Persistence and fate of tebufenozide (RH-5992) insecticide in terrestrial microcosms of a forest environment following spray application of two mimic® formulations
Title:
Persistence and fate of tebufenozide (RH-5992) insecticide in terrestrial microcosms of a forest environment following spray application of two mimic® formulations
Author:
Sundaram, K. M. S.
Appeared in:
Journal of environmental science and health. Part B, Pesticides, food contaminants, and agricultural wastes
Paging:
Volume 30 (1995) nr. 3 pages 321-358
Year:
1995
Contents:
A terrestrial microcosm study was conducted to study the persistence and metabolic fate of tebufenozide in clay loam soil, forest litter, spruce needles and shoots after spray application of aqueous flowable (AF) and emulsion suspension (ES) formulation of tebufenozide, MIMIC®, at 35, 70 and 140 g active ingredient (A.l.)/ha. Soil, litter, spruce needles and shoots were collected at intervals of time up to 460 d post-spray and analyzed by high-performance liquid chromatography (HPLC) for the intact chemical. Droplet density, size spectra (DN.5 and Dv.5) and initial deposit data were gathered using collection units consisting of Kromekote® cards, glass fibre filters and glass plates. Droplet density, size spectra and deposition varied according to the formulation type sprayed. Deposit levels increased with dosage and the ES formulation usually gave higher deposition on the collectors compared to the AF formulation. Initial deposits (μg/g, fresh weight) were higher (ca. 150 %) on the spruce needles than on the shoots and varied according to the dosage and type of formulation. Usually, the ES formulation deposited well on all the matrices studied. A significant loss of tebufenozide (ca. 40 to 50 %) from the needles was observed within the first 45 d after application, probably due to various physical and biological processes. Loss from the shoots during the same period was about 70 %. The higher loss in shoots was partly due to growth dilution. The remaining tebufenozide was found to dissipate gradually and persisted until snowfall. Tebufenozide residues, depending on the dosage and formulation, overwintered and persisted at detectable levels up to the end of summer in 1994. Similar trends in the dissipation of tebufenozide were also found in the soil and litter. However, tebufenozide dissipated slowly in the litter and persisted longer compared to the soil, indicating that the litter could act as a sink for the chemical. Tebufenozide showed a low degradation rate in all the matrices studied. The approximate range of DT50 values in soil, litter, spruce needles and shoots, irrespective of the type of formulation and dosage rate sprayed, were 32 to 45, 52 to 87, 30 to 49 and 15 to 22 d, respectively. Besides the A.I., only small amounts of different intact metabolites were found in the 62 d post-spray samples, indicating that other mechanisms were involved in the metabolic conversion of the molecule. Further metabolic studies using C-14 labelled tebufenozide, undercontrolled laboratory microcosms with accompanying mass balance, are necessary to understand its degradative pathways in forestry matrices.
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