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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 2019-07-09 to 2019-09-26
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:
EU Method C.18 (Adsorption / Desorption Using a Batch Equilibrium Method)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
Laboratory ambient temperature
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 100 mg/L test item
- Sampling interval: After the equilibration period soil and water phases of the test mixtures were separated by centrifugation at 4000 rpm for 5 minutes.
Soil and water phase samples were analysed for 2,5-Dimethoxytetrahydrofuran using the
previously validated analytical method. Aqueous phase was diluted tenfold with acetonitrile and then analysed by GC-MS.
Soil phase was analysed at the last sampling point (after 21-25 hours equilibration). Soil
phases were extracted twice with acetonitrile. The extracts were diluted with acetonitrile and
then analysed by GC-MS.
- Sample storage before analysis: not specified
Matrix no.:
#2
Matrix type:
silty clay loam
% Clay:
35.9
% Silt:
61.7
% Sand:
2.5
% Org. carbon:
2.98
pH:
6.69
Matrix no.:
#3
Matrix type:
loam
% Clay:
18.1
% Silt:
32.9
% Sand:
48.9
% Org. carbon:
1.21
pH:
6.25
Matrix no.:
#4
Matrix type:
silty clay loam
% Clay:
27.6
% Silt:
58.7
% Sand:
13.7
% Org. carbon:
1.91
pH:
7.07
Matrix no.:
#5
Matrix type:
sandy loam
% Clay:
15.3
% Silt:
25.5
% Sand:
59.3
% Org. carbon:
0.51
pH:
4.33
Matrix no.:
#6
Matrix type:
silty clay loam
% Clay:
31.5
% Silt:
61.9
% Sand:
6.7
% Org. carbon:
0.69
pH:
7.52
Details on matrix:
COLLECTION AND STORAGE
- Geographic location:
GPS X GPS Y
type 2 454922.3056 180016.1719
type 3 454855.5267 182058.4854
type 4 460950.2192 182021.3162
type 5 455135.9908 175802.8086
type 6: 460234.7541 180319.9312

- Collection procedures: not specified
- Sampling depth (cm): not specified
- Storage conditions: not specified
- Storage length: not specified
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): The air-dried soils were sieved to a particle size ≤ 2 mm. The moisture content of each soil was determined at 105 °C, on three aliquots with the help of a moisture analyser. For all calculations the dry mass of the soil was used.

PROPERTIES
- Soil texture/% sand/% silt/% clay: see above
- Horizon: not specified
- Soil series: not specified
- Soil order: not specified
- pH: see above
- Organic carbon (%): see above
- CEC (meq/100 g): not specified
- Carbonate as CaCO3: not specified
- Insoluble carbonates (%): not specified
- Extractable Cations (Ca, Mg, Na, K, H) (MEQ/100 g): not specified
- Special chemical/mineralogical features: not specified
- Clay fraction mineralogy: not specified
- Moisture at 1/3 atm (%): not specified
- Bulk density (g/cm3): not specified
- Biomass (e.g. in mg microbial C/100 mg, CFU or other): not specified
Details on test conditions:
TEST CONDITIONS
- Buffer: not used
- pH: Volume of the aqueous phases was too low for pH measurement; therefore pH was determined in a separate experiment with 12 g soil and 10 cm3 aqueous solution. Samples were centrifuged after 6 hours equilibration and the pH was determined. pH of aqueous phase: from 4.6 to 7.7.

TEST SYSTEM
- Type, size and further details on reaction vessel: 50 mL polypropylene centrifuge tubes
- Water filtered (i.e. yes/no; type of size of filter used, if any): Aqueous phase: 0.01 mol/l CaCl2 dissolved in ultra-pure water
- Amount of soil/sediment/sludge and water per treatment (if simulation test):
Tier 1, preliminary study:
The following soil to solution ratios (m/V) were applied:
25 g soil and 25 cm3 aqueous solution of the test item (ratio 1/1);
5 g soil and 25 cm3 aqueous solution of the test item (ratio 1/5);
1 g soil and 25 cm3 aqueous solution of the test item (ratio 1/25).
Tier 2, Screening Test:
All five soil types were used. The parallel method was applied with 6 g soil and 5 cm3 aqueous solution of the test item.
- Number of reaction vessels/concentration:
- Measuring equipment: GC-MS
- Test performed in closed vessels due to significant volatility of test substance: not specified

Tier 1, Preliminary Study:
- Control experiments: A control sample with only the test item in 0.01 M CaCl2 solution (no soil) was subjected to precisely the same steps as the test systems, in order to check the stability of the test item in CaCl2 solution and its possible adsorption on the surfaces of the test vessels.
Blank run per soil: the same amount of soil and 0.01 M CaCl2 solution (without test item) were subjected to the same test procedure. This served as a background control during the analysis to detect interfering compounds or contaminated soils.
- Equilibration before the test: Before the day of the experiment the air-dried soil samples were equilibrated by shaking with a volume of 22.5 cm3 of 0.01 M CaCl2 overnight.
- Preparation of the test mixtures: Afterwards, a 2.5 mL of the stock solution of the test item (Stock solution II) was added in order to adjust the final volume. This resulted in an initial concentration of the test item of approximately 100 mg/L (c0).
- Equilibration: The parallel method (as many replicates as the time intervals) was applied. The experiments were performed in duplicate or triplicate.
The mixtures were shaken with the overhead mixer. Aqueous phase of the mixtures was analysed after 2, 4, 6, 8 and 22 hours equilibration.
- Evaluation: The percentage adsorption ( ti A ) was calculated at each time point (ti) on the basis of the nominal initial concentration and the measured concentration at the sampling time (ti).

Tier 2, Screening Test:
- Adsorption kinetics at one concentration of the test item: All five soil types were used. The parallel method was applied with 6 g soil and 5 cm3 aqueous solution of the test item, because of the weak adsorption found in the course of the preliminary test. Concentration of the test item was approximately 100 mg/L in the aqueous phase. Analysis of the aqueous phase was performed by GC-MS in different time points.
- Control experiments: In every experiment two replicate blanks were run. They consisted of the soil and 0.01 M CaCl2 solution, without test item, and of weight and volume, respectively, identical to those of the experiment. Two replicate control samples with only the test item in 0.01 M CaCl2 solution (without
soil) were subjected to the same test procedure. They were analysed at the end of the experiment.
- Mass balance: In order to determine the mass balance the aqueous phase and extracts of the soil were analysed for the test item at the last time point.
- Evaluation: The percentage adsorption was calculated at each time point ( ti A ) and was plotted versus time. The distribution coefficient Kd at equilibrium, as well as the organic carbon normalized adsorption coefficient Koc was also calculated.

- Are the residues from the adsorption phase used for desorption: NA
Computational methods:
The chromatograms were evaluated with the help of LabSolutions GCMS solution software. The calculations were performed using Microsoft Office Excel. Weighted linear regression was computed with PASW Statistics.
Based on the measured concentrations adsorption characteristics were calculated using the following formulas:
The percentage adsorption was calculated from the concentration measured in the aqueous phase:
A%=100*(m0-Cadsaq*V0)/m0
Adsorbed material concentration on the soil (μg/g):
Cs=(m0-maq)/msoil
When both phases were analysed percent of the chemical adsorbed was calculated from the mass of test substance extracted from the soil:
A%=100*(mE/mc)
Adsorbed material concentration on the soil after the adsorption test (μg/g) (both phases were analysed):
Cs=mE/msoil
Mass Balance (%) was calculated with the following formula:
MB=100*(maq+mE)/m0; maq=caq.V0
The adsorption coefficient (Kd) (cm3/g) and the organic carbon normalized adsorption coefficient (Koc) (cm3/g) were determined as follows:
Kd=Cs/Caq; Koc=Kd*(100/%organic carbon)

Symbols used:
m0 initial mass of test substance (μg)
cm mass of test substance measured in the control solution at the end of the adsorption test (μg)
maq mass of test substance measured in the aqueous phase at the end of the adsorption test (μg)
mE mass of test substance extracted from the soil at the end of the adsorption test (μg)
msoil dry mass of the soil
c0 initial concentration of the test solution
caq concentration determined analytically in the aqueous phase (μg/mL)
V0 Initial volume of the aqueous phase (mL)
Key result
Sample No.:
#2
Type:
Kd
Value:
0.19 other: cm3/g
pH:
6.8
% Org. carbon:
2.98
Key result
Sample No.:
#2
Type:
Koc
Value:
6.4 other: cm3/g
pH:
6.8
Key result
Sample No.:
#3
Type:
Kd
Value:
0.077 other: cm3/g
pH:
6.4
% Org. carbon:
1.21
Key result
Sample No.:
#3
Type:
Koc
Value:
6.4 other: cm3/g
pH:
6.4
Key result
Sample No.:
#4
Type:
Kd
Value:
0.12 other: cm3/g
pH:
7.1
% Org. carbon:
1.91
Key result
Sample No.:
#4
Type:
Koc
Value:
6.4 other: cm3/g
pH:
7.1
Key result
Sample No.:
#5
Type:
Kd
Value:
0.094 other: cm3/g
pH:
4.6
% Org. carbon:
0.51
Key result
Sample No.:
#5
Type:
Koc
Value:
18 other: cm3/g
pH:
4.6
Key result
Sample No.:
#6
Type:
Kd
Value:
0.064 other: cm3/g
pH:
7.7
% Org. carbon:
0.69
Key result
Sample No.:
#6
Type:
Koc
Value:
9.2 other: cm3/g
pH:
7.7
Concentration of test substance at end of adsorption equilibration period:
Because of the weak adsorption of the test item, depletion in the aqueous phase was ≤ 20% at equilibrium.
Based on the results 2,5-Dimethoxytetrahydrofuran is considered to be stable in the time scale of the test.
Sample no.:
#2
Duration:
6 h
% Adsorption:
20
Remarks on result:
other: Mass balance: 95%
Sample no.:
#3
Duration:
6 h
% Adsorption:
10
Remarks on result:
other: Mass balance: 98%
Sample no.:
#4
Duration:
6 h
% Adsorption:
12
Remarks on result:
other: Mass balance: 100%
Sample no.:
#5
Duration:
6 h
% Adsorption:
18
Remarks on result:
other: Mass balance: 91%
Sample no.:
#6
Duration:
6 h
% Adsorption:
7
Remarks on result:
other: Mass balance: 99%
Transformation products:
not measured
Details on results (Batch equilibrium method):
Results, Tier1:
- Selection of optimal soil/solution ratios: The adsorbed test item amount was calculated from the decrease of the test substance concentration measured in the water phase. The results and the ratios chosen for the main test are:
Percentage adsorption
Soil/solution ratio (m/V) Soil type 2 Soil type 5
1/1 23% 32%
1/5 18% 27%
1/25 18% 2 5%
Ratios chosen for the main test 6/5 for all soil types.

- Control experiments: The stability of the test item in CaCl2 solution and its possible adsorption to the surface of the test vessels was checked with control samples containing the test item in 0.01 M CaCl2 without soil. After 22 hours agitation measured concentration was approximately 70% of the start concentration. The loss of concentration was attributed to an analytical error, therefore test item is considered stable in CaCl2 solution.
- Blank run per soil: No interfering component was on the chromatograms of soil type 5. Blank samples of soil type 2 were contaminated, because of a sample preparation error. In the course of Tier 2 blank samples were prepared again. No interference was detected in those samples.

Results, Tier2:
Control experiments: No interfering component was detected in the blank samples. The stability of the test item in CaCl2 solution was verified with control samples containing the test item in 0.01 M CaCl2 without soil. At the end of the experiments (after 21 - 25 hours agitation) measured concentrations were 93 - 99% of the start concentration. Therefore test item is considered stable in CaCl2 solution over the timescale of the experiments.
Mass balance: When the experiment was completed the phases were separated and the aqueous phase and extracts of the soil and test vessel walls were analysed for the test item and the mass balance was calculated for all five soil types according to the above formula.
The found percentages are summarised in the above table. Because of the weak adsorption of the test item, depletion in the aqueous phase was ≤ 20% at equilibrium.
Based on the results 2,5-Dimethoxytetrahydrofuran is considered to be stable in the time scale of the test.
Based on the charts the adsorption equilibration time is approximately 6 hours.
Validity criteria fulfilled:
not applicable
Conclusions:
The soil adsorption of 2,5-Dimethoxytetrahydrofuran was studied in five different European soils.
The following soil/solution ratio (m/V) was applied: 6/5.
Based on the mass balance 2,5-Dimethoxytetrahydrofuran was considered to be stable in the time scale of the test.
For the screening test five soils were used. The initial concentration of the test item was 100 mg/L. The adsorption equilibrium was reached after about 6 hours agitation. The adsorption coefficients Kd were in the range of 0.06 – 0.2 cm3/g and Koc were 6 – 18 cm3/g.
Executive summary:

The purpose of the study was to evaluate the adsorption behaviour of the test item on 5 different soil types, according to OECD 106 guideline and C18 method, and following GLP. The soils had a varying range of organic carbon content, clay content, soil texture and pH. It comprised two tiers:

Preliminary test:

Two types of soil were tested. Initial concentration of the test item was approximately 100 mg/L.

The optimal soil/solution ratios (m/V) chosen for the main test was 6/5.

Screening test:

Five different soils were used. Initial concentration of the test item was approximately 100 mg/L. The parallel method was applied. The adsorption equilibrium was reached after about 6 hour agitation. Based on the mass balance 2,5-Dimethoxytetrahydrofuran was considered to be stable in the time scale of the test.

The percentage adsorption was calculated at each time point. The adsorption coefficients, Kd and Koc were calculated at equilibrium:

Kd (cm3/g): 0.19 (type 2), 0.077 (type 3), 0.12 (type 4), 0.094 (type 5), 0.064 (type 6)

Koc (cm3/g): 6.4 (type 2), 6.4 (type 3), 6.4 (type 4), 18 (type 5), 9.2 (type 6)

Description of key information

The soil adsorption of 2,5-Dimethoxytetrahydrofuran was studied in five different European soils.

The following soil/solution ratio (m/V) was applied: 6/5.

Based on the mass balance 2,5-Dimethoxytetrahydrofuran was considered to be stable in the time scale of the test.

For the screening test five soils were used. The initial concentration of the test item was 100 mg/L. The adsorption equilibrium was reached after about 6 hours agitation. The adsorption coefficients Kd were in the range of 0.06 – 0.2 cm3/g and Koc were 6 – 18 cm3/g.

Key value for chemical safety assessment

Koc at 20 °C:
18

Additional information