Particulate-bound polycyclic aromatic hydrocarbons in the urban area of Milan (Italy)

Polycyclic aromatic hydrocarbons were monitored in samples from atmospheric particulate matter (PM) for more than two years ( July 2001-Dec 2003) in a background site of the urban area of Milan (Italy). Nine PAHs were sistematically analyzed in 24-h PM2.5 and PM10 samples by ultrasonic extraction and HPLC-FD analysis: BaA, CHR, BeP, BbF, BkF, BaP, BghiP, dBahA and IcdP. All of them were quite exclusively present in the particulate phase (96-100%). A strong seasonal trend was observed for PAHs concentrations, with maximum autumn-winter concentrations (Σ-9 PAHs (PM2.5) = 18.8 ± 6.9 ng m -3) and minimum spring-summer values (Σ-9 PAHs (PM2.5) = 1.2 ± 0.6 ng m -3).The same trend was observed for the PAHs relative contribution in atmospheric particles, with autumn-winter particles, which were about 6 folds richer in PAHs than spring-summer, mainly because of different meteorological conditions. Even if PAHs make up a very small fraction of particles (Σ-9 PAHs ≅ 0.2% of yearly PM concentration), high PAH concentration during winter indicate a different seasonal "toxicological quality" of atmospheric PM, as PAHs are known to be very toxic compounds which are considered to be responsible for evident health side effects in urban areas. The nine analyzed PAHs were strictly correlated to each other, and a quite constant PAH pattern was observed in the background urban site during all the year, with BaP (99/30/CE) being about 12% of total PAHs. The nine particulate-bound PAHs were usually distributed in fine particles ([PAHs]PM 2.5 >95%[PAHs]PM 10). Therefore PAH monitoring should focus mainly on this particle fraction (PM 2.5 or eventually PM1), which is also more harmful, being entirely within the respirable fraction of PM. Due to the extreme variability in PAH concentration, and to the complexity of host-particle interaction, caution is suggested before stating a predifinite role for PAHs (and related patho-physiological mechanisms), in the occurrence of pollution related health effects