Effects of an herbicide and insecticide mixture in aquatic mesocosms

The influence of a herbicide (atrazine, 0 or 50 ug per litre) on the bioavailability and effects of the pyrethroid insecticide esfenvalerate (0-1.71 ug per litre) was studied in 0.1-ha mesocosms. The mesocosms were stocked with bluegill (Lepomis macrochirus). Macrophyte communities in the mesocosms were initially dominated by Naja sp. (20 per cent) and Chara sp. (80 per cent). Atrazine altered the species composition and density of the macrophyte community and nearly eliminated the standing crop of Naja sp. It did not alter plant biomass, total system metabolism, or the bioavailability of the insecticide to zooplankton or fish. Synergism did not occur between the herbicide and insecticide because of the functional redundancy of the macrophyte community and the rapid aqueous dissipation rate of the insecticide. There are 43 references.