Speciation as a screening tool for the determination of heavy metal surface water pollution in the Guadiamar river basin

The Guadiamar river basin has traditionally received pollutants from two main sources: in its northern section of mining origin, and in its southern section (next to Doñana National Park) from urban-industrial and agricultural sources. In April 1998, the spill of 6 million m3 of mining wastes (acidic waters and sludge) severely polluted the Guadiamar river basin with heavy metals, which caused serious damage to the local ecosystem. There is a direct association between the physicochemical speciation of an element and its toxicity, biological activity, bioavailability, solubility, etc. This work describes a distribution study of the metals Zn, Cd, Pb and Cu by speciation analysis of surface waters in eleven sampling points of the Guadiamar river basin. Four metal fractions were determined using anodic stripping voltammetry: labile metal forms, H+ exchangeable metal forms, strongly inert forms (associated with organic and inorganic matter in solution), and forms associated with suspended matter. Total concentrations in surface waters followed the trend Zn > Cu > Pb > Cd. The speciation study showed that Zn and Cd were present to a large extent in available forms (labile and H+ exchangeable), while Pb and Cu were found mostly in the less available forms (strongly inert). Moreover, the available forms were found in the northern section (mining pollution) and the strongly inert forms in the southern section (urban, industrial and agricultural pollution). These results can illustrate the potential value of speciation to discern between different sources of pollution.