PAHs accumulation on leaves of six evergreen urban shrubs: A field experiment

Air pollution refers to the occurrence of toxic substances in the atmosphere which results in detrimental effects to human beings and living environments. Among the most common atmospheric pollutants, Polycyclic Aromatic Compounds (PAHs) are the most common substances originated by vehicles. The aim of the study was to investigate the accumulation of 16 PAHs in leaves of six evergreen shrubs frequently used in Italy for urban landscaping (Elaeagnus x ebbingei, Ilex aquifolium, Laurus nobilis, Ligustrum japonicum, Photinia x fraserii and Viburnum lucidum). The study was conducted in two sites: a public park and a high traffic square. Six samplings were performed in a period of 26 months during Winter. The plants tolerance was investigated considering leaf-extract pH, total chlorophyll, leaf ascorbic acid content and relative leaf water content. A morphological leaf characterization was also carried out considering stomatal density and cuticle width. Phenanthrene, fluoranthene, fluorene and pyrene were the major compounds yielded in the plant leaves accounting for about 83% of ΣPAHs, the contributions being 53%, 11.3%, 10.5% and 8.5%, respectively. Such compounds are related to vehicular emissions. The analysis of the PHAs accumulation and the evaluation of the plants tolerance also revealed that the efficiency in trapping 5- and 6-rings potentially carcinogenic PAHs such as benzo(b)fluoranthene, benzo(k)fluoranthene in plant leaves is highest for Elaeagnus x ebbingei, L. japonicum and L. nobilis while Elaeagnus x ebbingei and Photinia x fraserii resulted to be those most tolerant to air pollution. The role of plants in mitigating traffic pollution is confirmed.