Monitoring Microplastics in Biofiltration: Runoff and Media Sample Collection and Analysis

Abstract Submission: Urban runoff plays a key role in the entry of microplastics into water bodies. Microplastics, defined as plastic particles less than 5 mm long, are emerging contaminants that are not regulated nor commonly monitored in stormwater runoff. There is no design guidance to promote microplastic’s removal using best management practices (BMPs). There is a substantial data gap regarding the occurrence of microplastics in runoff entering and exiting biofiltration BMPs. This is partly due to the absence of standardized sampling and analysis methods compatible with typical BMP monitoring. To address these gaps, we are leveraging the Southern California Stormwater Monitoring Coalition (SMC) Regional BMP Monitoring Network and our experience in developing standardized methods for microplastics analysis, to develop protocols for sampling and analyzing runoff entering and exiting biofiltration and engineered media within biofiltration. During the past southern California wet season (February to April 2024), we successfully collected 10 sets of runoff samples (inflow, outflow, and equipment blanks) from 6 individual biofiltration-type BMPs. In the dry season (June to July 2024), we also collected engineered media samples from these BMPs. The runoff and media samples were analyzed in the SCCWRP laboratory for microplastics particle count, size distribution, and plastic-type. Media were also analyzed for particle- and pore-size distributions. These analyses aim to provide insights into whether existing BMPs effectively capture microplastics and whether engineered media specifications need to be redesigned to address this emerging contaminant.

Learning Objectives/Expected Outcome (Optional) :