Adsorption, transport and degradation of fipronil termiticide in three Hawaii soils

Background: The behavior of the termiticide fipronil in soils was studied to assess its potential to contaminate ground and surface water. This study characterizes (1) adsorption of fipronil in three different soils, (2) transport of fipronil through leaching and runoff under simulated rainfall in these soils and (3) degradation of fipronil to fipronil sulfide and fipronil sulfone in these soils. Results: The adsorption experiments showed a Freundlich isotherm for fipronil with K _oc equal to 1184 L kg ^-1. In the leaching experiments, the concentration of fipronil and its metabolites in leachate and runoff decreased asymptotically with time. The concentration of fipronil in the leachate from the three soils correlated inversely with soil organic carbon content. The degradation experiment showed that the half-life of fipronil in the soils ranged from 28 to 34 days when soil moisture content was 75% of field capacities, and that 10.7-23.5% of the degraded fipronil was transformed into the two metabolites (fipronil sulfide and fipronil sulfone). Conclusion: Fipronil showed large losses through leaching but small losses via runoff owing to low volumes of runoff water generated and/or negligible particle-facilitated transport of fipronil. The half-life values of fipronil in all three soils were similar.