Aqueous photochemical degradation of mefenamic acid and triclosan: role of wastewater effluent matrices.

In this study, photochemical degradation of two emerging pharmaceutical chemicals, mefenamic acid (MF) and triclosan (TCS), was investigated to clarify the role of treated wastewater effluent matrices on their environmental photolysis. Target compounds were individually exposed to simulated sunlight in different media: ultrapure buffered water and synthetic field water with treated municipal wastewater effluent. The results in ultrapure buffered water showed that the direct photolysis processes in aquatic environments are not relevant to the elimination of MF. However, in samples containing treated wastewater effluent, photochemical degradation of MF was clearly enhanced. Our results indicate that MF undergoes indirect photolysis by reactive intermediates produced in an effluent matrix. Further quenching experiments suggested that photochemically produced hydroxyl radicals and excited triplet state dissolved organic matter drive the degradation of MF. In contrast to MF, TCS photochemical degradation proceeds through rapid direct photolysis. TCS was quickly degraded in ultrapure buffered water but it is considerably hampered in samples containing wastewater effluent. The declined degradation of TCS in the synthetic field water was discussed in terms of underlying optical filter effects by coexisting chromophoric substances. Results emphasize the importance of taking local water chemistry into consideration when predicting natural attenuation of pharmaceutical chemicals in receiving areas.

Dynamics of dissolved organic matter in a wastewater effluent-impacted Japanese urban stream: characteristics, occurrence and photoreactivity of fluorescent components.

We report the results of using the excitation-emission matrix (EEM) method combined with parallel factor analysis (PARAFAC) to investigate the characteristics and occurrence of dissolved organic matter (DOM) in an urban stream impacted by effluent from a wastewater treatment plant (WWTP). The PARAFAC model divides the bulk EEM spectra into six individual fluorescent components with three humic-like components (C1-C3), two protein-like components (C4 and C5) and a wastewater-derived component (C6). In general, intensities of fluorescent components are abundant in WWTP effluent impacted samples, thus showing that such an effluent is a major source of DOM in urban rivers, but C5 is considered to have autochthonous sources within the stream. In areas where the effluent is released, the fluorescent intensity from components (except C5) gradually decreases as these components are transported downstream. However, concentrations of dissolved organic carbon remain almost constant downstream of the release area. These results would be attributed to degradation and/or modification of fluorophore. Photolysis experiments confirmed that fluorescent intensities can decrease with increase of irradiation times. C6 particularly showed a rapid photodegradation, remaining only 24.1% after 48 h photolysis. These findings would be important when assessing DOM source and water quality in aquatic environments by EEM-PARAFAC.

Characterisation of polycyclic aromatic hydrocarbons associated with indoor PM0.1 and PM2.5 in Hanoi and implications for health risks.

Polycyclic aromatic hydrocarbons (PAHs) associated with indoor PM pose a high risk to human health because of their toxicity. A total of 160 daily samples of indoor PM2.5 and PM0.1 were collected in Hanoi and analysed for 15 PAHs. In general, the concentrations of carcinogenic PAHs (car-PAHs) accounted for 21% ± 2%, 19.1% ± 2%, and 26% ± 3% of the concentrations of 15 PAHs in PM2.5, PM0.1-2.5, and PM0.1, respectively. Higher percentages of car-PAHs were found in smaller fractions (PM0.1), which can be easily deposited deep in the pulmonary regions of the human respiratory tract. The concentrations of 15 PAHs were higher in winter than in summer. The most abundant PAH species were naphthalene and phenanthrene, accounting for 11%-21% and 19%-23%, respectively. The PAH content in PM0.1 was almost twice as high as those in PM2.5 and PM0.1-2.5. Principal component analysis found that vehicle emissions and the combustion of biomass and coal were the main outdoor sources of PAHs, whereas indoor sources included cooking activities, the combustion of incense, scented candles, and domestic uses in houses. According to the results, 60%-90% of the PM0.1-bound BaP(eq) was deposited in the alveoli region, whereas 63%-75% of the PM2.5-bound BaP(eq) was deposited in head airways (HA), implying that most of the particles deposited in the HA region were PM0.1-2.5. The contributions of dibenz[a,h]anthracene and benzo[a]pyrene were dominant and contributed from 36% to 51% and 31%-50%, respectively, to the carcinogenic potential, whereas benzo[a]pyrene contributed from 30% to 49% to the mutagenic potential for both size fractions. The incremental lifetime cancer risk, simulated by Monte Carlo simulation, was within the limits set by the US EPA, indicating an acceptable risk for the occupants. These results provide an additional scientific basis for protecting human health from exposure to indoor PAHs.

Assessment of traffic-related chemical components in ultrafine and fine particles in urban areas in Vietnam.

Ultrafine particles (UFPs or PM0.1; aerodynamic diameter ≤ 0.1 µm) were monitored at a roadside site (RS) in a populated area of Hanoi, Vietnam. Meanwhile, UFPs and fine particles (FPs or PM2.5, aerodynamic diameter ≤ 2.5 µm) were monitored at an ambient site (AS), located at an on-campus a university, approximately 200 m away from the RS. Sampling was conducted in different seasons-summer, winter, and the transitional periods of summer-to-winter and winter-to-summer (STP and WTP, respectively). Carbonaceous and ionic species in UFPs and FPs-rarely investigated in the study area-were analyzed to observe the seasonal variations, characteristics of UFPs near the roadway, and spatial differences between the sites. The UFPs concentration at the AS was in the order of winter > STP > WTP > summer, whereas that of the FPs was winter > WTP > STP > summer. This seasonal variation of particle concentration was possibly affected by the meteorological conditions, which contribute to the highest concentration in winter. The higher FPs concentration in WTP than in STP resulted from the substantial increase in ionic concentrations, particularly sulfate, nitrate, and ammonium. This result indicates the effect of secondary formation processes under drizzle-like weather, which is typical during WTP in northern Vietnam. Compared with UFPs at the AS, traffic-related emissions were more noticeable in UFPs at the RS, including a higher EC concentration and lower OC/EC ratio. The possibility of particle growth under favorable conditions, including the presence of gas-phase pollutants and the availability of surface areas owing to high UFPs concentration in Hanoi, may explain the low correlation of the chemical components between UFPs and FPs in the sites. This study serves as a reference for further investigation of the relationship between UFPs and FPs under highly polluted conditions in big cities in Vietnam in future studies.

Mechanisms for removal of gaseous toluene in headspace using sonophysical and sonochemical effects at the gas-liquid interface.

We developed a new method for removing gaseous substances by using high frequency (200 kHz) ultrasonic irradiation of water, and the effects of ultrasonic irradiation on gas-phase toluene were evaluated quantitatively for the first time. The removal ratio of gaseous toluene increased with increasing ultrasonic power, but the reaction was inhibited by the addition of radical scavengers, indicating that ultrasonic irradiation not only accelerated the dissolution of gaseous toluene but also induced toluene decomposition. The contribution made by OH radicals to the decomposition of gaseous toluene at the gas-liquid interface was confirmed by the difference in removal ratios between addition of KI and addition of tert-butyl alcohol. The toluene removal mechanism was investigated by studying the logarithmic plots for toluene concentration at specified times. The results of this study clearly showed the promotion of gaseous toluene dissolution and the reaction via OH radicals at the gas-liquid interface by sonophysical and sonochemical effects with both effects contributing to the removal of gaseous toluene. Furthermore, the total organic carbon concentration in the aqueous phase increased with increasing reaction time, indicating that the toluene degradation products were trapped and decomposed into low-molecular-weight organic compounds in the aqueous phase.

Capturing of gaseous and particulate pollutants into liquid phase by a water/oil column using microbubbles.

A new method was developed to remove gaseous and particulate pollutants by capturing them in water using microbubbles. The capture efficiency of gaseous toluene and ultrafine carbon particles, which are hydrophobic substances, was remarkably improved compared to water-only conditions by adding a small amount of oily substances (4% volume fraction of water) to the water surface. The physicochemical properties of four types of oily substances were investigated. Rapeseed and mineral oil exhibited good capture efficiency during a capture experiment of high-concentration gaseous toluene for 96 h. Additionally, a long-term continuous capture experiment for 24 days revealed that the capture mechanisms of rapeseed and mineral oil were different. The toluene concentration in rapeseed oil reached saturation in the middle of the experiment while the capture efficiency of mineral oil remained constant. It was also shown that the emulsion formation greatly affected the capture of rapeseed oil. Thus, it is expected that a new gaseous pollutant treatment technology that can capture and remove gaseous/particulate pollutants regardless of their hydrophilic/hydrophobic properties could be developed in the future.

Improved ultrasonic degradation of hydrophilic and hydrophobic aldehydes in water by combined use of atomization and UV irradiation onto the mist surface.

Ultrasonic irradiation of 430 kHz, which induces both the chemical effect of pyrolysis and the physical effect of atomization, was carried out to achieve highly effective decomposition of organic substances in water with UV254 irradiation and H2O2 addition. To investigate the influence of physicochemical properties of the substrate on the degradation rate, three different aldehydes, namely, formaldehyde, acetaldehyde, and benzaldehyde, were selected as model substrates. Upon ultrasonic irradiation alone, the removal ratio of the hydrophobic substrate benzaldehyde reached 100% after 120 min, whereas the removal ratios of the hydrophilic substrates formaldehyde and acetaldehyde were only 21.1% and 53.0%, respectively. By combining ultrasonic atomization and UV254 irradiation, formaldehyde and acetaldehyde underwent effective gas-phase decomposition on the surfaces of the mist particles. Photolysis by UV254 irradiation mainly affected for the decomposition of aldehydes on the mist surface rather than the reaction of hydroxyl radicals derived from H2O2 made by water sonolysis. However, the addition of H2O2 effectively improved the decomposition and mineralization rates for both hydrophilic and hydrophobic aldehydes owing to the generation of hydroxyl radicals on the surfaces of the mist particles, which greatly contributed to the gas-phase decomposition. Consequently, the effective decomposition of organic pollutants was achieved regardless of their physicochemical properties in aqueous media.

Chemical characterization and source apportionment of ambient nanoparticles: a case study in Hanoi, Vietnam.

PM0.1 has been believed to have adverse short- and long-term effects on human health. However, the information of PM0.1 that is needed to fully evaluate its influence on human health and environment is still scarce in many developing countries. This is a comprehensive study on the levels, chemical compositions, and source apportionment of PM0.1 conducted in Hanoi, Vietnam. Twenty-four-hour samples of PM0.1 were collected during the dry season (November to December 2015) at a mixed site to get the information on mass concentrations and chemical compositions. Multiple linear regression analysis was utilized to investigate the simultaneous influence of meteorological factors on fluctuations in the daily levels of PM0.1. Multiple linear regression models could explain about 50% of the variations of PM0.1 concentrations, in which wind speed is the most important variable. The average concentrations of organic carbon (OC), elemental carbon (EC), water-soluble ions (Ca2+, K+, Mg2+, Na+, NH4+, Cl-, NO3-, SO42-, C2O42-), and elements (Be, Al, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sb, Ba, Tl, Pb, Na, Fe, Mg, K, and Ca) were 2.77 ± 0.90 µg m-3, 0.63 ± 0.28 µg m-3, 0.88 ± 0.39 µg m-3, and 0.05 ± 0.02 µg m-3, accounting for 51.23 ± 9.32%, 11.22 ± 2.10%, 16.28 ± 2.67%, and 1.11 ± 0.94%, respectively. A positive matrix factorization model revealed the contributions of five major sources to the PM0.1 mass including traffic (gasoline and diesel emissions, 46.28%), secondary emissions (31.18%), resident/commerce (12.23%), industry (6.05%), and road/construction (2.92%).

Combined sonochemical and short-wavelength UV degradation of hydrophobic perfluorinated compounds.

Perfluorochemicals (PFCs), which are common in the aquatic environment, are toxic substances that have high chemical and heat resistance because of their strong C-F bonds. We investigated the effect of ultrasonication and short-wavelength UV irradiation on the degradation of perfluorooctane, perfluoropropionic acid, and perfluorooctanoic acid, which are examples of hydrophobic, hydrophilic, and intermediate PFCs, respectively. The results confirmed that ultrasonication was more effective for decomposing hydrophobic PFCs and UV irradiation was more effective for decomposing hydrophilic PFCs. Therefore, defluorination of the degradation intermediates was improved by a combination of ultrasonication and UV irradiation. Our results can be applied to the decomposition treatment of PFCs that have various levels of water solubility in the aquatic environment.

Effect of ultrasonic frequency on size distributions of nanosized mist generated by ultrasonic atomization.

Ultrasonic atomization is used to produce fine liquid mists with diameter ranges below 100nm. We investigated the effect of the frequency on the size distribution of ultrasonic mist. A bimodal distribution was obtained for the mist generated by ultrasonic atomization with a wide-range particle spectrometer. The peak diameter decreased with increasing frequency, and the number concentration of the mist increased in the smaller range. We determined the relation between the size distribution of the mist and the ultrasonic frequency, and we proposed a generation mechanism for the ultrasonic nanosized mist based on the amount of water vapor around the liquid column. Increasing the power intensity and density by changing the surface diameter of the ultrasonic oscillator affected the number concentration and size distribution of the nanosized mist. Using this technique, the diameter of the mist can be controlled by changing the frequency of the ultrasonic transducer.

Aqueous secondary formation of brominated, chlorinated, and mixed halogenated pyrene in presence of halide ions.

We examined the secondary production of halogenated derivatives of polycyclic aromatic hydrocarbons (PAHs) in surface seawater. Pyrene was selected as the model compound and exposed to UV irradiation in synthetic seawater for various irradiation times. Pyrene underwent rapid photochemical reactions that produced various halogenated derivatives including 1-chloropyrene, 1-bromopyrene, three unidentified dichloropyrenes, and three unidentified bromochloropyrenes. The production of 1-chloropyrene (220-360 nM) was higher than that of 1-bromopyrene (7.3-12 nM), reflecting the high chlorine content of seawater. A pilot field survey was conducted to test the environmental implications of these results, and fresh, brackish, and seawater samples were collected in southwestern Japan. The variation in the concentration ratios between 1-chloropyrene and pyrene implied the presence of a specific source of 1-chloropyrene in coastal water, which can be partly explained by the secondary production observed in our photolysis experiments. In sum, the photochemical reactions of PAHs are a potential secondary source of halogenated PAHs, especially in marine environments heavily contaminated with PAHs.

Studies on size distribution and health risk of 37 species of polycyclic aromatic hydrocarbons associated with fine particulate matter collected in the atmosphere of a suburban area of Shanghai city, China.

Polycyclic aromatic hydrocarbons (PAHs) in suspended particulate matter (SPM) contribute significantly to health risk. Our objectives were to assess the size distribution and sources of 26 PAHs and 11 polycyclic aromatic compounds (PACs) in SPM in the suburban area, Shanghai city, China. Air sampling was carried out on the rooftop of a five-stories building in the campus of Shanghai University. An Andersen high-volume air sampler was employed to collect ambient size-segregated particles from August to September 2015. The toxic particulate PAHs were determined by the gas chromatography mass spectrometry. The concentrations of total PAHs (TPAHs) in SPM and PM1.1 (suspended particulate matter below 1.1 µm) were in the ranges of 4.58-14.5 ng m(-3) and 1.82-8.56 ng m(-3), respectively. 1,8-naphthalic anhydride showed the highest concentrations among 37 species of PAHs and PACs ranging 7.76-47.9 ng m(-3) and 1.50-17.6 ng m(-3) in SPM and PM1.1, respectively. The concentrations of high molecular weight 5-6 ring PAHs followed a nearly unimodal size distribution with the highest peak in PM1.1, while other lower molecular weight PAHs were not dependent on particle sizes. The toxicity analysis indicated that the carcinogenic potency of particulate PAHs primarily existed in PM1.1. Regarding meteorological parameters and other pollutants, the positive effect of humidity and NO2 over PAHs was confirmed. Diagnostic ration indicated that the particulate PAHs in Shanghai were mainly derived from motor-vehicle or petroleum combustion. The highest benzo[a]pyrene equivalent (BaPeq) in SPM and PM1.1 were 2.15 ng m(-3) and 1.43 ng m(-3) calculated by the toxicity equivalency factor, and 69.31 ng m(-3) and 47.81 ng m(-3) estimated by the potency equivalency factors, respectively. The highest contributors in the total carcinogenicity of the particulate PAHs were dibenzo[a,h]pyrene (46.2% and 45.0%) and benz[j]aceanthrylene (80.2% and 83.1%), respectively while benzo[a]pyrene is lower contributor than other carcinogenic PAHs.

Size distribution and sources of 37 toxic species of particulate polycyclic aromatic hydrocarbons during summer and winter in Baoshan suburban area of Shanghai, China.

The objectives of this study were to assess the size-segregated distribution and sources of 37 different species of particulate polycyclic aromatic hydrocarbons (PAHs) in a suburban area of Shanghai metropolitan City, China. The ambient particulate sampling was carried out on the rooftop of a five-stories building in Baoshan campus of Shanghai University. An Andersen high-volume air sampler was employed to collect ambient size-segregated particulate matter during summer of August to September and winter of November to December 2015. The high toxic PAHs were determined by a gas chromatography mass spectrometry. The concentrations of total PAHs in suspended particulate matter (SPM) and PM1.1 (suspended particulate matter below 1.1µm in diameter) in the suburban area of Shanghai were 4.58-14.5ng/m(3) and 1.82-8.56ng/m(3), respectively in summer, and 43.6-160ng/m(3) and 23.2-121ng/m(3), separately in winter. 1,8-Naphthalic anhydride (1,8-NA) showed the highest concentration among 37 different species of PAHs in the suburban area of Shanghai. The concentrations of high molecular PAHs (e.g. 5-6 ring PAHs) followed a nearly unimodal size distribution with the highest peaks in PM1.1. The diagnostic ration qualitatively indicated that PAHs in SPM of Shanghai were mainly derived from motor-vehicle or petroleum combustion in summer and from coal and biomass combustion in winter. According to the calculated toxicity equivalency factors based on the methods of Nisbet and Lagoy and the potency equivalency factors (PEF) recommended by U.S. EPA, the highest contributors in the total carcinogenicity of the PAHs in SPM and PM1.1 were dibenzo[a,h]pyrene (46.2% and 45.0% in summer), benzo[a]pyrene (44.4% and 43.8% in winter) and benz[j]aceanthrylene (80.2% and 83.1% in summer and 83.1% and 84.0% in winter), respectively. Therefore, benzo[a]pyrene seemed to be a lower contributor than other carcinogenic PAHs.

Photochemical and photocatalytic degradation of gaseous toluene using short-wavelength UV irradiation with TiO2 catalyst: comparison of three UV sources.

The feasibility of the use of short-wavelength UV (254+185 nm) irradiation and TiO2 catalyst for photodegradation of gaseous toluene was evaluated. It was clear that the use of TiO2 under 254+185 nm light irradiation significantly enhanced the photodegradation of toluene relative to UV alone, owed to the combined effect of photochemical oxidation in the gas phase and photocatalytic oxidation on TiO2. The photodegradation with 254+185 nm light irradiation was compared with other UV wavelengths (365 nm (black light blue lamp) and 254 nm (germicidal UV lamp)). The highest conversion and mineralization were obtained with the 254+185 nm light. Moreover, high conversions were achieved even at high initial concentrations of toluene. Catalyst deactivation was also prevented with the 254+185 nm light. Regeneration experiments with the deactivated catalyst under different conditions revealed that reactive oxygen species played an important role in preventing catalyst deactivation by decomposing effectively the less reactive carbon deposits on the TiO2 catalyst. Simultaneous elimination of photogenerated excess ozone and residual organic compounds was accomplished by using a MnO2 ozone-decomposition catalyst to form reactive species for destruction of the organic compounds.

Synergistic effects of high-frequency ultrasound on photocatalytic degradation of aldehydes and their intermediates using TiO2 suspension in water.

The degradation of model substances, benzaldehyde (C(6)H(5)CHO) and formaldehyde (HCHO), were investigated under various conditions, namely, ultrasound (US) irradiation, TiO(2) photocatalysis with UV irradiation (UV/TiO(2)), and the combination of sonophotocatalysis and UV irradiation (US/UV/TiO(2)), in order to clarify the synergistic effects between US and UV/TiO(2). US and UV/TiO(2) primarily contribute to the degradation of highly hydrophobic and hydrophilic substances, respectively. However, the degradation rate was found to depend on the chemical properties and concentration of not only the substances initially present, but also their decomposition intermediates. Here, the essential information for accurately evaluating the synergistic effects on reaction rate under US/UV/TiO(2) conditions is reported, with a focus on the behavior of decomposition intermediates.

Degradation of organic gases using ultrasonic mist generated from TiO2 suspension.

The photocatalytic degradation of organic gases with mist particles that were formed by ultrasonic atomization of a TiO(2) suspension was performed with three different ultraviolet light sources. Three aromatic volatile organic compounds (VOCs; toluene, p-xylene, and styrene) and aldehydes (formaldehyde and acetaldehyde) were chosen as model organic gases for the degradation experiment. Under UV(365) irradiation, toluene was decomposed by a photocatalytic reaction on the surface of mist particles. Under UV(254+185) irradiation, the removal efficiency and mineralization ratio of the VOC gases were higher than those under UV(365) or UV(254) irradiation. Under UV(254+185) irradiation, it was found that VOC gases were immediately degraded and converted to water-soluble intermediates by not only direct photolysis but also oxidation by OH radical, since the removal efficiency of several organic gases depended on the reaction rate with OH radical and the primary effect of generated ozone was to complete the mineralization of the intermediates. On the other hand, water-soluble aldehyde gases were rapidly trapped by mist particles before reaction on their surface. Furthermore, water-soluble intermediates that formed via the decomposition of VOC gases were completely trapped in the mist and were not detected at the reactor exit. Therefore, notable secondary particle generation was not observed, even under UV(254+185) irradiation. Based on these results as well as the size distribution of the mist droplets, it was found that primarily submicron-scale droplets contributed to the photocatalytic reaction. Lastly, we propose a mechanism for the degradation of organic gaseous pollutants on the surface of mist particles.