Tracking polycyclic aromatic hydrocarbons (PAHs) across Palermo with the invasive grass Cenchrus setaceus (syn. Pennisetum setaceum)

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants posing significant environmental and health risks. This study evaluates the suitability of the invasive grass Cenchrus setaceus (syn. Pennisetum setaceum) as a passive collector of PAHs contamination across urban and coastal areas of Palermo, Sicily. Sampling campaigns were conducted in August and December at 12 sites characterised by varying levels of traffic intensity and anthropogenic pressure. Sixteen priority PAHs were extracted from inflorescence tissues and quantified by GC-MS in selected ion monitoring mode. Seasonal variations in PAH concentrations, with total levels ranging from 86.2 to 254.1 ng g−1 in summer and from 49.4 to 1217 ng g−1 in winter, were confirmed by a one-way PERMANOVA (p = 0.0042). Low molecular weight PAHs predominated in summer, whereas intermediate and high molecular weight PAHs increased in winter. This reflects temperature-dependent gas-particle partitioning, deposition processes and emission patterns. Diagnostic isomeric ratios indicated predominantly mixed sources of PAHs, mainly driven by vehicular traffic and liquid fossil fuel combustion, with additional contributions from biomass and coal combustion, as well as minor petrogenic contributions. Our results demonstrate that C. setaceus, which is widely distributed along road verges and anthropized habitats, effectively integrates atmospheric PAHs deposition over time. This supports its potential use as a passive biomonitor. Furthermore, incorporating this species into urban and coastal environmental assessments could facilitate dual management, enabling contamination monitoring while promoting the valorisation of biomass into high value-added bio-based products within circular economy strategies.