New insights on mobility and bioavailability of heavy metals in soils of the Padanian alluvial plain (Ferrara Province, northern Italy)

tHeavy metals having both natural and anthropogenic origin are common contaminants in soils andsediments, and can be transferred and bioaccumulated at all levels of the food chain, posing seriousenvironmental concern to the local population. In this paper, agricultural soils from the Province ofFerrara (easternmost part of the Padanian Plain, northern Italy) were investigated to assess the levelsof potentially toxic metals in relation to their phytoavailability. Agricultural soils have been sampled inorder to identify the origin, mobility and bioavailability of heavy metals, collecting superficial and deeper(depths of 20–30 and 100–120 cm, respectively) horizons. The “total” XRF analyses properly elaboratedwith a statistical approach reveal that soils evolved from two distinct types of alluvial sediments, in turnrelated to the Po and Reno rivers; the former type is distinctively enriched in heavy metals (particularlyCr and Ni), reflecting the presence of femic and ultrafemic rocks in the hydrological basin of River Po. Theabsence of Top Enrichment Factors for Ni, Co, Cr, V, and Pb suggests that the content of these elements isnatural and unaffected by contamination, whereas superficial enrichments of Cu (and Zn) is ascribed toanthropogenic inputs related to agricultural activities. Multiple extraction tests using variously aggres-sive reactants (aqua regia, DTPA, EDTA, NH4NO3, and H2O) analyzed by ICP gave insights on the specificmobility of the distinct elements, which decreases in the following order: Pb > Cu > Cd > Co > >Ni > Cr. Tak-ing into consideration the elements that are inducing the main concerns, Cr appears scarcely mobile,whereas Ni could be more phytoavailable and has to be monitored in the local agricultural products.Cd although scarcely abundant has to be monitored for its mobility and toxicity, whereas Cu althoughabundant and extremely mobile doesn’t induce concerns as it is not hazardous for the living receptors.