Research Progress on Emerging Pollutants in Watershed Water Bodies: A Bibliometric Approach

Abstract

Watershed water bodies, as a key part of the Earth’s water cycle, were identified as an important destination for emerging pollutants. However, existing research primarily focused on single environmental zones, such as lakes or rivers, lacking a comprehensive understanding at the watershed scale. Scientific knowledge mapping and tools, such as Bibliometrics, VOSviewer, and CiteSpace, were employed to conduct a comprehensive analysis of literature on emerging pollutants in watershed water bodies from the WOSCC database. The results indicated that, from 2000 to 2024, research themes in this field gradually expanded from the identification and detection of pollutants to source analysis, environmental behavior, ecological effects, risk assessment, and social governance. Keyword co-occurrence analysis revealed high-frequency terms such as “waste-water,” “persistent organic pollutants,” “polycyclic aromatic hydrocarbons,” and pollutants related to sediments. Burst keyword analysis showed that early keywords like “polychlorinated biphenyls” were gradually replaced by more recent terms like “particles.” Additionally, it was found that cooperation between China and the United States was close, and research was increasingly interdisciplinary. Finally, the main challenges in the current research were summarized, and future research directions were proposed, aiming to provide theoretical support and data foundation for scientific studies and policymaking concerning emerging pollutants in watershed water bodies.

1. Introduction

In recent years, the issue of emerging pollutants (EP) has been increasingly highlighted, attracting widespread attention from all sectors of society. In response, a series of important documents, including the “Action Plan for Emerging Pollutant Control,” the “List of Key Control Emerging Pollutants (2023 Edition),” and the “Ecological and Environmental Monitoring Standards for Emerging Pollutants (2024 Edition),” were introduced by China. These documents aimed to clearly define and strengthen the investigation, monitoring, and supervision of emerging pollutants such as persistent organic pollutants (POPs), endocrine-disrupting chemicals (EDCs), antibiotics, and microplastics. Emerging pollutants were not only found in environmental media such as the atmosphere [1,2], water bodies [3,4,5], and soil [1,6], but they were also detected in human blood [7], urine [8], and breast milk [9]. They circulated throughout the body via the bloodstream, and when their concentrations exceeded certain thresholds, they were found to severely harm human health [10]. Emerging pollutants in the environment could enter water bodies through various pathways [11,12]. For instance, Liu et al. [13] found that most pharmaceuticals and personal care products (PPCPs) were indirectly discharged into natural water bodies through wastewater treatment plants.

Watershed water bodies, as an important part of the Earth’s water cycle, were identified as one of the main destinations for emerging pollutants. However, existing research on EP in aquatic environments was largely confined to isolated compartments such as lakes [14], rivers [15], and sewage treatment plants [16], with only a few studies comprehensively investigating emerging pollutants in different environmental compartments at the watershed scale. For example, although many studies had found that emerging pollutants were widely present in the surface water and sediments of the Yangtze River Basin [17,18], these studies mainly focused on the mainstream or a part of the watershed, lacking a holistic understanding of emerging pollutants across the entire watershed water bodies. In this study, “watershed water bodies” are defined as the full spectrum of aquatic systems within a watershed boundary, encompassing pollution sources (municipal or industrial effluents), natural transport pathways (rivers and streams), and ecological or human exposure endpoints (lakes, reservoirs, and drinking water sources). Therefore, a bibliometric approach was considered valuable for characterizing the current research landscape and thematic development of EP studies in watershed environments.

Bibliometric analysis, first proposed by Alan Pritchard in 1969 [19], was used to apply statistics and visualization techniques to analyze the frequency of keywords, publications from different countries, research institutions, journals, and academic disciplines, as well as social networks and their impact factors. This method has provided a way for scholars to identify new research directions and themes in scientific studies [20,21]. Bibliometric analysis has been widely applied in various research fields [19,22,23].

Therefore, bibliometric analysis was used in this paper to collect literature data on emerging pollutants in watershed water bodies from the Web of Science Core Collection (WOSCC) database. By using tools such as the R package Bibliometrix (version 4.3.2), VOSviewer (version 1.6.17), and CiteSpace (version 6.3.1) for visualization, a comprehensive analysis of publication numbers, research institutions, authors, countries, and keywords related to emerging pollutants in watershed water bodies was performed. The purpose of this analysis was to identify the geographical distribution, core author groups, and historical development of research in this field. In addition, this study sought to map current research hotspots and anticipate future thematic trends, thereby providing a reference framework to support continued scientific inquiry in the domain of watershed water bodies’ emerging pollutant research.

2. Data and Methods

2.1. Data Source

The Clarivate Analytics Web of Science Core Collection (WOSCC) database was selected as the data source for this study. This database was a comprehensive academic information platform, which not only included highly influential core academic journals but also covered a wide range of research fields, including natural sciences, social sciences, and biomedical sciences [23].

2.2. Data Collection

Based on the Science Citation Index Expanded (SCI-E) and Social Sciences Citation Index (SSCI) sub-databases of WOSCC, the search strategy used in this study involved the use of the following search terms: TS = ((“Watershed” OR “Watershed water bodies” OR “River basin”) AND (“Emerging pollutant*” OR “Emerging contaminant*” OR “Contaminant* of emerging concern*” OR “Persistent organic pollutant*” OR “POPs” OR “Endocrine-disrupting chemical*” OR “EDCs” OR “Antibiotic*” OR “Microplastic*” OR “MP” OR “Nanomaterial*” OR “Disinfection* by product*” OR “Perfluorinated alkyl substance*” OR “Per-and polyfluoroalkyl substance*” OR “Perfluorinated compound*” OR “Polychlorinated biphenyls” OR “Dichlorodiphenyltrichloroethane” OR “Pesticide*” OR “Pharmaceutical*” OR “Cosmetic*” OR “Personal care product*” OR “Surfactant*” OR “Cleaning product*” OR “Drug*” OR “Micropollutant*” OR “PPCPs”)). The document type was filtered to “Article,” and the language was restricted to English. The search was conducted on 1 February 2025, and the time range for the search was from 1 January 2000 to 31 December 2024. To ensure the accuracy of the data and literature, the titles and abstracts of each document were carefully reviewed, and duplicate or irrelevant documents were discarded [24]. After filtering, 823 highly relevant and valid documents were retained.

2.3. Data Analysis Methods

Bibliometric methods and scientific knowledge mapping were employed in this paper. The selected literature was downloaded in txt format from the WOSCC database and imported into the R package Bibliometrix (version 4.3.2) for comprehensive analysis [25]. By analyzing the publication number, subject distribution, countries, institutions, authors, and journals, the development trajectory and frontier trends of research on emerging pollutants in watershed water bodies were examined. Additionally, the VOSviewer (version 1.6.17) software was used to construct cooperation network maps among authors, institutions, and countries/regions [26]. Co-occurrence network analysis was conducted to quantify the co-occurrence information of keywords, revealing potential relationships between content associations and key features. Furthermore, CiteSpace (version 6.3.1) software was used to perform burst analysis on the keywords in the literature, identifying dynamic hotspots and trends in the research field [27].

3. Results

3.1. Basic Characteristics of Publications

3.1.1. Annual Publication Trends

The number of research publications was considered to reflect the progress and development trends of a field to some extent [28]. Figure 1 illustrates the annual publication trends of research on emerging pollutants in watershed water bodies from 2000 to 2024. The x-axis represented the years, and the y-axis represented the number of publications. Except for small fluctuations observed in certain years, the overall volume of literature in this research field showed an upward trend.

3.1.2. Types of Publications

The distribution of publication types related to research on emerging pollutants in watershed water bodies is shown in Figure 2, listing only the top 10 types of publications. Among them, “SCIENCE OF THE TOTAL ENVIRONMENT” accounted for the highest proportion (16.77%), followed by “ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH” (7.53%), “CHEMOSPHERE” (6.68%), and “ENVIRONMENTAL POLLUTION” (5.71%). Publications of other types were relatively rare.

3.2. Producing Countries and Cooperation

The number of articles published by a country/region was calculated based on the affiliation of the authors. International cooperative publications were attributed to all cooperating countries and included in the count of each country [20]. The statistical results indicated that, in recent years, the number of articles from China had increased sharply, rising from 46 articles in 2012 to 977 articles in 2024, showing rapid development and investment in the field of emerging pollutants in watershed water bodies (Figure 3). The number of publications from the United States also exhibited steady growth, although the increase was relatively moderate. From 46 publications in 2008 to 381 in 2024, the United States maintained a consistent output in the field of emerging pollutants in watershed water bodies. While the growth rate was slower than that of China, the foundational strength of the United States in this field remained notable. Other countries/regions such as Canada, Brazil, Japan, Germany, Spain, France, and India showed relatively moderate growth trends in their number of publications. From 2000 to 2024, the number of publications from these countries/regions grew from tens to hundreds of articles, indicating stable development in the field. Notably, Canada and Brazil experienced slightly faster growth compared to other countries/regions, reflecting a higher level of research activity in this area. Figure 4 depicts the specific cooperation relationships between countries/regions. As shown in Figure 4, cooperation among countries/regions was relatively close, especially among the top four producing countries: China, the United States, Canada, and Brazil.

3.3. Influential Institutions

A total of 285 institutions actively participated in global research on emerging pollutants in watershed water bodies.

Table 1. Top 10 institutions based on publications and citations in the field of emerging pollutants in watershed water bodies.

Rank	Institution	Country	Total Publications		Total Citations	Average Citation Per Paper
			No.	%
1	Chinese Academy of Sciences	China	131	15.92	4494	34.31
2	University of Chinese Academy of Sciences	China	120	14.58	4172	34.77
3	Chinese Research Academy of Environmental Sciences	China	53	6.44	1958	36.94
4	Consejo Superior de Investigaciones Cientificas (CSIC)	Spain	37	5	4193	113.32
5	Beijing Normal University	China	29	3.52	1196	41.24
6	Research Center for Eco-Environmental Sciences (RCEES)	China	28	3.4	1189	42.46
7	CSIC-Centro de Investigacion y Desarrollo Pascual Vila (CID-CSIC)	Spain	26	3.16	2962	113.92
8	CSIC-Instituto de Diagnostico Ambiental y Estudios del Agua (IDAEA)	Spain	26	3.16	2962	113.92
9	Institut Catala de Recerca de l’Aigua (ICRA)	Spain	23	2.79	2968	129.04
10	Centre National de la Recherche Scientifique (CNRS)	France	22	2.67	585	26.59

shows the top 10 institutions based on total publications and total citations in the field of emerging pollutants in watershed water bodies. Among these, five institutions were from China, four were from Spain, and one was from France. The three institutions with the highest global publication output in this field were the Chinese Academy of Sciences (131 publications), the University of Chinese Academy of Sciences (120 publications), and the Chinese Research Academy of Environmental Sciences (53 publications). Although these three institutions had a relatively low average citation rate per paper, they indicated significant contributions from China to the field. Notably, Spanish institutions such as CSIC, CID-CSIC, IDAEA, and ICRA demonstrated both high research output and high average citation rates—for instance, ICRA had an average citation count of 129.04 per paper, indicating high research quality. These institutions often operated with interdisciplinary teams and sustained funding, enabling more systematic and in-depth investigations. While Chinese institutions dominated in terms of publication quantity, Spanish institutions were more frequently involved in international collaborations. For example, CSIC maintained close partnerships not only with other European countries but also with North American scholars. Such collaborations enhanced both the visibility and citation rates of their publications. Moreover, Spanish institutions often published in high-impact journals such as Science of the Total Environment and Environmental Science & Technology, which contributed to the high citation rates.

Co-occurrence network analysis of institutions not only provided information on influential research institutions and potential collaborators but also helped scholars establish collaborations [29,30]. Figure 5 presents the co-occurrence network of institutions in the field of emerging pollutants in watershed water bodies. There were clear and close links between research teams. Well-established and influential institutions such as the Chinese Academy of Sciences and Beijing Normal University played central roles in the cooperation network, forming a highly dense collaboration network. Moreover, it was worth noting that most of the research institutions in this collaboration network were located in China, highlighting the importance of strengthening international cooperation, especially on global issues like emerging pollutants.

3.4. Influential Authors

Academic authors were not only considered outstanding contributors in a specific field but were also regarded as playing a crucial role in advancing scientific research [31]. According to the statistics, a total of 289 authors from around the world had made significant contributions to the research on emerging pollutants in watershed water bodies.

Table 2. Top 10 authors based on publications and citations in the field of emerging pollutants in watershed water bodies.

Rank	Authors	Total Publications	Institutions and Countries	Total Citations	Average Citation Per Paper
1	Barcelo, Damia	27	Consejo Superior de Investigaciones Cientificas (CSIC), Spain	3298	122.15
2	Ying, Guang-Guo	11	South China Normal University, China	567	51.55
3	Lin, Chunye	9	Beijing Normal University, China	445	49.44
4	He, Mengchang	8	Beijing Normal University, China	404	50.5
5	Yu, Gang	8	Tsinghua University, China	325	40.63
6	Lacorte, Silvia	7	Consejo Superior de Investigaciones Cientificas (CSIC), Spain	511	73
7	Li, Sijia	5	Northeast Normal University, China	91	18.2
8	Ju, Hanyu	4	Chinese Academy of Sciences, China	64	16
9	Wang, Haozheng	4	Beijing Normal University, China	369	92.25
10	Liu, Sheng	3	Hohai University, China	125	41.67

shows the top 10 authors with the highest publication output in this field from 2000 to 2024. Among these, eight scholars were from research institutions in China, and two were from research institutions in Spain. Barcelo Damia, from CSIC, Spain, was ranked first with 27 publications and 3298 total citations. His average citation per paper was 122.15, significantly higher than that of other scholars. This could be attributed to his early and systematic engagement in the field, which helped his work become widely cited and accumulate academic influence over time. Lin Chunye (Beijing Normal University, Beijing, China) with a total of 445 citations, He Mengchang (Beijing Normal University, Beijing, China) with 404 citations, and Wang Haozheng (Beijing Normal University, Beijing, China) with 369 citations, although having fewer publications (8–9 papers), had each an average citation rate exceeding 49 citations per paper, suggesting that their research had attracted considerable academic attention. Notably, Wang Haozheng, who had published only four papers, had an average citation rate of 92.25 per paper, indicating that his research had focused on hot topics or methodological innovations, resulting in higher individual impact. In contrast, some scholars (e.g., Li Sijia, Ju Hanyu) had relatively lower total citations and average citation rates, which could have been attributed to the novelty of their research direction, shorter publication times, or regionally focused research themes.

The analysis of the cooperation network revealed the dynamics of academic research teams and provided valuable insights for closely collaborating scholars [32]. Figure 6 depicts the collaboration network of authors in the field of emerging pollutants in watershed water bodies. It was shown that several tight-knit author groups existed, likely representing different research directions or subfields. For example, the brown node group, centered around “Lin, Chunye,” and the orange and red node groups, centered around “Ying, Guang-guo” and “Lu, Yonglong,” showed significant collaboration relationships and research influence. These core authors held high academic status and leadership in this field, and their research had played a pivotal role in the development of the field.

3.5. Highly Cited Publications

The number of citations for a publication was not only regarded as representing its academic impact but also indicated the research hotspots in a given period [33,34]. Table 3 lists the top 10 highly cited publications related to emerging pollutants in watershed water bodies based on total citations (TC). These publications were ranked by their total number of citations. The publication titled “The occurrence of antibiotics in an urban watershed: From waste-water to drinking water” by Watkinson et al. [35], published in 2009, was ranked first with a total of 931 citations, averaging 54.76 citations per year. Most of the highly cited publications were published between 2009 and 2019. In contrast, the studies by Khurshid et al. [36], Wu et al. [37], and Sresung et al. [38] showed zero total and average citations, as they were all published in late 2024, and the analysis in this study was limited to records indexed up to 31 December 2024.

Highly cited publications were not only considered scientifically impactful but also provided practical guidance for environmental management, pollution control, and public health policymaking. For example, the study by Carmona et al. [39] developed a liquid chromatography–tandem mass spectrometry (LC–MS/MS) method capable of simultaneously detecting multiple acidic pharmaceuticals and personal care products (PPCPs) in both water and sediment, with the innovative use of ammonium fluoride to enhance ionization efficiency. Mao et al. [40] proposed a novel internal standard-based approach to extract and quantify both extracellular DNA (eDNA) and intracellular DNA (iDNA) from water and sediment samples, thereby enabling more accurate tracking of antibiotic resistance genes (ARGs) and their persistence in sediments, significantly improving environmental monitoring accuracy. Watkinson et al. [35] demonstrated that wastewater treatment plants (WWTPs) served as major sources of antibiotics in surface water systems, offering policy-relevant insights into water reuse and discharge regulations. Ding et al. [41] employed principal component analysis (PCA) to examine the spatial distribution of microplastics in the Wei River Basin and their associations with land use and anthropogenic activities, thus providing data support and policy direction for regional microplastic pollution control. Sharma et al. [42] evaluated the potential health and ecological risks posed by PPCPs detected in groundwater—used as drinking water—along the Ganges River, offering critical scientific evidence to inform environmental and public health policy, and enhancing the interdisciplinary impact of their work.

Table 3. Top 10 highly cited publications related to emerging pollutants in watershed water bodies.

Rank	Title	Authors	Source	Type	Year	Total Citations	TC Per Year
1	The occurrence of antibiotics in an urban watershed: From wastewater to drinking water [35]	Watkinson, A.J.; Murby, E.J.; Kolpin, D.W.; Costanzo, S.D.	Science of the Total Environment	Article	2009	931	54.76
2	Occurrence and Transport of Tetracycline, Sulfonamide, Quinolone, and Macrolide Antibiotics in the Haihe River Basin, China [43]	Luo, Y.; Xu, L.; Rysz, M.; Wang, Y.Q.; Zhang, H.; Alvarez, P.J.J.	Environmental Science & Technology	Article	2011	813	54.2
3	Sources and sinks of microplastics in Canadian Lake Ontario nearshore, tributary and beach sediments [44]	Ballent, A.; Corcoran, P.L.; Madden, O.; Helm, P.A.; Longstaffe, F.J.	Marine Pollution Bulletin	Article	2016	475	47.5
4	Plastic Debris in 29 Great Lakes Tributaries: Relations to Watershed Attributes and Hydrology [45]	Baldwin, A.K.; Corsi, S.R.; Mason, S.A.	Environmental Science & Technology	Article	2016	474	47.4
5	Legacy and Emerging Perfluoroalkyl Substances Are Important Drinking Water Contaminants in the Cape Fear River Watershed of North Carolina [46]	Sun, M.; Arevalo, E.; Strynar, M.; Lindstrom, A.; Richardson, M.; Kearns, B.; Pickett, A.; Knappe, D.R.U.	Environmental Science & Technology Letters	Article	2016	468	46.8
6	Occurrence of acidic pharmaceuticals and personal care products in Tuna River Basin: From waste to drinking water [39]	Carmona, E.; Andreu, V.; Picó, Y.	Science of the Total Environment	Article	2014	401	33.42
7	Microplastics in surface waters and sediments of the Wei River, in the northwest of China [41]	Ding, L.; Mao, R.F.; Guo, X.T.; Yang, X.M.; Zhang, Q.; Yang, C.	Science of the Total Environment	Article	2019	392	56
8	Persistence of Extracellular DNA in River Sediment Facilitates Antibiotic Resistance Gene Propagation [40]	Mao, D.Q.; Luo, Y.; Mathieu, J.; Wang, Q.; Feng, L.; Mu, Q.H.; Feng, C.Y.; Alvarez, P.J.J.	Environmental Science & Technology	Article	2014	358	29.83
9	Assessment of the sources and inflow processes of microplastics in the river environments of Japan [47]	Kataoka, T.; Nihei, Y.; Kudou, K.; Hinata, H.	Environmental Pollution	Article	2019	337	48.14
10	Health and ecological risk assessment of emerging contaminants (pharmaceuticals, personal care products, and artificial sweeteners) in surface and groundwater (drinking water) in the Ganges River Basin, India [42]	Sharma, B.M.; Becanová, J.; Scheringer, M.; Sharma, A.; Bharat, G.K.; Whitehead, P.G.; Klánová, J.; Nizzetto, L.	Science of the Total Environment	Article	2019	324	46.29

Table 3. Top 10 highly cited publications related to emerging pollutants in watershed water bodies.

Rank	Title	Authors	Source	Type	Year	Total Citations	TC Per Year
1	The occurrence of antibiotics in an urban watershed: From wastewater to drinking water [35]	Watkinson, A.J.; Murby, E.J.; Kolpin, D.W.; Costanzo, S.D.	Science of the Total Environment	Article	2009	931	54.76
2	Occurrence and Transport of Tetracycline, Sulfonamide, Quinolone, and Macrolide Antibiotics in the Haihe River Basin, China [43]	Luo, Y.; Xu, L.; Rysz, M.; Wang, Y.Q.; Zhang, H.; Alvarez, P.J.J.	Environmental Science & Technology	Article	2011	813	54.2
3	Sources and sinks of microplastics in Canadian Lake Ontario nearshore, tributary and beach sediments [44]	Ballent, A.; Corcoran, P.L.; Madden, O.; Helm, P.A.; Longstaffe, F.J.	Marine Pollution Bulletin	Article	2016	475	47.5
4	Plastic Debris in 29 Great Lakes Tributaries: Relations to Watershed Attributes and Hydrology [45]	Baldwin, A.K.; Corsi, S.R.; Mason, S.A.	Environmental Science & Technology	Article	2016	474	47.4
5	Legacy and Emerging Perfluoroalkyl Substances Are Important Drinking Water Contaminants in the Cape Fear River Watershed of North Carolina [46]	Sun, M.; Arevalo, E.; Strynar, M.; Lindstrom, A.; Richardson, M.; Kearns, B.; Pickett, A.; Knappe, D.R.U.	Environmental Science & Technology Letters	Article	2016	468	46.8
6	Occurrence of acidic pharmaceuticals and personal care products in Tuna River Basin: From waste to drinking water [39]	Carmona, E.; Andreu, V.; Picó, Y.	Science of the Total Environment	Article	2014	401	33.42
7	Microplastics in surface waters and sediments of the Wei River, in the northwest of China [41]	Ding, L.; Mao, R.F.; Guo, X.T.; Yang, X.M.; Zhang, Q.; Yang, C.	Science of the Total Environment	Article	2019	392	56
8	Persistence of Extracellular DNA in River Sediment Facilitates Antibiotic Resistance Gene Propagation [40]	Mao, D.Q.; Luo, Y.; Mathieu, J.; Wang, Q.; Feng, L.; Mu, Q.H.; Feng, C.Y.; Alvarez, P.J.J.	Environmental Science & Technology	Article	2014	358	29.83
9	Assessment of the sources and inflow processes of microplastics in the river environments of Japan [47]	Kataoka, T.; Nihei, Y.; Kudou, K.; Hinata, H.	Environmental Pollution	Article	2019	337	48.14
10	Health and ecological risk assessment of emerging contaminants (pharmaceuticals, personal care products, and artificial sweeteners) in surface and groundwater (drinking water) in the Ganges River Basin, India [42]	Sharma, B.M.; Becanová, J.; Scheringer, M.; Sharma, A.; Bharat, G.K.; Whitehead, P.G.; Klánová, J.; Nizzetto, L.	Science of the Total Environment	Article	2019	324	46.29

3.6. Keywords

3.6.1. Topic Evolution Analysis

The research conducted by Watkinson et al. [35] in 2009 received the highest number of citations, and thus, 2009 was used as a boundary to analyze the evolution of research topics. Based on the Bibliometrix (version 4.3.2) software, Figure 7 visually presents the evolution of topics from 2000 to 2024. It was observed that in the early stages, research had mainly focused on pollutant identification and detection. As the research progressed, the focus gradually expanded to include source analysis, environmental behavior, ecological effects, and risk assessment. Furthermore, Figure 7 revealed the growing attention to emerging issues such as social governance and public participation in recent years.

Topic evolution analysis, proposed by Cobo et al. [48] in 2011, was used as a method based on bibliometric and co-word analysis to detect, quantify, and visualize the evolution of specific research areas. The core of this method was to divide research topics into four quadrants based on centrality (the degree of connection between clusters) and density (the degree of connection between keywords), revealing the development status and importance of different topics. In this study, the research period was divided into two stages, with 2009 serving as a boundary, and a two-phase strategic map was generated, as shown in Figure 8 and Figure 9. According to the definition by Cobo et al. [48], the first quadrant was considered well-developed, with strong centrality and high density, and it played a crucial role in the development of emerging pollutants research in watershed water bodies. The second quadrant was highly developed, with high centrality and low density, indicating that it was important but contributed less to the field. The third quadrant was underdeveloped, with low density and centrality, which suggested that the topics were either emerging or disappearing. The topics in the fourth quadrant had low centrality and high density, which typically represented fundamental concepts that supported the development of other topics. Each circle represented a cluster, and the larger the circle, the higher the frequency of keywords in that cluster.

During the time period shown in Figure 8, research had mainly focused on basic areas such as pollutant environmental behavior, ecological effects, and risk assessment. In contrast, during the period shown in Figure 9, although research in these basic areas continued, studies in applied areas, such as social governance, policy regulations, public participation, and pollution control technologies, began to emerge and became new research hotspots. As the research deepened, the study of emerging pollutants in watershed water bodies was no longer confined to the field of environmental science but had gradually integrated with disciplines such as chemistry, biology, sociology, and economics, forming an interdisciplinary research system. This interdisciplinary integration not only broadened the research field but also promoted innovations in research methods.

3.6.2. Keyword Co-Occurrence Analysis

VOSviewer, a software tool for building and visualizing bibliometric networks, was used in this study for keyword co-occurrence analysis [49]. The co-occurrence network of keywords was constructed, where each node represented a keyword, and the size of the node reflected the frequency of that keyword’s occurrence. The distance between nodes indicated the relatedness between keywords, with shorter distances representing stronger associations [50,51]. Figure 10 displays the keyword co-occurrence network, which was divided into four clusters. The red cluster consisted of the most common keywords, with “waste-water” being the most frequently occurring keyword. The green cluster focused on newly emerging pollutants such as “persistent organic pollutants” and “polycyclic aromatic hydrocarbons.” The blue and yellow clusters mainly involved various emerging pollutants in the sediments of the watershed water bodies. For example, the keyword “sediments” was located in the blue cluster, while “perfluorinated compounds” appeared in the yellow cluster. In Figure 11, the temporal distribution of co-occurring keywords was shown using VOSviewer. If the node color was close to yellow, it indicated that the keyword was in the early stages of development. Between 2018 and 2020, researchers had primarily focused on detecting newly emerging pollutants and their adverse environmental impacts. Currently, the focus of research has shifted to how to effectively treat and remove these emerging pollutants, providing prospects for the sustainable development of aquatic environments.

3.6.3. Keyword Burst Analysis

Burst keyword detection analysis was used to identify keywords that had experienced a rapid increase in frequency over a short period of time, revealing the hot topics that had emerged in recent years [52,53]. This method provided insights into how certain topics within the field of emerging pollutants in watershed water bodies had gained attention over time. A co-occurrence network of keywords from 2000 to 2024 in the field of emerging pollutants in watershed water bodies was constructed, and 104 burst keywords were detected during this period. The top 25 burst keywords, shown in Figure 12, were the most widely discussed during this time. According to the timeline, “polychlorinated biphenyls” was the first keyword to experience a burst, with a burst strength of 8.6, and it remained a research hotspot from 2007 to 2014. Following this, the keywords “samples” and “residues” emerged as popular topics between 2008 and 2013 and 2008 and 2011, respectively. As research progressed, the keyword “particles” gained widespread attention in recent years. The burst keyword detection provided further insights into the evolving trends in research on emerging pollutants in watershed water bodies.

3.6.4. Keyword Timeline Analysis

CiteSpace software was used in this study to perform a timeline visualization analysis of keywords in the field of emerging pollutants in watershed water bodies from 2000 to 2024 (Figure 13). This analysis systematically revealed the temporal and spatial characteristics of topic evolution in the field [54]. Through clustering analysis of high-frequency keywords, six core research clusters were identified. Within each cluster, keywords were distributed along the timeline according to their first appearance, clearly showing the historical origins and research development paths of pollutants. Specifically, “organochlorine pesticides” was identified as Cluster #0, with research spanning from 2000 to 2024. The next cluster, Cluster #1, included keywords such as “antibiotics,” “microplastics,” “perfluoroalkyl substances,” “microplastic,” “antibiotic resistance genes,” and “herbicides.” Clusters #0, #3, and #4 had timelines that nearly covered the entire research period, indicating that topics such as “organochlorine pesticides,” “perfluoroalkyl substances,” and “microplastic” were some of the most prominent research topics in the field of emerging pollutants in watershed water bodies. Cluster #6 had the shortest duration. At the same time, the timeline further revealed the generational evolution of research on emerging pollutants in watershed water bodies: early research had focused on the residual characteristics of traditional pesticides and antibiotics, while research in the mid-period had shifted toward the migration mechanisms of physical pollutants such as microplastics. In recent years, research has delved into complex pollution effects, such as the spread of resistance genes. This evolutionary trend was closely related to global pollutant control policies and the innovation of analytical techniques, providing quantitative evidence for understanding the paradigm shift in watershed water environment research.

4. Discussion

4.1. Policy Landscape

The frequent detection of emerging pollutants in watershed water bodies has attracted significant attention from national governments and international organizations, which have promoted the formulation and implementation of relevant policies. For instance, antibiotics were identified by the World Health Organization (WHO) as a major public health threat. In addition, the European Union issued the Water Framework Directive (WFD), and the United Nations Environment Programme (UNEP) launched the Stockholm Convention. These landmark legal documents not only provided a regulatory framework for the control of persistent organic pollutants (POPs) and other priority substances but also required member states to develop and implement national implementation plans (NIPs) to eliminate or reduce the release of POPs into the environment [55]. In recent years, China also released several key policy documents, such as the “List of Key Control Emerging Pollutants (2023 Edition)” and the “Ecological and Environmental Monitoring Standards for Emerging Pollutants (2024 Edition)”, which clearly defined the types of emerging pollutants to be prioritized and their distribution across environmental media. Nevertheless, existing policies covered only a small portion of known emerging pollutants and lacked concentration limits or risk thresholds for most potentially hazardous substances. Thus, continued research efforts were still needed to identify high-risk compounds and to revise and improve related regulations and standards.

4.2. Current Research Status and Major Challenges

Bibliometric analysis revealed a rapid increase in research activity concerning EP in watershed environments, with China, the United States, and Spain identified as the leading contributors. Research themes had expanded from contaminant identification to source tracking, environmental behavior, ecotoxicology, and risk governance, reflecting a growing diversification and systematization of the field. However, several key challenges persisted:

(1)

Most studies still focused on single environmental media, such as surface water, sediments, or wastewater discharge points, and lacked integrated modeling of cross-media and multi-pathway migration and fate processes at the watershed scale. This limitation hindered the comprehensive understanding and predictive capability regarding pollutant behavior.

(2)

Although advanced technologies such as mass spectrometry and non-target screening had matured, technical bottlenecks remained in identifying unknown compounds, degradation products, and mixture effects. Additionally, inconsistencies in sampling, treatment, and analytical protocols among studies weakened the comparability of data.

(3)

The impacts of public health emergencies, such as pandemics, on emerging pollutants in watershed water bodies have not been adequately addressed. For example, the COVID-19 pandemic has led to increased inputs of antiviral drugs, antibiotics, and personal protective equipment (e.g., masks and gloves) into aquatic environments, elevating both pharmaceutical and microplastic pollution levels. According to Liu et al. [56], among 23 major watersheds in China, 77.27% exhibited increased microplastic abundance during the pandemic, particularly in the middle and lower reaches of the Yangtze and Pearl Rivers. Despite this significant impact, related research remained scarce, and systematic investigations into the resulting changes in pollutant spectra and ecological health risks were still lacking. Future studies should prioritize this area.

4.3. Future Perspectives

Although substantial progress had been made in investigating EP in watershed systems, this study identified several unresolved challenges. Future research was recommended to focus on the following strategic directions:

(1)

Development of Integrated Watershed Simulation Models: Multi-media coupled models should be established to simulate the migration, transformation, and accumulation of contaminants across surface water, groundwater, sediments, and biota. These models should incorporate land use, hydrodynamic processes, and socioeconomic drivers to enable holistic risk assessments and policy scenario analyses.

(2)

Advancement of Interdisciplinary Monitoring Technologies: Portable biosensors, Internet-of-Things (IoT) devices for real-time detection, and AI-assisted analytics should be integrated to achieve high-frequency, low-cost, and spatially distributed monitoring of multiple contaminants, thus supporting regulatory enforcement and public health interventions.

(3)

Innovation in Green and Efficient Removal Technologies: Priority should be given to developing high-efficiency, low-energy, and byproduct-free removal techniques such as advanced oxidation processes, membrane filtration, and biologically integrated treatment systems. Emerging green technologies should also be explored to enhance the scalability and cost-effectiveness of contaminant removal in real-world water management contexts.

5. Conclusions

In this paper, bibliometric methods were used to systematically analyze the research on emerging pollutants in watershed water bodies from 2000 to 2024, revealing the research progress, hotspots, and future trends in this field. The results indicated that research on emerging pollutants in watershed water bodies gradually expanded from early topics such as pollutant identification and detection to include source analysis, environmental behavior, ecological effects, risk assessment, and social governance. Keyword analysis revealed that terms like “waste-water,” “persistent organic pollutants,” and “polycyclic aromatic hydrocarbons” were frequently found, while in recent years, emerging keywords such as “particles” have gradually gained attention.

Regarding national and institutional cooperation, it was found that China and the United States had made the most significant contributions to research in this field, and cooperation between the two countries was notably close. Chinese institutions, such as the Chinese Academy of Sciences and the University of Chinese Academy of Sciences, were recognized as occupying a crucial position in this field, while Spanish institutions like CSIC also played a significant role in international cooperation. Furthermore, the analysis of collaboration networks among authors showed that research on emerging pollutants in watershed water bodies was increasingly interdisciplinary, involving fields such as environmental science, chemistry, biology, and sociology.

Through an analysis of highly cited publications, extensive scholarly attention was found to have been directed in recent years toward emerging pollutants such as antibiotics and microplastics, particularly concerning their sources, transport pathways, and ecological impacts in watershed environments. Keyword burst analysis further revealed an evolution of research hotspots—from early emphasis on “polychlorinated biphenyls” to a more recent focus on “particles,” indicating a gradual shift toward the environmental behavior and remediation technologies of emerging pollutants. In the future, as environmental risk perception deepened and regulatory frameworks became increasingly refined, contaminants characterized by high persistence, bioaccumulation potential, and complex metabolic byproducts were anticipated to become the next focal point of research and management.

Despite notable advances, several critical challenges remained, including insufficient understanding of cross-media transport processes, limitations in detection technologies, and a lack of research on the impact of sudden pollution events. Future efforts should prioritize the development of integrated multi-media modeling, intelligent monitoring systems, and green removal technologies. In addition, enhanced international collaboration and stronger policy support were deemed essential to facilitate a transition from descriptive studies to those focused on mechanistic understanding and effective intervention. These efforts were expected to provide vital theoretical underpinnings and practical guidance for improving water environment governance and formulating precise watershed-scale management strategies.