László Wojnárovits

Hydroxyl radical induced degradation of ibuprofen

Pulse radiolysis experiments were used to characterize the intermediates formed from ibuprofen during electron beam irradiation in a solution of 0.1mmoldm(-3). For end product characterization (60)Co γ-irradiation was used and the samples were evaluated either by taking their UV-vis spectra or by HPLC with UV or MS detection. The reactions of OH resulted in hydroxycyclohexadienyl type radical intermediates. The intermediates produced in further reactions hydroxylated the derivatives of ibuprofen as final products. The hydrated electron attacked the carboxyl group. Ibuprofen degradation is more efficient under oxidative conditions than under reductive conditions. The ecotoxicity of the solution was monitored by Daphnia magna standard microbiotest and Vibrio fischeri luminescent bacteria test. The toxic effect of the aerated ibuprofen solution first increased upon irradiation indicating a higher toxicity of the first degradation products, then decreased with increasing absorbed dose.

A computer controlled pulse radiolysis laboratory

In this paper the computer controlled, automated pulse radiolysis laboratory of the Institute of Isotopes of the Hungarian Academy of Sciences, Budapest, is introduced. The system is equipped with a Linac type accelerator which produces 50 ns–2.6 μs pulses of 4 MeV electrons, with an optical detection system and with computerized data acquisition.

Electron-capture detection of aromatic hydrocarbons

Abstract The detectabilities and some parameters of electron + aromatic hydrocarbon reactions were investigated in a constant-current, variable-frequency electron-capture detector. It was found that lower alkylbenzenes give weak signals in the detector, polymethylbenzenes, styrene, indene, naphthalenes and biphenyl exhibit medium responses, whereas the response factors of aromatics with three rings and those of diphenylthylene, diphenylacetalyne and azulene are relativity high. On the basis of the temperature dependence of the response factors the electron affinities and the electron absorption and desorption rate constants were determined for many aromatics, and the magnitudes of the response factors are discussed.

Addition and elimination kinetics in OH radical induced oxidation of phenol and cresols in acidic and alkaline solutions

Abstract The rates of the two consecutive reactions, OH radical addition and H 2 O/OH − elimination, were studied by pulse radiolysis in highly acidic (pH=1.3–1.9) and alkaline (pH≈11) solutions, respectively, for phenol and for the three cresol isomers. The rate coefficient of the addition as measured by the build-up of phenoxyl radical absorbance and by a competitive method is the same (1.4±0.1)×10 10 mol −1 dm 3 s −1 both in acidic and alkaline solution. The rate coefficient of the H 2 O elimination in acidic solution is (1.6±0.2)×10 6 s −1 , whereas the coefficient of the OH − elimination in alkaline solutions is 6–8 times higher. The kinetics of the phenoxyl radical formation was described by the two-exponential equation of the consecutive reactions: the first exponential is related to the pseudo-first-order addition, while the second to the elimination reaction. No considerable structure dependence was found in the rate coefficients, indicating that the methyl substitutent in these highly acidic or alkaline solutions influences neither the addition nor the elimination rate.

Radiation-chemical reaction of 2,3,5-triphenyl-tetrazolium chloride in liquid and solid state

Abstract In pulse radiolysis of 2,3,5-triphenyl-tetrazolium chloride (TTC) at around 360 nm fast formation of intermediate tetrazolium radical was observed under both oxidizing and reducing conditions. In the latter case bimolecular formation of formazan, absorbing at around 480 nm, was observed. This reaction is accompanied by combination to the diformazan dimer, absorbing over the spectral range 500–550 nm. A polyvinyl-alcohol-based TTC film was produced and tested for dosimetry purposes: it gave a measurable response in the 1–100 kGy dose range by evaluating the 50 μm thick TTC films at the absorption maximum of 493 nm.

Ketoprofen removal by O3 and O3/UV processes: Kinetics, transformation products and ecotoxicity

Ozonation (O3) and its combination with ultraviolet radiation (O3/UV) were used to decompose ketoprofen (KET). Depending on the initial KET concentration, fourteen to fifty times faster KET degradation was achieved using combined O3/UV method compared to simple ozonation. Using both methods, formation of four major aromatic transformation products were observed: 3-(1-hydroxyethyl)benzophenone, 3-(1-hydroperoxyethyl) benzophenone, 1-(3-benzoylphenyl) ethanone and 3-ethylbenzophenone. In the combined treatment the degradation was mainly due to the direct effect of UV light, however, towards the end of the treatment, O3 highly contributed to the mineralization of small carboxylic acids. High (~90%) mineralization degree was achieved using the O3/UV method. Toxicity tests performed using representatives of three trophic levels of the aquatic ecosystems (producers, consumers and decomposers) Pseudokirchneriella subcapitata green algae, Daphnia magna zooplanktons and Vibrio fischeri bacteria showed that under the used experimental conditions the transformation products have significantly higher toxicity towards all the test organisms, than KET itself. The bacteria and the zooplanktons showed higher tolerance to the formed products than algae. The measured toxicity correlates well with the concentration of the aromatic transformation products, therefore longer treatments than needed for complete degradation of KET are strongly suggested, in order to avoid possible impact of aromatic transformation products on the aquatic ecosystem.

Elimination of diclofenac from water using irradiation technology

The effluents of wastewater treatment plants, usually directly emitted to the environment, often contain the anti-inflammatory drug diclofenac (DCF). The paper investigates DCF elimination using irradiation technology. Hydroxyl radical and hydrated electron reactive intermediates resulting from water radiolysis effectively degrade DCF and strongly reduce the toxicity of the solutions. ()OH attaches to one of the rings of DCF, and hydroxylated molecules, 2,6-dichloroaniline and quinoid type compounds are the products. Hydrated electron adds to the chlorine atom containing ring, in the reaction quinoid type compounds and 4-chloroacridine form. At a 0.1 mM DCF concentration, a ∼1 kGy absorbed dose is needed for the degradation of DCF molecules, but for mineralization of the products (in presence of O2) an order of magnitude higher dose is required. For irradiation of wastewater after biological treatment a ∼1 kGy dose is suggested. At this dose DCF and other drugs or metabolites present at μg L(-1) level are eliminated together with microorganism deactivation.

Analytical approaches to the OH radical induced degradation of sulfonamide antibiotics in dilute aqueous solutions

By combining a large variety of analytical techniques this study aimed at elaborating methods to follow up the degradation of sulfonamides in an advanced oxidation process (AOP): irradiation with ionizing radiation in dilute aqueous solution. In this process, besides other radicals, hydroxyl radicals are produced. As pulse radiolysis experiments show the basic initial reaction is hydroxyl radical addition to the benzene ring, forming cyclohexadienyl radical intermediates. In aerated solutions these radicals transform to peroxy radicals. Among the first formed products aromatic molecules hydroxylated in the benzene rings or in some cases in the heterocyclic rings were observed by LC-MS/MS. Chemical oxygen demand (COD) measurements indicate that at the early reaction period of degradation one hydroxyl radical induces incorporation of 1.5 O atoms into the products. Comparison of the COD and TOC (total organic carbon content) results shows gradual oxidation. Simultaneously with hydroxylation ring opening also takes place. The kinetics of inorganic SO4(2-) and NH4(+) formation, analyzed by ion chromatography, is similar to the kinetics of ring degradation (UV spectroscopy), however, there is a delayed formation of NO3(-). The latter ions may be produced in oxidative degradation of smaller N containing fragments. The S atoms of the sulfonamides remain in the solution (ICP-MS measurements) after degradation, whereas some part of the N atoms leaves the solution probably in the form of N2 (total nitrogen content (TN) measurements). Degradation is accompanied by a high pH drop due to formation of SO4(2-), NO3(-) and smaller organic acids. The degradation goes through many simultaneous and consecutive reactions, and with the applied methods the different stages of degradation can be characterized.

Radiation activation of cotton-cellulose prior to alkali treatment

The effect of alkali treatment on preirradiated cotton-cellulose was investigated using diffuse reflectance Fourier transformed infrared spectroscopy (DRIFT) and X-ray diffraction (XRD). The effect of two kinds of alkali solutions (NaOH and TMAH, tetramethyl ammonium hydroxide) on the crystalline structure of irradiated cotton-cellulose was compared. The transformation of cellulose I to cellulose II was observed applying DRIFT technique by the increase of the absorbance at 896 cm-1 and XRD. The results obtained by the two methods were in good correlation. An increase in carbonyl content (as detected by FTIR by measuring the absorbance at 1740 cm-1) was found in the samples due to oxidative degradation.

Degradation of organic molecules in advanced oxidation processes: relation between chemical structure and degradability.

Hydroxyl radical induced degradation of maleic acid, fumaric acid and 20 aromatic molecules was investigated in air saturated aqueous solutions. Hydroxyl radicals were generated by an advanced oxidation process (AOP), water radiolysis. Oxidation was followed by chemical oxygen demand (COD) and total organic carbon content (TOC) measurements. Up to ∼30-50% decrease of COD the dose dependence was linear. By the ratio of the decrease of COD and the amount of reactive radiolysis intermediates introduced into the solution the oxidation efficiencies were calculated. Efficiencies around 0.5-1 (O2 molecule built in products/OH) found for most of the compounds show that the one-electron-oxidant OH induces 2-4 electron oxidations. The high oxidation rates were explained by OH addition to unsaturated bonds and subsequent reactions of dissolved O2 with organic radicals. In amino substituted molecules or in Acid Red 1 azo dye, O2 cannot compete efficiently with unimolecular transformation of organic radicals and the efficiency is lower (0.2-0.5).