Anthropogenic contribution, transport, and accumulation of Polycyclic Aromatic Hydrocarbons in sediments of the continental shelf and slope in the Mediterranean Sea

A multidisciplinary approach, involving geochemical, sedimentological and oceanographic analyses, was employed to examine the distribution of Polycyclic Aromatic Hydrocarbons (PAHs) in a strongly anthropized area of the marginal Adriatic Sea (Mediterranean basin). The investigation into PAH distribution considered the grain size and biogeochemical properties of the sediments, as well as in relation to the main oceanographic processes and river inputs. Both biogeochemical and hydrographical inputs regulated the sedimentation of organic particles, influencing the distribution of PAHs. The results indicated PAH levels in 116 marine surface sediments ranging from 4 to 235 ng g-1 (average 55 ng g-1). The distribution of PAHs in Adriatic Sea surface sediments aligned with a higher clayey sedimentation in the deeper basin areas of the Middle Adriatic Depression

Mercury Content in Central and Southern Adriatic Sea Sediments in Relation to Seafloor Geochemistry and Sedimentology

Mercury contents were determined in surface sediments from the Central and Southern Adriatic Sea to gain insight into the processes, factors, and variables affecting its distribution. Mercury concentration was measured by thermal decomposition amalgamation atomic absorption spectrometry in samples collected by box-corer from Ancona to Santa Maria di Leuca during the CNR-PERTRE cruise (16/9-4/10/2016). Sediments were also evaluated for chemical-physical parameters (pH, Eh), biogeochemical composition (total carbon, inorganic carbon, total organic carbon, organic matter) and grain size. The average mercury concentration in the Adriatic Sea sediment was 0.053 mg/Kg (d.w.), range 0.011–0.12 mg/Kg (d.w.). Mercury content was mainly affected by grain size and organic matter (OM) distribution, whereas anthropic factors exerted a limited influence. Concentrations followed the distribution of sediment types (clay > silt > sand) due to Adriatic Sea hydrodynamics and were well below the regulatory limits in all sample

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

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

Electrical conduction and electroluminescence in nanocrystalline silicon-based light emitting devices

Electrical transport and light emission properties of plasma-enhanced chemical vapor deposition grown light emitting devices LEDs based on nanocrystalline silicon have been studied. Various active layer compositions have been used. Electroluminescence and current-voltage measurements have been performed on metal-oxide-semiconductor structures. We found that Poole–Frenkel emission and trap-assisted tunneling between traps located at the nanocrystalline silicon interfaces are consistent with the measurements. The interface trap density was estimated. Its dependence on the composition of the active layer is discussed. We propose an equivalent electrical circuit model for the LED based on complex impedance measurements. Nanocrystalline silicon electroluminescence in the near infrared region is explained by hot-electron injection and impact ionization mechanism. It is concluded that the trap-assisted tunneling and charge trapping limit the external power efficiency of this kind of devices. © 2008 American Institute of Physics