This study investigated the environmental fate of nursery-box-applied insecticides, fipronil and imidacloprid and metabolites of fipronil, in rice paddy through field and lysimeter monitoring as well as through model simulations. The at-sowing (AS) application of controlled-release formulation greatly reduced the imidacloprid concentrations in paddy water and soil as compared with the before transplanting (BT) application of conventional-release formulations. The influence of the application methods on concentrations of fipronil and fipronil sulfone in the paddy environment was not obvious. The AS application slightly reduced those concentrations in rice paddy environments. Fipronil sulfone persisted at appreciable concentrations in paddy water and surface soil. Photochemical degradation of fipronil along with production of its metabolites in paddy water proceeded within one to two days and similar behavior was observed for imidacloprid. A micro-paddy lysimeter (MPL) was able to reproduce the concentrations of the insecticide and its metabolite in the actual rice paddy by imposing appropriate water balance and environmental conditions. A newly developed numerical model was validated for simulating concentrations of nursery-box-applied insecticides and their metabolites in rice paddies with field monitoring data using key parameters determined from laboratory experiments. MPL and PCPF-M were shown to be alternative tools to assist field monitoring and to conduct eco-toxicological risk assessments of nursery-box applied pesticide and its metabolites in rice paddy.

Monitoring and modeling the environmental fate of nursery-box-applied insecticides and their metabolites in a rice paddy

248th National Meeting (2014)

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