Trace elements mobility in a saline coastal aquifer of the Po river lowland (Italy)

The effect of elevated salinity (> 50 g/l) on the mobility of trace elements (Br, Sc, Ti, Cr, Ni, Co, As, Cd, Pb and Zn) was studied, within a shallow coastal aquifer. The use of intensive depth profiles with resolution of 0.5. m in two different locations, gave insight into groundwater and sediment matrix interaction. The collected sediments were analyzed for major and trace elements via XRF powder pellets, while major ions in groundwater were analyzed via IC and trace elements via ICP-MS.The total concentration of trace elements within the aquifer matrix was higher in the fine sediments, since usually these elements concentrate in the clay fraction, while the concentration in groundwater generally increased with the ionic strength of the solution. The increase of salinity in conjunction with a high content in carbonates stimulated a release of Pb and Zn, suggesting surface complexation on carbonate and dolomite minerals. The elevated organic carbon content of the sediments induced reducing conditions throughout the aquifer, which further promoted trace elements dissolution. The only exceptions were V and As that did not followed this trend, most probably released by peaty layers and fertilizers leaching.