Microplastics Found in Tree Leaf Deposits Across Lahore Species

In one of the most comprehensive studies of its kind conducted in South Asia, researchers have mapped the invisible layer of plastic that settles on the leaves of urban trees, revealing that the foliage of Lahore’s streets is acting as a vast, passive trap for airborne microplastics. The study, led by Muhammad Shahid and Abdul Qadir of the College of Earth and Environmental Sciences at the University of the Punjab, along with Sidra Farooq, Rahib Hussain and Tahir Sattar, examined 15 tree species at 44 locations along a major urban corridor in Lahore, Pakistan, and found microplastic particle concentrations on leaf surfaces ranging from 0.93 to 9.23 particles per square centimeter. The findings, published in Archives of Environmental Contamination and Toxicology, offer the first systematic, city-scale assessment of foliar microplastic deposition in Pakistan and carry significant implications for how rapidly growing cities might design their urban forests to combat plastic pollution.

The research addresses a conspicuous gap in the microplastics literature. While the contamination of oceans, rivers, soils and even remote mountain snowpack by microscopic plastic debris has been documented extensively over the past decade, surprisingly few studies have systematically evaluated how much atmospheric microplastic is deposited on and retained by the leaves of urban trees. This omission is striking given that tree foliage is known to intercept substantial quantities of airborne particulate matter, and given that cities in densely populated regions of South Asia face some of the worst air quality in the world. Lahore, a metropolis of well over ten million people that has struggled with shrinking green cover, expanding urban sprawl and severe episodes of smog, provided an ideal natural laboratory for testing whether tree leaves could serve both as a record of airborne plastic pollution and as a potential mitigation tool.

The team’s sampling design was deliberately broad. Leaves were collected from 15 different plant species across 44 sites along a major urban corridor, allowing the researchers to capture the variability of pollution exposure across the city. Crucially, the study classified each species by leaf surface morphology, distinguishing smooth, leathery, hairy and glossy leaf surfaces, and specifically recorded the presence or absence of trichomes, the hair-like structures that protrude from the epidermis of many plants. This morphological framework allowed the team to test a long-standing hypothesis from air pollution research: that the physical texture of a leaf determines how effectively it captures and holds particles suspended in the air.

The results confirmed both the pervasiveness of the problem and the importance of leaf architecture. Microplastic concentrations on individual leaf surfaces varied nearly tenfold across species, from a low of 0.93 particles per square centimeter on Lagerstroemia indica, the crape myrtle, to a high of 9.23 particles per square centimeter on Morus alba, the white mulberry. When the data were aggregated by surface type, hairy leaves emerged as the most effective traps, retaining an average of 4.8 particles per square centimeter across nine sampled species. Smooth-leaved species followed with 3.8 particles per square centimeter across ten species, glossy surfaces held 2.7 particles per square centimeter across 13 species, and leathery leaves retained the least, at 2.6 particles per square centimeter across 12 species. Interestingly, these differences among surface types were not statistically significant, a result that suggests the deposition process is influenced by a complex interplay of factors rather than by texture alone. Nevertheless, the trend is consistent with mechanistic expectations: trichomes increase the surface area available for particle interception, create turbulent micro-boundary layers that slow airflow across the leaf, and physically entangle fibers that would simply bounce off or be re-entrained from a smoother surface.

Perhaps the most striking single finding concerns the white mulberry. With its combination of complex venation, waxy cuticle and hairy leaf surface, Morus alba accumulated more microplastics per unit area than any other species examined. The researchers identified it as the most suitable of all the plant species studied for biomonitoring and potentially for mitigating airborne plastic pollution in rapidly growing cities. The mulberry’s dense network of veins creates a topographically rough surface that disrupts laminar flow, while its trichomes act like a microscopic forest, snagging drifting fibers. In effect, the tree functions as a biological filter, passively scrubbing synthetic fibers from the air passing through its canopy.

To determine what kinds of plastic were actually settling on the leaves, the team turned to spectral analysis, using spectroscopic techniques to match the absorption signatures of extracted particles against reference polymer libraries. The analysis showed that fibers of polyethylene terephthalate, better known as PET, dominated the deposited material, accounting for 61.25 percent of identified polymers. Polyphenylene sulfide ranked second at 17.67 percent, followed by aramid polymer at 10.43 percent. The polymer fingerprint is telling. PET is the workhorse of synthetic textiles and beverage bottles, and the overwhelming predominance of PET fibers points directly to the shedding of clothing, upholstery and other textile products as the primary source of Lahore’s airborne plastic burden. Every wash cycle, every wearing of a synthetic garment releases microscopic fibers that can remain aloft for days and travel considerable distances before settling. Polyphenylene sulfide and aramid, by contrast, are high-performance engineering polymers used in industrial filtration, automotive components and protective fabrics, hinting at a contribution from the city’s industrial and vehicular activity.

One of the study’s most consequential observations concerns the vertical dimension of deposition. The researchers found an inverse relationship between microplastic load and the height at which leaves were sampled, with significantly lower deposition recorded above one meter. This height gradient carries important mechanistic implications. Lower portions of the canopy sit closer to ground-level emission sources, where road dust resuspension, tire wear, litter degradation and pedestrian activity continuously inject plastic particles into the near-surface air. In addition, particles deposited on upper branches may be washed downward by rain and intercepted again by lower foliage, causing microplastics that leach from the upper canopy to accumulate on leaves nearer the ground. Either way, the height effect means that the plastic burden measured on a tree is not uniform, and that sampling protocols which ignore canopy position may produce misleading estimates. It also means that the hedges, shrubs and low branches that people brush past every day on city streets are, in effect, the most heavily plastic-loaded surfaces in the urban forest.

The findings situate Lahore within a growing global picture. Studies in Paris, Dongguan, Shanghai and Beijing have documented synthetic fibers in atmospheric fallout, and researchers have traced microplastics to remote alpine and Arctic snow, demonstrating that plastic particles are now a routine component of the atmosphere. Terrestrial plants have been proposed as temporary sinks that slow the long-range atmospheric transport of these particles, and work on mangrove leaves and freshwater macrophytes has shown that foliage can be an important accumulation surface. What the Lahore study adds is a rigorous, species-resolved, city-scale dataset from a South Asian megacity, a region where such measurements have been largely absent despite the scale of the exposure. Previous work by some of the same research group had already documented airborne microplastic deposition across Lahore and microplastic contamination in the River Ravi and the city’s urban surface water system, but the new study is the first to systematically link that deposition to the specific trees lining the city’s corridors.

The health and environmental context is difficult to ignore. Microplastics have been shown in laboratory studies to induce gut microbiota disruption and metabolic changes in mammals, accumulate in tissues, alter soil properties and plant performance, and even exert direct radiative effects that may influence climate. Inhaled airborne fibers are a particular concern because of their small size and their prevalence in the air people breathe, especially in densely populated urban environments. While the current study did not assess human health outcomes directly, its demonstration that PET fibers blanket the leaves of street trees at concentrations approaching ten particles per square centimeter underscores how pervasive the exposure pathway may be, both for residents inhaling resuspended particles and for herbivores consuming contaminated foliage.

For urban planners, the study offers an actionable insight. If the choice of tree species influences how much airborne plastic a city’s green infrastructure can intercept, then species selection becomes a pollution control strategy. Planting hairy-leaved, structurally complex species such as Morus alba along traffic corridors could, in principle, enhance the capture and retention of atmospheric microplastics, just as similar logic has already been applied to the selection of urban trees for particulate matter and dust capture. The researchers caution that leaves act as temporary sinks rather than permanent ones, since intercepted particles can be washed to the ground, resuspended or redeposited, and the ultimate fate of the trapped plastic, often the soil beneath the canopy or the stormwater system, must be considered. Yet even temporary capture removes fibers from the breathing zone during the periods of highest exposure.

The study was funded by the Higher Education Commission of Pakistan under the National Research Program for Universities, and the authors acknowledge the laboratory and fieldwork support of the University of the Punjab. Its publication marks a milestone for environmental monitoring in the region, establishing a baseline against which future interventions, whether emission controls, waste management reforms or smarter urban forestry, can be measured. As microplastic pollution becomes an increasingly recognized component of urban air quality, the humble street tree is emerging not merely as an amenity but as an instrument: a living sensor whose leaves record, particle by particle and fiber by fiber, the synthetic chemistry of the air we all share.