From Sources to Solutions: The San Francisco Bay–Delta System as a Microcosm for Microplastic Science

Microplastics (MPs) are a pervasive and persistent class of pollutants found in nearly every aquatic habitat. Substantial advances have been made in characterizing MP sources, environmental transport, fate, and biological effects. However, significant challenges remain due to the vast diversity of MP characteristics, which complicates cross-study comparability, monitoring, and risk assessment. A central focus of this paper is the San Francisco Bay–Delta, one of the most intensively managed and studied estuarine systems in the world, which provides a valuable setting for advancing MP science within a real-world management context. California was the first jurisdiction to formally define MPs and has since implemented statewide monitoring strategies to support method development and the generation of actionable data. Work in this region can therefore serve as a model for management- and solutions-focused MP science. Drawing on discussions from a symposium focused on MP pollution in the San Francisco Bay–Delta, together with global and California-focused research, we highlight priorities, including stronger standardization, environmentally realistic studies, improved risk assessment frameworks, increased data accessibility and transparency, expanded community engagement, and upstream prevention. Together, these efforts are critical for informing MP research, monitoring, and management in the San Francisco Bay–Delta and beyond.