The mobility of thiobencarb and fipronil in two flooded rice-growing soils

Abstract

The mobility of the rice pesticides thiobencarb (S-[(4-chlorophenyl) methyl] diethylcarbamothioate) and fipronil ([5-amino-3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]pyrazole) were investigated in the glasshouse under flooded conditions using two Australian rice-growing soils. When using leakage rates of 10 mm day⁻¹, less than 20% of applied thiobencarb and fipronil remained in the water column after 10 days due to rapid transfer to the soil phase. Up to 70% and 65% of the applied thiobencarb and fipronil, respectively, were recovered from the 0–1 cm layer of soils. Only 5–7% of each pesticide was recovered from the 1–2 cm layer, and less than 2% was recovered from each 1 cm layer in the 2–10 cm region of the soils. Analysis of the water leaking from the base of the soil cores showed between 5–10% of the applied thiobencarb and between 10–20% of the applied fipronil leaching from the soil cores. The high levels of pesticide in the effluent was attributed to preferential flow of pesticide-laden water via soil macropores resulting from the wetting and drying process, worm holes and root channels.

Keywords:

• Sorption
• degradation
• diffusion
• leaching
• anaerobic
• flooded

Acknowledgments

The authors would like to thank the Cooperative Research Center for Sustainable Rice Production for providing the funding to undertake the work reported, and the EH Graham Centre for Agricultural Innovation for providing the funding to allow its publication. The authors would also like to thank Jan Skjemstad of Commonwealth Scientific and Industrial Research Organisation (CSIRO) Land and Water for performing char analysis on the soils.

Notes

*Using a 20 g sample.

**Using a 15 mL sample volume.