Persistent Organic Contaminants Research Articles

Application of Chelating Agents to Enhance Fenton Process in Soil Remediation: A Review

Persistent organic contaminants affecting soil and groundwater pose a significant threat to ecosystems and human health. Fenton oxidation is an efficient treatment for removing these pollutants in the aqueous phase at acidic pH. However, the in-situ application of this technology for soil remediation (where pHs around neutrality are required) presents important limitations, such as catalyst (iron) availability and oxidant (H2O2) stability. The addition of chelating agents (CAs), forming complexes with Fe and enabling Fenton reactions under these conditions, so-called chelate-modified Fenton process (MF), tries to overcome the challenges identified in conventional Fenton. Despite the growing interest in this technology, there is not yet a critical review compiling the information needed for its real application. The advantages and drawbacks of MF must be clarified, and the recent achievements should be shared with the scientific community. This review provides a general overview of the application of CAs to enhance the Fenton process for the remediation of soils polluted with the most common organic contaminants, especially for a deep understanding of the activation mechanisms and influential factors. The existing shortcomings and research needs have been highlighted. Finally, future research perspectives on the use of CAs in MF and recommendations have been provided.

Legacy contaminant-stable isotope-age relationships in Lake Ontario year-class Alewife (Alosa pseudoharengus)

Alewife (Alosa pseudoharengus) are the preferred prey species of the top piscivore predators in the Lake Ontario food web and are an essential constituent in the bioaccumulation of persistent organic contaminants. Year-class samples collected in 2016 represent the alewife age ranges of 2015 (Age-01) sequentially dating back to 2008 (Age-08). The most abundant contaminant measured in Lake Ontario alewife (151.5 ng/g) were total polychlorinated biphenyls (PCBs), increasing at a rate of 11.8 ng/g per year on an age-averaged concentration basis. Total mercury demonstrated the largest percent increase (240%) accumulated over alewife ages of 1–8 years. Average total concentrations of the most abundant polychlorinated dibenzo-p-dioxin isomer (2378-tetrachlorinated dibenzo-p-dioxin (TCDD), 1.3 pg/g) and polychlorinated dibenzofuran isomer (2378-tetrachlorinated dibenzofuran (2378-TCDF), 6.6 pg/g) comprised most of the overall total dioxin (2.5 pg/g) and total furan concentrations (8.7 pg/g). The vast majority (69%) of alewife total toxic equivalence (TEQ) was comprised of the non-ortho coplanar PCBs. Both mammal and avian wildlife protection values based on total TEQ were uniformly exceeded for the dioxin-like compounds measured in Lake Ontario alewife. Ontogenetic dietary influences expressed a significant impact on Age-01 alewife age-contaminant relationships and age-stable isotope concentrations and trends for legacy contaminants. Total Hg and all dioxin-like contaminants did not demonstrate the Age-01 ontogenetic dietary effects found in legacy contaminants. A prominent polychlorinated naphthalene (PCN) concentration peak measured in year-class Age-04 alewife was followed by a corresponding lake trout peak 3–4 years later illustrating a unique example of trophic-level contaminant uptake and concomitant integration delay.

Artificial neural network and molecular modeling for assessing the adsorption performance of a hybrid alginate-based magsorbent

The study reported herein describes a chemometric approach, based on an artificial neural network (ANN), to predict the adsorption performance of a new hybrid material. This composite adsorbent with magnetic properties (magsorbent) consists of a cross-linked alginate matrix that incorporates inorganic nanoparticles of cobalt ferrite. Instrumental physical–chemical techniques (FTIR, VSM, SEM, and EDX) were employed for material characterization. The produced magnetic-adsorbent was used to remove a persistent organic contaminant from aqueous solutions. Adsorption studies were carried out to assess the kinetics, isotherms, and thermodynamics parameters. The calculated free energy of adsorption ranged from 9.38 to 10.61 (kJ/mol) suggesting the retention mechanism based on ion-exchange. The good generalization capability of the ANN-model allowed establishing the optimal adsorption conditions by the model-based simulation. Under optimal conditions, the maximal removal efficiency of 96.54% was observed for an initial concentration of 110 mg/L of the pollutant. Details regarding the interactions at the molecular level were provided by computational chemistry methods. Molecular docking revealed that binding of the cationic organic pollutant to the cross-linked alginate matrix relied on hydrophobic and electrostatic interactions. Molecular dynamics simulation disclosed the behavior of the docked complex against the simulation time and in the presence of the explicit solvent.

Novel magnetically retrievable In2O3/MoS2/Fe3O4 nanocomposite materials for enhanced photocatalytic performance

The current work involves synthesis of hybrid nanomaterial of In2O3/MoS2/Fe3O4 and their applications as photocatalysts for disintegration of esomeprazole under visible light illumination. The data emerged from various analyses testified to the successful construction of the desired nano-scaled hybrid photocatalyst. Tauc plot gave the band gap of In2O3/MoS2/Fe3O4 to be ~ 2.15 eV. Synergistic effects of the integrant components enabled efficacious photocatalytic performances of the nanocomposite. The nanohybrid photocatalyst In2O3/MoS2/Fe3O4 showed photodecomposition up to ~ 92.92% within 50 min. The current work realizes its objective of constructing metal oxide based hybrid nano-photocatalyst supported on MoS2 sheets for activity in the visible spectrum, which displayed remarkable capacity of disintegrating emerging persistent organic contaminants and are magnetically recoverable.

Removal of persistent organic contaminants from wastewater using a hybrid electrochemical-granular activated carbon (GAC) system

A three-dimensional (3D) electrochemical flow-through reactor equipped with GAC packed bed, polarized by the electric field, was evaluated for the removal of persistent organic contaminants from real sewage effluent. The performance of the reactor was investigated for 27 consecutive runs at two anodic current densities, i.e., low current density (LCD) of 15 A m−2, and high current density (HCD) of 100 A m−2. In the HCD experiments, the adsorption ability of saturated GAC was increased, mainly due to the increase in the mesoporosity of GAC. A synergy between electrosorption/adsorption on GAC and electrooxidation was observed in terms of the removal of all target pollutants. DEET presented the highest synergy, ranging from 40% to 57%, followed by iopromide (22–46%), carbamazepine (15–34%) and diatrizoate (4–30%). The addition of GAC decreased the concentrations of toxic chlorate and perchlorate by 2-fold and 10-fold, respectively, due to their electrosorption on GAC. Also, 3D electrochemical system yielded lower concentrations of adsorbable organic iodide (AOI) and adsorbable organic chlorine (AOCl). Thus, addition of low amounts of GAC in electrochemical systems may be a low-cost and simple way of minimizing the formation and final effluent concentrations of toxic halogenated byproducts.

Highly Efficient Hydrated Electron Utilization and Reductive Destruction of Perfluoroalkyl Substances Induced by Intermolecular Interaction.

Perfluoroalkyl substances (PFASs) are highly toxic synthetic chemicals, which are considered the most persistent organic contaminants in the environment. Previous studies have demonstrated that hydrated electron based techniques could completely destruct these compounds. However, in the reactions, alkaline and anaerobic conditions are generally required or surfactants are involved. Herein, we developed a simple binary composite, only including PFAS and hydrated electron source chemical. The system exhibited high efficiency for the utilization of hydrated electrons to decompose PFASs. By comparing the degradation processes of perfluorooctanoic acid (PFOA) in the presence of seven indole derivatives with different chemical properties, we could conclude that the reaction efficiency was dependent on not only the yield of hydrated electrons but also the interaction between PFOA and indole derivative. Among these derivatives, indole showed the highest degradation performance due to its relatively high ability to generate hydrated electrons, and more importantly, indole could form a hydrogen bonding with PFOA to accelerate the electron transfer. Moreover, the novel composite demonstrated high reaction efficiency even with coexisting humic substance and in a wide pH range (4-10). This study would deepen our understanding of the design of hydrated electron based techniques to treat PFAS-containing wastewater.

A novel electrocatalytic filtration system with carbon nanotube supported nanoscale zerovalent copper toward ultrafast oxidation of organic pollutants

In this study, we designed an integrated electrochemical filtration system for catalytic activation of peroxymonosulfate (PMS) and degradation of aqueous microcontaminants. Composites of carbon nanotube (CNT) and nanoscale zero valence copper (nZVC) were developed to serve as high-performance catalysts, electrode and filtration media simultaneously. We observed both radical and nonradical reaction pathways, which collectively contributed to the degradation of model pollutants. Congo red was completely removed via a single-pass through the nZVCCNT filter (τ <2 s) at neutral pH. The rapid kinetics of Congo red degradation were maintained across a wide pH range (from 3.0–7.0), in complicated matrixes (e.g., tap water and lake water), and for the degradation of a wide array of persistent organic contaminants. The superior activity of nZVCCNT stems from the boosted redox cycles of Cu2+/Cu+ in the presence of an external electric field. The flow-through design remarkably outperformed the conventional batch system due to the convection-enhanced mass transport. Mechanism studies suggested that the carbonyl group and electrophilic oxygen of CNT served as electron donor and electron acceptor, respectively, to activate PMS to generate •OH and 1O2via one-electron transport. The electron-deficient Cu atoms are prone to react with PMS via surface hydroxyl group to produce reactive intermediates (Cu2+-O-O-SO3−), and then 1O2 will be generated by breaking the coordination bond of the metastable intermediate. The study will provide a green strategy for the remediation of organic pollution by a highly efficient and integrated system based on catalytic oxidation, electrochemistry, and nano-filtration techniques.

Computerized Pathway Generator for the UV/Free Chlorine Process: Prediction of Byproducts and Reactions.

The ultraviolet (UV)/free chlorine process is a very promising treatment technology to remove persistent organic contaminants (POCs, e.g., pharmaceutical and personal care products) from water. The radical chain reactions involved in the UV/free chlorine process are very complicated, and the reaction pathways for organic contaminants degradation are largely unknown. Therefore, we developed a computerized pathway generator that uses graph theory and experimentally determined reaction rules that were reported for the UV/free chlorine process. Our pathway generator predicts all possible intermediates, byproducts, and elementary reactions that are involved in the oxidation of organic contaminants. For example, the degradation of tricholoroethylene (TCE) produces 497 species (i.e., intermediates and byproducts) and 6608 elementary reactions. The predicted species from our pathway generator not only predict the major and stable byproducts that were observed in our experiments (e.g., CHCl2COOH, CHCl(OCl)COOH, etc.) but also include many other minor and toxic byproducts that were produced but not measured because they have a short lifetime. Overall, our pathway generator significantly improves our understanding of the reaction pathways that are involved in organic contaminant degradation in the UV/free chlorine process.

Surface modification of BiOBr/TiO2 by reduced AgBr for solar-driven PAHs degradation: Mechanism insight and application assessment

A novel solar active AgBr/BiOBr/TiO2 catalyst was synthesized by a facile coprecipitation method for solar-driven water remediation. The synthesized material composed of flower-like TiO2 nanoparticles loaded on BiOBr nanosheets and with homogeneous surface distributed Ag/AgBr nanoparticles. The internal electric field between BiOBr/TiO2 heterojunction greatly facilitated the charge carrier migration; the introduction of narrow band gap semiconductors (AgBr and BiOBr) promoted the visible light adsorption; and the Ag/AgBr nanoparticles acted as photosensitizer to further improve the light utilization. The new material showed 7.6- and 4.0-times activity of pure TiO2 and BiOBr under solar light, and the contribution of reactive species on anthracene degradation followed the order of h+ >O2•−> •OH. The degradation mechanism and pathway were proposed based on intermediates analysis and DFT calculation. The QSAR analysis revealed that the environmental risks of contaminants were greatly reduced during the photocatalysis process but some intermediates were still toxic. The high photocatalytic activity, stability and adaptability all indicated that this new material owns great application potential for cost-effective photocatalytic remediation of persistent organic contaminants under solar light.

Modeling the relationship between emerging and persistent organic contaminants in water, sediment and oysters from a temperate lagoon

The concentrations of emerging and persistent organic contaminants (EPOC) in oysters (CO) from Aveiro Lagoon are represented as a function of their concentrations in water (CW) and sediment (CS) using linear and generalized additive models (LM, GAM). Additionally, four sampling seasons, octanol/water partition coefficients (K) and type of EPOC (pyrethroids, flame-retardants, musks, UV filters, polycyclic aromatic hydrocarbons, others) are included in the models. The probabilities of detection of EPOC in water, sediment and oysters are analyzed by GAM. The behavior of contaminants in water is determined by K with a clear seasonal trend. Sediments are reservoirs for hydrophobic compounds with less seasonal variation. Seasonal changes are found for CO, the last being determined additively both by CW and hydrophobicity from one side and by CS and type of contaminants from the other side. The seasonal change of EPOC concentration in water, sediment and oysters is specific for each contaminant type.

Effect of UV/chlorine treatment on photophysical and photochemical properties of dissolved organic matter

Dissolved organic matter (DOM) is a ubiquitous component in effluents, DOM discharged with an effluent can affect the composition and properties of natural DOM in the receiving waters. As the photophysical and photochemical properties of effluent DOM can be changed by wastewater treatment processes, the effect of UV/chlorine treatment on the photophysical and photochemical properties of DOM was investigated using Suwannee River fulvic acid (SRFA) and Suwannee River natural organic matter (SRNOM) as representatives. Results showed that the absorbance of the two DOM was significantly decreased. The evolution trends of three representative photophysical parameters upon increase of chlorine dosages were observed. Also, a decrease in DOM aromaticity, molecular weight and electron-donating capacity was observed upon increasing chlorine dosage. Quantum yields of excited triplet state of DOM (3DOM*), singlet oxygen (1O2) and hydroxyl radicals (·OH) first decreases and then increased in the UV/chlorine systems upon increasing chlorine dosages due to the different reaction pathways of the two DOM. Moreover, 3DOM* can not only be regarded as a “controller” of other reactive intermediates, but also effectively promote the photodegradation of bezafibrate, which is classified as a persistent organic contaminant. This study gives deep insights into effects of UV/chlorine on the photophysical and photochemical properties of DOM, and is helpful for understanding the dynamic roles of DOM in the photodegradation of micropollutants.

Combining Chemical and Biological Oxidation for Sustainable Treatment of Chloronitrobenzene in Anoxic Groundwater

AbstractChloronitrobenzenes (CNBs) are important chemical intermediates that are resistant to natural degradation processes in anoxic environments. When receptors are threatened by CNB‐contaminated groundwater, advanced oxidation processes (AOPs) offer a rapid response to protect human health and the environment. While AOPs are effective for the transformation of persistent organic contaminants, driving chemical oxidation reactions to complete mineralization is often not energy‐ and cost‐efficient due to the formation of recalcitrant intermediates or competition by natural organic matter. In this study, we applied an electrochemical AOP to elucidate the degradation pathways and kinetics of CNB under varying treatment conditions and times. Nontargeted mass spectrometry revealed multiple ring hydroxylation and ring opening products such as dicarboxylic acids that became increasingly harder to chemically oxidize as treatment time progressed. To determine the universal biodegradability of the generated intermediates under anoxic conditions, AOP‐treated water samples collected at different stages of electrochemical oxidation were exposed to a microbial culture derived from generic rhizosphere soil. All ring opening products were completely biodegraded anaerobically within 28 days of microcosm incubation. While multiple oxygenated ring intermediates were substantially removed, CNB was stable in the absence of oxygen. Our findings demonstrate that the combination of limited and targeted chemical oxidation with subsequent biodegradation of incomplete oxidation products is a more sustainable approach than the exclusive application of AOPs for the treatment of groundwater contaminated with CNBs and likely other aromatic compounds.

Separation and Lithological Mapping of PFAS Mixtures in the Vadose Zone at a Contaminated Site

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are persistent organic contaminants of concern to human and environmental health. Several literature reviews and laboratory column experiments have been conducted to determine the transport parameters and to describe the fate of PFAS as they migrate in subsurface environments. However, there are very few case studies focusing on contaminated sites with high-resolution field data. Such studies are crucial for the validation of transport simulation models that have been developed from experimental studies, prior to their broader applications. The key purpose of this research was to evaluate lithological separations of PFAS fractions as they are transported in the vadose zone of a historically (1979) contaminated site where Aqueous Film Forming Foam (AFFF) formulations (3M Lightwater™ and Ansulite™) have been used for fire training exercises. Surface and subsurface soils, and groundwater samples were collected across the site and a total of 29 PFAS compounds were selected as target analytes. The results indicated a distinct profile of PFAS concentration with depth at most of the test bores, exhibiting separation of PFAS as transported in vadose zone soils. Perfluorooctanoic acid (PFOA), Perfluorooctane sulfonic acid (PFOS), and Perfluorohexane sulfonic acid (PFHxS) were the predominant compounds detected in the site samples and they have been found in near-surface soils (&amp;lt;3 m) with concentrations declining with depth. The concentration of the 6:2 fluorotelomer sulfonate showed little change with depth in most of the test bore wells. The percentage concentration of each compound relative to the sum of PFAS, and the ratio of PFHxS/PFOS with depth, suggested transformation processes. Despite the relatively high solubility of PFAS, and that the application of AFFF has been ceased for some years at the site, there were still significant concentrations of PFAS adsorbed to the vadose zone soils that acted as ongoing sources of contamination to groundwater.

Insight into the degradation of p-nitrophenol by visible-light-induced activation of peroxymonosulfate over Ag/ZnO heterojunction

In this report, the peroxymonosulfate activation over Ag/ZnO heterojunction under visible light (Ag/ZnO/PMS/Vis) for p-nitrophenol (p-NP) contaminant degradation was conducted in detail. Herein, the catalyst dosage was decreased, and the results showed that a dosage of 0.5 g L−1 Ag/ZnO and 4 mM PMS almost completely degraded 30 mg L−1 p-NP after 90 min of irradiation. In addition, the PMS activation mechanism of Ag/ZnO/PMS/Vis system was proposed by investigations of the influence of PMS concentration, the FTIR spectra, UV–Vis spectroscopy, and electrochemical analyses. Additionally, the role of SO4•– in the photocatalytic reaction is determined by a combination of a trapping test using isopropanol and tert-butanol as probe compounds and electron spin resonance (ESR) spectroscopy. This report provides a potential alternative to remove persistent organic contaminants in sewage using PMS incorporated with Ag/ZnO under visible light irradiation.

Organophosphate Esters in the Canadian Arctic Ocean

Eleven organophosphate esters (OPEs) were detected in surface water and sediment samples from yearly sampling (2013-2018) in the Canadian Arctic. In water samples, ∑chlorinated-OPEs (Cl-OPEs) concentrations exceeded ∑non-chlorinated-OPEs (non-Cl-OPEs) with median concentrations of 10 ng L-1 and 1.3 ng L-1, respectively. In sediment samples, ∑Cl-OPEs and ∑nonchlorinated-OPEs had median concentrations of 4.5 and 2.5 ng g-1, respectively. High concentrations of OPEs in samples from the Mackenzie River plume suggest riverine discharge as an OPE source to the Canadian Arctic. The prevalence of OPEs at other sites is consistent with long-range transport. The OPE inventory of the Canadian Arctic Ocean representative of years 2013-2018 was estimated at 450-16,000 tonnes with a median ∑11OPE mass of 4100 tonnes with >99% of the OPE inventory estimated to be in the water column. These results highlight the importance of OPEs as water-based Arctic contaminants subject to long-range transport and local sources. The high OPE inventory in the water column of the Canadian Arctic Ocean points to the need for international regulatory mechanisms for persistent and mobile organic contaminants (PMOCs) that are not covered by the risk assessment criteria of the Stockholm Convention.

Ecotoxicity profile of heavily contaminated surface water of two rivers in Tunisia

Persistent organic and inorganic contaminants generated by industrial effluent wastes poses a threat to the maintenance of aquatic ecosystems and public health. The Khniss and Hamdoun rivers, located in the central-east of Tunisia, receive regularly domestic and textile wastewater load. The present study aimed to survey the water quality of these rivers using physicochemical, analytical and toxicological approaches. In the physicochemical analysis, the recorded levels of COD and TSS in both samples exceed the Tunisian standards. Using the analytical approach, several metals and some textile dyes were detected. Indeed, 17 metals were detected in both samples in varying concentrations, which do not exceed the Tunisian standards. The sources of metals pollution can be of natural and anthropogenic origin. Three textile disperse dyes were detected with high levels compared to other studies: the disperse orange 37 was detected in the Khniss river with a concentration of 6.438 μg/L and the disperse red 1 and the disperse yellow 3 were detected in the Hamdoun river with concentrations of 3.873 μg/L and 1895 μg/L, respectively. Textile activities were the major sources of disperse dyes. For both samples, acute and chronic ecotoxicity was observed in all the studied organisms, however, no genotoxic activity was detected. The presence of metals and textile disperse dyes could be associated with the ecotoxicological effects observed in the river waters, in particular due to the industrial activity, a fact that could deteriorate the ecosystem and therefore threaten the human health of the population living in the study areas. Combining chemical and biological approaches, allowed the detection of water ecotoxicity in testing organisms and the identification of possible contributors to the toxicity observed in these multi-stressed water reservoirs.

Developing interim water quality criteria for emerging chemicals of concern for protecting marine life in the Greater Bay Area of South China

This study aimed to establish marine water quality criteria (MWQC) for emerging chemicals of concern (ECCs) for protecting aquatic life in the Greater Bay Area (GBA) of South China. Despite the frequent occurrence and elevated concentrations of these ECCs in the GBA, there is a lack of regional MWQC for these contaminants. We screened 21 common ECCs that were classified into the following six groups: (1) new persistent organic contaminants; (2) brominated flame retardants; (3) perfluoroalkyl and polyfluoroalkyl substances; (4) pharmaceutically active compounds (PhACs); (5) plasticizers; and (6) personal care products. Globally, MWQC for PhACs remain largely unavailable despite their increasing occurrence in marine environments. Using an integrative scientific approach, we derived interim MWQC for the GBA with specific protection goals. The approach described herein can be applied for the derivation of MWQC for ECCs and the establishment of guidelines for ecological risk assessment in the GBA and other regions.

Pesticide residues in food: distribution, route of exposure and toxicity: in review

The safety of food has significant impact on human health hence the increasing concern on safe food consumption. One of the recent issues that have globally attracted the concern of consumers is the presence of pesticide residues in food. These residual chemicals are persistent organic contaminants that have serious lethal effect on human health when exposed beyond certain levels. The fears of the envisaged increased in the global population has further increased the use of pesticides due to concern for food productivity and security. The present paper examines the presence of pesticide residues in food, their sources and strategies for reducing the concentrations of these toxic chemicals. Attempt is also made in reviewing the Risk Assessment of Pesticide Residue in Food.

Mycelium-producing Mushroom Calocybe indica (Milky Mushroom) as Bio-antagonist Against the Bacteria present in Marikina River.

Mushroom forming fungi are one of the nature’s most powerful decomposers and degrades a wide variety of environmentally persistent pollutants and organic contaminants by secreting strong extra cellular enzymes due to their aggressive growth and biomass production.&#x0D; This study assess the potential of Calocybe indica (Milky mushroom) as bio-antagonist against microorganism serves as pollutants on Marikina River through Heterotrophic plate count (HPC).&#x0D; The use of Calocybe indica (Milky mushroom) as the medium of mycoremediation effectively lessen the count of bacterial colonies in Marikina River’s water by creating a bio-antagonistic relationship with the bio-pollutants present on the water samples.&#x0D; Increasing the period of treatment and observation. Using of water samples from different depth from surface level down to aphotic region of the Marikina River. Identifying the strain of microorganisms present on the water. Using other mushroom to compare the potential of Calocybe indica to kill bio-pollutants should be done for the improvement of the study.

Evaluating Fugacity Model for Organic Contaminants in Waste Deposited in Khulna Landfill

Trichloroethylene, and Benzene etc. in different landfill components such as landfill gas (LFG), leachate and waste due to emission from a selected waste disposal site at old Rajbandh, Khulna, Bangladesh. Level III Fugacity model was implemented on the selected evaluative environment and Monte Carlo simulation was used to account the variability and uncertainty of the model inputs as well as to observe its effect on the model outputs. It was found that Trichloroethylene had the highest concentration in waste compartment with a magnitude of 2.0E-02 mol/m3 and most of the mass (52%) was accumulated in waste compartment. It was found that m-Xylene was the highly persistent organic contaminant as it spends the highest amount of time in the modelled landfill environment. Reaction was the main removal mechanism for Trichloroethylene as about 79% of the total amount was removed by oxidation and hydrolysis reaction. It is essential to know the behaviour of potential harmful contaminants for assessing human health hazards from landfill site. The outcome of level III Fugacity model like mass, concentrations, etc. of organic contaminants generated from a selected landfill will further be helpful for evaluating health hazards from landfill site at Khulna.&#x0D; Journal of Engineering Science 11(1), 2020, 67-82