Scanning electron microscope and statistical analysis of suspended heavy metal particles in San Luis Potosi, Mexico

Three hundred samples of urban aerosol were collected in high-volume sample rs from five urban locations situated near an important metallurgical plant in the city of San Luis Potosi, Mexico. Whole samples were analyzed by ato mic absorption (AA) for Pb, Cd, As, Cu, Ni, Fe and Cr. One hundred eighty o f these samples were subjected to X-ray microanalysis (EDS) coupled with a scanning electron microscope to classify individual particles according to their chemical or mineralogical composition. The principal component analysis (PCA) obtained from the bulk sample analys is, and X-ray microanalysis from individual particles, confirmed chemical a ssociations among elements directly and indirectly. PCA from bulk assays ma de the most effective use of X-ray microanalysis to characterize major part icle types. Some chemical associations would be difficult to detect using m icroanalysis, alone, for example, in anthropogenic complex phases. In this work, the combined use of microanalysis and statistical methods permitted i dentification of associations among elements. We observed an association of Pb-As-Cd and Fe-Mn among the samples. In a second order, Pb-Fe, Pb-Mn, Fe- As, Fe-Cd, Cd-Mn and As-Mn showed a lower association. Only Ni and Cu appea red unassociated with any other element analyzed by AA. We characterized th e mineral phases by size range, morphology and chemical composition using S EM-EDS to obtain a compositional approach of anthropogenic phases and pecul iar morphology and size. A high percentage of heavy metal particles smaller than 2 mu m were detected. (C) 2000 Elsevier Science Ltd. All rights reser ved.