Plastics and their pollution have been understood as inert, safe materials whose environmental impacts arise only after disposal, caused by careless consumers and poor waste management practices. This representation, constructed by industry over decades, reduces plastics pollution to a waste problem, one assumed solvable through clean-ups, recycling or technological fixes. This thesis challenges that simplification, by studying plastics pollution as an inseparable social-ecological challenge. This approach reveals plastics as deeply embedded in ecological degradation, toxic chemical use, dependency on fossil fuels, and systemic social injustice. Plastics pollution disrupts multiple Earth system processes, with many irreversible impacts. This requires governance approaches grounded in justice, equity, and planetary stewardship. 

Adopting a systems-based perspective, the research establishes plastics pollution as an issue of concern at planetary scale. It presents a multi-metric approach for characterizing the complex, large-scale and long-term impacts, and it also shows why a narrow focus on biophysical metrics is inadequate information for science-policy processes. With a particular focus on ongoing Plastics Treaty negotiations, it describes efforts by scientists with policy-influence to reframe the plastics pollution issue as an inseparable social-ecological challenge. 

Paper I situates plastics pollution within the planetary boundaries framework as a representative case of novel entities. Paper II traces how plastics pollution interacts with all other planetary boundaries, including climate change, biosphere integrity and biogeochemical flows, highlighting the need for multiple control variables across the full impact-pathway (i.e., from fossil fuel extraction and production to Earth system disruption). Paper III critiques narrow ecological framings, emphasizing the need for integrated responses that account for social, economic, and political drivers. Paper IV operationalizes this integration through an interdisciplinary multi-expert elicitation process, identifying quantifiable indicators that span environmental, human health, governance, and economic dimensions. Paper V applies a feminist discourse policy analysis to the Global Plastics Treaty negotiations, showing how dominant, industry-aligned representations shape the treaty’s ambition, while exposing sustainability “winners” and “losers” embedded in these representations.

Across all these papers, this thesis underscores the limitations of technocratic, single-metric governance approaches. It advances empirically derived indicators and analytical tools that can support more sustainable global governance, while stressing that sustainable solutions must operate across the full life-cycle of plastics, confront entrenched industrial interests, and address historical and structural injustices. It highlights the risks of science being instrumentalized or sidelined in policy contexts, and the need for deep reflection on these issues. These findings argue for transparent, power-aware science-policy interfaces that integrate plural knowledges, including marginalized voices to inform systemic solutions. They further show that while urgency is undeniable, slowing research and policy design to enable deliberation, trust-building, and co-production can yield more meaningful and equitable outcomes.