diethyl 1-(2,4-dichlorophenyl)-5-methyl-4,5-dihydro-1H-pyrazole-3,5-dicarboxylate

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

key study

Study period:

02 Jun 1992 - 12 Dec 1994

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP Guideline study

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-3 (Photodegradation Studies on Soil)

GLP compliance:

yes

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

other: Radioactivity was determined by LSC

Light source:

other: polychromatic light

Light spectrum: wavelength in nm:

290 - 800

Details on light source:

- Other: The spectrum of sunlight was simulated by an ORIGINAL HANAU SUNTEST
photoreactor (Hanau Quarzlampen GmbH, Hanau, Germany)

The light intensity was determined by a chemical actinometer (uranylsulfate/oxalate) to the 1.37fold value compared to that of 52° North at June and sea level.

Details on test conditions:

TEST SYSTEM
- Application procedure:
- Volume of test solution used/treatment: applied onto twelve 16 cm2 steel plates (17.1 µg active ingredient per plate)
- Method of application: soil samples treated with 17.1 g U-14C-dichlorophenyl-labelled AE F107892 per 16 cm2 at 25°C and approx. 40% mwrc for a total of 17 days taking into account day/night intervals of 12 hours each
- Details of traps for volatile, if any: Mineralisation and formation of volatile components were determined by suitably equipped traps.

MEASUREMENTS:
After 0, 1, 3, 8, 15 and 17 days, duplicate soil samples were extracted and analysed for test substance and transformation products by high performance liquid chromatography (HPLC) with radioanalytical detection techniques. Non-extractable residues were determined by combustion/LSC. In parallel, dark controls were investigated for comparison of profiles with those of irradiated samples.

Duration:

17 d

Temp.:

25 °C

Initial conc. measured:

17.1 other: µg U-14C-dichlorophenyl-labelled AE F107892

DT50:

5.6 d

Transformation products:

yes

Findings:

Recoveries ranged from approx. 84% to 103% of total applied radioactivity with an exception for one irradiation series at the two late sampling intervals (day 15: 74.0 %, day 17: 69.2 %).Further investigations for samples at day 17 by acidification and additional extraction of soil did not result in an increase in the material balance.

The extractable portion of radioactivity declined from 102.0% (irradiation series I) and 100.3% (series II) of applied dose by day 0 to values of 61.6% and 41.1%, respectively, by the end of the study, day 17. The non-extractable residues increased from 0.5% (series I) / 0.4% (series II) by day 0 to 19.0% / 18.9% by day 17. The formation of¹⁴C-carbon dioxide accounted for 3.9% of applied radioactivity at the end of the irradiation period. Other volatile material amounted to 5.2% of applied dose at the same time.

 

Metabolic profile:

The parent compound AE F107892 showed a decline from 96.4% (series I) / 95.3% (series II) of applied dose by day zero to 5.9% / 2.8% by day 17, respectively. The monoester compound mefenpyr-ethyl AE F113225 was observed as a major metabolite at peak values of 27.6% / 27.5% (series I / series II) by day 3. The pyrazole carboxylic acid AE F094270 was found as a minor component at maximum levels of 6.6% of applied radiolabel in the course of the study.

An unknown metabolite (reporting title “M8“) was detected at a peak value of 11.0 % of applied radiolabel (average, day 1) and subjected to extensive structure elucidation by gas chromatography (GC) and mass spectrometry (MS) with and without derivatisation and H-NMR. The efforts resulted in structural proposals proposing that the skeleton of the parent compound was still intact with an additional oxygen atom attached or inserted to it. Further unknown components were detected at <3.5 % of applied radiolabel.

 

The disappearance of AE F107892 was described by a simple first order kinetic approach. The disappearance time for 50 % (DT₅₀) was calculated to 5.6 days under approximation for outdoor conditions.

Description of key information

Phototransformation on soil is not a significant process for the elimination of the substance in the outdoor soil environment.

Key value for chemical safety assessment

Half-life in soil:

5.6 d

Additional information

A soil photolysis study was conducted according to EPA Guideline Subdivision N 161-3 (1995). Soil samples of 16 cm² each treated with 17.1 μg U-14C-dichlorophenyl-labelled parent substance were irridated at 25°C and approx. 40% mwrc for a total of 17 days taking into account day/night intervals of 12 hours each. The amount of test item applied referred to a maximum application rate of 90 g/ha in the field. The soil samples were extracted and analysed for test substance and transformation products by high performance liquid chromatography (HPLC) with radioanalytical detection techniques. Non-extractable residues were determined by combustion/LSC. In parallel, dark controls were investigated for comparison of profiles with those of irradiated samples.

The disappearance of the substance was described by a simple first order kinetic approach. The disappearance time for 50% (DT50) was calculated to 5.6 days under approximation for outdoor conditions.

Photolysis on soil surfaces is of limited contribution to the elimination of the parent compound from the outdoor environment. Phototransformation products observed undergo rapid further degradation as indicated by the significant formation of volatile radioactivity (14CO2). The phototransformation products formed can be assumed to be stabilized by the conditions of the experiment, for example, by sterilisation of soil from intensive irradiation and the use of acidic soil. Phototransformation products contain sub-structures similar to the parent compound (e. g. ester). This implies rapid conversion by other abiotic (i.e. hydrolysis) and microbially induced processes for a field situation. Considering the rapid biotically-induced hydrolysis of the parent compound this precursor is reduced significantly before phototransformation products as observed in the test may be formed under outdoor conditions. A significant extent or, accumulation of phototransformation products of the substance in a natural soil environment is thus highly unlikely.