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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
29-10-2013 to 09-12-2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study performed under GLP. All relevant validity criteria were met.
Qualifier:
according to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Deviations:
no
Qualifier:
equivalent or similar to guideline
Guideline:
EU Method C.18 (Adsorption / Desorption Using a Batch Equilibrium Method)
Deviations:
no
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
20 ± 2°C
Analytical monitoring:
yes
Details on sampling:
- Concentrations:
1. Determination of equilibrium time (adsorption kinetics): A stock solution of 45.0 mg test item in 10 mL acetonitrile was prepared (4500 mg/L). The stock solution was diluted in 0.01M CaCl2 solution to obtain a spike solution of 20 mg/L. A soil : solution ratio of 1:5 was selected for all soils. The adsorption kinetics experiment was initiated by adding a weighed volume of approximately 3 mL of spike solution to the pre-equilibrated soil slurries. The initial concentration of test item in the solution was approximately 2 mg/L.
2. Determination of adsorption isotherms: Two spike solutions of 4437 mg test item/L and 311.7 mg test item/L in acetonitrile were prepared. Adsorption isotherms were determined at a 1:5 soil : solution ratio. After equilibration, the samples were spiked with an appropriate amount of one of the spike solutions to obtain final test item concentrations in the test solutions of: 0.2, 1, 5, 10 and 20 mg/L. Controls (without soil) and blank sample (without test item) were also performed.
- Sampling interval:
1. Determination of equilibrium time (adsorption kinetics): After the various contact times (3, 6, 24 and 48 hours). Blanks and controls were sampled only after 48 hours. The pH of the supernatants (48 h) was measured.
2. Determination of adsorption isotherms: After 24 hours of contact time, the soil slurries were removed from the roller mixer and centrifuged for 5 minutes at 540 g and 20°C. Aliquots of 0.75 mL were taken and stored at ≤ -15°C until analysis. The pH of the supernatants was determined at the end of the experiment after decanting (one replicate of each soil at the highest and lowest concentration level).
- Sample storage before analysis:
1. Determination of equilibrium time (adsorption kinetics): stored at ≤ -15°C until analysis
2. Determination of adsorption isotherms: stored at ≤ -15°C until analysis
- Other: On the day of analysis, the samples were defrosted at room temperature. If necessary, the aqueous samples were further diluted with 0.01M aqueous CaCl2 to obtain concentrations within the calibration range. The (diluted) test samples were extracted in a 1:1 (v:v) ratio with cyclohexane containing the internal standard naphthalene at 1 mg/L. The shaking time was 30 seconds. Based upon the results of the preliminary experiments (without soil) it was concluded that adsorption to container materials was very high. As a consequence, glass vials used in adsorption kinetics and adsorption isotherm experiments were rinsed after each sampling with cyclohexane containing the internal standard at 1 mg/L in order to determine the fraction adsorbed to glass walls. Thus, in addition to the regular supernatant samples, samples from rinsing the test vessels were taken. If necessary, these latter samples were further diluted with cyclohexane containing the internal standard at 1 mg/L prior to analysis.
Matrix no.:
#1
Matrix type:
loamy sand
% Clay:
8.2
% Silt:
15.3
% Sand:
76.5
% Org. carbon:
1.74
pH:
5.5
CEC:
10.2 meq/100 g soil d.w.
Matrix no.:
#2
Matrix type:
sandy loam
% Clay:
8.7
% Silt:
28.2
% Sand:
63.1
% Org. carbon:
1
pH:
6.8
CEC:
10.7 meq/100 g soil d.w.
Matrix no.:
#3
Matrix type:
clay
% Clay:
40.7
% Silt:
34.5
% Sand:
24.8
% Org. carbon:
1.66
pH:
7.1
CEC:
26.9 meq/100 g soil d.w.
Details on matrix:
COLLECTION AND STORAGE
- Geographic location: #1: Speyer 2.2 soil : Hanhofen, Rheinland-Pfalz, Germany ; #2: Speyer 2.3 soil : Offenbach, Rheinland-Pfalz, Germany ; #3: Speyer 6S soil : Siebeldingen, Rheinland-Pfalz, Germany
- Collection procedures: Not reported.
- Sampling depth (cm): Not reported.
- Storage conditions: 4°C since receipt and then ambient temperature during study
- Storage length: ca. 5 months
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): Sieved (2 mm) air-dried soil samples were taken from storage in the laboratory.

PROPERTIES
See “Details on Matrix”. Additionally see attached background material.
Moisture content of the matrices was pre-determined prior to the study and was taken into account in all determinations. The moisture content of the soils was 1.07% : #1: Speyer 2.2 soil ; 1.11% : #2: Speyer 2.3 soil and 3.77% : #3: Speyer 6S soil.
Details on test conditions:
TEST CONDITIONS
- Buffer: Not applicable.
- pH: The pH of the supernatants was pH 6.1 for #1: Speyer 2.2 soil, pH 7.1 for #2: Speyer 2.3 soil and pH 7.4 for #3: Speyer 6S soil.
- Suspended solids concentration: Not applicable.
- other: Three or more experiments were conducted. Different conditions and test systems were used in the determination of each parameter. Described further, as appropriate.
Preliminary test: Stability of test item / adsorption to container material
Preliminary test: Determination of an appropriate soil : solution ratio
Definitive test:
1. Determination of equilibrium time (adsorption kinetics
2. Determination of adsorption isotherms

TEST SYSTEM
- Type, size and further details on reaction vessel: Glass containers used (less adsorption in preliminary testing than polypropylene containers)
- Water filtered (i.e. yes/no; type of size of filter used, if any): Tap water purified by a Milli-Q water purification system.
- Amount of soil/sediment/sludge and water per treatment (if simulation test): Not applicable.
- Soil/sediment/sludge-water ratio (if simulation test): Not applicable.
- Number of reaction vessels/concentration: See Details on Sampling.
- Measuring equipment: See identification and quantification of the test substance/product and other fields.
- Test performed in closed vessels due to significant volatility of test substance: Closed vessel use is presumed from definition of the containers.
- Method of preparation of test solution: See Details on Sampling.
- Are the residues from the adsorption phase used for desorption: Not applicable.
- Other:
Preliminary tests:
In the first preliminary test after 24 hours 68% was recovered in the water layer. This indicates that the test substance significantly adsorbs to the glass walls (less so than polypropylene). Separately, it was decided to select a soil: solution ratio of 1: 5, since it was shown that more soil would lead to less adsorption to the container walls.
1. Determination of equilibrium time (adsorption kinetics
The results of the adsorption kinetics experiment based on the analysis of the aqueous samples. Since the average adsorption of test item on the container walls was ≤6%, no correction was made for the adsorption on glass.
2. Determination of adsorption isotherms:
The fits of the Freundlich adsorption isotherms and parameters of Speyer 2.2, Speyer 2.3 and Speyer 6S soil were determined. Since the average adsorption of test item on the container walls was ≤4%, no correction was made for the adsorption on glass.
Computational methods:
- Adsorption and desorption coefficients (Kd): The adsorption coefficients Kd and Koc were obtained from the adsorption kinetics experiment and were calculated as follows:
Kd = Cs (eq)/Caq (eq)
and
Koc = Kd x 100 / %OC
- Freundlich adsorption and desorption coefficients: The Freundlich adsorption isotherm parameters (KFads and 1/nads) were calculated by fitting the Freundlich isotherm to the data.
Cs(eq) = KF ∙ Caq(eq)1/n
- Slope of Freundlich adsorption/desorption isotherms: See tables.
- Adsorption coefficient per organic carbon (Koc): See above.
- Regression coefficient of Freundlich equation. These were reported. See tables.
- Other: Not applicable.
Sample No.:
#1
Type:
log Koc
Value:
3.06 dimensionless
pH:
6.1
Temp.:
20 °C
Matrix:
Speyer 2.2 - Loamy sand
% Org. carbon:
1.74
Remarks on result:
other: Koc = 1155 mL/g
Sample No.:
#2
Type:
log Koc
Value:
3.03 dimensionless
pH:
7.1
Temp.:
20 °C
Matrix:
Speyer 2.3 - Sandy loam
% Org. carbon:
1
Remarks on result:
other: Koc = 1070 mL/g
Sample No.:
#3
Type:
log Koc
Value:
3.03 dimensionless
pH:
7.4
Temp.:
20 °C
Matrix:
Speyer 6S - Clay
% Org. carbon:
1.66
Remarks on result:
other: Koc = 1060 mL/g
Adsorption and desorption constants:
See table 1.
Recovery of test material:
See table 2 and table 3 and table 4. 1. Determination of equilibrium time (adsorption kinetics
The results of the adsorption kinetics experiment based on the analysis of the aqueous samples. Since the average adsorption of test item on the container walls was ≤6%, no correction was made for the adsorption on glass.
2. Determination of adsorption isotherms:
The fits of the Freundlich adsorption isotherms and parameters of Speyer 2.2, Speyer 2.3 and Speyer 6S soil were determined. Since the average adsorption of test item on the container walls was ≤4%, no correction was made for the adsorption on glass.
Transformation products:
not measured
Details on results (Batch equilibrium method):
PRELIMINARY TEST
- Sample purity: Same as definitive test.
- Weighed soil: Soil : solution ratios of approximately 1:2, 1:10 and 1:50 were investigated for all soils. 1: 5 was selected, since it was shown that more soil would lead to less adsorption to the container walls.
- Volume of CaCl2 solution: In preliminary test 1: diluted 0.01M CaCl2 solution to obtain a test solution of 10 mg/L ; in preliminary test 2: diluted in 0.01M CaCl2 solution to obtain a spike solution of 20 mg/L, with further dilution to obtain 2 mg/L test item concentrations.
- Initial test substance concentration: In preliminary test 1: 10 mg/L test item ; In preliminary test 2: 2 mg/L test item
- Test substance concentration in final solution: See above.
- Analytical test substance concentration in final solution: Analysed concentrations are reported in the full study repor.t
- Other: Glass containers and a soil: solution ratio of 1: 5 was selected, since it was shown that more soil would lead to less adsorption to the container walls.

MAIN TEST: PERFORMANCE
- Test material stability during adsorption/desorption phase: Yes (based on equilibrium period of 24 hours determined from preliminary testing).
- Experimental conditions maintained throughout the study: Yes
- Buffer/test substance interactions affecting sorption: Not applicable.
- Further chemical interactions: Not applicable.
- Buffer-catalyzed degradation of test substance: Not applicable.
- Anomalies or problems encountered (if yes): Some adsorption to test container glass, however was not deemed necessary to correct for the adsorption as this remained ≤6% in all definitive testing.
- Other observations: None.

TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount: Not applicable.

RESIDUES
- Total unidentified radioactivity (range) of applied amount: Not applicable.
- Extractable residues (% of applied amount at end of study period): Not applicable.
- Non-extractable residues (% of applied amount at end of study period): Not applicable.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: Not applicable.

RESULTS OF SUPPLEMENTARY EXPERIMENT (if any): Not applicable.

Table 1. Freundlich adsorption isotherm parameters for test item

Soil

Soil number

Soil type

KF

(mL/g)

KF,oc

(mL/g)

1/n

r2

log Koc

Data points

pH of supernatant

Speyer 2.2

#1

Loamy sand

20.1

1155

1.05

0.995

3.06

10

5.4-5.5

Speyer 2.3

#2

Sandy loam

10.7

1070

0.93

0.990

3.03

10

6.8-6.9

Speyer 6S

#3

Clay

17.6

1060

0.92

0.997

3.03

10

7.0-7.1

 

 

 

 

 

 

 

 

 

 

 

Other: Plots of primary data indicated increases of the adsorption of test item to all the soils in the first 3 hours of contact time. No significant increase in adsorption was observed between 24 and 48 hours contact time for Speyer 2.2 and Speyer 6S soils. For Speyer 2.3 soil a slight increase was observed between 24 and 48 hours of contact time. Based on the results of the kinetics experiment, it was decided to take samples after 24 hours of adsorption in the isotherms experiment with all soils. For Speyer 2.3 soil also 24 hours was selected to exclude degradation. No significant amounts of test item were detected in blank samples.

 

Table 2. Adsorption of test item to container materials

Container material

Contact Time (h)

Mean % recovery (n=2)

Polyproplyene

0

74.3

 

6

37.1

 

24

20.8

Glass

0

75.6

 

6

69.8

 

24

49.7

 

 

 

Glass (experiment 2)

0

110

 

24

68.2

 

 

 

 

Table 3. Adsorption of test item at different soil : solution ratios (first experiment - preliminary test 2)

Soil

Soil number

soil : solution ratio

% adsorption

 

 

 

 

Speyer 2.2

#1

1:2

95.9

 

 

1:10

88.1

 

 

1:50

82.1

 

 

 

 

Speyer 2.3

#2

1:2

93.1

 

 

1:10

84.4

 

 

1:50

79.1

 

 

 

 

Speyer 6S

#3

1:2

95.0

 

 

1:10

87.3

 

 

1:50

81.1

 

 

 

 

 

Table 4. Adsorption of test item at different soil : solution ratios (second experiment - preliminary test 2)

Soil

Soil number

soil : solution ratio

% adsorption total

% adsorption soil

 

 

 

 

 

Speyer 2.3

#2

1:10

57.2

39.7

 

 

1:50

44.0

22.5

 

 

 

 

 

Validity criteria fulfilled:
yes
Conclusions:
The test item adsorption coefficient (log Koc) for three different soils according to OECD Guideline 106 was Speyer 2.2 (loamy sand): 3.06, Speyer 2.3 (sandy loam): 3.3 and Speyer 6S (clay): 3.03 at 20 ± 2°C.
Executive summary:

The test item adsorption coefficient (log Koc) for three different soils according to OECD Guideline 106 was Speyer 2.2 (loamy sand): 3.06, Speyer 2.3 (sandy loam): 3.3 and Speyer 6S (clay): 3.03 at 20 ± 2°C. The study was performed in accordance with OECD TG 106 batch equilibrium method under GLP to assess the adsorption coefficient (Koc) of the test item to three different soils, including a loamy sand (Speyer 2.2 soil), a sandy loam (Speyer 2.3 soil) and a clay soil (Speyer 6S soil). Adsorption was studied using the batch equilibrium method and calculated as the difference between the initial test substance concentration and the concentration at sampling. All adsorption experiments were carried out in the dark at 20 ± 2°C. The experiments were performed at a 1:5 soil : solution ratio. Adsorption kinetics were determined at an initial test item concentration of approximately 2 mg/L. Adsorption equilibrium was reached after 24 hours for Speyer 2.2 and Speyer 6S. For Speyer 2.3 a slight increase of adsorption was observed between 24 and 48 hours. Adsorption isotherms were determined over a test item concentration range of 0.2 – 20 mg/L and a contact time of 24 hours. At the end of the isotherm experiment, the pH of the supernatant was measured for each soil at the lowest and highest test substance concentration. The pH was 5.5-5.4 for Speyer 2.2 soil, 6.8-6.9 for Speyer 2.3 soil and 7.0-7.1 for Speyer 6S soil. Adsorption of test item on Speyer 2.2 (%OC 1.74), Speyer 2.3 (%OC 1.0) and Speyer 6S (%OC 1.66) soil could be described by the Freundlich equation. The Freundlich adsorption coefficients for these three soils are summarised as: Speyer 2.2 (loamy sand): 3.06 (Koc: 1155 mL/g), Speyer 2.3 (sandy loam): 3.3 (Koc: 1070 mL/g) and Speyer 6S (clay): 3.03 (Koc: 1060 mL/g) at 20 ± 2°C.

Description of key information

log Koc = 3.06 (Koc: 1155 mL/g): Speyer 2.2 - loamy sand: pH 5.4-5.5; 3.03 (Koc: 1070 mL/g) : Speyer 2.3 - sandy loam: pH 6.8-6.9 and 3.03 (Koc: 1060 mL/g) : Speyer 6S (clay pH 7.0-7.1) at 20 ± 2°C and 1 atm, OECD TG 106, 2014

Key value for chemical safety assessment

Koc at 20 °C:
3.06

Additional information

Key study : OECD TG 106, 2014 : The test item adsorption coefficient (log Koc) for three different soils according to OECD Guideline 106 was Speyer 2.2 (loamy sand): 3.06, Speyer 2.3 (sandy loam): 3.3 and Speyer 6S (clay): 3.03 at 20 ± 2°C. The study was performed in accordance with OECD TG 106 batch equilibrium method under GLP to assess the adsorption coefficient (Koc) of the test item to three different soils, including a loamy sand (Speyer 2.2 soil), a sandy loam (Speyer 2.3 soil) and a clay soil (Speyer 6S soil). Adsorption was studied using the batch equilibrium method and calculated as the difference between the initial test substance concentration and the concentration at sampling. All adsorption experiments were carried out in the dark at 20 ± 2°C. The experiments were performed at a 1:5 soil : solution ratio. Adsorption kinetics were determined at an initial test item concentration of approximately 2 mg/L. Adsorption equilibrium was reached after 24 hours for Speyer 2.2 and Speyer 6S. For Speyer 2.3 a slight increase of adsorption was observed between 24 and 48 hours. Adsorption isotherms were determined over a test item concentration range of 0.2 – 20 mg/L and a contact time of 24 hours. At the end of the isotherm experiment, the pH of the supernatant was measured for each soil at the lowest and highest test substance concentration. The pH was 5.5-5.4 for Speyer 2.2 soil, 6.8-6.9 for Speyer 2.3 soil and 7.0-7.1 for Speyer 6S soil. Adsorption of test item on Speyer 2.2 (%OC 1.74), Speyer 2.3 (%OC 1.0) and Speyer 6S (%OC 1.66) soil could be described by the Freundlich equation. The Freundlich adsorption coefficients for these three soils are summarised as: Speyer 2.2 (loamy sand): 3.06 (Koc: 1155 mL/g), Speyer 2.3 (sandy loam): 3.3 (Koc: 1070 mL/g) and Speyer 6S (clay): 3.03 (Koc: 1060 mL/g) at 20 ± 2°C.

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