Joseph De Laat

Photodegradation of the steroid hormones 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) in dilute aqueous solution

The photochemical transformation of natural estrogenic steroid 17beta-estradiol (E2) and the synthetic oral contraceptive 17alpha-ethinylestradiol (EE2) has been studied in dilute non buffered aqueous solution (pH 5.5-6.0) upon monochromatic (254 nm) and polychromatic (lambda>290 nm) irradiation. Upon irradiation at 254 nm, the quantum yields of E2 and EE2 photolysis were similar and evaluated to be 0.067+/-0.007 and 0.062+/-0.007, respectively. Upon polychromatic excitation, and by using phenol as chemical actinometer, the photolysis efficiencies have been determined to be 0.07+/-0.01 and 0.08+/-0.01 for E2 and EE2, respectively. For both estrogens, photodegradation by-products were identified with GC/MS and LC/MS. In a first step, a model compound--5,6,7,8-tetrahydro-2-naphthol (THN)--, which represents the photoactive phenolic group, was used to obtain basic photoproduct structural informations. Numerous primary and secondary products were observed, corresponding to hydroxylated phenolic- or quinone-type compounds.

Transformation of carbendazim induced by the H2O2/UV system in the presence of hydrogenocarbonate ions : involvement of the carbonate radical

The transformation of the fungicide carbendazim by hydroxyl radicals generated by the photolysis (λexc. = 254 nm) of hydrogen peroxide in aqueous solution has been studied in the absence and in the presence of hydrogenocarbonate ions. In the presence of high concentrations of hydrogen peroxide, the second-order rate constant of the reaction of HO˙ radicals with carbendazim has been determined to be equal to (2.2 ± 0.3) × 109 L.mol−1.s−1. The identification of the main degradation by-products shows the existence of two different reaction sites for carbendazim induced degradation: the benzene ring and the methyl group. Good simulations of carbendazim disappearance have been obtained by kinetic modelling over a wide range of initial H2O2 concentrations. In the presence of hydrogenocarbonate ions, a quenching effect is observed and the simulations lead to an underestimation of the carbendazim disappearance. This is because of the involvement of the carbonate radicals, which react with carbendazim with a second-order rate constant evaluated to be equal to (6 ± 2) × 106 L.mol−1.s−1 by kinetic modelling. When the starting concentration of HCO3− is high enough, the elimination of carbendazim by CO3˙ becomes the major route of carbendazim transformation.

Hydroxyl radical involvement in the decomposition of hydrogen peroxide by ferrous and ferric-nitrilotriacetate complexes at neutral pH.

The relative rates of degradation of three hydroxyl radical probe compounds (atrazine, fenuron and parachlorobenzoic acid (pCBA)) by Fe(III)/H(2)O(2) (pH = 2.85), Fe(III)NTA/H(2)O(2) (neutral pH), Fe(II)/O(2), Fe(II)NTA/O(2), Fe(II)/H(2)O(2) and Fe(II)NTA/H(2)O(2) (neutral pH) have been investigated using the competitive kinetic method. Experiments were carried out in batch and in semi-batch reactors, in the dark, at 25 °C. The data showed that the three probe compounds could be degraded by all the systems studied, and in particular by Fe(II)NTA/H(2)O(2) and Fe(III)NTA/H(2)O(2) at neutral pH. The relative rate constants of degradation of the three probe compounds obtained for all the systems tested were identical and equal to 1.45 ± 0.03 and 0.47 ± 0.02 for k(Atrazine)/k(pCBA) and k(Fenuron)/k(pCBA), respectively. These values as well as the decrease of the rates of degradation of the probe compounds upon the addition of hydroxyl radical scavengers (tert-butanol, bicarbonate ions) suggest that the degradation of atrazine, fenuron and pCBA by Fe(II)NTA/O(2), Fe(II)NTA/H(2)O(2) and Fe(III)NTA/H(2)O(2) is initiated by hydroxyl radicals.

Effect of some parameters on the rate of the catalysed decomposition of hydrogen peroxide by iron(III)-nitrilotriacetate in water.

The decomposition rate of H(2)O(2) by iron(III)-nitrilotriacetate complexes (Fe(III)NTA) has been investigated over a large range of experimental conditions: 3 < pH < 11, [Fe(III)](T,0): 0.05-1 mM; [NTA](T,0)/[Fe(III)](T,0) molar ratios : 1-250; [H(2)O(2)](0): 1 mM-4 M) and concentrations of HO· radical scavengers: 0-53 mM. Spectrophotometric analyses revealed that reactions of H(2)O(2) with Fe(III)NTA (1 mM) at neutral pH immediately lead to the formation of intermediates (presumably peroxocomplexes of Fe(III)NTA) which absorb light in the region 350-600 nm where Fe(III)NTA and H(2)O(2) do not absorb. Kinetic experiments showed that the decomposition rates of H(2)O(2) were first-order with respect to H(2)O(2) and that the apparent first-order rate constants were found to be proportional to the total concentration of Fe(III)NTA complexes, were at a maximum at pH 7.95 ± 0.10 and depend on the [NTA](T,0)/[Fe(III)](T,0) and [H(2)O(2)](0)/[Fe(III)](T,0) molar ratios. The addition of increasing concentrations of tert-butanol or sodium bicarbonate significantly decreased the decomposition rate of H(2)O(2), suggesting the involvement of HO· radicals in the decomposition of H(2)O(2). The decomposition of H(2)O(2) by Fe(III)NTA at neutral pH was accompanied by a production of dioxygen and by the oxidation of NTA. The degradation of the organic ligand during the course of the reaction led to a progressive decomplexation of Fe(III)NTA followed by a subsequent precipitation of iron(III) oxyhydroxides and by a significant decrease in the catalytic activity of Fe(III) species for the decomposition of H(2)O(2).

Concentration levels of urea in swimming pool water and reactivity of chlorine with urea

This study investigated the reactivity of chlorine with urea which is the main nitrogen contaminant introduced into swimming pool water by bathers. In the first part of this study, analyses showed that the mean concentrations of urea and TOC determined from 50 samples of municipal swimming pool were equal to 18.0 μM (s.d. 11.7) and 3.5 mg C L(-1) (s.d. 1.6), respectively. The mean value for the urea contribution to the TOC content was 6.3% (s.d. 3.3). The rate of decomposition of urea in swimming pool water measured during the closure time of the facility was very slow (decay at the rate of ≈ 1% per hour in the presence of 1.6-1.8 mg L(-1) of free chlorine). In the second part of this work, experiments carried out with phosphate buffered solutions of urea ([Urea](0) = 1 mM; [Cl(2)](0)/[Urea](0): 0.5-15 mol/mol; pH 7.4 ± 0.2; reaction time: 0-200 h) showed that long term chlorine demand of urea was about 5 mol Cl(2)/mol of urea. Chlorination led to a complete mineralization of organic carbon into CO(2) for a chlorine dose of 3.5 mol/mol and to the formation of 0.7-0.8 mol NO(3)(-)/mol of urea for chlorine dose of 8-10 mol/mol. Experiments conducted with dilute solutions of urea ([Urea](0) = 50 μM; pH ≈ 7.3) confirmed that the degradation rate of urea by chlorine is very slow under conditions simulating real swimming pool water.

Effect of dissolved oxygen on the photodecomposition of monochloramine and dichloramine in aqueous solution by UV irradiation at 253.7 nm

The effect of dissolved oxygen on the photodecomposition of monochloramine (7.5 < pH < 10) and dichloramine (pH = 3.7 +/- 0.2) at 253.7 nm has been investigated. The kinetic study shows that the rate of photodecomposition of monochloramine is about two times faster in the absence of oxygen than in the presence of oxygen, is not significantly affected by pH and by the presence of hydroxyl radical scavengers (hydrogenocarbonate ion and tert-butanol). The apparent quantum yields of photodecomposition of monochloramine at 253.7 nm ([NH(2)Cl](0) approximately 1.5-2 mM, epsilon(253.7 nm) = 371 M(-1) cm(-1)) were equal to 0.28 +/- 0.03 and 0.54 +/- 0.03 mol E(-1) in oxygenated-saturated and in oxygen-free solutions, respectively. The photodecomposition rates or the apparent quantum yields of photodecomposition of dichloramine ([NHCl(2)](0) approximately 1.5-2 mM, pH = 3.7 +/- 0.2) in oxygen-free and in oxygen-saturated solutions were quite identical (Phi = 0.82 +/- 0.08 mol E(-1); epsilon(253.7 nm) = 126 M(-1) cm(-1)). Under O(2) saturation, UV irradiation of NH(2)Cl leads to the formation of nitrite ( approximately 0.37 mol/mol of NH(2)Cl decomposed), nitrate ( approximately 0.073 mol/mol) and does not form ammonia (<0.01 mol/mol). In oxygen-free solutions, monochloramine decomposes to form ammonia ( approximately 0.37 mol/mol). Photodecomposition of dichloramine did not lead to significant amounts of nitrite and nitrate in the presence and in the absence of oxygen. The nitrogen mass balances also indicate the formation of other nitrogen species (probably N(2) and/or N(2)O) during the photodecomposition of monochloramine and dichloramine by UV irradiation at 253.7 nm.

Monochloramination of Resorcinol: Mechanism and Kinetic Modeling

The kinetics of monochloramination of resorcinol, 4-chlororesorcinol, and 4,6-dichlororesorcinol have been investigated over the pH range of 5-12, at 23 +/- 2 degrees C. Monochloramine solutions were prepared with ammonia-to-chlorine ratios (N/Cl) ranging from 1.08 to 31 mol/mol. Under conditions that minimize free chlorine reactions (N/Cl > 2 mol/mol), the apparent second-order rate constants of monochloramination of resorcinol compounds show a maximum at pH values between 8.6 and 10.2. The intrinsic second-order rate constants for the reaction of monochloramine with the acid-base forms of the dihydroxybenzenes (Ar(OH)(2), Ar(OH)O(-), and Ar(O(-))(2)) were calculated from the apparent second-order rate constants. The stoichiometric coefficients for the formation of 4-chlororesorcinol by monochloramination of resorcinol and 4,6-dichlororesorcinol by monochloramination of 4-chlororesorcinol were found to be equal to 0.66 +/- 0.05 and 0.25 +/- 0.02 mol/mol, respectively at pH 8.6. A kinetic model that incorporates reactions of free chlorine and monochloramine with the different acid-base forms of resorcinol compounds simulated well the initial rates of degradation of resorcinol compounds and was useful to evaluate the contribution of free chlorine reactions to the overall rates of degradation of resorcinol at low N/Cl ratios.

Effect of some parameters on the formation of chloroform during chloramination of aqueous solutions of resorcinol

The effects of various factors (N/Cl ratio used to prepare monochloramine, monochloramine doses, pH and contact time) on the monochloramine demand and on the chloroform yield during chloramination of resorcinol have been investigated. Chloramination experiments were carried out at 24+/-1 degrees C, at pH values ranging from 6.5 to 12 using a bicarbonate/carbonate buffer and preformed monochloramine solutions prepared at pH 8.5 with N/Cl ratios ([NH(4)Cl](0)/[Total free Cl(2)](0) ranging from 1.0 to 150 mol/mol). Kinetic experiments ([Resorcinol](0)=5 or 100 microM, [NH(2)Cl](0)/[Resorcinol](0)=20 mol/mol, pH=8.5+/-0.1) showed a slow increase of the monochloramine consumption with reaction time. The monochloramine demands after reaction times of 7 days ([Resorcinol](0)=100 microM) and 14 days ([Resorcinol](0)=5 microM) were equal to 8.5 mol of NH(2)Cl/mole of resorcinol and were higher than the chlorine demands (approximately 7.3 mol/mol). Chloroform yields from monochloramination of resorcinol were lower than 8% (<80 mmol of CHCl(3)/mole of resorcinol) and were less than the yields obtained by chlorination (0.9-0.95 mol/mol). Chloroform productions increased with increasing monochloramine dose and reaction time and decreased with increasing pH values within the pH range 6.5-10. Chloroform formation markedly decreased when the N/Cl ratio increased from 1 to 1.5 mol/mol and was suppressed at N/Cl>100 mol/mol. The data obtained in the present work suggest that free chlorine released from monochloramine hydrolysis plays a significant role on the formation of chloroform during chloramination of resorcinol at N/Cl ratios close to unity (1.0

Effect of Chloride and Sulfate Ions on the Photoreduction Rate of Ferric Ion in UV Reactor Equipped with a Low Pressure Mercury Lamp

Abstract This study aims to demonstrate the effects of pH and of inorganic anions on the photoreduction of Fe(III). Effective quantum yields for the production of •OH radicals from iron(III) hydroxo species in pechlorate medium and in the present of chloride and sulfate anions were determined in the pH range 1-3. Experiments were carried out in batch at 25°C with a low-pressure mercury vapor lamp emitted at 253.7 nm. The method was based on measuring the pseudo-first-order rate constant of the photoreduction of Fe(III)-complexes in which tert-butanol scavenged the •OH at an identical rate. The results showed that the apparent quantum yield of photoreduction of Fe(III) increased when the pH increases, the values passed from 0.063 at pH 1 to 0.1 at pH 3 ([Fe(III)]0 = 1 mM and 3 mM). The effects of Cl- or SO42- on the photoreduction of Fe(III) depended on pH and on ion concentrations. The apparent quantum yield values increased in the present of anion Cl-, whereas those values decreased in the present of anion SO42-. For the Photo Fenton system, the effects of Cl- or SO42- were found to depend on pH, on the concentrations of the inorganic anions and to decrease the rate of decomposition of H2O2.