Methyl O-(4-amino-3,5-dichloro-6-fluoropyridin-2-yloxy)acetate

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1 May- 28 Aug 1995

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP-Guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1995

Report date:

1995

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Version / remarks:

Adopted in 1991

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Test material

Test material information

Constituent 1

Reference substance name:

Methyl O-(4-amino-3,5-dichloro-6-fluoropyridin-2-yloxy)acetate

EC Number:

407-550-4

EC Name:

Methyl O-(4-amino-3,5-dichloro-6-fluoropyridin-2-yloxy)acetate

Cas Number:

69184-17-4

Molecular formula:

Hill formula: C8 H7 Cl2 F N2 O3 CAS formula: C8 H7 Cl2 F N2 O3

IUPAC Name:

methyl 2-[(4-amino-3,5-dichloro-6-fluoropyridin-2-yl)oxy]acetate

Details on test material:

- Name of test material (as cited in study report): Fluroxypyr methyl ester
- Physical state: solid
- Analytical purity: 98.6%
- Lot/batch No.: non-radiolabelled material, AGR 218601; radiolabelled material, INV 92/29
- Radiochemical purity (if radiolabelling): > 96.2% on 20 March 1995
- Locations of the label (if radiolabelling): 2 and 6 positions in pyridine ring
- Specific activity (if radiolabelling): 26.6 mCi/mmole
- Storage condition of test material: as acetone solution in the dark at < -16 °C

Radiolabelling:

yes

Study design

Test temperature:

Ambient temperature

Batch equilibrium or other method

Analytical monitoring:

yes

Details on sampling:

Preliminary tests
1. Adsorption to test apparatus
- After the 16.5 hour shaking period, aliquots (10 µL) of each solution were sampled for analysis by Liquid Scintillation Counting (LSC) to determine any loss of radioactivity due to adsorption to the glass test apparatus. During the sampling procedure for each aliquot the pipette
tip was rinsed by dispensing a further volume (10 µL) of acetone into the appropriate LSC sample vial. This rinsing procedure was used as a precaution against adsorption of the test material by the plastic pipette tip. After decanting the solutions into new tubes and rinsing the original vials with acetone, portions of the rinses were sampled (50 µL) for analysis by LSC in order to quantify the extent of material desorbed from the glass tubes by the acetone and to achieve a radiochemical balance
2. Stability under test conditions (no soil)
- After the LSC analysis the solution was analysed by normal phase and reverse phase Thin-Layer Chromatography (TLC) (10 µL) to demonstrate the stability of the test materials under the test conditions
3. Stability of the test material in soil/water slurries: after the shaking period, aliquots (10 µL) of each solution were sampled for analysis by LSC to determine any loss of radioactivity in solution due to adsorption to the soil (at 10, 30 and 60 minutes and 2 and 24 hours after test initiation). During the sampling procedure for each aliquot the pipette tip was rinsed by dispensing a further volume (10 µL) of acetone into the appropriate LSC sample vial. This rinsing procedure was used as a precaution against adsorption of the test material by the plastic pipette tip. After LSC analysis, selected solutions were analysed by normal phase and reverse phase TLC to demonstrate the instability of the test materials under the test conditions
Screening test on main metabolite (Fluroxypyr)
- After the 16 hour shaking period and centrifugation, aliquots (10 µL) of each supernatant were sampled for analysis by LSC to determine any loss of radioactivity in solution due to adsorption to the soil. After LSC analysis, solutions were analysed by normal phase and reverse phase TLC (5 µL) to demonstrate the stability of the test materials under the test conditions

Details on matrix:

COLLECTION AND STORAGE
- Geographic location:
Soil 1: Speyer, Germany
Soils 2 and 3: Marcham,Oxfordshire, UK; Highworth, Oxfordshire, UK
Soil 4: Nimes, France
For details on soil properties see table 1 under "Any other information on materials and methods"
- Collection and soil preparation procedures: the soils were sieved to 2 mm and stored damp (at their original moisture content) refrigerated in the dark until required. Before use the moisture content was determined by oven-drying portions of each soil for ca 24 hours at 105°C and calculating weight loss

Details on test conditions:

Preliminary tests
- Aqueous solubility
The water solubility of fluroxypyr methyl ester was determined by a method complying with EEC Directive 84/449/EEC Annex 5, OECD Guidelines for Testing of Chemicals 1981 and EPA/FIFRA Subdivision D Series 63. The solubility was shown to be 28.0 mg/L (Knowles; 1991, GHE-P-2541). Therefore a nominal concentration of 4 mg/L was used for the study in order to comply with the maximum concentration of 5mg/mL permitted by OECD 106 (1981)
- Adsorption to test apparatus ans Stability under test conditions
This test was carried out in duplicate. Aliquots of the stock solutions were added to separate glass tubes (screw- capped, 8 dram capacity) and the solvent removed using a gentle stream of N2. A dose check (10 µL in triplicate) was carried out at the same time. Aqueous 0.01M CaCl2 solution (10 mL) was added to each tube to give a nominal concentration of 4 mg/L. The tubes were capped, shaken by hand and placed in an ultrasonic bath for 5 minutes. The samples were then shaken on a Gerhardt end-to end shaker (on setting 4 - 5, giving ca 1-2 cycles per second) for 16.5 hours at ambient temperature. Analysis was then carried out to determine any adsorption of radioactivity to the test apparatus, followed by chromatographic analysis to assess the stability of the stability of the test materials under the test conditions. Where losses of radioactivity from solution were observed the solutions were decanted into new glass tubes and the original tubes rinsed with acetone (2mL) by shaking for 5 minutes on an end-to end shaker. The rinses were analysed in order to quantify the extent of material desorbed from the glass tubes by the acetone
- Stability in soil/water slurries: a solution of 14C-fluroxypyr methyl ester in 0.01M aqueous calcium chloride was prepared, at a nominal concentration of 4.8mg/L. Seven 1g (dry weight equivalent) samples of each soil type contained in screw- capped glass tubes (8 dram) were dosed with a portion (5 mL) of the 14C-fluroxypyr methyl ester solution. At the same time a dose check was made by dispensing the same volume into an empty glass tube (no soil) and sampling for LSC (25 µL in triplicate). This blank was also used to check stability of the dosing solution during the test. The tubes (including the blank) were shaken on a Gerhardt end-to end shaker (on setting 4-5, giving ca 1-2 cycles per second) for up to 24 hours at ambient temperature. This speed ensured the soil was maintained in suspension, but it was not so vigorous as to cause breakdown of the soil structure. Samples were removed at 10, 30 and 60 minutes and 2 and 24 hours after the start of the experiment. Following centrifugation at 1,500 rpm for 5 minutes the supernatant was analysed to determine any adsorption of radioactivity to the soil. The 10 minute, 2 hour and 24 hour supernatants were analysed by TLC to determine the stability of the test materials under the test conditions, and to assess the extent of any hydrolysis of the ester to the acid product (fluroxypyr)
- Screening adsorption test on fluroxypyr:
- A solution of the 14C-testmaterial in 0.01M aqueous calcium chloride was prepared, at a nominal concentration of 4mg/L . The actual concentration obtained was 3.7460 mg/L. Duplicate 1 g (dry weight equivalent) samples of each soil type contained in pre-weighed, screw-capped glass tubes (8 dram) were dosed with a portion (5 mL) of the 14C- test material solution. At the same time a dose check was made by dispensing the same volume into an empty glass tube (no soil) and sampling for LSC (25 µL in triplicate. This blank was also used to check the purity of the dosing solution at the beginning of the test and its stability during the test. The tubes (including the blank) were shaken on a Gerhardt end-to end shaker 1-2 cycles per second) for 16 hours at ambient temperature. Following centrifugation at 1,500 rpm for 5 minutes the supernatant was analysed to determine the extent of adsorption of radioactivity to the soil. The supernatants were also analysed by TLC to demonstrate the stability of the test materials under the test conditions

Results and discussion

Results: Batch equilibrium or other method

Transformation products:

yes

Identity of transformation products

No.:

#1

Reference

Reference substance name:

Unnamed

IUPAC name:

Fluroxypyr (acid)

Identifier:

common name

Identity:

Fluroxypyr (acid)

Details on results (Batch equilibrium method):

- Fluroxypyr methyl ester hydrolysed rapidly to fluroxypyr in the presence of soil, with only 37% - 50% of the radioactivity present as ester after 10 minutes (normal phase TLC results). As a result of the instability of the test substance in aqueous-soil slurries it was not possible to calculate an adsorption coefficient
- The results of the screening test for the hydrolysis product fluroxypyr showed adsorption to be between 12.9% and 21.3%. Mean Koc values obtained were in the range 32.6 mL/g to 71.0 mL/g. These results indicate that fluroxypyr would be potentially mobile/very mobile in the soils tested

Any other information on results incl. tables

see details on results

Applicant's summary and conclusion

Conclusions:

No adsorption coefficient could be estimated due to the hydrolytical instability of fluroxypyr methyl ester