2-Pyridinecarboxylic acid, 4-amino-3,6-dichloro-

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:

17 August 2006 to 15 December 2006

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

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Specific details on test material used for the study:

Purity: 98%

Radiolabelling:

yes

Test temperature:

25 °C

Analytical monitoring:

yes

Details on sampling:

All samples were removed after 22 hours of shaking. Test samples and controls were fortified with 0.50 mL of the appropriate dosing solution in 0.01 M CaCl₂; the blanks were fortified with 0.50 mL of untreated 0.01 M CaCl₂.

Aqueous and organic solutions were stored refrigerated when not undergoing analysis. Extracted soil pellets were allowed to air dry at ambient temperatures prior to combustion analysis.

Details on matrix:

COLLECTION AND STORAGE
Description of Soil Collection and Storage for M696 Lufa 3A Loam
- Geographic location: Altluβheim, Baden-Württemberg, Germany (Meadow (grass and weeds) with apple trees, no rain for ca. 6 days. No pesticide use for past 5 years)
- Collection procedures: Spade
- Sampling depth (cm): 20
- Storage conditions: 4 °C (± 5 °C)
- Storage length: Approximately 3 months
- Soil preparation: Sieved through 2 mm screen

Description of Soil Collection and Storage for M697 Site Gl Sandy Loam
- Geographic location: Barrow on Trent, Derbyshire, UK (Permanent grass field with ridge and furrow. MCPA/2,4-D applied spring 2005)
- Collection procedures: By spade from shallow pit in topsoil after turf removal
- Sampling depth (cm): 5 - 12
- Storage conditions: 4 °C (± 5 °C)
- Storage length: Approximately 3 months
- Soil preparation: Sieved through 2 mm screen

Description of Soil Collection and Storage for M698 Site FH Clay Loam
- Geographic location: Hertfordshire, England (Ground cover of artichokes. No pesticide application for over 5 years)
- Collection procedures: By spade
- Sampling depth (cm): 5 - 20
- Storage conditions: 4 °C (± 5 °C)
- Storage length: Approximately 3 months
- Soil preparation: Sieved through 2 mm screen

Description of Soil Collection and Storage for M699 Lufa 5M Sandy Loam
- Geographic location: Mechtersheim, Rheinland-Pfalz, Germany (Weeds, no rain for ca. 6 days. No pesticide application for 4 years)
- Collection procedures: By spade
- Sampling depth (cm): ca. 20
- Storage conditions: 4 °C (± 5 °C)
- Storage length: Approximately 3 months
- Soil preparation: Sieved through 2 mm screen

Description of Soil Collection and Storage for M700 Languedoc Loam
- Geographic location: Languedoc, Roujan, France (Former vineyard that has been in woodland for more than 15 years. No pesticide use during recent woodland history)
- Collection procedures: By spade from soil surface after scraping away 5 cm litter/humus layer
- Sampling depth (cm): 5 - 20
- Storage conditions: 4 °C (± 5 °C)
- Storage length: Approximately 3 months
- Soil preparation: Sieved through 2 mm screen

Description of Soil Collection and Storage for M701 Site J2 Clay Loam
- Geographic location: Empingham, Rutland, UK (Arable field ploughed out of 2 year grass ley in 2000, sown in winter wheat and oilseed rape since then. In winter wheat in 2006. Range of pesticides applied for winter wheat and oilseed rape)
- Collection procedures: By spade from cultivated and sown topsoil
- Sampling depth (cm): 0 - 20 within topsoil
- Storage conditions: 4 °C (± 5 °C)
- Storage length: Approximately 3 months
- Soil preparation: Sieved through 2 mm screen

Following sampling, all soils were handled at all times in accordance with ISO/DIS 10381-6

PROPERTIES
See Table 1.

Details on test conditions:

EXPERIMENTAL APPARATUS
Nalgene polycarbonate centrifuge tubes (35 mL) were used as the sample containers. Duplicate test samples, controls (containing test material but no soil), and blanks (containing soil but no test material) were prepared. The appropriate amount of soil for each soil type (based on 5 g oven-dry weight equivalents) was added to a weighed and labelled sample container for the test samples and blanks. Next, 9.5 mL of 0.01 M CaCl₂ solution was added to each test sample, blank, and control. Test samples and blanks were placed on a horizontal shaker and allowed to pre-equilibrate overnight in an incubator set at 25 °C. The control samples were placed on a horizontal shaker and allowed to equilibrate overnight on the laboratory benchtop at room temperature. All samples were removed after 22 hours of shaking. Test samples and controls were fortified with 0.50 mL of the appropriate dosing solution in 0.01 M CaCl₂; the blanks were fortified with 0.50 mL of untreated 0.01 M CaCl₂.

NOMINAL SAMPLE CONCENTRATIONS
The container sorption test was conducted at 0.5 µg/mL. Freundlich adsorption coefficients for the test material were established at nominal concentrations of 5.0, 1.0, 0.5, 0.1, and 0.05 µg/mL.

PREPARATION OF TEST SOLUTIONS
The test material was dissolved in acetonitrile to prepare a concentrated stock solution. Aliquots were removed for assay by LSC to determine the amount of 14C received. Next, the acetonitrile was evaporated under nitrogen and the 14C-test material residues were reconstituted in 0.01 M CaCl₂ solution. Aliquots removed for LSC analysis determined the concentration of the stock solution to be approximately 100 µg/mL. The stock solution was stored in a refrigerator when not in use.
All dose solutions were prepared so that the desired amount of test material would be delivered in 500 µL of CaCl₂ solution to 9.5 mL of CaCl₂ solution for a total of 10 mL of solution. The dose solution was applied to the surface of the aqueous layer of each sample.
To prepare the dose solutions, the stock solution was diluted with the appropriate amount of 0.01 M CaCl₂.
Aliquots of each dose solution were taken for LSC analysis to verify concentration.

STUDY DESIGN
- SAMPLE CONTROLS
Sample controls were used to check for sorption of the test material to the test container walls. 9.5 mL of 0.01 M CaCl₂ was added to the tubes and shaken on a horizontal shaker at room temperature for approximately 22 hours. Next, the controls were dosed with 0.500 mL of the 100-, 20-, 10-, 2-, and 1-µg/mL dosing solutions, for nominal sample concentrations of 5-, 1-, 0.5-, 0.1-, and 0.05-µg/mL. Control samples were dosed in duplicate and equilibrated for 48 hours. After the equilibration period, the control sample solutions were analysed by LSC.

- SAMPLE BLANKS
Blanks contained soil and CaCl₂ solution, but no test material. Duplicate samples of each soil type were weighed into the test containers at the desired soil mass, 5 g dry weight. 0.01 M CaCl₂ solution was added to obtain the proper volume, 9.5 mL. The blanks were shaken on a horizontal shaker in an incubator set at 25 °C for approximately 22 hours. Next, 0.50 mL of untreated 0.01 M CaCl₂ solution was added to the blanks. Blanks were then equilibrated for another 48 hours. The aqueous and soil phases were separated by centrifugation and aliquots of the aqueous phase were counted by LSC.

- SAMPLE pH
The pH of an aliquot of the CaCl₂ solution was measured. Since pH may play an important role in the sorption process, the pH of representative soil blanks and samples were tested after equilibration.

- FREUNDLICH ADSORPTION ISOTHERMS
All six soils were evaluated using a nominal soil:solution ratio of 1:2, an adsorption equilibration time of 48 hours, and 35-mL polycarbonate centrifuge tubes for test containers. Duplicate samples per soil type were prepared for each of the five sample concentrations.
Approximately 5 g (oven dry weight equivalent) moist soil was weighed into centrifuge tubes and 9.5 mL of 0.01 M CaCl₂ solution was added. The samples were shaken in a horizontal shaker in an incubator set at 25 °C to pre-equilibrate overnight. After approximately 22 hours of pre-equilibration, the samples were removed from the shaker and fortified with 14C-test material in 0.5 mL of 0.01 M CaCl₂. The test material was applied at nominal concentrations of 0.05, 0.1, 0.5, 1, and 5 µg/mL. The samples were returned to the shaker and were shaken for 48 hours in the dark at 25 °C. At the end of the 48 hours, the samples were spun in a centrifuge for 30 minutes at 3500 rpm. The adsorption solution was decanted into a 24-mL glass vial. The weight of the adsorption solution was recorded, and triplicate aliquots were removed for LSC analysis. Representative 5 µg/mL adsorption solutions were prepared and analysed by HPLC to prove the stability of the test material during the adsorption test.
Following the removal of the adsorption solution, the soil samples were extracted three times with acetonitrile:1.0 N HCl (90: 10) solution by shaking for 60 minutes (30 minutes for the second and third extracts), centrifuging (2500 rpm for 10 minutes), and decanting into a 40-mL glass vial. The extracts were pooled and weighed to determine final volume (based on density). Aliquots of the soil extracts were analysed by LSC. Representative 5 µg/mL soil extracts were prepared and analysed by HPLC.
Extracted soil pellets were allowed to air dry for approximately 3 days. Sub-samples of the air-dry extracted pellets were combusted for mass balance determination.

- PREPARATION FOR HPLC ANALYSIS
Filtration of the aqueous samples was necessary prior to HPLC analysis. A 0.10 mL aliquot was filtered through a syringe filter (PTFE, 0.2 µm pore size) into a 2-mL volumetric flask. The syringe filter was rinsed with 1.5 mL of a water:(acetonitrile:methanol, 1:1) (90:10) +0.1 % formic acid solution. The rinse was collected in the same volumetric flask and the sample was brought to volume with the 90:10 solution. Aliquots were taken for LSC analysis.
Concentration and filtration of the organic extracts was necessary prior to HPLC analysis. A 5-mL aliquot of each soil extract was transferred to a 15-mL centrifuge tube. The pH of each soil extract was checked with pH paper. The soil extract for the M697 sandy loam was the only extract that needed to be neutralised to between pH 6 and 8. The M697 neutralised extract was spun in a centrifuge at 2000 rpm for 5 minutes. The supernatant was transferred to a new centrifuge tube. All soil extracts were then concentrated under a stream of nitrogen to less than 0.5 mL volume using a Turbovap evaporator. The waterbath was set at 30 °C. The concentrate was filtered through a 0.2 µm PTFE filter into a 2-mL volumetric flask. The filter was rinsed with a water:(acetonitrile:methanol , 1:1) (90:10) +0.1 % formic acid solution; the final volume of each sample was 2 mL. Aliquots were taken for LSC analysis.
The precipitate formed during the neutralisation of the M697 soil extract was reconstituted in 5 mL of acetonitrile:1 N HCl (90: 10) extraction solution. Aliquots were taken for LSC analysis.

- EXPERIMENTAL CONDITIONS AND MONITORING
Samples and blanks were equilibrated on horizontal shakers inside a temperature-controlled and monitored incubator set at 25 °C. Samples were maintained in the dark during equilibration. Incubator temperatures were monitored with Camille system. The Temperature Monitoring Coordinator was alerted if any temperature controlled devices were out of the acceptable range for more than 1 hour. Controls were equilibrated at room temperature; temperatures of the controls were not monitored.

Key result

Sample No.:

#1

Type:

Kd

Value:

0.17 other: mL/g

Remarks on result:

other: average of all samples

Key result

Sample No.:

#1

Type:

Koc

Value:

9 other: mL/g

Remarks on result:

other: average of all samples

Stability of the Test Material

The radiochemical purity of the test material prior to dosing was determined. The radiochemical stability of the test material throughout the various tests was demonstrated by HPLC analysis of representative samples of the adsorption solutions and organic extracts. The test material was stable throughout all tested phases of the study.

 

Analytical Methodology

- Verification of Extraction Procedures

The average amount of radioactivity recovered by combustion of the extracted air-dried soil was generally less than 10 % of applied, indicating the extraction procedure was acceptable at removing radioactive residues from the soil.

- Verification of Chromatographic Procedures

HPLC column recoveries were determined by comparing the radioactivity in a direct count of an aliquot of each sample analysed by HPLC with the sum of the radioactivity eluted from the column.

- Mass Balance

Mass balance was calculated as the sum of the radioactivity recovered from the adsorption supernatant, the organic extract, and combustion of the extracted soil pellet. The average mass balance for test material adsorption isotherm samples was 98.3 ± 1.9 % (range 94.8-103.0 %).

 

Results of Tier 1 Tests

- Sample Containers

Neither container type showed adsorption to the container; therefore either would be suitable. Due to possible glass breakage, the polycarbonate centrifuge tubes were chosen for use in this study.

- Sample Controls

In general, greater than 95 % of the applied radioactivity was recovered in the aqueous phase, indicating that the test material did not stick to the sample container. For one control dosed with 0.05-µg/mL, only 90 % of the applied radioactivity was recovered in the aqueous phase, indicating that some sorption of the test material to the sample vessel took place. However, the presence of soil in the sample would greatly mitigate the sorption of the test material to the container. Soil samples were extracted with organic solvent to account for any sorption to the test container.

- Sample Blanks

No radioactivity was observed in any sample blank.

 

Freundlich Adsorption Isotherms

The amount of radioactivity remaining in the aqueous phase after the adsorption equilibrium period varied by soil type, but was consistent across all sample concentrations. Approximately 85-100 % of the applied radioactivity was present in the adsorption phase. Likewise, 0-16 % of the applied radioactivity was sorbed to the soil after the adsorption phase.

Only parent test material was present in any of the samples analysed by HPLC, proving the stability of the test material over the course of the isotherm test.

Adsorption Freundlich constants were calculated on all six soils. Adsorption KF values ranged from 0.05 to 0.20 µg^1-1/nmL^1/ng^-1. The linear correlation coefficients (R²) ranged from 0.622 to 0.985. The 1/n values ranged from 0.44 to 0.80, indicating some non-proportional dependence on concentration. KF,oc values ranged from 2.1 to 15.2 µg^1-1/nmL^1/ng^-1.

 

Storage Stability

Adsorption supernatants were analysed by LSC within one day of sampling and by HPLC within 2 weeks of sacrifice. Soil samples were extracted and analysed for radioactivity by LSC within 3 days of sacrifice. HPLC analyses of soil extracts were conducted within 2 weeks of sampling.

The test material did not degrade in the samples, proving stability of the test material over the storage period.

Table 2: Summary of Results

Soil type	M696 Loam	M697 Sandy Loam	M698 Clay Loam	M699 Sandy Loam	M700 Loam	M701 Clay Loam
Amount adsorbed* (%)	7.3 (1.4-15.5)	10.9 (5.2-14.6)	5.2 (0.3-8.4)	6.9 (1.8-9.7)	6.2 (1.7-9.1)	7.6 (1.7-10.8)
Adsorption Kd (mL/g)	0.16	0.27	0.12	0.15	0.14	0.17
Adsorption Koc (mL/g)	9.3	5.9	5.2	21.1	4.3	8.3
Adsorption KF (µg^1-1/nmL^1/ng^-1)	0.09	0.20	0.05	0.11	0.09	0.11
Adsorption KFoc (µg^1-1/nmL^1/ng^-1)	5.3	4.4	2.1	15.2	2.7	5.0
1/n	0.63	0.80	0.44	0.78	0.68	0.67

*Expressed as percent of the applied radioactivity. Amount adsorbed to soil calculated by subtracting the amount in solution from the amount applied to the test system.

Validity criteria fulfilled:

yes

Conclusions:

After 48 hours of equilibration, between 0.3 and 15.5 % of the applied test material was adsorbed in the six soils. Test material adsorption Kd values ranged from 0.01 to 0.37 mL/g, (average of 0.17 ± 0.08 mL/g). Adsorption Koc values ranged from 0.3 to 29.4 mL/g, (average of 9.0 ± 7.1 mL/g).
Adsorption test material KF values ranged from 0.05 to 0.2 µg^(1 -1/n)mL^(1/n) g^-1 with correlation coefficients of 0.622 to 0.985, and 1/n values of 0.44 to 0.80. KF,oc values ranged from 2.1 to 15.2 µg^(1 -1/n)mL^(1/n)g^-1.

Executive summary:

The adsorption of the test material was investigated in a study which was conducted under GLP conditions and in accordance with the standardised guideline OECD 106.

The adsorption characteristics of the test material were studied in six soil types, a loam (M696, pH 7.5, 1.7 % organic carbon) from Germany, a sandy loam (M697, pH 6.3, 4.6 % organic carbon) from the UK, a clay loam (M698, pH 7.6, 2.2 % organic carbon) from the UK, a sandy loam (M699, pH 7.4, 0.7 % organic carbon) from Germany, a loam (M700, pH 7.6,3.2 % organic carbon) from France, and a clay loam (M701, pH 7.5, 2.1 % organic carbon) from the UK.

The adsorption phase of the study was carried out by equilibrating fresh soil with the test material at nominal concentrations of 0.1, 0.2, 1.0, 2, and 10 mg a.i. per kg soil. Equilibration was conducted in the dark in an incubator set at 25 °C. The equilibrating solution used was 0.01 M CaCl₂, with a soil:solution ratio of 1:2 (5 g oven dry soil to 10 mL solution). Samples were equilibrated for 48 hours.

Soil and aqueous phases were separated by centrifugation after the adsorption phase. Soil samples were extracted three times with 90:10 acetonitrile:1.0 N HCl, centrifuged, and the extracts decanted and combined. Residues in aqueous solution and organic extracts were assayed LSC. 14C residue remaining in the soil pellet after extraction was determined by oxidative combustion. Adsorption parameters were calculated using the Freundlich adsorption isotherms.

Representative samples of each soil type were analysed by HPLC to determine stability of the test material over the course of the study. All test material samples contained 95 % parent or greater, proving their stability through the adsorption and extraction phases.

The average mass balance in all six soils at the end of the adsorption phase was 98.3 ± 1.9 % of the applied for the test material.

After 48 hours of equilibration between 0.3 and 15.5 % of the applied test material was adsorbed in the six soils. Adsorption Kd values ranged from 0.01 to 0.37 mL/g, (average of 0.17 ± 0.08 mL/g). Adsorption Koc values ranged from 0.3 to 29.4 mL/g, (average of 9.0 ± 7.1 mL/g).

Adsorption test material KF values ranged from 0.05 to 0.2 µg^(1 -1/n)mL^(1/n) g^-1 with correlation coefficients of 0.622 to 0.985, and 1/n values of 0.44 to 0.80. KF,oc values ranged from 2.1 to 15.2 µg^(1 -1/n)mL^(1/n)g^-1.

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

8 August 2001 to 20 December 2002

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:

EPA OPPTS 835.1220 (Sediment and Soil Adsorption / Desorption Isotherm)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: EPA Guideline Subdivision N 163-1 (Leaching and Adsorption/Desorption Studies)

Deviations:

no

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Specific details on test material used for the study:

Purity: 99.5%

Radiolabelling:

yes

Test temperature:

5 and 25 °C

Analytical monitoring:

yes

Details on sampling:

Tier 1, Tier 2, Tier 3
Duplicate samples were removed from the shaker and analysed at 2, 4, 8, 24, and 48 hours after initiation of shaking. Blank samples were analysed at the same times and in the same manner except that after aliquots were removed for analysis, the samples were mixed to break the soil pellet and returned to the shaker.
Control samples were analysed only at 24 hours.

Details on matrix:

COLLECTION AND STORAGE
- Collection procedures: Hand trowels were used to collect 10-12 samples from a 50-ft by 50-ft plot. The soil samples were transferred to 5-gallon plastic buckets and shipped to the testing facility.
- Storage conditions: soils were stored in a refrigerator unit set at 4 °C until use
- Soil preparation: soils were passed through a #10 mesh (2 mm) sieve

PROPERTIES
See Table 1.

Details on test conditions:

EXPERIMENTAL APPARATUS
For each tier, 24 mL glass vials with Teflon-lined caps were used as the sample containers. Duplicate samples and controls (containing test material but no soil) were prepared in each tier. The blank samples (containing soil but no test material) were prepared in duplicate in Tiers 1 and 2, and in single replicates in Tier 3 desorption kinetics and soil metabolism study tests.
For each tier, the appropriate amount of soil for each soil type (based on dry weight equivalents) was added to a sample container. Then, the appropriate amount of 0.01 M CaCl₂ solution was added using a 10-mL electronic pipette. Next, the samples were placed on a horizontal shaker and allowed to equilibrate overnight in an incubator set at 25 °C. This same procedure was followed for studying soils M568 and M599 for the temperature dependence test, except the incubator was set at 5 °C.

PREPARATION OF APPLICATION SOLUTIONS
The 14C-test material was dissolved in acetonitrile and a purity check was performed. Next, a 10 µg/mL stock solution of the test material was prepared in 0.01 M CaCl₂ by adding a portion of the test material to a 200-mL volumetric flask. The acetonitrile was evaporated under nitrogen and the stock solution was brought to volume with 0.01 M CaCl₂. Separate aliquots of this 10 µg/mL stock solution were used to dose test samples at 0.5 µg/mL, for the preliminary tests, Tier 1, Tier 2, and Tier 3 desorption kinetics test, and the Isotherm test.
Several additional dosing solutions were prepared for the isotherm test. The concentrations of these dosing solutions were 1.0, 2.0, 20 and 60 µg/mL.
All five dose solutions (1.0, 2.0, 10, 20, and 60 µg/mL) for the isotherm test were analysed by LSC prior to dosing to ensure correct concentration.

APPLICATION RATES
The application rate for the Tier 1, Tier 2, Tier 3 desorption kinetics, and temperature-dependent (5 °C) tests, as well as the soils from the aerobic soil metabolism study, was 0.5 µg/mL, (1.0 µg a.i./g soil). The soils for the isotherm test were dosed at 0.05, 0.1, 0.5, 1.0, and 5 µg/mL (0.1, 0.2, 1.0, 2.0, and 10 µg a.i./g soil).

STUDY DESIGN
- MATRIX INTERFACE
Using two of the eight soil types, one with a high clay content and low organic matter content (M599) and one with a low clay content and high organic matter content (M568), the matrix effects of the soil on the analysis of 14C-test material was evaluated. Moist soil (5 g dry weight) was weighed into 24-mL glass vials and 0.01 M CaCl₂ was added to bring the total water volume to 4.75 mL. Two control samples and one blank sample per soil containing no test material were analysed concurrently. The samples were shaken for approximately 4.5 hours and the solution removed by centrifugation and decantation. The calcium chloride phases were fortified with 14C-test material to a nominal concentration of 0.5 µg/mL (0.25 mL of the 10 µg/mL dose solution).
Triplicate aliquots (0.1 mL) of the fortified samples were analysed by LSC. The fortified CaCl₂ phases were then filtered through Whatman 13 mm filters (0.45 µm pore size) before HPLC analysis.

- METHODOLOGY
The adsorption phase of the study was carried out by equilibrating fresh soil with test material at 0.1, 0.2, 1.0, 2.0 and 10 mg a.i./kg soil in the dark at 25 °C for 48 hours. The equilibrating solution used was 0.01 M CaCl₂, with a soil:solution ratio of 1:2. The desorption phase of the study was carried out by adding approximately the amount of 0.01 M CaCl₂ removed for adsorption and equilibrating in the dark at 25 °C for 2 hours. The samples were desorbed once.
Two soils, M568 and M599, were used to examine the temperature dependence of the adsorption and desorption of the test material using incubations at 5 °C.
The supernatant solution after adsorption and desorption was separated by centrifugation and the test material residues were analysed by HPLC with fraction collection. The fractions were then assayed by LSC. The soils were extracted three times with 90:10 acetone:1.0 N HCl. The extracts were concentrated using a turbo evaporator and analysed by HPLC with fraction collection. The 14C residue remaining in the soil after extraction was determined by oxidative combustion. The adsorption and desorption parameters were calculated using the Freundlich adsorption and desorption isotherms.

SOILS FROM AEROBIC SOIL METABOLISM STUDY
Approximately 5 g (oven dry weight equivalent) moist soil of M610, M611, M615, and M623 (used in an additional aerobic soil metabolism study) were weighed into glass tubes, 0.01 M CaCl₂ was added (9.49 mL), and the samples were shaken in a horizontal shaker in an incubator set at 25 °C to equilibrate overnight. After approximately 18 hours of equilibration, the samples were removed from the shaker and fortified with the nominal concentration of 0.50 µg/mL, 14C-test material in 0.01 M CaCl₂ for a final volume of 10 mL. The samples were returned to the shaker and were shaken for 48 hours in the dark at 25 °C. At the end of the 48 hours, the adsorption solution was removed as for Tier I and analysed by LSC. Single replicates of the adsorption solutions for each of the soil types were analysed by HPLC.
Samples were extracted, concentrated and analysed by HPLC as for Tier 1. Aliquots of extracted, air-dried soils were combusted to obtain a material balance.

Key result

Sample No.:

#1

Type:

Kd

Value:

0.22 other: mL/g

Remarks on result:

other: average of all samples

Key result

Sample No.:

#1

Type:

Koc

Value:

10 other: mL/g

Remarks on result:

other: average of all samples

Material Balance

The stability of the test material during the adsorption phase and desorption phases averaged 99.1 ± 0.5 % in the adsorption solution (isotherm test, highest concentration only). The mass balance at the end of the adsorption phase of the study was 98.2 ± 3.4 % of the applied in all of the soils (Preliminary Tier I and Tier 2 tests and aerobic soil metabolism soils at 48 hour equilibrium, soil:solution ratio of 1:2). The mass balance at the end of the desorption phase was 98.7 ± 1.5 % of the applied in all of the soils (Preliminary Tier 3 desorption test at 2 hour equilibrium and temperature dependence test). The mass balance of the isotherm test was 99.7 ± 2.3 % of the applied in all of the soils.

 

Preliminary Test to Determine Filter Sorption

The test material did not sorb to the Whatman 13 mm syringe filters used in the study.

 

Preliminary Test to Determine Container Sorption

The sorption test showed that less than 1 % of the test material sorbed to the container; therefore, this container was appropriate for conducting this study.

 

Matrix Interface Preliminary Test

Duplicates of two soils (M568 and M599) and controls were evaluated for matrix interference. For the M568 soil, 92 and 93 % of the applied radioactivity was detected in the solution; for soil M599, 91 and 90 % of the applied radioactivity was detected in solution; and for the controls 94 and 95 % of the applied radioactivity was in solution. These samples, as well as blank samples of each soil type, were analysed by HPLC and shown to contain greater than 99 % test material. Therefore, no matrix interference was noted. Since this test used a 1:1 soil:solution ratio, it represented the worst case scenario for matrix interference. Thus, other soil:solution ratios were not expected to demonstrate matrix interference.

 

Tier 1 Test (to Determine Soil:Solution Ratio and Adsorption Equilibration Time)

Four soil:solution ratios were evaluated using two soils. The soil:solution ratios were nominally 1:1, 1:2, 1:5, and 1:10 for soils M568 and M599. Results showed that the 1:2 soil:solution ratio was the most appropriate for determining the sorption characteristics of the test material. All blank soil samples contained no radioactivity.

The concentration recovery for the M599 extraction solution was low, 82.8 %; most likely it was due to the low total amount of radioactivity. The test material did not degrade in either the adsorption solution or the extraction solution. Overall, 98-100 % of the radioactivity in those solutions remained as test material. Mass balance was calculated for the 48 hour samples at the 1:2 soil:solution ratio and was greater than 99 % of applied radioactivity.

 

Tier 2 Test (to Determine Adsorption Equilibration Time)

Using a soil:solution ratio of 1:2, the remaining six soils were evaluated for adsorption equilibration time. Since M568 and M599 soils were evaluated in Tier 1, these data were used and the procedures were not repeated for these soil types. All blank soil samples contained no radioactivity.

Adsorption equilibrium was achieved in the preliminary Tiers 1 and 2 tests within 48 hours. The radioactive components remained in the adsorption solution, with generally less than 13 % of the applied radioactivity sorbed to the soil for seven soils. The M616 soil (clay loam from North Dakota, USA) had approximately 26 % of the applied radioactivity sorbed to the soil.

The 48-hour soils were extracted and one replicate for each soil type was concentrated. These concentrates and the adsorption solutions were analysed by HPLC. The analyses showed that the test material did not degrade; the radioactivity in the concentrates and the adsorption solutions was at least 98 % parent. Mass balance was measured at the 48 hour time point only. It was acceptable for all soils (94.9-108.5 % of applied).

From the preliminary Tiers 1 and 2 tests, an adsorption equilibration period of 48 hours was chosen for equilibration.

 

Tier 3 (to Determine Desorption Equilibration Time - Desorption Kinetics Test)

Desorption equilibration times were determined by dosing all eight soils at a nominal concentration of 0.5 µg/mL, in 0.01 M CaCl₂, using a soil:solution ratio of 1:2, and an adsorption equilibration time of approximately 48 hours.

All blank soil samples contained no radioactivity. Desorption equilibration was achieved rapidly, within two hours for all eight soils. Generally the adsorption solution contained greater than 87 % (72 % in M616 soil) of the applied radioactivity while the desorption solution contained less than 6 % (10 % in M616 soil) of the applied radioactivity. The adsorption and desorption solutions for the 2 hour time point samples were analysed by HPLC. The radioactivity was greater than 98 % parent for all solutions.

The 2-hour time point soils were extracted. While M546, M549, M568, and M617 soils had acceptable concentration recoveries, M579, M584, M599, and M616 soils had low concentration recoveries. These soils formed a precipitate when the acidic extraction solutions were brought to between pH 6 and 8 with 1.0 N NaOH. The precipitates were dissolved in acetone and thoroughly mixed by vortex and sonication. The precipitate solutions were then centrifuged and the rinsate was added to the neutralised extraction solution to be concentrated. To analyse the amount of radioactivity remaining in the precipitate, it was re-dissolved in acetone and analysed by LSC. The activity recovered in the precipitate accounted for the loss of activity during concentration. These concentrated extracts were analysed by HPLC and greater than 90 % of the radioactivity in the samples was recovered as parent (except for M584, which was 82.2 %).

Mass balance was calculated for the 2 hour desorption time point only; it was acceptable for all soils (96.2-101.3 %).

From the preliminary Tier 3 desorption kinetics test, a desorption equilibration period of at least two hours was chosen to allow equilibrium.

 

Isotherm Test

- Mass Balance and Degradation of Parent

The aqueous phase of all eight soils was dosed at nominal concentrations of 0.05, 0.1, 0.5, 1.0, and 5.0 µg/mL using a soil:solution ratio of 1:2, an adsorption equilibration time of approximately 48 hours, and a desorption equilibration time of 2 hours.

The average mass balance for all samples was 99.7 %.

An average of 92.8 % (69.3-101.2 %) of the applied radioactivity remained in the adsorption solution, while an average of 2.4 % (0.0-9.7 %) was recovered in the desorption solution. An average of 2.7 % (0.0-14.7 %) of the applied was recovered in the organic extract. The soil pellet contained an average of 1.8 % (0.1-6.7 %) of the applied radioactivity.

Single replicates of the adsorption and desorption solutions dosed at 5 µg/mL, for each soil type were analysed by HPLC. The test material was stable throughout the equilibration period; the adsorption and desorption solutions were composed of 98.3-100.0 % parent. Single replicates of the soil extracts dosed at 5 µg/mL, for each soil type were concentrated and analysed by HPLC. The concentration recoveries for the M579, M584, and M599 soils were low in the concentrated extracts; however, when the radioactivity in the concentrated extract was combined with the radioactivity contained in the precipitate formed after neutralisation, the overall recovery was acceptable. These concentrated extracts were analysed by HPLC and showed that the test material did not degrade. The extracts contained 97.1-99.6 % parent.

 

- Adsorption and Desorption Constants

The adsorption Kd values ranged from 0.00 to 1.04 mL/g, while the adsorption Koc values ranged from 0.0 to 38.9 mL/g.

The test material may be considered potentially mobile with desorption Kd values ranging from no measurable desorption to 405.94 mL/g and desorption Koc values ranging from 0.00 to 40594 mL/g. Generally, the desorption Kd values were higher than the adsorption constants.

Desorption constants were not calculated for soils M549 and M599 (both clay soils from the UK and Mississippi, USA, respectively) because no discernable (below LOD) test material was desorbed from the soil.

 

- Freundlich Constants

Adsorption KF values ranged from 0.01 to 0.73 µg^(1 -1/n)mL^(1/n)g^-1. The linear correlation coefficients (R²) ranged from 0.893 to 0.999. The 1/n values ranged from 0.32 to 1.52, indicating some non-proportional dependence on concentration.

Desorption KF values ranged from 1.24 to 3.09 µg^(1 -1/n)mL^(1/n)g^-1. The linear correlation coefficients (R²) ranged from 0.833 to 1.000.

The 1/n values ranged from 0.61 to 1.00, again indicating some non-proportional dependence on concentration.

 

- Temperature Dependence Test

M568 and M599 soils were fortified at 0.5 µg/mL, and incubated at 5 °C, instead of 25 °C. Mass balance was acceptable with an average of 99.1 % of applied radioactivity.

An average of 93.3 % of the applied radioactivity remained in the adsorption solution, while an average of 5.1 % was recovered in the desorption solution of the M568 soil. No discernable (below LOD) amount of test material desorbed from the M599 soil. An average of 1.0 % of the applied was recovered in the organic extract. The soil pellet contained an average of 2.2 % of the applied radioactivity.

The concentrations of test material in the soil and solution following the adsorption and desorption phases were not corrected for the average amount of parent because the radioactivity in all phases was greater than 90 % parent in all samples analysed in Tiers 1, 2, and 3. Therefore, the radioactivity in each phase was considered to be all test material.

The adsorption Kd values ranged from 0.02 to 0.30 mL/g with adsorption Koc values which ranged from 1.6 to 7.8 mL/g. The desorption Kd and Koc values were only calculated for the M568 soil because no test material was desorbed from the M599 soil.

Comparing these results to the isotherm test results for the same soils fortified at the same concentration shows that temperature does not affect adsorption or desorption.

 

Soils from Aerobic Soil Metabolism Study

Five soils were evaluated in the aerobic soil metabolism study with test material: M610, M611, M615, M616, and M623. The properties of M616 sorption were studied during the isotherm test. Adsorption constants were evaluated for the other four soils. The blank samples contained no measurable radioactivity.

An average of 62.8 % of the applied radioactivity remained in the adsorption solution. An average of 28.7 % of the applied was recovered in the organic extract. The soil pellet contained an average of 4.4 % of the applied radioactivity.

The concentrations of test material in the soil and solution following the adsorption and desorption phases were not corrected for the average amount of parent because the radioactivity contained in the adsorption and extraction solutions was 96.1-99.9 % parent. Therefore, the radioactivity in each phase was considered to be all test material. Mass balance was acceptable with an average of 95.9 % of applied radioactivity.

The adsorption Kd values ranged from 0.07 to 0.41 mL/g with the adsorption Koc values ranging from 5.5 to 27.2 mL/g.

Soils from Aerobic Soil Metabolism Study

Five soils were evaluated in an aerobic soil metabolism study: M610, M611, M615, M616 and M623. The properties of M616 sorption were studied during the isotherm test. Adsorption constants were evaluated for the other four soils. The blank samples contained no measurable radioactivity.

An average of 62.8 % of the applied radioactivity remained in the adsorption solution. An average of 28.7 % of the applied was recovered in the organic extract. The soil pellet contained an average of 4.4 % of the applied radioactivity.

The concentrations of test material in the soil and solution following the adsorption and desorption phases were not corrected for the average amount of parent because the radioactivity contained in the adsorption and extraction solutions was 96.1-99.9 % parent. Therefore, the radioactivity in each phase was considered to be all test material. Mass balance was acceptable with an average of 95.9 % of applied radioactivity.

The adsorption Kd values ranged from 0.07 to 0.41 mL/g with the adsorption Koc values ranging from 5.5 to 27.2 mL/g.

 

Storage Stability

For the isotherm, temperature-dependence, and soils from aerobic soil metabolism study tests, adsorption and desorption supernatants were analysed by LSC within one day of sampling and by HPLC within 4 days of sampling. The soils were extracted within 4 days of sampling. The soil extracts were analysed by LSC within one day of extraction and by HPLC within 10 days of extraction. As the samples were analysed within two weeks of sacrifice and test material did not degrade in the samples, determination of storage stability was unnecessary.

Table 2: Summary of Results

Soil type	M546 Silt Loam	M549 Clay	M568 Silty Clay Loam		M579 Sand	M584 Loam	M599 Clay		M616 Clay Loam	M617 Loamy sand
Temperature (°C)	25	25	25	5	25	25	25	5	25	25
Amount adsorbed* (%)	2.3 (0.8-3.7)	1.3 (0.0-2.9)	12.2 (8.4-15.7)	12.1	3.2 (1.3-5.2)	4.1 (1.7-8.1)	0.6 (0.0-1.8)	1.4	26.7 (20.4-30.7)	7.2 (4.2-10.4)
Adsorption Kd (mL/g)	0.053 (0.019-0.087)	0.036 (0.000-0.064)	0.308 (0.207-0.406)	0.298	0.072 (0.027-0.118)	0.089 (0.037-0.176)	0.024 (0.000-0.039)	0.029	0.853 (0.613-1.035)	0.162 (0.093-0.223)
Adsorption Koc (mL/g)	5.31 (1.92-8.67)	0.87 (0.00-1.99)	7.96 (5.34-10.50)	7.71	4.52 (1.72-7.37)	8.91 (3.75-17.62)	0.81 (0.00-2.58)	1.95	23.69 (17.03-28.75)	27.00 (15.56-38.87)
Amount desorbed**	26.3 (13.8-37.7)	0.0	36.6 (33.9-40.2)	42.2	58.6 (26.4-110.7)	7.3 (0.0-16.1)	0.0	0.0	33.5 (30.8-39.8)	46.3 (27.3-59.9)
Desorption Kd (mL/g)	7.47 (3.67-13.87)	0.00	3.81 (3.25-4.26)	2.97	2.91 (0.00-5.77)	79.8 (0.0-405.94)	0.00	0.00	4.63 (3.52-5.20)	2.65 (1.38-5.44)
Desorption Koc (mL/g)	747 (367-1387)	0	98 (84-110)	77	182 (0-361)	7988 (0-40 594)	0	0	129 (98-144)	442 (230-907)

*Amount adsorbed to the soil calculated by subtracting the amount remaining in solution from the amount applied to the solution.

**Expressed as a percentage of the adsorbed

 

Table 3: Summary of Results from Soils used in Aerobic Soil Metabolism Study

Soil type	M610 Clay Loam	M611 Loam	M615 Sandy Loam	M623 Heavy Clay
Amount adsorbed* (%)	3.3	3.1	0.6	1.8
Adsorption Kd (mL/g)	0.409	0.395	0.066	0.211
Adsorption Koc (mL/g)	27.24	11.62	5.51	6.21

*Amount adsorbed to the soil calculated by subtracting the amount remaining in solution from the amount applied to the solution.

Validity criteria fulfilled:

yes

Conclusions:

The sorptive behaviour of the test material may be characterised as potentially mobile for all soil types tested. The average adsorption Kd value was 0.22 mL/g (range 0.00-1.04 mL/g); the corresponding average Koc value was 10.0 mL/g (range 0.0 to 38.9 mL/g). Adsorption Kf values ranged from 0.01 to 0.73 mL/g, averaging 0.17 mL/g, with correlation coefficients of 0.893 to 0.999, and 1/n values of 0.32 to 1.52. For the soils where test material sorbed, the average desorption Kd value was 13.97 mL/g (range 0.00-405.94 mL/g), the corresponding average Koc value was 1341 mL/g (range 0.0 to 40594 mL/g). Desorption Kf values ranged from 1.24 to 3.09 mL/g, averaging 2.17 mL/g, with correlation coefficients of 0.833 to 1.000, and 1/n values of 0.61 to 1.00.
The findings from this study therefore show that the test material sorbs weakly to soil; however, the test material does have a short half-life under aerobic soil conditions, and the sorption of test material does increase with soil contact time. These factors, as well as a low application rate will mitigate the leaching potential of the test material and the risk to groundwater.

Executive summary:

The adsorption and desorption of the test material was investigated in a study which was conducted under GLP conditions and in accordance with the standardised guidelines EPA Guideline Subdivision N 163-1, OECD 106 and EPA OPPTS 835.1220.

The adsorption/desorption characteristics of radiolabelled test material were studied in eight soil types in a batch equilibrium experiment: a silt loam (M546) [pH 7.8, organic carbon 1.0 %] from Thessaloniki (Greece), a clay (M549) [pH 7.5, organic carbon 3.2 %] from Faringdon (United Kingdom), a silty clay loam (M568) [pH 7.8, organic carbon 3.9 %] from Manitoba (Canada), a sand (M579) [pH 6.6, organic carbon 1.6 %] from Bedfordshire (England), a loam (M584) [pH 6.1, organic carbon 1.0 %] from Charentilly (France), a clay (M599) [pH 6.9, organic carbon 1.5 %] from Mississippi (USA), a clay loam (M616) [pH 4.8, organic carbon 3.6 %] from North Dakota (USA), and a loamy sand (M617) [pH 4.5, organic carbon 0.6 %] from North Carolina (USA).

The adsorption characteristics of radiolabelled test material were also studied in four soils: a clay loam (M610) [pH 4.6, organic carbon 1.5 %] from Kansas (USA), a loam (M611) [pH 7.5, organic carbon 3.4 %] from Manitoba (Canada), a sandy loam (M615) [pH 7.3, organic carbon 1.2 %] from North Dakota (USA), and a heavy clay (M623) [pH 7.5, organic carbon 3.4 %] from Texas (USA).

The adsorption phase of the study was carried out by equilibrating fresh soil with test material at 0.1, 0.2, 1.0, 2.0 and 10 mg a.i./kg soil in the dark at 25 °C for 48 hours. The equilibrating solution used was 0.01 M CaCl₂, with a soil:solution ratio of 1:2. The desorption phase of the study was carried out by adding approximately the amount of 0.01 M CaCl₂ removed for adsorption and equilibrating in the dark at 25 °C for 2 hours. The samples were desorbed once.

Two soils, M568 and M599, were used to examine the temperature dependence of the adsorption and desorption of the test material using incubations at 5 °C.

The supernatant solution after adsorption and desorption was separated by centrifugation and the test material residues were analysed by HPLC with fraction collection. The fractions were then assayed by LSC. The soils were extracted three times with 90:10 acetone:1.0 N HCl. The extracts were concentrated using a turbo evaporator and analysed by HPLC with fraction collection. The 14C residue remaining in the soil after extraction was determined by oxidative combustion. The adsorption and desorption parameters were calculated using the Freundlich adsorption and desorption isotherms.

The stability of the test material during the adsorption phase and desorption phases averaged 99.1 ± 0.5 % in the adsorption solution (isotherm test, highest concentration only). The mass balance at the end of the adsorption phase of the study was 98.2 ± 3.4 % of the applied in all of the soils (Preliminary Tier 1 and Tier 2 tests and aerobic soil metabolism soils at 48 hour equilibrium, soil:solution ratio of 1:2). The mass balance at the end of the desorption phase was 98.7 ± 1.5 % of the applied in all of the soils (Preliminary Tier 3 desorption test at 2 hour equilibrium and temperature dependence test). The mass balance of the isotherm test was 99.7 ± 2.3 % of the applied in all of the soils.

After 48 hours of equilibration, 2.3, 1.3, 12.2, 3.2, 4.1, 0.6, 26.7 and 7.2 % of the applied test material was adsorbed in soils M546, M549, M568, M579, M584, M599, M616, and M617, respectively. The adsorption Kd values ranged from 0.00 to 1.04 mL/g, with an average of 0.22 ± 0.28 mL/g. The adsorption Koc values ranged from 0.0 to 38.9 mL/g, with an average of 10.0 mL/g. At the end of the desorption, 26.3, 0.0, 36.6, 58.6, 7.3, 0.0, 33.5 and 46.3 % of the adsorbed amount was desorbed from soils M546, M549, M568, M579, M584, M599, M616 and M617, respectively. The desorption Kd values ranged from 0.00 to 405.94 mL/g, with an average of 13.96 ± 54.36 mL/g. The desorption Koc ranged from 0.0 to 40 594 mL/g, with an average of 1301 mL/g. The desorption Kd and Koc values were higher than those obtained for adsorption.

Description of key information

Koc = 10.0 mL/g (average of 8 soil types), EPA Guideline Subdivision N 163-1, OECD 106, EPA OPPTS 835.1220. Rutherford (2002)
Adsorption Koc = 9.0 mL/g (average of 6 soil types), OECD 106. Laughlin (2006)

Key value for chemical safety assessment

Koc at 20 °C:

10

Additional information

Two studies, investigating the adsorption/desorption of the test material in soils, are available. Both studies were conducted under GLP conditions and in accordance with standardised guidelines. Both studies were assigned a reliability score of 1 in line with the criteria of Klimisch et al. (1997).

 

In the first study, reported by Rutherford (2002), the adsorption and desorption of the test material was investigated in a study which was conducted under GLP conditions and in accordance with the standardised guidelines EPA Guideline Subdivision N 163-1, OECD 106 and EPA OPPTS 835.1220.

The adsorption/desorption characteristics of radiolabelled test material were studied in eight soil types in a batch equilibrium experiment: a silt loam (M546) [pH 7.8, organic carbon 1.0 %] from Thessaloniki (Greece), a clay (M549) [pH 7.5, organic carbon 3.2 %] from Faringdon (United Kingdom), a silty clay loam (M568) [pH 7.8, organic carbon 3.9 %] from Manitoba (Canada), a sand (M579) [pH 6.6, organic carbon 1.6 %] from Bedfordshire (England), a loam (M584) [pH 6.1, organic carbon 1.0 %] from Charentilly (France), a clay (M599) [pH 6.9, organic carbon 1.5 %] from Mississippi (USA), a clay loam (M616) [pH 4.8, organic carbon 3.6 %] from North Dakota (USA), and a loamy sand (M617) [pH 4.5, organic carbon 0.6 %] from North Carolina (USA).

The adsorption characteristics of radiolabelled test material were also studied in four soils: a clay loam (M610) [pH 4.6, organic carbon 1.5 %] from Kansas (USA), a loam (M611) [pH 7.5, organic carbon 3.4 %] from Manitoba (Canada), a sandy loam (M615) [pH 7.3, organic carbon 1.2 %] from North Dakota (USA), and a heavy clay (M623) [pH 7.5, organic carbon 3.4 %] from Texas (USA).

The adsorption phase of the study was carried out by equilibrating fresh soil with test material at 0.1, 0.2, 1.0, 2.0 and 10 mg a.i./kg soil in the dark at 25 °C for 48 hours. The equilibrating solution used was 0.01 M CaCl₂, with a soil:solution ratio of 1:2. The desorption phase of the study was carried out by adding approximately the amount of 0.01 M CaCl₂ removed for adsorption and equilibrating in the dark at 25 °C for 2 hours. The samples were desorbed once.

Two soils, M568 and M599, were used to examine the temperature dependence of the adsorption and desorption of the test material using incubations at 5 °C.

The supernatant solution after adsorption and desorption was separated by centrifugation and the test material residues were analysed by HPLC with fraction collection. The fractions were then assayed by LSC. The soils were extracted three times with 90:10 acetone:1.0 N HCl. The extracts were concentrated using a turbo evaporator and analysed by HPLC with fraction collection. The 14C residue remaining in the soil after extraction was determined by oxidative combustion. The adsorption and desorption parameters were calculated using the Freundlich adsorption and desorption isotherms.

The stability of the test material during the adsorption phase and desorption phases averaged 99.1 ± 0.5 % in the adsorption solution (isotherm test, highest concentration only). The mass balance at the end of the adsorption phase of the study was 98.2 ± 3.4 % of the applied in all of the soils (Preliminary Tier 1 and Tier 2 tests and aerobic soil metabolism soils at 48 hour equilibrium, soil:solution ratio of 1:2). The mass balance at the end of the desorption phase was 98.7 ± 1.5 % of the applied in all of the soils (Preliminary Tier 3 desorption test at 2 hour equilibrium and temperature dependence test). The mass balance of the isotherm test was 99.7 ± 2.3 % of the applied in all of the soils.

After 48 hours of equilibration, 2.3, 1.3, 12.2, 3.2, 4.1, 0.6, 26.7 and 7.2 % of the applied test material was adsorbed in soils M546, M549, M568, M579, M584, M599, M616, and M617, respectively. The adsorption Kd values ranged from 0.00 to 1.04 mL/g, with an average of 0.22 ± 0.28 mL/g. The adsorption Koc values ranged from 0.0 to 38.9 mL/g, with an average of 10.0 mL/g. At the end of the desorption, 26.3, 0.0, 36.6, 58.6, 7.3, 0.0, 33.5 and 46.3 % of the adsorbed amount was desorbed from soils M546, M549, M568, M579, M584, M599, M616 and M617, respectively. The desorption Kd values ranged from 0.00 to 405.94 mL/g, with an average of 13.96 ± 54.36 mL/g. The desorption Koc ranged from 0.0 to 40 594 mL/g, with an average of 1301 mL/g. The desorption Kd and Koc values were higher than those obtained for adsorption.

 

In the second study, reported by Laughlin (2006), the adsorption of the test material was investigated in a study which was conducted under GLP conditions and in accordance with the standardised guideline OECD 106.

The adsorption characteristics of the test material were studied in six soil types, a loam (M696, pH 7.5, 1.7 % organic carbon) from Germany, a sandy loam (M697, pH 6.3, 4.6 % organic carbon) from the UK, a clay loam (M698, pH 7.6, 2.2 % organic carbon) from the UK, a sandy loam (M699, pH 7.4, 0.7 % organic carbon) from Germany, a loam (M700, pH 7.6,3.2 % organic carbon) from France, and a clay loam (M701, pH 7.5, 2.1 % organic carbon) from the UK.

The adsorption phase of the study was carried out by equilibrating fresh soil with the test material at nominal concentrations of 0.1, 0.2, 1.0, 2, and 10 mg a.i. per kg soil. Equilibration was conducted in the dark in an incubator set at 25 °C. The equilibrating solution used was 0.01 M CaCl₂, with a soil:solution ratio of 1:2 (5 g oven dry soil to 10 mL solution). Samples were equilibrated for 48 hours.

Soil and aqueous phases were separated by centrifugation after the adsorption phase. Soil samples were extracted three times with 90:10 acetonitrile:1.0 N HCl, centrifuged, and the extracts decanted and combined. Residues in aqueous solution and organic extracts were assayed LSC. 14C residue remaining in the soil pellet after extraction was determined by oxidative combustion. Adsorption parameters were calculated using the Freundlich adsorption isotherms.

Representative samples of each soil type were analysed by HPLC to determine stability of the test material over the course of the study. All test material samples contained 95 % parent or greater, proving their stability through the adsorption and extraction phases.

The average mass balance in all six soils at the end of the adsorption phase was 98.3 ± 1.9 % of the applied for the test material.

After 48 hours of equilibration between 0.3 and 15.5 % of the applied test material was adsorbed in the six soils. Adsorption Kd values ranged from 0.01 to 0.37 mL/g, (average of 0.17 ± 0.08 mL/g). Adsorption Koc values ranged from 0.3 to 29.4 mL/g, (average of 9.0 ± 7.1 mL/g).

Adsorption test material KF values ranged from 0.05 to 0.2 µg^(1 -1/n)mL^(1/n) g^-1 with correlation coefficients of 0.622 to 0.985, and 1/n values of 0.44 to 0.80. KF,oc values ranged from 2.1 to 15.2 µg^(1 -1/n)mL^(1/n)g^-1.

 

Overall, the test material was found to sorb weakly to soil; however, the test material did have a short half-life under aerobic soil conditions, and the sorption of the test material was found to increase with soil contact time. These factors, as well as a low application rate mitigate the leaching potential of the test material and the risk to groundwater.