane sulfonic acid CF3(CF2)3SO3H
Expiration date: 07/06/2001

Radiolabelling:

no

Test temperature:

Temperature range from 17.0 - 19.1 °C for Tier 1, 19.5 - 22.7 °C for Tier 2, and 18.2 -19.3 °C for Tier 3.

Analytical monitoring:

yes

Details on sampling:

Tier 1 preliminary study: Two soil types ( Don Uglem Loam and Kittson Clay) were tested in tier 1 test. Triplicate samples were prepared for each soil type and at three soil to solution ratios of 1/1, 1/5 and 1/25. The samples were mixed in 50 mL centrifuge tubes at 32 rpm at 17.0 – 19.1 °C until adsorption equilibrium was reached. Samples were collected over a 48-hour period of continuous mixing. At the specific sample intervals (4, 8, 24 and 48 hours), all samples were centrifuged, and an aliquot (1 mL) of the aqueous phase was removed for analysis. After the removal, the samples were remixed with the aqueous phase and returned to the mixing apparatus until next sampling interval. Following the last sampling after 48 hours, the samples were centrifuged, aqueous phase was recovered and the soil was extracted with methanol for analysis of PFBS. The concentration of PFBS in solution and soil was analyzed by LC/MS.

Tier 2 Sorption Kinetics test: Broeren Clay loam, Goose river sediment and NIST sludge were tested in the tier 2 test. The solid to solution ratio were 1:1 for soil and sediment (20 g to 20 mL), and 1:5 (5 g to 40 ml) for the sludge. Triplicate samples were prepared for each matrix at specified solid to solution ratios. Triplicate control (test substance in 0.01 M CaCl2 with so solid) and triplicate blank ( solid and 0.01 M CaCl2 with no test substance) were also prepared. The test procedure was performed in the same manner as the preliminary test. Aqueous samples were collected at 2, 4, 6, 8, and 24 hours of contact time and the concentration of PFBS in solution was analyzed by LC/MS. At 24 hours the soil, sediment and sludge were collected and analyzed for PFBS concentration by LC/MS.

Tier 3: Adsorption/desorption isotherms were determined on all matrices at a solid/solution ratio: 1:1 for soil and sediment (20 g to 20 mL) and 1:5 (5 g to 40 ml) for the sludge. Five nominal concentrations of PFBS (50, 100, 250, 500, and 1000 ug/L) were used. Triplicate samples and triplicate blanks were used. The concentration were well above the detection limit of 10 ug/L. The adsorption was performed in the same manner as the tier 1 and tier 2 studies, except that the aqueous phase was analyzed at 24 hours as determined to be the equilibrium time. The concentration of PFBS in solution was analyzed by LC/MS.

Following removal of the adsorption solutions, all remaining solids were remixed with 0.01 M CaCl2 solution without PFBS for desorption. The volume of solution used were same as the adsorption. The equilibrium concentration in the solutions were determined by LC/MS. Following the desorption, methanol extraction were performed only for the solid samples for which the adsorption and desorption solution concentration did not account for > 90 % of the fortified concentration. The extraction was performed using a wrist action shaker for 30 minutes followed by 30 min sonication. Samples were centrifuged and supernatant were decanted. The extraction were performed twice, and the both extracts were combined, concentrated and analyzed by LC/MS.

Matrix no.:

#1

Matrix type:

loam

% Clay:

11

% Silt:

50

% Sand:

39

% Org. carbon:

4.9

pH:

7.4

CEC:

23.9 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

clay loam

% Clay:

33

% Silt:

46

% Sand:

21

% Org. carbon:

2.6

pH:

6

CEC:

24.7 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

clay

% Clay:

62

% Silt:

22

% Sand:

16

% Org. carbon:

2.6

pH:

7.2

CEC:

54.5 meq/100 g soil d.w.

Matrix no.:

#4

Matrix type:

other: river sediment

% Clay:

19

% Silt:

42

% Sand:

39

% Org. carbon:

1.3

pH:

7.7

CEC:

17.5 meq/100 g soil d.w.

Matrix no.:

#5

Matrix type:

other: Sludge (100% organic matter)

Details on matrix:

COLLECTION AND STORAGE
- Geographic location:
Don Uglem Loam (Latitude: 47°44', Longitude: 97°48'); Broeren Clay Loam (Latitude: 47°42', Longitude: 97°40'); Kittson Clay (Latitude: 48°62', Longitude: 96°89'); Goose River sediment (Latitude: 47°45', Longitude: 97°37');
- Sampling depth (cm): 0 - 6"
- Sampling date:10/19/2000, and 10/21/2000
- Storage conditions: 2 - 6 °C

Key result

Sample No.:

#1

Type:

Koc

Value:

0 - 50

Adsorption and desorption constants:

The adsorption constant (k) for the three soil and the sediment tested were 0.
The estimated K value for sludge was 0.5.
The Freundlich adsorption and desorption isotherm were calculated only for the sludge since the soil and sediment demonstrated no adsorption.
The Adsorption isotherm for sludge had Kf (ad) = 0.3 with 1/n of 1.2840;
The desorption isotherm for sludge had Kf(des) = 0.001 with 1/n of 2.6055

Transformation products:

not measured

Details on results (Batch equilibrium method):

From the tier 1 and tier 2 stuies, PFBS showed no adsorption to the three soils and the Goose River sediment tested. The total % of applied PFBS recoveries were 74.8 – 102.7%. The estimated adsorption coefficient (K) was 0 for each soil and sediment.

In tier 2 study, only sludge showed adsorption, the estimated K value for sludge was 0.5. The equilibrium was reached by 24 hours. The average % of applied PFBS recoveries was 72.9% for sludge. Given an approximate fraction organic carbon of 0.5 for organic matter, a rough estimate of Koc is ca. 1 for sludge.

In tier 3 study, the % of applied PFBS recoveries were 90.3% ( 77.2 -105.1%) for Don Uglem loam; 105.9% ( 89.5 -126.8%) for Kittson Clay; 101.7% ( 91.5 -116.8%) for Broeren Clay loam; 117.4% ( 107.6 -128.9%) for Goose rive sediment; and 79.1% (68.9 -93.5%) for NIST sludge.

The Freundlich adsorption and desorption isotherm were calculated only for the sludge since the three soils and sediment demonstrated no adsorption.
The Adsorption isotherm for sludge was log (x/m) = 1.2840 log (Ce) -0.5470, corrlation coefficient = 0.9790, Kf (ad) = 0.3 with n=0.779;
The desorption isotherm for sludge was log (x/m) = 2.6055 log (Ce) -5.8621, corrlation coefficient = 0.9198, Kf(des) = 0.001 with n= 0.3838;

Table 3_ Tier 3 Freundlich adsorption isotherm for Sludge

initial PFBS conc. (ug/L)	rep	sludge (x/m) (ng/g)	Sludge Log x/m	CaCl2 solution Ce (ng/mL)	Log Ce (ng/mL)	K (x/m)/Ce
38	1	15.95	1.203	23	1.362	0.7
	2	16.65	1.222	24	1.38	0.7
	3	9.5	0.978	31	1.491	0.3
Avg						0.6
79	1	49.9	1.698	46	1.663	1.1
	2	46.46	1.667	45	1.653	1
	3	63.58	1.803	46	1.663	1.4
Avg						1.2
196	1	140.45	2.148	115	2.061	1.2
	2	109.09	2.038	113	2.053	1
	3	124.96	2.097	113	2.053	1.1
Avg						1.1
391	1	450.69	2.654	260	2.415	1.7
	2	347.48	2.541	257	2.41	1.4
	3	371.98	2.571	254	2.405	1.5
Avg						1.5
758	1	829.59	2.919	526	2.721	1.6
	2	854.92	2.932	536	2.729	1.6
	3	715.78	2.822	532	2.726	1.3
Avg						1.5

 

Table 4_ Tier 3 Freundlich Desorption isotherm for sludge 

initial PDBS conc. (ug/L)	rep	sludge (x/m) (ng/g)	Sludge Log x/m	CaCl2 solution Ce (ng/mL)	Log Ce (ng/mL)	K (x/m)/Ce
196	1	4.86	0.687	27.77	1.444	0.2
	2	2.24	0.35	21.77	1.338	0.1
	3	0	--	25.11	1.4	0
Avg						0.1
391	1	91.04	1.959	73.01	1.863	1.2
	2	102.58	2.011	49.82	1.697	2.1
	3	102.38	2.01	54.16	1.734	1.9
Avg						1.7
758	1	247.57	2.394	116.65	2.067	2.1
	2	190.88	2.281	133.93	2.127	1.4
	3	277.84	2.444	87.82	1.944	3.2
Avg						2.2

 

Validity criteria fulfilled:

yes

Conclusions:

The measured adsorption coeffiecient was 0 for the tested soils and sediment. The measured adsorption coeffiecient was 0.3 for the tested sludge. PFBS has very high mobility (Koc 0 - 50) in the tested soil, sediment, and sludge. Results are directly applicable to PFBSK+.

Executive summary:

The adsorption/desorption behavior of PFBS on soils, sediments and sludge was performed according to OECD 106 guideline.

This study was conducted on the tiered approach. The tier 1 study was conducted on two soil types (Don Uglem Loam and Kittson Clay) to determine any adsorption to test vessel, the ratio of soil to solution, and equilibrium mixing time. The tier 2 study was conducted on a third soil (Broeren Clay loam ), a sediment (Goose river sediment ) and a sludge (NIST sludge) to determine the sorption kinetics. Finally the tier 3 study was performed on all matrices at a solid/solution ratio: 1:1 for soil and sediment (20 g to 20 mL) and 1:5 (5 g to 40 ml) for the sludge using five nominal concentrations of PFBS (50, 100, 250, 500, and 1000 ug/L) to to determine the adsorption and desorption isotherms.

The adsorption constant (k) for the three soil and the sediment tested were 0. The estimated K value for sludge was 0.5 from tier 2 study. The Freundlich Adsorption isotherm for sludge had Kf (ad) of 0.3 with 1/n of 1.2840; the Freundlich desorption isotherm for sludge had Kf(des) of 0.001 with 1/n of 2.6055. The Freundlich adsorption and desorption isotherms were calculated only for the sludge since the soil and sediment demonstrated no adsorption. The low sorption of PFBS to all five matrices tested (three soils, sediment, and sludge) placed PFBS in the very high mobility class (Koc = 0 - 50).

This is a guideline stud conducted under GLP. Because PFBS is a strong acid and will exist entirely in anionic form at pH values mandated by the test guideline, results are equivalent to testing on the salt. Therefore, results for PFBS are directly applicable to PFBSK+. Therefore, it is considered reliable without restriction.

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

documentation insufficient for assessment

Justification for type of information:

The study examines soil-water distribution of the anion PFBS- in a laboratory setting. As PFBS is a strong acid that will exist predominantly in ionic form in the environment, this study is relevant to the examination of PFBSK+ distribution coefficient in soils.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Batch sorption experiment

GLP compliance:

no

Type of method:

other: Single-point distribution coefficient

Media:

soil

Specific details on test material used for the study:

Perfluorobutanesulfonate from Sigma-Aldrich (St. Louis, MO USA)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 10 µg/L
- Sampling interval: Once, at 14 days
- Sample storage before analysis: No

Matrix no.:

#1

Matrix type:

other: topsoil amended with sand

% Sand:

> 75

% Org. carbon:

0.4

Matrix no.:

#2

Matrix type:

sandy loam

% Clay:

19

% Silt:

19

% Sand:

62

% Org. carbon:

2

Matrix no.:

#3

Matrix type:

loam

% Clay:

19

% Silt:

36

% Sand:

45

% Org. carbon:

6

Details on matrix:

Matrix 1 was a 3:1 mixture of washed play sand and a topsoil obtained from a local (Golden, CO USA) nursery. Matrices 2 and were obtained from a commercial laboratory (Agvise Labs, Northwood, ND USA).

Details on test conditions:

Triplicate batch experiments were prepared for each soil. Aliquots of soil (1 g) were added to 50-ml polypropylene centrifuge tubes and spiked with 1g/L sodium azide and 10 µg/L of each of several perfluoroalkyl acid substance. Reclaimed wastewater (50 mL) was then added to each tube. Tubes were shaken for 14 days and then centrifuged to collect soil and aqueous phases. Both phases were analyzed.

Sample No.:

#1

Type:

Kd

Value:

1.04 L/kg

Matrix:

Topsoil amended with sand

% Org. carbon:

0.4

Remarks on result:

other: St. dev., 0.08 (n=3)

Remarks:

No further details on test conditions

Sample No.:

#1

Type:

log Koc

Value:

2.42 dimensionless

Matrix:

Topsoil amended with sand

% Org. carbon:

0.4

Remarks on result:

other: no further details on test conditions

Sample No.:

#2

Type:

Kd

Value:

1.42 L/kg

Matrix:

Sandy loam

% Org. carbon:

2

Remarks on result:

other: St. dev., 0.02 (n=3)

Remarks:

no further details on test conditions

Sample No.:

#2

Type:

log Koc

Value:

1.85 dimensionless

Matrix:

Sandy loam

% Org. carbon:

2

Remarks on result:

other: no further details on test conditions

Sample No.:

#3

Type:

Kd

Value:

1.88 L/kg

Matrix:

Loam

% Org. carbon:

6

Remarks on result:

other: St. Dev., 0.23 (n=3)

Remarks:

no further details on test conditions

Sample No.:

#3

Type:

log Koc

Value:

1.5 dimensionless

Matrix:

Loam

% Org. carbon:

6

Remarks on result:

other: no further details on test conditions

Adsorption and desorption constants:

The average log Koc over the three soils was 1.92

Validity criteria fulfilled:

not applicable

Conclusions:

The average log Koc over three soils was 1.92

Executive summary:

A batch soil sorption experiment was done ancillary to a plant bioconcentration study of PFBS. Three soils having organic carbon contents of 0.4%, 2%, and 6% were incubated for 14 days with a mixture perfluoroalkyl acid substances including PFBS. The study did not monitor concentration over time to establish equilibrium. Little information was provided on soil chemistry or conditions during sorption. The reliability of this study cannot be established.

Reference 3

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

Study report is unclear whether substance was tested as free acid or salt. As PFBS is a strong acid that will exist predominantly in ionic form in the environment, invertebrates would be exposed to PFBS- anions regardless of the original material (PFBS acid v. potassium salt v. another ionic material). Therefore, this study is relevant to the examination of bioaccumulation in terrestrial invertebrates

Qualifier:

no guideline followed

Principles of method if other than guideline:

Batch sorption experiment

GLP compliance:

no

Type of method:

batch equilibrium method

Media:

soil

Specific details on test material used for the study:

perfluorobutanesulfonate (PFBS) from Wellington Laboratories

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Batch Sorption Experiments: Five-point sorption isotherms were measured for a mixture perfluoroalkyl acid (PFAAs) including PFBS in three soils. The initial aqueous concentrations were 0.5, 5, 50, 500, and 1000 μg/L for each PFAAs. Triplicate batch reactors were prepared for each soil type and concentration in 50 mL polypropylene centrifuge tubes with 15 g of soil and 40 mL of AGW (artificial groundwater), spiked with 20 µl of PFAA mix spiking solution. The batch tubes were vortexed, and equilibrated on a shaker table for 10 days based on previous studies.

At the completion of the 10 day sorption experiments, the tubes were centrifuged at 2,700 rpm (1467 RCF) for 20 min. The aqueous phase was removed and diluted appropriately so that the aqueous sample concentration falls within the linear range of the calibration curve. The diluted aqueous samples were analyzed directly via LC−MS/MS.

The solid phase from all centrifuge tubes was extracted with 10 mL solvent mixture of 99:1 (v/v) methanol and ammonium hydroxide. The samples were vortexed and placed in a heated (30 °C) sonication bath for one hour. Each tube was subsequently removed and placed on a shaker table for two hours. The samples were then centrifuged at 2,700 rpm (1467 RCF) for 20 minutes and the extract was decanted into a clean, 20 mL glass scintillation vial. This procedure was repeated twice for a total of three extraction cycles. After each round of extraction, the extract was evaporated to dryness under nitrogen. The final extraction was reconstituted with 700 μL of 99:1 (v/v) methanol and acetic acid (acidic methanol). The reconstituted extract was transferred to a microcentrifuge tube containing 20-40 mg of ENVI-Carb (Supelco Inc., Bellefante, PA), vortexed by hand for thirty seconds, and centrifuged at 17,000 RCF for 30 minutes. An aliquot of the samples were diluted appropriately in an autosample vial, vortexed 30 seconds, prior to direct injection LC-MS /MS analysis. All final samples were 8.6% of a solution of 70/30 made with acidic methanol and dilution water, 1.4% of 70/30 containing 0.3 ng of surrogate solution, and 90%Milli-Q water.

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

9

% Silt:

1

% Sand:

81

% Org. carbon:

1.7

pH:

6.1

Bulk density (g/cm³):

1.14

Matrix no.:

#2

Matrix type:

loam

% Clay:

25

% Silt:

42

% Sand:

33

% Org. carbon:

4.5

pH:

7.8

Bulk density (g/cm³):

0.92

Matrix no.:

#3

Matrix type:

sandy clay loam

% Clay:

33

% Silt:

20

% Sand:

47

% Org. carbon:

0.8

pH:

5.2

Bulk density (g/cm³):

1.11

Details on test conditions:

TEST CONDITIONS:
Composition of artificial groundwater (AGW):
MnSO4∙H20: 1 (mg/L), 0.01(mM);
Na2SO4: 180 (mg/L), 1.27 (mM);
NaCl: 113 (mg/L), 1.93 (mM);
NaHCO3: 40 (mg/L), 0.48 (mM);
HCl: pH to 6.5

TEST SYSTEM
- Type, size and further details on reaction vessel: 50 mL polypropylene centrifuge tubes.
- Soil/sediment/sludge-water ratio (if simulation test):15g soil in 40 mL water, i.e 0.375 g/mL
- Number of reaction vessels/concentration: three

Key result

Type:

log Koc

Value:

1.79 dimensionless

Matrix:

soil

% Org. carbon:

>= 0.8 - <= 4.5

Remarks on result:

other:

Remarks:

pH and temperature not reported

Adsorption and desorption constants:

The Freundlich adsorption isotherm were expressed as:
Log Cs = Log Kf + n Log Cw
where Cs is the concentration in the soil, Cw is the concentration in the aqueous phase, Kf is the Freundlich sorption coefficient, and n describes isotherm linearity.

The PFBS adsorption isotherm for Loamy Sand (soil A) was: Log Cs = 0.81 log (Cw) - 0.64 (R^2 = 0.99);
The PFBS adsorption isotherm for Loam (soil B) was: Log Cs = 0.82 log (Cw) - 0.13 (R^2 = 1.00);
The PFBS adsorption isotherm for Sandy Clay Loam (soil C) was: Log Cs = 1.05 log (Cw) - 0.19 (R^2 = 1.00);

Transformation products:

not measured

Details on results (Batch equilibrium method):

Concentration-specific solid−water distribution coefficients (Kd values, L/kg) were calculated for PFBS and each soil at two aqueous concentrations. Interpolated values were calculated at a concentration of 5 nM (0.0015 mg/L) and at a concentration of 0.35 mg/L to represent differing trends at the upper end of the isotherm (Table 2).
For Loamy Sand soil, the Kd values were 0.80 L/Kg and 0.28 L/Kg for concentration 0.0015 mg/L and 0.35 mg/L;
For Loam soil, the Kd values were 2.35 L/Kg and 0.90 L/Kg for concentration 0.0015 mg/L and 0.35 mg/L;
For Sandy Clay Loam soil, the Kd values were 0.46 L/Kg and0.61 L/Kg for concentration 0.0015 mg/L and 0.35 mg/L.

Kd values at 5 nM were normalized to foc and averaged to obtain concentration-specific Koc (L/Kg oc) values. PFBS has an average log Koc of 1.79 (± 0.10) at concentration of 5 nM (0.0015 mg/L) for the three soil tested .

Table 1. Soil adsorption isotherm from Batch experiments (Guelfo 2013)

Soil type	Measured PFBS in aqueous phase (ug/L) (Min – Max)	Measured PFBS in solid phase (ug/kg) (Min – Max)	No. of obs.	Log Kf (mg/kg)  (mg/L) -n	n	R^2
Loamy sand (soil A)	2.61 – 1071.33	1.61 – 227.92	15	-0.64 (±0.07)	0.81 (±0.04)	0.99
Loam  (Soil B)	1.88 - 938	3.69 – 701.22	15	-0.13 (±0.05)	0.82 (±0.03)	1.00
Sandy Clay loam (Soil C)	0.56 – 1000.67	0.27 – 685.04	15	-0.19 (±0.03)	1.05 (±0.01)	1.00

 

Table 2. Interpolated Kd from the batch experiment (Guelfo 2013)

Soil type	Measured PFBS in aqueous phase, Cw,  (mg/L)	Measured PFBS in solid phase,  Cs, (mg/kg)	Kd (L/Kg)	Log Kd
Loamy sand (soil A)	0.0015	0.00119	0.80	-0.10
Loamy sand (soil A)	0.35	0.10	0.28	-0.55
Loam  (Soil B)	0.0015	0.00351	2.35	0.37
Loam  (Soil B)	0.35	0.31	0.90	-0.05
Sandy Clay loam (Soil C)	0.0015	0.00068	0.46	-0.34
Sandy Clay loam (Soil C)	0.35	0.21	0.61	-0.22

Validity criteria fulfilled:

yes

Conclusions:

PFBS has a concentration-specific average log Koc of 1.79 (± 0.10) at concentration of 5 nM (0.0015 mg/L) for the three soil tested with organic carbon range from 0.8 - 4.5%.

Executive summary:

A batch sorption experiment was performed for PFBS in three soils (Loamy Sand, Loam, Sandy Clay Loam, organic carbon range from 0.8 - 4.5%) at initial aqueous concentrations of 0.5, 5, 50, 500, and 1000 μg/L PFBS. Triplicate samples were prepared for each soil and concentration in 50 mL polypropylene centrifuge tubes with 15 g of soil and 40 mL of AGW (artificial groundwater). The samples were mixed and equilibrated on a shaker table for 10 days. At the end of the 10 day sorption period, the tubes were centrifuged. The aqueous phase was removed and diluted foranalysis PFBS concentration directly via LC/MS/MS. The solid phase from each sample was extracted three times with 10 mL solvent mixture of 99:1 (v/v) methanol and ammonium hydroxide. Each time the extract was evaporated to dryness under nitrogen. The final extraction was reconstituted, cleaned with ENVI-Carb, centrifuged, and an aliquot of the samples were diluted for analysis via LC/MS/MS.

The Freundlich adsorption isotherms for each soil had R^2 of ≥ 0.99. Concentration-specific solid−water distribution coefficients (Kd values, L/kg) were calculated for PFBS and each soil at two aqueous concentrations (0.0015 mg/L, 0.35 mg/L). Kd values at 0.0015 mg/L ranged from 0.46 to 2.35 (L/Kg) and were normalized to organic carbon and averaged to obtain concentration-specific Koc (L/Kg oc) values. PFBS has an average log Koc of 1.79 (± 0.10) at concentration of 0.0015 mg/L for the three soil tested.

This study was performed according generally accepted scientific principles and is well document. It is considered reliable with restriction, and a supporting study.

Description of key information

PFBS did not sorb to soils or sediment in a test done under OECD106. Results are directly applicable to PFBS-K salt.

Additional information

In the key study, the sorption of PFBS was determined in a tiered batch sorption study using three soils, a sediment, and a sludge sample. Because PFBS is a strong acid (Hammett acidity of -13.2) and will exist entirely in anionic form at pH values mandated by the test guideline, results for PFBS are equivalent to testing on the potassium salt. The adsorption constant (k) for the three soils and the sediment tested was determined to be 0. The estimated K value for sludge was 0.5 from the Tier 2 portion of the study. Given 100% organic matter content, a rough estimate for Koc of ca.1 may be derived from the Tier 2 sludge test. The Freundlich isotherm for sludge had Kf (ads) of 0.3 with 1/n of 1.2840 and a Kf(des) of 0.001 with 1/n of 2.6055. The Freundlich adsorption and desorption values were calculated only for the sludge since the soils and sediment demonstrated no adsorption. The low sorption of PFBS to all five matrices tested (three soils, sediment, and sludge) places PFBS in the very high mobility class (Koc = 0 - 50). In a supporting study, a batch sorption experiment was performed for PFBS in three soils (Loamy Sand, Loam, and Sandy Clay Loam. The organic carbon content ranged from 0.8 - 4.5%). At initial aqueous concentrations of 0.5, 5, 50, 500, and 1000 µg/L PFBS, the Freundlich adsorption isotherms for each soil had R² of ≥0.99. Concentration-specific solid−water distribution coefficients (Kd values, L/kg) were calculated for PFBS for each soil type at two aqueous concentrations (0.0015 mg/L, 0.35 mg/L). Kd values at 0.0015 mg/L ranged from 0.46 to 2.35 (L/Kg) and were normalized to organic carbon and averaged to obtain concentration-specific Koc (L/Kg) values. PFBS has an average log Koc of 1.79 (± 0.10) at concentration of 0.0015 mg/L for the three soils tested. In a third adsorption study, the average log Koc for three soils was 1.92. Owing to lack of information, the reliability of this result cannot be assessed.