SEASONAL ANALYSIS OF THE TOXICITY OF HEAVY METALS IN THE SURFACE SEDIMENT OF AN URBAN STREAM (MATO GROSSO DO SUL, BRAZIL)

Abstract

The Imbirussu Stream, located in the northwestern region of the city of Campo Grande/MS, passes through several densely populated neighborhoods and an Industrial Park, receiving a large intake of potentially toxic substances, including heavy metals. These substances end up being deposited in the sediment and may return to the water column, causing many impacts to the aquatic ecosystem. Thus, this study aimed to: a) assess the concentrations of heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in the sediment; b) perform acute ecotoxicological tests using Daphnia similis and Danio rerio as bioindicators and c) evaluate the effects of seasonality on the obtained results. The samples were collected in February/2013 (Rainy period) and August/2013 (Dry period) from the source to near its mouth in the Anhanduí River. Cultivation of organisms and toxicity tests were performed according to NBR 12.713/2009 and NBR 15.088/2011. The analysis of sediment samples were performed according to the methods described in the manual Standard Methods for the Examination of Water and Wastewater, 22nd ed. With the values obtained in the analysis it became clear the input of heavy metals into the stream due to the effluents discharged by the industries installed in the Industrial Park. The obtained results showed the influence of seasonality, because the metal concentrations were higher in the dry period than they were in the rainy one. These results were confirmed by the tests, since acute toxic effects to the organisms occured only in the dry season.

Key Words: Acute toxicity, Danio rerio, Daphnia similis, heavy metals, sediment pollution.