In order to assess the influencing factors of the presence of mercury in a river within the Savanna biome (Cerrado), we surveyed total mercury (THg) in bottom sediment from 50 lakes along 750 km of the Middle Araguaia floodplain. The sampling sites included non-urban and urban surroundings over three distinct geomorphologies. We measured water physicochemical parameters at each site and tested statistically if land use nested within the geological formation influenced the THg concentration in bottom sediments and related water parameters. Multivariate results indicate that the interaction between geological groups and land use is statistically significant (p < 0.05). Nested ANOVA and Tukey HSD tests confirmed that the geological formation with its nested land use influences the THg, pH, DO, conductivity, and TDS (p < 0.05). THg was significantly lower in Quaternary terrains (p < 0.05) and differed significantly between non-urban and urban areas in Neoproterozoic terrains (p = 0.02). The spatial projections of the THg eigenvector on the main axes with the scoring factors of the Neoproterozoic/Paleoproterozoic terrains, and urban/non-urban, confirmed the spatial correlations. These results indicate that the association of land use and geology could be the main driver of THg in the bottom sediments of lakes from the Middle Araguaia floodplain.

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.

Macrophytes are fundamental photosynthetic organisms for functioning freshwater ecosystems, identified as potential bioindicators of mercury (Hg) in the environment. We quantified the concentrations of total Hg (THg) in water and macrophytes (Paspalum repens Berg.) from 17 lakes on the Araguaia River floodplain, aiming to compare the bioconcentration factor (BCF) in the aerial tissues and roots; evaluate the translocation factor (TF) between plant tissues; and assess the influence of environmental factors and land use on THg concentrations in water and macrophytes. The BCF was significantly higher in roots (1.29 ± 0.32) than in aerial tissues (0.41 ± 0.34), with low TF between plant tissues (0.14 ± 0.06). The highest concentrations of THg in water were determined in lakes with higher land use intensity and a pH close to neutral, indicating the transport of particulate-bound Hg and the immobilization in the water column. In contrast, wetlands were priority areas for the bioconcentration of THg in macrophytes, associated with sulfate, dissolved oxygen, and oxidation–reduction potential in the water. Thus, although P. repens is not a suitable bioindicator of Hg mobilization by anthropogenic land use in our study area, our results suggest the potential of macrophytes as bioindicators of sites that are favorable to Hg methylation.

A emissão de mercúrio (Hg) por atividades antrópicas tornou-se um processo capaz de modificar o seu ciclo biogeoquímico natural. Os sedimentos são o principal compartimento para a metilação do Hg nos ecossistemas aquáticos, enquanto os solos superficiais são os maiores reservatórios de Hg nos ambientes terrestres. O objetivo deste estudo foi caracterizar as concentrações médias de mercúrio total (HgT) nos sedimentos dos córregos da Estação Ecológica de Águas Emendadas (ESECAE), em conjunto com a distribuição espacial do Hg nos solos superficiais da reserva, analisada a partir de dados secundários. Dados de sensoriamento remoto foram empregados para avaliar a influência da paisagem local nas concentrações médias de HgT. A concentração de mercúrio total (HgT) no sedimento variou de 16,12 a 96,80 ng.g-1, com média de 41,46 ± 28,01 ng.g-1. A avaliação do uso e cobertura do solo demonstrou que as áreas antrópicas são predominantes no entorno da ESECAE. A combinação entre o modelo digital de elevação e os autovetores indicou a orientação do HgT nos solos superficiais em direção às menores altitudes, favorecendo o acúmulo nos córregos. A tendência da distribuição decrescente do HgT de fora para o centro da ESECAE e as maiores concentrações nos córregos marginais às rodovias indicam a influência das atividades humanas desenvolvidas no entorno da área de estudo. Portanto, a combinação das análises espaciais foi eficaz para a determinação da distribuição de mercúrio nos solos superficiais e definição de locais mais vulneráveis à poluição.