Varied influence of aged microplastics and related leachates on phosphorus transformation and release from the sediments

Microplastics (MPs) accumulate and age in freshwater sediments, releasing leachates that may alter sediment nutrient cycling. While phosphorus (P) is crucial for freshwater eutrophication, previous studies have rarely focused on MPs leachates. Herein, this work investigated the effects of polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), and related leachates on the sediment P cycling. Results indicated that aged MPs and leachates regulated the expression of P cycling functional genes via inducing DOM components and structures, and microbial communities, thereby affecting the P cycling. The primary mechanism by which aged MPs and leachates affect sediment P involved facilitating the transformation of Al-bound P into Fe (III)-bound P and organic P. Leachates containing microbial-utilizable organic matter exerted a more significant impact on converting Al-bound P into organic P. Besides, incubation and adsorption experiments revealed that aged MP could enhance P release from sediments while leachate inhibited. The effects of different aged MPs and leachate on P release vary. Compared to the control group (0.496 mg/L), P concentration in the overlying water was the highest in 5% PE-MPs (0.659 mg/L) and the lowest in 1% LPE (0.189 mg/L). These results provided new insights into the involvement of aged MPs and leachates in freshwater nutrient cycling.