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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:
2018-07-23 to 2018-11-27
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)
Version / remarks:
2000
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.18 (Adsorption / Desorption Using a Batch Equilibrium Method)
Version / remarks:
2008
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
20-25°C
Analytical monitoring:
yes
Details on sampling:
The soil suspensions were centrifuged after agitation at ≥ 4000 rpm to separate the phases, followed by analysing the concentration of the test item in aqueous phase by LC-MS. For analysis of the soil, the aqueous phase was decanted and the soil was extracted. During tier 1, test vessels were extracted and rinsed with acetonitrile / ultrapure water 50/50 containing 1 % formic acid to determine test vessel adsorption. Extracts were also analysed by LC-MS.
Matrix no.:
#1
Matrix type:
other: Silty sand (LUFA 2.1)
% Clay:
4.1
% Silt:
10.5
% Sand:
85.4
% Org. carbon:
0.718
pH:
4.9
CEC:
2.4 meq/100 g soil d.w.
Matrix no.:
#2
Matrix type:
other: Loamy sand (LUFA 2.2)
% Clay:
8.5
% Silt:
11.3
% Sand:
80.2
% Org. carbon:
1.47
pH:
5.4
CEC:
7.6 meq/100 g soil d.w.
Matrix no.:
#3
Matrix type:
other: Silty sand (LUFA 2.3)
% Clay:
8.6
% Silt:
29.3
% Sand:
62.1
% Org. carbon:
0.412
pH:
5.9
CEC:
4.9 meq/100 g soil d.w.
Matrix no.:
#4
Matrix type:
other: Clayey loam (LUFA 2.4)
% Clay:
25.2
% Silt:
42.3
% Sand:
32.6
% Org. carbon:
1.74
pH:
7.4
CEC:
22 meq/100 g soil d.w.
Matrix no.:
#5
Matrix type:
other: Loamy sand (LUFA 5M)
% Clay:
10.2
% Silt:
31.1
% Sand:
58.7
% Org. carbon:
0.916
pH:
7.3
CEC:
10 meq/100 g soil d.w.
Details on matrix:
COLLECTION AND STORAGE
- Geographic location: Landwirtschaftliche Untersuchungs- und Forschungsanstalt LUFA Speyer, Obere Langgasse 40, 67346 Speyer, Germany
Standard LUFA soils 2.1, 2.2, 2.3, 2.4 and 5M in contact to 0.01 M CaCl2-solution were used for this study. These matrices have varying adsorption capacities in relation to their content of organic matter, clay, pH and cation exchange capacity. All soils are air-dried and sieved to a maximum particle size of 2 mm by the distributor.

Storage at test facility Room temperature, in closed containers

Expiry date LUFA 2.1 (batch: F2.1 2817): 2022-07-24
LUFA 2.2 (batch: F2.2 4016): 2021-10-24
LUFA 2.3 (batch: F2.3 4116): 2021-10-24
LUFA 2.4 (batch: F2.4 4116): 2021-10-24
LUFA 5M (batch: F5M 5015): 2020-12-17
Details on test conditions:
Soil / Solution ratio Test volume: 40mL
Tier 1: 1:40 and 1:10
Tier 2 and Tier 3: 1:10

Sampling points Tier 1: 2h, 5h and 24h for soil / solution ratio 1:40
Tier 1: 2h, 4h and 24h for soil / solution ratio 1:10
Tier 2: 1h, 2h, 4h, 6h, 24h
Desorption kinetics: 2h, 4h, 6h, 24h and 48h
Adsorption Isotherms: 24h for LUFA soil 2.1
4h for the other soils

Agitation By horizontal shaker. Frequency was adjusted to avoid sedimentation of soil particles during treatment. 
Test temperature The temperature was mainly in the range of 20 to 25 °C during the course of the study. Deviations from this temperature range were brief periods (<< 1h) between 18 and 20 °C during tier 1. Furthermore the temperature reached a minimum of 17.3 °C during a conditioning phase for the desorption kinetics. For details refer to section 5.

Test vessels 50 mL disposable centrifugation tubes

Concentration 2 mg test item /L (concentration used for adsorption kinetics)
1 mg test item /L
0.2 mg test item /L
0.1 mg test item /L
0.02 mg test item /L

Stock solutions Stock solutions of 2, 1, 0.2, 0.1 and 0.02 g/L of the test item in methanol were prepared.

Preparation of the soil samples (conditioning) The soils were weighed into the test vessels and an appropriate volume of 0.01 M CaCl2-solution was added. After agitation overnight (12 h minimum), the samples were used for adsorption experiments.

Preparation of the samples (adsorption experiments) The soil samples were conditioned as described above. 0.1 volume-% (0.04 mL) of the stock solutions were added in order to adjust the test concentrations. Afterwards, the samples were agitated.

Preparation of the samples (desorption experiments) Samples at adsorption equilibrium were used for this purpose. After completion of the adsorption experiments the test vessels were centrifuged, weighed and the supernatant was replaced by fresh 0.01 M CaCl2-solution. Then the test vessels were agitated again to investigate the desorption behavior of the test item.

Replicates All samples were prepared in duplicate.

CONTROLS CaCl2-solution was conditioned as described above, followed by separation of the aqueous phase by centrifugation. Then the aqueous phase was fortified acc. to the concentrations used for the test item samples to verify the stability of the test item in the aqueous phase under test conditions. The samples were agitated as long as the test item sample with the longest agitation period.

Replicates Duplicates (tier 1)

BLANK Blank samples were prepared for all soils as described for the test item samples but without fortification with the test item. The samples were agitated as long as the samples with the longest agitation period.

Replicates Duplicates (tier 1), single (tier 2)
Type:
Koc
Value:
77 057 L/kg
pH:
5.8
Temp.:
20 °C
Matrix:
LUFA 2.1
% Org. carbon:
0.718
Type:
Koc
Value:
45 361 L/kg
pH:
6.3
Temp.:
20 °C
Matrix:
LUFA 2.2
% Org. carbon:
1.47
Type:
Koc
Value:
151 587 L/kg
pH:
6.8
Temp.:
20 °C
Matrix:
LUFA 2.3
% Org. carbon:
0.412
Type:
Koc
Value:
95 475 L/kg
pH:
7.3
Temp.:
20 °C
Matrix:
LUFA 2.4
% Org. carbon:
1.74
Type:
Koc
Value:
183 082 L/kg
pH:
7.2
Temp.:
20 °C
Matrix:
LUFA 5M
% Org. carbon:
0.916
Key result
Type:
Koc
Remarks:
geom. mean
Value:
98 478 L/kg
pH:
7
Temp.:
20 °C
% Org. carbon:
>= 0.412 - <= 1.74
Phase system:
solids-water in soil
Type:
Kp
Value:
553 L/kg
Temp.:
20 °C
pH:
5.8
Matrix:
LUFA 2.1
% Org. carbon:
0.718
Phase system:
solids-water in soil
Type:
Kp
Value:
667 L/kg
Temp.:
20 °C
pH:
6.3
Matrix:
LUFA 2.2
% Org. carbon:
1.47
Phase system:
solids-water in soil
Type:
Kp
Value:
625 L/kg
Temp.:
20 °C
pH:
6.8
Matrix:
LUFA 2.3
% Org. carbon:
0.412
Phase system:
solids-water in soil
Type:
Kp
Value:
1 661 L/kg
Temp.:
20 °C
pH:
7.3
Matrix:
LUFA 2.4
% Org. carbon:
1.74
Phase system:
solids-water in soil
Type:
Kp
Value:
1 677 L/kg
Temp.:
20 °C
pH:
7.2
Matrix:
LUFA 5M
% Org. carbon:
0.916
Key result
Phase system:
solids-water in soil
Type:
Kp
Remarks:
geom. mean
Value:
915 L/kg
Temp.:
20 °C
pH:
7
% Org. carbon:
>= 0.412 - <= 1.74
Transformation products:
not measured
Conclusions:
The test item concentrations in the aqueous phase in the lower application concentrations could not be determined at the end of the agitation phase due to the nearly quantitative depletion of the test item. Therefore, no direct analytical method (parallel analysis of samples of soil and aqueous phase) could be applied. Rather, a linear adsorption behavior was assumed with the consequence that the test item concentrations in the aqueous phase for the application concentrations K2 – K5 were extrapolated from the experimental derived values in tier 2. Furthermore, the test item concentration in soil was experimentally determined for all concentration levels and all soils. But, the decreasing mass balances and the calculation of the adsorption isotherms showed a nonlinear adsorption and therefore that no extrapolation of the test item concentrations for the aqueous phase is possible. For this reason, no adsorption isotherms could be calculated. Either fast formation of non-extractable residues (NERs), relatively increasing in the lower application levels, or biodegradation of the test item in soil could be possible explanations for the nonlinear adsorption behavior. The test item is readily biodegradable as shown in a modified Sturm test according to OECD 301B (Maischak, Noack ID: 180326EJ AST18175, 2018). In addition, it is worthy of mention that there was no significant decrease in the mass balances of an adsorption / desorption study according to OECD 106 recently conducted with another cationic amine derivative (Goller, Noack ID: 170524EJ CAD18111, 2018). The test item used in the last-mentioned study is not readily biodegradable as shown in a headspace test according to OECD 310 (Maischak, Noack ID: 170524EJ AHT18110, 2018). For this reason, it is more likely that biodegradation is responsible for the decreasing mass balances and the nonlinear adsorption behaviour.
Furthermore, no distribution coefficients Kdes were determined because the test item concentrations in the soils should decrease during the course of the experiment due to biodegradation. Therefore, no reference point for the calculation of the endpoints was available. The measured low concentrations in the aqueous phase at the end of the desorption experiment show that desorption is not relevant.
Only organic carbon normalized distribution coefficients Koc for the highest application level (K1) could be derived because the direct analytical method (parallel analysis of test vessel adsorption, test item concentration in the aqueous phase and soil) was applied. Values ranged from 45361 to 183082 mL/g with a geometric mean value of 98478 mL/g. For the distribution coefficient Kd a geometric mean value of 915 mL/g was derived.The test item adsorbs to all tested soils with Koc values > 5000 and is therefore immobile in soils according to McCall et al.
Executive summary:

The adsorption / desorption behavior of the test item C16 Alkylamidopropyltrimethylammonium Chloride was investigated in five different soils according to OECD guideline 106 and Council Regulation (EC) No. 440/2008, C.18. Distribution coefficients Kd and organic carbon normalized distribution coefficients Koc ere determined with a single concentration. Furthermore, investigations about the desorption behaviour and the degree of the adsorption as a function of the test item loading level (Freundlich adsorption isotherms) in the aqueous phase were performed. No endpoints could be reliably derived for these experiments due to the reasons given below. The test item was analysed by LC-MS/MS. Relevant properties of the used soils are given in Table 1. Experiments for adsorption and desorption kinetics were conductedwith a nominal test item concentration of 2 mg test item/L (K1). Additional concentrationsof 1, 0.2, 0.1 and 0.02 mg test item/L (K2 – K5) were used for the determination of the Freundlich adsorption isotherms.

 

Table1:   Relevant Characteristics of Test Matrices

 

Soils

 

LUFA 2.1

LUFA 2.2

LUFA 2.3

LUFA 2.4

LUFA 5M

batch

F2.1 2817

F2.2 4016

F2.3 4116

F2.4 4116

F5M 5015

Soil Type1)

Silty sand

Loamy sand

Silty sand

Clayey loam

Loamy sand

pH (0.01 M CaCl2)3)

4.9

5.4

5.9

7.4

7.3

Organic Carbon [%]2)

0.718

1.47

0.412

1.74

0.916

Clay (<0.002 mm) [%]2)

4.1

8.5

8.6

25.2

10.2

Silt (0.002-0.063 mm) [%]2)

10.5

11.3

29.3

42.3

31.1

Sand (0.063-2 mm) [%]2)

85.4

80.2

62.1

32.6

58.7

Cation Exchange Capacity [mval/100g]2)

2.4

7.6

4.9

22

10

1)according to German DIN

2)determined at Agrolab Agrar und Umwelt GmbH (non-GLP)

3) Analyses data sheet provided by LUFA

 

Results of Tier 1

Tier 1– Test Vessel Adsorption

Experiments in tier 1 showed that the test item is prone for adsorption to the vessel surfaces of the polypropylene centrifugation tubes. Test item controls (the test item dissolved and agitated in the test vessel without soil) prepared in0.01 M CaCl2 or in soil eluates of LUFA 2.2 and LUFA 2.4 showed a test vessel adsorption of approximately 10%. For this reason, no test item controls were prepared and analysed during the further experiments because being useless for the interpretation and assessment of the study results. In addition, the test vessel adsorption in soil suspension of all soils was determined. Two different soil / solution ratios (1:10 and 1:40) were tested with the soils LUFA 2.2 and LUFA 2.4 for this purpose. The test vessel adsorption was lower in the samples with the higher soil /solution ratio. A soil / solution ratio of 1:10 was used for the further experiments during this study. The test vessel adsorption ranged from 0.6 to 3.3% under this condition for all tested soils.

 

Tier 1– Adsorption Kinetics

The test item depletion of the test item in the aqueous phase in soil suspensions with a soil / solution of 1:10 was nearly quantitative within 2 hours of the experiments with the soils LUFA 2.2 and LUFA 2.4. These results were obtained by the indirect method; only the concentration of the test item in the aqueous phase was determined. An agitation time of 24 hours was used for the adsorption kinetic experiments in tier 2 based on these experiments. The agitation time was reduced to 4 hours during the experiments for the adsorption isotherms in all soils except for the soil LUFA 2.1.

 

Tier 1– Parental Mass Balance

The parental mass balance for the test item was determined in all soils with an application concentration of 2 mg/L, a soil / solution ratio of 1:10 and after an agitation time of 4 hours for the soils LUFA 2.2, 2.3, 2.4 and 5M. 24 hours of agitation were used for the soil LUFA 2.1. The parental mass balances were finally calculated by taking into account the test item recovery on the test vessel surfaces, in the aqueous phase and in the soil. The extraction method for soil was optimized prior to these experiments by preparing samples in the soil LUFA 2.4. This soil was used for this purpose because this soil has the highest amount of organic carbon and clay. These parameters have a significant impact on the adsorption of organic compounds in soils. In general, high values for these parameters are responsible for high adsorption and fast / increased formation of non-extractable residues (NERs). A harsh extraction with an accelerated solvent extractor (ASE) was finally used for extraction of the test item It is more likely to obtain the best extraction efficiency with an ASE for aged samples than with an extraction at ambient temperature because the ASE extraction uses a combination of elevated temperature and pressure. Further experiments during method development indicated a decline of test item recovery in extracts of aged soil samples. Mass balances between 57 and 92% were obtained.

 

Results Tier 2– Adsorption Kinetics

These experiments confirmed the results of tier 1. The test item depletion in the aqueous phase ranged from 96 to 99% after 24 hours of agitation. Only the aqueous phase was analysed during these experiments. It was decided to waive further analysis of the aqueous phase during the determination of the adsorption isotherms duringtier 3based on these results. The concentrations of the test item in the aqueous phase were often in the lower range of the calibration with only low dilution factors. In consequence, concentrations lower than the lowest calibration level would have been obtained in the lower application concentrations during the determination of the adsorption isotherms. For this reason, the measurement of theses samples was useless for the determination of the adsorption isotherms.

 

Results Tier 3

Results Tier 3– Desorption Kinetics

Only samples of the aqueous phase were analysed for this purpose. Test item concentrations in the aqueous phase lower than 1% related to the applied test item amount (2 mg test item/L) were determined in the desorption kinetic experiments. The desorption is negligible under the used experimental conditions (24 hours adsorption and 48 hours desorption). Therefore, no experiments for the determination of the desorption isotherms were conducted.

 

ResultsTier 3– Adsorption Isotherms

Analysis during the determination of the adsorption isotherms were performed by analysing soil extracts of all concentration levels. The concentrations in the aqueous phase were calculated from the corresponding data of the adsorption kinetics and extrapolating the adsorption in % also to the lower concentration levels based on the assumption that the adsorption behavior is linear. Table 2 presents the obtained data.

Table2:      Freundlich Adsorption Isotherms

Applied test item concentrations: 2, 1, 0.2, 0.1, 0.02 mg/L

Volume of aqueous phase:        40 mL

Soil Type

msoil[g]

r2

1/n

KFads

KFOC

LUFA 2.1

3.88

0.995

1.47

3243

451638

LUFA 2.2

3.71

0.997

1.14

1121

76255

LUFA 2.3

3.84

0.997

1.20

1340

325155

LUFA 2.4

3.62

0.995

1.10

2460

141384

LUFA 5M

3.70

0.992

1.11

2582

281835


msoil
      = used amount of soil (dry weight) [g]

n           = regression constant

KFads      = Freundlich adsorption coefficient [µg1-1/n(mL)1/ng-1]

KFOC      = Freundlich adsorption coefficient normalized to content of organic carbon [µg1-1/n(mL)1/ng-1]

 

A further assessment for the results of these experimentswasperformed because the values for the inverse regression constant 1/n (slope of the linear regression) were not plausible. These values were ≥ 1.1 and are not between 0.7 and 1 as expected for a Freundlich adsorption behavior. Furthermore, a strong decrease of the extracted test item amount from the soils was observed towards the lower application concentrations. This fact is in accordance to the implausible values for the inverse regression constants 1/n indicating a significant nonlinear adsorption behaviour. For this reason, individual organic carbon normalized distribution coefficients Koc were calculated (see Table 3) per application level and for all soils and compared with the organic carbon normalised Freundlich adsorption coefficients KFoc. Table3 indicates that the organic carbon normalized distribution coefficients Koc are lower than the corresponding organic carbon normalised Freundlich adsorption coefficients KFoc. Furthermore, a decrease of these values towards the lower application levels was determined. These data clearly indicate that the adsorption is significantly nonlinear.

 

Table3:      Individual organic carbon normalized Distribution Coefficients Koc

Applied test item concentrations: 2, 1, 0.2, 0.1, 0.02 mg/L

Volume of aqueous phase:        40 mL

Application Level

 

KOC

LUFA 2.1

LUFA 2.2

LUFA 2.3

LUFA 2.4

LUFA 5M

K1

77057

45361

151587

95475

183082

K2

57954

42678

149890

86546

171219

K3

18510

37103

95755

62844

105760

K4

15737

25591

76229

66114

105856

K5

9870

25420

68902

62717

123801

 

 

Conclusions and Impact on the Study Endpoints

The test item concentrations in the aqueous phase in the lower application concentrations could not be determined at the end of the agitation phase due to the nearly quantitative depletion of the test item. Therefore, no direct analytical method (parallel analysis of samples of soil and aqueous phase) could be applied. Rather, a linear adsorption behavior was assumed with the consequence that the test item concentrations in the aqueous phase for the application concentrations K2 – K5 were extrapolated from the experimental derived values in tier 2. Furthermore, the test item concentration in soil was experimentally determined for all concentration levels and all soils. But, the decreasing mass balances and the calculation of the adsorption isotherms showed a nonlinear adsorption and therefore that no extrapolation of the test item concentrations for the aqueous phase is possible. For this reason, no adsorption isotherms could be calculated. Either fast formation of non-extractable residues (NERs), relatively increasing in the lower application levels, or biodegradation of the test item in soil could be possible explanations for the nonlinear adsorption behavior. The test item is readily biodegradable as shown in a modified Sturm test according to OECD 301B (Maischak, Noack ID: 180326EJ AST18175, 2018). In addition, it is worthy of mention that there was no significant decrease in the mass balances of an adsorption / desorption study according to OECD 106 recently conducted with another cationic amine derivative (Goller, Noack ID: 170524EJ CAD18111, 2018). The test item used in the last-mentioned study is not readily biodegradable as shown in a headspace test according to OECD 310 (Maischak, Noack ID: 170524EJ AHT18110, 2018). For this reason, it is more likely that biodegradation is responsible for the decreasing mass balances and the nonlinear adsorption behaviour.

Furthermore, no distribution coefficients Kdes were determined because the test item concentrations in the soils should decrease during the course of the experiment due to biodegradation. Therefore, no reference point for the calculation of the endpoints was available. The measured low concentrations in the aqueous phase at the end of the desorption experiment show that desorption is not relevant.

Only organic carbon normalized distribution coefficients Koc for the highest application level (K1) could be derived because the direct analytical method (parallel analysis of test vessel adsorption, test item concentration in the aqueous phase and soil) was applied. Values ranged from 45361 to 183082 mL/g with a geometric mean value of 98478 mL/g. For the distribution coefficient Kd a geometric mean value of 915 mL/g was derived.The test item adsorbs to all tested soils with Koc values > 5000 and is therefore immobile in soils according to McCall et al.

Description of key information

The test item concentrations in the aqueous phase in the lower application concentrations could not be determined at the end of the agitation phase due to the nearly quantitative depletion of the test item. Therefore, no direct analytical method (parallel analysis of samples of soil and aqueous phase) could be applied. Rather, a linear adsorption behavior was assumed with the consequence that the test item concentrations in the aqueous phase for the application concentrations K2 – K5 were extrapolated from the experimental derived values intier 2. Furthermore, the test item concentration in soil was experimentally determined for all concentration levels and all soils. But, the decreasing mass balances and the calculation of the adsorption isotherms showed a nonlinear adsorption and therefore that no extrapolation of the test item concentrations for the aqueous phase is possible. For this reason, no adsorption isotherms could be calculated. Either fast formation of non-extractable residues (NERs), relatively increasing in the lower application levels, or biodegradation of the test item in soil could be possible explanations for the nonlinear adsorption behavior. The test item is readily biodegradable as shown in a modified Sturm test according to OECD 301B (Maischak, Noack ID: 180326EJ AST18175, 2018). In addition, it is worthy of mention that there was no significant decrease in the mass balances of an adsorption / desorption study according to OECD 106 recently conducted with another cationic amine derivative (Goller, Noack ID: 170524EJ CAD18111, 2018). The test item used in the last-mentioned study is not readily biodegradable as shown in a headspace test according to OECD 310 (Maischak, Noack ID: 170524EJ AHT18110, 2018). For this reason, it is more likely that biodegradation is responsible for the decreasing mass balances and the nonlinear adsorption behaviour.

Furthermore, no distribution coefficients Kdes were determined because the test item concentrations in the soils should decrease during the course of the experiment due to biodegradation. Therefore, no reference point for the calculation of the endpoints was available. The measured low concentrations in the aqueous phase at the end of the desorption experiment show that desorption is not relevant.

Only organic carbon normalized distribution coefficients Koc for the highest application level (K1) could be derived because the direct analytical method (parallel analysis of test vessel adsorption, test item concentration in the aqueous phase and soil) was applied. Values ranged from 45361 to 183082 mL/g with a geometric mean value of 98478 mL/g. For the distribution coefficient Kd a geometric mean value of 915 mL/g was derived.The test item adsorbs to all tested soils with Koc values > 5000 and is therefore immobile in soils according to McCall et al.

Cationic surfactants adsorb to soil or sediment mainly via ionic interaction with negatively charged surfaces and there is poor correlation between adsorption and organic carbon content. Hence, sorption should not be normalized to organic matter and it is better to rely on Kd rather than Koc. When organic matter is not determining the distribution in soil, sediment and suspended sediment there is no difference in adsorption to these three compartments (based on dry weight) as the organic matter content is the only variable. Therefore, it was considered to be more relevant to use the mean Kd value of 915.22 L/kg to further calculate the partition coeffcients of soil-water, sediment-water and suspended-sediment matter.

Key value for chemical safety assessment

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
3.14
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in sediment)
Value in L/kg:
2.66
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in suspended matter)
Value in L/kg:
2.36
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in raw sewage sludge)
Value in L/kg:
1.44
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in settled sewage sludge)
Value in L/kg:
1.44
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in activated sewage sludge)
Value in L/kg:
1.44
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in effluent sewage sludge)
Value in L/kg:
1.44
at the temperature of:
20 °C

Additional information

The adsorption / desorption behavior of the test item C16 Alkylamidopropyltrimethylammonium Chloride was investigated in five different soils according to OECD guideline 106 and Council Regulation (EC) No. 440/2008, C.18. Distribution coefficients Kd and organic carbon normalized distribution coefficients Koc were determined with a single concentration. Furthermore, investigations about the desorption behaviour and the degree of the adsorption as a function of the test item loading level (Freundlich adsorption isotherms) in the aqueous phase were performed. No endpoints could be reliably derived for these experiments due to the reasons given below. The test item was analysed by LC-MS/MS. Relevant properties of the used soils are given in Table 1. Experiments for adsorption and desorption kinetics were conductedwith a nominal test item concentration of 2 mg test item/L (K1). Additional concentrationsof 1, 0.2, 0.1 and 0.02 mg test item/L (K2 – K5) were used for the determination of the Freundlich adsorption isotherms.

 

Table1:   Relevant Characteristics of Test Matrices

 

Soils

 

LUFA 2.1

LUFA 2.2

LUFA 2.3

LUFA 2.4

LUFA 5M

batch

F2.1 2817

F2.2 4016

F2.3 4116

F2.4 4116

F5M 5015

Soil Type1)

Silty sand

Loamy sand

Silty sand

Clayey loam

Loamy sand

pH (0.01 M CaCl2)3)

4.9

5.4

5.9

7.4

7.3

Organic Carbon [%]2)

0.718

1.47

0.412

1.74

0.916

Clay (<0.002 mm) [%]2)

4.1

8.5

8.6

25.2

10.2

Silt (0.002-0.063 mm) [%]2)

10.5

11.3

29.3

42.3

31.1

Sand (0.063-2 mm) [%]2)

85.4

80.2

62.1

32.6

58.7

Cation Exchange Capacity [mval/100g]2)

2.4

7.6

4.9

22

10

1)according to German DIN

2)determined at Agrolab Agrar und Umwelt GmbH (non-GLP)

3) Analyses data sheet provided by LUFA

 

Results of Tier 1

Tier 1– Test Vessel Adsorption

Experiments in tier 1 showed that the test item is prone for adsorption to the vessel surfaces of the polypropylene centrifugation tubes. Test item controls (the test item dissolved and agitated in the test vessel without soil) prepared in0.01 M CaCl2 or in soil eluates of LUFA 2.2 and LUFA 2.4 showed a test vessel adsorption of approximately 10%. For this reason, no test item controls were prepared and analysed during the further experiments because being useless for the interpretation and assessment of the study results. In addition, the test vessel adsorption in soil suspension of all soils was determined. Two different soil / solution ratios (1:10 and 1:40) were tested with the soils LUFA 2.2 and LUFA 2.4 for this purpose. The test vessel adsorption was lower in the samples with the higher soil /solution ratio. A soil / solution ratio of 1:10 was used for the further experiments during this study. The test vessel adsorption ranged from 0.6 to 3.3% under this condition for all tested soils.

 

Tier 1– Adsorption Kinetics

The test item depletion of the test item in the aqueous phase in soil suspensions with a soil / solution of 1:10 was nearly quantitative within 2 hours of the experiments with the soils LUFA 2.2 and LUFA 2.4. These results were obtained by the indirect method; only the concentration of the test item in the aqueous phase was determined. An agitation time of 24 hours was used for the adsorption kinetic experiments in tier 2 based on these experiments. The agitation time was reduced to 4 hours during the experiments for the adsorption isotherms in all soils except for the soil LUFA 2.1.

 

Tier 1– Parental Mass Balance

The parental mass balance for the test item was determined in all soils with an application concentration of 2 mg/L, a soil / solution ratio of 1:10 and after an agitation time of 4 hours for the soils LUFA 2.2, 2.3, 2.4 and 5M. 24 hours of agitation were used for the soil LUFA 2.1. The parental mass balances were finally calculated by taking into account the test item recovery on the test vessel surfaces, in the aqueous phase and in the soil. The extraction method for soil was optimized prior to these experiments by preparing samples in the soil LUFA 2.4. This soil was used for this purpose because this soil has the highest amount of organic carbon and clay. These parameters have a significant impact on the adsorption of organic compounds in soils. In general, high values for these parameters are responsible for high adsorption and fast / increased formation of non-extractable residues (NERs). A harsh extraction with an accelerated solvent extractor (ASE) was finally used for extraction of the test item It is more likely to obtain the best extraction efficiency with an ASE for aged samples than with an extraction at ambient temperature because the ASE extraction uses a combination of elevated temperature and pressure. Further experiments during method development indicated a decline of test item recovery in extracts of aged soil samples. Mass balances between 57 and 92% were obtained.

 

Results Tier 2– Adsorption Kinetics

These experiments confirmed the results of tier 1. The test item depletion in the aqueous phase ranged from 96 to 99% after 24 hours of agitation. Only the aqueous phase was analysed during these experiments. It was decided to waive further analysis of the aqueous phase during the determination of the adsorption isotherms during tier 3 based on these results. The concentrations of the test item in the aqueous phase were often in the lower range of the calibration with only low dilution factors. In consequence, concentrations lower than the lowest calibration level would have been obtained in the lower application concentrations during the determination of the adsorption isotherms. For this reason, the measurement of theses samples was useless for the determination of the adsorption isotherms.

 

ResultsTier 3

ResultsTier 3– Desorption Kinetics

Only samples of the aqueous phase were analysed for this purpose. Test item concentrations in the aqueous phase lower than 1% related to the applied test item amount (2 mg test item/L) were determined in the desorption kinetic experiments. The desorption is negligible under the used experimental conditions (24 hours adsorption and 48 hours desorption). Therefore, no experiments for the determination of the desorption isotherms were conducted.

 

ResultsTier 3– Adsorption Isotherms

Analysis during the determination of the adsorption isotherms were performed by analysing soil extracts of all concentration levels. The concentrations in the aqueous phase were calculated from the corresponding data of the adsorption kinetics and extrapolating the adsorption in % also to the lower concentration levels based on the assumption that the adsorption behavior is linear. Table 2 presents the obtained data.

Table2:      Freundlich Adsorption Isotherms

Applied test item concentrations: 2, 1, 0.2, 0.1, 0.02 mg/L

Volume of aqueous phase:        40 mL

Soil Type

msoil[g]

r2

1/n

KFads

KFOC

LUFA 2.1

3.88

0.995

1.47

3243

451638

LUFA 2.2

3.71

0.997

1.14

1121

76255

LUFA 2.3

3.84

0.997

1.20

1340

325155

LUFA 2.4

3.62

0.995

1.10

2460

141384

LUFA 5M

3.70

0.992

1.11

2582

281835


msoil
      = used amount of soil (dry weight) [g]

n           = regression constant

KFads      = Freundlich adsorption coefficient [µg1-1/n(mL)1/ng-1]

KFOC      = Freundlich adsorption coefficient normalized to content of organic carbon [µg1-1/n(mL)1/ng-1]

 

A further assessment for the results of these experiments was performed because the values for the inverse regression constant 1/n (slope of the linear regression) were not plausible. These values were ≥ 1.1 and are not between 0.7 and 1 as expected for a Freundlich adsorption behavior. Furthermore, a strong decrease of the extracted test item amount from the soils was observed towards the lower application concentrations. This fact is in accordance to the implausible values for the inverse regression constants 1/n indicating a significant nonlinear adsorption behaviour. For this reason, individual organic carbon normalized distribution coefficients Koc were calculated (see Table 3) per application level and for all soils and compared with the organic carbon normalised Freundlich adsorption coefficients KFoc. Table 3 indicates that the organic carbon normalized distribution coefficients Koc are lower than the corresponding organic carbon normalised Freundlich adsorption coefficients KFoc. Furthermore, a decrease of these values towards the lower application levels was determined. These data clearly indicate that the adsorption is significantly nonlinear.

 

Table3:      Individual organic carbon normalized Distribution Coefficients Koc

Applied test item concentrations: 2, 1, 0.2, 0.1, 0.02 mg/L

Volume of aqueous phase:        40 mL

Application Level

 

Koc

LUFA 2.1

LUFA 2.2

LUFA 2.3

LUFA 2.4

LUFA 5M

K1

77057

45361

151587

95475

183082

K2

57954

42678

149890

86546

171219

K3

18510

37103

95755

62844

105760

K4

15737

25591

76229

66114

105856

K5

9870

25420

68902

62717

123801