Reducing uncertainty and confronting ignorance about the possible impacts of weathering plastic in the marine environment

Plastic is ubiquitous in the global oceans. Weathering of plastic generates microplastic and releases chemical additives, and likely also produces nanoplastic and chemical fragments cleaved from the polymer backbone. However, plastic weathering in the marine environment is not well understood in terms of time scales for fragmentation and degradation, the evolution of morphology and surface properties, and hazards of the chemical mixture liberated by weathering. Biofilms that form on plastic affect weathering, vertical transport, toxicity and uptake of plastic by marine organisms, and are also under-investigated. Laboratory studies, field monitoring and models of the impact of weathering on plastic debris are needed to reduce uncertainty in hazard and risk assessments for known and suspected adverse effects. Scientists and decision-makers must also recognize that plastic in the oceans may have unanticipated effects about which we are currently ignorant. Exposure of the global oceans to plastic debris cannot be readily reversed, and constitutes a planetary boundary threat if it is causing an unrecognized effect on a vital Earth system process. Possible impacts that we are currently ignorant of can only be confronted by vigilant monitoring of plastic in the oceans, and discovery-oriented research related to the possible effects of weathering plastic.