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Application of magnetic composites for the removal of organic pollutants from wastewaters: a mini-review
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ScienceDirect Materials Today: Proceedings 19 (2019) 910–916
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BraMat 2019
Application of magnetic composites for the removal of organic pollutants from wastewaters: a mini-review Irina Fierascua, Toma Fistosa,b,*, Anda Maria Baroia,b, Roxana Ioana Brazdisa,b a
National Institute for Research & Development in Chemistry and Petrochemistry – ICECHIM Bucharest, Emerging Nanotechnologies Group, 202 Spl. Independentei, 060021, Bucharest, Romania b University of Bucharest, Chemistry Department, 90-92 Sos. Panduri, 050663, Bucharest, Romania
Abstract One of the causes of water pollution is represented by the various organic compounds originating from different industries, such as pharmaceutical or textile industry, agriculture, etc. This issue has been a major concern for scientists, who have been trying to develop efficient processes for the removal of organic pollutants. Studied methods include photocatalytic oxidation, adsorption and separation. It has been observed that all these processes present a number of disadvantages such as the necessary energy, the efficiency of the method and its costs. The present review describes the main sources of organic pollutants and their possible health effects, as well as some of the magnetic composite materials used for pollutant removal. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 11th International Conference on Materials Science & Engineering, BraMat 2019 Keywords: magnetic composites; organic pollutants; adsorption.
1. Introduction Persistent organic pollutants (POPs) represent organic compounds resistant to the chemical, biological and photocatalytic action of environmental agents. They are typically halogenated compounds with low water solubility and high lipophilicity; these compounds are also semi-volatile, allowing them to pass in the gaseous phase at the environmental temperature. The process of volatilization of POPs can be repeated, so they can accumulate at a relatively long distance from the area in which they were initially used. As a result, these compounds can be transported over long distances by atmospheric air and thus easily reach food and drinking water [1].
* Corresponding author. Tel.: +4-021-315-32-99; fax: +4-021-312-34-93. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 11th International Conference on Materials Science & Engineering, BraMat 2019
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The large class of POPs can be divided in two sub-classes: polycyclic aromatic hydrocarbons and halogenated hydrocarbons. To the halogenated hydrocarbons class belongs organochlorines, one of the most resistant to degradation types of compounds, extensively used and marketed in the past. It is well known that more chlorinated biphenyls tend to accumulate more easily in the human body and metabolize and eliminate slowly than less chlorinated biphenyls [2]. These substances can affect the endocrine and the reproductive system, thyroid functions, as well as glucose and lipid metabolism. Aquatic ecosystems are very exposed to compounds which are acting as endocrine disruptors, the sources of contamination and the level of action being different for each compound. Some endocrine disruptors can bioaccumulate in the tissues and organs of aquatic organisms and become, in their turn, sources of pollution. The toxicity of these compounds can be influenced by various factors, such as pH, temperature, dissolved oxygen, water hardness, etc. Besides the threat to natural ecosystems and human health, those environmental issues also represent a challenge for the scientific world, which needs to adapt to the numerous side-effects of industrialization and urbanization. Thus, despite many thorough studies, remediation technologies, environmental monitoring, and the assessment of pollution-related problems, the environmental issues tends to grow exponentially and also tends to expand. Pollutants are omnipresent and versatile and go from one environmental compartment to another, with or without changes in their chemical and physical properties [3]. 2. Main sources of organic pollutants and possible health effects POPs include a wide range of organic compounds with different physicochemical properties. Their hazards are related to their high persistence in the environment and the bioaccumulation and biomagnification properties in living tissues. Following the Stockholm Convention, POPs were divided into four categories, namely: subject to elimination of production and use (aldrin, hexachlorobenzene, mirex, endrin, chlordecone, chlordane, dieldrin, heptachlor, toxaphene, lindane etc.), restricted in production and use (pentachlorobenzene, hexabromobiphenyl), unintentionally produced (pentachlorobenzene, hexachlorobenzene, polychlorinated dibenzofurans) and chemicals under investigation (chlorinated naphthalene, short-chained chlorinated paraffins, hexachlorobutadiene, pentachlorophenol) [4]. Aldrin is an organic chlorinated pesticide used until it was banned in 1970. As aspect it is a colorless solid used for soil and seed treatment. Chlordane is an organic chlorinated pesticide, used for corn or citrus crops and lawns or gardens. It was banned by the United States Environmental Protection Agency in 1983 [4]. Dichloro-diphenyl trichloroethane (DDT) is an effective, inexpensive insecticide use since 1940. It has been observed that this compound can penetrate and can be stored in food, soil and the human body, ultimately producing cancer. It was forbidden to use in 1970. Polychlorinated biphenyls represent a class of industrial chemicals, consisting of two benzene rings and chlorine atoms. They were used as cooling agents and as dielectric fluid in condensation processes and were banned in 1970. Is presented as a clear and viscous solution without taste or smell [5]. From the origin point of view, POPs can originate from different industrial processes, waste and very often from pesticide and insecticide farming. Because of their physical properties, they are easy to enter and accumulate in the environment, most often being found in air and water. They are scattered very easily through water stream and air currents over long distances from the place of deposition; another factor contributing to the distribution of POPs is weather, such as rain or snow. As a result of accumulation, they most often get into fish, seafood and vegetables, and thus they easily reach humans, being able to cause serious affections [6]. Chen et al. [7] have investigated the agricultural farmlands irrigated in the northern China by effluents from biological treatment plants that receive sewage and industrial wastewater. Both residues of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) were found in soils irrigated with underground water and effluents. The results have shown that wastewater irrigation can cause the accumulation of PAHs in soils close to the points of discharge. The compounds of the PAHs category identified in polluted soils were benzo[b]fluoroethane, benzo[a]pyran, indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene and benzo[g,h,i]perylene. Minh et al. [8] have studied pollution with POPs, in particular dichlorobiphenyl-trichloroethane and its metabolites (DDTs), hexachlorocyclohexanes (HCHs), chlordane, hexachlorobenzene (HCB), and polychlorinated biphenyls (PCBs) from different soils in Cambodia, India, and Vietnam. They came to the conclusion that in the soil
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was predominant DDTs, PCBs, and HCHs. The DDT compound component confirmed their use in populated zones, which leads to an increase of DDT in the discarding area. Based on the existence of HCH isomers, it was concluded that they were used in different countries. In recent years, excess of persistent organic pollutants (POPs) have been used (such as polychlorinated biphenyls - PCBs or organochlorine pesticides - OCPs) in the development of industries and agriculture. It is thought that in China were produced about 4.9 million tons of hexachlorocyclohexane (HCHs) and 400 thousand tons of dichlorobiphenyl-trichloroethane and its metabolites (DDTs) [9]. POPs are dangerous pollutants because they tend to bioaccumulate and are non-degradable in the environment. It has been found that in a pollutant environment most people have POPs in their body, being found even at the embryonic level, affecting the fetus [10]. Human exposure to POPs can lead to several types of health disorders such as obesity, hormonal, neurological and reproductive disorders, cancer, cardiovascular disease and diabetes. Zhou et al. [11] described the functioning mechanisms of POPs in the development of various health problems, using zebrafish as an aquatic animal model. The conclusion of the study was that mechanisms are very complex, being mainly mediated by aryl hydrocarbon receptors (AhR) pathways. Considering that the effects of POP are synergistic and additive on the environment and organisms, their study is quite difficult. Sometimes mixtures of POPs are studied simultaneously, in order to identify their effects in real-life situations. Endocrine disruptors are considered all the chemicals that interfere with the endocrine system, affecting hormone functions, resulting in negative effects of the reproductive, neurological and immune system. The most common endocrine disrupting pesticides are organochlorine pesticides (DDT, mirex, endosulfan, toxaphene, chlordane and dieldrin), these compounds functioning by altering estrogen and sexual organs functions [12]. Papadopoulou et al. [13] investigated the effects of prenatal exposure to POPs on the endocrine system, including in the study 231 mothers and their newborns from Greece (Crete) and Spain (Barcelona), and 476 mothers and their children measured between 1 and 2 years from Greece. According to the results presented, several types of pesticides were transmitted from mothers to unborn babies (organochlorine pesticides, polychlorinated biphenyls and polychlorinated diphenyl ethers), with concentrations higher in the mother’s serum than umbilical cord and placentas [13]. Effects on newborns include low weight, length and circumference of the chest, as presented by Giwercman et al. [14], caused by the change of the Y:X chromosomes ratio in sperm, result of the exposure to PCBs and p,p’-DDE. Cardiovascular diseases are the main causes of mortality in the world, including hypertension, angina pectoris, cardiac arrhythmias, etc. The occurrence of cardiovascular disease increases when social, behavioral and metabolic factors are involved along with POPs pollution. It is known that most POPs are lipophilic in nature and are accumulated in lipoproteins, leading to many cardiovascular system problems. The main POPs compounds that contribute to cardiovascular problems are organochlorine pesticides, polychlorinated biphenyls and polybrominated biphenyl (PBB). Valera et al. [15] examined the polychlorinated pesticide (PCB) and organochlorine pesticide (OCP) effects on hypertension in Arctic populations. Hypertension was measured by linear regression using POPs as continuous variables. Finally, it was found that the high level of dioxin and PCB is associated with the metabolism of the syndrome. In the case of POPs exposure, blood pressure, triglycerides and glucose levels increased. Cancer is an unpredictable disease, characterized by the uncontrolled growth of abnormal cells, being considered the most lethal disease (responsible for 21% of the annual deaths). In the case of cancer, healthy cells begin to behave differently due to internal and external factors. High POP concentrations in low density lipoproteins are responsible for various types of cancer [16]. Yu et al. [17] studied the risk of cancer associated with seafood. The authors noticed that aquatic products can contain organochlorine pesticides, polybrominated diphenyl ethers, polychlorinated dibenzo-p-dioxins, dibenzofurans, polychlorinated biphenyls (PCBs), including dioxin-like PCBs. The conclusion of the study was the cancer risk increases for global consumers by consumption of aquatic products, the exposure to different classes of POPs being specific for each of the areas studied (for example, Europeans were found to be more exposed to polychlorinated dibenzo-p-dioxins, dibenzofurans and dioxin-like PCBs, while the Americans and Asians had a higher exposure levels to organochlorine pesticides and PCBs, by consumption of marine fish) [17]. Arrebola et al. [18] studied the association of human exposure to POPs with serum lipid levels and obesity on 368 people in Spain. The POPs were analyzed in adipose tissues, using Cox-regression models, establishing a direct
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relationship between POP exposure and serum lipids/obesity. Mathur et al. [19] evaluated the correlation between the concentrations of DDT and its metabolites (DDE, dieldrin, heptachlor, etc.) and breast cancer occurrence in the case of women in Jaipur, India, observing a high risk of breast cancer with increased levels of POPs. Hardel et al. [20] studied various POPs levels on patients with prostate cancer. In the adipose tissue samples collected from cancer patients, the study identified higher levels of polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), chlordane and polybrominated diphenyl ethers (PBDE), compared with the controls. The authors concluded that prostate cancer may be related to the presence of certain POPs. Ghisari et al. [21] investigated how polymorphic genes are affected during xenobiotic metabolism and estrogen biosynthesis. They calculated the serum level of 115 individuals and noticed the direct relationship between the high concentration of perfluoro-octane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) with breast cancer in Inuit women. Obesity is a disease associated with an excess of fat in body, contributing to various health problems, including cardiovascular problems, cancer, osteoarthritis, obstructive sleep apnea, etc. [22]. Barnes et al. [23] argue that obesity will be the main disease of the 21st century, with a recorded obesity rate of 74.1% in the United States and over 60% in Canada and the United Kingdom. Several studies associated the obesity situations with the accumulation of POPs. Dirinck et al. [24] studied the potential correlation between obesity and POPs presence, in a cohort of obese and lean adult men and women. The results of the study showed a positive relationship between the concentration of β-hexachlorocyclohexane and the body mass index (BMI), a negative relationship between the level of PCBs and BMI and no statistically significant relationship between serum levels of dichloro-diphenyldichloroethylene and BMI, concluding that the diabetogenic effect of low-dose exposure to POPs is more complex than a simple obesogenic effect [24]. Lee et al. [25] studied the correlation between presence of low dose POPs and the future apparition of adiposity, dyslipidemia, and insulin resistance. The authors reported that the exposure to POPs can contribute to the development of these affections, common precursors of type 2 diabetes and cardiovascular diseases. Donat-Vargas et al. [26] analyzed 12,313 people with different levels of POPs in the body and noted that obesity was present in 621 cases; moreover, its appearance was correlated with the POPs levels in their diet. Diabetes is a severe disease that can affect the whole body, which involves the accumulation of sugar in the blood, and the body cannot produce enough insulin. In cases of serious forms of diabetes, people can suffer vascular accidents, heart diseases, kidney failure, ulcer, eye disorders [27]. In Japan, a study conducted on 1,374 subjects aged 15-73 years highlighted the fact that chlorinated pesticides and polychlorinated biphenyls interfere with the development of metabolic syndrome (insulin resistance). After the study, a connection between metabolic syndrome and different POP compounds (polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polychlorinated biphenyls) was observed [28]. Airaksinen et al. [29] investigated the association between the occurrence of several POPs (oxychlordane, trans-nonachlor, 1,1-dichloro-2,2-bis-(p-chlorophenyl)-ethylene, polychlorinated biphenyl) and type 2 diabetes. The experiment involved 8,760 subjects born in Helsinki and 1.642.24 times higher types of 2 diabetes were reported in association with high POPs levels. In the same time, the association between type 2 diabetes with oxychlordane and trans-nonachlor was much higher in the case of overweight individuals. The study of Rignell-Hydbom et al. [30] also found an association between p,p’-DDE exposure and type 2 diabetes. 3. Magnetic composites for organic pollutants removal Nowadays, in the aquatic environment there are pollutants that change the physical, chemical and biological properties of water. Several studies present the removal of organic pollutants using innovative materials. For example, adsorption of methylene blue was presented by Wu et al. [31] on rhamnolipid-functionalized graphene oxide (RL-GO) hybrid. Sorption is often used to remove different pollutants, as the method represents a low-cost, simple, efficient and versatile solution [31]. It has been discovered that graphene and its derivatives are very useful in the absorption of environmental pollutants, such as aromatic compounds, dyes, heavy metal ions, combined pollutants, etc. In particular, graphene oxide (GO) has been applied in many ways to the treatment of waste water and its purification because it has a large contact surface and a variety of O-containing functionals groups such as
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hydroxide, epoxide, carbonyl and carboxyl groups. The separation modes involving these types of absorbents are often complicated by their dispersion in water. The introduction of Fe3O4 nanoparticles (NPs) into GO and reduced graphene oxide (RGO) can increase the absorption capacity and even favor the process. In the same time, introduction of the magnetic phase reduces the costs usually associated with the separation stage. Huang et al. [32] synthesized and characterized magnetic graphene oxide (MGO), magnetically chemically-reduced graphene (MCRG) and magnetic annealing-reduced graphene (MARG). The obtained materials also include iron and oxygen contents that have sorption capabilities. Graphene oxide (GO) was obtained from natural graphite flakes using a modified Hummers method. The adhesive (GO) was exfoliated by sonication and dialyzed to remove acids and other impurities, and co-precipitation of FeCl3×6H2O and FeSO4×7H2O produced nanoparticles of Fe3O4 (NPs). The GO solution was added dropwise to the Fe3O4 NPs solution, with the formation of MGO. After reduction of the synthesized MGO with hydrazine hydrate, MCRG was obtained by a 500 °C expansion under N2 using MGO as the precursor. MGO, MCRG, and MARG of different oxygen contents were used as magnetic graphene adsorbents. Tetracycline (TC) was selected as organic pollutant model to investigate adsorption processes of magnetic graphene materials. MGO proved to be the best adsorbent for TC, which should be attributed to a larger number of Ocontaining functional groups. The experimental results demonstrated that the absorption capacity for MGO was 252 mg/g [32]. Zhang et al. [33] synthesized Fe3O4 NPs with diameter of approx. 10 nm to remove aromatic hydrocarbons such as phenol an aniline from aqueous solutions. The NPs were obtained by the co-precipitation method, using FeCl2×4H2O and FeCl3×6H2O. The obtained nanoparticles were separated from the solution with an external magnetic field and rinsed several times with deoxygenated water. The pollutant removal experiments were carried out in buffer solution (NaH2PO4–Na2HPO4) containing NPs in which aniline or phenol were added. The removal of the aromatic compounds was achieved after 6 hours, the total organic carbon abatement efficiency for phenol and aniline were 42.79% and 40.38%, respectively. To demonstrate the effectiveness of the tested compounds, compared analysis was performed before and after the catalytic process. Prior to the reaction, the nanoparticles had a diameter of approximately 10 nm and a spherical shape; after the adsorption, the diameter of some nanoparticles increased and the shape changed. The paramagnetic behavior of the compound was demonstrated by placing a magnet near the vessel with the containing nanoparticles aqueous solution. Following the proximity of the magnet, the solution became clear in just a few seconds. It was observed that the effectiveness of the adsorption process was directly proportional to the concentration of the nanoparticles used [33]. Zhang et al. [34] synthesized core-shell Fe3O4/C magnetic nanomaterials, with an approximate diameter of 250 nm, using a two steps procedure, for removing organic dyes from aqueous solutions. Fe3O4 magnetic nanospheres were synthesized by mixing FeCl3×6H2O with ethylene glycol, as a solvent and reducing agent, until FeCl3 was dissolved, followed by the addition of anhydrous sodium acetate. The reaction was considered completed when a clear solution was obtained. Finally, the obtained nanospheres were rinsed several times with warm water and ethanol. The absorption of the used dyes (methylene blue – MB and cresol red - CR) was evaluated using UV–vis spectrometry. The dyes were adsorbed from the solution in proportion of 90% in 2.5 hours. The adsorption capacities of the proposed material for MB and CR were established to be 44.38 mg/g and 11.22 mg/g, respectively [34]. Another solution for removing POPs from water matrix was applied by Zhang et al. [35]. The authors photocatalytic removed 2,2-bis (4-hydroxyphenyl) propane (BPA) with a core-shell-shell magnetic composite material BiOBr@SiO2@Fe3O4. The magnetic composite material was obtained in three steps: first step involved the synthesis of the Fe3O4 microspheres, followed by the magnetic SiO2@ Fe3O4 core-shell composite microspheres, and finally the synthesis of the BiOBr@SiO2@Fe3O4 material. Following the experiments, it was demonstrated that the synthesized material had superior photocatalytic properties, compared with the commercial TiO2 photocatalyst (P25) (87% degradation of BPA using the synthesized material, compared with a 27.2% degradation achieved using the commercial product, after 50 min under visible light irradiation). Moreover, the composite can be easily separated from the reaction solution using an external magnetic field [35].
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Fierascu et al. [36] proposed core-shell magnetic composites (copper and nickel ferrite cores, with a chitosan shell) for the efficient removal of pharmaceutical endocrine disrupting compounds (naproxen sodium and diltiazem hydrochloride). The presented results suggested that the nickel ferrite/chitosan composite showed the highest affinity towards the adsorption of Na naproxen (89% removal after 48 hours), while the best results for the adsorption of diltiazem HCl were obtained for the copper ferrite/chitosan composite (56% at 48 hours). The magnetic composites (having saturation magnetization determined by magnetization versus magnetic field strength investigations at room temperature of 2.5 emu/g and 6.8 emu/g, respectively) were also easily removed from the test solution by using an external magnetic field. 4. Conclusions The persistence and health effects of organic pollutants represents an important area of research, and new alternatives for their removal being currently proposed. POPs pollution has been known since the 1970s, but more attention has been paid to it in recent years. Due to their physical properties, namely lipophilicity and solubility, they can spread very easily and quickly into water, soil and air, and then into human food. In the living organisms, they can affect various systems and cause a series of serious affections, such as endocrine disorders, reproductive system problems, cardiovascular problems, cancer, obesity, diabetes, and even death. Considering the potential treat both to the environment and the human health, efforts are focused towards the identification of new, more efficient solutions for their removal. The application of magnetic materials (especially core-shell materials, with a magnetic core and an active shell) represents a viable alternative in the targeted area. As the presented short literature review proves, it is possible to remove persistent organic pollutants from water using magnetic nanomaterials. Various types of nanomaterials with magnetic properties (such as Fe3O4, Fe3O4/C, BiOBr@SiO2@Fe3O4, nickel and copper ferrite/chitosan) have been used for the removal of organic pollutants. Their magnetic properties allow the rapid removal of the materials, together with the pollutants, from the solution using an external magnetic field. The approach can be easily translated to the industrial scale, being a cost-effective alternative to the currently applied methods. Thus, the reduction of the POPs levels in the environment can lead to an increase not only in the environmental status, but also to the diminishment of the health effects those pollutants can cause. Acknowledgements This work was supported by Romanian Ministry of Research and Innovation - MCI through INCDCP-ICECHIM Bucharest 2019-2022 Core Program PN. 19.23 - Chem-Ergent, Project No.19.23.03.01 and contract 31PFE/2018 TRANS - CHEM. References [1] K.C. Jones, P. de Voogt, Environ. Pollut. 100 (1999) 209-221. [2] L. Ritter, K.R. Solomon, J. Forget, M. Stemeroff, C. O’Leary, IPCS, 1995, available at: https://www.who.int/ipcs/assessment/en/pcs_95_39_2004_05_13.pdf. [3] D.O. Carpenter, Rev. Environ. Health. 26 (2011) 61-69. [4] Stockholm Convention on Persistent Organic Pollutants, 2014, available at https://www.wipo.int/edocs/lexdocs/treaties/en/unep-pop/trt_unep_pop_2.pdf. [5] S. Corsolini, S. Focardi, in: F. Faranda, L. Guglielmo, A. Ianora (Eds.), Springer-Verlag, Berlin, 2000, pp. 575-584. [6] J. Jacob, Int. J. Biosci. Biochem. Bioinforma. 3 (2013) 657-661. [7] Y. Chen, C. Wang, Z. Wang, Environ. Int. 31(2005) 778-783. [8] N. H. Minh, T. B. Minh, N. Kajiwara, T. Kunisue, A. Subramanian, H. Iwata, T. S. Tana, R. Baburajendran, S. Karuppiah, P. H. Viet, B. C. Tuyen, S. Tanabe, Arch. Environ. Contam. Toxicol. 50 (2006) 474-481. [9] H. Zhi, Z. Zhao, L. Zhang, Chemosphere 119 (2015) 1134-1140. [10] O. M.L. Alharbi, A. A. Basheer, R. A. Khattab, I. Ali, J. Molec. Liquids 263 (2018) 442–453. [11] H. Zhou, H.Wu, C. Liao, X. Diao, J. Zhen, L. Chen, Q. Xue, Toxicol. Mech. Methods 20 (2010) 279-286. [12] T. Damstra, S.W. Page, J.L. Herrman, T. Meredith, J. Epidemiol. Community Health 56 (2002) 824-825. [13] E. Papadopoulou, M. Vafeiadi, S. Agramunt, K. Mathianaki, P. Karakosta, A. Spanaki, H. Besselink, H. Kiviranta, P. Rantakokko, K. Sarri, A. Koutis, L. Chatzi, M. Kogevinas, Sci. Total Environ. 461-462 (2013) 222-229.
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BraMat 2019
Application of magnetic composites for the removal of organic pollutants from wastewaters: a mini-review Irina Fierascua, Toma Fistosa,b,*, Anda Maria Baroia,b, Roxana Ioana Brazdisa,b a
National Institute for Research & Development in Chemistry and Petrochemistry – ICECHIM Bucharest, Emerging Nanotechnologies Group, 202 Spl. Independentei, 060021, Bucharest, Romania b University of Bucharest, Chemistry Department, 90-92 Sos. Panduri, 050663, Bucharest, Romania
Abstract One of the causes of water pollution is represented by the various organic compounds originating from different industries, such as pharmaceutical or textile industry, agriculture, etc. This issue has been a major concern for scientists, who have been trying to develop efficient processes for the removal of organic pollutants. Studied methods include photocatalytic oxidation, adsorption and separation. It has been observed that all these processes present a number of disadvantages such as the necessary energy, the efficiency of the method and its costs. The present review describes the main sources of organic pollutants and their possible health effects, as well as some of the magnetic composite materials used for pollutant removal. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 11th International Conference on Materials Science & Engineering, BraMat 2019 Keywords: magnetic composites; organic pollutants; adsorption.
1. Introduction Persistent organic pollutants (POPs) represent organic compounds resistant to the chemical, biological and photocatalytic action of environmental agents. They are typically halogenated compounds with low water solubility and high lipophilicity; these compounds are also semi-volatile, allowing them to pass in the gaseous phase at the environmental temperature. The process of volatilization of POPs can be repeated, so they can accumulate at a relatively long distance from the area in which they were initially used. As a result, these compounds can be transported over long distances by atmospheric air and thus easily reach food and drinking water [1].
* Corresponding author. Tel.: +4-021-315-32-99; fax: +4-021-312-34-93. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 11th International Conference on Materials Science & Engineering, BraMat 2019
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The large class of POPs can be divided in two sub-classes: polycyclic aromatic hydrocarbons and halogenated hydrocarbons. To the halogenated hydrocarbons class belongs organochlorines, one of the most resistant to degradation types of compounds, extensively used and marketed in the past. It is well known that more chlorinated biphenyls tend to accumulate more easily in the human body and metabolize and eliminate slowly than less chlorinated biphenyls [2]. These substances can affect the endocrine and the reproductive system, thyroid functions, as well as glucose and lipid metabolism. Aquatic ecosystems are very exposed to compounds which are acting as endocrine disruptors, the sources of contamination and the level of action being different for each compound. Some endocrine disruptors can bioaccumulate in the tissues and organs of aquatic organisms and become, in their turn, sources of pollution. The toxicity of these compounds can be influenced by various factors, such as pH, temperature, dissolved oxygen, water hardness, etc. Besides the threat to natural ecosystems and human health, those environmental issues also represent a challenge for the scientific world, which needs to adapt to the numerous side-effects of industrialization and urbanization. Thus, despite many thorough studies, remediation technologies, environmental monitoring, and the assessment of pollution-related problems, the environmental issues tends to grow exponentially and also tends to expand. Pollutants are omnipresent and versatile and go from one environmental compartment to another, with or without changes in their chemical and physical properties [3]. 2. Main sources of organic pollutants and possible health effects POPs include a wide range of organic compounds with different physicochemical properties. Their hazards are related to their high persistence in the environment and the bioaccumulation and biomagnification properties in living tissues. Following the Stockholm Convention, POPs were divided into four categories, namely: subject to elimination of production and use (aldrin, hexachlorobenzene, mirex, endrin, chlordecone, chlordane, dieldrin, heptachlor, toxaphene, lindane etc.), restricted in production and use (pentachlorobenzene, hexabromobiphenyl), unintentionally produced (pentachlorobenzene, hexachlorobenzene, polychlorinated dibenzofurans) and chemicals under investigation (chlorinated naphthalene, short-chained chlorinated paraffins, hexachlorobutadiene, pentachlorophenol) [4]. Aldrin is an organic chlorinated pesticide used until it was banned in 1970. As aspect it is a colorless solid used for soil and seed treatment. Chlordane is an organic chlorinated pesticide, used for corn or citrus crops and lawns or gardens. It was banned by the United States Environmental Protection Agency in 1983 [4]. Dichloro-diphenyl trichloroethane (DDT) is an effective, inexpensive insecticide use since 1940. It has been observed that this compound can penetrate and can be stored in food, soil and the human body, ultimately producing cancer. It was forbidden to use in 1970. Polychlorinated biphenyls represent a class of industrial chemicals, consisting of two benzene rings and chlorine atoms. They were used as cooling agents and as dielectric fluid in condensation processes and were banned in 1970. Is presented as a clear and viscous solution without taste or smell [5]. From the origin point of view, POPs can originate from different industrial processes, waste and very often from pesticide and insecticide farming. Because of their physical properties, they are easy to enter and accumulate in the environment, most often being found in air and water. They are scattered very easily through water stream and air currents over long distances from the place of deposition; another factor contributing to the distribution of POPs is weather, such as rain or snow. As a result of accumulation, they most often get into fish, seafood and vegetables, and thus they easily reach humans, being able to cause serious affections [6]. Chen et al. [7] have investigated the agricultural farmlands irrigated in the northern China by effluents from biological treatment plants that receive sewage and industrial wastewater. Both residues of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) were found in soils irrigated with underground water and effluents. The results have shown that wastewater irrigation can cause the accumulation of PAHs in soils close to the points of discharge. The compounds of the PAHs category identified in polluted soils were benzo[b]fluoroethane, benzo[a]pyran, indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene and benzo[g,h,i]perylene. Minh et al. [8] have studied pollution with POPs, in particular dichlorobiphenyl-trichloroethane and its metabolites (DDTs), hexachlorocyclohexanes (HCHs), chlordane, hexachlorobenzene (HCB), and polychlorinated biphenyls (PCBs) from different soils in Cambodia, India, and Vietnam. They came to the conclusion that in the soil
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was predominant DDTs, PCBs, and HCHs. The DDT compound component confirmed their use in populated zones, which leads to an increase of DDT in the discarding area. Based on the existence of HCH isomers, it was concluded that they were used in different countries. In recent years, excess of persistent organic pollutants (POPs) have been used (such as polychlorinated biphenyls - PCBs or organochlorine pesticides - OCPs) in the development of industries and agriculture. It is thought that in China were produced about 4.9 million tons of hexachlorocyclohexane (HCHs) and 400 thousand tons of dichlorobiphenyl-trichloroethane and its metabolites (DDTs) [9]. POPs are dangerous pollutants because they tend to bioaccumulate and are non-degradable in the environment. It has been found that in a pollutant environment most people have POPs in their body, being found even at the embryonic level, affecting the fetus [10]. Human exposure to POPs can lead to several types of health disorders such as obesity, hormonal, neurological and reproductive disorders, cancer, cardiovascular disease and diabetes. Zhou et al. [11] described the functioning mechanisms of POPs in the development of various health problems, using zebrafish as an aquatic animal model. The conclusion of the study was that mechanisms are very complex, being mainly mediated by aryl hydrocarbon receptors (AhR) pathways. Considering that the effects of POP are synergistic and additive on the environment and organisms, their study is quite difficult. Sometimes mixtures of POPs are studied simultaneously, in order to identify their effects in real-life situations. Endocrine disruptors are considered all the chemicals that interfere with the endocrine system, affecting hormone functions, resulting in negative effects of the reproductive, neurological and immune system. The most common endocrine disrupting pesticides are organochlorine pesticides (DDT, mirex, endosulfan, toxaphene, chlordane and dieldrin), these compounds functioning by altering estrogen and sexual organs functions [12]. Papadopoulou et al. [13] investigated the effects of prenatal exposure to POPs on the endocrine system, including in the study 231 mothers and their newborns from Greece (Crete) and Spain (Barcelona), and 476 mothers and their children measured between 1 and 2 years from Greece. According to the results presented, several types of pesticides were transmitted from mothers to unborn babies (organochlorine pesticides, polychlorinated biphenyls and polychlorinated diphenyl ethers), with concentrations higher in the mother’s serum than umbilical cord and placentas [13]. Effects on newborns include low weight, length and circumference of the chest, as presented by Giwercman et al. [14], caused by the change of the Y:X chromosomes ratio in sperm, result of the exposure to PCBs and p,p’-DDE. Cardiovascular diseases are the main causes of mortality in the world, including hypertension, angina pectoris, cardiac arrhythmias, etc. The occurrence of cardiovascular disease increases when social, behavioral and metabolic factors are involved along with POPs pollution. It is known that most POPs are lipophilic in nature and are accumulated in lipoproteins, leading to many cardiovascular system problems. The main POPs compounds that contribute to cardiovascular problems are organochlorine pesticides, polychlorinated biphenyls and polybrominated biphenyl (PBB). Valera et al. [15] examined the polychlorinated pesticide (PCB) and organochlorine pesticide (OCP) effects on hypertension in Arctic populations. Hypertension was measured by linear regression using POPs as continuous variables. Finally, it was found that the high level of dioxin and PCB is associated with the metabolism of the syndrome. In the case of POPs exposure, blood pressure, triglycerides and glucose levels increased. Cancer is an unpredictable disease, characterized by the uncontrolled growth of abnormal cells, being considered the most lethal disease (responsible for 21% of the annual deaths). In the case of cancer, healthy cells begin to behave differently due to internal and external factors. High POP concentrations in low density lipoproteins are responsible for various types of cancer [16]. Yu et al. [17] studied the risk of cancer associated with seafood. The authors noticed that aquatic products can contain organochlorine pesticides, polybrominated diphenyl ethers, polychlorinated dibenzo-p-dioxins, dibenzofurans, polychlorinated biphenyls (PCBs), including dioxin-like PCBs. The conclusion of the study was the cancer risk increases for global consumers by consumption of aquatic products, the exposure to different classes of POPs being specific for each of the areas studied (for example, Europeans were found to be more exposed to polychlorinated dibenzo-p-dioxins, dibenzofurans and dioxin-like PCBs, while the Americans and Asians had a higher exposure levels to organochlorine pesticides and PCBs, by consumption of marine fish) [17]. Arrebola et al. [18] studied the association of human exposure to POPs with serum lipid levels and obesity on 368 people in Spain. The POPs were analyzed in adipose tissues, using Cox-regression models, establishing a direct
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relationship between POP exposure and serum lipids/obesity. Mathur et al. [19] evaluated the correlation between the concentrations of DDT and its metabolites (DDE, dieldrin, heptachlor, etc.) and breast cancer occurrence in the case of women in Jaipur, India, observing a high risk of breast cancer with increased levels of POPs. Hardel et al. [20] studied various POPs levels on patients with prostate cancer. In the adipose tissue samples collected from cancer patients, the study identified higher levels of polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), chlordane and polybrominated diphenyl ethers (PBDE), compared with the controls. The authors concluded that prostate cancer may be related to the presence of certain POPs. Ghisari et al. [21] investigated how polymorphic genes are affected during xenobiotic metabolism and estrogen biosynthesis. They calculated the serum level of 115 individuals and noticed the direct relationship between the high concentration of perfluoro-octane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) with breast cancer in Inuit women. Obesity is a disease associated with an excess of fat in body, contributing to various health problems, including cardiovascular problems, cancer, osteoarthritis, obstructive sleep apnea, etc. [22]. Barnes et al. [23] argue that obesity will be the main disease of the 21st century, with a recorded obesity rate of 74.1% in the United States and over 60% in Canada and the United Kingdom. Several studies associated the obesity situations with the accumulation of POPs. Dirinck et al. [24] studied the potential correlation between obesity and POPs presence, in a cohort of obese and lean adult men and women. The results of the study showed a positive relationship between the concentration of β-hexachlorocyclohexane and the body mass index (BMI), a negative relationship between the level of PCBs and BMI and no statistically significant relationship between serum levels of dichloro-diphenyldichloroethylene and BMI, concluding that the diabetogenic effect of low-dose exposure to POPs is more complex than a simple obesogenic effect [24]. Lee et al. [25] studied the correlation between presence of low dose POPs and the future apparition of adiposity, dyslipidemia, and insulin resistance. The authors reported that the exposure to POPs can contribute to the development of these affections, common precursors of type 2 diabetes and cardiovascular diseases. Donat-Vargas et al. [26] analyzed 12,313 people with different levels of POPs in the body and noted that obesity was present in 621 cases; moreover, its appearance was correlated with the POPs levels in their diet. Diabetes is a severe disease that can affect the whole body, which involves the accumulation of sugar in the blood, and the body cannot produce enough insulin. In cases of serious forms of diabetes, people can suffer vascular accidents, heart diseases, kidney failure, ulcer, eye disorders [27]. In Japan, a study conducted on 1,374 subjects aged 15-73 years highlighted the fact that chlorinated pesticides and polychlorinated biphenyls interfere with the development of metabolic syndrome (insulin resistance). After the study, a connection between metabolic syndrome and different POP compounds (polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polychlorinated biphenyls) was observed [28]. Airaksinen et al. [29] investigated the association between the occurrence of several POPs (oxychlordane, trans-nonachlor, 1,1-dichloro-2,2-bis-(p-chlorophenyl)-ethylene, polychlorinated biphenyl) and type 2 diabetes. The experiment involved 8,760 subjects born in Helsinki and 1.642.24 times higher types of 2 diabetes were reported in association with high POPs levels. In the same time, the association between type 2 diabetes with oxychlordane and trans-nonachlor was much higher in the case of overweight individuals. The study of Rignell-Hydbom et al. [30] also found an association between p,p’-DDE exposure and type 2 diabetes. 3. Magnetic composites for organic pollutants removal Nowadays, in the aquatic environment there are pollutants that change the physical, chemical and biological properties of water. Several studies present the removal of organic pollutants using innovative materials. For example, adsorption of methylene blue was presented by Wu et al. [31] on rhamnolipid-functionalized graphene oxide (RL-GO) hybrid. Sorption is often used to remove different pollutants, as the method represents a low-cost, simple, efficient and versatile solution [31]. It has been discovered that graphene and its derivatives are very useful in the absorption of environmental pollutants, such as aromatic compounds, dyes, heavy metal ions, combined pollutants, etc. In particular, graphene oxide (GO) has been applied in many ways to the treatment of waste water and its purification because it has a large contact surface and a variety of O-containing functionals groups such as
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hydroxide, epoxide, carbonyl and carboxyl groups. The separation modes involving these types of absorbents are often complicated by their dispersion in water. The introduction of Fe3O4 nanoparticles (NPs) into GO and reduced graphene oxide (RGO) can increase the absorption capacity and even favor the process. In the same time, introduction of the magnetic phase reduces the costs usually associated with the separation stage. Huang et al. [32] synthesized and characterized magnetic graphene oxide (MGO), magnetically chemically-reduced graphene (MCRG) and magnetic annealing-reduced graphene (MARG). The obtained materials also include iron and oxygen contents that have sorption capabilities. Graphene oxide (GO) was obtained from natural graphite flakes using a modified Hummers method. The adhesive (GO) was exfoliated by sonication and dialyzed to remove acids and other impurities, and co-precipitation of FeCl3×6H2O and FeSO4×7H2O produced nanoparticles of Fe3O4 (NPs). The GO solution was added dropwise to the Fe3O4 NPs solution, with the formation of MGO. After reduction of the synthesized MGO with hydrazine hydrate, MCRG was obtained by a 500 °C expansion under N2 using MGO as the precursor. MGO, MCRG, and MARG of different oxygen contents were used as magnetic graphene adsorbents. Tetracycline (TC) was selected as organic pollutant model to investigate adsorption processes of magnetic graphene materials. MGO proved to be the best adsorbent for TC, which should be attributed to a larger number of Ocontaining functional groups. The experimental results demonstrated that the absorption capacity for MGO was 252 mg/g [32]. Zhang et al. [33] synthesized Fe3O4 NPs with diameter of approx. 10 nm to remove aromatic hydrocarbons such as phenol an aniline from aqueous solutions. The NPs were obtained by the co-precipitation method, using FeCl2×4H2O and FeCl3×6H2O. The obtained nanoparticles were separated from the solution with an external magnetic field and rinsed several times with deoxygenated water. The pollutant removal experiments were carried out in buffer solution (NaH2PO4–Na2HPO4) containing NPs in which aniline or phenol were added. The removal of the aromatic compounds was achieved after 6 hours, the total organic carbon abatement efficiency for phenol and aniline were 42.79% and 40.38%, respectively. To demonstrate the effectiveness of the tested compounds, compared analysis was performed before and after the catalytic process. Prior to the reaction, the nanoparticles had a diameter of approximately 10 nm and a spherical shape; after the adsorption, the diameter of some nanoparticles increased and the shape changed. The paramagnetic behavior of the compound was demonstrated by placing a magnet near the vessel with the containing nanoparticles aqueous solution. Following the proximity of the magnet, the solution became clear in just a few seconds. It was observed that the effectiveness of the adsorption process was directly proportional to the concentration of the nanoparticles used [33]. Zhang et al. [34] synthesized core-shell Fe3O4/C magnetic nanomaterials, with an approximate diameter of 250 nm, using a two steps procedure, for removing organic dyes from aqueous solutions. Fe3O4 magnetic nanospheres were synthesized by mixing FeCl3×6H2O with ethylene glycol, as a solvent and reducing agent, until FeCl3 was dissolved, followed by the addition of anhydrous sodium acetate. The reaction was considered completed when a clear solution was obtained. Finally, the obtained nanospheres were rinsed several times with warm water and ethanol. The absorption of the used dyes (methylene blue – MB and cresol red - CR) was evaluated using UV–vis spectrometry. The dyes were adsorbed from the solution in proportion of 90% in 2.5 hours. The adsorption capacities of the proposed material for MB and CR were established to be 44.38 mg/g and 11.22 mg/g, respectively [34]. Another solution for removing POPs from water matrix was applied by Zhang et al. [35]. The authors photocatalytic removed 2,2-bis (4-hydroxyphenyl) propane (BPA) with a core-shell-shell magnetic composite material BiOBr@SiO2@Fe3O4. The magnetic composite material was obtained in three steps: first step involved the synthesis of the Fe3O4 microspheres, followed by the magnetic SiO2@ Fe3O4 core-shell composite microspheres, and finally the synthesis of the BiOBr@SiO2@Fe3O4 material. Following the experiments, it was demonstrated that the synthesized material had superior photocatalytic properties, compared with the commercial TiO2 photocatalyst (P25) (87% degradation of BPA using the synthesized material, compared with a 27.2% degradation achieved using the commercial product, after 50 min under visible light irradiation). Moreover, the composite can be easily separated from the reaction solution using an external magnetic field [35].
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Fierascu et al. [36] proposed core-shell magnetic composites (copper and nickel ferrite cores, with a chitosan shell) for the efficient removal of pharmaceutical endocrine disrupting compounds (naproxen sodium and diltiazem hydrochloride). The presented results suggested that the nickel ferrite/chitosan composite showed the highest affinity towards the adsorption of Na naproxen (89% removal after 48 hours), while the best results for the adsorption of diltiazem HCl were obtained for the copper ferrite/chitosan composite (56% at 48 hours). The magnetic composites (having saturation magnetization determined by magnetization versus magnetic field strength investigations at room temperature of 2.5 emu/g and 6.8 emu/g, respectively) were also easily removed from the test solution by using an external magnetic field. 4. Conclusions The persistence and health effects of organic pollutants represents an important area of research, and new alternatives for their removal being currently proposed. POPs pollution has been known since the 1970s, but more attention has been paid to it in recent years. Due to their physical properties, namely lipophilicity and solubility, they can spread very easily and quickly into water, soil and air, and then into human food. In the living organisms, they can affect various systems and cause a series of serious affections, such as endocrine disorders, reproductive system problems, cardiovascular problems, cancer, obesity, diabetes, and even death. Considering the potential treat both to the environment and the human health, efforts are focused towards the identification of new, more efficient solutions for their removal. The application of magnetic materials (especially core-shell materials, with a magnetic core and an active shell) represents a viable alternative in the targeted area. As the presented short literature review proves, it is possible to remove persistent organic pollutants from water using magnetic nanomaterials. Various types of nanomaterials with magnetic properties (such as Fe3O4, Fe3O4/C, BiOBr@SiO2@Fe3O4, nickel and copper ferrite/chitosan) have been used for the removal of organic pollutants. Their magnetic properties allow the rapid removal of the materials, together with the pollutants, from the solution using an external magnetic field. The approach can be easily translated to the industrial scale, being a cost-effective alternative to the currently applied methods. Thus, the reduction of the POPs levels in the environment can lead to an increase not only in the environmental status, but also to the diminishment of the health effects those pollutants can cause. Acknowledgements This work was supported by Romanian Ministry of Research and Innovation - MCI through INCDCP-ICECHIM Bucharest 2019-2022 Core Program PN. 19.23 - Chem-Ergent, Project No.19.23.03.01 and contract 31PFE/2018 TRANS - CHEM. References [1] K.C. Jones, P. de Voogt, Environ. Pollut. 100 (1999) 209-221. [2] L. Ritter, K.R. Solomon, J. Forget, M. Stemeroff, C. O’Leary, IPCS, 1995, available at: https://www.who.int/ipcs/assessment/en/pcs_95_39_2004_05_13.pdf. [3] D.O. Carpenter, Rev. Environ. Health. 26 (2011) 61-69. [4] Stockholm Convention on Persistent Organic Pollutants, 2014, available at https://www.wipo.int/edocs/lexdocs/treaties/en/unep-pop/trt_unep_pop_2.pdf. [5] S. Corsolini, S. Focardi, in: F. Faranda, L. Guglielmo, A. Ianora (Eds.), Springer-Verlag, Berlin, 2000, pp. 575-584. [6] J. Jacob, Int. J. Biosci. Biochem. Bioinforma. 3 (2013) 657-661. [7] Y. Chen, C. Wang, Z. Wang, Environ. Int. 31(2005) 778-783. [8] N. H. Minh, T. B. Minh, N. Kajiwara, T. Kunisue, A. Subramanian, H. Iwata, T. S. Tana, R. Baburajendran, S. Karuppiah, P. H. Viet, B. C. Tuyen, S. Tanabe, Arch. Environ. Contam. Toxicol. 50 (2006) 474-481. [9] H. Zhi, Z. Zhao, L. Zhang, Chemosphere 119 (2015) 1134-1140. [10] O. M.L. Alharbi, A. A. Basheer, R. A. Khattab, I. Ali, J. Molec. Liquids 263 (2018) 442–453. [11] H. Zhou, H.Wu, C. Liao, X. Diao, J. Zhen, L. Chen, Q. Xue, Toxicol. Mech. Methods 20 (2010) 279-286. [12] T. Damstra, S.W. Page, J.L. Herrman, T. Meredith, J. Epidemiol. Community Health 56 (2002) 824-825. [13] E. Papadopoulou, M. Vafeiadi, S. Agramunt, K. Mathianaki, P. Karakosta, A. Spanaki, H. Besselink, H. Kiviranta, P. Rantakokko, K. Sarri, A. Koutis, L. Chatzi, M. Kogevinas, Sci. Total Environ. 461-462 (2013) 222-229.
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