Plastic pellet spills and leakages during maritime transportation: a transdisciplinary approach to understand the complex causal pathways

Plastic pellets form the second largest source of microplastics in the marine environment and are found around the world. The origin of plastic pellet pollution is often linked to land-based industrial sites and transportation. However, recent spills resulting from accidents with ships have highlighted the significance of maritime shipping as a source of plastic pellet pollution. In addition, plastic pellets may be released from ships into the ocean as a result of operational leakages during maritime transportation. Although the need to address plastic pellet pollution from ships has been globally recognized, the scale and causal pathways behind this source have not been comprehensively documented and knowledge and data remain fragmented across resources and stakeholders. In order to advance the understanding of the causal pathways of plastic pellet spills and leakages during maritime transportation, this paper applied a transdisciplinary approach using mixed methods. These included expert and stakeholder consultations, systematic review of literature and industry data, and ultimately, the integration of all data in the form of cause-consequence diagrams. Causal pathways of plastic pellet spills and leakages during maritime transportation were found to be of four types of events, namely leaking containers, container damage, container lost overboard and loss of the vessel. Both the causes and consequences of these events were described, as such providing a basis for the identification of a comprehensive set of interventions. Mandatory requirements for the transport of plastic pellets should build upon a comprehensive set of interventions, addressing prevention as well as spill response.