Polycyclic aromatic hydrocarbon (PAH) levels in indoor air and their associated health risks for children across Europe.

Polycyclic aromatic hydrocarbons (PAHs) are compounds with well-established negative health effects. In this study, the levels of the 16 Environmental Protection Agency (EPA) - PAHs were determined in air and deposited dust in different indoor environments, including schools, homes and sports halls in six metropolitan areas across Europe (Athens, Barcelona, Colchester, Copenhagen, Helsinki and Lisbon). However, naphthalene, acenaphthylene, anthracene, and dibenz[ah]anthracene were excluded from the final dataset due to analytical limitations. Results showed considerable spatial variability, suggesting that the highest median PAH concentrations (>50,000 pg/m3) in both schools and homes are linked to emissions from intensive local residential wood burning and poor ventilation, while the lowest PAH concentrations were observed in south-western Europe (<10,000 pg/m3). The levels of high-molecular weight (HMW) PAHs were generally higher in schools compared to homes likely due to greater occupancy and accumulation of outdoor-derived particles. Low molecular weight (LMW) PAHs, on the other hand, were more prominent in homes and associated with household practices (e.g., cleaning and ventilation frequency). In addition to active air sampling, indoor air concentrations were also estimated based on concentrations in the deposited dust samples. However, this methodology underestimated HMW-PAHs. The estimated Excess Cancer Risk for a 5-year primary education exposure period (ECR5) across all monitored sites ranged from 10-8 to 10-5, remaining below the unacceptable risk value of 10-4, which was used as a contextual reference within the USEPA cancer risk assessment framework. Nevertheless, these findings highlight the need for continuous proactive strategies to reduce PAH exposure and improve indoor air quality, particularly in environments occupied by children.