River Cabuçu-Piraquê, a tributary of Sepetiba Bay, has a history of pollution for decades, but without a systematic study of the origins and fate of trace elements such as cadmium and zinc, in its environmental compartments. The bioaccumulation of these elements can cause serious damage to the biota of mangroves in its estuary, and to human consumers of local fisheries. In this study, it was evaluated the current state of contamination of water and sediment from that river by means of various parameters (concentration of dissolved oxygen and ammonium and phosphate ions, among others), as well as the occurrence of the transport and accumulation of these metals in the estuary´s sediment fraction brought by the bay waters during high tides. Concentrations of cadmium and zinc above those considered safe by Brazilian law were found both in the fine fraction (< 63 µm) of sediment, averages of 5 and 1351 mg kg-1 , respectively, and at high tide waters, 0.09 and 0.31 mg dm-3 , respectively. Both metals were found only in the most bioavailable operating fractions of waters, while sediment average values of 92 % were found for Cd, and 97 % for Zn at same fractions. From the concentrations of these metals in water from the saline wedge generated by the bay, it was possible to infer such an influx into the estuary from the material present in the bay waters, and this transport process may be shipping a major contributor to contamination of the local mangroves.

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