Assessment of trace metals concentrations in Timbó River Estuary sediments, Pernambuco-Brazil

Abstract

Timbó River Estuary is located in the Metropolitan Region of Recife, among the cities Paulista, Abreu e Lima and Igarassu. It has an approximate area of 1397 hectares, and is affected by human action, especially that related to urban pressure and industrial activities. This work aims to determine the hydrological parameters and heavy metals concentrations (Zn, Mn, Cr, Cu, Ni, Cd and Fe), in rainy and dry periods. Hydrological parameters were measured at four points in the main channel of the river, according to Standard Methods for Examinations of Water and Wastewater. Sediment samples were submitted to acid process in a sample digester using the microwave and, for the quantification of metals, using the Optical Emission Spectrometer with Inductively Accolade Plasma (ICPOES). Results indicated that Timbó water is compromised concerning dissolved oxygen values (DO); and concerning dissolved oxygen saturation which indicated oversaturation in the most stations sampled. The maximum values of zinc (723 mg.kg-1), manganese (438 mg.kg-1), chrome (338 mg.kg-1) and iron (62840 mg.kg-1) were above those of reference, also presenting concentrations higher than the guide-values adopted by the Canadian Counselor of Environmental Minister. However, pH values (reduced conditions) and the organic load tend to immobilize metals in the sediment by adsorption and precipitation mechanisms making them less available to the other aquatic compartments.