Assessment of Pesticides in the Chasqueiro Irrigation District, Southern Brazil, an Agricultural Area of International Importance

Despite the importance of the Mirim-Sao Goncalo Basin in providing drinking and irrigation water for rice crops, both in Brazil and Uruguay, occurrence of pesticides in its surface waters has been poorly studied. In this study, five sampling campaigns were carried out in three tributaries of the Mirim Lagoon and in the Chasqueiro Dam. Temporal and spatial occurrence of 97 pesticides was investigated employing extraction by solid-phase extraction, while determinations were performed by liquid chromatography tandem mass spectrometry. Twenty-four pesticides were detected in the water samples (10 herbicides, 8 fungicides, and 6 insecticides). Quinclorac, bentazone, and tricyclazole were the ones found at the highest concentrations (from 0.018 to 2298 mu g L-1), and azoxystrobin and tricyclazole were the most frequent (78%). Rivers in the irrigation district (Chasqueiro and Canhada) exhibited the highest pesticide concentrations. Regarding pesticide classes, herbicides were detected at higher frequency and levels at the beginning of rice cultivation, fungicides were found at the end of the period, and insecticides were detected at lower concentrations, but at similar levels, throughout the period. Significant correlation among some pesticides and pH, electrical conductivity, biochemical oxygen demand, turbidity, and total solids was found. These parameters are related to diffuse sources of contamination that reinforce the contribution of agricultural activities to the detected contamination pattern. Thus, results show that the agricultural area contributes to the occurrence of pesticides in surface waters. It is important to highlight that pesticide contamination can seriously affect the quality of water bodies and to emphasize the need for proper assessment of the water quality in this lagoon of international importance.

Automated summary

This study investigates the occurrence of pesticides in the Mirim-Sao Goncalo Basin, an important water source for rice crops in Brazil and Uruguay. The results show that 24 pesticides were detected in the surface waters, with herbicides being the most frequently detected class. The study highlights the contribution of agricultural activities to the pesticide contamination in the water bodies.