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 (Branchiura sowerbyi) to enhance MP biodegradation in sediments. Bioturbation significantly enhanced MP degradation in sediments (P < 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 (Thaumarchaeota) and bacteria (Nitrospirae), 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.