Characteristics, Possible Origins, and Health Risk Assessment of Trace Elements in Surface Waters of the Han River Watershed, South Korea.

To safeguard aquatic environments in and around the Han River watershed in South Korea, a multivariate statistical evaluation of trace elements, a trace element concentration analysis and source determination, and a human health risk assessment were conducted on 10 trace elements at 25 sites. The results demonstrated that the Han River watershed was mainly affected by anthropogenic activities (traffic/industrial activity). The range of concentrations was arranged in descending order: Fe (217.13 ± 301.03 µg/L) > Mn (102.36 ± 153.04 µg/L) > Zn (23.33 ± 79.63 µg/L) > Ba (29.05 ± 12.37 µg/L) > Ni (5.14 ± 11.57 µg/L) > Cu (3.80 ± 3.56 µg/L) > Pb (0.46 ± 0.52 µg/L) > Se (0.06 ± 0.04 µg/L) > Cd (0.01 ± 0.01 µg/L) > Ag (0.004 ± 0.013 µg/L). The hazard index values of trace elements in surface water for combined pathways (ingestion and dermal contact) were < 1.0 for both adults and children, indicating no possible human health hazards. The estimated total cancer risk did not exceed the acceptable limit (1 × 10-4) for adults and children. The findings of this study provide data-driven guidelines for water environment policy decisions in the study area.

Spatio-Temporal Distribution and Influencing Factors of Human and Veterinary Pharmaceuticals in the Tributary Surface Waters of the Han River Watershed, South Korea.

Human and veterinary pharmaceuticals are being increasingly used for disease treatment; hence, their distribution and factors influencing them in the aquatic environment need to be investigated. This study observed the effect of human and animal populations, usage, purchasing criteria (prescription vs. non-prescription), and land use to identify the spatio-temporal distribution of eight pharmaceuticals at twenty-four sites of the tributaries of the Han River watershed. In rural areas, the mean concentration (detection frequency) of non-prescription pharmaceuticals (NPPs) was higher (lower) compared to that of prescription pharmaceuticals (PPs); in urban areas, a reverse trend was observed. Pharmaceutical concentrations in urban and rural areas were mainly affected by wastewater treatment plants (WWTPs) and non-point sources, respectively; concentrations were higher downstream (4.9 times) than upstream of the WWTPs. The concentration distribution (according to the target) was as follows: human-veterinary > human > veterinary. Correlation between total concentration and total usage of the pharmaceuticals was high, except for NPPs. Most livestock and land use (except cropland) were significantly positively correlated with pharmaceutical concentrations. Concentrations were mainly higher (1.5 times) during cold seasons than during warm seasons. The results of this study can assist policymakers in managing pharmaceutical pollutants while prioritizing emerging pollutants.

Influence of Zooplankton and Environmental Factors on Clear-Water Phase in Lake Paldang, South Korea.

Lake Paldang is a complex water system with both fluvial and lacustrine characteristics and the largest artificial dam lake in South Korea. In this study, the different occurrence patterns and causes of the clear-water phase (CWP) were investigated using water quality and hydrological factors at four sites in Lake Paldang. Among the environmental and other factors associated with CWP occurrence, secchi depth and turbidity exhibited significant correlations with precipitation, hydraulic retention time (HRT), and individual and relative abundance (RA) of zooplankton (Cladocera) (p < 0.01). Hence, a change in the HRT because of precipitation could alter the CWP. The Cladocera individuals and RA showed significant correlations with the water temperature, indicating that the emergence of Cladocera in spring as the water temperature rises could cause the CWP. Sensitivity assessments conducted using Bayesian models demonstrated different CWP occurrence sensitivity relationships for the river-type, lake-type, and shallow and deep sites. Turbidity, secchi depth, and zooplankton factors also showed sensitive relationships with CWP occurrence for all sites. The sensitivity to precipitation and HRT was higher in the river-type sites. The lake-type sites, with common Cladocera emergence and long HRT, favored CWP occurrence. Thus, CWP occurrence was dependent on the site characteristics and climate conditions.

Occurrence, Potential Sources, and Risk Assessment of Volatile Organic Compounds in the Han River Basin, South Korea.

Increasing public awareness about the aesthetics and safety of water sources has shifted researchers' attention to the adverse effects of volatile organic compounds (VOCs) on humans and aquatic organisms. A total of 17 VOCs, including 10 volatile halogenated hydrocarbons and seven volatile non-halogenated hydrocarbons, were investigated at 36 sites of the Han River Basin, which is the largest and most important drinking water source for residents of the Seoul metropolitan area and Gyeonggi province in South Korea. The VOC concentrations ranged from below detection limits to 1.813 µg L-1. The most frequently detected VOC was 1,2-dichloropropane, with a detection frequency of 80.56%, as it is used as a soil fumigant, chemical intermediate, and industrial solvent. In terms of geographical trends, the sampling sites that were under the influence of sewage and industrial wastewater treatment plants were more polluted with VOCs than other areas. This observation was also supported by the results of the principal component analysis. In the present study, the detected concentrations of VOCs were much lower than that of the predicted no-effect concentrations, suggesting low ecological risk in the Han River. However, a lack of available ecotoxicity data and limited comparable studies warrants further studies on these compounds.

Review of MXene-based nanocomposites for photocatalysis.

Since multilayered MXenes (Ti3C2Tx, 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.

Temporal-spatial variation and environmental risk assessment of pharmaceuticals in tributaries of the Han River watershed, South Korea.

Eight compounds from three categories of pharmaceuticals [5 antibiotics, 2 non-steroidal anti-inflammatory drugs, and 1 anti-epileptics] were monitored at 24 sites in the tributaries of the Han River watershed in South Korea, 2016. The seasonal occurrence, temporal-spatial variation, potential compound source(s), and a risk assessment of this watershed, which is the largest drinking water source in the country, were investigated. Clarithromycin was detected most frequently (72.2%) with the greatest median concentration (0.151 ± 0.072 µg L-1), followed by carbamazepine and sulfamethoxazole. The seasonality of the pharmaceuticals was observed, with higher concentrations and detection frequencies in spring than in summer and autumn; this was possibly caused by lower levels of microbial activities associated with lower water temperatures than other seasons. In terms of geographical variation, urban areas had higher pharmaceutical concentrations than rural areas, which was attributed to the former's high population density and largest wastewater treatment plants (WWTPs) regardless of season. The total concentration and detection frequency of WWTPs were 12.4 and 2.5 times higher in downstream sites than upstream sites, thereby conveying that WWTPs were the main source for the presence of pharmaceuticals in tributaries. According to the results produced from calculations of the risk quotient (RQ) of aquatic organisms, clarithromycin and sulfamethazine were identified as posing relatively high ecological risk (RQ > 1) during the spring that was identified for this study. This study can provide policymakers with scientific support for prioritizing pollutant management and collections of global data on emerging pollutants.

Pharmaceutical compounds in tributaries of the Han River watershed, South Korea.

The Han River watershed is the largest and most important source of drinking water for the residents of the Seoul metropolitan area and the Gyeonggi province in South Korea. The tributaries of the watershed are vulnerable to contamination by effluents from nearby wastewater treatment plants (WWTPs) and non-point sources. In this study, a one-year monitoring study was performed to investigate the occurrence of 13 pharmaceuticals in 24 tributaries of the Han River watershed in October 2015. From the 13 pharmaceuticals, 12 were found in at least one sample, with the exception of chlortetracycline, which was not detected. The three most frequently detected compounds were clarithromycin (95.8%), carbamazepine (66.7%), and lincomycin (62.5%). Compounds found in high concentrations included clarithromycin (5.2675 µg L-1), ibuprofen (1.9646 µg L-1), and carbamazepine (1.1009 µg L-1). The total concentration of 12 pharmaceuticals in the Seoul metropolitan area (0.7128 µg L-1) was higher than that in the Gyeonggi area (0.3177 µg L-1) possibly due to the large-scale WWTPs located upstream. However, in IHR-3, which is located at the very upstream of the tributary and is not impacted by a WWTP, pharmaceuticals were not detected. This can be explained by the fact that most pharmaceuticals derived from WWTPs are related to human activity. The risk quotients (RQs) for the target pharmaceuticals were calculated on the basis of their presence in tributaries, and all pharmaceuticals presented RQs < 0.01, indicating that potential environmental impacts should be low. These results will be useful to monitor and assess the potential environmental risks of pharmaceuticals in the surface water.

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.

Ultrasonic degradation of acetaminophen and naproxen in the presence of single-walled carbon nanotubes.

Ultrasonic (US) and single-walled carbon nanotube (SWNT)-catalyzed ultrasonic (US/SWNT) degradation of a pharmaceutical (PhAC) mixture of acetaminophen (AAP) and naproxen (NPX) used as analgesics was carried out in water. In the absence of SWNTs, maximum degradations of AAP and NPX occurred at a high frequency (1000 kHz) and under acidic conditions (pH 3) and different solution temperatures (25 °C at 28 kHz and 35 °C at 1000 kHz) during US reactions. Rapid degradation of PhACs occurred within 10 min at 28 kHz (44.5% for AAP; 90.3% for NPX) and 1000 kHz (39.2% for AAP; 74.8% for NPX) at a SWNT concentration of 45 mgL(-1) under US/SWNT process, compared with 28 kHz (5.2% for AAP; 10.6% for NPX) and 1000 kHz (29.1% for AAP; 46.2% for NPX) under US process. Degradation was associated with the dispersion of SWNTs; small particles acted as nuclei during US reactions, enhancing the H2O2 production yield. NPX removal was greater than AAP removal under all US-induced reaction and SWNT adsorption conditions, which is governed by the chemical properties of PhACs. Based on the results, the optimal treatment performance was observed at 28 kHz with 45 mgL(-1) SWNTs (US/SWNT) within 10 min.

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.

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.

Wastewater treatment plants (WWTPs)-derived national discharge loads of perfluorinated compounds (PFCs).

The discharge of perfluorinated compounds (PFCs) was investigated for 15 wastewater treatment plants (WWTPs), comprising 25% of total domestic wastewater and 23% of total industrial wastewater produced in Korea. PFCs concentrations in influent, effluent, and sludge were greater in industrial wastewater than in the majority of domestic wastewater. Individual PFCs were found to have differing industrial sources, with perfluorocarboxylates used in fabric/textiles, paper-mill, and dyeing industries, and perfluoroalkylsulfonates occurring in oil/chemical and metal-plating/processing industries. Total WWTP-derived national discharge loads were calculated based on the average concentrations in effluents and the total volume of wastewaters produced in Korea. The average WWTP-derived national discharge loads of individual PFCs were 0.04-0.61 ton/year, with 63% of perfluorooctanoate being from domestic wastewater, and 75% of perfluorooctanesulfonate being from industrial wastewater. These estimates accounted for the majority of national emissions, based on measurements in major river mouths, indicating the major contribution of WWTPs to PFC occurrence in Korean aquatic environments. Both the per capita emission factor (µg/capita/day) for domestic discharge, and area-normalized national discharge loads (g/capita/km(2)/day) for all wastewaters were several factors lower in Korea than in Japan or Europe, which is consistent with the lower levels of human exposure to PFCs in Korea.

Perchlorate removal in Fe0/H2O systems: Impact of oxygen availability and UV radiation.

In this study, the removal of perchlorate (0.016mM) using Fe(0)-only (325 mesh, 10g L(-1)) and Fe(0) (10g L(-1)) with UV (254nm) reactions were investigated under oxic and anoxic conditions (nitrogen purging). Under anoxic conditions, only 2% and 5.6% of perchlorate was removed in Fe(0)-only and Fe(0)/UV reactions, respectively, in a 12h period. However, under oxic conditions, perchlorate was removed completely in the Fe(0)-only reaction, and reduced by 40% in the Fe(0)/UV reaction, within 9h. The pseudo-first-order rate constant (k(1)) was 1.63×10(-3)h(-1) in Fe(0)-only and 4.94×10(-3)h(-1) in Fe(0)/UV reaction under anoxic conditions. Under oxic conditions, k(1) was 776.9×10(-3)h(-1) in Fe(0)-only reaction and 35.1×10(-3)h(-1) in the Fe(0)/UV reaction, respectively. The chlorine in perchlorate was recovered as chloride ion in Fe(0)-only and Fe(0)/UV reactions, but lower recovery of chloride under oxic conditions might due to the adsorption/co-precipitation of chloride ion with the iron oxides. The removal of perchlorate in Fe(0)/UV reaction under oxic conditions increased in the presence of methanol (73%, 9h), a radical scavenger, indicating that OH radical can inhibit the removal of perchlorate. The removal of perchlorate by Fe(0)-only reaction under oxic condition was highest at neutral pH. Application of the Langmuir-Hinshelwood model indicated that removal of perchlorate was accelerated by adsorption/co-precipitation reactions onto iron oxides and subsequent removal of perchlorate during further oxidation of Fe(0). The results imply that oxic conditions are essential for more efficient removal of perchlorate in Fe(0)/H(2)O system.

A Fenton-like degradation mechanism for 1,4-dioxane using zero-valent iron (Fe0) and UV light.

In this study, the degradation mechanism of 1,4-dioxane using zero-valent iron (Fe0) in the presence of UV light was investigated kinetically. The degradation of 1,4-dioxane in Fe0-only, photolysis, and combined Fe0 and UV reactions followed the kinetics of a pseudo-first-order model. The degradation rate constant (19 x 10(-4)min(-1)) in the combined reaction with UV-C (4.2 mW cm(-2)) and Fe0 (5 mg L(-1)) was significantly enhanced compared to Fe0-only (4.8 x 10(-4) min(-1)) and photolytic reactions (2.25 x 10(-4)min(-1)), respectively. The removal efficiency of 1,4-dioxane in combined reaction with Fe0 and UV within 4 h was enhanced by increasing UV intensity at UV-C region (34% at 4.2 mW cm(-2) and 89% at 16.9 mW cm(-2)) comparing with the removal in the combined reaction with Fe0 and UV-A (29% at 2.1 mW cm(-2), and 33% at 12.6 mW cm(-2)). It indicates that 1,4-dioxane was degraded mostly by OH radicals in the combined reaction. The degradation patterns in both Fe(0)-only and combined reactions were well fitted to the Langmuir-Hinshelwood model, implying that adsorption as well as the chemical reaction occurred. The transformation of Fe0 to Fe2+ and Fe3+ was observed in the Fe0-only and combined reactions, and the transformation rate of Fe0 was improved by UV irradiation. Furthermore, the reduction of Fe3+ was identified in the combined reaction, and the reduction rate was enhanced by an increase of UV energy. Our study demonstrated that the enhancement of 1,4-dioxane removal rate occurred via an increased supply of OH radicals from the Fenton-like reaction induced by the photolysis of Fe0 and H2O, and with producing less sludge.