Potential Discharge of Microplastics in Surface Runoff—Bucharest Case Study

Plastic particles reach and accumulate the water systems through various routes, including dry/wet deposition or surface runoff. Considering that there are not many studies about the sources of microplastics (MPs) in surface runoff and their contribution to water systems, this study aims to estimate for the first time for a city in Romania (Bucharest) the sources and number of MPs that are discharged by surface runoff, by employing three different scenarios. Sources, such as traffic, artificial terrains, paints, and plasters, have been included in the analysis. Results show that surface runoff contains a number of at least 123,148 × 109 particles per year. Most MPs originate from tire wear and football fields. Also, after the wastewater treatment processes, surface runoff contributes with over 4.98 MPs L−1 to the receiving water body. A solution to reducing MPs in surface runoff is to develop an effective traffic management plan, with improved road surfaces or driving style.