Leaching tests: useful tools for the risk assessment of contaminated sediments.

In recent years, the importance of trace metal mobile fractions rather than total contents in environmental matrices is increasing in risk assessment evaluation of contaminated sites. In this study different leaching/extraction tests, aimed at the measurements of mobile fractions of trace metals and standardized at European Committee for Standardization (CEN) for the characterization of waste, have been compared with those adopted by the Italian legislation for soils. All these procedures have been applied on Venice Lagoon sediments, in order to extend the appliance of these methods to sediments and to verify the consistency of the results when different leaching tests are applied on the same sample. The results show that these tests can be applied successfully to sediments and confirm that leaching/extraction methods based on the main parameters controlling the remobilisation of trace metals are useful tools for risk-assessment, because they can allow a "transparent" interpretation in the light of key environmental variables (such as pH and DOC) controlling metal mobility. Further the use of geochemical models in support to leaching allows the assessment of trace metals mobility in the long-term.