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Administrative data

Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
11 August - 05 September, 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2017
Report Date:
2017

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: particulate/powder
Details on test material:
White solid
Radiolabelling:
not specified

Study design

Test temperature:
The temperature was in the range of 23±2°C.

Batch equilibrium or other method

Analytical monitoring:
yes
Details on sampling:
Preliminary test:
Five soils were sterilized beforehand including red soil, black soil, paddy soil, meadow soil and moisture soil which were used as the test soils. As the solution/soil ratio was 1: 1, there was not obvious adsorption on red soil, black soil and paddy soil after 24h agitation, so the next steps of these three soils were terminated, however, notable adsorption occurred on the meadow soil and moisture soil, so these two soils were subjected to the next tests.

Adsorption kinetics and desorption percentage:
the concentrations in both phases were measured after the 4th, 6th and 48th hour of agitation. The results indicated:adsorption equilibrium on meadow soil and moisture soil were quickly achieved, i.e. 4 hours; and on which 52.0% adsorption on meadow soil and 68.7% on moisture soil were achieved. Because these adsorption percentage were >50%,
solution/soil ratio 1: 1 was employed in the next adsorption isotherms test. The 22nd hour samples were subjected to a desorption test for another 24 hours, which
implied that the adsorption on meadow soil and moisture soil might be irreversible.
Matrix propertiesopen allclose all
Matrix type:
other: Moisture soil
% Clay:
24.6
% Silt:
24.2
% Sand:
51.2
% Org. carbon:
1.22
pH:
7.87
CEC:
3.5 other: cmol/kg
Matrix type:
other: Meadow soil
% Clay:
10.1
% Silt:
43.4
% Sand:
46.5
% Org. carbon:
1.46
pH:
8.51
CEC:
6.8 other: cmol/kg
Matrix type:
other: Red Soil
% Clay:
32
% Silt:
20.3
% Sand:
47.7
% Org. carbon:
0.77
pH:
5.48
CEC:
2.2 other: cmol/kg
Matrix type:
other: Black Soil
% Clay:
24.6
% Silt:
24.2
% Sand:
50.1
% Org. carbon:
5.27
pH:
6.51
CEC:
34.1 other: cmol/kg
Matrix type:
other: Paddy Soil
% Clay:
18.1
% Silt:
17.1
% Sand:
64.8
% Org. carbon:
1.96
pH:
6.88
CEC:
6.8 other: cmol/kg
Details on matrix:
0.0l mol/L CaCh solution and sterilized soils.
Five typical soils were solected with discrepancies in texture, clay content, organic matter content, and pH value as the test soils. The soils were sieved through 2 mm and stored under room temperature. The soils used in the preliminary test were: paddy soil, meadow soil, red soil, black soil, and moisture soil. The meadow and moisture soils were chosen following the preliminary study for the experiement.
Details on test conditions:
Test Method:
Solution preparation: Preparation of 0.01 mol/L CaCb solution: 1.11 g CaCb was dissolved in 1000 mL ultra-water.

Soil sterilization: All the soils used in the study were sterilized beforehand under 121 °C for 30 mins.

Batch equilibrium method
Tier I-preliminary test:
The solubility in water of the test item was 8984.9 mg/L with the log Pow of -1.33, the adsorption on soils might vary slightly. Therefore, the present test
employed solution/soil ratio of 1: 1 to evaluate the adsorption percentage, each soil was run in duplicate. 20.0 g of soil was weighed and put into 250 mL centrifugal tube, and 20.0 mL of 0.01 mol/L aCh solution was added. The centrifugal tubes were placed into a shaking incubator and agitated at 160rpm for 24 hours at 23±2 'C in order to achieve pre-equilibrium. After pre-equilibration, 102.0 µL of stock solution of 1964.1 mg/L was added into the aqueous phase to achieve a nominal concentration of 10 mg/L. Then another 24h agitation was run to reach the adsorption equilibrium. The two control units were also performed in same condition, 1) 20.0 g blank soil with 20.0 mL 0.01 mol/L CaCh solution but without the test item, 2) 20.0 mL 0.01 mol/L CaCh solution with the test item of 10 mg/L but without soil. After 24h agitation, the aqueous phase was separated from the soil phase by means of high speed centrifugation at 5000 rpm for 5 min. The concentration of the test item in the supernatant solution and soil phase were directly measured. As the concentrations in both phases were determined, the adsorption percentage and mass balance were achieved for all of the five soils. The test item was considered stable during the test period if the mass balance was 2:90% of the initial content. The Batch Equilibrium Method was to be terminated if the adsorption percentage was <20%. The soil that had an adsorption percentage >20% was used in the Tier 2 test.

Tier 2-adsoprtion kinetics and desportion at one signal concentration:
The main operation was identical with Tier 1, the initial concentration was also 10 mg/L, and each soil was run in duplicate.

Equilibrium time: the concentration in both aqueous and soil phases were measured on the 4th, 6th, 22nd, and 48th hours.

Desorption percentage: Both phases were separated on the 22nd hour when adsorption equilibrium was reached and the volume of supernatant solution was recorded, and then an equal volume of 0.01 mol/L CaCh solution substitutes for that to go to the desorption test. Afterwards, another 24h agitation was done to reach the desorption equilibrium. The adsorption of test item can be considered as reversible if the desorption >75% of the content adsorbed on soil, or else it is irreversible.

Tier 3-adsorption isotherms:
Five test concentrations covering two orders of magnitude (5-500 mg/L) were run, and the Freundlich adsorption coefficients were calculated. Each
concentration was done in duplicate.

Sample analysis:
Aqueous phase: separated from soil phase and measured by LC/MS/MS after dilution;

Soil phase: a mixture of acetonitrile and water was employed as the extraction solvent, shaking at 190 rpm for 60 min, then the solvent was measured
by LC/MS/MS after dilution.

Results and discussion

Adsorption coefficientopen allclose all
Key result
Sample No.:
#1
Type:
log Kd
Value:
0.623 dimensionless
Remarks on result:
not measured/tested
Remarks:
Moisture soil
Key result
Sample No.:
#2
Type:
log Koc
Remarks:
Meadow soil
Value:
2.695 dimensionless
Remarks on result:
not measured/tested

Results: Batch equilibrium or other method

Recovery of test material:
The recovery test in 0.01 mol/L CaCh solution was set at three concentrations, i.e. 0.1 mg/L, 10.0 mg/L and 500 mg/L. The mean recovery
rate was in the range of 92.4%-98.6% with RSD in the range of 0.7%-5.6%. The recovery test in soils was set tat hree concentrations, i.e. 0.5 mg/kg, 10.0 mg/kg and 250 mg/kg, the mean recovery rate was in the range of 87.8%-106. 7% with RSD in the range of 0.5%-6.2%. The present analysis method met the quality criteria.
Transformation products:
not specified
Details on results (Batch equilibrium method):
Tier I-preliminary test:
The solution/soil ratio was set 1: 1 and the initial concentration was 10 mg/L in the preliminary test, residual concentration in both aqueous and soil phases of the five soils were determined after 24h agitation. After 24 hours agitation, the mass balance of red soil, black soil, and paddy soil was 105.2%, 102.4% and 99.7%, respectively; the corresponding percentage was -1.5%, -3.3% and 1.5%, which indicated that the test item in these three soils were chemically stable and had extremely low adsorption, so the adsorption test on these three soils were terminated. After 24 hours agitation, the mass balance of meadow soil and moisture soil was 45.2% and 50.2%, the adsorption percentage was 75.7% and 57.7%, respectively. The results implied that the test item in these two soils were not
stable and obvious adsorption occurred. Additionally, the adsorption percentages were both >50%, so those two soils were directly subjected to the Tier 2.

Tier 2-adsorption kinetics and desorption at one signal concentration Equilibrium time:
the adsorption percentage of meadow soil on the 4th, 6th, and 48h hour was 52.0%, 45.8% and 39.8%, respectively; while that of moisture soil was 68.7%, 66.2% and 70.0%, respectively. The results implied that adsorption equilibrium was quickly achieved, i.e. 4 hours, a remarkable increase was not discovered during the 48 hours. So the 4 hour was considered as equilibrium time in the next steps.

Adsorption percentage-optimal solution/soil ratio:
the adsorption percentage was 52.0% on meadow soil and 68.7% on moisture soil on the 4th hour, so the solution/soil ratio of 1: 1 was used in the Tier 3 test

Mass balance:
the mass balance of meadow soil on the 4th, 6th, and 48 th hour was 21.2%, 19.5% and 10.6%, respectively; while that in moisture soil was 55.8%, 54.6% and 38.6%. And that was 18.1 % on meadow soil and 26.0% on moisture soil of the 22nd samples which supernatant solution was replaced by about 11 mL blank CaCh solution to go to 24 hour desorption. The results indicated: 1) the test item was not chemically stable during test period; 2) the blank CaCh solution might accelerate transformation of test item in moisture soil.

Desorption percentage:
because a certain proportion of test item was transformed in aqueous/soil systems, the desorption percentage was not accurately calculated. The content desorbed from soil was considered as the difference of content of aqueous phase after 24 hours agitation and content of residual solution after centrifugation when adsorption equilibrium was reached. However, the differences of meadow soil and moisture soil were both negative, so the adsorption of test item was considered to be irreversible.

Tier 3-adsorption isotherms:
The meadow soil and moisture soil were test soils, solution/soil ratio of 1: 1, 4 hour as the equilibrium time, and the concentration of 5, 10, 50, 100 and 500 mg/Lin the adesorption isotherms tests.

Meadow soil: isotherm equation logCs=O. 7697 X logCe+0.6233, logKJ was 0.6233, logKoc was 2.695

Moisture soil: isotherm equation logCs=0.6082 X logCe+0.1798, logKi was 0.1798, logl
The test item was moderately adsorbed on soils in the present study




Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
The test item Difluorosulfonamide HCl has a moderate adsorption potential.