Prometryn

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1 Oct 1987

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Pesticide Assessment Guidelines, Subdivision N, Section 163-1 of the Environmental Protection Agency

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

approximately 25°C

Analytical monitoring:

yes

Details on sampling:

See 'Details on test conditions'

Matrix no.:

#1

Matrix type:

clay loam

% Clay:

32

% Silt:

47

% Sand:

21

% Org. carbon:

2.9

pH:

7

CEC:

21 meq/100 g soil d.w.

Bulk density (g/cm³):

1.19

Matrix no.:

#2

Matrix type:

sand

% Clay:

2

% Silt:

1

% Sand:

97

% Org. carbon:

0.17

pH:

5.4

CEC:

1.1 meq/100 g soil d.w.

Bulk density (g/cm³):

1.59

Matrix no.:

#3

Matrix type:

sandy loam

% Clay:

5

% Silt:

35

% Sand:

60

% Org. carbon:

0.41

pH:

4.6

CEC:

3.4 meq/100 g soil d.w.

Bulk density (g/cm³):

1.59

Matrix no.:

#4

Matrix type:

silt loam

% Clay:

13

% Silt:

58

% Sand:

29

% Org. carbon:

0.64

pH:

7

CEC:

13 meq/100 g soil d.w.

Bulk density (g/cm³):

1.18

Details on matrix:

- The study was conducted with the following soil types: Kewaunee clay loam (Winnebago County, Wisconsin), Plainfield sand (Adams County, Wisconsin), California sandy loam (Citrus Heights, California) , and Mississippi silt loam (Greenville, Mississippi). Before use, the soils were air-dried and passed through a 2-mm sieve. Physical analysis was performed by the University of Wisconsin-Extension Soil and Forage Laboratory. Field moisture capacity and bulk density were measured by the lab. Physical characteristics of the soils tested are summarized in Table 1 in “Any other information on materials and methods incl tables”.

Details on test conditions:

PRELIMINARY STUDIES
- Preliminary studies were conducted to determine the solubility, stability, and potential adsorption to glassware of 14C-substance in aqueous 0.01M Ca(NO3)2 at various concentrations. A preliminary study was also conducted to determine an appropriate solution:soil ratio and the adsorption equilibrium time of 14C-substancesubstance in aqueous 0.01M Ca(NO3)2 at a target concentration of 10.0 µg/mL on the soils selected for study.
- Preparation of Test Material Solution: A 10.2µg/ml solution of 14C-substance was prepared by combining appropriate amounts of radioactive and nonradioactive substance in aqueous 0.01M Ca(NO3)2. The radioactivity concentration of the solution was determined by LSC analysis of duplicate aliquots. The total substance concentration was determined from the mean of the LSC results and the calculated specific activity of the test material in solution (7,559 dpm/µg).
- Solubility of Test Material: Approximately 2-, 10-, and 20-fold dilutions of the 10.2 µg/mL test material solution were prepared for verification of the 14C-substance solubility in aqueous 0.01M Ca(NO3)2. The solution concentration of 14C-substance was determined by LSC analysis of duplicate aliquots. The total substance ( radioactive and nonradioactive) solution concentration was determined from the mean of the LSC results and the calculated specific activity of the 14C-substance in the 10.2-µg/mL test material solution (7,559 dpm/µg). The theoretical concentrations (0.500, 1.00, 5.00, and 10.0 µg/mL) versus Individual actual concentrations of 14C-substance (0.513, 0.518, 1.02, 1.02, 5.04 , 5.08, 10.1, and 10.2 µg/mL) were analyzed by linear regression.
- Stability of Test Material: The stability of 14C-substance in a 10.2 µg/mL aqueous 0.01M Ca(NO3)2 solution prepared with radioactive and nonradioactive substance was determined by TLC analysis. The solution was prepared and allowed to stand at room temperature under fluorescent lighting for approximately 24 hours before analysis. The radiopurity of 14C-substance in solution was compared with the original radiopurity determined by the lab.
- Adsorption of Test Material to Glass: Ten milliliters of the 0.516 µg/mL test material solution was placed in each of 10 glass culture tubes. The 10 samples were placed in a shaker set at approximately 25°C. Two tubes per time point were removed at approximately 1, 2, 5, and 8 hours of equilibration. Duplicate 1.0-mL aliquots from each tube were analyzed by LSC. The radioactivity remaining in solution at each Interval was compared with the solution radioactivity at Hour 0.
- Adsorption Equilibrium Time: Forty samples (10 per soil type) of soil in test material solution were prepared in glass culture tubes by adding 10.0 mL of the 10.2 µg/mL test material solution to an aliquot of Kewaunee clay loam (approximately 1 g) , Plainfield sand (approximately 2 g), California sandy loam (approximately 1 g) , Mississippi silt loam (approximately 1 g). The tubes were capped and placed 1n a shaker set at approximately 25°C. At approximately 1 , 2, 5 , 8, and 24 hours, duplicate samples of each soil type were removed from the shaker and centrifuged. Duplicate 1.0-mL aliquots of each supernatant were removed for LSC analysis to determine the concentration of 14C-substance 1n solution. The mean percentage of 14C-substance adsorption to soil versus time was plotted for each soil type. The plotted data were used to determine the equilibrium time of the 14C-substance adsorption to soil and the soil solution ratio used in the definitive study.

DEFINITIVE STUDY
- Preparation of Test Material Solutions: A 10.1 µg/mL solution of 14C-substance was prepared by combining appropriate amounts of radioactive and nonradioactive substance 1n aqueous 0.01M Ca(NO3)2. Three dilutions of the 10.1 µg/mL solution were prepared at concentrations of 0.511, 1.01, and 5.04 µg/mL, respectively. The radioactivity concentration of the solutions was determined by LSC analysis of duplicate aliquots. The total substance concentration was determined from the mean of the LSC results and the calculated specific activity of the test material in solution (7,002 dpm/µg).
- Adsorption of Test Material to Soil: Thirty two samples (two samples/soil type/test material concentration) of soil in test material solution were prepared in glass culture tubes by adding 10.0 mL of the 0.511-, 1.01-, 5.04-, or 10.1 µg/mL test material solutions to an aliquot of Kewaunee clay loam (approximately 1 g) Plainfield sand (approximately 2 g), California sandy loam (approximately 1 g), or Mississippi silt loam (approximately 1 g) . The tubes were capped and placed in a shaker set at approximately 25°C. After approximately 2 hours, the samples were removed from the shaker and centrifuged. A 5.00-mL aliquot of supernatant was removed, and duplicate 1.0-mL aliquots were analyzed by LSC. The LSC data were used to calculate the soil and solution concentrations and the percentage of 14C-substance adsorption to soil.
- Desorption of Test Material from Soil: After completion of the adsorption phase, 5.00 mL of fresh aqueous 0.01M Ca(NO3)2 was added to each sample container to re-establish the 10.0-mL solution volume. The tubes were capped and placed in a shaker set at approximately 25°C. After approximately 2 hours, the samples were removed from the shaker and centrifuged. Duplicate 1.0-mL aliquots of the supernatant were analyzed by LSC. The LSC data were used to calculate the concentrations and the percentage of 14C-substance desorption from soil.

Duration:

2 h

Initial conc. measured:

0.511 other: mg/L

Temp.:

25 °C

Remarks:

for all soil types used in this experiment

Duration:

2 h

Initial conc. measured:

1.01 other: mg/L

Temp.:

25 °C

Remarks:

for all soil types used in this experiment

Duration:

2 h

Initial conc. measured:

5.04 other: mg/L

Temp.:

25 °C

Remarks:

for all soil types used in this experiment

Duration:

2 h

Initial conc. measured:

10.1 other: mg/L

Temp.:

25 °C

Remarks:

for all soil types used in this experiment

Duration:

2 h

Temp.:

25 °C

Remarks:

for all soil types used in this experiment

Key result

Sample No.:

#1

Type:

Koc

Value:

113 dimensionless

pH:

7

Temp.:

25 °C

Matrix:

Clay Loam

% Org. carbon:

2.9

Key result

Sample No.:

#2

Type:

Koc

Value:

363.2 dimensionless

pH:

5.4

Temp.:

25 °C

Matrix:

Sand

% Org. carbon:

0.17

Key result

Sample No.:

#3

Type:

Koc

Value:

493 dimensionless

pH:

4.6

Temp.:

25 °C

Matrix:

Sandy loam

% Org. carbon:

0.41

Key result

Sample No.:

#4

Type:

Koc

Value:

148.6 dimensionless

pH:

7

Temp.:

25 °C

Matrix:

Silt loam

% Org. carbon:

0.64

Sample No.:

#1

Phase system:

solids-water in soil

Type:

other: desorption kd

Value:

4.739 dimensionless

Temp.:

25 °C

pH:

7

Matrix:

Clay loam

% Org. carbon:

2.9

Sample No.:

#2

Phase system:

solids-water in soil

Type:

other: desorption kd

Value:

1.071 dimensionless

Temp.:

25 °C

pH:

5.4

Matrix:

Sand

% Org. carbon:

0.17

Sample No.:

#3

Phase system:

solids-water in soil

Type:

other: desorption kd

Value:

2.87 dimensionless

Temp.:

25 °C

pH:

4.6

Matrix:

Sandy loam

% Org. carbon:

0.41

Sample No.:

#4

Phase system:

solids-water in soil

Type:

other: desorption kd

Value:

1.681 dimensionless

Temp.:

25 °C

pH:

7

Matrix:

Silt loam

% Org. carbon:

0.64

Adsorption and desorption constants:

- Adsorption of Test material to soil (definitive study): The equilibrium adsorption constant (Kd, anti-log of the y-intercept) was calculated from results of the linear regression analysis of the soil and solution log concentrations of 14C-substance. The calculated Kd values were 3.323 (Kewaunee clay loam), 0.6410 (Plainfield sand), 2.030 (California sandy loam), and 0.9614 (Mississippi silt loam) (Table 2 in “Any other information on results incl tables”). The sorption coefficient was calculated for each soil: 113.0 (Kewaunee clay loam), 363.2 (Plainfield sand), 493.0 (California sandy loam), and 148.6 L/kg (Mississippi silt loam) (Table 2 in “Any other information on results incl tables”).
- Desorption of Test material to soil (definitive study): Equilibrium desorption constant values were calculated: 4.7392 (Kewaunee clay loam), 1.0706 (Plainfield sand), 2.8704 (California sandy loam), and 1.6795 (Mississippi silt loam) (Table 2 in “Any other information on results incl tables”). The desorption Kd was greater than the adsorption Kd for all soil types.

Remarks on result:

other: See Table 1 in "Any other information on results incl tables".

Remarks on result:

other: See Table 1 in "Any other information on results incl tables".

Transformation products:

not specified

Details on results (Batch equilibrium method):

PRELIMINARY STUDIES
- Solubility of Test Material: The test material , 14C-substance, was soluble in aqueous 0.01M Ca(NO3)2 solution at all concentrations tested. Linear regression analysis demonstrated that the plot of theoretical concentration (0.500, 1.00, 5.00, and 10.0 µg/mL) versus individual actual concentration. (0.513, 0.518, 1.02, 1.02, 5.04, 5.08, 10.1, and 10.2 µg/mL) was linear with a y-intercept of 0.0036, a slope of 1.0140, and a correlation coefficient of 0.9999.
- Adsorption of Test Material to Glass: The mean percentage of radioactivity adsorbed to glass from a 0.516-µg/mL solution of 14C-substance in aqueous 0.01M Ca(NO3)2 ranged from 4.0% at Hour 1 to 11.8% at Hour 8. Since the mean percentage of adsorption at Hour 2, the equilibrium time chosen for the definitive study, was only 6.1%, no correction factor for adsorption to glass was required.
- Adsorption Equilibrium Time: A plot of the percentage of 14C-substance [10.2 µg/ml in aqueous 0.01M Ca(NO3)2] that adsorbed to soil versus time (1, 2, 5, 8, and 24 hours) for each soil type demonstrated that the adsorption equilibrium of 14C-substance was reached after 2 hours of equilibration at approximately 25°C. Soil solution ratios of 1:10 (Kewaunee clay loam, California sandy loam, and Mississippi silt loam) and 2:10 (Plainfield sand) demonstrated measurable adsorption. The above soil solution ratios of 1:10 and 2:10 and the equilibrium time of 2 hours were used in the definitive study.

DEFINITIVE STUDY
- Adsorption of Test Material to Soil: The percentage of 14C-substance adsorbed at the concentrations tested ranged from 35.3% to 19.0% (Kewaunee clay loam), 13.7% to 5.0% (Plainfield sand) , 21.8% to 10.2% (California sandy loam) , and 12.7% to 4.5% (Mississippi silt loam) (Table 1 in “Any other information on results incl tables”). The percentage of adsorption decreased with Increasing test material concentration for all soils tested. Linear regression analysis demonstrated that the plot of the soil .and solution log concentrations for four concentrations of 14C-substance after approximately 2 hours of Incubation at 25°C was linear for all soil types. Correlation coefficients of -0.9818 (Kewaunee clay loam), -0.9780 (Plainfield sand), -0.9960 (California sandy loam), and -0.9676 (Mississippi silt loam) were calculated (Table 2 in “Any other information on results incl tables”). The equilibrium adsorption constant (Kd, anti-log of the y-intercept) was calculated from results of the linear regression analysis of the soil and solution log concentrations of 14C-substance. The calculated Kd values were 3.323 (Kewaunee clay loam), 0.6410 (Plainfield sand), 2.030 (California sandy loam), and 0.9614 (Mississippi silt loam) (Table 2 in “Any other information on results incl tables”). The sorption coefficient was calculated for each soil: 113.0 (Kewaunee clay loam), 363.2 (Plainfield sand), 493.0 (California sandy loam), and 148.6 L/kg (Mississippi silt loam) (Table 2 in “Any other information on results incl tables”). The slope of the regression line (1/n) was less than one for each soil, indicating a decrease in relative adsorption with an increase in initial concentration (Table 2 in “Any other information on results incl tables”).
- Desorption of Test Material From Soil: The percentage of desorption was highest (generally 15% to 20%) in the soils that demonstrated a greater affinity to adsorb 14C-substance (California sandy loam and Kewaunee clay loam), indicating that some of the test material was loosely bound to the
soil. Desorption of the test material from Plainfield sand and Mississippi silt loam was extremely low and erratic due to the small percentage of adsorption (Table 1 in “Any other information on results incl tables”). Equilibrium desorption constant values were calculated: 4.7392 (Kewaunee clay loam), 1.0706 (Plainfield sand), 2.8704 (California sandy loam), and 1.6795 (Mississippi silt loam) (Table 2 in “Any other information on results incl tables”). The desorption Kd was greater than the adsorption Kd for all soil types.

Table 1. Summary of the Individual Adsorption and Desorption Results of 14C-substance at Four Concentrations in Aqueous 0.01M Ca(NO3)2

Initial Solution concentration	Adsorption concentration			Adsorption	Desorption
(µg/mL)	Sample number	Solution (Cw) (µg/mL)	Soil (Cs) (µg/g)	(%)	(%)
Kewaunee Clay Loam
0511	1A	0.331 (-0.4802)	1.78 (0.2514)	35.5	13.0
	1B	0.411 (-0.3862)	0.984 (-0.072)	19.5	0.4
1.01	2A	0.725 (-0.1397)	2.75 (0.4387)	28.2	17.7
	2B	0.731 (-0.1361)	2.79 (0.4453)	27.6	19.3
5.04	3A	3.94 (0.5955)	10.5 (1.023)	21.8	14.8
	3B	3.97 (0.5987)	10.5 (1.023)	21.1	15.7
10.1	4A	8.18 (0.9125)	19.0 (1.280)	19.0	6.9
	4B	8.10 (0.9083)	19.9 (1.298)	19.7	15.0
Plainfield Sand
0511	1A	0.443 (-0.3536)	0.336 (-0.4734)	13.2	10.1
	1B	0.448 (-0.3487)	0.312 (-0.5061)	12.2	6.1
1.01	2A	0.890 (-0.0506)	0.585 (-0.2327)	11.8	13.2
	2B	0.872 (-0595)	0.664 (-0.1779)	13.7	-12.0
5.04	3A	4.58 (0.6607)	2.29 (0.3593)	9.1	-8.5
	3B	4.51 (0.6545)	2.56 (1.4088)	10.4	-13.5
10.1	4A	9.55 (0.9798)	2.66 (0.4244)	5.4	-23.2
	4B	9.58 (0.9813)	2.49 (0.3954)	5.0	4.8
California Sandy Loam
0511	1A	0.400 (-0.3979)	1.09 (0.0357)	21.8	15.1
	1B	0.403 (-0.3947)	1.08 (0.0320)	21.1	30.0
1.01	2A	0.859 (-0.660)	1.49 (0.1742)	14.9	18.9
	2B	0.827 (-0.0825)	1.79 (0.2518)	18.1	17.8
5.04	3A	4.35 (0.6384)	6.75 (0.8292)	13.6	20.0
	3B	4.42 (0.6452)	6.07 (0.7834)	12.3	17.4
10.1	4A	9.06 (0.9569)	10.2 (1.010)	10.2	10.1
	4B	8.96 (0.9522)	11.1 (1.045)	11.2	-39.4
Mississippi Silt Loam
0511	1A	0.459 (-0.3382)	0.484 (-0.3152)	10.2	2.5
	1B	0.455 (-0.3420)	0.566 (-0.2553)	10.9	1.4
1.01	2A	0.930 (-0.0315)	0.796 (-0.991)	7.9	7.7
	2B	0.935 (-0.0292)	0.747 (-0.1267)	7.4	25.8
5.04	3A	4.40 (0.6432)	6.21 (0.7928)	12.7	-5.0
	3B	4.70 (0.6717)	3.39 (0.5301)	6.7	16.0
10.1	4A	9.63 (0.9836)	4.54 (0.6570)	4.5	-16.6
	4B	9.37 (0.9716)	7.05 (0.8482)	7.1	-17.0

Note: Values in parentheses are log values of the concentration values.

 

Table 2. Results of the Linear Regression Analysis of the Adsorption and Desorption Soil and Solution Log Concentrations of Four Concentrations of 14C-substance in Aqueous 0.01M Ca(NO3)2 for Four Soils.

Soil	Anti-log of y- intercept (Kd)	Slope (1/n)	Correlation coefficient	Sorption coefficient (Koc)
Adsorption
Kewaunee clay loam	3.323	0.8432	-0.9818	113.0
Plainfield sand	0.6410	0.7070	-0.9780	363.2
California sandy loam	2.030	0.7557	-0.9960	493.0
Mississippi silt loam	0.9614	0.8574	-0.9676	148.6
Desorption
Kewaunee clay loam	4.7392	0.8329	-0.9916	NA
Plainfield sand	1.0706	0.7704	-0.9636	NA
California sandy loam	2.8704	0.8790	-0.9798	NA
Mississippi silt loam	1.6814	0.9258	-0.9576	NA

 

Validity criteria fulfilled:

not specified

Conclusions:

The test material in aqueous 0.01M Ca(NO3)2 was stable and soluble at the concentrations tested. Adsorption of the substance to glass was approximately 6.0% after 2 hours of equilibration at 25°C. Linear regression analysis of adsorption data demonstrated that the plot of the soil and solution log concentrations of 14C-substance at the concentrations tested was linear for all soil types (correlation coefficient of at least -0.9676). The slope of the regression line (1/n) was less than one for each soil. The adsorption Kd values were 3.323 (Kewaunee clay loam), 0.6410 (Plainfield sand), 2.030 (California sandy loam), and 0.9614 (Mississippi silt loam). 14C-substance was not strongly adsorbed to the Plainfield sand and Mississippi silt loam soils. The Koc values were 113.0 (Kewaunee clay loam), 363.2 (Plainfield sand), 493.0 (California sandy loam), and 148.6 L/kg (Mississippi silt loam). The desorption values were 4.7392 (Kewaunee clay loam), 1.0706 (Plainfield sand), 2.8704 (California sandy loam), and 1.6814 (Mississippi silt loam).

Executive summary:

The adsorption and desorption characteristics of the test material, radioactive substance on four representative agricultural soils (Kewaunee clay loam, Plainfield sand, California sandy loam, Mississippi silt loam) were studied. The study was conducted according to the Pesticide Assessment Guidelines, Subdivision N, Section 163-1 of the Environmental Protection Agency and in compliance with GLP criteria. Preliminary studies indicated that 14C-substance in aqueous 0.01M Ca(NO3)2 was stable and soluble at the concentrations tested. Adsorption of the test material to glass was minimal (approximately 6% after 2 hours). A preliminary study of the adsorption of the test material in aqueous 0.01M Ca(NO3)2 to soil was conducted to establish the soil:solution ratio (1:10 for 3 soils and 2:10 for one soil) and the equilibration time (2 hours) for the definitive study. Soil-solution samples were prepared for each soil type in 0.511 , 1.01, 5.04, and 10.1 µg/mL solutions of test material in aqueous 0.01M Ca(NO3)2. The samples were equilibrated for 2 hours at approximately 25°C. After centrifuging, the supernatant was analyzed by liquid scintillation counting (LSC) to determine adsorption. Solution removed from each sample for analysis was replaced by an equal volume of fresh aqueous 0.01M Ca(NO3)2. The samples were equilibrated for 2 hours at approximately 25°C and analyzed by LSC to determine desorption. Linear regression analysis demonstrated that the plot of the soil and solution log concentrations for the above solutions was linear for all soil types (correlation coefficient of at least -0.9676). The slope of the regression line (1/n) was less than one for each soil. The adsorption Kd values were 3.323 (Kewaunee clay loam), 0.6410 (Plainfield sand), 2.030 (California sandy loam), and 0.9614 (Mississippi silt loam). 14C-substance was not strongly adsorbed to the Plainfield sand and Mississippi silt loam soils. The Koc values were 113.0 (Kewaunee clay loam), 363.2 (Plainfield sand), 493.0 (California sandy loam), and 148.6 (Mississippi silt loam). The desorption Kd values were 4.7392 (Kewaunee clay loam), 1.0706 (Plainfield sand), 2.8704 (California sandy loam), and 1.6814 (Mississippi silt loam).

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 Jan 1991 to 28 Feb 1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Pesticide Assessment Guidelines, Subdivision N, Section 163-1 of the Environmental Protection Agency

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

25 °C

Analytical monitoring:

yes

Details on sampling:

See 'Details on test conditions'

Matrix no.:

#1

Matrix type:

sand

% Clay:

1

% Silt:

11

% Sand:

88

% Org. carbon:

0.35

pH:

7.9

CEC:

3 meq/100 g soil d.w.

Bulk density (g/cm³):

1.24

Matrix no.:

#2

Matrix type:

loamy sand

% Clay:

3

% Silt:

13

% Sand:

84

% Org. carbon:

0.99

pH:

7.7

CEC:

7 meq/100 g soil d.w.

Bulk density (g/cm³):

1.49

Matrix no.:

#3

Matrix type:

silt loam

% Clay:

17

% Silt:

66

% Sand:

17

% Org. carbon:

1.74

pH:

6.5

CEC:

16 meq/100 g soil d.w.

Bulk density (g/cm³):

1.37

Matrix no.:

#4

Matrix type:

silty clay loam

% Clay:

34

% Silt:

51

% Sand:

15

% Org. carbon:

0.67

pH:

6.9

CEC:

30 meq/100 g soil d.w.

Bulk density (g/cm³):

1.59

Details on matrix:

- Test Soils: All soils (i.e., agricultural sand, loamy sand, silt loam and silty clay loam) were supplied by PTRL East, Inc. and were obtained from Fayette County, Kentucky. All four soils used in this study satisfied the soil requirement for the state of Arizona, ie., pH of >6.2 to <8.0 and organic carbon content of less than or equal to 2.6%.
- Physicochemical Characterization: Soil properties including pH, cation exchange capacity, field capacity, organic matter and percent composition of agricultural sand, silt and clay were supplied by PTRL and determined by Commonwealth Technology, Lexington, Kentucky. Bulk density was performed by the University of Kentucky, Lexington, Kentucky. Soil characterization results and the USDA soil series classifications are presented in Table 1 in “Any other information on materials and methods incl tables”.
- Preparation of Soils: Soils were air dried at room temperature (approximately 25 ºC) and passed
through a 2 mm screen prior to use.
- Sample Identification: All test systems were identified by, at least, sample i.d. (including replicate and concentration).

Details on test conditions:

PRELIMINARY TRIALS
- Preliminary adsorption trials were conducted to determine the appropriate soil to water ratio and the time to equilibrium. The highest recommended label rate for a single application is 9.0 ppm. However, due to insolubility of substance in 0.01 N CaCl2 at that concentration the study was conducted at 1 ppm. A nominal concentration of 1.0 ppm [14C]substance was made by weighing 1.3 mg of [14C]substance and adding the material to 27 mL of 1, 4-Dioxane. This solution was then added to 1,350 mL of filter sterilized 0.01 N CaCl2. 1,4-Dioxane was used as a co-solvent (2%) due to difficulties encountered in solubilizing the test material. Thirty mL of the nominal 1.0 ppm [14C]substance solution in 0.01N CaCl2 and 1.0, 5.0, 10.0, 15.0 and 20.0 g of each soil type were used to determine the amount of soil necessary to obtain 20-80% adsorption (linear portion of the
isotherm). Five sets of duplicate 50 mL Teflon® centrifuge tubes were prepared, each set with one soil weight and 30 mL of the [14C]substance solution (1.0 ppm). Duplicate tubes containing 5.0 g of each soil type and 30 mL 0.01 N CaCl2 were used for background determinations. Two tubes containing only 30 mL of 1.0 ppm were prepared to demonstrate any adsorption of [14C]substance to the Teflon®tubes. All tubes were placed in a shaking water bath (approximately 90 oscillations/min.) maintained in the dark at 25°C. Triplicate 0.5 mL aliquots were taken at 3, 20 and 24 hours. Water bath temperature was read at time zero and at each sampling time. Temperature throughout preliminary trials was 25.0 ± 0ºC. At each sampling time, tubes were centrifuged at approximately 2,000 G for approximately 10 minutes and the supernatants were removed and radioassayed immediately. Then the soil in the tubes was resuspended into the adsorption solution and tubes were returned to the water bath. At the last sampling, the tubes were centrifuged and the supernatant was decanted. Soils were air dried (with the aid of a fan), then combusted for subsequent radioassay. From the data obtained in the preliminary trials it was determined that 20 g of agricultural sand soil, 15 g of loam sand soil, 10 g of silt loam and 10 g of silty clay loam soil (with 30 mL of treatment solution) would be required to achieve adsorption within 20-80% adsorption range and that equilibration was established in 24 hours. It was also determined that there was little adsorption of [14C]substance to the Teflon® tubes. Solutions in the blank tubes were radioassayed at 3, 20 and 24 hours.

DEFINITIVE PHASE
- Preparation of Test Solution: A stock solution of [14C]substance was prepared such that 1 mL of 0.01 N CaCl2 (2% dioxane) contained 0.01 µCi. 0.8 mg of [14C]substance were weighed and added to 13 mL of 1, 4-Dioxane. This solution was then added to 750 mL of filter sterilized 0.01N CaCl2 and then radioassayed. From this solution, which was 1.0 ppm, concentrations of 0.76, 0.50, 0.25 and 0.10 ppm were made. Each concentration met protocol requirement of being within 5% of the calculated value.
- Sorption Measurements: Teflon® centrifuge tubes were prepared in duplicate with 20 g of agricultural sand soil, 15 g of loamy sand,10 g of silt loam and 10 g silty clay loam soil as determined by the preliminary trials. To each tube, 30 mL of the appropriate solution was added and tubes were placed in a shaking water bath and maintained in the dark at 25°C. Duplicate tubes containing 5.0 g of each soil type and 30 mL 0.01N CaCl2 were used for background determinations. Two tubes, containing only 30 mL of 1.0 ppm solution were also placed in the water bath to demonstrate adsorption, if any of [14C]substance to the Teflon® tubes. After 24 hours the tubes were centrifuged (same conditions as in the preliminary trials), supernatants were decanted and immediately radioassayed (3 X 0.5 mL) for determination of adsorption isotherms. The adsorption solutions of the agricultural sand and silty clay loam were also analyzed by HPLC to determine the stability of [14C]substance under the conditions of the study. Desorption isotherms were then determined by resuspending each of the soil pellets with fresh 0.01 N CaCl2 solution (volume added was equivalent to volume of adsorption solution decanted), then placing the tubes back into the shaking
water bath for an additional 24 hours in the dark at 25*C. After centrifugation, supernatants were removed and radioassayed as previously described. Temperature of the water bath was taken 6 times during the 48 hour period giving a mean of 25.0 ± 0°C. Soils were air dried (with the aid of a fan) and combusted for quantitation of radiocarbon.

Duration:

24 h

Temp.:

25 °C

Remarks:

with concentration 1.0, 0.76, 0.50, 0.25, 0.10 and 0.0 ppm in all soils used in this experiment

Duration:

24 h

Temp.:

25 °C

Remarks:

all soils used in this experiment

Key result

Sample No.:

#1

Type:

Koc

Value:

246.57 dimensionless

pH:

7.9

Temp.:

25 °C

Matrix:

Agricultural sand

% Org. carbon:

0.35

Key result

Sample No.:

#2

Type:

Koc

Value:

169.43 dimensionless

pH:

7.7

Temp.:

25 °C

Matrix:

Loamy sand

% Org. carbon:

0.99

Key result

Sample No.:

#3

Type:

Koc

Value:

116.8 dimensionless

pH:

6.5

Temp.:

25 °C

Matrix:

Silt loam

% Org. carbon:

1.74

Key result

Sample No.:

#4

Type:

Koc

Value:

447.99 dimensionless

pH:

6.9

Temp.:

25 °C

Matrix:

Silt clay loam

% Org. carbon:

0.67

Key result

Sample No.:

#1

Phase system:

solids-water in soil

Type:

other: desorption Koc

Value:

1 353.4 dimensionless

Temp.:

25 °C

pH:

7.9

Matrix:

Agricultural sand

% Org. carbon:

0.35

Key result

Sample No.:

#2

Phase system:

solids-water in soil

Type:

other: desorption Koc

Value:

460.49 dimensionless

Temp.:

25 °C

pH:

7.7

Matrix:

Loamy sand

% Org. carbon:

0.99

Key result

Sample No.:

#3

Phase system:

solids-water in soil

Type:

other: desorption Koc

Value:

400.71 dimensionless

Temp.:

25 °C

pH:

6.5

Matrix:

Silt loam

% Org. carbon:

1.74

Key result

Sample No.:

#4

Phase system:

solids-water in soil

Type:

other: desorption Koc

Value:

1 419.96 dimensionless

Temp.:

25 °C

pH:

6.9

Matrix:

Silt clay loam

% Org. carbon:

0.67

Adsorption and desorption constants:

The adsorption/desorption coefficients (Kd values) for [14C]substance were determined to be 0.8630/4.7369 for agricultural sand, 1.6943/4.6049 for loamy sand, 2.0557/7.0525 for silt loam and 3.1807/10.0817 for silty clay loam (Table 2 in “Any other information on results incl tables”). The adsorption/desorption constants (Koc values) for [14C]substance were determined to be 246.57/1,353.40 for agricultural sand, 169.43/460.49 for loamy sand, 116.80/400.71 for silt loam and 447.99/1,419.96 for silty clay loam (Table 2 in “Any other information on results incl tables”).

Sample no.:

#1

Duration:

24 h

% Adsorption:

>= 40.8 - <= 60

Remarks on result:

other: Agricultural sand

Sample no.:

#2

Duration:

24 h

% Adsorption:

>= 46.7 - <= 62.3

Remarks on result:

other: Loamy sand

Sample no.:

#3

Duration:

24 h

% Adsorption:

>= 42.3 - <= 55.3

Remarks on result:

other: Silt loam

Sample no.:

#4

Duration:

24 h

% Adsorption:

>= 52.3 - <= 58.8

Remarks on result:

other: Silt Clay Loam

Sample no.:

#1

Duration:

24 h

% Desorption:

>= 15.8 - <= 20.9

Remarks on result:

other: Agricultural sand

Sample no.:

#2

Duration:

24 h

% Desorption:

>= 15.9 - <= 22.7

Remarks on result:

other: Loamy sand

Sample no.:

#3

Duration:

24 h

% Desorption:

>= 27.5 - <= 32

Remarks on result:

other: Silt loam

Sample no.:

#4

Duration:

24 h

% Desorption:

>= 22.1 - <= 27.2

Remarks on result:

other: Silt Loam Clay

Transformation products:

no

Details on results (Batch equilibrium method):

- Radiochemical Purity of [14C]Substance: The radiochemical purity of [14C]substance used in this study was verified prior to use in the preliminary trials to be 100% by HPLC analysis.
- Stability of [14C]Substance: HPLC analysis of unlabelled substance was performed prior to and following sampling to determine its stability (See Figure 2). HPLC analysis of treatment solution at the time of study initiation (100%) and upon adsorption in agricultural sand (100%) and silty clay loam (100%) soils showed [14C]substance to be stable in the test system. The radiochemical purity of [14C]substance determined after termination of sampling in the definitive phase (100%) established the stability of the test material at the test site.
- Mass Balance of [14C]Substance: Mass balance summaries of [14C]substance equivalents recovered in the preliminary trials. The mean mass balance for the preliminary trials in all four soils was 95.3 ± 4.3%. The mean mass balance for all four soils was 102.1 ± 4.3% of the applied radiocarbon.
- Adsorption/Desorption of [14C]substance: Throughout the preliminary trials and definitive phase of the study, blank tubes containing only test solution were radioassayed to demonstrate any adsorption of [14C]substance to the Teflon® tubes. In all cases, there was no adsorption of the [14C]substance to the Teflon® tubes.
- A summary of the percent adsorption and desorption of [14C]substance at five concentrations with four soil types is presented in Table 1 in “Any other information on results incl tables”. The percent adsorbed (mean of two replicates) ranged between 47.2 and 56.2 and the percent desorbed (mean of two replicates) ranged between 18.3 and 28.9 of the amount adsorbed. The adsorption and desorption solution concentrations (Ce) and soil concentrations (x/m) observed are summarized in Table 2 in “Any other information on results incl tables”. The regression calculations for the Freundlich equation for the four soil types are also provided in Table 2 in “Any other information on results incl tables”. Based on the use of Koc values to predict leaching potential, where values greater than 5,000 denote immobility of a chemical in soil and values between 150 and 500 denote moderate mobility in soil, substance is predicted to have moderate mobility in each of the four soil types.

 Table 1. Definitive Phase: Summary of Percent Adsorption/Desorption of [14C]-substance with Four Soil Types.

Soil Types	Initial Aqueous concentration (ppm)	Percent absorbed	Percent Desorbed
Agricultural sand	0.10	60.0	17.3
	0.25	47.7	15.8
	0.50	43.6	17.6
	0. 76	43.8	19.7
	1.00	40.8	20.9
	Mean ± SD	47.2 ± 7.6	18.3 ± 2.0
Loamy sand	0.10	58.9	15.9
	0.25	62.3	20.5
	0.50	56.5	22.5
	0. 76	50.6	22.7
	1.00	46.7	22.0
	Mean ± SD	55.0 ± 6.3	20.7 ± 2.8
Silt loam	0.10	55.3	28.4
	0.25	54.6	27.5
	0.50	48.3	32.0
	0. 76	45.3	27.6
	1.00	42.3	29.0
	Mean ± SD	49.2 ± 5.7	28.9 ± 1.8
Silt Loam Clay	0.10	58.8	26.8
	0.25	58.5	25.5
	0.50	57.4	26.9
	0. 76	54.0	27.2
	1.00	52.3	22.1
	Mean ± SD	56.2 ± 2.9	25.7 ± 2.1

 

 

Table 2. Adsorption/Desorption Constants For [14C]-substance in Four Soil Types

Soil Types	Study phase	Percent organic matter	Percent Organic carbon	Kd	Koc (Kdx100)/(%organic carbon)	n (1/slope)
Agricultural sand	Adsorption	0.6	0.35	0.860	246.57	1.3899
	Desorption	0.6	0.35	4.7369	1353.40	1.1179
Loamy sand	Adsorption	1.7	1.00	1.6943	169.43	1.2706
	Desorption	1.7	1.00	4.6049	460.49	1.1995
Silt loam	Adsorption	3.0	1.76	2.0557	116.80	1.2737
	Desorption	3.0	1.76	7.0525	400.71	1.0174
Silt Loam Clay	Adsorption	1.2	0.71	3.1807	447.99	1.1240
	Desorption	1.2	0.71	10.0817	1419.96	0.9512

 

Validity criteria fulfilled:

not specified

Conclusions:

Adsorption/desorption isotherms with [14C]substance were determined using four soil types. Adsorption constants (Koc values) of 246.57, 169.43, 116.80, 447.99 in agricultural sand, loamy sand, silt loam and silty clay loam soils, respectively, predict the substance to be moderately mobile in all four soil types.

Executive summary:

Adsorption/desorption isotherms with [14C]-substance were determined using four soil types which varied in cation exchange capacity (CEC), percent organic matter (OM), and texture. The study was conducted in accordance with EPA N Series 163-1 and in compliance with GLP criteria. Aqueous test solutions of [14C]substance in 0.01 N calcium chloride (CaCl2) (2% dioxane as co-solvent) were prepared at the concentrations of 1.0, 0.76, 0.50, 0.25, 0.10 and 0.0 ppm. The adsorption phase was conducted at 25°C for approximately 24 hours in a shaking water bath with 15 g of loamy sand soil, 10 g silt loam, 10 g silty clay loam soil, and 20 g of agricultural sand soil plus 30 mL of test solution in Teflon® centrifuge tubes. The tubes were centrifuged and the test solutions were decanted. The desorption phase was conducted under the same conditions after fresh 0.01 N CaCl2 was added to the tubes used in the adsorption phase. The volume added was equivalent to the volume of adsorption solution decanted. The mean material balance in all soils was 102.1 + 4.3% of the applied radiocarbon. The adsorption/desorption coefficients (Kd values) for [14C]substance were determined to be 0.8630/4.7369 for agricultural sand, 1.6943/4.6049 for loamy sand, 2.0557/7.0525 for silt loam and 3.1807/10.0817 for silty clay loam soils. Adsorption increased with increasing organic matter and clay content of the test soils. Differences in the composition of the organic matter and clay content of the test soils are the probable causes for the differences observed in the ranking of Koc values. The adsorption/desorption constants (Koc values) for [14C]substance were determined to be 246.57/1,353.40 for agricultural sand, 169.43/460.49 for loamy sand, 116.80/400.71 for silt loam and 447.99/1,419.96 for silty clay loam. Based on the use of Koc values to predict leaching potential, where Koc values between 150 and 500 denote moderate mobility of a chemical in soil, the substance is predicted to have moderate mobility in all four soil types.

Description of key information

The arithmetic mean Koc for the soil adsorption of the substance was determined to be 262.4 L/kg, EPA 163 -1, Saxena 1987, Kesterson 1991.

Key value for chemical safety assessment

Koc at 20 °C:

262.4

Additional information

Summary of the Koc values for the substance
USDA	Name / Origin	OC*	pH	Kf/Kd*	Koc*	1/n	Author / Year
Sand	Plainfield, Wisconsin, USA	0.17	5.4	0.64	363	0.71	Saxena, 1987
Silt loam	Mississippi, USA	0.64	7.0	0.96	149	0.86
Sandy loam	California, USA	0.41	4.6	2.03	493	0.76
Clay loam	Kewaunee, Wisconsin, USA	2.9	7.0	3.3	113	0.84
Sand	Kentucky, USA	0.36	7.9	0.86	247	0.7195	Kesterson, 1991
Loamy sand	Kentucky, USA	1.0	7.7	1.69	169	0.7870
Silt loam	Kentucky, USA	1.76	6.5	2.06	117	0.7855
Silty clay loam	Kentucky, USA	0.68	6.9	3.18	448	0.8897
Arithmetic mean Koc				1.8	262.4	0.7940

* Units: OC(%), Kf/Kd and Koc (mL/g)