How to obtain large amounts of location- and time-specific PM2.5 with homogeneous mass and composition? A possible approach, from particulate collection to chemical characterization

A suitable protocol for the collection, extraction, and characterization of a large quantity of a local and current fine particulate matter (PM2.5) was developed, to provide homogeneous PM2.5 amounts for use in in vitro and in vivo toxicological assays rather than a generic and obsolete standard reference material (SRM). PM2.5 samples were collected at an outdoor urban background site in Como, Northern Italy, using a high-volume air sampler (500 L/min) equipped with polytetrafluoroethylene (PTFE)-coated glass fiber filters (eight sampling campaigns of 24–96 h each, from February to April 2019). PM2.5 was extracted from the filters by sequential sonication steps and the final pooled extract was filtered to remove the glass fibers released during extraction. Several PM2.5 aliquots (n = 55) were then prepared from the PM2.5 dry residue for i) a chemical characterization of the elements, inorganic ions, and the carbonaceous fraction and ii) in vivo and in vitro studies. The proposed protocol allowed a large amount of ambient PM2.5 (>300 mg) to be collected within a reasonably short time. An average extraction efficiency of 75% was achieved, and the chemical analyses conducted on a set of PM2.5-replicates revealed a satisfactory level of precision, ranging from 3% (anions and OC) to 10% (trace metals and EC), thereby confirming the possibility of obtaining aliquots with homogeneous mass and composition. Finally, the emerging differences with the SRM 1648a elemental composition suggest the importance of location- and time-specific particulate testing, which is truly representative of the actual exposure scenario for specific populations.