A bibliometric analysis and literature review of earthworms used as bio-indicators for assessing soil heavy metal pollution

Earthworms serve as valuable bioindicators for assessing soil contamination due to their high sensitivity to pollutants. Nevertheless, there is still a lack of a thorough overview of recent advancements and emerging trends in the application of earthworms for assessing the risks associated with soil heavy metal pollution. In this study, the current research status of earthworms in relation to soil heavy metal pollution over the past two decades is examined by utilizing the Web of Science database. A total of 1068 publications were analyzed utilizing VOSviewer and Bibliometrix tools, revealing that zinc, copper, cadmium and lead are the most extensively studied heavy metals concerning soils and earthworms. There is a significant emphasis on understanding the bioaccumulation, bioavailability, toxic effects, and toxicological mechanisms of soil heavy metals in earthworms. Furthermore, it is noteworthy that interests have recently surged regarding the impacts of gut microbiota, biochar, microplastics, and climate change on the interactions between soil heavy metals and earthworms. In light of these findings, the absorption, accumulation, toxic responses, and underlying toxicological mechanisms of soil heavy metals in earthworms are reviewed based on recent literature. Finally, bottlenecks encountered when employing earthworms as bio-indicators for monitoring environmental and health risks associated with soil heavy metals as well as potential opportunities for future research endeavors are discussed in detail.