Landscape risk analysis for pesticides applied to rice paddies

The use of geographical information system (GIS) datasets in combination with mathematical modeling has been proven a powerful tool for modeling refinement at higher tier assessment in all crop situations. This study constitutes the first attempt to predict pesticide exposure in surface-water and groundwater systems of a rice watershed using a combination of GIS and modeling. A rice-cultivated watershed in the region of Lombardy, province of Pavia, Italy was selected. The community of Tromello is bypassed by the river Terdoppio, which along with drainage canals and streams creates a rice watershed of 467 ha, comprising 201 paddies. The watershed was conceptualized using a combination of the rice water quality (RICEWQ 1.6.4v) and river water quality (RIVWQ 2.02) models. Spatial GIS data (land use, soil properties and hydrology), on-site scouting and personal interviews with the farmers were used for modeling parameterization. Application of RICEWQ in each of the paddies provided groundwater predicted environmental concentrations for the herbicides propanil and molinate. Groundwater predicted concentrations did not exceed 0.1 mu g/L in any of the propanil-treated paddies, unlike molinate, whose predicted concentrations exceeded 0.1 mu g/L in 7 of the 31 molinate-treated paddies. Pesticide mass and water releases from paddies were used as inputs for canals, streams and the river, and the fate of propanil and molinate was simulated with RIVWQ. Comparison of the predicted concentrations of molinate and propanil for the year 1999 at the most downstream point of the simulated segment of the river Terdoppio, with measured values obtained from approximately the same point of the river showed a relatively good agreement. These results indicate that the combination of GIS with validated models can be a useful option for higher tier exposure assessment and modeling refinement in rice-paddy areas