Saturday, 15 July 2006

Clay Mineralogy and Trace Elements Content in Volcanic Polluted Soils from South Italy.

Mariavittoria Zampella1, Paola Adamo1, Laurent Caner2, Sabine Petit2, and Dominique Righi2. (1) Dipartimento di Scienze del Suolo, della Pianta e dellĺAmbiente, Univ di Napoli Federico II, Via UniversitÓ 100, 80055 Portici, Napoli, Italy, (2) Univ de Poitiers, UMR CNRS 6532 HydrASA, 40, Avenue du Recteur Pineau, 86022, Poitiers, France

The Cr and Cu contaminated volcanic agricultural soils from the Solofrana river valley (south-western Italy) were investigated for clay mineralogy and trace elements content. Cr contamination originated from deposition of polluted sediments on the soil surface by overflowing events and from irrigation with water of the Solofrana river, polluted by Cr-rich effluents from tanning plants. Copper contamination was more likely due to past agricultural large use of fertilizers and pesticides. Soil profiles from an area subject to overflowing events (P1) and from an area irrigated with the Solofrana river contaminated water (P2), a control soil (neither flooded, nor irrigated) (C) and river sediment (S) were studied in order to investigate the occurrence of Cr, Cu, Ni and Zn in the <2.0 Ám and <0.1 Ám fractions and the distribution of trace metal-bearing fine particles in the soil matrix. Quartz, feldspars, carbonates, vermiculite, chlorite, smectites, illite/mica, kaolinite and halloysite at 1.0 nm were detected by XR-diffraction in the <2.0 Ám fraction. Poor crystalline halloysite (proto-halloysite) at 1.0 nm was the main component of the <0.1 Ám fraction along with small amounts of illite/mica and kaolinite. Oxalate and dithionite-citrate extractions suggested the presence of allophanic materials. Thermal analysis showed the occurrence of organo-mineral complexes. According with optical microscopy observations of soil thin sections, the fine material carried on soil by river water occurs, in P1, as surface massive structured flooded layers, in P2, as round microaggregates incorporated in the soil matrix and pore deposits. In both soils translocation of fine particles along the pore network was evidenced by occurrence of silt and clay coatings at different depths. SEM/WDS analyses showed that, in all polluted soil and sediment samples, more than 50% of Cr and Cu total content was associated with the <2.0 Ám fraction. Cr and Cu were always more concentrated in the fine than in the coarse clay fraction, although fine particles from surface soil horizons had higher Cr (273-1638 mg kg-1) and Cu (105-243 mg kg-1) content compared with those separated from deeper horizons (Cr 13-63 mg kg-1; Cu 18-24 mg kg-1). Results suggest in the studied soils a risk of progressive migration down the soil profile of trace metals bound to colloids in the soil water flow.

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