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Atmospheric microplastics as vectors of heavy metals and trace elements in tropical urban air: SEM–EDX and ICP–MS evidence from Metro Manila, Philippines
Original title: Atmospheric microplastics as vectors of heavy metals and trace elements in tropical urban air: SEM–EDX and ICP–MS evidence from Metro Manila, Philippines
Summary
Tiny plastic particles floating in the air over Manila can pick up metals like zinc, copper, and even toxic ones like lead and mercury, essentially acting as tiny hitchhiker rides for pollution. The good news: based on current levels, breathing these particles in doesn't appear to pose a meaningful health risk. Still, metal buildup on these particles increased sharply during the dry season, and as plastics break down into smaller, more easily inhaled pieces, scientists say this is worth continuing to watch.
Suspended atmospheric microplastics (SAMPs) may function as mobile carriers of airborne contaminants, yet their heavy metal and trace element associations in tropical urban environments remain poorly characterized. We investigated heavy metal and trace element association with SAMPs collected from six cities across Metro Manila, Philippines, using SEM-EDX surface analysis (78 particles: 26 fibers, 29 films, 23 fragments) and ICP-MS bulk quantification of pooled fiber SAMPs across three sampling months. SEM-EDX revealed morphotype-dependent elemental patterns: fragments carried the highest diversity (Zn, Ba, Ca, Si), fibers were selectively enriched in Fe (9.33 wt%) and Ni (4.75 wt%), and films uniquely accumulated Mo, Nb, and Ti. ICP-MS of the three monthly fiber pools (n = 3 temporal observations, without analytical replicates) indicated Zn and Cu among the dominant associated metals, with total loading increasing 22-fold from March (320 μg/g) through April (1096 μg/g) to June (7168 μg/g). Because these pools included co-collected glass-fiber filter material, reported concentrations represent upper-bound estimates, and filter-derived elements (notably Fe, Al, Si) are interpreted with caution and de-emphasized accordingly. We hypothesize that the progressive dry-season metal enrichment reflects the convergence of intensified emissions, loss of wet-deposition scavenging, and cumulative weathering-driven growth of surface sorption sites during the pre-monsoon period. Priority toxic metals Pb, Cr, and Hg were consistently detected, suggesting SAMPs may function as vectors for toxic metals in tropical urban air. A proxy screening-level inhalation assessment indicated that hazard quotients and incremental lifetime cancer risks for all SAMP-associated metals remained below regulatory thresholds of concern even under upper-bound assumptions (Cr(VI) ILCR ≤2.0 × 10; hazard index ≪ 1), indicating that the inhalation risk from currently observed SAMP-bound metals is negligible while underscoring the need for size-resolved exposure assessment as particles fragment toward the respirable range.