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Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption, other
Type of information:
experimental study
Adequacy of study:
key study
Study period:
April 4, 2003 to May 28, 2004
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
performed acc. to an older version of OECD 106 (adopted 1981) and with several limitations: e.g. 3 instead of 5 soils, only on-time measurements, no determination of equilibration time, kinetics not determined
Qualifier:
according to
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Version / remarks:
adopted 12 May 1981
Deviations:
no
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
23.2 ± 0.8 °C (room temperature)
Analytical monitoring:
yes
Details on sampling:
The following was performed for 3 soil types: Soil (approx. 2 g) and aqueous CaCl2 solution (12 mL) were mixed in test tubes and spiked with small volumes (0.1 mL) of test item solution (in duplicate, with soil blanks). After overnight mixing, the CHCI3 layer was transferred to a 1.8 mL glass crimp-top vial and stored at 4 °C awaiting GC-FID analysis.
Matrix no.:
#1
Matrix type:
Podzol
% Clay:
3
% Silt:
8
% Sand:
89
% Org. carbon:
1.12
pH:
5.1
CEC:
12.2 meq/100 g soil d.w.
Matrix no.:
#2
Matrix type:
Gleysol
% Clay:
25
% Silt:
56
% Sand:
19
% Org. carbon:
0.24
pH:
5.7
CEC:
20.6 meq/100 g soil d.w.
Matrix no.:
#3
Matrix type:
Brunisol
% Clay:
30
% Silt:
69
% Sand:
1
% Org. carbon:
4.59
pH:
9
CEC:
9.7 meq/100 g soil d.w.
Details on matrix:
COLLECTION AND STORAGE SOIL #1, PODZOL
- Geographic location: Squamish-Alicer Lake, Provincial Park (49° 46' 43.5" / 123° 06' 49.2")

PROPERTIES
- Horizon: Bmz
- Soil taxonomic classification: US comprehensive soil classification system
- Soil classification system: O.HFP, Orthic Humic Podzol
- Soil series: NA
- Soil order: Podzolic
- Carbonate as CaCO3: 1.89
- Organic matter content (%): 1.9 (converted acc. to ECHA guidance R.16 in organic carbon content: 1.12%)
- Extractable Cations (Ca, Mg, Na, K, H) (MEQ/100 g): Ca: 0.0, Mg: 0.0, K: 0.0025

COLLECTION AND STORAGE SOIL #2, GLEYSOL
- Geographic location: Delta-Agricultural plot, Boundary Bay (49° 05' 09.9" / 123° 01' 23.1")

PROPERTIES
- Horizon: Bnt
- Soil taxonomic classification: US comprehensive soil classification system
- Soil classification system: O.HG, Orthic Humic Gleysol
- Soil series: Ladner
- Soil order: Gleysolic
- Carbonate as CaCO3: 1.28
- Organic matter content (%): 1.0 (converted acc. to ECHA guidance R.16 in organic carbon content: 0.24%)
- Extractable Cations (Ca, Mg, Na, K, H) (MEQ/100 g): Ca: 5.3, Mg: 8.7, K: 0.3

COLLECTION AND STORAGE SOIL #3, BRUNISOL
- Geographic location: Kootenay Site 9, Golden (51° 85' 0.6" / 116° 59' 45.5")

PROPERTIES
- Horizon: C
- Soil taxonomic classification: US comprehensive soil classification system
- Soil classification system: E.EB, Eluviated Eutric Brunisol
- Soil series: Wapta
- Soil order: Brunisolic
- Carbonate as CaCO3: 21.84
- Organic matter content (%): 7.8 (converted acc. to ECHA guidance R.16 in organic carbon content: 4.59%)
- Extractable Cations (Ca, Mg, Na, K, H) (MEQ/100 g): Ca: 2.0, Mg: 3.9, K: 0.3
Details on test conditions:
Test Solutions
Calcium Chloride Solution (CaCl2 Solution): CaCl2.2H20 (1.449 g) was dissolved in DIW for a solution volume of 1.00 L (0.01 M).
Test item solution in CH3CN: Test item (7.2 µL) was dissolved in 5.00 mL of CH3CN (acetonitrile) solution in a volumetric flask (1.5483 mg/mL; based on density of 1.0752 g/mL).

Soils Hydration
Soil (2.0 ± 0.1 g) and Calcium Chloride Solution (12.0 mL, glass pipette) were added to ca. 15-mL glass screw-cap test tubes. The contents of the tubes were mixed (tumbled end-over-end; ca. 1 rev/5 sec) overnight to pre-equilibrate the soils.

Adsorption and Wash Solutions
After soil hydration, test item solution (100 µL) was added to the tubes with hydrated soils. The contents of the tubes were mixed (tumbled end-over-end, ca. 1 rev/5 sec) for 16.3 hours. The tubes were centrifuged (2000 rpm, 20 min). The pH's of the blank adsorption solutions were measured using a calibrated pH meter.
The adsorption solutions (10.0 mL) were transferred to ca. 15-mL glass screw-cap test tubes and extracted with 2.00 mL of CHCI3 as described in details on analytical method.
The remainders of the adsorption solutions in the ca. 15-mL glass screw-cap test tubes were discarded, leaving the damp soil pellets in the tubes.

Wash-1: Calcium chloride solution was added to the marks on the test tubes containing soil pellets. The pellets were re-suspended (vortex mixer) and the contents of the tubes were mixed for 16.3 hours. The contents of the tubes were centrifuged and the soil solutions (supernatants) were aliquoted to ca. 15-mL glass screw-cap test tubes as described above and extracted with CHCI3 as described in details on analytical method. The vials were stored at ca. 4 °C awaiting GC-FID analysis. The remainders of the supernatants were discarded, leaving the soil pellets in the tubes.

Wash-2: Calcium Chloride Solution was again added to the marks on the test tubes containing soil pellets. The pellets were re-suspended and the contents of the tubes were mixed for 67 hours. The contents of the tubes were processed as described for wash-1. The vials were stored at ca. 4 °C awaiting GC-FID analysis.

The test temperature was 23.2 ± 0.8 °C.
Sample No.:
#1
Duration:
16.3 h
Initial conc. measured:
77.4 mg/kg soil d.w.
pH:
5.1
Temp.:
>= 23 - <= 24.6 °C
Remarks:
concentration added to soil / 2 replicates
Sample No.:
#2
Duration:
16.3 h
Initial conc. measured:
77.4 mg/kg soil d.w.
pH:
5.7
Temp.:
>= 23 - <= 24.6 °C
Remarks:
concentration added to soil / 2 replicates
Sample No.:
#3
Duration:
16.3 h
Initial conc. measured:
77.4 mg/kg soil d.w.
pH:
9
Temp.:
>= 23 - <= 24.6 °C
Remarks:
concentration added to soil / 2 replicates
Sample no.:
#1
Duration:
3.5 d
Conc. of adsorbed test mat.:
57 mg/kg soil d.w.
pH:
5.1
Temp.:
22.5 °C
Remarks:
2 replicates
Sample no.:
#2
Duration:
3.5 d
Conc. of adsorbed test mat.:
34 mg/kg soil d.w.
pH:
5.7
Temp.:
22.5 °C
Remarks:
2 replicates
Sample no.:
#3
Duration:
3.5 d
Conc. of adsorbed test mat.:
69 mg/kg soil d.w.
pH:
9
Temp.:
22.5 °C
Remarks:
2 replicates
Computational methods:
- Adsorption coefficient per organic carbon (Koc):
Koc = K' *100/%OC (organic carbon content)
K', adsorption coefficient (concentration in soil/concentration in solution): K' = Cs / Cw

- Freundlich adsorption and desorption coefficients: not performed
- Slope of Freundlich adsorption/desorption isotherms: not performed
Sample No.:
#1
Type:
Koc
Value:
877 L/kg
pH:
5.1
Temp.:
23.2 °C
Matrix:
#1: Podzol
% Org. carbon:
1.9
Remarks on result:
other: 887 ± 176 L/kg
Key result
Sample No.:
#2
Type:
Koc
Value:
1 197 L/kg
pH:
5.7
Temp.:
23.2 °C
Matrix:
#2: Gleysol
% Org. carbon:
0.4
Remarks on result:
other: 1197 ± 105 L/kg
Sample No.:
#3
Type:
Koc
Value:
659 L/kg
pH:
9
Temp.:
23.2 °C
Matrix:
#3: Brunisol
% Org. carbon:
21.84
Remarks on result:
other: 659 ± 3 L/kg
Adsorption and desorption constants:
See summary table in any other information on results.
Recovery of test material:
See summary table in any other information on results.
Concentration of test substance at end of adsorption equilibration period:
See summary table in any other information on results.
Concentration of test substance at end of desorption equilibration period:
See summary table in any other information on results.
Sample no.:
#1
Duration:
16.3 h
% Adsorption:
>= 69.3 - <= 77.1
Remarks on result:
other: 2 replicates
Sample no.:
#2
Duration:
16.3 h
% Adsorption:
>= 42.1 - <= 46.5
Remarks on result:
other: 2 replicates
Sample no.:
#3
Duration:
16.3 h
% Adsorption:
>= 89.5 - <= 89.6
Remarks on result:
other: 2 replicates
Sample no.:
#1
Duration:
3.5 d
% Desorption:
>= 24.5 - <= 34
Remarks on result:
other: 2 replicates
Sample no.:
#2
Duration:
3.5 d
% Desorption:
>= 56 - <= 68
Remarks on result:
other: 2 replicates
Sample no.:
#3
Duration:
3.5 d
% Desorption:
>= 26.2 - <= 27.4
Remarks on result:
other: 2 replicates
Transformation products:
not measured
Remarks:
because the test item is stable
Details on results (Batch equilibrium method):
Three soils were representing a range of soil organic matter content (0.4 % - 7.8 %) and clay content (3 % - 30 %). The results showed that 73 ± 4 %, 44 ± 2 %, and 90 ± 0 % of test item adsorbed to soil-1, soil-2, and soil-3, respectively. After the adsorption period, 29 ± 5 %, 62 ± 6 %, and 27 ± 1 % of the adsorbed test item desorbed from soil-1, soil-2, and soil-3, respectively, after two washes. The extents of adsorption were directly related to soil organic matter contents. The adsorption coefficients (K; mL/g) were 17 ± 3, 4.8 ± 0.4, and 51.4 ± 0.3 for soil-1, soil-2, and soil-3, respectively. The adsorption coefficients expressed as a function of soil organic carbon content (Koc; mL/g) were 887 ± 176, 1197 ± 105, and 659 ± 3 for soil-1, soil-2, and soil-3, respectively.

For summary table of results see also any other information on results.


Statistics:
Recorded data for sample duplicates were averaged (arithmetic mean).

Summary study resulst / Adsorption parameters

Parameters Soil (a & b are replicates)
1a 1b 2a 2b 3a 3b
Dry weight of soil (g) 2 2 2 2 2 2
Original volume of solution employed (mL) 12 12 12 12 12 12
Volume of solution obtained after the adsorption step (mL) 10.5 10.5 10.3 10.3 10.3 10.3
Quantity of test substance added (μg) 154.8 154.8 154.8 154.8 154.8 154.8
Concentration of substance remaining in the solution (V) in the adsorption step (μg/mL) 3.97 2.95 6.91 7.47 1.34 1.36
Adsorbed % 69.30% 77.10% 46.50% 42.10% 89.60% 89.50%
Concentration of substance in the first wash step (μg/mL) 2.38 1.83 3.32 3.53 2.98 2.9
Concentration of substance in the second wash step (μg/mL) 1.66 1.37 1.77 2.09 0.95 0.87
Desorbed % 34.00% 24.50% 56% 68% 27.40% 26.20%
Percent of original quantity found remaining on adsorbent after desorption % 66.00% 75.50% 44% 32% 72.60% 73.80%
Quantity of test substance in soil (µg) 107.2276 119.3753 71.9279 65.2142 138.7138 138.5628
Adsorbed (μg/g) 53.6 59.7 36 32.6 69.4 69.3
K' (mL/g) 13.52 20.2 5.21 4.37 51.65 51.11
K'oc (mL/g) 711.4 1063.3 1301.5 1091.6 662.1 655.3
Organic matter % 1.90% 1.90% 0.40% 0.40% 7.80% 7.80%
Clay % 3.00% 3.00% 25.00% 25.00% 30.00% 30.00%
Validity criteria fulfilled:
not applicable
Conclusions:
The adsorption coefficients expressed as a function of soil organic carbon content (Koc; mL/g) were 887 ± 176, 1197 ± 105, and 659 ± 3 for soil-1, soil-2, and soil-3, respectively.
Executive summary:

This study investigated the adsorption / desorption characteristic of 3-chloro-o-xylene to soil. The study was performed according to OECD 106 (adopted 1981) and in compliance with GLP. Three different types of soil were equilibrated with aqueous solutions of the test substance 3-chloro-o-xylene for 16.3 hr, after which the soil solutions were analyzed.The soils were washed twice with calcium chloride solution, and the washes were also analyzed for the test compound.

Three soils were representing a range of soil organic matter content (0.4 % - 7.8 %) and clay content (3 % - 30 %). The results showed that 73 ± 4 %, 44 ± 2 %, and 90 ± 0 % of test item adsorbed to soil-1, soil-2, and soil-3, respectively. After the adsorption period, 29 ± 5 %, 62 ± 6 %, and 27 ± 1 % of the adsorbed test item desorbed from soil-1, soil-2, and soil-3, respectively, after two washes. The extents of adsorption were directly related to soil organic matter contents. The adsorption coefficients (K; mL/g) were 17 ± 3, 4.8 ± 0.4, and 51.4 ± 0.3 for soil-1, soil-2, and soil-3, respectively. The adsorption coefficients expressed as a function of soil organic carbon content (Koc; mL/g) were 887 ± 176, 1197 ± 105, and 659 ± 3 for soil-1, soil-2, and soil-3, respectively.

The study was performed acc. to an older version of OECD 106 (adopted 1981) and with several limitations: e.g. three instead of five soils, only on-time measurements, no determination of equilibration time and kinetics. Despite the deficiencies, the derived Koc values were considered adequate and reliable, indicating that the test substance has the property to adsorb to soil. The derived Koc values were used for the environmental hazard assessment of the test substance.

Description of key information

The adsorption coefficient Koc was: 887 ± 176, 1197 ± 105, and 659 ± 3 (mL/g) for three different types of soil (tested range of soil organic matter content: 0.4 % - 7.8 %; clay content: 3 % - 30 %). The Koc used as key value was 1197 (mL/g) / log Koc of 3.1 (OECD 206, 2004)

Key value for chemical safety assessment

Koc at 20 °C:
1 197

Additional information

A reliable key study investigated the adsorption / desorption characteristic of 3-chloro-o-xylene to soil. The study was performed according to OECD 106 (adopted 1981) and in compliance with GLP. Three soils were used, representing a range of soil organic matter (0.4 % - 7.8 %) and clay content (3 % - 30 %). Results show that the extents of adsorption were directly related to soil organic matter contents. The adsorption coefficients expressed as a function of soil organic carbon content (Koc; mL/g) were 887 ± 176, 1197 ± 105, and 659 ± 3 for soil-1, soil-2, and soil-3, respectively. The study was performed acc. to an older version of OECD 106 (adopted 1981) and with several limitations. Despite the deficiencies, the derived Koc values were considered adequate and reliable, indicating that the test substance has the property to adsorb to soil. The derived Koc values were used for the environmental hazard assessment of the test substance.