Introduction

In recent decades, emerging contaminants (ECs) have attracted significant concern globally due to their probable chronic and acute toxicity (Tong et al. 2022). A new class of ECs identified includes pharmaceutical drugs in combination with personal care products, commonly referred to as pharmaceuticals and personal care products (PPCPs) (Zenobio et al. 2015). PPCPs are an extraordinary, diversified group of organic compounds utilized in human health, veterinary medicine, agricultural practices, and cosmetic care (sunscreens, fragrances, personal hygiene products, and nutritional substances) (Barceló and Petrovic 2007; Eriksson et al. 2003). These so-called new ECs are highly bioactive, polar, optically active, and present in trace concentrations (Barceló and Petrovic 2007). PPCPs have drawn remarkable attention in recent years due to the following reasons: (i) present along with their metabolites and transformation products (Daughton and Ternes 1999; Liu and Wong 2013) with varying physical, chemical, biological properties and having a unique mode of biochemical action (Boxall et al. 2012); (ii) ubiquitous and have been detected in wastewater treatment plants (WWTPs), drains, surface water (river, lakes, sea, oceans), sediments, soils (vadose zone and saturated soils), groundwater, drinking water, air, wetlands, sewage sludge, landfills, septic tanks, humans, and biota; (iii) difficult to remove using conventional WWTPs, thus continuously re-enter the water cycle and behave similarly as persistent pollutants, hence termed as “pseudo-persistent compounds” (Ellis 2006); (iv) some PPCPs are present in low concentration, hence may not be ecotoxic when acting singly, but, in mixtures, may elicit significant toxicity (Cleuvers 2003). The improved analytical methods for the detection have led to an increasing concern about the fate of PPCPs (Kalyva 2017). The detrimental effect due to the PPCPs calls for an effective treatment system. Some advanced technologies such as membrane filtration, ultrafiltration, ozonation, UV, reverse osmosis, granular-activated carbon, and conventional disinfection with chlorine are successful in removing some of the ECs. However, their application is limited due to high cost (Beltrán et al. 2008; Sui et al. 2011; Matamoros et al. 2007; Roberts and Thomas 2006). Also, the difference in the physicochemical properties of these PPCPs makes it almost impossible to design a robust treatment system. An alternative is thus required to keep a check on the increasing concentration of the PPCPs in the environment.

To better manage PPCPs in the environment, it is crucial to understand their origin, environmental interaction (fate), and transport deportment (Tong et al. 2022). The typical investigatory process for determining FTP is by conducting routine monitoring of the contaminants in the environment, which is spatially and temporally cumbersome (Trinh et al. 2016). Thus, monitoring data cannot be used alone for determining the relative magnitudes of various sources and cannot meet real-time prediction demands for emergent events, though it provides some understanding of the environmental behavior and exposure routes (Lindim et al. 2016; Song et al. 2016; Wang et al. 2012). Hence, mathematical modeling comes to the rescue, which can predict the concentration of the contaminant in various media with reasonable accuracy (Lindim et al. 2017). Therefore, it is required to have deep insight into the fate and transport processes occurring in the environment, which will serve as an input in the fate and transport model of the PPCPs.

Today, comprehensive studies have been conducted regarding the FTP in the environment, viz. water, sediments, soil, groundwater, air, landfills, etc. The PPCPs on human consumption are not absorbed and wholly metabolized by humans, thus ending up in raw sewage in several manners (Kasprzyk-Hordern et al. 2008). Few PPCPs are conjugated in the body before excretion. These conjugated forms are generally broken down in sewage treatment plants (STPs) and may be transformed into the parent compound (Karnjanapiboonwong et al. 2011). The PPCPs may also get into the environment via leaching from landfills, unlawful disposal, and industries, the primary source of PPCPs being the STPs (Archer et al. 2017). Their presence in raw sewage may affect the performance of STPs, causing toxicity in microorganisms, affecting marine life, and contaminating groundwater and food crops (Drillia et al. 2005). After being discharged from the STPs, the PPCPs present in sewage cause contamination in the receiving water bodies (Liu and Wong 2013). Effluents from WWTPs (reclaimed water) are also used in irrigation to reduce water supply demand, which serves as an introductory pathway for PPCPs in the soil (Kinney et al. 2006; Pedersen et al. 2005). The PPCPs adsorbed onto the active sludge in STPs enter the soil on sludge land application, and the reclaimed wastewater used in agricultural irrigation with PPCPs gets into the soil, reaches the groundwater, and, finally, the drinking water (Drillia et al. 2005).

Many studies have investigated the source, transport, distribution, transformation, migration, and risk assessment of PPCPs (Charuaud et al. 2019; Yang et al. 2019; Li et al. 2021; Al-baldawi et al. 2021; Anand et al. 2022; Atugoda et al. 2021; Li et al. 2021; Martínez-Alcalá et al. 2021; Ohoro et al. 2022; Shaheen et al. 2022; Wang et al. 2022). Still, many gaps remain about the complex ecological system’s occurrence, fate, and transformation due to the diversity and different physicochemical properties in the varying environment (Yuan et al. 2020). However, most of these studies focus on some aspects and partial processes of the PPCPs, thereby revealing incomplete behavior and dynamics (Ebele et al. 2017; Liu et al. 2019a, b). Due to deferring monitoring time, targeted PPCPs, analytical methods, regional characteristics, etc., it is very cumbersome to monitor and quantify the whole life cycle of PPCPs from human consumption to the destination (Yuan et al. 2020). Thus, the area still needs to be wholly explored to quantify the risk due to these PPCPs.

While studying any field, having information on the present, past, and future research trends is of prime importance. Bibliometric analysis is a powerful tool for analyzing research articles quantitatively. It benefits the researcher by providing easily comprehendible visual information and a brief research topic review. The bibliometric analysis assisted in evaluating a considerable amount of data that included countries, authors, institutions, sponsors, journals, and keywords (Reshadi et al. 2021). Also, the relationship between countries, journals, and research centers (acknowledged by their affiliations) may be known by citations and co-citation analysis. The number of times of occurrences of keywords helps reveal the research field’s present, past, and future trends. The content analysis helped to gain an in-depth understanding of the FTP study in the environment originating from its source, i.e., STPs to its sink (sediment/soil/groundwater/oceans, etc.). The paper does not aim to give any additional technical understanding of FTP; rather, it briefs the research trends and delivers a contextual outlook on environmental FTP studies. Also, to the best of the authors’ knowledge, prior studies have been conducted in the area, but bibliometric analysis has been done for the first time on the topic of FTP. The study presents a statistical analysis based on research published in the Scopus database between 1996 and 2021 intended to identify publication growth and trends, top journals, authors, countries, sponsors, institutions, and keywords involved in FTP. Also, the paper provides a synopsis of the research trends, hotspots, and a contextual perspective on the FTP study. The outcome of this study will broaden the current state of the art of modeling FTP and its future prospectives. Additionally, the work may serve as a critical review in risk assessment studies. The paper aims to assist engineers, researchers, and policy makers to gain prior knowledge on how to manage the increasing environmental concentration of PPCPs.

Methodology

The leading databases of bibliographical details are Scopus and Web of Science (WOS). As stated in a study (Reshadi et al. 2021), WOS encompasses only 54% of the journal titles in Scopus, whereas Scopus covers around 84% of the journal titles incorporated in WOS. It is, thus, inferred that Scopus covers a more significant number of journals, and there is a possibility of more significant results for a similar search. Therefore, Scopus has been selected to retrieve the raw data regarding the FTP-related studies. Furthermore, the extracted raw data is subjected to bibliometric analysis, data mining, and content analysis using R software, Biblioshiny, MS Excel, and VOS viewer software.

Raw data extraction

To ensure maximum coverage of FTP publications, Scopus database was used to extract the FTP-related documents from 1996 to 2021. The preliminary selection of documents was based on the title, abstract, and keywords (TITLE-ABS-KEY) using the following terms: (“fate” OR “Distribution”) AND transport of (“Pharmaceuticals” OR “Personal Care Products” OR “PPCPs” OR “Pharmaceuticals and Personal Care Products”) in the (“environment” OR “Soil” OR “Sediment” OR “Water” OR “Sewage” OR “Air” OR “Landfills” OR “Sewage treatment plants”). A pictorial representation of the research framework is shown in Fig. 1. The language of the documents was restricted to English, and the types of documents shortlisted were articles and reviews. These criteria resulted in a total of 577 documents.

Fig. 1
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Pictorial representation of the research framework

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Data analysis

This research employed a mixed analytical method to map the scientific articles on FTP. Integrating bibliometric analysis, text mining, and content analysis illuminated the applied research technique. Collectively, the information was extracted from a massive database of literature, and a snapshot of FTP trends, characteristics, evolution, research themes, and future perspectives was drawn.

Bibliometric analysis is a powerful statistical tool, which has been increasingly used in recent years for analyzing various published research and map** scientific articles. The bibliometric analysis braces researchers in the identification of research directions in the future. The bibliometric analysis is conducted here using VOSviewer and Biblioshiny software to map the FTP research and yield relationships between articles, journals, countries, keywords, citations, and co-citation networks. Various bibliometric parameters are presented to identify research hotspots and statistically map the analyzed bibliometric information on scientific publications in the last 25 years. Moreover, text mining analysis was conducted on the abstracts and titles of the extracted paper by conducting a “co-occurrence” algorithm on the author and index keywords within the dataset. A text mining method is a tool for extricating information from a massive collection of documents in text format. Consequently, the conceptual structure, hotspots, trends, and latent research themes in the FTP research were identified.Content analysis is conducted to yield an additional in-depth apprehension of the study’s qualitative findings. The data is clustered using a bibliographic coupling, followed by qualitative content analysis on the top fifteen influential articles within each cluster to identify the theoretical orientation of the FTP research.

Data visualizations and interpretation-tools used

VOSviewer, Biblioshiny, and MS Office tools were used to analyze the collected information. The interpretation, visualization, and analysis of bibliometric networks (collaboration and co-occurrence networks) were done using VOSviewer software. For data mining, VOSviewer and MS excel have been used interactively. R software and Biblioshiny have been exploited to study the author’s performance and construct the Tree plot and Sankey diagram.

Primary data statistics

Research growth trend

The basic information from the raw data obtained from Scopus on FTP research is tabulated in Table 1. The FTP databases comprise 577 documents from 1996 to 2021, published in 213 data sources. The retrieved documents have an average of 7.18 years from publications, 69.23 mean citations per article, and 7.472 average citations per year. A total of 38,588 references have been used in the documents. The collected papers have 8106 keywords plus index keywords, 1892 author keywords, 2418 authors, and 2925 author appearances. Among the articles extracted, 18 are single authored, and 2400 authors have appeared in multi-authored documents.

Table 1 Key evidence of FTP study in Scopus database
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The number of publications on the FTP during the last 25 years is shown in Fig. 2. It is apparent that the research study has grown continually and started ascending after 2007. A handful of studies have been done before 2000s, and a continuous rise in the research is recorded since early 2000s, with the highest number of publications in 2016. The growth trends indicate that although FTP research has old roots, significant attention has been gained for two decades. The three main phases deduced from the growth trend are the stagnant, fluctuation, and booming phases of the research area. Before 2001, there was a stationary phase as the number of publications per year was reported to be insignificant. The study entered a fluctuating phase from 2001 to 2007, as the number of publications fluctuated smoothly around a general trend upward. The changes became sharper after 2007 when the research entered a blooming phase and the number of publications rose from 10 in 2007 to 48 in 2021.

Fig. 2
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The publication growth trend in FTP research

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The growth trends might be associated beyond scientific interest, particularly with catastrophic events such as the sudden decline in the vulture population in the Indian subcontinent (Shultz et al. 2004) that happened due to the increasing concentration of PPCP, diclofenac in the environment. Also, these PPCPs are not easily removed by the conventional WWTPs (Reyes et al. 2021). Hence, they have found their way to the environment, wherein they accumulate (Deblonde et al. 2013; Gao et al. 2012) and persist in the background for months and years, causing detrimental effects on the ecosystem (Monteiro and Boxall 2009).

Thematic areas of FTP study from 1996 to 2021

The thematic areas are linked to article classification as seen in Fig. 3. Environmental science tops the category with 324 articles published, followed by pharmacology, toxicology and pharmaceutics, chemistry, biochemistry, genetics, and molecular biology, medicine, engineering, agricultural and biological sciences, and materials science and earth and planetary sciences with 175, 108, 74, 44, 32, 28, 27, 26, and 20 publications, respectively.

Fig. 3
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Distribution of FTP publications among ten major research categories

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Data analysis

Bibliometric analysis—citation analysis of the collected FTP literature

Productive and domineering articles

The trend of the study on FTP has rapidly influenced novel publications’ mean and total citations. The mean citations per article and total mean citations per year are depicted in Fig. 4, the citations being rounded to a whole number. It is clear from Fig. 2 that the publication rate increased in recent years, because of which the mean citations/document declined. The mean total citation/year also seeks a similar trend with the mean citations per document till 2019. The critical evidence conferred that FTP research documents have 69.23 average citations/document and 7.472 average citations/year/document. The section analyzes and demonstrates the highest cited articles in the FTP research field. The top 20 most cited papers in FTP can be seen in Table 2.

Fig. 4
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Distribution of mean citations per document and mean citation per year

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Table 2 Top 20 papers with the highest citations in FTP study
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Productivity and dominance of sources

Based on the Scopus data collected, the 577 documents extracted were published in a total of 213 journals. However, 143 journals have had only 1 article published in the study area. A list of the top 20 journals in the FTP is provided in Table 3. These top 20 journals published 51.47% of the total documents. Science of the Total Environment with 74 articles (34.74%) secures the topmost rank among the journals, followed by Chemosphere, Water Environment Research, Water Research, and Environmental Pollution published 28, 23, 21, and 18 articles in the field, thus accounting for 13.15%, 10.8%, 9.86%, and 8.45% of all the publications, respectively. Table 3 also highlights the journals’ “h,” “g,” and “m” indexes.

Table 3 Top 20 most productive sources in publishing research in FTP
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Productivity and dominance of countries

According to Scopus data, 577 articles were published by authors from 66 countries. However, 12 countries published only one article. Table 4 summarizes the top 20 countries involved in the study based on various parameters. The parameters to assess the performance of a country are the total number of articles (NoA) published, possessing single authorship by the country, the number of articles having the first authorship, its H- Index, collaboration among the countries, and the citation analysis. The top five productive countries based on the total number of articles published in the research area are the USA (35.01%), China (12.48%), Germany (9.53%), the UK (8.67%), and Canada (6.59%). A country’s ranking is based on the single authorship (SA), which indicates the number of articles written by a single country. First authorship (FA) shows the number of articles having the first author of the country, the USA, China, Germany, UK, and Canada. The H Index (H-I) of the country indicates the country’s overall performance by the Scientific Journal Ranking (SJR) in the area of “environmental engineering.” It does not particularly relate to FTP. According to H Index, the highest productive countries are the USA, China, India, the UK, and Canada. The collaboration among the top 20 countries is shown in Fig. 5. The thickness of the lines indicates the number of collaborations, and the order of maximum collaboration as apprehended from Fig. 5 is USA-China, USA-Canada, USA-Spain, and USA-UK. The countries located in the center, i.e., the USA imply the highest tendency of collaboration. The countries with marginal positions, such as India and Belgium, indicate their secluded research efforts. The highest ranking based on the collaborations (link and total link strength (TLS)), as seen in Table 4, are the USA, UK, China, and Germany. The parameter link in the table indicates the number of collaborations with other countries in the top-20 list, and the total link strength suggests the total number of documents in which the country has collaborated with all other countries involved in the research of FTP. The countries are also ranked based on the articles’ total number of citations (TC) and the normalized citation score (NCS). The NCS is equal to the total citations of a particular country divided by the mean citations of all the articles published in the same year by other countries. The NCS is of paramount importance as it is a correction of the fact that older articles get more time to be cited.

Table 4 Ranking of top 20 countries based on parameters assessing the country’s productivity
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Fig. 5
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Research collaboration among the top 20 countries

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The growth trend in the research area of the top 5 countries is depicted in Fig. 6. It is observed that, since 2000, the USA is dominating all other countries. A few reasons for the increased research in the USA in the context of PPCPs could be due to increased scientific output and environmental awareness and the search for technologies to take care of the harm posed due to the increasing PPCP concentrations in the environment. The sponsorship information of the research from various countries is tabulated in Table 5. The maximum number of sponsors is from the USA, followed by China. The dominance of the USA here may be because of the strong support of the government of the USA in monitoring water resources.

Fig. 6
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Scientific progress in FTP research of top 5 countries

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Table 5 Top 20 funding sponsors of FTP research projects
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Dynamic authors in FTP research

A total of 2418 distinct authors have published their work in the area. The average count of authors per article is 4.19. Among 2418 authors, 2100 have published only one document, and 18 papers are single authored. Information regarding the top 25 authors in FTP research based on the number of articles (NoA) is tabulated in Table 6, and based on citations is tabulated in Table 7. The top 20 universities/institutes to which the maximum number of authors are affiliated can be seen in Fig. 7, where 40, 38, and 27 authors are affiliated with the University of California, University of Copenhagen, and Ghent University, respectively. Also, the affiliations of the top authors are tabulated in Tables 6 and 7. Overall, USA’ and Spain’s researchers have secured the top 5 positions. Figure 8 depicts the co-authorship network of the top 50 authors in FTP research. It is seen that only 37 authors had collaborations. Tables 6 and 7 also provide co-authorship information of authors, including links, total link strength, and normalized citation score. The top 25 authors’ production over the years can be seen in Fig. 9. The top authors have been active after 2006, and the average publication year of the top 25 authors, along with the H-I index of the authors, can be seen in Tables 6 and 7.

Table 6 Top twenty-five most productive authors in publishing research articles on FTP
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Table 7 Top twenty-five productive authors of most cited articles in FTP research
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Fig. 7
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Top 20 universities to which the authors are affiliated

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Fig. 8
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Co-authorship network among the top 50 dominant authors in FTP research

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Fig. 9
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Top 25 authors’ production over the years

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Data mining-text mining and co-occurrence analysis of the keywords

The 577 articles were analyzed rigorously to identify the evolved themes and research topics. Also, the keywords were analyzed to determine research hotspots in FTP.

Text mining—identification of research themes

The text mining analysis revealed the studies on FTP focused on eight research themes as shown in Table 8. The identified prepotent themes including the PPCPs category, hazardous effects, occurrence of PPCPs, PPCPs in organisms, remediation, FTP-governing processes, and assessment in the environment are presented and discussed in the section.

Table 8 Top seven themes in FTP studies
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The first theme is based on the variety of PPCPs present in the environment. The PPCPs include an extraordinarily diverse class of chemicals employed in human health, agricultural practices, veterinary medicines, and cosmetic care (Barceló and Petrovic 2007). PPCPs can be broadly classified into steroids, personal care products, and non-steroidal pharmaceuticals. The steroids comprise estrogens, progestogens, estrogen antagonistics, androgens and glucocorticoids, phytoestrogens, and veterinary growth hormones (Ebele et al. 2017). The non-steroidal pharmaceuticals incorporate agents used in blood and blood-forming organs, dermatological drugs, antibiotics, analgesics, anti-inflammatories, anti-depressants, and allergy- and asthma-treating agents (Guerra et al. 2014; Ebele et al. 2017). Personal care products (PCPs) include disinfectants, conservation agents, fragrances, and UV screens (Ebele et al. 2017). Synthetic musk fragrances used in inexpensive fragrances, cleaning products, air fresheners, and various hygiene and household products are some PCPs in the aquatic environment. They have recently received growing attention (Smital et al. 2004). Artificial sweeteners have been consumed in large quantities in beverages, food, PPCPs, and animal feed (Gan et al. 2013).

These PPCPs are unique ECs that cause human physiological disturbances and toxicity to the ecosystem even if present in trace concentration (Ebele et al. 2017). Theme 2 pertains to the hazardous effects caused due to these PPCPs. The fragrance materials (Vecchiato et al. 2018), artificial sweeteners (Lange et al. 2012), phenols, and their metabolites (Hammam et al. 2015) have the property of long-range transport and persistence. The phenols, a component in the pharmaceutical drug, reveal peroxidative capacity, being toxic to the nervous, digestive, and reproductive systems. Also, being hematotoxic and hepatotoxic, they cause carcinogenesis and mutagenesis in humans and other organisms (Hammam et al. 2015). Carbamazepine is known to disrupt the expression of the neurotransmitter system in freshwater species (Yang et al. 2018). Diclofenac, a well-known pharmaceutical responsible for the drastic reduction of the vulture population, exceeded the environmental quality standard in the river water (Gimeno et al. 2018). Veterinary antibiotics cause water pollution and are associated with human health and ecological risks (Wöhler et al. 2021). The increasing demand for UV filters/sunscreen used as PCPs has led to its abundance in various geographic locations, leading to an ecotoxicological threat (Astel et al. 2020). The UV filters in environmental mixtures are identified as the prime driver of mixture toxicity since they protract antibiotic contamination of aquatic and engineered environments (Grgić et al. 2021). Some UV filters get adsorbed on microplastics and cause neurotoxic effects. They also induce oxidative damage and accelerate genotoxicity with exposure time (O'Donovan et al. 2020). The excessive use of antibiotics in the environment leads to high levels of antibiotic-resistance genes (Xu et al. 2017). Owing to the hydrophilic nature of PPCPs, they tend to adsorb onto plastic surfaces, hence being found to co-exist with microplastics (Atugoda et al. 2021). PPCPs tend to bioaccumulate, biomagnify, and cause endocrine disruption and eutrophication (Cui and Schröder 2016; Mearns et al. 2019, 2020).

The PPCPs enter the ecosystem via industrial, urban transport, agricultural activities, animal feeding operations, hospitals, and pharmaceutical manufacturers (León et al. 2020; Zhao et al. 2021). They then find their route to the whole ecosystem, be it drinking water (Yee et al. 2021), surface water, wastewater, sediment, sludge, soil, sewage, WWTPs, tissue residues, biosolids, seawater, groundwater, septic systems, wetlands, plants, reclaimed wastewater, and landfills (Ramakrishnan et al. 2015). The studies about the occurrence of these PPCPs in the environment are categorized in the third theme. These PPCPs contaminate surface water along with groundwater. Still, they are primarily present in higher concentration in surface water, indicating the generality of wastewater discharges into the streams, which then acts as the primary pollutant source (Conkle et al. 2010; Llamas-dios et al. 2021; Wilkinson et al. 2017a, b). The PPCPs from WWTPs find their way to surface water (Zhao et al. 2021), and then to sediments (León et al. 2020) and soils at various geographical locations (Stefano et al. 2021). Reclaimed wastewater for irrigation also serves as a contamination route of soil (Qin et al. 2015) and groundwater and then bio-transfers to various living organisms until it finally reaches human receptors (García-Santiago et al. 2017). The PPCPs have been detected in the hyporheic zone, where surface and groundwater meet (Hohne et al., 2021). The PPCPs exhibiting long-range transport may travel and reach the seawater (Vecchiato et al. 2017). Moreover, septic tanks may also contribute to contamination of surface water and shallow groundwater (Yang et al. 2017).

Along with the environment, these PPCPs have been detected in living organisms, including birds, fishes, microbes, mammals, plankton, turtles, algae, and invertebrates (Peng et al. 2018), rats, and nonhuman primates (Mearns et al. 2016, 2018, 2019, 2020; Peng et al. 2018). This has been grouped under the theme PPCPs in organisms.

Various treatment technologies are available for these contaminants, which are covered in the sixth theme. Many of the PPCPs can be obliterated using the advanced oxidation process (Shahid et al. 2021). The anaerobic membrane bioreactors and the microalgae/fungal strains are also promising methods of PPCP removal (Shahid et al. 2021). Electrochemical oxidation and membrane separation are also efficacious in removing these ECs (Shahid et al. 2021). Advanced wastewater treatment technologies such as UV C radiation are useful in degrading antibiotics and minimizing UV filter effects (Grgić et al. 2021). The ethylene and propylene oxide shows a high removal rate in Moving Bed Biofilm Reactors (MBBR) and conventional activated sludge WWTPs (Tisler et al. 2021). However, adequate water treatment technologies for PPCPs are still lacking, and the traditional treatment system comprising the tertiary treatment still needs to be upgraded (Corominas et al. 2021; Dang et al. 2020). Artificial groundwater recharge and bank filtration are prime, effective, and low-cost techniques for treating surface water and microbes, along with organic and inorganic contaminant removal (Heberer et al. 2004).

The sixth theme, fate and transport processes, concentrates on the governing mechanisms of transport and the fate of PPCPs from their source to sinks. The pH and dissolved organic matter affect the FTP in wastewater treatment plants (Zhang et al. 2014). After being released from the source, PPCPs are exposed to various processes such as sorption to soil and sediments, abiotic photolysis and hydrolysis, biotic degradation (Biošić et al. 2017; Khan et al. 2020; Shu et al. 2021), and biotransformation (Navrátilová et al. 2020). The transport of pharmaceuticals occurs via water channels where aquatic colloids and sediments play a significant role in acting as a sink for these pollutants (Khan et al. 2020). The PPCPs are ionizing chemicals that dissociate and have electrical interactions with biota and organic matter in surface water (Trapp et al. 2010). The in-river degradation and deconjugation and the effect of acidity and polarity in the contaminant’s partitioning to suspended particulate matter, photochemical degradation, biotransformation, and dilution are potential fate processes in multiple river systems (Wilkinson et al. 2017a, b). The hydrophobic ECs have the highest concentration and detection frequency possibly because hydrophobic compounds have a higher retardation factor compared to hydrophilic contaminants, which are easily transported by the flow of water resulting in a widespread and homogeneous distribution (Llamas-dios et al. 2021). The hydrophilic contaminants have a higher concentration in the lower basin and tend to accumulate in the groundwater (Llamas-dios et al. 2021). The dissolved organic matter (DOM) plays an essential role in the photodegradation of pharmaceuticals in pure and natural water (Carmosini and Lee 2009; G. Zhang et al. 2017) by forming contaminant-DOM complexes affecting the environmental transport of PPCPs (Hernandez-Ruiz et al. 2012). Season plays a significant role in the concentration of PPCPs detected in surface water (Cantwell et al. 2016). The ability of PPCPs to be retained in the surface layer of soil depends upon the background concentration, soil characteristics, pH, solubility, pKa of a compound, and soil organic content (Hari et al. 2005; Stefano et al. 2021; Revitt et al. 2015; Wegst-Uhrich et al. 2014). The FTP of ionizable organic contaminants in the subsurface is influenced by soil pH, concentration, clay and organic matter type (ion exchange capacity), soil’s strength as a base or acid (acid dissociation constant), the lipophilicity (n-octanol water partition co-efficient), soil aeration, temperature, moisture content, emission mode (continuous or episodic), and the pattern of pharmaceutical use (Lees et al. 2016). Some PPCPs have high retention at low pH, possibly due to electrostatic cation exchange and interaction of π-π electron donor–acceptor at pH 3 and cation exchange at high pH 5 and 7. The PPCPs enter the soil via reclaimed wastewater and biosolids; their adsorption may be governed by colloids such as clay, which act as significant transport of PPCPs in the subsurface (** into groundwater and contaminating the latter (Qin et al. 2015).

Cluster 2 mainly focuses on the documents based on the “processes governing fate and transport study” and the “environmental risk assessment” due to these PPCPs. The first group is inclined toward the FTP study in the environment (Atugoda et al. 2021; Ebele et al. 2017; Liu et al. 2019a, b; Vieno and Sillanpää 2014; Westerhoff et al. 2005), and the prime process of FTP study, i.e., sorption (Wu et al. 2016) and degradation (Yu et al. 2013). Abiotic and biotic processes govern the FTP in the environment (Petrie et al. 2018). Photolysis is the main fate-governing process in the surface water, and biodegradation is the prime fate process in the wastewater and soil (Durán-álvarez et al. 2015). Bio-degradation and/or chemical transformation of PPCPs is the key fate process in the WWTPs (Subedi and Kannan 2015). The WWTPs are one of the significant disposal pathways for PPCPs (Richardson and Ternes 2011). The PPCPs present in the liquid phase in WWTPs can be effectively removed by sorption to suspended particulate matter or sludge, transformation, or biodegradation to increase the sludge retention time (Snip et al., 2014; Subedi and Kannan 2015). In the aquatic environment, sorption and degradation (biodegradation and photodegradation) are the chief processes determining the contaminant fate, where sediments and aquatic colloids act as major sinks (Khan et al. 2020). The presence of nitrates, carbonates, and dissolved organic matter accelerates the photolysis of some PPCPs in freshwater (Petrie et al. 2018). Dissolved oxygen (DO) also plays a significant role in the photo transformation of PPCPs (Zhang et al. 2017). The contaminant’s physio-chemical properties govern the FTP in the water–sediment matrix (vapor pressure, solubility, and lipophilicity), environmental situations (temperature, pH, irradiation, and redox situation), and the existing microbial community (Wu et al. 2010; Luo and Angelidaki 2014). The volatile PPCPs exhibit long-range and short-range (local) contamination, thus causing a threat to the polar regions as well (Mandaric et al. 2019). Atmospheric deposition and photo transformation are the main processes governing FTP in the air (McLachlan et al. 2010). The soil properties and aerobic conditions govern the fate of PPCPs (Koba et al. 2016). Adsorption, degradation, and migration (Sui et al. 2015) serve as the main governing parameters in the subsurface. The persistence of PPCPs and their metabolites in the soil leads to groundwater contamination, causing adverse effects on humans as it is a significant source of drinking water supply in many countries (Koba et al. 2016; Sui et al. 2015). The sources of PPCP contamination in the groundwater include contaminated surface water, wastewater, septic tanks, landfills, sewer leakage, and livestock breeding (Sui et al. 2015). Risk assessment studies dominate the second group of cluster 2 (Picó et al. 2020; Verlicchi et al. 2012). The recent trend for managing contaminants having different physicochemical properties is to follow a risk-based approach. A decision analysis framework that evaluates other remediation options by combining health risks (individual, population, residual) and different costs to deliver the most cost-effective process serves as an alternate remedial measure for the contaminants (Naidu et al. 2016).

The articles related to the physicochemical properties of pharmaceuticals and their carrier post-consumption in humans/animals are dominant in the third cluster. Oral intake of pharmaceuticals for humans is a favorable route to the target site of action. However, water-insoluble drugs are incapable of permeating the gastrointestinal (GI) tract, which requires a carrier/transporter/drug delivery vehicle to deliver them effectively without being degraded using this route (Poonia et al. 2016). Hence several drug delivery vehicles are researched to be of prime importance in drug metabolism, distribution, adsorption, and excretion (Bergström et al. 2016; Evers et al. 2018). The environmental fate of these carriers of pharmaceuticals, e.g., CeO2 nanoparticles, depends on their physicochemical properties (Dahle and Arai 2015). Additionally, various properties of PPCPs, such as log solubility in water (Bannan et al. 2016), log P, polar surface area, hydrogen bond donors, and several hydrogen bond acceptors (Benet et al. 2011) have been discussed. The metabolism of the drugs owing to post-consumption by humans and their physiological fate (Date et al. 2010), their diffusivity through the biological membrane (Camenisch et al. 1998; Neupane et al. 2020), and the human gut wall (Thelen & Dressman 2009) is also discussed. The distribution coefficient between the immiscible aqueous and non-aqueous phases measures the degree to which the small molecules prefer one phase over another at a particular pH (Rustenburg et al. 2016). The most lipophilic molecules are least soluble in water (Box and Comer 2008). Water solubility is the governing factor of drug access to biological membranes (Faller and Ertl 2007). These pharmaceuticals enter the environment via the excretion of humans/animals and pose several risks to the ecosystem. Ionization, intrinsic solubility (log S), and lipophilicity (log P) have a significant impact on the transport properties of pharmaceuticals (Box and Comer 2008). Knowledge about the fate of pharmaceuticals is limited to some compounds; very few lab experiments under controlled conditions mimicking the natural environment have been conducted, and only a few data sets are available focusing on field studies. Thus, sufficient data gaps exist regarding pathways of degradation and transformation processes, making it difficult to understand the fate of these compounds in complex natural systems (Khan et al. 2020).

Implications for research: research hotspot and directions for future studies

Based on the insights provided by the bibliometric, text mining, and qualitative content analysis conducted, the implication for future studies is presented in the section. After attentive consideration, four areas of study are identified as potential gaps in research and directions for future studies to better position the FTP research agenda in line with the PPCPs.

  • The detrimental effects of the PPCPs have paved a path for future researchers to design a robust treatment system for the complete removal of the PPCPs, which is lacking in both developed, develo**, and underdeveloped countries. COVID-19 has led to a surge in the usage of PPCPs either as medication or preventive measures, e.g., antibiotics and sanitizer (Dindarloo et al. 2020), reaching the WWTPs. These PPCPs have entered the drinking water supply via groundwater, which is an alarming situation for humans. Though present in trace amounts, its continuous introduction has reported high concentrations in the various niches of the world (Ebele et al. 2017). Also, the property of persistence and bioaccumulation calls for immediate action. Thus, there is an urgent call for a sturdy treatment system; otherwise, it may result in what the world has witnessed in the form of the extinction of various species from the earth and many disturbances in the whole ecosystem.

  • The escalated use of antibiotics gives rise to antibiotic-resistant bacteria (ARBs) and antibiotic-resistant genes (ARGs) (Koch et al. 2021). The advent of resistance among bacteria and the distribution of resistant genes may lead to an increase in potentially pathogenic and resistant organisms and excessive growth of exogenic pathogens (Rashid et al. 2012). The escalating amount of ARGs and ARBs would lead to the evolution of microbial structure via ecological niche occupation, thus enhancing the enforcement of target selection, which may cause an imbalance in the microbial ecosystem (Chen et al. 2021a, b). Along with the bacterial ecosystem, humans have been affected due to the emergence of ARBs and ARGs. COVID-19-infected patients have shown high prevalence of antimicrobial resistance in the body, which may lead to severe health issues in the future (Ahmed et al. 2022). A call for strict compliance in the usage of antibiotics and employment of antibiotic stewardship programs at private or public institutions is recommended.

  • The FTP studies in a multimedia environment, considering all the multimedia compartments and phases in which the contaminants exist, are also limited. The transformation of the PPCPs from their release, transport, and, finally, to their destination has not been investigated in the true sense for most of the PPCPs. Also, the synergistic effect of the contaminants co-existing in the environment is unexplored. Thus, the researchers have a good opportunity in the field to explore the fate and transport of the PPCPs

  • Several models are developed to simulate the fate and transport processes in a single compartment (air, water, soil, groundwater, STPs, etc.) or in combination. The models may be employed in risk assessment and future contaminant concentration prediction. This may be used in policymaking and as an alternative to control the environmental PPCPs. Unfortunately, there are only limited studies considering all the media in one single model and mimicking the actual scenario existing in the field from the release of PPCPs to its fate. Therefore, there is a great scope in exploring the FTP area.

Conclusions

The study aimed to provide an inclusive map of FTP research over the last 25 years. Based on the bibliometric analysis, the research growth trend has been blooming since the early 2000s, having the maximum research published in 2016. Researchers from 66 different countries contributed to this field, USA and China leading the research area. Since the introduction of FTP research, various themes and topics have been continually added to the research field. An investigation of over 500 publications, along with their citations and bibliographic information, reveals that various ecological disturbances have been observed since the introduction of numerous types of PPCPs in the environment. The orientation of the research in this study ranges from the detection of the PPCPs in the ecosystem to the transport and fate of the PPCPs in the environment and the remediation measures taken for managing the PPCPs in the environment.

Due to the lack of proper treatment technologies, the PPCPs released primarily from WWTPs have found their route to the sediments, soil, groundwater, drinking water, and even biota wherein they tend to bioaccumulate, biomagnify, and cause endocrine disruption and eutrophication. Attempts have been made for the PPCP remediation, ranging from fate and transport models to risk assessment studies, in order to keep a check on the increasing concentration of PPCPs in the environment, which requires an in-depth understanding of the fate and transport processes that these PPCPs are subjected to. The research, after careful review, highlights the critical fate and transport processes occurring in the environment from its sources to sinks. The fate and transport processes in WWTPs are adsorption and degradation governed by factors including the pH and dissolved organic matter. The critical FTP processes in surface water include sorption to sediments and colloids, volatilization, abiotic photolysis, hydrolysis, biotic degradation, and biotransformation of contaminants. DO, dilution, seasonal variations and organic matter are the prime factors that affect the FTP in surface water. The processes of FTP in soils include advection, dispersion, adsorption, and degradation that are governed by key factors including soil characteristics, pH, solubility and pKa of PPCPs, soil organic content, the lipophilicity, soil aeration, temperature, moisture content, emission mode, and the pattern of pharmaceutical use. Volatilization does not significantly affect FTP processes in soil.

Moreover, these PPCPs are ubiquitous and detected in almost the whole ecosystem, and their synergistic effects have attracted significant importance. Thus, there is an urgent need for the remediation of these emerging contaminants, especially after the COVID-19 pandemic, which has lead to an enormous increase in the concentration of the PPCPs and antibiotic-resistant genes and antibiotic-resistant bacteria. In the absence of an effective treatment system, modeling of these PPCPs to forecast their increasing environmental concentration and their risk assessment studies can be an alternate solution to keep a check on the ever-increasing concentration of these PPCPs. Otherwise, there can be catastropic effects in the near future as happened before due to the increase in diclofenac, a PPCP that leads to a sudden decline in the vulture population in the Indian sub-continent. The study will be beneficial to the researchers to gain a prior knowledge of the PPCPs’ fate and transport in the environment, which will further benefit as being the primary step in managing the increasing concentration of these contaminants in the environment.