Life Cycle Assessment and Source Apportionment of Microplastic Pollution in Urban Stormwater Systems: Implications for Blue-Green Infrastructure

Abstract

Microplastic pollution carried by urban stormwater is a route from land to aquatic ecosystems that we still understand poorly. This study ran a multi-scale life cycle assessment (LCA) and source apportionment of microplastic emissions, transport, and fate through the stormwater system of Tehran, Iran, a megacity of 9.6 million people spread across a 2,840 km² catchment. Over 12 months, spanning both dry and wet weather, we collected 432 stormwater samples from 24 monitoring stations across four land-use types: high-density residential, commercial, industrial, and transportation corridors. From these samples we isolated, identified, and quantified 18,547 microplastic particles ranging from 10 µm to 5 mm, using FTIR microscopy and Raman spectroscopy. Concentrations averaged 142.4 ± 38.6 particles L⁻¹ in runoff and 78.6 ± 22.4 particles L⁻¹ in the receiving water, with polyethylene (38.4%), polypropylene (24.7%), and polystyrene (14.2%) making up most of what we found. To trace these particles back to their sources, we built a hybrid framework combining positive matrix factorization (PMF) with material flow analysis (MFA), which pointed to six categories: tire wear (28.4%), textile fiber shedding (22.7%), packaging degradation (18.6%), personal care products (11.2%), construction materials (10.4%), and atmospheric deposition (8.7%). The LCA, carried out under ISO 14040/14044 using the ReCiPe 2016 endpoint methodology, put the global warming potential at 0.84 kg CO₂-eq per kg of microplastic emitted, freshwater ecotoxicity at 1.42 × 10⁻³ CTU, and cumulative energy demand at 26.4 MJ kg⁻¹. We then modeled three blue-green infrastructure (BGI) scenarios, bioswales, bioretention cells, and green roofs, to see how much of this pollution could realistically be intercepted. A hybrid BGI portfolio covering 30% of the catchment cut microplastic emissions to receiving waters by 67.4%, lowered GWP by 58%, and returned a benefit-to-cost ratio of 4.2.