Research progress of persistent organic pollutants in water: classification, sources, potential risks, and treatment approaches Open Access

During the surge of industrialisation, post-World War II, the wide usage of persistent organic pollutants (POPs) has begun. These synthetic chemicals were cheaper than their natural predecessors, and hence, POPs were introduced into commercial use for economy's benefit (Duttagupta et al. 2020b). They proved efficient in pest and disease control, agriculture, industry, etc. Since POPs survive for a long time in the biosphere and transmit from one species to another via the food chain, they have a severe unfortunate effect that has been endangering human health and the ecosystem for decades (Boulkhessaim et al. 2022). POPs are hazardous chemical substances that have recently received a lot of attention internationally. These chemicals possess specific physical and chemical properties that enable them to bioaccumulate, resist degradation, and travel long distances. Polychlorinated biphenyls (PCBs), dichloro-diphenyl-trichloroethane (DDT), and dioxins are some of the most well-known POPs. POPs have been quantified in every continent and significant climate (Fitzgerald & Wikoff 2014).

Persistence, toxicity, bioaccumulation, and long-distance transport are the four basic properties of POPs. Due to their resistance to numerous environmental processes, including chemical, biological, and photolytic destruction, POPs last for a long time. They are poor in water solubility and high in lipid solubility (hence the term ‘lipophilic’), which causes them to bioaccumulate in fatty tissues of living beings (Fitzgerald & Wikoff 2014). As a result, the food chain is biomagnified. Therefore, the highest POP concentrations are found in creatures at the top of the food chain and are typically present everywhere in the environment and biota, including humans (Fernandez et al. 2007). Through a process known as the ‘grasshopper effect,’ their semi-volatility makes it easier for them to fly over vast distances in the air or absorb into airborne or waterborne particulate matter (Liu et al. 2023).

Every living species, including humans, carry a certain amount of POPs in their bodies near or at the danger level. Even the smallest amount of POPs can threaten animal and human tissues, lead to cancers, damage the nervous system, cause immune system diseases, and cause reproductive and developmental disorders (Mishra et al. 2022). Exposure to POPs has been linked to a number of ecotoxicological outcomes, including immunotoxicity, dermal impacts, congenital impairments, cancer, decreased reproductive function, and population decreases in general. Numerous wildlife species suffer immunodeficiencies as a result of specific POPs, including PCBs, chlordane, hexachlorobenzene (HCB), dioxins, toxaphene, and DDT (Lee et al. 1998; Devi 2020). Exposure to POP also causes reproductive problems in mink, and population declines in porpoises, dolphins, seals, and beluga whales. Humans experience a wide range of health impacts from genotoxicity to reproductive abnormalities, immune system changes, elevated cancer risk, endocrine disruption, neurobehavioural impairment, and increased birth defects when exposed to even low amounts of POPs. POPs can be passed from mothers to their unborn children through the placenta and through breast milk in mammals, including humans. It is important to remember, though, that breastfeeding has benefits that outweigh the alleged concerns.

Many different combustion processes, including those used in power plants, industrial boilers, furnaces, incinerators, and home heating equipment, are thought to produce POPs. Full-scale combustion facilities have the potential to be significant POP generators due to the massive mass flow of flue gas released by a plant. Total POP emissions from small combustion appliances like wood stoves and home oil furnaces can also be significant due to the enormous number of installed units close to highly inhabited areas (Lee et al. 1998; Adithya et al. 2021).

Around 90 nations, including the European Union, joined forces to create the historic Stockholm Convention in May 2001 to address the problem of POPs. There are now 179 parties in the convention. Twelve main POPs, often referred to as the ‘Dirty Dozen’, are included in Table 1 and are subject to reduction or eradication under this treaty (Fitzgerald & Wikoff 2014). These include polychlorinated-dibenzo-p-dioxins (PCDDs), PCBs, polychlorinated dibenzofurans (PCDFs), toxaphene, aldrin, endrin, DDT, chlordane, dieldrin, mirex, heptachlor, and HCB. Since then, tributyltin and carcinogenic polycyclic aromatic hydrocarbons (PAHs) have been included (Fernandez et al. 2007; El-Shahawi et al. 2010). The convention imposes obligations on parties, including conducting research, locating POP-contaminated areas, identifying POP-contaminated areas, limiting and eradicating the manufacture and use of POPs, and providing financial support and incentives for the convention. Before becoming a party, a state or regional economic integration organisation must submit to the depositary a method of certification, acceptance, approval, or accession. POPs were known to be both a blessing and a curse, with the latter eventually outweighing the former. We will conduct a thorough analysis of POPs and their classifications in this article, as well as their sources, characteristics, impacts on the environment and living things throughout the world, mitigation strategies, and so on.

Table 1

Compound diagram, uses and effects of dirty dozen introduced by the Stockholm Convention

Sl no. .	Name of the compound .	Compound diagram .	Main uses .	Environmental effects .	References .
1	Aldrin		Pesticides	Easily converted to dieldrin	Fitzgerald & Wikoff (2014)
2	Chlordane		Insecticides	Slow environmental degradation	Fitzgerald & Wikoff (2014)
3	DDT		Pesticides	Bioaccumulation in water	El-Shahawi et al. (2010)
4	Dieldrin		Control termites and textile pests	Effects on the nervous system, liver, and immunity in animals	Nowak et al. (2019)
5	Endrin		Insecticides	Soil contaminant and slow degradation	Marshall et al. (2002)
6	Heptachlor		Control soil insects and termites	Toxic to aquatic animals and can bioaccumulate in fish and freshwater invertebrates	Nizzetto et al. (2010)
7	Hexachlorobenzene		Fungicide	Persistence in the environment, potential to bioaccumulate, and toxicity to humans and the environment	Tanabe et al. (1987)
8	Mirex		Control fire ants	Damage to aquatic life	Nizzetto et al. (2010)
9	Toxaphene		Insecticide and control tics and mites in livestock	Gets accumulated in fatty tissues of various organisms	Parra-Arroyo et al. (2022)
10	PCBs		Heat exchange fluids in capacitors, additives in paints	Carcinogen in humans and various other organisms	Weber et al. (2018); Lau et al. (2017)
11	PCDDs		Unintentionally formed	Extremely stable in the environment and can bioaccumulate in fatty tissues	Eduljee & Dyke (1996)
12	PCDFs		Unintentionally formed	Extremely stable in the environment and can bioaccumulate in fatty tissues	Eduljee & Dyke (1996)

Sl no. .	Name of the compound .	Compound diagram .	Main uses .	Environmental effects .	References .
1	Aldrin		Pesticides	Easily converted to dieldrin	Fitzgerald & Wikoff (2014)
2	Chlordane		Insecticides	Slow environmental degradation	Fitzgerald & Wikoff (2014)
3	DDT		Pesticides	Bioaccumulation in water	El-Shahawi et al. (2010)
4	Dieldrin		Control termites and textile pests	Effects on the nervous system, liver, and immunity in animals	Nowak et al. (2019)
5	Endrin		Insecticides	Soil contaminant and slow degradation	Marshall et al. (2002)
6	Heptachlor		Control soil insects and termites	Toxic to aquatic animals and can bioaccumulate in fish and freshwater invertebrates	Nizzetto et al. (2010)
7	Hexachlorobenzene		Fungicide	Persistence in the environment, potential to bioaccumulate, and toxicity to humans and the environment	Tanabe et al. (1987)
8	Mirex		Control fire ants	Damage to aquatic life	Nizzetto et al. (2010)
9	Toxaphene		Insecticide and control tics and mites in livestock	Gets accumulated in fatty tissues of various organisms	Parra-Arroyo et al. (2022)
10	PCBs		Heat exchange fluids in capacitors, additives in paints	Carcinogen in humans and various other organisms	Weber et al. (2018); Lau et al. (2017)
11	PCDDs		Unintentionally formed	Extremely stable in the environment and can bioaccumulate in fatty tissues	Eduljee & Dyke (1996)
12	PCDFs		Unintentionally formed	Extremely stable in the environment and can bioaccumulate in fatty tissues	Eduljee & Dyke (1996)

View Large

POPs are hazardous organic compounds that take an extended period to break down naturally in the atmosphere and can build up in living things and ecosystems. Because of POPs' durability in ecosystems, biological magnification, and biological accumulation in ecosystems, as well as their serious adverse impacts on human health, there are substantial worries about them at the global level. POPs are divided into three different groups – pesticides, chemicals used in industry, and unintentional creation (Nguyen et al. 2020; Tang 2021).

The two categories of POPs, intentional and unintentional, are outlined in Table 2 (Kodavanti et al. 2014). Intentional POPs consist of pesticides and industrial chemicals, whose prolonged usage harm the surroundings. Some of them are PCBs, hexachlorobenzenes (HCB)s, aldrin, mirex, and furans. POPs were developed around the early 1920s. With the boom in the industrial sector, after World War II, commercially useful POPs began to see a global distribution. POPs boosted crop productions too, conquering the agricultural industry. However, the manufacturing and agricultural sectors did not start to rely substantially on POPs until the 1940 and 1950s (Kodavanti et al. 2014).

Table 2

Chemical structure of intentional and unintentional POPs

View Large

Pesticides have most positively affected the economy; however, when it is over the permissible limits, they are said to have adverse effects on various environmental aspects and humans due to their pervasive manifestation and toxicity. Therefore, efforts should be made to mitigate pesticide residues by employing effective detection properly (Parra-Arroyo et al. 2022). Some of the most commonly used pesticides are PCBs, pentachlorophenol, dioxins (dibenzofurans), DDT, HCB, mirex, aldrin, chlordane, and toxaphene.

Methods like chromatography and mass spectrometry have proven to be useful in detecting pesticides (Stachniuk & Fornal 2015; Pang et al. 2016); however, metal–organic frameworks (MOFs) are considered to be quite effective in detecting POPs. In MOFs, ligands are linked metal ions or clusters that create three-dimensional structures (Vikrant et al. 2018). MOFs with well-defined structures, crystalline structure, and comparatively high porosity may reach upward of 7,000 m²/g in some cases (Farha et al. 2012).

Some industrial chemicals that heavily contribute to pollution are perfluorinated compounds, polybrominated diphenyl ethers (PBDEs), DDT, and PCBs. These chemicals have adverse effects on wildlife due to the discharge of chemicals into streams, rivers, and lakes, which often leads to bioaccumulation of toxins in the upper-trophic level predators through the food chain (Karthigadevi et al. 2021; Qiao & Xiong 2021). Higher concentrations of POPs found in food have chronic adverse health effects, including cancer, neurotoxicity, disruption of the endocrine system, and damage to the developing foetus (Chen et al. 2021; Tripathi et al. 2022).

Unintentionally produced POPs (UP-POPs) are unwanted by-products produced during chemical processes. Unintentional POPs are volatile and toxic and cause health hazards. Some commonly traced UP-POPs are HCB, PCDF, PCBs, and PCDDs (Kodavanti et al. 2014). Polychlorinated naphthalenes are a separate class of POPs that can develop through a variety of processes and thermal procedures (Odabasi et al. 2017; Weber et al. 2018). Iron ore sintering, municipal waste incineration, and materials that come into contact with food are the main sources of UP-POPs (Tuppurainen et al. 1998; Winkler 2015; Shen et al. 2021).

The sources can be broadly classified into primary and secondary sources. The term ‘primary sources’ describes sources whose emission levels are controllable. The secondary sources, also called re-emissions, are those whose emission levels cannot be controlled. These sources are described in detail in the following sections.

Primary sources produce POPs intentionally for one or more goals, unintentionally as by-products of industrial operations, or accidentally in response to human action (Breivik et al. 2004).

From the dirty dozen POPs named by the Stockholm Convention initially, nine of them are pesticides. They are HCB, dieldrin, aldrin, heptachlor, DDT, endrin, mirex, and chlordane. These pesticides are used because they are stable chemically in ecological conditions. Pesticides, like toxaphene congeners, have a half-life of 14 years, and some were found as residues in water more than a decade after they had been banned. Banned and obsolete pesticides have been used, contributing to the emission levels of POPs in water bodies, which Food and Agriculture Organisation (FAO) recognizes as a significant global issue. Due to their proximity to human activities, the pesticides are of great concern in bays and harbours. POP levels must be monitored by sticking to the limits prescribed for groundwater, fishery water, drinking water, and seawater (Hu et al. 2007).

PCBs and PBDEs are the key representatives of industrially produced POPs. Although PCBs have peaked in the past, PBDEs have been produced in high volumes in recent years. HCB was also intentionally created until the Stockholm Convention banned it (Rashed & Summers 2022).

The most common POPs, produced unintentionally, are PCDDs and PCDFs. Currently, the emission and concentration levels cannot be appropriately estimated due to the diversity in production and usage. However, certain reliable sources can be listed, including clinical waste, emissions from sinter factories, iron and steel industries, non-ferrous metal processes, and coal combustion (Shen et al. 2021).

HCB is considered to be a miscellaneous POP. Due to its thermodynamic stability, HCB is generated in tiny amounts in various reactions where it persists. In manufacturing numerous chlorine-containing insecticides, for instance, residues of HCB are generated during the chlorination stage. HCB is also produced in high-energy reactions combining chlorine and graphite-like compounds like soot (Fenstad et al. 2016).

More studies are needed to enhance the quantifiable knowledge of the comparative significance of primary emissions versus re-emissions for numerous POPs, even though the perceived significance of primary emissions versus re-emissions into the atmosphere for POPs has indeed been mentioned in a variety of studies. For certain POPs, it is necessary to consider the relative significance of natural emissions in respect to the regional and global mass balance. The PCDD/Fs provide as helpful examples from this perspective. In the instance of PCDD/Fs, a growing number of data suggest that dioxins have likely been found in the environment for much longer than the beginning of the ‘chlorine business.’ The multimedia component of chemical release may be crucial for assessing the overall ecological consequences of such chemicals under specific circumstances and for the highly volatile POPs. For example, industrial wastewaters directly release some volatile substances into aquatic habitats. These compounds might subsequently vaporize out of the aqueous solution into the environment. Further ambient dosage estimations out of which patterns can be inferred are required, in addition to the obvious need for enhanced emission characterisation, to make comparisons with simulations and act as a checking on emission data. The ultimate objective is to enhance and safeguard the environment that all people live in (Kallenborn et al. 2013). Over the years, newly identified POPs have been added to the list, which had originally consisted of 12 POPs. Among these chemicals are a few that have been detected in freshwater regions. Table 3 comprises the research on POPs found in the water of several regions globally. The chemicals listed are either identified as POPs or potential POPs.

Because of their propensity to accumulate bioaccumulative over time, POPs are known as the silent killers. They can be found in all parts of our surroundings, including in humans, animals, and plants. These are the cause of several deadly illnesses and environmental issues. POPs are linked to a variety of disorders, including obesity, diabetes, cancer, hormonal imbalances, heart disease, issues with reproduction, and environmental issues (Alharbi et al. 2018). The most prevalent POPs are mirex, dioxins, PCBs, polychlorinated dibenzodioxins (PCDDs), PBDEs, PCDFs, HCB, and chlorinated hydrocarbons, such as aldrin, DDT, endrin, and dieldrin. These can be found in a wide range of goods and products, such as flame retardants, wood floor finishes, hydraulic fluids, adhesives, coatings for electrical wiring and electronic components made of polyvinyl chloride, foams, paints, computers, textiles, televisions, furniture, and cars, as well as industrial and commercial surfactants (Islam et al. 2018). The main pollutants that cause POP contamination include dioxins, dibenzofurans, PAHs, organochlorine pesticides (OCPs), and PCBs. Since these substances are not biodegradable, they stay in the environment abnormally intact for extended periods of time. Furthermore, the long-range transport, persistence, and propensity for biological accumulation of these chemicals make them extremely concerning. Once they go into the food chain, they develop in the body's fatty tissue and have the potential to have a negative impact on both the environment and human health (Gaur et al. 2018).

POPs poison food, water, and other organisms higher up in the food chain, including humans, polar bears, killer whales, and eagles. There is proof that a large number of individuals globally may currently have enough POPs in their body fat, where they can build up and have a major negative impact on health that can result in disease and even death. In recent years, some POPs have also been linked to decreased immunity in young children and adults, as well as to an increase in infections at the same time. They have also been linked to developmental abnormalities, neurobehavioural impairment, malignancy, and the induction or promotion of tumours and cancer. Certain POPs are also thought to be significant risk factors in the development of breast cancer in humans. When POPs are taken at a younger age, there can be serious side effects, including birth defects, cancer, multiple tumours, immune system disorders, reproductive issues, decreased resistance to disease, stunted growth, and long-term impairment of brain function (El-Shahawi et al. 2010).

The interrelationship between air, water, animals, and people in the environment is intricate. Directly or indirectly, these identities' consequences harm the ecosystem. POPs consequently interfere with biotic, abiotic, social, cultural, and technical aspects of the environment. The natural balance is upset by POP pollution, putting the ecosystem and the welfare of all living creatures in peril. POPs build up in aquatic animals, causing them to die. As a result, there is a disparity in the ecology of the sea. POPs often last more than 20 years in the environment, with a few lasting a century. HCB, DDT, PCDDs, endrin, furans, and mirex can last 10–20 years in the environment. The grasshopper effect, which involves cyclic volatilisations and condensations, is visible in POPs. These chemicals relocate to cooler regions from warmer ones. When the temperature drops, these settle down, but when the temperature rises, they evaporate. This cyclic movement of POPs might sometimes affect global warming (Everaert & Baeyens 2002; Altarawneh et al. 2009).

Concentrations of POPs are typically lower in the polar climates than in warm climates. While some POPs (such as PCBs and DDTs) are declining, other POPs (such as fluorinated and brominated flame retardants) are growing in polar animals. The rise in global production and usage of these pollutants is the primary cause of this rise. Concentrations of POPs in glaucous gulls, canines, and grizzly bears from these regions have been demonstrated through laboratory and field research to exceed the impact thresholds, suggesting that the current POP levels alter behavioural, biochemical, physiological, and immunological variables (Ismail et al. 2018).

A vast variety of contaminants has always polluted our globe. Organic pollutants that are resistant to degradation are known as persistent pollutants for an extended period of time despite being resistant to environmental deterioration (Ritter et al. 1995). POPs are divided into intentional POPs and unintentional POPs. They are in charge of biomagnification because the toxins build up and are transferred via the food web to the animals at higher trophic levels. As a result, it may be claimed that everyone in the current situation has POPs in their bodies. Recent studies have discovered POPs in foetuses and embryos as well. Exposure to these POPS results in a number of health problems, including obesity, cancer, cardiovascular disease, diabetes, and hormone disruption. The United States Environmental Protection Agency (EPA) states that PCBs are the most dangerous POPs and that dioxins are the toxic POPs that cause cancer (Tanabe et al. 1987; Safe 1990). The following sections highlight a few health issues related to POPs.

Endocrine-disrupting chemicals, commonly referred to as POPs, are compounds that mimic various hormones and interfere with their function, leading to a variety of disorders such as diabetes, reproductive problems, and stunted growth (Jacobson et al. 1990a, 1990b; Alharbi et al. 2018). These substances attach to proteins, which interferes with hormone function (Predieri et al. 2020). These substances contain c-halogen molecules that can withstand various types of degradation (Gonsioroski et al. 2020; Dichiarante et al. 2021), such as PCBs, phthalates, PBDEs, dioxins, and pesticides. From conception until death, the body's biological activities are regulated by the endocrine system, according to the research by Nowak et al. (2019), Yilmaz et al. (2020), and Dahiya et al. (2021). Development, growth, and maturation are controlled by the endocrine system (Street & Bernasconi 2020; Dahiya et al. 2021). Pesticides, fungicides, and other chemicals frequently result in endocrine disruption. Substances that interact with the hormone system are known as ‘endocrine disruptors’ which frequently have harmful consequences on the body, including weight gain, sluggish reflexes, and impaired visual recognition that are visible from an early age (Street & Bernasconi 2020).

White blood cell development that is out of the ordinary leads to the condition known as cancer. Cancer is a fatal illness that poses a threat to life because it accounts for 21% of fatalities worldwide (Ali et al. 2011). Different malignancies occur due to higher POP distribution in low-density lipoproteins, including PCDDs, PBDEs, PCBs, and dibenzofurans (PCDD/Fs) (Ljunggren et al. 2014). The existence of these POPs in marine life is caused by biomagnification. Therefore, eating seafood raises your risk of developing cancer.

Obesity is a disorder involving excessive fat, which might lead to other complications (Chaput et al. 2012). Other complications associated with obesity are osteoarthritis and cardiovascular diseases (Thayer et al. 2012). The United States has the highest rate of obesity, close to 74%. A few reviews are based on the role of POPs in obesity (Hectors et al. 2011; Myre & Imbeault 2014). However, a positive correlation was found between endocrine disruption and POPs, leading to obesity, which is one of the complications of endocrine disruption. When gene expression levels of obesity markers were evaluated, it was found that PCBs were a major contributing factor to obesity (Pereira-Fernandes et al. 2014).

It is a disease that impacts the blood vessels or the heart. About 17 million people per year pass away from cardiovascular illness, with hypertension accounting for one-third of these deaths. Cardiovascular disorders are one of the leading causes of mortality (Alharbi et al. 2018). The four most typical cardiovascular conditions are arrhythmia, excessive blood pressure, cardiac arrest, and coronary heart disease. Since POPs are known to be lipophilic, the majority of them accumulate in the body and cause cardiovascular problems by biomagnification (Ljunggren et al. 2014). POPs including PCBs, polybrominated biphenyl, and organochlorine insecticides cause cardiovascular disorders. High levels of dioxins and PCBs were found to be associated with hypertension, elevated triglycerides, and hyperglycaemia.

When the pancreas either produces insufficient amounts of insulin or is unable to utilise the insulin that is produced, it results in a persistent illness called diabetes. The two most common types of diabetes are type 1 and type 2 diabetes. The pancreas produces very little or no insulin, which leads to type 1 diabetes. On the other hand, type 2 diabetes affects the way body produces insulin. Stroke, heart disease, kidney failure, foot gangrene are long-term effects of diabetes. Bioaccumulation of POPs in humans leads to the emergence of diabetes as well. The development of the metabolic syndrome has been directly attributed to PCBs and chlorinated pesticides. In addition, a link was established between dioxins and metabolic syndrome. According to the authors, type 2 diabetes is about 1.6–2.25 times more prevalent when POP concentrations are high. Moreover, it was shown that connections between type 2 diabetes and the chemicals trans-nonachlor and oxychlordane were significantly higher in obese people. It was assessed whether PCBs and a number of other chemicals increased the likelihood of developing diabetes (Carpenter 2008). The National Health and Nutrition Examination was used by two distinct parties to conduct a survey on a random sample of American inhabitants. It was determined that these POPs are main reasons for developing diabetes in people. According to research, the precise mechanism is unknown due to its complexity, but it is conceivable that these POPs could change how much insulin is produced.

The wastes produced by numerous industrial operations, the production of chemicals, and their by-products all contain POPs (Eduljee & Dyke 1996). POP has special physicochemical characteristics that permit them to resist degradation, and traverse bioaccumulate over great distances. POPs can enter freshwater and marine habitats by runoff, atmospheric deposition, effluent emissions, and other methods. POPs have a limited solubility in water, which causes them to bind tightly to the particulate matter in aquatic sediments. This paves the way for many harmful effects that can be seen in human beings and wildlife. People are most likely affected by these substances through the contaminated food and water that they consume or due to exposure to the industries that produce these chemicals. Table 3 presents the concentrations of POPs in different types of water sources. Studies have shown the abnormalities caused in the aquatic life residing in the contaminated water bodies and subsequent effects on their predators. It is necessary to detect POPs, gather information on their sources, brainstorm, and implement methods to reduce their production and effects (Zimmerman et al. 2000; Lau et al. 2017; Wagner et al. 2021).

Several methods are being used to detect the existence of POPs. POPs are difficult to analyse in water samples because in order to detect concentrations at environmental levels, substantial sample volumes would be required owing to their low solubilities. The traditional technique of analysis is using fish tissue; however, biological sampling must be take into account, and additional issues include migration, analyte metabolism, predation, disease, or the possible arrival of a foreign species. The surface-enhanced Raman scattering (SERS) (Sakai et al. 2001; Guerrini et al. 2008) method uses a molecular assembler and can be used to identify molecules that have been adsorbed onto a metal surface and to determine their most plausible orientation. Due to their incapacity to reach the metal surface, the majority of POPs, with the exception of a few, do not respond to this procedure, which is problematic. Some insecticides seemed to be effective in getting the analyser to come dangerously close to the metal surface. However, pesticides that contain a lot of halogen atoms behave very inertly in SERS. They have no attraction for the metal, and hence, SERS cannot directly detect them. Semipermeable membrane devices (SPMDs) (Abad et al. 2000) have proven to be rather efficient, especially compared to traditional chemical analyses. Usually, the tissue of the fish residing in the sample water is analysed, and SPMD has detected low solubility herbicides that cannot be detected commonly in surface water. Fouling factors are used for effective results. Creation of novel sensing components such as MOFs can offer a sizable active surface area as well as the capacity to be stable during target molecule adsorption and desorption. In addition, conceivable is functionalisation. In essence, they are arrangements of inorganic nodes guided by organic linkers. The resulting 3D network has a clear structure, crystallinity, and a sizable amount of porosity. This provides significant sensitivity for detecting guest molecules; in this case, it is the POPs.

There are methods and improvements in the methods mentioned earlier, which are in the process of development. The sources for the POPs that are either intentionally or unintentionally produced are usually from industries, especially the ones that manufacture pesticides. PCBs are POPs that are intentionally produced because they are useful in industrial applications, as heat exchange fluids, power transformers, and sizable capacitors. DDT (trichloroethane) is a controversial pesticide because it is a very effective chemical yet very harmful to the environment. Some manufacturing processes including trash incineration produce POPs unintentionally (Sakai et al. 1999; Abad et al. 2001). Table 4 summarises the sources of the discussed POPs.

To put a bar on the jeopardising effects of these POPs, numerous measures have been taken to eliminate or reduce emissions of dioxins and other related substances. As mentioned earlier, Stockholm Convention on POPs (2001) has been implemented by many countries that propose banning 21 POPs for commercial usage. If treatment is not carried out properly, it may result in accidental production or release of POPs in the environment. Basel Convention (with effect from 1992) had a set of guidelines that also contained numerous POPs destruction and irreversible transformation methods. Table 5 summarises the reduction methods discussed.

The use of microorganisms in biodegradation is an environmentally sustainable and cost-effective method for eliminating organic contaminants from soil and water. By cleaning up the environment, the biodegradation process aims to maintain regular biological activities in the surrounding environment. It is a process called biodegradation wherein live microorganisms break down complex chemical molecules into simpler ones. The utilisation of economical and cost-effective inputs yields better outcomes using biodegradation technology, which is highly favoured over conventional approaches. Since biodegradation is a more popular, cost-effective, and environmentally beneficial solution to the issue caused by organic contaminants, it can thus be taken into consideration (Gaur et al. 2018). POPs can be removed via microbial decomposition; however, this process is frequently hampered by the low bioavailability of POPs. For soil bioremediation, it is crucial to increase the bioavailability of POPs (Ren et al. 2018). Microalgae have demonstrated the ability to remove POPs from the environment through a variety of methods. Among the several methods, biodegradation is one of the best methods that completely eliminate POPs from the environment. As a result, employing microalgae to remove POPs offers a practical substitute for efficiently clean polluted environments and wastewater while also conserving resources (Singh et al. 2022).

The adsorption procedure has shown to be a more successful way to remove POPs and, for the most part, comply with discharge requirements. POPs from aqueous solutions may be efficiently adsorbent by nanomaterials. An adsorptive clearance effectiveness of >70% was attained for the majority of POPs. Electrostatic contact, hydrophobic interaction, and hydrogen bonding are the main processes for POPS absorption by nano-adsorbents. For around three cycles, nano-adsorbent may maintain an adsorptive removal of >90% POPs and can be reused for up to 10 cycles. There are difficulties with secure disposal and environmental toxicity of adsorbents (Ighalo et al. 2022). Technologies that are both economical and energy efficient for removing POPs from water include adsorptive removal and photocatalytic degradation. Both have garnered significant interest in treating wastewater worldwide. In terms of adsorptive removal and photocatalytic degradation of POPs for water remediation, MOFs – a class of recently created multifunctional porous materials – have demonstrated enormous promise and a bright future (Pi et al. 2018).

Adsorption removal of persistent POPs is a simple, practical solution, especially in decentralised systems and locations that are remote, whereas photocatalytic removal of POPs is an excellent, efficient, and durable technique (Ahmad et al. 2022). For the very successful elimination of POPs, it is essential to create novel adsorbents and catalysts for photosynthesis with the appropriate structure, adjustable chemistry, and maximal adsorption sites. MOFs are a type of recently developed multifunctional porous substances that have enormous potential for adsorption and photocatalytic destruction of POPs in case of cleaning water (Naghdi et al. 2023). Due to their unique chemical and physical features, cyclodextrins are inexpensive and eco-friendly pollution adsorbents (Trojanowicz et al. 2020; Titchou et al. 2021). Cyclodextrins are also widely reported to be functionalised using a variety of processes, and they are also extremely simple to employ. In addition, a number of derivatives of cyclodextrin are known, and a few of them are offered commercially. By adopting a variety of techniques, such as adsorption, cyclodextrin- and cyclodextrin-functionalised materials might be utilised to remove various contaminants (Wacławek et al. 2022).

Photochemical processes (advanced oxidation processes) have a number of benefits, but one of the most advantageous is how good it is at producing extremely reactive oxidising free radicals of OH in situ from water. POPs in sewage can be treated successfully using hydrodynamic cavitation technique as well as other cutting-edge oxidation techniques according to investigations (Badmus et al. 2018). These contaminants cannot be reduced by conventional wastewater treatment systems. Adsorption removal and photocatalytic breakdown of POPs in water have been found to be energy and cost-effective remedies (Wang et al. 2019). For their attempts to clean the wastewater produced across the world, both systems have drawn considerable attention.

The fundamental ideas and fundamental workings of photocatalysts based on titanium dioxide substances, light-assisted Fenton systems, metal oxides, framework materials like MOFs and polyoxometalates, as well as metal-free and hybrid photocatalysts for POPs removal, are described for potential uses in addressing POPs pollution in the surroundings. The crucial issues for the new contaminants are the enhancements of photocatalytic efficiency, particularly the elimination of POP mechanism using traditional and improved process, the design and optimisation of photoreactors, and the incorporation of technological advances. These issues demand extensive study in the near future (Nguyen et al. 2020).

POPs, including such PCB lubricants from dismantled transformers and chlorinated pesticides, may be included in in a hazardous waste mixture for burning in a specialised waste incinerator. It might include pollutants contaminated with POPs, such as commercial waste and activated carbon screens used to clean the exhaust gases in burning facilities (Abad et al. 2000; Abad et al. 2001). To get rid of these POPs, incinerator's processing parameters are modified. Nevertheless, once the burning gases are cooled down, more POPs are produced, chiefly PCDD/Fs and PCBs (Sakai et al. 1999, 2001). These POPs are found in the incineration residues, especially in the fly and furnace ashes and in the gas cleaning residues, in addition to being emitted with the flue gases at the stack (Everaert & Baeyens 2002; Altarawneh et al. 2009).

An ionised gas-like material called plasma is made up of electron-deprived and electron-positron atoms. Numerous properties of plasma, including electric conversion efficiency, quick response, high thermal capacity, and high energy, offer distinct advantages and promising prospects for effective disposal of POPs wastes (Girolkar et al. 2021).

Using a non-combustion process, plasma arc technology can be applied to manage organic fluoride in phenyl chlorosilane residue, industrial waste, and HFC23 (Zhu & Kang 2014).

Antibacterial bimetallic Ag-Cu nanoparticles were made via green synthesis for catalytic reduction of POPs (Ismail et al. 2018). It was concluded that Ag-Cu/T.P. is extremely suitable for the catalytic reduction of organic molecules due to its abundance, affordability, and effective catalytic degradation. Natural coagulants like Xantham and Guar gum are effective in treating POPs, and it is a well-recommended option due to their various salient features, including their abundance, cheap maintenance, and biodegradable biopolymer properties (Pariatamby & Kee 2016). POPs are removed from sewage and sources of water using ionising radiation (Trojanowicz 2020).

The wastewater treatment industry is one area where the circular economy may be used. Consideration of wastewater recovery and reuse, for instance, appears to be a great way to boost water supplies while lowering environmental effects. Wastewater can be sufficiently treated by the technique to be safe for human use. Agricultural, industrial, urban, environmental, or recreational uses are the most popular uses of recovered wastewater because this concept is still unpopular with most people and is referred to as the ‘yuck factor’. Nevertheless, there are many opportunities to implement the circular economy if we consider not just the resource worth of water but also the materials present in these effluents. As an illustration, it is commonly recognised that wastewater may be used to recover energy and nutrients. Other potential uses include the recovery of metals, organic and inorganic chemicals, biomolecules, and more. However, there are also ways to implement a circular economy in the water sector, such as by making money off of sewage sludge (Guerra-Rodríguez et al. 2020). Therefore, while both POP regulation and climate action, which heavily emphasises plastic recycling, are necessary for a circular economy, they are incompatible. The development of recycling methods, which allow for the separation and safe destruction of such materials, is one way to address this disparity (Wagner & Schlummer 2020).

This review article aims to give the readers an insight into the growing concern about the effects of POPs in water bodies. It throws light on the potential environmental and public health risks. Despite tighter controls at the national and international levels, the general public is nevertheless exposed to POPs at levels that might have long-term consequences on their health. POPs are present in extremely minute amounts and cannot be properly removed by traditional methods. Based on the contaminants' physicochemical properties, a sophisticated treatment must be selected. The unique features of nanomaterials, which are excellent for many environmental applications, have transformed the field of wastewater treatment. The research in the coming years will hopefully be able to change the situation, but the urge to reduce the production of these chemicals will always remain.

Some strategies could be implemented to reduce POPs or find suitable and safer alternatives to these contaminants. The strategies include functional substitution, chemical management, and chemical safety analysis. It has been concluded that studies done on POPs should not only focus on their risk factors but also on their function. These approaches pave the way for decision-making and can produce safer chemicals in the long run. The chemical function is an important criterion that might help synthesize safer chemicals. Chemists design chemicals to have specific properties that have specific functions. This enables chemists to reduce the toxicity of chemicals. One can consider the end-use function as an alternative, as it involves degreasing and other methods that achieve the same.

POPs use can be reduced by identifying alternatives to replace them that are way safer for global health and the environment. The functional substitution approach provides an easier and more feasible method for finding safe alternatives, which leaves us with many options that replace the chemicals with higher toxic content with safe alternative. With expanding research in nanotechnology, nanomaterials, based on their nature, can prove to be a promising remedy for removing POPs with high efficiency. Climate change has an effect on POP exposure concerns and transport processes in a variety of media, including air–soil gas exchange, emissions from melting glaciers, air–water gas exchange, and bioaccumulation in food web.

The augmentation of POP re-emission from soil, water, and glaciers, as well as the increase in POP concentrations in the world's polar areas, are only a few of the many effects of climate change. Therefore, it is urgent to increase the development and investigation of greener, more sustainable alternatives for POP mitigation. Adopting phytoremediation, a widely utilised integrated approach that uses bacteria and plants to break down toxins, could remove POPs without harming the environment. However, the primary focus is on maximum eradication of POPs usage rather than removal of POPs.

Aindrila Mandal, C. S. Poorva, S. Lohita: investigation, methodology, and writing – review and editing. P. Senthil Kumar: conceptualisation, validation, and supervision. B. Senthil Rathi, Gayathri Rangasamy: conceptualisation, resources, and formal analysis.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.