A review on the remediation of microplastics using constructed wetlands: Bibliometric, co-occurrence, current trends, and future directions.

Massive prevalence of microplastics (MPs) in the environment has become one of the world's most serious environmental concerns. Human dependence on plastics has created a constant flow of MPs from different sources into natural environment, which has raised public concern regarding consequences of MPs coming into contact with the natural environment. Deploying constructed wetlands (CWs) to reduce MPs pollution is considered a promising method, however there are still barriers for breakthroughs in this technology, particularly knowledge gaps in the mechanisms affect removal process. Recognising this, we provide a comprehensive summary of current advances and theories regarding the mechanisms of occurrence in this research area. In this work, the bibliometric methods were first used to identify annual publication trends and topical topics of research interest. The selected documents were then statistically analyzed using VOSviewer and the 'bibliometrix' package in R to derive the annual productivity of countries or organizations, the most relevant affiliations, the most relevant authors, the most relevant sources, textual analysis, co-occurrence analysis, and cluster analysis of keywords. Finally, detailed information concerning the removal of MPs by CWs was summarised, covering the most common operational and design parameters (i.e., structure types, wetland plants, substrate materials, and microbial communities), to reveal how these parameters can be adjusted for more efficient MPs removal rate. Challenges and future directions were additionally proposed. It is hoped that the review will help identify current research trends, provide insight into the mechanisms of the removal process, and contribute further to the development of this important area.