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Adsorption / desorption

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Endpoint:
adsorption / desorption: screening
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
The test was performed with substance analogue TMAH. The rationale for read-across is attached in IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
Type:
Koc
Value:
87.3 L/kg
Temp.:
20 °C
% Org. carbon:
1.87
Remarks on result:
other: KFoc in Speyer 2.2 soil, 1/n 0.84, r^2 0.9981, 10 datapoints
Type:
Koc
Value:
585 L/kg
Temp.:
20 °C
% Org. carbon:
0.94
Remarks on result:
other: KFoc in Speyer 2.3 soil, 1/n 0.64, r^2 0.9988, 10 datapoints
Type:
Koc
Value:
1 017 L/kg
Temp.:
20 °C
% Org. carbon:
1.64
Remarks on result:
other: KFoc in Speyer 6S soil, 1/n 0.77, r^2 0.9975, 10 datapoints
Type:
Koc
Value:
563 L/kg
Temp.:
20 °C
Remarks on result:
other: Mean KFoc, 1/n 0.75
Concentration of test substance at end of adsorption equilibration period:
Analysed concentration in the liquid phase after 48 h (adsorption kinetics):
Speyer 2.2 soil: 7.46 mg/L
Speyer 2.3 soil: 4.62 mg/L
Speyer 6S soil: 5.77 mg/L
Details on results (Batch equilibrium method):
Determination of equilibrium time (adsorption kinetics):
The graphs show a rapid increase of the adsorption of TMAH pentahydrate to all the soils in the first 3 hours of contact time. After 24 hours contact time equilibration was reached. No TMAH pentahydrate was detected in the blank samples.

Determination of adsorption isotherms:
Adsorption isotherms could be described by the Freundlich equation. The fits of the Freundlich adsorption isotherms to the data are shown bellow in the field "any other information on results incl. tables".

The pH of the supernatants after 48 h (adsorption kinetics) was 5.6 for Speyer 2.2 soil and 7.0 for Speyer 2.3 and Speyer 6S soil.

At the end of the isotherm experiment, the pH was 5.6-5.7 for Speyer 2.2 soil, 7.0 for Speyer 2.3 and Speyer 6S soil.

Table: Koc and Kd values of TMAH pentahydrate determined during adsorption kinetics test at an initial nominal concentration of 10 mg/L

Type

Value

Temperature

% Org. carbon

Remarks

Koc

35

20 °C

1.87

Speyer 2.2 (Loamy sand)-48 h

Kd

0.7

20 °C

1.87

Speyer 2.2 (Loamy sand)-48 h

Koc

258

20 °C

0.94

Speyer 2.3 (Sandy loam)-48 h

Kd

2.4

20 °C

0.94

Speyer 2.3 (Sandy loam)-48 h

Koc

452

20 °C

1.64

Speyer 6S (Clay)-48 h

Kd

7.4

20 °C

1.64

Speyer 6S (Clay)-48 h

 

Validity criteria fulfilled:
yes
Conclusions:
The adsorption behavior of TMAH pentahydrate was studied in three different soils, including a loamy sand (Speyer 2.2 soil; %oc 1.87), a sandy loam (Speyer 2.3 soil; %oc 0.94) and a clay soil (Speyer 6S soil; %oc 1.64).
The KFoc value of TMAH pentahydrate was 87 (1/n 0.84), 585 (1/n 0.64) and 1017 (1/n 0.77) in three different soils (mean KFoc 563, 1/n 0.75). This result is read across to TEAH.
Executive summary:

The adsorption behavior of TMAH pentahydrate was studied in three different soils, including a loamy sand (Speyer 2.2 soil; %oc 1.87), a sandy loam (Speyer 2.3 soil; %oc 0.94) and a clay soil (Speyer 6S soil; %oc 1.64).

Adsorption kinetics were determined at an initial TMAH pentahydrate concentration of approximately 10 mg/L. A rapid increase of the adsorption of TMAH pentahydrate to the soils in the first 3 hours contact time was observed for all three soils. The adsorption plateau was reached after 24 hours for all three soils.

Adsorption isotherms were determined over a TMAH pentahydrate concentration range of 0.25 – 25 mg/L and a contact time of 24 hours. TMAH pentahydrate adsorption isotherms could be described by the Freundlich equation.

The KFoc value of TMAH pentahydrate was 87 (1/n 0.84), 585 (1/n 0.64) and 1017 (1/n 0.77) in three different soils (mean KFoc 563, 1/n 0.75).

This result is read across to TEAH.

Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
28 November 2012 - 8 February 2013
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
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
All adsorption experiments were carried out at 20 ± 2°C.
Analytical monitoring:
yes
Details on sampling:
After the various contact times (3, 6, 24 and 48 hours), the slurries were removed from the roller mixer and centrifuged for 5 minutes at 845 g and 20°C (the controls were not centrifuged). After centrifugation, a 2 mL aliquot of the supernatant was taken from each sample and stored at ≤ -15°C until analysis. Blanks were sampled after 48 hours only.

Determination of equilibrium time (adsorption kinetics):
- Initial concentration: approx. 10 mg/L
- Sampling interval: 3, 6, 24 and 48 h

Determination of adsorption isotherms:
- Concentrations: 0.25, 1, 2.5, 10 and 25 mg/L
- Sampling time: 24 h
Details on matrix:
Three different soils, representative for agricultural soils in Europe and North America. Sieved (2 mm) air-dried soil samples were taken from storage in the lab. Storage was at ambient temperature and time between sampling and the start of the test did not exceed three years.

Soil 1:
Designation: Speyer 2.2 soil
- Classification: Loamy sand
- pH: 5.5
- Organic carbon (%): 1.87
- CEC (meq/100 g): 10
- Moisture: 1.19% (determined prior to start)

Soil 2:
Designation: Speyer 2.3 soil
- Classification: Sandy loam
- pH: 6.8
- Organic carbon (%): 0.94
- CEC (meq/100 g): 11
- Moisture: 2.04% (determined prior to start)

Soil 3:
Designation: Speyer 6S soil
- Classification: Clay
- pH: 7.1
- Organic carbon (%): 1.64
- CEC (meq/100 g): 24
- Moisture: 5.35% (determined prior to start)
Details on test conditions:
TEST SYSTEM
- Type, size and further details on reaction vessel: 50 mL polypropylene containers
- Solution: 0.01 M CaCl2 solution (7.35 g calcium chloride dihydrate/5L Milli-Q water)
- Water: Milli-Q water (tap water purified by a Milli-Q water purification system (Millipore, USA))
- Amount of soil and water per treatment:
For Speyer 2.2 and Speyer 2.3 soil approx. 15 g plus 27 mL 0.01 M CaCl2 solution
For Speyer 6S soil approx. 4.5 g plus 40.5 mL 0.01 M CaCl2 solution
- Soil-solution ratio: 1:2 for Speyer 2.2 and Speyer 2.3 soil, and 1:10 for Speyer 6S soil
- Number of reaction vessels/concentration: 1 vial per sampling point (kinetics); 2 samples per soil and concentration (isotherms)
- Measuring equipment: HPLC-UV and pH meter
- Test performed in closed vessels in the dark on a roller mixer
- Method of preparation of test solution
Adsorption kinetics: A stock solution of 102.3 mg TMAC in 10 mL Milli-Q was prepared (10.2 g/L). The stock solution was diluted in 0.01 M CaCl2 solution to obtain a spike solution of 100 mg/L.
Adsorption isotherms: Two stock solutions of 33.8 mg and 308.4 mg TMAC in 25 mL Milli-Q water were prepared (1.35 g/L and 12.3 g/L , respectively). A series of spike solutions of 2.5, 10 and 25 mg/L were prepared by dilution of the 1.35 g/L solution in 0.01 M CaCl2 solution and spike solutions of 100 and 250 mg/L were prepared by dilution of the 12.6 g/L solution in 0.01 M CaCl2 solution.

PRELIMINARY EXPERIMENTS
The adsorption of TMAH pentahydrate on the surface of the glass and polypropylene vessels and the stability of the test substance in 0.01M CaCl2 solution were assessed by equilibrating a 10 mg/L solution in test vessels under identical experimental conditions (duplicate samples per vessel material per contact time).

Soil:solution ratios of approximately 1:2, 1:10 and 1:50 were investigated. The soil:0.01 M CaCl2 slurries were equilibrated overnight on a roller mixer prior to spiking with a 100 mg/L solution to obtain a final TMAH pentahydrate concentration in the test solutions of approximately 10 mg/L.

DETAILS EQUILIBRIUM TIME DETERMINATION (ADSORPTION KINETICS):
The slurries were equilibrated on a roller mixer overnight prior to spiking. The adsorption kinetics experiment was initiated by adding a weighed volume of approximately 3 ml (Speyer 2.2 and 2.3 soil) and 4.5 mL (Speyer 6S soil) of spike solution to the pre-equilibrated soil slurries to obtain the selected soil:solution ratio. A control without soil was included, as well as a blank sample of each soil (soil without test substance). The samples were placed on a roller mixer. The pH of the supernatants (48 h) was measured .

DETAILS ADSORPTION ISOTHERMS DETERMINATION:
The slurries were equilibrated for at least 16 h on a roller mixer prior to spiking. After equilibration, the samples were spiked with an appropriate amount of spike solution to obtain the desired test concentration. Controls without soil were included as well as a blank sample for each soil system using a known amount of 0.01 M CaCl2 solution and no test substance. At the end of the experiment the pH of the supernatants was determined after decanting (one replicate of each soil at the highest and lowest concentration level).
Sample No.:
#1
Duration:
48 h
Initial conc. measured:
9.84 other: mg/L (Speyer 2.2 soil)
pH:
5.5
Sample No.:
#2
Duration:
48 h
Initial conc. measured:
9.8 other: mg/L (Speyer 2.3 soil)
pH:
6.8
Sample No.:
#3
Duration:
48 h
Initial conc. measured:
9.84 other: mg/L (Speyer 6S soil)
pH:
7.1
Computational methods:
The Freundlich adsorption isotherm parameters (KF and 1/n) were calculated by fitting the data to the Freundlich isotherm. Organic carbon-normalised Freundlich adsorption coefficients (KF,oc) were also determined. KF = Freundlich adsorption coefficient (ml/g); n = regression constant.
Type:
Koc
Value:
92 L/kg
Temp.:
20 °C
% Org. carbon:
1.87
Remarks on result:
other: KFoc in Speyer 2.2 soil, 1/n 0.82, r^2 0.982, 10 datapoints
Type:
Koc
Value:
567 L/kg
Temp.:
20 °C
% Org. carbon:
0.94
Remarks on result:
other: KFoc in Speyer 2.3 soil, 1/n 0.64, r^2 0.991, 10 datapoints
Type:
Koc
Value:
979 L/kg
Temp.:
20 °C
% Org. carbon:
1.64
Remarks on result:
other: KFoc in Speyer 6S soil, 1/n 0.78, r^2 0.99, 10 datapoints
Type:
Koc
Value:
546 L/kg
Temp.:
20 °C
Remarks on result:
other: Mean KFoc, 1/n 0.75
Concentration of test substance at end of adsorption equilibration period:
Analysed concentration in the liquid phase after 48 h (adsorption kinetics):
Speyer 2.2 soil: 6.99 mg/L
Speyer 2.3 soil: 4.36 mg/L
Speyer 6S soil: 5.42 mg/L
Details on results (Batch equilibrium method):
Determination of equilibrium time (adsorption kinetics):
The graphs show a rapid increase of the adsorption of TMAC pentahydrate to all the soils in the first 3 hours of contact time. After 3 hours contact time equilibration was reached. No TMAC pentahydrate was detected in the blank samples.

Determination of adsorption isotherms:
Adsorption isotherms could be described by the Freundlich equation. The fits of the Freundlich adsorption isotherms to the data are shown bellow in the field "any other information on results incl. tables".

The pH of the supernatants after 48 h (adsorption kinetics) was 5.6 for Speyer 2.2 soil and 7.0 for Speyer 2.3 and Speyer 6S soil.

At the end of the isotherm experiment, the pH was 5.6-6.0 for Speyer 2.2 soil, 7.0-7.1 for Speyer 2.3 and 6.9-7.1 for Speyer 6S soil.

Table: Koc and Kd values of TMAC determined during adsorption kinetics test at an initial nominal concentration of 10 mg/L

pe

Value

Temperature

% Org. carbon

Remarks

Koc

44

20 °C

1.87

Speyer 2.2 (Loamy sand)-48 h

Kd

0.8

20 °C

1.87

Speyer 2.2 (Loamy sand)-48 h

Koc

270

20 °C

0.94

Speyer 2.3 (Sandy loam)-48 h

Kd

2.5

20 °C

0.94

Speyer 2.3 (Sandy loam)-48 h

Koc

525

20 °C

1.64

Speyer 6S (Clay)-48 h

Kd

8.6

20 °C

1.64

Speyer 6S (Clay)-48 h

Validity criteria fulfilled:
yes
Conclusions:
The adsorption behavior of TMAC was studied in three different soils, including a loamy sand (Speyer 2.2 soil; %oc 1.87), a sandy loam (Speyer 2.3 soil; %oc 0.94) and a clay soil (Speyer 6S soil; %oc 1.64). The adsorption behavior of TMAC was studied in three different soils, including a loamy sand (Speyer 2.2 soil; %oc 1.87), a sandy loam (Speyer 2.3 soil; %oc 0.94) and a clay soil (Speyer 6S soil; %oc 1.64). Adsorption isotherms were determined over a TMAC concentration range of 0.25 - 25 mg/L and a contact time of 24 hours. TMAC adsorption isotherms could be described by the Freundlich equation.
The KFoc value of TMAC was 92 (1/n 0.82), 567 (1/n 0.64) and 979 (1/n 0.78) in three different soils (mean KFoc 546, 1/n 0.75). This result is read across to TEAH.
Executive summary:

The adsorption behavior of TMAC was studied in three different soils, including a loamy sand (Speyer 2.2 soil; %oc 1.87), a sandy loam (Speyer 2.3 soil; %oc 0.94) and a clay soil (Speyer 6S soil; %oc 1.64).

Adsorption kinetics were determined at an initial TMAC concentration of approximately 10 mg/L. A rapid increase of the adsorption of TMAC to the soils in the first 3 hours contact time was observed for all three soils. The adsorption plateau was reached after 3 hours for all three soils.

Adsorption isotherms were determined over a TMAC concentration range of 0.25 - 25 mg/L and a contact time of 24 hours. TMAC adsorption isotherms could be described by the Freundlich equation.

The KFoc value of TMAC was 92 (1/n 0.82), 567 (1/n 0.64) and 979 (1/n 0.78) in three different soils (mean KFoc 546, 1/n 0.75). This result is read across to TEAH.

Description of key information

The KFoc of read-across candidates TMAH pentahydrate and TMAC was determined in three different soils, in accordance with OECD guideline 106 and GLP (see read-across justification in IUCLID section 13)
The KFoc value of TMAH pentahydrate was 87 (1/n 0.84), 585 (1/n 0.64) and 1017 (1/n 0.77) in three different soils (mean KFoc 563, 1/n 0.75).
The KFoc value of TMAC was 92 (1/n 0.82), 567 (1/n 0.64) and 979 (1/n 0.78) in three different soils (mean KFoc 546, 1/n 0.75).
The mean KFoc value of TMAH and TMAC was 555 (1/n 0.75).

Key value for chemical safety assessment

Koc at 20 °C:
555

Additional information

There are two relevant studies available for structural analogues TMAH pentahydrate and TMAC.

The mean KFoc value of TMAH and TMAC was 555 (1/n 0.75)

Brands (2013a,b) carried out OECD106 studies with TMAH pentahydrate and TMAC which can be regarded as representative for the tetramethylammonium cation. The mean KFoc values (for 3 tested soil types) were 563 and 546 for TMAH pentahydrate and TMAC, respectively. The fact that these values do not differ significantly indicates that the different anions (hydroxide and chloride) did not influence the adsorption. The results of both studies can be used for the calculation of a mean KFoc value in a weight of evidence approach.

Brands(2013a) (TMAH pentahydrate):

The adsorption behavior of TMAH pentahydrate was studied in three different soils, including a loamy sand (Speyer 2.2 soil; %oc 1.87), a sandy loam (Speyer 2.3 soil; %oc 0.94) and a clay soil (Speyer 6S soil; %oc 1.64).

Adsorption kinetics were determined at an initial TMAH pentahydrate concentration of approximately 10 mg/L. A rapid increase of the adsorption of TMAH pentahydrate to the soils in the first 3 hours contact time was observed for all three soils. The adsorption plateau was reached after 24 hours for all three soils.

Adsorption isotherms were determined over a TMAH pentahydrate concentration range of 0.25 – 25 mg/L and a contact time of 24 hours. TMAH pentahydrate adsorption isotherms could be described by the Freundlich equation. The KFoc value of TMAH pentahydrate was 87 (1/n 0.84), 585 (1/n 0.64) and 1017 (1/n 0.77) in three different soils (mean KFoc 563, 1/n 0.75).

Brands (2013b)(TMAC):

The adsorption behavior of TMAC was studied in three different soils, including a loamy sand (Speyer 2.2 soil; %oc 1.87), a sandy loam (Speyer 2.3 soil; %oc 0.94) and a clay soil (Speyer 6S soil; %oc 1.64).

Adsorption kinetics were determined at an initial TMAC concentration of approximately 10 mg/L. A rapid increase of the adsorption of TMAC to the soils in the first 3 hours contact time was observed for all three soils. The adsorption plateau was reached after 3 hours for all three soils.

Adsorption isotherms were determined over a TMAC concentration range of 0.25 - 25 mg/L and a contact time of 24 hours. TMAC adsorption isotherms could be described by the Freundlich equation.

The KFoc value of TMAC was 92 (1/n 0.82), 567 (1/n 0.64) and 979 (1/n 0.78) in three different soils (mean KFoc 546, 1/n 0.75).