Heavy Metal Pollution In The Paso Del Norte Region:Historical Reconstruction And Source Interpretation

A unique and complex situation of heavy metal pollution arose in the El Paso del Norte region, one of the largest and oldest metropolitan areas on the US-Mexican border. This region with its complex topography is home to more than 2.2 million people sharing the same environment. Although many studies have been conducted in the region to identify the sources of environmental contamination, the cumulative history of heavy metal pollution is still incomplete. In order to identify the patterns of heavy metal dispersion and to test the hypothesis that the American Smelting and Refining Company (ASARCO) was a considerable contributor to local heavy metal pollution, we have studied attic dust as a medium of investigation of air pollution history via environmental forensic methods. Undisturbed attic dust provides an integrated history of atmospheric loading of particulates emanating from geological, biological, and anthropogenic sources and helps reconstruct past air pollution events on a local scale. Ninety-six attic dust samples were collected from surfaces in 15 houses and buildings of varying ages in two neighborhoods, Kern Place and Government Hill areas of El Paso, and from a downtown Ciudad Juarez location (Victoria Theater). Fifty-one combined dust samples and twelve combined samples of unpolluted buried soil horizons were extracted with Aqua Regia and were analyzed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Concentration values of 17 major and trace elements in the dusts and soil were utilized for calculation of their enrichment factors (EFs). In order to further clarify the sources of heavy metals, the EF data were processed by summary statistics, Pearson correlation analyses, MANCOVA Willklsquos Lambda test, Cluster and Principal Component (PCA) statistical methods. viii All the statistical analyses identified the same group of elements, six heavy metals/metalloids, associated with smelting processes. The mean EFs of Pb (263), As (81), Cd (333), Sb (644), Cu (475) and Zn (376) appeared abnormally high in contrast to other elements\u27 EFs (&le10) in all locations, suggesting their anthropogenic origin. At the same time the EFs of these elements were much higher in attic dusts collected from Kern Place compared to Government Hill the latter being more distantly located from the ASARCO smelter. Dust from the newest attics and attic surfaces (pipes, ducts, storage containers) post-dating the 2000s showed lower heavy metals EF values than the dust collected on adjacent surfaces that werepresent during the smelter operation. A fundamental change in the EFs distribution of heavy metals/metalloids occurred after 1966, and it was the year when ASARCO constructed an 828 foot (252.4 m) smokestack. The strongest correlations (r &ge 0.92, p &le0.0001) were observed among Pb, As, Cd, Cu and Sb, being the highest from the attic dust sampled in Kern Place area. These metals/metalloids (with minor exceptions) were also grouped together into one cluster and factor, signifying their common source, non-ferrous ore smelting. Based on the evidence provided by the dust analyses, it is concluded that the identified heavy metals were predominantly emitted from the smelter stack and were preferentially deposited in the surrounding area. The emissions could have followed wind trajectories near the surface along the Rio Grande valley rather than mixing to heights resulting in movement over the Franklin Mountains and deposited on the east side of El Paso