Occurrence, drivers, and environmental implications of pesticides in surface waters from one of Brazil's last agricultural frontiers: Spatial–seasonal patterns

The intensification of agricultural activities, driven by population growth, has resulted in significant impacts on the quality and availability of water resources. This expansion increases the likelihood of pesticide contamination, affecting both water quality and aquatic ecosystems. In regions of intensive agricultural production, such as the Cerrado biome (MATOPIBA region), crop management practices require careful attention due to the potential presence of pesticide residues in surface waters. In this context, the present study aimed to assess the spatial and temporal distribution of pesticides in surface waters of the Uruçuí-Preto River basin, encompassing both the dry and rainy seasons. To achieve this, water samples were collected at 10 sites distributed along approximately 300 km of the river's main course, during four strategically selected months (February, March, April, and August) to capture the pronounced seasonal contrasts between periods of higher rainfall and drought. Pesticide residues were determined using Solid-Phase Microextraction followed by analysis via Liquid Chromatography-Tandem Mass Spectrometry. The results revealed the presence of multiple chemical groups of pesticides, with clomazone standing out as it was detected at all sampling points in August, the month with the lowest precipitation (dry season). The higher number of detections recorded during this period indicates that reduced rainfall favors the accumulation of residues in surface waters. In contrast, during the rainy months, a dilution effect and increased mobilization of compounds were observed, although occasional detections still occurred. Overall, the findings highlight the strong influence of seasonality and agricultural practices on water quality, underscoring the need for continuous monitoring and policies that promote the safe management of pesticides in the region.