Twenty fifth year of global research in heavy metal removal (1998-2023) : A bibliometric analysis of a modelling on phytoremediation and heavy metals

Due to its severe ecological effects worldwide, heavy metals pollution is a serious issue. Even at low levels in the environment, heavy metals bioaccumulate in food chains will have an adverse effect on all life forms that can not be reserved and when present in water with an excess number, are a key risk for aquatic life. Environmentally friendly method to remove dangerous levels of heavy metals from the contaminated environment is phytoremediation and computational modelling to predict heavy metal removal with phytoremediation has become more important in recent years. Accordingly, the aim of the study is to identify the most significant journal in terms of cited papers, authors, institutions, and countries using VOSviewer software to map graphically the bibliographic material by employing bibliographic coupling and co-citation from all the document published in the journal between 1999 and 2023 using Scopus database. Phytoremediation, heavy metals, and modelling used as hot research topic keywords. The structured information could be useful for identifying research hotspots and gaps in this filed and understand research trends.


Introduction
A significant amount of metal mining waste has been produced as a result of the irresponsible exploitation of the world's natural resources, endangering both human health and the environment [1].Numerous environmental issues, such as the major "contamination of soil, water," creatures, and food, have been caused by the extensive "use of heavy metals in industry and" metal mining.Even at low quantities, when heavy metals are discharged into the environment, they can build up in the soil and spread to people through a variety of routes, including ingestion, skin contact, and soil inhalation (air) [2].Statistics show that each year, nations all over the world emit an average of "5 million tonnes of Pb, 15 million tonnes of Mn, 3.4 million tonnes of Cu, and 1 million tonnes of Ni into the soil" [3].Heavy 1314 (2024) 012105 IOP Publishing doi:10.1088/1755-1315/1314/1/012105 2 metals are easily collected, easily converted "into more hazardous methyl compounds, and can even accumulate in the human body at harmful concentrations through the food" chain.Heavy metals cannot be digested by soil microbes [4].Heavy metal contamination is a significant problem due to its severe ecological effects on the entire world.

Figure 1.
Assessment of heavy metal pollution from anthropogenic activities and remediation strategies" [5] The removal of heavy metals from the soil using hyperaccumulating plant, that can accumulate heavy metals in their roots, shoots, and leaves is known as phytoremediation [6].Due to its low cost and simplicity of use, phytoremediation has become more popular than other physical and chemical techniques such soil replacement, washing laws, and solidification [7].Phytoremediation is a method that is environmentally acceptable for removing hazardous amounts of heavy metals from damaged environments, and computational modelling to forecast heavy metal removal with phytoremediation has gained importance recently.
Bibliometric "or the Scientometric analysis is the research area which helps to analyse current trends in the literature regarding a particular area and provides guidelines and motivations for future research work.It basically provides a general outline and overall structure of the research area" [8].The study's objective is to determine which journal is the most significant "in terms of cited papers, authors, institutions, and countries" by using the VOSviewer software "to map graphically the bibliographic material using bibliographic coupling and co-citation" from "all the documents published in the journal between 1999 and 2023 using the" Scopus database.Keywords for popular research topics include modeling, heavy metals, and phytoremediation.The structured data may be helpful for understanding research trends, locating research gaps and hotspots in this area.

Methods
In this study, "we have gathered bibliometric data from the most widely referred repositories" (Scopus).The "VOS Viewer was used to analyze relevant documents (journal articles) produced by the Scopus" database."In order to fully capture information released throughout the years, the publications of modelling at phytoremediation of heavy metals were gathered using the Scopus" database.This is especially crucial for data consistency and accuracy that needed for historical analysis and trend prediction.The "keyword which has been used for the search query" are : phytoremediation, heavy metals, and modelling."Nodes in VOSviewer maps come in a range of hues and sizes.Size of a node affects frequency of occurrence.The color of a node indicates its relationship to other nodes that have a similar color" [9]..A number of tags were found, including author, title, abstract, nation, citation record, author affiliation, etc. Scopus displayed 88 documents whereas made up of articles (81.81%), reviews (5.68%), conference paper 4.54%, book chapter 3.40% and book 2.27%.The keywords that has been used also filtered by subject are, such as : limited to Environmental Science; "Agricultural and Biological Science; Medicine; Chemistry; Engineering; Biochemistry, genetics and Molecular Biology; Earth and Planetary Sciences; Chemical Engineering; Immunology and Microbiology; Energy; Business, Management and Accounting; and Social" Sciences.

Figure 2. Bibliometric Analysis"
The results of the search instructions for the Scopus database were exported in CSV format.Only journal papers in English were used in this analysis, which covered the year 1999 through 2023".

TITLE-ABS-KEY (phytoremediation AND heavy AND metals AND modeling) AND LANGUAGE (english)
87 records were selected for indepth results Include : Article, Review, Conference paper, Book chapter, Editorial, Book.

Worldwide publication trends
There was interest in the topic during this time period, as evidenced by the volume of research output.
The high cost and lengthy laboratory-based heavy metals removal procedure has been targeted for reduction used computer-aided modelling.A total of 87 original articles were published between the years 1998 and 2023 representing 86,13% of all papers within the scope of the study.The top 10 most productive nations "in terms of publications," as reported Scopus, are shown in this section based on the data that was extracted.Figure 5 shown the order of the countries sorted by document by country or territory.More than 10 papers have been published in ten different nations in total.It's interesting to note that Germany produced paper less than 10 but has the highest citations (1761) with the research topic : "plant responses to abiotic stresses: Heavy metal-induced oxidative stress and protection by mycorrhization" [10].United States in the second rank of top cited countries with 234 citations and produced more than fifth documents.
The top fifth sites or journals that are publishing the most regularly in the developing field of subject area are shown in Figure 6."A journal is a periodic publication (monthly, annually, etc.) with the aim of advancing and tracking the development of the discipline it represents" [8].and Engineering (both 4.6%), Earth and Planetary Sciences (4.0%), and others are additional disciplines that received considerable research.

Author participation and citation analysis
Based on the quantity of publications, the most productive author from Scopus are extracted and sorted [8].Table 1 lists the authors in order of their overall number of citations across all of the publications, which was used to compile a ranking of the most significant author.Schutzendubel Andres and Andrea Polle, "who was the most productive author and the most influential author with" 1761 citations.In Scopus, Schutzendubel Andres and Andrea Polle followed by French and Zhou with 170 and 132 citations each.There are two authors, Brennan and Robinson with top cited of fifth."On the other hand, Scopus' ranking of the most influential authors does not contain a single author from the most productive list, this might be because a bigger number of academics and readers can participate in indexing because to Scopus's comprehensive coverage of international conferences and publications" [8].The h-index is used as an impact parameter to evaluate an author's output and its influence on research in their sphere of influence.

Keyword co-occurrence related to phytoremediation, heavy metals and modelling
Three main cluster have been identified, mapped, labelled as follows.Phytoremediation, soil pollution and heavy metal are the prominent cluster member, and modelling appears as an interesting blue cluster member (with 14 total link strength).Based on content analysis the research focus of each cluster are : remediation "technology to remove heavy" metals "from soil and" model simulation was created to simulating extraction "and translocation of heavy metals in" plants.
As can be seen, phytoremediation is surrounded by phytoextraction, bioremediation, modelling, heavy metals, numerical model, plants, and soil pollutants.The most popular terms used by authors in Scopus are visualized in Figure 8."Due to Scopus's indexing of papers from a variety of sources, the circular node's depiction of the keywords' intensity may be more" intense.We can also see that one keyword, populus, is different from the others in the top list of" keywords.Phytoremediation belongs to old research topic, but when it combine with numerical model to make a simulation for heavy metal adsorption it becomes an emerging and trending research topic (Figure 9) and from the analysis of density visualization we've got 3 cluster with 242 total link strength.Figure 10.shown that heavy metals and modeling are in the same cluster.It means that possible to use a modeling form simulating the number of heavy metal and combined with phytoremediation as the technology.Numerical model can be used as an empirical models attempt to describe observed phenomena, for example to simulate the uptake and translocation of heavy metals in plants.

Figure 3 .
Figure 3. Depicts the search command used for this study.Each part of document's (title and abstract, author's names, country and institution of affiliation, author keywords, number of publications annually, citation counts, and journal titles) are all included in the data export"

Figure 5 .
Figure 5. Document by country or territory"

Figure 6 .
Figure 6.Document per year by source"

Table 1 .
"Top 5 most cited authors and articles on phytoremediation of heavy metals and modelling method"