Determination of REE in urban park soils from Sao Paulo city for fingerprint of traffic emission contamination

The study of rare earth elements (REE) distribution in urban environments has become very interesting in the last years, due to the increasing industrial use of these elements. The REE La, Ce and Nd are used in automobile converter catalysts to stabilize the catalyst support and to enhance the oxidation of pollutants. The honeycomb structure has a typical association of a high Ce (and often also La) concentration combined with high concentrations of Platinum Group Elements. Due to thermal and mechanical wear of catalysts, fine particles enriched in REE are released to the environment. These catalyst particles can accumulate in urban soils, mainly in soils located near high density traffic roads. The aim of this paper was to study the REE distribution and ratios in surface soil samples collected in fourteen urban public parks of Sao Paulo city, to assess the influence of vehicular emissions. Instrumental Neutron Activation Analysis (INAA) was used for the REE analysis. The diagrams normalized to chondrite values showed an enrichment of the light REE (La to Sm), in contrast to the heavy REE (Eu to Lu), with a negative anomaly of Eu. The results obtained indicated that the enrichment in REE is not clearly attributed to vehicular traffic, because of high background values associated to the natural geological composition of the soils. (author)