Ecological risks associated to trace metals of contaminated sediments from a densely urbanized tropical eutrophic estuary.

The sediment contamination by trace metals in coastal aquatic ecosystems is a worldwide environmental problem, since metals can be toxic, persistent, and bioaccumulated. In case of natural events, such as storms, or anthropogenic activities, like dredging, the sediment resuspension to the water column occurs and can solubilize metals, probably increasing their bioavailability and consequently the risk to aquatic life. This study evaluated the bioavailability on reactive trace metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in estuarine sediments from Iguacu and Meriti Rivers, both in the drainage basin of Guanabara Bay (Rio de Janeiro, Brazil). Additionally, a discussion about the anthropogenic interference throughout time of six short sediments cores, calculating three different indexes (contamination factors, CF; potential ecological risk index for a single heavy metal, Eif for short; potential ecological risk, PERI) was performed. It was considered as reactive phase, the metal concentrations obtained using a weak acid extraction (in HCl 1 mol L-1 solution). Zn presented high concentrations after resuspension, being above effect range medium (ERM) (52.81 to 1337.4 mg kg-1). The CF indicated very high contamination degree for Cu (14.62 to 17.96) and Zn (27.80 to 35.85) for both rivers. The Eif for short presented higher risk to Cu and Zn for Iguacu and Meriti rivers. PERI index classified Meriti River samples as severely contaminated (238.10 to 351.62).