BEHAVIOR OF AN ALGINATE-KAOLIN BASED CONTROLLED-RELEASE FORMULATION OF THE HERBICIDE THIOBENCARB IN SIMULATED ECOSYSTEMS

An alginate-kaolin based controlled-release formulation of the herbicide thiobencarb, TCR-1, was prepared. The distribution, bioaccumulation and persistence of thiobencarb from this formulation were compared to those from a commercial granular formulation, 10 G, in flooded paddy soil under controlled conditions and in simulated aquatic systems and rice paddy/fish systems under greenhouse conditions. Persistence of the total residues and thiobencarb parent increased significantly in the soil treated with TCR-1, and at the end of a 49-day incubation 32.5% of the applied herbicide was recovered as the parent from the soil treated with TCR-1, compared to only 15.2% from the soil treated with 10G. Slower release into water and less accumulation in fish tissues were found in the simulated aquatic system treated with TCR-1. A lower concentration was detected in the paddy water in the simulated rice paddy/fish system treated with TCR-1 over the duration of a 66-day greenhouse experiment. Fish and rice plants accumulated less residues from the system treated with TCR-1 than from that with commercial formulation 10G. The overall results indicated that the persistence of thiobencarb in the controlled-release formulation was prolonged in water and soil, and the potential impact on non-target components such as rice plants and fish was concurrently reduced.