Toxic inflammatory effects of filters frequently used for the collection of airborne particulate matter

Epidemiological studies indicate that exacerbations of airway diseases and cardio-respiratory mortality have been associated with high levels of particulate air pollution. In the search for explanatory mechanisms, there is a need to collect particulate matter (such as PM10/PM2.5) onto filters for biological analysis. The removal of airborne particulate matter from a filter into solution involves agitation of the samples to release the particles and this is done by such methods as high-speed vortexing. Since it is possible that components of filters could contaminate the preparation and interfere with biological investigations it is necessary to find an inert filter suitable for both particulate collection and biological analysis. Extracts of the following six filters were assessed for toxicological activity both in vivo and in vitro:-Millipore AP20, Whatman GF/A, Whatman WCN, Gelman TF1000, Gelman DM800 and polycarbonate (PC). Treatment with the extract of either Whatman GF/A, Gelman DM800 or Millipore AP20 filters for 24 h significantly (p<0.001) decreased the metabolic competence of A549 cells, as measured by MTT (3-(4,5-dimetholthiazol-2,5-diphenyl tetrazolium bromide) reduction. In addition instillation of filter extracts into rat lungs was carried out to investigate their ability to cause inflammation. The cellular components of the bronchoalveolar lavage fluid (BALF) were analysed for the number of neutrophils, as markers of inflammation. After 24 h the filter extract of the Millipore AP20, polycarbonate (PC), Whatman WCN and Whatman GF/A induced a significant (P<0.001) influx of neutrophils into the rat lung. Finally the ability of each filter to absorb phosphate buffer solution (PBS) was assessed. The Whatman GF/A increased in weight 13 fold and the Millipore AP20 8 fold. In comparison the polycarbonate and the Gelman TF1000 were hydrophobic. These results suggest that of the six filters tested, the Teflon Gelman TF1000 filter was the most suitable for the collection and subsequent biological analysis of airborne particulate matter, as it releases little in the way of toxic material.