2-chloro-N-[[[4-(trifluoromethoxy)phenyl]amino]carbonyl]benzamide

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

29 October 2002 - 19 November 2002.

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

This study was carried out in a GLP-certified laboratory and in adherence with OECD 106, and US EPA 163-1 guidelines.

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:

other: EPA 163-1

Version / remarks:

1982

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Specific details on test material used for the study:

The radiolabelled test material 14C-triflumuron has a batch number of C-915 and a purity of 99.8%. Specific activity: 40.7 mCi/mMol.

Radiolabelling:

yes

Test temperature:

20 ±1°C.

Analytical monitoring:

yes

Remarks:

Liquid chromatography mass spectroscopy with electrospray ionization (LC/ESI-MS) and High Performance Liquid Chromatography (HPLC).

Details on sampling:

The appropriate soil amount, as determined in Preliminary Test I, was pre-equilibrated in 0.01 M CaCl2-HgCl2, prior to addition of treatment solution. The tests were conducted in duplicate and carried out at a concentration of 0.0125 µg triflumuron/mL (as in Preliminary Test I). The samples were shaken for a period of 8, 24, 48, and 72 hours. At each sampling interval the samples were centrifuged, and aliquots (1 or 2 mL depending on concentration) were taken from the supernatant for LSC. To confirm stability of triflumuron in this test, HPLC analysis was performed on aliquots of the 24-hour interval test systems. Radioactivity in the soil was determined by combustion to obtain material balance.

Aliquots from liquid samples were prepared for LSC by adding 5 or 15 mL (depending on the volume of the test system aliquot size) of Ultima Gold liquid scintillation cocktail (Packard Instrument Co.). LSC was performed using either a Model A2700 or Model 1600TR Packard Tri-Carb liquid scintillation counter which were equipped with automatic external standardization. All values were corrected for instrument efficiency. The LSC protocol includes automatic background subtraction, where the first vial counted contains only cocktail. The average dpm after a 10-minute count of this vial is automatically subtracted from the dpm of each sample. The limit of sensitivity and greatest probable error for these analyses are listed in Appendix 8 and 9.

After removal of desorption supernatants, hydrolyzed potato starch (Fisher Scientific, Pittsburg, PA) was added to wet soil (~0.4 g) and mixed well. Multiple soil pellets were made from each test system soil. In the Preliminary Tests, hydromatrix (Sample Preparation Products, Harbour City, CA) was mixed with wet soils (instead of starch), and this may have resulted in inefficient combustion of soils leading to lower material balances. Soil pellets were placed in combustion thimbles along with a cellulose pad. A Packard Model 307 Oximate 80 sample oxidizer was used to combust samples, and combustaid (Packard) was added to each sample prior to oxidation. The 14CO2 was trapped in 6 mL Carbosorb-E (Packard) and 15 mL PermaFluor E+ (Packard). The samples were radioassayed by LSC and corrected for oxidizer efficiency and average background counts.

Matrix no.:

#1

Matrix type:

clay loam

% Clay:

32.8

% Silt:

47.2

% Sand:

20

% Org. carbon:

1.7

pH:

6.8

CEC:

18.9

Bulk density (g/cm³):

1.2

Matrix no.:

#1

Matrix type:

silt loam

% Clay:

24.8

% Silt:

63.6

% Sand:

11.8

% Org. carbon:

2.5

pH:

7

Bulk density (g/cm³):

1.2

Matrix no.:

#2

Matrix type:

loam

% Clay:

10.8

% Silt:

40

% Sand:

49.2

% Org. carbon:

0.66

pH:

6.2

Bulk density (g/cm³):

1.52

Matrix no.:

#2

Matrix type:

loamy sand

% Clay:

7.6

% Silt:

6

% Sand:

86.4

% Org. carbon:

0.6

pH:

6.2

Bulk density (g/cm³):

1.51

Matrix no.:

#3

Matrix type:

silty clay

% Clay:

50.8

% Silt:

48

% Sand:

1.2

% Org. carbon:

0.92

pH:

5.4

Bulk density (g/cm³):

1.23

Matrix no.:

#3

Matrix type:

sandy loam

% Clay:

12.8

% Silt:

27.6

% Sand:

59.8

% Org. carbon:

0.3

pH:

5.6

CEC:

4.9

Bulk density (g/cm³):

1.54

Details on matrix:

Soil characteristics: Preliminary Tests I and II (Matrix #1), Preliminary Tests I, II, and the definitive tests (Matrix #2). Used only in the definitive tests (Matrix #3)

Details on test conditions:

Temperature: 20 ±1°C (Environmental Chamber).

Lighting: Dark.

Shaker: Benchtop Shaker.

Centrifuge: 20 min at centrifugation force of ~ 2700G.

Duration:

24 h

Duration:

24 h

Key result

Sample No.:

#1

Type:

Koc

Value:

13 209

Matrix:

Sandy loam, loamy sand, silty clay and loam.

Adsorption and desorption constants:

The constants of the adsorption isotherms according to Freundlich were calculated by linear regression. The KF-ads determined for sandy loam, loamy sand, silty clay, and loam were 90.0, 9.8, 30.0, and 114.4 mL/g, respectively, with a mean of 61.1 mL/g. The Koc-ads values for sandy loam, loamy sand, silty clay, and loam were 30,006; 1,629; 3,257; and 17,339 mL/g, respectively, with a mean Koc-ads of 13,058 mL/g.

The proportion of adsorbed triflumuron that was desorbed from the sandy loam ranged from 42.9 to 71.3%. The proportion of adsorbed triflumuron that was desorbed from the loamy sand ranged from 41.8 to 60.0%. The percentage of adsorbed triflumuron that desorbed from the silty clay and loam ranged from 59.8 to 75.6% and 42.6 to 57.2%, respectively. The constants of the desorption isotherms according to Freundlich were calculated by linear regression. The KF-des determined for sandy loam, loamy sand, silty clay, and loam were 91.8, 4.3, 174.2, 113.3 mL/g, respectively, with a mean of 95.9. The Koc-des values for sandy loam, loamy sand, silty clay, and loam were 30,612; 711; 18,931; and 17,166 mL/g respectively, with a mean Koc-des of 16,855 mL/g.

Data on the slope of Freunlich adsorption/desorption isotherms (1/n), and regression coefficient (R2):

1/n: 1.24 (Sandy loam), 0.85 (Loamy sand), 1.03 (Silty clay), 1.21 (Loam), 1.08 (Mean)

R2: 0.96 (Sandy loam), 0.96 (Loamy sand), 1.00 (Silty clay), 0.99 (Loam), 0.98 (Mean)

Recovery of test material:

For the sandy loam, the material balances ranged from 97.3 to 110.0% of the applied radioactivity, with an overall mean of 100.4%. For the loamy sand the material balances ranged from 94.2 to 102.1% of the applied radioactivity, with an overall mean of 96.5%. For the silty clay, the material balance ranged from 95.4 to 108.7% of the applied radioactivity, with an overall mean of 99.9% . For the loam, the material balance ranged from 97.7 to 110.9% of the applied radioactivity, with an overall mean of 101.5%.

Concentration of test substance at end of adsorption equilibration period:

Sandy loam: At equilibrium (µg/0.6 g) 0.009 ± 0.0008 - 0.16 ± 0.03 (20.9-35.5% adsorbed).

Loamy sand: At equilibrium (µg/0.6 g) 0.10 ± 0.01 - 0.038 ± 0.002 (22-32.6% adsorbed).

Silty clay: At equilibrium (µg/0.6 g) 0.012 ± 0.0008 - 0.070 ± 0.0007 (28.8-31% adsorbed)

Loam: At equilibrium (µg/0.6 g) 0.013 ± 0.0003 - 0.19 ± 0.02 (30.6-42.7% adsorbed)

Concentration of test substance at end of desorption equilibration period:

Sandy loam: At equilibrium (µg/0.6 g) 0.028 ± 0.006 - 0.002 ± 0.001 (55.1-71.3% of adsorbed).

Loamy sand: At equilibrium (µg/0.6 g) 0.037 ± 0.0005 - 0.033 ± 0.0002 (45.6-60% adsorbed).

Silty clay: At equilibrium (µg/0.6 g) 0.015 ± 0.001 - 0.042 ± 0.009 (59.8-75.6% adsorbed).

Loam: At equilibrium (µg/0.6 g) 0.094 ± 0.01 - 0.05 ± 0.0002 (42.6-57.2% adsorbed).

Sample no.:

#1

% Adsorption:

100.4

Remarks on result:

other: Sandy loam (overall mean)

Sample no.:

#2

% Adsorption:

96.5

Remarks on result:

other: Loamy sand (overall mean)

Sample no.:

#3

% Adsorption:

99.9

Remarks on result:

other: Silty clay (overall mean)

Sample no.:

#4

% Adsorption:

101.5

Remarks on result:

other: Loam (overall mean)

Preliminary test 1 and 2:

Preliminary Test I, Determination of Appropriate Soil:Solution Ratio:

Preliminary Test I showed a dependence of the adsorption rate on the soil:solution ratio in all soils used. The radioactivity in the 36 mL of solution ranged from an average of 24.7 to 72.8% of the applied radioactivity. Thus, the adsorption ranged from an average of 27.2 to 75.3% of the applied radioactivity after shaking for a period of 24 hours. The soil amount to be used in the Preliminary Test II and the Definitive Test was determined to be 0.6 g for all soils.

The stability of triflumuron was determined by HPLC of representative samples. The clay loam, silt loam, and loamy sand soils showed considerable degradation after 24 hours. The 0.01M CaCl2-HgCl2 solution was used for Preliminary Test II.

Preliminary Test II: Determination of Equilibration Time, Stability, and Sorption to Glass. This test showed that in all soils an equilibrium was reached within 24 hours. The concentration of the triflumuron in the supernatant did not change more than 5% within the time period of 24 to 48 hours.

For the Definitive Test, a 24-hour equilibrium time was chosen. Material balances ranged from an average of 71.5 to 91.8% of the applied radioactivity. The mean material balance for the sandy loam, silt loam, clay loam, and loamy sand was 89.0, 71.5, 74.1, and 91.8 respectively. The clay loam and silt loam were replaced with a loam from Benoit, MS, and a silty clay from Stilwell, KS for the definitive tests due to material balance difficulties.

Determination of Stability of Test Substance: Triflumuron was unstable in soil-containing test systems of Preliminary Test I. The region of interest (ROI%) from HPLC analyses as a degradate ranged from 7.1 to 51.3%. Thus,
Preliminary Test II was conducted using a sterilizing agent (50 mg HgCl2/L) and 0.01 M CaCl2.

Determination of Sorption to Glass and Abiotic Degradation: Test systems were radioassayed to determine if sorption to glass occurred. In Preliminary Test I, adsorption to glass of samples containing 0.3 g soil ranged from 0.8 to 7.9% of the applied radioactivity. In Preliminary Test II at the 24-hour interval, the percentage of applied radioactivity that adhered to glass ranged from 0.5 to 3.1% in soil-containing test systems. In a control test system (no soil present) at the 24-hour interval of Preliminary Test II, 31% of the applied triflumuron adhered to the glass.

Validity criteria fulfilled:

yes

Conclusions:

The Freundlich adsorption coefficients (KF) were determined for triflumuron in sandy loam,
loamy sand, silty clay, and loam. The normalized adsorption coefficient (Koc) can be used to
compare mobility tendencies in these soils. According to the classification of McCall et al.1 and based on the results of this study, triflumuron is considered to immobile in soil types tested (mean classification from four soils), with a mean Koc value determined in this study of 13,209.

Executive summary:

The adsorption and desorption characteristics of triflumuron were investigated on 4 different soils: a sandy loam from Frederick, Oklahoma; a loamy sand from Byromville, Georgia; a silty clay from Stilwell, Kansas; and a loam from Benoit, Mississippi. [Phenoxy-UL-14C]triflumuron was applied at actual concentrations corresponding to 0.0125, 0.00628, 0.00325, 0.00114, 0.000128 μg per mL of 0.01 M CaCl2 (with 50 mg HgCl2/L) solution. The soil to solution ratio used for all soils was 1:60. The lowest concentration (0.000128 μg/mL) was problematic due to low radioactivity per test system (~1000 dpm per test system) and near background levels in supernatants. Thus, only the four highest concentrations were used in determining adsorption characteristics for triflumuron in this study.

After a 24-hour pre-equilibration period, triflumuron adsorbed to the soil at a range from 20.9 to 42.7% of the applied radioactivity. The adsorption constants KF, determined by means of the Freundlich adsorption isotherm, as well as the soil carbon-based sorption coefficient Koc, were calculated. The KF-ads (expressed as mL/g) and additional information are presented.

Desorption tests showed that between 39.6 and 71.5% of the adsorbed triflumuron was desorbed from the soils. Based on the results of this study triflumuron is considered to be immobile (mean classification from four soils).

Description of key information

The Freundlich adsorption coefficients (KF) were determined for triflumuron in sandy loam, loamy sand, silty clay, and loam. The normalized adsorption coefficient (Koc) can be used to compare mobility tendencies in these soils. According to the classification of McCall et al and based on the results of this study, triflumuron is considered to immobile in soil types tested (mean classification from four soils), with a mean Koc value determined in this study of 13,209.

Key value for chemical safety assessment

Koc at 20 °C:

13 209