Microbe-Mediated Degradation of Polyethylene and Release of Associated Pollutants under Simulated Dark Environments

Polyethylene (PE) dominates global packaging waste, yet its fate remains poorly understood in dark, anoxic environments such as ocean sediments and landfills, which represent important reservoirs for discarded plastics. In this study, 800-day microcosm experiments were performed with PE samples retrieved from an active landfill site with distinct landfill durations. Results demonstrated that anaerobic microbes slowly degrade PE while enhancing the release of secondary pollutants, such as nanoplastics (NPs) and phthalate esters (PAEs). Microbial colonization increased the surface roughness of PE samples and the abundance of oxygenated functional groups, driving oxidative chain scission, NP release (2.4-4.3 × 10¹¹ particles mL^-1 leachate), and PAE biodegradation. Logarithmic curves derived from an improved Polymer Aging Index revealed a midage acceleration window, with PE buried for 7 years being the most susceptible to microbial attack. PE-associated microbial communities were dominated by deterministic assembly processes, with functional taxa being the dominant drivers of PE aging, and PAE degraders exhibiting dual-threshold dynamics. Together, this study identifies a coupled oxidation-biodegradation-fragmentation feedbacks mechanism that governs the fate of PE in landfills, highlighting the dual microbial role in degrading PE and amplifying associated pollutant release.