TIME EVOLUTION OF PB(II) SPECIATION IN PAMPA SOIL FRACTIONS

G. FERREYROA; A. MONTENEGRO; M. B. TUDINO; R. LAVADO; F. MOLINA

Bahìa Blanca

Congreso; XXIV Congreso Argentino de la Ciencia del Suelo; 2014

Soil pollution by heavy metals, particularly lead is an important environmental concern; the bioavailability of such pollutants is strongly dependent on its chemical form, thus it is expected that it will be modified by the soil composition and climate conditions. Here, the speciation of Pb(II) in soil fractions as a function of time is studied, using a selective sequential extraction method. The sample came from an Argentinean Pampas region, and was extensively characterized, including Rietveld analysis of the silt+clay fraction XRD pattern to find the major mineral components. A shelter experiment was run twice, once in winter, once in summer. The results show different speciation time profiles in both cases, showing faster changes in winter due to higher water content. The summer experiment corresponds to an earlier stage in the speciation profile evolution compared with winter. The soluble/exchangeable fraction decreases with time in summer (after 60 days decays, from an initial value of 21.4 %, to 11.5 %) but shows a lower and relatively constant value in the winter run (10.3-9.6 %). A high proportion is found to be adsorbed onto the stable (aluminosilicates+quartz) mineral fraction (between 40 and 60 % approximately). The results strongly suggest that, even at a short time after soil pollution with Pb, only a low fraction is bioavailable (10.6 % on average). The most stable (mineral incorporated) form is observed to increase with time (from 10 % to about 20 %). Soil water content appears to be more important than temperature in determining the differences between the two experiments. Additionally, Pb speciation in a long-term polluted soil is being analyzed.