sodium 2-{N-[(3,5-difluorophenyl)carbamoyl]ethanehydrazonoyl}nicotinate

Biodegradation in soil

Description of key information

The test substance (diflufenzopyr) degraded with a moderate rate under aerobic conditions with a half-life of about 18 days. The test substance degraded to a number of products. Metabolites M1 (8-Methyl-5-hydroxy-pyrido(2,3 d)-pyridazinone), M9 (8-Methylpyrido(2,3-d)pyridazine-2,5(1H,6H)-dione) and CO2 were the only degradation products found in excess of 10% TAR (total applied radiation) during the course of the study. 

Key value for chemical safety assessment

Half-life in soil:

18 d

at the temperature of:

20 °C

Additional information

Key study (BASF 2001):

An aerobic soil metabolism study of 14C-labelled test substance (diflufenzopyr) (phenyl and pyridine labels) was conducted at 20 ± 1° C in accordance with US EPA Guideline 162-1 Aerobic Soil Metabolism SETAC Guideline Procedure for Assessing the Environmental Fate and Ecotoxicity of Pesticides, March 1995.

The study duration was 312 days for phenyl label and 328 days for pyridine label. The soil used in this study was characterized as Sandy Loam. For phenyl label, samples were taken at time 0, 7, 14, 30, 64, 97, 122, 215 and 312 days after treatment (DAT) for analysis. For pyridine label, samples were taken at time 0, 6, 14, 34, 69, 90, 132, 196, 273 and 328 days after treatment for analysis.

The test substance degraded with an aerobic half-life of approximately 18 days The average material balance for phenyl label experiment was 96.19% TAR and the average material balance for pyridine label experiment was 100.77% TAR. About 30.13% TAR and 45.07% TAR were found as 14CO2 (cumulative) for the phenyl label and pyridine label experiments respectively at the end of the study.

The test substance was the largest radioactive residue at every sampling interval. The degradation products PH1, PH2, M4, PH3, M2, PH4, M23, PH5 and M5 were minor. PH2, M4 and M5 were the only degradation products that exceeded 2% TAR during the study duration. The maximum amounts of the degradation products PH2, M4 and M5 found during the study period were 4.02% TAR, 5.82% TAR and 3.89% TAR respectively and all declined over time. Metabolites M1 (8-Methyl-5-hydroxy-pyrido(2,3 d)-pyridazinone), M9 (8-Methylpyrido(2,3-d)pyridazine-2,5(1H,6H)-dione) and CO2 were the only degradation products found in excess of 10% TAR during the course of the study.

Metabolites found in excess of 2% TAR were positively identified by a combination of HPLC cochromatography and Mass Spectrometry techniques.

Supporting study (Sandoz, 1996):

The study of aerobic soil metabolism of 14C-Pyridinyl-labelled test substance (difluenzopyr sodium salt) and 14C-Phenyl-labelled test substance (difluenzopyr sodium salt) were conducted in a midwestern loam soil at 23° ± 1° C in darkness using the maximum application rate (0.2 lb, a.e./acre). The study was conducted to satisfy 40 CFR 158 registration requirements as described in EPA Pesticide Assessment Guidelines, Subdivision N, Environmental Fate: Section 162-1 (October, 1982), FIFRA Accelerated Registration Phase 3 Technical Guidance (USEPA, 1989), and two EPA Pesticide Reregistration Rejection Rate Analysis reports (1993 and 1995). The half-lives of test test substance (difluenzopyr), applied as 14C-Pyridinyl-labelled test substance (difluenzopyr sodium salt) and 14C-Phenyl-labelled test substance (difluenzopyr sodium salt), were determined to be 10.1 and 8.6 days, respectively, using first order degradation kinetics. The average material balance of 14C-pyridinyl system and 14C-phenyl system was 93.3% and 98.0%, respectively. The major metabolites (>=10% of the applied) of 14C-pyridinyl-labelled test substance (difluenzopyr sodium salt) treated aerobic soil were CO2, M5 (carbamoyl phthalazinone), and M9 (2-keto phthalazinone). Ml (phthalazinone) was identified as a siginif icant, yet minor metabolite of 14C-pyridinyl-labelled test substance (difluenzopyr sodium salt) treated soil. CO2 and M5 were the major metabolites in 14C-phenyl- Diflufenzopyr sodium salt treated soil. Minor amounts (1-2% of the applied) of two to three other degradation products were also detected in soil treated with 14C-phenyl-labelled test substance (difluenzopyr sodium salt). The nature of the aerobic soil metabolism is now well understood, Ml, M5, M9, and CO2 are the only metabolites significantly formed in soil. Since standard of M5 easily degrades into Ml in pure organic solvent(s) with time, all residue work will convert parent as a non-radiolabeled residue method and M5 to Ml for tolerance study.