Sauce Chico River and Napostá Grande Creek as a potential source of heavy metals to Bahía Blanca estuary

DEL BLANCO, L.; BOTTÉ, S.E.; CHIARELLO, M.N.; ARLENGHI, J.; FREIJE, R.H.; MARCOVECCHIO, J.E.

Buzios/Rio de Janeiro, Brasil

Simposio; 4th International SYMPOSIUM ENVIRONMENTAL GEOCHEMISTRY IN TROPICAL COUNTRIES; 2004

Departamento de Geoquímica da Universidade Federal Fluminense

Bahía Blanca estuary (in the southest Atlantic littoral of Buenos Aires province, in Argentina), with roughly 80 km length and a total surface of 1300 km2 during high tide, receives several pollutant inputs from municipal sewages, industrial effluent discharges and harbour operations (including oil storage and transport, cargo vessel circulation, artisanal fishery boats, dredging and refule). Also both the continental runoff and atmospheric deposition must be mentioned as potential sources of heavy metals within the estuary. Concerning with the transport of land materials to the estuary, mainly linked with both human activities as well as natural processes, the Sauce Chico river and the Napostá Grande stream are the most important natural tributaries to Bahía Blanca coastal system. It is interesting to remark that the Napostá Grande stream is the unique natural water flow crossing through Bahía Blanca city, and flowing toward the estuary. In order to characterize the metal transport through the tributaries to the estuary, as much in its dissolved forms as in the bound to the suspended material ones, and the possible environmental impact that they suffer by the anthropic activity, a study of the heavy metal concentrations was made in waters and surface sediments of Sauce Chico river and Napostá Grande stream. Samples of water and surface sediments from Napostá Grande Stream, after crossing the city of Bahía Blanca, and from Sauce Chico River were monthly collected from March 2002 to May 2003. The dissolved metals were extracted by chelation with ammonium pyrrolidine-dithiocarbamate (APDC) followed by extraction into metil iso-butil ketone (MIBK) according to a modification of the method described by Koirtyohann & Wen. Sediments were digested in a mixture of concentrated nitric and perchloric acids, according to the method modified by Marcovecchio et al. Heavy metals (Cu, Zn, Cd, Pb, Cr, Ni, Mn and Fe) were measured by flame atomic absorption spectrometry. The obtained results have allowed to present a preliminary masses balance for this environment, and suggested that in this study area, metals concentrations are comparable with those measured in pristine rivers and non contaminated seawater and both water flows contribution magnitudes were similar.