Microplastics Affect Sediment Phosphorus Transformation: Based on the Interplay of Bioturbation and Microbial Regulation

Anthropogenic activities frequently cause the accumulation of phosphorus (P) and microplastics (MPs) in river sediments. MP contamination can alter the transformations of sediment phosphorus, thereby elevating the risks of river eutrophication and impeding ecosystem health. Notably, the environmental behavior of MPs can be changed by benthic animals. Nevertheless, it is still unclear how bioturbation affects the interaction of MPs and P transformation. This study investigated the impact mechanism of typical MPs (polypropylene, polystyrene, and polylactic acid) on sediment P fractions in the presence of benthic animals ( Branchiura sowerbyi ). The results revealed that MP accumulation increased inorganic P contents (5.98% to 9.08%) and decreased organic P contents (22.57% to 70.72%), promoting organic P mineralization in sediments. The decrease in labile P (total P extracted from water) content and the increase in total dissolved P concentration indicated that MP accumulation accelerated the release of labile P from sediments into overlying water. Bioturbation aggravated the aging degree of MPs and further strengthened the effects of MP accumulation on P transformation. A mathematical model verified that MP characteristics (types and aging degree of MPs) affected the biomarkers of phoD -encoding bacteria, which indirectly altered P fractions in sediments by regulating the generation of alkaline phosphatase. The study demonstrated the microbial mechanism of P fraction transformation mediated by MPs and bioturbation in sediments, providing information for river eutrophication control and ecological risk management.