Family farming in the eastern Amazon, and particularly in northeastern Pará, is characterized by the implementation of semi-perennial industrial crops with heavy application of pesticides. This study was carried out with the main objective of evaluating the mobility of pesticides, in particular dimeatoate, in the unsaturated zone of the Cumari creek watershed, in the municipality of Igarapé-Açu (PA). In the area, the aquifer is constituted by inconsolable sand-clay and sand-silt sediments belonging to the Post-Barreiras period. Specifically, the objective was to analyze the potential for contamination of groundwater by pesticides. The objective was also to quantify the geochemical process of sorption, relating it to the physical and chemical characteristics of the unsaturated zone. A mapping of the areas where passion fruit is cultivated was carried out, since a high volume of pesticides is used in this culture, together with a survey of the agricultural pesticides used in the area. Subsequently, the risk of groundwater contamination was assessed using the GUS index (Groundwater Ubiquity Score). This index has as parameters the half-life values of the compound in the soil (DT50) and the coefficient of adsorption to organic matter (Koc). In addition, manual auger drilling was carried out in order to collect sediment samples from the unsaturated zone for laboratory analysis. In the laboratory stage, the granulometry, mineralogy, natural pH and organic matter content of the different levels of the unsaturated zone were determined, aiming at its characterization. This step also included the sorption experiment and the determination of dimethoate. Based on the risk analysis, it was found that dimethoate has the greatest potential to contaminate groundwater, with a GUS index ranging from 2.36 to 3.36. The sorption experiment showed that, in percentage terms, the sorption of dimethoate by sediments in the unsaturated zone ranged from 2.5% to 3.2%. These data confirmed the high potential for groundwater contamination by this substance, which is mainly due to its mobility and low retention. It was also verified that the amount of organic matter and the pH exert a greater influence on the sorption of dimethoate.
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