Dimantine

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

2000-05-09 to 2000-07-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP Guideline study. Justification for read-across see chemical safety report chapter 1.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2000

Report date:

2000

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

other: soil sediment and sludge

Test material

Test material information

Constituent 1

Reference substance name:

Octadecylamine

EC Number:

204-695-3

EC Name:

Octadecylamine

Cas Number:

124-30-1

Molecular formula:

C18H39N

IUPAC Name:

octadecan-1-amine

Radiolabelling:

yes

Study design

Test temperature:

20°C ± 2°C

Batch equilibrium or other method

Analytical monitoring:

yes

Details on sampling:

See section "Details on test conditions"

Details on matrix:

#1 - SOIL 1: SSLRC Standard soil No 164 (Cranfield 164)
- Geographic location: Farditch Farm, Buxton, Derbyshire, United Kingdom. OS map reference
SK104691
PROPERTIES
- Soil texture:
- Particle size distribution(USDA):
% silt (2-53 μm): 63.24
% sand (53-2000 μm): 15.00
% clay (< 2 μm): 20.04

- Particle size distribution (DIN)
% silt (2-63 μm): 70.08
% sand (63-2000 μm): 9.87
% clay (< 2 μm): 20.04
- Horizon: 10-20 cm
- pH: 6.3-6.8
- Organic carbon (%): 3.8
- CEC (meq/100 g): 21.8

#2 - SOIL 2: SSLRC Standard soil No 266 (Cranfield 266)
- Geographic location: Posher Farm, Ufton, Warwicks, United Kingdom. OS map reference SP
37076231
PROPERTIES
- Soil texture:
- Particle size distribution(USDA):
% clay (< 2 μm) 50.17
% silt (2-53 μm) 29.00
% sand (53-2000 μm) 20.84

- Particle size distribution (DIN)
% clay (< 2 μm) 51.63
% silt (2-63 μm) 29.77
% sand (63-2000 μm) 18.60
- Horizon: 0-20 cm
- pH: 7.4-8.6
- Organic carbon (%): 1.5
- CEC (meq/100 g): 23.1

#3 - SEDIMENT:
- Details on collection: The sediment was sampled from Oostvaardersplassen (OVP) on May 10, 2000. Oostvaardersplassen
is an area endiked from the lake IJssel (IJsselmeer), situated near Lelystad, The Netherlands. The lake
has been closed for river Rhine water for approximately 35 years.
- Textural classification (i.e. %sand/silt/clay): silt loam (% clay (< 2 μm): 18.70, % silt (2 μm – 63 μm): 69.02, % sand (63 μm – 2 mm): 12.28)
- pH: 7.6 - 8.0
- Organic carbon (%): 2.4
- CEC (meq/100 g): 13.6

#4 - SEWAGE SLUDGE:
- Type of sludge:
- Source of sludge: The sewage sludge was sampled from the municipal wastewater treatment plant Waterschap De
Maaskant in ’s-Hertogenbosch, The Netherlands on May 15, 2000 from a basin containing so-called
return sludge, which had been thickened two to three times
- Oxygen status:
Texture: Silty Clay
% clay (< 2 μm): 45.93
% silt (2 μm – 63 μm): 51.57
% sand (63 μm – 2 mm): 2.50
% organic carbon: 30.1
% organic matter: 51.9
pH-H2O: 7.2
pH-CaCl2: 6.8
CEC (meq/100g): 54.9

Details on test conditions:

1) Test system preparation
Prior to being used for the experiment the soils, sediment and sewage sludge were irradiated at Gammaster B.V. in Ede, The Netherlands on June 4, 2000. The materials were kept in plastic containers and were subjected to a dose of 25.0 kGy average in a JS6500 Tote Box Irradiator.
Although the irradiation was not performed under GLP-conditions, Gammaster is certified with the national and international Quality Assurance System Standards NEN-ISO 9002 and EN 46002.
Representative samples of soils I (Cranfield 164 silt loam) and II (Cranfield 266 clay), sediment (OVP) and sewage sludge (DB1) were taken from storage and their moisture content was determined after oven drying at 105°C until constant weight.

2) Treatment solutions
For the kinetics experiment, a stock solution (A) containing 2.519 MBq/mL 14C-octadecylamine in methanol was prepared. This is equivalent to 335 μg 14C-octadecylamine/mL. The radiochemical purity of the stock solution was determined by thin layer chromatography (TLC). In addition, a stock solution containing 1.140 mg/mL unlabelled octadecylamine was prepared in methanol. From these stock solutions the following treatment solution was prepared in methanol:
Treatment solution 1 : 979 μg/mL with a specific activity of 512 Bq/μg.
Prior to the isotherm experiment, it was found that the radiochemical purity of the stock solution (A) at that moment was only 87%. It was therefore purified by a combination of TLC and repeated extraction of isolated plate material with methanol. With the purified material a stock solution (B) containing 0.387
MBq/mL 14C-octadecylamine in methanol was prepared. This is equivalent to 51.3 μg 14Coctadecylamine/mL. The radiochemical purity of the stock solution (B) was determined by TLC. In addition, a stock solution containing 1.028 mg/mL unlabelled octadecylamine was prepared in methanol. From these stock solutions the following treatment solutions were prepared in methanol:
Treatment solution 2 : 102 μg/mL with a specific activity of 1604 Bq/μg
Treatment solution 3 : 201 μg/mL with a specific activity of 774 Bq/μg
Treatment solution 4 : 502 μg/mL with a specific activity of 323 Bq/μg
The concentrations were determined by liquid scintillation counting (LSC) of the solutions prior to use. The radiochemical purity of all treatment solutions was also determined by TLC.

3) Pre-equilibration of test systems
Prior to the start of all adsorption-desorption experiments, a precisely known amount of approximately 100 mg of soil or sediment or approximately 1000 mg of sludge was weighed out in glass vials and a known amount of approximately 10 mL (soil and sediment) or 9 mL (sludge) of 0.01 M aqueous CaCl2
solution was added. The vials were sealed and placed on a shaker for at least 16 hours for preequilibration. Soils were equilibrated at 20°C ± 2°C.

4) Adsorption kinetics
The purpose of this part of the study was to determine the times required to reach adsorption and desorption equilibrium. Treatment solution 1 (as defined in paragraph 2) was used for these experiments. Experiments were performed at a soil:solution ratio of 1:100 and were carried out at 20°C ± 2°C.
The adsorption kinetics experiments were initiated by adding 10 μL of treatment solution 1 to a total of ten pre-equilibrated test system slurries for each test system (two per test system per sampling time point and two per test system for TLC analysis after 3 and 24 hours). Liquid scintillation counting of 10 μL aliquots of treatment solution 1 just prior to, during and immediately after spiking of the test system solutions indicated that this was equivalent to a dose of 10.36 μg octadecylamine. Hence, the initial concentration of test chemical in the test system solution was 1.036 μg/mL and the amount of organic
co-solvent (methanol) in the test system solution was 0.1%. The vials were sealed and placed on a shaker. After 1, 3, 6 and 24 hours sampling was performed and the appropriate samples were centrifuged at 4000 rpm (3023 g) for 5 minutes at 20°C. The weight of the supernatant was determined after careful decanting and radioactivity was determined by LSC of the whole supernatant (Ultima Gold XR). The test system was removed from the vials with a spatula. Last traces of test system were removed by twice adding 0.5 mL of Milli-Q water and removing the slurry with a pipette. To recover any test material that had adsorbed to the container walls, 5 mL of methanol were added to the empty containers and the containers were closed with the original caps. Then they were shaken for one minute and the methanol phase was collected. This procedure was repeated once and the methanol phases were combined, weighed and activity was determined by LSC of a 1 mL aliquot. The desorption part of the kinetics experiment was conducted after the adsorption isotherm experiment.

5) Adsorption isotherms and desorption kinetics
The adsorption isotherm experiment was initiated by adding a specific volume of stock solution (B) or treatment solutions 2, 3 or 4 to twelve pre-equilibrated test system slurries per test system (two replicates per concentration, one additional sample for mass balance determination and one additional sample for TLC analysis). Two samples per test system were spiked with 7.8 μL of stock solution (B), two with 39 μL of stock solution (B), four samples (including the ones intended for mass balance determination and TLC analysis) were spiked with 100 μL of treatment solution 2, another two samples were spiked with 100 μL of treatment solution 3 and finally two samples were spiked with 100 μL of treatment solution 4. For the sediment OVP test system one sample was erroneously spiked with twice the spike volume of treatment solution 2 (and therefore used as the sample for TLC analysis). As a result, for the sewage sludge DB1 test system only three samples could be spiked with treatment solution 2. Hence, the sample used for determination of the mass balance for this test system functioned at the same time as the duplicate. The test system:solution ratio used was 1:100 and the initial concentrations were approximately 0.04, 0.2, 1, 2 and 5 μg/mL.
The solutions in contact with the test system contained ≤ 1% of organic co-solvent (methanol). The test system slurries were placed on a shaker at 20°C ± 2°C. At adsorption equilibrium (3 hours as determined according to paragraph 4), the test system slurries were centrifuged at 4000 rpm (3023 g) for 5 minutes at 20°C. The weight of the supernatant was determined after careful decanting and radioactivity was determined by LSC of the whole supernatant (Ultima Gold XR). The test system was removed from the vials with a spatula. Last traces of test system were removed by twice adding 0.5 mL of Milli-Q water and removing the slurry with a pipette. To recover any test substance that had adsorbed to the container walls, 5 mL of methanol were added to the empty containers and the containers were closed with the original caps. Then they were shaken and the methanol phase was collected. This procedure was repeated once and the methanol phases were combined, weighed and activity was determined by LSC of a 1 mL (weighed) aliquot. The desorption kinetics step of the experiment was performed with two samples (spiked with treatment solution 2) per test system except for the sewage sludge DB1, for which only one sample could be used (the other samples had been used for mass balance determination and TLC analysis). After removal of the supernatant of the adsorption step, the test system was transferred to a clean vial by means of a spatula and a total of 1 mL of Milli-Q water. To each vial was added 9 mL of aqueous 0.01M calcium chloride solution and the vials were sealed and placed on a shaker at 20°C ± 2°C. At the sampling times of 47 hours and 166 hours, one sample per test system was centrifuged for 5 minutes at 4000 rpm (3023 g) at 20 °C. The weight of the supernatant was determined after careful decanting and radioactivity was determined by LSC of the whole supernatant (Ultima Gold XR). The test system was removed from the vials by twice adding 0.5 mL of Milli-Q water and removing the slurry with a pipette. To recover any test substance that had adsorbed to the container walls, 5 mL of methanol were added to the empty containers and the containers were closed with the original caps. Then they were shaken for one minute and the methanol phase was collected. This procedure was repeated once and the methanol phases were combined, weighed and activity was determined by LSC of a 1 mL (weighed) aliquot.

6) Stability of test chemical during the experiments
Thin Layer Chromatography (TLC) was used to assess the stability of octadecylamine during the experiments. TLC was performed with adsorption kinetics samples obtained after 3 and 24 hours and with adsorption isotherm samples that had been spiked with treatment solution 2 (one sample per test system). The supernatant was analysed directly. The test system was transferred to a vial with 0.5-1.0 mL Milli-Q water and extracted with methanol. This extract was subjected to TLC. A subsample of the combined methanol phases used for recovery of test substance from the container walls was also TLC’ed. Additionally, TLC was used for purification of the radiolabelled test substance prior to the isotherm experiment .
All TLC experiments were performed on Silica-60 F254 plates (20x20 cm, Merck) using methanol:acetic acid (97:3 v/v) as mobile phase.

7) Mass balances
The A replicates of the kinetics-samples obtained after 3 and 24 hours and four isotherm samples that had been spiked with treatment solution 2 (one sample per test system) were used for the determination of a complete mass balance. Hereto, the test system that was removed from the vials was transferred to a weighing scoop. After addition of 0.5 mL acetone (to prohibit biodegradation of the test substance) the test system was air dried and combusted on a Harvey OX500 biological oxidizer while trapping the released 14CO2 in Picosolve-300 scintillation cocktail. Activity was determined byLSC.

Duration of adsorption equilibration

Duration of adsorption equilibration 1

Sample No.:

#1

Duration:

3 h

Temp.:

20 °C

Duration of adsorption equilibration 2

Sample No.:

#2

Duration:

3 h

Temp.:

20 °C

Duration of adsorption equilibration 3

Sample No.:

#3

Duration:

3 h

Temp.:

20 °C

Duration of adsorption equilibration 4

Sample No.:

#4

Duration:

3 h

Temp.:

20 °C

Duration of desorption equilibration

Duration of desorption equilibration 1

Sample no.:

#1

Duration:

47 h

Temp.:

20 °C

Duration of desorption equilibration 2

Sample no.:

#2

Duration:

47 h

Temp.:

20 °C

Results and discussion

Adsorption coefficient

Adsorption coefficient 1

Type:

Kd

Remarks:

Cranfield 164 soil in L/kg

Value:

243

Temp.:

20 °C

% Org. carbon:

3.8

Remarks on result:

other: for lowest pore water conc. at ads. equilib. 9 µg/L

Adsorption coefficient 2

Type:

Kd

Remarks:

Cranfield 266 soil in L/kg

Value:

409

Temp.:

20 °C

% Org. carbon:

1.5

Remarks on result:

other: for lowest pore water conc. at ads. equilib. 8 µg/L

Adsorption coefficient 3

Type:

Kd

Remarks:

Sediment OVP in L/kg

Value:

600

Temp.:

20 °C

% Org. carbon:

2.4

Remarks on result:

other: for lowest pore water conc. at ads. equilib. 5 µg/L

Adsorption coefficient 4

Type:

Kd

Remarks:

Activated sludge DB in L/kg

Value:

693

Temp.:

20 °C

% Org. carbon:

30.1

Remarks on result:

other: for lowest pore water conc. at ads. equilib. 5 µg/L

Adsorption coefficient 5

Type:

log Koc

Remarks:

Cranfield 164 soil

Value:

3.805

Temp.:

20 °C

% Org. carbon:

3.8

Remarks on result:

other: for lowest pore water conc. at ads. equilib. 9 µg/L

Adsorption coefficient 6

Type:

log Koc

Remarks:

Cranfield 266 soil

Value:

4.436

Temp.:

20 °C

% Org. carbon:

1.5

Remarks on result:

other: for lowest pore water conc. at ads. equilib. 8 µg/L

Adsorption coefficient 7

Type:

log Koc

Remarks:

Sediment OVP

Value:

4.398

Temp.:

20 °C

% Org. carbon:

2.4

Remarks on result:

other: for lowest pore water conc. at ads. equilib. 5 µg/L

Adsorption coefficient 8

Type:

log Koc

Remarks:

Activated sludge DB

Value:

3.362

Temp.:

20 °C

% Org. carbon:

30.1

Remarks on result:

other: for lowest pore water conc. at ads. equilib. 5 µg/L

Results: Batch equilibrium or other method

Adsorption and desorption constants:

See section "Any other information on results including tables"!

Recovery of test material:

See table 1 section "any other information on materials and methods including tables"!

Concentration of test substance at end of adsorption equilibration period:

See table 1 section "any other information on materials and methods including tables"!

Mass balance (%) at end of adsorption phase

Mass balance (%) at end of adsorption phase 1

Sample no.:

#1

Duration:

3 h

% Adsorption:

80.2

Mass balance (%) at end of adsorption phase 2

Sample no.:

#2

Duration:

3 h

% Adsorption:

91.3

Mass balance (%) at end of adsorption phase 3

Sample no.:

#3

Duration:

3 h

% Adsorption:

88.1

Mass balance (%) at end of adsorption phase 4

Sample no.:

#4

Duration:

3 h

% Adsorption:

80.1

Mass balance (%) at end of desorption phase

Mass balance (%) at end of desorption phase 1

Sample no.:

#1

Duration:

166 h

% Desorption:

24.2

Mass balance (%) at end of desorption phase 2

Sample no.:

#2

Duration:

166 h

% Desorption:

19.1

Mass balance (%) at end of desorption phase 3

Sample no.:

#3

Duration:

166 h

% Desorption:

16.6

Mass balance (%) at end of desorption phase 4

Sample no.:

#4

Duration:

47 h

% Desorption:

5.7

Transformation products:

yes

Details on results (Batch equilibrium method):

See section "Any other information on results including tables"!

Any other information on results incl. tables

Adsorption isotherms and desorption kinetics

Radioactivity was measured in the supernatant (SN) and in the methanol washings of the glass container walls. Subtraction of these two values from the total applied activity should give the activity that had adsorbed to the test system. For one sample per test system (spiked with treatment solution 2) the activity adsorbed to the test system was determined by combustion and a mass balance was calculated. The results are presented in Table 3. As can be seen, mass balances were all >90%, as specified by the guideline, hence proving the validity of the method used and indicating that calculating the activity that had adsorbed to the test system from the other experimentally determined values (total activity in supernatant, on glass and initially applied) was correct.

Table 3:

Sample	Total activity in SN 1)	Total activity on glass 1)	Total activity on test system (calculated) 1)	Total activity on test system (combustion) 1)	Mass balance (%)
Cranfield 164	75887	104845	800848	767499	96.60
Cranfield 266	48924	25045	907612	878244	97.01
OVP	51268	31249	899063	880494	98.11
DB1	102322	48468	830790	769821	93.79

 1) In dpm. Total activity applied: 981580 dpm.

From the various total activities that were measured and calculated the concentrations of octadecylamine adsorbed on test system and in solution were calculated. The mean value of the two replicates was then further used for calculation of the Freundlich adsorption parameters. These are presented in Table 4. Based on the classification given by Mensink and the values for the Kom obtained from the adsorption isotherm, octadecylamine can be considered immobile (Kom>100) in all test systems investigated. The fitted Freundlich isotherms appear to have a convex shape, whereas usually such isotherms are concave. The reason for this difference is that, because of its typical surfactant structure, the adsorption of the test substance need not be limited to adsorption of a monolayer. Multilayer adsorption is a well-known phenomenon for surfactants and octadecylamine may also be expected to show multilayer (i.e. bilayer) adsorption.

Table 4:

Test system	K (F) ads [µg^(1 -1/n)(cm³)^(1/n) g^(-1)]	K (F, om) ads [µg^(1 -1/n)(cm³)^(1/n) g^(-1)]	1/n	r2
Cranfield 164	3065	46437	1.5384	0.9857
Cranfield 266	30053	1155884	1.8897	0.9858
Sediment OVP	6433	155466	1.4478	0.9679
Sludge DB1	821	1583	1.0322	0.9990

Stock solution (B) and treatment solutions 2, 3 and 4, although of high radiochemical purity, still showed the presence of two metabolites at a Rf value of 0 and 0.9, respectively, and these metabolites were again encountered in several isotherm samples. The metabolite at Rf 0.9 was encountered in all test system extracts, as well as in the supernatant and container wall extract of sludge DB1, thus confirming its high adsorptivity. Purity of octadecylamine extracted from the test system was high for the two Cranfield soils and the sediment (93-96%) and moderate (62%) for the sludge DB1. In the container wall extracts of the two Cranfield soils and the sediment OVP only octadecylamine was found, whereas the sludge DB1 container wall extract contained 90% octadecylamine and 10% of metabolite Rf 0.9. Finally, the supernatant chromatograms for the two Cranfield soils and the OVP sediment appeared to indicate instability of the test substance, but as the amount of activity present in the sample was low, these values were treated as unreliable. The DB1 supernatant contained 79% octadecylamine as well as 4% of metabolite Rf0 and 17% of metabolite Rf0.9. The reason for the decrease in purity of the test substance is not clear. Biodegradation is unlikely as the test systems had been irradiated prior to testing and the decrease was also observed for a test substance solution not in contact with any test system. The guideline recommends that under these circumstances both phases (soil and solution) are to be analysed. This has been done.

Because of the limited number of samples available for the desorption kinetics experiment after the adsorption isotherm experiment, and the fact that each vial could be sampled only once (total supernatant, removal of test system, washing of the container walls) a limited number of samplings could be performed in the desorption kinetics experiment. For results see Table 5.

Table 5: Desorption kinetics:

Test system	% desorption after 47 hours	% desorped after 166 hours
Cranfield 164	24.4	24.2
Cranfield 266	13.7	19.1
Sediment OVP	No result	16.6
Sludge DB 1	5.7	No result

The result clearly show that octadecylamine desorption occurs to a lesser extent than adsorption and is slower than adsorption for all test systems.

Applicant's summary and conclusion

Validity criteria fulfilled:

not applicable

Remarks:

Valid study due to reliable exp. results and comprehensible documentation; however, OECD 106 does not state explicit validity criteria.

Conclusions:

Octadecylamine can be considered immobile in Cranfield 164 silt loam soil, Cranfield 266 clay soil, Oostvaardersplassen sediment silt loam and sewage sludge DB1 silty clay.

Executive summary:

The objective of this study was to obtain information on the adsorption/desorption behaviour of octadecylamine on soil, sediment and sludge. Adsorption parameters were determined compliant to GLP using the batch equilibrium method according to OECD 106 (reliability category 1) in two soils which represent major agricultural areas in Europe and North America, one sediment and one sewage sludge:

Cranfield 164 soil [21.8% clay, 6.6% organic matter, silt loam], Cranfield 266 soil [50.2% clay, 2.6% organic matter, clay], Oostvaardersplassen sediment [18.7% clay, 4.1% organic matter, silt loam] and sewage sludge DB1 [45.9% clay, 51.9 % organic matter, silty clay]. These test systems encompass a range of % clay and % organic material.

Because of the strong adsorption of octadecylamine on the container materials, an alternative set-up for performance of the study was developed. In this method, activity was determined in the supernatant and on the container walls. Activity adsorbed to the test system was calculated from these results and the initial activity applied. Adsorption and desorption kinetics were determined at an initial concentration of approximately 1 μg/mL. Adsorption isotherms were determined over a concentration range from approximately 0.04 to 5 μg/mL. All adsorption-desorption experiments were carried out at 20°C ±2°C.

Mass balances thus obtained for the adsorption isotherm experiment were all >90%, indicating the validity of the test set-up.

Octadecylamine can be considered immobile in Cranfield 164 silt loam soil, Cranfield 266 clay soil, Oostvaardersplassen sediment silt loam and sewage sludge DB1 silty clay.

K_{F,o m}^adsvalues, obtained from the Freundlich adsorption isotherm, were

46*10³µg^1-1/n(cm³)^1/ng^-1for Cranfield 164 silt loam, 1/n = 1.5384,

1.2*10⁶µg^1-1/n(cm³)^1/ng^-1for Cranfield 266 clay, 1/n = 1.8897,

1.6*10⁵µg^1-1/n(cm³)^1/ng^-1for Oostvaardersplassen sediment silt loam, 1/n = 1.4478 and

1.6*10³µg^1-1/n(cm³)^1/ng^-1for sewage sludge DB1 silty clay, 1/n = 1.0322.

For all test systems r²> 0.96.