Prevalence of Microplastics in Influent and Effluent Wastewater

Author: Benjamin-Rafael Mingoa

Faculty Supervisor: Archana Anand

Department: Biology

Microplastics (MPs) are defined as plastic particles that are smaller than 5 mm. Major sources of MPs include synthesized fibers, plastic bags, household products, and plastic bottles. As these products are worn, used, or exposed to natural phenomena such as rain or wind, they are susceptible to erosion and degrade into smaller particles. Due to the size of MPs, they easily pass through many water filtration systems. MPs have the capacity to accumulate inorganic and organic pollutants from urban environments and gradually release them post-migration into marine and freshwater systems such as the San Francisco Bay or the Pacific Ocean. This project aims to quantify microplastic concentration in influent and effluent water from the San Francisco Southeast Treatment Plant, which handles 80% of San Francisco City’s wastewater. 500 mL samples of composite influent and effluent water were collected weekly for 4 weeks in the summer and 4 weeks in the winter. The samples were filtered through Whatman 1 filter paper and stained using Nile red (0.01 mg/mL in acetone and distilled water). The dyed samples were analyzed using ultraviolet microscopy to identify the abundance of plastic particles before and after treatment at the wastewater treatment plant.