Global trends and prospects in research on heavy metal pollution at contaminated sites

Soil contamination by heavy metals is a global environmental challenge, poses a serious risk to plant life, human health, and global food supply. In recent years, advanced and effective remediation strategies for heavy metal-contaminated soils have developed rapidly, and a systematic summarization of this progress is important. Based on 2822 bibliographic data (2014-2023) acquired from the Web of Science Core Collection, the research status, hotspots and trends of heavy metal-contaminated sites worldwide had been synthetically analyzed in scientometrics. The results showed that China, India, and the USA were the most active countries in related research, and the main research subjects were the assessment of contaminated sites and remediation methods. The keywords showed 3 co-occurrence clusters, focusing on site characterization, phytoremediation and physical-chemical remediation. The time zone view shows a multidisciplinary amalgamation tendency particular in methods such as using artificial intelligence and remote sensing to predict spatial distribution and migration characteristics of heavy metals. Regarding the types of contaminated sites, the most frequently studied are mining sites and industrial waste sites. Among heavy metals, Cd, Pb, and Zn are the most commonly studied pollutants. The heavy metal contamination in soil, ranked by the geo-accumulation index, is as follows: Cd (5.91) > Pb (4.12) > Zn (3.73) > Cu (2.37) > Cr (1.85) > Ni (1.34). In terms of remediation technologies, the frequency of utilization is ranked as follows: phytoremediation > microbial remediation > soil washing > electrokinetic remediation > oxidation reduction > solidification/stabilization > thermal desorption > soil replacement. Additionally, phytoremediation and soil washing are the most effective technologies for removing Cd, Pb, and Zn. The insights derived from this study contribute to a deeper understanding of the state-of-the-art in this field and help to develop/select applicable methods for the effective remediation of heavy metal-contaminated sites.