Challenges and Initiatives to Operationalize the Planetary Boundaries for Novel Entities.

The planetary boundaries framework offers a science-based perspective on maintaining Earth system stability and safeguarding human well-being. For novel entities, however, monitoring and governance remain fragmented, with no quantitative boundary being defined or operationalized yet due to the high variation and diversity of substance emissions, exposure, and effects. Here, we synthesize progress and key implementation gaps in defining and applying a planetary boundary for novel entities. We propose an action-based framework that embeds DPSIR (Drivers-Pressures-State-Impacts-Responses) within iterative PDCA (Plan-Do-Check-Act) cycles and leverages chemical footprint approaches to derive policy-relevant metrics and control variables. This framework aims to translate the planetary boundary for novel entities from an abstract early warning concept into an actionable tool for guiding global chemicals management within a safe and just operating space.