Effects of dredging at Aratu port in All Saints Bay, Brazil: monitoring the metal content in water and sediments.

Abstract

This work reports the chemical monitoring of saline water and sediments at Aratu port, All Saints Bay, Brazil, when subjected to a deep dragging process (DDP) over a 2-year period (2010-2012). The aim of this work was to detect which metals had possible deleterious effects on the biota. It analyzed percentage of silt + clay and TOC and metal concentrations (As, Cd, Cu, Cr, Ni, Pb, and Zn) before, during, and after the DDP. The determination of metal concentration in sediments used the following techniques: atomic absorption spectrometer with flame, also with hydrate generation, and cold vapor spectrophotometry. The DDP disturbed the concentrations of metals in sediments and water, but 15months after the DDP, only Cu and Zn were detectable on the bottom saline water, and 20months after the DDP, only Zn was detectable in water. This fact indicates that these metals were longer available for absorption by the marine biota with probable deleterious effect. Indeed, studies by others during the DDP in Aratu port, indicated the decrease from 50 to 40 of the number of microalgae species identified. On the other hand, in the sediments, 20months after the DDP, the concentrations of As, Cr, Cu, Pb, and Hg, returned to the original values, but Ni and Zn did not return to their original values. Comparison with studies by others indicated that the sediments from dredging were inappropriate for disposal at sea. This work indicated that the metals Cu, Ni, and Zn are the most deleterious elements to the marine environment.