Assessment of microplastic release from geofabrics used in erosion control at construction sites

Microplastic (MP) pollution in urban environments is an emerging concern, yet limited data exist on contributions from active construction sites. This study investigated the abundance and characteristics of MP particles in stormwater, including their release from geofabric materials at a construction site following major rainfall events. Polyethylene terephthalate (PET) emerged as the dominant polymer, accounting for 28.79% of the total MP load across all samples, followed by PP, PE, and PU. This dominance was due to its high concentration in downstream samples collected within the construction zone, where PET averaged 61.74 MPs/L and accounted for 53.33% of the MPs at that location. In comparison, the concentrations declined to 6.74 MPs/L at the outlet site. This reduction reflects the influence of stormwater management features such as sediment basins, riprap-lined channels, and vegetated strip filters, which retained more than 90% of MP particles. However, estimated event-based loads indicated that between 1.42 × 10⁶ and 4.60 × 10⁶ MPs/event (mean: 2.61 × 10⁶ MPs/event) were discharged to receiving waters, including approximately 1.69 × 10⁶ PET MPs/event derived from geofabric shedding. These findings demonstrate that even when stormwater best management practices (SBMPs) are implemented effectively, construction sites can be substantial sources of MP pollution. This study highlights the need for long-term monitoring, flow-based load estimations, and targeted improvements to SBMP design to minimise MP export and better manage pollution risks during rainfall-driven events. Keywords: stormwater, microplastic, construction sites, pollution, geofabrics