Microbial Degradation of Plastics in Freshwater Environments

Plastic pollution is an increasing concern in freshwater ecosystems, yet the roles of polymer chemistry, environmental context, and microbial community composition in governing degradation remain poorly resolved. This study examined plastic–microbe interactions across river, creek, and pond environments using gravimetric mass loss, scanning electron microscopy (SEM), and 16S rRNA gene sequencing. Four polymers were evaluated: biodegradable polyhydroxyalkanoate (PHA) and polylactic acid (PLA), and conventional low-density polyethylene (LDPE) and polyethylene terephthalate (PET). Rapid biofilm formation occurred on all plastic surfaces, indicating widespread microbial colonization; however, measurable degradation was strongly polymer-dependent. PHA exhibited rapid and extensive mass loss across environments, approaching complete degradation after four months in river and pond settings, whereas PLA, LDPE, and PET showed limited mass loss despite substantial colonization. Environmental context influenced degradation intensity, but these effects amplified degradation only when polymer chemistry permitted breakdown. Microbial community analyses showed that substrate presence influenced beta diversity more than alpha diversity, and differential abundance patterns revealed overlapping enriched taxa across polymers. Overall, degradation was governed primarily by polymer chemistry and environmental conditions, while microbial composition played a secondary, indirect role.