Occurrence, transport, and detection techniques of emerging pollutants in groundwater

Review Highlights

• •Environmental occurrence and transport of emerging pollutants.
• •Transition to portable and in-situ detection techniques.
• •Emergent pollutants removal from waters.

Abstract

Emerging pollutants (EPs) are a group of different contaminants, such as hormones, pesticides, heavy metals, and drugs, usually found in concentrations between the order of ng and µg per liter. The global population's daily city and agro-industrial activities release EPs into the environment.  Due to the chemical nature of EPs and deficient wastewater treatment and management, they are transported to superficial and groundwater through the natural water cycle, where they can potentially cause harmful effects on living organisms. Recent efforts have focused on developing technology that allows EPs quantification and monitoring in real-time and in situ. The newly developed technology aims to provide accessible groundwater management that detects and treats EPs while avoiding their contact with living beings and their toxic effects. This review presents some of the recently reported techniques that have been applied to advance the detection of EPs in groundwater and potential technologies that can be used for EP removal.

Graphical abstract

Specifications table

Subject area:	Environmental Science
More specific subject area:	Ground water
Name of the reviewed methodology:	N.A.
Keywords:	Quantification, Methods, Biosensors, Sustainable management.
Resource availability:	Scopus, Web of Science.
Review question:	How emergent pollutants gets into groundwater? Which are the typical technologies used for it quantification? How can be improved typical technologies? Which new technologies and techniques has been developed in the recent years? How can be treated, and removed emergent pollutants from water?

Introduction: occurrence and transport of emerging pollutants

The presence of emerging pollutants (EPs) such as personal care products, pesticides, endocrine disrupting compounds, artificial sweeteners, pharmaceuticals, as well as products derived from their transformation has gained interest in the last few years. Due to their concentration in the environment (between ngL⁻¹ and µgL⁻¹) these products were previously not detectable and in most of the cases, there was no established concentration llimitsto protect living organisms from these contaminants [1,2]. Due to different human activities, the development, use and emission of EPs have increased [3]. Wastewater and septic systems are considered one of the more important sources of EPs discharges as they often lack the necessary treatment technologies to remove them fully. Leaks in sewer lines, landfills, animal feeding operations, agriculture, wastewater irrigation, leachates, among others, are other potential sources of EPs that enter groundwater [1,4,5].

Groundwater is typically used as a drinking water source, which with the presence of EPs, may represent a risk to human health [6]. Negative effects in humans and animals have been observed after exposure to EP concentrations as low as µg L⁻¹. Some of the reported effects of EPs on health include hormonal interference, genotoxicity, carcinogenicity, endocrine disruption, and immune toxicity [3]. Since conventional technologies are not able to remove these contaminants, and the lack of regulations that control use, and discharges into the environment, many of these contaminants such as pesticides [6,7], hormones [6], pharmaceutical compounds [4,5], cosmeceutical [4], and artificial sweeteners [8,9], to mention some, had been found in groundwater.

According to Stefano et al. [6], the presence of EPs in groundwater is associated with the geology of the aquifers. They discuss that most of the EPs detected were found in a porous aquifer as it allowed the transport of contaminants across its walls. On the other hand, aquifers covered by clay and sediments still have EPs presence but less frequently and in lower concentrations. Lesser et al., [4], mentioned that the nature of the EPs is the factor that most influences the presence and persistence of EPs in groundwater. The reason why some EPs studied in their research were not found in groundwater samples or in lower concentrations depended on their volatility. Bexfield et al. [5], mentioned that in the case of pharmaceuticals and hormones, factors such as consumption trends, human metabolization, and absorption rates were the main contributors to their detection in groundwater. EPs are strongly influenced by geographic location of their use pattern. Li et al. [8], published that some pharmaceuticals, such as antivirals and antibiotics for diseases with an incidence in Africa, are commonly found and in higher concentration in surface and groundwater than pharmaceuticals used in Western countries. In addition, in third-world countries with low family income, personal care products and some daily consumption products such as artificial sweeteners are less frequently used, so their concentration in wastewater is much lower than in developed countries. In this context, in non-agricultural areas, such as residential houses, restaurants, commercial shops, etc., artificial sweeteners have been suggested as a marker of groundwater contamination due to their high concentrations (μg l-1) [8,9]. On the other hand, in agricultural areas, artificial sweeteners can be found but concentration and occurrence will be lower than in rural areas, and others EPs such as pesticides and antibiotics are more likely to be found. Some antibiotics are excreted through feces, where they can remain for long periods of time; in addition, several antibiotics are soluble in water, which is why they have negligible sorption with the soil, which allows them to spread quickly into groundwater. Likewise, pesticides that include various compounds, such as fungicides, herbicides, insecticides, and growth promoters, are introduced to groundwater, where they have been detected in parts per billion (ppb) ranges or even lower due it uses in agriculture practices. The use of these contaminants influences their concentration in shallow waters due to the crop fields; the pollutants migrate to rivers, streams, or hydrographic basins through surface runoff [9].

The detection of emerging pollutants in groundwater has aroused the interest in the constant improvement of detection techniques and technologies that make possible the detection of these compounds. Due to EPs potential effects on human health, it is necessary to develop detection techniques that can identify and quantify compounds in concentrations at least as low as parts per billion, and if possible, even lower. This review presents novel technologies and materials developed to improve EP detection and quantification in groundwater as well as a brief description of treatment methods that can remove different EPs from groundwater.

Existing methods for the detection of emerging pollutants

As previously discussed, EP occurrence in water can be associated with different factors such as the pollutant nature, the environmental conditions, and characteristics. Sample collection is critical to keep the organic/biological molecules desired to detect. In WWTPs the collection method depends on the sample, source, and the influent container collector. When sampling effluents, samples are taken in two steps, first the water is taken by pumping from the source and later the sample is filtered [10]. Sample preparation depends on the following analytical method and the desired molecule detection. Some possible preparations steps include liquid-liquid extraction methods with organic solvents, acidification, centrifugation, filtration [11].

The evaluation of EPs in wastewater samples is generally achieved using chromatography, Liquid (LC) or Gas (GC), coupled with mass spectrometry (MS) techniques [12]. Tandem mass spectrometry is a preferred technique due to its sensibility and selectivity in complex matrices, such as environmental samples, although it is not appropriate when screening in an untargeted approach [13]. Another approach is the use of high-resolution mass spectrometry (HRMS) coupled to GC or LC, which is more selective and sensitive and allows for a wide screening of organic micropollutants [12]. LC- HRMS can identify ions in the sample and includes techniques such as Orbitrap, time of flight and Q-orbitrap. GC coupled to MS is widely used due to its accuracy, although it requires a derivatization reaction which increases the complexity of the analysis and can lead to the degradation or even loss of the pollutant being analyzed. Analyzing water samples can be very complex, particularly when the matrix contains multiple pollutants that share mass-to-charge ratios, elute similarly, and or affect the matrix in a similar manner [13]. Furthermore, point source monitoring systems are needed to provide relevant information in real time about contaminants and its presence. Even though traditional analysis allows for a high sensitivity and specificity, these methods are too expensive, time consuming, require trained personal, need additional sample preparation, and may provide logistical challenges [14], [15], [16]. New technologies are needed to overcome these obstacles. Most efforts have focused their attention on in field monitoring and generally use nanomaterials or biological components to provide sensitive, transportable, environmentally friendly, and dependable detectors (Fig. 1).

Fig. 1.

Comparison between EPs detection with Current vs Emerging monitoring technology. The figure shows different EPs that reach surface and lastly ground water, the workflow and equipment to evaluate water quality. In contrast, portable sensor technology has been studied to overtake the task as affordable, simple and in situ use to monitor EPs. High-Performance Liquid Chromatography (HPLC), High-Performance Liquid Chromatography/Mass Spectrometry (HPLC/MS), Gas Chromatography (GC), Ultra Performance Liquid Chromatography (UPLC), High-Resolution Mass Spectrometry (HRMS), Liquid Chromatography (LC).

As previously mentioned, different works have developed and evaluated a variety of biologic, electric and chemical materials in the construction of sensors that allows a simplified detection of EPs in real time and point source. Table 1 shows an extensive review of the more recently developed techniques for the detection of EPs such as pesticides, herbicides, hormones, pharmaceuticals, heavy metals, persistent organic pollutants, among others, and the detection limit reached by each technique. Most of the reported techniques consist of portable sensors such as biosensors [17], [18], [19] and carbon-based sensors[16,18,20]. Another reported technique is the use of some materials such as covalent organic frameworks [21] or nanoparticles [22], [23], [24], [25], [26], [27], [28] in combination with conventional sensors or biosensors to improve the detection limits. Finally, another option is the application of electrochemical methods such as strips and sensors [14,29]. Moreover, the search of techniques that allow for lower detection limits has prompted the application of the combination of materials and principles, for example the combination of biosensors with carbon dots [18], and electrochemical sensors with nanoparticles or colorimetric devices [15,23,30,31]. These improvements to detection techniques and devices have allowed the detection and quantification of EPs in concentrations of as low as 0.001 pgL⁻¹, which represents a step forward in EP control and the transition to a sustainable management of groundwater.

Table 1.

Recently developed techniques for the detection of EPs in groundwater and its concentration limit detection.

Technique	Contaminant group	Contaminant	Range of detection	Reference
Fluorescent green carbon dots	Pesticides	Diazinon	>0.25	[20]
		Amicarbazone	>0.5
		Glyphosate	>2
Fluorescent carbon dots conjugated with acetylcholinesterase (fluorescent biosensor)	Organophosphate pesticides (µg L−1)	pure chlorpyrifos (CPF), profenofos (PF), and a commercial formulation called Lorsban	0.14–2.05	[18]
Acetylcholinesterase/Carbon Dots Fluorescent Biosensor		pure chlorpyrifos Lorsban	> 0.14
			>2.05
Paper-Based Electrochemical Strips			>1.3	[14]
3D-printed sensor Nanomaterial-enhanced	Herbicides (µg L−1)	Atrazine	> 0.24	[22]
		Acetochlor	>3.20
Porous Pyrolyzed Paper-Based Electrochemical Detector	Nutrients (µg L−1)	Phosphate	> 0.03	[29]
Fluorescent sensor	Persistent Organic Pollutants (µM)	Benzo[a]pyrene	>10 × 106*	[17]
Covalent Organic Frameworks-Functionalized Lanthanide-Doped Nanocrystals		Perfluorooctane sulfonate (PFOS)	1.8 × 10−7 – 0.18	[21]
nano-carbons non aqueous	Aromatic nitro-phenols compounds (µM)	Para-nitro phenol	0–616	[28]
		Dinitro phenol	0–670
		Trinitro phenol	0–412
RIANA solid-phase fluoroimmunoassay	Herbicide (µg L−1)	Atrazine	> 0.155	[19]
		Isoproturon	> 0.046
		Estrone	> 0.084
carbon electrode Aptamer/Carbon Nanodots Screen printed	Hormones (µM)	Estrogens	0.1–1.0 × 10−6	[16]
Combine oxide/silver nanowires and silver nanoparticles			1–90
Carbon conductive ink, Glass varnish-based			0.1–8.0
carbon nanotubes			1.2 *
carbon nanotubes			1.6 *
MIP Coated poly (ANIco-MSAN) s			0.001 × 10−9 –1000 × 10−9*
(TSMEIPs) poly (AN-co-MSAN)			3.6 × 10−6 to 73.0 × 10−6*
Disposable stochastic sensors maltodextrin nanostructures based	Pharmaceutical (µM)	Ibuprofen,	1 × 10−9– 0.001	[27]
		Ketoprofen
		Flurbiprofen	1 × 10−9 −0.010
Electrochemical immunosensor nanoparticles based		Ciprofloxacin (CPX)	0.001 × 10−3–1000 × 10−3*	[23]
Electrochemical sensor with reduced graphene nanoribbons		Sulfamethoxazole (SMX) Trimethoprim (TMP)	0.09	[31]
			0.04
Self-assembled gold nano islands	Heavy metals (µg L−1)	Arsenic (As3+)	> 0.085	[24]
Disposable electrochemical sensors		Cd(II)	17.5 −21.8	[30]
		Pb (II)	8.1–10.4
Paper-based colorimetric devices		Fe, Ni and Cu	100 to 300	[15]
Paper-based electrochemical devices			0.9 to 10.5
Polyester fiber membranes as flexible surface-enhanced Raman scattering substrates	Artificial sweetener (mg L−1)	sodium saccharin	> 0.3	[32]
Graphene oxide-silver nanoparticules composite		Saccharin	> 0.7	[25]
Nanocoated fiber biosensing		Perfluorooctanoic acid	156 – 625 × 10 3	[26]

^⁎mgL⁻¹.

Biosensors use a natural bio recognition element such as the complementarity of nucleic acids, or the specificity of immunological components for the development of assays [22]. One of the advantages that biosensors have over other more robust techniques is the lack of a pretreatment that is normally required when analyzing environmental samples using conventional techniques such as FT- Raman spectrophotometry, Fourier transform infrared spectroscopy (FTIR), different chromatographys, and other colorimetric techniques. Additionally, they can be less expensive than their traditional counterparts as well as allow for real time detection. Biosensors can be used for contaminant monitoring while more sensitive techniques can be used to confirm detection or quantify more accurately if needed [18]. To enhance physical and chemical properties and surface area for the increase of sensor interaction with the analyte, many biosensors use nanomaterials. The two most widely reported mechanisms of detection are optical and electrochemical. Optical sensors reduce the time needed for analysis, are cost effective and allow for point of care detection. Ledesma et al. [17], reported the development of a Benzo[a]pyrene (BaP) sensor that employs the sensitivity of fluorescence spectroscopy and uses the copolymer of 1-(4 vinylbenzyl) thymine (VBT) and vinyl phenyl sulfonate (VPS) to enhance the luminescence of the contaminant. This study proposed an alternative use of emerging monitoring technology (shown in Fig. 1) where detection can occur at room temperature with relatively available and easy to use equipment.

The use of carbon materials has been extensively reported in situ sensors due to their availability and biocompatibility. For example, carbon dots (CDs) are biocompatible, soluble, and easily synthesized [18,33]. CDs generally are semi spherical and smaller than 10 nm and can combine to form amorphous or nanocrystalline structures. They consist of oxygen and nitrogen containing groups which can be modified to other groups that facilitate interaction with the target. Additionally, they can be synthesized from fruit juices and peels. Out of the different synthesis methods, hydrothermal carbonization, a high temperature and pressure method, can be carried out in only one step, avoiding the use of hazardous chemicals. CDs are often used to detect a wide variety of metal ions as Cd²⁺, Pb²⁺, Ag⁺, Cu²⁺, Fe³⁺, Hg²⁺, and K⁺to mention a few [18,33]. Moreover, CDs have been explored for the detection of pesticides. One study reports the synthesis of a CD turn-off fluorescent-based sensor made by a hydrothermally treated cauliflower. The sensor was tested on a real sample of cherry tomato and proved to be sensitive, reproducible, cost effective while also being simple [33]. Gaviria et al. [18], developed a biosensor for chlorpyrifos detection using AChE as its biological sensing element, and CDs and graphene oxide (GO) as a florescent transductor and quenching agent to enhance its optical properties. The sensor's limit of detection was 0.14 for pure chlorpyrifos and Lorsban, and 2.05 µg L⁻¹ for commercial chlorpyrifos. This sensor was selective against other compounds commonly found in drinking water such as other proteins and glucose. The sensor responded strongly to methomyl, a carbamate type pesticide structurally like organophosphates, and slightly responded to cypermethrin a pyrethroid type pesticide, although it could not successfully detect profenofos, another organophosphate [18].

Covalent organic frameworks (COFs) are a material based on a crystalline porous polymer with advantageous physical properties (density, porosity, big surface area), and stability. Upconversion nanoparticles (UCNPs) transform low energy light such as wavelengths near infrared into higher energy forms such as visible and ultraviolet light though two photon or multiphoton mechanisms. UCNPs diverge from other fluorophores as they are auto fluorescent, highly stable, have sharp emission bands and are more resistant to photobleaching. Li et al. [21] proposes a fluorescence approach to detect low concentrations of PFOS using UCNPs combined with COFs. Their approach involves creating a fluorescent probe from the solvothermal growth of COFs modified to allow their deposition on the surface of UCNPs. PFOS, the analytes of their study, quenches the probe fluorescence at varying concentrations. Furthermore, the probe's sensitivity can be enhanced using a surfactant. Black carbon (BC) is an emissive nanocarbon that can be used for detection of contaminants as well as the photodegradation of multiple dyes. BC has been used to sense nitro phenolic compounds (N-PhOHs), a family of compounds that are highly toxic and carcinogenic. N-PhOHs are present in explosives, pharmaceuticals, fireworks, and dyes and in the environment can be found in contaminated soil and water. Fluorescent probe-based method is simple, cost effective, quick and of a low detection limit [28]. The advantage of using gold to formulate nanoparticles (AuNPs) lies in its electrical as well as optical properties. AuNPs can be chemically functionalized with thiols, amino acids among other functional groups through strong bonds, providing enhanced bonding with the target molecule [24].

The use of electrochemical methods is less prone to interference by the turbidity or color of the sample as is common with colorimetric based methods which is preferable for environmental samples. Electrochemical sensors are economical, quick, sensitive, and simple to use. Despite the ease of scalability of bare electrodes, they are often not sensitive enough for their feasible application. In this sense, electrode surfaces are often modifying to amplify signals, and provide antifouling, by different nanomaterials and nanoparticles. On the other hand, these materials are not easily translated into commercial applications [29]. Shimizu at al. [29], reported the construction of pyrolyzed paper-based electrode, increasing its sensitivity using isopropanol to trigger its capillarity abolishing the effect of fouling media [29]. A work by Fuletra et al. [24], proposed a sensor highly selective to As₃⁺ using DTH (1,12-dodecane thiol, 1, 4-dithiothreitol (DTT)). The sensor has an electrode functionalized with APTMS to bond with gold nano islands formed by a bilayer of Au seed with di-thio. This method allowed for easy fabrication and was advantageous over the use of colloidal films as it has an adjustable island density, no DTH agglomeration, and high signal-to-noise ratio (SNR), PDCA (2, 4-Pyridinedicarboxylic acid) was employed to reduce interferences and enhancing sensitivity. The sensor was used to analyze contaminated water samples to corroborate their feasibility [24].

As paper is widely accessible, foldable, light, biodegradable, and inexpensive, it has been widely studied as the support for many in-field sensors [29]. Paper-based sensors have also been recently explored as they have the advantage of being easily disposed of and are of low cost. Paper-based lateral flow immunoassays (LFIA) are an economical, portable, and simple technology that requires no specific training. This technology has been used to detect organophosphorus compounds, pathogens, and glucose. At present their main limitations are their lack of sensitivity. One widely used approach to counteract this limitation is their coupling with other detection platforms of electrochemical, optical, and mass-based nature, with the electrochemical method being the most common. The sensitivity of this method is the electrochemical scanning method, the mechanism of reaction, and the nature of the detection platform. One solution is printing electrodes, but this requires additional steps during fabrication [22]. Even though enzymes are widely used due to their substrate specificity and catalytic activity, they have drawbacks such as their low stability, low activity outside of optimal conditions as well as the high cost associated with purification and storage. To overcome these challenges the use of enzyme mimicking materials has been explored such as in a study by Ruan et al. [22], that detailed a high-performance multiplex herbicide residue sensor using palladium/platinum nanoparticles that simulated an antibody biorecognition element and served as an electrochemical indicator of herbicide residues. They used an electrochemical analyzer to overcome the limitations of a purely colorimetric LFIA system. Additionally, the sensor was 3D printed due to this method's flexibility, low cost, quick and customizable properties. The sensor was used to quantify atrazine and acetochlor [22].

Another paper-based device are screen-printed electrodes (SPEs) which have performances comparable to glassy carbon electrodes when analyzing metals. The advantage of SPEs lies in the ease of their alteration though the conditions of printing and materials used to optimize detection capabilities. On the other hand, they are not suitable for metal stripping analysis as the nature of their electrodes does not facilitate metal reduction at their surface. Also, their surface can easily delaminate during testing therefore, additional steps must be taken when analyzing metals to improve their performance. For example, coating the electrodes with bismuth allows for insensitivity to dissolved oxygen as well as a more environmentally friendly option in comparison to mercury-based electrodes. New conducting polymers have been achieved through the integration of bismuth and carbon nanomaterials for their application in electrochemical sensors. Additionally, materials such as graphitic nitride (g-C3N4) have been reported to be suitable carbon like structures yet their use in electrochemical sensors for heavy metal detection hasn't been widely explored [30]. A study by Zheng et al. [30], employed electrochemical sensors to detect Pb (II) and Cd (II). The sensor electrodes were altered with Bi/g-C₃N₄ materials and Bi nanoparticles to increase sensitivity. The sensors were successfully tested on buffer solution and tap water [30]. Another study by Cioffi et al. [14], developed a sensor out of common office paper, Whatman No.1. This study uses material that is less expensive in comparison to other similar sensors and commonly available. The sensor uses cholinesterase enzymes as its biological element which responds to organophosphates, enzyme-like Prussian blue as an indicator of enzymatic activity and the electrical conductivity of the printed element is amplified by carbon nanoaggregates. This sensor's innovation lies in that it combines all its elements in the same drop. The sensor was tested quantifying paraoxon (ng mL⁻¹) in different matrices as well as in samples from a small farm in Napoles (Italy), the obtained data was corroborated using LC−MS/MS method [14]. Other paper-based detection systems include μPADs that are paper-based microfluidic devices that employ colorimetric detection while ePADs are similar but use electrochemical detection. Silva-Neto et al. [15] created a plug-and-play (PnP) assembly allowing the simultaneous detection of different metals in river water samples. It combines the benefits of both colorimetric and electrochemical detection. Both devices (colorimetric and electrochemical) used paper substrates upon which they added flexible polymers that could be folded according to the desired analysis, their PnP strategy. To guarantee proper connection, reproducibility across uses, and simplify the device's handling, an external holder was 3D printed connecting the ePAD and voltmeter. The same report details the device's analytical performance such as its sensitivity, selectivity, accuracy, and reliability [15].

Treatment technologies for emerging pollutants removal

The need to develop methodologies and technologies for the treatment of groundwater has increased along with the diverse activities that intensify the contamination of groundwater and decrease the availability of drinking water [34]. Currently there are many technologies for water treatment based on reverse osmosis processes, advanced oxidation, adsorption with activated carbon, electrochemical reduction, and ion exchange (Fig. 2). However, these technologies are usually expensive processes to implement and operate on a large scale [35,36]. To overcome these limitations, different emerging technologies such as the use of microalgae, rhizofiltration, and diverse nanomaterials have been developed (Fig. 2).

Fig. 2.

Emerging treatment technologies for the treatment of emergent contaminants in groundwater.

Systems based on microalgae have been found as effective, sustainable, and profitable alternatives for antibiotics and pesticides removal in wastewater. Ferrando & Matamoros, [37], studied a strategy for groundwater treatment with co-immobilized microalgae in different supports for further biodegradation of various contaminants, demonstrating that microalgae immobilized in loofah and foam materials improve attenuation of organic contaminants up to 51%, after 10 days of treatment in a batch study. Microalgae combined with bacteria have been tested in a bioreactor using polyurethane foam followed by a cork filter as a support for the immobilization of the microorganisms. This system proved to be efficient for the removal of nitrates, pesticides such as atrazine and bromacil, and antibiotics such as sulfamethoxazole and sulfacetamide present in groundwater. The prototype presented an attenuation of nitrates of 58%, and up to 95% for antibiotics and pesticides, where biodegradation was the main process identified for the attenuation of the contaminants studied [36].

Rhizofiltration is a phytoremediation method that can positively impact groundwater contamination through its very broad absorption and root precipitation capacity for organic and inorganic contaminants. It also has the advantage that it absorbs the contaminant without degrading it, avoiding the generation of more toxic degradation compounds. To achieve better elimination, easy-to-cultivate, fast-growing plants with a high capacity for accumulating pollutants and low maintenance costs should be selected for this application [38]. A study by Ji et al. [39], showed that the hydroxyl and sulfate radicals activated with ferrous ions (Fe (II)) are highly effective for the chemical oxidation of antibiotics such as ciprofloxacin and sulfamethoxazole. The sustainable use of Graphene Sand Hybrid from the pyrolysis of low-quality dates for the removal of tetracycline by adsorption proved to be profitable and effective with a maximum adsorption capacity of 46.4 mg g⁻¹ [40].

Another promising approach with great research attention are the advanced nanomaterials such as nanoenzymes that have unique physicochemical properties and the ability to catalytically mimic the biological reactions of different enzymes with lower costs, high efficiency, selectivity, and structural stability, which are limiting properties in the use of enzymes in some bioprocesses. These properties have been very effective in the environmental area for the development of detection and remediation technologies for emerging contaminants in water [41,42].

After detection and quantification of EPs, removal technologies for its treatment are key for the transition to sustainable management of groundwater and to avoid EPs transport through the water and trophic chain to human consumption to ensure water quality and avoid their negative effects on health.

Conclusions

Current social and environmental conditions have pushed the improvement of traditional methods used for the detection of EPs in groundwater. Traditional methods are time consuming, expensive and require sample preparation, which limits the identification of sources, monitoring of sites, and early response to the presence of EPs in waters. This review identifies the development of sensors as a promising tool in the monitoring of EPs in waters. Most of the recently reported research has focused its efforts in the use of biological components, carbon based, and nano sized materials in the construction and improvement of sensors, as well as the combination of techniques and materials that reach low detection limits with high specificity.  The ideal method for the detection of EPs should be: i) portable, allowing in site monitoring; ii) cheap, for its large-scale construction and application; iii) not sensitive to interferences, to avoid sample pretreatment; and iv) possessing a low detection limit, able to detect concentrations competitive with conventional technologies. In this sense, future research should continue focusing on the combination of materials, and principles that avoid the usual limitations in order to obtain better methods. Finally, development of new technologies for water treatment focused on the removal of Eps should be a priority area to ensure water security. The new technologies for the elimination of emerging contaminants have to be sustainable, effective, and environmentally friendly. These technologies must remove as much contaminant as possible and recover treated water at a low cost and with low energy consumption. In the same way, the treatments should be able to integrate several elimination techniques to comply with the regulated concentrations. In this case, developed microalgae and nanomaterials biotechnology can be fundamental key techniques for groundwater treatment.

Ethics statements

Not applicable

CRediT authorship contribution statement

Karina G. Coronado-Apodaca: Conceptualization, Investigation, Writing – original draft, Visualization. Sofía E. Rodríguez-De Luna: Conceptualization, Investigation, Writing – original draft. Rafael G. Araújo: Conceptualization, Investigation, Writing – original draft, Visualization. Mariel Araceli Oyervides-Muñoz: Investigation, Writing – original draft. Georgia María González-Meza: Writing – review & editing, Investigation. Lizeth Parra-Arroyo: Conceptualization, Investigation, Writing – original draft. Juan Eduardo Sosa-Hernandez: Conceptualization, Investigation, Writing – original draft, Visualization, Writing – review & editing. Hafiz M.  N. Iqbal: Conceptualization, Writing – review & editing, Resources. Roberto Parra-Saldivar: Conceptualization, Writing – review & editing, Resources.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

• No data was used for the research described in the article.