Effects of micro/nanoplastics on microorganisms and plants in constructed wetlands during the nitrogen removal process: A review

The occurrence of microplastics (MPs) and nanoplastics (NPs) in the ecosystem has received widespread attention, with research showing that their impact differs from that of conventional pollutants due to the complexity of their effect mechanisms. Constructed wetlands (CWs) as an effective wastewater treatment system using plants, substrates and biofilms can remove MPs/NPs from water bodies. MPs/NPs retained within the systems may have an impact on microorganisms, plants and other aspects of the ecological environment, thus affecting the nitrogen removal performance of CWs. Furthermore, the large specific surface area and abundant adsorption sites of MPs/NPs can result in their adsorption of coexisting environmental pollutants, heightening the potential risks posed by MPs/NPs to the ecological CWs environment. Recent studies have investigated the potential impacts of MPs/NPs on microorganisms and plants in the aquatic environments and in the soil. However, the interrelationships between MPs/NPs, microorganisms and plants in CWs and their ultimate impact on nitrogen removal are not fully understood. Therefore, it is necessary to summarize the current research progress. This review evaluates the effects of MPs/NPs and MPs/NPs carrying environmental pollutants on the nitrogen-transforming microorganisms and plant growth in CWs. The effects of changes in nitrogen-transforming microbial communities and plant growth on nitrogen removal in CWs were analyzed. This paper aims to propose practical suggestions and directions for future research on CWs and their relationship with MPs/NPs by reviewing the mechanism of influence of MPs/NPs on microbial and plant nitrogen removal in CWs.