Navigating knowledge gaps: An emissions inventory approach to understand plastic pollution from international shipping.

Plastic pollution is a complex environmental problem, requiring tailored solutions based on an understanding of contributing sources and mechanisms. Shipping activities significantly affect local plastic loads and, to respond to this ongoing problem, the International Maritime Organization (IMO) is coordinating efforts to address plastic emissions from international shipping. A global, sector-specific assessment could inform such actions, but is currently not feasible due to fragmented and missing data. In this study, a generic plastic emissions inventory framework of ship-sourced plastic flows was developed and parametrised at global scale, based on the current state of knowledge and data. Building on the concept of "key categories" from the domain of greenhouse gas emissions, key flows were identified based on their relative contributions to overall emissions and uncertainty. Among the quantifiable flows, abandoned, lost and discarded fishing gear, mismanaged plastic waste, container loss and self-polishing antifouling paints were identified as key categories. Four flows could not be quantified due to a lack of data and were therefore assessed qualitatively. Priority data gaps were identified for each key flow. The study provides a comprehensive and structured framework to support science-based policy development within the context of the IMO Action Plan on Plastic Pollution and Marine litter. Additionally, its underlying methodological principles can be applied more broadly in other domains of plastic pollution to provide a basis for structured and science-based knowledge and policy development.