Preliminary results on the distribution and solubility of heavy metals in urban and suburban soils of Ravenna

Three location types of different environmental impact were identified in the district of Ravenna, a city park, a suburban pinewood and rural arable fields. In this paper we reported the preliminary results about the relationship between land use and soil management and chemical fractionation of heavy metals. The distribution and solubility of Cr, Ni, Cu, Zn, Cd and Pb was determined by water and LMWOAs extraction procedures in A1 and A2 horizons of 13 soils. In general the maximum potentially toxic element concentrations were associated with soil collected from the pinewood, and tended to decrease with depth. The upper layer enrichment of the pinewood soils clearly revealed an anthropogenic origin of pollution. Under the pinewood, the metal levels presented a rather similar distribution pattern in terms of ranking of extractive power by the single extraction procedures, with Zn and Ni being more dissolved than Cu by the use of LMWOAs extractant. However, both readily available pools were demonstrated to be more enriched in Ni, Zn, Cd and Pb compared to city park and arable soils. City park and arable soils were highly endowed in Cu. The highest concentrations were particularly shown by the arable soil under orchard, due to frequent fungicide applications. Single extractions were compared to dissolved metals in aqua regia by bivariate correlation. By comparison, pinewood soils showed higher relationships between soil pseudo-total contents and metal concentrations by single extraction procedures than city park plus arable soils. The highest correlation coefficients were found for Zn and Cd by water extraction, and for Cu and Pb by LMWOAs extraction. Both water and LMWOAs pools exhibited poor correlation with pseudo-total contents of Cr and Ni