Health risk assessment of uranium intake from private residential drinking groundwater facilities based on geological characteristics across the Republic of Korea.

Groundwater contributes to an average of 8 % of the total water source capacity in the Republic of Korea. Hence, private residential households in rural areas in Korea are still using groundwater for drinking without any regular water quality inspection. This can increase the risk of exposure to natural radionuclides like uranium through drinking groundwater. This study investigated the uranium level in drinking groundwater all over the country by analyzing 11,451 samples from private residential drinking groundwater facilities and compared the exposure amount and its associated carcinogenic and non-carcinogenic risk based on the geological characteristics of the aquifer. Results yield that although the average hazard quotient (HQ) and excess cancer risk (ECR) of exposure to natural uranium through drinking groundwater were respectively below 1 and 1 × 10-6 and do not indicate a potential health hazard, significantly high HQ and ECR up to respectively 70 and 4 × 10-4 in samples where the aquifer is the Jurassic granite observed. Accordingly, regular water quality investigation and onsite treatment methods are required to provide healthy drinking water in such areas.

Prediction of groundwater quality index to assess suitability for drinking purpose using averaged neural network and geospatial analysis.

Groundwater quality management is pivotal for ensuring public health and ecological resilience. However, the conventional water quality indices often face challenges related to parameter selection, geographic coverage, and scalability. The integration of machine learning and spatial analysis represents a promising methodological shift, allowing for high accuracy and adaptive management strategies. The Safe Groundwater Project in Unsupplied Areas (2017-2020) employed a comprehensive Groundwater Quality Index (GQI) to evaluate potable groundwater quality across South Korea, utilizing a large dataset comprising 28 water quality parameters and 3552 wells. This study revealed that over 50 % of the evaluated wells (Total 8326 wells) were inappropriate as sources of drinking water, indicating a pressing need for policy revision. The averaged neural network model achieved a high predictive accuracy of approximately 95 % for GQI grades, outperforming other classification models. The introduction of 2D spatial analysis in conjunction with machine learning algorithms notably increased the predictive accuracy for unevenly distributed groundwater samples. Moreover, this combined approach enabled the intuitive visualization of groundwater vulnerability across various regions, which can inform targeted interventions for effective resource allocation and management. This research represents a methodologically robust, interdisciplinary approach that holds significant implications for a framework for future groundwater quality management and vulnerability assessment.

Characterization of seasonal behaviors of naturally occurring radioactive materials in a groundwater borehole using an in situ monitoring system.

Understanding the temporal behaviors of naturally occurring radioactive materials is important for safeguarding groundwater as a secure water resource for drinking, agriculture, and industry usage. This study reports the vertical profiles of 238U concentration and 222Rn activity and the management of in situ monitoring systems during intensive field sampling of a national groundwater-monitoring borehole for seven years (2015-2021). The aim was to capture the seasonal characteristics of the 238U concentrations and 222Rn activity. Both factors were low in the rainy season and high in the winter season, reflecting the dilution effect of rainfall recharge. The 238U and 222Rn behaviors were associated with water-rock interactions of calcite dissolution in fracture zones filled with carbonate minerals. Furthermore, multilayer perceptron models estimated the 238U concentration and 222Rn activity with reasonable regression and classification accuracy. Hydrometeorological indicators (temperature and groundwater-level fluctuations) were more important estimators of 238U concentration and 222Rn activity than geochemical process indicators. The regression accuracy performance was higher at deeper sampling depths, where seasonality in the 238U and 222Rn behaviors dominated. From the predicted distributions of 238U concentrations and 222Rn activities, we could estimate the ranges of 238U concentrations and 222Rn activities emerging from groundwater boreholes. High exposure threats from 238U and 222Rn during groundwater usage were found in the winter season. When the multilayer perceptron models use the entire in situ monitoring data at refined temporal resolution, we can quickly determine the naturally occurring radioactive materials and further develop the national groundwater-monitoring borehole equipped with the in-situ monitoring system, supplementing the occasionally obtained field-measurement data.

Uranium Concentrations in Private Wells of Potable Groundwater, Korea.

Uranium (U) is one of the typical naturally occurring radioactive elements enriched in groundwater through geological mechanisms, thereby bringing about adverse effects on human health. For this reason, some countries and the World Health Organization (WHO) regulate U with drinking water standards and monitor its status in groundwater. In Korea, there have been continuous investigations to monitor and manage U in groundwater, but they have targeted only public groundwater wells. However, the features of private wells differ from public ones, particularly in regard to the well's depth and diameter, affecting the U distribution in private wells. This study was initiated to investigate U concentrations in private groundwater wells for potable use, and the significant factors controlling them were also elucidated through statistical methods. The results obtained from the analyses of 7036 groundwater samples from private wells showed that the highest, average, and median values of U concentrations were 1450, 0.4, and 4.0 µg/L, respectively, and 2.1% of the wells had U concentrations exceeding the Korean and WHO standard (30 µg/L). In addition, the U concentrations were highest in areas of the Jurassic granite, followed by Quaternary alluvium and Precambrian metamorphic rocks. A more detailed investigation of the relationship between U concentration and geology revealed that the Jurassic porphyritic granite, mainly composed of Daebo granite, showed the highest U contents, which indicated that U might originate from uraninite (UO2) and coffinite (USiO4). Consequently, significant caution should be exercised when using the groundwater in these geological areas for potable use. The results of this study might be applied to establish relevant management plans to protect human health from the detrimental effect of U in groundwater.

Time from Exposure to Diagnosis among Quarantined Close Contacts of SARS-CoV-2 Omicron Variant Index Case-Patients, South Korea.

To determine optimal quarantine duration, we evaluated time from exposure to diagnosis for 107 close contacts of severe acute respiratory syndrome coronavirus 2 Omicron variant case-patients. Average time from exposure to diagnosis was 3.7 days; 70% of diagnoses were made on day 5 and 99.1% by day 10, suggesting 10-day quarantine.

Importation and Transmission of SARS-CoV-2 B.1.1.529 (Omicron) Variant of Concern in Korea, November 2021.

In November 2021, 14 international travel-related severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.529 (omicron) variant of concern (VOC) patients were detected in South Korea. Epidemiologic investigation revealed community transmission of the omicron VOC. A total of 80 SARS-CoV-2 omicron VOC-positive patients were identified until December 10, 2021 and 66 of them reported no relation to the international travel. There may be more transmissions with this VOC in Korea than reported.

Ni0.67Fe0.33 Hydroxide Incorporated with Oxalate for Highly Efficient Oxygen Evolution Reaction.

As the oxygen evolution reaction (OER) imposes a high energy barrier during electrochemical water splitting, designing highly efficient, stable, and cost-effective electrocatalysts for OERs is an ongoing challenge. In this study, we present a facile approach to prepare villi-shaped Ni-Fe hydroxides incorporated with oxalate derived from Ni-Fe oxalate through the in situ precipitation growth and subsequent immersion in an alkaline solution. The electrode with an optimized Ni-Fe ratio improves the OER kinetics, on which the electronic structure of the active site is adjusted based on a mutual effect between the adjacent nickel and iron atoms. The OER performance was significantly better than that of monometallic Ni(OH)2 and pristine Ni foam, with a low overpotential of 277 mV at 100 mA cm-2 and excellent stability. The enhanced OER performance is ascribed to the advanced intrinsic electrocatalytic activity of the electrode as a result of the synergetic effect of optimized Ni-Fe ratio mixing at the atomic level which leads to an increased surface area, a high number of active sites, and a reduced charge transfer resistivity.

Characterizing land use effect on shallow groundwater contamination by using self-organizing map and buffer zone.

Nitrate-nitrogen (NO3-N) contamination in groundwater is a major problem of drinking and domestic waters in rural areas. This study revealed the influence of land use type on shallow alluvial groundwaters in a typical rural area in South Korea by applying a self-organizing map (SOM), principal component analysis (PCA), and hierarchical cluster analysis (HCA). The uncertainty of spatial information on land use was improved by using a buffer zone of the average influence radius of 32.65 m surrounding wells. Two major land-use types, forests (44.9%) and rice fields (28.8%), occupied a total of 73.7% of the rural area. The higher concentrations of NO3-N in public facilities and livestock areas were demonstrated to directly recharge groundwater pollutants. NO3-N contamination in rice paddies, which also contained chlorine (Cl) and sulfate (SO4), was assessed according to the nutrients and residual salt in the soil. In addition, different NO3-N concentrations for the same land use indicate various biochemical reactions and NO3-N recharge types into the groundwater system. The shallow groundwaters in the study area were classified into three clusters according to their chemical constituents and land-use properties, especially NO3-N concentration, including pH, Cl, and SO4, using a SOM, PCA, and HCA. Unlike existing studies, we applied a buffer zone based on the Cooper-Jacob equation to obtain an improved SOM model prediction accuracy approximately 10% greater than that using the original dataset.

Contribution of nitrate-nitrogen concentration in groundwater to stream water in an agricultural head watershed.

This study characterized nitrate-nitrogen (NO3-N) concentrations in groundwater and stream water in an agricultural head watershed in South Korea and identified the pollution load of NO3-N as a result of the groundwater entering streams using field surveys, analyses of chemical constituents, and numerical modeling. The mean NO3-N concentration in groundwater was 7.373 mg/L, which is approximately 1.9 times higher than concentrations found in stream water. The groundwater and stream water samples belonged to the Ca-HCO3 type. The concentration of NO3-N in groundwater tended to increase in the lowland areas downstream. There was seasonal variations of NO3-N in both the groundwater and stream water samples, with increases in concentration during the dry season (January-April) and decreases during the wet season (June-October). The NO3-N load in stream water to that in groundwater (R) was higher during the wet season (September) than the dry season (March), with R distinctly increasing in upstream areas relative to downstream areas, indicating that during the wet season, a large amount of NO3-N is introduced into stream water from groundwater. By analyzing the relationship between groundwater and stream water and through NO3-N transport modeling, it was revealed that in the watershed, the nitrate-N load in stream water is greatly augmented by inputs from groundwater, particularly in the middle and downstream areas.

Efficacy of in situ well-based denitrification bio-barrier (WDB) remediating high nitrate flux in groundwater near a stock-raising complex.

This study assessed the feasibility of an in situ well-based denitrification bio-barrier (WDB) for managing groundwater contaminated with high-strength nitrate. To evaluate the efficacy of WDB using fumarate as a carbon source and/or electron donor, three sequential single-well push-pull tests (SWPPTs) were conducted at six test sites. The values of the isotope enrichment factor (ɛ) ranging from -6.5‰ to -22.6‰ and the detection and degradation of nitrite and nitrous oxide confirmed complete in situ denitrification of nitrate to nitrogen gas. The ratio of the first-order rate coefficient of fumarate to nitrate (k1,fum/k1,NO3) was obtained to estimate the amount and frequency of fumarate injection for the effective design of WDB. At three sites, the ratios ranged from 0.67 to 0.80, while the other two sites showed higher ratios of 2.97 and 2.20 than the theoretical values and significant amounts of sulfate reduction, theoretically equivalent to 6.5% of total fumarate consumption. Considering the theoretical mole ratio of fumarate to nitrate of 0.98, the amount and frequency of fumarate injection is site specific. During the operating WDB, the average annual nitrate mass degraded (95% CI) was 2.2 ± 1.0 kg N/yr/well. The amount of N reduced by one well of WDB is equivalent to treating 110 m3 of groundwater at 30 mg N/L to the level of 10 mg N/L for one year. WDB would be an effective remediation option for managing high nitrate flux in groundwater.

Air-Stable Aerophobic Polydimethylsiloxane Tube with Efficient Self-Removal of Air Bubbles.

The adherence of underwater air bubbles to surfaces is a serious cause of malfunction in applications such as microfluidics, transport, and space devices. However, realizing spontaneous and additional unpowered transport of underwater air bubbles inside tubes remains challenging. Although superhydrophilic polydimethylsiloxane (PDMS) tubes are attracting attention as air bubble repellents, superhydrophilic PDMS, which is fabricated via oxygen plasma treatment, has a disadvantage in that it is weak against aging. Here, we present a tube with the ability to self-remove air bubbles, which overcomes the drawback of rapid aging. PDMS containing Silwet L-77 with a hierarchical nano-microstructure exhibiting subaqueous aerophobicity was fabricated. We conducted adherence and saturation experiments of air bubbles using the fabricated PDMS tube with Silwet L-77 to investigate the mechanism of bubbles adhering to and separating from the fabricated tube surface. The developed PDMS with Silwet L-77 exhibits a strong self-removal effect with an air bubble removal of 97.7%. The adherence and saturation experiments suggest that the transparent superhydrophilic-underwater aerophobic PDMS is a potentially exceptional tool for spontaneously separating air bubbles attached to tube surfaces.

Occurrence and distribution of pharmaceutical and personal care products, artificial sweeteners, and pesticides in groundwater from an agricultural area in Korea.

This study investigated the occurrence and distribution of 33 pharmaceutical and personal care products (PPCPs), five artificial sweeteners (ASs), and six pesticides in groundwater in rural agricultural and rural non-agricultural area in South Korea. A total of 31 target compounds (15 antibiotics, four anthelmintics, seven other PPCPs, four ASs, and one pesticide) were detected in agricultural groundwater at concentrations from not detected (ND) to 49.3 ng/L for PPCPs, ND to 1340 ng/L for ASs, and ND to 116 ng/L for pesticides. Four target compounds (two PPCPs and two ASs) were detected in rural non-agricultural groundwater in the range of 0.085-5.74 ng/L for PPCPs and 5.64-1330 ng/L for ASs. Among the target compounds, ASs, especially acesulfame (detection frequency 69% in rural agricultural areas and 100% in the rural non-agricultural area) were predominantly detected in both agricultural (mean: 32.9 ng/L) and non-agricultural (mean: 536 ng/L) groundwater, but different occurrence patterns were observed according to the sources of contamination. Known markers of sewage leakage were detected in both agricultural and non-agricultural groundwater samples (e.g., acesulfame (69% and 100%), caffeine (88% and 100%), and crotamiton (62% and 100%)), while compounds related to agricultural activities were only observed in agricultural groundwater (e.g., sulfathiazole (38%), sulfamethoxazole (31%), oxfendazole (69%), and carbofuran (42%)).

The Application of REDOR NMR to Understand the Conformation of Epothilone B.

The structural information of small therapeutic compounds complexed in biological matrices is important for drug developments. However, structural studies on ligands bound to such a large and dynamic system as microtubules are still challenging. This article reports an application of the solid-state NMR technique to investigating the bioactive conformation of epothilone B, a microtubule stabilizing agent, whose analog ixabepilone was approved by the U.S. Food and Drug Administration (FDA) as an anticancer drug. First, an analog of epothilone B was designed and successfully synthesized with deuterium and fluorine labels while keeping the high potency of the drug; Second, a lyophilization protocol was developed to enhance the low sensitivity of solid-state NMR; Third, molecular dynamics information of microtubule-bound epothilone B was revealed by high-resolution NMR spectra in comparison to the non-bound epothilone B; Last, information for the macrolide conformation of microtubule-bound epothilone B was obtained from rotational-echo double-resonance (REDOR) NMR data, suggesting the X-ray crystal structure of the ligand in the P450epoK complex as a possible candidate for the conformation. Our results are important as the first demonstration of using REDOR for studying epothilones.