New insights for microplastic degradation: Synergistic degradation mechanisms of microplastics and atrazine in sediments

Microplastics (MPs) and pesticides are widely distributed in sediments and can interact with each other to form complex pollutants, thereby altering their environmental impacts. However, it remains unclear whether this process affects the microbial degradation of MPs and pesticides. In this study, 90-day microcosm incubation experiment was conducted using polystyrene (PS), polyethylene (PE), polyethylene terephthalate (PET), polylactic acid (PLA), and atrazine (ATZ). MPs were recovered from the sediments after incubation. Metagenomic analysis was subsequently conducted to investigate the plastisphere microbes, while chemical characterization was performed to examine the surface structure of MPs. It was found that ATZ adsorption increased the mass loss of MPs by 47.37%, 139.44%, 174.67%, and 284.00% for PS, PE, PET, and PLA, respectively. Metagenomic binning analysis revealed that plastispheres enriched MPs and ATZ-degrading microbes, including Glycine, Aquabacterium, Azospirillum, and Pantoea, which carried degradation genes (PaaA, PaaK, PaaG, HSD17B4, alkR, ALDH, and aprE). All four types of MPs were degraded to acetyl-CoA by these functional microbes with distinct metabolic pathways. Acetyl-CoA and the ATZ-derived intermediates (hydroxyatrazine, cyanuric acid, and N-isopropylammelide) involved in the tricarboxylic acid cycle, facilitating the co-metabolism of MPs and ATZ. The study provides a new insight into the degradation mechanism of MPs in the presence of other emerging contaminants.