Electron-beam treatment of aromatic hydrocarbons that can be air-stripped from contaminated groundwater. 1. Model studies in aqueous solution

As a model for the electron-beam degradation of volatile aromatics (benzene, toluene, ethylbenzene, xylenes, BTEX) in groundwater strip gas, to be reported in Part 2, the gamma-radiolysis of benzene has been studied in aqueous solutions. Addition of *OH to the aromatic ring gives rise to hydroxycyclohexadienyl radicals which either dimerize or disproportionate. The various dimers undergo acid-catalyzed water elimination yielding biphenyl. Phenol is formed upon disproportionation directly, but also via dihydroxycyclohexadiene which subsequently undergoes acid-catalyzed water elimination. Co-radiolysis of benzene with nitrite generates *NO2 in addition to the hydroxycyclohexadienyl radical. These not only interact with one another (product: nitrobenzene via nitro-hydroxycyclohexadienes) but the *NO2 radical is also capable of abstracting cyclohexadienylic hydrogens. This reaction leads to the formation of 2- and 4-nitrophenol and to further nitrated products that were not identified. These are suggested to be formed in an analogous reaction of *NO2 with the hydroxycylohexadienyl dimers. The effect of O2 on these reactions and the relevance for the gas-phase radiolysis of BTEX is discussed.     

Substrate interactions in BTEX and MTBE mixtures by an MTBE-degrading isolate

Groundwater contaminant plumes from recent accidental gasoline releases often contain the fuel oxygenate MTBE (methyl tert-butyl ether) together with BTEX (benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene) compounds. This study evaluates substrate interactions during the aerobic biotransformation of MTBE and BTEX mixtures by a pure culture, PM1, capable of utilizing MTBE for growth. PM1 was unable to degrade ethylbenzene and two of the xylene isomers at concentrations of 20 mg/L following culture growth on MTBE. In addition, the presence of 20 mg/L of ethylbenzene or the xylenes in mixtures with MTBE completely inhibited MTBE degradation. When MTBE-grown cells of PM1 were exposed to MTBE/benzene and MTBE/toluene mixtures, MTBE degradation proceeded, while the degradation of benzene and toluene was delayed for several hours. Following this initial lag, benzene and toluene were degraded rapidly, while the rate of MTBE degradation slowed significantly. MTBE degradation did not increase to previous rates until benzene and toluene were almost entirely degraded. The lag in benzene and toluene degradation was presumably due to the induction of the enzymes necessary for BTEX degradation. Once these enzymes were induced, sequential additions of benzene or toluene were degraded rapidly, and growth on benzene and toluene was observed. The results of this study suggest that BTEX and MTBE degradation occurs primarily via two independent and inducible pathways. If subsurface microbial communities behave similarly to the culture used in this study, the observed severe inhibition of MTBE degradation by ethylbenzene and the xylenes and the partial inhibition by benzene and toluene suggest thatthe biodegradation of MTBE in subsurface environments would most likely be delayed until MTBE has migrated beyond the BTEX plume.     

Evidence for very tight sequestration of BTEX compounds in manufactured gas plant soils based on selective supercritical fluid extraction and soil/water partitioning

Benzene, toluene, ethylbenzene, o-, m-, and p-xylenes (BTEX), and polycyclic aromatic hydrocarbons (PAHs) were extracted from eight manufactured gas plant (MGP) soils from sites that had been abandoned for several decades. Supercritical fluid extraction (SFE) with pure carbon dioxide demonstrated the presence of BTEX compounds that were highly sequestered in both coal gas and oil gas MGP soils and soots. Benzene was generally the slowest compound to extract from all samples and was even more difficult to extract than most two- to five-ring PAHs found on the same samples. Since the solubility of benzene in carbon dioxide is 2-5 orders of magnitude higher than the solubilities of PAHs, these results demonstrate that benzene was more tightly sequestered than toluene, ethylbenzene, xylenes, or the multi-ring PAHs. Additional evidence for very tight binding was based on the fact that BTEX concentrations determined using either SFE or with methylene chloride sonication were much higher than those obtained by the U.S. EPA purge-and-trap method, especially for benzene (whose concentration was underestimated by as much as 1000-fold by the EPA method). However, soil/water desorption showed little benzene mobility, and Kd values for benzene were 1-2 orders of magnitude higher than those calculated based on literature sorption K(OC) values. These results indicate that environmentally relevant concentrations of benzene may be better represented by mild extraction methods than by methods capable of extracting tightly bound benzene.     

Kinetic modeling of TiO2-catalyzed photodegradation of trace levels of microcystin-LR

A kinetic model has been developed to investigate the relative importance of major pathways for the photocatalytic degradation of trace levels of the cyanobacterial toxin microcystin-LR (MLR) in solutions containing a complex suite of dissolved organic matter and to test the sensitivity of MLR degradation to rate constants of the key processes. The kinetic model incorporates adsorption of the trace contaminant, other organics and oxygen on the particle surface, surface reactions between adsorbed radical and nonradical species, desorption of surface radical species, solution phase radical reactions, and radical termination pathways. Under conditions where the contaminant adsorbs strongly to semiconductor surface sites, rapid degradation is observed, and a primary degradation step appears to involve reaction between surface-located long-lived organic radicals (formed from hydroxyl radical scavenging by the bulk organic) and adsorbed trace contaminant. MLR degradation is relatively insensitive to changes in light intensity under these strongly adsorbing conditions but highly dependent under weakly adsorbing conditions and when solution phase degradation is important. While not verified independently, desorption of surface bound superoxide appears to lead to the production of organic peroxyl radicals through reaction of superoxide with the bulk organic. These solution phase organic peroxyl radicals are highly reactive and appear to be the primary source of trace contaminant degradation under conditions where the trace contaminant shows no observable adsorption and surface degradation is negligible. Under alkaline conditions, adsorption of carbonate onto the particle surface results in scavenging of surface hydroxyl radicals to form surface carbonate radicals that rapidly quench surface bound superoxide. This prevents organic peroxyl production, the primary agent of solution-phase trace contaminant degradation.     

Rate constants for the gas-phase reactions of a series of alkylnaphthalenes with the nitrate radical

Naphthalene and its methyl-, ethyl-, and dimethyl-derivatives are semivolatile polycyclic aromatic hydrocarbons expected to be in the gas phase in ambient atmospheres and are subject to nighttime degradation by gas-phase reactions with the nitrate (NO3) radical. Using a relative rate method, rate constants for the gas-phase reactions of NO3 radicals with a series of alkylnaphthalenes have been measured at 298 +/- 2 K and atmospheric pressure of air. The compounds studied were 1- and 2-methylnaphthalene (1- and 2-MN), 1- and 2-ethylnaphthalene (1- and 2-EN), and the 10 dimethylnaphthalene isomers (1,2-, 1,3-, 1,4-,1,5-, 1,6-, 1,7-, 1,8-, 2,3-, 2,6-, and 2,7-DMN). Sampling in Riverside, CA showed that these alkylnaphthalenes were readily detected in ambient air, with the exception of 1,8-DMN. The reactions of naphthalene and the alkylnaphthalenes with NO3 radicals proceed by initial addition of the radical to form an aromatic-NO3 adduct (with rate constant k(a)) which either decomposes back to reactants (with rate constant kb) or reacts with NO2 to form products (with rate constant k(c). Using naphthalene as the reference compound, the values of (k(a)k(c)/k(b)) obtained for the NO3 radical reactions (in units of 10(-28) cm(6) molecule(-2) S(-1), indicated errors are two least-squares standard deviations) were as follows: 1-MN, 7.15 +/- 0.37; 2-MN, 10.2 +/- 1.0; 1-EN, 9.82 +/- 0.69; 2-EN, 7.99 +/- 0.99; 1,2-DMN, 64.0 +/- 2.3; 1,3-DMN, 21.3 +/- 1.2; 1,4-DMN, 13.0 +/- 0.5; 1,5-DMN, 14.1 +/- 1.3; 1,6-DMN, 16.5 +/- 1.8; 1,7-DMN, 13.5 +/- 0.7; 1,8-DMN, 212 +/- 59; 2,3-DMN, 15.2 +/- 0.5; 2,6-DMN, 21.2 +/- 1.6; 2,7-DMN, 21.0 +/- 1.5.     

Product study of the gas-phase BrO-initiated oxidation of Hg0: evidence for stable Hg1+ compounds

Mercury is a key toxic environmental pollutant, and its speciation affects its bioavailability. BrO radicals have been identified as key oxidants during mercury depletion events observed in Arctic and sub-Arctic regions. We report the first experimental product study of BrO-initiated oxidation of elemental mercury at atmospheric pressure of ca. 0.987 bar and T= 296+/-2 K. We used chemical ionization and electron impact mass spectrometry, gas chromatography coupled to a mass spectrometer, a MALDI-TOF mass spectrometer, a cold vapor atomic fluorescence spectrometer, and high-resolution transmission electron microscopy coupled to energy dispersive spectrometry. BrO radicals were formed using visible and UV photolysis of Br2 and CH2Br2 in the presence of ozone. We have analyzed the products in the gas phase, on suspended aerosols and on wall deposits, and identified HgBr, HgBrO/HgOBr, and HgO as reaction products. Mercury aerosols with a characteristic width of ca. 0.2 microm were observed as products. We herein discuss the implications of our results to the chemistry of atmospheric mercury and its potential implications in the biogeochemical cycling of mercury.     

Reactions of semivolatile organics and their effects on secondary organic aerosol formation

Secondary organic aerosol (SOA) constitutes a significant fraction of total atmospheric particulate loading, but there is evidence that SOA yields based on laboratory studies may underestimate atmospheric SOA. Here we present chamber data on SOA growth from the photooxidation of aromatic hydrocarbons, finding that SOA yields are systematically lower when inorganic seed particles are not initially present. This indicates that concentrations of semivolatile oxidation products are influenced by processes beyond gas-particle partitioning, such as chemical reactions and/or loss to chamber walls. Predictions of a kinetic model in which semivolatile compounds may undergo reactions in both the gas and particle phases in addition to partitioning are qualitatively consistent with the observed seed effect, as well as with a number of other recently observed features of SOA formation chemistry. The behavior arises from a kinetic competition between uptake to the particle phase and reactive loss of the semivolatile product. It is shown that when hydrocarbons react in the absence of preexisting organic aerosol, such loss processes may lead to measured SOA yields lower than would occur under atmospheric conditions. These results underscore the need to conduct studies of SOA formation in the presence of atmospherically relevant aerosol loadings.     

Benzene: a secondary pollutant formed in the three-way catalyst

Benzene emissions from a relevant proportion of today's gasoline-driven passenger cars and light-duty vehicles can increase by up to 2 orders of magnitude when driving at high engine load (e.g., on highways). Under such conditions, post-catalyst benzene levels exceeded those found pre-catalyst. As a consequence, formation of benzene in the catalyst was postulated. To further reduce ambient air concentrations of benzene,these critical operating conditions must be carefully avoided. Here, we report in detail to what extent and at what operating conditions catalyst-induced benzene and toluene formation can occur. For that purpose, a EURO-1 passenger car (1.8 L, model year 1995)fulfilling the valid regulations, equipped with a new, two-layered, Pd-CeO2-Al2O3/Rh-ZrO2-Al2O3 three-way catalyst was operated at steady state on a chassis dynamometer at 100, 125, and 150 km/h at variable air to fuel ratios. Pre- and post-catalyst exhaust gas concentrations of benzene, toluene, C2-, and C3-benzenes were monitored at a time resolution of 0.5 Hz by means of chemical ionization mass spectrometry. A net benzene formation window, ranging from pre-catalyst exhaust gas temperatures of 600-730 degrees C and lambda-values of 0.83-0.95, with a pronounced minimum at 0.87, was observed. Dealkylation reactions of aromatic hydrocarbons are assumed to be the major pathway leading to benzene.     

BTEX plume dynamics following an ethanol blend release: geochemical footprint and thermodynamic constraints on natural attenuation

In this 10 year study, Brazilian gasoline (100 L, containing 24% ethanol by volume) was released to a sandy aquifer to evaluate the natural attenuation of benzene, toluene, ethylbenzene, and total xylenes (BTEX) in the presence of ethanol. Groundwater concentrations of BTEX, ethanol, and degradation products (e.g., acetate and methane) were measured over the entire plume using an array of monitoring well clusters, to quantify changes in plume mass and region of influence. Ethanol biodegradation coincided with the development of methanogenic conditions while acetate (a common anaerobic metabolite) accumulated. The benzene plume expanded beyond the 30 m long monitored area and began to recede after 2.7 years, when ethanol had disappeared. Theoretical calculations suggest that the transient accumulation of acetate (up to 166 mg L(-1)) may have hindered the thermodynamic feasibility of benzene degradation under methanogenic conditions. Yet, benzene removal proceeded relatively fast compared to literature values (and faster than the alkylbenzenes present at this site) after acetate concentrations had decreased below inhibitory levels. Thus, site investigations of ethanol blend releases should consider monitoring acetate concentrations. Overall, this study shows that inhibitory effects of ethanol and acetate are relatively short-lived, and demonstrates that monitored natural attenuation can be a viable option to deal with ethanol blend releases.     

Dicarbonyl products of the OH radical-initiated reactions of naphthalene and the Cl- and C2-alkylnaphthalenes

Naphthalene and the C1- and C2-alkylnaphthalenes are the most abundant polycyclic aromatic hydrocarbons (PAHs) in urban atmospheres. Their major atmospheric loss process is by gas-phase reaction with hydroxyl (OH) radicals. In this study, we have used in situ direct air sampling atmospheric pressure ionization mass spectrometry (API-MS) as well as gas chromatography-mass spectrometry (GC/MS) techniques to investigate the products of the gas-phase reactions of OH radicals with naphthalene, naphthalene-ds, 1- and 2-methylnaphthalene (MN), 1- and 2-MN-dio, 1- and 2-ethylnaphthalene (EN), and the 10 isomeric dimethylnaphthalenes (DMNs). The major reaction products are ring-opened dicarbonyls that are 32 mass units higher in molecular weight than the parent compound, one or more ring-opened dicarbonyls of lower molecular weight resulting from loss of two P-carbons and associated alkyl groups, and ring-containing compounds that may be epoxides. Phthalic anhydride and alkyl-substituted phthalic anhydrides were observed as second generation products. The position of alkyl-substitution on the naphthalene ring is a key factor determining the ring cleavage site and the isomeric product distribution.     

The role of free radicals and antioxidants: How do we know that they are working?

This review briefly discusses how free radicals are formed and the possible participation of free radicals in disease. The review describes the basic radical reactions and the types of products that are formed from the free‐radical reactions of cellular constituents. In many cases, in vivo free‐radical oxidation can be detected by measuring products that were derived from radical reactions. Since aerobic organisms generate oxygen‐containing free radicals during oxygen metabolism, they carry chemicals and enzymes that reduce the threat posed by these radicals. The more common sources of in vivo free radicals are described in the article as well as the methods used by cells to protect themselves from free‐radical damage. Generation of free radicals in vivo also may be the result of exposure to certain chemical agents present in the environment Many of these agents cause pathologic changes to the exposed tissues and organs by initiating free‐radical reactions.     

Transformation and removal of bisphenol A from aqueous phase via peroxidase mediated oxidative coupling reactions: efficacy, products, and pathways

A systematic investigation of the feasibility of and mechanisms for transformation and removal of bisphenol A (BPA) from aqueous phase via oxidative coupling mediated by horseradish peroxidase is described. It is demonstrated that BPA can be effectively transformed into precipitable solid products in HRP-mediated oxidative coupling reactions. A total of 13 reaction intermediates and products are identified using LC/MS and GC/MS techniques, and with the help of ab initio molecular modeling, detailed reaction pathways are proposed. It is postulated that two BPA radicals are coupled primarily by the interaction of an oxygen atom on one radical and propyl-substituted aromatic carbon atom on another, followed by elimination of an isopropylphenol carboncation. All intermediates or products detected can be interpreted as resulting from either coupling or substitution reactions between BPA and other intermediates or products. The efficacy of the reaction at low substrate concentrations is demonstrated using a sensitive analytical procedure involving solid-phase extractions. The results suggest that catalyzed oxidative coupling reactions may be important natural transformation pathways for estrogenic phenolic compounds and indicate their potential use as an efficient means for removal of estrogenicity from waters and wastewaters.     

顶空-气质联用内标法检测印刷油墨中的苯及苯系物

建立了-种以氟苯为内标,利用顶空-气相色谱质谱联用技术测定印刷油墨中苯、甲苯、乙苯、邻,间,对-二甲苯(BTEX)的方法,此方法BTEX的定性检出限为0.02～0.05 μg/g,平均回收率在96%～103%之间,RSD<6%.同时利用此方法对不同颜色的UV印刷油墨和凹印油墨中BTEX成份进行分析,结果表明,两类不同颜...     

FTIR kinetic, product, and modeling study of the OH-initiated oxidation of 1-butanol in air

A kinetic and product study was performed on the reaction of OH radicals with 1-butanol in a 480 L indoor photoreactor and also in the EUPHORE outdoor smog chamber in Valencia, Spain. Long path in situ FTIR spectroscopy and gas chromatography with photoionization detection were used to analyze reactants and products. Using a kinetic relative rate technique, a rate coefficient of k(OH + 1-butanol) = (8.28 +/- 0.85) x 10(-12) cm3 s(-1) was measured in 740 Torr synthetic air at 298 +/- 2 K. The reaction products observed and their fractional molar yields were (in percent) butanal (51.8 +/- 7.1), propanal (23.4 +/- 3.5), ethanal (12.7 +/- 2.2), and formaldehyde (43.4 +/- 2.4). In addition, the results support the probable formation of 4-hydroxy-2-butanone. Propanal, ethanal, and formaldehyde could also be formed in secondary reactions of some of the primary aldehydic products. However, under the conditions employed in the experiments, the contribution from secondary reactions is very minor. On the basis of the product studies, a detailed atmospheric degradation mechanism was constructed and tested against experimental data by chemical box model calculations. Measured and simulated concentration-time profiles for selected reactants were in excellent agreement.     

Formation of secondary organic aerosol by reactive condensation of furandiones, aldehydes, and water vapor onto inorganic aerosol seed particles

Volatile furandiones and aldehydes are significant atmospheric oxidation products of aromatic compounds. The mechanism of secondary organic aerosol formation by these compounds was probed using particle chamber observations and macroscale simulations of condensed phases. Growth of inorganic seed aerosol was monitored in the presence of humidity and high concentrations of 2,5-furandione (maleic anhydride), 3-methyl-2,5-furandione (citraconic anhydride), benzaldehyde, and trans-cinnamaldehyde. Particle growth commenced when the gas-phase saturation level of each organic compound and water vapor (relative to its pure liquid), when summed together, reached a threshold near one, implying the formation of a nearly ideal mixed organic/aqueous phase. However, these organics are immiscible with water at the high mole fractions that would be expected in such a phase. Highly acidic dicarboxylic acids produced by the reactions between furandiones and water were shown to rapidly acidify an aqueous phase, resulting in greatly increased benzaldehyde solubility. Thus, the uptake of these organics onto particles in the presence of humidity appears to be reaction-dependent. Finally, it is shown that dicarboxylic acids produced in these reactions recyclize back to furandiones when subjected to normal GC injector temperatures, which could cause large artifacts in gas/particle phase distribution measurements.     

Secondary organic aerosol formation from aromatic precursors. 2. Mechanisms for lumped aromatic hydrocarbons

Quantitative kinetic and physical phase partitioning models of secondary organic aerosol (SOA) formation resulting from the reactions of lumped aromatic species were integrated into a state of the art mechanism for gas-phase reactions (SAPRC). Aromatic and aerosol precursor species were aggregated based on their rate of reaction with OH radicals. Model parameters for the lumped model species were estimated based on the properties of individual compounds making up the lumped parameters. The model was applied to estimate the contribution of aromatic precursors to the formation of SOA in Houston, TX.     

Effect of oxidative deterioration on flavour and aroma components of lemon oil

Reactions of five major components (citral, α- and β-pinene, limonene and γ-terpinene) of lemon oil in the presence of Cu catalysts and air have been shown to lead to significant oxidation of α- and β-pinene and γ-terpinene, even when the catalyst concentration was comparable to that present in copper-plumbed tap water. Addition of commercial antioxidants (BHA and tocopherol) generally led to suppression of oxidation. UV degradation of these compounds in the presence of air was most significant for γ-terpinene and limonene which gave products similar to those obtained from the Cu-catalysed thermal reactions. Citral gave different products, mainly photocitrals, in contrast to the thermal reactions. The sensitivity of lemon oil to temperature and the presence of air was confirmed.     

A bench-scale constructed wetland as a model to characterize benzene biodegradation processes in freshwater wetlands

In wetlands, a variety of biotic and abiotic processes can contribute to the removal of organic substances. Here, we used compound-specific isotope analysis (CSIA), hydrogeochemical parameters and detection of functional genes to characterize in situ biodegradation of benzene in a model constructed wetland over a period of 370 days. Despite low dissolved oxygen concentrations (<30 μM), the oxidation of ammonium to nitrate and the complete oxidation of ferrous iron pointed to a dominance of aerobic processes, suggesting efficient oxygen transfer into the sediment zone by plants. As benzene removal became highly efficient after day 231 (>98% removal), we applied CSIA to study in situ benzene degradation by indigenous microbes. Combining carbon and hydrogen isotope signatures by two-dimensional stable isotope analysis revealed that benzene was degraded aerobically, mainly via the monohydroxylation pathway. This was additionally supported by the detection of the BTEX monooxygenase gene tmoA in sediment and root samples. Calculating the extent of biodegradation from the isotope signatures demonstrated that at least 85% of benzene was degraded by this pathway and thus, only a small fraction was removed abiotically. This study shows that model wetlands can contribute to an understanding of biodegradation processes in floodplains or natural wetland systems.     

Effect of oxygen in a thin-film rotating disk photocatalytic reactor

A novel experimental procedure was developed to measure oxygen mass transfer during the oxygenation of water in a thin film of a rotating disk photocatalytic reactor (RDPR). The increase in dissolved oxygen (DO) of initially deaerated water was monitored with time in the reactor vessel at different disk angular velocities after exposure of the reactor to the atmosphere. Oxygenation was predominantly achieved by oxygen mass transport through the thin liquid film carried by the disk and to a much lesser extent by direct oxygenation of the water in the reactor vessel via a surface renewal mechanism. A mathematical model was developed to simulate the phenomenon considering both cases of presence and absence of oxygen mass transport limitations. In the latter case, the model considered that the amount of liquid carried by the disk was saturated with oxygen when returning to the reactor vessel. On the basis of the model and the experimental data, it was proven that mass-transfer limitations existed until the water in the reactor vessel became saturated with oxygen. Results obtained from the model were validated by an alternative analysis using dimensionless groups characteristic to the system. The study revealed that the mass-transfer coefficient increased linearly with disk angular velocity and thus disk Reynolds number. The results showed that oxygen mass-transfer limitations decreased with increasing disk angular velocity, mainly due to an increase in the overall mass-transfer coefficient. In the presence of UV radiation, the influence of oxygen on the photocatalytic oxidation of 4-chlorobenzoic acid was investigated in the RDPR operated in batch and continuous mode. The photocatalytic reactions occurred in a thin film of liquid carried by the disk in the presence of UV radiation and ST-B01 composite spherical ceramic (SiO2/Al2O3) balls coated with anatase TiO2 catalyst. It was found that the initial degradation rate followed Langmuir kinetics with respect to oxygen concentration in the gas phase. When the oxygen concentration in the gas phase surpassed that in air, the degradation rates did not improve significantly, suggesting that operation with air instead of oxygen is most probably a more realistic practical choice. Measurements of DO during the presence and absence of UV radiation suggested that the photocatalytic reactions were mainly oxygen concentration-limited rather than oxygen mass-transfer-limited.     

Effect of platinum deposits on TiO2 on the anoxic photocatalytic degradation pathways of alkylamines in water: dealkylation and N-alkyation

Most photocatalytic degradation (PCD) reactions of aquatic pollutants require the presence of dissolved oxygen and hence do not occur in anoxic suspensions. We investigated the PCD reactions of alkylamines in anoxic water using TiO2 deposited with Pt nanoparticles. Unlike typical PCD reactions, the absence of dissolved oxygen increases the PCD rates of alkylamines on Pt/TiO2 and generates products that are different from those formed on pure TiO2. In particular, N-alkylated amines (e.g., (CH3)3N produced from (CH3)2NH) as well as dealkylated amines are generated in a deaerated Pt/TiO2 suspension. This anoxic N-alkylation pathway is enabled only in the presence of Pt deposits on TiO2 and is applicable only to neutral alkylamines and not to alkylammonium cations. The Pt surface appears to interactwith the lone-pair electron on the N atom and catalyze the anoxic degradation of alkylamines mainly through a radical mechanism. Methyl radicals generated on Pt participate in the N-methylation reaction. The presence of intermediate methyl radicals on the Pt surface was verified by the detection of CH4 and CH3CH3 gases evolved during the PCD of (CH3)3N in an anoxic Pt/TiO2 suspension, whereas no such products were observed in a pure TiO2 suspension. The anoxic PCD of N-methylethylamine on Pt/TiO2 also produces both N-ethylated and N-methylated amines as byproducts, which indicates that both methyl and ethyl radicals are generated during the anoxic degradation process. From a practical point of view, the present finding that undesirable alkylated amines can be produced on Pt/TiO2 in anoxic conditions indicates that caution is necessary when applying Pt/TiO2 photocatalyst to the treatment of water that contains amines.