Metal mobility after resuspension of contaminated sediments from a tropical urban bay

Abstract

Dredging activities are recurrent in coastal cities, however, they can cause the remobilization of contaminants, increasing the risk to the biota. Guanabara Bay is a complex eutrophic estuary that undergoes dredging in several areas during the year. The Meriti River estuary is silted up and highly contaminated by metals, such as Cr, Cu, and Zn, due to the discharge of untreated sewage. In this sense, the present study aims to evaluate the remobilization of metals in the sediment (Cr, Cu, Fe, Mn, Ni, Pb, and Zn) and bioavailability after resuspension. Twelve sampling points were collected along 4 transects. The resuspension experiments were performed at two intervals: 1 h (T1) and 24 h (T2) and followed protocols from previous studies. In general, all metals are remobilized after resuspension. -  In addition, the bioavailability change (BC) index was applied., which showed 54% remobilization of Cr after T2. The transects closer to the river showed less remobilization after resuspension, which may be related to the saline gradient. Zn was the only metal that exceeded CONAMA Resolution 454/12 level 2 after resuspension, indicating a significant anthropogenic input to the area. Although organic matter (OM) is one of the main regulators of bioavailability in this study, the results suggest that there is an interference of bacterial activity in the dynamics of OM degradation, which directly impacts the bioavailability of metals after resuspension.