Environ Sci Pollut Res DOI 10.1007/s11356-014-3991-4
RESEARCH ARTICLE
Adsorption/desorption and bioavailability of methamphetamine in simulated gastrointestinal fluids under the presence of multiwalled carbon nanotubes Jing Zhang & Zhenhu Xiong & Lei Wang & Kai Zhang
Received: 11 August 2014 / Accepted: 12 December 2014 # Springer-Verlag Berlin Heidelberg 2015
Abstract Adsorption/desorption and desorption hysteresis of methamphetamine (MMA) on carbon nanotubes (CNTs) as well as bioavailability of MMA were studied in simulated gastrointestinal fluids and background fluids. Adsorption of MMA in near-neutral (weak alkaline) intestinal fluid was enhanced, while adsorption of MMA on CNTs in acid gastric fluid was suppressed. Desorption of MMA is divided into fast and slow stages, and fast desorption conducting in the gastric fluid lasted shortly and slow desorption occurred in intestinal fluid; pepsin can enhance the release of MMA in gastrointestinal system. While, the acidic condition in gastric fluid is the main factor which causes the release of MMA. The amount of MMA released from CNTs in different fluids follows the order gastric > background (pH=2.0) > intestinal (fed) > intestinal
(fasted) > background (pH=7.5). These findings in the simulated gastrointestinal system suggest that the release of MMA from CNTs could be promoted by biomacromolecules (such as pepsin and bile salts in digestive tract); thus, the bioavailability of MMA is enhanced.
Responsible editor: Philippe Garrigues
Carbon nanotubes (CNTs) are new types of nanomaterials that can be classified into single-walled carbon nanotubes and multiwalled carbon nanotubes according to their layers (Minoia et al. 2012). Because π–π electron system on the surface of graphene layers, CNTs can have great affinity capacity to the chemicals, such as pesticides, dyes, and persistent organic pollutants and metal ions, heavy metal ions in water environment by donor–acceptor interaction and other ways (hydrophobic interaction, hydrogen bonding interaction, and electrostatic interaction); therefore, CNTs become potential adsorbents for wastewater treatment and water purification (Ren et al. 2011). In this sense, there are several possible pathways for CNTs to become available to the organisms. For instance, CNTs have been used for biological medicine and food packaging, which causes it to have the opportunity to enter the human body directly. Besides, CNTs in the environment could be ingested by terrestrial plants and aquatic life, and thus enter the food chain and lead to adverse effects on the human beings. Methamphetamine (MMA, C10H15N) belongs to the amphetamine-type stimulants and the structure was given in
Highlights • Adsorption/desorption and desorption hysteresis of MMA on CNTs in vitro gastrointestinal fluid were studied. • Adsorption of MMA on CNTs can be enhanced in near-neutral (weak alkaline) intestinal fluid. • Desorption of MMA from CNTs may be strengthened by pepsin in the gastric fluid. • The release of MMA from CNTs follows the order gastric fluid > background solution (pH=2.0) > intestinal fluid (fed) > intestinal fluid (fasted) > background solution (pH=7.5). • Desorption of MMA in digestive system increases the bioavailability of MMA to aquatic organisms. Electronic supplementary material The online version of this article (doi:10.1007/s11356-014-3991-4) contains supplementary material, which is available to authorized users. J. Zhang : Z. Xiong (*) : L. Wang Tianjin Key Laboratory of Water Quality Science and Technology, School of Municipal and Environmental Engineering, Tianjin Chenjian University, Tianjin 300384, People’s Republic of China e-mail: [email protected] K. Zhang Tianjin Municipal Public Security Bureau Narcotics Corps, Tianjin 300240, People’s Republic of China
Keywords Methamphetamine . Gastrointestinal fluids . Carbon nanotubes . Adsorption/desorption . Bioavailability
Introduction
Environ Sci Pollut Res
the supplementary information Fig. S1. Because the appearance of MMA is similar to the ice, it is commonly known as "ice." MMA can cause some pharmacology and toxicological effects, such as psychological dependence, central nervous excitement, appetite inhibition, and hallucinogenic situations (Dean et al. 2013); thus, it has been prohibited by the psychoactive substance of the United Nations Office of Drug and Crime (UNODC). However, MMA prescription drugs are legitimate and used in the treatment of sleepiness, cerebral inflammation, Parkinson syndrome, alcoholism, and obesity. In recent years, amphetamine-type stimulants represented by MMA rapidly spreads around the world through illegal or legal consumption and synthesis approach in private laboratories (Duane et al. 2005; Herman-Stahl et al. 2006); the crime behavior in this long-term abuse caused serious adverse effects to the society. According to the research, after metabolism in the human body, the majority of MMA was not metabolized and excreted in the urine, and then entered the sewage system. Owing to MMA and its metabolite being difficult to be removed by wastewater treatment process, they will be discharged into surface water and underground water with effluent. In aqueous environment, the MMA which has not been metabolized may form complexes with different kinds of nanoparticles including CNTs and enter the gastrointestinal tracts through a variety of ways. Once the MMA carried by CNTs releases in the digestive tract, it will produce biological availability. However, MMA is a chemical with strong hydrophilic character and physiological effect; the adsorption/desorption mechanism of MMA on the CNTs will be different from that of hydrophobic compounds under physiological conditions. Nevertheless, the physical chemical behaviors and bioavailability of MMA in the gastrointestinal tract are less known. It is necessary to research the physical and chemical behavior of the complex of CNTs with organic pollutants in the gastrointestinal tract. However, the study about effects of CNTs to biological systems often focuses on hydrophobic organic chemicals; for example, Wang et al. (2011) studied the adsorption of phenanthrene and desorption of adsorbed phenanthrene on the CNTs in simulated gastric fluid. They proposed that the pepsin and bile salt in digestive fluid may prom ote the release of hydrophobic com pounds (phenanthrene) from the CNTs and increase the bioavailability of adsorbed phenanthrene. In general, the hydrophobic compounds have low solubility in water, and the main fate for them is adsorption on the nanoparticles. Because many of the environmental important compounds are ionic form, their environmental behavior may be completely different with hydrophobic organic chemicals. Therefore, the adsorption of ionizable organic contaminants on the CNTs has drawn attention. For example, Sun et al. (2014) exposed carp to water-containing CNTs and pentachlorophenol (PCP) to evaluate the facilitated transport of PCP in
carp in vivo and the desorption of PCP from CNTs in simulated digestive fluid; after 21-day exposure of PCP to carps, they found that CNTs promoted bioaccumulation of PCP. In this study, the batch experiments of MMA on multiwalled carbon nanotube (it was abbreviated to CNTs in the paper) in simulated gastrointestinal fluids (presence of pepsin or bile salt) were carried out to investigate the adsorption/desorption characteristics of MMA on/from CNTs. Gastrointestinal model was used for studying the release process of adsorbed MMA on the CNTs in vitro and assessing the effect of CNTs on bioavailability of released MMA was achieved.
Materials and experiments Materials CNTs were purchased from the Chinese Academy of Science, Chengdu Organic Chemistry Co. LTD. The average outer diameter and inner diameter of the CNT was 8–15 and 3– 5 nm, respectively, and the average length was 50 μm and surface area was 200 m2/g. The CNTs were purified with HNO3 before used to reduce the content of metal catalyst and amorphous carbon. Methamphetamine (MMA) hydrochloride was from Tianjin Municipal Public Security Bureau Narcotics Corps, which was dissolved in methanol and stored in a refrigerator at 4 °C. In order to facilitate HPLC detection and the concentration of MMA used to adsorption experiment was 3–13 mg/L, this concentration range benefitted to the experimental operation and did not affect the experimental results even though it is larger than environmental content. Pepsin (potency 1: 10,000; grade: high-purity grade; pH 2–4; store at 2–8 °C) and bile salts (residue on ignition intestinal fluid (fed) > background solution (pH=2.0) > gastric fluid. Fast desorption took place in gastric fluid, and corresponding desorption percent was about 80 %. Desorption hysteresis was observed in the desorption process of MMA from CNTs, pepsin, and bile salts which contributed to the releasing of MMA. Desorption of MMA from CNTs in different fluids follows the following order: gastric fluid > background solution (pH=2.0) > intestinal fluid (fed) > intestinal fluid (fasted) > background solution (pH=7.5). The experiment carried out in in vitro gastrointestinal system showed that MMA bound by CNTs in natural water can enter into organisms; the physical or chemical conditions in the digestive tract of aquatic organisms can enhance the releasing of MMA from CNTs and promote the bioavailability of MMA. However, no matter the results are universal or not, further researches are required. Acknowledgments This research was supported by the National Nature Science Foundation of China (grant number: 50878138). We appreciate our colleagues who participated in this work.
References Barnier C, Ouvrard S, Robin C, Morel JL (2014) Desorption kinetics of PAHs from aged industrial soils for availability assessment. Sci Total Environ 470:639–645 Chi W, Hao L, Shaohua L, Hao Z, Zhenyu W, Bo P, Baoshan X (2013) Coadsorption, desorption hysteresis and sorption thermodynamics of sulfamethoxazole and carbamazepine on graphene oxide and graphite. Carbon 65:243–51
Dean AC, Groman SM, Morales AM, London ED (2013) An evaluation of the evidence that methamphetamine abuse causes cognitive decline in humans. Neuropsychopharmacology 38: 259–274 Duan L, Palanisami T, Liu Y, Dong Z, Mallavarapu M, Kuchel T, Semple KT, Naidu R (2014) Effects of ageing and soil properties on the oral bioavailability of benzo a pyrene using a swine model. Environ Int 70:192–202 Duane DD, Heimburger GE, Chu TT (2005) Prescription methamphetamine in narcolepsy: frequency, cognitive and behavioral effects. Sleep 28:A213–A213 Fei Y-h, X-d L, X-y L (2011) Organic diagenesis in sediment and its impact on the adsorption of bisphenol A and nonylphenol onto marine sediment. Mar Pollut Bull 63:578–582 Feldman EP, Stefanovich LI, Terekhova YV (2014) Influence of adsorption or desorption and surface diffusion on the formation kinetics of open half-monolayer coverage. Phys Rev E 89 Gong Y, Zhao X, O’Reilly SE, Qian T, Zhao D (2014) Effects of oil dispersant and oil on sorption and desorption of phenanthrene with Gulf Coast marine sediments. Environ Pollut 185:240–249 Herman-Stahl MA, Krebs CP, Kroutil LA, Heller DC (2006) Risk and protective factors for nonmedical use of prescription stimulants and methamphetamine among adolescents. J Adolesc Health 39:374– 380 Kim JK, Jung KH, Jang JH, Huh DS (2014) Hydrophobic interactionmediated reversible adsorption-desorption of nanoparticles in the honeycomb-patterned thermoresponsive poly(N-isopropylamide) hydrogel surface. Polym Bull 71:1375–1388 Li J, Hou L, Du P, Yang J, Li K, Xu Z, Wang C, Zhang H, Li X (2014) Estimation of amphetamine and methamphetamine uses in Beijing through sewage-based analysis. Sci Total Environ 490:724–32 Makino Y (2012) Simple HPLC method for detection of trace ephedrine and pseudoephedrine in high-purity methamphetamine. Biomed Chromatogr 26:327–330 Minoia A, Chen L, Beljonne D, Lazzaroni R (2012) Molecular modeling study of the structure and stability of polymer/carbon nanotube interfaces. Polymer 53:5480–5490 Monsef Shokri M, Ahmadian S, Akbari N, Khajeh K (2014) Hydrophobic substitution of surface residues affects lipase stability in organic solvents. Mol Biotechnol 56:360–8 Motaghian HR, Hosseinpur AR (2014) Impact of sewage sludge application on zinc desorption kinetics in some calcareous soils. Environ Earth Sci 71:4647–4655 Nam S-W, Choi D-J, Kim S-K, Her N, Zoh K-D (2014) Adsorption characteristics of selected hydrophilic and hydrophobic micropollutants in water using activated carbon. J Hazard Mater 270:144–152 Panda M, Kabir ud D (2013) Solubilization of polycyclic aromatic hydrocarbons by gemini-conventional mixed surfactant systems. J Mol Liq 187:106–113 Ren X, Chen C, Nagatsu M, Wang X (2011) Carbon nanotubes as adsorbents in environmental pollution management: a review. Chem Eng J 170:395–410 Sun H, Ruan Y, Zhu H, Zhang Z, Zhang Y, Yu L (2014) Enhanced bioaccumulation of pentachlorophenol in carp in the presence of multi-walled carbon nanotubes. Environ Sci Pollut Res 21:2865– 2875 Wang J, Wang F, Yao J, Wang R, Yuan H, Masakorala K, Choi MMF (2013) Adsorption and desorption of dimethyl phthalate on carbon nanotubes in aqueous copper(II) solution. Colloids Surf Physicochem Eng Asp 417:47–56 Wang Z, Zhao J, Song L, Mashayekhi H, Chefetz B, Xing B (2011) Adsorption and desorption of phenanthrene on carbon nanotubes in simulated gastrointestinal fluids. Environ Sci Technol 45:6018– 6024
Environ Sci Pollut Res Wu W, Sun H (2010) Sorption-desorption hysteresis of phenanthrene— effect of nanopores, solute concentration, and salinity. Chemosphere 81:961–967
Yang K, Jing Q, Wu W, Zhu L, Xing B (2010) Adsorption and conformation of a cationic surfactant on single-walled carbon nanotubes and their influence on naphthalene sorption. Environ Sci Technol 44:681–687
RESEARCH ARTICLE
Adsorption/desorption and bioavailability of methamphetamine in simulated gastrointestinal fluids under the presence of multiwalled carbon nanotubes Jing Zhang & Zhenhu Xiong & Lei Wang & Kai Zhang
Received: 11 August 2014 / Accepted: 12 December 2014 # Springer-Verlag Berlin Heidelberg 2015
Abstract Adsorption/desorption and desorption hysteresis of methamphetamine (MMA) on carbon nanotubes (CNTs) as well as bioavailability of MMA were studied in simulated gastrointestinal fluids and background fluids. Adsorption of MMA in near-neutral (weak alkaline) intestinal fluid was enhanced, while adsorption of MMA on CNTs in acid gastric fluid was suppressed. Desorption of MMA is divided into fast and slow stages, and fast desorption conducting in the gastric fluid lasted shortly and slow desorption occurred in intestinal fluid; pepsin can enhance the release of MMA in gastrointestinal system. While, the acidic condition in gastric fluid is the main factor which causes the release of MMA. The amount of MMA released from CNTs in different fluids follows the order gastric > background (pH=2.0) > intestinal (fed) > intestinal
(fasted) > background (pH=7.5). These findings in the simulated gastrointestinal system suggest that the release of MMA from CNTs could be promoted by biomacromolecules (such as pepsin and bile salts in digestive tract); thus, the bioavailability of MMA is enhanced.
Responsible editor: Philippe Garrigues
Carbon nanotubes (CNTs) are new types of nanomaterials that can be classified into single-walled carbon nanotubes and multiwalled carbon nanotubes according to their layers (Minoia et al. 2012). Because π–π electron system on the surface of graphene layers, CNTs can have great affinity capacity to the chemicals, such as pesticides, dyes, and persistent organic pollutants and metal ions, heavy metal ions in water environment by donor–acceptor interaction and other ways (hydrophobic interaction, hydrogen bonding interaction, and electrostatic interaction); therefore, CNTs become potential adsorbents for wastewater treatment and water purification (Ren et al. 2011). In this sense, there are several possible pathways for CNTs to become available to the organisms. For instance, CNTs have been used for biological medicine and food packaging, which causes it to have the opportunity to enter the human body directly. Besides, CNTs in the environment could be ingested by terrestrial plants and aquatic life, and thus enter the food chain and lead to adverse effects on the human beings. Methamphetamine (MMA, C10H15N) belongs to the amphetamine-type stimulants and the structure was given in
Highlights • Adsorption/desorption and desorption hysteresis of MMA on CNTs in vitro gastrointestinal fluid were studied. • Adsorption of MMA on CNTs can be enhanced in near-neutral (weak alkaline) intestinal fluid. • Desorption of MMA from CNTs may be strengthened by pepsin in the gastric fluid. • The release of MMA from CNTs follows the order gastric fluid > background solution (pH=2.0) > intestinal fluid (fed) > intestinal fluid (fasted) > background solution (pH=7.5). • Desorption of MMA in digestive system increases the bioavailability of MMA to aquatic organisms. Electronic supplementary material The online version of this article (doi:10.1007/s11356-014-3991-4) contains supplementary material, which is available to authorized users. J. Zhang : Z. Xiong (*) : L. Wang Tianjin Key Laboratory of Water Quality Science and Technology, School of Municipal and Environmental Engineering, Tianjin Chenjian University, Tianjin 300384, People’s Republic of China e-mail: [email protected] K. Zhang Tianjin Municipal Public Security Bureau Narcotics Corps, Tianjin 300240, People’s Republic of China
Keywords Methamphetamine . Gastrointestinal fluids . Carbon nanotubes . Adsorption/desorption . Bioavailability
Introduction
Environ Sci Pollut Res
the supplementary information Fig. S1. Because the appearance of MMA is similar to the ice, it is commonly known as "ice." MMA can cause some pharmacology and toxicological effects, such as psychological dependence, central nervous excitement, appetite inhibition, and hallucinogenic situations (Dean et al. 2013); thus, it has been prohibited by the psychoactive substance of the United Nations Office of Drug and Crime (UNODC). However, MMA prescription drugs are legitimate and used in the treatment of sleepiness, cerebral inflammation, Parkinson syndrome, alcoholism, and obesity. In recent years, amphetamine-type stimulants represented by MMA rapidly spreads around the world through illegal or legal consumption and synthesis approach in private laboratories (Duane et al. 2005; Herman-Stahl et al. 2006); the crime behavior in this long-term abuse caused serious adverse effects to the society. According to the research, after metabolism in the human body, the majority of MMA was not metabolized and excreted in the urine, and then entered the sewage system. Owing to MMA and its metabolite being difficult to be removed by wastewater treatment process, they will be discharged into surface water and underground water with effluent. In aqueous environment, the MMA which has not been metabolized may form complexes with different kinds of nanoparticles including CNTs and enter the gastrointestinal tracts through a variety of ways. Once the MMA carried by CNTs releases in the digestive tract, it will produce biological availability. However, MMA is a chemical with strong hydrophilic character and physiological effect; the adsorption/desorption mechanism of MMA on the CNTs will be different from that of hydrophobic compounds under physiological conditions. Nevertheless, the physical chemical behaviors and bioavailability of MMA in the gastrointestinal tract are less known. It is necessary to research the physical and chemical behavior of the complex of CNTs with organic pollutants in the gastrointestinal tract. However, the study about effects of CNTs to biological systems often focuses on hydrophobic organic chemicals; for example, Wang et al. (2011) studied the adsorption of phenanthrene and desorption of adsorbed phenanthrene on the CNTs in simulated gastric fluid. They proposed that the pepsin and bile salt in digestive fluid may prom ote the release of hydrophobic com pounds (phenanthrene) from the CNTs and increase the bioavailability of adsorbed phenanthrene. In general, the hydrophobic compounds have low solubility in water, and the main fate for them is adsorption on the nanoparticles. Because many of the environmental important compounds are ionic form, their environmental behavior may be completely different with hydrophobic organic chemicals. Therefore, the adsorption of ionizable organic contaminants on the CNTs has drawn attention. For example, Sun et al. (2014) exposed carp to water-containing CNTs and pentachlorophenol (PCP) to evaluate the facilitated transport of PCP in
carp in vivo and the desorption of PCP from CNTs in simulated digestive fluid; after 21-day exposure of PCP to carps, they found that CNTs promoted bioaccumulation of PCP. In this study, the batch experiments of MMA on multiwalled carbon nanotube (it was abbreviated to CNTs in the paper) in simulated gastrointestinal fluids (presence of pepsin or bile salt) were carried out to investigate the adsorption/desorption characteristics of MMA on/from CNTs. Gastrointestinal model was used for studying the release process of adsorbed MMA on the CNTs in vitro and assessing the effect of CNTs on bioavailability of released MMA was achieved.
Materials and experiments Materials CNTs were purchased from the Chinese Academy of Science, Chengdu Organic Chemistry Co. LTD. The average outer diameter and inner diameter of the CNT was 8–15 and 3– 5 nm, respectively, and the average length was 50 μm and surface area was 200 m2/g. The CNTs were purified with HNO3 before used to reduce the content of metal catalyst and amorphous carbon. Methamphetamine (MMA) hydrochloride was from Tianjin Municipal Public Security Bureau Narcotics Corps, which was dissolved in methanol and stored in a refrigerator at 4 °C. In order to facilitate HPLC detection and the concentration of MMA used to adsorption experiment was 3–13 mg/L, this concentration range benefitted to the experimental operation and did not affect the experimental results even though it is larger than environmental content. Pepsin (potency 1: 10,000; grade: high-purity grade; pH 2–4; store at 2–8 °C) and bile salts (residue on ignition intestinal fluid (fed) > background solution (pH=2.0) > gastric fluid. Fast desorption took place in gastric fluid, and corresponding desorption percent was about 80 %. Desorption hysteresis was observed in the desorption process of MMA from CNTs, pepsin, and bile salts which contributed to the releasing of MMA. Desorption of MMA from CNTs in different fluids follows the following order: gastric fluid > background solution (pH=2.0) > intestinal fluid (fed) > intestinal fluid (fasted) > background solution (pH=7.5). The experiment carried out in in vitro gastrointestinal system showed that MMA bound by CNTs in natural water can enter into organisms; the physical or chemical conditions in the digestive tract of aquatic organisms can enhance the releasing of MMA from CNTs and promote the bioavailability of MMA. However, no matter the results are universal or not, further researches are required. Acknowledgments This research was supported by the National Nature Science Foundation of China (grant number: 50878138). We appreciate our colleagues who participated in this work.
References Barnier C, Ouvrard S, Robin C, Morel JL (2014) Desorption kinetics of PAHs from aged industrial soils for availability assessment. Sci Total Environ 470:639–645 Chi W, Hao L, Shaohua L, Hao Z, Zhenyu W, Bo P, Baoshan X (2013) Coadsorption, desorption hysteresis and sorption thermodynamics of sulfamethoxazole and carbamazepine on graphene oxide and graphite. Carbon 65:243–51
Dean AC, Groman SM, Morales AM, London ED (2013) An evaluation of the evidence that methamphetamine abuse causes cognitive decline in humans. Neuropsychopharmacology 38: 259–274 Duan L, Palanisami T, Liu Y, Dong Z, Mallavarapu M, Kuchel T, Semple KT, Naidu R (2014) Effects of ageing and soil properties on the oral bioavailability of benzo a pyrene using a swine model. Environ Int 70:192–202 Duane DD, Heimburger GE, Chu TT (2005) Prescription methamphetamine in narcolepsy: frequency, cognitive and behavioral effects. Sleep 28:A213–A213 Fei Y-h, X-d L, X-y L (2011) Organic diagenesis in sediment and its impact on the adsorption of bisphenol A and nonylphenol onto marine sediment. Mar Pollut Bull 63:578–582 Feldman EP, Stefanovich LI, Terekhova YV (2014) Influence of adsorption or desorption and surface diffusion on the formation kinetics of open half-monolayer coverage. Phys Rev E 89 Gong Y, Zhao X, O’Reilly SE, Qian T, Zhao D (2014) Effects of oil dispersant and oil on sorption and desorption of phenanthrene with Gulf Coast marine sediments. Environ Pollut 185:240–249 Herman-Stahl MA, Krebs CP, Kroutil LA, Heller DC (2006) Risk and protective factors for nonmedical use of prescription stimulants and methamphetamine among adolescents. J Adolesc Health 39:374– 380 Kim JK, Jung KH, Jang JH, Huh DS (2014) Hydrophobic interactionmediated reversible adsorption-desorption of nanoparticles in the honeycomb-patterned thermoresponsive poly(N-isopropylamide) hydrogel surface. Polym Bull 71:1375–1388 Li J, Hou L, Du P, Yang J, Li K, Xu Z, Wang C, Zhang H, Li X (2014) Estimation of amphetamine and methamphetamine uses in Beijing through sewage-based analysis. Sci Total Environ 490:724–32 Makino Y (2012) Simple HPLC method for detection of trace ephedrine and pseudoephedrine in high-purity methamphetamine. Biomed Chromatogr 26:327–330 Minoia A, Chen L, Beljonne D, Lazzaroni R (2012) Molecular modeling study of the structure and stability of polymer/carbon nanotube interfaces. Polymer 53:5480–5490 Monsef Shokri M, Ahmadian S, Akbari N, Khajeh K (2014) Hydrophobic substitution of surface residues affects lipase stability in organic solvents. Mol Biotechnol 56:360–8 Motaghian HR, Hosseinpur AR (2014) Impact of sewage sludge application on zinc desorption kinetics in some calcareous soils. Environ Earth Sci 71:4647–4655 Nam S-W, Choi D-J, Kim S-K, Her N, Zoh K-D (2014) Adsorption characteristics of selected hydrophilic and hydrophobic micropollutants in water using activated carbon. J Hazard Mater 270:144–152 Panda M, Kabir ud D (2013) Solubilization of polycyclic aromatic hydrocarbons by gemini-conventional mixed surfactant systems. J Mol Liq 187:106–113 Ren X, Chen C, Nagatsu M, Wang X (2011) Carbon nanotubes as adsorbents in environmental pollution management: a review. Chem Eng J 170:395–410 Sun H, Ruan Y, Zhu H, Zhang Z, Zhang Y, Yu L (2014) Enhanced bioaccumulation of pentachlorophenol in carp in the presence of multi-walled carbon nanotubes. Environ Sci Pollut Res 21:2865– 2875 Wang J, Wang F, Yao J, Wang R, Yuan H, Masakorala K, Choi MMF (2013) Adsorption and desorption of dimethyl phthalate on carbon nanotubes in aqueous copper(II) solution. Colloids Surf Physicochem Eng Asp 417:47–56 Wang Z, Zhao J, Song L, Mashayekhi H, Chefetz B, Xing B (2011) Adsorption and desorption of phenanthrene on carbon nanotubes in simulated gastrointestinal fluids. Environ Sci Technol 45:6018– 6024
Environ Sci Pollut Res Wu W, Sun H (2010) Sorption-desorption hysteresis of phenanthrene— effect of nanopores, solute concentration, and salinity. Chemosphere 81:961–967
Yang K, Jing Q, Wu W, Zhu L, Xing B (2010) Adsorption and conformation of a cationic surfactant on single-walled carbon nanotubes and their influence on naphthalene sorption. Environ Sci Technol 44:681–687
