The sediments of the Venice Lagoon (Italy) evaluated in a screening risk assessment approach: part I--application of international sediment quality guidelines.

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 1) 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 2) define sustainable and environmentally correct ways of managing sediments that are to be dredged for navigational purposes or in relation to other interventions (i.e., ex situ management). This study reports on a critical comparison of chemical quality of sediments in Venice Lagoon and its subregions. Data on the Venice Lagoon were compiled from several studies conducted during the past decade on surface sediment contamination; temporal variation and risks for contaminants at depth were not addressed. The comparison of observed pollutant concentrations with local and internationally used sediment quality guidelines (SQGs) was used as a tool to benchmark different sites and for a tier I (screening) ecological risk assessment. Meaning and relevance of a number of SQGs are discussed, together with the options available for carrying out the comparison with sediment data. The screening of the Venice Lagoon sediment quality is discussed from a risk-assessment perspective and appropriate values for use in an in situ-ex situ management framework are suggested. Although there were some differences depending upon which specific SQGs were applied, different SQGs provided the same general picture of screening risk in Venice Lagoon: Although there are geographic differences, median levels for several contaminants in surface sediments exceeded a number of SQGs. Many contaminants exceed threshold effects SQGs, and Hg exceeds probable effects SQGs in most sub-basins except the southern Lagoon. 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). Ranges are high in all areas, therefore any remedial or disposal decision should use site-specific data.

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.

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.