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Adsorption / desorption

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Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 2014-10-23 to 2014-11-20
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study without detailed documentation
Qualifier:
according to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Deviations:
no
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil
Specific details on test material used for the study:
Lot No.: KNC110310
Purity: 100.0%
Radiolabelling:
no
Test temperature:
23±2 ℃
Analytical monitoring:
yes
Details on sampling:
- Tier 1-Preliminary test:
The test item concentration of the aqueous phase was analyzed after centrifugation and filtration at 2, 4, 6, 8, 24, 48, 96 and 120 h.

- Tier 2-Adsorption kinetics at one concentration of the test item:
Determination of concentration oftest item in aqueous phase was conducted at 2, 4, 6, 8, 24, 48, 96 and 120 h.

- Tier 3-Desorption kinetics at one concentration of the test item:
The aqueous phases were separated by centrifugation and the aqueous phases were removed as much as possible. Then concentration of the aqueous phase was analyzed after 2, 4, 6, 24, 30, 72, 96 and 120 h.

- Tier 4-Adsorption isotherms:
The test item concentrations of aqueous phases were determined after 120 h.

- Tier 5-Desorption isotherms:
The test item concentrations of aqueous phases were determined when it reached desorption equilibrium time.

- Tier 6-Mass balance:
The test item concentrations in the soils #1, #2 were determined.
Matrix no.:
#1
Matrix type:
loam
% Org. carbon:
6.82
pH:
6.85
CEC:
27.1 other: cmol/kg
Matrix no.:
#2
Matrix type:
silty clay
% Org. carbon:
1.52
pH:
6.58
CEC:
10.5 other: cmol/kg
Matrix no.:
#3
Matrix type:
silty clay loam
% Org. carbon:
5.82
pH:
6.96
CEC:
21.2 other: cmol/kg
Matrix no.:
#4
Matrix type:
silt loam
% Org. carbon:
1.83
pH:
6.42
CEC:
6.59 other: cmol/kg
Matrix no.:
#5
Matrix type:
silt loam
% Org. carbon:
6.35
pH:
7.01
CEC:
23.3 other: cmol/kg
Details on matrix:
- Preparation of test soil:
The soils were air-dried ambient temperature (preferably between 20-25℃) after collection. The soils were sieved to a particle size ( ≤2 mm), and distributed uniformly. The moisture content of each soil was determined with heating at 105℃. For all calculations the mass of soil refers to oven dry mass.
Details on test conditions:
- Tier 1-Preliminary test:
Two soil types (#1 and #2) and three soil/solution ratios below were suggested to determine the optimal soil/solution.
50 g soil and 50 mL aqueous solution (0.01 mol/L CaCl2 solution) of the test item (soil/solution ratio 1/1)
10 g soil and 50 mL aqueous solution (0.01 mol/L CaCl2 solution) of the test item (soil/solution ratio 1/5)
2 g soil and 50 mL aqueous solution (0.01 mol/L CaCl2 solution) of the test item (soil/solution ratio 1/25)
One control sample with only the test item in 0.01 mol/L CaCl2 solutions (no soil) was subjected to precisely the same steps as the test systems, in order to check the stability of the test item in 0.01 mol/L CaCl2 solution and its possible adsorption on the surfaces of the test vessels.
A blank sample with the same amount of soil and total volume of 50 mL 0.01 mol/L CaCl2 solutions (without test item) was subjected to the same test procedure. This served as a background control during the analysis to detect whether there are interference substances or soils are contaminated.
All the experiments, including controls and blanks, were performed in duplicate.

- Tier 2-Adsorption kinetics at one concentration of the test item:
The optimal soil/solution ratio for soil #1, #3 and #5 was 1/1 and for soil #2, #4 was 1/5. A treatment of one concentration (2500 mg/L) for each soil was done, and the determination was performed at each time point. In every experiment, a blank sample which consisted of the soil and 0.01 mol/L CaCl2 solution without test item, and a control sample with only the test item in 0.01 mol/L CaCl2 solution (without soil) were subjected to the same test procedure.

- Tier 3-Desorption kinetics at one concentration of the test item:
The soils, the soillsolution ratios, the concentration of the test solution (2500 mg/L) were selected the same as the adsorption kinetics study. The mixture of soil with solution was shaken until adsorption equilibrium was reached on the water bath shaker at 23±2 ℃ for 120 h. Then, the aqueous phases were separated by centrifugation and the aqueous phases were removed as much as possible. The volume of solution removed was replaced by an equal volume of 0.01 mol/L CaCl2 solution without test item. The mixture of soil with the new solution was mixed and shaken. Then concentration of the aqueous phase was analyzed after 2, 4, 6, 24, 30, 72, 96 and 120 h. In every experiment one blank was run. It consisted of the soil and 0.01 mol/L CaCl2 solution, without test item. A control sample with only the test item in 0.01 mol/L CaCl2 solution (without soil) was subjected to the same test procedure.

- Tier 4-Adsorption isotherms:
Five test item concentrations (750, 1000, 1500, 2000 and 2500 mg/L) were used in five soils respectively for the adsorption isotherms test. This test was performed as describe above (Tier 2).

- Tier 5-Desorption isotherms:
Desorption isotherms test was performed as describe above five concentration were set separately (750, 1000, 1500, 2000 and 2500 mg/L).

- Tier 6-Mass balance:
On the base of Tier 2, the test item concentrations in the soils #1, #2 were determined.
Duration:
120 h
Temp.:
23 °C
Duration:
72 h
Temp.:
23 °C
Remarks:
For soil #1, #3 and #5
Sample no.:
#2
Duration:
2 h
Temp.:
23 °C
Sample no.:
#4
Duration:
96 h
Temp.:
23 °C
Computational methods:
Please refer to the "Adsorption-desorption PSF-58 - DATA ANALYSIS" in attached backgroud material.
Sample No.:
#1
Type:
Koc
Value:
5.51 other: cm3/g
Temp.:
23 °C
Matrix:
Loam (Black soil)
% Org. carbon:
6.82
Sample No.:
#2
Type:
Koc
Value:
59.4 other: cm3/g
Temp.:
23 °C
Matrix:
Silty clay (Red soil)
% Org. carbon:
1.52
Sample No.:
#3
Type:
Koc
Value:
8.16 other: cm3/g
Temp.:
23 °C
Matrix:
Silty clay loam (Paddy soil)
% Org. carbon:
5.82
Sample No.:
#4
Type:
Koc
Value:
50.9 other: cm3/g
Temp.:
23 °C
Matrix:
Silty loam (Moisture soil)
% Org. carbon:
1.83
Sample No.:
#5
Type:
Koc
Value:
7.13 other: cm3/g
Temp.:
23 °C
Matrix:
Silty loam (Meadow soil)
% Org. carbon:
6.35
Sample no.:
#1
Duration:
120 h
% Adsorption:
93.9
Sample no.:
#2
Duration:
120 h
% Adsorption:
92.7
Transformation products:
not measured
Details on results (Batch equilibrium method):
- TIER1-PRELIMINARY TEST:
For soil #1, with the soil/solution ratio of 1/25, it reached equilibrium at 6 h with the percentage adsorption of 11.2 %, with the ratio of 1/5, the percentage adsorption was 23.2 % at 120 h, and with the ratio of 1/1, and the percentage adsorption was 25.6 % at 120 h. So for soil #1, #3 and #5 with high content of organic carbon, the soil/solution ratio of 1/1 was selected. For soil #2, with the soil/solution ratio of 1/25, the adsorption percentage was 8.80 % at 96 h, with the ratio of 1/5, the adsorption percentage was 12.8 % at 96 h, and with the ratio of 1/1, and the adsorption percentage was 12.8 % at 96 h. So for soil #2 and #4, the soil/solution ratio of 1/5 was selected. The adsorption equilibration time was achieved at 120 h. Tthere was no adsorption on the test vessels and the test item was stable in CaCl2 solution during the test time.

- TIER 2-ADSORPTION KINETICS AT ONE CONCENTRA TION OF THE TEST ITEM:
The distribution coefficient Kd of five soils were 0.376, 0.903, 0.475, 0.931 and 0.453 cm3/g and the organic carbon normalized adsorption coefficient Koc were 5.51, 59.4, 8.16, 50.9 and 7.13 cm3/g, respectively.

- TIER 3-DESORPTION KINETICS AT ONE CONCENTRATION OF THE TEST ITEM:
The desorption coefficient Kdes of five soils were 0.327, 2.09, 0.275, 1.41 and 0.639 cm3/g and desorption percentage were 75.4 %, 70.5 %, 78.4 %, 78.0 % and 61.0 %, respectively.

- TIER 4-FREUNDICH ADSORPTION ISOTHERMS:
Freudlich adsorption coefficient (K_F^ads) of five soils were 0.100, 52.2, 3.70, 8.45 and 2.92〖μg〗^(1-1/n) 〖(cm3)〗^(1/n)/ g, respectively and the value of 1/n were 0.798 ~ 1.51.

- TIER 5- FREUNDICH DESORPTION ISOTHERMS
Freudlich desorption coefficient (K_F^des) of five soils were 249, 0.0000115, 0.0000725, 0.495 and 17.5〖μg〗^(1-1/n) 〖(cm3)〗^(1/n)/ g, respectively and the value of 1/n were -0.181 ~ 3.32.

- TIER 6-MASS BALANCE:
When the nominal concentration was 2500 mg/L at the beginning of the test, the mass balances of #1, #2 soils were 93.9 % and 92.7 % respectively.
Validity criteria fulfilled:
not specified
Conclusions:
Based on the results, when reached adsorption equilibrium, the distribution coefficient Kd of five soils were 0.376, 0.903, 0.475, 0.931 and 0.453 cm3/g. Freudlich adsorption coefficient (K_F^ads) of five soils were 0.1 00, 52.2, 3.70, 8.45 and 2.92〖μg〗^(1-1/n) 〖(cm3)〗^(1/n)/ g, respectively
Executive summary:

The test was designed to evaluate the adsorption behavior of the test item on different soil types in order to predict its distribution under different environmental conditions. The study procedures described in this report were designed according to OECD 106.

Five soils which characterized by different physic-chemical properties such as pH, organic carbon content and soil texture were selected. To determine the adsorption/desorption behavior, tests of different tiers comprising preliminary test, adsorption kinetic test and adsorption isotherm test were carried out using batch equilibrium method.

The optimal soil/water ratios of test item in soil #1, #3 and #5 were 1/1, and the optimal soil/water ratios of test item in soil #2 and #4 were 1/5. The distribution of test item in soil/solution phase reached equilibrium after shaken at a constant temperature for 120 h. The distribution coefficient (Kd) of test item in the above five soil types were 0.376, 0.903, 0.475, 0.931 and 0.453 cm3/g and the adsorption coefficient (Koc) of that were 5.51, 59.4, 8.16, 50.9 and 7.13 cm3/g respectively. Desorption coefficient of test item in five soils were 0.327, 2.09, 0.275, 1.41 and 0.639 cm3/g respectively. Freudlich adsorption coefficient of five soils were 0.1 00, 52.2, 3.70, 8.45 and 2.92, respectively. Freudlich desorption coefficient of five soils were 249, 0.0000115, 0.0000725, 0.495 and 17.5, respectively and the value of 1/n were -0.181 ~ 3.32. When the nominal concentration was 2500 mg/L at the beginning of the test, the mass balances of #1, #2 soils were 93.9 % and 92.7 % respectively.

Description of key information

The adsorption behavior of the test item on different soil types were evaluated based on OECD 106. The distribution coefficient (Kd) of test item in the above five soil types were 0.376, 0.903, 0.475, 0.931 and 0.453 cm3/g and the adsorption coefficient (Koc) of that were 5.51, 59.4, 8.16, 50.9 and 7.13 cm3/g respectively.

Key value for chemical safety assessment

Koc at 20 °C:
26.22

Additional information

 Mean value of five soils (5.51, 59.4, 8.16, 50.9 and 7.13 cm3/g respectively)