DOI: Alessandro Amorosi and Irene Sammartino
Authors: 10.5176/2251-3353_GEOS13.28
Abstract: When defining the status of soils in relation to metal pollution, one of the major issues is the reliable assessment of natural metal concentrations, i.e., background values. Through integrated sedimentological and geochemical analyses of 1,418 samples from the Po Plain (Italy), collected at 709 sampling stations at two distinct depths (120-130 cm and 20-30 cm, respectively), we document that the natural spatial distribution of five potentially toxic metals (Cr, Ni, Cu, Pb and Zn) can be predicted as function of three major factors: sediment provenance, grain size and soil maturity. Background values of Cr and Ni invariably exceed the threshold limits where alluvial and coastal sediments are supplied by ultramafic (ophiolite-rich) sources. Within the individual provenance domains, natural metal concentrations are strongly influenced by transport and accumulation processes, with a general tendency towards higher concentrations in the finest-grained fractions. Once background values are established on the basis of data from the deeper samples, geochemical anomalies (reflecting anthropogenic pollution) can promptly be identified and estimated calculating the geoaccumulation index from topsoil samples. The use of sedimentological criteria to fingerprint the geochemical composition of distinct depositional facies is presented here as a pragmatic tool to enhance predictability of natural metal contents in sediments, with obvious positive feedbacks for legislative purposes and environmental protection. The new type of geochemical map derived from this work is currently applied by the Emilia-Romagna authorities in lieu of the mono-leveled values established by the Italian environmental agencies.
Keywords: Background values, Metal pollution, Geochemical mapping, Geochemical anomalies, Sedimentology, Po Plain, Italy
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