Chemistry and fate of fenvalerate and esfenvalerate.

Fenvalerate is listed under Class IV of the U.S. Food and Drug Administration (USFDA) Surveillance Index Classification, indicating a low hazard potential to humans from both exposure and toxicological standpoints; thus, minimal monitoring is required (Reed 1981; Eisler 1992). To date, monitoring efforts have been of limited value in evaluating concentrations of fenvalerate and its subsequent risk to the environment. Few regulations currently exist for protection of sensitive natural resources against fenvalerate or esfenvalerate, although current application rates may be lethal to many nontarget species, including bees, fish, and aquatic invertebrates. Additional monitoring is recommended to measure residues in the environment and evaluate risks associated with use. It is clear that both fenvalerate and esfenvalerate are considerably less harmful to the environment and most nontarget organisms than most other insecticides. They are considerably less persistent and more selective in their toxicity, except for their high degree of toxicity to fish and aquatic invertebrates. However, they are moderately persistent in soils and, because of low water solubilities, high octanol-water partition coefficients (Kow), and moderate persistence, both fenvalerate and esfenvalerate have been identified as having the potential to accumulate in aquatic sediments and biota (Nowell et al. 1999). Numerous studies of fenvalerate dynamics in soils indicate that it is relatively immobile and readily degraded. In almost all cases, the degradation products formed are less toxic than the parent insecticide. However, some degradation products from fenvalerate may demonstrate elevated toxicity, and more research into and increased monitoring of abiotic degradation may be warranted. Results from environmental monitoring are minimal at best and do not adequately support research done in the laboratory. These results are critical for accurately determining the risk these insecticides pose to the environment. The pyrethroids are poised to fill the gap left in the insecticide market with the impending suspension of many of the organophosphates and possibly at least some carbamates. One agent, chlorpyrifos, has already been heavily restricted by the U.S. Environmental Protection Agency (USEPA), and one manufacturer has ceased production. The environmental risk posed by both fenvalerate and esfenvalerate can change significantly with increased application, and current information is not sufficient to adequately assess the risk that a dramatic rise in use would pose. Future efforts should focus on increased environmental monitoring and research on esfenvalerate fate with increased and repeated application. Pyrethroids, including fenvalerate and esfenvalerate, have also recently been linked to endocrine disruption (Garey and Wolff 1998; Go et al. 1999). Endocrine disruption is an emerging field, and more research is essential in documenting and managing these types of effects. Research into the bioavailability and dynamics of esfenvalerate at the sediment-water interface is also of key importance. Current information indicates that resuspension or desorption from soils should be minimal, but this is not equivalent to the fraction of sediment-sorbed esfenvalerate that may be bioavailable to sensitive aquatic species. In terms of risk, fenvalerate and esfenvalerate are significant improvements over many of their predecessors, but it is clear that more information is needed to fully support this conclusion.