Avaliação das influências espaço-temporais e de maré nas concentrações de metais em água e sedimentos estuarinos no entorno de um polo industrial amazônico

Abstract

Formed by the Tocantins River and smaller tributaries such as the Guamá and Capim rivers, the Pará River Estuary is an important ecosystem, serving as a shelter and reproduction site for many fish species and contributing to nutrient recycling in the aquatic environment. However, this area suffers from constant discharges of domestic and industrial effluents. The town of Barcarena, located in Pará and approximately 40 km from the state capital (Belém), plays a significant role in the state’s economy by hosting an industrial hub focused on the aluminum, kaolin, and steel industries. This study aims to characterize the temporal and spatial variation in the presence of metals and metalloids in both surface water (total, dissolved, and particulate fractions) and sediment across various points with differing levels of urban and industrial influence in Barcarena, PA. Water and sediment samples were collected during different seasonal periods throughout 2023 and 2024. During the sampling period, several phenomena were observed, particularly those related to the El Niño–Southern Oscillation (ENSO). The year 2023 was marked by the occurrence of La Niña, while 2024 was characterized by El Niño conditions. Sampling was performed in triplicate during both low and high tides at each site. Ten different metals (Al, Ba, Cd, Fe, Pb, Mn, Ni, Cr, As, and Hg) were analyzed in both water and sediment samples using Atomic Absorption Spectrometry with Flame Atomization, Graphite Furnace, Cold Vapor Mercury, and Hydride Generation techniques. The results showed no statistically significant differences between the different tidal conditions (high and low tide). Overall, the metals that exhibited higher concentrations across the sites were Al, Fe, Mn, and Ba, in both environmental matrices. This outcome was expected, as these elements naturally occur at high concentrations in the area's geological formation (Barreiras Formation). Although the region presented high metal concentrations, this pattern is most likely related to the local geology. However, anthropogenic factors may also contribute to elevated metal levels, as observed at certain highly impacted sites characterized by poor basic sanitation and direct discharge of domestic effluents and contamination from open-air dumps. These residues ultimately become sources of metal and metalloid input into the environment, especially for elements such as Pb, Hg, and As, in both water and sediment. These elements are often associated with domestic sewage, improper solid waste disposal, and open dumpsites. Our results also highlight important conclusions regarding the influence of ENSO on metal distribution in water and sediment in the Amazon region. Higher metal concentrations in both water and sediment were observed during the El Niño period compared to the La Niña period. Therefore, we conclude that environmental assessments in the Amazon region especially those involving metal monitoring in environmental matrices, should carefully consider the natural background input of these elements into abiotic compartments in order to accurately identify potential contamination arising from anthropogenic activities such as urbanization and industrialization.