Environmental trade-offs in plastic waste management pathways: A critical synthesis of comparative life cycle assessment studies.

Plastic waste remains a major challenge for sustainable polymer science, requiring solutions that align with circular economy principles. This review provides a structured critical synthesis of comparative life cycle assessment (LCA) studies on waste management strategies, including mechanical recycling (MR), chemical recycling (CR), pyrolysis (PY), energy recovery (ER), incineration (IN), and landfill disposal (LF). Results show that MR was most frequently associated with lower impacts for clean polymer streams, cutting greenhouse gas emissions by up to 70% relative to virgin production. CR and PY were often reported as relevant options for mixed or contaminated plastics, though they remain energy-intensive with global warming potentials 30-50% higher than MR. ER and IN reduce volumes but often offset benefits through additional emissions, while LF was frequently ranked among the least favorable options. Beyond benchmarking, we identify persistent methodological gaps across LCAs, including variable system boundaries, omission of microplastic impacts, and limited techno-economic integration. Notably, 88% of studies emphasize global warming, whereas fewer than 50% address eutrophication or human health, constraining comparability and policy relevance. By consolidating fragmented evidence across waste streams and treatment routes, this review maps recurring methodological patterns and environmental trends relevant to future LCA studies and plastic waste management strategies.