The effects of seasonal weather on the genotoxicity, cytokinetic properties, cytotoxicity and organochemical content of extracts of airborne particulates in Mexico City.

Extracted organic material (EOM) from PM10 airborne particles collected during three distinct seasons in Mexico City was assayed for genotoxicity, cytokinetic effects and cytotoxicity. Using sister chromatid exchange (SCE) for genotoxicity, replication index (RI) and mitotic index (MI) for cytokinetics, and microscopic evaluation (cell death) for cytotoxicity on human lymphocytes exposed to increasing concentrations of EOM, this study showed that the extent of genotoxic, cytokinetic, and cytotoxic change caused by pollutants depended at least in part on the seasonal weather. Bioactivated extracts of samplings in April (warm and dry), August (warm and rainy) and November (cool and dry) produced the highest rate of genotoxicity (SCE) in November and the lowest rate in April. Without bioactivation the rates were still highest in November but equally low in April and August. Thus, almost all of the genotoxic responses in the bioactivation experiments during these latter months were from promutagens. However, in November equally large amounts of mutagens and promutagens were present. Cytokinetics (RI and MI) showed steady decreases as the concentration of EOM was increased, independent of bioactivation and weather. Cytotoxicity (cell death) occurred when higher concentrations of EOM were used. EOM was the least cytotoxic in April and most cytotoxic in November. Bioactivation was not required for cytokinetic change and cytotoxicity, suggesting that the agents involved may be different from the genotoxic agents. Using gas chromatography/mass spectroscopy (GC/MS) it could be shown that the type of pollutant chemicals in the EOM also depended on the weather. In particular, all 15 polycyclic aromatic hydrocarbons (PAH) studied were present in November EOM whereas four different PAH were absent in the other 2 months. Generally the amounts were less in the EOM collected in April and August. Conversely, nitro-PAH compounds were greater in number in April EOM but higher in amount in November EOM. The significance of these findings is discussed.