Factors Influencing the Adsorption of Fipronil on Soils

Abstract

A comparative study of the adsorption of fipronil, a phenylpyrazole acridicide, on two Sahelian soils (Saguia and Banizoumbou in Niger) and a Mediterranean soil (Montpellier) has shown that this phenomenon is dependent on the level of organic matter (OM): the adsorption coefficients (K f) were, respectively, 4.3 (Saguia, 0.1% OM), 7.3 (Banizoumbou, 0.3% OM), and 45.5 (Montpellier, 6.5% OM). The partial destruction of the OM of the Montpellier soil sample by oxidation with hydrogen peroxide confirmed the fundamental role of this component: the values of log K OM were practically constant (2.8−2.9) for OM levels ranging from 6.5 to 1.1%. Following the Giles classification, the adsorption isotherms of the two Sahelian soils seemed to be type S, characteristic of soils with low OM content. For natural Montpellier soil, the shape of the isotherm began close to type S but changed rapidly to type C. The temperature and the methanol cosolvent level were factors influencing the adsorption. For the Banizoumbou soil, increasing the temperature (from 22 to 35 °C) caused an increase in K f (from 7.3 to 9.3) and modification of the mechanism of the fipronil−soil interaction. K f decreased exponentially as the methanol fraction of the binary mixture increased. The quantitative study of the adsorption of fipronil on the soil demonstrated the influence of the soil/water ratio: K f increased proportionately as the soil/water ratio decreased. Keywords: Fipronil; adsorption; soil; temperature; cosolvent; soil/water ratio

Concentration-Dependent Degradation of Three Termiticides in Soil Under Laboratory Conditions and Their Bioavailability to Eastern Subterranean Termites (Isoptera: Rhinotermitidae)

“…The result is that over a certain range of concentration, more Þpronil molecules will be present in the aqueous phase. In the case of Þpronil it was also demonstrated that there was a signiÞcant decrease in adsorption coefÞcient as the soil organic matter and clay content decreased (Bobe et al 1997). This explains more bioavailability of the Þpronil in soils with lower organic matter because of the small amount of organic phase available for Þpronil molecules.…”

“…Few data are available on the degradation of Þpronil (Bobe et al 1997) and even less so for the rates applied as termiticides. When applied at Þeld application rates (8 g [AI]/ha), 75% of the Þpronil degraded within 3 d, and the four metabolites were detected (Bobe et al 1998).…”

“…At low rates in soil, it has low soil afÞnity, due to strong competition from the aqueous phase. Adsorption increases as concentration increases (Bobe et al 1997). However, at termiticide application rates of 0.06 Ð 0.125%, the adsorption process exhibits a reverse phenomenon, whereby there is a decrease in adsorption coefÞcient with an increase in concentration (Kamble and Saran 2005).…”

“…This explains more bioavailability of the Þpronil in soils with lower organic matter because of the small amount of organic phase available for Þpronil molecules. Lower water solubility of Þpronil offers a lower leaching potential as demonstrated by Bobe et al (1997) and a higher persistence, the latter being more important for a durable termiticide treatment.…”

Environmental fate and toxicology of fipronil

“…6) The parent insecticide and its degradation products each possesses unique dissipation kinetics which are presented below.…”