Luca Giorgio Bellucci

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.

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.

An Integrated Approach to the Assessment of Pollutant Delivery Chronologies to Impacted Areas: Hg in the Augusta Bay (Italy)

Assessing pollution levels and trends in heavily impacted environments is important but hardly achievable due to the difficulty of recovering suitable undisturbed sediment records. An integrated approach is here presented to solve this kind of problem. It was adopted in the Augusta Bay (Italy) for the study of Hg historical inputs and present trends. Archive information on dredging and mud disposal, together with bathymetry and high-resolution seismic profiles, were used to identify suitable sampling sites. Undisturbed sediment cores were collected in the port and bay. Sediments were analyzed for depth distributions of radiotracers ((210)Pb and (137)Cs), Hg, and main sediment parameters (magnetic susceptibility, grain size, dry bulk density, mineralogy, and organic carbon and nitrogen contents). Hexachlorobenzene (HCB) was also analyzed as an additional time tracer, since its production history in the area was well-known. Results show that peak Hg contamination (up to 575 mg·kg(-1)) was reached in the 1970s. Technological improvements and waste treatment in the following years determined a consistent decrease, but high concentrations still affect surficial sediments (0.25-92 mg·kg(-1)). Hg-HCB correlation suggests that this situation is likely the effect of resuspension and redistribution of deep sediments by dredging and naval traffic.

Polycyclic aromatic hydrocarbons in sediments of the Venice Lagoon

Three sediment cores were collected in the Venice Lagoon: two from mud flats (E, F) and one from the San Giuliano Canal (I1), which borders the industrial district. Samples were analysed for the 15 polycyclic aromatic hydrocarbons (PAHs) listed as priority pollutants by the U.S. EPA. Sediment chronologies were established using both 137Cs and 210Pb activity-depth profiles, and confirmed by independent information. The highest levels of PAHs, up to 16,474 μg kg−1, characterise the sediment from the industrial canal. In lagoon sediments maximums were 618–1,531 μg kg−1, while surficial values were 315 and 810 μg kg−1. Dated concentration-depth profiles suggest that highest inputs occurred in the first half of last century and were followed by significant decreases. The industrial activities played a major role in the PAH contamination of lagoon sediments, as suggested by the high concentration gradients in the study area. The main source, based on the information provided by the relative abundance of congeners, is represented by high temperature combustion processes. Petrogenic sources may have influenced some samples, whereas the effects of selective transport and diagenesis are difficult to assess. The sediment of the industrial canal has the potential to occasionally cause adverse effects in sensitive species.

Recognizing different impacts of human and natural sources on the spatial distribution and temporal trends of PAHs and PCBs (including PCB-11) in sediments of the Nador Lagoon (Morocco).

The Nador Lagoon holds a major interest in present-day Moroccan socioeconomic development. This environment is exposed to a number of potential polluting sources, such as mine tailings, urban and industrial dumping, and untreated wastewater inputs from surrounding cities. The aim of this study was to assess concentrations and trends of persistent contaminants such as PCBs and PAHs and to identify their origin. The non-Aroclor PCB-11 was determined for the first time in the lagoon sediments. Chronology and source assessment helped identifying the timing and nature of inputs and post-depositional processes controlling the two classes of contaminants: PAHs present a typical mixed petrogenic signature, with the exception of sediments deposited in the period 1930-1960 near the city of Nador, when pyrogenic inputs prevailed; PCBs show signs of microbial anaerobic degradation from 1950 to 1990, probably linked to changing hydrodynamic conditions in the South-Western part of the lagoon where agricultural inputs are dominant. The presence of PCB-11 is linked to specific productions and might be affected by degradation processes. Presently, different land uses (e.g., urban and agricultural areas) appear to be the key factors in controlling the level and composition of PAHs and PCBs in lagoon sediments. Total PAH and PCB levels are low (from 21.6 to 108 ng g(-1) and from 2.50 to 20.7 ng g(-1), respectively) but recent increasing values and the potential threat to humans and biota require continuous and constant monitoring.

Bioturbation experiments in the Venice Lagoon

Short experiments (14–21 days) were carried out during autumn 1998 and spring 1999 at one selected site of the Venice Lagoon to measure bioturbation activities and mixing rates, as well as to obtain quantitative information on benthos functionality. Fluorescent sediment particles (luminophores, 63–350 μm) were introduced as pulse inputs at the sediment surface. The concentration–depth profiles of the tracer were simulated with a new advection–diffusion–non local model applied under non-steady state conditions. This allowed the quantification of the mixing parameters associated with different mechanisms: biodiffusion (Db), bioadvection (W) and non-local mixing (Ke, z1, z2). A parameter RS (removed sediment) was also calculated to account for the flux of sediment due to non-local transport. Results show that bioturbation was dominated by biodiffusion in autumn and by bioadvection in spring. Mean mixing parameters Db, W, and RS changed from 3.09 to 0.87 cm2 y−1, from 0.93 to 15.50 y−1 and from 5.85 to 7.79 g cm−2 y−1, respectively.