Extending responsibility: Port-based downscaling targets for the global plastic treaty

The Global Plastic Treaty (GPT) calls for systemic action to curb marine plastic pollution. This paper examines the strategic role of the Port of Santos (SE Brazil), the busiest in the South Atlantic, in advancing GPT implementation through midstream port-based governance. We analyse 19 years of bulk cargo operations (2005-2024) to identify key chemicals and operators in the plastic supply chain. Four chemical cargoes, i.e., naphthas, other naphthas, styrene, and vinyl acetate, are identified as midstream indicators of plastic production. These account for over 7 million tons, with four operators handling more than 90 % of this volume in recent years. By targeting these actors and cargoes, we argue that national implementation of GPT can be accelerated through locally enforceable, port-based interventions. Our findings underscore the value of ports as governance nodes that bridge global treaty commitments with actionable, place-based policies.