Role of broad- and needle- leaf morphology in capturing particulate matter and emerging pollutants in urban environments

Abstract

Urban air pollution remains one of the key environmental and public health issues, with particulate matter (PM) acting as a major carrier of harmful contaminants. This study explored the occurrence of emerging and established contaminants, including radiopharmaceuticals, heavy metals, and rare earth elements within PM deposited on the broad- and needle- leaf surfaces of urban trees. Broad- and needle- leaf samples of Hedera helix L., Pinus sylvestris and Thuja occidentalis were collected from an urban-industrial area in Gliwice, Poland. The morphology of the leaf surfaces and the composition of PM deposited on the leaves were examined using scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM/EDS). A quantitative analysis of particle fractions (large, coarse, fine) was performed through sequential filtration and gravimetric weighing following the washing of the plant material. The results indicated that the PM capture capacity of broad- and needle- leaf species depends on the morphological traits intrinsic to the species. The plant species with the greatest potential for retention of particulate matter was P. sylvestris, where deposited particles constituted 0.33% of the total mass of the P. sylvestris needle- leaves. Particulate matter can be characterised by compounds containing potentially toxic elements: heavy metals such as As, Sb, Cr, Ni, Cu, Zn, Pb, Cd, and Hg; other elements such as Ba, Ti, Fe, Mn, and Ag; as well as various trace elements, including rare earth elements. Particulate matter is also likely to carry radiopharmaceuticals such as those containing Tc and Re. Monitoring the elemental content of PM provides valuable information on the source and distribution of pollutants in the environment, including emerging pollutants such as radiopharmaceuticals.