(2) In ESI highly Cited Papers

There were 859 unique author keywords recorded in 395 ESI highly cited papers of MPs research, among which a total of 26 author keywords (manually standardized) appeared at least five times. The co-occurrence network analysis of these 26 author keywords were shown in Figure 5. "Microplastic" (the biggest dot, Occurrence = 198) was undoubtedly the most frequently used author keyword in ESI highly cited papers of MPs research, followed by "marine environment pollution" (occurrence = 72), "marine debris" (occurrence = 59), "sediments" (occurrence = 40), "ingestion" (occurrence = 28), "freshwater" (occurrence = 24), "nanoplastic" (occurrence = 23), "fish" (occurrence = 21), "accumulation" (occurrence = 13), "mussels" (occurrence = 12), ranked second to tenth. Most of these keywords were the same as those in publications extracted from WoSCC, and they also contributed to exploring the global hotspots of MPs-related research in the next section.

**Figure 5.** Co-occurrence network diagram of author keywords appearing in a minimum of five ESI highly cited papers, between 2010 and 2019.
