Evolução temporal da qualidade ambiental na Baía de Sepetiba

Abstract

Sepetiba Bay is a large, ellipsoidal, coastal body, and it is one of the largest bays located in Rio de Janeiro. The region has been suffering a process of urbanization and an increase in industrial activity. Both of these processes influenced the environmental quality of this ecosystem, contributing to eutrophication, contamination by metals and other pollutants. This work aims to study the process of metal contamination occurring in the region through eight cores (SP1-SP8) and to compare their metal concentrations with several coastal regions around the world. In addition to inferring the state of environmental quality in the SP5 core region for the last 100 years or so. For the study of contamination by metals, granulometric and geochemical analyzes were performed, such as: Total organic carbon and elemental concentrations. In addition, index such as: Enrichment Factor (EF), Ecological Risk Index (RI), Geoaccumulation Index (Igeo) and Potential Ecological Risk Index (PERI) were determined. From the results obtained, it was possible to observe that there is an increasing concentration trend of potentially toxic elements (PTEs), from the bottom to the top in most of the studied cores (SP3, SP5, SP7 and SP8) which is related to industrial growth in the region and anthropogenic sources. Although Companhia Ingá Mercantil is identified as one of the main contaminants of Cd and Zn in the region, the distribution of EF and PERI results suggest that there are regions far from this polluting source that are more enriched and present greater potential ecological risk than some closer locations, despite the expectations. This fact may be related to the hydrodynamics of the region, which favors the metal concentrations in some areas. In the study of the environmental quality of the SP5 core region, granulometric, mineralogical, geochemical, micropaleontological analyzes and Pb210 and Cs137 dating were performed. With the analyzed data, it was possible to infer that the area is moderately to heavily polluted by metals such as Cd, Zn and Sn. This contamination occurred mainly from the 1970s onwards, however, this is not the only factor that modifies environmental quality. The region has been suffering from eutrophication processes which have been affecting the establishment of diversified foraminifera assemblages, with a predominance of opportunistic specimens, such as Ammonia tepida. The values of the ecological quality ratio (EQS) based on benthic foraminifera assemblages allowed us to infer that the environmental quality of the bay was poor during the period of operation of Cia. Ingá and worsened after the waste disposal event in 1996. However, it has been recovering since then.