Effects of surfactants on the adsorption of pyrethroids to inorganic surfaces

Adsorption experiments were conducted with the pyrethroid insecticide bifenthrin, the anionic surfactant linear alkyl benzene sulfonate (LAS) and concrete, sand and aggregate to characterize the effects of surfactants on the sorption affinity of pyrethroids to these mineral-based surfaces. Surfactants are key components of commercial pyrethroid formulations and in previous field simulations they facilitated the transport of pyrethroids from urban hard surfaces. In the absence of LAS, adsorption capacities of solids were in the following order sand = aggregate > concrete. Sorption of bifenthrin to concrete and aggregate in the presence of LAS at concentrations above, below and at critical micelle concentration (CMC) was studied. With increasing LAS concentrations adsorption affinities for the solids tested decreased, indicating that the aqueous phase activity of bifenthrin was lowered in the presence of surfactant. Adsorption parameter values for concrete were further used for modeling wash-off of bifenthrin from concrete surfaces and the predicted profile was compared with measured wash-off during previous field studies. This work could be of practical interest in devising mitigation and management practices that protect surface waters from water quality degradation caused by pyrethroid use.