Journal Scan

Abstract

This work aims to investigate the spatial and temporal distribution of trace metals in sediment samples taken from the Nerbioi-Ibaizabal River estuary (Bilbao, Basque Country) over the course of a long-term surveillance monitoring programme from 2005 to 2010. Sediment Quality Guidelines (SQGs) and the geoaccumulation indexes (Igeo) were used to assess the environmental risk posed by metal content in the estuary sediment.Sediment was collected at eight different sites in the estuary every three months over the period of investigation. A total of 14 elements (Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V and Zn) were selected and the concentration of each was measured in all samples. Additionally, conductivity, pH and the concentration of carbonate, total organic carbon and fulvic and humic acids were also measured in those samples collected in sampling campaigns from March 2006 to October 2008.The concentration of most of the metals systematically decreased over the period of investigation. There are still some points of the estuary (those located in the surroundings of the Gobela and Galindo tributaries), however, where concentrations of As, Cd, Cu, Pb and Zn are significantly higher than the background values estimated for the area. According to the mean Effects Range Median quotients (mERMqs) calculated for these sites, sediments may still pose a toxicological threat to living organisms. Metal content in inner estuary sediment is low.Specific point sources of metals to the estuary, together with background contamination of diffuse origin, are probably responsible for this situation.