RESUMO
The possible genotoxicity of small particulate matter has been under investigation for the last 10 years. Diesel exhaust particles (DEP) are considered as "probably carcinogenic" (IARC group 2A) and a number of studies show genotoxic effects of urban particulate matter (UPM). Carbon black (CB) is carcinogenic in rats. In this study the cytotoxic and genotoxic potency of these three particle types was investigated by exposing human cells (A549 and THP-1 cell lines) in vitro to CB, DEP (SRM 1650, NIST), and UPM (SRM 1648, NIST) for 48 hr. Cytotoxicity was assessed using the Alamar Blue assay, whereas genotoxicity was assessed using the single-cell gel electrophoresis (comet assay). The particles were characterized with regard to their mean diameter in tissue culture medium (CB 100 nm, DEP 400 nm, UPM 2 microm), their total carbon content (CB 99%, DEP 85%, UPM 15%), and their acid-soluble metal composition (UPM >> CB approximately DEP). The concentrations ranged from 16 ng/ml to 16 microg/ml for cytotoxicity tests and from 16 ng/ml to 1.6 microg/ml for genotoxicity tests. In both assays, paraquat was used as a reference chemical. The CB, DEP, and UPM particles showed no significant cytotoxicity. However, all three particles were able to cause significant DNA damage, although to a different extent in the two cell lines. The genotoxicity of washed particles and dichloromethane extracts was also investigated. In THP-1 cells CB washed particles and DEP extracts caused significant DNA damage. This difference in effect may be related to differences in size, structure, and composition of the particles. These results suggest that CB, DEP, and UPM are able to cause DNA damage and, therefore, may contribute to the causation of lung cancer. More detailed studies on influence of size, structure, and composition of the particles are needed.