Evaluation of optimal size of illite adsorbent for 137Cs removal in contaminated artificial lake.

Since the Chernobyl and the Fukushima Daiichi disasters, contamination caused by radioactive accidents has attracted increasing attention. The present study evaluated immediate cleanup of 137Cs dissolved in surface water reservoir using an illite adsorbent, simulating an event of 137Cs contamination at Lake Paldang, South Korea. The study was conducted in two parts: (1) calculation of the residence time (tr) of illite adsorbent, and (2) evaluation of the adsorption time (ta) of illite adsorbent. tr was calculated based on physical properties (e.g., density, diameter, shape, and roughness) of the illite adsorbent at designated depth of surface water. Subsequently, ta was measured for 4 illite adsorbents (Korea01-Illite, Korea02-Illite, USA-Illite, and China-Illite) at 100 and 100,000 µg/L Cs, via kinetic adsorption experiment. Upon spraying of illite adsorbents with 50-150 µm diameter to locations where lake depth was between 6.5 m and 25.5 m, tr ranged from 0.132 to 3.300 h ta of 4 illite adsorbents was shorter than 0.6 and 2.5 h, for respective tests using 100 and 100,000 µg/L Cs. Based on the two characteristic times (tr and ta), the optimal particle diameter for the 4 illite adsorbents were evaluated at available lake depths in Lake Paldang. The study revealed that the USA-Illite is the efficient adsorbent at 100 µg/L Cs; in contrast, China-Illite could serve as the effective adsorbent at 100,000 µg/L Cs. Also, it was suggested that adsorbent efficiency had seasonal variations; tr was 2 h longer in winter than summer. In general, the study suggests that in the event of 137Cs contamination at Lake Paldang, Korea01-Illite is likely the best adsorbent to remove 137Cs due to its removal efficiency and accessibility from the illite deposit in Korea.

Effects of radiation and temperature on iodide sorption by surfactant-modified bentonite.

Bentonite, which is used as an engineered barrier in geological repositories, is ineffective for sorbing anionic radionuclides because of its negatively charged surface. This study modified raw bentonite using a cationic surfactant (i.e., hexadecyltrimethylammonium [HDTMA]-Br) to improve its sorption capability for radioactive iodide. The effects of temperature and radiation on the iodide sorption of surfactant-modified bentonite (SMB) were also evaluated under alkaline pH condition similar to that found in repository environments. Different amounts of surfactant, equivalent to the 50, 100, and 200% cation-exchange capacity of the bentonite, were used to produce the HDTMA-SMB for iodide sorption. The sorption reaction of the SMB with iodide reached equilibrium rapidly within 10 min regardless of temperature and radiation conditions. The rate of iodide sorption increased as the amount of the added surfactant was increased and nonlinear sorption behavior was exhibited. However, high temperature and γ-irradiation ((60)Co) resulted in significantly (∼2-10 times) lower iodide Kd values for the SMB. The results of FTIR, NMR, and XANES spectroscopy analysis suggested that the decrease in iodide sorption may be caused by weakened physical electrostatic force between the HDTMA and iodide, and by the surfactant becoming detached from the SMB during the heating and irradiation processes.

Uptake mechanism for iodine species to black carbon.

Natural organic matter (NOM) plays an important role in determining the fate and transport of iodine species such as iodide (I(-)) and iodate (IO3(-)) in groundwater system. Although NOM exists as diverse forms in environments, prior iodine studies have mainly focused on uptake processes of iodide and iodate to humic materials. This study was conducted to determine the iodide and iodate uptake potential for a particulate NOM (i.e., black carbon [BC]). A laboratory-produced BC and commercial humic acid were used for batch experiments to compare their iodine uptake properties. The BC exhibited >100 times greater uptake capability for iodide than iodate at low pH of ~3, while iodide uptake was negligible for the humic acid. The uptake properties of both solids strongly depend on the initial iodine aqueous concentrations. After uptake reaction of iodide to the BC, X-ray absorption fine structure spectroscopy results indicated that the iodide was converted to electrophilic species, and iodine was covalently bound to carbon atom in polycyclic aromatic hydrocarbons present in the BC. The computed distribution coefficients (i.e., Kd values) suggest that the BC materials retard significantly the transport of iodide at low pH in environmental systems containing even a small amount of BC.

Enhanced immobilization of Prussian blue through hydrogel formation by polymerization of acrylic acid for radioactive cesium adsorption.

In this study, a hydrogel impregnated with powder activated carbon (PAC), MAA-PAC, was synthesized through the polymerization of acrylic acid (AA) and PB was immobilized using the carboxyl group of AA. In this process, an adsorbent with an enhancement of PB content and stability of immobilization was developed through the additional supply of Fe3+ ions by the layer by layer (LBL) assembly. XRD, FT-IR, SEM (EDS), TEM (EDS, mapping), and TG analyzes of the LBL and non-LBL groups were performed to confirm the change of PB content in the adsorbent as the LBL assembly was applied. The stability of PB immobilization was confirmed during the washing process after the synthesis of the adsorbent. When the LBL assembly process was applied as a PB immobilization strategy, the PB content in the adsorbent was improved and PB leakage was not observed during the washing process. The maximum adsorption (qm) for cesium in the MAA-PAC-PB LBL group that showed high PB content was 40.03 mg/g, and the adsorption isotherm was more suitable for the Langmuir model than the Freundlich model. The LBL group showed a high removal efficiency of 99.81% and a high DF value (525.88) for radioactive cesium (120 Bq/g). These results demonstrate the potential efficiency of the MAA-PAC-PB LBL group for the decontamination of radioactive cesium-contaminated water systems. Furthermore, it was verified that the LBL group of MAA-PAC-PB could be used as an adsorbent without an additional design of the existing water treatment facility. This can an economical decontamination method for removing radioactive cesium.

Evaluation of multiple PRPs' contributions to soil contamination in reclaimed sites around an abandoned smelter.

Although soil contamination must be remediated by the polluters under current legal frameworks in numerous countries, the allocation of responsibilities for soil clean-up is still challenging in the case of multiple potentially responsible parties (PRPs). This study evaluated the individual contributions of two PRPs (Owners A & B) to heavy metal contamination in the soil environment near an abandoned smelter and compared the results with those from the conventional Gore Factor (GF) method. The soil in the study area was widely contaminated by various heavy metals. In particular, the arsenic concentration exceeded the local regulatory level of 25 mg kg-1 at all investigated sites. Arsenic components were frequently observed in the form of iron oxides, and they decreased with increasing distance from the smelter chimney. This distribution supported the premise that the arsenic mainly originated from the chimney through oxidation processes of iron-containing ores under high temperature. The GF results attributed greater responsibility to Owner A than Owner B, while the estimated arsenic masses (based on the field investigation) indicated the contrary. These results could be caused by insufficient information for the GF evaluation, because the change in smelter ownership and long history of contamination obscure important data, such as the amount of total refined ores and the efficiency of air pollution prevention facilities in the smelter. Therefore, more field-based approaches must be considered more importantly for the evaluation of multiple PRPs' remediation responsibilities, especially in areas with long-term contamination.

In-depth compositional analysis of water-soluble and -insoluble organic substances in fine (PM2.5) airborne particles using ultra-high-resolution 15T FT-ICR MS and GC×GC-TOFMS.

Airborne particulate matter consisting of ionic species, salts, heavy metals and carbonaceous material is one of the most serious environmental pollutants owing to its impacts on the environment and human health. Although elemental and organic carbon compounds are known to be major components of aerosols, information on the elemental composition of particulate matter remains limited because of the broad range of compounds involved and the limits of analytical instruments. In this study, we investigated water-soluble and -insoluble organic compounds in fine (PM2.5) airborne particles collected during winter in Korea to better understand the elemental compositions and distributions of these compounds. To collect ultra-high-resolution mass profiles, we analyzed water-soluble and -insoluble organic compounds, extracted with water and dichloromethane, respectively, using an ultra-high-resolution 15 T Fourier transform ion cyclotron resonance (15T FT-ICR) mass spectrometer in positive ion mode (via both electrospray ionization [ESI] and atmospheric pressure photoionization [APPI] for water-extracts and via APPI for dichloromethane-extracts). In conjunction with the FT-ICR mass spectrometry (MS) data, subsequent two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS) data were used to identify potentially hazardous organic components, such as polycyclic aromatic hydrocarbons. This analysis provided information on the sources of ambient particles collected during winter season and partial evidence of contributions to the acidity of organic content in PM2.5 particles. The compositional and structural features of water-soluble and -insoluble organic compounds from PM2.5 particles are important for understanding the potential impacts of aerosol-carried organic substances on human health and global ecosystems in future toxicological studies.

A predictive estimation method for carbon dioxide transport by data-driven modeling with a physically-based data model.

In this study, a data-driven method for predicting CO2 leaks and associated concentrations from geological CO2 sequestration is developed. Several candidate models are compared based on their reproducibility and predictive capability for CO2 concentration measurements from the Environment Impact Evaluation Test (EIT) site in Korea. Based on the data mining results, a one-dimensional solution of the advective-dispersive equation for steady flow (i.e., Ogata-Banks solution) is found to be most representative for the test data, and this model is adopted as the data model for the developed method. In the validation step, the method is applied to estimate future CO2 concentrations with the reference estimation by the Ogata-Banks solution, where a part of earlier data is used as the training dataset. From the analysis, it is found that the ensemble mean of multiple estimations based on the developed method shows high prediction accuracy relative to the reference estimation. In addition, the majority of the data to be predicted are included in the proposed quantile interval, which suggests adequate representation of the uncertainty by the developed method. Therefore, the incorporation of a reasonable physically-based data model enhances the prediction capability of the data-driven model. The proposed method is not confined to estimations of CO2 concentration and may be applied to various real-time monitoring data from subsurface sites to develop automated control, management or decision-making systems.

Comparison of physicochemical properties between fine (PM2.5) and coarse airborne particles at cold season in Korea.

Although it has been well-known that atmospheric aerosols affect negatively the local air quality, human health, and climate changes, the chemical and physical properties of atmospheric aerosols are not fully understood yet. This study experimentally measured the physiochemical characteristics of fine and coarse aerosol particles at the suburban area to evaluate relative contribution to environmental pollution in consecutive seasons of autumn and winter, 2014-2015, using XRD, SEM-EDX, XNI, ICP-MS, and TOF-SIMS. For these experimental works, the fine and coarse aerosols were collected by the high volume air sampler for 7 days each season. The fine particles contain approximately 10 µg m(-3) of carbonaceous aerosols consisting of 90% organic and 10% elemental carbon. The spherical-shape carbonaceous particles were observed for the coarse samples as well. Interestingly, the coarse particles in winter showed the increased frequency of carbon-rich particles with high contents of heavy metals. These results suggest that, for the cold season, the coarse particles could contribute relatively more to the conveyance of toxic contaminants compared to the fine particles in the study area. However, the fine particles showed acidic properties so that their deposition to surface may cause facilitate the increase of mobility for toxic heavy metals in soil and groundwater environments. The fine and coarse particulate matters, therefore, should be monitored separately with temporal variation to evaluate the impact of atmospheric aerosols to environmental pollution and human health.

Distribution and potential health risk of groundwater uranium in Korea.

Chronic exposure even to extremely low specific radioactivity of natural uranium in groundwater results in kidney problems and potential toxicity in bones. This study was conducted to assess the potential health risk via intake of the groundwater containing uranium, based on the determination of the uranium occurrence in groundwater. The groundwater was investigated from a total of 4140 wells in Korea. Most of the groundwater samples showed neutral pH and (sub-)oxic condition that was influenced by the mixing with shallow groundwater due to long-screened (open) wells. High uranium contents exceeding the WHO guideline level of 30 µg L(-1) were observed in the 160 wells located mainly in the plutonic bedrock regions. The statistical analysis suggested that the uranium component was present in groundwater by desorption and re-dissolution processes. Predominant uranium phases were estimated to uranyl carbonates under the Korean groundwater circumstances. These mobile forms of uranium and oxic condition facilitate the increase of potential health risk downgradient. In particular, long-term intake of groundwater containing >200 µg U L(-1) may induce internal exposure to radiation as well as the effects of chemical toxicity. These high uranium concentrations were found in twenty four sampling wells of rural areas in this study, and they were mainly used for drinking. Therefore, the high-level uranium wells and neighboring areas must be properly managed and monitored to reduce the exposure risk for the residents by drinking groundwater.

Heterogeneous carbonaceous matter in sedimentary rock lithocomponents causes significant trichloroethylene (TCE) sorption in a low organic carbon content aquifer/aquitard system.

This study evaluated the effects of heterogeneous thermally altered carbonaceous matter (CM) on trichloroethylene (TCE) sorption for a low fraction organic carbon content (foc) alluvial sedimentary aquifer and aquitard system (foc=0.046-0.105%). The equilibrium TCE sorption isotherms were highly nonlinear with Freundlich exponents of 0.46-0.58. Kerogen+black carbon was the dominant CM fraction extracted from the sediments and accounted for >60% and 99% of the total in the sands and silt, respectively. Organic petrological examination determined that the kerogen included abundant amorphous organic matter (bituminite), likely of marine origin. The dark calcareous siltstone exhibited the greatest TCE sorption among aquifer lithocomponents and accounted for most sorption in the aquifer. The results suggest that the source of the thermally altered CM, which causes nonlinear sorption, was derived from parent Paleozoic marine carbonate rocks that outcrop throughout much of New York State. A synthetic aquifer-aquitard unit system (10% aquitard) was used to illustrate the effect of the observed nonlinear sorption on mass storage potential at equilibrium. The calculation showed that >80% of TCE mass contained in the aquifer was sorbed on the aquifer sediment at aqueous concentration <1000 µgL(-1). These results show that sorption is likely a significant contributor to the persistence of a TCE groundwater plume in the aquifer studied. It is implied that sorption may similarly contribute to TCE persistence in other glacial alluvial aquifers with similar geologic characteristics, i.e., comprised of sedimentary rock lithocomponents that contain thermally altered CM.

Transfer of antibiotic resistance plasmids in pure and activated sludge cultures in the presence of environmentally representative micro-contaminant concentrations.

The presence of antibiotics in the natural environment has been a growing issue. This presence could also account for the influence that affects microorganisms in such a way that they develop resistance against these antibiotics. The aim of this study was to evaluate whether the antibiotic resistant gene (ARG) plasmid transfer can be facilitated by the impact of 1) environmentally representative micro-contaminant concentrations in ppb (part per billion) levels and 2) donor-recipient microbial complexity (pure vs. mixed). For this purpose, the multidrug resistant plasmid, pB10, and Escherichia coli DH5α were used as a model plasmid and a model donor, respectively. Based on conjugation experiments with pure (Pseudomonas aeruginosa PAKexoT) and mixed (activated sludge) cultures as recipients, increased relative plasmid transfer frequencies were observed at ppb (µg/L) levels of tetracycline and sulfamethoxazole micro-contaminant exposure. When sludge, a more complex community, was used as a recipient, the increases of the plasmid transfer rate were always statistically significant but not always in P. aeruginosa. The low concentration (10 ppb) of tetracycline exposure led to the pB10 transfer to enteric bacteria, which are clinically important pathogens.

Can chlorofluorocarbon sorption to black carbon (char) affect groundwater age determinations?

Although adsorption is not generally considered important in low f(oc) (fraction organic carbon) aquifers, we show that chlorofluorocarbon (CFC) adsorption to black carbon (BC) is sufficiently large to retard transport and affect groundwater ages obtained with CFCs. Sorption isotherms of CFC-11, -12, and -113 to synthetic wood char were nonlinear (Freundlich n = 0.71-0.94) while humic acid isotherms were linear. Moreover, sorption to char was 10-1000 times greater than to humic acid for all three CFCs at the lowest observed concentrations, C(w)/S approximately 10(-8)-10(-7). We used the observed isotherms for char and humic acid to represent sorption to BC and amorphous organic matter, respectively, in a dual mode model to estimate retardation factors for a low f(oc) aquifer (= 0.06% gC g(-1)). The estimated retardation factors for the char-containing aquifer (presumed BC fraction = 9% of f(oc)) were approximately 6.8-10.6 at C(w)/S = 10(-8) and >5 times those estimated assuming amorphous organic matter partitioning only. The results indicate that unless CFC adsorption to BC is evaluated in transport, the groundwater age determined may be biased toward older than true ages. The CFC data archived in BC-containing aquifers may contain information about its adsorbent properties that could be useful to predict retardation of other chlorinated organic contaminants.