Lost in definition: unravelling microplastics from marine coatings through bibliometrics science mapping in thematic analysis and systematic narrative literature review

Abstract Marine coatings used on merchant ships have recently emerged as a source of microplastics in marine environments. Marine coatings encompass all paints and coatings applied to various parts of a ship, primarily for anti-corrosion, antifouling anti-skid, heat-resistance, and cosmetic enhancement. However, marine coatings on merchant ships have evaded classification and were not included in the microplastic literature until recently. The purpose of this study is to examine the current state of the absence of a unified definition on a global scale, identify the factors that contribute to the exclusion of marine coatings under the microplastic classification and to analyse the thematic mapping and evolution of the keywords “definition”, “classification”, and “paint” or “marine coatings” in the field of microplastics. We conducted science mapping analysis using Bibliometrix software to examine 1078 papers and carried out a systematic narrative literature review to examine the current state of a standardised definition of microplastics and whether the absence of such impedes a unified interpretation and study of microplastics from marine coatings. Based on the science mapping analysis, this research indicates that “definition” and “paint” have become important keywords in the domain of microplastic research lately, playing a vital role in structuring the field. Meanwhile, the systematic narrative literature review unveiled that the absence of a standardised definition remains a subject of considerable debate, resulting in marine coatings evading classification as microplastics. With this study, we aim to advocate for the establishment of more precise guidelines and policies pertaining to microplastic pollution in marine environments and to promote the adoption of a unified approach towards the definition and classification of microplastics for the purposes of legislation and research. This will also path the way for the collection of better data on microplastic emissions from marine coatings, thereby closing the knowledge gap in this area.