Reaction mass of potassium trifluoroacetate and potassium trifluoromethanesulphinate

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 19 March 2012 to may 2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

GLP study, OECD 106 compliant but with deviations.

Qualifier:

according to guideline

Guideline:

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

Deviations:

yes

Remarks:

The pH of the aqueous phase before and after contact with soil has not been determined. The clay content of the tested soils has not been determined.

Qualifier:

according to guideline

Guideline:

EU Method C.18 (Adsorption / Desorption Using a Batch Equilibrium Method)

Deviations:

yes

Remarks:

The pH of the aqueous phase before and after contact with soil has not been determined. The clay content of the tested soils has not been determined.

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Samples with the same soil/solution ratio were prepared, as many as the time intervals at which it was desired to study the adsorption kinetics. In the preliminary study, samples were collected sequentially over a 48 h period of mixing (in the test at 4, 8, 24, 48 h). After centrifugation and filtration, the aqueous phase of the first tube was recovered as completely as possible and was measured after 4 h, that of the second tube after 8 h, that of the third after 24 h, etc.

Details on matrix:

COLLECTION AND STORAGE
- Geographic location: China
- Collection procedures: The soil samples were transported using containers and under temperature conditions which guarantee that the initial soil properties were not significantly altered.
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): The soils were air-dried at ambient temperature (20~25 °C). Disaggregating was performed with minimal force, so that the original texture of the soil would be changed as little as possible. The soils were sieved to a particle size ≤0.3 mm. Careful homogenization was recommended, as this enhances the reproducibility of the results. The moisture content of each soil was determined on three aliquots with heating at 105°C until there is no significant change in weight. For all calculations the mass of soil refers to oven dry mass, i.e. the weight of soil corrected for moisture content.

PROPERTIES
Soil Number Soil Types pH Organic Carbon (%) Texture
A Black Soil (Hei LongLongjiang)6.15 2.35 Silt Loam
B Red Soil (Jiangxi) 4.57 0.71 Clay loam
C Paddy Soil (Jiangsu) 6.58 3.20 Loam
D Red Soil/ Black Soil (1:1) 5.36 1.21 Clay loam/ Silt Loam
E Red Soil/ Paddy Soil (1:1) 5.58 1.64 Clay loam/ Loam

Details on test conditions:

Test 1: Preliminary test:
Two soil types (A and B) and three soil/solution ratios described as follows were adopted.
- 50 g soil and 50 mL aqueous solution of the test substance (ratio 1/1);
- 10 g soil and 50 mL aqueous solution of the test substance (ratio 1/5);
- 2 g soil and 50 mL aqueous solution of the test substance (ratio 1/25).

One control sample with only the test substance in 0.01 M CaCl2 solution (no soil) was subjected to precisely the same steps as the test systems, in order to check the stability of the test substance in CaCl2 solution and its possible adsorption on the surfaces of the test vessels.
A blank run per soil with the same amount of soil and total volume of 50 mL 0.01 M CaCl2 solutions (without test substance) were subjected to the same test procedure. This serves as a background control during the analysis to detect interfering compounds or contaminated soils.
All the experiments, including controls and blanks, were performed in duplicate.
The air-dried soil samples were equilibrated by shaking with a minimum volume of 49.7 mL of 0.01 mol/L CaCl2 overnight (12 h) before the day of the experiment. Afterwards, 0.300 mL of the stock solution (1046 mg/L) of the test substance was added, and the theoretical concentration for TFSK and TFAK is 195.602 and 174.682 mg/L, respectively. This volume of the stock solution added does not exceed 10% of the final 50 mL volume of the aqueous phase in order to change as little as possible the nature of the pre-equilibration solution
The mixture was shaken until adsorption equilibrium was reached. Parallel method was applied: Samples with the same soil/solution ratio were prepared, as many as the time intervals at which it was desired to study the adsorption kinetics. In the preliminary study, samples were collected sequentially over a 48 h period of mixing (in the test at 4, 8, 24, 48 h). After centrifugation and filtration, the aqueous phase of the first tube was recovered as completely as possible and was measured after 4 h, that of the second tube after 8 h, that of the third after 24 h, etc.
The percentage adsorption Ati was calculated at each time point (ti) on the basis of the nominal initial concentration and the measured concentration at the sampling time (ti), corrected for the value of the blank. Plots of the Ati versus time were generated in order to estimate the achievement of equilibrium plateau. The Kd value at equilibrium was also calculated. Based on this Kd value, appropriate soil/solution ratios were selected from OECD 106 Guideline, so that the percentage adsorption reached above 20% and preferably >50%.

Test 2: Adsorption Kinetics at One concentration of test substance:
Five soils were selected and used. There was an advantage to including some or all of the soils used in the preliminary study, if appropriate, among these five soils. In this case, Test 2 had not been repeated for the soils used in preliminary study.
The equilibration time (48h), the soil/solution ratio (1:1), the weight of the soil sample (10g), the volume of the aqueous phase in contact with the soil (10mL) and the concentration of the test substance in the solution (1mg/L) were chosen based on the preliminary study results. Analysis was performed approximately after 2, 4, 8, 24 and 48 h contact time.
Each experiment (one soil and one solution) was done at least in duplicate to allow estimation of the variance of the results. In every experiment one blank was run. It consisted of the soil and 0.01 mol/L CaCl2 solution, without test substance, and of weight and volume, respectively, identical to those of the experiment. A control sample with only the test substance in 0.01 mol/L CaCl2 solution (without soil) was subjected to the same test procedure, serving to safeguard against the unexpected.
The percentage adsorption was calculated at each time point Ati and was plotted versus time. The distribution coefficient Kd and Koc at equilibrium was calculated.
The linear Kd value was generally accurate to describe sorption behaviour in soil and represents an expression of inherent mobility of chemicals in soil.
When the soil/solution ratio is 1:1, the adsorption percentages of the test substance in all five soils were more than 25% in the preliminary study. Therefore, the desorption part in soil of the test was conducted.

Test 3: Desorption kinetics:
For five soil which is chosen to proceed with the desorption study, samples with the same soil/solution ratio as in the adsorption kinetics experiment are prepared. In every experiment (one soil, one solution) one blank is run. It consists of the soil and 0.01 M CaCl2 solution, without test substance, and of weight and volume, respectively, identical to those of the experiment. As a control sample the test substance in 0.01 M CaCl2 solution (without soil) is subjected to the same test procedure. All the mixtures of the soil with the solution is agitating until to reach adsorption equilibrium (as determined before in Tier 2). Then, the phases are separated by centrifugation and the aqueous phases are removed as much as possible. The volume of solution removed is replaced by an equal volume of 0.01 M CaCl2 without test substance and the new mixtures are agitated again. The aqueous phase is recovered as completely as possible and is measured after 2h, 4h, 8h, 24h and 48h.

Test 4: Adsorption isotherms:
Five concentrations for TFAK (0.4, 0.6, 0.8, 1.0 and 1.2 mg/L) and TFSK (0.2, 0.3, 0.4, 0.5 and 0.6 mg/L) were used. The same soil/solution ratio per soil was kept along the study. The adsorption test was performed as described above, with the only difference that the aqueous phase was analyzed only once at the time necessary to reach equilibrium (48 h) as determined before in Test 2. The equilibrium concentrations in the solution were determined and the amount adsorbed was calculated from the depletion of the test substance in the solution. The adsorbed mass per unit mass of soil was plotted as a function of the equilibrium concentration of the test substance.

Test 5: Desorption isotherms:
Five test substance concentrations were used. The same soil/solution ratio per soil was kept along the study. The desorption test is performed as described in the section “Desorption kinetics”, with the only difference that the aqueous phase is analyzed only once at desorption equilibrium. The amount of the test substance desorbed is calculated.

Computational methods:

- Adsorption: The adsorption Ati was defined as the percentage of substance adsorbed on the soil related to the quantity present at the beginning of the test, under the test conditions. If the test substance was stable and did not adsorb significantly to the container wall, Ati was calculated at each time point ti.
- Adsorption coefficients (Kd): The distribution coefficient Kd was the ratio between the content of the substance in the soil phase and the mass concentration of the substance in the aqueous solution, under the test conditions, when adsorption equilibrium was reached.
- Adsorption coefficient per organic carbon (Koc): The organic carbon normalized adsorption coefficient Koc relates the distribution coefficient Kd to the content of organic carbon of the soil sample.
- Freundlich adsorption coefficients: The Freundlich adsorption isotherms equation related the amount of the test substance adsorbed to the concentration of the test substance in solution at equilibrium.
The data were treated as under "Adsorption" and, for each test tube, the content of the test substance adsorbed on the soil after the adsorption test ( ), elsewhere denoted as x/m) was calculated.
- Desorption: The desorption is defined as the percentage of the test substance which is desorbed, related to the quantity of substance previously adsorbed.
- Freundlich desorption coefficients: The Freundlich desorption isotherms equation relates the content of the test substance remaining adsorbed on the soil to the concentration of the test substance in solution at desorption equilibrium.

Key result

Type:

Kd

Remarks:

TFAK

Value:

>= 0.44 - <= 2.2 other: cm3 g-1

% Org. carbon:

>= 0.71 - <= 3.2

Key result

Type:

Kd

Remarks:

TFSK

Value:

>= 0.316 - <= 0.715 other: cm3 g-1

% Org. carbon:

>= 0.71 - <= 3.2

Key result

Type:

Koc

Remarks:

TFAK

Value:

>= 18.7 - <= 309 other: cm3 g-1

% Org. carbon:

>= 0.71 - <= 3.2

Key result

Type:

Koc

Remarks:

TFSK

Value:

>= 13.5 - <= 67.5 other: cm3 g-1

% Org. carbon:

>= 0.71 - <= 3.2

Details on results (HPLC method):

Not applicable.

Adsorption and desorption constants:

The highest Kd value obtained was 2.195 cm3/g for TFAK with soil B, which corresponds to a koc value of 309 cm3/g. All other Kd values, for both TFAK and TFSK, were in the range of 0.316 and 1.027, corresponding to Koc values between 13.45 and 62.598.

Recovery of test material:

From the data, a depletion more than the standard error of the analytical method of control samples was not observed, so it was stated that the test substance was stable in the test period and hadn’t adsorbed to the surface of test vessels. Mass balance has not been defined as the depletion of the test item for the blank sample were relative low, so it was considered that the test item distributed in the water and soil under the water/soil system

Concentration of test substance at end of adsorption equilibration period:

Adsorption Kinetics at One Concentration of the Test Substance
Test 1: the Kd value of TFAK in A soil is 0.440 cm3.g-1 and that in B soil is 2.195 cm3.g-1. The Koc value in A soil is 18.729 cm3 g-1 and that in red soil is 309.184 cm3.g-1. The Kd value of TFSK in A soil is 0.316 cm3.g-1 and that in B soil is 0.479 cm3.g-1. The Koc value in A soil is 13.450 cm3 g-1 and that in red soil is 67.519 cm3.g-1
Test2: the Kd values of TFAK in three soil types were 0.953, 0.992 and 1.027 cm3.g-1, respectively. The Koc values in the three soil types were 29.776, 81.998 and 62.598 cm3.g-1. The Kd values of TFSK in three soil types were 0.559, 0.601 and 0.715 cm3.g-1, respectively. The Koc values in the three soil types were 17.466, 49.707 and 43.600 cm3.g-1.

Adsorption Isotherms
Test 4: The results showed that the Freundlich adsorption coefficient values in the five soils (A, B, C, D and E) are 0.111, 0.188, 0.213, 0.151 and 0.137 μg -1/n (cm3)1/n g-1 respectively, the n values for the five soils are 0.319, 0.511, 0.675, 0.603 and 0.617. The adsorption isotherms for TFAK on four soils (B, C, D and E) followed the Freundlich adsorption isotherms equation, because the correlative coefficients are higher than 0.9. For TFSK, the Freundlich adsorption coefficient values in the five soils (A, B, C, D and E) are 0.068, 0.103, 0.116, 0.081 and 0.086 μg -1/n (cm3)1/n g-1 respectively, the n values for the five soils are 0.287, 0.428, 0.475, 0.405 and 0.429. The adsorption isotherms on three soils (B, C and E) followed the Freundlich isotherms adsorption equation, because the correlative coefficients are higher than 0.9.

Concentration of test substance at end of desorption equilibration period:

Desorption Kinetics
Test 3: The desorption coefficient (Kdes) values of TFAK in A, B, C, D, E soil are 3.733, 3.226, 2.744, 3.682 and 3.056 cm3.g-1, respectively, and the Kdes values of TFSK are 1.358, 1.909, 2.505, 1.874 and 2.410 cm3.g-1 in above soils respectively; in addition, the max percentage of desorption (Dti) of TFAK and TFSK is 27.3% and 43.3% in above soils respectively, and the total desorption is less than 75% of the amount adsorbed. Therefore, the adsorption of the test substance on five soils has a low reversibility.

Test 5: Desorption Isotherms
The results of desorption isotherms show that the Freundlich desorption coefficient values in the five soils (A, B, C, D and E) are 0.092, 0.115, 0.162, 0.111 and 0.117 μg -1/n (cm3)1/n g-1 respectively, the n values for the five soils are 0.190, 0.274, 0.282, 0.233 and 0.244 respectively. The desorption isotherms for TFAK, on four soils (B, C, D and E) followed the Freundlich desorption isotherms equation, because the correlative coefficients are higher than 0.9. For TFSK, the Freundlich desorption coefficient values in the five soils (A, B, C, D and E) are 0.078, 0.082, 0.116, 0.071 and 0.080 μg -1/n (cm3)1/n g-1 respectively, the n values for the five soils are 0.126, 0.279, 0.178, 0.145 and 0.141 respectively. The desorption isotherms on three soils (C, D and E) followed the Freundlich desorption isotherms equation, because correlative coefficients are higher than 0.9.

Details on results (Batch equilibrium method):

The results show that optimal soil/aqueous ratio is 1:1, the appropriate adsorption equilibrium time is 48 h because the percentage adsorption reached was above 20% in soil A and above 50% in soil B.

Recovery of the substance in the test medium:

TFAK-Nominal Concentration (mg/L)	Measured Concentration (mg/L)	Recovery Rate (%)	Mean Recovery rate (%)	RSD (%)
0.05	0.0459	91.8	96.9	4.69
	0.0493	98.6
	0.0502	100.4
1.00	0.930	93.0	97.8	4.41
	0.989	98.9
	1.01	101.4

TFSK-Nominal Concentration (mg/L)	Measured Concentration (mg/L)	Recovery Rate (%)	Mean Recovery rate (%)	RSD (%)
0.05	0.0443	88.6	89.9	3.22
	0.0466	93.2
	0.0439	87.8
1.00	0.941	94.1	90.3	3.93
	9.98	99.8
	10.0	100.0

Test concentration of Blank Samples (no soil)

Time(h)	0	4	8	24	48
Con.(mgL^-1)/TFAK	1.05	0.93	0.92	0.92	0.92
Con.(mgL^-1)/TFSK	0.53	0.50	0.44	0.44	0.42

Adsorption data of the preliminary test:

Time(h)	TFAK-Ati(%)
	A Soil			B Soil
	ratio* 1/25	ratio 1/5	ratio 1/1	ratio 1/25	ratio 1/5	ratio 1/1
4	10.3	9.35	5.51	11.3	21.2	60.5
8	10.5	12.4	7.57	13.8	22.1	61.3
24	11.2	13.2	10.6	13.8	24.0	64.6
48	25.0	19.1	29.8	34.1	30.0	68.2
Kd (cm^3g^-1)	0.440			2.195
Koc(cm^3g^-1)	18.729			309.184
Time(h)	TFSK-Ati(%)
	A Soil			B Soil
	ratio 1/25	ratio 1/5	ratio 1/1	ratio 1/25	ratio 1/5	ratio 1/1
4	18.6	18.7	12.7	89.9	89.8	95.0
8	20.3	18.9	15.1	88.7	91.1	94.7
24	20.3	20.4	15.5	88.3	91.2	95.8
48	20.4	23.2	23.3	89.0	93.4	96.4
Kd (cm^3g^-1)	0.316			0.479
Koc(cm^3g^-1)	13.450			67.519

Results for Adsorption kinetics:

Time(h)	TFAK-Ati(%)
	C	D	E
2	57.5	46.8	49.6
4	48.3	46.8	45.8
8	52.5	49.0	46.8
24	50.4	45.9	46.1
48	48.0	48.9	50.0
Kd(cm^3g^-1)	0.953	0.992	1.027
Koc(cm^3g^-1)	29.776	81.998	62.598
Time(h)	TFSK-Ati(%)
	C	D	E
2	45.8	27.4	39.6
4	28.7	31.8	39.2
8	33.5	34.2	43.6
24	28.0	28.0	41.2
48	35.1	36.8	41.0
Kd(cm^3g^-1)	0.559	0.601	0.715
Koc(cm^3g^-1)	17.466	49.707	43.600

Results for Desorption kinetics:

Time(h)	TFAK-Dti(%)
	A	B	C	D	E
2	23.3	19.3	27.4	24.9	23.6
4	28.1	21.7	23.4	19.0	23.3
8	21.5	23.1	24.2	20.7	26.3
24	19.7	26.2	27.3	21.9	24.8
48	21.8	24.1	27.3	21.9	25.2
Kd(cm^3g^-1)	3.733	3.226	2.744	3.682	3.056
Time(h)	TFSK-Dti(%)
	A	B	C	D	E
2	23.0	30.0	36.3	37.4	29.0
4	47.0	30.9	32.7	29.8	34.9
8	42.8	33.4	37.6	35.5	30.5
24	37.7	34.0	27.9	32.2	24.8
48	43.3	34.9	29.2	35.6	29.9
Kd(cm^3g^-1)	1.358	1.909	2.505	1.874	2.410

Validity criteria fulfilled:

yes

Conclusions:

In the adsorption kinetics experiment performed on the five soils, the highest Kd value obtained was 2.195 cm3/g for TFAK with soil B, which corresponds to a koc value of 309 cm3/g. All other Kd values, for both TFAK and TFSK, were in the range of 0.316 and 1.027, corresponding to Koc values between 13.45 and 62.598. All these results show that TFAK and TFSK have a low adsorption onto the soils tested, and are not completely desorbed.

Executive summary:

In this study (2013), Adsorption / Desorption of the test substance Reaction mass of potassium trifluoromethanesulphinate (TFSK) and potassium trifluoroacetate (TFAK) was conducted using a batch equilibrium method, under GLP conditions and following the OECD 106 guideline.

As the test substance is a reaction mass containing two constituents in water, the adsorption-desorption potential of each constituent, i.e. potassium trifluoroacetate (TFAK) and potassium trifluoromethanesulphinate (TFSK), was determined.

Five type soils with different pH, texture, and organic carbon contents sampling from Hei Longjiang, Jiangxi, Jiangsu provinces of china were selected. Batch equilibrium method was adopted, and Tier 1, Tier 2, and Tier 3 tests were performed to determine the adsorption characteristics of TFAK and TFSK in this study.

The results show that optimal soil/aqueous ratio is 1:1 and the appropriate adsorption equilibrium time is 48 h. The adsorption coefficient (Kd) values of TFAK in the fives soils were 0.440, 2.195, 0.953, 0.992 and 1.027 cm3.g-1, respectively, and the Koc values of TFAK were 18.729, 309.184, 29.776, 81.998 and 62.598 cm3.g-1 in the above soils respectively. The adsorption coefficient (Kd) values of TFSK in the five soils were 0.316, 0.479, 0.559, 0.601 and 0.715 cm3.g-1, respectively, and the Koc values of TFSK were 13.450, 67.519, 17.466, 49.707 and 43.600 cm3.g-1 in above soils respectively. These results show that TFAK and TFSK have a low adsorption onto the soils tested.

The results of desorption kinetics show that the desorption coefficient (Kdes) values of TFAK in the five soils were 3.733, 3.226, 2.744, 3.682 and3.g-1, respectively, and the Kdes values of TFSK were 1.358, 1.909, 2.505, 1.874 and3.gabove soils respectively; in addition, the max percentage of desorption (Dti) of TFAK and TFSK is 27.3% and 43.3% in above soils respectively, and the total desorption is less than 75% of the amount adsorbed. Therefore, the adsorption of the test substance on five soils has a low reversibility.

Adsorption isotherms and desorption isotherms experiments were also performed.

Description of key information

The koc range values obtained in experimental study were the following:
TFAK: 18.729-309.184 (corresponding log koc: 1.27 – 2.49)
TFSK: 13.45 – 67.519 (corresponding log koc: 1.13 – 1.83)

Key value for chemical safety assessment

Koc at 20 °C:

13.45

Additional information

A reliable study on the Adsorption / Desorption of the test substance Reaction mass of potassium trifluoromethanesulphinate (TFSK) and potassium trifluoroacetate (TFAK) is available. It has been conducted using a batch equilibrium method, under GLP conditions and following the OECD 106 guideline. As the test substance is a reaction mass containing two constituents in water, the adsorption-desorption potential of each constituent, i.e. potassium trifluoroacetate (TFAK) and potassium trifluoromethanesulphinate (TFSK), was determined.

Five type soils with different pH, texture, and organic carbon contents sampling from Hei Longjiang, Jiangxi, Jiangsu provinces of china were selected. Batch equilibrium method was adopted, and Tier 1, Tier 2, and Tier 3 tests were performed to determine the adsorption characteristics of TFAK and TFSK in this study.

The results show that optimal soil/aqueous ratio is 1:1 and the appropriate adsorption equilibrium time is 48 h. The adsorption coefficient (Kd) values of TFAK in the fives soils were 0.440, 2.195, 0.953, 0.992 and 1.027 cm3.g-1, respectively, and the Koc values of TFAK were 18.729, 309.184, 29.776, 81.998 and 62.598 cm3.g-1 in the above soils respectively. The adsorption coefficient (Kd) values of TFSK in the five soils were 0.316, 0.479, 0.559, 0.601 and 0.715 cm3.g-1, respectively, and the Koc values of TFSK were 13.450, 67.519, 17.466, 49.707 and 43.600 cm3.g-1 in above soils respectively. These results show that TFAK and TFSK have a low adsorption onto the soils tested.

The results of desorption kinetics show that the desorption coefficient (Kdes) values of TFAK in the five soils were 3.733, 3.226, 2.744, 3.682 and 3.056 cm3.g-1, respectively, and the Kdes values of TFSK were 1.358, 1.909, 2.505, 1.874 and 2.410 cm3.g-1 in above soils respectively; in addition, the max percentage of desorption (Dti) of TFAK and TFSK is 27.3% and 43.3% in above soils respectively, and the total desorption is less than 75% of the amount adsorbed. Therefore, the adsorption of the test substance on five soils has a low reversibility.

Adsorption isotherms and desorption isotherms experiments were also performed.