Cytotoxicity of PM2.5 and PM2.5-10 ambient air pollutants assessed by the MTT and the Comet assays

Ambient air particulate matters are classified into two distinct modes in s ize distribution, namely the coarse and fine particles. Correlation between high particulate concentration and adverse effects on human populations ha s long been recognized, however the toxicology of these adverse effects has not been clarified. In the current report, the cytotoxic effects of the so lvent-extractable organic compounds (SEOC) from fine particles smaller than 2.5 mum (PM2.5) and from coarse particles between 2.5-10 mum (PM2.5-10) we re studied. Nine 24 h consecutive monthly samples were tested to determine the correlation between cytotoxicity and total SEOC in two size fractions o f particulate air pollution. Cytotoxicity of SEOC was measured by two micro -scale mammalian cells-based bioassays: the MTT cell proliferation assay, a nd the Comet assay for the detection of DNA damage. A well-defined mammalia n cell line - Rat 6 rodent fibroblast was employed in the study. The SEOC e xtracts of air particulate matters were sub divided into two equal parts. O ne part was dissolved in DMSO, the other in KOH/hexane and then conjugated with bovine serum albumin to produce a lipid-soluble fraction for testing. The DMSO fraction would contain mainly the polycyclic aromatic hydrocarbons (PAH), alkanes and alkanols, while the lipid-soluble fraction would be enr iched with fatty acids. The results from MTT assay showed that cytotoxicity of the PM2.5 was much more severe than the PM2.5-10. suggesting that toxic SEOC were confined to the fine particles. By and large, the DMSO solubles were much more toxic than the lipid solubles. The degree of cytotoxicity of the DMSO soluble samples is positively correlated to the amount of particu lates present in the ambient air. For the PM2.5, the winter samples were si gnificantly more toxic than the summer samples in terms of cell killing, wh ich seemed to be a direct reflection of the total loading of organic matter in the samples. Results from Comet assays showed that SEOC samples of PM2. 5 derived from winter months induced DNA damage at dosages resulting in no obvious cell killing in the MTT assay. Thus, long-term exposure to non-kill ing dosage of air pollutants may lead to the accumulation of DNA lesions, w hich may be one of the mechanisms responsible for the chronic adverse healt h effects of particulate air pollution. (C) 2000 Elsevier Science B.V. All rights reserved.