Monitoramento ambiental do médio rio Tocantins: elementos potencialmente tóxicos e essenciais em água, sedimentos e peixes, biomarcadores e implicações para a saúde ribeirinha

Abstract

The Tocantins–Araguaia basin is one of the largest hydrographic systems in South America, spanning the states of Maranhão, Tocantins, and Pará, and is part of the Brazilian Legal Amazon. Despite draining extensive Cerrado and tropical forest ecosystems, this basin has undergone significant environmental degradation in recent decades due to agricultural expansion, deforestation, and the introduction of non-native species. This scenario is particularly relevant for riverine communities along the middle Tocantins River, which depend on the river for water supply, recreation, and fish consumption. In this context, fish can act as biomonitors of contaminant exposure in aquatic environments, as they integrate ecological processes and represent an important food and economic resource. Thus, the aim of this study was to perform environmental monitoring of the middle Tocantins River through an integrated approach, including the analysis of physicochemical water parameters, the determination of potentially toxic and essential elements in water, sediments, and fish, and the assessment of enzymatic biomarkers in native fish species. Sampling was conducted at four sites: P1 (Beira Rio – urban area), P2 (Bananal village), P3 (Embiral village), and P4 (Cidelândia village). The thesis is structured into five chapters. Chapter 1 presents a literature review on the Tocantins–Araguaia basin and ecotoxicological aspects related to contaminants in aquatic environments. Chapter 2 describes a socio-environmental study assessing riverine perceptions of water quality through structured questionnaires. The results showed that 34% of respondents consume and commercialize native fish, 62% use them for subsistence consumption, and 4% do not consume fish. Additionally, 84% reported the absence of sewage systems, highlighting high dependence on water and fish resources and significant socio-environmental vulnerability. Chapter 3 evaluated potentially toxic and essential elements in water, along with physicochemical parameters. Aluminum, copper, iron, magnesium, and selenium exceeded regulatory limits at certain sites and periods, with seasonal variations influenced by climatic factors. Site P1 exhibited higher electrical conductivity, total dissolved solids, chlorophyll, and nitrogen compounds, indicating anthropogenic influence and potential risks associated with untreated water consumption. In Chapter 4, sediment analysis revealed elevated concentrations of aluminum, iron, manganese, and selenium, as well as chromium, nickel, copper, zinc, and lead exceeding quality guidelines, particularly in areas influenced by urban activities. Higher concentrations during the rainy season highlighted the role of seasonality in contaminant mobilization and deposition processes. Chapter 5 investigated the bioaccumulation of potentially toxic and essential elements and enzymatic responses in native fish species (Psectrogaster amazonica and Caenotropus labyrhinthicus). Elevated concentrations of arsenic, lead, and selenium were detected in fish tissues, exceeding recommended limits. Enzymatic activities (AChE, AST, ALT, and ALP) indicated physiological responses associated with environmental exposure and were interpreted as sublethal alterations, without allowing direct inference of causality or specific mechanisms. Overall, the results indicate that the dynamics of elements in the middle Tocantins River are controlled by the interaction between natural processes and anthropogenic influences. The concentrations of elements such as iron, aluminum, and manganese partly reflect the regional geochemical background, characterized by highly weathered tropical soils, while physicochemical parameters and spatial patterns indicate the influence of human activities, particularly in urban areas. The observed bioaccumulation in fish and enzymatic responses indicate organism exposure to environmental contaminants and associated physiological alterations. These findings, combined with the strong dependence of riverine populations on water and fish resources, highlight the importance of integrated environmental monitoring approaches that consider regional specificities and their implications for environmental health and food safety, in line with the One Health framework