Pore water trace metal chemistry in polluted sediments of a tropical estuary of SE Brazil

The Sepetiba Bay is a shallow water body semi enclosed located on the west side of Rio de Janeiro City. Almost 80% of flesh water discharge, from the St Francisco canal, coming from the northern side of the bay develops an estuarine environment. Fishing and tourism are some of the most important economic activities in the area. During 35 years a zinc/cadmium smelter has polluted the bay. The objective of this investigation is to demonstrate the diagenetic processes and cadmium remobilization into pore water from the contaminated sediments. Two sites were selected to compare diagenetic processes. Site P1 is located next to domestic effluents discharge into the bay and approximately 20km away from the smelter. Site P2 is located near the same smelter and next to the Mazomba estuary, which is not influenced directly by domestic effluents. Peeper samplers of 25 cells with a resolution of 2.5 cm were deployed at both the sites. After a 3-weeks period of equilibrium, the pore waters were separated from the cells and analyzed immediately （within 24 h） for alkalinity, NH3 and reactive soluble phosphorus on a spectrophotometer. An ICP-AESΣH2S spectrometer was used to analyze Na, Mg, Li, Ba, Sr, Si, Fe and Mn. Total and labile dissolved Cd in pore waters were determined by differential-pulse stripping voltametry. The dissolved constituents in the pore waters have shown that the intensities of diagenetic reactions are different between sites. The reactions are stronger at site P1 site than at site P2, especially between 7.5 cm and 22.5 cm, which is evident by the organic rich sediment.

Pore water trace metal chemistry in polluted sediments of a tropical estuary of SE Brazil