Characterization and in vitro biological effects of concentrated particulate matter from Mexico City

Abstract

Coarse and fine particles were collected using an ambient particle concentrator (VACES system) in the north, center and south regions of Mexico City during May and November of 2003 with the aim of collecting enough particulate matter (PM) to examine their chemical and physical characteristics, biological content, and toxicity potential. The chemical, morphological and biological composition of PM was determined, together with the redox activity, induction of apoptosis and DNA damage. Carbonaceous species determined by thermal-optical transmittance (TOT) showed that the highest concentrations were found in PM 2.5 from the north and in PM 10 from the center. When analyzed by inductively coupling plasma (ICP), levels of metals were higher in the coarse fraction, mainly in the north. Morphological analysis by Scanning Electron Microscope & Energy Dispersive X-ray Spectrometer (SEM-EDX) is shown. Bacteria, fungi and endotoxin were present mostly in the coarse samples from the north. Fine PM had higher redox activity, than the coarse PM assessed by the dithiothreitol (DTT) assay. Early apoptotic cell death assessed by annexin V was observed in A549 cells exposed to PM from all regions, particularly with those collected in May. The fine fraction from the south induced higher apoptotic cell death compared to the coarse fraction, in contrast, the coarse fraction from the north induced significantly higher apoptosis than the fine fraction. All PM samples induced DNA damage assessed by the comet assay on THP-1 cells when exposed to a concentration of 10 μg/mL, the highest DNA damage was produced by both particle fractions collected in the north in May and November. In conclusion, PM from the north showed a higher metal and biological content, apoptotic cell death induction and more extensive DNA damage. Also, fine PM fractions from all sampled regions showed more redox activity than the coarse fraction. In summary, location, season and size of PM collection influenced their chemical, morphological and biological composition and thus their toxicity to cells.