Drinking Water Limit Research Articles

Arsenic Release and Attenuation Processes in a Groundwater Aquifer During Anaerobic Remediation of TCE with Biostimulation

AbstractArsenic in groundwater in excess of the drinking water limit is usually from natural sources. The release of As, however, can be amplified by anthropogenic inputs of carbon, including those associated with the remediation of chlorinated solvents such as trichloroethylene (TCE). Large laboratory columns (15.2 cm diameter, 183 cm long) packed with aquifer solids from a TCE contaminated site near Hill Air Force Base (Utah) were fed with groundwater containing TCE and were biostimulated, bioaugmented, and monitored for TCE dechlorination over 7.5 years. This is a basin‐fill aquifer with As bearing geologic features. The objective of this study was to evaluate the biogeochemical changes that affect As solubilization that occurred after 7.5 years of feeding the columns with either whey or two formulations of Newman Zone® emulsified oil, and a no carbon addition control. The columns were analyzed in 10.16 cm sections for pore water and sediment quality parameters, parameters descriptive of redox conditions, and As geochemistry. The whey treatment resulted in 52.9% (±1.36%) (average ± standard deviation) of the total As in the solids leaching from the columns. The oil treatments promoted loss of 20.9% (±6.40%) of the total As. Arsenic solubility was associated with strongly reducing conditions developed with whey addition, leading to dissolution of crystalline Fe oxides and release of As. Arsenic was attenuated within the oil treated columns with As associated with carbonates in the lower layers. A consequence of adding whey, resulting in the desired full dechlorination of TCE in this aquifer, is the mobilization of As in groundwater.

Simultaneous removal of fluoride and arsenic from well water by electrocoagulation

The co-occurrence of fluoride and arsenic in groundwater presents a problem in many, mostly arid, regions of Latin America and the world. These pollutants cause significant health problems and are difficult to remove simultaneously from drinking water. In this study, the electrocoagulation process for the simultaneous removal of fluoride and arsenic was evaluated in well from the state of Durango, Mexico, in order to both solve the local problem and determine how to apply the method generally. Tests were carried out with different times, concentrations, initial pH values, and electric current densities, with iron and aluminum as electrode materials. The removal efficiencies in simultaneous presence were 85.68% for fluoride and approximately 100% for arsenic. The final concentrations for both pollutants were below the drinking water limits established by the World Health Organization (WHO) and Mexican regulations. The optimum conditions of the electrocoagulation process found were a current density of 4.5 mA/cm2, an initial pH of 5, and a treatment time of 15 min, considering initial fluoride and arsenic concentrations of 5 mg/L and 80 μg/L, respectively.

Kinetic Reactive Transport Modelling of CCS Disaster Scenarios: CO2 or Brine Leakage from a CO2 Reservoir into a Freshwater Aquifer

Potential disaster scenarios of CO2 geological storage (CGS) are CO2 escape and brine displacement to protected freshwater aquifers via unexpected pathways. Present study evaluates the geochemical aspects of such events in the vicinity of potential CGS sites in Hungary. This is primarily possible by reactive transport modelling using the open source PHREEQC. Solution and mineral compositions, electrical conductivity and porosity are simulated in time and space. Main results predict an increase of ion-concentrations in the freshwater; some ions may even exceed drinking water limit values either in the case of CO2 and brine leakage. Finally, electrical conductivity of water is suggested to record for a cost-effective, early detection of both scenarios.

Trends and probabilistic stability index for evaluating groundwater quality: The case of quaternary alluvial and quartzite aquifer system of India

This study proposed a novel groundwater-quality stability index (GQSI), which considers probabilistic estimate of reliability and resilience based on multi-year dataset. The developed index is validated and optimized adopting optimum index factor approach. The vulnerabilities of different groundwater quality parameters are also computed to provide an insight about the deviations of their concentrations from the safe drinking water limits. The application of the developed stability index is demonstrated through a case study in quaternary alluvial and quartzite aquifer system of India. In addition, trends in the groundwater quality parameters are identified by using variance-corrected Mann-Kendall test, and trends are quantified by using Sen's slope estimation test. Box-whisker plots revealed that EC and TDS mostly exceed their maximum permissible limits prescribed for drinking water in the southern and southwest hard-rock formations. Whereas, most parameters do not cross their maximum desirable limits in the central and northern alluvial formations. Increasing trends of potassium and bicarbonate, and decreasing trends of carbonate, calcium, sulfate, and fluoride are found prominent. The GQSI values indicated high stability of groundwater quality under older alluvium geology and low stability under the gneiss and mica-schist. Results of the GQSI are found in agreement with that of groundwater-quality index (GQI) at 84% sites, which proved adequacy of the developed GQSI. Also, three classes (‘low’/‘poor’, ‘moderate’, and ‘high’/‘good’) of both the GQSI and GQI showed a good coherence at 83, 78, and 87% sites. However, GQSI is more advantageous than GQI due to former's statistical framework, consistency and comparability over different areas. Three optimum index factors, i.e., TDS, pH and nitrate, are found to have the maximum impact on overall groundwater quality with their largest variations. Results of the optimum groundwater-quality stability index (OGQSI) and GQSI closely matched with each other, and a significant linear relationship (R2 = 0.70) existed between them. Therefore, OGQSI is a cost-effective approach for adequate monitoring and satisfactory evaluation of the groundwater quality in low-income nations.

A geologically-based approach to map arsenic risk in crystalline aquifers: Analysis of the Tampere region, Finland

The study illustrates the critical role of accurate geological structural mapping to delineate crystalline aquifer zones more prone to high health risk due to elevated dissolved As in drinking wells. The analysis revisits the results from more than 1200 groundwater samples collected over ten years from domestic wells across the Tampere region (Finland). It is demonstrated that the highest dissolved As concentrations in the region (up to 2230 μg/L) are exclusively found near major faults and deformation zones (FDZs) detected via geophysical and geological surveys, and that a clear correlation exists between dissolved concentrations and the distance from the FDZs (r). Almost all values exceeding the drinking water limit (10 μg/L) occur at r < 8 km, while concentrations above 100 μg/L occur at r < 4 km. Solid-phase As concentrations in bedrock show less dependency on FDZ than aqueous concentrations. This behavior is explained considering different mechanisms, which include enhanced sulfide oxidation and fracture connectivity, promoting preferential transport of dissolved As to FDZs and mixing of waters from different redox zones, mobilizing preferentially As(III) or As(V). Fe hydro-oxides may also precipitate/dissolve preferentially because of FDZs, while residence time may influence the contact time between water and As-bearing minerals. It is concluded that the accurate mapping of FDZs, and in general of structural geology, provides an important preliminary information to identify where localized, site-specific characterization of hydrogeology and geochemistry is more urgent to reduce As-related health risk from groundwater intake.

EPA blasted for failing to set drinking water limits for ‘forever chemicals’

EPA blasted for failing to set drinking water limits for ‘forever chemicals’

Polyvinyl alcohol-stabilized granular Fe–Mn binary oxide as an effective adsorbent for simultaneous removal of arsenate and arsenite

ABSTRACT A novel granular Fe–Mn (GFM) binary oxide sorbent, with a diameter of approximate 2.0 mm and a length of 2.0–3.0 mm, was successfully prepared using extrusion granulation method in this study. The GFM sorbent is highly porous with a BET-specific surface area of 210.3 m2/g. It shows high effectiveness in simultaneously adsorbing As(V) and As(III). The maximal sorption capacities for As(V) and As(III) are 33.2 and 50.7 mg/g at pH 7.0 ± 0.1, respectively, which are superior to most of granular sorbents reported in the literature. The present Ca2+, Mg2+, humic acids and fulvic acids do not have obvious influence on the arsenic sorption. But, coexisting anions affect negatively arsenic sorption in the following order: H2PO4 − > SiO3 2− > HCO3 − > SO4 2−. NaOH solution is an effective eluent for regeneration of the arsenic-loaded GFM. The GFM packed in the fixed-bed column can treat approximately 3400 and 6500 bed volumes of simulated groundwater containing 233 μg/L As(V) and As(III), respectively, before the arsenic concentration in the effluent reached a drinking water limit of 10 μg/L. The features of high effectiveness, selectivity and reusability make the GFM a potential alternative to remove simultaneously As(V) and As(III) from groundwater.

Seasonal antimony pollution caused by high mobility of antimony in sediments: In situ evidence and mechanical interpretation.

Antimony (Sb) mobilization in sediments and its impact on water quality remained to be studied. In this study, high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) technique were used to measure soluble Sb and labile Sb in sediment-overlying water profiles for a full year in a eutrophic region of Lake Taihu. Results showed that the highest mean concentrations of soluble Sb in overlying water (11.27 and 6.99 μg/L) appeared in December 2016 and January 2017, due to oxidation of Sb(III) to Sb(V) by Mn and Fe oxides, all of which exceeded the surface or drinking water limits set by China, United States and European Union. From April to November 2016, the concentrations of soluble Sb remained low with small monthly fluctuations and mean values ranging from 1.79 to 2.93 μg/L. This was attributed to the predominance of insoluble Sb(III) in sediments under anoxic conditions. The concentration of soluble Sb was slightly higher in summer than in autumn, due to the complexation of Sb(III) with DOM, as shown under anaerobic incubation. The mobility of inorganic Sb in sediments was mostly determined by the transition between Sb(III) and Sb(V), with Sb pollution in bottom water during winter being of concern.

Investigation of the water quality of daily used surface-sources for drinking and irrigation by the population of Segou in the center of Mali.

This study evaluates the quality and pollution status of source surface waters in Segou, Mali. The nature, sources, and extent of pollution of Comatex Stream, Cerfitex Pond, and Sonikoura River were studied for a period of twelve months (July 2016-June 2017). Analysis included 209 water samples collected from eleven different locations in the study area. Laboratory and field analysis were realized using the standard methods and concerned eleven parameters including four physicals, six chemicals and one bacteriological. Also, organoleptic parameters were observed. Most of the average values of parameters addressing the quality of water were significantly higher (P < 0.05) in both the stream and river compared to the pond. Fecal coliform counts (FCC) were not in significant correlation with the temperature; pH and turbidity; but had a significant and positive correlation (P < 0.05) with conductivity: total dissolved solids (TDS); total suspended solids (TSS); Cl-; PO4 -P; NO3 -N and 5-day biochemical oxygen demand (BOD5). Analysis of samples revealed a level of FCC that is above the permissible limit for both drinking water and of fresh vegetable irrigation water. In all, there is a pressing need to inform the public about the state of water bodies and the application of relevant laws regarding the proper treatment of sewage before it is discharged into surface water.

Influence of application of manganese ore in constructed wetlands on the mechanisms and improvement of nitrogen and phosphorus removal

Vertical up-flow constructed wetlands (CWs) with manganese ore (Mn ore) as media (M-CWs) were developed to treat simulated polluted river water. The results showed that the average removal efficiencies for NH4-N, NO3-N, TN and TP were 91.74%, 83.29%, 87.47% and 65.12% in M-CWs, respectively, which were only 79.12%, 72.90%, 75.85% and 43.23% in the CWs without Mn ore (C-CWs). Nutrient mass balance showed that nitrogen (N) removal was improved by enhanced microbial processes, media storage and plant uptake in M-CWs. Moreover, almost 50% of phosphorus (P) was retained by media storage because of the adsorption processes on Mn ore. It was found that addition of Mn ore enhanced denitrification as the relative abundance of denitrifying bacteria increased. The produced Mn(II) and more abundant Gammaproteobacteria confirmed alternative N removal pathways including anoxic nitrification coupled to Mn ore reduction and denitrification using Mn(II) as electron donor. Mn(II) concentration in the effluent of M-CWs was below the drinking water limit of 0.1 mg/L, which makes them environmentally-friendly.

Factors affecting the occurrence of lead and manganese in untreated drinking water from Atlantic and Gulf Coastal Plain aquifers, eastern United States—Dissolved oxygen and pH framework for evaluating risk of elevated concentrations

Groundwater samples collected during 2012 and 2013 from public-supply wells screened in the Atlantic and Gulf Coastal Plain aquifers of the eastern and southeastern U.S. rarely contained lead or manganese concentrations that exceeded drinking-water limits, despite having corrosive characteristics. Data indicate that the occurrence of dissolved lead and manganese in sampled groundwater, prior to its distribution or treatment, was related to several explanatory factors including the presence of source minerals, hydrologic position along the flow path, water-rock interactions, and associated geochemical conditions such as pH and dissolved oxygen (DO) concentrations. Elevated concentrations of lead compared to health-based benchmarks were associated with groundwater that is acidic (pH ≤ 6.5), oxygenated (DO ≥ 2 mg/L), and closer to recharge zones (relatively young water). Elevated concentrations of manganese were associated with groundwater that is acidic to neutral (pH ≤ 7.5), has low DO (<2 mg/L), and further from recharge zones (relatively old). Under these geochemical conditions, minerals that could sequester lead or manganese tended to be undersaturated, and adsorption by hydrous ferric oxide was limited. Under neutral to alkaline pH conditions, precipitation of impure calcium carbonate or phosphate compounds containing traces of lead or manganese (solid solutions) could maintain low concentrations of the trace elements. Additionally, adsorption of lead or manganese cations by hydrous ferric oxides (HFO) could be another attenuating factor where conditions are oxidizing and dissolved inorganic carbon concentrations are relatively low. A DO/pH framework was developed as a screening tool for evaluating risk of elevated lead or manganese, based on the occurrence of elevated lead and manganese concentrations and the corresponding distributions of DO and pH in the Atlantic and Gulf Coastal Plain aquifers. Validation of the DO/pH framework was accomplished using an independent national dataset that showed consistent results for elevated lead (pH ≤ 6.5; DO ≥ 2 mg/L) and manganese (pH ≤ 7.5; DO < 2 mg/L).

Entry of biocides and their transformation products into groundwater via urban stormwater infiltration systems

Biocides are, inter alia, applied as preservatives on facades to prevent the growth of microorganisms. Their incomplete mineralization results in new compounds, so-called transformation products (TPs). Rain causes that both applied biocides and their TPs leach from facades with stormwater into the urban aquatic environment. This study is the first to investigate the introduction of the biocides Diuron, Terbutryn, and Octylisothiazolinone (OIT) and their TPs into the groundwater via urban stormwater infiltration systems. In this study, the TPs of these biocides were created by laboratory photolysis and elucidated using LC-HRMS. The results were then used to analyze TPs by LC-MS/MS in stormwater and groundwater samples, which were taken from an urban swale-trench system and from groundwater wells upgradient and downgradient of the infiltration system. A sprinkling experiment was conducted to evaluate facades as a contamination source. Biodegradation tests were conducted to determine bio-persistence of biocides and their TPs.Fourteen TPs were identified under laboratory photolysis. TP-186, TP-210, and TP-256 of Terbutryn were hitherto unknown. Nine TPs were qualitatively detected in environmental water samples. Parent compounds, TP-219 of Diuron and TP-212, TP-214, and TP-226 of Terbutryn were detected at a maximum concentration of 140 ng L−1 during stormwater events. Concentrations in groundwater were considerably below German drinking water limits, but were higher in groundwater samples downgradient from the investigated swale-trench system than in those collected upgradient. Neither the biocides nor most of their TPs were readily biodegradable under simulated surface water conditions. The results show that entry of biocides and their TPs into groundwater is caused by infiltration of urban stormwater.

Arsenic-hypertolerant and arsenic-reducing bacteria isolated from wells in Tucumán, Argentina.

Arsenic-hypertolerant bacteria were isolated from arsenic-contaminated well water from the village of Los Pereyra in Tucumán province, Argentina. Microorganisms that biotransform arsenic are a major factor in arsenic mobilization in contaminated aquifers. Groundwater analyses showed a level of arsenic contamination (mean concentration of 978 μg·L-1) that exceeds the safe drinking water limit of 10 μg·L-1 recommended by the World Health Organization and the Argentine Food Code. There was considerable spatial variability in the concentration of arsenic in each of the wells analyzed and in the distribution of the major anions HCO3-, SO42-, and Cl-. Eighteen bacterial strains were characterized. Six strains belonging to the Actinobacteria phylum were able to grow in media with 20 mmol·L-1 As(III) or 200 mmol·L-1 As(V) and were also highly resistant to Cr, Cd, and Cu. Their ability to biotransform arsenic was examined by speciation of the products by high-performance liquid chromatography inductively coupled plasma mass spectrometry. In addition, two strains, Brevibacterium sp. strain AE038-4 and Microbacterium sp. strain AE038-20, were capable of aerobic arsenate reduction, which suggests that these strains could increase the mobility of arsenic by formation of more mobile As(III).

Enhanced triclosan and nutrient removal performance in vertical up-flow constructed wetlands with manganese oxides

Limited concentrations of oxygen in constructed wetlands (CWs) have inhibited their ability to remove emerging organic contaminants (EOCs) at μg/L or ng/L levels. Manganese (Mn) oxides were proposed as a solution, as they are powerful oxidants with strong adsorptive capabilities. In the present study, triclosan (TCS) was selected as a typical EOC, and CW microcosms with Mn oxides (birnessite) coated sand (B-CWs) and without (C-CWs) were developed to test the removal capacities of TCS and common nutrients. We found that the addition of Mn oxides coated sand significantly improved removal efficiencies of TCS, NH4-N, COD, NO3-N and TP (P < 0.05). The average concentration of Mn(II) effluent was 0.036 mg L−1, mostly lower than the drinking water limit. To gain insight into the mechanisms of pollution removal, Mn transformation, dissolved oxygen (DO) distribution, bacterial abundance, and microbial community composition were also investigated. Maximum Mn(II) was detected at 20 cm height of the B-CWs in anoxic zone. Although Mn-oxidizing bacteria existed in the layer of 30–50 cm with 103–104 CFU g−1 dry substate, Mn oxides were only detected at height from 40 to 50 cm with rich oxygen in B-CW. The quantities of bacterial 16S rRNA, amoA, narG and nosZ were not significantly different between two systems (P > 0.05), while Illumina high-throughput sequencing analysis revealed that the abundance of denitrifying bacteria was significant higher in B-CWs, and the abundance of Gammaproteobacteria that have a recognized role in Mn transformation were significantly increased. The results indicated that Mn oxides could enhance TCS and common pollutants removal in both anoxic and aerobic areas through the recycling of Mn between Mn(II) and biogenic Mn oxides.

Accessing effects and signals of leakage from a CO2 reservoir to a shallow freshwater aquifer by reactive transport modelling

CO2 geological storage is a transitional technology for the mitigation of climate change. In the vicinity of potential CO2 reservoirs in Hungary, protected freshwater aquifers used for drinking water supplies exist. Effects of disaster events of CO2 escape and brine displacement to one of these aquifers have been studied by kinetic 1D reactive transport modelling in PHREEQC. Besides verifying that ion concentrations in the freshwater may increase up to drinking water limit values in both scenarios (CO2 or brine leakage), total porosity of the rock is estimated. Pore volume is expected to increase at the entry point of CO2 and to decrease at further distances, whereas it shows minor increase along the flow path for the effect of brine inflow. Additionally, electrical conductivity of water is estimated and suggested to be the best parameter to measure for cost-effective monitoring of both worst-case leakage scenarios.

Breakthrough dynamics of s-metolachlor metabolites in drinking water wells: Transport pathways and time to trend reversal

We present the results of a two years study on the contamination of the Luxembourg Sandstone aquifer by metolachlor-ESA and metolachlor-OXA, two major transformation products of s-metolachlor. The aim of the study was twofold: (i) assess whether elevated concentrations of both transformation products (up to 1000 ng/l) were due to fast flow breakthough events of short duration or the signs of a contamination of the entire aquifer and (ii) estimate the time to trend reversal once the parent compound was withdrawn from the market. These two questions were addressed by a combined use of groundwater monitoring, laboratory experiments and numerical simulations of the fate of the degradation products in the subsurface.Twelve springs were sampled weekly over an eighteen month period, and the degradation rates of both the parent compound and its transformation products were measured on a representative soil in the laboratory using a radiolabeled precursor. Modelling with the numeric code PEARL simulating pesticide fate in soil coupled to a simple transfer function model for the aquifer compartment, and calibrated from the field and laboratory data, predicts a significant damping by the aquifer of the peaks of concentration of both metolachlor-ESA and –OXA leached from the soil. The time to trend reversal following the ban of s-metolachlor in spring protection zones should be observed before the end of the decade, while the return of contaminant concentrations below the drinking water limit of 100 ng/l however is expected to last up to twelve years. The calculated contribution to total water discharge of the fast-flow component from cropland and short-circuiting the aquifer was small in most springs (median of 1.2%), but sufficient to cause additional peaks of concentration of several hundred nanograms per litre in spring water. These peaks are superimposed on the more steady contamination sustained by the base flow, and should cease immediately once application of the parent compound stops.

A Study of Groundwater Characteristics by Using of Groundwater Quality Index and Pollution Index in Zubair District, Basra Province, Iraq

Abstract The present work evaluated the groundwater quality index (GWQI) depending on some physicochemical analyses of thirteen groundwater samples in the Zubair district in Basra Province, Iraq. The collected groundwater samples were subjected to an extensive physicochemical analysis to evaluate the characteristics of water for drinking purpose according to Iraqi standard. For calculating the (GWQI), twelve water quality parameters were considered; turbidity, pH, chloride, total dissolved solids, total hardness (TH), electrical conductivity (EC), sodium, sulphate, phosphate, calcium, nitrate, and magnesium. The analysis of the results reveals that all the samples surpassed the portability of drinking water limits. High values of the (GWQI) in the obtained groundwater samples could possibly be caused by the higher values of electrical conductivity, total hardness, chloride, total dissolved solids and sodium within the groundwater. The calculated GWQI values ranged from 73.36 to 595.92. The pollution index (PI) was calculated for the study area with values ranged from 2.97 to 8.26. Correlation coefficients amongst the chosen water parameters exhibited some strong relationships. Finally, the analysis shows that the groundwater in this particular area needs to be treated before its consumption, and in addition, it usually needs to avoid the hazard of contamination. Principal component analysis (PCA) and cluster analysis (CA) indicate that the acquiring-data from groundwater samples are explained 90.5 % of the variance in the data with a four-component system that explains a large portion of the total variance of collected data.

Hexavalent Chromium in Drinking Water

The risk assessment of chromium in drinking water is complex. To better understand this complexity, the essential information on exposure, analytical and treatment methods, toxicology, and mode of action (MOA) on which agencies based their risk assessments are provided. Humans are exposed to an average of 0.2–2 μg hexavalent chromium per liter in drinking water through natural erosion of soil and rocks or by contamination from industrial sources. Internationally, drinking water limits for total chromium range from 50 to 100 μg/L. These values are based on intestinal toxicity data from experimental animals, since human toxicity data via the oral route are lacking. MOA analysis supports a progression from noncancer to cancer effects via a nonmutagenic MOA and therefore a threshold approach is appropriate for the risk assessment of chromium in drinking water. Drinking water limits derived from this approach are measureable by available analytical methods and achievable by available treatment technologies, and are protective of both cancer and noncancer effects.

Efficient removal of arsenate from oxic contaminated water by colloidal humic acid-coated goethite: Batch and column experiments

Abstract Arsenic (As) contamination of groundwater frequently occurs and there is a need for cost-effective in situ remediation techniques. The injection of iron oxide colloids coated with humic substances has been proposed. This technology is based on injecting mobile humic acid-coated goethite colloids that are subsequently deposited by aggregation in the contaminated zone where the ionic strength is large, thereby creating an in situ reactive barrier for As. While coagulation and deposition are desirable for colloid immobilization, its effect on adsorption properties have been previously overlooked. This study was set up to investigate if i) humic acid-coated goethite colloids retain their As(V) adsorption properties after coagulation in quartz sand and ii) if batch As(V) adsorption data can predict As immobilization in columns at variable flow conditions. Equilibrium batch adsorption experiments showed that humic acid-coated goethite colloids coagulated and deposited on quartz sand have equal As(V) adsorption capacity, but two-fold lower affinity than humic acid-goethite colloids in suspension. This results indicated that there were some interactions between the sand and colloids but the overall adsorption capacity was not affected. Column experiments using sand coated with humic acid-goethite colloids (2.80 mg goethite g−1 sand) and stepwise injection of As(V) (1–4.9 mg As L−1) showed a highly efficient As(V) removal from the liquid phase as the outflow As(V) concentrations remained below the drinking water limit (10 μg As L−1) until about 45% of the sorbent capacity (30 mg As g−1 goethite) was reached. The flow rate dependent leachate As concentrations, including responses to stop-flow events, illustrated non-equilibrium sorption. The equilibrium batch adsorption parameters failed to predict the observed As(V) breakthrough curves, which were better fitted with a chemical non-equilibrium consideration. This study confirms the feasibility of the technology on lab-scale but suggests that safety factors must be embedded to account for As(V) by-pass flow that could occur during field applications.

Covalent Organic Frameworks as a Decorating Platform for Utilization and Affinity Enhancement of Chelating Sites for Radionuclide Sequestration.

The potential consequences of nuclear events and the complexity of nuclear waste management motivate the development of selective solid-phase sorbents to provide enhanced protection. Herein, it is shown that 2D covalent organic frameworks (COFs) with unique structures possess all the traits to be well suited as a platform for the deployment of highly efficient sorbents such that they exhibit remarkable performance, as demonstrated by uranium capture. The chelating groups laced on the open 1D channels exhibit exceptional accessibility, allowing significantly higher utilization efficiency. In addition, the 2D extended polygons packed closely in an eclipsed fashion bring chelating groups in adjacent layers parallel to each other, which may facilitate their cooperation, thereby leading to high affinity toward specific ions. As a result, the amidoxime-functionalized COFs far outperform their corresponding amorphous analogs in terms of adsorption capacities, kinetics, and affinities. Specifically, COF-TpAb-AO is able to reduce various uranium contaminated water samples from 1 ppm to less than 0.1 ppb within several minutes, well below the drinking water limit (30 ppb), as well as mine uranium from spiked seawater with an exceptionally high uptake capacity of 127 mg g-1 . These results delineate important synthetic advances toward the implementation of COFs in environmental remediation.