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 depolymerize 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 13 C-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.