This study evaluates the use of mercury (Hg) concentrations in fish muscle tissue to determine a species’ trophic position (TP) in its environment. A campaign conducted in 2019 along 375 km in the middle Araguaia River basin, Brazil, resulted in 239 organisms from 20 species collected. The highest total mercury (THg) concentrations were found in Pellonacastelnaeana (6.93 µg·g⁻¹, wet weight) and in Triportheus elongatus (3.18 µg·g⁻¹, wet weight), whose TPs were different according to the FishBase database. However, they occupied the same trophic level in this study. The intra-specific comparison showed a difference in Hg concentrations between individuals captured in distinct sites. The study of the biota–sediment accumulation factor (BSAF) showed that spatiality interferes with a species’ TP. Statistical analyses revealed that when we used a predicted species’ TP based on each individual’s size, it explained 72% of the variability in THg concentration across all fish species. Multiple regression analysis confirmed that standard length and FishBase values are positively associated with THg (R² = 0.943). These results point to Hg as a viable indicator of a fish species’ TP since it reflects regional, biological, and environmental factors, as demonstrated here for the middle Araguaia River.

The use of pesticides in agriculture can leave residues in the treated crops. Pesticides are also potential contaminants of ground and surface water, as reported in many countries. The development of efficient analytical methods to quantify pesticides in water samples is a challenge due to the low levels present. The objective of this work was to develop and validate a method for pesticide analysis in water using sample lyophilization followed by UHPLC–MS/MS and to determine pesticide levels in samples from a Brazilian hydrographic basin. In total, 77 compounds were included, of which 28 were considered only qualitatively. The method was applied to analyze 142 water samples collected during the dry and rainy seasons of 2021–2022, of which 90 were surface and 52 were groundwater samples. In total, 19 compounds were detected in the samples (≥LOD), mainly atrazine (72.5%), atrazine-2-hydroxy (50%), fipronil (18.3%), and pirimiphos-methyl (15.5%). Most compounds (17) were detected during the rainy season regardless of the environmental compartment. Twenty-five samples had quantified levels of the compounds (≥LOQ), of which 80% were collected during the dry season, and 58.3% were groundwater samples (up to 1.045 µg L⁻¹ of 2,4-D in an artesian well). The highest concentrations found in surface water were of atrazine-2-hydroxy (0.171 and 0.179 µg L⁻¹), levels that represent a potential risk to aquatic organisms (risk quotient of 1.1). This work provides an analytical method for determining pesticides in water that can be applied to other environmental pollutants. Although the levels found in the samples complied with Brazilian legislation, constant monitoring should be conducted in the region to guarantee safe levels of the pesticide in water.

The Brazilian savanna (Cerrado Biome) is one of the most important regions in the world in terms of food production, with the use of fertilizers based on nitrogen, phosphorus and potassium (NPK). When not applied properly, fertilizers can alter and affect water quality. The objective of this study was to evaluate the presence of these compounds in surface and groundwater in the Upper Jardim River Hydrographic Unit, Federal District, thus characterizing seasonal variations during the dry and rainy seasons in two periods. A total of 207 groundwater samples and 23 surface water samples were collected in the years 2014, 2015, 2019 and 2020. The parameters analyzed were pH and nitrate, nitrite, ammonium, phosphate and potassium ions. In groundwater samples, pH values were significantly higher and ion levels lower in samples collected during the early years (except for nitrate), and the ammonium concentrations were lower in the dry season than the rainy (in 2014 and 2019). In surface samples, total phosphorus levels were significantly higher in the rainy/2019 compared to the rainy/2020 season, while this tendency was inverted for potassium during the dry season. The use of NPK-based fertilizers has increased considerably in recent years in the region due to the expansion of the agricultural area, and although the results of the study show that concentrations in water are much lower than the maximum values allowed by Brazilian legislation, continuous monitoring is necessary to guarantee water quality.