SORPTION OF FIPRONIL AND ITS METABOLITES ON SOILS FROM SOUTH AUSTRALIA

Abstract

This paper reports on the sorption of fipronil [(±)-5-amino-1-(2,6-dichloro-α,α,α-trifluoro-p-tolyl)-4-trifluoromethyl-sulfinylpyrazole-3-carbonitrile] and its two main metabolites, desulfynil and sulfide derivatives on a range of soils from South Australia. The Freundlich sorption coefficient (K_f) values for fipronil on the soils ranged from 1.94 to 4.84 using a 5% acetonitrile/water mixture as the soil solution. Its two metabolites had a higher sorption affinity for soils, with K_f values ranging from 11.09 to 23.49 for the sulfide derivative and from 4.70 to 11.77 for the desulfynil derivative. Their sorption coefficients were found to be better related to the soil organic carbon than clay content.

The presence of cosolvents in soil solutions had a significant influence on the sorption of fipronil. The Freundlich sorption coefficients showed a log linear relationship with the fractions of both acetonitrile and methanol in solutions. The sorption coefficient of fipronil on Turretfield soil in the aqueous solution was estimated to be from 13.80 to 19.19. Methanol had less effect on the sorption of fipronil than acetonitrile. The K_d values for fipronil on the eight soils using a 5% methanol/water mixture were from 5.34 to 13.85, which reflect more closely the sorption in the aqueous solution. The average K_oc value for fipronil on the eight South Australian soils was calculated to be 825 ± 214.

Keywords:

• Fipronil
• Metabolites
• Termiticide
• Sorption
• Cosolvent
• Soil

ACKNOWLEDGMENTS

The authors would like to thank Aventis Australia for the financial support for the work. Thanks go to Ms Julie Smith for the help in GC instrumentation. The authors also wish to thank internal reviewers, Drs Z. Chen, E. Smith and M. Mallavarapu in CSIRO for their useful comments.