Análise da contaminação e distribuição espacial de metais pesados em áreas de influência de mineração em um estuário tropical na Amazônia

Abstract

Tropical estuaries are often impacted by heavy metals, but the spatial distribution and contamination of these pollutants have been insufficiently investigated between sediments and water in South America, especially in the little-studied regions of the Amazon. In order to contribute to this gap, this study investigated the spatial distribution and contamination of heavy metals (Cd, Cu, Fe, Mn and Zn) in the surface waters and sediments of the Pará River Estuary (PRE) (Pará, Brazil), which has been affected by various mining activities. Thus, different procedures were integrated, including a systematic review of the literature on tailings spill events and impacts derived from these events, sedimentary and mineralogical characterization, estimation of organic matter in the sediment, physical-chemical parameters of the water, determination of metals in the sediment and water, contamination assessment indices and statistical analyses. The results showed that the kaolin tailings storage systems in Barcarena-PA are more unsafe than the alternative disposal systems reported in the literature, resulting in kaolin tailings leaking into regional water bodies and spreading areas used for bathing. On the other hand, the disposal of bauxite tailings in the area prioritizes alternative systems with higher solids content, facilitating control actions. In addition, the bauxite and kaolin tailings had predominantly silty fractions and mineralogy marked by the presence of aluminum hydroxides. All the samples showed low concentrations of heavy metals in the sediments, suggesting the action of resuspension in an area with predominantly sandy sediments. As an exception, Cd showed high concentrations in Murucupi and Furo do Arrozal, which triggered high levels of contamination in these areas. All the sampling sites indicated that there was a high concentration of heavy metals and a high degree of contamination of the water, except in the vicinity of Vila do Conde. Furthermore, high ecological risks are associated with the metals present in the water from anthropogenic activities, compromising the quality of the estuarine ecosystem.