| Summary: | Concerns over the adverse effects of pesticides on human health and the environment have led to the development of stricter pesticide regulations and the outright banning of many pesticides in the U.S. Bifenthrin and fipronil are important pesticides used in the nursery industry for the control of imported fire ants (Solenopsis invicta Buren, S. richteri Forel, and their hybrids) to meet the requirements of the Imported Fire Ant Quarantine. Nurseries typically use highly-organic media ("soilless" media) and little is known about the fate of these pesticides when used with these media.
Our research measured the influence of irrigation frequency and time on the degradation of bifenthrin and fipronil in a nursery medium composed of 90% pine bark and 10% mason sand. Media samples and media leachate samples were collected over a period of 180 days. Levels of bifenthrin, fipronil, and fipronil metabolites (MB45950, MB46136, MB46513) were measured using gas chromatography with electron capture detection (GC/ECD) and gas chromatography secondary ion mass spectrometry (GCMS/SIMS).
Bifenthrin levels in the nursery potting media initially dropped and then remained constant throughout the study. Fipronil levels in nursery potting media decreased over time. Levels of the fipronil metabolite MB45950 in potting media fluctuated over time, while the levels of this metabolite increased over time in media
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