ethametsulfuron-methyl (ISO); methyl 2-[(4-ethoxy-6-methylamino-1,3,5-triazin-2-yl)carbamoylsulfamoyl]benzoate

Toxicity to terrestrial plants

Administrative data

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1986

Report date:

1986

Reference 2

Reference Type:

other company data

Title:

Unnamed

Year:

1987

Report date:

1987

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

other: Pesticide Assessment Guidelines, Subdivision O, Residue Chemistry, 171-2: Nature of Residue in Plants, US EPA 540/9-82-023

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: U. S. EPA Pesticide Assessment Guidelines, Subdivision O, 171-4

Deviations:

no

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Reference substance 002

Cas Number:

97780-06-8

Test material form:

solid

Details on test material:

Purity: 85-99%

Specific details on test material used for the study:

[phenyl(U)-14C]-test substance (specific activity: 39.9 µCi/mg; radiochemical purity: >96%)
[triazine(U)-14C]-test substance(specific activity: 49.6 µCi/mg; radiochemical purity: >95%)
[triazine(U)-13C/14C]-test substance (specific activity: 29.8 µCi/mg; radiochemical purity: >95%)

Sampling and analysis

Analytical monitoring:

no

Test substrate

Vehicle:

yes

Test organisms

Species:

Brassica napus

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Canola
- Variety: Westar

Study design

Test type:

other: Metabolism

Study type:

other: Green house study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

31 d

Test conditions

Test temperature:

27-30°C

pH:

6.5

Nominal and measured concentrations:

application rate: 30, 100 g a.i./ha

Reference substance (positive control):

no

Results and discussion

Effect concentrations

Effect concentrations 1

Key result

Species:

Brassica napus

Duration:

31 d

Remarks on result:

other: The major metabolite recovered in the aqueous fraction of the extracts of the intermediate samples is methyl 2-[[[[(4-hydroxy-6-methylamino-amino-1,3,5-triazin-2-yl)]carbonyl]amino]sulfonyl]benzoate, present at 0.004-0.008 ppm when treated at 30 g a.i./ha

Remarks:

Metabolite was present at 0.004-0.008 ppm when treated at 30 g a.i./ha

Effect concentrations 2

Key result

Species:

Brassica napus

Duration:

31 d

Remarks on result:

other: Total radioactive residues in the mature seed were 0.008-0.012 ppm from plants treated at 30 g a.i./ha

Effect concentrations 3

Key result

Species:

Brassica napus

Duration:

31 d

Remarks on result:

other: Total radioactive residues in the mature seed were 0.010-0.020 ppm from plants treated at 100 g a.i./ha

Applicant's summary and conclusion

Conclusions:

The major metabolite recovered in the aqueous fraction of the extracts of the intermediate samples is methyl 2-[[[[(4-hydroxy-6-methylamino-amino-1,3,5-triazin-2-yl)]carbonyl]amino]sulfonyl]benzoate.

A second radiolabeled metabolite isolated from the excised canola seedlings has been tentatively identified as methyl 2-[[[[4-amino-6-hydroxy-1,3,5-triazin-2-yl]-amino]carbonyl]amino]sulfonyl]benzoate

Executive summary:

The test substance is an experimental oil seed rape herbicide for post-emergent control of grasses and broadleaf weeds. The study was conducted according to U.S. EPA Guidelines, Subdivision O, 171-2. This study investigates the metabolic fate of the test substance in greenhouse grown Westar variety canola treated at the 2- to 3-leaf growth stage with the current recommended maximum application rate of 30 g a.i./ha. Additional plants were treated at an exaggerated use rate of 100 g a.i./ha to generate higher levels of metabolites for isolation and identification. Both phenyl- and triazine-labeled test substance were examined. The results for both labels were similar:

Overall levels of radioactivity in the plants dropped rapidly from an initial level of ca. 1 ppm immediately after treatment to 0.013-0.020 ppm (calculated as test substance) 31 days after treatment. Total radioactivity (test substance equivalents) in the seed from mature plants treated at 30 g a.i./ha ranged from 0.008-0.012 ppm.

Test substance levels decreased from an initial concentration of ca. 1 ppm to 0.002-0.007 ppm in plants analysed 31 days after treatment; no test substance (<0.0005 ppm) was detected in the mature seed.

The initial metabolite has been tentatively identified as methyl 2-[[[[(4-hydroxy-6-methylamino-amino-1,3,5-triazin-2-yl)]carbonyl]amino]sulfonyl]benzoate; it is recovered in the aqueous fraction of the extracts of the intermediate plant samples and is the major metabolite 31 days after application.

The terminal test substance metabolites in the mature seed were also in the aqueous fractions of the extract but were more polar than methyl 2-[[[[(4-hydroxy-6-methylamino-amino-1,3,5-triazin-2-yl)]carbonyl]amino]sulfonyl]benzoate.

In order to provide a more complete picture of the decline of radiolabelled test substance and its degradates in greenhouse-grown canola treated with radiolabelled test substance at 30 and 100 g a.i./ha, several samples have been analysed in addition to those reported above. Plant samples removed 60 days after treatment and two additional seed samples have been analysed. Also, the metabolism of [triazine(U)-13C/14C]test substance has been investigated in excised canola seedlings at the 4-leaf growth stage to generate larger quantities of metabolites for isolation and identification. Total radioactive residues in the foliage of plants treated at 30 g a.i./ha declined rapidly from ca. 1 ppm immediately after treatment to 0.007-0.009 ppm 60 days after treatment. Corresponding test substance levels dropped from ca. 1 ppm to <0.0005 ppm over the same period. The identity of the major initial metabolite in canola foliage, tentatively identified by co-chromatography above, has been confirmed using mass spectrometry as methyl 2-[[[[(4-hydroxy-6-methylamino-amino-1,3,5-triazin-2-yl)]carbonyl]amino]sulfonyl]benzoate. The compound was isolated from excised canola seedlings incubated in a 4 ppm solution of [triazine(U)-13C/14C]test substance. A second radiolabelled metabolite isolated from the excised canola seedlings has been tentatively identified as methyl 2-[[[[4-amino-6-hydroxy-1,3,5-triazin-2-yl]-amino]carbonyl]amino]sulfonyl]benzoate based on mass spectral evidence. Total radioactive residues in the mature seed were 0.008-0.012 ppm from plants treated at 30 g/ha and 0.010-0.020 ppm from plants treated at 100 g/ha, based on combustion data; the extracted radiolabelled seed residue was highly polar as judged by its behaviour when subjected to reverse phase liquid chromatography and did not appear to be subject to hydrolysis catalysed by ß-glucosidase.