Global Research Activities on Micro(nano)plastic Toxicity to Earthworms

Micro(nano)plastics are emerging contaminants that have been shown to cause various ecotoxicological effects on soil biota. Earthworms, as engineers of the ecosystem, play a fundamental role in soil ecosystem processes and have been used as model species in ecotoxicological studies. Research that evaluates micro(nano)plastic toxicity to earthworms has increased greatly over the last decade; however, only few studies have been conducted to highlight the current knowledge and evolving trends of this topic. This study aims to visualize the research status and knowledge structure of the relevant literature. Bibliometrics and visualization analyses were conducted using co-citations, cooperation networks and cluster analysis. The results showed that micro(nano)plastic toxicity to earthworms is an emerging and increasingly popular topic, with 78 articles published from 2013 to 2022, the majority of which were published in the last two years. The most prolific publications and journals involved in this topic were also identified. In addition, the diversity of cooperative relationships among different countries and institutions confirmed the evolution of this research field, in which China contributed substantially. The high-frequency keywords were then determined using co-occurrence analysis, and were identified as exposure, bioaccumulation, soil, pollution, toxicity, oxidative stress, heavy metal, microplastic, Eisenia foetida and community. Moreover, a total of eight clusters were obtained based on topic knowledge clustering, and these included the following themes: plastic pollution, ingestion, combined effects and the biological endpoints of earthworms and toxic mechanisms. This study provides an overview and knowledge structure of micro(nano)plastic toxicity to earthworms so that future researchers can identify their research topics and potential collaborators.