Polycyclic aromatic hydrocarbons and elements in tree barks in a Brazilian metropolis

Biomonitoring can be essential for air pollution assessment since active sampling methods might be costly and involve complicated logistics. In this context, the study focused on sampling tree barks near a petrochemical complex in an urban area in the Metropolitan Area of São Paulo (Brazil). These samples were chemically characterized, with the determination of polycyclic aromatic hydrocarbons (PAHs), metals, and metalloids. Fluoranthene and pyrene were the most abundant PAH in half of the samples, representing 20% or more of total PAHs. The PAH diagnostic ratios indicated that the samples were affected by local light-duty vehicular emissions. However, they also suggested different contributions of industrial sources and heavy-duty vehicles. Fe, Zn, Mn, and Cu were the most abundant elements, and considering the enrichment factors (EF), Zn, Cd, Cu, Sn, and Pb were more associated with anthropogenic sources (EF > 25). EFs were higher for some samples collected in the northwest vicinity of the complex, which were more affected by the industry plumes, especially concerning Zn and Cd. Ni and V, previously associated with industrial emissions, presented relatively lower EFs than other elements. Both species also presented moderate correlations. Low Cu/Zn ratios suggested a relatively high Zn abundance compared to other sources, suggesting an extra source for this species in this industrial-impacted area. These results suggested a combination of different anthropogenic sources affecting the composition of tree barks in that area and zinc as a possible local emission fingerprint.