Benthic Fauna Enhance Biodegradation of Microplastics in Riparian Sediments: Reactive Oxygen, Keystone Microbes, and Metabolites

Microplastics (MPs) are biodegraded slowly in riparian sediments due to their stable chemical properties and high polymerization. Thus, we proposed a technique involving the benthic fauna (<i>Branchiura sowerbyi</i>) to enhance MP biodegradation in sediments. Bioturbation significantly enhanced MP degradation in sediments (<i>P</i> < 0.05). Compared to MPs in sediments without benthic fauna, bioturbation resulted in a 2.08-, 2.19-, and 1.68-fold increase in weight loss for polystyrene (PS), polypropylene (PP), and polylactic acid (PLA), respectively. The bioturbation of benthic fauna could not only promote ^·OH generation to cause a higher aging degree of MPs and destroy the structure of MPs but also reshape the keystone microbial community of the plastisphere, thereby enhancing MP degradation to low-molecular-weight products. The contributions of biotic and abiotic factors to MP degradation were found to be 46.9-57.0% and 43.0-53.1%, respectively. Metabolomics further indicated that (-)-alpha-Bisabolol was the main metabolite in the degradation of PLA, whereas hexadecanedioate was the main metabolite in the degradation of PS and PP. These metabolite-related metabolic pathways might be mediated by ammonia-oxidizing archaea (<i>Thaumarchaeota</i>) and bacteria (<i>Nitrospirae</i>), implying that MP degradation might occur in parallel with nitrification. This study has the potential to inform the remediation of MP pollution in riparian zones.