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Review

The Bibliometric Analysis of Microplastics in Soil Environments: Hotspots of Research and Trends of Development

by
Tingting Yang
,
Jinning Liu
,
Hongfei Zhu
,
Lei Zhu
,
Tao Kong
and
Shanshan Tai
*
College of Environmental Sciences and Engineering, Liaoning Technical University, Fuxin 123000, China
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(9), 7122; https://doi.org/10.3390/su15097122
Submission received: 27 March 2023 / Revised: 14 April 2023 / Accepted: 17 April 2023 / Published: 24 April 2023
(This article belongs to the Special Issue Microplastics in the Soil: Pollution and Sustainable Solutions)
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Abstract

:
Microplastics are persistent and complex contaminants and have been recognized as a global concern. Recently, increasing efforts have been devoted to studying the influence of microplastics on soils. However, the complexity of microplastics and the diversity of extraction methods result in a lack of systematic analysis and comprehensive review in this field. In this paper, we used CiteSpace software to summarize the development of this field. Then, we visualized and analyzed the knowledge structure, research hotspots, and trend directions of this field. We found that the number of publications escalated dramatically, and 281 institutions in 69 countries have published articles in this field. Among them, China was the most productive contributor. However, according to the scientific collaboration analysis, we found that more than 90% of the authors who contributed to the field had no close connection. In co-occurrence analysis for subject categories, we found that the research in this field covered environmental science, engineering, ecology, and agriculture. Additionally, the effect of soil microplastics on agriculture was the most important problem in scientific research. The keyword co-occurrence cluster analysis revealed a total of 6 clusters, including “Identification” (#0), “Microbial community” (#1), “Oxidative stress” (#2), “Adsorption” (#3), “Porous media” (#4), and “Abundance” (#5). We discussed several aspects in detail, including detection methods, characteristics, environmental effects, adsorption capacity, removal and degradation, and toxicity. According to these results, we summarized the current research hotspots and evaluated future research trends in soil microplastics. This study is the first to specifically visualize the research field, and these results provide a reference for future research in the field of soil microplastics.

1. Introduction

Microplastic pollution has been a widespread scientific concern in recent years because a large amount of discarded plastic is flooding into the environment with the increase in plastics, and it remains in the environment for a long time [1]. The bulk of plastic fragments will break into small pieces of plastic [2]. Pieces with a diameter less than 5 mm are defined as microplastics, which are the source of microplastic pollution. Many studies have focused on marine microplastic pollution because the first observation of microplastic pollution was found in marine environments. However, the concentrations of microplastics are much higher in soils than in marine environments [3]. On the one hand, some studies have shown that there is a 4- to 23-fold greater amount of plastic released into the terrestrial environment compared to the marine environment annually [4]. On the other hand, microplastics are more likely to be deposited in soils than in marine environments [5]. Moreover, terrestrial ecosystems are believed to be the source of microplastics in the ocean [6]. Therefore, it is important to pay attention to microplastics in soils.
The first study on microplastic pollution in soil was carried out in 2012 [1]; since then, more and more studies have focused on soil microplastics. The routes by which microplastics enter the soil are diverse, including soil amendments with compost [7], sewage sludge [8], plastic mulching [9], irrigation, littering, and atmospheric deposition [10]. Once microplastics enter the soil, they may have an adverse effect on soil ecosystems. For example, microplastics could affect the soil’s physical properties, including increasing evapotranspiration [11] and changing the soil bulk density and soil porosity [12]. Microplastics could have an impact on soil microbial communities; Wang found that microplastics have caused a significant decline in the diversity of soil microbes [13]. Meanwhile, they also affect soil fauna [14,15] and plants [16]. Terribly, microplastics may indirectly threaten human beings through the food chain [17]. Thus, microplastic pollution in soils has become an important issue among researchers.
The study of soil microplastics could be divided into the following themes: detection methods, characteristics, environmental effects, adsorption capacity, removal and degradation, and toxicity. In order to better understand the research trends and hotspots of soil microplastics, it is necessary to analyze the development of research comprehensively. Although some studies have summarized the distribution and contamination conditions of soil microplastics using meta-analysis [18], analyzed the effect on soil quality and soil ecosystems by combining meta-analysis with experimental results [19,20], or compared and optimized multiple detection methods through review papers [21], most studies have only focused on one aspect of soil microplastics. They did not discuss soil microplastic pollution in its entirety. Therefore, we used CiteSpace, which is a bibliometric analysis method software, to provide a new and comprehensive viewpoint on soil microplastics [22].
In this paper, we used quantitative literature analysis to investigate the current knowledge about microplastic pollution in soils. Furthermore, we cover all the important current research and evaluate research trends in the future. The aims of this paper were as follows: (a) to achieve a better understanding of the studies on microplastic pollution in soil; (b) to analyze the research status of microplastic pollution in soil in depth; and (c) to make suggestions for future research. Therefore, this paper discussed the development status of soil microplastics comprehensively and analyzed hotspots of soil microplastics further. It is important to provide suggestions for future research directions.

2. Data Acquisition and Methods

The data were retrieved from the Web of Science (WoS) Core Collection, and the search term was “microplastic* and soil*” with a cutoff time of 2021. The WoSCC indexes “Science Citation Index-Expanded (SCI-E)” and “Conference Proceedings Citation Index-Science (CPCI-S)”. The search was conducted in December 2021. We refined the search results by the document types “Articles”, “Review Articles”, and “Proceedings Papers”. The data consisted of 721 publications, including 566 articles, 9 proceedings papers, and 146 reviews.
In this study, we used CiteSpace (5.8 R2) as the visualization software to perform co-occurrence network analysis of keywords [23]. The cooperative analysis of the country, institution, and author is shown by the contributing countries. The research hotspots in a field were identified by the journal articles with frequency of use of popular keywords. Therefore, the node types “Country”, “Author”, “Institution”, and “Keyword” were selected in the software to generate co-occurrence maps. Other parameters were set as follows: (1) the time slice: one year; (2) the top keywords: 50; (3) the cluster was generated by applying K-core clustering; and (4) the cluster labels were automatically extracted by the log-likelihood rate (LLR). Furthermore, a node with a relatively high BC value (≥0.1) indicated its vital role in mapping and extensive connections to other nodes [24].
In the results of visualization, the number or frequency of nodes was indicated by the size of the nodes (the thicker the circle of nodes, the more frequently terms appear), and the strength of the association was indicated by the thickness of the lines (the thicker the line between the nodes, the closer they are to each other) [25]. Co-occurrence analysis refers to counting the frequency of occurrence of a group of words in the study literature and measuring their affinity through their co-occurrence. Cluster analysis refers to grouping and classifying objects according to their similarity. Burst detection can detect a drop or increase in the use of a particular keyword.

3. Results

3.1. Publication Contribution

The publication contribution demonstrates the development of a field. There were 68 countries involved in studies of soil microplastics, indicating that the field has raised global concern. The top five countries based on publication contributions on soil microplastics are shown in Figure 1. Although soil microplastics were first mentioned in 2012, the first research paper indexed in WoS that referred to the negative effects of microplastics on the soil’s ecological environment was published in 2016. Among the top five countries, Germany, the Netherlands, and Australia published papers in 2016. China was the leading country from 2017 to 2021, with 311 accumulated publications, and the average growth rate was 150%. The total number of publications continued to increase dramatically until 2021. The results showed that China contributed the most research on soil microplastics.

3.2. Scientific Collaboration Analysis

The analysis of scientific collaboration revealed the distribution and intensity of cooperation and showed the importance and relevance of the countries, institutions, and authors [26]. There were 281 institutions in 69 countries that were covered since 2016. Among them, the countries “China”, “Germany”, “Finland”, “Japan”, “USA”, “France”, “Australia”, and “Netherlands” had high centrality, with values of 0.42, 0.16, 0.13, 0.12, 0.11, 0.11, 0.10, and 0.10, respectively (Table 1). This result indicated that the above countries had extensive connections with other countries. Additionally, the Chinese Academy of Sciences (CAS) was the greatest contributor by far (Figure 2) and had the highest centrality (the value is 0.64). This result indicated that the Chinese Academy of Sciences had extensive connections with other institutions. Although there was a total of 752 authors who contributed to this field, more than 90% of the authors had no connection (the centrality values were equal to zero) (Figure 3). The results indicated that more cooperation and communication are needed in this field, and, based on the bibliometric analysis, we concluded that a leadership team has not yet been formed.

3.3. Subject Category Analysis

The analysis of subject categories is a reflection of the integration of subjects in a field. The subject categories of this field were environmental science, engineering, ecology, and agriculture (Figure 4A). The high centrality and frequency of related publications reflect the gravity center. We found that this field revolved around environmental sciences and ecology (Frequency = 512, Centrality = 0.28) (Figure 4B). These results showed that more attention has been given to soil microplastics in the field of environmental science and ecology. Additionally, the subject category with the highest centrality was “Agriculture” (Centrality = 0.40), indicating that the effect of soil microplastics on agriculture is the most important concern in scientific research. Although the subject category of “Endocrinology & Metabolism” recently had low centrality and frequency, its inclusion revealed that researchers are not only focusing on the ecological effects of microplastics on soils but also trying to explore the mechanism of the impact of microplastics.

3.4. Keyword Co-Occurrence Analysis

The keyword co-occurrence network reflected the core content of articles [24,27]. The largest node was “pollution”, with a frequency value of 191, with “soil” and “microplastic” excepted (Figure 5). The results showed that an increasing number of researchers are addressing the pollution from soil microplastics. Moreover, we should monitor which keywords have been taken seriously more recently. For example, atmospheric fallout with a frequency value of 10 was the largest node that first appeared in 2021, indicating that global atmospheric fallout is also a source of microplastics in soils. Surface deposits and landfill deposits may spread into the atmosphere and then transfer to the soil [28], making it more difficult to control soil microplastics.

3.5. Cluster Analysis

Cluster analysis can reveal research hotspots in a field. We carried out the LLR algorithm to show the co-occurrence clusters of the keywords, which was an effective way to identify hot topics and emerging trends. As shown in Figure 6, 6 clusters, including “Identification” (#0), “Microbial community” (#1), “Oxidative stress” (#2), “Adsorption” (#3), “Porous media” (#4), and “Abundance” (#5), were obtained. According to the clusters and research content, we summarized the hot topics as follows.

3.6. Identification Methods for Soil Microplastics

The cluster “identification” had 63 keywords, and the mean publication year was 2018. The identification of soil microplastics is the basis of this field and directly affected the accuracy and references of research. Although the presence of plastic in soil was mentioned in 2012, the amount was not quantified. We think the limiting factor was the identification technique [29]. Therefore, many studies have focused on identification methods for soil microplastics. The process of identification includes the destruction of soil aggregates, separation, and purification. In the first step, microplastic particles should be distinguished from soil particles by the destruction of soil aggregates. The methods of separating microplastics from soils include density separation [30], froth flotation [31], magnetic extraction [32], electrostatic separation [33], solvent extraction separation [34], and oil separation [32]. Microplastics isolated from soils usually have many organic components on the surface, and they should be removed to avoid interference with the identification of microplastics. The methods of purification include hydrogen peroxide oxidation [35], acid and alkaline digestion [36], and enzymatic digestion [37].
The keywords with a high frequency were related to soil and pollution, marine environment, etc. and grouped into cluster #0 (Figure 6a). The keywords with marine environment had the highest centrality value (0.08) and had a relatively high frequency value (101) in this cluster. Additionally, the most cited references of the marine environment stated that the identification of microplastics in the marine environment will provide a reference that is likely to be identified in soils [4]. Therefore, we think that the identification of microplastics in marine environments is very important for the soil environment. The identification methods and techniques for soil microplastics are derived from marine environments. For example, the density of flotation easily identifies microplastics in soil and marine environments [38,39].

3.7. Environmental Effects and Removal of Soil Microplastics

The mean publication year for the cluster “microbial community” was 2018. The microbial community is one of the important controls affecting soil processes [40] and sustaining soil function. Moreover, the microbial community is an important biological indicator of soil quality [41]. Therefore, the effect of microplastics on the microbial community has been a focus. Several studies reported the relationship between soil microplastics and the soil microbial community and the effects of microplastics on the soil microbial community [42,43,44].
The cluster “microbial community” had 56 keywords, including “microplastics”, “exposure”, and “degradation” which appeared with high frequency (Figure 6b). Many studies focused on the effect of microplastic exposure on soil microbial communities. For the keyword exposure, the majority of the cited articles concluded that microplastics were transmitted to the soil in diverse ways, including physical, biological, and anthropogenic mechanisms [45]. We think that microplastic exposure, as a potential agent of global change in terrestrial systems, could cause changes in the soil microbial community. One reason is that soils may be the first receptacle for plastics and likely act as long-term sinks for microplastic debris [1]. Another reason is that soil microplastics have an extremely long degradation time [46]. Therefore, the degradation of microplastics in soils has received more attention. Degradable plastics are currently used and promoted [47]. For example, biodegradable plastics have partly been used as alternatives to conventional plastics. However, degradable plastics in soils still pose a significant problem. Because degradable plastics are more susceptible to degradation, they can generate more microplastics than conventional plastics [48]. The effect of degradable plastics on the soil environment remains uncertain. Therefore, we should study the feasibility of degradable plastics as an alternative to conventional plastics. Meanwhile, many studies have focused on microbial strains to degrade microplastics in soils [49]. For example, Zhang identified a bacterium that degrades polyvinyl chloride and proposed a biodegradation pathway.

3.8. Toxicity of Soil Microplastics

The third cluster was labeled “oxidative stress”. In a contaminated environment, the balance between reactive oxygen species and antioxidant responses is disturbed, which can often stimulate oxidative stress [50]. Many studies reported that microplastics could harm the soil fauna through oxidative stress [51,52,53]. For example, Sun found that the gastrointestinal walls of Achatina fulica were damaged, and its liver underwent oxidative stress [54]. Song found that microplastic exposure could reduce the total antioxidant capacity in snail liver tissues [55]. Moreover, an increasing number of studies have reported that oxidative stress caused by microplastic exposure could affect the soil biota [54,56]. Thus, the oxidative stress affected by microplastic exposure should be studied thoroughly. In this cluster, the highest centrality keyword was “ingestion” (centrality value = 0.1) (Figure 6c), and the earliest publication year was 2016. The most cited article with the keyword ingestion introduced the ingestion of microplastics by Lumbricus terrestris and discussed the concentration of accumulation [56]. Meanwhile, many studies provided direct evidence that microplastics can accumulate in plants. For example, Li found that microplastics were taken up by crops via crack entry [57]. However, whether microplastics are transmitted through the food chain and have toxic effects on human health should be studied further.

3.9. Adsorption Capacity of Soil Microplastics

The fourth cluster, labeled “adsorption”, consisted of 43 keywords. The mean publication year for this cluster was 2019. Many studies reported that microplastics in soils can accumulate heavy metal or organic pollutants [4,58]. The reason is that microplastics have a small particle size, large surface area, and high hydrophobicity in soils [59,60]. The fifth cluster was “porous media”, and it consisted of 41 keywords. The highest frequency value of keywords was “sorption”. The most cited article of these keywords discussed the sorption of persistent organic pollutants, heavy metals, and antibiotics by soil microplastics [61,62]. Many studies have been conducted on the sorption behavior of heavy metal or organic pollutants. However, the sorption mechanisms of microplastics on heavy metal or organic pollutants in porous media remain unclear. Therefore, we should pay more attention to fully understanding the sorption mechanisms. Moreover, soil microplastics could also affect the sorption and migration of heavy metal or organic pollutants in porous media. Microplastics act as carriers of pollutants in the soil and can indirectly change the bioavailability of heavy metals, pesticides, or other complex substances. For example, soil microplastics could increase the mobility of Cd in soils and could expand the scope of Cd [63]. Wu found that microplastics slowed the rapid adsorption stage of pesticides in soil. Therefore, it is important to study compound pollution with microplastics and organic pollutants in soils.
In the cluster with adsorption, the highest frequency value of keywords was “water” (Figure 6d). The most cited article with this keyword reported that biodegradation was affected by the water absorption of plastic materials [64]. Water absorption could allow microbes to access bulk material. Therefore, the different water absorption of microplastics should be considered in biodegradation.

3.10. Characteristics of Soil Microplastics

The sixth cluster, “abundance”, consisted of 41 keywords. The soil environment is a sink for microplastic debris, and its abundance of microplastics is one of the important characteristics. However, research on the abundance of microplastics in soils may be a major challenge. This is influenced by the identification methods and techniques. Meanwhile, the most cited article on plastic debris suggested that the abundance of plastic debris (<5 mm) is important for understanding the potential effects of microplastic pollution [4]. Therefore, we think that it is important to summarize the abundance of microplastics in different soil types.

3.11. Keyword Bursts

Keyword bursts represent the use of certain keywords, and these keywords within a specific period were sharply increased in a certain field. Therefore, it could partially reflect the dynamics of the study field and the potential development of research questions [65,66].
The strongest bursts of keywords refer to the hottest topics or the most studied. The nine keywords with the strongest bursts are shown in Figure 7a. Among these keywords, “ingestion” was the strongest and had the longest duration. According to the results of the clusters, we found that the ingestion of soil microplastics in plants received attention. The most recent keyword was “extracting microplastics”. We think that the high requirements for extracting microplastics requires in-depth study. For example, microplastic particles were isolated using density separation with a NaCl solution, but microplastics with a high density, such as polyethylene glycol terephthalate and polyvinyl chloride, could not be extracted [67]. Thus, the extraction of microplastics should be given more attention. Additionally, in Figure 7a, we found that researchers focused more attention on the sources of soil microplastics through other keyword bursts.
The keyword bursts with the longest duration indicated that it had attracted research interest in the long term (Figure 7a). The keyword bursts with the longest duration included nine keywords, and both “ingestion” and “marine environment” were the strongest keyword bursts. The results showed that ingestion of biota and the effect of the marine environment of microplastics were the most concerning problems and were also studied for a long duration. Moreover, the keyword burst with the longest duration was “bacterial community”. We think that the result indicates that the soil bacterial community has received continuous attention. However, soil fungal communities also played an important role in soil ecosystems for functions and processes [68,69]. Thus, the fungal communities should receive attention in studies of soil microplastics.

3.12. Coreference Analysis

The coreference analysis is the research developmental background of this field. The labels extracted from relevant papers demonstrate the relationship between these papers. A coreference cluster network was also constructed in this study (Figure 8), and the network was divided into 13 coreference clusters. Based on the coreference analysis results, the five largest clusters were summarized (Table 2). The silhouette represents the homogeneity of clusters, and the value ranged from 0 to 1; the size refers to the number of publications of clusters. According to Table 2, the values of the five largest clusters ranged from 0.722 to 0.899, indicating that these clusters significantly differed in the network.
The largest cluster (#0), labeled gut microbiome, has 133 members, and the silhouette value is 0.722 (Table 2). The second largest cluster (#1), labeled as case study, has 125 members, and the silhouette value is 0.899 (Table 2). The most relevant reference of these two clusters was J Huang, H Chen, Y Yang, Y Zhang and B Gao [70]. Huang conducted a systematic review of the occurrences, sources, and analytical methods in soils and groundwater. Additionally, Huang also demonstrated that microplastics have potential effects on animals via the gut microbiome. Many studies found that microplastics in soils could have an effect on soil animals [56], plants [71], microbiota, soil functions and structures [72], and even humans [73]. However, the effects of microplastics on soil animals have received more attention, and we think that the effects may be more influential and convincing. Furthermore, Huang summarized the global spatial distribution of microplastic abundance in soils and groundwater and confirmed that most microplastic occurrence cases in soils are recorded above or near mega groundwater aquifers globally. Therefore, we think that microplastics migrate between soil and groundwater, which may result in greater ecological risk. For example, the microplastics in soils could have vertical migration from soils into groundwater [74]. The transport of microplastics includes not only vertical migrations but also horizontal migrations. However, the migration concentration and depth of microplastics between soil and groundwater are not known. The topic of the transport of microplastics is important in the soil environment [5,43] and needs to be studied deeply.
In Table 2, the third largest cluster (#2) has 78 members, and the silhouette value was 0.791. It was labeled separating microplastics. Cluster #2 of the reference was similar to cluster #0 of the keyword. Therefore, we think that the separation of microplastics is very important to microplastic research. Additionally, the fourth largest cluster (#3) had 52 members, the silhouette value was 0.871, and it is labeled adsorption behavior. In cluster (#2) and cluster (#3), the most relevant reference was Q Birch, P Potter, P Pinto, D Dionysiou and S Al-Abed [75]. Birch et al. summarized the adsorption behavior of soil microplastics. They found that microplastics in soils adsorb toxic compounds and transport them long distances in many ways. This causes incalculable potential risk to the soil environment. For example, Bergami indicated that microplastics have entered Antarctic terrestrial food webs [76]. Therefore, we think that microplastics should be studied deeply in the field of global soil biogeochemical cycles. The silhouette value was 0.881 with the fifth largest cluster (#4), and a wastewater treatment plant was the label. In cluster #4, the most relevant reference was P Koyuncuoğlu and G Erden [77]. This explains the ecological risks of wastewater treatment plants to the soil environment. The microplastics of wastewaters are transferred and accumulate in sewage sludge. Then, sewage sludge is used in agricultural irrigation, which results in microplastic pollution. Therefore, wastewater treatment plants are the main source of agricultural soil pollution.
As shown in Table 3, the articles of Lwanga EH (2016), Horton AA (2017) and Nizzetto L (2016) were highly cited. The top item by citation was Lwanga EH (2016), with a citation count of 202. The ecological impact of microplastics on soils has been summarized at various levels [78]. Thus, we think it is necessary to study microplastics at multiple scales. The second most highly cited paper was Horton AA (2017), which has a citation count of 182 [4]. Horton evaluated the relevant data from marine microplastic literature and determined the applicability of this information to terrestrial systems. Furthermore, further research into the soil environment was suggested. The third most highly cited papers were carried out by Nizzetto L (2016), with 173 citation counts. Nizzetto also suggested that municipal wastewater treatment plants are likely to represent a major input of microplastics to agricultural soils [79]. We think that it provides strong support for sources of microplastics in agricultural soil. Therefore, farmers, wastewater treatment operators, and the general public should raise their awareness to protect agricultural soils.

4. Discussion

Microplastics in soils have attracted increasing attention all over the world in recent years. Although some reviews have reported this topic, traditional literature review studies have a bias in the selection of publications. They may lack key literature and important information. However, the bibliometric analysis of CiteSpace can cover all papers within a selected time period and could avoid missing key literature and important information. Moreover, the results could provide research hotspots and potential development insights into certain scientific fields. Therefore, this paper used CiteSpace software to obtain a more objective result for further research on soil microplastics.

4.1. Analysis of the Literature

Using publication contribution analysis, we found that the study of soil microplastics started late. We think that this may be caused by the extraction and detection methods, which were inadequate [80], or the harmful effects of microplastics on soils being the result of long-term pollution.
Additionally, some studies reported that most of the available studies on microplastics focused on China [81]. We also found that China has the most research on soil microplastics in the world in terms of the publication contribution. On the one hand, China accounts for 30% of the world’s plastic production [81], which means that China must pay more attention to the ecological effects of soil microplastics on environmental change than other counties. On the other hand, China is known for strong scientific research.

4.2. Analysis of Cooperation Networks

In the scientific collaboration analysis, we found that the main countries that contributed more research had extensive connections with other countries/regions. However, more than 90% of the authors who contributed to the field had no close connection. We think that one of the reasons may be that different countries or regions have different levels of economic development, modes of agricultural production, and population densities. This could lead to soil properties or the types and concentrations of microplastics varying greatly in different study areas. For example, the abundance of microplastics in agricultural soils in Yunnan was 0.34 to 0.36 items/kg [82], and the abundance of soil microplastics in southern Germany was 7100 to 42,960 items/kg [83]. These studies showed that soil microplastics have high spatial heterogeneity, and the abundance of microplastics in different soils varies greatly [84]. Therefore, the assessment of the ecological impacts of soil microplastics is inconsistent. Additionally, we think that another reason is that soil microplastics exist in many soil types, such as agricultural areas, industrial areas, roadsides [85], and so on. This could lead to researchers’ focus being relatively scattered. Therefore, there is no consensus on the research emphasis of soil microplastics. In conclusion, we think that most researchers have not reached a consensus about the research of soil microplastics, which leads to rare communication and cooperation in this field.

4.3. Co-Occurrence Analysis for Subject Categories

More attention has been given to soil microplastics in the field of environmental science and ecology by subject category analysis, and some studies have also shown that microplastic pollution is the second most important scientific issue in the field of environment and ecology [86]. Furthermore, the results of this study showed that the effect of soil microplastics on agriculture was the most important problem in scientific research. We think one of the reasons is that agricultural activities such as plastic mulching, organic fertilization, or wastewater irrigation could increase the opportunities for agricultural soils to receive microplastics. The other reason is that microplastics in agricultural soil pass into human food via the food chain. Many studies have reported that microplastics have a potential transfer pathway from agricultural soil or crops to human food [87,88,89].

5. Research Frontier Analysis

5.1. Analysis for Keyword Co-Occurrence

Some studies determined that the main sources of soil microplastics come from agricultural practices, including mulching film, sludge, and wastewater irrigation [80]. In this study, we found that atmospheric fallout was the largest node in 2021 that first appeared in keyword co-occurrence analysis. On the one hand, we think that an increasing number of researchers are paying attention to the influence of atmospheric deposition on soil microplastics. Compared with other sources, microplastics may be transported to remote areas during atmospheric deposition; for example, winds may transport lighter plastic items to soils on other lands [90]. A specific example is the study performed by Allen who analyzed atmospheric microplastic deposition samples from the French Pyrenees and found microplastic transport up to 95 km through the atmosphere [91]. On the other hand, soil microplastic pollution caused by atmospheric deposition is more difficult to control. Therefore, we think that quantifying the contribution rate of atmospheric deposition to soil microplastics is one of the key goals for future studies.

5.2. Analysis for Clustering

Microplastics in soil environments are increasingly being reported, and efficient separation and identification of microplastics are required for assessing environmental risk [32]. Compared to the marine environment, soil microplastics are difficult to collect and identify. For example, some microplastics can be strongly adsorbed by soil particles. Alternatively, there are different sizes and types, which may impact the effectiveness of flotation and separation, so diverse flotation solutions are needed to adjust to various soil samples [67,92,93,94]. Therefore, the identification methods of microplastics applicable to various soil environments should be explored. There are many identification methods for soil microplastics at present, and many studies have chosen different identification methods or the same identification methods with different reagents. This leads to variation in the quantitative and qualitative microplastic counts. For example, the abundance of soil microplastics has used different units, such as items/kg [95], particles/kg [96], or pieces/kg [97]. Thus, it is difficult to compare the results and make assessments for global trends in microplastic distribution. Therefore, there is an urgent need to establish standardized methods and uniform protocols for the quantification of soil microplastics. Above all, more accurate methods and techniques of identification and standardized methods or uniform protocols of identification are the hot and difficult focus of future research in this field.
Many studies have found that the effect of microplastics on the soil microbial community is dependent on the type, dose, shape, size, and soil conditions [98,99]. For example, Zhu found that microplastics at a concentration of 2% are enough to alter wheat rhizosphere soil microbial community composition, but the influence varies among three different types of microplastics [100]. Feng found that a 2% concentration of polyethylene could alter soil bacterial community diversity, but the number of OTUs with a 0.2% concentration of polyethylene showed no significant difference from the control [99]. Ng found that the variation in the treatment of the bacterial community was higher in high LDPE treatments than in the controls and low LDPE treatment [101]. Additionally, most studies thought that microplastics could alter the soil microbial community [101], but Helmberger found that an obvious effect on the soil microbial community was generated only when the concentration of microplastics exceeded a certain threshold [102]. However, most of these studies were based on different soils and sizes and types of microplastics as objects, leading to difficulty in generalizing trends across these studies. Therefore, we think that the study of the impact of microplastics on the soil microbial community should consider multiple angles in future research and identifying the thresholds of impact (including time of exposure, range of concentration, range of size, and so on) is the key issue to be addressed. Moreover, some studies have found that biodegradable microplastics could produce even more microplastic particles [103,104,105], or biodegradable microplastics have chemical additives that may harm the soil microbial community [106]. For example, Li found that excessive biodegradable microplastics could decrease the diversity and richness of the soil bacterial community [107]. Therefore, whether biodegradable microplastics become a solution to global microplastic pollution should be further studied.
Many studies have reported that the effects of microplastics on plants are mainly reflected in the indicators of oxidative stress [108,109], and microplastics also intensify the oxidative stress responses in soil animals [110,111]. For example, Zhang found that soil microplastics altered soil physicochemical properties and then produced oxidative stress damage to plants and soil animals [20]. However, few studies have focused on the relationship between oxidative stress and soil properties. Therefore, we think an assessment of the effect of soil microplastics on oxidative stress in plants and soil animals should consider the influence of soil microplastics on soil ecosystems. Alternatively, the correlation between oxidative stress and soil properties should be studied thoroughly.
Many studies have reported that microplastics generally have a strong adsorption capacity for other pollutants. They have a small size and large specific surface area. This makes the microplastics able to serve as a vector to transfer other pollutants in porous media [98,112]. For example, Roams found that pesticides could migrate from the surface to the interior of plastic film or soil and then concentrate under the influence of microplastics [113]. The competitive adsorption of microplastics results in the decreased bioavailability of hydrophobic organic compounds in soil porewater [114]. However, these studies focused on the objective description of the existence of adsorption behavior at present, reported the adsorption of organic pollutants or heavy metals on microplastics, or posed a potential risk to the soil environment [115]. For example, Yu found that the strong adsorption capacity of microplastics could inhibit the activities of enzymes [116]. We think that it is important to study the interaction between other pollutants and microplastics to evaluate the risk to soil organisms. Therefore, the additional impact of soil microplastic absorbability should be explored to study the impact of soil microplastics on the soil environment, especially the interaction between soil microplastics and organic pollutants. Moreover, little is known about the mechanisms of microplastics on heavy metal or organic pollutants in porous media, which is also a key issue for future research.
In remediation of soil microplastic pollution, exploiting suitable remediation technology is one of the fundamental ways to solve the problem. Among them, bioremediation technology may be the best choice, which can be used to degrade microplastics using plants or microorganisms in the soil system [49]. Some studies have shown that bacteria can degrade microplastics due to their natural ability to degrade long-chain fatty acids. For example, Park obtained a degraded strain to degrade microplastics using enzymatic chain scission [117]. However, the soil environment is very complex. It not only requires single bioremediation technology but also complex degrade strains or technology [118]. For example, the soil can be contaminated by microplastics combined with heavy metals or pesticides. Therefore, it is important to study the remediation of complex contamination in the future.

6. Conclusions

In this study, we used CiteSpace software to analyze a large number of publications and visually reviewed the academic progress and achievements in this field. We summarized the research hotspots and proposed the focus and direction of future research in the field of soil microplastics. The research trends of soil microplastics in the future are as follows:
(1)
Increasing cooperation and communication are needed in this field.
(2)
In terms of identification, developing standardized methods or uniform protocols is an important and challenging aspect of future research.
(3)
The influence thresholds of microplastics on the soil microbial community should be studied thoroughly, including the time of exposure, range of concentration, range of size, and so on. Additionally, quantifying the contribution rate of atmospheric deposition to soil microplastics is one of the key points of future studies.
(4)
Whether degradable microplastics become a solution to global microplastic pollution should be determined. However, we should pay more attention to separating microbial strains to degrade microplastics in soils.
(5)
Whether microplastics are transmitted through the food chain and are toxic to human health should be investigated in the future.
(6)
The migration concentration and depth of microplastics between soil and groundwater should be studied deeply in the future.
(7)
It is necessary to study the effect of compound pollution with microplastics and organic pollutants in soils. In addition, it is important to study the remediation of complex contamination in the future.

Author Contributions

Conceptualization: S.T.; data curation: T.Y., S.T. and J.L.; formal analysis: T.Y.; funding acquisition: T.Y. and S.T.; investigation: T.Y., J.L. and S.T.; methodology: T.Y. and H.Z.; resources: T.Y., T.K. and L.Z.; software: T.Y., J.L., L.Z. and S.T.; supervision: H.Z., L.Z., T.K. and S.T.; writing—original draft: T.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Liaoning Province Education Administration (LJKMZ20220681) and the Liaoning Province Education Administration (LJKZ0365).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Rillig, M.C. Microplastic in terrestrial ecosystems and the soil? Environ. Sci. Technol. 2012, 46, 6453–6454. [Google Scholar] [CrossRef] [PubMed]
  2. Wang, W.; Ge, J.; Yu, X.; Li, H. Environmental fate and impacts of microplastics in soil ecosystems: Progress and perspective. Sci. Total Environ. 2019, 708, 134841. [Google Scholar] [CrossRef] [PubMed]
  3. Xu, B.; Liu, F.; Cryder, Z.; Huang, D.; Lu, Z.; He, Y.; Wang, H.; Lu, Z.; Brookes, P.; Tang, C.; et al. Microplastics in the soil environment: Occurrence, risks, interactions and fate—A review. Crit. Rev. Environ. Sci. Technol. 2019, 50, 2175–2222. [Google Scholar] [CrossRef]
  4. Horton, A.; Walton, A.; Spurgeon, D.; Lahive, E.; Svendsen, C. Microplastics in freshwater and terrestrial environments: Evaluating the current understanding to identify the knowledge gaps and future research priorities. Sci. Total Environ. 2017, 586, 127–141. [Google Scholar] [CrossRef] [PubMed]
  5. Jambeck, J.; Geyer, R.; Wilcox, C.; Siegler, T.; Perryman, M.; Andrady, A.; Narayan, R.; Law, K. Marine pollution. Plastic waste inputs from land into the ocean. Science 2015, 347, 768–771. [Google Scholar] [CrossRef]
  6. Sheela, A.M.; Manimekalai, B.; Dhinagaran, G. Review on the distribution of microplastics in the oceans and its impacts: Need for modeling-based approach to investigate the transport and risk of microplastic pollution. Environ. Eng. Res. 2022, 27. [Google Scholar] [CrossRef]
  7. Vithanage, M.; Ramanayaka, S.; Hasinthara, S.; Navaratne, A. Compost as a carrier for microplastics and plastic-bound toxic metals into agroecosystems. Curr. Opin. Environ. Sci. Health. 2021, 24, 100297. [Google Scholar] [CrossRef]
  8. Hurley, R.; Nizzetto, L. Fate and occurrence of micro(nano)plastics in soils: Knowledge gaps and possible risks. Curr. Opin. Environ. Sci. Health. 2018, 1, 6–11. [Google Scholar] [CrossRef]
  9. Zhang, Z.; Peng, W.; Duan, C.; Zhu, X.; Wu, H.; Zhang, X. Microplastics pollution from different plastic mulching years accentuate soil microbial nutrient limitations. Gondwana Res. 2021, 108, 91–101. [Google Scholar] [CrossRef]
  10. Braun, M.; Amelung, W. Plastics in soil: Analytical methods and possible sources. Sci. Total Environ. 2017, 612, 422–435. [Google Scholar]
  11. Machado, A.; Lau, C.; Kloas, W.; Bergmann, J.; Bachelier, J.; Faltin, E.; Becker, R.; Görlich, A.; Rillig, M. Microplastics Can Change Soil Properties and Affect Plant Performance. Environ. Sci. Technol. 2019, 53, 6044–6052. [Google Scholar] [CrossRef] [PubMed]
  12. Jiang, X.; Liu, W.; Wang, E.; Tingzhang, Z.; Xin, P. Residual plastic mulch fragments effects on soil physical properties and water flow behavior in the Minqin Oasis, northwestern China. Soil Tillage Res. 2017, 166, 100–107. [Google Scholar] [CrossRef]
  13. Wang, J.; Lv, S.; Zhang, M.; Chen, G.; Zhu, T.-B.; Zhang, S.; Teng, Y.; Christie, P.; Luo, Y. Effects of plastic film residues on occurrence of phthalates and microbial activity in soils. Chemosphere 2016, 151, 171–177. [Google Scholar] [CrossRef]
  14. Lei, L.; Liu, M.; Song, Y.; Lu, S.; Hu, J.; Cao, C.; Xie, B.; Shi, H.; He, D. Polystyrene (nano)microplastics cause size-dependent neurotoxicity, oxidative damage and other adverse effects in Caenorhabditis elegans. Environ. Sci. Nano. 2018, 5, 2009–2020. [Google Scholar] [CrossRef]
  15. Lei, L.; Wu, S.; Lu, S.; Liu, M.; Song, Y.; Fu, Z.; Shi, H.; Raley-Susman, K.; He, D. Microplastic particles cause intestinal damage and other adverse effects in zebrafish Danio rerio and nematode Caenorhabditis elegans. Sci. Total Environ. 2017, 619, 1–8. [Google Scholar] [CrossRef]
  16. Jiang, X.; Chen, H.; Liao, Y.; Ye, Z.; Li, M.; Klobučar, G. Ecotoxicity and genotoxicity of polystyrene microplastics on higher plant Vicia faba. Environ. Pollut. 2019, 250, 831–838. [Google Scholar] [CrossRef] [PubMed]
  17. Huerta, E.; Vega, J.; Ku-Quej, V.; Chi, J.; Cid, L.; Chi, C.; Escalona-Segura, G.; Gertsen, H.; Salánki, T.; Ploeg, M.; et al. Field evidence for transfer of plastic debris along a terrestrial food chain. Sci. Rep. 2017, 7, 1407. [Google Scholar] [CrossRef]
  18. Wei, H.; Wu, L.; Liu, Z.; Saleem, M.; Chen, X.; Xie, J.; Zhang, J. Meta-analysis reveals differential impacts of microplastics on soil biota. Ecotoxicol. Environ. Saf. 2022, 230, 113150. [Google Scholar] [CrossRef]
  19. Qiu, Y.F.; Zhou, S.L.; Zhang, C.C.; Zhou, Y.J.; Qin, W.D. Soil microplastic characteristics and the effects on soil properties and biota: A systematic review and meta-analysis. Environ. Pollut. 2022, 313, 120183. [Google Scholar] [CrossRef]
  20. Zhang, J.; Ren, S.; Xu, W.; Liang, C.; Li, J.; Zhang, H.; Li, Y.; Liu, X.; Jones, D.L.; Chadwick, D.R.; et al. Effects of plastic residues and microplastics on soil ecosystems: A global meta-analysis. J. Hazard. Mater. 2022, 435, 129065. [Google Scholar] [CrossRef]
  21. Fok, L.; Lam, T.; Li, H.-X.; Xu, X.-R. A meta-analysis of methodologies adopted by microplastic studies in China. Sci. Total Environ. 2019, 718, 135371. [Google Scholar] [CrossRef] [PubMed]
  22. Chen, C. Searching for intellectual turning points: Progressive knowledge domain visualization. Proc. Natl. Acad. Sci. USA 2004, 101, 5303–5310. [Google Scholar] [CrossRef] [PubMed]
  23. Chen, C. Science Mapping: A Systematic Review of the Literature. J. Data Inf. Sci. 2017, 2, 1–40. [Google Scholar] [CrossRef]
  24. Liu, K.; Guan, X.; Li, C.; Zhao, K.; Yang, X.; Fu, R.; Li, Y.; Yu, F.-M. Global perspectives and future research directions for the phytoremediation of heavy metal-contaminated soil: A knowledge mapping analysis from 2001 to 2020. Front. Environ. Sci. Eng. 2022, 16, 1–20. [Google Scholar] [CrossRef]
  25. Chen, C.M.; Hu, Z.G.; Liu, S.B.; Tseng, H. Emerging trends in regenerative medicine: A scientometric analysis in CiteSpace. Expert Opin. Biol. Ther. 2012, 12, 593–608. [Google Scholar] [CrossRef]
  26. Zhang, X.; Zhang, Y.; Wang, Y.; Fath, B. Research progress and hotspot analysis for reactive nitrogen flows in macroscopic systems based on a CiteSpace analysis. Ecol. Model. 2021, 443, 109456. [Google Scholar] [CrossRef]
  27. Ouyang, W.; Wang, Y.; Lin, C.; He, M.; Hao, F.; Liu, H.; Zhu, W. Heavy metal loss from agricultural watershed to aquatic system: A scientometrics review. Sci. Total Environ. 2018, 637, 208–220. [Google Scholar] [CrossRef]
  28. Zhang, B.; Yang, X.; Chen, L.; Chao, J.; Teng, J.; Wang, Q. Microplastics in soils: A review of possible sources, analytical methods, and ecological impacts. J. Chem. Technol. Biotechnol. 2020, 95, 2052–2068. [Google Scholar] [CrossRef]
  29. Sun, C.J.; Ding, J.F.; Gao, F.L. Methods for microplastic sampling and analysis in the seawater and fresh water environment. Method Enzymol. 2021, 648, 27–45. [Google Scholar]
  30. Cao, J.H.; Zhao, X.N.; Gao, X.D.; Zhang, L.; Hu, Q.; Siddique, K.H.M. Extraction and identification methods of microplastics and nanoplastics in agricultural soil: A review. J. Environ. Manag. 2021, 294, 112997. [Google Scholar]
  31. Huang, L.L.; Wang, H.; Wang, C.Q.; Zhao, J.Y.; Zhang, B. Microwave-assisted surface modification for the separation of polycarbonate from polymethylmethacrylate and polyvinyl chloride waste plastics by flotation. Waste Manag. Res. 2017, 35, 294–300. [Google Scholar] [CrossRef] [PubMed]
  32. He, D.F.; Zhang, X.T.; Hu, J.N. Methods for separating microplastics from complex solid matrices: Comparative analysis. J. Hazard. Mater. 2021, 409, 124640. [Google Scholar] [CrossRef] [PubMed]
  33. Felsing, S.; Kochleus, C.; Buchinger, S.; Brennholt, N.; Stock, F.; Reifferscheid, G. A new approach in separating microplastics from environmental samples based on their electrostatic behavior. Environ. Pollut. 2018, 234, 20–28. [Google Scholar] [CrossRef] [PubMed]
  34. Fuller, S.; Gautam, A. A Procedure for Measuring Microplastics using Pressurized Fluid Extraction. Environ. Sci. Technol. 2016, 50, 5774–5780. [Google Scholar] [CrossRef] [PubMed]
  35. Wang, J.; Li, J.Y.; Liu, S.T.; Li, H.Y.; Chen, X.C.; Peng, C.; Zhang, P.P.; Liu, X.H. Distinct microplastic distributions in soils of different land-use types: A case study of Chinese farmlands. Environ. Pollut. 2021, 269, 116199. [Google Scholar] [CrossRef]
  36. Enders, K.; Lenz, R.; Beer, S.; Stedmon, C.A. Extraction of microplastic from biota: Recommended acidic digestion destroys common plastic polymers. ICES J. Mar. Sci. 2017, 74, 326–331. [Google Scholar] [CrossRef]
  37. Mbachu, O.; Jenkins, G.; Pratt, C.; Kaparaju, P. Enzymatic purification of microplastics in soil. Methodsx. 2021, 8, 10125. [Google Scholar] [CrossRef]
  38. Zhang, S.; Yang, X.; Gertsen, H.; Peters, P.; Salánki, T.; Geissen, V. A simple method for the extraction and identification of light density microplastics from soil. Sci. Total Environ. 2017, 616, 1056–1065. [Google Scholar] [CrossRef]
  39. Wang, W.; Ndungu, A.W.; Li, Z.; Wang, J. Microplastics pollution in inland freshwaters of China: A case study in urban surface waters of Wuhan, China. Sci. Total Environ. 2017, 575, 1369–1374. [Google Scholar] [CrossRef]
  40. Fierer, N.; Schimel, J.; Holden, P.; Fierer, N.; Schimel, J.P.; Holden, P.A. Variations in microbial community composition through two soil depth profiles. Soil Biol. Biochem. 2003, 35, 167–176. [Google Scholar] [CrossRef]
  41. Zhang, G.S.; Zhang, F.X.; Li, X.T. Effects of polyester microfibers on soil physical properties: Perception from a field and a pot experiment. Sci. Total Environ. 2019, 670, 1–7. [Google Scholar] [CrossRef] [PubMed]
  42. Huang, Y.; Yanran, Z.; Wang, J.; Zhang, M.; Jia, W.; Qin, X. LDPE microplastic films alter microbial community composition and enzymatic activities in soil. Environ. Pollut. 2019, 254, 112983. [Google Scholar] [CrossRef] [PubMed]
  43. Alimi, O.S.; Budarz, J.F.; Hernandez, L.M.; Tufenkji, N. Microplastics and Nanoplastics in Aquatic Environments: Aggregation, Deposition, and Enhanced Contaminant Transport. Environ. Sci. Technol. 2018, 52, 1704–1724. [Google Scholar] [CrossRef] [PubMed]
  44. Ren, X.W.; Tang, J.C.; Liu, X.M.; Liu, Q.L. Effects of microplastics on greenhouse gas emissions and the microbial community in fertilized soil. Environ. Pollut. 2020, 256, 113347. [Google Scholar] [CrossRef]
  45. Machado, A.; Kloas, W.; Zarfl, C.; Hempel, S.; Rillig, M. Microplastics as an emerging threat to terrestrial ecosystems. Glob. Chang. Biol. 2017, 24, 1405–1416. [Google Scholar] [CrossRef]
  46. Lin, Z.; Jin, T.; Zou, T.; Xu, L.; Xi, B.; Xu, D.; He, J.; Xiong, L.; Tang, C.; Peng, J.; et al. Current progress on plastic/microplastic degradation: Fact influences and mechanism. Environ. Pollut. 2022, 304, 119159. [Google Scholar] [CrossRef]
  47. Meng, K.; Ren, W.J.; Teng, Y.; Wang, B.B.; Han, Y.J.; Christie, P.; Luo, Y.M. Application of biodegradable seedling trays in paddy fields: Impacts on the microbial community. Sci. Total Environ. 2019, 656, 750–759. [Google Scholar] [CrossRef]
  48. Zhou, J.; Jia, R.; Brown, R.W.; Yang, Y.; Zeng, Z.; Jones, D.L.; Zang, H. The long-term uncertainty of biodegradable mulch film residues and associated microplastics pollution on plant-soil health. J. Hazard. Mater. 2023, 442, 130055. [Google Scholar] [CrossRef]
  49. Chen, Z.; Zhao, W.Q.; Xing, R.Z.; Xie, S.J.; Yang, X.G.; Cui, P.; Lu, J.; Liao, H.P.; Yu, Z.; Wang, S.H.; et al. Enhanced in situ biodegradation of microplastics in sewage sludge using hyperthermophilic composting technology. J. Hazard. Mater. 2020, 384, 121271. [Google Scholar] [CrossRef]
  50. Kaur, R.; Kaur, J.; Mahajan, J.; Kumar, R.; Arora, S. Oxidative stress-implications, source and its prevention. Environ. Sci. Pollut. Res. Int. 2013, 21, 1599–1613. [Google Scholar] [CrossRef]
  51. Lu, Y.; Zhang, Y.; Deng, Y.; Jiang, W.; Zhao, Y.; Geng, J.; Ding, L.; Ren, H. Uptake and Accumulation of Polystyrene Microplastics in Zebrafish (Danio rerio) and Toxic Effects in Liver. Environ. Sci. Technol. 2016, 50, 4054–4060. [Google Scholar] [CrossRef] [PubMed]
  52. Alomar, C.; Sureda, A.; Capó, X.; Guijarro, B.; Tejada, S.; Deudero, S. Microplastic ingestion by Mullus surmuletus Linnaeus, 1758 fish and its potential for causing oxidative stress. Environ. Res. 2017, 159, 135–142. [Google Scholar] [CrossRef] [PubMed]
  53. Pflugmacher, S.; Tallinen, S.; Kim, Y.; Kim, S.; Esterhuizen, M. Ageing affects microplastic toxicity over time: Effects of aged polycarbonate on germination, growth, and oxidative stress of Lepidium sativum. Sci. Total Environ. 2021, 790, 148166. [Google Scholar] [CrossRef] [PubMed]
  54. Sun, W.; Meng, Z.; Li, R.; Renke, Z.; Jia, M.; Yan, S.; Tian, S.; Zhou, Z.; Zhu, W. Joint effects of microplastic and dufulin on bioaccumulation, oxidative stress and metabolic profile of the earthworm (Eisenia fetida). Chemosphere 2020, 263, 128171. [Google Scholar] [CrossRef] [PubMed]
  55. Song, Y.; Cao, C.; Qiu, R.; Hu, J.; Liu, M.; Lu, S.; Shi, H.; Raley-Susman, K.; He, D. Uptake and adverse effects of polyethylene terephthalate microplastics fibers on terrestrial snails (Achatina fulica) after soil exposure. Environ. Pollut. 2019, 250, 447–455. [Google Scholar] [CrossRef]
  56. Huerta, E.; Gertsen, H.; Gooren, H.P.A.; Peters, P.; Salánki, T.; Ploeg, M.; Besseling, E.; Koelmans, A.; Geissen, V. Microplastics in the Terrestrial Ecosystem: Implications for Lumbricus terrestris (Oligochaeta, Lumbricidae). Environ. Sci. Technol. 2016, 50, 2685–2691. [Google Scholar] [CrossRef]
  57. Li, L.Z.; Luo, Y.M.; Li, R.J.; Zhou, Q.; Peijnenburg, W.; Yin, N.; Yang, J.; Tu, C.; Zhang, Y.C. Effective uptake of submicrometre plastics by crop plants via a crack-entry mode. Nat. Sustain. 2020, 3, 929–937. [Google Scholar] [CrossRef]
  58. Hodson, M.; Duffus-Hodson, C.; Clark, A.; Prendergast-Miller, M.; Thorpe, K. Plastic Bag Derived-Microplastics as a Vector for Metal Exposure in Terrestrial Invertebrates. Environ. Sci. Technol. 2017, 51, 4714–4721. [Google Scholar] [CrossRef]
  59. Wang, T.; Yu, C.C.; Chu, Q.; Wang, F.H.; Lan, T.; Wang, J.F. Adsorption behavior and mechanism of five pesticides on microplastics from agricultural polyethylene films. Chemosphere 2020, 244, 125491. [Google Scholar] [CrossRef]
  60. Muller, A.; Becker, R.; Dorgerloh, U.; Simon, F.G.; Braun, U. The effect of polymer aging on the uptake of fuel aromatics and ethers by microplastics. Environ. Pollut. 2018, 240, 639–646. [Google Scholar] [CrossRef]
  61. Wang, J.; Liu, X.; Li, Y.; Powell, T.; Wang, X.; Wang, G.; Zhang, P. Microplastics as contaminants in the soil environment: A mini-review. Sci. Total Environ. 2019, 691, 848–857. [Google Scholar] [CrossRef] [PubMed]
  62. Li, J.; Guo, K.; Cao, Y.; Wang, S.; Song, Y.; Zhang, H. Enhance in mobility of oxytetracycline in a sandy loamy soil caused by the presence of microplastics. Environ. Pollut. 2020, 269, 116151. [Google Scholar] [CrossRef] [PubMed]
  63. Zhang, S.W.; Han, B.; Sun, Y.H.; Wang, F.Y. Microplastics influence the adsorption and desorption characteristics of Cd in an agricultural soil. J. Hazard. Mater. 2020, 388, 121775. [Google Scholar] [CrossRef] [PubMed]
  64. Ng, E.L.; Huerta, E.; Eldridge, S.; Johnston, P.; Hu, H.; Geissen, V.; Chen, D. An overview of microplastic and nanoplastic pollution in agroecosystems. Sci. Total Environ. 2018, 627, 1377–1388. [Google Scholar] [CrossRef] [PubMed]
  65. Cui, X.; Guo, X.; Wang, Y.; Wang, X.; Zhu, W.; Shi, J.; Lin, C.; Gao, X. Application of remote sensing to water environmental processes under a changing climate. J. Hydrol. 2019, 574, 892–902. [Google Scholar] [CrossRef]
  66. Bi, L.H.; Zhou, S.R.; Ke, J.J.; Song, X.M. Knowledge-Mapping Analysis of Urban Sustainable Transportation Using CiteSpace. Sustainability. 2023, 15, 958. [Google Scholar] [CrossRef]
  67. Crawford, C.B.; Quinn, B. Microplastic separation techniques. In Microplastic Pollutants; Elsevier Limited: Amsterdam, The Netherlands, 2017; pp. 203–218. [Google Scholar]
  68. Crowther, T.; van den Hoogen, J.; Wan, J.; Mayes, M.; Keiser, A.; Mo, L.; Averill, C.; Maynard, D. The global soil community and its influence on biogeochemistry. Science 2019, 365, eaav0550. [Google Scholar] [CrossRef]
  69. Tedersoo, L.; Bahram, M.; Põlme, S.; Kõljalg, U.; Yorou, N.S.; Wijesundera, R.; Ruiz, L.V.; Vasco-Palacios, A.M.; Thu, P.Q.; Suija, A.; et al. Global diversity and geography of soil fungi. Science 2014, 346, 1256688. [Google Scholar] [CrossRef]
  70. Huang, J.; Chen, H.; Yang, Y.; Zhang, Y.; Gao, B. Microplastic pollution in soils and groundwater: Characteristics, analytical methods and impacts. Chem. Eng. J. 2021, 425, 131870. [Google Scholar] [CrossRef]
  71. Boots, B.; Russell, C.; Green, D. Effects of Microplastics in Soil Ecosystems: Above and below Ground. Environ. Sci. Technol. 2019, 53, 11496–11506. [Google Scholar] [CrossRef]
  72. Rillig, M. Microplastic Disguising as Soil Carbon Storage. Environ. Sci. Technol. 2018, 52, 6079–6080. [Google Scholar] [CrossRef] [PubMed]
  73. Prata, J.; Da Costa, J.; Lopes, I.; Duarte, A.; Rocha-Santos, T. Environmental exposure to microplastics: An overview on possible human health effects. Sci. Total Environ. 2019, 702, 134455. [Google Scholar] [CrossRef] [PubMed]
  74. Wanner, P. Plastic in agricultural soils—A global risk for groundwater systems and drinking water supplies?—A review. Chemosphere 2020, 264, 128453. [Google Scholar] [CrossRef] [PubMed]
  75. Birch, Q.; Potter, P.; Pinto, P.; Dionysiou, D.; Al-Abed, S. Sources, transport, measurement and impact of nano and microplastics in urban watersheds. Rev. Environ. Sci. Bio/Technol. 2020, 19, 275–336. [Google Scholar] [CrossRef] [PubMed]
  76. Bergami, E.; Rota, E.; Caruso, T.; Birarda, G.; Vaccari, L.; Corsi, I. Plastics everywhere: First evidence of polystyrene fragments inside the common Antarctic collembolan Cryptopygus antarcticus. Biol. Lett. 2020, 16, 20200093. [Google Scholar] [CrossRef]
  77. Koyuncuoğlu, P.; Erden, G. Sampling, pre-treatment, and identification methods of microplastics in sewage sludge and their effects in agricultural soils: A review. Environ. Monit. Assess. 2021, 193, 1–28. [Google Scholar] [CrossRef]
  78. Zhang, M.G.; Tan, M.M.; Ji, R.; Ma, R.H.; Li, C.L. Current Situation and Ecological Effects of Microplastic Pollution in Soil. Rev. Environ. Contam. Toxicol. 2022, 260, 11. [Google Scholar] [CrossRef]
  79. Nizzetto, L.; Futter, M.; Langaas, S. Are Agricultural Soils Dumps for Microplastics of Urban Origin. Environ. Sci. Technol. 2016, 50, 10777–10779. [Google Scholar] [CrossRef]
  80. He, D.; Luo, Y.; Lu, S.; Liu, M.; Song, Y.; Lei, L. Microplastics in soils: Analytical methods, pollution characteristics and ecological risks. TrAC Trends Anal. Chem. 2018, 109, 163–172. [Google Scholar] [CrossRef]
  81. Zhang, Z.; Zhao, S.; Chen, L.; Duan, C.; Zhang, X.; Fang, L. A review of microplastics in soil: Occurrence, analytical methods, combined contamination and risks. Environ. Pollut. 2022, 306, 119374. [Google Scholar] [CrossRef]
  82. Zhang, G.S.; Liu, Y.F. The distribution of microplastics in soil aggregate fractions in southwestern China. Sci. Total Environ. 2018, 642, 12–20. [Google Scholar] [CrossRef]
  83. Piehl, S.; Leibner, A.; Loder, M.G.J.; Dris, R.; Bogner, C.; Laforsch, C. Identification and quantification of macro- and microplastics on an agricultural farmland. Sci. Rep. 2018, 8, 17950. [Google Scholar] [CrossRef]
  84. Zhang, Z.; Cui, Q.; Chen, L.; Zhu, X.; Zhao, S.; Duan, C.; Zhang, X.; Song, D.; Fang, L. A critical review of microplastics in the soil-plant system: Distribution, uptake, phytotoxicity and prevention. J. Hazard. Mater. 2022, 424, 127750. [Google Scholar] [CrossRef]
  85. Zhang, M.Y.; Liu, L.H.; Xu, D.Y.; Zhang, B.H.; Li, J.J.; Gao, B. Small-sized microplastics (<500 μm) in roadside soils of Beijing, China: Accumulation, stability, and human exposure risk. Environ. Pollut. 2022, 304, 119121. [Google Scholar]
  86. Sengupta, S.; Dey, S. Microplastic Menace in Soil Environment: Source, Impact and the Way Forward. Agric. Food 2020, 2, 845–848. [Google Scholar]
  87. He, D.F.; Zhang, Y.L.; Gao, W. Micro(nano)plastic contaminations from soils to plants: Human food risks. Curr. Opin. Food Sci. 2021, 41, 116–121. [Google Scholar] [CrossRef]
  88. Liu, Y.Y.; Guo, R.; Zhang, S.W.; Sun, Y.H.; Wang, F.Y. Uptake and translocation of nano/microplastics by rice seedlings: Evidence from a hydroponic experiment. J. Hazard. Mater. 2022, 421, 126700. [Google Scholar] [CrossRef]
  89. Wang, L.W.; Wu, W.M.; Bolan, N.S.; Tsang, D.C.W.; Li, Y.; Qin, M.H.; Hou, D.Y. Environmental fate, toxicity and risk management strategies of nanoplastics in the environment: Current status and future perspectives. J. Hazard. Mater. 2021, 401, 123415. [Google Scholar] [CrossRef]
  90. Zylstra, E.R. Accumulation of wind-dispersed trash in desert environments. J. Arid. Environ. 2013, 89, 13–15. [Google Scholar] [CrossRef]
  91. Allen, S.; Allen, D.; Phoenix, V.R.; Le Roux, G.; Jimenez, P.D.; Simonneau, A.; Binet, S.; Galop, D. Atmospheric transport and deposition of microplastics in a remote mountain catchment. Nat. Geosci. 2019, 12, 339–344. [Google Scholar] [CrossRef]
  92. Corradini, F.; Meza, P.; Eguiluz, R.; Casado, F.; Huerta-Lwanga, E.; Geissen, V. Evidence of microplastic accumulation in agricultural soils from sewage sludge disposal. Sci. Total Environ. 2019, 671, 411–420. [Google Scholar] [CrossRef] [PubMed]
  93. Scheurer, M.; Bigalke, M. Microplastics in Swiss Floodplain Soils. Environ. Sci. Technol. 2018, 52, 3591–3598. [Google Scholar] [CrossRef] [PubMed]
  94. Liebezeit, G.; Dubaish, F. Microplastics in Beaches of the East Frisian Islands Spiekeroog and Kachelotplate. Bull. Environ. Contam. Toxicol. 2012, 89, 213–217. [Google Scholar] [CrossRef] [PubMed]
  95. Ding, L.; Wang, X.L.; Ouyang, Z.Z.; Chen, Y.H.; Wang, X.X.; Liu, D.S.; Liu, S.S.; Yang, X.M.; Jia, H.Z.; Guo, X.T. The occurrence of microplastic in Mu Us Sand Land soils in northwest China: Different soil types, vegetation cover and restoration years. J. Hazard. Mater. 2021, 403, 123982. [Google Scholar] [CrossRef]
  96. Li, S.T.; Ding, F.; Flury, M.; Wang, Z.; Xu, L.; Li, S.Y.; Jones, D.L.; Wang, J.K. Macro- and microplastic accumulation in soil after 32 years of plastic film mulching. Environ. Pollut. 2022, 300, 118945. [Google Scholar] [CrossRef]
  97. Huang, Y.; Liu, Q.; Jia, W.Q.; Yan, C.R.; Wang, J. Agricultural plastic mulching as a source of microplastics in the terrestrial environment. Environ. Pollut. 2020, 260, 114096. [Google Scholar] [CrossRef]
  98. Wang, F.Y.; Wang, Q.L.; Adams, C.A.; Sun, Y.H.; Zhang, S.W. Effects of microplastics on soil properties: Current knowledge and future perspectives. J. Hazard. Mater. 2022, 424, 127531. [Google Scholar] [CrossRef]
  99. Feng, X.; Wang, Q.; Sun, Y.; Zhang, S.; Wang, F. Microplastics change soil properties, heavy metal availability and bacterial community in a Pb-Zn-contaminated soil. J. Hazard. Mater. 2022, 424, 127364. [Google Scholar] [CrossRef]
  100. Zhu, J.; Liu, S.; Wang, H.; Wang, D.; Zhu, Y.; Wang, J.; He, Y.; Zheng, Q.; Zhan, X. Microplastic particles alter wheat rhizosphere soil microbial community composition and function. J. Hazard. Mater. 2022, 436, 129176. [Google Scholar] [CrossRef]
  101. Ng, E.L.; Lin, S.Y.; Dungan, A.M.; Colwell, J.M.; Ede, S.; Huerta Lwanga, E.; Meng, K.; Geissen, V.; Blackall, L.L.; Chen, D. Microplastic pollution alters forest soil microbiome. J. Hazard. Mater. 2021, 409, 124606. [Google Scholar] [CrossRef]
  102. Helmberger, M.S.; Tiemann, L.K.; Grieshop, M.J. Towards an ecology of soil microplastics. Funct. Ecol. 2020, 34, 550–560. [Google Scholar] [CrossRef]
  103. Green, D.S.; Boots, B.; Sigwart, J.; Jiang, S.; Rocha, C. Effects of conventional and biodegradable microplastics on a marine ecosystem engineer (Arenicola marina) and sediment nutrient cycling. Environ. Pollut. 2016, 208, 426–434. [Google Scholar] [CrossRef] [PubMed]
  104. Lambert, S.; Wagner, M. Formation of microscopic particles during the degradation of different polymers. Chemosphere 2016, 161, 510–517. [Google Scholar] [CrossRef] [PubMed]
  105. Meng, F.R.; Yang, X.M.; Riksen, M.; Geissen, V. Effect of different polymers of microplastics on soil organic carbon and nitrogen—A mesocosm experiment. Environ. Res. 2022, 204, 111938. [Google Scholar] [CrossRef]
  106. Zhang, M.; Jia, H.; Weng, Y.X.; Li, C.T. Biodegradable PLA/PBAT mulch on microbial community structure in different soils. Int. Biodeterior. Biodegrad. 2019, 145, 104817. [Google Scholar] [CrossRef]
  107. Li, C.; Cui, Q.; Li, Y.; Zhang, K.; Lu, X.; Zhang, Y. Effect of LDPE and biodegradable PBAT primary microplastics on bacterial community after four months of soil incubation. J. Hazard. Mater. 2022, 429, 128353. [Google Scholar] [CrossRef]
  108. Pignattelli, S.; Broccoli, A.; Renzi, M. Physiological responses of garden cress (L. sativum) to different types of microplastics. Sci. Total Environ. 2020, 727, 138609. [Google Scholar] [CrossRef]
  109. Qi, R.M.; Jones, D.L.; Li, Z.; Liu, Q.; Yan, C.R. Behavior of microplastics and plastic film residues in the soil environment: A critical review. Sci. Total Environ. 2020, 703, 134722. [Google Scholar] [CrossRef]
  110. Chen, K.Y.; Tang, R.G.; Luo, Y.M.; Chen, Y.C.; Ei-Naggar, A.; Du, J.H.; Bu, A.; Yan, Y.; Lu, X.H.; Cai, Y.J.; et al. Transcriptomic and metabolic responses of earthworms to contaminated soil with polypropylene and polyethylene microplastics at environmentally relevant concentrations. J. Hazard. Mater. 2022, 427, 128176. [Google Scholar] [CrossRef]
  111. Zhou, Y.F.; Liu, X.N.; Wang, J. Ecotoxicological effects of microplastics and cadmium on the earthworm Eisenia foetida. J. Hazard. Mater. 2020, 392, 122273. [Google Scholar] [CrossRef]
  112. Wang, Q.L.; Adams, C.A.; Wang, F.Y.; Sun, Y.H.; Zhang, S.W. Interactions between microplastics and soil fauna: A critical review. Crit. Rev. Environ. Sci. Technol. 2022, 52, 3211–3243. [Google Scholar] [CrossRef]
  113. Ramos, L.; Berenstein, G.; Hughes, E.A.; Zalts, A.; Montserrat, J.M. Polyethylene film incorporation into the horticultural soil of small periurban production units in Argentina. Sci. Total Environ. 2015, 523, 74–81. [Google Scholar] [CrossRef] [PubMed]
  114. Wang, J.; Coffin, S.; Sun, C.L.; Schlenk, D.; Gan, J. Negligible effects of microplastics on animal fitness and HOC bioaccumulation in earthworm Eisenia fetida in soil. Environ. Pollut. 2019, 249, 776–784. [Google Scholar] [CrossRef] [PubMed]
  115. Huffer, T.; Metzelder, F.; Sigmund, G.; Slawek, S.; Schmidt, T.C.; Hofmann, T. Polyethylene microplastics influence the transport of organic contaminants in soil. Sci. Total Environ. 2019, 657, 242–247. [Google Scholar] [CrossRef]
  116. Yu, H.; Fan, P.; Hou, J.; Dang, Q.-L.; Cui, D.; Xi, B.; Tan, W. Inhibitory effect of microplastics on soil extracellular enzymatic activities by changing soil properties and direct adsorption: An investigation at the aggregate-fraction level. Environ. Pollut. 2020, 267, 115544. [Google Scholar] [CrossRef]
  117. Park, S.Y.; Kim, C.G. Biodegradation of micro-polyethylene particles by bacterial colonization of a mixed microbial consortium isolated from a landfill site. Chemosphere 2019, 222, 527–533. [Google Scholar] [CrossRef]
  118. Shah, A.A.; Hasan, F.; Akhter, J.I.; Hameed, A.; Ahmed, S. Degradation of polyurethane by novel bacterial consortium isolated from soil. Ann. Microbiol. 2008, 58, 381–386. [Google Scholar] [CrossRef]
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Figure 1. The top five countries with their accumulated number of publications from 2016 to 2021. The abscissa represents year of publication, and the ordinate represents the number of publications.
Figure 1. The top five countries with their accumulated number of publications from 2016 to 2021. The abscissa represents year of publication, and the ordinate represents the number of publications.
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Figure 2. Cooperation networks for institutions that have performed research on soil microplastics. The different color of the line between the nodes represents the time when the relevant institutions appeared, where dark colors represent earlier years and light colors represent later years. In addition, the size of the purple circles represents centrality, where big circles represent high centrality.
Figure 2. Cooperation networks for institutions that have performed research on soil microplastics. The different color of the line between the nodes represents the time when the relevant institutions appeared, where dark colors represent earlier years and light colors represent later years. In addition, the size of the purple circles represents centrality, where big circles represent high centrality.
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Figure 3. Author cooperation network in the field of soil microplastics. The different color of the line between the nodes represents the time when the relevant institutions appeared, where dark colors represent earlier years and light colors represent later years.
Figure 3. Author cooperation network in the field of soil microplastics. The different color of the line between the nodes represents the time when the relevant institutions appeared, where dark colors represent earlier years and light colors represent later years.
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Figure 4. (A) Evolution of the co-occurrence of subject categories. The color of the line between the nodes represents the time when the relevant subject categories appeared, where dark colors represent the earlier year and light colors represent the later year. In addition, the size of the purple circles represents centrality, where big circles represent high centrality. (B) Top 34 subject categories and their superposition of frequency and centrality. The top abscissa represents frequency of subject categories, and the scale is from 0 to 600. The bottom abscissa represents centrality of subject categories, and the scale is from 0 to 0.45. The ordinate represents different subject categories.
Figure 4. (A) Evolution of the co-occurrence of subject categories. The color of the line between the nodes represents the time when the relevant subject categories appeared, where dark colors represent the earlier year and light colors represent the later year. In addition, the size of the purple circles represents centrality, where big circles represent high centrality. (B) Top 34 subject categories and their superposition of frequency and centrality. The top abscissa represents frequency of subject categories, and the scale is from 0 to 600. The bottom abscissa represents centrality of subject categories, and the scale is from 0 to 0.45. The ordinate represents different subject categories.
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Figure 5. Keyword co-occurrence network. The color of the line between the nodes represents the time when the relevant keyword appeared, where dark colors represent the earlier year and light colors represent the later year.
Figure 5. Keyword co-occurrence network. The color of the line between the nodes represents the time when the relevant keyword appeared, where dark colors represent the earlier year and light colors represent the later year.
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Figure 6. Clusters of the keywords in microplastic-related articles. The color of the line between the nodes represents the time when the relevant keyword appeared, where dark colors represent the earlier year and light colors represent the later year. In addition, the size of the purple circles represents centrality, where big circles represent high centrality. Each cluster was drawn in detail to better study the hot topics in the soil microplastic field over the study period: ((a) Cluster #0; (b) Cluster #1; (c) Cluster #2; (d) Cluster #3; (e) Cluster #4; (f) Cluster #5).
Figure 6. Clusters of the keywords in microplastic-related articles. The color of the line between the nodes represents the time when the relevant keyword appeared, where dark colors represent the earlier year and light colors represent the later year. In addition, the size of the purple circles represents centrality, where big circles represent high centrality. Each cluster was drawn in detail to better study the hot topics in the soil microplastic field over the study period: ((a) Cluster #0; (b) Cluster #1; (c) Cluster #2; (d) Cluster #3; (e) Cluster #4; (f) Cluster #5).
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Figure 7. Top nine keywords with strongest and longest citation bursts ((a) strongest citation bursts; (b) longest citation bursts).
Figure 7. Top nine keywords with strongest and longest citation bursts ((a) strongest citation bursts; (b) longest citation bursts).
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Figure 8. Coreference cluster network. The color of the line between the nodes represents the time when the relevant keyword appeared, where dark colors represent the earlier year and light colors represent the later year.
Figure 8. Coreference cluster network. The color of the line between the nodes represents the time when the relevant keyword appeared, where dark colors represent the earlier year and light colors represent the later year.
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Table
Table 1. The count and centrality in different countries.
Table 1. The count and centrality in different countries.
CountCentralityYear (First Appear)Countries/Regions
3110.422017China
730.162016Germany
110.132018Finland
120.122018Japan
870.112017USA
190.112017France
570.102016Australia
390.102016Netherlands
Table
Table 2. Summary of the five largest clusters.
Table 2. Summary of the five largest clusters.
ClusterSizeSilhouetteLabel (LLR)Average Year
#01330.722gut microbiome2015
#11250.899case study2018
#2780.791separating microplastics2017
#3520.871adsorption behavior2018
#4500.881wastewater treatment plant2018
Table
Table 3. Top 10 highly cited papers.
Table 3. Top 10 highly cited papers.
Cited FrequencyAuthorSourceDOI
202Lwanga EH (2016)Environ Sci Technol10.1021/acs.est.5b05478
182Horton AA (2017)Sci Total Environ10.1016/j.scitotenv.2017.01.190
173Nizzetto L (2016)Environ Sci Technol10.1021/acs.est.6b04140
167Blasing M (2018)Sci Total Environ10.1016/j.scitotenv.2017.08.086
162Scheurer M (2018)Environ Sci Technol10.1021/acs.est.7b06003
160Zhang GS (2018)Sci Total Environ10.1016/j.scitotenv.2018.06.004
153Machado AAD (2018)Global Change Biol10.1111/gcb.14020
153Fuller S (2016)Environ Sci Technol10.1021/acs.est.6b00816
150Machado AAD (2018)Environ Sci Technol10.1021/acs.est.8b02212
144Geyer R (2017)Sci Adv10.1126/sciadv.1700782
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Yang, T.; Liu, J.; Zhu, H.; Zhu, L.; Kong, T.; Tai, S. The Bibliometric Analysis of Microplastics in Soil Environments: Hotspots of Research and Trends of Development. Sustainability 2023, 15, 7122. https://doi.org/10.3390/su15097122

AMA Style

Yang T, Liu J, Zhu H, Zhu L, Kong T, Tai S. The Bibliometric Analysis of Microplastics in Soil Environments: Hotspots of Research and Trends of Development. Sustainability. 2023; 15(9):7122. https://doi.org/10.3390/su15097122

Chicago/Turabian Style

Yang, Tingting, Jinning Liu, Hongfei Zhu, Lei Zhu, Tao Kong, and Shanshan Tai. 2023. "The Bibliometric Analysis of Microplastics in Soil Environments: Hotspots of Research and Trends of Development" Sustainability 15, no. 9: 7122. https://doi.org/10.3390/su15097122

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