Mauro Frignani

Distribution of heavy metals in sediments of the Venice Lagoon: the role of the industrial area

We sampled eighteen stations in the lagoon and nine in the canals of the industrial area of Porto Marghera. At each lagoon site a short core, 10 cm long, was taken and immediately extruded to obtain four slices 2.5 cm thick. Surficial sediment samples from the canals were 2-8 cm thick. Samples were analysed for As, Cd, Hg, Pb and Zn after acid extraction. Maximum values are seen in sediments taken from the oldest part of the industrial area (up to 132, 70, 48, 929, 8295 microg g(-1) for As, Cd, Hg, Pb and Zn, respectively), whereas the highest concentrations in the lagoon are much lower (25, 5.0, 2.3, 114, 1115 microg g(-1) for As, Cd, Hg, Pb and Zn, respectively). Metal distributions are not driven by sediment characteristics, such as grain size composition and organic carbon content: the strong gradients reflect the relative importance of the sources. In fact, a series of factories have been treating minerals for many years for the production of metals and chemicals. Concentration-depth profiles in lagoon sediments suggest that the contamination is decreasing, thus confirming the trends shown by previous core data. Since the release of metals from the industrial plants has been reduced, the polluted sediments stored in the industrial canals are presently the most likely source of toxic metals to the lagoon environment. The influence of this source can be seen in the still high levels found in the lagoon sample closest to the industrial area.

Polychlorinated biphenyls in sediments of the Venice Lagoon

Twenty-four surficial sediment samples, representing different environments within the Venice Lagoon, were analyzed for polychlorinated biphenyls (PCBs) in order to assess degrees of pollution, sources, areal distribution, and potential risk for the environment. Concentrations in surficial sediments range from 2 to more than 2049 microg kg(-1) dw. The maximum is probably due to the discharge of industrial wastes into the Brentella Canal, within the first Industrial Area. Lagoon samples are 11-205 times less contaminated, being influenced by pollutants stored in the canals only occasionally. Congener profiles distinguish PCBs in two main categories. The baseline pollution is probably due to a variety of sources within the lagoon system, whereas less chlorinated PCBs were discharged into the Brentella Canal. Our estimates suggest that, due to high concentrations, toxic equivalents (TEQs) of PCBs are comparable to those relative to PCDD/Fs for the least contaminated samples, whereas they are lower in case of heavy PCDD/F contamination.

Lead-210 as a tracer of atmospheric input of heavy metals in the northern Venice Lagoon

Abstract A chronology for the accumulation of a salt marsh core taken in the Venice Lagoon has been obtained from the activity-depth profile of excess 210 Pb , a naturally occurring radionuclide supplied to the marsh from the atmosphere. Over the past century, the accretion rate of the marsh increased from 0.07–0.08 cm yr−1 to a maximum (0.2 cm yr−1) in ∼1970, followed by a decrease to ∼0.18 cm yr−1. The increase and recent constancy of accretion of the marsh follow the historical pattern of sea level change due to natural and human-induced (groundwater extraction) causes. The 210 Pb chronology is used to determine depositional histories of anthropogenic trace metals, defined as metal concentration in excess of the background value determined at depth in the core. Several patterns are evident: fluxes of excess Ag and Cd increase to the present, Ni and Zn show increasing fluxes to ∼1970 with factor-of-two decreases in recently deposited material. Lead shows high and variable fluxes between 1940 and 1984, with recent decreases. Copper fluxes display a broad peak around 1960. Recent (∼1990) metal fluxes recorded in the marsh core agree within factors of 1.5 to 4 with directly measured (1993–1994) atmospheric fluxes in wet and dry deposition at a site in Venice. The data show that Cu and Pb inputs to the marsh can be accounted for by atmospheric deposition and significant fractions (27–42%) of Cd, Ni and Zn can be supplied by this pathway. Excess 210 Pb inventories in both marsh and subtidal sediments from the Venice Lagoon are consistent with atmospheric supply of this radionuclide. If we assume that atmospheric supply of trace metals is the dominant source of heavy metal contaminants to the marsh, integrated deposition of excess metals in the marsh core, normalized to that of excess 210 Pb , can be used to determine upper limits on the atmospheric contribution of trace metals to lagoon sediments. The results demonstrate that point source inputs of Cu, Ni, Pb and Zn are evident in sediments near the mainland, especially near Porto Marghera, but atmospheric inputs of Pb (and possibly Zn) tend to dominate in the northern and eastern portions of the lagoon.

Sediment accumulation rates in the southern Barcelona continental margin (NW Mediterranean Sea) derived from 210Pb and 137Cs chronology

Sediment cores were collected from the southern Barcelona continental margin, including the Foix canyon, in order to study sediment accumulation in this area. For this purpose, 210Pb, 137Cs and, to a lesser extent, 239,240Pu and heavy metals, were determined in sediment sections using state-of-the-art techniques. 210Pb concentration profiles and 137Cs, 239,240Pu and heavy metals profile features were used to establish the sediment chronologies. Further information was also obtained from granulometric analyses. The magnitudes studied and correlated in this work included surface activities, mixing rates, accumulation rates and inventories. Sediments on the continental shelf showed a varied degree of mixing (except possibly CN-23), sedimentation rates were relatively small and the sedimentary material probably had a common origin. Cores from the slope showed less mixing and, in cores CN-36 and EB-2, located in the Foix canyon axis, the 137Cs signal vs. depth was clear and well preserved. Accumulation rates and total 210Pb inventories were maximum in core CN-36 at mid-slope of the canyon, which was considered to be an active depocenter. Core CN-38, collected on the open slope, showed a much smaller accumulation rate. Therefore, it was concluded that shelf material is being transported alongshore by the prevailing currents and becomes focused in the canyon, which is acting as a natural trap. Within the canyon this material is preferentially deposited at a mid-slope depocenter. Little extra material reaches the lower canyon area. In this area, core EB-2 appeared to show signs of the presence of resuspended material, possibly derived from the canyon walls. Finally, observed changes in sedimentation rates during the 1930s could not be explained on the basis of current knowledge and this is suggested to be an important subject for further research.

Accumulation rates and137Cs distribution in sediments off the Po River delta and the Emilia-Romagna coast (northwestern Adriatic Sea, Italy)

Abstract Sediment accumulation rate studies were conducted using 210 Pb and 137 Cs with the aim of understanding recent and present sedimentation patterns on the Italian Adriatic continental shelf. Since there is no simple model governing the delivery of radionuclides to coastal sediments a variety of approaches were used to estimate dry mass accumulation rates. At many sites there was little divergence between the various estimates, and the mean value is taken to be a reliable estimate of the net sediment accumulation rate. At other sites greater variation was observed. Reasons for these variations can include both secular changes in accumulation rates, and interruptions to the process of sedimentation arising from, for example, sediment mixing, scouring and focussing. At these sites best estimates of accumulation rates are given on the basis of an assessment of the most appropriate dating technique. Highest mass accumulation rates are found near the Po river (up to 1.80 ± 0.29g cm −2 year −1 ), reflecting the large supply of sedimentary materials from this source. South of the delta accumulation rates were much lower, ranging from 0.22 ± 0.06 to 0.39 ± 0.06g cm −2 year −1 . At a number of sites the 137 Cs activity versus depth profile had a well defined peak (resulting from weapon fallout) which served to identify the depth corresponding to 1963, providing a valuable check on the 210 Pb derived accumulation rates. At other sites this peak was too broad or confused to be a valuable reference. The distribution of 210 Pb and 137 Cs reflect their different geochemical behaviour and sources, and provide information on the process of sediment accumulation.

Metal fluxes to the sediments of the northern Venice Lagoon

Eighteen short cores were analyzed for major and trace metals (Al, Fe, Ca, Mg, Mn, Si, K, Ti, Pb, Zn, Cu, Ni, Cr), 210Pb, 137Cs, and other sediment characteristics, so as to describe the chronology of pollution and calculate metal concentration factors and fluxes. Substantial evidence was found that trace metal profiles are influenced by anthropogenic sources and by changes in sediment composition. Only Zn presents concentrations (up to 13.1 μmol g−) and concentration factors (1.3 to 13.2) that can be attributed to heavy contamination. Pb, Cu and Ni, in this order, are less significant. The areal distribution of concentrations and inventories reflects the importance of direct sources, in particular the industrial area of Porto Marghera and the Dese river. The inventories of excess metals, above pre-industrial levels, were determined for each core and the three different parts of the study area, the amounts of Zn accumulated in sediments are 11.0 Mmol, 5.1 Mmol and 0.37 Mmol in the Campalto, S. Erasmo, and Palude di Cona areas, respectively. Ruxes were also calculated and compared with those suggested for the atmospheric delivery by Cochran et al. [(1995)b. Atmospheric fluxes of heavy metal contaminants to the Venice Lagoon, Rapp. Comm. Int. Mer Medit., 34, 136.], the atmospheric contribution is predominant or significant in many cases, especially at sites far from the major local inputs. Concentrations and fluxes show a significant increase in the anthropogenic metal supply starting from the second decade of this century, with maximum inputs in the period between the (1930)s and the (1970)s. At some stations a decrease in heavy metal contamination of surficial sediments was found and this could be ascribed to a reduced input of pollutants in recent years.

Accumulation of polychlorinated dibenzo-p-dioxins and dibenzofurans in sediments of the Venice Lagoon and the industrial area of Porto Marghera.

Two sediment cores collected from the central Venice Lagoon and five from the canals of the nearby industrial area were studied in order to assess the temporal evolution of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) delivery and present trends. The most polluted site is C12, in the Brentella Canal, with a total equivalent (TEQ) concentration of 2858 and 64,130 ng kg-1 at the surface and at 18-20 cm depth, respectively. High values can be also found in the Nord Industrial Canal and in the Salso Canal: 3000 and 2500 ng kg-1, respectively. Lagoon samples are much less contaminated, with TEQ downcore maxima of 22 and 53 ng kg-1, being influenced by pollutants stored in sediments of the canals only occasionally. Sediment chronology, based on 210Pb and 137Cs activity-depth profiles, shows that the highest fluxes occurred in the 1970s and early 1980s, and that pollution is now decreasing. Homologue profiles can distinguish PCDD/Fs from different sources: combustion for octachlorinated dibenzo-p-dioxin (OCDD) and stripping of VCM for octachlorinated dibenzofuran (OCDF) alone, whereas several activities carried out in the past within the industrial area can be responsible of the overall contamination by furans.

Accumulation of polychlorinated biphenyls in sediments of the Venice Lagoon and the industrial area of Porto Marghera

Sediment cores, collected at seven sites in the Venice Lagoon and within the canals of the industrial area were analyzed for polychlorinated biphenyls (PCBs) in order to assess the chronology of pollution and its present trends. The surficial concentration of PCBs is very high (more than 2049 microg kg(-1)) only in the Brentella Canal, probably due to a very recent contaminating episode. Very high values downcore (up to 41,639 microg kg(-1)) can be found in different parts of the industrial area, especially in the canals Lusore-Brentelle and Salso. Lagoon samples are much less contaminated (2.7-123 microg kg(-1)), being influenced only occasionally by polluted sediments resuspended from the canals. Sediment chronology shows that the delivery of contaminants peaked in the 1970s-early 1980s, decreasing since at most sites. Congener profiles distinguish PCBs in two main categories: heavy congeners characterize a baseline pollution, probably due to a large variety of sources within the lagoon system, whereas a mixture of light PCBs was discharged into the canals Brentella and Salso.

PBDEs and PCBs in sediments of the Thi Nai Lagoon (Central Vietnam) and soils from its mainland.

Concentration and distribution of PCBs, PCB 11, and PBDEs in both surficial sediment and soil samples, taken from a zone subject to recent accelerated development, were investigated to assess the environmental quality and understand both natural and anthropogenic processes that influence contaminant behaviors. Values of PCB and PBDE are in the lower range of those reported in literature, typical of low impacted coastal zones. This could be due to efficient processes of resuspension and removal. Contaminants in the lagoon showed higher concentrations in sediments from sites close to the city and the outfalls of the industrial area, while soils showed maximum values in the northern samples. In addition, congener patterns and statistical analyses suggest the presence of effective degradation processes, especially for PBDEs, with the exception of the most concentrated samples that may indicate a direct input. PCB 11 is a significant component (up to 18%) in most lagoon sediments. Its presence is strongly associated with fine particles, thus the distribution seems to be driven mainly by the system hydrodynamic and does not trace the sources. Due to evaporation, only flooded agricultural soils show a similar relative abundance of this congener.

Particle fluxes and biogeochemical processes in an area influenced by seasonal retreat of the ice margin (northwestern Ross Sea, Antarctica)

Abstract Fluxes of biogenic components were determined using time-series sediment trap samples collected at site B (74°01.50′S, 175°05.55′E) in the northern Joides Basin of the Ross Sea from December 1994 to January 1996. In most cases, a great part of the material collected by traps (200 and 540 m depth) was biogenic, opal being the most abundant constituent followed by organic matter. The composition of particles shows a seasonal pattern in the upper trap, which is much less evident at depth. Fluxes showed a marked seasonality due to the presence, in winter, of ice cover. During the sampling period, mass fluxes varied from 0.03 to 120 mg m −2 day −1 and from 24 to 393 mg m −2 day −1 at the upper and bottom level, respectively. Values of 0–64 mg m −2 day −1 of biogenic silica and 0–7.8 mg m −2 day −1 of organic carbon were obtained at 200 m depth. Near-bottom fluxes were almost always much higher: 11–141 and 1.5–19 mg m −2 day −1 , respectively. 210 Pb fluxes are lower than expected, and this means that particles sink rapidly without reaching an equilibrium with the radiotracer. A mechanism of focusing affects the bottom trap and much more, the seafloor. At site B, we measured particle fluxes that are much lower than those obtained at other locations in the Ross Sea. This can be due to low production and export during the sampling period, and underlies the necessity to further investigate the interannual variability of these processes.