Geochemical control of heavy metal concentrations and distribution within Bahía Blanca Estuary (Argentina)

Abstract

Chromium and lead concentrations and distribution have been fully studied within Bahía Blanca estuary inner area, which is strongly influenced by urban and industrial stress. Not only metals dissolved in estuarine water but also those included in sediments and suspended particulate matters (SPM) were measured. In all cases, internationally standardized protocols were applied to metal measurements, including analytical quality check test through analysis of certified reference materials. Total metal contents from surface sediments and SPM were compared with those from a historical database of the area, as well as with values representing the natural geochemical baseline within the system. Results showed that heavy metal pollution is mainly localized in the areas both close to the industrial effluents discharge system and to the urban sewage outfall discharge. Data from sequential extractions indicate that metals from anthropogenic sources (i.e. Pb) are potentially more mobile than those inherited from geological parent material (i.e. Cr). The influences of other potential sources of metals (i.e. streams, runoff) were also considered. SPM was clearly identified as the main carrier of the studied heavy metals within the system, and its significance to metals input into sediments and/or biota was verified. Finally, the normalization of measured metal concentrations against background reference elements (i.e. Al or Fe) has allowed to identify that most of the measured Cr was lithogenic. While a significant percentage of Pb was from anthropogenic origin within Bahía Blanca estuary.