Evaluation of Toxicity Induced by PM 10 and PM 2.5 from Three Different Zones of México City in Relation with Their Composition

Contributed by Universidad Nacional Autónoma de Mexico, Universidad Autónoma Metropolitana, Instituto Nacional de Cancerología Multidisciplinary Group

Figure 1. PM 2.5 levels in three different zones of Mexico City.

Health effects related to air pollution exposures have been reported to be very similar in cities around the world. Ambient concentrations of criteria pollutants (e.g., ozone, particulate matter (PM), SO 2, NOx) correlate with increases in mortality, emergency room visits, asthma attacks, school absenteeism or impaired pulmonary function. Although these effects are probably the result of exposures to a mixture of contaminants, epidemiology has shown that PM has the strongest effect.

Most of those epidemiologic studies relied on PM monitoring that only evaluate concentration ( ?g/m 3) and size as defined by the aerodynamic diameter. They established correlations in which smaller particles have stronger effects, indicating deeper PM penetration into the respiratory system. However, there are other variables besides PM size and concentration that could be considered if we were looking at different health outputs. For example, little is known about the participation of PM in chronic diseases such as cancer or atherosclerosis or in the impairment of the immune system that could result in an increase of infectious diseases. Adverse health effects could be related to particle composition. We do not know if PM emitted from different sources (industry, motor vehicles, natural) would represent the same risk, due to differences in size and composition. Preliminary experimental studies from our group indicated that there are differences in the effects induced in cells exposed to PM from the north, center and south of Mexico City, suggesting that such differences could be related to particle composition besides particle size, since the PM sources differ by location. The lack of direct evidence on particle composition and particle size distribution on the PM 10 used in that study, motivated the present one which has the aim of collecting large amounts of PM 10 and PM 2.5 in three zones of Mexico City. The selected zones have differences in the predominant PM sources: North (industry) at FES Iztacala; Center (traffic) at La Merced and South (traffic and vegetation) at CCA, UNAM. PM samples will allow for: morphological analysis and analysis for elements, organic compounds, black carbon, and microorganisms and some of their products. Parallel experimentation will asses the impact of PM samples on cells: the induction of death, secretion of pro-inflammatory cytokines and DNA damage.

Figure 2. Configuration of the Mobile

Preliminary results indicate that PM 2.5 levels between January and July of 2002 vary both by region and time of the year (Figure 1). Levels were higher in the North. Levels diminished in all zones at the beginning of the rainy season. Due to technical problems with the monitors, we could not sample simultaneously in all three zones during the whole period.

Morphologic analysis of the PM samples indicate the presence of soil particles in the three zones and elemental analysis indicates a higher metal content in the particles from the North and the Center than in the South (Figure 2). These differences are more important in the coarse fraction than in the fine one. Total carbon is ~50% in the samples from the three zones and elemental carbon is higher in the fine fraction to about the same degree in all regions. Detailed analysis of organic compounds content is underway. The analysis for biologic components in the PM indicates the presence of endotoxin. PM 10 had the higher endotoxin content than PM 2.5 . The highest concentration was found on PM 10 from the South (406 EU/mg). Endotoxin content partially correlated with the activation of serum complement (serum complement is a potent defense mechanism strongly activated by endotoxin), suggesting that other components capable of activating serum complement may be present in the PM. Additionally, toxicological evaluation indicates that PM 10 were able to produce OH radicals and cell death (Figure 3) and this activity is related to the metal content in the PM 10 .

Figure 3. PM 10 induced a concentration dependent cell death on monocytic cells. This is only observed in proliferating cells. Particles from the Center are the most potent

At the present time we can conclude that there are differences in the levels and composition of PM obtained from three different zones in Mexico City. These differences account for differences in cellular responses induced by in vitro exposure to the PM. We have accomplished approximately 70% of our goals and new results will allow for further correlations.

This work is supported by the Integrated Program on Urban, Regional and Global Air Pollution with funds from Comisión Ambiental Metropolitana.