Maria Antonopoulou

A review on advanced oxidation processes for the removal of taste and odor compounds from aqueous media.

In view of the global concern about the occurrence of taste and odor (T&O) compounds in waters for drinking water supply and the necessity for the development of more innovative and efficient technologies for water treatment and depuration, the focus of this study is to provide a state of the art overview on current knowledge for the application of advanced oxidation technologies for the treatment of T&O compounds in aquatic media. The most representative and newly emerging compounds belonging to the major groups of T&O compounds, such as geosmin, methylisoborneol, benzothiazoles, mercaptans and sulfides as well as aromatic and other miscellaneous T&O compounds, are included in the systematic overview. The current data has been compiled and extensively discussed in terms of the degree of degradation, reaction kinetics, effect of operational parameters and water quality, identity of intermediate and final products and possible transformation pathways.

Sonochemical degradation of ethyl paraben in environmental samples: Statistically important parameters determining kinetics, by-products and pathways.

The sonochemical degradation of ethyl paraben (EP), a representative of the parabens family, was investigated. Experiments were conducted at constant ultrasound frequency of 20 kHz and liquid bulk temperature of 30 °C in the following range of experimental conditions: EP concentration 250-1250 μg/L, ultrasound (US) density 20-60 W/L, reaction time up to 120 min, initial pH 3-8 and sodium persulfate 0-100mg/L, either in ultrapure water or secondary treated wastewater. A factorial design methodology was adopted to elucidate the statistically important effects and their interactions and a full empirical model comprising seventeen terms was originally developed. Omitting several terms of lower significance, a reduced model that can reliably simulate the process was finally proposed; this includes EP concentration, reaction time, power density and initial pH, as well as the interactions (EP concentration)×(US density), (EP concentration)×(pHo) and (EP concentration)×(time). Experiments at an increased EP concentration of 3.5mg/L were also performed to identify degradation by-products. LC-TOF-MS analysis revealed that EP sonochemical degradation occurs through dealkylation of the ethyl chain to form methyl paraben, while successive hydroxylation of the aromatic ring yields 4-hydroxybenzoic, 2,4-dihydroxybenzoic and 3,4-dihydroxybenzoic acids. By-products are less toxic to bacterium V. fischeri than the parent compound.

Photodegradation of ethyl paraben using simulated solar radiation and Ag3PO4 photocatalyst

In this work, the solar light-induced photocatalytic degradation of ethyl paraben (EP), a representative of the parabens family, was studied using silver orthophosphate, a relatively new photocatalytic material. The catalyst was synthesized by a precipitation method and had a primary crystallite size of ca 70nm, specific surface area of 1.4m2/g and a bandgap of 2.4eV. A factorial design methodology was implemented to evaluate the importance of EP concentration (500-1500μg/L), catalyst concentration (100-500mg/L), reaction time (4-30min), water matrix (pure water or 10mg/L humic acid) and initial solution pH (3-9) on EP removal. All individual effects but solution pH were statistically significant and so were the second-order interactions of EP concentration with reaction time or catalyst concentration. The water matrix effect was negative (all other effects were positive) signifying the role of humic acid as scavenger of the oxidant species. Liquid chromatography-time of flight mass spectrometry revealed the formation of methyl paraben, 4-hydroxybenzoic acid, benzoic acid and phenol as primary transformation by-products; these are formed through dealkylation and decarboxylation reactions initiated primarily by the photogenerated holes. Estrogenicity assays showed that methyl paraben was more estrogenic than EP; however, parabens are slightly estrogenic compared to 17β-estradiol.

Photocatalytic and photoelectrocatalytic degradation of the drug omeprazole on nanocrystalline titania films in alkaline media: Effect of applied electrical bias on degradation and transformation products.

Photocatalytic and photoelectrocatalytic degradation of the drug omeprazole has been studied in the presence of nanocrystalline titania films supported on glass slides or transparent FTO electrodes in alkaline environment. Its photocatalytic degradation rate was assessed by its UV absorbance and by HPLC, while its transformation products were analyzed by HR-LC-MS. Based on UV absorbance, omeprazole can be photocatalytically degraded at an average rate of 6.7×10(-4)min(-1) under low intensity UVA irradiation of 1.5mWcm(-2) in the presence of a nanoparticulate titania film. This corresponds to degradation of 1.4mg of omeprazole per gram of the photocatalyst per liter of solution per hour. The photodegradation rate can be accelerated in a photoelectrochemical cell by applying a forward bias. In this case, the maximum rate reached under the present conditions was 11.6×10(-4)min(-1) by applying a forward bias of +0.6V vs. Ag/AgCl. Four major transformation products were successfully identified and their profiles were followed by HR-LC-MS. The major degradation path includes the scission of the sulfoxide bridge into the corresponding pyridine and benzimidazole ring derivates and this is accompanied by the release of sulfate anions in the reaction mixture.

Evaluation of toxicity and genotoxicity of 2-chlorophenol on bacteria, fish and human cells.

Due to the extensive use of chlorophenols (CPs) in anthropogenic activities, 2-Chlorophenol (2-CP), among other CPs, can enter aquatic ecosystems and can be harmful to a variety of organisms, including bacteria, fish and humans, that are exposed directly and/or indirectly to such contaminated environments. Based on the existing knowledge and in order to move a step forward, the purpose of this study is to investigate the toxic and mainly the genotoxic effects of 2-CP using a combination of bioassays. The tests include the marine bacterium Vibrio fischeri and micronuclei induction in the erythrocytes of Carassius auratus as well as in cultured human lymphocytes. The results obtained reveal that 2-CP is able to induce dose-dependent toxic and genotoxic effects on the selected tested concentrations under the specific experimental conditions.

A Multidisciplinary Assessment of River Surface Water Quality in Areas Heavily Influenced by Human Activities

The present study could serve as a multidisciplinary approach for the assessment of river surface water quality with the use of chemical and biological methods. Specifically, physicochemical parameters, heavy metals, and pesticides were measured in water samples from three different stations (sampling station S1, S2, and S3) along Asopos River (Greece). In parallel, algal species (primary producers)—such as Scenedesmus rubescens and Chlorococcum sp.; consumer invertebrate species, such as the fairy shrimp Thamnocephalus platyurus and the rotifer Brachionus calyciflorus; as well as human lymphocytes—were exposed to those samples for assessing their toxic and genotoxic/mutagenic effects. According to the results, although the values of almost all of the physicochemical parameters tested, heavy metals (zinc, cadmium, lead, and mercury) and pesticides were lower than or within the respective environmental quality standards, thus offering no clear evidence for their natural or anthropogenic origin. Values recorded for nickel, chromium, hexavalent chromium, and malathion represent a typical case of mixed influence from natural and anthropogenic enrichments. In contrast, the algal growth arrest, the acute toxic effects on the freshwater invertebrates, and the increased micronuclei frequencies observed in human lymphocytes showed the presence of human-derived hazardous substances, which were hardly determinable with the use of conventional chemical methods. Given that the presence of priority pollutants in river surface waters, heavily burdened by anthropogenic activities, could give no clear evidence for their biological risk, the results of the present study showed that chemical and biological assays should be applied in parallel, thus serving as a reliable tool for the assessment of river water quality.

Photocatalytical removal of fluorouracil using TiO2-P25 and N/S doped TiO2 catalysts: A kinetic and mechanistic study.

In the present study, the photocatalytic activity of TiO2-based photocatalysts toward degradation and mineralization of the anti-cancer drug 5-fluorouracil (5-FU) in aqueous phase was investigated under simulated solar and visible irradiation. Commercial TiO2 (P25) and N/S-doped TiO2 catalysts synthesized by a simple sol-gel method were used as photocatalysts. TiO2 P-25 was found to be the most photoactive catalyst for the removal of 5-FU, under simulated solar irradiation. Among N/S-doped TiO2 catalysts, the one with molar Ti:N/S ratio equal to 0.5 was the most efficient under simulated solar irradiation. In contrast, under visible irradiation the catalyst with equimolar Ti:N/S ratio showed the highest performance for the removal of 5-FU. Scavenging experiments revealed that HO radicals and h+ were the major reactive species mediating photocatalytic degradation of 5-FU using TiO2 P-25 and N/S-doped TiO2 catalysts, under simulated solar irradiation. On the other hand, the essential contribution of 1O2 and O2- in the degradation of 5-FU under visible light was proved. The transformation products (TPs) of 5-FU, were identified by LC-MS-TOF suggesting that defluorination followed by hydroxylation and oxidation are the main transformation pathways, under all the studied photocatalytic systems.

Photo-Fenton and Fenton-like processes for the treatment of the antineoplastic drug 5-fluorouracil under simulated solar radiation

In the present study, photo-Fenton and Fenton-like processes were investigated for the degradation and mineralization of the antineoplastic drug 5-fluorouracil (5-FU). For the optimization of photo-Fenton treatment under simulated solar light (SSL) radiation, the effects of several operating parameters (i.e., 5-FU concentration, Fe3+, and oxidant concentration) on the treatment efficiency were studied. According to the results, SSL/[Fe(C2Ο4)3]3−/Η2Ο2 process was the most efficient, since faster degradation of 5-FU and higher mineralization percentages were achieved. All the applied processes followed quite similar transformation routes which include defluorination-hydroxylation as well as pyrimidine ring opening, as demonstrated by the transformation products identified by high resolution mass spectrometry analysis. The toxicity of the treated solutions was evaluated using the Microtox assay. In general, low toxicity was recorded for the initial solution and the solution at the end of the photocatalytic treatment, while an increase in the overall toxicity was observed only at the first stages of SSL/Fe3+/Η2Ο2 and SSL/Fe3+/S2O82− processes.

The role of acetone in the [omim][BF4]-mediated adverse effects on tissues of mussels, human lymphocytes and the fruit fly Drosophila melanogaster

The present study investigated [omim][BF4]-mediated adverse effects on biological models widely used in toxicological studies. Specifically, mussels of the genus Mytilus, human lymphocytes and fruit flies of the species Drosophila melanogaster, were exposed to [omim][BF4] at concentrations ranging from micro- to milligrams per liter, with or without the presence of acetone as a carrier solvent and thereafter [omim][BF4]-mediated adverse effects were analyzed appropriately (stress indices, such as lipid peroxidation byproducts, acetylcholinesterase/AChE activity and micronucleus/MN formation frequency, in mussel gills, Cytokinesis Block Micronucleus/CBMN assay and SMART test in human lymphocytes and fruit flies respectively). LC-MS-TOF analysis was also performed for elucidating [omim][BF4] mode of action in the presence of the carrier solvent. The results showed the toxic potential of [omim][BF4], as well as acetones ability to attenuate [omim][BF4]-mediated toxicity in almost all cases, probably due to the significant effect of acetone on the hydrophilic-lipophilic character and the viscosity of [omim][BF4], as well as its interaction and permeability on the cell membranes. The slight involvement of acetone in the attenuation of [omim][BF4]-mediated genotoxic effects on D. melanogaster could be due to species feeding experimental conditions, thus favoring the induction of antioxidant defense system against the [omim][BF4]-mediated effects in all cases.

Laboratory calibration of twelve pesticides using polar organic chemical integrative samplers

Passive sampling is an emerging tool for monitoring micropollutants in surface waters and enables the determination of time-weighted average (TWA) concentration over extended sampling periods. For the determination of TWA concentration, the sampling rates (Rs) for the compounds of interest are required. Laboratory calibration experiments were conducted in order to determine the sampling rates of 12 selected pesticides using Polar Organic Chemical Integrative Samplers (pest-POCIS). The experiments were performed on the basis of static renewal exposure of pest-POCIS under stirred conditions for different time intervals up to 28 days. The recoveries of target pesticides ranged between 71 % and 120 % with relative standard deviation (RSD) <18%. Detection limits (LODs) and quantification limits (LOQs) ranged between 0.5 and 6 ng L−1 and 1.6 and 19.7 ng L−1, respectively. The uptake in POCIS for the studied pesticides followed a linear pattern throughout the 28 days of exposure, except for fipronil. The calculated sampling rates ranged from 0.030 L day−1 to 0.223 L day−1. The pesticides pirimiphos methyl, clofentezine, cyprodinil, fipronil and kresoxim methyl have never been studied before in calibration experiments using pest-POCIS passive samplers. Using the described analytical procedure, trace levels (ng L−1) of the target pesticides could be determined in surface waters.