Distribution of mercury and other heavy metals in core sediments of the northern Adriatic Sea

Seven sediment cores were collected along a transect about 20 km off from the mouth of the Po River, in the northern Adriatic Sea (Italy). Cores were characterised by different depositional sequences associated with late Pleistocene-Holocene lowstand (LST), transgressive (TST) and highstand (HST) system tracts. Sediment samples were analysed for mercury, copper, nickel, chromium, manganese and iron, as well as for total organic matter. Metal distribution generally showed vertical and spatial variability ascribed to grain size effects with no significant anthropogenic perturbation. Conversely, mercury showed vertical profiles characterised by surface enrichment, with concentrations in the upper layer (50-230 ng g super(-1)) exceeding 3-11 times the background value of 20 ng g super(-1) determined in bottom cores. Surface maxima were attributed to anthropogenic mercury delivered mainly by the Po River.