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Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
01/09/2001 - 18/12/2001
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP, Guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: EPA OPP Guideline No. 163-1
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: Annex, Revision 3 (draft) by the Food Agriculture Organization of United Nations (August 28, 1993)
Deviations:
no
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
yes
Test temperature:
20 °C
Details on study design: HPLC method:
Not applicable
Analytical monitoring:
yes
Details on sampling:
Dinotefuran was tested in the following concentrations during the advanced test: 0.964, 0.243, 0.049, 0.024, and 0.010 mg/L. The amount of organic solvent (acetone) did not exceed 0.3% at the top concentration and 0.1% at the remaining concentrations.
Details on matrix:
Details on soil, see Table A7.1.3-1.
Details on test conditions:
Preliminary test:
Adsorption behaviour of dinotefuran was studied using two soil types (loamy sand and silt loam) which were tested in this part of the study. Soil samples of 20 g, 4 g, and 1 g respectively, were shaken each with 20 mL of 0.01 M CaCl2 solution, at the test concentration of 0.259 mg 14C-dinotefuran/L. Soil/aqueous phase suspensions were incubated in sealed Teflon® centrifuge tubes on a shaker. Tubes were shaken at about 200 strokes per minute in the dark at 20 °C.

Screening test:
the adsorption was studied in six different soil types (loamy sand, silt loam, loam, sandy loam, clay loam and sand) by means of adsorption kinetics at a single concentration to determine the distribution coefficients kd and Koc. The soil/solution ratio of 1/1, the weight of the soil sample (10 g), and the volume of the aqueous phase of 10 mL were chosen. Duplicate samples were set-up for each interval.

Advanced test:
For adsorption isotherms and desorption kinetics/desorption isotherms, with respect to the results obtained in the preliminary and screening tests, the study of the adsorptive behavior of 14C-dinotefuran on soil and its potential mobility was continued by determining Freundlich adsorption isotherms. The procedure for the adsorption isotherms test was similar to that used in the preliminary and screening tests. The desorption experiment was carried out on each sample used in the test for the determination of the adsorption isotherms. After the adsorption, the mixture was centrifuged and the aqueous phase was removed. The volume of supernatant was replaced by an equal volume of 0.01 M CaCl2 without test item. The new mixture was agitated and aliquots of 100 µL were taken from the same sample and analyzed after 4 and 24 hours. Volume of these aliquots did not exceed 4 % of the total aqueous solution volume in order to avoid significantly changing the soil/solution ratio and decreasing the mass of solute available for desorption. A greater aliquot of 1 mL was taken and analyzed after 47 hours.
Computational methods:
See table below
Key result
Sample No.:
#1
Type:
Koc
Value:
6 other: cm3/g
% Org. carbon:
2.17
Key result
Sample No.:
#2
Type:
Koc
Value:
22 other: cm3/g
% Org. carbon:
1
Key result
Sample No.:
#3
Type:
Koc
Value:
42 other: cm3/g
% Org. carbon:
2.4
Key result
Sample No.:
#4
Type:
Koc
Value:
45 other: cm3/g
% Org. carbon:
1.6
Key result
Sample No.:
#5
Type:
Koc
Value:
42 other: g/cm3
% Org. carbon:
2.9
Details on results (HPLC method):
Not applicable
Adsorption and desorption constants:
Soil loamy sand silt loam loam sandy loam clay loam
KF 0.119 0.215 1.009 0.713 1.221
Koc 6 22 42 45 42
n 1.18 1.14 1.18 1.14 1.12
Kdes,F 1.4 1.8 9.5 3.4 8.7
Kdes,oc 66 178 397 213 299
n 1.02 0.98 0.96 1.00 0.94
Recovery of test material:
The balance of the radioactivity applied was 99.5% for loamy sand, 99.8% for silt loam, and 99.2% for sand. In the supernatant, amounts of 84.4%, 82.4%, and 96.0% of the radioactivity applied were detected for soils loamy sand, silt loam and sand, respectively. Extracted was 11.9%, 11.1%, and 2.1% for soils loamy sand, silt loam and sand, respectively. The direct combustion of the extracted soil recovered 3.1%, 6.3%, and 2.1% for soils loamy sand, silt loam and sand, respectively.
Concentration of test substance at end of adsorption equilibration period:
See tables below
Concentration of test substance at end of desorption equilibration period:
See tables below
Transformation products:
no
Details on results (Batch equilibrium method):
See tables below
Statistics:
Not applicable

Table 2:  Results of preliminary test: distribution of dinotefuran between aqueous phase and soil (1: Speyer 2.2, 2: Senozan) after adsorption at three different soil to aqueous phase ratios

Sample

Ratio

m

[g]

V0

[cm3]

m(ads)s

[µg]

m(ads)aq

[µg]

Kd

[cm3/g]

Kd*ratio

[cm3/g]

Koc

[cm3/g]

Soil 1 (loamy sand)

Sample A

Sample B

Mean

1:1

 

20

20

 

20

20

 

0.69

0.66

 

4.5

4.5

4.5

 

0.154

0.147

0.150

 

0.15

0.15

0.15

 

7

7

7

Soil 1 (loamy sand)

Sample A

Sample B

Mean

1:5

 

4

4

 

20

20

 

0.22

0.15

 

5.0

5.0

5.0

 

0.227

0.152

0.189

 

0.05

0.03

0.04

 

10

7

9

Soil 1 (loamy sand)

Sample A

Sample B

Mean

1:20

 

1

1

 

20

20

 

0.13

0.05

 

5.1

5.1

5.1

 

0.506

0.204

0.355

 

0.03

0.01

0.02

 

23

9

16

Soil 2 (silt loam)

Sample A

Sample B

Mean

1:1

 

20

20

 

20

20

 

1.1

1.0

 

4.1

4.2

4.1

 

0.264

0.241

0.252

 

0.26

0.24

0.25

 

26

24

25

Soil 2 (silt loam)

Sample A

Sample B

Mean

1:5

 

4

4

 

20

20

 

0.2

0.3

 

4.9

4.9

4.9

 

0.243

0.292

0.267

 

0.05

0.06

0.05

 

24

29

27

Soil 2 (silt loam)

Sample A

Sample B

Mean

1:20

 

1

1

 

20

20

 

0.1

0.1

 

5.1

5.1

5.1

 

0.315

0.364

0.340

 

0.02

0.02

0.02

 

32

36

34

m = mass of soil (g)

V0= initial volume of the aqueous phase in contact with the soil (cm3)

m(ads)s = mass of the test item adsorbed on the soil at adsorption equilibrium (µg)

m(ads)aq = mass of test item in the solution at adsorption equilibrium (µg)

Kd = distribution coefficient (cm3/g)

Koc = distribution coefficient related to the organic carbon content of the soil (cm3/g)

Table 3:                  Results of preliminary test: mass balance in percent of radioactivity applied for soil 1(Speyer 2.2) and soil 2 (Senozan)

Sample

Ratio

mass applied

[µg]

(ads)aq

[%]

(ads)extract

[%]

(ads)residue

[%]

recovery

[%]

Soil 1 (loamy sand)

Sample A

Sample B

Mean

1:1

 

5.2

5.2

 

86.7

87.2

86.9

 

5.6

2.5

4.0

 

4.3

4.3

4.3

 

96.5

94.0

95.2

Soil 2 (silt loam)

Sample A

Sample B

Mean

1:1

 

5.2

5.2

 

79.1

80.6

79.9

 

8.1

8.8

8.5

 

9.5

7.7

8.6

 

96.8

97.1

96.9

(ads)aq                  : percent of the amount applied remaining in the aqueous phase

(ads)extract    : percent of the amount applied being extracted after the adsorption step

(ads)residue    : percent of the amount applied remaining unextracted in the soil

 

Table 4:  Results of screening test: distribution of dinotefuran between aqueous phase and soil after adsorption to six different soils

Sample

Ratio

m

[g]

V0

[cm3]

m(ads)s

[µg]

m(ads)aq

[µg]

Kd

[cm3/g]

Kd*ratio

[cm3/g]

Koc

[cm3/g]

Soil 1 (loamy sand)

Sample A

Sample B

Mean

1:1

 

10

10

 

10

10

 

0.85

0.79

 

 

4.3

4.4

4.4

 

0.196

0.180

0.188

 

0.20

0.18

0.19

 

9

8

9

Soil 2 (silt loam)

Sample A

Sample B

Mean

1:1

 

10

10

 

10

10

 

0.89

0.97

 

 

4.3

4.2

 

 

0.207

0.229

0.218

 

0.21

0.23

0.22

 

21

23

22

Soil 5 (loam)

Sample A

Sample B

Mean

1:1

 

10

10

 

10

10

 

3.0

2.9

 

 

1.7

1.7

1.7

 

1.752

1.664

1.708

 

1.75

1.66

1.71

 

73

69

71

Soil 6 (sandy loam)

Sample A

Sample B

Mean

1:1

 

10

10

 

10

10

 

2.2

2.2

 

 

2.5

2.4

2.4

 

0.868

0.918

0.893

 

0.87

0.92

0.89

 

54

57

56

Soil 7 (clay loam)

Sample A

Sample B

Mean

1:1

 

10

10

 

10

10

 

2.9

2.8

 

 

2.3

2.3

2.3

 

1.235

1.223

1.229

 

1.24

1.22

1.23

 

43

42

42

Soil 8 (sand)

Sample A

Sample B

Mean

1:1

 

10

10

 

10

10

 

0.2

0.2

 

 

5.0

5.0

5.0

 

0.046

0.043

0.044

 

0.05

0.04

0.04

 

51

48

49

m = mass of soil (g)

V0= initial volume of the aqueous phase in contact with the soil (cm3)

m(ads)s = mass of the test item adsorbed on the soil at adsorption equilibrium (µg)

m(ads)aq = mass of test item in the solution at adsorption equilibrium (µg)

Kd = distribution coefficient (cm3/g)

Koc = distribution coefficient related to the organic carbon content of the soil (cm3/g)

Table 5   Results of advanced test: distribution of14C-dinotefuran between aqueous phase and soil after desorption. Evaluation according to the Freundlich desorption isotherms

 

Soil 1 (loamy sand)

Concentration Ci (µg/cm3)

0.964

0.243

0.049

0.024

0.010

m(des)s (µg)

Sample A

Sample B

Mean (µg)

Mean (% of applied)

 

0.47

0.54

0.51

5.27

 

0.26

0.24

0.25

10.32

 

0.06

0.06

0.06

11.92

 

0.02

0.02

0.02

9.94

 

0.01

0.01

0.01

11.45

m(des)s / m(soil) (µg/g)

log(m(des)s / m(soil))

c(des)aq (µg/cm3)

log(c(des)aq)

0.051

-1.294

0.035

-1.456

0.025

-1.601

0.015

-1.820

0.006

-2.235

0.003

-2.483

0.002

-2.621

0.002

-2.784

0.001

-2.959

0.001

-3.192

 

 

Soil 2 (silt loam)

Concentration Ci (µg/cm3)

0.964

0.243

0.049

0.024

0.010

m(des)s (µg)

Sample A

Sample B

Mean (µg)

Mean (% of applied)

 

0.98

0.93

0.95

9.88

 

0.38

0.35

0.36

14.92

 

0.008

-2.087

0.005

-2.335

 

0.04

0.03

0.04

14.95

 

0.02

0.01

0.02

15.75

m(des)s / m(soil) (µg/g)

log(m(des)s / m(soil))

c(des)aq (µg/cm3)

log(c(des)aq)

0.095

-1.021

0.061

-1.213

0.036

-1.441

0.021

-1.687

0.008

-2.087

0.005

-2.335

0.004

-2.443

0.002

-2.335

0.002

-2.820

0.001

-2.993

 

 

Soil 5 (loam)

Concentration Ci (µg/cm3)

0.964

0.243

0.049

0.024

0.010

m(des)s (µg)

Sample A

Sample B

Mean (µg)

Mean (% of applied)

 

4.60

4.68

4.64

48.13

 

1.24

1.30

1.27

52.36

 

0.26

0.28

0.27

55.00

 

0.15

0.15

0.15

63.70

 

0.06

0.06

0.06

61.82

m(des)s / m(soil) (µg/g)

log(m(des)s / m(soil))

c(des)aq (µg/cm3)

log(c(des)aq)

0.464

-0.334

0.047

-1.328

0.127

-0.896

0.016

-1.785

0.027

-1.571

0.005

-2.315

0.015

-1.814

0.002

-2.720

0.006

-2.226

0.001

-1.132

 

Soil 6 (sandy loam)

Concentration Ci (µg/cm3)

0.964

0.243

0.049

0.024

0.010

m(des)s (µg)

Sample A

Sample B

Mean (µg)

Mean (% of applied)

 

3.12

3.02

3.07

31.85

 

0.96

0.96

0.96

39.64

 

0.20

0.21

0.20

41.92

 

0.10

0.10

0.10

42.75

 

0.04

0.04

0.04

44.44

m(des)s / m(soil) (µg/g)

log(m(des)s / m(soil))

c(des)aq (µg/cm3)

log(c(des)aq)

0.307

-0.513

0.093

-1.033

0.096

-1.017

0.026

-1.591

0.020

-1.689

0.006

-2.208

0.010

-1.987

0.003

-2.531

0.004

-2.370

0.001

-2.917

 

 

Soil 7 (clay loam)

Concentration Ci (µg/cm3)

0.964

0.243

0.049

0.024

0.010

m(des)s (µg)

Sample A

Sample B

Mean (µg)

Mean (% of applied)

 

4.74

4.74

4.74

49.15

 

1.31

1.32

1.31

54.17

 

0.28

0.28

0.28

57.19

 

0.14

0.14

0.14

56.56

 

0.06

0.06

0.06

58.20

m(des)s / m(soil) (µg/g)

log(m(des)s / m(soil))

c(des)aq (µg/cm3)

log(c(des)aq)

0.474

-0.324

0.058

-1.240

0.131

-0.881

0.022

-1.659

0.028

-1.555

0.005

-2.302

0.014

-1.865

0.002

-2.607

0.006

-2.252

0.001

-3.040

Ci = initial concentration in the supernatant before adsorption (µg/cm3)

m(des)s = mass of the test item remaining adsorbed on the soil at desorption equilibrium (µg)

m = mass of soil (1 g)

c(des)aq = concentration of test item in the solution at desorption equilibrium (µg/cm3)

Validity criteria fulfilled:
yes
Conclusions:
An estimation of the dinotefuran Koc values in soil resulted in values between 6 and 45 with 1/n values ranging 1.12 to 1.18 derived in the advanced test. Koc values derived in the screening test ranged between 9 to 71.
The adsorption/desorption test performed on six soils: loamy sand, silt loam, loam, sandy loam, clay loam, and sand confirmed the estimated values. The test item was shown to be stable in the aqueous solution as well as in the soil/solution mixture during the test. In addition, the mass balance showed that no losses of radioactivity occurred. The adsorption and desorption kinetics indicated that equilibrium was reached after about 24 to 48 hours of agitation.
The calculated Kdesoc values were higher than those obtained for the adsorption isotherms, indicating the in part irreversibility of the adsorption. According to the classification system found in the literature, dinotefuran has a very high mobility in soils.

Description of key information

The adsorption and desorption of dinotefuran has been shown to be influenced by the organic content of the soil matrix. The arithmetic mean KOC value of 31.4 L.kg-1 (from the advanced study using 5 different soil types) suggests that the compound would not adsorb strongly to soil and would very easily undergo desorption, suggesting a potential for high mobility in the soil compartment.

Key value for chemical safety assessment

Koc at 20 °C:
31.4

Additional information