Characterization and in vitro biological effects of concentrated particulate matter from Mexico City
Introduction
Exposure to ambient particulate matter (PM) represents a significant health risk in major urban centers, such as Mexico City (Téllez-Rojo et al., 2000; Pope et al., 2002). The chemical and physical properties and toxicological mechanisms by which PM causes adverse health effects are still uncertain. PM aerodynamic size has become a relevant factor when studying PM toxicity due to its ability to penetrate the respiratory system; i.e., fine particles reach the deeper regions of the lungs, whereas coarse PM may be deposited in upper regions of the airways. PM chemical components mediate toxic response and could thus be relevant in the induction of adverse health effects in humans (Ghio, 2004). Previous work showing the high content of metals in coarse and fine PM from Mexico City (Mugica et al., 2002) suggests they could play an important role in damage to cells. Fine PM potentially may owe its toxicity to its content of organic compounds, metals and other reactive chemical compounds (Lighty et al., 2000). Alfaro-Moreno et al. (2002) reported that in vitro studies in human pulmonary cells and murine macrophages exposed to PM10 from the northern and central regions of Mexico City showed higher toxic effects than those from the southern region (cytotoxicity, DNA breakage and apoptotic cell death).
A complex challenge to study the underlying factors in PM toxicity is to obtain enough PM to perform controlled laboratory studies. To address this issue the southern california particle center and supersite (SCPCS) has developed a versatile aerosol concentration enrichment system (VACES), allowing collection of large amounts of PM by size fraction. The size fractionated PM is collected in concentrated PM suspensions by connecting the output flows of each parallel concentrator to a liquid impinger (BioSampler™), used in a modified configuration in order to collect particles under near-ambient pressure (Kim et al., 2001). The SCPCS joined efforts with air pollution researchers from four Mexican institutions: Centro de Investigación y de Estudios Avanzados (CINVESTAV), Universidad Autónoma Metropolitana (UAM-A), Universidad Nacional Autónoma de México (UNAM) and Instituto Nacional de Cancerología (INCan), to install and operate for the first time the VACES system in Mexico City, integrating an interdisciplinary group of scientists specialized in PM studies (Mexican Consortium for particulate matter studies).
The toxicological evaluation of PM exposure is often limited by the amount of PM that can be collected, therefore the aim of this study was to collect PM from ambient air in Mexico City with a particle/virtual impactor concentrator to examine them for their chemical and physical characteristics, biological content, and potential toxicity. PM were collected in the northern, central and southern regions of Mexico City in May and November of 2003 and their carbon and metal content, morphology and redox activity were determined, together with their cytotoxic potential assessed by apoptotic cell death and DNA damage induction.
Section snippets
PM collection
Coarse (2.5–10 μm) and fine (<2.5 μm) PM were collected in the north—industrial (Xalostoc), center—commercial (Merced) and south—residential (Pedregal) regions of Mexico City during 4 continuous days in May and November of 2003, representing the warm and cold-dry seasons. Particles were collected using the particle concentrator VACES system, which consists of three parallel sampling lines, each one operating with an intake flow rate of 110 L/min (Kim et al., 2001). Briefly, coarse particles were
Particulate carbon and metal content
Ambient PM10 concentrations during the sampling period were 115.64, 110.84 and 55.91 μg m−3 in the north, center and south, respectively. PM2.5 levels were 47.22, 70.8 and 33.4 μg m−3, respectively. The total amount of coarse and fine PM from the 4 days of the particle concentrator collection ranged from 20 to 59 mg and from 14 to 38 mg, respectively. Total carbon (TC), the sum of organic (OC) and elemental carbon (EC), accounted for 20–39% of PM10 mass, and for 27–58% of PM2.5 mass. The highest
Acknowledgments
Financed by UC MEXUS-CONACYT Collaborative Grant and the UCLA-Fogarty Program, Southern California Particle Center and Supersite (EPA-STAR R82735201), Southern California Environmental Health Center, National Institute of Environmental Health Sciences (NIEHS) Grant #5 P30 ES07048-07 and the California Air Resources Board (98-416). The authors wish to acknowledge the support from the Mexico City Monitoring Network, particularly Armando Retama and Rafael Ramos, and Centro Nacional de
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