Historical Trends of Trace Metals in the Sepetiba Bay Sediments: Pollution Indexes, Fluxes and Inventories

The environmental condition of surface sediments in Sepetiba Bay is influenced by trace metals derived from human activities. Four sediment cores were collected from both the inner (Coroa Grande and Enseada das Garças) and outer (Guaratiba and Marambaia) areas of the bay. Trace metals content varied considerably, with the highest values recorded at Enseada das Garças (e.g., Cd: 2.4 mg kg−1; Zn: 393 mg kg−1), and lowest at Marambaia Barrier Island (e.g., Cd: <0.001 mg kg−1; Zn: 3.35 mg kg−1). Mean annual metal fluxes have increased since the 1950s, especially for Cd (from 8 × 10−5 to 0.4 g m−5 y−1) and Zn (from 4.0 to 68.7 g m−2 y−1). However, a decreasing trend has been observed since the 2000s. Pollution indexes indicated that Cd poses the highest contamination and ecological risk in recent layers of the inner bay, and moderate risk at the Marambaia Barrier Island (maximum values of Cd: 0.67 mg kg−1 and Zn: 94.9 mg kg−1). Metal distribution patterns are influenced by mineral phases and sediment dynamics. Findings emphasize the need to monitor other metals like Cu and Pb, besides the historical heavy loadings of Cd and Zn, considering recent industrial and port expansions in the Sepetiba Bay region.