Removal of phthalates from aqueous solution by different adsorbents: a short review

A Review of the Analysis of Phthalates by Gas Chromatography in Aqueous and Food Matrices

As a commonly well-known industrial chemical, phthalates are produced in high volumes to be used in various consumer products (e.g., plasticizers, medical devices, construction materials, and toys) to enhance softness, durability, transparency, and flexibility. Phthalates are generally not chemically bonded to the polymer chain of the plastic in which they are mixed. Thus, they may leach, migrate, or evaporate into indoor/outdoor air, and foodstuffs. In this review, a comprehensive overview of several sample preparation methods coupled with gas chromatography for the analysis of phthalates in various kinds of complex matrices, with a focus on the last 20 years' worth of papers. The review begins by highlighting the environmental significance of phthalate pollution along with the various routes to their exposure to general population. Then, the discussion is extended to cover the pretreatment and extraction techniques for phthalates for their quantitation based on gas chromatographic approach. Finally, the present and future challenges for the detection of phthalates in aqueous and food matrices are discussed.

Adsorptive removal of dimethyl phthalate using peanut shell-derived biochar from aqueous solutions: equilibrium, kinetics, and mechanistic studies

Rise in polymer industry and extensive use of their products leads to leaching of phthalate esters and distributed into the different matrices of the environment. This chemical group has the potential to hamper the life of living organisms and ecosystem. Thus, it is essential to develop cost-effective adsorbents capable of removing these harmful compounds from the environment. In this work, peanut hull-derived biochar was taken as the adsorbent, and DMP was selected as the model pollutant or adsorbates. The biochars of different properties were produced at three pyrolysis temperatures (i.e., 450, 550, and 650 °C) to check how temperature affected the adsorbent properties and adsorption performance. Consequently, the performance of biochars for DMP adsorption was thoroughly studied by the combination of experiments and compared with commercial activated carbon (CAC). All the adsorbents are meticulously characterized using various analytical techniques and used for adsorption DMP from aqueous solutions. The results suggested that adsorption was favoring chemisorption with multi-layered adsorption as adsorption kinetics and isotherm are in good alignment with pseudo-second-order kinetics and Freundlich isotherm, respectively. Further, thermodynamic study revealed DMP adsorption on adsorbent is physically spontaneous and endothermic. The removal efficiency order of four adsorbent was as follows: BC650 > CAC > BC550 > BC450 with maximum efficiency of 98.8% for BC650 followed by 98.6% for CAC at optimum conditions. And as it is a short carbon chain PAE, dominant mechanisms of adsorption for DMP onto porous biochar were H-bonding, π-π EDA interactions, and diffusion within the pore spaces. Therefore, this study can provide strategies for the synthesis of biochar for effectively removing DMP from aqueous solution.

Phthalate esters: occurrence, toxicity, bioremediation, and advanced oxidation processes

Phthalic acid esters are emerging pollutants, commonly used as plasticizers that are categorized as hazardous endocrine-disrupting chemicals (EDCs). A rise in anthropogenic activities leads to an increase in phthalate concentration in the environment which leads to various adverse environmental effects and health issues in humans and other aquatic organisms. This paper gives an overview of the research related to phthalate ester contamination and degradation methods by conducting a bibliometric analysis with VOS Viewer. Ecotoxicity analysis requires an understanding of the current status of phthalate pollution, health impacts, exposure routes, and their sources. This review covers five toxic phthalates, occurrences in the aquatic environment, toxicity studies, biodegradation studies, and degradation pathways. It highlights the various advanced oxidation processes like photocatalysis, Fenton processes, ozonation, sonolysis, and modified AOPs used for phthalate removal from the environment.

Molecular evaluation of the metabolism of estrogenic di(2-ethylhexyl) phthalate in Mycolicibacterium sp

BACKGROUND

Di(2-ethylhexyl) phthalate (DEHP) is a widely detected plasticizer and a priority pollutant of utmost concern for its adverse impact on humans, wildlife and the environment. To eliminate such toxic burden, biological processes are the most promising ways to combat rampant environmental insults under eco-friendly conditions. The present study investigated the biochemical and molecular assessment of the catabolic potential of Mycolicibacterium sp. strain MBM in the assimilation of estrogenic DEHP.

RESULTS

A detailed biochemical study revealed an initial hydrolytic pathway of degradation for DEHP followed by the assimilation of hydrolyzed phthalic acid and 2-ethylhexanol to TCA cycle intermediates. Besides the inducible nature of DEHP-catabolic enzymes, strain MBM can efficiently utilize various low- and high-molecular-weight phthalate diesters and can grow under moderately halotolerant conditions. Whole genome sequence analysis exhibited a genome size of 6.2 Mb with a GC content of 66.51% containing 6,878 coding sequences, including multiple genes, annotated as relevant to the catabolism of phthalic acid esters (PAEs). Substantiating the annotated genes through transcriptome assessment followed by RT-qPCR analysis, the possible roles of upregulated genes/gene clusters in the metabolism of DEHP were revealed, reinforcing the biochemical pathway of degradation at the molecular level.

CONCLUSIONS

A detailed co-relation of biochemical, genomic, transcriptomic and RT-qPCR analyses highlights the PAE-degrading catabolic machineries in strain MBM. Further, due to functional attributes in the salinity range of both freshwater and seawater, strain MBM may find use as a suitable candidate in the bioremediation of PAEs.

Occurrence, source, ecological risk, and mitigation of phthalates (PAEs) in agricultural soils and the environment: A review

The widespread distribution of phthalates (PAEs) in agricultural soils is increasing drastically; however, the environmental occurrence and potential risk of PAEs in agricultural systems remain largely unreviewed. In this study, the occurrence, sources, ecotoxicity, exposure risks, and control measures of PAEs contaminants in agricultural soils are summarized, and it is concluded that PAEs have been widely detected and persist in the soil at concentrations ranging from a few μg/kg to tens of mg/kg, with spatial and vertical variations in China. Agrochemicals and atmospheric deposition have largely contributed to the elevated contamination status of PAEs in soils. In addition, PAEs cause multi-level hazards to soil organisms (survival, oxidative damage, genetic and molecular levels, etc.) and further disrupt the normal ecological functions of soil. The health hazards of PAEs to humans are mainly generated through dietary and non-dietary pathways, and children may be at a higher risk of exposure than adults. Improving the soil microenvironment and promoting biochemical reactions and metabolic processes of PAEs are the main mechanisms for mitigating contamination. Based on these reviews, this study provides a valuable framework for determining future study objectives to reveal environmental risks and reduce the resistance control of PAEs in agricultural soils.

Remediation of phthalate acid esters from contaminated environment—Insights on the bioremedial approaches and future perspectives

Phthalates are well-known emerging pollutants that are toxic to the environment and human health. Phthalates are lipophilic chemicals used as plasticizers in many of the items for improving their material properties. These compounds are not chemically bound and are released to the surroundings directly. Phthalate acid esters (PAEs) are endocrine disruptors and can interfere with hormones, which can cause issues with development and reproduction, thus there is a huge concern over their existence in various ecological surroundings. The purpose of this review is to explore the occurrence, fate, and concentration of phthalates in various environmental matrices. This article also covers the phthalate degradation process, mechanism, and outcomes. Besides the conventional treatment technology, the paper also aims at the recent advancements in various physical, chemical, and biological approaches developed for phthalate degradation. In this paper, a special focus has been given on the diverse microbial entities and their bioremedial mechanisms executes the PAEs removal. Critically, the analyses method for determining intermediate products generated during phthalate biotransformation have been discussed. Concluisvely, the challenges, limitations, knowledge gaps and future opportunities of bioremediation and their significant role in ecology have also been highlighted.

Catalytic ozonation with vanadium oxide-doped TiO2 nanoparticles for the removal of di-2-ethylhexyl phthalate

Among various plastic additives, di-2-ethylhexyl phthalate (DEHP) has been a great concern due to its high leaching potential and harmful effects on both human and the ecosystem. For the effective oxidation and mineralization of DEHP by ozone in the existing TiO₂ catalytic processes, the heterogeneous catalyst, vanadium oxide (V₂O₅)-incorporated TiO₂ (V₂O₅/TiO₂), was synthesized. The generation of hydroxyl radicals was promoted by cyclic redox reactions of vanadium atoms in V₂O₅/TiO₂ via the increase of surface oxygen vacancies by the replacement of V⁵⁺ species in the lattice of TiO₂. The catalytic ozonation in the presence of V₂O₅/TiO₂ exhibited the significantly higher degradation of DEHP with the pseudo-second-order kinetic constant of 1.7 × 10⁵ mM^-1min^-1 and the removal efficiency of 58.7% after 60 s in 2 mg/L of ozone. The degradation of DEHP was initiated by the shortening of the alkyl-side chain followed by the opening of esterified benzene moieties.

A review on the removal of phthalate acid esters in wastewater treatment plants: from the conventional wastewater treatment to combined processes

In the past decades, phthalate acid esters (PAEs), as a new class of recalcitrant environmental contaminant, have attracted increasing concern due to their potential hazards to reproductive system. wastewater treatment plants (WWTPs) are generally regarded as a crucial barrier to prevent a variety of contaminants from introducing into aquatic environment. This paper reviews the occurrence, fate, and removal efficacy of six widely appearing PAEs in conventional wastewater treatment. PAEs removal appears to be compound- and process-dependent. Advanced treatment processes, including activated carbon, advanced oxidation process (AOPs), membrane filtration, and membrane bioreactor, show good performance in PAEs elimination, but many methods have been commercially limited by toxic byproducts, high operation, and maintenance costs. Even though combined processes are qualified as a promising alternative, further studies are required to optimize these processes, especially the competitiveness between technique and economy.

Phthalates removal from wastewater by different methods - a review

Phthalate esters are commonly used as plasticizers to improve the durability and workability of polymeric materials, locating and identifying them in various contexts has become a major challenge. Because of their ubiquitous use in plastic packaging and personal care items, as well as their tendency to leach out of these materials, phthalates have been detected in a variety of aquatic situations, including surface water, groundwater, drinking water, and wastewater. Phthalate esters have been shown to affect reproductive health and physical growth by disrupting the endocrine system. As a result, developing energy-efficient and effective technologies to eliminate these harmful substances from the atmosphere has become more important and urgent. This paper examines the existing techniques for treating phthalates and degradation mechanisms, as well as knowledge gaps and future research directions. These technologies include adsorption, electrochemical, photocatalysis, membrane filtration and microbial degradation. Adsorption and photo catalysis are the most widely used techniques for phthalate removal, according to the literature survey papers.

Phthalates in the environment: characteristics, fate and transport, and advanced wastewater treatment technologies

Phthalates are well-known emerging contaminants that harm human health and the environment. Therefore, this review aims to discuss about the occurrence, fate, and phthalates concentration in the various environmental matrices (e.g., aquatic, sediment, soil, and sewage sludge). Hence, it is necessary to treat sources containing phthalates before discharging them to aqueous environment. Various advanced wastewater treatments including adsorption process (e.g., biochar, activated carbon), advanced oxidation processes (e.g., photo-fenton, ozonation, photocatalysis), and biological treatment (membrane bioreactor) have been successfully to address this issue with high removal efficiencies (70-95%). Also, the degradation mechanism was discussed to provide a comprehensive understanding of the phthalate removal for the reader. Additionally, key factors that influenced the phthalates removal efficiency of these technologies were identified and summarized with a view towards pilot-scale and industrial applications.

Biodegradation of di-(2-ethylhexyl) phthalate by novel Rhodococcus sp. PFS1 strain isolated from paddy field soil

Di-(2-ethylhexyl)-phthalate (DEHP) is the phthalate ester frequently utilized as a plasticizer, commonly found in cosmetics, packaging materials; moreover, it has carcinogenic and mutagenic effects on humans. In the current study, we isolated the soil bacterium Rhodococcus sp. PFS1 and to assess its DEHP degradation ability in various environmental conditions. The strain PFS1 was isolated from paddy field soil and identified by the 16S rRNA sequencing analyses. The strain PFS1 was examined for its biodegradation ability of DEHP at various pH, temperature, salt concentration, glucose concentration, and high and low concentrations of DEHP. Moreover, the biodegradation of DEHP at a contaminated soil environment by strain PFS1 was assessed. Further, the metabolic pathway of DEHP degradation by PFS1 was analyzed by HPLC-MS analysis. The results showed that the strain PFS1 effectively degraded the DEHP at neutral pH and temperature 30 °C; moreover, expressed excellent DEHP degradation at the high salt concentration (up to 50 g/L). The strain PFS1 was efficiently degraded the different tested phthalate esters (PAEs) up to 90%, significantly removed the DEHP contamination in soil along with native organisms which are present in soil up to 94.66%; nevertheless, the PFS1 alone degraded the DEHP up to 87.665% in sterilized soil. According to HPLC-MS analysis, DEHP was degraded into phthalate (PA) by PFS1 strain via mono(2-ethylehxyl) phthalate (MEHP); then PA was utilized for cell growth. These results suggest that Rhodococcus sp. PFS1 has excellent potential to degrade DEHP at various environmental conditions especially in contaminated paddy field soil.

Electro-Fenton approach in oxidative degradation of dimethyl phthalate - The treatment of aqueous leachate from landfills

Herein, the dimethyl phthalate (DMP) contamination, as an emerging pollutant, has been cost-effectively removed from landfill leachate through an advanced oxidation process, that is the electro-Fenton (EF) process. For this purpose, a quadratic polynomial model was developed via response surface methodology (RSM). Furthermore, the analysis of variance (ANOVA) was performed for evaluating the significance of the proposed assumptions. The actual removal rate of 99.1% was obtained with optimal values of 4 mg L^-1 of initial DMP concentration, 50 mM Na₂SO₄, 600 μL L^-1 H₂O₂, 8-minute electrolytic time, solution pH 3 and 6 mA cm^-2 current density for the process variables and was consistent with the expected 99.6% removal rate. Satisfactory correlation coefficients were obtained, and a non-significant value of 0.0618 for model mismatch confirmed that the proposed model is extremely important and can successfully predict the effectiveness of DMP removal. The kinetics of the process and the effect of the presence of some radical scavengers were studied to understand the exact mechanism of DMP degradation. Therefore, it was observed that the reaction of hydroxyl radicals with DMPs followed the first-order kinetics model. Moreover, it was established that the optimal ratio of H₂O₂/Fe²⁺ mole was 1.6 and the electricity consumption was 0.157 kWh m^-3. The elaborated treatment model used to remove DMP from landfill leachate showed that DMP contamination was effectively removed with a 95.6% removal efficiency in the investigating process.

Evaluation of adsorption ability of cyclodextrin-calixarene nanosponges towards Pb2+ ion in aqueous solution

Different cyclodextrin-calixarene nanosponges (CyCaNSs) have been characterized by means of FFC-NMR relaxometry, and used as sorbents to remove Pb²⁺ ions from aqueous solutions. Considering that the removal treatments may involve polluted waters with different characteristics, the adsorption experiments were performed on solutions without and with the addition of background salts, under different operational conditions. The adsorption abilities and affinities of the nanosponges towards Pb²⁺ ions were investigated by measuring the metal ion concentration by means of Inductively Coupled Plasma Emission Spectroscopy (ICP-OES) and Differential Pulse Anodic Stripping Voltammetry (DP-ASV). The acid-base properties of nanosponges and of metal ion as well as their interactions with the other interacting components of the systems have been considered in the evaluation of adsorption mechanism. Recycling and reuse experiments on the most efficient adsorbents were also performed. On the grounds of the results obtained, post-modified CyCaNSs appear promising materials for designing environmental remediation devices.

Remediation strategies for mitigation of phthalate pollution: Challenges and future perspectives

Phthalates are a group of emerging xenobiotic compounds commonly used as plasticizers. In recent times, there has been an increasing concern over the risk of phthalate exposure leading to adverse effects to human health and the environment. Therefore, it is necessary to not only understand the current status of phthalate pollution, their sources, exposure routes and health impacts, but also identify remediation technologies for mitigating phthalate pollution. Present review article aims to inform its readers about the ever increasing data on health burdens posed by phthalates and simultaneously highlights the recent advancements in research to alleviate phthalate contamination from environment. The article enumerates the major phthalates in use today, traces their environmental fate, addresses their growing health hazard concerns and largely focus on to provide an in-depth understanding of the different physical, chemical and biological treatment methods currently being used or under research for alleviating the risk of phthalate pollution, their challenges and the future research perspectives.

Simultaneous removal of nitrogen and dimethyl phthalate from low-carbon wastewaters by using intermittently-aerated constructed wetlands

Phthalic acid esters (PAEs) such as dimethyl phthalate (DMP) have been widely used as a plasticizer in society, which pose severe harm to human health. In this study, the potential of DMP elimination and nitrogen removal from low-carbon wastewaters by intermittently-aerated subsurface flow constructed wetlands (SSFCWs) was evaluated, and the effect of the influent DMP concentrations on nitrogen removal was also investigated. The results showed a better removal of DMP (88.5-97.8%) was obtained in CWs under different influent DMP concentrations, and the high removal of COD (86.7-95.0%) and NH₄⁺-N (95.5-98.7%) was also achieved simultaneously. The maximum TN removal (48.7%) was observed at an influent DMP concentration of 10 mg L^-1. Furthermore, the TN removal and DMP reduction had a good fitting relationship (R² = 0.71) in CWs under different influent DMP concentrations. The analysis of DMP decomposition processes demonstrated that DMP was degraded into some smaller molecular fractions, and DMP degradation intermediates mainly including monomethyl phthalate (MMP) and phthalate (PA), which might provide a potential carbon source for the denitrification processes in CWs. These findings could contribute to a better understanding of DMP removal mechanism and provide useful guidance for the practical application of CWs for treating wastewater containing phthalates.

Preparation of multi-walled carbon nanotubes based magnetic multi-template molecularly imprinted polymer for the adsorption of phthalate esters in water samples

Taking the advantages of surface imprinting, multi-template imprinting and magnetic separation, a novel magnetic multi-template molecularly imprinted polymer (mag-MMIP@MWCNTs) was prepared by using MWCNTs as support material, Fe₃O₄ as magnetic core, and dimethyl phthalate (DMP), diethyl phthalate (DEP), and dibutyl phthalate (DBP) as template molecules. This composite was characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), and the Brunauer-Emmett-Teller (BET) analysis, and was used for the simultaneous adsorption of DMP, DEP, and DBP in aqueous solution. The effects of solution pH, contact time, PAEs initial concentration, temperature, adsorption selectivity, and reusability were investigated and discussed in detail. The results demonstrated that mag-MMIP@MWCNTs exhibited fast kinetics, good magnetic separation, and excellent selectivity for the adsorption of three phthalate esters (PAEs). The adsorption kinetics followed pseudo second-order kinetic model and the adsorption thermodynamics followed Langmuir isothermal model very well, and the maximum adsorption capacities (Q_max) of DMP, DEP, and DBP were obtained as 0.95, 1.38, and 7.09 mg g^-1, respectively. The Scatchard analysis revealed that the template-polymer system had a two-site binding behavior. The adsorption thermodynamic studies indicated that the adsorption processes were exothermic and spontaneous, and dominated by physical adsorption relying on hydrogen bond, hydrophobic interaction, and van der Waals force. Mag-MMIP@MWCNTs also showed good reproducibility and reusability for simultaneous adsorption of the three PAEs. The potential application of mag-MMIP@MWCNTs was proved by the removal of DMP, DEP, and DBP spiked in environmental water samples.

Optimization of reactive media for removing organic micro-pollutants in constructed wetland treating municipal landfill leachate

The removal of organic micro-pollutants (OMPs) from landfill leachate in constructed wetland (CW) media having different material mixtures of sand (S), clay (C), and iron powder (Fe) was investigated using experimental column study. The use of S:C:Fe media consisting of 60:30:10% (w/w) and cattail as vegetation was found optimum for the removals of 2,6-DTBP, BHT, DEP, DBP, and DEHP at 67.5-75.4% during long-term operation of 373 days. Adsorption and biodegradation were confirmed as predominant mechanisms for their removal in CW media but their contribution in total removal varied depending on chemical properties of OMPs. Adsorption kinetic could be well explained by pseudo-second-order whereas biodegradation kinetic followed first-order reaction. The adsorption affinity of OMPs to CW media was S:C:Fe > S:C > S in descending order. This study demonstrated high and sustainable removal of OMPs during long-term operation of CW with the optimized reactive media.

Partition and Fate of Phthalate Acid Esters (PAEs) in a Full-Scale Horizontal Subsurface Flow Constructed Wetland Treating Polluted River Water

When used as highly produced chemicals and widely used plasticizers, Phthalate acid esters (PAEs) have potential risks to human life and the environment. In this study, to assess the distribution and fate of PAEs, specifically inside a full-scale horizontal subsurface flow constructed wetland, four PAEs including dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), and bis (2-ethylhexyl) phthalate (DEHP) were investigated. In effluent, PAEs concentration decreased 19.32% (DMP), 19.18% (DEP), 19.40% (DBP), and 48.56% (DEHP), respectively. Within the wetland, PAEs partitioned in water (0.18–1.12 μg/L, 35.38–64.92%), soil (0.44–5.08 μg/g, 1.02–31.33%), plant (0.68–48.6 μg/g, 0.85–36.54%), air and biological transformation (2.72–33.21%). The results indicated that soil and plant adsorption contributed to the majority of PAE removal, digesting DMP (19.32%), DEP (19.18%), DBP (19.40%), and DEHP (48.56%) in constructed wetlands. Moreover, the adsorption was affected by both octanol/water partition coefficient (Kow) and transpiration stream concentration factors (TSCF). This work, for the first time, revealed the partition and fate of PAEs in constructed wetlands to the best of our knowledge.

Removal efficiency and mass balance of polycyclic aromatic hydrocarbons, phthalates, ethoxylated alkylphenols and alkylphenols in a mixed textile-domestic wastewater treatment plant

In this work the occurrence and fate of polycyclic aromatic hydrocarbons (PAHs), phthalic acid esters (PAEs), mono and diethoxylate alkylphenols (AP_1-2EOs) and alkylphenols (APs) have been investigated during a two-weeks period in a facility treating mixed textile-domestic wastewater (Prato, Italy). The wastewater treatment plant (WWTP) consists of primary sedimentation, activated sludge biological oxidation, secondary sedimentation, clariflocculation and ozonation. The sludge is treated within the facility by thickening, dewatering and final incineration, thus providing the almost quantitative removal of the adsorbed micropollutants. Naphthalene (50%), di(2-ethylhexyl) phthalate (74%) and branched 4-nonylphenols (59%) were the individual main representative compounds of each class in the influent wastewater, which showed concentration ranges of 5.6-66, 85-290 and 21-133μg/L for PAHs, PAEs and APs+AP_1-2EOs, respectively. The WWTP efficiently removed PAHs, PAEs and APs+AP_1-2EOs, providing effluent concentrations of 0.075-0.16ng/L 0.38-9.9μg/L and 0.53-1.4μg/L. All targeted priority and priority-hazardous micropollutants showed effluent concentrations in line with the European environmental quality standards (EQS), even though for di(2-ethylhexyl) phthalate and benzo(a)pyrene after correction for the dilution factor of the recipient. The WWTP performance was evaluated by mass balance, verifying its accuracy by monitoring Pb and Cd as conservative species. The biological treatment sections provided mass losses of 85.5%, 74.5% and 56.8% for APs+AP_1-2EOs, PAEs and PAHs, highlighting efficient biotransformation performances of the activated sludge process. However, for the more volatile PAHs (e.g. naphthalene), a significant contribution of stripping cannot be excluded. A remarkable mass loss was also determined in the ozonation stage for PAEs (72.9%) and especially PAHs (97.0%), whereas a lower efficiency was observed for APs+AP_1-2EOs (41.3%). The whole plant allowed for obtaining an almost quantitative removal (96.7-98.4%) for all targeted compounds.

Carbon and hydrogen isotopic fractionation during abiotic hydrolysis and aerobic biodegradation of phthalate esters

We systematically investigated the changes of carbon and hydrogen isotope signatures of three phthalate esters (PAEs) during (i) abiotic hydrolysis over the pH range of 2, 7 and 10, and (ii) aerobic biodegradation initiated by hydrolysis by Rhodococcus opacus strain DSM 43250. Significant carbon isotopic fractionation was exhibited under all investigated conditions. Hydrogen isotopic fractionation was observed in some experiments and is hypothesized to be a secondary isotope effect due to the absence of a hydrogen bond cleavage during hydrolysis. Dual stable isotope analysis (Λ = Δδ²H/Δδ¹³C) resulting from abiotic hydrolysis and aerobic biodegradation showed similar magnitudes for dimethyl phthalate (DMP) and diethyl phthalate (DEP). The calculated carbon apparent kinetic isotope effects (AKIE_C) for the hydrolytic pathway (CO bond cleavage) of PAEs fall within an expected range of 1.03-1.09, with the exception of lower AKIE_C values for dibutyl phthalate (DBP) during hydrolysis at pH 2 and aerobic biodegradation. The lower AKIE_C of DBP at pH 2 and aerobic biodegradation is likely related to a transition state from reactant-like to tetrahedral intermediate-like structure. Abiotic and biotic hydrolysis of PAEs resulted in similar AKIE_C and Λ values due to the CO bond cleavage pathway, indicating the potential of dual isotope analysis to detect and quantify hydrolytic processes of PAEs in the environment. The pronounced primary carbon and typically low secondary or absent hydrogen isotopic fractionation might form a typical pattern to identify the hydrolytic reaction of PAEs in the environment. The characteristic Λ values of the hydrolytic reaction were different from Λ values of chemical oxidation of PAEs and showed diagnostic potential of dual HC isotope analysis to analyze reactions.

Automated on-line monitoring of the TiO2-based photocatalytic degradation of dimethyl phthalate and diethyl phthalate

An automated on-line system for monitoring the TiO₂-based photocatalytic degradation of dimethyl phthalate and diethyl phthalate.

Degradation of Diallyl Phthalate (DAP) by Fenton Oxidation: Mechanistic and Kinetic Studies

In this work, the degradation and mineralization of Diallyl Phthalate (DAP) in water by Fenton oxidation was investigated. The effects of different experimental parameters including the initial pH, the hydrogen peroxide (H2O2) dose, the catalyst (Fe2+) dose, the iron source, and the DAP concentration on the rate and the yield of DAP degradation by Fenton oxidation were evaluated. DAP and its intermediates were quantified by high performance liquid chromatography (HPLC) analysis and the measurement of total organic carbon (TOC) during Fenton oxidation. The results obtained confirmed that hydroxyl radicals (HO•) generated from Fenton’s reaction were capable of completely eliminating DAP from water. Fenton oxidation of 100 mg/L DAP aqueous solution at pH = 3.2 required 1000 mg/L H2O2 and 50 mg/L Fe2+. Under these conditions, more than TOC removal exceeded 95% after 300 min Fenton oxidation. The competition kinetics method was used to determine an absolute rate constant of 7.26.109 M−1 s−1 for the reaction between DAP and HO• radicals. HPLC analysis showed that phthalic acid, 1,2-dihydroxybenzene, 1,2,4-trihydroxybenzene, maleic acid, formic acid and oxalic acid were the main intermediates formed during DAP degradation. Accordingly, a simple DAP degradation mechanism by the Fenton reaction was proposed. These promising results proved the potential of Fenton oxidation as a cost-effective method for the decontamination of wastewaters containing phthalates.

Biodegradation of di-(2-ethylhexyl) phthalate by a halotolerant consortium LF

A halotolerant bacterial consortium capable of degrading di-(2-ethylhexyl) phthalate (DEHP) was enriched from activated sludge. Community analysis revealed that LF contained seven families and seven genera of bacteria. The predominant species was Gordonia sp. (54.93%), Rhodococcus. sp. (9.92%) and Achromobacter sp. (8.47%). The consortium could degrade 93.84% of 1000 mg/l DEHP after 48 h incubation. The optimal temperature and pH for LF to degrade DEHP were 30 °C and 6.0, respectively. LF degraded more than 91% of DEHP with salt concentrations ranging from 0–3%. The inoculum size had great effects on DEHP degradation (incubation time < 24h). LF could degrade high concentrations of DEHP (from 100 to 2000 mg/l) with the degradation ratio above 92% after 72 h incubation. Kinetics analysis revealed that the degradation of DEHP by LF was best fitted by the first-order kinetics when the initial concentration ranged from 100 to 2000 mg/l. The main intermediates (2-ethylhexyl pentyl phthalate, butyl (2-ethylhexyl) phthalate (BEHP), mono-ethylhexyl phthalate (MEHP), mono-hexyl phthalate (MHP), mono-butyl phthalate (MBP)) in DEHP degradation process were identified using gas chromatography–mass spectrometry (GC-MS), and a new complex biochemical pathway was proposed. Furthermore, LF could also degrade dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), di-n-octyl phthalate (DOP) and phthalic acid (PA).

Removal of bisphenol A and 2,4-Di-tert-butylphenol from landfill leachate using plant- based coagulant

Landfill leachate contain persistent organic pollutants (POPs), namely, bisphenol A (BPA) and 2,4-Di-tert-butylphenol, which exceed the permissible limits. Thus, such landfill leachate must be treated before it is released into natural water courses. This article reports on investigations about the removal efficiency of POPs such as BPA and 2,4-Di-tert-butylphenol from leachate using locust bean gum (LBG) in comparison with alum. The vital experimental variables (pH, coagulant dosage and stirring speed) were optimised by applying response surface methodology equipped with the Box-Behnken design to reduce the POPs from leachate. An empirical quadratic polynomial model could accurately model the surface response with R² values of 0.928 and 0.954 to reduce BPA and 2,4-Di-tert-butylphenol, respectively. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were performed on treated flocs for further understanding. FTIR analysis revealed that the bridging of pollutant particles could be due to the explicit adsorption and bridging via hydrogen bonding of a coagulation mechanism. SEM micrographs indicated that the flocs produced by LBG have a rough cloudy surface and numerous micro-pores compared with alum, which enabled the capture and removal of POPs from leachate. Results showed that the reduction efficiencies for BPA and 2,4-Di-tert-butylphenol at pH 7.5 were 76% and 84% at LBG dosage of 500 mg·L^-1 and 400 mg·L^-1, respectively. Coagulant dosage and pH variation have a significant effect on POPs reduction in leachate. Coagulation/flocculation using LBG could be applied for POPs reduction in leachate as a pre-treatment prior to advanced treatments.

Sorption of organic pollutants frequently detected in stormwater: evaluation of five potential sorbents

Adsorption filtration is one of the most promising techniques for removal of dissolved, colloidal and particulate pollutants from stormwater. The aim of this study was to compare the capacity of five filter materials - cellulose, chitosan, chitosan-covered bark, pine bark and polypropylene/polyethylene (PP/PE) fibres - to sorb organic pollutants frequently detected in stormwater, including polycyclic aromatic hydrocarbons (PAHs), alkylphenols and phthalates. In batch tests, synthetic stormwater spiked with a mixture of the organic compounds was contacted with the materials for up to 24 h. The compounds were then liquid-liquid extracted and analysed using GC-MS. Cellulose and chitosan showed very low sorption capacity for the organic contaminants, whereas >70% of the initial concentration of most tested compounds was removed using PP/PE fibres, and >80% with pine bark and chitosan-covered bark. The highest adsorption capacity was found for PAHs (up to 44 µg/g) using PP/PE fibres and bark. For all tested compounds, maximum sorption was approached within 30 min using these materials.

Removal of organic contaminants in bioretention medium amended with activated carbon from sewage sludge

Bioretention, also known as rain garden, allows stormwater to soak into the ground through a soil-based medium, leading to removal of particulate and dissolved pollutants and reduced peak flows. Although soil organic matter (SOM) is efficient at sorbing many pollutants, amending the bioretention medium with highly effective adsorbents has been proposed to optimize pollutant removal and extend bioretention lifetime. The aim of this research was to investigate whether soil amended with activated carbon produced from sewage sludge increases the efficiency to remove hydrophobic organic compounds frequently detected in stormwater, compared to non-amended soil. Three lab-scale columns (520 cm³) were packed with soil (bulk density 1.22 g/cm³); activated carbon (0.5% w/w) was added to two of the columns. During 28 days, synthetic stormwater-ultrapure water spiked with seven hydrophobic organic pollutants and dissolved organic matter in the form of humic acids-was passed through the column beds using upward flow (45 mm/h). Pollutant concentrations in effluent water (collected every 12 h) and polluted soils, as well as desorbed amounts of pollutants from soils were determined using GC-MS. Compared to SOM, the activated carbon exhibited a significantly higher adsorption capacity for tested pollutants. The amended soil was most efficient for removing moderately hydrophobic compounds (log K _ow 4.0-4.4): as little as 0.5% (w/w), carbon addition may extend bioretention medium lifetime by approximately 10-20 years before saturation of these pollutants occurs. The column tests also indicated that released SOM sorb onto activated carbon, which may lead to early saturation of sorption sites on the carbon surface. The desorption test revealed that the pollutants are generally strongly sorbed to the soil particles, indicating low bioavailability and limited biodegradation.

Organic Pollutants in Shale Gas Flowback and Produced Waters: Identification, Potential Ecological Impact, and Implications for Treatment Strategies

Organic contaminants in shale gas flowback and produced water (FPW) are traditionally expressed as total organic carbon (TOC) or chemical oxygen demand (COD), though these parameters do not provide information on the toxicity and environmental fate of individual components. This review addresses identification of individual organic contaminants in FPW, and stresses the gaps in the knowledge on FPW composition that exist so far. Furthermore, the risk quotient approach was applied to predict the toxicity of the quantified organic compounds for fresh water organisms in recipient surface waters. This resulted in an identification of a number of FPW related organic compounds that are potentially harmful namely those compounds originating from shale formations (e.g., polycyclic aromatic hydrocarbons, phthalates), fracturing fluids (e.g., quaternary ammonium biocides, 2-butoxyethanol) and downhole transformations of organic compounds (e.g., carbon disulfide, halogenated organic compounds). Removal of these compounds by FPW treatment processes is reviewed and potential and efficient abatement strategies are defined.

Adsorption of Phthalates on Municipal Activated Sludge

Phthalates (PAEs) are commonly detected in discharge of municipal wastewater treatment plants. This study investigated the removal of six typical PAEs with activated sludge and the results revealed that concentrations of aqueous PAEs decreased rapidly during the beginning 15 min and reached equilibrium within 2 hours due to the adsorption of activated sludge. The process followed first-order kinetic equation, except for dioctyl phthalate (DOP). The factors influencing the adsorption were also evaluated and it was found that higher initial concentrations of PAEs enhanced the removal but affected little the adsorption equilibrium time. The adsorption of PAEs favored lower operating temperature (the optimum temperature was approximately 25°C in this research), which could be an exothermic process. Additionally, lower aqueous pH could also benefit the adsorption.

Phenyl-functionalized mesoporous silica materials for the rapid and efficient removal of phthalate esters

Phthalate esters (PAEs) are a group of endocrine disrupting compounds, which have been widely used as plasticizers. To alleviate the environmental and health threats from water resources polluted by PAEs, we prepared phenyl functionalized mesoporous silica materials (ph-SBA-15) were synthesized by a simple post-modification approach for rapid and efficient removal of low concentration of di-n-butyl phthalate (DBP) from aqueous solution. Mesostructure, texture, surface chemistry and surface charges were systemically characterized. The obtained ph-SBA-15 possesses a highly ordered mesostructure, a high surface area (418m²/g), uniform mesopores (6.5nm) and high-density organic groups around 11wt.%. Batch adsorption experiments revealed that phenyl modified SBA-15 had an excellent ability to remove DBP with the maximum adsorption capacity up to ∼40mg/g at 25°C. The thermodynamics and kinetics for the adsorption were also investigated, demonstrating an exothermic, multi-layer and fast adsorption process. In addition, DBP adsorption was found to be sensitive to the pH and the uptake was observed to be greatest at around pH 7.0. Furthermore, this material can be effectively regenerated by ethanol.

Study on the Mechanism of Interaction between Phthalate Acid Esters and Bovine Hemoglobin

Phthalate acid esters (PAEs) are widely used in plastic products as a series of chemical softeners. However, PAEs, which now exist in many environmental media such as the atmosphere, water, and soil, have been shown to be environmental endocrine disruptors. Hemoglobin is a functional protein that carries oxygen in the red blood cells of animals. This study aims at revealing the interactions between bovine hemoglobin (BHb) and PAEs using spectroscopic and molecular modeling methods. The results indicate that the selected representative PAEs-dimethyl phthalate (DMP), diethyl phthalate (DEP), and dibutyl phthalate (DBP)-can interact with BHb to form BHb-PAE complexes with one binding site, mainly relying on hydrophobic forces, with the affinity order DMP > DEP > DBP, opposite to the order of side-chain length. The binding of PAEs can cause conformational and micro-environmental changes in BHb, which may affect the physiological functions of Hb. Furthermore, molecular docking was applied to define the specific binding sites, the results of which show that all the three PAEs can bind into the central cavity of BHb. The study contributes to expound the toxic mechanism of PAEs in vivo from the point of hematological toxicology.

Detection of phthalate esters in seawater by stir bar sorptive extraction and gas chromatography-mass spectrometry

We developed the stir bar sorptive extraction (SBSE)-gas chromatography-mass spectrometry (GC-MS) method to detect 15 kinds of PAEs in seawater. The stir bars (20mm in length and 1mm in film thickness) coated with 150μL of polydimethylsiloxane (PDMS) were found to demonstrate the optimal extraction of PAEs. The optimal conditions were as follows: extraction time of 2h, extraction temperature of 25°C, sodium chloride of 5%, methanol of 10%, analytical time of 50min, and methanol-acetonitrile (4:1) as the solvent. SBSE-GC-MS revealed that under the set temperature, the chromatographic peaks of all 15 PAEs can appear with complete separation. The detection limit ranged from 0.07μg/L to 5.71μg/L, whereas the limit of quantification ranged from 0.023μg/L to 193μg/L, and the correlation coefficients between the chromatographic peak area and concentration of the PAEs were greater than 0.92.

Novel Functionalized Polythiophene-Coated Fe₃O₄ Nanoparticles for Magnetic Solid-Phase Extraction of Phthalates

Poly(phenyl-(4-(6-thiophen-3-yl-hexyloxy)-benzylidene)-amine) (P3TArH) was successfully synthesized and coated on the surface of Fe₃O₄ magnetic nanoparticles (MNPs). The nanocomposites were characterized by Fourier transform infra-red (FTIR), X-ray diffractometry (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, analyzer transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). P3TArH-coated MNPs (MNP@P3TArH) showed higher capabilities for the extraction of commonly-used phthalates and were optimized for the magnetic-solid phase extraction (MSPE) of environmental samples. Separation and determination of the extracted phthalates, namely dimethyl phthalate (DMP), diethyl phthalate (DEP), dipropyl phthalate (DPP), dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), dicyclohexyl phthalate (DCP), di-ethylhexyl phthalate (DEHP) and di-n-octyl phthalate (DNOP), were conducted by a gas chromatography-flame ionization detector (GC-FID). The best working conditions were as follows; sample at pH 7, 30 min extraction time, ethyl acetate as the elution solvent, 500-µL elution solvent volumes, 10 min desorption time, 10-mg adsorbent dosage, 20-mL sample loading volume and 15 g·L-1 concentration of NaCl. Under the optimized conditions, the analytical performances were determined with a linear range of 0.1⁻50 µg·L-1 and a limit of detection at 0.08⁻0.468 µg·L-1 for all of the analytes studied. The intra-day (n = 7) and inter-day (n = 3) relative standard deviations (RSD%) of three replicates were each demonstrated in the range of 3.7⁻4.9 and 3.0⁻5.0, respectively. The steadiness and reusability studies suggested that the MNP@P3TArH could be used up to five cycles. The proposed method was executed for the analysis of real water samples, namely commercial bottled mineral water and bottled fresh milk, whereby recoveries in the range of 68%⁻101% and RSD% lower than 7.7 were attained.

Sorption of DOM and hydrophobic organic compounds onto sewage-based activated carbon

Treatment of stormwater via sorption has the potential to remove both colloidal and dissolved pollutants. Previous research shows that activated carbon produced from sewage sludge is very efficient in sorbing hydrophobic organic compounds (HOCs), frequently detected in stormwater. The aim of this research was to determine whether the presence of dissolved organic matter (DOM) has a negative effect on the adsorption of HOCs onto sludge-based activated carbon (SBAC) in batch adsorption tests. Batch adsorption tests were used to investigate the influence of two types of DOM - soil organic matter and humic acid (HA) technical standard - on the sorption of HOCs onto SBAC, and whether preloading adsorbent and adsorbates with DOM affects HOC sorption. The results indicate that soil DOM and HAs do not have a significant negative effect on the adsorption of HOCs under tested experimental conditions, except for a highly hydrophobic compound. In addition, preloading SBAC or HOCs with DOM did not lead to lower adsorption of HOCs. Batch adsorption tests appear to be inefficient for investigating DOM effects on HOC adsorption, as saturating the carbon is difficult because of high SBAC adsorption capacity and low HOC solubility, so that limited competition occurs on the sorbent.

Removal of endocrine disruptor di-(2-ethylhexyl)phthalate by modified polythiophene-coated magnetic nanoparticles: characterization, adsorption isotherm, kinetic study, thermodynamics

Superparamagnetic nanosorbent poly(phenyl(4-(6-thiophen-3-yl-hexyloxy)-benzylidene)-amine)/Fe₃O₄ nanoparticles (Fe₃O₄@P3TArH) were successfully synthesized via a simplistic method for the enhanced extraction of potent endocrine disruptor, di-(2-ethylhexyl)phthalate (DEHP).

Effective remediation of phenol,2,4-bis(1,1-dimethylethyl) and bis(2-ethylhexyl) phthalate in farm effluent using Guar gum--A plant based biopolymer

This study was carried out to evaluate the efficiency of Guar gum in removing Persistent Organic Pollutants (POPs), viz. phenol,2,4-bis(1,1-dimethylethyl) and bis(2-ethylhexyl) phthalate (DEHP), from farm effluent. The removal efficiency was compared with alum. The results indicated that 4.0 mg L(-1) of Guar gum at pH 7 could remove 99.70% and 99.99% of phenol,2,4-bis(1,1-dimethylethyl) and DEHP, respectively. Box Behnken design was used for optimization of the operating parameters for optimal POPs removal. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy studies were conducted on the flocs. SEM micrographs showed numerous void spaces in the flocs produced by Guar gum as opposed to those produced by alum. This indicated why Guar gum was more effective in capturing and removal of suspended particles and POPs as compared to alum. FTIR spectra indicated a shift in the bonding of functional groups in the flocs produced by Guar gum as compared to raw Guar gum powder signifying chemical attachment of the organics present in the effluent to the coagulant resulting in their removal. Guar gum is highly recommended as a substitute to chemical coagulant in treating POPs due to its non-toxic and biodegradable characteristics.

Monitoring of phthalates in foodstuffs using gas purge microsyringe extraction coupled with GC-MS

Phthalate esters (PAEs) are commonly used as nonreactive plasticisers in vinyl plastics to increase the flexibility of plastic polymers. Numerous studies have indicated that the PAEs as a class of endocrine-disrupting chemicals. In addition, the studies have also shown that a major source of human exposure to phthalates is the diet. To date, the largest problem in PAEs analysis is the high blank value because PAEs are widely used in various applications and products. To overcome this shortcoming, gas purge microsyringe extraction (GP-MSE) was applied, which established a new and low-blank-value analytical method for PAE analysis to analyse PAEs in foodstuffs. In this study, GP-MSE was used as a clean-up method, and the overall recoveries ranged from 85.7 to 102.6%, and the RSD was less than 10%. More importantly, this method can overcome the problem of the high blank value in PAE analysis. This method was applied for measuring PAEs in 78 foodstuffs. The results showed that a wide variety of PAE concentrations were found in the different groups, and the content of PAEs (varies from 658 to 1610 ng g(-1) fresh weight) is greatest in seafood. The concentrations were in the following order: DEHP>DBP>DEP≈DMP>BBP≈DNOP. Finally, the daily intake of PAEs was estimated for adults based on the levels of PAEs in foodstuffs. The total EDIdiet values of 3.2 and 12.9 μg kg(-1) bw d(-1) were calculated for DEHP based on the mean and highest concentrations in foodstuffs, respectively.