The sediments of the venice lagoon (Italy) evaluated in a screening risk assessment approach: Part II—lagoon sediment quality compared to hot spots, regional, and international case studies

Abstract

The objective of this study was to carry out a critical comparison of data on the screening quality of surface sediments in Venice Lagoon (VL; main lagoon and its subbasins, Porto Marghera [PM], and Venice City Canals) and in other transitional and coastal ecosystems with various levels of human impact (urbanization and industrialization). To put VL in terms of reference and industrialized sites in the region, case studies were selected from the North Adriatic Region; to gain insight into how VL sediments compared to transitional areas throughout the world, case studies also were selected from a number of regions internationally. In order to compare regional levels of contamination, statistically processed sediment contaminant levels within a region (minimum, maximum, mean, and median), not individual sample values, are compared. The screening quality (relative to a variety of sediment quality guidelines) and the drivers of screening risk (based upon contaminant mixtures) of the VL sediments and other coastal and transitional sites are compared and discussed. The VL sediments have hazard quotients on the low end of the range typical of moderately urbanized and industrialized sites and higher than background conditions among the case studies reviewed. The Hg levels in the VL were generally higher than at other sites, and other contaminants were either equivalent or lower. Although sediments have somewhat higher levels of some contaminants and lower levels of other contaminants in PM and Venice City (VC) canals, levels for most contaminants are comparable to case studies with high levels of anthropogenic impact. For many contaminants of interest, PM (and for some, VC) sediments have some of the highest levels of any case study reviewed. How PM and VC rank when compared to other highly industrialized sites depends upon how data are synthesized and how ranges are taken into account. Actual risk must be evaluated using a weight-of-evidence approach, because natural background levels and site-specific bioavailability will differ both regionally and internationally.

The sediments of the venice lagoon (Italy) evaluated in a screening risk assessment approach: Part I—application of international sediment quality guidelines

“…Figures 6 and 7 clearly show also how the 2 hot spots in the lagoon, PM and Venice City canals, significantly differ from the open lagoon. These 2 sites are discussed in greater detail in the companion paper (Apitz, Barbanti, et al 2007).…”

“…As can be seen in the contour plots in Figures 2 and 3, sediment contaminant levels are highly heterogeneous in most areas of the lagoon and there are large ranges between the minimum and maximum values in each area (Table 4). Examination of the raw data (see Apitz, Barbanti, et al 2007) for a graphical view of the data ranges, means, and media) revealed that, in most cases, the mean sediment chemistry values also are much higher than the median values, suggesting that the means are dominated by the few hot spot areas in a region. However, because dredging projects and other potential activities can span large and heterogeneous areas, hot spot data were not treated as outliers to be removed from the dataset, but as part of the data range that represents the range of sediment quality in the regions.…”

“…These datasets were kept separate from data on Venice City Canals (VC) and Porto Marghera (PM), based upon evidence that these 2 sites are not only confined geographically, but also represent hot spots of contamination. Data on the surface sediment chemistry in Venice and the PM canals were taken from a previous compilation (Barbanti et al 2001) and are compared to data in the main Venice Lagoon in the companion paper (Apitz, Barbanti, et al 2007).…”

“…Using SQGs as benchmarks, the Venice Lagoon sediments also are compared to hot spots in the lagoon (Venice City Canals and Porto Marghera), to other sites within the Adriatic Region, and to a suite of international lagoon and estuarine sediments, subjected to a range of anthropogenic pressures. The results of this comparison are the subject of the companion paper (Apitz, Barbanti, et al 2007). Because the bulk of both these studies have been carried out on regionally averaged data, our analysis will address sustainable risk management issues at the basin‐scale, while assessment and management at the site‐specific scale would require more focused analysis.…”

“…In both cases, risk can be defined simply as the likelihood that adverse effects may occur or are occurring as a result of exposure to one or more stressors. In practice, however, risk means different things to different people (and at different points in the decision process) and it can be said that the concept of absolute risk should be combined with more complex evaluation, such as relative risk, uncertainty in risk estimation, regional versus site‐specific risk, trade‐off between risks posed by different options, and socio‐economic risk (NRC 1997; Apitz and Power 2002; Sorensen et al 2004; Bridges et al 2006; Apitz, Carlon, et al 2007). Thus, the ERA process, which is carried out to identify the potential risk, either in place or to a proposed disposal site, of a contaminated sediment, is just 1 part of an overall decision and management process.…”