Chemical Properties and Biological Effects of Particles from the Subway System of Mexico City

Uribe-Ramirez Marisela (1) Uriarte-Ramos Ada G (1) Melgar-Paniagua Eva (1) Mugica-Alvarez Violeta (2) Soberanes-Arias Saul (3) Budinger G.R. Scott (3) Osornio-Vargas Alvaro (4) Blanco-Jimenez Salvador (5) Campos-Ramos A.Arturo (5) Cardenas Beatriz (5) Rivera Olivia (6) Retama Armando (6) Barbier Olivier (1) De Vizcaya-Ruiz Andrea (1)

(1) Departamento de Toxicologia, CINVESTAV-IPN, Mexico City, MX; (2) Universidad Autónoma Metropolitana-Azcapotzalco, Mexico City, MX; (3) Division of Pulmonary and Critical Care Medicine, Department of Medicine, Northwestern University Feinberg School of Medicine and Jesse Brown VA Medical Center, Chicago, IL; (4) INCan, SSA, Mexico City, MX; (5) Instituto Nacional de Ecología, Mexico City, MX; (6) Sistema de Monitoreo Atmosférico, Secretaria del Medio Ambiente, GDF, Mexico City, MX.

     Abstract Number: 348
     Last modified: November 9, 2009

Abstract
Although exposure to particulate matter (PM) is associated with adverse cardio-respiratory effects, little is known about the biological effects of PM from confined environments such as subways. This is relevant, considering the large number of users potentially exposed (3 million people/day use the subway system of Mexico City) to a specific PM source. A diverse mixture of organic (PAH) and inorganic compounds (minerals, metals, ions) -which have been directly implicated with the generation of reactive oxygen species (ROS)- compose PM. This study aims to investigate chemical properties of PM10 and PM2.5 sampled in an underground platform of the subway (S) system of Mexico City (Metro) and above ground ambient air (AG) (commercial/residential area) and their ability to induce in vitro biological effects. High (Tisch) and low (AirMetrics) volume samplers were operated 24 h to collect PM10 and PM2.5 in Nov-Dec 2008. Teflon filters were conditioned before and after sampling (40±5% humidity and 22±3 oC during 48 h) prior PM gravimetric determination. Elemental content was measured by energy dispersive X-ray fluorescence (XRF), and redox activity using the dithiothreitol (DTT) assay. Biological effects such as cell viability (cristal violet), intracellular ROS generation (2’,7’-dichlorodihydrofluorescein diacetate) and mitochondrial membrane potential (Deltapsim) (Mitotracker green), were evaluated in alveolar epithelial A549 cells exposed to PM. Our data show that PM10 and PM2.5 concentrations were about 10% higher in the S compared to AG. XRF analysis showed that PM10 from the S contained a 1.1-fold and 2-fold higher levels of mineral elements and metals (mainly Fe, Cu and Mn), respectively, than PM10 from AG. On the other hand, AG PM2.5 showed a higher content of mineral elements compared to S ambient air, but PM2.5 from the S showed higher content of metals. S PM2.5 redox activity was 1.4-fold higher than AG PM2.5, however PM10 from the S showed the highest redox activity, 5.2-fold higher compared to S PM2.5. Exposure of human alveolar epithelial A549 cells to non-cytotoxic concentrations (10, 20 and 40 µg/cm2) of S and AG PM10 and PM2.5 for 24 h induced the generation of intracellular ROS, the effect was higher for PM10 from the S than S PM2.5 or AG PM10 and PM2.5. Exposure to PM from the S induced a more pronounced reduction in mitochondrial membrane potential than AG PM. No differences between PM10 and PM2.5 were observed. Although exposures to PM in the subway could be relatively short, the intensity of observed PM related biological effects could be relevant in terms of adverse health effects. Our results suggest that while PM concentrations in the subway were not significantly higher from those above ground ambient air, they showed a higher redox potential and mitochondrial derived ROS intracellular generation, imposing them a larger toxic potential. Metal content could be explaining it. More studies are underway to further investigate the toxicity and potential human implications of these findings. Acknowledgments and grant information: Sistema de Transporte Colectivo – Metro; Project financed by: Instituto de Ciencia y Tecnología del Distrito Federal, GDF.