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Environmental fate & pathways

Adsorption / desorption

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Administrative data

Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report Date:
2010

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Deviations:
no
Qualifier:
according to
Guideline:
other: U.S. EPA Pesticide Assessment Guidelines, Subdivision N, 163-1 (1982)
Deviations:
no
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid
Details on test material:
Purity: 85-99%
Specific details on test material used for the study:
Radiochemical purity: 97.1%; Specific activity: 39.55 µCi/mg
Radiolabelling:
yes
Remarks:
phenyl label

Study design

Test temperature:
20 ± 2°C

Batch equilibrium or other method

Analytical monitoring:
yes
Matrix propertiesopen allclose all
Matrix no.:
#1
Matrix type:
clay loam
% Clay:
32
% Silt:
48
% Sand:
20
% Org. carbon:
2.9
pH:
6.4
CEC:
27.2 meq/100 g soil d.w.
Bulk density (g/cm³):
1.1
Matrix no.:
#2
Matrix type:
loam
% Clay:
12
% Silt:
46
% Sand:
42
% Org. carbon:
0.5
pH:
8.2
CEC:
11.2 meq/100 g soil d.w.
Bulk density (g/cm³):
1.09
Matrix no.:
#3
Matrix type:
sandy loam
% Clay:
14
% Silt:
32
% Sand:
54
% Org. carbon:
1.4
pH:
7.7
CEC:
9.2 meq/100 g soil d.w.
Bulk density (g/cm³):
1.12
Matrix no.:
#4
Matrix type:
silty clay
% Clay:
44
% Silt:
44
% Sand:
12
% Org. carbon:
1.8
pH:
7.6
CEC:
19.1 meq/100 g soil d.w.
Bulk density (g/cm³):
1.06
Matrix no.:
#5
Matrix type:
sandy loam
% Clay:
9
% Silt:
24
% Sand:
67
% Org. carbon:
1.2
pH:
5.7
CEC:
6.1 meq/100 g soil d.w.
Bulk density (g/cm³):
1.22
Duration of adsorption equilibration
Duration:
24 h
Initial conc. measured:
>= 0.003 - <= 0.3 other: µg/mL
Temp.:
>= 18 - <= 22 °C
Remarks:
For all the samples
Duration of desorption equilibration
Duration:
24 h
Conc. of adsorbed test mat.:
0.3 other: µg/mL
Temp.:
20 °C
Remarks:
For all the samples

Results and discussion

Adsorption coefficientopen allclose all
Key result
Sample No.:
#1
Type:
Kd
Value:
19.37 other: mL/g
Matrix:
Clay loam
% Org. carbon:
2.9
Key result
Sample No.:
#2
Type:
Kd
Value:
0.22 other: mL/g
Matrix:
Loam
% Org. carbon:
0.5
Key result
Sample No.:
#3
Type:
Kd
Value:
0.56 other: mL/g
Matrix:
Sandy loam
% Org. carbon:
1.4
Key result
Sample No.:
#4
Type:
Kd
Value:
0.83 other: mL/g
Matrix:
Silty clay
% Org. carbon:
1.8
Key result
Sample No.:
#5
Type:
Kd
Value:
3.66 other: mL/g
Matrix:
Sandy loam
% Org. carbon:
1.2
Key result
Sample No.:
#1
Type:
Koc
Value:
667.9 other: mL/g
Matrix:
Clay Loam
Key result
Sample No.:
#2
Type:
Koc
Value:
44.6 other: mL/g
Matrix:
Loam
Key result
Sample No.:
#3
Type:
Koc
Value:
39.7 other: mL/g
Matrix:
Sandy Loam
Key result
Sample No.:
#4
Type:
Koc
Value:
45.9 other: mL/g
Matrix:
Silty Clay
Key result
Sample No.:
#5
Type:
Koc
Value:
305.2 other: mL/g
Matrix:
Sandy Loam

Results: Batch equilibrium or other method

Recovery of test material:
The average material balance ranged from 97.2 to 107.9% and is within the acceptable guideline range of 90-110% of the applied radioactivity.
Mass balance (%) at end of desorption phaseopen allclose all
Sample no.:
#1
Duration:
24 h
% Desorption:
107.9
Sample no.:
#2
Duration:
24 h
% Desorption:
107.1
Sample no.:
#3
Duration:
24 h
% Desorption:
101.6
Sample no.:
#4
Duration:
24 h
% Desorption:
97.2
Sample no.:
#5
Duration:
24 h
% Desorption:
104.1
Transformation products:
no

Applicant's summary and conclusion

Conclusions:
Average sorption coefficient
Kd: 4.93 mL/g
Kom: 129.0 mL/g
Koc: 220.7 mL/g

Total percent of test item desorbed after both desorption intervals (DT):
Drummer soil: 31.9%
Porterville soil: 39.9%
Nambsheim soil: 44.4%
Lleida soil: 39.4%
Sassafras soil: 82.8%
Executive summary:

The adsorption and desorption properties of the test substance in five different soils was investigated in the laboratory using 14C-test substance according to the procedures outlined in U.S. EPA Pesticide Assessment Guidelines, Subdivision N, 163-1 and OECD Guideline for the Testing of Chemicals, OECD 106 (January 2000). The adsorption coefficients Kd, Kom, and Koc, and the Freundlich adsorption isotherm parameters KF, KFom, KFoc and 1/n were calculated for Drummer, Porterville (California), Lleida, Nambsheim and Sassafras #16 soils.

The texture of the soils included a clay loam (Drummer), a loam (Porterville or California), two sandy loams (Nambsheim and Sassafras #16) and a silty clay (Lleida). The percent organic matter (Walkley-Black method) of the soils ranged from 0.9-5.0% and the pH in 0.01 M CaCl2 ranged from 5.0-7.9.

Adsorption experiment was performed using the batch equilibration method on the soils with five nominal test concentrations (0.003, 0.015, 0.03, 0.15 and 0.3 µg/mL) of the test item prepared in 0.01 M CaCl2. Two desorption cycles were performed on samples treated at the highest test concentration.

A 1:1, 1:5, or 1:10 (w/v) soil-to-solution ratio was used in the definitive testing. The sorption coefficients Kd, Kom and Koc were calculated for each soil at each concentration of the test item. A summary of the average sorption coefficients for each soil is given in the table below:

SOIL

Kd(mL/g)

Kom(mL/g)

Koc(mL/g)

Drummer

19.37

387.4

667.9

Porterville

0.22

24.8

44.6

Nambsheim

0.56

23.2

39.7

Lleida

0.83

26.6

45.9

Sassafras #16

3.66

183.1

305.2

Average

4.93

129.0

220.7

The values for the Freundlich adsorption isotherm parameter KF, KFom, KFoc, and 1/n were derived from the linear form of the Freundlich equation for all soils. A summary of the adsorption isotherm parameters for each soil is given in the table below:

SOIL

KF

KFOM

KFOC

1/n

R2

Drummer

10.66842

213.368

367.877

0.8697

0.9998

Porterville

0.19774

21.971

39.548

0.9754

0.9804

Nambsheim

0.36000

15.000

25.714

0.8879

0.9985

Lleida

0.74114

23.908

41.174

0.9771

0.9837

Sassafras # 16

1.46994

73.497

122.495

0.7827

0.9837

Average

2.68745

69.549

119.362

0.8986

0.9892

The percent 14C-test substance desorbed from the soils during two desorption intervals (D1 and D2) was calculated and totalled (DT) for all soils at the highest test solution concentration. The DT values ranged from 31.9% in the Drummer soil to 44.4% in the Nambsheim soil. In general, lower desorption values were observed in second desorption interval for all soils. The lowest desorption was observed in Drummer and Porterville soils in the first and second desorption interval, respectively whereas, the highest desorption was observed in Sassafras #16 soils in both desorption intervals (D1 and D2). A summary of the average percent desorption for each soil is given in the table below:

SOIL

D1(%)

D2(%)

DT(%)

Drummer

16.0

15.9

31.9

Porterville

24.5

15.5

39.9

Nambsheim

25.5

18.9

44.4

Lleida

24.0

15.4

39.4

Sassafras # 16

58.3

24.5

82.8