Speciation of lead in contaminated soil under the influence of plants and phosphate amendment type C. Diyab, F. Juillot1, C. Dumat, G. Morin', M. Benedetti2 and A. Mariotti LBI, Laboratoire de Biogéochimie Isotopique, UMR 7618 du CNRS, INRA-Paris 6, 4 place Jussieu, Tour 26 4e Étage Case 120, 75252 Paris cedex 05, France 1 LMCP, UMR 7590 du CNRS, Paris 6 & 7, IPGP, France 2 LGM, UMR 7047 du CNRS, Paris 6, France Abstract The toxicity of an element and its behaviour depend on its chemical form (speciation) and concentration. The objective of our work is to study the speciation of Pb under the influence of phosphate amendments (solide, soluble) and type of plants : peas, tomato (pH variation, organie acid complexes formation) in a polluted soil near one of Europe's largest lead contaminated area in the north of France. Chemical and physical methods were used to determine the speciation of lead in rhizospheric soil (chemical extraction, pFX, EXAFS, SEM.). Me formation oflead phosphate complexe was confirme in rhizospheric soil of both plants. Quantity and chemical structure of phosphate lead complexe formed in soil, varied with the type of plante and phosphate amendement added. Analysis of organic acids secreted by the two plantes were performed to understand the effect oforganic acidson the speciation oflead in the rhizospheric soil. 1. Materials and Methods 1. 1 Studied site The studied site was contaminated by the emission of a pyrometallurgical factory near Evin-Malmaison where the content of Pb and Zn is higher than 2000 ppm. This site corresponds to a historical pollution due to atmospheric metal deposition (primarily Pb, Zn, but also Cu, Cd and Cr) (Figure 1 localization of the site noted P2). This strongly contaminated site is responsible of a non-point source pollution affecting the close agricultural perimeter. A top soil (pH 5, 5) under poplar plantation was retained for this work : it bas not been cultivated since the beginning of anthropic pollution and has not received phosphate amendments. The concentrations of lead and zinc are very important, approximately 2500 ppm and 4000 ppm respectively. Moreover, on this site many studies were completed in order to determine the speciation of the metals in the non rhizospheric soil and in the soi ! solution (Juillot, 1998 ; Morin et al., 1999 ; Dumat et al., 2001), which concluded that in this soil lead is mainly related to the organic matter and adsorbed on iron hydroxides. After sampling, the soil was air dried, disaggregated and passed through a 2 nm sieve.-, nalysis of total soil lead, in bulk and cultived soil