From Plastisphere to Biorecycling: A Critical Review of Plastic Biodegradation Scales, Risks, and Policy Needs

Plastic pollution has reached planetary scale, with 25-35 Mt leaking annually and cumulative environmental stocks projected to exceed 710 Mt by 2040. This critical review demonstrates that natural microbial biodegradation is 2-4 orders of magnitude too slow to offset inputs: PET and polyester-PU achieve only 5-30% mass loss under optimal conditions, while dominant polyolefins (PE, PP), PS and PVC remain effectively recalcitrant. Engineered enzymes can now depolymerise more than 90% of post-consumer PET within hours, enabling the emergence of the first commercial biorecycling plants in recent years. Yet these advances are polymer-specific, produce contaminated wastewater, and risk accelerating additive release and toxic intermediate formation if hyper-active degraders enter natural ecosystems. True biologically mediated circularity demands immediate integration of ¹³C-validated field monitoring, mandatory biosafety assessment, hybrid routes for mixed plastics, comprehensive life-cycle analysis of degradation products, and binding production caps via the Global Plastics Treaty. Without rigorous ecological oversight, biotechnological approaches to plastic degradation could introduce new environmental risks.