| Abstract |
A number of studies carried out in recent years have shown the presence of a wide range of contaminants in the Venice Lagoon. It is important to have a good understanding of the ecological quality of Venice Lagoon sediments, in order to: i) define and locate areas where a threat to the environment is present and therefore an intervention is needed (i.e. in situ assessment and management); and ii) define sustainable and environmentally correct ways of managing sediments which are to be dredged for navigational purposes or in relation to other interventions (i.e., ex situ management).To examine how various regional and international SQGs ‘classed’ screening risk in Venice Lagoon sediments, data on median contaminant levels in surface sediments in Venice Lagoon resulting from a literature review were compared to a range of local and international sediment quality guidelines (SQGs). Then data on sediment contaminant levels in various areas and sub-basins of Venice Lagoon (main Lagoon, Porto Marghera and Venice City Canals) and in other regional and international transitional and coastal ecosystems with various levels of human impact (urbanization and industrialization) were evaluated based upon a selected consensus-based SQG. Finally, screening sediment quality for all of Venice Lagoon was mapped and contoured, relative to this consensus-based SQG and briefly compared with direct toxicity measurement through a battery of bioassays.SQGs allow the sediment areas to be put in terms of potential, or screening, risk. Although there were some differences depending upon which specific SQGs were applied, the Venice SQGs and other international SQGs provided the same general picture of screening risk in Venice Lagoon despite geographic differences. Venice Lagoon South has the lowest screening risk levels, Venice Lagoon Central/North has the highest (and is nearest to the Porto Marghera and Venice City Canals sites).The Venice Lagoon sediments have hazard quotients on the low end of the range of moderately urbanized and industrialized sites and higher than background case studies reviewed. Hg levels in the Venice Lagoon were generally higher than equivalent sites, while other contaminants were either equivalent or lower. In Porto Marghera (PM) and Venice City Canals (VC), for many contaminants of interest, PM, and for some, VC sediments have the highest levels of any case study reviewed. Ranges are high, so in all cases, remedial or disposal decisions should be based upon site-specific (and preferably tiered) data.The use of hazard quotients makes it possible to compare screening risks due to different mixes of contaminants within and between sites, but results should be interpreted with caution. How these sites rank when compared to some of the other highly industrialized sites depends upon how data are synthesized and communicated. Actual risk must be evaluated using a weight of evidence (WOE) approach, as site-specific bioavailability and background levels will differ both regionally and internationally.Whilst there are subtle differences, the current Venice sediment classifications (A, B and C) ‘performed’ in a similar manner to SQGs in similar classes, suggesting that regions of Venice Lagoon would not be classified much differently if other SQGs such as TEL, ERL, PEL, ERM or AET were adopted. The Italian sediment quality objectives, on the other hand, are significantly more conservative than any other SQGs examined, with the exception of the Flemish Reference values. A number of European nations are considering criteria based upon contaminant levels in relatively pristine modern sites, or based upon derivations of historical (pre-anthropogenic) contaminant levels. When used as a standard, such an approach lacks discriminating power, designating almost all sediments within an urbanized or industrialized region as of concern, or even, in many cases, mandating action or prohibiting various management approaches in a large percentage of sediments. While generally based upon the laudable desire to return sites to unimpacted levels, there is a risk that overprotective criteria have the opposite effect: by designating too large a percentage of sediments as requiring management or control, limited resources may be improperly allocated. Which set of SQGs is most ‘appropriate’ for the Venice Lagoon sediments depends upon the questions being asked. However, the Venice classifications are currently being used as pass-fail criteria, without consideration of site-specific conditions. The fact that they performed similarly to SQGs in similar classes suggests that any work to develop more site-specific SQGs (with the same general decision classes) would probably not make much difference in how sediments were ultimately classified and managed unless the fundamental approach was changed from a pass-fail to a tiered and WOE approach integrated in a comprehensive decision framework. For Venice Lagoon, and for other regions, although SQGs should be developed with care, in a scientifically defensible and risk-based manner, an equally or more important issue to be addressed is their role in overall decision frameworks. |
