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Adsorption / desorption

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Endpoint:
adsorption / desorption: screening
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
28 April 1995 - 23 May 1995
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP-Guideline study with acceptable restrictions. Degradation products were not described in the study. Test conducted with the source substance thiram (CAS No. 137-26-8)
Qualifier:
according to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Deviations:
no
Guideline:
other: EPA 540/9-82-021, Subdivision N; Section 163-1; October 1982
Deviations:
no
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
yes
Details on study design: HPLC method:
Combustion of soil:
Soil samples were combusted in a stream of oxygen at 800°C with copper oxide as catalyst.
Analytical monitoring:
yes
Details on matrix:
Details on table below
Details on test conditions:
Aqueous solvent:
0.01 M CaCl2 solution was used as the aqueous solvent phase.
Preparation of the stock solution:
Approximately 1 mg of the radiolabelled test item was dissolved in 1 ml of acetone and afterwards an aliquot of 10 µL was filled up to 10 mL with the same solvent as given above. After measurement by LSC (liquid scintillation counting) the content of 14C-THIRAM in the stock solution was determined to be 1.39 mg/mL.
Application solutions:
Application solution no. 1:
0.2 mL of the stock solution (0.278 mg of radiolabelled THIRAM) was mixed with 0.05 mL of a solution of unlabelled test item in acetone in concentration of 5.51 mg/mL. The resulting solution was dissolved in 0.01 M CaCl2 to a volume of 550 mL. The actual concentration of THIRAM was determined by LSC to be 1.069 mg/L.
Application solution 2, 3, 4:
Appropriate volumes of the application solution 1 were diluted with 0.01 M CaCl2 solution to a volume of 300 mL to obtain the application solutions no. 2, 3 and 4 in concentration of 0.201 mg, 0.041 mg and 0.010 mg THIRAM per litre, respectively.
Stability of the test item during application:
The stability of the radiolabelled test item in the application solution was determined by high-pressure liquid chromatography (HPLC) before and after (about 30 min.) the start of the adsorption test.
Additionally, the application solution in aqueous CaCl2 phase (1 mg/mL) in two control tubes without soil (control samples) was checked for parent compound by HPLC after 12 hours of shaking (adsorption step for four hours and two desorption steps, each for 4 hours).
Soil preparation:
The air dried soil samples were equilibrated by shaking with 0.01 M CaCl2 solution (2:1, vol : mass) overnight, then centrifuged at about 2000 g for 10 minutes. Afterwards the supernatant was discarded and the solution remaining in soil gravimetrically determined.
Blank test per soil with the same amount of soil and total volume of CaCl2 solution was subjected to the same test procedure. This served as a background control during the analysis to detect interfering compounds or contaminated soils.
Two replicates per test soil and one replicate per control and blank sample were prepared for the main test.
Type:
Koc
Value:
2 245
Remarks on result:
other: Soil I
Type:
Koc
Value:
24 526
Remarks on result:
other: Soil II
Type:
Koc
Value:
6 359
Remarks on result:
other: Soil III
Type:
Koc
Value:
12 899
Remarks on result:
other: Soil IV
Type:
log Koc
Value:
3.3
Remarks on result:
other: Soil I
Type:
log Koc
Value:
4.4
Remarks on result:
other: Soil II
Type:
log Koc
Value:
3.8
Remarks on result:
other: Soil III
Type:
log Koc
Value:
4.1
Remarks on result:
other: Soil IV

Adsorption and desorption of THIRAM in soils I to IV as a function of time from the pre-test (values in percent of applied radioactivity).

Soil I
New York

Soil II
Illinois 1A

Soil III
Illinois site 1

Soil IV
IOWA 1A

Radioactivity in % applied:

Time (hours)

Adsorbed RA

Desorbed RA

Adsorbed RA

Desorbed RA

Adsorbed RA

Desorbed RA

Adsorbed RA

Desorbed RA

0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

1

60.9

3.5

42.9

1.5

51.0

4.9

71.0

3.9

2

76.5

3.9

66.3

1.7

65.4

5.3

79.8

4.8

3

84.4

4.1

82.2

1.8

73.6

5.6

84.1

5.4

4

88.1

4.3

91.1

1.8

79.4

5.8

88.3

6.1

5

89.7

4.5

94.8

1.9

82.7

5.8

88.5

6.5

6

90.5

4.7

96.0

2.0

84.6

6.2

88.1

6.8

Freundlich adsorption / desorption constants calculated for four soils used in the study

Soil type

Organic carbon
[%]

Clay content
[%]

Freundlich adsorption

Freundlich desorption

Ka[mL/g]

Koc[mL/g]

R

1/n

Kd
[ml/g]

Koc
[ml/g]

1/n

R

I: sandy loam

2.41

14.8

54.1

2245

0.9955

1.036

781.2

32414

1.271

0.9963

II: loamy sand

0.61

7.5

149.6

24526

0.9964

1.149

1762.1

288869

1.264

0.9995

III: silt loam

1.06

16.8

67.4

6359

0.9974

1.104

841.4

79381

1.225

0.9976

IV: loam

2.04

25.2

263.1

12899

0.9891

1.126

1679.7

82340

1.156

0.9935

Ka: Adsorption constant,
Kd: desorption constant,
Koc(a): adsorption constant as a function of the organic content,
Koc(d): desorption constant as a function of the organic content,
1/n: slope of the adsorption / desorption isotherm,
R: correlation coefficient

Balance of the applied radioactivity in the soil-water systems treated with14C-THIRAM at a concentration of 1mg/L

Sample

Soil I:
sandy loam

Soil II:
loamy sand

Soil III:
silt loam

Soil IV:
loam

µg*

%**

µg*

%**

µg*

%**

µg*

%**

Aqueous phase (W)

A
B
Mean
SD***

2.83
2.94
2.88
0.054

10.58
10.98
10.78
0.200

1.78
1.82
1.80
0.019

6.65
6.79
6.72
0.072

4.39
4.36
4.38
0.016

16.44
16.32
16.38
0.059

3.36
3.34
3.35
0.009

12.58
12.51
12.54
0.034

Soil
Extract

A
B
Mean
SD***

15.57
15.63
15.60
0.028

58.26
58.47
58.36
0.103

14.15
13.63
13.89
0.259

52.92
50.98
51.95
0.970

11.74
11.84
11.79
0.047

43.92
44.28
44.10
0.177

12.67
12.80
12.74
0.066

47.41
47.90
47.65
0.248

Soil
Combustion

A
B
Mean
SD***

7.40
7.00
7.20
0.200

27.68
26.19
26.94
0.747

10.14
10.19
10.17
0.023

37.94
38.12
38.03
0.087

9.23
8.76
9.00
0.236

34.53
32.77
33.65
0.883

9.12
9.01
9.06
0.052

34.10
33.71
33.91
0.194

TOTAL

25.68

96.08

25.85

96.70

25.16

94.13

25.16

94.10

Calculation was performed by means of EXCEL 4.0 using not rounded values.
*= Values expressed as parent equivalents in micrograms.
**= Values in % of the applied radioactivity (RA).
*** = Standard deviation.

Adsorption andDesorption of parent radioactivity (RA) from soil sediments (soils I to IV) after equilibration with14C-THIRAM at various initial concentrations Ci

Ci
(µg/
ml)

Sam-ple

Soil I

Soil II

Soil III

Soil IV

RA
ads

RA
des

RA
ads

RA
des

RA
ads

RA
des

RA
ads

RA
des

[%]*

D1
[%]

[%]

[%]*

D1
[%]

[%]

[%]*

D1
[%]

[%]

[%]*

D1
[%]

[%]

1.07

A
B
Mean

88.50
84.42
86.46

1.15
1.23
1.19

1.67
1.80
1.74

93.31
92.11
92.71

0.76
0.75
0.76

1.17
1.15
1.16

82.87
83.16
83.01

1.00
1.01
1.00

1.48
1.47
1.47

86.30
85.84
86.07

0.45
0.29
0.37

0.60
0.43
0.51

0.20

A
B
Mean

84.39
84.11
84.25

2.26
2.44
2.40

3.44
3.53
3.48

93.48
93.51
93.49

1.10
1.05
1.07

1.62
1.54
1.58

81.82
82.17
81.99

1.94
1.43
1.68

2.77
2.30
2.54

74.68
74.67
74.67

0.58
1.06
0.82

0.68
1.34
1.01

0.04

A
B
Mean

79.58
79.99
79.79

3.36
3.30
3.33

4.67
4.56
4.61

89.74
90.16
89.95

1.46
1.54
1.50

2.18
2.20
2.19

74.55
74.27
74.41

2.43
2.41
2.42

3.35
3.25
3.30

72.80
71.97
72.39

0.85
0.53
0.69

1.12
0.65
0.89

0.01

A
B
Mean

84.56
85.78
85.17

3.78
3.61
3.70

5.12
5.03
5.08

87.42
88.37
87.89

2.31
2.19
2.25

3.22
2.96
3.09

78.47
76.03
77.25

2.46
2.58
2.52

3.44
3.45
3.44

77.30
76.52
76.91

0.75
1.12
0.93

0.89
1.40
1.14

Calculation was performed by means of EXCEL 4.0 using not rounded values.
RA ads = Radioactivity adsorbed.
RA des = Radioactivity desorbed
D1= Amount of radioactivity (RA) desorbed after the first desorption step.
Dtotal= Total radioactivity desorbed during both desorption steps: D1 + D2.
* = Percentage from the radioactivity totally applied to the system.

Validity criteria fulfilled:
yes
Conclusions:
Based on the range of the Koc values it can be concluded that THIRAM is strongly adsorbed by soil components.
According to the scheme introduced by McCall (1980, mobility classes of pesticides) as well as Briggs (Proc. 7th British Insecticide and Fungicide Conference, Nottingham, UK, 83 86, 1973), the mobility of the test item can be classified as very low mobile to immobile for all soils used in the study
Executive summary:

Materials and methods:The adsorption and desorption of THIRAM was investigated in four different soils (soil I: sandy loam, soil II: loamy sand, soil III: silt loam and soil IV: loam) varying in clay content, organic carbon content and pH value using the14C-labelled test item.

The analysis was performed in accordance with OECD Guidelines for Testing of Chemicals, No. 106.

The radioactivity in all samples was determined on a Packard liquid scintillation counter. Furthermore the stock solution, application solutions as well as aqueous phases and organic soil extracts were analysed by HPLC.

Results and discussion:The adsorption experiment showed that the adsorption of14C-THIRAM reached equilibrium after about four hours.

The equilibrium concentrations of total radioactivity found for soils I to IV (mass balance) in the aqueous phase after adsorption were 10.8%, 6.7%, 16.4% and 12.5%, respectively. The corresponding values for the amount adsorbed onto the soils were 85.3%, 90.0%, 77.8% and 81.6% of the radioactivity initially applied.

The radioactivity in the aqueous phases after the adsorption step consisted of THIRAM as well as of degradation products, whereas the soil extracts contained mainly the parent compound.

The total recoveries ranged from 94.1% for soil IV to 96.7% for soil II with a mean value for the four soils of 95.3%.

The adsorption tests indicated very high adsorption levels of14C-THIRAM onto the four soils analysed, whereas the amounts adsorbed did not depend on the organic carbon content and on the concentration level of test item.
The maximum amounts adsorbed were 86.5%, 93.5% 83.0% and 86.1% of the applied radioactivity for soil I to IV, respectively. For the same soils the maximum amounts desorbed as14C-THIRAM in a first desorption step were 3.7 %, 2.3 %, 2.5 % and 0.9 %, only.

The results indicate that THIRAM was bound to the chosen soils specifically.

Endpoint:
adsorption / desorption
Remarks:
other: calculation
Type of information:
calculation (if not (Q)SAR)
Remarks:
Migrated phrase: estimated by calculation
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Scientifically accepted calculation method
Principles of method if other than guideline:
Calculated using KOCWIN v2.00, a subroutine of the computer program EPI Suite™ (Estimation Program Interface for Windows, version 4.0. Syracuse Research Corporation, Syracuse, NY, USA) U.S. Environmental Protection Agency, OPPT
Type:
log Koc
Value:
3.9 - 4.2

Description of key information

Disulfiram shows potential for adsorption to the soil (log Koc of 3.3 (sandy loam) to 4.4 (loamy sand) L/kg).

Key value for chemical safety assessment

Additional information

No data on the adsorption/desorption potential of disulfiram (CAS No. 97-77-8) were available. Therefore, a conclusion based on data from an analogue substance had to be drawn. The adsorption potential of tetramethylthiuram disulfide (CAS No. 137-26-8), substance structurally and composition related to tetraethylthiuram disulfide, was investigated in a study.This test was conducted according to OECD Guideline No.106: Adsorption/Desorption using a Batch Equilibrium Method (2000) and EPA’s Pesticide Assessment Guidelines, CFR 40, Subdivision 163-1 (1982) under GLP conditions.14C-thiram was tested in 4 soil types obtaining log Koc values of 3.3 (sandy loam), 4.4 (loamy sand), 3.8 (silt loam) and 4.1 L/kg (loam).

The results from the KOCWIN v2.00 show that the predicted log Koc values for disulfiram are within the range obtained in the experimental study with the analogue substance.