Geochemical investigation of trace metal pollutants in the Oreto river, Palermo (Italy)

In the past, three main rivers, named Kemonia, Papireto and Oreto, were present in the plain of Palermo, in northwestern Sicily. Today, only the latter one has been preserved from the unregulated urban expansion. Fortunately, over the last ten years, attention and consciousness towardsthe Oreto river and its delicate ecosystem has grown considerably, also thanks to many associations and citizens’ committees involved in protecting, preserving and valorising the precious area. In this context, our study is focused on a hydrogeochemical investigation of its surface water quality. The Oreto river flows for about 20 km within a catchment area of about 130 km2. Over the past three years, numerous water sampling campaigns have been carried out in order to measure the main physicalchemical parameters (EC, T, DO, Eh and pH) and analyse the major constituents (Na, K, Ca, Mg, S, Cl, F, N, Alkalinity) together with a large suite of trace elements (including those potentially toxic). Sampling sites include the river mouth, several springs, poorly purified (or untreated) urban sewage discharges, and the main river confluences. Waters are of bicarbonatealkaline earth composition, as a result of waterrock interaction processes and reflect the dominance of limestone sequences outcropping in the area. The effects of anthropogenic pressure on the river system become more evident in urban areas, where untreated sewage flows have a significant impact on water quality: negative Eh values, decrease in dissolved oxygen, increase in EC and nitrogen species. Many of the trace elements (Cu, Pb, Ni, Cr, Fe, Al, Sb and Sn) also show increasing trends from the springs to the estuary, highlighting the fingerprint of the anthropogenic sources.