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

Abstract

Abstract The environmental condition of surface sediments in Sepetiba Bay is influenced by the presence of trace metals derived from human activities. The trace metals contents vary considerably, with the highest values recorded in the inner part of the bay (Cd: 2.4 , Cu: 18.8, Ni: 12.2 , Pb: 20.4, Zn: 393 mg kg-1) and the lowest at Marambaia Barrier Island area (Cd: non-detected, Cu: 2.6, Ni: 0.2, Pb: 0.2, Zn: 3.35 mg kg-1). Mean annual fluxes of trace metals have increased since the 1950s, especially for Cd (8 x 10-5 to 0.4 g m-2 y-1) and Zn (4.0 to 60.9 g m-2 y-1) at Enseada das Garças. However, decreasing patterns towards the surface occur for all elements since the 2000’s. Pollution indexes reveal that Cd is the most concerning trace metal in Sepetiba Bay, with "high contamination and ecological risk" in recent layers of the inner area and “moderate contamination and ecological risk” at Marambaia Barrier Island region. Mineral phases and ligands are critical in the metal's distribution, due to the dynamic environment, continuously altered by natural and anthropogenic remobilization events. After examining the trends in Cd and Zn over the past 50 years regarding the point source of pollution, it is time to investigate other metals of concern, such as Cu and Pb, especially given the growth of industrial and harbor activities in the Sepetiba Bay basin. Other point and non-point pollution sources for the system are expected. Recent episodes of sediment remobilization raise concerns about the release of contaminants into the water column, increasing their bioavailability and toxicity.