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 Ksa 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.

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.

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).

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.

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.

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

ß-cyclocitral and ß-ionone are ones of major algal odorants produced by oxidation of the ß-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. ß-ionone showed faster degradation compared to ß-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 ß-ionone and 50% removal of ß-cyclocitral. Unlike ß-ionone, ß-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 ß-ionone was the main site for chloroform production. Several byproducts during UV photolysis and UV-chlorination of ß-ionone were identified by GC-MS, and these were degraded with further reaction by UV-induced isomerization, OH radical, and bond scission mechanisms. ß-cyclocitral was formed as byproducts during UV-chlorination of ß-ionone. Based on degradation byproducts, the degradation pathways of ß-ionone and ß-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 ß-cyclocitral and ß-ionone.

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.

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.

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 (NOx) 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 CO2-eq yr-1 for A facility and 32,916 ton CO2-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 NOx removal system was used, whereas there was no difference in CO2 emissions.

Optimization of naproxen and ibuprofen removal in photolysis using a Box-Behnken design: effect of Fe(III), NO3-, and humic acid.

This study investigated the roles and optimum conditions of four independent variables [ultraviolet (UV) intensity, Fe(III), NO3 (-), and humic acid (HA) concentration] in the photolytic removal of naproxen (NPX) and ibuprofen (IBP) in water using a response surface method based on the Box-Behnken design. Lab-scale experiments used analysis of variance and t-test statistics to test the significance of independent variables and their interactions. Predicted levels of NPX and IBP removals were found to be in good agreement with experimental levels (R(2) = 0.9891 for NPX and 0.9936 for IBP). UV intensity and HA were the most positively and negatively significant variables (P < 0.001), respectively. However, Fe(III) and NO3 (-) ions had a less significant impact (P > 0.05). This result implies that NPX was removed by both direct photolysis (photons) and indirect reaction (OH radical), while IBP was removed mainly by the OH radical. NPX was more susceptible to the OH radical than IBP (kOH/NPX = 8.24 × 10(9) M(-1)s(-1) and kOH/IBP = 7.51 × 10(9) M(-1)s(-1)). According to a quadratic regression model, the predicted maximum removal efficiencies for NPX and IBP were 71.66% and 63.58% when the predicted optimum ratio of UV (mW cm(-2)):Fe(III) (mg/L):NO3(-) (mg/L):HA (mg/L) was 6.3:0.94:0:0 and 6.3:0.94:20:0, respectively, which was similar to the respective experimental NPX and IBP removal values of 70.21% and 62.16%. Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of Environmental Science and Health, Part A, to view the supplemental file.

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.

Optimization of photolysis of diclofenac using a response surface methodology.

This study investigates the effects of environmental parameters such as UV intensity (X(1), 2.1 ∼ 6.3 mW/cm(2)), Fe(III) (X(2), 0 ∼ 0.94 mg/L), NO(3)(-) (X(3), 0 ∼ 20 mg/L) and humic acid (X(4), 0 ∼ 30 mg/L) on the removal efficiency of diclofenac (DCF, Y), and optimization using a response surface methodology (RSM) based on Box-Behnken design (BBD). According to analysis of variance and t-test results (p < 0.001), the proposed quadratic BBD model based on a total of 29 experimental runs fitted well to the experimental data. Moreover, the determination coefficient (R(2) = 0.990) and adjusted determination coefficient (R(a)(2) = 0.981) indicated that this model is adequate with a high goodness-of-fit. Variables of X(1), X(2) and X(3) had significant positive contributions (p < 0.001), while X(4) had significant negative contribution to the DCF removal (p < 0.001). A Pareto analysis showed that X(4) was the most important factor (57.18%) in DCF photolytic removal. The predicted and observed DCF removal were 94.98 and 94.2% under optimal conditions (X(1) = 6.29 mW/cm(2), X(2) = 0.75 mg/L, X(3) = 15.65 mg/L and X(4) = zero), respectively. The RSM not only gives valuable information on the interactions between these photoreactive species (UV intensity, Fe(III), NO(3)(-), and humic acid) that influence DCF removal, but also identifies the optimal conditions for effective DCF removal in water.

Occurrence of disinfection by-products in tap water distribution systems and their associated health risk.

The concentrations of trihalomethanes (THMs), including chloroform, bromodichloromethane, dibromochloromethane, and bromoform, and haloacetic acids (HAAs; monochloroacetic acid, monobromoacetic acid, dibromoacetic acid, dichloroacetic acid, and trichloroacetic acid) were measured in tap waters passing through water distribution systems of six water treatment plants in Seoul, Korea, and their associated health risks from exposure to THMs through ingestion, dermal contact, and inhalation were estimated using a probabilistic approach. The concentration ranges for total THMs and HAA5 were 3.9-53.5 and

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.

Carbamazepine degradation by photolysis and titanium dioxide photocatalysis.

We investigated the degradation of carbamazepine by photolysis/ultraviolet (UV)-C only and titanium dioxide photocatalysis. The degradation of carbamazepine by UV-only and titanium-dioxide-only (adsorption) reactions were inefficient, however, complete degradation of carbamazepine was observed by titanium dioxide photocatalysis within 30 min. The rate of degradation increased as initial carbamazepine concentration decreased, and the removal kinetics fit well with the Langmuir-Hinshelwood model. The addition of methanol, a radical scavenger, decreased carbamazepine removal, suggesting that the hydroxide radical played an important role during carbamazepine degradation. The addition of oxygen during titanium dioxide photocatalysis accelerated hydroxide radical production, thus improving mineralization activity. The photocatalytic degradation was more efficient at a higher pH, whereas the removal of carbamazepine and acridine (a major intermediate) were more efficient under aerobic conditions. The mineralization of carbamazepine during photocatalysis produced various ionic by-products such as ammonium and nitrate by way of nitrogen dioxide.

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.

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.