Impacts of conventional and biodegradable microplastics on greenhouse gas emissions and microbial communities in lake sediment under diverse aging methods

Microplastics (MPs) are crucial in regulating microbial communities, thereby influencing greenhouse gas (GHG) emissions in freshwater ecosystems. MPs’ presence in lake sediment has been confirmed to be aged, necessitating a reassessment of their influence on GHG emissions. This study aims to investigate the impacts of MPs with various aging methods on organic carbon decomposition and GHG release in urban lake sediments. During the four-week duration of the microcosm experiment, the conventional polyethylene (PE) and biodegradable Poly (butylene-adipate-co-terephthalate) (PBAT) MPs were subjected to ultraviolet (UV) radiation, advanced oxidation processes (AOPs) and biological aging methods to investigate their impacts on carbon dioxide (CO2) and methane (CH4) emissions from lake sediment. Compared to pristine PE, pristine PBAT significantly exacerbated the detrimental impact on CO2 and CH4 emissions by 21.61% and 43.13%, respectively, mainly due to 10% increase in dissolved organic carbon (DOC) and 22.65% increase in microbial biomass carbon (MBC). The surface morphology and functional groups of MPs were changed obviously after aging, thereby influencing the decomposition potential of organic carbon and capacity of microbial reproduction. The aging process of PBAT reduced the available nutrients for microbial activity due to its rapid degradation, leads to a pronounced inhibitory effect on microbial respiration. Besides, MPs aging altered the microbial relative abundance of phyla Firmicutes, Actinobacteria, as well as families Lutispora and Azospirillaceae, thus exerting influence on capacity and anaerobic proportion of microbial respiration.