Effects of an herbicide and insecticide mixture in aquatic mesocosms

Abstract

The ecological risk of pesticides is estimated from data generated on single chemicals. However, agricultural chemicals frequently occur in the environment as herbicide and insecticide mixtures. This study investigated the effects of an herbicide and insecticide mixture in 0.1-ha mesocosms to determine if the herbicide would alter the bioavailability of the insecticide to fish and zooplankton. Mesocosms were treated with either 0 or 50 μg/L atrazine (six mesocosms each) to create two levels of herbicide classification. A series of six concentrations of the pyrethroid insecticide esfenvalerate (0–1.71 μg/L) was applied on two dates within each herbicide level (0 or 50 μg/L). Atrazine altered species composition of macrophytes but did not alter plant biomass, total system metabolism, or the bioavailability of the insecticide to zooplankton or fish. Potential ecological synergisms (i.e., increased effects of the insecticide due to the herbicide) did not occur because of the functional redundancy of the macrophyte community and the rapid aqueous dissipation rate of the pyrethroid insecticide.