Effects on Water Quality of Pesticide use in Farmland Under Intensive Soil Management in Southern Brazil

Poor soil management and intensive use of pesticides causes serious damage to soil and water quality in Brazil. To confirm this, two studies were conducted in an area with intensive farming in Southern Brazil with objectives to evaluate the level of pesticides in the river adjacent to the farmland during different seasons (river study) and to know the potential contamination resulting from surface runoff (runoff study). The river study was performed with samples from river water and riverbed sediment obtained over one year period with three months sampling period intervals (different seasons) on dry days (base flow effect). The runoff study was performed in the laboratory with simulated rainfall after recent pesticide application. The pesticides analyzed were Tebuconazole, Metalaxyl, Deltamethrin, Chlorothalonil, Glyphosate and its Metabolite-aminomethylphosphonic acid. They represented the most commonly used pesticides in the studied region. None of the pesticides tested were found in the river water or riverbed sediment samples at any sampling period. The detection limit in river water samples for Glyphosate and its metabolite was 5μg L-1 while it was 1 μg L-1 for the other pesticides. The runoff study (one hour rainfall) demonstrated that all the pesticides were present at high levels. It was 36μg L-1 for Tebuconazole, 3.24 μg L-1 for Metalaxyl, and 5.74 μg L-1 for Chlorothalonil in runoff samples, suggesting a high probability of contamination in downstream environments during intense rainfall events after recent pesticides application. The results highlight the importance of good management practices to prevent pesticides contamination of downstream environments due to runoff from agricultural lands.