Metagenomic insights into density-driven plastic stratification in open dumpsites: implications for waste management and bioremediation

Abstract

Open dumpsites in developing countries constitute a critical nexus of plastic contamination and microbial ecology. However, the mechanistic interplay between polymer density-driven stratification and niche-specific microbial adaptation remains unexplored. This study presents the first integrated metagenomic investigation linking density-mediated plastic segregation to depth-stratified microbial community assembly and metabolic functionality in a tropical open dumpsite. Depth profiling revealed that low-density polyethylene dominated the layers closer to the surface, whereas polypropylene and polyethylene terephthalate were concentrated in the bottom layers. A stratification pattern was subsequently detected in adjacent soil microplastic profiles, indicating density-dependent dispersal mechanisms. Metagenomic sequencing revealed distinct microbial niches aligned with plastic layers: surface zones favoured aerobic Proteobacteria and Actinobacteria, whereas anoxic depths enriched anaerobic taxa and pathways for methane metabolism, alternative carbon fixation, and dissimilatory processes. These findings highlight plastic density as an important driver of vertical microplastic migration and indigenous microbial community structuring, informing predictive modelling of contamination risk trajectories and the design of depth-targeted bioremediation strategies using adapted native consortia. This work advances fundamental understanding of density-driven ecological structuring in anthropogenic waste systems while providing an evidence-based framework for optimizing site-specific waste stabilization and developing indigenous microbial solutions for plastic remediation in regions dependent on uncontrolled dumping.