Assessment of metals in sediments in a tributary of Guadalquivir River (Spain). Heavy metal partitioning and relation between the water and sediment system

A physical-chemical characterisation of the sediments of the Guadaira River in Southwest Spain has been carried out, determining twenty-three parameters per sample. Non-treated urban sewage and industrial wastewaters from olive oil and table olives affect this river. The factor analysis of the data shows high organic matter contents with metallic pollution. Consequently, points downstream stand out because of very high organic and metallic pollution (Zn, Pb, Cr, Cu and Cd, in order of abundance, showing concentrations in sediments ranging from 50-7500 times those of waters). Heavy metals partitioning studies can be a good approach to show the real activity of these metals in the aquatic environment. We applied Tessier's analytical sequential extraction scheme to sediments. Sediments would be in general mildly hazardous because we found low levels of easily interchangeable metals in the first fraction. Nevertheless, that is not the case in the river's last stretch, precisely where sediments are most abundant, the heavy metal levels largest and dredgings are made periodically. Here, their disposal is of concern; since the actual use of these sediments as organic amendment for agricultural soils is unacceptable. Interaction between waters and sediments in the riverbed by means of correlation, factor and cluster analysis on waters and sediments data, was investigated. With this approach we concluded that in the final stretch there is a problem of contamination of both, sediments and waters. However, in the middle course only sediments are actually polluted. This corresponds to the previous research, when the situation of waters in this zone was even worse.