Distribution and Occurrence of Microplastics in Foliar Deposition Across Tree Species in Lahore

Despite global concern over microplastic (MP) pollution, only a few studies have systematically evaluated the deposition and retention of atmospheric MP on urban tree foliage at the city scale, particularly in densely populated regions of South Asia. Here, the study present the first comprehensive assessment of foliar MP deposition in Lahore, Pakistan, examining the influence of leaf surface morphology and canopy height across 15 plant species at 44 locations along a major urban corridor. The leaves of the selected tree species were identified for smooth, leathery, hairy, and glossy surfaces, and the presence of trichomes (hair-like structures) was taken into account. Microplastic particle concentration on leaves varied between 0.93 n/cm to 9.23 n/cm; the highest MPs were quantified on the Morus alba leaves (i.e., 9.23 n/cm), and the lowest were noted on Lagerstroemia indica leaves (i.e., 0.93 n/cm). Morphologically, the highest number of MPs (4.8 n/cm) was adhered to the hairy surface leaves (n = 9), followed by smooth surface leaves (3.8 n/cm) (n = 10), glossy surfaces (2.7 n/cm) (n = 13), and the lowest was on the leathery surface leaves, i.e., 2.6 n/cm (n = 12), and were not statistically different. The spectral analysis confirmed that fibers of polyethylene terephthalate (61.25%) were the dominant polymer, followed by polyphenylene sulfide (17.67%) and aramid polymer (10.43%). An inverse relationship of MPs with the height where leaves were sampled, signifying lesser deposition above 1 m. There have been other studies within cities, and other publications have noted the influence of the tree and leaf morphology. Lower heights in the canopy are closer to ground-level emissions source or they accumulate microplastic particles that leach (wash off) from the upper canopy. Among all the plant species, Morus alba (n = 5) are most suitable species having complex venation, waxy, and hairy leaf morphology that can enhance biomonitoring and potentially mitigate airborne plastic pollution in rapidly growing cities.