2,2-Difluoroethyl Acetate

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption, other

Remarks:

Study performed according to OECD TG 106 (batch equilibrium method) with the use of a range of actual soils which thus represents a more realistic scenario than the OECD TG 121 (HPLC method) study also available (see the supporting study).

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 11 january 2016 to 30 may 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2000

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

20°C - 25°C

Analytical monitoring:

yes

Details on sampling:

Sampling details were not the same in the different tests performed in the context of this study and are detailed below in the field "Details on test conditions".

Matrix no.:

#1

Matrix type:

loam

% Org. carbon:

6.54

pH:

7.28

CEC:

28.87 other: cmol/kg

Matrix no.:

#2

Matrix type:

silt loam

% Org. carbon:

1.36

pH:

4.6

CEC:

11.53 other: cmol/kg

Matrix no.:

#3

Matrix type:

silty clay loam

% Org. carbon:

5.36

pH:

6.81

CEC:

22.9 other: cmol/kg

Matrix no.:

#4

Matrix type:

silt loam

% Org. carbon:

1.39

pH:

7.84

CEC:

7.08 other: cmol/kg

Matrix no.:

#5

Matrix type:

silt loam

% Org. carbon:

6.85

pH:

7.96

CEC:

22.13 other: cmol/kg

Details on matrix:

COLLECTION AND STORAGE
- Geographic location:
1=A Jilin (Black soil) 125.73°/42.28°
2=B Jiangxi (Red soil) 117.01°/28.23°
3=C Jiangsu (Paddy soil) 120.30°/31.60°
4=D Shandong (Yellow soil) 116.06°/34.81°
5=E Gansu (Meadow soil) 100.40°/38.90°
- Collection procedures and sampling depth (cm): The top soils of depth of 10 cm to 15 cm were collected, and these soils were not polluted by fertilisers, pesticides and other chemicals.
- Storage conditions: The soil samples were transported using containers and under temperature conditions which guarantee that the initial soil properties were not significantly altered.
- Storage length: no data available.
- Soil preparation: The soils were air-dried at ambient temperature (20°C - 25°C). The soils were sieved to a particle size of 0.3 mm. 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
See table 1 below.

Details on test conditions:

TEST 1: PRELIMINARY STUDY
Three aspects were investigated in the preliminary study:
(1) Selection of optimal soil/solution ratios:
The five soil types and three soil to solution ratios were tested:
Ratio 1/1: 50 g soil /50 mL aqueous solution of test substance.
Ratio 1/5: 10 g soil /50 mL aqueous solution of test substance.
Ratio 1/50: 1 g soil /50 mL aqueous solution of test substance.
One control sample with only the test substance in 0.01 mol/L CaCl2 solution (no soil) was subjected to precisely the same steps as the test system, in order to check the stability of the test substance in CaCl2 solution and its possible adsorption on the surface of the test vessels.
A blank run per soil with the same amount of soil and total volume of 50 mL 0.01 mol/L CaCl2 solutions (without test substance) was subjected to the same test procedure. This served as a background control during the analysis to detect interfering compounds or contaminated soils.
All the experiments, including control and blank, were performed in duplicate.
The air-dried soil samples were equilibrated by shaking with a minimum volume of 50 mL of 0.01 mol/L CaCl2 overnight (12h) before the day of the experiment. Afterwards, 1 mL of the stock solution (10000 mg/L) of the test substance was added.
The mixtures were shaken until adsorption equilibrium was reached. The analysis of the test substance in the aqueous solution was performed according to the parallel method: 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 this test, the samples were collected sequentially over a 36h period of mixing (at 2, 4, 6, 10, 18, 24, 36h). After centrifugation and filtration, the aqueous phase of the first tube was recovered as completely as possible and was measured after 2h, that of the second tube after 4h, that of the third tube after 6h, etc.
The percentage of adsorption At was calculated at each time point on the basis of the nominal initial concentration and the measured concentration at the sampling time, corrected for the value of the blank. The appropriate soil/solution ratio allowing reaching a percentage of adsorption above 50% was selected from this preliminary study.
(2) Determination of adsorption equilibration time and of the amount of test substance adsorbed at equilibrium:
Plots of At versus time permit estimation of the achievement of the adsorption equilibrium and the amount of test substance adsorbed at equilibrium. Equilibration time was the time the system needed to reach a plateau.
(3) Adsorption on the surface of the test vessel and stability of the test substance:
Such information was derived by analyzing the control samples.

TEST 2: ADSORPTION KINETICS AT ONE CONCENTRATION OF THE TEST SUBSTANCE
The adsorption was studied in five different soil types by means of adsorption kinetics at a single concentration and the distribution coefficients Kd and Koc were determined.
The equilibration time (24 h), the soil solution ratio (1:50 for A, C, E soils and 1:5 for B, D soils), the weight of the soil sample (1 g for A, C, E soils and 10 g for B, D soils), the volume of the aqueous phase in contact with the soil (50 mL) and the concentration of the test substance in the solution (100 mg/L) were chosen based on the preliminary study results.
The percentage of adsorption was calculated at each time point At. The distribution coefficients Kd and Koc at equilibrium were calculated.

TEST 3: DESORPTION KINETICS
Because the adsorption percentages of the test substance in soils were more than 25% in the preliminary study, a desorption experiment was conducted. The desorption was studied in the five different soil types by means of desorption kinetics at a single concentration and the desorption coefficients Kdes were determined.
For the five soils, samples with the same soil/solution ratio as in the adsorption kinetics experiment were prepared. In every experiment (one soil, one solution), one blank was run. It consisted of the soil and 0.01 mol/L CaCl2 solution, without test substance and of weight and volume identical to those of the experiment. As a control sample, the test substance in 0.01 mol/L CaCl2 solution (without soil) was subjected to the same test procedure.
All the mixtures of the soil with the solution were agitated until reaching the adsorption equilibrium (as determined before in test 2). Then, the phases were separated by centrifugation and the 48 mL aqueous phases were removed. The volume of solution removed was replaced by an equal volume of 0.01 mol/L CaCl2 without test substance and the new mixtures were agitated again. The aqueous phase was recovered as completely as possible and was measured alter 2 h, 4h, 6h, 10h, 18h, 24h and 48h.
The percentage desorption Dt was calculated at each time point and plotted versus time. The desorption coefficient Kdes at equilibrium was also calculated.

TEST 4: ADSORPTION ISOTHERMS
The Freundlich adsorption isotherms were determined to assess the influence of concentration on the extent of adsorption on soils.
Five test substance concentrations (A, C, E soils: 50, 100, 200, 400 and 500 mg/L; B and D soils: 10, 20, 50, 100 and 200 mg/L) were used to conduct adsorption isotherms for all five soils. 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 (24 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 of mass of soil was plotted as a function of the equilibrium concentration of the test substance.

TEST 5: DESORPTION ISOTHERMS
The Freundlich desorption isotherms were also determined to assess the influence of concentration on the extent of desorption on soils.
Five test substance concentrations (same as for adsorption isotherms) were used to conduct desorption isotherms for B soil. The same soil/solution ratio per soil was kept along the study (i.e. 1:25). The desorption test is performed as the "Desorption kinetics" test 3, with the only difference that the aqueous phase was analysed only once, at desorption equilibrium. The amount of the test substance desorbed was calculated. The content of test substance remaining adsorbed on soil at desorption equilibrium was plotted as a function of the equilibrium concentration of the test susbtance in solution.

TEST 6: MASS BALANCE
The mass balance (MB) was calculated at the end of the adsorption test as being the percentage of test substance that can be analytically recovered versus the nominal amount of test substance at the beginning of the test.

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

100 other: mg/l

Remarks:

Sample 1= A. The initial conc. measured is not detailed. The soil/solution ratio is 1:50. The weight of soil sample is 1g. The volume of aqueous phase in contact with soil is 50 mL and the concentration of the test substance in solution is 100 mg/L.

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

100 other: mg/l

Remarks:

Sample 2= B. The initial conc. measured is not detailed. The soil/solution ratio is 1:5. The weight of soil sample is 10g. The volume of aqueous phase in contact with soil is 50 mL and the concentration of the test substance in solution is 100 mg/L.

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

100 other: mg/l

Remarks:

Sample 3= C. The initial conc. measured is not detailed. The soil/solution ratio is 1:50. The weight of soil sample is 1g. The volume of aqueous phase in contact with soil is 50 mL and the concentration of the test substance in solution is 100 mg/L.

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

100 other: mg/l

Remarks:

Sample 4=D. The initial conc. measured is not detailed. The soil/solution ratio is 1:5. The weight of soil sample is 10g. The volume of aqueous phase in contact with soil is 50 mL and the concentration of the test substance in solution is 100 mg/L.

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

100 other: mg/l

Remarks:

Sample 5= E. The initial conc. measured is not detailed. The soil/solution ratio is 1:50. The weight of soil sample is 1g. The volume of aqueous phase in contact with soil is 50 mL and the concentration of the test substance in solution is 100 mg/L.

Sample no.:

#1

Duration:

48 h

Conc. of adsorbed test mat.:

100 other: mg/L

Remarks:

Sample 1= A. The initial conc. measured is not detailed. Similar as adsorption experiment + separation of phases by centrifugation. Then aqueous phases are replaced by equal volume of 0.01 mol/L CaCl2 without DFEA.

Sample no.:

#1

Duration:

48 h

Conc. of adsorbed test mat.:

100 other: mg/L

Remarks:

Sample 2 = B. The initial conc. measured is not detailed. Similar as adsorption experiment + separation of phases by centrifugation. Then aqueous phases are replaced by equal volume of 0.01 mol/L CaCl2 without DFEA.

Sample no.:

#1

Duration:

48 h

Conc. of adsorbed test mat.:

100 other: mg/L

Remarks:

Sample 3 = C. The initial conc. measured is not detailed. Similar as adsorption experiment + separation of phases by centrifugation. Then aqueous phases are replaced by equal volume of 0.01 mol/L CaCl2 without DFEA.

Sample no.:

#1

Duration:

48 h

Conc. of adsorbed test mat.:

100 other: mg/L

Remarks:

Sample 4 = D. The initial conc. measured is not detailed. Similar as adsorption experiment + separation of phases by centrifugation. Then aqueous phases are replaced by equal volume of 0.01 mol/L CaCl2 without DFEA.

Sample no.:

#1

Duration:

48 h

Conc. of adsorbed test mat.:

100 other: mg/L

Remarks:

Sample 5 = E. The initial conc. measured is not detailed. Similar as adsorption experiment + separation of phases by centrifugation. Then aqueous phases are replaced by equal volume of 0.01 mol/L CaCl2 without DFEA.

Computational methods:

Adsorption percentage at the different time points (At), distribution coefficient (Kd), organic carbon normalized adsorption coefficient (Koc), Freundlich adsorption isotherms equation and Freundlich adsorption coefficient (Kads,F), desorption percentage at the different time points (Dt), desorption coefficient (Kdes), Freundlich desorption isotherms equation and Freundlich desorption coefficient (Kdes,F) and mass balance (MB) were calculated as recommended in the OECD 106 guideline.

Key result

Sample No.:

#1

Type:

Kd

Value:

45.3 other: cm3/g

Matrix:

Soil / Loam

% Org. carbon:

6.54

Remarks on result:

other: Corresponding to a Koc value of 692 cm3/g (Log Koc = 2.84)

Key result

Sample No.:

#2

Type:

Kd

Value:

7.6 other: cm3/g

Matrix:

Soil / Silt loam

% Org. carbon:

1.36

Remarks on result:

other: Corresponding to a Koc value of 560 cm3/g (Log Koc = 2.75)

Key result

Sample No.:

#3

Type:

Kd

Value:

57.4 other: cm3/g

Matrix:

Soil / Silt clay loam

% Org. carbon:

5.36

Remarks on result:

other: Corresponding to a Koc value of 1070 cm3/g (Log Koc = 3.03)

Key result

Sample No.:

#4

Type:

Kd

Value:

8.7 other: cm3/g

Matrix:

soil / silt loam

% Org. carbon:

1.39

Remarks on result:

other: Corresponding to a Koc value of 628 cm3/g (Log Koc = 2.80)

Key result

Sample No.:

#5

Type:

Kd

Value:

127 other: cm3/g

Matrix:

soil / silt loam

% Org. carbon:

6.85

Remarks on result:

other: Corresponding to a Koc value of 1857 cm3/g (Log Koc = 3.27)

Sample no.:

#1

Duration:

24 h

% Adsorption:

76.2

Sample no.:

#2

Duration:

24 h

% Adsorption:

85.8

Sample no.:

#3

Duration:

24 h

% Adsorption:

81.7

Sample no.:

#4

Duration:

24 h

% Adsorption:

83.9

Sample no.:

#5

Duration:

24 h

% Adsorption:

88.6

Transformation products:

not measured

TEST 1 - PRELIMINARY STUDY

The data obtained from preliminary test were shown in Table 2.

The results showed the concentration of test substance almost reached equilibration at 24 hours in all soils, so the equilibration time of 24h was selected for the further tests.

At this time, the adsorption percentage were greated than 50% in A, C, E soils (soil/solution ration 1:50) and B, D soils (soil/solution ration 1:5).

During the appropriate adsorption equilibrium time of 24h, the test substance was almost stable in the 0.01 mol/L CaCl2 solution. This means that there was no adsorption of the test substance on the surface of the test vessels.

The test substance was not detected in the blank control consisting of soil and 0.01 mol/L CaCl2 solutions, suggesting that the soils were not contaminated and can be used for the further tests.

 

Table 2: Adsorption percentages (At) during preliminary test

Time (h)	Soil A=1			Soil B=2			Soil C=3			Soil D=4			Soil E=5
	1/50	1/5	1/1	1/50	1/5	1/1	1/50	1/5	1/1	1/50	1/5	1/1	1/50	1/5	1/1
2	7.7	33.6	55.8	0	16.7	16.7	12.4	45.3	62.3	0	9.8	17.7	10.7	45.1	76.4
4	11.3	65.9	100	0	20.5	40.5	17.5	78.9	89.1	4.85	14.7	32.2	30.3	77.7	100
6	16.0	74.6	100	5.41	33.2	53.2	25.2	92.1	100	8.01	24.1	50.3	41.4	89.3	100
10	23.2	82.3	100	6.74	50.2	70.2	38.5	96.6	100	8.76	45.4	61.4	54.8	100	100
18	54.8	95.1	100	9.32	63.5	83.5	58.1	100	100	10.4	64.8	86.9	72.7	100	100
24	60.0	96.2	100	10.5	66.0	96.0	62.0	98.7	100	12.8	69.4	94.4	75.0	100	100
36	61.4	96.0	100	10.2	62.5	97.6	64.7	100	100	14.5	70.5	93.8	74.8	100	100

 

TEST 2 - ADSORPTION KINETICS AT ONE CONCENTRATION OF THE TEST SUBSTANCE

The adsorption kinetics data were shown in Table 3.

The Kd values in the five soil types calculated according to the determined concentration of test substance in soil were 45.3, 7.6, 57.4, 8.7 and 127 cm³/g respectively. The corresponding Koc values were 692, 560, 1070, 628 and 1857 cm³/g; giving a mean Koc value of 961 cm³/g. The corresponding Log Koc values were 2.84, 2.75, 3.03, 2.80 and 3.27; giving a mean Log Koc value of 2.98.

 

Table 3: Results for adsorption kinetics

Time (h)	At (%)
	Soil A = 1	Soil B = 2	Soil C = 3	Soil D = 4	Soil E = 5
2	7.70	16.7	12.4	9.80	10.7
4	11.3	20.5	17.5	14.7	30.3
6	16.0	33.2	25.2	24.1	41.4
10	23.2	50.2	38.5	45.4	54.8
18	54.8	63.5	58.1	64.8	72.7
24	60.0	66.0	62.0	69.4	75.0
Kd (cm^3/g)	45.3	7.6	57.4	8.7	127
Koc (cm^3/g)	692	560	1070	628	1857

At: adsorption percentage at the time point t (%)

Kd: distribution coefficient

Koc: organic carbon normalized adsorption coefficient

 

TEST 3 - DESORPTION KINETICS

During the desorption period of 48h, the test substance was not detected in the supernatant of A, B, C, D and E soils.

 

TEST 4 - ADSORPTION ISOTHERMS

The adsorption isotherms data and calculated results were shown in Table 4 and Table 5.

The test substance adsorption isotherms on the five soils preferably followed Freundlich adsorption equation; correlative coefficients being all superior to 0.9. The Freundlich adsorption coefficient (Kads,F) values in the five soils were 227, 22.6, 325, 20.8 and 337 µg ^1-1/n (cm³)^1/n g^-1 respectively. The 1/n values for soils A, B, C, D, E were 0.7216, 0.7329, 0.7288, 0.8794, 0.7760, respectively.

 

Table 4: Adsorption isotherms data

C0 (mg/L)	Soil A = 1		Soil B = 2		Soil C = 3		Soil D = 4		Soil E = 5
	Cs (eq)	Caq (eq)	Cs (eq)	Caq (eq)	Cs (eq)	Caq (eq)	Cs (eq)	Caq (eq)	Cs (eq)	Caq (eq)
1	1755	15.6	39.6	2.24	2042	9.78	40.1	2.02	2041	10.0
2	3102	39.2	75.8	5.15	3321	34.6	75.8	4.91	3924	23.1
3	5765	87.0	180	14.7	6629	69.4	194	11.4	7199	58.9
4	10408	196	332	35.0	13858	127	374	25.6	15510	96.0
5	12806	249	566	89.1	15431	196	714	57.9	16582	175

C0: test concentrations: A,C,E soils: 50, 100, 200, 400 and 500 mg/L; B, D soils: 10, 20, 50, 100 and 200 mg/L.

Cs (eq): content of the substance adsorbed on the soil at adsorption equilibrium (µg g^-1).

Caq (eq): mass concentration of the substance in the aqueous phase at adsorption equilibrium (µg cm^-3).

With

Vo was equal to 50 cm³ (initial volume of the aqueous phase in contact with the soil).

msoil (= oven dry mass) was equal to 0.98, 9.80, 0.985, 9.95 and 0.98 g for A, B, C, D and E soils, respectively.

 

Table 5: Results of adsorption isotherms

Soil types	Freundlich adsorption equation	KF	1/n
A = 1	Y=0.7216x+2.3568, R^2 = 0.9979	227	0.7216
B = 2	y= 0.7329x+1.3537, R^2 = 0.9954	22.6	0.7329
C = 3	y= 0.7288x+2.5122, R^2 = 0.9512	325	0.7288
D = 4	y=0.8794x+1.3184, R^2= 0.9957	20.8	0.8794
E = 5	y=0.7760x+2.5282, R^2 = 0.9679	337	0.7760

Where: y = logCs(eq) and x = logCaq(eq)

Kads,F: Freundlich adsorption coefficient (µg ^1-1/n (cm³)^1/n g^-1)

 

TEST 5 - DESORPTION ISOTHERMS

The test substance desorption isotherms on five soils didn't followed Freundlich desorption equation.

 

TEST 6 - MASS BALANCE

See the results in the field above entitled "Mass balance (%) at end of adsorption phase".

Validity criteria fulfilled:

not applicable

Conclusions:

The Kd values of 2,2-Difluoroethyl acetate in the five studied soils were 45.3, 7.6, 57.4, 8.7 and 127 cm3/g.
The corresponding Koc values were 692, 560, 1070, 628 and 1857 cm3/g, respectively; giving a mean Koc value of 961 cm3/g.
The corresponding Log Koc values were 2.84, 2.75, 3.03, 2.80 and 3.27, respectively; giving a mean Log Koc value of 2.98.
The Freundlich adsorption coefficient (Kads, F) values in the five soils were 227, 22.6, 325, 20.8 and 337 µg 1-1/n (cm3)1/n g-1.

Executive summary:

The adsorption/desorption potential of 2,2-Difluoroethyl acetate was investigated in a study performed according to the OECD test guideline 106 under GLP compliance, using the batch equilibrium method on five soils.

The soils were selected based on the three following parameters considered to be largely responsible for the adsorptive capacity: organic carbon, clay content and soil texture, and pH. The soils selected for this study were from Jilin (Black soil A), Jiangxi (Red soil B), Jiangsu (Paddy soil C), Shandong (Yellow soil D), Gansu (Meadow soil E).

Batch equilibrium method was followed with the three Tiers being covered by the different tests below:

* Tier 1: Preliminary test:

     - Test 1: This test was performed to determine for each soil the optimal soil/solution ratio, the equilibration time for adsorption, the amount of test substance adsorbed at equilibrium, the adsorption of the test substance on the surface of the test vessels and its stability during the test period. 

* Tier 2: Kinetics tests

     - Test 2: The adsorbtion kinetics were determined in all five soils at a single concentration after 24h of agitation using a soil-to-solution ratio of 1:50 for A, C and E soils and 1:5 ratio for B and D, as determined from the results of the preliminary test (test 1). Kd  and Koc values were determined.

     - Test 3: Because the adsorption percentages of the test substance in soils were more than 25% in the preliminary study, a desorption experiment was conducted. The desorption was studied in the five different soil types by means of desorption kinetics at a single concentration.

* Tier 3: Freundlich isotherms tests

     - Test 4: The Freundlich adsorption isotherms were determined to assess the influence of concentration on the extent of adsorption on soils. Five test substance concentrations were used to conduct adsorption isotherms for all five soils. 

     - Test 5: The Freundlich desorption isotherms were also determined to assess the influence of concentration on the extent of desorption on soils. Five test substance concentrations (same as for adsorption isotherms) were used to conduct desorption isotherms for B soil. 

Based on test 2, the Kd values of 2,2-Difluoroethyl acetate in the studied five soils were 45.3, 7.6, 57.4, 8.7 and 127 cm3/g. The corresponding Koc values were 692, 560, 1070, 628 and 1857 cm3/g, respectively; giving a mean Koc value of 961 cm³/g. The corresponding Log Koc values were 2.84, 2.75, 3.03, 2.80 and 3.27, respectively; giving a mean Log Koc value of 2.98.

During the desorption equilibrium time of 48 h (test 3), the test substance was not detected in the supernatant of A, B, C, D and E soils.

The test substance adsorption isotherms (test 4) on five soils preferably followed Freundlich adsorption equation, correlative coefficients are all more than 0.9. The Freundlich adsorption coefficient (Kads,F) values in the five soils are 227, 22.6, 325, 20.8 and 337 µg ^1-1/n (cm³)^1/n g^-1. The 1/n value for the different soils was between 0.722 and 0.8794.

Desorption isotherms experiment (test 5) showed that the correlative coefficient of the test substance desorption isotherms on five types of soil didn't followed Freundlich adsorption equation.

Reference 2

Endpoint:

adsorption / desorption: screening

Remarks:

Study performed according to OECD TG 121 (using HPLC) which is known to be a method of screening and estimation of adsorption potential.

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

From 21 october to 20 november 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))

Version / remarks:

2001

GLP compliance:

yes (incl. QA statement)

Type of method:

HPLC estimation method

Media:

soil/sewage sludge

Radiolabelling:

no

Test temperature:

40°C ± 0.8 °C

Details on study design: HPLC method:

EQUIPMENT
- Apparatus: Agilent Model 1100/1200 High Performance Liquid Chromatograph (HPLC).
- Type, material and dimension of analytical (guard) column: Chromatographic separations were achieved using an Poroshell 120 EC-CN column (100 x 3.0 mm, 2.7 μm particle size).
- Detection system: Agilent Series 1100 variable wavelength UV detector.
- Other conditions:
* Stop time: 30.00 minutes.
* Flow rate: 0.500 mL/min
* Over temperature: 40°C.
* Primary analytical wavelength: 205 nm

MOBILE PHASES
- Type: Prepared in situ by the HPLC system from reservoirs containing MeOH and H2O:
* Solvent A (45.0%): HPLC-grade H2O.
* Solvent B (55.0%): MeOH.
- Experiments with additives carried out on separate columns: no.
- pH: 6.5.
- Solutes for dissolving test and reference substances: Solutions of test substance and urea dead marker were prepared in methanol. Primary stock solutions of reference substances were prepared in acetonitrile and were then used to prepare standard solutions in methanol.

DETERMINATION OF DEAD TIME
- Method: by inert substances which are not retained by the column. The column dead time was determined by injections of the urea calibration reference standard solution prior to and following analysis of 2,2-Difluoroethyl acetate.

REFERENCE SUBSTANCES
- Identity: Urea (dead marker, CAS 57-13-6), Acetanilide (CAS 103-84-4), Phenol (CAS 108-95-2), Naphthalene (CAS 91-20-3), Phenanthrene (85-01-8), 1,1-Bis(4-chlorophenyl)-2,2,2-trichloroethane, 98%; 4,4’-DDT (CAS 50-29-3).

DETERMINATION OF RETENTION TIMES
- Quantity of test substance introduced in the column: 20.0 µL.
- Quantity of reference substances: 20.0 µL.
- Intervals of calibration: The six calibration reference standard solutions were injected prior to and after the test substance to determine retention times over the total run time. The test substance solutions were each injected following the initial injections of the reference standard solutions and were analyzed under the same chromatographic conditions as for the reference standard solutions.

REPETITIONS
- Number of determinations for reference substances: 2.
- Number of determinations for 2,2-Difluoroethyl acetate: 3.

EVALUATION
- Calculation of capacity factors k' using retention times: The capacity factors, k, were calculated for each test substance peak and each reference substance peak using the following equation:
k = (tR - t0)/t0
where:
* tR is the retention time of the test substance or reference substance peak.
* t0 is the column dead time established with urea.
A correlation graph of Log(k) versus Log(Koc) for the reference substances was plotted and fitted to a regression equation in the form y = mx + b. The calibration curve had a coefficient of determination (R2) of 0.9923 and a correlation coefficient (R) of 0.9961.
- Determination of the log Koc value: Log Koc values for each test substance peak were calculated by substituting the calculated logarithm of the capacity factor for each test substance peak into the linear regression equation for the calibration curve.

Key result

Type:

log Koc

Value:

1.02 dimensionless

pH:

6.5

Temp.:

40 °C

Remarks on result:

other: SD: +/- 0.013

Details on results (HPLC method):

- Retention times of reference substances used for calibration: see table 1 below.
- Details of fitted regression line (log k' vs. log Koc): The following equation was obtained for the reference standard calibration curve: y = 0.2943x - 1.0651, with a coefficient of determination (R²) of 0.9923 and a correlation coefficient (R) of 0.9961.
- Graph of regression line attached (see below).
- Average retention data for test substance: 1.23 min (SD: 0.002).

Table 1: Calibration reference substances retention times, capacity factors, and Log K_OC values

Reference Standard	Concentration (mg/L)	Retention Time (minutes)	Capacity Factor (k)*	Log k	log KOC**
Urea	200	1.048 1.047	N/A	N/A	N/A
Acetanilide	40.0	1.237 1.235	0.181 0.179	-0.743 -0.747	1.25
Phenol	25.0	1.266 1.266	0.209 0.209	-0.681 -0.681	1.32
Naphthalene	10.0	1.748 1.748	0.669 0.669	-0.175 -0.175	2.75
Phenanthrene	10.0	2.467 2.478	1.355 1.366	0.132 0.135	4.09
DDT	25.0	4.917 4.912	3.694 3.689	0.568 0.567	5.63

N/A: Not applicable

*: Capacity factor (k) is the standard retention time minus the mean column dead time (1.048 minutes for urea) divided by the mean column dead time.

**: Log K_OC values for all the reference substances are based on literature values provided in OECD 121 guideline.

 

Table 2: Log adsorption coefficients (Log Koc) for 2,2-Difluoroethyl acetate

Sample Number	Retention Time (minutes)	Mean (Standard Deviation)	Capacity Factor (k)	Mean (Standard Deviation)	Log k	KOC	Mean (Standard Deviation)	Capacity Factor (k)	Mean (Standard Deviation)
1	1.226	1.23 (0.002)	0.170	0.172 (0.0015)	-0.769	10.2	10.5 (0.030)	1.01	1.02 (0.013)
2	1.229		0.173		-0.761	10.8		1.03
3	1.228		0.172		-0.764	10.6		1.02

2,2-Difluoroethyl acetate reproducibly eluted as one peak on the UV detector. This peak (mean retention time = 1.228 min) eluted prior to the first reference standard (acetanilide, mean retention time = 1.236 min) and as such was an extrapolated value. The capacity factor for 2,2-Difluoroethyl acetate was calculated based on the retention time and the results for the three injections were averaged. The corresponding mean Log Koc for 2,2-Difluoroethyl acetate was extrapolated from the calibration curve as 1.02.

Validity criteria fulfilled:

not applicable

Conclusions:

The log Koc of 2,2-Difluoroethyl acetate for soil/sewage sludge was calculated to be equal to 1.02 +/- 0.013 at 40°C.

Executive summary:

The adsorption potential of 2,2-Difluoroethyl acetate was investigated in a study performed according to OECD test guideline 121 under GLP compliance, using High Performance Liquid Chromatography (HPLC).

One solution of 2,2-Difluoroethyl acetate at a nominal concentration of 5.00 mg/mL was prepared in a solvent composition matched to the mobile phase of the HPLC system and consisted of 55% methanol (MeOH): 45% reagent water (H2O) (v/v). Three aliquots of this preparation were ampulated for further HPLC/UV analysis.

Six reference substances, consisting of urea and five calibration reference standards (Acetanilide, Phenol, Naphthalene, Phenanthrene, 1,1-Bis(4-chlorophenyl)-2,2,2-trichloroethane), were also prepared in the mobile phase solvent composition at a nominal concentration (range 10.0-200 mg/L) selected to provide desired ultraviolet (UV) detector response. Urea was used to determine the column dead time. The five calibration reference standards, with known experimentally established Koc values, were used to prepare a calibration curve by plotting the logarithms of their capacity factors against their log KOC values, giving a linear regression equation. The capacity factors of the reference standards were calculated from their retention times and the retention time of urea. The adsorption coefficient of 2,2-Difluoroethyl acetate was then estimated using the calibration curve constructed from all reference items. 

The calibration reference standard solutions were sequentially injected into the HPLC system followed by single injections of each test substance solution aliquot. The calibration reference standards injection sequence was repeated following the test substance injections. The HPLC system was operated under standardized isocratic, reverse-phase operating conditions. The retention times of the test substance and the reference standards were accurately measured. The dead time of the instrument was also measured, and capacity factors were calculated for each reference substance. The calibration curve was then constructed by plotting the capacity factor (log k) for the reference standards against their adsorption coefficients (log Koc). Linear regression analysis was conducted and gave the following equation: y = 0.2943 x - 1.0651, with a coefficient of determination (R²) of 0.9923 and a correlation coefficient (R) of 0.9961.

2,2-Difluoroethyl acetate reproducibly eluted as one peak on the UV detector. This peak (mean retention time = 1.228 min) eluted prior to the first reference standard (acetanilide, mean retention time = 1.236 min) and as such thus required that Log Koc of 2,2-Difluoroethyl acetate be extrapolated from the calibration curve.

Under the chromatographic conditions specified, the mean Log Koc of 2,2-Difluoroethyl acetate was extrapolated from the calibration curve to be 1.02 ± 0.013.

Description of key information

The Koc values of 2,2-Difluoroethyl acetate in five soils were 692, 560, 1070, 628 and 1857 cm3/g; giving a mean Koc value of 961 cm3/g. The corresponding Log Koc values were 2.84, 2.75, 3.03, 2.80 and 3.27, respectively; giving a mean Log Koc value of 2.98.

Key value for chemical safety assessment

Koc at 20 °C:

1 857

Additional information

Two experimental studies performed under GLP compliance and in accordance with OECD test guidelines 121 and 106 were assigned a Klimisch score of 1. The OECD 121 method (HPLC method) is known to be a method of screening and estimation of adsorption potential. The OECD test guideline 106 (batch equilibrium method) uses a range of actual soils and thus represents a more realistic scenario than the OECD 121 method. For this reason, the studies performed according to OECD test guidelines 106 and 121 were flagged as key and supporting studies, respectively.

The key value for the chemical safety assessment (i.e. the Koc value used to derive the PNECs for the soil and sediment compartments using the equilibrium partitioning method) was selected to be the highest value obtained during the OECD TG 106 study, as a worst case scenario (i.e. K_oc = 1857 L/kg).