Pulsed exposure of the macrophyte Lemna minor to herbicides and the mayfly Neocloeon triangulifer to diamide insecticides

Pesticides applied to agricultural land can enter aquatic ecosystems through runoff or leaching during precipitation events. In a lotic system, these events result in a pulse of exposure to biota living in these systems. The concentration of pesticide increases, peaks, and then gradually declines, and this pulsed exposure may occur multiple times over the course of a growing season. The dynamic nature of exposure to pesticides in the environment is not often mimicked in the laboratory testing of the toxicity of pesticides. The present study investigated the potential latent effects of a 24-h pulsed exposure of metolachlor, metribuzin, MCPA (2-methyl-4-chlorophenoxyacetic acid), MCPP (methylchlorophenoxypropionic acid or mecoprop), dicamba, and 2,4-D to the aquatic macrophyte Lemna minor followed by a 5-day recovery period. The relative sensitivity of L. minor to the herbicides were, in this decreasing order: metolachlor > metribuzin >2,4-D > MCPA > MCPP > dicamba. This study also investigated the effects of short-term exposures of the diamide insecticides cyantraniliprole and chlorantraniliprole on the survival of the larvae of the parthenogenetic mayfly Neocloeon triangulifer. The median lethal concentrations (96-h LC50s) for cyantraniliprole and chlorantraniliprole were 8.60 and 2.92 μg/L, respectively.