POTENTIALLY HARMFUL ELEMENT (PHE) OCCURRENCE AND PHASE PARTITIONING IN THE RIVER MOUTHS OF THE GULF OF TRIESTE (NORTHERN ADRIATIC SEA)

Potentially harmful elements (PHEs) are supplied to estuarine environments in association with freshwater inputs affected by several anthropogenic sources [1]. The present work aims to understand the PHE (Pb, Hg, Cs, As, Zn, Cu, Ni, Co, Fe, Mn, Cr) partitioning between particulate (> 0.45 μm), colloidal (0.45 μm - 10 kDa) and dissolved (< 10 kDa) fractions in river mouths of the Gulf of Trieste (northern Adriatic Sea). In order to achieve these objectives, CTD (Hydrolab H2O Multiprobe) vertical profiles of salinity, temperature and turbidity were recorded before sampling to identify the water masses. The surface samples were collected at variable depth, according to the salinity trend and along the salinity gradient, whereas the bottom water samples were representative of salt water intrusion. In addition, the main physico-chemical parameters (T, pH, Eh, DO and EC) were measured in situ (pH-meter PH25, Conductivity-meter CM35+ by Crison Instruments). Samples were filtered through 0.45 μm filters (Millipore HA, Ø 47 mm) to isolate the particulate fraction which was aciddigested through a total dissolution in a closed microwave system (Multiwave PRO, Anton Paar). The filtrate samples were ultrafiltered through 10 kDa membranes (Vivaflow 200, Sartorius). All sample aliquots were analysed for PHE determination by means of Inductively Coupled Plasma Mass Spectrometry (Nexion 350x Perkin Elmer), whereas Hg was analysed via Cold Vapor Atomic Fluorescence Spectrometry (Mercur Analytic Jena). Hydrodynamic conditions at the river mouths showed the presence of two distinct layers due to the freshwater input and salinity vertical profiles displayed a sharp halocline or mixing layer depending on the river discharge. Elevated PHE contents were detected in the particulate and dissolved fractions and in some parts, PHEs seem to be associated with the colloidal fraction. As expected, Hg reaches elevated values in the particulate fraction of the Isonzo River [2]. The Timavo River samples showed elevated concentrations of PHEs, most likely due to wastewater discharge from a paper mill located near the river mouth. Information on PHE mobility can be provided by the correlations observed between PHE content and salinity, which appear to have an important role in PHE phase partitioning.