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Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
April - Nov 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Qualifier:
according to guideline
Guideline:
EPA OPPTS 835.1110 (Activated Sludge Sorption Isotherm)
Qualifier:
according to guideline
Guideline:
other: EMA Guideline on the Environmental Risk Assessment of Medicinal Products for Human Use (EMEA/CHMP/SWP/4447/00).
Version / remarks:
Adopted 01 June 2006.
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil/sewage sludge
Radiolabelling:
yes
Test temperature:
20 ± 2°C
Details on study design: HPLC method:
A stock solution containing 1.38 MBq LBQ657/mL (based on triplicate analysis by LSC; RSD 1.1%) in acetonitrile was used. This is equivalent to a concentration of 287 mg LBQ657/L. A spike solution was prepared by diluting the stock solution with 0.01 M CaCl2 solution to 3.27 mg LBQ657/L (15.7 kBq/mL based on triplicate analysis by LSC; RSD 0.4%).
The experiment described in section "Details on sampling" was repeated using sterilised Speyer 2.3 and Speyer 6S soil slurries at a soil:solution ratio of 1:2 and sterilised Tilburg and Aa & Maas sludge at a sludge:solution ratio of 1:10. The sludges (approximately 3 g sludge and 27 mL of 0.01 M CaCl2 solution) and the soils (approximately 15 g soil and 27 mL of 0.01 M CaCl2 solution) were autoclaved at 121°C for 20 minutes prior to equilibration. All sludge and soil slurries were equilibrated in glass containers on a roller mixer at 20 ± 2°C for four days in the dark prior to spiking. The adsorption-desorption kinetics experiment was initiated by adding a volume of 3 mL of spike solution to the pre-equilibrated sludges and soil slurries. Hence, the initial concentration of LBQ657 in the solution was approximately 0.3 mg/L.
A blank sample was included for each test system using the same amounts of soil and 0.01 M CaCl2 solution without test substance. Two control samples were also included, containing known amounts of 0.01 M CaCl2 solution and spike solution without a test system.
The samples were placed on a roller mixer at 20 ± 2°C in the dark. At the adsorption sampling times (3, 6, 24 and 48 hours), the slurries were removed from the roller mixer and centrifuged for 5 minutes at 160 g and 20°C. After centrifugation, a 100 µL aliquot of the supernatant was taken from each sample (including blanks) for determination of activity by LSC. Directly after sampling, the slurries were mixed well and placed back on the roller mixer until the next sampling event. After 48 hours of adsorption, the remaining supernatant of each test system was decanted and weighed.
Subsequently, an approximately equal weight of fresh 0.01 M CaCl2 solution was added to the test systems (B and Bl replicates). The vials were closed and placed on the roller mixer. At the desorption sampling times (3, 6, 24 and 30 hours), the slurries were removed from the roller mixer and centrifuged (5 minutes at 160 g and 20°C). After centrifugation a 100 µL aliquot of the supernatant was taken from each sample for the determination of activity by LSC. After the final desorption sampling event, the remaining supernatant was decanted and weighed.
At the end of the adsorption and desorption phases, the supernatants were filtered and analysed on HPLC. Filtration of the samples was necessary to remove all soil/sludge particles before HPLC analysis. After filtration a subsample was counted with LSC. The pH of the supernatants after the adsorption and desorption phase of the kinetics experiment (one replicate of each test system) was determined on the day of decanting.
At the end of the adsorption/desorption period after removal of the supernatant, the soils and sludges were allowed to dry to the air at room temperature for 33-34 days.
The adsorption part was conducted in duplicate for each test system (replicate A and B). The desorption part was conducted with replicates B and Bl only. Mass balances were determined after the adsorption part (replicate A) and after the desorption part (replicate B). Mass balances included radioactivity in samples taken for analysis, radioactivity in decanted supernatant after adsorption and/or desorption and radioactivity in test system
Analytical monitoring:
yes
Details on sampling:
A stock solution containing 711 kBq LBQ657/mL (based on triplicate analysis by LSC; RSD 1.7%) in acetonitrile was used. This is equivalent to a concentration of 148 mg LBQ657/L. A spike solution was prepared by diluting the stock solution with 0.01 M CaCl2 solution to 2.84 mg LBQ657/L (13.6 kBq/mL based on triplicate analysis by LSC; RSD 0.6%).
Based on the experiment a soil:solution ratio of 1:2 and sludge:solution ratio of 1:10 was selected. The sludges (approximately 3 g sludge and 27 mL of 0.01 M CaCl2 solution) and the soils (approximately 15 g soil and 27 mL of 0.01 M CaCl2 solution) were equilibrated in polypropylene tubes on a roller mixer at 20 ± 2°C overnight in the dark prior to spiking. The adsorption-desorption kinetics experiment was initiated by adding a volume of 3 mL of spike solution to the pre-equilibrated sludge and soil slurries. Hence, the initial concentration of LBQ657 in the solution was approximately 0.3 mg/L.
A blank sample was included for each test system using the same amounts of soil and 0.01 M CaCl2 solution without test substance. Two control samples were also included, containing known amounts of 0.01 M CaCl2 solution and spike solution without a test system.
The samples were placed on a roller mixer at 20 ± 2°C in the dark. At the adsorption sampling times (3, 6, 24 and 48 hours), the slurries were removed from the roller mixer and centrifuged for 5 minutes at 540 g and 20°C. After centrifugation, a 100 µL aliquot of the supernatant was taken from each sample (including blanks) for determination of activity by LSC. Directly after sampling, the slurries were mixed well and placed back on the roller mixer until the next sampling event. After 48 hours of adsorption, the remaining supernatant of each test system was decanted and weighed.
Subsequently, an approximately equal weight of fresh 0.01 M CaCl2 solution was added to the test systems (B and Bl replicates). The vials were closed and placed on the roller mixer. At the desorption sampling times (3, 6, 24 and 30 hours), the slurries were removed from the roller mixer and centrifuged (5 minutes at 540 g and 20°C). After centrifugation a 100 µL aliquot of the supernatant was taken from each sample for the determination of activity by LSC. After the final desorption sampling event, the remaining supernatant was decanted and weighed.
The decanted supernatants (after both the adsorption and the desorption phase) were analysed by HPLC. The pH of the supernatants after the adsorption and desorption phase of the kinetics experiment (one replicate of each test system) was determined on the day of decanting.
At the end of the adsorption/desorption period after removal of the supernatant, Speyer 2.2 soil was allowed to dry to the air at room temperature for 26- 27 days to determine the mass balance. Mass balances of the other soils and sludges were determined in the second kinetics test.
The adsorption part was conducted in duplicate for each test system (replicate A and B). The desorption part was conducted with replicates B and Bl only. Mass balances were determined after the adsorption part (replicate A) and after the desorption part (replicate B) for Speyer 2.2. Mass balances included radioactivity in samples taken for analysis, radioactivity in decanted supernatant after adsorption and/or desorption and radioactivity in soil or sludge
Details on matrix:
Adsorption and desorption parameters of LBQ657 were determined in two different sludges and in three different soils. Sieved (2 mm) freeze-dried and oven-dried sludge samples and sieved (2 mm) air-dried soil samples were taken from storage. Storage was at ambient temperature. Moisture content was determined at WIL Research Europe after oven drying until constant weight. Soil and sludge parameters are summarised in Table:

Designation Classification (USDA) % OC CEC (meq/100g) pH
Tilburg sludge Sludge 41.2 104 6.1
Aa & Maas sludge Sludge 43.7 92 5.6
Speyer 2.2 soil Loamy sand 1.74 10 5.5
Speyer 2.3 soil Sandy loam 1.0 11 6.8
Speyer 6S soil Clay 1.66 27 7.1
% OC percentage organic carbon
CEC cationic exchange capacity
Details on test conditions:
Radioactivity in solution was determined by counting an aliquot in 10 mL of Ultima Gold cocktail on a Liquid Scintillation Counter. The limit of quantification (LOQ) was considered 5 times the average background (125 dpm).
Combustion was performed on an oxidizer. The 14CO2 released during combustion was trapped in Oxysolve C-400 cocktail. Radioactivity was measured by LSC.
Prior to measurement, the oxidizer was tested for blanks and for efficiency of the combustion process. Samples of about 25 mg filtration paper were used as test matrix. Background response was determined and a blank check was performed by combustion of non-spiked samples. Efficiency of the combustion process was determined as the ratio of the radioactivity collected after combustion of a spiked paper filter, and the nominal radioactivity which was spiked directly into the scintillation cocktail after combustion of a non-spiked sample. All these determinations were performed in duplicate. The efficiency test was performed before and after each sample series. The acceptance criterion for the efficiency was 90% and was always met. Sample measurements were corrected for background response and for efficiency of the combustion process.
Key result
Sample No.:
#1
Type:
Kd
Value:
9.3 L/kg
Matrix:
Tilburg; Sludge
% Org. carbon:
41.2
Key result
Sample No.:
#2
Type:
Kd
Value:
19.7 L/kg
Matrix:
Aa & Maas; Sludge
% Org. carbon:
43.7
Key result
Sample No.:
#3
Type:
Kd
Value:
6.4 L/kg
Matrix:
Speyer 2.2; Loamy sand
% Org. carbon:
1.74
Key result
Sample No.:
#4
Type:
Kd
Value:
0.4 L/kg
Matrix:
Speyer 2.3, Sandy loam
% Org. carbon:
1
Key result
Sample No.:
#5
Type:
Kd
Value:
0.7 L/kg
Matrix:
Speyer 6S; Clay
% Org. carbon:
1.66
Details on results (HPLC method):
The graphs show that for Tilburg sludge and Speyer 2.3 and Speyer 6S soil equilibrium was reached after approximately 24 hours. The amount of LBQ657 adsorbed to soil and sludge after 48 hours of contact time was approximately 45% for Tilburg sludge, 16% for Speyer 2.3 soil and 23% for
Speyer 6S soil. For Aa & Maas sludge equilibrium was reached after approximately 6 hours of contact time. The amount of LBQ657 adsorbed to Aa & Maas sludge after 48 hours of contact time was approximately 64%.
The graphs show that desorption equilibrium for Speyer 6S soil and Aa & Maas and Tilburg sludge was reached after approximately 24 hours. For Speyer 2.3 desorption equilibrium was reached after approximately 30 hours of contact time.
At the end of the adsorption and desorption phases, the supernatants were filtered and analysed on HPLC.
Validity criteria fulfilled:
yes
Executive summary:

 


Based upon the results of the 48 hours samples taken in the adsorption kinetics experiment and 30 hours in the desorption kinetics experiment, the following adsorption coefficients (Kd and Koc) were calculated:


Test system       Texture              %oc              Kd          Koc            Kdes


                       (USDA)                                 (mL/g)   (mL/g)         (mL/g)


Tilburg              Sludge              41.2              9.3              22.8        45.7


Aa & Maas      Sludge               43.7              19.7           48.8           72.7


Speyer 2.2       Loamy sand       1.74              6.4             38.0          5.8


Speyer 2.3      Sandy loam       1.0               0.4             39.2          4.1


Speyer 6S       Clay                    1.66              0.7             40.6        4.3

Description of key information

 


Based upon the results of the 48 hours samples taken in the adsorption kinetics experiment and 30 hours in the desorption kinetics experiment, the following adsorption coefficients (Kd and Koc) were calculated:


Test system       Texture              %oc              Kd          Koc            Kdes


(USDA)                                                      (mL/g)       (mL/g)         (mL/g)


Tilburg            Sludge               41.2              9.3              22.8        45.7


Aa & Maas      Sludge                43.7              19.7           48.8          72.7


Speyer 2.2      Loamy sand        1.74              6.4             38.0          5.8


Speyer 2.3      Sandy loam         1.0               0.4             39.2          4.1


Speyer 6S       Clay                   1.66              0.7             40.6         4.3

Key value for chemical safety assessment

Koc at 20 °C:
40

Additional information