9,9-bis-(methoxymethyl)fluorene

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

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)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.1110 (Activated Sludge Sorption Isotherm)

Deviations:

no

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20 +/- 2°C

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Adsorption/desorption isothers: 0.05, 0.2, 1, 2 and 5 mg/L. For the determination of equilibrium time (adsorption/desorption kinetics) the initial concentration in solution was 1 mg/L.
- Adsorption and desorption kinetics: samples taken at 3, 6, 24 and 48 hours.
- Adsorption and desorption isotherms: 3 hours of contact time.

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

3

% Silt:

11

% Sand:

86

% Org. carbon:

0.71

pH:

4.9

CEC:

4.3 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

loamy sand

% Clay:

8

% Silt:

15.8

% Sand:

76.2

% Org. carbon:

1.61

pH:

5.4

CEC:

9.7 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

sandy loam

% Clay:

6.5

% Silt:

33.8

% Sand:

59.7

% Org. carbon:

0.67

pH:

5.7

CEC:

7.5 meq/100 g soil d.w.

Matrix no.:

#4

Matrix type:

loam

% Clay:

26

% Silt:

41

% Sand:

33

% Org. carbon:

1.98

pH:

7.2

CEC:

30.6 meq/100 g soil d.w.

Matrix no.:

#5

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.

Matrix no.:

#6

Matrix type:

other: Loam (used for isotherm study)

% Clay:

25.8

% Silt:

41.1

% Sand:

33.1

% Org. carbon:

1.99

pH:

7.4

CEC:

32.9 meq/100 g soil d.w.

Matrix no.:

#7

Matrix type:

other: Clay (used for isotherm study)

% Clay:

40.5

% Silt:

34.1

% Sand:

25.4

% Org. carbon:

1.78

pH:

7.2

CEC:

27.3 meq/100 g soil d.w.

Details on matrix:

COLLECTION AND STORAGE
Adsorption and desorption parameters of the test item were determined in five different soils. Sieved (2 mm) air-dried soil samples were taken from storage. Storage was at ambient temperature and did not exceed three years after sampling for the soils. Moisture content was determined after oven drying until constant weight. Soils were taken from various areas in Germany.

PROPERTIES
- As per table 'matrix properties'.

Details on test conditions:

Confirmation of Identity of 14C-Labeled Test Item:
To confirm the identity of the 14C-labeled test item a 14C-labeled stock solution and unlabeled stock solution were prepared in acetonitrile. Both stock solution were analyzed with LC.

Solubility:
Solubility in 0.01M CaCl2 was determined by dissolving the test item in 0.01 M CaCl2 at a nominal concentration of approximately 50 mg/L in glass containers. After stirring/shaking for 24 hours at room temperature, the excess test item was removed (by filtration) after which the test item concentration was determined.

Test substance stability in the test system:
To test the adsorption of the test item to test container walls and the stability in 0.01 M CaCl2 solution, the test solution was incubated on a roller mixer for 48 hours. The initial test item concentration was approximately 1 mg/L. Radioactivity was determined after 3, 6, 24 and 48 hours. Additionally, subsamples were taken for LCanalysis at all time points. During initial testing, adsorption was observed in both polypropylene and glass vessels. Adsorption to container material experiment was repeated using regular and silanized glass vessels following the procedure as described above. Furthermore vessels were flushed with 0.01 M CaCl2 solution and containers flushed with unlabelled test item to investigate possible adsorption.

Determination of appropriate test system/solution ratio:
Soil:solution ratios of 1:2, 1:10 and 1:50 were investigated for Speyer 2.1, Speyer 2.3 and Speyer 6S soil in order to determine an appropriate ratio for the kinetics and isotherm experiments.

The soils were equilibrated in polypropylene tubes on a roller mixer overnight. After equilibration, the samples were spiked with stock solutions. The initial test item concentration was approximately 1 mg/L. The samples were placed on a roller mixer. After 24 hours of contact time, the containers were removed from the roller mixer and centrifuged. Aliquots were taken for LSC analysis. Additionally, sub-samples were taken for LC analysis.

Because the measured adsorption was below 50% for soil:solution ratios of 1:10 and 1:50 the procedure as described was repeated using soil:solution ratios of 1:1, 1:2 and 1:50. Soil:solution ratios of 1:1, 1:2 and 1:50 were investigated for Speyer 2.1, Speyer 2.3 and Speyer 6S soil in order to determine an appropriate ratio for the kinetics and isotherm experiments. Aliquots of 0.01 M CaCl2 solution were added to soil. The soils were equilibrated in glass tubes on a roller mixer for at least 12 hours. After equilibration, the samples were spiked with stock solutions. The initial test item concentration was approximately 1 mg/L. The samples were placed on a roller mixer. After 24 hours of contact time, the containers were removed from the roller mixer and centrifuged. Aliquots were taken for LSC analysis. Additionally, sub-samples were taken for LC analysis. Furthermore the vials of the ratio of 1:2 samples were cleaned using water and later flushed using acetonitrile to determine a possible increase of adsorption to the wall in presence of soil.

Determination of equilibrium time:
A stock solution of the test item in acetonitrile at a level of 1.42 MBq/mL (based on triplicate analysis by LSC; RSD 0.48%) was used. This is equivalent to a test item concentration of 372 mg/L. The radiochemical purity of the test item in the stock solution was determined by LC-analysis on the day of the test. Based on previous experiments, a soil:solution ratio of 1:2 was selected. The soils (approximately 15 g soil and 30 mL 0.01 M CaCl2 solution) were equilibrated in glass vials on a roller mixer overnight prior to spiking. The adsorption-desorption kinetics experiment was initiated by adding a volume of stock solution to the pre-equilibrated slurries. Hence, the initial concentration of the test item in the solution was approximately 1 mg/L.

At the beginning, middle and at the end of the spiking procedure, the same amount of spike solution was pipetted in a volumetric flask, which were made up to volume using acetonitrile. LSC analysis indicated that the concentration in the test systems was between 0.985 and 1.02 mg/L (based on triplicate analysis by LSC of 1 mL aliquots; RSD 1.7%). A blank sample was included for each test system using the same amounts of soil and 0.01 M CaCl2 solution without test item. 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 in the dark. At the adsorption sampling times (3, 6, 24 and 48 hours), the soil suspensions were removed from the roller mixer and centrifuged. After centrifugation, an aliquot of the supernatant was taken from each sample (including blanks) for determination of activity by LSC. Directly after sampling, the test systems 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. The vials were closed and placed on the roller mixer.

At the desorption sampling times (3, 6, 24 and 48 hours), the soil suspensions were removed from the roller mixer and centrifuged. After centrifugation, an 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 analyzed by LC. 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. After removal of the supernatant at the end of the adsorption and desorption phase, the slurries were allowed to dry to the air at room temperature. The adsorption part was conducted in duplicate for each test system. The desorption part was conducted with certain replicates only. Mass balances were determined after the adsorption part and after the desorption part for each test system. Mass balances included radioactivity in samples taken for analysis, radioactivity in decanted supernatant after adsorption and/or desorption and radioactivity in test system.

Determination of adsorption/desorption isotherms:
Due to the short adsorption and desorption equilibrium time, the determination of Adsorption/Desorption Isotherms were measured at different days with different stock solutions. Concentrations of 0.2, 0.05, 1, 2 and 5 mg/L were used on study.

Soil suspensions (soil:solution ratio of 1:2) in glass containers were equilibrated on a roller mixer overnight prior to spiking. A blank sample was included for each test system using a known amount of 0.01 M CaCl2 solution and no test item. Two control samples for each test system were also included, containing known amounts of 0.01 M CaCl2 solution and spike solution but without soil. The adsorption-desorption isotherms experiment was initiated by adding the spike volume to the ten pre-equilibrated soil slurries (two replicates per concentration). The samples were incubated on a roller mixer. After 3 hours of contact time, the soil suspensions were removed from the roller mixer and centrifuged. The activity in the supernatant was determined by LSC. The supernatants were decanted and weighed. The decanted supernatant was replaced by an approximately equal, known volume of fresh 0.01 M CaCl2 solution. The suspensions were mixed well and placed on a roller mixer for 3 hours. The suspensions were centrifuged. The activity in the supernatant was determined by LSC. The adsorption and desorption parts of the isotherms experiments were conducted in duplicate for each test system. The pH of the supernatants after the adsorption and desorption parts of the experiment (one replicate of highest and lowest concentration of each test system) was determined after decanting.

Sample No.:

#1

Duration:

48 h

Initial conc. measured:

1.01 other: µg/mL

pH:

5.82

Temp.:

>= 18 - <= 22 °C

Remarks:

Adsorption equilibrium was observed to gradually increase from between 3 and 48 hours. As such, adsorption equilibrium was set as 48 hours (the maximum time in the guideline)

Sample No.:

#2

Duration:

24 h

Initial conc. measured:

>= 1.01 - <= 1.02 other: µg/mL

pH:

6.3

Temp.:

>= 18 - <= 22 °C

Remarks:

Adsorption equilibrium was observed to gradually increase from between 3 and 48 hours. As such, adsorption equilibrium was set as 48 hours (the maximum time in the guideline)

Sample No.:

#3

Duration:

24 h

Initial conc. measured:

1.01 other: µg/mL

pH:

6.51

Temp.:

>= 18 - <= 22 °C

Remarks:

Adsorption equilibrium was observed to gradually increase from between 3 and 48 hours. As such, adsorption equilibrium was set as 48 hours (the maximum time in the guideline)

Sample No.:

#4

Duration:

24 h

Initial conc. measured:

>= 0.999 - <= 1 other: µg/mL

pH:

6.86

Temp.:

>= 18 - <= 22 °C

Remarks:

Adsorption equilibrium was observed to gradually increase from between 3 and 48 hours. As such, adsorption equilibrium was set as 48 hours (the maximum time in the guideline)

Sample No.:

#5

Duration:

24 h

Initial conc. measured:

>= 0.985 - <= 0.99 other: µg/mL

pH:

6.94

Temp.:

>= 18 - <= 22 °C

Remarks:

Adsorption equilibrium was observed to gradually increase from between 3 and 48 hours. As such, adsorption equilibrium was set as 48 hours (the maximum time in the guideline)

Sample no.:

#1

Duration:

3 h

Conc. of adsorbed test mat.:

18.7 other: µg

pH:

6.37

Temp.:

20 °C

Sample no.:

#2

Duration:

3 h

Conc. of adsorbed test mat.:

24.7 other: µg

pH:

6.58

Temp.:

20 °C

Sample no.:

#3

Duration:

3 h

Conc. of adsorbed test mat.:

17.6 other: µg

pH:

6.81

Temp.:

20 °C

Sample no.:

#4

Duration:

3 h

Conc. of adsorbed test mat.:

16.9 other: µg

pH:

6.9

Temp.:

20 °C

Sample no.:

#5

Duration:

3 h

Conc. of adsorbed test mat.:

23.9 other: µg

pH:

6.86

Temp.:

20 °C

Computational methods:

All calculations were based on formulas given in the OECD 106 guideline. In line with this guideline, 1 mL of aqueous solution is considered to weigh 1 g.

Adsorption and desorption coefficients Kd and Kdes were obtained from the adsorption-desorption kinetics experiment. The Freundlich adsorption and desorption isotherm parameters (KF^ads/des and 1/n^ads/des) were calculated by fitting the data to the Freundlich isotherm KF,oc^ads values were also determined.

Sample No.:

#1

Type:

Koc

Value:

511 L/kg

pH:

5.82

Temp.:

20 °C

Matrix:

Loamy sand

% Org. carbon:

0.71

Sample No.:

#2

Type:

Koc

Value:

520 L/kg

pH:

6.3

Temp.:

20 °C

Matrix:

Loamy sand

% Org. carbon:

1.61

Sample No.:

#3

Type:

Koc

Value:

423 L/kg

pH:

6.51

Temp.:

20 °C

Matrix:

Sandy loam

% Org. carbon:

2.83

Sample No.:

#4

Type:

Koc

Value:

391 L/kg

pH:

6.86

Temp.:

20 °C

Matrix:

Loam

% Org. carbon:

1.99

Sample No.:

#5

Type:

Koc

Value:

468 L/kg

pH:

6.94

Temp.:

20 °C

Matrix:

Clay

% Org. carbon:

1.78

Sample No.:

#1

Type:

Kd

Value:

3.63 dimensionless

pH:

5.82

Temp.:

20 °C

Matrix:

Loamy sand

% Org. carbon:

0.71

Sample No.:

#2

Type:

Kd

Value:

8.37 dimensionless

pH:

6.31

Temp.:

20 °C

Matrix:

Loamy sand

% Org. carbon:

1.61

Sample No.:

#3

Type:

Kd

Value:

2.83 dimensionless

pH:

6.51

Temp.:

20 °C

Matrix:

Sandy loam

% Org. carbon:

0.67

Sample No.:

#4

Type:

Kd

Value:

7.74 dimensionless

pH:

6.86

Temp.:

20 °C

Matrix:

Loam

% Org. carbon:

1.99

Sample No.:

#5

Type:

Kd

Value:

7.77 dimensionless

pH:

6.94

Temp.:

20 °C

Matrix:

Clay

% Org. carbon:

1.78

Adsorption and desorption constants:

Results provided in 'any other information on results incl. tables'.

Recovery of test material:

Mass balances were determined for one sample of each test system after the adsorption and desorption stage of the kinetics experiment. The mass balances of Speyer 2.4 (loam) was in the acceptable range of 90-110%, indicating that no activity was lost during the timeframe of the experiment. The mass balances of Speyer 2.1 (loamy sand), Speyer 2.2 (loamy sand), Speyer 2.3 (sandy loam) and Speyer 6S (clay) were not in the range of 90-110%.

Control samples analyzed at the same time points as the soil samples showed a decrease in recovery from approximately 90% at 3 hours to approximately 72% at 48 hours. As adsorption to the wall cannot be observed and no test item degradation was apparent in LC chromatograms, the reason for this decrease is unknown. However because of this the only time point to provide a reasonable accurate isotherm response would after 3 hours. For that reason it was decided to take samples after 3 hours of adsorption and after 3 hours of desorption in the isotherms experiment.

Mass balances were determined for one sample of each test system after the adsorption and desorption stage of the isotherms experiment. The mass balances were in the range of 81-98%. The control samples indicated a loss of 6 - 24% in activity during the course of the experiments. Reason for this loss, as has been described before, has been thoroughly investigated however, no clear reason could be observed.

Concentration of test substance at end of adsorption equilibration period:

The amount of test item adsorbed to soil after 48 hours of contact time was 64% (Speyer 2.1), 80% (Speyer 2.2), 58% (Speyer 2.3), 79% (Speyer 2.4) and 78% (Speyer 6S).

Concentration of test substance at end of desorption equilibration period:

At the end of the adsorption and desorption phases, the supernatants were analyzed by LC. In the chromatograms of the supernatants of all soils, no other peak than the test item peak was observed, indicating that the test item was stable during the time frame of the experiment.

Remarks on result:

other: results do not fit within IUCLID constraints

Remarks on result:

other: results do not fit within IUCLID constraints

Transformation products:

not measured

Details on results (Batch equilibrium method):

Preliminary results (stability/container adsorption):
This experiment was performed to test the adsorption of test item to container walls and its stability in 0.01 M CaCl2 solution. The amount of radioactivity recovered in the solutions after 48 hours of contact time with the container material in the absence of soil was between 38% and 39% of the nominal applied activity in polypropylene vials and between 79% and 83% in glass containers. These results indicate that the adsorption of test item to the polypropylene container is 61% and to the glass container is 19%. Based on analysis by LC, 100% test item was recovered in the test solutions in both glass vials and polypropylene containers after 48 hours of contact time.

Since the observed recovery was low in both glass and polypropylene containers, the test was repeated using both regular and silanized glass vials. Vials were also flushed after 48 hours using acetonitrile and additionally vials containing soil were flushed after incubation to determine if the presence of soil causes adsorption to the wall. No difference was measured between flushed containers and normal containers. Also no additional effect of the presence of soil in relation to adsorption to the wall was detected. Since chromatograms did not reveal additional signals the test item was considered stable in CaCl2 solution for at least 48 hours. The stability of the test item in CaCl2 solution was confirmed by the control samples of the kinetics experiment. Adsorption results were comparable between glass and silanized glass vials and for that reason further tests were performed in glass vials.

Determination of an Appropriate Test System:Solution Ratio:
Based on analysis by LC, 100% test item was recovered in the test solution with Speyer 2.2, Speyer 2.3 and Speyer 6S soil. Therefore the test item was stable when in contact with soil for at least 24 hours. The stability of the test item when in contact with soil was confirmed by the samples of the kinetics experiment. Based on the results of this test a second preliminary experiment was performed using soil:solution ratios of 1:1, 1:2 and 1:50. Based on analysis by LC, 100% test item was recovered in the test solution with Speyer 2.2, Speyer 2.3 and Speyer 6S soil. Therefore the test item was stable when in contact with soil for at least 24 hours. The stability of the test item when in contact with soil was confirmed by the samples of the kinetics experiment.

Determination of equilibrium time (adsorption and desorption kinetics):
The radiochemical purity of the test item in the spike solution was 100% on the day of spiking. Adsorption equilibrium was observed to gradually increase between 3 and 48 hours. For this reason adsorption equilibrium was set at the maximum time as described in the guidelines, 48 hours. The amount of test item adsorbed to soil after 48 hours of contact time was 64% (Speyer 2.1), 80% (Speyer 2.2), 58% (Speyer 2.3), 79% (Speyer 2.4) and 78% (Speyer 6S). Desorption equilibrium for all soils was reached after approximately 24 hours. At the end of the adsorption and desorption phases, the supernatants were analyzed by LC. In the chromatograms of the supernatants of all soils, no other peak than the test item peak was observed, indicating that the test item was stable during the time frame of the experiment. The pH of the remaining supernatants ranged from 5.8 to 7.3 after adsorption and from 6.4 to 6.9 after desorption. Mass balances were determined for one sample of each test system after the adsorption and desorption stage of the kinetics experiment.

The mass balances of Speyer 2.4 was in the acceptable range of 90-110%, indicating that no activity was lost during the timeframe of the experiment. The mass balances of Speyer 2.1, Speyer 2.2, Speyer 2.3 and Speyer 6S were not in the range of 90-110%. Control samples analyzed at the same time points as the soil samples showed a decrease in recovery from approximately 90% at 3 hours to approximately 72% at 48 hours. As adsorption to the wall cannot be observed and no test item degradation was apparent in LC chromatograms, the reason for this decrease is unknown. However because of this the only time point to provide a reasonable accurate isotherm response would after 3 hours. For that reason it was decided to take samples after 3 hours of adsorption and after 3 hours of desorption in the isotherms experiment.

Adsorption/desorption kinetics and isotherms:
Adsorption of the substance to soil is concentration and soil dependent and varies between approximately 40% and 75%. Desorption was measured to be between approximately 10% and 30% soil and concentration level dependent.

The adsorption is close to linear with a slight L-shaped isotherm shape indicating that the substance has a moderate to high affinity for soil at the initial stages of adsorption, however if more adsorption sites are filled adsorption is becoming more difficult.

Based on KFads results adsorption capacity appears to be higher for Speyer 2.2, 2.4 and 6S. However, when results are normalized for OC the adsorption capacity is comparable between the different soils indicating that the OC content is the most important factor in determining the adsorption capacity of soil for the substance.

Desorption is according to the same pattern and shape as adsorption. Normalized desorption is comparable between the different soils. Since the KF,ocdes is slightly larger than the KF,ocads this would be an indication that the adsorption is not completely reversible, however results are comparable which is also the case for the 1/n values indicating that adsorption and desorption is of comparable rate.

Statistics:

Not applicable.

Overall Results:

Test system	Texture [USDA]	Organic carbon [%]	Kd	Koc [mL/g]	KF^ads [mL/g]	KF,oc^ads [mL/g]	KF^des [mL/g]	KF,oc^des [mL/g]
Speyer 2.1	Loamy sand	0.71	3.63	511	1.63	229	2.16	304
Speyer 2.2	Loamy sand	1.61	8.37	520	4.27	265	5.13	319
Speyer 2.3	Sandy loam	0.67	2.83	423	1.43	213	1.95	290
Speyer 2.4	Loam	1.99	7.74	391	4.46	224	5.21	262
Speyer 6S	Clay	1.78	7.77	468	4.76	267	5.84	328

Mass Balances after adsorption/desorption kinetics experiment:

Test system	Recovery after adsorption phase	Recovery after desorption phase
	Replicate A [% of applied]	Replicate B [% of applied]
Speyer 2.1	80%	77%
Speyer 2.2	89%	87%
Speyer 2.3	75%	80%
Speyer 2.4	91%	91%
Speyer 6S	78%	84%

Validity criteria fulfilled:

yes

Conclusions:

Determined Koc values ranged from 391 to 520 in the varying soil types used (Kd ranged from 2.83 to 8.37). Adsorption of the substance to soil is concentration and soil dependent and varies between approximately 40% and 75%. Desorption was measured to be between approximately 10% and 30% soil and concentration level dependent.

Description of key information

An OECD guideline 106 study was conducted with radio-labelling of the test substance to determine adsorption/desorption kinetics and isotherms. The highest Koc value from the 5 soil types tested is used as the key value for chemical safety assessment.

Key value for chemical safety assessment

Koc at 20 °C:

520