Evaluation of the Role of Benzo(a)pyrene as Carcinogenic Index of PM₁₀ bound PAHs in Italian Urban Sites

European Air Quality Directive defines benzo(a)pyrene as the chemical index for Polycyclic Aromatic Hydrocarbons (PAHs) carcinogenicity and sets a limit for its concentration in PM10 to address the exposure risk associated with the class. It also mandates monitoring six additional PAHs at a limited number of selected sites to assess the benzo(a)pyrene's contribution to the class in ambient air. For this aim, as part of the "Reti Speciali" project, benzo(a)pyrene and seven other PAHs were measured at 10 urban sites across Italy in 2016-2019 and the spatial and temporal pattern of these compounds were analyzed to evaluate benzo(a)pyrene's effectiveness in representing the carcinogenicity of the entire PAHs class. Results showed that in Italy, benzo(a)pyrene accounted for 61% ± 4.4% of total carcinogenicity when benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, dibenzo(a-h)anthracene, and indenopyrene were considered, and about 5% less when chrysene was also added. This value varies by site (from 51%± 11% in Taranto to 66% ± 7.5% in Cosenza) and decreases in summer due to benzo(a)pyrene's strong photochemical degradation. In Europe, this percentage is generally similar or lower. For instance, in the United Kingdom, across 24 urban sites, it averages 56%± 2.9%. These findings suggest that benzo(a)pyrene does not represent the overall carcinogenicity of PAHs nor a constant percentage, highlighting the need to further investigate the use of benzo(a)pyrene as the sole marker of PAHs toxicity.