Microenvironmental air and soil monitoring of contaminants: An evaluation of indoor and outdoor levels in Chihuahua City

Marcos Delgado-Rios, University of Texas at El Paso


Like most of the cities around the world Chihuahua City suffers atmospheric and soil pollution. This is a problem that requires immediate attention from both public authorities and the scientific community. Although it is known that high levels of heavy metals are present in the airborne particulate matter, soil and dust in many urban regions, the information about personal exposure to these pollutants in Chihuahua City is nonexistent. This study focuses on the analysis and characterization of lead and arsenic in the airborne and soil particulate matter present in the interiors of households and their surrounding outdoor environments in the southern part of Chihuahua City. The sampling area chosen for this study was located in the southern part of Chihuahua City. An atmospheric sampling point selected by the Centro de Investigación en Materiales Avanzados (CIMAV) was selected as a geographical center, with a 2 km radius forming the sampling area. The households selected for analyses were located on Lombardo Toledano Street, a high-traffic street. The main objectives of this study were to establish the maximum exposure level in outdoor and indoor environments for particulate matter less than 10 μm (PM 10), Pb, and As, to determine the background level of Chihuahua City for these same elements, to determine the isotopic ratios of Pb206 and Pb207 in the indoor and outdoor atmospheric samples, and to verify if the source of the pollution is from anthropogenic and/or natural sources. Additionally, a comparison of the analytical data from X-ray fluorescence (XRF) versus the analytical data from inductively coupled plasma with optical emission spectroscopy (ICP-OES) was conducted. The comparison of these techniques was based on sample preparation, speed of analysis, and accuracy of results. In the case of sample preparation, two extraction techniques were performed for a comparison of the extraction/leaching of Pb and As from the samples. These microwave-assisted extraction techniques used either concentrated nitric acid (HNO3) or aqua regia (a mixture of HNO3 and HCl, in 1:4 ratio) for elemental extraction. Statistical tools such as F-test, paired-data test, t-test and ANOVA were used to compare the analytical results between ICP-OES and XRF and the indoor/outdoor sampling study. ^ This study concluded that no statistical differences existed between the indoor and outdoor levels in the studied households for Pb and As concentrations. The results also showed that the most important sources of PM10 and Pb in the indoor environment were the transport and resuspension of external dust. The result further indicated that the inorganic As is associated with the fine particulate matter and is for the most part naturally occurring. In general the hypothesis that the exposure to environmental particulate matter, Pb and As is the same for indoor and outdoor environments can be accepted for the majority of the sampling houses. The isotopic ratios for the indoor samples were somewhat larger than the corresponding outdoor isotopic Pb sample ratios, reaching background levels from several regions around the world. The outdoor Pb isotopic ratios are similar to those found in the polluted-zones from smelting activities. The digestion of soil using HNO3 and aqua regia did not affect the extraction of Pb and As. The analytical techniques XRF and ICP-OES produced similar results for the determination of As in soil samples. However, these techniques produced different results for Pb determinations. These differences were, more than likely, associated to the digestion/extraction methodology. XRF techniques can successfully substitute other analytical techniques such as ICP-OES in the quantification of some trace elements in soil samples. ^

Subject Area

Atmospheric Sciences|Environmental Sciences

Recommended Citation

Delgado-Rios, Marcos, "Microenvironmental air and soil monitoring of contaminants: An evaluation of indoor and outdoor levels in Chihuahua City" (2007). ETD Collection for University of Texas, El Paso. AAI3291009.