The impacts of microplastics and biofilms mediated interactions on sedimentary nitrogen cycling: A comprehensive review

The environmental problems caused by microplastics (MPs) are becoming more serious. Sediments are important environmental assets and tend to accumulate MPs and nitrogen (N). Microbes are crucial for the cycling of N in benthic ecosystems, and the presence of MPs can alter the microbial community and N transformation. Moreover, various factors can significantly impact the N availability regulated by MPs, including their type, size, and concentration, by interfering with microbial diversity, enzyme activities and related coding genes. This paper mainly reviews the research progresses on the impacts of MPs in sediment coupled with the contribution of biofilm. Furthermore, the response and mechanism of MPs to microorganism-mediated N cycling, such as ammonia oxidation, denitrification, and N fixation, are spotlighted as areas of primary concern along with the role of MPs in accelerating or impeding the N cycle. Finally, the research gaps that require further multidisciplinary investigations are raised. The knowledge gained from this review will provide insights into the detrimental impacts of MPs on benthic ecosystem and urge future research to establish different approaches about formation of MPs-biofilm under different environmental scenarios to evaluate the multidimensional impacts.