Assessment of Metals in Sediments in a Tributary of Guadalquiver River (Spain). Heavy Metal Partitioning and Relation between the Water and Sediment System

Abstract

A physical-chemical characterisation of the sedimentsof the Guadaira River in Southwest Spain has beencarried out, determining twenty-three parameters persample. Non-treated urban sewage and industrialwastewaters from olive oil and table olives affectthis river. The factor analysis of the data showshigh organic matter contents with metallicpollution. Consequently, points downstreamstand out because of very high organic and metallicpollution (Zn, Pb, Cr, Cu and Cd, in order ofabundance, showing concentrations in sediments rangingfrom 50–7500 times those of waters). Heavy metals partitioning studies can be a goodapproach to show the real activity of these metals in theaquatic environment. We applied Tessier's analytical sequential extraction scheme to sediments.Sediments would be in general mildly hazardous because wefound low levels of easily interchangeable metals in the first fraction. Nevertheless, that is not thecase in the river's last stretch, precisely wheresediments are most abundant, the heavy metal levelslargest and dredgings are made periodically. Here,their disposal is of concern; since the actual use ofthese sediments as organic amendment for agriculturalsoils is unacceptable.Interaction between waters and sediments in theriverbed by means of correlation, factor and clusteranalysis on waters and sediments data, wasinvestigated. With this approach we concluded that inthe final stretch there is a problem of contaminationof both, sediments and waters. However, in the middlecourse only sediments are actually polluted. Thiscorresponds to the previous research, when thesituation of waters in this zone was even worse.