Abstract

Pesticide mobility in soils depends on physico-chemical characteristics, environment, edaphic conditions, applications and crop management. Pesticide movement via leaching through the soil profile and surface runoff are primary processes, defined by the sorption constant (kd and koc). High Koc values means low mobility in soil, low probability to impact aquatic communities. To reduce impacts it is important to preserve the riparian zone. A study was conducted in the Tijeral river catchment (37°43'21''S; 72°35'50''W, Chile). The catchment has 11,059 hectares, with 1,745 hectares cultivated with apples, an intensive pesticide application, a humid Mediterranean climate and silt loam soil. The study was conducted to determine Kd and normalized to organic carbon content (Koc) for atrazine, carbaryl, chlorpyrifos, glyphosate and tebuconazole, and its relation with impact on biological water quality index (BWQI). Benthonic community was observed in four points through a multi-habitat sampling: Ti1 (agriculture use); Ti2 (before apple orchard); Ti3 (agriculture and forestry use) and Ti4 (reference point native vegetation). The BWQI was determined with BMWP-Ch. In each point the riparian quality index (RQI) was characterized. Glyphosate presented a strong koc (13,260.7 L kg-1) the other pesticides were lower. The results showed moderate to low probability for pesticides to arrive in water. The BWQI had a gradient from the upper part (Ti4) to the output point (Ti1). The RQI was regular for Ti4 and poor for the others. The studied pesticides showed strong to moderate affinity for this soil, assuming that has not a direct effect on the aquatic organisms biodiversity. RQI was low, potentially driven by erosion following rainfall; related with the benthic community response. These results suggest the need to work on the causal relationship of biological water quality and fate of pesticides.