Quantifying Microplastic Loads from Urban Stormwater Runoff Using Pyrolysis-GC/MS: Insights from a Coastal Creek in South Korea

Microplastics (MPs) are widely recognized as emerging contaminants that threaten aquatic ecosystems and human health. Stormwater runoff serves as a major transport pathway, mobilizing MPs accumulated on urban surfaces into receiving waters; however, quantitative information on rainfall-driven MP mobilization remains limited.

This study quantified the emission characteristics and loads of MPs discharged during a 14-mm rainfall event at Samhocheon, a coastal urban creek connected to Masan Bay, South Korea.

Time-weighted stormwater sampling was conducted, and mass-based MP concentrations were determined using pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) following organic matter removal and density separation. The baseline MP concentration prior to rainfall was 6.13 μg/L. Concentrations increased sharply during the initial runoff phase, peaking approximately 1.5 hours after runoff onset, and gradually declined with decreasing rainfall intensity. The event mean concentration (EMC) was 11.93 μg/L. Polypropylene, polyethylene, and polyvinyl chloride were the dominant polymers, accounting for 60–80% of MPs.

Tire wear particles (TWPs), quantified using styrene–butadiene rubber as a proxy, contributed 20–68% of the total MP load. The total MP (>20 μm) load discharged to Masan Bay during the event was 100.3 g based on Py-GC/MS data, with 84% (84.5 g) mobilized during the first 20% of the runoff duration. This estimate was comparable to the FTIR-based load (62.32 g) calculated from particle dimensions.

Overall, the findings demonstrate the utility of Py-GC/MS as a complementary technique to FTIR for MP monitoring and highlight early-stage stormwater runoff as a critical period for MP mobilization. These results emphasize the need for targeted urban watershed management strategies to reduce MP emissions to aquatic environments.