Biodegradable Microplastics Affect the Wheatgrass Traits, Fe Plaque Development Involved in Sb Accumulation, and Microbial Community Functions in Antimony-Contaminated Riparian Wetlands

Alternative biodegradable plastics have been the primary protocols to alleviate traditional plastic pollution in terrestrial systems. However, few studies have investigated the risks of biodegradable microplastics (MPs) and their combination with antimony (Sb) in wetlands. In this study, polyhydroxyalkanoate (PHA), polylactic acid (PLA), and poly(butyleneadipate-co-terephthalate) (PBAT) MPs (0.5 and 2.5 wt %) and Sb(III)/Sb(V) were individually or jointly exposed to wheatgrass in waterlogged riparian wetland sediments. Results showed that root/shoot lengths and root branches were more sensitive to coexposure of Sb(III) with PLA/PHA MPs. Coexposure of Sb(III) and PLA MPs led to a plummet, but coexposure of Sb(V) with PLA presented a significant promotion on microbial activities. PLA and PHA (2.5 wt %) MPs presented a great impact on Fe plaque development, and their combination with Sb significantly increased Sb accumulation in roots. Meanwhile, PBAT MPs promoted transfer factors and bioaccumulation factors of Sb in wheatgrass shoots under Sb(V) amendment. In addition, except for single Sb(V) exposure, the treatments of MPs with Sb led to a stimulation on carbon utilization by microbes in flooded wetland soil. In summary, this study provided information for evaluating potential threats of biodegradable plastics and MPs if present in high concentrations in Sb- or other heavy-metal-contaminated riparian wetlands.