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The water and oxygen contents of the vadose zone change cyclically depending upon the meteorological condition (e.g., intermittent rainfall), which can affect the biogeochemical reactions that govern the fate of arsenic (As). To simulate and evaluate the transient behavior of As in this zone when subjected to repeated wet and dry conditions, soil column experiments with different soil properties were conducted. Three wetting–drying cycles resulted in the fluctuation of water and dissolved oxygen contents, and consequently, the reduction–oxidation potential in the soil columns. Under these circumstances, the biotic reduction of As(V) to As(III) was observed, especially in the column filled with soils enriched in organic matter. Most of the As was found to be associated with soil particles rather than to be dissolved in the pore water in all of the columns tested. Retention of As was more preferable in the soil column with a higher Fe content and bulk density, which provided more sorption sites and reaction time, respectively. However, a considerable amount of soil-bound As could be remobilized and released back to the pore water with the repetition of wetting and drying due to the transformation of As(V) to As(III). [Display omitted] • Transient behaviors of As in vadose zone were studied under varying water content. • Most of the As released in vadose zone was associated with soil particles. • Higher Fe content and dry density of soil medium increased the retention of As. • With repeated wetting and drying, As(V) was biotically reduced to As(III). • The reduction enhanced the As remobilization and release into pore water. [ABSTRACT FROM AUTHOR]

• Microplastic (MP; 10‒90 μm) removal was studied during drinking water treatment. • Sequential coagulation and sand filtration could completely remove MPs ≥ 45 μm. • Some of the MPs < 20 μm passed through sand, which were fragmented in UV oxidation. • UV and UV/H 2 O 2 treatments leached out organics, increasing bacterial toxicity. The effectiveness of traditional drinking water treatment plants for the removal of Microplastics (MPs) in the size range of tens of micrometers is currently uncertain. This study investigated the behavior and removal efficiency of four different sized polystyrene MPs (10−90 μm in diameter) in a simulated cascade of coagulation/sedimentation, sand filtration, and UV-based oxidation over technically relevant time frames. In the coagulation and sand filtration steps, the larger the MP size, the better it was removed. The coagulant type and water characteristics (i.e., pH and the presence of natural organic matter) influenced the coagulation efficiency for MPs. X-ray microcomputed tomography technique and two-site kinetic modeling were used to identify the mechanisms involved in sand filtration. The MPs > 20 μm could be completely retained in sand by straining, while the attachment to the sand surface was likely responsible for the retention of MPs < 20 μm. However, approximately 16% of 10 μm MPs injected passed through the sand, which were further fragmented by UV oxidation. UV/H 2 O 2 treatment promoted the MP fragmentation and chemical leaching more significantly than UV treatment, resulting in a higher toxicity for UV/H 2 O 2 -treated water. Our findings pave the way for deeper understanding of how MPs behave and transform in a sequential drinking water treatment process. [Display omitted] [ABSTRACT FROM AUTHOR]

• The radius of investigation during the recovery phase of pumping tests is analyzed. • Exact (semi-analytical) and approximate (fully analytical) solutions are derived. • The radius of investigation can be significantly larger than at the end of pumping. • The maximum radius of investigation can be reached long after pumping is stopped. • Pumping rate and duration, and apparent measurement resolution are key parameters. Pumping tests are routinely performed to characterize aquifers. In particular, recovery tests involve analyzing the residual drawdown after the termination of pumping. Evaluating the radius of investigation of pumping tests is important for test design and interpretation. However, the radius of investigation during the recovery phase has rarely been discussed in the literature. Here, we derive exact (semi-analytical) and approximate (fully analytical) solutions for the radius of investigation during the recovery phase, and present a sensitivity analysis for typical parameter values. During recovery, the radius of investigation shows non-monotonic behavior: it first increases, then decreases, and eventually vanishes. The maximum radius can be up to five times larger than that at the end of the pumping phase in the investigated range of parameter values. However, the conditions yielding a large radius of investigation are such that the time at which the maximum occurs is relatively large: up to one hundred times the pumping duration, depending on the parameters. Thus, in practice, one may need to find a compromise between the size of the investigated area and the time required for the test. In addition to the aquifer parameters, we observe that the pumping rate and duration, and the apparent measurement resolution are key parameters controlling the radius of investigation during recovery. Finally, the approach is applied to a field example. This study provides fundamental insight on the radius of investigation of recovery tests as well as practical solutions, thereby facilitating the design and interpretation of recovery tests in practice. [ABSTRACT FROM AUTHOR]

Riverbank filtration is a commonly-used technology that improves water quality by passing river water through aquifers. In this study, a riverbank filtration site in Busan, South Korea, was investigated to understand the spatiotemporal evolution of high iron and sulfate concentrations observed in the riverbank-filtered water. Discrepancies between the nonreactive transport results and field measurements suggest that iron-sulfate-related geochemical reactions play a major role in the spatiotemporal evolution of the hydrochemical properties. Pyrite oxidation was hypothesized to be the main process driving the release of iron and sulfate. To test this hypothesis, a reactive transport model was developed, that implemented pyrite oxidation as a kinetic process and subsequent ferrous iron oxidation and ferric iron precipitation as equilibrium processes. The model accurately captured the temporal evolution of sulfate; however, iron concentrations were underestimated. Sensitivity tests revealed that adjusting reaction constants significantly improved the prediction of iron concentrations. The results of this study suggest that pyrite oxidation can affect the hydrochemistry of riverbank-filtered water and highlight the potential limitations of using theoretical reaction constants in field modeling applications. Unlabelled Image • High concentrations of iron and sulfate were observed in riverbank filtered water. • A reactive transport model with pyrite oxidation reproduced iron and sulfate levels. • Pyrite oxidation can explain the release of iron and sulfate at the field site. • The discrepancies between theoretical and field reaction constants are discussed. [ABSTRACT FROM AUTHOR]

Evaluating and predicting the natural attenuation capacity (AC) of a vadose zone is essential for determining groundwater vulnerability to contamination from upper sources. However, it remains unclear how the physicochemical properties of vadose zone soils affect AC owing to their complexity and spatial heterogeneity. In this study, we developed a regression model for estimating the AC of a vadose zone against diesel using datasets from different soils with a wide range of physicochemical properties. Among the 17 properties, six (i.e., organic matter (OM), total phosphorous (TP), coefficient of uniformity, particle size (D 30 ), van Genuchten's n, saturation degree (SD)) were selected as primary regressors. The results indicate that biogeochemical factors, including OM and TP, have decisive effects on the AC. Finally, the regression model was expanded to a GIS-based spatial model and applied to Namyangju, Korea using the index-overlay method. The produced AC map showed a nonmonotonic decrease along the depth, and the areas closer to the water bodies generally represented low AC values, most likely due to the lower OM, TP, and higher SD. This study provides an empirical basis for future research initiatives for spatial and temporal AC dynamics, which complements conventional intrinsic groundwater vulnerability models such as DRASTIC., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Arsenic (As) is a widespread environmental contaminant that poses a significant threat to ecosystems and human health. Although previous studies have qualitatively revealed the effects of individual soil properties on the transport and fate of As in the vadose zone, their integrated impacts remain obscure. Moreover, studies investigating the retardation factor therein, which is a key parameter for comprehending As transport in the vadose zone, are extremely limited. In this study, we investigated the interplay of soil properties with As transport and retention within the vadose zone, while focusing on the retardation factor of As. We employed steady-state unsaturated water-flow soil column experiments coupled with a mobile-immobile model and multiple linear regression analysis to elucidate the dependence of As retardation factors on the soil properties. In the mobile water zone, iron and organic matter contents emerged as the two most influential properties that impedes As mobility. Whereas, in the immobile water zone, the coefficient of uniformity and bulk density were the most influential factors that enhanced As retention. Finally, we derived an empirical equation for calculating the As retardation factors in each zone, offering a valuable tool for describing and predicting As behavior to protect the groundwater resources underneath., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

In natural environments, the fate and migratory behavior of metalloid contaminants such as antimony (Sb) significantly depend on the interfacial reactivity of mineral surfaces. Although boehmite (γ-AlOOH) is widely observed in (sub)surface environments, its underlying interaction mechanism with Sb oxyanions at the molecular scale remains unclear. Considering Sb-contaminated environmental conditions in this study, we prepared boehmite under weakly acidic conditions for use in the systematic investigation of interfacial interactions with Sb(III) and Sb(V). The as-synthesized boehmite showed a nanorod morphology and comprised four crystal facets in the following order: 48.4% (010), 27.1% (101), 15.0% (001), and 9.5% (100). The combined results of spectroscopic analyses and theoretical calculations revealed that Sb(III) formed hydrogen bonding outer-sphere complexation on the (100), (010), and (001) facets and that Sb(V) preferred to form bidentate inner-sphere complexation via mononuclear edge-sharing configuration on the (100), (001), and (101) facets and binuclear corner-sharing configuration on the (010) facet. These findings indicate that the facet-mediated thermodynamic stability of the surface complexation determines the interaction affinity toward the Sb species. This work is the first to document the contribution of boehmite to (sub)surface media, improving the ability to forecast the fate and behavior of Sb oxyanions at mineral-water interfaces., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Aquifer storage and recovery (ASR) is a promising approach for managing water resources that enhances water quality through biogeochemical reactions occurring within aquifers. Iron (hydr)oxides, which are the predominant metallic oxides in soil, play a crucial role in degrading dissolved organic carbon (DOC), primarily through a process known as dissimilatory iron reduction (DIR). However, the efficiency of this reaction varies depending on the mineralogy and composition of the aquifer, and this understanding is essential for adequate water quality in ASR. The objective of this study is to investigate the impact of iron (hydr)oxide on acetate, as an organic carbon source, attenuation during the ASR. To achieve this, three sets of laboratory sediment columns were prepared, each containing a different type of iron (hydr)oxide minerals: ferrihydrite, goethite, and hematite. Following an acclimation period of 28 days to simulate the microcosm within an aquifer, the columns were continuously supplied with the simulated river water spiked with acetate (DOC 40-60 mg L -1 ), and the acetate concentration in the effluent was monitored. The result revealed that the column containing ferrihydrite achieved 97% acetate attenuation through DIR with anoxic conditions (DO < 0.1 mg L -1 ), while the goethite and hematite columns exhibited limited attenuation rates of 40 and 50%, respectively. Furthermore, the efficiency of acetate attenuation in the ferrihydrite columns increased with the content of ferrihydrite but experienced a rapidly declined at higher contents (3-4%), possibly due to the partial conversion of ferrihydrite to goethite as a result of the interaction between ferrihydrite and the Fe(II) produced during DIR. Additionally, an analysis of the microbial community demonstrated that microorganisms known to possess the ability to reduce iron (hydr)oxides under anaerobic conditions were abundant in the ferrihydrite columns., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Water and wastewater treatment plants (WWTPs) receive various types of microplastics (MPs), with fibers and fragments being dominant shapes. Here we investigated the removal behavior and transformation of MPs (polypropylene and polyethylene terephthalate fibers and fragments) in simulated water and wastewater treatment units, including activated sludge process, coagulation, sand filtration, and advanced oxidation/disinfection. Sand filtration demonstrated the highest average efficiency in removing MPs (98 %), followed by activated sludge process (61 %) and coagulation (55 %), which was associated with their physicochemical properties (shape, size, density, surface functional groups, etc). In activated sludge process and coagulation, the polymer type had a greater impact on the removal of MPs than the particle shape, while in sand filtration, the particle shape played a more important role. When subjected to the long-term operation and backwashing of sand filters, approximately 15 % of the initially filtered fragments broke through the sand media, with nearly no fibers escaping. UV-based advanced oxidation and chlorination induced the leaching of dissolved organic matters with different molecular characteristics from fragment MPs, resulting in varying levels of cytotoxicity and bacterial toxicity. Our study provides important information for predicting the fate of MPs and mitigating their impacts in WWTPs., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Despite the role of the vadose zone protecting groundwater from contamination, the non-stationarity in this zone makes it difficult to predict the behavior of petroleum hydrocarbons (PH) therein. In laboratory soil columns with sandy and sandy loam soils, we simulated a vadose zone subjected to repeated groundwater-level fluctuation (GLF) to evaluate the behavior of PH under hydrodynamic conditions. The GLF vertically redistributed the PH, the extent of which was pronounced in the sandy soil with a high initial concentration due to the enhanced transport of the immiscible PH through the larger pores. The frequency of GLF did not show a substantial effect on the extent of PH redistribution but largely affected their attenuation. The greater GLF hindered PH volatilization by maintaining a high degree of water saturation, while the subsequent development of a local anaerobic regime inhibited biodegradation, which was more apparent in the sandy loam. Finally, a specific potential risk index was introduced to quantitatively compare the potential risk of PH contamination in different vadose zones exposed to GLF. Overall, the sandy soil contaminated with the higher total PH (TPH) concentration showed markedly higher potential risk indices (i.e., 18.4-29.0%), while the ones comprised of the sandy loam showed 0.6-4.9%, which increased under the greater number of GLF cycles., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Jaeshik Chung reports financial support was provided by Korea Environmental Industry and Technology Institute. Seunghak Lee reports financial support was provided by National Research Foundation of Korea. Seunghak Lee reports financial support was provided by Korea Institute of Science and Technology. Seunghak Lee reports administrative support was provided by KU-KIST., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Aquifer storage and recovery (ASR) is a promising water management technique in terms of quantity and quality. During ASR, iron (Fe) (hydr)oxides contained in the aquifer play a crucial role as electron acceptors in attenuating dissolved organic carbon (DOC) in recharging water through dissimilatory iron reduction (DIR). Considering the preference of electron acceptors, nitrate (NO 3 ⁻), possibly coexisting with DOC as the prior electron acceptor to Fe (hydr)oxides, might influence DIR by interrupting electron transfer. However, this phenomenon is yet to be clarified. In this study, we systematically investigated the potential effect of NO 3 ⁻ on DOC attenuation during ASR using a series of sediment columns representing typical aquifer conditions. The results suggest that DOC attenuation could be enhanced by the presence of NO 3 ⁻. Specifically, total DOC attenuation was notably higher than that from the stoichiometric calculation simply employing NO 3 ⁻ as the additional electron acceptor to Fe (hydr)oxides, implying a synergetic effect of NO 3 ⁻ in the overall reactions. X-ray photoelectron spectroscopy analyzes revealed that the Fe(II) ions released from DIR transformed the Fe (hydr)oxides into a less bioavailable form, inhibiting further DIR. In the presence of NO 3 ⁻, however, no aqueous Fe(II) was detected, and another form of Fe (hydr)oxide appeared on the sediment surface. This may be attributed to nitrate-dependent Fe(II) oxidation (NDFO), in which Fe(II) is (re)oxidized into Fe (hydr)oxide, which is available for the subsequent DOC attenuation. These mechanisms were supported by the dominance of DIR-relevant bacteria and the growth of NDFO-related bacteria in the presence of NO 3 ⁻., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background and Objectives : To optimally predict lymph node (LN) failure after definite radiotherapy (RT) in head and neck cancer (HNC) with LN metastases, this study examined radiomics models extracted from CT images of different periods during RT. Materials and Methods : This study retrospectively collected radiologic and clinical information from patients undergoing definite RT over 60 Gy for HNC with LN metastases from January 2010 to August 2021. The same largest LNs in each patient from the initial simulation CT (CTpre) and the following simulation CT (CTmid) at approximately 40 Gy were indicated as regions of interest. LN failure was defined as residual or recurrent LN within 3 years after the end of RT. After the radiomics features were extracted, the radiomics alone model and the radiomics plus clinical parameters model from the set of CTpre and CTmid were compared. The LASSO method was applied to select features associated with LN failure. Results : Among 66 patients, 17 LN failures were observed. In the radiomics alone model, CTpre and CTmid had similar mean accuracies (0.681 and 0.697, respectively) and mean areas under the curve (AUC) (0.521 and 0.568, respectively). Radiomics features of spherical disproportion, size zone variance, and log minimum 2 were selected for CTpre plus clinical parameters. Volume, energy, homogeneity, and log minimum 1 were selected for CTmid plus clinical parameters. Clinical parameters including smoking, T-stage, ECE, and regression rate of LN were important for both CTpre and CTmid. In the radiomics plus clinical parameters models, the mean accuracy and mean AUC of CTmid (0.790 and 0.662, respectively) were more improved than those of CTpre (0.731 and 0.582, respectively). Conclusions : Both models using CTpre and CTmid were improved by adding clinical parameters. The radiomics model using CTmid plus clinical parameters was the best in predicting LN failure in our preliminary analyses.

Background and Objective: Gliomas are graded using multimodal magnetic resonance imaging, which provides important information for treatment and prognosis. When modalities are missing, the grading is degraded. We propose a robust brain tumor grading model that can handle missing modalities., Methods: Our method was developed and tested on Brain Tumor Segmentation Challenge 2017 dataset (n = 285) via nested five-fold cross-validation. Our method adopts adversarial learning to generate the features of missing modalities relative to the features obtained from a full set of modalities in the latent space. An attention-based fusion block across modalities fuses the features of each available modality into a shared representation. Our method's results are compared to those of two other models where 15 missing-modality scenarios are explicitly considered and a joint training approach with random dropouts is used., Results: Our method outperforms the two competing methods in classifying high-grade gliomas (HGGs) and low-grade gliomas (LGGs), achieving an area under the curve of 87.76% on average for all missing-modality scenarios. The activation maps derived with our method confirm that it focuses on the enhancing portion of the tumor in HGGs and on the edema and non-enhancing portions of the tumor in LGGs, which is consistent with prior expertise. An ablation study shows the added benefits of a fusion block and adversarial learning for handling missing modalities., Conclusion: Our method shows robust grading of gliomas in all cases of missing modalities. Our proposed network might have positive implications in glioma care by learning features robust to missing modalities., Competing Interests: Declaration of Competing Interest None., (Copyright © 2022. Published by Elsevier B.V.)

Various hydrogeochemical processes can modify the quality of river water during riverbank filtration (RBF). Identifying the subsurface processes responsible for the bank-filtered water quality is challenging, but essential for predicting water quality changes and determining the necessity of post-treatment. However, no systematic approach for this has been proposed yet. In this study, the subsurface hydrogeochemical processes that caused the high concentrations of total iron (Fe) and sulfate (SO 4 2- ) in the bank-filtered water were investigated at a pilot-scale RBF site in South Korea. For this purpose, water quality variations were monitored in both the extraction well and the adjacent river over five months. The volumetric mixing ratio between the river water and the native groundwater in the RBF well was calculated to understand the effect of mixing on the quality of water from the well and to assess the potential contribution of subsurface reactions to water quality changes. To identify the subsurface processes responsible for the evolution of Fe and SO 4 2- during RBF, an inverse modeling based on the chemical mass balance was conducted using the water quality data and the calculated volumetric mixing ratio. The modeling results suggest that pyrite oxidation by abundant O 2 present in an unsaturated zone could be a primary process explaining the evolution of total Fe and SO 4 2- during RBF at the study site. The presence of pyrite in the aquifer was indirectly supported by iron sulfate hydroxide (Fe(SO 4 )(OH)) detected in oxidized aquifer sediments., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V. part of Springer Nature.)

The biodiesel containing fatty acid methyl esters (FAMEs) are blended with refined diesel products. Here, we evaluate relative FAME composition ratio as a potential index to discriminate the pollution origin in diesel-contaminated soil. Artificially contaminated soil was prepared to mimic the release of petroleum products using four different refined diesels; in addition, the contaminated soil was put under natural weathering conditions. The variations in the relative FAME composition ratio was compared with those of the corresponding diesel origin using principal component analysis (PCA) for 60 days. All soil samples could be classified into four groups according to diesel origin using two principal components. The proposed method can be used to discriminate the specific diesel pollution origin in contaminated soils., (© 2021. The Author(s).)

A hybrid process of managed aquifer recharge with pre-oxidation was investigated as part of a multiple-barrier approach for safe water production. This study evaluated O 3 and O 3 /H 2 O 2 for the pre-oxidation of urban surface water prior to managed aquifer recharge (MAR) and compared their effectiveness with respect to trace organic contaminants (TrOCs), biostability, and trihalomethane formation potential. The combination of pre-oxidation and MAR was performed using long-term column studies, and the results confirmed the removal of 64 and 56% dissolved organic carbon by using O 3 and O 3 /H 2 O 2 , respectively. MAR combined with O 3 and O 3 /H 2 O 2 achieved >50% removal of dissolved organic carbon with the first 5 days of residence time. O 3 alone showed better performance in alleviating trihalomethane formation potential during chlorination compared to using O 3 /H 2 O 2 . The pre-oxidation of urban surface water was effective in attenuating selected TrOCs (35 - >99% removal), and subsequent MAR achieved >99% removal of selected TrOCs within the first 5 days, regardless of pretreatment methods examined in this study. The results of this study provide an understanding of the effects of O 3 and O 3 /H 2 O 2 as pre-oxidation processes on urban surface water prior to MAR, as well as the resulting impact on MAR., (Copyright © 2019 Elsevier B.V. All rights reserved.)

We propose a parameter server system for distributed ML, which follows a Stale Synchronous Parallel (SSP) model of computation that maximizes the time computational workers spend doing useful work on ML algorithms, while still providing correctness guarantees. The parameter server provides an easy-to-use shared interface for read/write access to an ML model's values (parameters and variables), and the SSP model allows distributed workers to read older, stale versions of these values from a local cache, instead of waiting to get them from a central storage. This significantly increases the proportion of time workers spend computing, as opposed to waiting. Furthermore, the SSP model ensures ML algorithm correctness by limiting the maximum age of the stale values. We provide a proof of correctness under SSP, as well as empirical results demonstrating that the SSP model achieves faster algorithm convergence on several different ML problems, compared to fully-synchronous and asynchronous schemes.