Diazinon Accumulation and Dissipation in Oryza sativa L. Following Simulated Agricultural Runoff Amendment in Flooded Rice Paddies

Flooded post-harvest rice paddies were examined as systems for reducing diazinon (organophosphate insecticide) concentrations in stormwater runoff. Two paddies were cultivated in Oryza sativa L. and amended with a 3-h simulated stormwater diazinon runoff event. Initial diazinon adsorption peaked at 347 and 571 μg kg (3% mass load reduction) for mean above-ground plant tissue concentrations in each pond, respectively. Subsequent senescence of above-ground tissue showed significant decreases in tissue mass (r=0.985) and adsorbed diazinon mass (90±4% and 82±1%) within 1 month of amendment. There were no corollary increases in water column diazinon concentrations. Furthermore, control O. sativa tissue placed within the treatment ponds had below-detectable levels of diazinon throughout the decomposition phase, suggesting a lack of within pond transference of dissipated diazinon. This study shows the relative effectiveness of diazinon adsorption by post-harvest rice plants and a potential mitigation strategy of senescence and pesticide degradation for contaminated tailwater.