1 Introduction

Bisphenol A (2,2-bis (4-hydroxyphenyl) propane) is widely used for production of polycarbonates, epoxy resins and other plastics [1]. Its global production exceeds 3.8 million tons per annum [2]. It has enormous resistance to biodegradation and chemical degradation, it is easily found in surface water and industrial waste in high concentrations [3]. Bisphenol A is one of the chemicals suspected to act like hormones in the living system. It has a weak oestrogen-like effect, endocrine, and mutagenic effect and have been indicated as one of risk factor for breast cancer [1, 4]. It can caused obesity, diabetes and cardiac ailment in the human body [2]. BPA also affects plant growth by modifying the level of single endogenous hormones and growth-stress hormone ratios in the roots because of BPA absorption by the roots [5]. Bisphenol A is used in the production of polycarbonate plastics to improve their clearness, production of epoxy resin metal cans, baby bottles, water tanks, food and beverage containers, production of healthcare equipment and kitchenware, Exposure to dietary BPA occurs due to heating of cans during sterilization of food which causes BPA to drip into the can content from the epoxy layer of the wall [6]. An enormous amount of wastewater holding BPA is generated in plastic producing industries and discharged into the environment mainly water bodies, thereby accumulating BPA in the surface water [7].

Several techniques have been innovated and developed for removing Bisphenol A from the environment including bioremediation and conventional physical and chemical approaches [8]. The biological removal of Bisphenol mainly focuses on the use of microbial products rather than the microorganisms themselves. For instance, the use of microbial secreted catalysts such as laccase, lignin peroxidase and manganese-dependent peroxidase secreted by White-rot basidiomycetes offers some advantages including not being toxic, catalytic competence, specificity for substrate and reduced reaction period [9].

The non-biological methods for remediating BPA include thermal degradation, membrane separation, Adsorption strategy and oxidative degradation [10]. Remediation techniques such as adsorption [11] and photocatalytic methods [11] are faced with at least any of the following constraints: slow removal, secondary toxic accumulation and high cost. The adoption of hydroxyl radicals (HO⋅), produced from Fenton or related procedures, are very effective organic compounds [3, 12]. The Fenton method needs an acidic pH environment and is accompanied with mass production of sludge, thereby reducing it practical application [13]. The mixed Fenton process could subdued these weaknesses but has fairly low efficacy considering the reaction time and low H2O2utilization rate [13].

The persistence of Bisphenol A and its remediation challenges necessitates global evaluation of the research into the remediation strategies to enhance formation of novel and globally acceptable strategies that can result in effective remediation. Although several researchers [8, 9, 13] have conducted experiments on various means of remediating the BPA contaminated environment and reported their findings as well as reviews Bisphenol A contamination and its removal, a mixed-method science global mapping analysis of research trends on BPA remediation is still lacking. The present study aimed to map the global research treads on Bisphenol A remediation between 1992 and 2021.

The analyses were based on yearly and country research productivity, most productive researchers and their averaged citations, sole and co-authorship, thematic and keywords evolutions, keywords analysis, authors and country collaborations/networking. Environmental and health impact of Bisphenol A and techniques for Bisphenol A remediation were further discussed under appropriate headings. The present analysis recognises research success, focus and gaps on Bisphenol A removal approaches and techniques and offer the researchers in this field the resources needed to identify present and future research priorities. This study will be helpful to policymakers and government in the allocation of funds for Bisphenol A remediation. The study found a global growth in BPA remediation research with more research output from advanced countries and few from developing countries.

2 Materials and methods

2.1 Data synthesis

Primary studies published from 1992 to 2021on Bisphenol remediation elucidations were sought in Scopus, PubMed, and Web of Science databases. PubMed is best database for biomedical sciences, Scopus host largest literature and web of science has the best quality. In this study we harnessed the strengths of the three databases. Data were retrieved from the databases with title specific algorithm enlisting ‘Bisphenol* AND (removal OR remediat* OR bioremediat* OR biodegrad*)’. Records were filtered to publication/document type, ‘article’ in WOS and Scopus and by ‘NOT review’ in PubMed. In all databases, documents in year 2022 were excluded for reproducibility. A total of 1376 (WOS = 557, Scopus = 561, PubMed = 258) documents retrieved from the database were pooled together in Rstudio for duplicate removal and data normalization using the bibliometrix package [14]. An initial pre-processing resulted in 709 duplicated documents removed leaving 667 articles. There was further processing to remove other non-primary articles unavoidably introduced by the lack of a primary article-specific filter in PubMed. In all, there were 640 articles as the final dataset for the analysis. The 640 datasets were analysed for trend, explanatory attributes, and productivity metrics in R Version 4.2.1. The hybrid quantitative and qualitative analyses (mixed methods) included explanatory analyses such as annual production, average citations/article and (co)-author metrics (i.e., collaboration index, authors’ appearances, authors count, (co-)authors/article, articles/author, and single-/multi-authored articles), productivity metrics of the top twenty-three authors/entities (nations, institutions, and sources) and the linked h-index and/or citation rate was further assessed. Finally, the thematic areas in BPA’s remediation research were determined qualitatively using unsupervised k-means clustering of the author-keywords via co-word analysis, metric multidimensional scaling or multiple correspondence analysis [14]. Thematic evolution of BPA remediation was evaluated based using simple centre co-word algorithm [15, 16]. In all approaches in the thematic areas and thematic evolution, Porter’s stemming algorithm was implemented to stemmed inflectional terms to their roots [17].

3 Results and discussion

3.1 Research output trend on bisphenol removal

Table 1 represents a summary of information on Bisphenol A remediation studies retrieved from Scopus, Web of Science and PubMed. A total of 640 documents comprising 625 journal articles, 2 book chapters, 11 proceedings, 1 English abstract and 1 evaluation study were published in the three research databases considered from 1992 to 2021, corresponding to the search terms “Bisphenol* AND (removal OR remediat* OR bioremediat* OR biodegrad*)”. These studies were published by 1903 authors with 2.07 authors/article and 0.336 article/author, 4.31 co-authors/article, and a collaborative index of 2.99. The collaboration index which shows a great partaking of co-authorship per document [18] is low here. While 1899 of the authors were involved in multi-authored documents, only 4 were involved in single authorship. The average citation of each document and average citations per year per doc stands at 29.5 and 4.3. Research productivity surged from 1 article in 1992 to 93 articles in 2021. Bibliometrically, the quantity of manuscripts published on a specific topic signifies the research output on that topic [19]. An annual growth rate of 17.35% recorded indicates a broad research effort on Bisphenol removal and bioremediation from 1992 to 2021. The collaboration on bisphenol and related contaminants is expected to grow due to continuous incessant global Bisphenol contamination and the unrelenting curiosity of the governments and relevant organisations to overcome the challenges of environmental degradation in general [20]. Teamwork in scientific studies is now a days becoming a norm prompted by the interdisciplinary nature, complication and high cost of modern scientific research [21].

Table 1 Summary of information retrieved on Bisphenol, 1992–2021
Full size table

The funding bodies nowadays integrate research collaboration as condition for awarding research grants [22]. Collaboration among researchers is encouraged to cross-fertilize research ideas across specializations, yearning to gain skills and expertise or mentoring new scientists as well as the need for a sophisticated instrument in environmental remediation research [23]. The increase in global production of BPA (about 5 million tons per year) should attract research interest in BPA remediation, thus calling for the emergence of new researchers in this field across the globe [24, 25].

3.2 Annual research trends

Figure 1 depicts the annual research productivity and average citation of published articles per year on Bisphenol A removal from 1992 to 2021. As earlier mentioned, the annual growth rate stood at 17.5%, indicating that studies on Bisphenol A remediation are increasing over time. Although only 5 studies were reported between the years 1992 and 1999 with some of the years witnessing no publication, the number of research reports began to increase from 2000 to 2010 but was steadily low (1 to 14 articles). A firm surge in research productivity was recorded from the year 2011 (27 publications) and peaked at 93 articles in 2021 accounting for 14.53%). The average total citation correspondingly swung across the years under review but peaked at 9.12% in 2018. The increased research on Bisphenol A (BPA) remediation can be attributed to both scientific and societal concerns such as environmental or ecological effects, endocrine disruption and other health effects as captured in the later part of this work, Government’s regulations on dangerous chemicals user and community Awareness, general increased in global research Alliance, general advancements in technology, multidisciplinary approach to remedy pollution, Sustainable Practices and Green Chemistry [10, 26].

Fig. 1
figure 1

Annual research output on Bisphenol from 1992 to 2021 and annual mean total citations per year. The productivity continue to surged over the years and peaked to 93 articles in 2021

Full size image

The highest articles of 93 still appear low in comparison with publications on related contaminants such as arsenic, the annual research output trend on BPA removal is expected to continue to surge rapidly due to increasing global interest in the elimination of BPA contamination, global interest in environmental remediation, improved laboratory facilities and increase funding support for research in general [25, 27].

3.3 The top prolific researchers on Bisphenol removal

Table 2 shows the list of the top 20 authors on BPA remediation. Zhang whose first publication appears in the year 2006 tops the list, he authored/co-authored 23 documents (3.59%) and recorded h-index of 15 with a citation of 1001. Liu who came second began his publication in 2009, he authored/co-authored 21(3.28%) articles with a total citation of 760 and an h-index of 13. Wang who started writing on BPA removal in 2011 published 17 (2.66) with a total citation of 419 and an h-index of 10, thus occupying the third position. Chen et al. shares the 7th position with each having 13 (2.03) articles and 319, 476, 500 and 399 citations, respectively. Although Zhou started publication lately in 2010, he has the highest citation of 884 and occupies 6th position considering the number of articles 14 (2.19).

Table 2 Topmost 20 productive authors on Bisphenol remediation studies from 1992 to 2021
Full size table

A further in-depth study revealed that most of these top authors are concentrated in developed and industrialized nations such as Japan, China, USA and South Korea. Few of these top authors come from emerging countries such as Malaysia and India, an equivalent trend of general research productivity from such low-income nations.

3.4 Most cited articles on Bisphenol remediation

Citations are not a seamless index to appraise a researcher's influence in a given area of specialization [23]. The journal type (close or open access) as well as the indexing of the journal in which an article is published can affect the number of researchers who reads and cites the article. Self and erroneous citations can give the wrong metrics, and the petite number of articles used can positively impact the topmost cited articles. Researchers based in underdeveloped nations has little or no contact with closed-access journals especially if their affiliations lack enough funding that could enable them to subscribe to relevant article databases [28]. As depicted in Table 3, the 5 topmost cited documents were published in the years 2015, 2005, 2016, 2018, and 2009. Similarly, articles published from 2017 to 2018 also made the list of the top 20 most cited articles. Thus, the progressive tendency of the citations suggests that they accumulate over time. The documents published in recent times would not have sufficient time to attain much citations because citations grow with year [29].

Table 3 Most global cited documents on Bisphenol remediation from 1992 to 2021
Full size table

The overall citations of the topmost 23 articles ranged from 365 to 109 and the total citation per year of between 45.6 to 27.3. The majority of the articles were published in environmental-based journals such as Applied Catalysis B: Environmental (4 articles), Water resources (2), Environmental Science and Technology (3 articles), Applied Environmental Microbiology (1 article), few of the articles were published in chemistry and toxicological based journals such as Chemical Engineering Journal (3 articles), Chemical communication (1), Chemosphere (3 articles), Journal of Hazardous Materials (2) and Environmental Toxicology and Chemistry(1 article). Others are the Journal of Colloid and Interface Science (1) and Bioresource Technology (1). Most of the topmost cited documents focused on oxidative elimination of BPA, fabrication of novel products and composites that enhance BPA removal from water as well as immobilization of enzymes and use of activated carbons for removing BPA. For instance, in the topmost cited document, Sharma et al. [12] used a sulphate radical-based innovative oxidation process that adopts activated peroxymonosulfate (PMS) as an oxidant to eliminate BPA and achieved 96.7 ± 0.05% removal at the optimized conditions of the operating parameters (initial pH of 5.15, temperature of 29 ± 3 ˚C PMS dose of 0.66 mM). Bautista-Toledo et al. [3], the second most cited article, investigated the performance of dissimilar activated carbons in the removal and adsorption efficiency of BPA from water and related the removal efficiency to the chemical nature of the carbon surface and the pH of the liquid medium. Some other most cited articles [8, 11, 30] immobilized laccase to removed BPA from aqueous solution, synthesized superoxide radical and singlet oxygen from PMS to achieved 99.3% BPA removal and fabricated a three-dimensional hydrogel of titanium dioxide (TiO2)-graphene to remove BPA and achieved over 90% efficiency after 10 cycles.

Some of the topmost cited articles also applied bioremediation as an efficient way of removing BPA. Lobos et al. [31] isolated a new bacterium tagged strain MV1 from plastic wastewater sludge and used it to effectively achieve BPA removal. Tsutsumi et al. [32] extracted peroxidase and laccase from a lignin-degrading basidiomycetes and used it to degrade BPA and nonylphenol (NP). Other researchers such as Yüksel et al. [33] and Mu et al. [34] used nanofiltration, reverse osmosis membranes and other separation techniques to achieve BPA remediation. The coverage of various novel remediation techniques and innovations by the most cited articles on BPA removal can be linked to the general advance analytical instrumentation and advancement of pollution detection and remediation.

3.5 Top prolific countries and academic institutions on Bisphenol remediation

Table 4 shows the research output on BPA removal and remediation for the 20 topmost productive countries. China (n = 267, 41.7%), Japan (n = 53, 8.3%), USA (n = 33, 5.2%) and Korea (n = 28, 4.4%) occupies the first to fourth position considering the total number of published articles and overall citation. Iran, India, Poland and Malaysia occupy 4th to 8th positions with 27, 23, 23 and 20 publications and 788, 607, 441 and 299 total citations, respectively. Brazil, Turkey, Spain, Singapore, Thailand, Canada, Argentina, France, Saudi Arabia, Australia and Finland occupies positions 9th to 20th. China is also the topmost country in terms of both single country publications (236 articles) and multiple country publications (31) followed by Japan and Korea in terms of single country publications and the USA and Malaysia in terms of multiple country publications.

Table 4 Top productive countries on Bisphenol A remediation research from 1992 to 2021
Full size table

The leading role of China in BPA remediation studies is not unconnected with a high number of BPA-producing industries in China, high investment in environmental remediation to maintain a safe environment in a highly industrialized countries and a recent general surge in number of scientific researchers from China [28, 35]. Moreover, the economic and financial growth rate of a nation has been implicated in directly influencing its research outputs because the universities and other research institutes largely depends on funding from the governments and companies to fund their research [36]. China and Japan had 0.43 and 0.08 frequency of publication, other topmost countries have between 0.01 and 0.05. Asian countries found in the list included Japan, China, Malaysia, Korea and India while only South Africa and Algeria are the only African countries found in the bottom of the list of the top 20 countries in terms of citation. This may be due to general low research output from Africa that is attributable to lack of adequate funds, laboratory facilities and low number of researchers,

The elevated level of BPA contamination in developed and developing nations and the accessibility of research funds from government agencies and industries could serve as the motivating factors for the researchers in these countries to carry out more research on how to remediate this contaminant. In addition to the worthwhile budget for research, economic status, availability of modern facilities and available research sponsorship, the research productivity in these countries can be linked to a growing collaboration with relevant organizations across national boundaries [36]. China, Japan and the USA have been reported to play dominating roles in research that focus on global challenges [28, 37]. Factors such as stable and itch free government transitions intercontinental collaboration, and progressive economy which are common in these countries also determines a country's prominence in research [38].

3.6 Top relevant academic institutions

The topmost academic institutions associated with BPA remediation and the quantity of documents they produced are as shown in Fig. 2. Harbin Institute of Technology, China tops the list with 23 publications followed by Research Centre for Eco-Environmental Sciences, University of Chinese Academy of Sciences Institute of Environmental Assessment and Water Research and Rwth Aachen University with 21, 19, 18 and 18 articles respectively. Guangzhou Institute of Geochemistry and University of Cincinnati each has 17 articles, Tsinghua University and University of Quebec has 16 articles each, while other topmost affiliations published between 14 and 10 articles.

Fig. 2
figure 2

Topmost academic institutions linked to Bisphenol A remediation from 1992 to 2021

Full size image

Academic institutions from Asia particularly China dominate the top relevant academic institutions affiliated with Bisphenol remediation-related research. The dominance of Chinese institutions in Bisphenol removal research may also be driven by environmental pollution fears in China, strict regulations, health factors and China’s desire to participate in global efforts of eliminating recalcitrant pollutants [26]. These corroborate the earlier finding in Table 4, which shows China to be the topmost country that has reported research findings on BPA remediation. In addition, China has major BPA manufacturing industries such as Lanxing Epoxy Plant, Chang Chun Petrochemical, Shuangfu Fine Chemical and many more as reviewed in the work of Huang, Wong [39], thus making China the largest growing BPA market in the world.

3.7 Keywords co-occurrence, conceptual framework and thematic evolutions

The keyword co-occurrence in BPA remediation studies is as depicted in Fig. 3. Each circle-coloured node depicts a specific keyword. The magnitude of the nodes (keywords) depicts the frequency of their occurrence in BPA remediation research, the edges indicate co-occurrence linkages of the words with one another, the colours of the nodes signify co-occurrence clusters. The stiffness of the lines between any two words shows the level of co-occurrence. Forty-eight (48) relevant keywords were encountered during this bibliometric mapping on BPA remediation. The most prominent keywords were Bisphenol A followed by adsorption as indicated by the two bold nodes (Fig. 3). Other relevant words include biodegradation, peroxymonosulphate, immobilization, endocrine disruptors, wastewater treatment, water treatment, membrane bioreactor, endocrine disrupting compounds, peroxidase, removal, activated carbon, photocatalysis, sorption water purification, etc.

Fig. 3
figure 3

Keywords co-occurrence on Bisphenol A removal research from 1992 to 2021

Full size image

Most journals make it an inevitable requirement for authors to provide not less than 5 keywords that captures the major contents of their work when submitting their manuscript for consideration.[40]. The keywords are provided beneath the abstract of the manuscripts. This helps to streamline the quest for documents online and help the journal managers to identify relevant manuscript assessors or referees. This also help to show the research progression in a particular field of study, especially on the Web of Science or Scopus [28, 41].

In the present study, the frequency of reappearance of the keywords was employed for comprehending the trend of publication on BPA remediation. The utmost pertinent keywords associated with BPA remediation articles mirror the research climax from 1992 to 2021 as reviewed. These keywords indicate that the greatest and persisting challenge of BPA contamination is associated with water as signified by the occurrence of the words such as wastewater treatment, water treatment, water purification, activated sludge, biochar and membrane bioreactor. This is because water acts as the major route of contact for humans with most pollutants [42]. Other co-occurring words such as peroxymonosulphate, photocatalysis, nanocomposites, persulphate and carbon nanotubes are associated with BPA remediation strategies and fabrication of novel products that aid BPA remediation as earlier detailed in most cited articles. These words also reflect BPA co-contamination with other pollutants and the research efforts to achieve their effective remediation strategies in general. This is strengthened by the common conceptual outlined co-words depicted in Fig. 4 such as catalysis, carbon nanotubes, immobilization, sorption, removal and oxidation. The popular conceptual frames in recovered documents measured by K-means clustering show the research on BPA remediation focuses on the use of photocatalysis, sorption, immobilization, oxidation–reduction and use of enzymes such as laccases. The conceptual framework also focused on the effect of Bisphenol A on living organisms as indicated by the concepts; endocrine disrupting compounds, endocrine disruptors and estrogenic activity (Fig. 4).

Fig. 4
figure 4

Common conceptual frames linked to Bisphenol A remediation. The 640 retrieved documents showed

Full size image

The evolutions of the theme of BPA removal studies from 1992 to 2021 are as represented in Fig. 5. Themes such as Bisphenols, Bisphenol a (bpa), Bisphenol a, Bisphenol-a, absorption and host–guest interaction were common from 1992 to 2015. This points toward the fact that the research focus then was basically on recognising Bisphenol contamination (theme Bisphenol), its effect on living forms (theme host guest reaction) and how to conventionally remove Bisphenol through absorption (theme absorption). Between 2016 to 2019, the themes evolved to include themes such as Bisphenol A, emerging contaminants, biodegradation, adsorbent, betacyclodextrin, peroxymonosulphate and anthracite particles. These themes indicate that the research focus shifted from basic knowledge on Bisphenol A contamination and its effect on living forms to novel removal strategies that included biodegradation, fabrication of novel products like or using betacyclodextrin, peroxymonosulphate and anthracite particles that facilitate BPA removal. In the last two years (2020–2021), the theme evolved to include activated carbon, photocatalysis and removal mechanisms. This signifies further research focusing on the use of activated carbon, photocatalysis and more novel removal mechanisms. Recent and general research themes on the removal of pollutants such as bioaugmentation, phytobial remediation, phytoremediation, bioflocculation and bioflocculant cationization, Nano phytoremediation, biostimulation and genetic alterations of microbes and plants as alternative approaches for remediating Bisphenol contaminants were not captured due to their low appearances.

Fig. 5
figure 5

Thematic evolution on Bisphenol A removal research from 1992 to 2021 two K-means clusters that reflects concepts regularly linked to BPA remediation

Full size image

3.8 Authors and collaboration networks on BPA remediation

To further comprehend the research progress on BPA remediation, author’s collaboration and country’s collaboration network were analysed using authorship and corresponding authors' countries as the inclusion criteria. The author’s collaboration network is portrayed in Fig. 6. Each node stands for an author. The magnitude of respective nodes (authors) indicates the rate of their involvement in co-authoring articles, the edges represent co-author relationships while the node colours signify collaboration groups. The line between the authors shows the collaboration path while thickness of the line signifies the magnitude of involvements in the collaborations. The authors’ network covers 46 nodes (authors) with Zhang Y, Li Y, and Liu Y being the prominent authors as indicated by their nodes. These 3 authors participated in more articles than others. This is presented in Table 2 which lists the 3 authors as the topmost productive researchers considering their research output and citations While Zhang and Liu have authored/co-authored 23 documents (1001 citations) and 21 documents (760 citations) Li Y had 16 documents (502 citations), respectively.

Fig. 6
figure 6

Authors’ collaborations on Bisphenol remediation. Each node signifies a different author’s collaboration. The connecting lines represents collaboration paths. The number of lines from the nodes signifies the number of co-authorships

Full size image

The country collaboration network is depicted in Fig. 7. The country collaboration involves 30 nodes (countries) with 9 clusters. The countries include China, Japan, Malaysia, Korea, India (Asian countries) South Africa, Egypt, Morocco, Tunisia and Nigeria (African countries). Other countries involved in collaboration includes Canada, Italy, France, Saudi Arabia, Germany, USA and Finland. The results depicted in Fig. 7 revealed China to be the most prominent country as indicated by the size of the node. China appears in the largest cluster that involves other most productive countries such as Japan, USA, India and Korea. Looking at the 30 countries involved in collaboration, a few of them only collaborated with one country as indicated by the collaboration pathway. For example, South Africa, Israel, Italy, and Spain only collaborated with Iran, Singapore, the United Kingdom and Algeria, respectively. Previous studies have shown the collaboration networks among authors from developing countries and developed countries to be generally low [28, 43, 44]. The collaborations among researchers living in advanced nations like the United States, Japan and China has generally stayed high, collaborations with and among developing and less developed countries appears very low. Research collaborations are capable of nurturing high-level expertise, division of labour and utilization of enough resources and skills to overcome global and pressing challenges that require research attention [28, 45].

Fig. 7
figure 7

International collaboration networks on Bisphenol remediation. The nodes signify dissimilar countries while the length of the nodes represents the strength of a country in collaborating with other countries. The lines indicates collaborative path among the countries

Full size image

4 Environmental and health impact of Bisphenol A

4.1 The environmental impact

Globally, it was estimated that, in the annual production of 6 billion pounds of products, Bisphenol ranked as one of the utmost applied substance for producing polycarbonate plastics and epoxy resin [46]. BPAs are stable, bio-accumulative and highly durable compounds capable of degrading ecological setup and affecting human health [1]. Due to its high prevalence, it is common to encounter it in the environment. The major route of contact with BPA is leakage of the interior coating site of canned materials that provide protection [4]. These canned items include polycarbonate water bottles, preservative vessels and toddler bottles. BPA can also be found in different products such as toys, nail polish, lotions, soaps, shampoo, electric instruments, automobile paths and tires. The refluxing of plastics was also reported to produce a galore quantity of BPA in the environment [6].

The major determinant of BPA leaked from polycarbonate containers into liquids are temperature and soil types [47, 48]. The entire half-life of BPA in the soil is solely dependent on these two determinants. Mostly, BPA gets degraded in the soil with a range period of 1 to 10 days, but in freshwater settings, the accumulation vis-à-vis degradation is quite minimal. It was reported that BPA took 4.6 days to be degraded under aerobic conditions. Though BPA is not a fast-accumulating chemical, its availability in the environment signals a strong need for its reduction in an urban environment and encourages the use of recycling production [49].

4.2 Bisphenol A induced toxicity in reproduction systems

According to the report of Ma et al. [50] BPA causes sterility in both males and females by slowing down the control of sex hormones in the body. It was also reported that BPA toxicity causes a decline in the amount of cortisol in the serum vis-a-vis increasing the level of progesterone and luteinizing hormones in the body. The differences in the thickness of the endometrial wall in women were due to BPA toxicity [51]. Women in the age range of less than 37 years had a strong relationship in the level of BPA in urine and wall of endometrial thickness. Moreover, women of the age category greater than 37 years revealed a negative correlation.

4.3 Bisphenol A induced toxicity in growing systems

Previous studies have informed that early contact to Bisphenol A in offspring causes mental retardation in offspring. During puberty, boys and girls were found to contain high levels of BPA [52]. In adult pregnant women, exposure to BPA severely affected the developmental state of their unborn babies. On this note, male children were reported to display some unusual behavior or attitude in school which is a result of the high level of BPA [15]. Sometimes, the effect of BPA in children is asymptomatic during postnatal exposure. Moreover, during prenatal, they mostly expressed behavior like anxiety, mode swing, lack of sleep and epileptic depression [53].

4.4 BPA induced metabolic disorders

High exposure to BPA was reported to interfere with the activity of neuroendocrine function and several problems in the metabolic system [1]. For instance, a study conducted on some men indicated that the level of BPA is equal to the concentration of glucose in plasma thereby simplifying the accumulation of sugar for the immediate development of type 2 diabetes [54]. An investigation by Barboza et al. [7] revealed that BPA causes injury in the axial muscle leading to the rudimentary swimming capacity in zebrafish larvae. Other effects include impaired enzyme activity, gene damage and chromosomal disorder [55]. It also affects the endocrine system by clipping receptors located in the thyroid hormone thereby suppressing the thyroid hormone transcription [56]. Future research can be conducted to investigate the relationship between BPA-induced thyroid expression and ecological responses such as growth, behavior and development. As a result of the magnitude of the negative effect of BPA, countries have taken the step of providing strict regulatory policies. For example, France was reported to ban the use of BPA in polycarbonate bottles used for infant feeding. The USA through its food and drug administration has also issued a banned policy on BPA from baby goods. Canadian minister of health suggested that general guidelines need to be in place to minimized the situation [57].

5 Techniques for Bisphenol A remediation

Due to the clear understanding of how BPA has severely affected our environment and as well as the public health sector, researchers have delved into finding a lasting solution to reducing its impact. Some of these methods of remediating BPA include thermal degradation, membrane separation, Adsorption strategy and oxidative degradation.

5.1 Thermal degradation

A study reported by Tian et al. [58] discovered that BPA can be degraded via thermal degradation. In their study, they reflux a combination of bass and fish fillet in the bath at a temperature of 100 °C for 60 min. Results obtained using ultrasound-aided extraction and high-performance liquid chromatography coupled with quadruple time of flight mass spectrometry (HPLC-QTOF-M) revealed about 33 and 35% removal of BPA in incurred and spiked fish respectively. Furthermore, degradation was not observed in the water model signifying that the breakdown of Bisphenol A is majorly depends on matrix.

5.2 Membrane separation

Membrane separation is another tool used for BPA removal from the environment [59]. Several researchers reported that this method is efficient due to its low cost, easy operation and produce clear effluent [60]. Examples of such methods are reverse osmosis and nanofiltration and both have low permeability and retain a large amount of BPA. Moreover, some emerging novel membranes have been developed [61]. For example, β-cyclodextrin (β-CD), a modified graphene oxide (GO) nanosheets-based AF membrane been shown to have a high capacity of BPA removal the conventional reverse osmosis and nanofiltration accounting for ~ 100% capability to regenerate when clean with ethanol [61]. Also, the piezoelectric membrane was developed using SnS2 nanosheet coated carbon nanofibres (CNFs) by Tian et al. [58]. The new synthesis generates a hydroxyl free radical that could provide better BPA degradation than the aluminum-made one.

5.3 Adsorption strategies

In the last five (5) years, research trend has indicated a clear trend of improved speedy adsorption of Bisphenol A from water, soil and wastewater. The common adsorbent used is activated carbon because of its physical nature and ability to be modified for enhanced function. For example, heteroatom modified with N, S, and B has been shown to capture BPA with enhanced adsorption ability within a short equilibrium time [62]. The doped modification provides a positive effect because of the elevated electronegativity of the doper atoms and its equivalent size to C. The study of Zhong et al. [63] fabricated a recyclable magnetic covalent organic framework with β-ketoenamine linkage (Fe3O4@COF(TpPa-1)) that showed 1220.97 mg/g BPA adsorption. The principle underlining the BPA removal was due to the availability carbonyl functional groups and amine in TpPa-1. Furthermore, Allam et al. [64] investigated the effect of the newly developed N-NiO@N-Fe2O3@N-ZnO nano metal oxide framework for BPA removal and the results show 96% removal in 80 min at an administered 100 mg of the nano-sorbent. Again, a modified form of Iron-clay-cyclodextrin composite has been demonstrated to show adsorption of over 90% of BPA.

5.4 Oxidative degradation

In an aquatic environment, photocatalytic oxidation is a cheap and eco-friendly approach for BPA removal. For instance, Li et al. [65] created a MIL-88B (Fe)/persulfate/visible light system for photocatalytic degradation of BPA. The results show that the new synthesized product could degrade BPA at a rate of BPA (0.107/min). Such efficiency was due to the formation of several reactive species (SO4-⋅, O2-⋅, OH⋅) in galore amount capable of providing better results. Similarly, an efficient BPA degradation was reported by Oguzie et al. [66] when they fabricated cobalt-ion activated peroxymonosulfate. The synthesis attains a degradation efficiency of 100%. A photoelectrocatalytic and SO4-based technology was used by Zhang et al. [42]to report 100% degradation efficiency in 90 min time.

In another study conducted by Gan et al. [67], a complete degradation of 0.025 mM of BPA within 10 min was reported when using 0.5 g/L of δ-MnO2 impregnated with Kenaf carbon fiber (KCF). The mechanism behind it is that the KCF graphite structure facilitates higher electron transfer between δ-MnO2 and BPA leading to the degradation effect. Zorzo et al. [68] in their attempt to improve the economy of the oxidation process, utilized a UV-solar/H2O2 system. Results indicated that 89.2% BPA was degraded at optimum conditions of pH (5.0) and H2O2 concentration (350 mg/L). Wang et al. [69]] synthesized titanium dioxide@aspartic acid-β-cyclodextrin@reduced graphene oxide (TiO2@ACD@RGO) composite capable of releasing O2 and H+ as the dominant reactive species. About 85.6% of BPA was removed by the composite in 60 min under UV radiation via photocatalytic oxidation.

6 Conclusion

This study presents a deep insight and understanding of the global research trends on Bisphenol A between 1992 and 2021. The study found a global growth in BPA remediation-related research with high research outputs from advanced countries and less from emerging countries. China was the most productive country whereas other top productive countries have sought collaboration. The study found low research output from underdeveloped countries. Although prediction of emerging research themes and emphasis in each field of study is hardly possible in a bibliometric evaluation due to the low appearance of recent themes and keywords, the present analysis indicated a recent focus on fabrication of novel products and adsorbents, use and immobilization of enzymes, bioremediation, photocatalysis and optimization of activated carbons to achieve remediation at environmental and biological matrices. The discoveries of the present study will offer the researchers, especially the environmental scientist, the bisphenol emitting industries and the government the opportunity to identify the research trend on BPA removal and major contributors with new scientific discoveries and emerging areas of interest. Such informations could guide the research focus in developing new and cost-effective strategies for remediation of Bisphenol and related contaminants. The findings of this study will also be useful to academic institutions in terms of benchmarking and comparing their performance against peers and competitors. This benchmarking aids in strategic planning, improving research quality, and enhancing institutional prestige and visibility. The findings of this research will also guide the government, research institutes and industries in allocating and awarding research grant to eliminate bisphenol from the global environment. This study provides a first. There is need to bridge the research gap by boosting global collaboration and provision of general and global guidelines and standard operating procedures on BPA detection and removal to achieve a global BPA remediation.

Like every other bibliometric analysis, this study is not free of limitations such as restricted use of only Web of Science, PubMed and Scopus. Articles published in journals that are not indexed in these databases were excluded from this analysis. Other limitations include the use of selected search titles and the inclusion of some categories of articles such as meeting abstracts, short notes and documents written in non-English languages. Furthermore, the detailed contents and results of the articles analysed were not captured in this survey except in a few cases. The recently published documents after 2021 that fall outside the survey period were not captured irrespective of their importance, relevance, contents and citations.