Selective oxidation of key functional groups in cyanotoxins during drinking water ozonation

Chemical kinetics were determined for the reactions of ozone and hydroxyl radicals with the three cyanotoxins microcystin-LR (MC-LR), cylindrospermopsin (CYN) and anatoxin-a (ANTX). The second-order rate constants (k(O3)) at pH 8 were 4.1 +/- 0.1 x 10(5) M(-1) s(-1) for MC-LR, approximately 3.4 x 10(5) M(-1) s(-1) for CYN, and approximately 6.4 x 10(4) M(-1) s(-1) for ANTX. The reaction of ozone with MC-LR exhibits a k(O3) similar to that of the conjugated diene in sorbic acid (9.6 +/- 0.3 x 10(5) M(-1) s(-1)) at pH 8. The pH dependence and value of k(O3) for CYN at pH > 8 (approximately 2.5 +/- 0.1 x 10(6) M(-1) s(-1)) are similar to deprotonated amines of 6-methyluracil. The k(O3) of ANTX at pH > 9 (approximately 8.7 +/- 2.2 x 10(5) M(-1) s(-1)) agrees with that of neutral diethylamine, and the value at pH < 8 (2.8 +/- 0.2 x 10(4) M(-1) s(-1)) corresponds to an olefin. Second-order rate constants for reaction with OH radicals (*OH), k(OH) for cyanotoxins were measured at pH 7 to be 1.1 +/- 0.01 x 10(10) M(-1) s(-1) for MC-LR, 5.5 +/- 0.01 x 10(9) M(-1) s(-1) for CYN, and 3.0 +/- 0.02 x 10(9) M(-1) s(-1) for ANTX. Natural waters from Switzerland and Finland were examined for the influence of variations of dissolved organic matter, SUVA254, and alkalinity on cyanotoxin oxidation. For a Swiss water (1.6 mg/L DOC), 0.2, 0.4, and 0.8 mg/L ozone doses were required for 95% oxidation of MC-LR, CYN, and ANTX, respectively. For the Finnish water (13.1 mg/L DOC), >2 mg/L ozone dose was required for each toxin. The contribution of hydroxyl radicals to toxin oxidation during ozonation of natural water was greatest for ANTX > CYN > MC-LR. Overall, the order of reactivity of cyanotoxins during ozonation of natural waters corresponds to the relative magnitudes of the second-order rate constants for their reaction with ozone and *OH. Ozone primarily attacks the structural moieties responsible for the toxic effects of MC-LR, CYN, and ANTX, suggesting that ozone selectively detoxifies these cyanotoxins.     

Treatment of volatile organic chemicals on the EPA Contaminant Candidate List using ozonation and the O3/H2O2 advanced oxidation process

Seven volatile organic chemicals (VOCs) on the EPA Contaminant Candidate List together with 1,1-dichloropropane were studied for their reaction kinetics and mechanisms with ozone and OH radicals during ozonation and the ozone/ hydrogen peroxide advanced oxidation process (O3/H2O2 AOP) using batch reactors. The three aromatic VOCs demonstrated high reactivity during ozonation and were eliminated within minutes after ozone addition. The high reactivity is attributed to their fast, indirect OH radical reactions with k(OH,M) of (5.3-6.6) x 10(9) M(-1) s(-1). Rates of aromatic VOC degradation are in the order 1,2,4-trimethylbenzene > p-cymene > bromobenzene. This order is caused by the selectivity of the direct ozone reactions (k(O3,M) ranges from 0.16 to 304 M(-1) s(-1)) and appears to be related to the electron-donating or -withdrawing ability of the substituent groups on the aromatic ring. The removal rates for the five aliphatic VOCs are much lower and are in the order 1,1-dichloropropane > 1,3-dichloropropane > 1,1-dichloroethane > 2,2-dichloropropane > 1,1,2,2-tetrachloroethane. The second-order indirect rate constants for the aliphatic VOCs range from 0.52 x 10(8) to 5.5 x 10(8) M(-1) s(-1). The relative stability of the carbon-centered intermediates seems to be related to the relative reactivity of the aliphatic VOCs with OH radicals. Except for 1,3-dichloropropane, ozonation and the O3/H2O2 AOP are not effective for the removal of other aliphatic VOCs. Bromide formation during the ozonation of bromobenzene indicates that bromate can be formed, and thus, ozonation and O3/H2O2 AOP may not be suitable for the treatment of bromobenzene.     

Oxidation of pharmaceuticals during ozonation and advanced oxidation processes

This study investigates the oxidation of pharmaceuticals during conventional ozonation and advanced oxidation processes (AOPs) applied in drinking water treatment. In a first step, second-order rate constants for the reactions of selected pharmaceuticals with ozone (k(O3)) and OH radicals (k(OH)) were determined in bench-scale experiments (in brackets apparent k(O3) at pH 7 and T = 20 degrees C): bezafibrate (590 +/- 50 M(-1) s(-1)), carbamazepine (approximately 3 x 10(5) M(-1) s(-1)), diazepam (0.75 +/- 0.15 M(-1) s(-1)), diclofenac (approximately 1 x 10(6) M(-1) s(-1)), 17alpha-ethinylestradiol (approximately 3 x 10(6) M(-1) s(-1)), ibuprofen (9.6 +/- 1.0 M(-1) s(-1)), iopromide (<0.8 M(-1) s(-1)), sulfamethoxazole (approximately 2.5 x 10(6) M(-1) s(-1)), and roxithromycin (approximately 7 x 10(4) M(-1) s(-1)). For five of the pharmaceuticals the apparent k(O3) at pH 7 was >5 x 10(4) M(-1) s(-1), indicating that these compounds are completely transformed during ozonation processes. Values for k(OH) ranged from 3.3 to 9.8 x 10(9) M(-1) s(-1). Compared to other important micropollutants such as MTBE and atrazine, the selected pharmaceuticals reacted about two to three times faster with OH radicals. In the second part of the study, oxidation kinetics of the selected pharmaceuticals were investigated in ozonation experiments performed in different natural waters. It could be shown that the second-order rate constants determined in pure aqueous solution could be applied to predict the behavior of pharmaceuticals dissolved in natural waters. Overall it can be concluded that ozonation and AOPs are promising processes for an efficient removal of pharmaceuticals in drinking waters.     

Oxidation of antibacterial molecules by aqueous ozone: moiety-specific reaction kinetics and application to ozone-based wastewater treatment

Ozone and hydroxyl radical (*OH) reaction kinetics were measured for 14 antibacterial compounds from nine structural families, to determine whether municipal wastewater ozonation is likely to result in selective oxidation of these compounds' biochemically essential moieties. Each substrate is oxidized by ozone with an apparent second-order rate constant, k'(O3,app) > 1 x 10(3) M(-1) s(-1), at pH 7, with the exception of N(4)-acetylsulfamethoxazole (K'(O3,app) is 2.5 x 102 M(-1) s(-1)). k'(O3,app) values (pH 7) for macrolides, sulfamethoxazole, trimethoprim, tetracycline, vancomycin, and amikacin appear to correspond directly to oxidation of biochemically essential moieties. Initial reactions of ozone with N(4)-acetylsulfamethoxazole, fluoroquinolones, lincomycin, and beta-lactams do not lead to appreciable oxidation of biochemically essential moieties. However, ozone oxidizes these moieties within fluoroquinolones and lincomycin via slower reactions. Measured k'(O3,app) values and second-order *OH rate constants, k'(*OH,app) were utilized to characterize pollutant losses during ozonation of secondary municipal wastewater effluent. These losses were dependent on k'(O3,app), but independent of k'(*OH,app). Ozone doses > or =3 mg/L yielded > or =99% depletion of fast-reacting substrates (K'(O3,app) > 5 x 10(4) M(-1) s(-1)) at pH 7.7. Ten substrates reacted predominantly with ozone; only four were oxidized predominantly by .OH. These results indicate that many antibacterial compounds will be oxidized in wastewater via moiety-specific reactions with ozone.     

Degradation of ozone-refractory organic phosphates in wastewater by ozone and ozone/hydrogen peroxide (peroxone): the role of ozone consumption by dissolved organic matter

Ozonation is very effective in eliminating micropollutants that react fast with ozone (k > 10(3) M(-1) s(-1)), but there are also ozone-refractory (k < 10 M(-1) s(-1)) micropollutants such as X-ray contrast media, organic phosphates, and others. Yet, they are degraded upon ozonation to some extent, and this is due to (?)OH radicals generated in the reaction of ozone with organic matter in wastewater (DOM, determined as DOC). The elimination of tri-n-butyl phosphate (TnBP) and tris-2-chloroisopropyl phosphate (TCPP), added to wastewater in trace amounts, was studied as a function of the ozone dose and found to follow first-order kinetics. TnBP and TCPP concentrations are halved at ozone to DOC ratios of ～0.25 and ～1.0, respectively. The (?)OH rate constant of TCPP was estimated at (7 ± 2) × 10(8) M(-1) s(-1) by pulse radiolysis. Addition of 1 mg H(2)O(2)/L for increasing the (?)OH yield had very little effect. This is due to the low rate of reaction of H(2)O(2) with ozone at wastewater conditions (pH 8) that competes unfavorably with the reaction of ozone with wastewater DOC. Simulations based on the reported (No?the et al., ES&T 2009, 43, 5990-5995) (?)OH yield (13%) and (?)OH scavenger capacity of wastewater (3.2 × 10(4) (mgC/L)(-1) s(-1)) confirm the experimental data. Based on a typically applied molar ratio of ozone and H(2)O(2) of 2, the contribution of H(2)O(2) addition on the (?)OH yield is shown to become important only at high ozone doses.     

Kinetics of aqueous ozone-induced oxidation of some endocrine disruptors

This study investigated aqueous ozone-induced oxidation of six endocrine disruptors (EDs: 4-n-nonylphenol, bisphenol A, 17alpha-ethinylestradiol, 17beta-estradiol, estrone, and estriol). In the first part, ED ozonation kinetics were studied over a pH range of 2.5-10.5 at 20 +/- 2 degrees C and in the presence of tert-butyl alcohol. Under these conditions, for each studied compound, the apparent ozone rates presented minima at acidic pH (pH < 5) and maxima at basic pH (pH > 10). In the second part, to explain this pH dependence, elementary reactions, i.e., reactions of ozone with neutral and ionized ED species, were proposed, and the intrinsic constants of each of them were calculated. The reactivity of ozone with ionized EDs (i.e. 1.06 x 10(9)-6.83 x 10(9) M(-1) s(-1)) was found to be 10(4)-10(5) times higher than with neutral EDs (i.e. 1.68 x 10(4) M(-1) s(-1)-2.21 x 10(5) M(-1) s(-1)). At pH > 5, ozone reacted to the greatest extent with dissociated ED forms. Finally, to assess the potential of ozone for inducing ED oxidation in water treatment conditions, the expected removal rates for each of the studied EDs were determined on the basis of the kinetic study at pH = 7 and 20 +/- 2 degrees C. For all EDs considered, O3 exposures of only approximately 2 x 10(-3) mg min L(-1) were calculated to achieve > or = 95% removal efficiency. The ozonation process could thus highly oxidize the studied EDs under water treatment conditions.     

Oxidation of N-nitrosodimethylamine (NDMA) precursors with ozone and chlorine dioxide: kinetics and effect on NDMA formation potential

The oxidation of N-nitrosodimethylamine (NDMA) precursors chlorine dioxide (ClO2). Second-order rate constants for the reactions of model NDMA precursors (dimethylamine (DMA) and 7 tertiary amines) with ozone (kapp at pH 7 = 2.4 x 10(-1) to 2.3 x 10(9) M(-1) s(-1)), ClO2 (kapp at pH 7 = 6.7 x 10(-3) to 3.0 x 10(7) M(-1) s(-1)), and hydroxyl radical (*OH) (kapp at pH 7 = 6.2 x 10(7) to 1.4 x 10(10) M(-1) s(-1)) were determined, which showed that the selected NDMA precursors, with the exception of dimethylformamide (DMFA) can be completely transformed via their direct reaction with ozone. During ozonation, DMFA may be partially transformed through oxidation by the secondary oxidant *OH. ClO2 was also shown to effectively transform most of the precursors, with the exceptions of DMA and DMFA. In the second part of the study, the NDMA formation potentials (NDMA-FP) in synthetic and natural waters were measured with and without pre-oxidation with ozone and ClO2. A significant reduction in the NDMA-FPs was observed after complete transformation of the model NDMA precursors. Ozonation generally led to more effective reduction of the NDMA-FP than ClO2. For most of the precursors, the formation of DMA could account for the NDMA-FPs remaining after complete transformation of the model NDMA precursors. In contrast, dimethylethanolamine and dimethyldithiocarbamate yielded other NDMA precursors (not DMA) as their oxidation products. Pre-oxidation by ozone and ClO2 of several natural waters showed behavior similar to that of the oxidation of model NDMA precursors with a reduction of the NDMA-FP by 32-94% for various natural water sources.     

Catalytic ozonation of gaseous reduced sulfur compounds using wood fly ash

The feasibility of reusing wood ash as an inexpensive catalyst in a catalytic ozonation process has been demonstrated. Catalytic ozonation was demonstrated to oxidize H2S, methanethiol (MT), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS) at low temperatures (23-25 degrees C). The process oxidized 25-50% of an inlet MT stream at 70 ppmv without the formation of DMDS (contrary to ash plus oxygen in air), oxidized 90-95% of an 85 ppmv stream of DMS, and oxidized 50% of a 100 ppmv DMDS stream using 2 g of wood ash at a space velocity of 720 h(-1) using ozone concentrations ranging from 100 to 300 ppmv. Similarly, 60-70% conversion of a 70 ppmv H2S stream was achieved with 2 g of ash in 1.1 s without catalytic deactivation (approximately 44 h). The overall oxidation rate of H2S, DMS, and DMDS increased with increasing ozone concentration contrary to the oxidation rate of MT, which was independent of ozone concentration. Dimethyl sulfoxide and dimethyl sulfone were identified as the primary end products of DMS oxidation, and SO2 was the end product of H2S and MT oxidation.     

Photolysis of ozone in aqueous solutions in the presence of tertiary butanol

The ozone decomposition quantum yield (phi) in millimolar and higher-concentration aqueous tertiary butanol solution is 0.64 +/- 0.05 (observed over a wavelength range from 250 to 280 nm) and rises toward lower tertiary butanol concentrations (phi approximately 1.5 at 10(-5) M at pH 2) on account of the onset of the well-known *OH-radical-induced chain reaction. The destruction of the organic is initiated by hydrogen-atom abstraction through OH radicals which are produced via the reaction of the photolytically generated O(1D) with the solvent water at a quantum yield of phi(*OH) of about 0.1. There is no decomposition of ozone in the dark on the time scale of the photolysis experiment. The efficiency of tertiary butanol destruction with respect to ozone consumption ([O3]0 = 3 x 10(-4) M), defined by the ratio delta[t-BuOH]/delta[O3], termed eta(t-BuOH), is 0.26 at millimolar tertiary butanol concentrations, determined at the stage of essentially complete ozone consumption. It diminishes toward lower tertiary butanol concentrations (delta[t-BuOH]/delta[O3] approximately 0.17 at [t-BuOH]0 = 1 x 10(-4) M). Part of the effect of the ozone, apart from being a source of *OH radicals, rests on the intervention of HO2*/O2*- which is produced in the course of the peroxyl-radical chemistry of the tertiary butanol in this dioxygen-saturated environment and converted into further *OH radical by reaction with ozone. Moreover in this system, organic free radicals and peroxyl radicals react with the ozone. On the basis of the experimental and mechanistic-simulation data, the quantum yield of direct (by hv) ozone cleavage in aqueous solution is estimated at about 0.5.     

Oxidation kinetics of selected taste and odor compounds during ozonation of drinking water

The applicability of ozonation to mitigate taste and odor problems in drinking water was investigated. Second-order rate constants of eleven taste and odor compounds with ozone and hydroxyl radicals were determined under laboratory conditions. Measured rate constants for the reaction with hydroxyl radicals are between 3 x 10(9) and 10(10) M(-1)s(-1) and for ozone: kbeta-cyclocitral = 3890 +/- 140 M(-1)s(-1); kgeosmin = 0.10 +/- 0.03 M(-1)s(-1); k3-hexen-1-ol = 5.4 +/- 0.5 x 10(5) M(-1)s(-1); kbeta-ionone = 1.6 +/- 0.13 x 10(5) M(-1)s(-1); k2-isopropyl-3-methoxypyrazine = 50 +/- 3 M(-1)s(-1); k2-methylisoborneol = 0.35 +/- 0.06 M(-1)s(-1); k2,6-nonadienal = 8.7 +/- 0.4 x 10(5) M(-1)s(-1); k1-penten-3-one = 5.9 +/- 0.1 x 10(4) M(-1)s(-1); k2,6-di-tert-butyl-4-methylphenol (BHT) = 7.4 +/- 0.2 x 10(4) M(-1)s(-1); k2,4,6-tribromoanisole = 0.02 +/- 0.01 M(-1)s(-1); k2,4,6-trichloroanisole = 0.06 +/- 0.01 M(-1)s(-1). Experiments conducted in natural waters showed that the removal efficiency during ozonation can be reliably predicted with the determined second-order rate constants. Ozonation is a powerful tool capable of oxidizing most of the taste and odor compounds to more than 50% under typical drinking water treatment conditions. For ozone-resistant taste and odor compounds, the application of advanced oxidation processes may be appropriate.     

Standard Gibbs free energies of reactions of ozone with free radicals in aqueous solution: quantum-chemical calculations

Free radicals are common intermediates in the chemistry of ozone in aqueous solution. Their reactions with ozone have been probed by calculating the standard Gibbs free energies of such reactions using density functional theory (Jaguar 7.6 program). O(2) reacts fast and irreversibly only with simple carbon-centered radicals. In contrast, ozone also reacts irreversibly with conjugated carbon-centered radicals such as bisallylic (hydroxycylohexadienyl) radicals, with conjugated carbon/oxygen-centered radicals such as phenoxyl radicals, and even with nitrogen- oxygen-, sulfur-, and halogen-centered radicals. In these reactions, further ozone-reactive radicals are generated. Chain reactions may destroy ozone without giving rise to products other than O(2). This may be of importance when ozonation is used in pollution control, and reactions of free radicals with ozone have to be taken into account in modeling such processes.     

Stoichiometry of ozonation of environmentally relevant olefins in saturated hydrocarbon solvents

The double bond-to-ozone reaction stoichiometry was quantified for ozonation of several environmentally relevant unsaturated fatty acids and monoterpenes in saturated hydrocarbon solvents. Olefins with initial concentrations from 30 microM to 3mM were injected in a solvent (n-hexadecane, nonane, or cyclohexane) while an ozone-oxygen mixture was slowly bubbled through the solution. The number of ozone molecules consumed by the injection was quantified in the outgoing flow, and the expected 1:1 double bond-to-ozone reaction stoichiometry was observed only under subambient temperature conditions (T < 250 K). At room temperature, the effective number of double bonds oxidized by each ozone molecule increased to 2-5, with a higher degree of oxidation occurring at lower initial olefin concentrations. The observed enhancement in the stoichiometry is consistent with a competition between direct ozonation and free radical initiated oxidation of double bonds, with free radicals being produced by slow reactions between dissolved ozone and solvent molecules.     

Sonochemical decomposition of phenol: evidence for a synergistic effect of ozone and ultrasound for the elimination of total organic carbon from water

Advanced oxidation processes (AOPs) for water and wastewater treatment are often handicapped by their inability to completely eliminate total organic carbon (TOC). In order to explore the capability of the combination of ultrasonic irradiation with ozone for the rapid removal of TOC, we examined the degradation rates of dissolved phenol (C6H5OH) in water with high-frequency ultrasound over the range of 200-1000 kHz, with ozone and with the combined application of sonication and ozonation. When ozone and ultrasound are applied simultaneously, a pronounced synergistic effect is observed that leads to the complete and rapid elimination of TOC at enhanced reaction rates. At longer reaction times, phenol oxidation by 03 leads to oxalate and formate, which accounts for the majority of the residual TOC. However, the combination of US (ultrasound) and ozone together readily oxidizes HCO2- and C2O4(2-) to CO2 while they prove to be relatively resistant to further oxidation to CO2 by O3 alone.     

Oxidation of the antiviral drug acyclovir and its biodegradation product carboxy-acyclovir with ozone: kinetics and identification of oxidation products

The oxidation of the antiviral drug acyclovir (ACV) and its main biotransformation product carboxy-acyclovir (carboxy-ACV) by ozone was investigated. Both compounds have recently been detected in surface water, and carboxy-ACV has also been detected in drinking water. The experiments revealed a strong pH dependence of the oxidation of ACV and carboxy-ACV with reaction rate constants increasing by 4 orders of magnitude between the protonated, positively charged form (k(ox,PH(+)), ～2.5 × 10(2) M(-1) s(-1)) and the deprotonated, negatively charged form (k(ox,P(-)), 3.4 × 10(6) M(-1) s(-1)). At pH 8 a single oxidation product was formed which was identified via LC-LTQ-Orbitrap MS and NMR as N-(4-carbamoyl-2-imino-5-oxoimidazolidin)formamido-N-methoxyacetic acid (COFA). Using Vibrio fischeri , an acute bacterial toxicity was found for COFA while carboxy-ACV revealed no toxic effects. Ozonation experiments with guanine and guanosine at pH 8 led to the formation of the respective 2-imino-5-oxoimidazolidines, confirming that guanine derivatives such as carboxy-ACV are undergoing the same reactions during ozonation. Furthermore, COFA was detected in finished drinking water of a German waterworks after ozonation and subsequent activated carbon treatment.     

Multiphase decomposition of novel oxygenated organics in aqueous and organic media

Prior to the massive use of new oxygenated solvents, data on their multiphase reactivity must be obtained to assess their environmental fate and impact on water and air quality. For this, the kinetics and mechanisms of the photochemical and photocatalytic degradation of selected oxygenated solvents by common tropospheric oxidants (such as OH and ozone) must be characterized. We studied the oxidation kinetics of new oxygenated solvents as pure organic liquids and in an aqueous medium by ozone and bythe OH radical, respectively. The studied chemicals are all unsaturated compounds, having none, one, or two ether groups. The results indicate that the OH reaction proceeds atthe diffusion limit by addition to the double bond. The reactive uptake coefficients associated with the reaction initiated by ozone are of the order of 10(-3). The reactions of compounds with two double bonds are very fast and probably occur at the surface. This kinetic information demonstrates that organic solvents in an organic medium or in an aqueous droplet will be oxidized rapidly by these oxidation reactions. These reactions, however, are not significant sinks for ozone and OH radicals.     

Product study of the OH, NO3, and O3 initiated atmospheric photooxidation of propyl vinyl ether

A product study is reported on the gas-phase reactions of OH and NO3 radicals and ozone with propyl vinyl ether (PVE). The experiments were performed in a 405 L borosilicate glass chamber in synthetic air at 298 +/- 3 K using long path in situ FTIR spectroscopy for the analysis of the reactants and products. In the presence of NO(x) (NO + NO2) the main products for the OH-radical initiated oxidation of PVE were propylformate and formaldehyde with molar formation yields of 78.6 +/- 8.8% and 75.9 +/- 8.4%, respectively. In the absence of NO(x) propylformate and formaldehyde were formed with molar formation yields of 63.0 +/- 9.0% and 61.3 +/- 6.3%, respectively. In the reaction of NO3 radicals with PVE propylformate 52.7 +/- 5.9% and formaldehyde 55.0 +/- 6.3% were again observed as major products. The ozonolysis of PVE led to the production of propylformate, formaldehyde, hydroxyperoxymethyl formate (HPMF; HC(O)OCH2OOH), and CO with molar formation yields of 89.0 +/- 11.4%, 12.9 +/- 4.0%, 13.0 +/- 3.4%, and 10.9 +/- 2.6%, respectively. The formation yield of OH radicals in the ozonolysis of PVE was estimated to be 17 +/- 9%. Simple atmospheric degradation mechanisms are postulated to explain the formation of the observed products.     

Removal of estrogenic activity and formation of oxidation products during ozonation of 17alpha-ethinylestradiol

This study investigated the oxidation of the oral contraceptive 17alpha-ethinylestradiol (EE2) during ozonation. First, the effect of ozone (O3) on the estrogenic activity of aqueous solutions of EE2 was studied using a yeast estrogen screen (YES). It could be shown that O3 doses typically applied for the disinfection of drinking waters were sufficient to reduce estrogenicity by a factor of more than 200. However, it proved impossible to completely remove estrogenic activity due to the slow reappearance of 0.1-0.2% of the initial EE2 concentration after ozonation. Second, oxidation products formed during ozonation of EE2 were identified with LC-MS/MS and GC/MS and the help of the model compounds 5,6,7,8-tetrahydro-2-naphthol (THN) and 1-ethinyl-1-cyclohexanol (ECH), which represent the reactive phenolic moiety and the ethinyl group of EE2. Additionally, oxidation products of the natural steroid hormones 17beta-estradiol (E2) and estrone (E1) were identified. The chemical structures of the oxidation products were significantly altered as compared to the parent compounds, explaining the diminished estrogenic activity after ozonation. Overall,the results demonstrate that ozonation is a promising tool for the control of EE2, E2, and E1 in drinking water and wastewater.     

Organic aerosol formation during the atmospheric degradation of toluene

Organic aerosol formation during the atmospheric oxidation of toluene was investigated using smog chamber systems. Toluene oxidation was initiated by the UV irradiation of either toluene/air/NOx or toluene/air/CH3ONO/NO mixtures. Aerosol formation was monitored using scanning mobility particle sizers and toluene loss was monitored by in-situ FTIR spectroscopy or GC-FID techniques. The experimental results show that the reaction of OH radicals, NO3 radicals and/or ozone with the first generation products of toluene oxidation are sources of organic aerosol during the atmospheric oxidation of toluene. The aerosol results fall into two groups, aerosol formed in the absence and presence of ozone. An analytical expression for aerosol formation is developed and values are obtained for the yield of the aerosol species. In the absence of ozone the aerosol yield, defined as aerosol formed per unit toluene consumed once a threshold for aerosol formation has been exceeded, is 0.075 +/- 0.004. In the presence of ozone the aerosol yield is 0.108 +/- 0.004. This work provides experimental evidence and a simple theory confirming the formation of aerosol from secondary reactions.     

Kinetics and mechanistic aspects of As(III) oxidation by aqueous chlorine, chloramines, and ozone: relevance to drinking water treatment

Kinetics and mechanisms of As(III) oxidation by free available chlorine (FAC-the sum of HOCl and OCl-), ozone (O3), and monochloramine (NH2Cl) were investigated in buffered reagent solutions. Each reaction was found to be first order in oxidant and in As(III), with 1:1 stoichiometry. FAC-As(III) and O3-As(III) reactions were extremely fast, with pH-dependent, apparent second-order rate constants, k'app, of 2.6 (+/- 0.1) x 10(5) M(-1) s(-1) and 1.5 (+/- 0.1) x 10(6) M(-1) s(-1) at pH 7, whereas the NH2Cl-As(III) reaction was relatively slow (k'app = 4.3 (+/- 1.7) x 10(-1) M(-1) s(-1) at pH 7). Experiments conducted in real water samples spiked with 50 microg/L As(III) (6.7 x 10(-7) M) showed that a 0.1 mg/L Cl2 (1.4 x 10-6 M) dose as FAC was sufficient to achieve depletion of As(III) to <1 microg/L As(III) within 10 s of oxidant addition to waters containing negligible NH3 concentrations and DOC concentrations <2 mg-C/L. Even in a water containing 1 mg-N/L (7.1 x 10(-5) M) as NH3, >75% As(III) oxidation could be achieved within 10 s of dosing 1-2 mg/L Cl2 (1.4-2.8 x 10(-5) M) as FAC. As(III) residuals remaining in NH3-containing waters 10 s after dosing FAC were slowly oxidized (t1/2 > or = 4 h) in the presence of NH2Cl formed by the FAC-NH3 reaction. Ozonation was sufficient to yield >99% depletion of 50 microg/L As(III) within 10 s of dosing 0.25 mg/L O3 (5.2 x 10(-6) M) to real waters containing <2 mg-C/L of DOC, while 0.8 mg/L O3 (1.7 x 10(-5) M) was sufficientfor a water containing 5.4 mg-C/L of DOC. NH3 had negligible effect on the efficiency of As(III) oxidation by O3, due to the slow kinetics of the O3-NH3 reaction at circumneutral pH. Time-resolved measurements of As(III) loss during chlorination and ozonation of real waters were accurately modeled using the rate constants determined in this investigation.     

Atmospheric chemistry of perfluoroalkanesulfonamides: kinetic and product studies of the OH radical and Cl atom initiated oxidation of N-ethyl perfluorobutanesulfonamide

Perfluorooctanesulfonamides [C8F17SO2N(R1)(R2)] are present in the atmosphere and may, via atmospheric transport and oxidation, contribute to perfluorocarboxylates (PFCA) and perfluorooctanesulfonate (PFOS) pollution in remote locations. Smog chamber experiments with the perfluorobutanesulfonyl analogue N-ethyl perfluorobutanesulfonamide [NEtFBSA; C4F9SO2N(H)CH2CH3] were performed to assess this possibility. By use of relative rate methods, rate constants for reactions of NEtFBSA with chlorine atoms (296 K) and OH radicals (301 K) were determined to be kCL) = (8.37 +/- 1.44) x 10(-12) and kOH = (3.74 +/- 0.77) x 10(-13) cm3 molecule(-1) s(-1), indicating OH reactions will be dominant in the troposphere. Simple modeling exercises suggestthat reaction with OH radicals will dominate removal of perfluoroalkanesulfonamides from the gas phase (wet and dry deposition will not be important) and that the atmospheric lifetime of NEtFBSA in the gas phase will be 20-50 days, thus allowing substantial long-range atmospheric transport. Liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis showed that the primary products of chlorine atom initiated oxidation were the ketone C4F9SO2N(H)COCH3; aldehyde 1, C4F9SO2N(H)CH2CHO; and a product identified as C4F9SO2N(C2H5O)- by high-resolution MS but whose structure remains tentative. Another reaction product, aldehyde 2, C4F9SO2N(H)CHO, was also observed and was presumed to be a secondary oxidation product of aldehyde 1. Perfluorobutanesulfonate was not detected above the level of the blank in any sample; however, three perfluoroalkanecarboxylates (C3F7CO2-, C2F5CO2-, and CF3CO2-) were detected in all samples. Taken together, results suggest a plausible route by which perfluorooctanesulfonamides may serve as atmospheric sources of PFCAs, including perfluorooctanoic acid.