Disentangling natural and anthropogenic sedimentation: current and past pollution impact on Sepetiba Bay (southeastern Brazil)

Densely populated coastal areas have been degraded by pollution caused by anthropogenic activities, including urban solid waste and domestic and industrial effluents. This study aims to distinguish the impacts of the legacy of past industrial activity from those of present-day iron ore exportation in Sepetiba Bay (SE Brazil). To this end, physicochemical, textural, mineralogical, geophysical, and geochemical data were analyzed in 73 surface sediment samples distributed throughout SB. The results show distinct sedimentary processes between the outer and inner zones of Sepetiba Bay, influenced by marine and continental activities. SB’s outer sector is characterized by well-sorted medium and coarse sand. Sediments enriched in felsic minerals were found in areas under strong marine processes. In the inner sector of the bay, fine to coarse silt sediments predominate, enriched in phyllosilicates, namely kaolinite and vermiculite and metals; this area is influenced by the fluvial input and the intense weathering process of the crystalline rocks found in the region's watershed; it displays high toxicity caused by potentially toxic elements (PTEs), mainly caused by a legacy of former industrial activity. Additionally, SB is experiencing another impact, as indicated by relatively high values of goethite, magnetite, and magnetic susceptibility associated with iron ore transport, loading, and export activities. The ore accidentally introduced into SB is causing a sharp increase in Fe and Mn in this coastal system. Thus, the statistical results suggest that SB is still suffering the impact of past pollution, in addition to current pollution. Therefore, it is necessary to implement a continuous, efficient environmental monitoring program to mitigate the problems identified in this study. • Disentangling natural and anthropogenic sedimentation • Current and past pollution in Sepetiba Bay (SE Brazil) • The legacy of past industrial activity related to high-purity zinc production • Current impact caused by iron ore transportation and exportation • Metal and mineral contamination