The effect of a common pyrethroid insecticide on wetland communities

Abstract

Within the past decade, the use of pyrethroid insecticides has drastically increased. While they are known to be directly toxic to aquatic organisms, based primarily on lab experiments, they are not expected to commonly contaminate aquatic ecosystems given their high binding affinities to organic material. However, increasing evidence suggest that pyrethroids do enter aquatic ecosystems via direct application, drift, and run-off. Despite the risks of these highly toxic chemicals, the full suite of direct and indirect effects of pyrethroid insecticides in wetland communities are not well understood. To address this gap, we examined the direct and indirect consequences of a common pyrethroid, permethrin, in complex aquatic mesocosms consisting of three trophic levels and 13 animal species. We found that permethrin was more lethal than laboratory toxicity assays suggest. Even the lowest concentrations of permethrin led to declines and extinctions in animals species across multiple trophic levels. The only animal species not negatively affected by permethrin were snails (Helisoma trivolvis and Physa acuta) and red-spotted newts (Notophthalmus viridescens). We also found that the direct effects of permethrin on anurans triggered indirect effects that facilitated periphyton abundance and increased the mass of those anurans that survived. As the use of pyrethroid insecticides continue to increase, understanding the direct and indirect effects of these insecticides on aquatic systems is critical to developing generalizations about their overall impact.