Determination of mercury in the sediments of the Adriatic sea in relation to their geochemical and sedimentological characterization.

The aim of this research was to investigate the mercury content in the superficial sediments of the Adriatic Sea in relation to the depositional processes present and to the Holocene evolution. To do this, above the analysis of mercury in the surface sediment, were considered the data of the biogeochemical composition (TC, IC, TOC, TN, OM, major and minor elements) and of the sediment granulometry. Surface sediment samples were collected during the PERTRE oceanographic campaign, conducted in September-October 2016 by the ISMAR-CNR institute of Ancona [1]. Altogether 107 samples were collected by box-corer, in an area of the Central Southern Adriatic Sea that goes from the waters in front of Potenza Picena (MC) to those off the coast of Santa Maria di Leuca (LE) (Fig. 1).The granulometry (Fig. 2) and the geochemistry data (Fig. 3) [2], as already partially highlighted above [3], indicate a current silty coarse deposition zone near the coast, an area of mainly fine clayey deposition that extends to the center of the Adriatic in the deepest areas and a coarser (silicatic and carbonatic) outer zone towards the center of the basin in the less profound areas in which the coarse sediments are variously deposited during the last glacial period. For what concerns the mercury [4], values between 0.0106 and 0.123 mg/kg have been found, with an average value of 0.0526 mg/kg. From the surface distribution map of mercury (Fig. 4), a distribution in three bands can be observed, which traces the particle size distribution (Fig. 2) and the geochemistry (Fig. 3). Going eastwards there is a coastal strip with low values of mercury, linked to the scarce presence of fine material, with which the metals have a greater affinity, for the removal effected by the wave motion at low depths. This is followed by a central band in correspondence with the main accretion zone of the fine holocene accretion wedge. Finally, at the center of the basin, an external area is encountered in which mercury concentrations decrease due to the reduction of recent Holocene contributions. From this general trend differs the southernmost coastal zone (between Ostuni and Otranto) where mercury values also increase near the coast, such coastal increases could be of probable anthropic origin. Further observations on the distribution of mercury can be inferred from the association with the distribution of the organic substance (Fig. 5) and from the correlation with the PAHs (Fig. 6). In the first case, the highest concentrations of mercury are recorded in sediment samples characterized by higher concentrations of organic substance that also coincide with the higher concentrations of fine material, confirming the high affinity of this element with the two components. In the second case, the highest concentrations of mercury are recorded in sediment samples characterized by higher concentrations of Polycyclic Aromatic Hydrocarbons (PAH) that are found in the southernmost coastal area confirming a possible anthropic origin.