U, TH and lanthanides in street soils of Sao Paulo city, Brazil

The study of lanthanide distribution in urban environments has become of interest over the last years, due to the increased industrial use of these elements. Sao Paulo is the 6th largest metropolitan region of the world, with about 20 million inhabitants in its metropolitan area, more than 9 million motor vehicles and intense industrial activity. There is little information on U, Th, and lanthanide contents in urban soils, and there are as of yet no reference values for these elements in soils of Sao Paulo city. The present study aimed to determine U, Th and lanthanide concentrations in soils adjacent to avenues of highly dense traffic downtown in Sao Paulo city, to assess their possible sources and potential environmental impacts. The analytical technique employed was Instrumental Neutron Activation Analysis (INAA). Th and U levels ranged from 4.0 to 37.0 mg kg-1 and from 1.6 to 18.7 mg kg-1, respectively. These values are higher than literature values for U and Th in Brazilian superficial soils. The results obtained for the lanthanides indicate enrichment in La and Ce. However, a possible anthropogenic source should be investigated since high background values of these elements may be associated to the natural geological composition of the soils. (author)