Soil erosion and transport of Imidacloprid and Clothianidin in the upland field under simulated rainfall condition.

Surface runoff has been recognized as an important medium of pesticides transport to surface water and groundwater causing critical risk to the aquatic ecosystem. Although total pesticide transport in surface runoff in most cases reported being below 1% of applied mass, much larger losses may occur in extreme cases. In this study, surface runoff potential of Imidacloprid and Clothianidin was investigated in an upland field with 5% slope under two simulated rainfall experiments of 70 mm/h intensity. Additionally, the downward movement of the pesticides was determined in soil (n = 87) taken at several depths on different time scales. The result showed that the second rainfall experiment caused more surface runoff than first rainfall experiment, and accounted 30.0 mm and 21.2 mm of applied rainfall, respectively. The cumulative surface runoff developed during first and second rainfall experiments was equal to 30% and 44% of the applied rainfall, respectively. The sediment transport in runoff was relatively higher in second rainfall than first rainfall, and was mostly stable after 30 min of rainfall. The chemical masses of Imidacloprid and Clothianidin were primarily transported in runoff sediments than runoff water and accounted for 10.8% and 7.93% of the applied mass, respectively. The transport of Imidacloprid both in runoff water and sediment was 1-2 times greater than that of Clothianidin. The concentrations of both pesticides were measured highest in the second fraction of runoff (10 min) collected during the first experiment. In soil, the transport of both pesticides prior to rainfall experiment was 1-2 times greater than post-rainfall experiments. The concentration of these pesticides decreased continuously with the time in the upper layer of soil; while a gradual increase of the pesticides mass was observed in the second soil layer. The cumulative mass transport of both pesticides was directly proportional to the cumulative runoff depth.