L. Menegazzo Vitturi

Heavy metal content and lithological properties of recent sediments in the Northern Adriatic

Heavy metal (Hg, Pb, Cd, Cu, Cr, Ni, Co, Zn and Fe) concentrations, textural characters and mineralogical compositions have been determined on 246 surface sediment samples from the Northern Adriatic Italian sea area. The relationship between the heavy metals content and the pelite (< 63 μm fraction) percentage has been studied. All the metals resulted accumulated in the fine fraction with the following percentages (Hg, 95%; Zn, 86%; Pb, 82%; Cu, 79%; Cd, 74%; Ni, 70%; Cr, 65%; Co, 65% and Fe, 64%). The specific surface area has been measured on 44 samples and correlated to metal values. A fairly good (50% and more variation explained) linear correlation co-efficient has been found for Ni and Cu in the entire area, less significant correlation for other metals. In order to discriminate between natural and anthropogenic origin the metal concentrations on the whole sediment has been normalized on the basis of the pelite percentage. In the areal distributions drawn with the corrected values, zones contaminated by industrial discharges have been identified mainly in front of the lagoon of Venice.

Geochemical considerations on trace element distributions in suspended matter and sediments at the river-sea interface, Adige River mouth, northern Adriatic sea

Abstract The particulate matter at the Adige River mouth has been investigated in order to determine the natural geochemical processes in the estuarine environment, and the anthropogenic influence on the biogeochemical cycling of heavy metals. The determination of suspended matter and sediment physico-chemical characteristics (grain size, mineralogy, organic matter content, specific surface area), and of concentrations of major and trace elements in the Adige River mouth in different hydrological conditions, has shown that this mouth acts as a trap for most heavy metals. Heavy metals were found to be preferentially bonded to the particulates, and in the estuarine mixing zone scavenging of most dissolved metals occurs, due to salinity and pH gradients, and to the formation of new particulate organic matter. The surface characteristics of suspended particulate matter [fine grain size, abundance of clay minerals, large specific surface area (SSA), organic and inorganic coatings] favour the adsorption of heavy metals. The sedimentation pattern (rapid deposition due to flocculation of fine particles, and to low environmental energy and estuarine circulation) causes accumulation of particulate matter, enriched in heavy metals, in the prodelta zone. Moderate anthropogenic influence on Cu, Pb, Cd, and Cr concentrations has been recognised in the Adige River. The environmental fate of these elements is determined by the same natural processes, and therefore accumulation in front of the river mouth occurs. The elevated partitioning in the organic phase of the anthropogenically influenced elements, could favour their mobility in different environmental conditions.

Sedimentation of riverborne material in a shallow shelf sea: Adige River, Adriatic Sea

Fast sedimentatio of fine grained riverborne suspended matter occurs in the prodelta zone of the Adige River mouthdue to deceleration of river flow and spreading into the low-energy environment in front of the river mouth. Process is probably associated with flocculation processin brackish water.

The role of suspended matter in the biogeochemical cycles in the Adige River estuary (Northern Adriatic Sea)

Abstract Suspended matter and sediments from the Adige River mouth were analysed in an attempt to elucidate the transfer of heavy metals from the river to the sea. The vertical profile of grain-size spectra of suspended matter in front of the river mouth has shown that the riverine particles are limited to the upper brackish layer. Particulate matter was found to have a large specific surface area, up to 20 m 2 g −1 in the estuarine sample. High quantities of quartz and phyllosilicates (micas and clay minerals) were found in the riverine suspended matter. The quartz content of the suspended matter from the brackish layer was found to be diminishing and with the organic matter becoming the essential component (22%). Higher levels of trace metals were usually detected in suspended matter samples (40 ppm Ni, 200 ppm Cr, 60 ppm Pb, 100 ppm Cu, 320 ppm Zn, and 0·9 ppm Cd) than in sediments. The observed similarity of physico-chemical, mineralogical and geochemical characteristics of riverine suspended matter and recent marine sediments, indicates that most of the riverborne particulate matter is deposited in the proximity of the Adige River mouth. The peculiar characteristics of the chromium level (high bulk concentration and its abundance in the organic fraction of the particular matter) when compared to the other trace metals, indicates the anthropogenic influence on its biogeocycle.

DDT and PCBs in sediments of the Venice gulf

Abstract The concentrations of ?DDT and PCBs in surface sediments collected in the Gulf of Venice are reported. The contribution of the lagoon and of the rivers to sea sediment contamination is discussed. Fresh waters reaching the sea through the lagoon or directly from rivers are responsible for relatively high ?DDT concentrations. The Porto Marghera industrial zone located in the inner border of the lagoon is probably the main PCB source. Two transport mechanisms have been identified: mobilization of suspended solids by tidal movements and direct dumping of industrial tailing and/or dredged materials from the lagoon canals.

Suspended matter properties and its role in pollutant transfer from the river to the sea. Case study: Adige River-Adriatic Sea.

Abstract Suspended matter and bottom sediments have been investigated in the Adige River estuary (Northern Adriatic Sea) and their role in the heavy metals transfer from land to sea. The observed similarity of the geochemical and mineralogical composition between the riverine suspended matter and the marine sediments just at the Adige mouth reveals that most of the riverborne suspended particles settle in the prodelta area together with the associated heavy metals. Among the various toxic elements examinated, chromium has a peculiar behaviour, which indicates the mans influence on its biogeocycle.

Distribution and behaviour of 137Cs in nearshore sediments of the northern Adriatic and at the Adige river estuary, northern Italy

Abstract This paper reports the results of determinations of137Cs and other radionuclides in bottom sediments and suspended matter collectedin a coastal zone of the northern Adriatic off the lagoon of Venice and at the estuary of the Adige River. The activity, behaviour and distribution of137Cs and some natural radionuclides were determined in materials sampled up to 1984. Various artificial radionuclides (134Cs,103Ru,106Ru, together with137Cs introduced by the accident Chernobyl) were detected samples collected in 1986. The study of the distribution of137Cs as a function of sediment properties showed that this radionuclide preferentially accumulates in the finest particles (6–12 phi, i.e. 16-0.24 μm range) and is taken up by adsorpion surface processes. This radioisotope has been used as tracer for recent sedimentary processes occurring in the study area and also as a tracer for predicting the fate of other inorganic and organic pollutants reaching the sediments by natural process. Exceptionally high values of radioactivity were observed after the Chernobyl accident in the estuary of the Adige River, particularly in suspended matter.

Geochemical characteristics of Western Ross Sea (Antarctica) sediments

Abstract A geochemical study of bottom sediments from 50 stations in various Ross Sea sedimentary environments, ranging from the coastal strip to the external platform, situated off Southern Victoria Land between the David and Mariner glaciers has demonstrated the silicate nature of these sediments and significant variations in the major element concentrations. The presence and concentrations of the trace elements studied (Cr, Ni, Co, V, Cu, Pb, Zn and Cd) differ from one geographic area to another, and within a given basin. A statistical analysis of the geochemical variables using the cluster method shows that Si is independent of the other elements, which group into associations. A multivariate statistical analysis based on geochemical, granulometric and environmental parameters identifies five distinct sediment groups located in different areas of sedimentation and with peculiar geochemical characteristics. Group 1, on the external platform, which comprises very fine sediments, is characterised by the highest contents of Mg, LOI, Cr, Ni and V, and of Cu and Zn. Group 2, from the banks formed by pelitic sands, is distinguished on the basis of lower Cu and Zn and higher Cr and Si. Group 3, on the internal platform consisting of sandy sediments, comprises high values of Na, Al, Ca and Pb and low values of Zn and V. Group 4, in the coarse coastal sands, is enriched in Co and Ca, Na, K and Al. Group 5, formed by materials with different grain-size distribution located south of Coulman Island, is distinguished by a very high content of Zn, Fe, Ti and Na, with Cr, Co, Pb and Si being found at lower levels. The materials are glacial-detrital, are derived from the rocky hinterland formations, and are reworked by transport and deposition processes depending on the energy level of the marine sedimentary environments. Given the scarcity of comparison data from the hinterland rocks it is difficult to establish the parent rocks of these glaciomarine sediments on the basis of geochemical data alone. Only in the case of the sediments south of Coulman Island can one be certain of a contribution from the McMurdo volcanics. For the external platform sediments, the highest contents of Si and L.O.I. confirm the input of material from biogenic neoformation.