STRATEGY FOR CLAIMING AN ENVIRONMENTAL ATTENUATION OF HEAVY METALS

Contaminated sites recovery is time consuming and involves increasingly high costs, despite in presence of limited economic resources availability. The existing legislation or guidelines currently stand on the total soil content of pollutants. On the contrary, within the frame of a natural attenuation process, it becomes fundamental to establish pollutants ultimate fate in the environment, and to adopt a strategy in order to realize in-situ pollutant attenuation. As far as organic pollutants are concerned, several chemical/biological processes have been alreadyproposed for a complete remediation. If concerning heavy metals, the environmental attenuation can only be seen as a reduction of their mobility and availability to plants and other environmental resources. Unfortunately, the understanding of heavy metal geochemical processes has been limited by a lack of simple procedures of work. In this framework, the need of a new technique, devoted to study metal bindings and mobility in interstitial pore water and their bioavailability, has arisen. A diffusive gradient technique in thin film (DGT) has already been used to measure fluxes of trace metal in sediments and soils. The fluxes are induced through a chelating resin separated from the soil by a diffusion gel layer. In a real case history the mobile pool of Cu and Ni in polluted soil, both straight in the field and in a laboratory reconstructed microcosm has been studied. The DGT deployment directly in-situ provided specific and reliable information on the metals binding and desorption kinetics. In this way it has been possible to quantify the mobility of the heavy metal cations with a paramiter called “effective concentration” (CE). Within this frame the DGT gives the desired information for avoiding the risk of underestimate, or uselessly assert the contamination of a site. The protocol adopted identifies also a useful strategy to monitor the attenuation process.