Pesticide transport modelling in soil for risk assessment of groundwater contamination

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Abstract
The risk of groundwater contamination with pesticides applied to soil surface depends on the soil properties, the agricultural practices, the climatic influences, and on the properties of the pesticides themselves. The EXSOL model was developed for the simulation of the transport and fate of pesticides and organics in soils. The dynamics of mobility, accumulation and degradation can be studied under various soil and climatic conditions. Transient water flow is provided from a simulation model of the field water balance. The percentages of the herbicide 2,4,5‐trichlorophenoxyacetic acid in a luvisol soil after a single application in summer are compared with model calculations using sorption coefficients from laboratory column studies. The calculated percentages lie within the measured range, except for those in the deeper soil layer. The underestimation can be explained with preferential flow in macropores which may have occurred during the heavy rainfall six days after application.