Fate of the herbicide sulfometuron methyl (Oust®) and effects on invertebrates in drainages of an intensively managed plantation

Abstract

The off-site movement and impacts on water quality and aquatic ecosystems of sulfometuron methyl applied as the herbicide Oust® to catchments in short-rotation plantations in the coastal plain of South Carolina were studied. Sulfometuron methyl was applied at the rate of 0.053 kg active ingredient·ha–1 to 5.4- and 5.9-ha catchments (C5 and C6, respectively). Off-site movement of sulfometuron methyl in drainage ditches was observed between application on 14 March 2001 and 14 June 2001 for the first five flow-producing rain events on C5 and the first four events on C6. The maximum observed concentrations (24 µg·L–1 on C5 and 23 µg·L–1 on C6) occurred during the first storm. Subsequent maximum concentrations for flow-producing storms were 10.0, 5.0, 0.5, and 0.1 µg·L–1 on C5 and 15.1, 6.7, and 0.5 µg·L–1 on C6. Pulsed inputs of sulfometuron methyl to stormflow were ephemeral and the maximum concentration for each storm event lasted 15 min or less. The faunal communities observed in these drainage ditches were dominated by a diversity of invertebrates typical of wetland habitats, such as midges, mosquitoes, water beetles, physid snails, and water fleas. Negative effects of sulfometuron methyl treatment on these communities in treated watersheds were not observed.