pymetrozine (ISO); (E)-4,5-dihydro-6-methyl-4-(3-pyridylmethyleneamino)-1,2,4-triazin-3(2H)-one

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

26 Feb 2000 to 28 Aug 2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

[14C]-labelled at position 2 of pyridine ring

DT50:

18.8 d

Test condition:

25 °C; ~ 7.8E-03 W/cm

DT50:

4.9 d

Test condition:

25 °C; ~ 7.8E-03 W/cm; Dissolved phase

Degradation of the test substance on viable soil under photolytic conditions did not follow first-order kinetics. The test substance degraded with a half life in the dissolved phase of 4.9 days and a rate constant of 0.14218 per day. The DT50 for the irradiated incubation was approximately 18.8 days. 14C-Pyridinyl-labelled test substance on viable soil under non-irradiated conditions was not first order kinetics either. The test substance degraded with a half life in the dissolved phase of 7.2 days and a rate constant of 0.09613 per day. The DT50 for the nonirradiated incubation was observed at approximately 18.2 days.

 

Photolytic degradation of the test substance led to the formation of 11 degradates for the irradiated incubation as opposed to 14 degradates for the non-irradiated incubation. These degradates were qualitatively and quantitatively very similar. Each degradate accounted for less than an average of 9.51 % of total dose for the irradiated incubation and 8.76% of total dose for the non-irradiated incubation. Volatiles accounted for up to an average of 8.86% of the total dose for the irradiated incubations and 8.90% of the total dose for the non-irradiated incubations. Precipitation of the KOH fractions indicated CO2 was the major volatile component. Evidence from this study indicates that photolysis is a minor contributing factor to the degradation of the test substance on soil. The test substance and its degradates bind to the soil quickly and are not released under mild or mild/basic extractions. The major bound residues are only released with 0.5 M sodium hydroxide extraction. Humin/Humic/Fulvic characterization indicated the residues were bound to the fulvic soil fraction. Only three degradates, M3, M10, and M1, were co-chromatographed with reference standards. Only the test substance and two degradates, M1 and M3, were present in large enough quantity to be confirmed by mass spectral analysis.

Validity criteria fulfilled:

not specified

Conclusions:

The test substance degraded with a half life in the dissolved phase of 4.9 days and a rate constant of 0.14218 per day; the DT50 for the irradiated incubation was 18.8 days. Under dark conditions, the test substance degraded with a half life in the dissolved phase of 7.2 days and a rate constant of 0.09613 per day; the DT50 was 18.2 days.

Executive summary:

A soil photolysis study was conducted with 14C-Pyridinyl-labelled test substance, in accordance with US EPA Environmental Fate Data Requirement 40 CFR Section 158 (Subdivision N, Series 161-3) and in compliance with GLP criteria. The photodegradation rate of the test substance was studied under artificial light at an average dose rate of 0.093 ppm which compares to the maximum recommended field use rate. The irradiated samples were irradiated with a xenon arc lamp for 12 hours per day at an average daily intensity of approximately 7.8E-03 W/cm . Samples were incubated up to 30 days as either irradiated or non-irradiated (dark control) samples. All samples were maintained at approximately 25°C. Harvest of samples was frequent enough to permit an accurate determination of the degradation half life and to monitor the formation and decline of degradates.

Degradation of the test substance on viable soil under photolytic conditions did not follow first-order kinetics. The test substance degraded with a half life in the dissolved phase of 4.9 days and a rate constant of 0.14218 per day. The DT50 for the irradiated incubation was approximately 18.8 days. 14C-Pyridinyl-labelled test substance on viable soil under non-irradiated conditions was not first order kinetics either. The test substance degraded with a half life in the dissolved phase of 7.2 days and a rate constant of 0.09613 per day. The DT50 for the nonirradiated incubation was observed at approximately 18.2 days.

 

Photolytic degradation of the test substance led to the formation of 11 degradates for the irradiated incubation as opposed to 14 degradates for the non-irradiated incubation. These degradates were qualitatively and quantitatively very similar. Each degradate accounted for less than an average of 9.51 % of total dose for the irradiated incubation and 8.76% of total dose for the non-irradiated incubation. Volatiles accounted for up to an average of 8.86% of the total dose for the irradiated incubations and 8.90% of the total dose for the non-irradiated incubations. Precipitation of the KOH fractions indicated CO2 was the major volatile component. Evidence from this study indicates that photolysis is a minor contributing factor to the degradation of the test substance on soil. The test substance and its degradates bind to the soil quickly and are not released under mild or mild/basic extractions. The major bound residues are only released with 0.5 M sodium hydroxide extraction. Humin/Humic/Fulvic characterization indicated the residues were bound to the fulvic soil fraction. Only three degradates, M3, M10, and M1, were co-chromatographed with reference standards. Only the test substance and two degradates, M1 and M3, were present in large enough quantity to be confirmed by mass spectral analysis.

Description of key information

The DT50 for the irradiated incubation was 18.8 days; EPA Subdivision N, Series 161-3 - Sparrow 2000.

Information on this endpoint is not part of Annex VIII data requirements; all included studies are marked as supporting information and considered in the CSA.