Regional geochemical baselines and controlling factors for trace metals in sediments from the Poxim river, Northeast Brazil

Abstract

The Poxim river hydrographic sub-basin comprises four freshwater rivers, Poxim-Açu, Poxim-Mirim, Poxim and Pitanga, and is located in the East of Sergipe State, Northeast of Brazil. The present work investigates the distribution, the factors controlling concentrations, and toxicity risks of the metals Co, Cr, Cu, Li, Mn, Ni, Pb, Zn, Al and Fe, in surface sediments of the four rivers. Toxicity was evaluated using the Consensus-based Sediment Quality Guidelines for freshwater ecosystems. Spearman correlation analysis did not indicate any association of the metals with organic matter, however strong, moderate and weak correlations with aluminium, iron, and manganese, respectively, suggested that clay minerals were the main carrier of metals to sediments. Concentrations of metals in all samples were below the TEC (threshold effect concentration), indicating that for these trace metals adverse effects on aquatic biota should rarely occur. A geochemical baseline for the region was defined using lithium as reference element. Metal enrichments due to anthropogenic influence were only observed at three sites. At other sites, enrichment factors were indicative of a large predominance of naturally occurring metals in the sediments. © 2009 Sociedade Brasileira de Química.