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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:
03 November 2008 through 31 March 2009
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
No desorption phase nor mass balance performed.
Qualifier:
according to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of method:
batch equilibrium method
Media:
soil
Specific details on test material used for the study:
NECTARYL :
- Batch No. : 9000751030
- Purity : 96 %
- Expiry Date : 14 May 2009
Radiolabelling:
no
Test temperature:
20 +/- 2 °C
Analytical monitoring:
yes
Details on sampling:
The study was performed with three soils of differing physico-chemical properties : Speyer 2.2 (Matrix #1), Speyer 2.3 (Matrix # 2) and Speyer 6S (Matrix #3).

Determination of the choice of Soil : Solution ratio :
An initial experiment was performed to determine the soil to solution ratio that should be applied for the adsorption kinetics and adsorption isotherm experiments.
The test soils were agitated on a roler mixer for 24 hour contact time at a soil : solution ratio of 1 : 10, 1 : 50 and 1 : 100.

Determination of Equilibrium Time (Adosprtion Kinetics) :
A soil : solution ratio of 1 : 50 was chosen. Test soils were agitated on a roler-mixer for four days at 20 +/- 2 °C. Following equilibration, the samples were spiked with the test item at a concentration of 1.0 mg/L. Samples were taken and prepared following a contact time of 3, 6, 24 and 48 hours.

Determination of Adsorption Isotherms :
The adsorption kinetics phase of the study indicatedf that a plateau had been attained by 24 hours. The adsorption isotherm part of the study was, therefore, conducted with a contact time of 24 hours. Adsorption isotherms for the three test soils were developed using initial concentrations at 0.20, 1.00, 4.99, 9.99, 20.0 mg/L, in duplicate.


Matrix no.:
#1
Matrix type:
loamy sand
% Clay:
6.4
% Silt:
12.7
% Sand:
80.9
% Org. carbon:
2.16
pH:
5.4
CEC:
10 meq/100 g soil d.w.
Matrix no.:
#2
Matrix type:
loamy sand
% Clay:
9.4
% Silt:
31.9
% Sand:
58.7
% Org. carbon:
0.98
pH:
6.4
CEC:
8 meq/100 g soil d.w.
Matrix no.:
#3
Matrix type:
clay loam
% Clay:
42.1
% Silt:
37
% Sand:
20.9
% Org. carbon:
1.75
pH:
7.2
CEC:
22 meq/100 g soil d.w.
Details on matrix:
All soils sampled from the 0 - 20 cm horizon.
Sample No.:
#1
Phase system:
soil-water
Type:
other: Freundlich-Partition Coefficient (Kf), normalised to Organic Carbon
Remarks:
Kf, OC
Value:
4 930 L/kg
Temp.:
20 °C
Matrix:
Speyer 2.2 (Loamy Sand - Matrix #1)
% Org. carbon:
2.16
Sample No.:
#2
Phase system:
soil-water
Type:
other: Freundlich-Partition Coefficient (Kf), normalised to Organic Carbon
Remarks:
Kf, OC
Value:
5 530 L/kg
Temp.:
20 °C
Matrix:
Speyer 2.3 (Loamy Sand - Matrix #2)
% Org. carbon:
0.98
Sample No.:
#3
Phase system:
soil-water
Type:
other: Freundlich-Partition Coefficient (Kf), normalised to Organic Carbon
Remarks:
Kf, OC
Value:
5 469 L/kg
Temp.:
20 °C
Matrix:
Speyer 6S (Clayey Loam - Matrix #3)
% Org. carbon:
1.75
Key result
Phase system:
soil-water
Type:
other: Mean Freundlich-Partition Coefficient (Kf), normalised to Organic Carbon
Remarks:
Mean Kf, OC
Value:
5 310 L/kg
Temp.:
20 °C
Matrix:
Mean Kf, OC for the three soils studies, mean Freundlich-Partition Coefficient (Kf), normalised to Organic Carbon
% Org. carbon:
>= 0.98 - <= 2.16
Adsorption and desorption constants:
Freundlich Adsorption Isotherm derived Partition Coefficients :

Speyer 2.2 (Matrix #1) - Kf = 106.5 L/kg; Kf, OC = 4930 L/kg; Kf, OM = 2860 L/kg

Speyer 2.3 (Matrix #2) - Kf = 54.2 L/kg; Kf, OC = 5530 L/kg; Kf, OM = 3208 L/kg

Speyer 6S (Matrix #3) - Kf = 95.7 L/kg; Kf, OC = 5469 L/kg; Kf, OM = 3172 L/kg
Recovery of test material:
A mass balance approach was not performed.
Details on results (Batch equilibrium method):
Adsorption of Nectaryl on soil could be described by a Freundlich adsorption isotherm. The Freundlich-Partition Coefficient (Kf), normalised to Organic Carbon (Kf, OC) values determined for the three different soils :

- Speyer 2.2 (Matrix #1) : 4930 L/kg

- Speyer 2.3 (Matrix #2) : 5530 L/kg

- Speyer 6S (Matrix #3) : 5469 L/kg

The test item, Nectaryl, can be considered as IMMOBILE in soil.
Validity criteria fulfilled:
yes
Conclusions:
Adsorption of Nectaryl on soil could be described by a Freundlich adsorption isotherm. The Freundlich-Partition Coefficient (Kf), normalised to Organic Carbon (Kf, OC) values determined for the three different soils :

- Speyer 2.2 (Matrix #1) : 4930 L/kg

- Speyer 2.3 (Matrix #2) : 5530 L/kg

- Speyer 6S (Matrix #3) : 5469 L/kg

The test item, Nectaryl, can be considered as IMMOBILE in soil.

Description of key information

Adsorption of Nectaryl on soil could be described by a Freundlich adsorption isotherm.  The Freundlich-Partition Coefficient (Kf), normalised to Organic Carbon (Kf, OC) values determined for the three different soils :

- Speyer 2.2 (Matrix #1) : 4930 L/kg

- Speyer 2.3 (Matrix #2) : 5530 L/kg

- Speyer 6S (Matrix #3) : 5469 L/kg

The average of Koc for the three soils studied was 5310 L/kg (LogKoc = 3.725).

The test item, Nectaryl, can be considered as IMMOBILE in soil.

Key value for chemical safety assessment

Koc at 20 °C:
5 310

Additional information

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