Development of ionic-liquid-impregnated activated carbon for sorptive removal of PFAS in drinking water treatment

Adsorption of per- and poly-fluoroalkyl substances (PFAS) on activated carbon (AC) is considerably hindered by the surface water constituents, degrading the ability of the AC adsorption process to remove PFAS in drinking water treatment. Herein, we developed ionic-liquid-impregnated AC (IL/AC) as an alternative to AC for PFAS sorption and demonstrated its performance with real surface water for the first time. Ionic liquids (ILs) of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (IL(C2)) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (IL(C6)) were selected from among 272 different ILs using the conductor-like screening model for realistic solvents (COSMO-RS) simulation. Impregnation of the ILs in AC was verified using various analytical techniques. Although the synthesized IL/ACs were less effective than pristine AC in treating PFAS in deionized water, their performances were less impacted by the surface water constituents, resulting in comparable or sometimes better performances than pristine AC for treating PFAS in surface water. The removal efficiencies of 10 wt% IL(C6)/AC for six PFAS were 1.40-1.96 times higher than those of pristine AC in a surface water sample containing 2.6 mg/L dissolved organic carbon and millimolar-level divalent cation concentration. PFAS partitioning from the surface water to ILs was not hindered by dissolved organic matter and was enhanced by the divalent cations, indicating the advantages of IL/ACs for treating significant amounts of PFAS in water. The synthesized IL/ACs were effective at treating coexisting pharmaceutical and personal-care products in surface water, showcasing their versatility for treating a broad range of water micropollutants.

Removal characteristics of 53 micropollutants during ozonation, chlorination, and UV/H2O2 processes used in drinking water treatment plant

The removal of 53 emerging micropollutants (MPs), including 10 per- and polyfluorinated substances (PFASs), 25 pharmaceuticals and personal care products (PPCPs), 7 pesticides, 5 endocrine disrupters (EDCs), 3 nitrosamines, and 3 taste and odor compounds (T&Os), by chlorination, ozonation, and UV/H2O2 treatment was examined in deionized water and surface waters used as the raw waters in drinking water treatment plants (DWTPs) in South Korea. The UV/H2O2 treatment was effective in the removal of most MPs, whereas chlorination was selectively effective for 19 MPs, including EDCs (>70 %). MPs containing aromatic ring with electron-donating functional group, or primary and secondary amines were effectively removed by chlorination immediately upon reaction initiation. The removal of MPs by ozonation was generally lower than that of the other two processes at a low ozone dose (1 mg L-1), but higher than chlorination at a high ozone dose (3 mg L-1), particularly for 16 MPs, including T&Os. Compared in deionized water, the removals of MPs in the raw water samples were lower in all three processes. The regression models predicting the rate constants (kobs) of 53 MPs showed good agreement between modeled and measured value for UV/H2O2 treatment (R2 = 0.948) and chlorination (R2 = 0.973), despite using only dissolved organic carbon (DOC) and oxidant concentration as variables, whereas the ozonation model showed a variation (R2 = 0.943). Our results can provide the resources for determining which oxidative process is suitable for treating specific MPs present in the raw waters of DWTPs.

Kinetics and proposed mechanisms of hexafluoropropylene oxide dimer acid (GenX) degradation via vacuum-UV (VUV) photolysis and VUV/sulfite processes

We investigated the degradation of hexafluoropropylene oxide dimer acid (GenX) in water via VUV photolysis and VUV/sulfite reactions under nitrogen-saturated conditions. Approximately 35% and 90% of GenX were degraded in 3 h in the VUV photolysis and VUV/sulfite reaction. While GenX removal rate was highest at pH 6 in VUV photolysis, it increased under alkaline pHs, especially at pH 10, in VUV/sulfite reaction. Radical scavenging experiments showed that, while both eaq- and •H contributed to VUV photolysis, eaq- played a significant role and •OH had a negative effect during VUV/sulfite reaction. Two transformation products (TPs) (TFA and PFPrA) were identified in VUV photolysis, whereas five TPs (TFA, PFPrA, TP182, TP348, and TP366) were identified in VUV/sulfite reaction by LCMS/MS and LCQTOF/MS. Defluorination of GenX was observed with the defluorination efficiency after 6 h reaching 17% and 67% in the VUV photolysis and VUV/sulfite reactions, respectively. Degradation mechanism for GenX based on the identified TPs and the theoretical calculation confirmed the susceptibility of GenX to nucleophilic attack. The initial reactions for GenX decomposition were C-C and C-O bond cleavage in both reactions, whereas sulfonation followed by decarboxylation was observed only in the VUV/sulfite reaction. ECOSAR ecotoxicity simulation showed that the toxicities of the TPs were not as harmful as those of GenX.

Reductive degradation mechanism of perfluorooctanoic acid (PFOA) during vacuum ultraviolet (VUV) reactions combining with sulfite and iodide

In this study, PFOA removal and defluorination were examined during vacuum ultraviolet (VUV) photolysis in the presence of sulfite and sulfite/iodide conditions. PFOA (24 μM) degradation rate constant (kobs) and defluorination amount in VUV photolysis, and VUV/sulfite, and VUV/sulfite/iodide reactions under nitrogen-purging condition were 5.50 × 10-3, 7.26 × 10-2, 1.60 × 10-1 min-1, and 34.6, 72.7, 73.9% in 6 h, respectively. When tert-butanol (t-BuOH), NO2-, and NO3- ions were added as radical scavengers, hydrated electrons (eaq-) was confirmed as the main species responsible for degrading PFOA and mediating defluorination in VUV-based reactions. While, during VUV photolysis, short-chain perfluoroalkyl carboxylic acids (PFCAs), such as PFHpA, PFHxA, PFPeA, and PFBA, were mainly produced as transformation products (TPs) by the chain-shortening mechanism, additional 14 and 15 TPs were identified in the VUV/sulfite and VUV/sulfite/iodide reactions by LC-QTOF/MS, respectively. The main degradation mechanisms in these reactions are H-F exchange (e.g., TP395 (m/z = 394.9739) and TP377 (m/z = 376.9838)), •SO3--F exchange (TP474, m/z = 474.9323), carbon double bond formation by defluorination (e.g., TP392 (m/z = 392.9455), TP410 (m/z = 410.9355), and TP436 (m/z = 436.9347)), and H-F exchange followed by hydration reaction (TP393, m/z = 392.9773), respectively. PFOA degradation pathways were proposed for these VUV-based reactions based on the identified TPs, their time profiles, and the density functional theory (DFT). Finally, the toxicity of PFOA and its TPs produced during three reactions were assessed using ECOSAR simulation.

Non-target screening of volatile organic compounds in spray-type consumer products and their potential health risks

Widespread use of spray-type consumer products can raise significant concerns regarding their effects on indoor air quality and human health. In this study, we conducted non-target screening using gas chromatography-mass spectrometry (GC-MS) to analyze VOCs in 48 different spray-type consumer products. Using this approach, we tentatively identified a total of 254 VOCs from the spray-type products. Notably, more VOCs were detected in propellant-type products which are mostly solvent-based than in trigger-type ones which are mostly water-based. The VOCs identified encompass various chemical classes including alkanes, cycloalkanes, monoterpenoids, carboxylic acid derivatives, and carbonyl compounds, some of which arouse concerns due to their potential health effects. Alkanes and cycloalkanes are frequently detected in propellant-type products, whereas perfumed monoterpenoids are ubiquitous across all product categories. Among the identified VOCs, 12 compounds were classified into high-risk groups according to detection frequency and signal-to-noise (S/N) ratio, and their concentrations were confirmed using reference standards. Among the identified VOCs, D-limonene was the most frequently detected compound (freq. 21/48), with the highest concentration of 1.80 mg/g. The risk assessment was performed to evaluate the potential health risks associated with exposure to these VOCs. The non-carcinogenic and carcinogenic risks associated with the assessed VOC compounds were relatively low. However, it is important not to overlook the risk faced by occupational exposure to these VOCs, and the risk from simultaneous exposure to various VOCs contained in the products. This study serves as a valuable resource for the identification of unknown compounds in the consumer products, facilitating the evaluation of potential health risks to consumers.

Comparison of sampling methods for the determination of volatile organic compounds in consumer aerosol sprays

Many studies have evaluated the hazardous substances contained in various household chemical products. However, for aerosol spray products there is currently no international standard sampling method for use in a component analysis. The aim of this study was to develop an appropriate sampling method for the analysis of volatile organic compounds (VOCs) in consumer aerosol sprays. Two different sampling methods, spraying (into a vial) and perforating (and transferring the contents into a vial), were used to evaluate the levels of 16 VOC components in eight different aerosol spray products. All eight products contained trace amounts of hazardous VOCs, and a quantitative analysis showed that, for the same product, VOC concentrations were higher when spraying than when perforating. Using the spraying method, average toluene, ethylbenzene, p-xylene, o-xylene, and styrene concentrations were 1.80-, 2.10- 2.25-, 2.03-fold, and 1.28-fold higher, respectively, than when using the perforating method. The spraying method may provide more realistic estimates of the user's exposure to harmful substances and the associated health risks when using spray products. Of the two representative methods widely used to analyze harmful substances in consumer aerosol sprays, the spraying method is recommended over the perforating method for the analysis of VOCs.

Polyaromatic hydrocarbon thin film layers on glass, dust, and polyurethane foam surfaces

An investigation was conducted into the dynamic behavior of two polyaromatic hydrocarbon (PAH) semi-volatile organic compound (SVOC) naphthalene (NAP) and benzo [ghi]perylene (BghiP) in air and on various surfaces including glass, dust, and polyurethane foam (PUF) to understand their interaction with different media. A confocal fluorescence microscope and an infrared microscope were employed to detect and monitor the concentration-, time-, and temperature-dependent changes of the aromatic NAP and BghiP species on the surfaces. Infrared two-dimensional mapping of the vibrational characteristic peaks was used to track the two PAHs on the surfaces. Gas chromatography-mass spectrometry (GC-MS) was employed to measure the gaseous concentrations. The sorption of NAP and BghiP on the surfaces was estimated using Arizona desert sand fine (ISO 12103-1 A2) dust and organic contaminant household (SRM 2585) dust. The surface-to-air partition coefficients of NAP and BghiP were estimated on the different surfaces of glass, dust, and PUF. Molecular dynamic simulations were performed on dust surfaces based on the Hatcher model to understand the behavior of NAP and BghiP on dust surfaces. The Weschler-Nazaroff model was introduced to predictPAH film accumulation on the surfaces, providing a better understanding of PAH interaction with different environmental media. These findings could contribute to developing effective strategies to mitigate the adverse impact of PAHs on the environment and human health.

Temporal and spatial distribution of microplastic in the sediment of the Han River, South Korea

Sediments are sinks for microplastics (MPs) in freshwater environments. It is, therefore, necessary to investigate the occurrence and fate of accumulated MPs in the sediments, which pose a risk to aquatic organisms. We conducted the first comprehensive investigation of MPs in riverine sediment in South Korea to examine the temporal and spatial distribution of MPs in the sediment at the two main branches and downstream of the Han River. The average abundance of MPs over all sites was 0.494 ± 0.280 particles/g. Spatially, the MP abundance at three sites in the North Han River (0.546 ± 0.217 particles/g) was higher than those in the South Han River (0.383 ± 0.145 particles/g) and downstream of the Han River (0.417 ± 0.114 particles/g). The abundances of MPs before dams at two upstream sites were significantly higher than that at other sites because of the slow river flow velocity attributed to the artificial structure. The abundance of MPs after the mosoon season (October, 0.600 ± 0.357 particles/g) was higher than that before the mosoon season (April, 0.389 ± 0.099 particles/g). The most common polymer types observed were polyethylene (>38%) and polypropylene (>24%). Irrespective of the location and season, greater than 93% of MPs identified were fragments, and the remaining were fibers. The concentrations of TOC, TN, and TP in the sediment were positively correlated with MP abundance. MP abundance was also positively correlated with clay and silt fractions of the sediment; however, it was negatively correlated with sand fraction. This study provides a basis for the management of MP pollution by offering findings related to critical factors influencing MP abundance in sediment.

Equilibria of semi-volatile isothiazolinones between air and glass surfaces measured by gas chromatography and Raman spectroscopy

Trace amounts of semi-volatile organic compounds (SVOCs) of the two isothiazolinones of 2-methylisothiazol-3(2H)-one (MIT) and 2-octyl-4-isothiazolin-3-one (OIT) were detected both in the air and on glass surfaces. Equilibria of SVOCs between air and glass were examined by solid phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS). Surface to air distribution ratios of K_sa for MIT and OIT were determined to be 5.10 m and 281.74 m, respectively, suggesting more abundant MIT in the gas phase by a factor of ∼55. In addition, a facile method of silver nanocube (AgNC)-assisted surface-enhanced Raman scattering (SERS) has been developed for the rapid and sensitive detection of MIT and OIT on glass surfaces. According to MIT and OIT concentration-correlated SERS intensities of Raman peaks at ∼1585 cm^-1 and ∼1125 cm^-1, respectively. Their calibration curves have been obtained in the concentration ranges between 10^-3 to 10^-10 M and 10^-3 to 10^-11 M with their linearity of 0.9986 and 0.9989 for MIT and OIT, respectively. The limits of detection (LODs) of the two isothiazolinones were estimated at 10^-10 M, and 10^-11 M for MIT and OIT, respectively. Our results indicate that AgNC-assisted SERS spectra are a rapid and high-ultrasensitive method for the quantification of MIT and OIT in practical applications. The development of analytical methods and determination of the Ksa value obtained in this study can be applied to the prediction of the exposure to MIT and OIT from various chemical products and dynamic behaviors to assess human health risks in indoor environments.

Analysis of semi-volatile organic compounds in indoor dust and organic thin films by house type in South Korea

In this study, semi-volatile organic compounds (SVOCs) in samples of indoor dust and organic thin films obtained from 100 residential houses in South Korea, were examined, based on both target analysis using gas chromatography-mass spectrometry (GC-MS) and non-target analysis by gas chromatography-quadrupole time-of flight mass spectrometry (GC-QTOF-MS) screening. In the targeted approach, phthalates and polycyclic aromatic hydrocarbons (PAHs) were analyzed in dust and organic film samples, to find that both these classes of SVOCs were detected in dust and organic film samples, with the median concentrations of eight phthalates (Σ₈ phthalate) and 16 PAHs (Σ₁₆ PAH) being 1015.93 μg/g and 1824.97 ng/g in the dust samples, and 75.79 μg/m² and 2252.78 ng/m² in the organic film samples, respectively. Among the phthalates, in all house types. bis(2-ethylhexyl) phthalate (DEHP) was detected at the highest concentration, followed by dibutyl phthalate (DBP) and diisobuthyl phthalate (DiBP), with DEHP levels found to be highest in dwelling houses. DEHP levels were found to be significantly associated with building age and renovation status. Lower levels of DEHP were detected in houses less than 10 years old or that had undergone renovation in the previous 10 years. Among the assessed PAHs, a significant correlation was detected between benzo(a)pyrene in dust and building age (p < 0.05). These findings imply that the inhabitants of older houses are at a greater risk of exposure to SVOCs originating from indoor dust and organic films. Non-target screening of selected dust and organic film samples using GC-QTOF-MS data revealed the presence of numerous SVOC compounds, including triphenylphosphine oxide, (Z)-9-octadecenamide, and cyclosiloxanes, along with certain organophosphate flame retardants including tris(1-chloro-2-propyl) phosphate (TCPP) and tris(1,3-dichloroisopropyl) phosphate (TDCPP), and plasticizers. These compounds identified in the non-target screening are of emerging concern, and their presence in dust and organic films needs to be estimated.

Degradation of iopromide during the UV-LED/chlorine reaction: Effect of wavelength, radical contribution, transformation products, and toxicity

Three different UV-LED wavelengths (265, 310, and 365 nm) were used in the UV-LED/chlorine reaction to investigate the degradation mechanism of iopromide (IPM) at different wavelengths, a representative iodinated contrast media compound. The degradation rate (k'_IPM) increased from pH 6-8 at 265 nm, but, decreased as the pH increased up to 9 at 310 nm and 365 nm. Radical scavenging experiments showed that reactive chlorine species (RCS) are the dominant radical species at all wavelengths, but a higher contribution of OH• was observed at lower pH and longer wavelengths. The contribution of RCS decreased but the contribution of OH• increased as the wavelength increased. Among RCS, the largest contribution was found to be ClO•. Total nine transformation products (TPs) were identified by LC-QTOF-MS during the UV-LED/chlorine reaction at 265 nm. Based on the identified TPs and their time profiles, we proposed a degradation pathway of IPM during UV-LED/chlorine reaction. The Microtox test using V. fischeri showed that no significant increase in toxicity was observed at all wavelengths. The synergistic effect of UV-LED and chlorine was greater at a higher wavelength by the electrical efficiency per order (EEO) calculation.

Propiconazole degradation and its toxicity removal during UV/H2O2 and UV photolysis processes

Propiconazole (PRO) is a triazole fungicide that is frequently detected in the water. In this study, we investigated the kinetics and degradation mechanism of PRO during the UV photolysis and UV/H₂O₂ processes. PRO was removed by the pseudo-first-order kinetics in both processes. The removal of PRO was enhanced by increasing H₂O₂ concentration in the UV/H₂O₂ process. The highest removal under neutral conditions, and lower removal of PRO were observed in acidic and alkaline pHs in the UV/H₂O₂ process. The presence of natural water ingredients such as Cl^-, NO₃^-, humic acid acted as radical scavengers, but HCO₃^- ion acted as both radical promoter and scavenger in the UV/H₂O₂ process. The transformation products (TPs) of PRO during both processes were identified using LC-QTOF/MS. Four TPs ([M+H]⁺ = 238, 256, 306, and 324) were identified during UV photolysis, and six TPs ([M+H]⁺ = 238, 256, 306, 324, 356, and 358) were identified in the UV/H₂O₂ process. Among the identified TPs, TP with [M+H]⁺ values of 356 and 358 were newly identified in the UV/H₂O₂ process. In addition, ionic byproducts, such as Cl^-, NO₃^-, formate (HCOO^-), and acetate (CH₃COO^-), were newly identified, indicating that significant mineralization was achieved in the UV/H₂O₂ process. Based on the identified TPs and ionic byproducts, the degradation mechanisms of PRO during two processes were proposed. The major reactions in both processes were ring cleavage and cyclization, and hydroxylation by OH radicals. The Microtox test with Vibrio fischeri showed that, while the toxicity of the reaction solution increased first, then gradually decreased during UV photolysis, the UV/H₂O₂ process initially increased toxicity at 10 min due to the production of TPs, but toxicity was completely removed as the reaction progressed. The results obtained in this study imply that the UV/H₂O₂ process is an effective treatment for eliminating PRO, its TPs, and the resulting toxicity in water.

Advanced microplastic monitoring using Raman spectroscopy with a combination of nanostructure-based substrates

Micro(nano)plastic (MNP) pollutants have not only impacted human health directly, but are also associated with numerous chemical contaminants that increase toxicity in the natural environment. Most recent research about increasing plastic pollutants in natural environments have focused on the toxic effects of MNPs in water, the atmosphere, and soil. The methodologies of MNP identification have been extensively developed for actual applications, but they still require further study, including on-site detection. This review article provides a comprehensive update on the facile detection of MNPs by Raman spectroscopy, which aims at early diagnosis of potential risks and human health impacts. In particular, Raman imaging and nanostructure-enhanced Raman scattering have emerged as effective analytical technologies for identifying MNPs in an environment. Here, the authors give an update on the latest advances in plasmonic nanostructured materials-assisted SERS substrates utilized for the detection of MNP particles present in environmental samples. Moreover, this work describes different plasmonic materials-including pure noble metal nanostructured materials and hybrid nanomaterials-that have been used to fabricate and develop SERS platforms to obtain the identifying MNP particles at low concentrations. Plasmonic nanostructure-enhanced materials consisting of pure noble metals and hybrid nanomaterials can significantly enhance the surface-enhanced Raman scattering (SERS) spectra signals of pollutant analytes due to their localized hot spots. This concise topical review also provides updates on recent developments and trends in MNP detection by means of SERS using a variety of unique materials, along with three-dimensional (3D) SERS substrates, nanopipettes, and microfluidic chips. A novel material-assisted spectral Raman technique and its effective application are also introduced for selective monitoring and trace detection of MNPs in indoor and outdoor environments.

Occurrence and characteristics of microplastics in fish of the Han River, South Korea: Factors affecting microplastic abundance in fish

This study examined the abundance of microplastics (MPs) in 106 fish from 22 species inhabiting three sites of the Han River, South Korea. In total, 1753 MPs from 106 fish samples were identified with an average abundance of 15.60 ± 13.45 MPs per individual fish (MPs indiv^-1) in the North Han River, 16.35 ± 12.32 MPs indiv^-1 in the South Han River, and 20.14 ± 10.01 MPs indiv^-1 in downstream of the Han River, indicating that the fish in the downstream of the Han River was the most contaminated by MPs. The dominant size of MPs detected in fish ranged between 0.1 and 0.2 mm, and the most common polymer types found in fish were polypropylene (PP) (≥40%) and polyethylene (PE) (≥23%), followed by polytetrafluoroethylene (PTFE) (≥16%) at all sampling locations. A significant correlation was observed between the log-transformed number of MPs with log-transformed fish length (p < 0.01) and with log-transformed fish weight (p < 0.01). The Kruskal-Wallis test disclosed a significant difference in the number of MPs among the feeding habits (p < 0.01), indicating that omnivorous and insectivorous fish contained more MPs than carnivorous and herbivorous fish. In addition, fish habitat result showed that pelagic fish contained a higher level of MPs than demersal fish, but no significant differences in the number of MPs among fish habitats were observed (p > 0.05).

Surface-dependent gas equilibrium of semi-volatile organic compounds on glass, wood, and polyurethane foam using SPME-GC/MS

The surface-dependent evaporation behavior of phthalates as semi-volatile organic compounds (SVOCs) on glass, wood, and polyurethane foam (PUF) was investigated. Three phthalates of di-2-ethylhexyl phthalate (DEHP), butyl benzyl phthalate (BBP), and dibutyl phthalate (DBP) were studied to compare the amount of gases vaporized from their surfaces. A 10 mL silicate glass vial was used to compare the gas equilibrium of the phthalates after 2 h. The gases accumulated in the air were transferred to a solid-phase microextraction (SPME) column and analyzed by gas chromatography-mass spectrometry (GC-MS). As correlated with the physicochemical properties of the phthalates, including molecular weights and vapor pressure, the surface-air partition coefficients (K_sa) were found to be in the range of 10¹-10⁵ m, 10⁶-10⁷ m, and 10⁷-10⁹ m on glass, wood, and PUF, respectively, implying that a significant amount of phthalates are retained on wood and PUF surfaces as compared to glass, and only a trace amount of phthalates can be volatilized into the air, especially the less volatile DEHP. The three-dimensional (3D) morphologies of glass and wood were also examined using a white-light interferometric surface profile microscope and an atomic force microscope (AFM). In contrast to smooth glass surfaces within the sub-micrometer vertical range, the wood surfaces exhibited uneven irregular structures at a height of 5-30 μm. The rough wood surfaces were found to adsorb substantial amounts of gases to prevent the effective volatilization of phthalates into the air, especially the low molecular DBP. Our results imply that wood and PUF surfaces may be superior to glass surfaces in storage and reduction of phthalates in the air, especially DBP.

Removal of tetramethylammonium hydroxide (TMAH) in semiconductor wastewater using the nano-ozone H2O2 process

In this study, we used a nano-ozone bubble to enhance the efficiency of the ozone/H₂O₂ process for the degradation of tetramethylammonium hydroxide (TMAH) found in semiconductor wastewater at high levels. The nano-ozone bubble significantly increased ozone mass transfer rate compared to that of the macro-ozone bubble. The half-life of nano-ozone bubbles was 23 times longer than that of the nano-ozone bubbles. Due to the high ozone mass transfer rate and its durability, the nano-ozone bubble increased the TMAH degradation rate compared to that of the macro-ozone. The addition of H₂O₂ significantly increased the TMAH degradation rate constant by OH production during the nano-ozone bubbles/H₂O₂ process. The optimum conditions for TMAH removal was 25 °C and pH 10. Within 90 min of the nano-ozone/H₂O₂ process, TOC removal was 65 % while 80 % of nitrogen was converted into nitrate (NO₃^-) with 95 % of TMAM removal. Decreases in acute (40-fold) and chronic (2-fold) toxicity were achieved after applying the nano-ozone/H₂O₂ process to TMAH containing wastewater. However, there was no significant chronic toxicity decrease during the nano-ozone/H₂O₂ process of TMAH.

Review of MXene-based nanocomposites for photocatalysis

Since multilayered MXenes (Ti₃C₂T_x, a new family of two-dimensional materials) were initially introduced by researchers at Drexel University in 2011, various MXene-based nanocomposites have received increased attention as photocatalysts owing to their exceptional properties (e.g., rich surface chemistry, adjustable bandgap structures, high electrical conductivity, hydrophilicity, thermal stability, and large specific surface area). Therefore, we present a comprehensive review of recent studies on fabrication methods for MXene-based photocatalysts and photocatalytic performance for contaminant degradation, CO₂ reduction, H₂ evolution, and N₂ fixation with various MXene-based nanocomposites. In addition, this review briefly discusses the stability of MXene-based nanophotocatalysts, current limitations, and future research needs, along with the various corresponding challenges, in an effort to reveal the unique properties of MXene-based nanocomposites.

Degradation of cyclophosphamide during UV/chlorine reaction: Kinetics, byproducts, and their toxicity

Cyclophosphamide (CP) is a widely used anticancer drug and an immunosuppressant. Since CP is nonbiodegradable, it is hardly removed by the conventional wastewater treatment processes, resulting in continuous detection in surface water. In this study, the degradation of CP during the UV-B/chlorine reaction was investigated. CP was not degraded by UV-B photolysis and chlorination only but was effectively degraded in the UV-B/chlorine reaction with pseudo-first-order kinetics. Acidic pH conditions in the UV-B/chlorine reaction showed the most effective removal of CP. More than 56% of the CP was mineralized within 8 h of the reaction. Seven organic transformation products (TPs) (m/z = 141.01, 192.10, 198.03, 212.01, 258.01, 274.00, and 276.02, respectively) and four inorganic byproducts (NH₄⁺, NO₃^-, HCOO^-, and PO₄^3-) were identified using LC-qTOF/MS and ion chromatography, respectively. Microtox test based on bioluminescence inhibition showed that the toxicity inhibition increased to 88% as the reaction proceeded during the UV/chlorine reaction, probably due to the production of TPs, especially TP 258 (m/z = 258.01). The results of this study imply that the toxicity of TPs needs to be reduced when applying a UV-B/chlorination process to treat CP in water.

Benzophenone-3 degradation via UV/H2O2 and UV/persulfate reactions

The degradation of benzophenone-3 (BP3) in water via the UV/H₂O₂ and UV/persulfate (UV/PS) reactions was investigated. The degradation of BP3 exhibited pseudo-first-order kinetics in both reactions. The degradation efficiency of BP3 was higher in the UV/PS reaction than in the UV/H₂O₂ reaction. In both reactions, the observed rate constants (k_obs) of BP3 degradation were highest at pH 6 and increased linearly with increasing dosage of H₂O₂ and persulfate. The second-order rate constants of BP3 with •OH (k_{•OH_BP3}) and •SO₄^- (k_•SO4-_{_BP3}) were determined to be 1.09 (± 0.05) × 10¹⁰ and 1.67 (± 0.04) × 10⁹ M^-1 s^-1, respectively. The k_obs values of BP3 were affected by water components such as HCO₃^-, NO₃^-, Cl^-, and Br^- ions, as well as humic acid. Based on the identified transformation products (TPs), the degradation pathway of BP3 during both reactions was a hydroxylation reaction. The inhibition of bioluminescence in Vibrio fischeri due to BP3 and its TPs decreased more quickly in the UV/PS reaction than in the UV/H₂O₂ reaction. The results suggest that the UV/PS process is a better alternative to the UV/H₂O₂ process for removing BP3 and its toxicity in water.

Nanostructured Raman substrates for the sensitive detection of submicrometer-sized plastic pollutants in water

We prepared novel Raman substrates for the sensitive detection of submicron-sized plastic spheres in water. Anisotropic nanostar dimer-embedded nanopore substrates were prepared for the efficient identification of submicron-sized plastic spheres by providing internal hot spots of electromagnetic field enhancements at the tips of nanoparticles. Silver-coated gold nanostars (AuNSs@Ag) were inserted into anodized aluminum oxide (AAO) nanopores for enhanced microplastic (MP) detection. We found that surface-enhanced Raman scattering (SERS) substrates of AuNSs@Ag@AAO yielded stronger signals at the same weight percentages for polystyrene MP particles with diameters as small as 0.4 μm, whereas such behaviors could not be observed for larger MPs (diameters of 0.8 μm, 2.3 μm, and 4.8 μm). The detection limit of the submicrometer-sized 0.4 μm in our Raman measurements were estimated to be 0.005% (∼0.05 mg/g =50 ppm) along with a fast detection time of only a few min without any sample pretreatments. Our nano-sized dimensional matching substrates may provide a useful tool for the application of SERS substrates for submicrometer MP pollutants in water.

Thyroid disrupting effects of perfluoroundecanoic acid and perfluorotridecanoic acid in zebrafish (Danio rerio) and rat pituitary (GH3) cell line

Due to global restriction on perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), the use of long-chain perfluoroalkyl substances (PFASs, C > 8) and their environmental occurrences have increased. PFOS and PFOA have been known for thyroid disruption, however, knowledge is still limited on thyroid disrupting effects of long-chain PFASs (C > 10). In this study, two long-chain perfluorinated carboxylic acids (PFCAs), i.e., perfluoroundecanoic acid (PFUnDA) and perfluorotridecanoic acid (PFTrDA), were chosen and investigated for thyroid disrupting effects, using zebrafish embryo/larvae and rat pituitary cell line (GH3). For comparison, PFOA was also added as a test chemical and also investigated for its thyroid disruption potential. Following a 5 d exposure to PFTrDA, zebrafish larvae showed upregulation of the genes responsible for thyroid hormone synthesis (tshβ, nkx2.1, nis, tpo, mct8) and (de)activation (dio1, dio2). In contrast, both PFUnDA and PFOA induced no regulatory changes except for upregulation of a thyroid metabolism related gene (ugt1ab). Morphological changes such as decreased eyeball size, increased yolk sac size, or deflated swim bladder, occurred following exposure to PFUnDA, PFTrDA, and PFOA. In GH3 cells, exposure to PFUnDA and PFTrDA upregulated Tshβ gene, suggesting that these PFCAs increase thyroid hormone synthesis through stimulation by Tsh. In summary, both long-chain PFCAs could cause transcriptional changes of thyroid regulating genes that may lead to increased malformation of the zebrafish larvae, but the pathway of thyroid disruption appears to be different by the chain length. Confirmation and validation in adult fish following long term exposure are warranted.

Effects of 2-ethylhexyl-4-methoxycinnamate (EHMC) on thyroid hormones and genes associated with thyroid, neurotoxic, and nephrotoxic responses in adult and larval zebrafish (Danio rerio)

One of the most widely used UV filters, 2-ethylhexyl-4-methoxycinnamate (EHMC), has been widely detected in the environment. While its endocrine disruption potential has often been reported, toxicological information on EHMC is limited. This study was conducted to determine the thyroid, neurological and renal toxicity potentials of EHMC in adult male and embryo-larval zebrafish (Danio rerio). Following 21 d of exposure, plasma T3 concentration decreased in a concentration-dependent manner in adult zebrafish. Several genes related to thyroid hormone regulation were also downregulated in the brain, thyroid, and liver of the adult fish. In addition, upregulation of syn2a in the brain and downregulation of podocin and wt1a in the kidney were observed following the exposure in adult fish. In zebrafish larvae, following 120 h exposure to EHMC, whole-body T3 and T4 contents decreased, and thyroid hormone-related genes were downregulated. However, several genes showed different patterns of transcription in the larvae; for example, mbp and etv1 genes were downregulated and podocin was upregulated. Unlike adult fish, the larval fish showed significant genetic changes related to neurotoxicity. The hypothyroidism induced in the larval fish by the exposure might be potentially associated with the neurotoxic potential of EHMC. The implications of the observed hormonal and transcriptional-level changes in zebrafish at different life stages following long-term exposure warrant further investigation.

Spectroscopic analysis of microplastic contaminants in an urban wastewater treatment plant from Seoul, South Korea

In this study, a systematic multi-spectroscopic analysis of microplastics (MPs) sampled from a metropolitan area of Seoul was undertaken to elevate understanding of the role of wastewater treatment plants (WWTPs) in eliminating suspended contaminants including MPs before releasing the effluent water into the environment. We analyzed pollutants in influent and effluent samples from a WWTP in Seoul, South Korea. Spectroscopic and microscopic methods were used to analyze MPs. Fourier-transform infrared (FT-IR) spectroscopy in the wavenumber region between 4000 and 715 cm^-1 was employed to estimate the abundance of MPs in wastewater. Stereomicroscope images and Nile red staining were used to facilely identify MPs in both influents and effluents to compare the results with those of FT-IR data. Hyperspectral imaging could identify MPs in the influent sample with the reflection method at 400-900 nm. Our preliminary results indicate that the most observed MPs after the wastewater were filtered by a 45 μm stainless steel mesh filter were polyethylene (PE) and polypropylene (PP). The total number of the prevalent MPs in influent samples decreased significantly. Nanostructure particles could be found by field-emission scanning electron microscopy (FE-SEM). Our combined multi-spectroscopic study should be helpful to provide a guideline for the rapid spectroscopic analysis of freshwater in the Han River, Seoul, South Korea.

Kinetics and degradation mechanism of tris (1-chloro-2-propyl) phosphate in the UV/H2O2 reaction

Tris (1-chloro-2-propyl) phosphate (TCPP) is a chlorinated organic phosphate used in various applications as a flame retardant and plasticizer. TCPP is a known suspected carcinogen and is not effectively removed by traditional water treatments such as biological, chlorination, and UV irradiation. In this study, the UV/H₂O₂ reaction was employed to degrade TCPP in water. TCPP was effectively degraded in the UV/H₂O₂ reaction by pseudofirst-order kinetics. The second-order rate constant of the reaction between the TCPP and OH radical was determined to be 4.35 (±0.13) × 10⁸ M^-1 s^-1 using the competition kinetics with nitrobenzene as a reference compound. The degradation of TCPP was affected by the amount of H₂O₂, pH, and coexisting water components such as HCO₃^-, NO₃^-, and humic acid. Approximately 64.2% of total organic carbon (TOC) in TCPP was mineralized in 12 h during the UV/H₂O₂ reaction, whereas chloride (Cl^-) and phosphate (PO₄^3-) ions were identified as ionic byproducts with the recoveries of 96% chlorine (Cl) and 50% phosphorus (P). Five organic transformation products (TPs) of TCPP were also identified using LC-qTOF/MS. Considering the identified TPs, the main degradation pathway of TCPP during the UV/H₂O₂ reaction was found to be OH-radical-induced hydroxylation. Finally, a 70% decrease in bioluminescence inhibition in Vibrio fischeri was observed during the UV/H₂O₂ reaction, and the time-toxicity profile was similar to the time-peak area profile of TPs. The result of this study implies that TCPP can be efficiently removed with significant mineralization and toxicity reduction by the UV/H₂O₂ process.

Energy-efficient erythromycin degradation using UV-LED (275 nm)/chlorine process: Radical contribution, transformation products, and toxicity evaluation

In this study, we investigated the degradation mechanism of erythromycin (ERY) during UV-LED/chlorine treatment using a 275-nm ultraviolet light-emitting diode (UV-LED). This wavelength is known to generate fewer disinfection byproducts (DBPs), and to have higher energy and photon yield efficiency compared to low pressure mercury (LP-UV) lamp which emits 254 nm of UV radiation. The degradation of ERY during the UV-LED/chlorine reaction followed pseudo-first-order kinetics. While Cl• and ClO• radicals along with other secondary radicals played key roles in the degradation of ERY at alkaline pH conditions, •OH radical was the main contributor at acidic pH conditions. Using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QToF-MS), we tentatively identified six byproducts. Trace amounts of DBPs, such as chloroform (CHCl₃) and chlorate (ClO₃^-) ions, were also detected at less than 0.3 mg/L. There was no residual antibiotic effect at the end of the UV-LED/chlorine reaction due to the complete degradation of important moieties, such as macrolide, in ERY. Toxicity decreased by 20% after 20 min during the UV-LED/chlorine process of ERY (1.0 mg/L) degradation. Finally, we confirmed the inactivation of ARB and ARG during the UV-LED/chlorine process.

Behavioral characteristics to airborne particles generated from commercial spray products

Commercial spray products are commonly used in daily life and airborne particles generated by these products may cause adverse health effects. Our study was aimed to characterize the behaviors of airborne particles from spray products and to determine the deposition loss rate. Four categories of spray products with highly frequent use - air fresheners, fabric deodorants, window cleaners, and a bathroom cleaner - were selected for the study. The products were applied in a cleanroom according to the instructions for use. Airborne particles (10-10,000 nm) were measured within the breathing zone of a user with a scanning mobility particle sizer and an optical particle spectrometer. Additionally, filter sampling was performed to examine the morphological characteristics of the particles using a field emission-scanning electron microscope (FE-SEM). The initial concentration and particle size distribution varied among different spray types and products. Two propellant-type air fresheners that we tested showed a high initial concentration of smaller sized particles. However, one of these and all hand-pressure type propellants showed a low initial concentration in all size ranges. We observed that particles in nucleation mode (10-31.6 nm) decreased and aggregated particles shifted to accumulation mode (100-1,000 nm) over time. The FS-SEM analysis confirmed the aggregation of nano-sized particles for all products. The deposition loss rates of various particle sizes depended on the initial concentration and distribution of particle sizes. For two air fresheners with high initial concentrations, the loss rate of small-sized particles was higher than that of the other products whereas the particle loss rate of large-sized particles was higher, regardless of initial concentration. The results of this study can give us useful information in the behaviors of airborne particles in the consumer spray products and resulting exposure assessment especially in the application to the exposure modeling of spray products.

Greenhouse gas emissions from advanced oxidation processes in the degradation of bisphenol A: a comparative study of the H2O2/UV, TiO2 /UV, and ozonation processes

To estimate greenhouse gas (GHG) emissions and degradation rate constants (k_obs) from H₂O₂/UV-C, TiO₂/UV-C, and ozonation processes in the degradation of bisphenol A (BPA), the laboratory scale experiments were conducted. In the H₂O₂/UV-C process, the fastest degradation rate constant (k_obs = 0.353 min^-1) was observed at 4 mM of H₂O₂, while the minimum GHG emission was achieved at 3 mM of H₂O₂. In the TiO₂/UV-C process, the fastest rate constant (k_obs = 0.126 min^-1) was achieved at 2000 mg/L of TiO₂, while the minimum GHG emission was observed at 400 mg/L of TiO₂. In the ozonation process, GHG emissions were minimal at 5 mg/L of O₃, but the degradation rate constant kept on increasing as the O₃ concentration increased. There were three major types of GHG emissions in the advanced oxidation processes (AOPs). In the ozonation process, most of the GHG emissions were generated by electricity consumption. TiO₂/UV-C process accounted for a significant portion of the GHGs generated by the use of chemicals. Finally, the H₂O₂/UV-C process produced similar GHG emissions from both chemical inputs and electricity consumption. The carbon footprint calculation revealed that for the treatment of 1 m³ of water contaminated with 0.04 mM BPA, the H₂O₂/UV-C process had the smallest carbon footprint (0.565 kg CO₂ eq/m³), followed by the TiO₂/UV-C process (3.445 kg CO₂ eq/m³) and the ozonation process (3.897 kg CO₂ eq/m³). Our results imply that the increase in removal rate constant might not be the optimal parameter for reducing GHG emissions during the application of these processes. Graphical abstract .

Occurrence of microplastics in the Han River and riverine fish in South Korea

Microplastic pollution has been paid attention due to the possibly global threat to human health and ecosystem in recent years. In this study, we investigated the distribution of microplastics in the Han River and its tributaries, South Korea, and in six species of inhabiting fish, namely carp (C. carpio), crucian carp (C. cuvieri), bluegill (L. macrochirus), bass (M. salmoides), catfish (S. asotus), and snakehead (C. argus). We found that the concentration of microplastics in the surface waters (0 m) was 0-42.9 particles/m³ (mean: 7.0 ± 12.9 particles/m³) compared to 20.0-180.0 particles/m³ (mean: 102.0 ± 50.3 particles/m³) at a depth of 2 m. Concentrations in the river tributaries ranged from 1.2 to 234.5 particles/m³ (mean: 91.1 ± 72.3 particles/m³). The most common types the plastic identified were polyethylene (PE), silicone, and polystyrene, while polytetrafluoroethylene (PTFE), polyethylene, and polyester dominated in the tributaries. With respect to shape, >73% of the recovered microplastics were fragments and the rest were fibers in the water. We also measured the concentration of microplastics in the intestines of fish, which ranged from 4 to 48 particles/fish (mean: 22.0 ± 16.0 particles/fish). The most common types of plastic found in the sampled fish were polytetrafluoroethylene (PFTE), polyethylene (PE), and rayon, and >94% of all the microplastic found in fish was in the form of fragments with the remainder being fibers. The concentrations of microplastic in the gills of fish ranged from 1 to 16 particles/fish (mean: 8.3 ± 6.0 particles/fish). In contrast, no microplastic was found in the flesh of the sampled fish. Our results imply that the ingestion of microplastics by fish is more closely related to habitat rather than feeding habits.

Concentration and distribution of per- and polyfluoroalkyl substances (PFAS) in the Asan Lake area of South Korea

Seasonal and spatial variations in per- and polyfluoroalkyl substances (PFAS) concentrations in different environmental media in the Asan Lake area of South Korea were investigated by measuring liquid chromatography-tandem mass spectrometry (LC-MS/MS). The mean concentrations of Σ₁₆ PFAS in the different media were in the ranges of 20.7-98.2 pg/m³ in air, 17.7-467 ng/L in water, 0.04-15.0 ng/g dry weight (dw) in sediments, and not detected (n.d.)-12.9 ng/g dw in soils, and the mean concentrations of Σ₁₉ PFAS in fish ranged from n.d. to 197 ng/g wet weight. The most frequently detected PFAS were perfluorooctanoic acid (PFOA) in air and soils, perfluoropentanoic acid (PFPeA) in water, and perfluorooctane sulfonate (PFOS) in sediment and fish. Long-chain PFAS species dominated over short-chain PFAS in most media samples except for the water phase. Sediment-water partition coefficients (log K_d) and bioaccumulation factors (log BAF) of PFAS were calculated using measured concentrations in water, sediments, and fish. Log K_d of PFAS tended to increase with increasing CF₂ units of PFAS, and perfluorodecanoic acid (PFDA) and PFOS showed the highest log BAF value (> 3.0) in all fish species. These results indicate that longer-chain PFAS, especially PFOS, can be effectively accumulated in biota such as fish.

Rapid screening for ecotoxicity of plating and semiconductor wastewater employing the heartbeat of Daphnia magna

Industrial wastewater discharge is one of major threats to the sustainability of aquatic environment. Rapid and sensitive detection of toxic wastewater discharge and appropriate control if necessary are therefore crucial. In the present study, a 1 h Daphnia magna exposure with heartbeat as an observation endpoint was developed and assessed for its utility as a rapid toxicity screening measure. Two types of metal-rich industrial wastewater, i.e., metal plating and the semiconductor industry were chosen as target samples, and the 1 h heartbeat assay was applied. Based on a literature search, four metals, i.e., Cu, Cr, Ni and Zn were identified as major chemicals of ecotoxicological concerns in these wastewaters. The effective concentrations determined for each metal from the D. magna 1 h heartbeat test were comparable to those derived from the conventional D. magna 48 h immobilization test. Copper sulfate (CuSO₄) was determined as the most toxic, followed by potassium dichromate (K₂Cr₂O₇), nickel sulfate (NiSO₄) and zinc sulfate (ZnSO₄). For ternary mixtures, the 1 h heartbeat test showed also comparable responses to those of the 48 h immobilization test, suggesting its utility for screening the toxicity of simple metal mixtures. For the site-sampled metal plating water, the rapid heartbeat assay showed similar responses to those of the 48 h immobilization assay. However, for the semiconductor industry wastewater, clearly different responses were observed in both the heartbeat and immobilization assays, probably due to the influence of other contaminants with different modes of action that are present in the wastewater. Our observations showed that the D. magna 1 h heartbeat test can be considered as a rapid ecotoxicity screening measure for certain wastewaters with simple metal mixtures.

Occurrence and Fate of Micropollutants in Private Wastewater Treatment Facility (WTF) and Their Impact on Receiving Water

This study investigated the occurrence and removals of micropollutants in the sewage treatment tank (STT) which is a typical private wastewater treatment facility used in the rural communities in Korea, and their impact on receiving water. STTs were selected in eight provinces to examine the regional difference in the composition of micropollutant occurrence. We measured ten selected micropollutants in influents and effluents of STTs, as well as upstream and downstream of its receiving surface water. The dominant micropollutants in the influent of the STTs were caffeine (13,346 ng/L), acetaminophen (11,331 ng/L), ibuprofen (1440 ng/L), and naproxen (1313 ng/L), in agreement with the amounts produced annually in Korea. In the effluent, caffeine (1912 ng/L), acetaminophen (1586 ng/L), naproxen (475 ng/L), and ibuprofen (389 ng/L) were detected in relatively high concentrations. The composition of micropollutants in STT influents showed little regional variation by provinces, suggesting that the consumption pattern of these micropollutants did not show regional variation. The removal efficiencies of the selected micropollutants at the STTs ranged from 12% (carbamazepine) to 88% (acetaminophen), lower than typical removal by sewage treatment plants (STPs). This result is probably due to the automatic operation systems and simple treatment processes in STTs compared with STPs. The concentrations of selected micropollutants upstream of the receiving water were generally lower compared with those observed downstream, indicating that effluent from STTs was the main source. The per capita discharge loads of STTs and annual emissions rates (kg/year) from private wastewater treatment facilities were estimated for the selected micropollutants.

Degradation kinetics and pathways of β-cyclocitral and β-ionone during UV photolysis and UV/chlorination reactions

β-cyclocitral and β-ionone are ones of major algal odorants produced by oxidation of the β-carotene that exists in algae cells. These compounds degraded the quality of drinking water therefore it needed to be treated in drinking water treatment by advanced oxidation processes. In this study, UV photolysis and UV-chlorination reactions along with chlorination to remove these odorants in water were compared. Kinetics of three reactions were well fitted at pseudo-first order model. Among three reactions, UV-chlorination was the most effective due to generation of OH and Cl radicals. β-ionone showed faster degradation compared to β-cyclocitral due to the existence of double bond in the alkyl carbon chain. In addition, radical contributions of degradation of odorants were examined. During UV-chlorination, UV photolysis contributed around 50% of removal for two odorants. OH radical took part of 36% removal of β-ionone and 50% removal of β-cyclocitral. Unlike β-ionone, β-cyclocitral was not degraded by reactive chlorine species during UV-chlorination. Acidic pH was favorable for UV-chlorination due to different quantum yield and radical scavenging effect by chlorine species. Formation of trace amount of chloroform was observed during UV-chlorination. The methyl ketone group of β-ionone was the main site for chloroform production. Several byproducts during UV photolysis and UV-chlorination of β-ionone were identified by GC-MS, and these were degraded with further reaction by UV-induced isomerization, OH radical, and bond scission mechanisms. β-cyclocitral was formed as byproducts during UV-chlorination of β-ionone. Based on degradation byproducts, the degradation pathways of β-ionone and β-cyclocitral of UV photolysis and UV-chlorination were suggested based on the identified byproducts. This study showed UV-chlorination process can be applied for degrading odorants like β-cyclocitral and β-ionone.

Distribution of phthalate esters in air, water, sediments, and fish in the Asan Lake of Korea

Phthalate esters (PEs) are the most commonly used plasticizers and one of the endocrine disrupting chemicals (EDCs) which are extensively present in various environment. Therefore, it is important to examine the levels and distribution of phthalates in multimedia environment. This study investigated the seasonal and spatial variation of 14 PEs in air, water, sediments, and fish in the Asan Lake. Asan Lake is one of the largest artificial lakes in Korea, and is surrounded by industrial complex and farmlands. The PEs were found to be present throughout the study area. The mean concentration of total PEs (∑₁₄ PEs) was 3.92-33.09 ng/m³ in air, not detected (n.d.)-2.29 μg/L in water, 3.6-8973 μg/kg dry weight (dw) in sediment, and n.d.-1081 μg/kg dw in fish, respectively. The most frequently detected phthalate in the samples was di(2-ethylhexyl) phthalate (DEHP), and followed by di-n-butyl phthalate (DBP). The concentrations of PEs in water and sediment samples tended to decrease moving downstream of Asan Lake. Bioaccumulation of PEs showed that benthic feeding fish such as crucian carp or skygager contained higher levels of DEHP. Partitioning of DEHP and DBP between water and sediment was calculated using paired sediment/water samples and fugacity fraction (ff). High ff value (ff = 0.89 ± 0.1) of DBP and low ff value of DEHP (ff = 0.24 ± 0.1) confirmed that DEHP is the most abundant PEs in the sediment, and DBP is the second most abundant PEs except DEHP in water. Our results can provide important information of the distribution and behavior of PEs in the lake environment.

Degradation mechanism of cyanide in water using a UV-LED/H2O2/Cu2+ system

In this study, we developed a UV-LED/H₂O₂/Cu²⁺ system to remove cyanide, which is typically present in metal electroplating wastewater. The results showed the synergistic effects of UV-LED, H₂O₂, and Cu²⁺ ions on cyanide removal in comparison with UV-LED photolysis, H₂O₂ oxidation, UV-LED/H₂O₂, and H₂O₂/Cu²⁺ systems. Cyanide was removed completely in 30 min in the UV-LED/H₂O₂/Cu²⁺ system, and its loss followed pseudo-first order kinetics. Statistically, both H₂O₂ and Cu²⁺ ions showed positive effects on cyanide removal, but Cu²⁺ ions exhibited a greater effect. The highest cyanide removal rate constant (k = 0.179 min^-1) was achieved at pH 11, but the lowest was achieved at pH 12.5 (k = 0.064 min^-1) due to the hydrolysis of H₂O₂ (pK_a of H₂O₂ = 11.75). The presence of dissolved organic matter (DOM) inhibited cyanide removal, and the removal rate constant exhibited a negative linear correlation with DOM (R² = 0.987). The removal rate of cyanide was enhanced by the addition of Zn²⁺ ions (from 0.179 to 0.457 min^-1), while the co-existence of Ni²⁺ or Cr⁺⁶ ion with Cu²⁺ ion reduced cyanide removal. The formation of OH radicals in the UV-LED/H₂O₂/Cu²⁺ system was verified using an aminophenyl fluorescence (APF) probe. Cyanate ions and ammonia were detected as the byproducts of cyanide decomposition. Finally, an acute toxicity reduction of 64.6% was achieved in the system within 1 h, despite a high initial cyanide concentration (100 mg/L). In terms of removal efficiency and toxicity reduction, the UV-LED/H₂O₂/Cu²⁺ system may be an alternative method of cyanide removal from wastewaters.

Development of water quality criteria of ammonia for protecting aquatic life in freshwater using species sensitivity distribution method

Ammonia is deemed one of the most important pollutants in the freshwater environment because of its highly toxic nature and ubiquity in surface water. This study thus aims to derive the criteria for ammonia in freshwater to protect aquatic life because there are no water quality criteria for ammonia in Korea. Short-term lethal tests were conducted to perform the species sensitivity distribution (SSD) method. This method is widely used in ecological risk assessment to determine the chemical concentrations to protect aquatic species. Based on the species sensitivity distribution method using Korean indigenous aquatic biota, the hazardous concentration for 5% of biological species (HC₅) value calculated in this study was 44mg/L as total ammonia nitrogen (TAN). The value of the assessment factor was set at 2. Consequently, the criteria for ammonia were derived as 22mg/L at pH7 and 20°C. When the derived value was applied to the monitoring data nationwide, 0.51%, 0.09%, 0.18%, 0.20%, and 0.35% of the monitoring sites in Han River, Nakdong River, Geum River, Youngsan River, and lakes throughout the nation, respectively, exceeded this criteria. The Ministry of Environment in Korea has been considering introducing water quality standard of ammonia for protecting aquatic life. Therefore, our results can provide the basis for introducing the ammonia standard in Korea.

Effect of nitrate, carbonate/bicarbonate, humic acid, and H2O2 on the kinetics and degradation mechanism of Bisphenol-A during UV photolysis

In this study, the effects of natural water components (nitrate, carbonate/bicarbonate, and humic acid) on the kinetics and degradation mechanisms of bisphenol A (BPA) during UV-C photolysis and UV/H₂O₂ reaction were examined. The presence of NO₃^- (0.04-0.4 mM) and CO₃^2-/HCO₃^- (0.4-4 mM) ions increased BPA degradation during UV photolysis. Humic acid less than 3 mg/L promoted BPA degradation, but greater than 3 mg/L of humic acid inhibited BPA degradation. During the UV/H₂O₂ reaction, all water matrix components acted as radical scavengers in the order of humic acid > CO₃^2-/HCO₃^- > NO₃^-. All of the degradation reactions agreed with the pseudo-first-order kinetics. While eight byproducts (m/z = 122, 136, 139, 164, 181, 244, 273, 289) were identified in UV-C/NO₃^- photolysis reaction, four (m/z = 122, 136, 164, 244) and three byproducts (m/z = 122, 136, 164) were observed during UV-C/NO₃^-/CO₃^2-/HCO₃^- and UV-C/CO₃^2-/HCO₃^- reactions. Nitrogenated and hydrogenated byproducts were first observed during the UV-C/NO₃^- photolysis, but only hydrogenated byproducts as adducts were detected during the UV-C/NO₃^-/CO₃^2-/HCO₃^- photolysis. Nitrogenated and hydrogenated byproducts were formed in the early stage of degradation by OH or NO₂ radicals, and these byproducts were subsequently degraded into smaller compounds with further reaction during UV-C/NO₃^- and UV-C/NO₃^-/CO₃^2-/HCO₃^- reactions. In contrast, BPA was directly degraded into smaller compounds by β-scission of the isopropyl group by CO₃^-/HCO₃ radicals during UV-C/CO₃^2-/HCO₃^- reaction. Our results imply that the water components can change the degradation mechanism of BPA during UV photolysis.

Interaction between Diethyldithiocarbamate and Cu(II) on Gold in Non-Cyanide Wastewater

A surface-enhanced Raman scattering (SERS) detection method for environmental copper ions (Cu2+) was developed according to the vibrational spectral change of diethyldithiocarbamate (DDTC) on gold nanoparticles (AuNPs). The ultraviolet-visible (UV-Vis) absorption spectra indicated that DDTC formed a complex with Cu2+, showing a prominent peak at ~450 nm. We found Raman spectral changes in DDTC from ~1490 cm-1 to ~1504 cm-1 on AuNPs at a high concentration of Cu2+ above 1 μM. The other ions of Zn2+, Pb2+, Ni2+, NH₄⁺, Mn2+, Mg2+, K⁺, Hg2+, Fe2+, Fe3+, Cr3+, Co2+, Cd2+, and Ca2+ did not produce such spectral changes, even after they reacted with DDTC. The electroplating industrial wastewater samples were tested under the interference of highly concentrated ions of Fe3+, Ni2+, and Zn2+. The Raman spectroscopy-based quantification of Cu2+ ions was able to be achieved for the wastewater after treatment with alkaline chlorination, whereas the cyanide-containing water did not show any spectral changes, due to the complexation of the cyanide with the Cu2+ ions. A micromolar range detection limit of Cu2+ ions could be achieved by analyzing the Raman spectra of DDTC in the cyanide-removed water.

Degradation mechanisms of Microcystin-LR during UV-B photolysis and UV/H2O2 processes: Byproducts and pathways

The removal and degradation pathways of microcystin-LR (MC-LR, [M+H]⁺ = 995.6) in UV-B photolysis and UV-B/H₂O₂ processes were examined using liquid chromatography-tandem mass spectrometry. The UV/H₂O₂ process was more efficient than UV-B photolysis for MC-LR removal. Eight by-products were newly identified in the UV-B photolysis ([M+H]⁺ = 414.3, 417.3, 709.6, 428.9, 608.6, 847.5, 807.4, and 823.6), and eleven by-products were identified in the UV-B/H₂O₂ process ([M+H]⁺ = 707.4, 414.7, 429.3, 445.3, 608.6, 1052.0, 313.4, 823.6, 357.3, 245.2, and 805.7). Most of the MC-LR by-products had lower [M+H]⁺ values than the MC-LR itself during both processes, except for the [M+H]⁺ value of 1052.0 during UV-B photolysis. Based on identified by-products and peak area patterns, we proposed potential degradation pathways during the two processes. Bond cleavage and intramolecular electron rearrangement by electron pair in the nitrogen atom were the major reactions during UV-B photolysis and UV-B/H₂O₂ processes, and hydroxylation by OH radical and the adduct formation reaction between the produced by-products were identified as additional pathways during the UV-B/H₂O₂ process. Meanwhile, the degradation by-products identified from MC-LR during UV-B/H₂O₂ process can be further degraded by increasing H₂O₂ dose.

Emission of greenhouse gases from waste incineration in Korea

Greenhouse gas (GHG) emission factors previously reported from various waste incineration plants have shown significant variations according to country-specific, plant-specific, and operational conditions. The purpose of this study is to estimate GHG emissions and emission factors at nine incineration facilities in Korea by measuring the GHG concentrations in the flue gas samples. The selected incineration plants had different operation systems (i.e., stoker, fluidized bed, moving grate, rotary kiln, and kiln & stoker), and different nitrogen oxide (NO_x) removal systems (i.e., selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR)) to treat municipal solid waste (MSW), commercial solid waste (CSW), and specified waste (SW). The total mean emission factors for A and B facilities for MSW incineration were found to be 134 ± 17 kg CO₂ ton^-1, 88 ± 36 g CH₄ ton^-1, and 69 ± 16 g N₂O ton^-1, while those for CSW incineration were 22.56 g CH₄ ton^-1 and 259.76 g N₂O ton^-1, and for SW incineration emission factors were 2959 kg CO₂ ton^-1, 43.44 g CH₄ ton^-1 and 401.21 g N₂O ton^-1, respectively. Total emissions calculated using annual incineration for MSW were 3587 ton CO₂-eq yr^-1 for A facility and 11,082 ton CO₂-eq yr^-1 for B facility, while those of IPCC default values were 13,167 ton CO_2-eq yr^-1 for A facility and 32,916 ton CO_2-eq yr^-1, indicating that the emissions of IPCC default values were estimated higher than those of the plant-specific emission factors. The emission of CSW for C facility was 1403 ton CO₂-eq yr^-1, while those of SW for D to I facilities was 28,830 ton CO₂-eq yr^-1. The sensitivity analysis using a Monte Carlo simulation for GHG emission factors in MSW showed that the GHG concentrations have a greater impact than the incineration amount and flow rate of flue gas. For MSW incineration plants using the same stoker type in operation, the estimated emissions and emission factors of CH₄ showed the opposite trend with those of NO₂ when the NO_x removal system was used, whereas there was no difference in CO₂ emissions.

Desorption of micropollutant from spent carbon filters used for water purifier

In this study, to examine the accumulated micropollutants in the spent carbon filter used in the water purifier, first, the method to desorb micropollutant from the activated carbon was developed and optimized. Then, using this optimized desorption conditions, we examined which micropollutants exist in spent carbon filters collected from houses in different regions in Korea where water purifiers were used. A total of 11 micropollutants (caffeine (CFF), acetaminophen (ACT), sulfamethazine (SMA), sulfamethoxazole (SMZ), metoprolol (MTP), carbamazepine (CBM), naproxen (NPX), bisphenol-A (BPA), ibuprofen (IBU), diclofenac (DCF), and triclocarban (TCB)) were analyzed using LC/MS-MS from the spent carbon filters. CFF, NPX, and DCF had the highest detection frequencies (>60%) in the carbon filters (n = 100), whereas SMA, SMZ, and MTP were only detected in the carbon filters, but not in the tap waters (n = 25), indicating that these micropollutants, which exist less than the detection limit in tap water, were accumulated in the carbon filters. The regional micropollutant detection patterns in the carbon filters showed higher levels of micropollutants, especially NPX, BPA, IBU, and DCF, in carbon filters collected in the Han River and Nakdong River basins where large cities exist. The levels of micropollutants in the carbon filter were generally lower in the regions where advanced oxidation processes (AOPs) were employed at nearby water treatment plants (WTPs), indicating that AOP process in WTP is quite effective in removing micropollutant. Our results suggest that desorption of micropollutant from the carbon filter used can be a tool to identify micropollutants present in tap water with trace amounts or below the detection limit.

Effects of molecular size fraction of DOM on photodegradation of aqueous methylmercury

This study investigated the photodegradation kinetics of MeHg in the presence of various size fractions of dissolved organic matter (DOM) with MW < 3.5 kDa, 3.5 < MW < 10 kDa, and MW > 10 kDa. The DOM fraction with MW < 3.5 kDa was most effective in MeHg photodegradation. Increasing UV intensity resulted in the increase of photodegradation rate of the MeHg in all size of DOM fractions. Higher rates of MeHg degradation was observed at higher pH. For the portion of MW < 3.5 kDa, the photodegradation rate of MeHg increased with increasing DOM concentration, indicating that radicals such as singlet oxygen (¹O₂) radicals can be effectively produced by DOM. At higher portion of MW > 3.5 kDa, the inhibition of MeHg degradation was observed due to the effect of DOM photo-attenuation. Our result indicates that radical mediated reaction is the main mechanism of photodegradation of MeHg especially in the presence of MW < 3.5 kDa. Our results imply that the smaller molecular weight fraction (MW < 3.5 kDa) of DOM mainly increased the photodegradation rate of MeHg.

Degradation mechanisms of geosmin and 2-MIB during UV photolysis and UV/chlorine reactions

We conducted chlorination, UV photolysis, and UV/chlorin reactions to investigate the intermediate formation and degradation mechanisms of geosmin and 2-methylisoborneol (2-MIB) in water. Chlorination hardly removed geosmin and 2-MIB, while the UV/chlorine reaction at 254 nm completely removed geosmin and 2-MIB within 40 min and 1 h, respectively, with lesser removals of both compounds during UV photolysis. The kinetics during both UV photolysis and UV/chlorine reactions followed a pseudo first-order reaction. Chloroform was found as a chlorinated intermediate during the UV/chlorine reaction of both geosmin and 2-MIB. The pH affected both the degradation and chloroform production during the UV/chlorine reaction. The open ring and dehydration intermediates identified during UV/chlorine reactions were 1,4-dimethyl-adamantane, and 1,3-dimethyl-adamantane from geosmin, 2-methylenebornane, and 2-methyl-2-bornene from 2-MIB, respectively. Additionally, 2-methyl-3-pentanol, 2,4-dimethyl-1-heptene, 4-methyl-2-heptanone, and 1,1-dichloro-2,4-dimethyl-1-heptane were newly identified intermediates from UV/chlorine reactions of both geosmin and 2-MIB. These intermediates were degraded as the reaction progressed. We proposed possible degradation pathways during the UV photolysis and UV/chlorine reactions of both compounds using the identified intermediates.

Characteristics of methane and nitrous oxide emissions from the wastewater treatment plant

The nitrous oxide (N2O) and methane (CH4) emissions were measured from a municipal wastewater treatment plant (WWTP) using a flux chamber to determine the emission factors. The WWTP treats sewage using both the activated-sludge treatment and anaerobic/anoxic/aerobic (A(2)O) methods. Measurements were performed in the first settling, aeration, and secondary settling basins, as well as in the sludge thickener, sludge digestion tank, and A(2)O basins. The total emission factors of N2O and CH4 from the activated-sludge treatment were 1.256gN2O/kg total nitrogen (TN) and 3.734gCH4/kg biochemical oxygen demand (BOD5), respectively. Those of the advanced treatment (A(2)O) were 1.605gN2O/kg TN and 4.022gCH4/kgBOD5, respectively. These values are applicable as basic data to estimate greenhouse gas emissions.

Adsorption characteristics of diclofenac and sulfamethoxazole to graphene oxide in aqueous solution

The adsorptive properties of graphene oxide (GO) were characterized, and the binding energies of diclofenac (DCF) and sulfamethoxazole (SMX) on GO adsorption were predicted using molecular modeling. The adsorption behaviors of DCF and SMX were investigated in terms of GO dosage, contact time, and pH. Additionally, the effects of sonication on GO adsorption were examined. GO adsorption involves "oxygen-containing functional groups" (OCFGs) such as COOH, which exhibit negative charges over a wide range of pH values (pH 3-11). DCF (-18.8 kcal mol(-1)) had a more favorable binding energy on the GO surface than SMX (-15.9 kcal mol(-1)). Both DCF and SMX were removed from solution (adsorbed to GO), up to 35% and 12%, respectively, within 6h, and an increase in GO dosage enhanced the removal of DCF. Electrostatic repulsion occurred between dissociated DCF/SMX and the more negatively charged GO at basic pH (>pKa). The sonication of GO significantly improved the removal of DCF (75%) and SMX (30%) due to dispersion of exfoliated GO particles and the reduction of OCFGs on the GO surface. Both DCF and SMX in the adsorption isotherm were explained well by the Freundlich model. The results of this study can be used to maximize the adsorption capacities of micropollutants using GO in water treatment processes.

Molecular marker characterization and source appointment of particulate matter and its organic aerosols

This study was carried out to identify possible sources and to estimate their contribution to total suspended particle (TSP) organic aerosol (OA) contents. A total of 120 TSP and PM2.5 samples were collected simultaneously every third day over a one-year period in urban area of Incheon, Korea. High concentration in particulate matters (PM) and its components (NO3(-), water soluble organic compounds (WSOCs), and n-alkanoic acids) were observed during the winter season. Among the organics, n-alkanes, n-alkanoic acids, levoglucosan, and phthalates were major components. Positive matrix factorization (PMF) analysis identified seven sources of organic aerosols including combustion 1 (low molecular weight (LMW)-polycyclic aromatic hydrocarbons (PAHs)), combustion 2 (high molecular weight (HMW)-PAHs), biomass burning, vegetative detritus (n-alkane), secondary organic aerosol 1 (SOA1), secondary organic aerosol 2 (SOA2), and motor vehicles. Vegetative detritus increased during the summer season through an increase in biogenic/photochemical activity, while most of the organic sources were prominent in the winter season due to the increases in air pollutant emissions and atmospheric stability. The correlation factors were high among the main components of the organic carbon (OC) in the TSP and PM2.5. The results showed that TSP OAs had very similar characteristics to the PM2.5 OAs. SOA, combustion (PAHs), and motor vehicle were found to be important sources of carbonaceous PM in this region. Our results imply that molecular markers (MMs)-PMF model can provide useful information on the source and characteristics of PM.

Spatial and temporal variation of total mercury and methylmercury in lacustrine wetland in Korea

The spatial and temporal variations of total mercury (THg) and methylmercury (MeHg) concentrations (n = 120, respectively) in water and sediments of the Yangsuri lacustrine wetland in Korea were measured. The average concentrations of THg and MeHg in surface water were 2.04 ± 1.97 and 0.05 ± 0.05 ng L(-1), respectively. The concentrations of THg and MeHg in sediments ranged from 1.28 to 85.83 and ≤0.01 to 0.35 ng g(-1), respectively, and varied depending on the location. In the vegetated zone located near residential areas, the highest concentrations of THg and MeHg in both surface water and sediments were obtained near the residential areas, especially during the fall season. This result might be due to increased methylation rate of Hg by water turnover in the fall season. While THg and MeHg concentrations in water were not correlated, they were significantly correlated in sediment (r = 0.75; P < 0.01). Log-transformed Hg concentrations in sediments were highly correlated with log-transformed organic matter (OM) and acid volatile sulfide (AVS) concentrations (P < 0.01). We also collected five species of fish near the output point of the wetland, and MeHg concentrations in fish tissue varied from 21.30 to 154.66 μg kg(-1) w/w, which was significantly dependent on fish species (P < 0.05). This is the first reported study which measured the levels of mercury, especially MeHg in the wetlands, and freshwater fish species in Korea.