A pH-based biosensor for detection of arsenic in drinking water

Arsenic contaminated groundwater is estimated to affect over 100 million people worldwide, with Bangladesh and West Bengal being among the worst affected regions. A simple, cheap, accurate and disposable device is required for arsenic field testing. We have previously described a novel biosensor for arsenic in which the output is a change in pH, which can be detected visually as a colour change by the use of a pH indicator. Here, we present an improved formulation allowing sensitive and accurate detection of less than 10 ppb arsenate with static overnight incubation. Furthermore, we describe a cheap and simple high-throughput system for simultaneous monitoring of pH in multiple assays over time. Up to 50 samples can be monitored continuously over the desired time period. Cells can be stored and distributed in either air-dried or freeze-dried form. This system was successfully tested on arsenic-contaminated groundwater samples from the South East region of Hungary. We hope to continue to develop this sensor to produce a device suitable for field trials.     

A rapid field detection method for arsenic in drinking water.

In this study, a rapid colorimetric method for arsenic detection was developed. Different reagents containing magnesium turnings in combination with a series of acids were tested for arsine generation. The arsine was then allowed to react with auric chloride on Whatman filter paper No. 3, which in turn changed color. The detection time and detection limit were measured for each acid. Oxalic acid was found to be the most appropriate acid among all the acids used for detection in this study. It took 10 min to detect 10 ppb arsenic concentration and only 1 min to detect concentrations higher than 50 ppb. This method thus reduced the detection time for arsenic and has the potential to develop better field kit.     

A study of method robustness for arsenic speciation in drinking water samples by anion exchange HPLC-ICP-MS

Regulating arsenic species in drinking waters is a reasonable objective, since the various species have different toxicological impacts. However, developing robust and sensitive speciation methods is mandatory prior to any such regulations. Numerous arsenic speciation publications exist, but the question of robustness or ruggedness for a regulatory method has not been fully explored. The present work illustrates the use of anion exchange chromatography coupled to ICP-MS with a commercially available "speciation kit" option. The mobile phase containing 2 mM NaH(2)PO(4) and 0.2 mM EDTA at pH 6 allowed adequate separation of four As species (As(III), As(V), MMAA, DMAA) in less than 10 min. The analytical performance characteristics studied, including method detection limits (lower than 100 ng L(-1) for all the species evaluated), proved the suitability of the method to fulfill the current regulation. Other parameters evaluated such as laboratory fortified blanks, spiked recoveries, and reproducibility over a certain period of time produced adequate results. The samples analyzed were taken from water utilities in different areas of the United States and were provided by the U.S. EPA. The data suggests the speciation setup performs to U.S. EPA specifications but sample treatment and chemistry are also important factors for achieving good recoveries for samples spiked with As(III) as arsenite and As(V) as arsenate.     

Effect of chlorine on adsorption/ultrafiltration treatment for removing natural organic matter in drinking water

In drinking water treatment, prechlorination is often applied in order to control microorganisms and taste-and-odor-causing materials, which may influence organics removal by adsorption and membrane filtration. Thus, the addition of chlorine into an advanced water treatment process using a hybrid of adsorption and ultrafiltration (UF) was investigated in terms of natural organic matter (NOM) removal and membrane permeability. A comparison between two adsorbents, iron oxide particles (IOP) and powdered activated carbon (PAC), was made to understand the sorption behavior for NOM with and without chlorination. Chlorine modified the properties of dissolved and colloidal NOM in raw water, which brought about lower TOC removal, during IOP/UF. The location of IOPs, whether they were in suspension or in a cake layer, affected NOM removal, depending on the presence of colloidal particles in feedwater. Chlorine also played a role in reducing the size of particulate matter in raw water, which could be in close association with a decline in permeate flux after chlorination.     

Adsorption ability of Ga5N10 nanomaterial for removing metal ions contamination from drinking water by DFT

The electronic, magnetic, and thermodynamic properties of alkali/alkaline earth metal ion-adsorbed gallium nitride nanocage (Ga₅N₁₀_NC) have been investigated using density functional theory. The results denote that alkali/alkaline earth-metal ion-adsorbed Ga₅N₁₀_NC systems are stable compounds, with the most stable adsorption site being the center of the cage ring. The partial density of states (PDOS) can estimate a certain charge assembly between Li⁺, Na⁺, K⁺/ Be²⁺, Mg²⁺, Ca²⁺ and Ga₅N₁₀_NC which indicate the complex dominant of metallic features as: Ca²⁺ > Mg²⁺ > Be²⁺ >> K⁺ > Na⁺ > Li⁺. For confirmation of magnetic-alignment of Ga₅N₁₀_NC, monovalent (M⁺) and divalent (M²⁺) metal ions were added to the sample to measure the effects of metals on the magnetic-alignment properties of Ga₅N₁₀_NC. Furthermore, the reported results of NMR spectroscopy have exhibited that both M⁺ and M²⁺ can be optimized to achieve optimal alignment of nanocage in the presence of an applied magnetic field; however, chemical shift anisotropy spans for Ca²⁺– and Mg²⁺–containing samples is due to Ca²⁺ and Mg²⁺ ions binding to Ga₅N₁₀_NC. Regarding IR spectroscopy, Li⁺@ Ga₅N₁₀_NC and Be²⁺@ Ga₅N₁₀_NC with more electronegativity appear the most fluctuations through adsorption process. Moreover, based on NQR analysis, Ca²⁺ has shown a different graph of electric potential during trapping in Ga₅N₁₀_NC compared to other metal cations. Based on the results of $$ amounts in this research, the selectivity of metal ion adsorption by gallium nitride nanocage (ion sensor) has been approved as: K⁺>Na⁺> Li⁺ in alkali metals and Ca²⁺>Mg²⁺> Be²⁺ in alkaline earth metals.     

Determination of surface properties of iron hydroxide-coated alumina adsorbent prepared for removal of arsenic from drinking water

A novel type adsorbent was prepared by in situ precipitation of Fe(OH)3 on the surface of activated Al2O3 as a support material. The iron content of the adsorbent was 0.31+/-0.003% m/m (56.1 mmol/g); its mechanical and chemical stability proved to be appropriate in solutions. The total capacity of the adsorbent was 0.12 mmol/g, and the pH of zero point of charge, pH(zpc) = 6.9+/-0.3. Depending on the pH of solutions, the adsorbent can be used for binding of both anions and cations, if pH(eq) < pH(zpc) anions are sorbed on the surface of adsorbent (S) through [SOH2+] and [SOH] groups. A graphical method was used for the determination of pH(iep) (isoelectric points) of the adsorbent and values of pH(iep) = 6.1+/-0.3 for As(III) and pH(iep) = 8.0+/-0.3 for As(V) ions were found. The amount of surface charged groups (Q) was about zero within the a pH range of 6.5-8.6, due to the practically neutral surface formed on the adsorption of As(V) ions. At acidic pH (pH 4.7), Q = 0.19 mol/kg was obtained. The adsorption of arsenate and arsenite ions from solutions of 0.1-0.4 mmol/L was represented by Langmuir-type isotherms. A great advantage of the adsorbent is that it can be used in adsorption columns, and low waste technology for removal of arsenic from drinking water can be developed.     

Analytical methods for inorganic arsenic in water: a review

Inorganic arsenic, a term which encompasses both As (III) and As (V) species, constitutes the highest toxicological risk associated with arsenic in water in contrast to the organic arsenic species. Different determination methods of inorganic arsenic have been developed over 40 years providing timely and efficient risk assessments of inorganic arsenic contamination world wide. The current report gives an overview of more than 100 papers, regarding existing methods for analysis of As (III) and As (V) in water, including various spectroscopic, ICP and electrochemical techniques. Recent field portable analytical applications are also reviewed.     

Molecular-mass distribution of dissolved organic matter of water sources and drinking water of Ufa

Using the size-exclusion chromatography method, the molecular-mass distribution of dissolved organic matter of drinking water and water sources of Ufa is studied. The influence of seasonal changes and various water treatment stages on the molecular-mass distribution of dissolved organic matter is shown.     

Optimization of a GFAAS method for determination of total inorganic arsenic in drinking water

The new 10 μg l⁻¹ arsenic standard in drinking water has been a spur to the search for reliable routine analytical methods with a limit of detection at the μg l⁻¹ level. These methods also need to be easy to handle due to the routine analyses that are required in drinking water monitoring. Graphite furnace atomic absorption spectrometry (GFAAS) meets these requirements, but the limit of detection is generally too high except for methods using a pre-concentration or separation step. The use of a high-intensity boosted discharge hollow-cathode lamp decreases the baseline noise level and therefore allows a lower limit of detection. The temperature program, chemical matrix modifier and thermal stabilizer additives were optimized for total inorganic arsenic determination with GFAAS, without preliminary treatment. The optimal furnace program was validated with a proprietary software. The limit of detection was 0.26 μg As l⁻¹ for a sample volume of 16 μl corresponding to 4.2 pg As. This attractive technique is rapid as 20 samples can be analysed per hour. This method was validated with arsenic reference solutions. Its applicability was verified with artificial and natural groundwaters. Recoveries from 91 to 105% with relative standard deviation <5% can be easily achieved. The effect of interfering anions and cations commonly found in groundwater was studied. Only phosphates and silicates (respectively at 4 and 20 mg l⁻¹) lead to significant interferences in the determination of total inorganic arsenic at 4 μg l⁻¹.     

A review of cyanobacteria and cyanotoxins removal/inactivation in drinking water treatment

This review focuses on the efficiency of different water treatment processes for the removal of cyanotoxins from potable water. Although several investigators have studied full-scale drinking water processes to determine the efficiency of cyanotoxin inactivation, many of the studies were based on ancillary practice. In this context, “ancillary practice” refers to the removal or inactivation of cyanotoxins by standard daily operational procedures and without a contingency operational plan utilizing specific treatment barriers. In this review, “auxiliary practice” refers to the implementation of inactivation/removal treatment barriers or operational changes explicitly designed to minimize risk from toxin-forming algae and their toxins to make potable water. Furthermore, the best drinking water treatment practices are based on extension of the multibarrier approach to remove cyanotoxins from water. Cyanotoxins are considered natural contaminants that occur worldwide and specific classes of cyanotoxins have shown regional prevalence. For example, freshwaters in the Americas often show high concentrations of microcystin, anatoxin-a, and cylindrospermopsin, whereas Australian water sources often show high concentrations of microcystin, cylindrospermopsin, and saxitoxins. Other less frequently reported cyanotoxins include lyngbyatoxin A, debromoaplysiatoxin, and β-N-methylamino-l-alanine. This review focuses on the commonly used unit processes and treatment trains to reduce the toxicity of four classes of cyanotoxins: the microcystins, cylindrospermopsin, anatoxin-a, and saxitoxins. The goal of this review is to inform the reader of how each unit process participates in a treatment train and how an auxiliary multibarrier approach to water treatment can provide safer water for the consumer.     

A concise review on microbial remediation cells (MRCs) in soil and groundwater radionuclides remediation

Currently, the existing microbial radionuclides transformations processes are not completely understood. Bacteria, however, solubilize radionuclides by direct enzymatic reduction, or indirectly by its metabolites and by facilitating electrochemical redox systems. Microbes exchange electrons from proteins, organelles, metabolites to metals and electrodes have strengthened the novel bioremediation methods. In contrast, MRCs based on this redox behavior has offered considerable value over traditional treatment because of growing renewable and conception of energy incentives methods. Moreover, MRCs provides a flexible platform that enables us to access integrated treatment process of generating power and for recovering valuable resources from the contaminated sites.     

Recent advances in electrochemical water technologies for the treatment of antibiotics: A short review

This short review presents a critical overview of the most recent works published in the literature related to the use of electrochemical advanced oxidation processes (EAOPs) for the treatment of antibiotics present in synthetic and real wastewaters. The first section focuses on novelties within the traditional EAOPs, including electrochemical oxidation and electrochemical Fenton-based processes. The second section is devoted to new electrochemical technologies, including heterogeneous electro-Fenton, electrochemically activated persulfate processes, and combined processes. Future perspectives about these processes are also presented to aid the continuous evolution of research in the area.     

A review on biological sources,chemistry and pharmacological activities of pinostrobin

Pinostrobin, a dietary bioflavonoid discovered more than 6 decades ago in the heart-wood of pine (Pinus strobus), has depicted many pharmacological activities including anti-viral, anti-oxidant, anti-leukaemic, anti-inflammatory and anti-aromatase activities. It is an inhibitor of sodium channel and Ca²⁺ signalling pathways and also inhibits intestinal smooth muscle contractions. In spite of the fact that pinostrobin has an application as functional foods, till-to-date no comprehensive review on pinostrobin has been carried out. Hence, the present review deals with the biological sources, chemistry and pharmacological activities of pinostrobin.     

Natural organic matter removal by coagulation during drinking water treatment: A review

Natural organic matter (NOM) is found in all surface, ground and soil waters. An increase in the amount of NOM has been observed over the past 10-20 years in raw water supplies in several areas, which has a significant effect on drinking water treatment. The presence of NOM causes many problems in drinking water and drinking water treatment processes, including (i) negative effect on water quality by causing colour, taste and odor problems, (ii) increased coagulant and disinfectant doses (which in turn results in increased sludge volumes and production of harmful disinfection by-products), (iii) promoted biological growth in distribution system, and (iv) increased levels of complexed heavy metals and adsorbed organic pollutants. NOM can be removed from drinking water by several treatment options, of which the most common and economically feasible processes are considered to be coagulation and flocculation followed by sedimentation/flotation and sand filtration. Most of the NOM can be removed by coagulation, although, the hydrophobic fraction and high molar mass compounds of NOM are removed more efficiently than hydrophilic fraction and the low molar mass compounds. Thus, enhanced and/or optimized coagulation, as well as new process alternatives for the better removal of NOM by coagulation process has been suggested. In the present work, an overview of the recent research dealing with coagulation and flocculation in the removal of NOM from drinking water is presented.     

Preparation of trimethylchlorosilane-modified acid vermiculites for removing diethyl phthalate from water

A hybrid organic-inorganic material based on vermiculite was prepared to remove diethyl phthalate (DEP) from aqueous solution. Natural vermiculite was activated with HCl to improve the specific surface area and was then modified by silanization using trimethylchlorosilane. Organovermiculite prepared by ion exchange with hexadecyl trimethylammonium bromide (HDTMAB) was also tested for comparison. The leaching of 2 mol L(-1) HCl at 80°C increased the specific surface area of vermiculite from 14.4 to 500.0m(2)g(-1), and the average pore-diameter was decreased from 7.90 nm to 2.75 nm. Fourier transform infrared spectroscopy (FTIR) spectra indicated that trimethysilyl groups were grafted covalently on the surface of acid vermiculites. The specific surface area of trimethylchlorosilane-modified acid vermiculites (TMAVs) (355.4 m(2) g(-1)) was much larger than that of organovermiculite (6.0 m(2) g(-1)). The isotherm adsorption experiments of DEP showed that TMAVs exhibited linear isotherms, suggesting that the uptake of DEP was controlled by partitioning mechanism. The maximal partition coefficient (K(d)) of TMAVs was 3.1 times higher than that of organovermiculite, implying that TMAVs had stronger organic affinity than organovermiculite. The results demonstrate that the adsorption capacity and mechanism of organoclays were controlled by the specific surface area and organic loading, whereas the length of alkyl chain of organic modifier was not the key factor.     

Monitoring arsenic in the environment: a review of science and technologies with the potential for field measurements

This review examines available field assays and other technologies with the potential to measure and monitor arsenic in the environment. The strengths and weaknesses of the various assays are discussed with respect to their sensitivity, ability to detect the chemical states of arsenic, performance in various media, potential interferences, and ease of operation. The state of the science and development efforts of selected technologies is presented.     

砷镉复合污染稻田修复研究进展

我国农田土壤重金属污染严重,其中稻田土壤砷镉(As/Cd)复合污染形势严峻。相较于其他粮食作物,水稻具有更强的积累As/Cd能力,稻米中As/Cd通过食物链进入人体会对人类健康带来危害。因此,修复As/Cd复合污染稻田土壤,降低稻米As/Cd含量,对保障我国粮食安全生产意义重大。本文综述农田As/Cd复合污染现状及危害,讨论了As/Cd有效性影响因素及水稻中As/Cd吸收转运机制,详细探讨了稻田中As/Cd污染的修复方法。最后针对目前修复技术提出存在的不足和展望,以期为As/Cd复合污染稻田土壤修复提供一定的指导。     

Preparation and characterization of a novel adsorbent for removing lipophilic organic from water

The initial twelve persistent organic pollutants (POPs) in Stockholm Convention on Persistent Or-ganic Pollutions include many organochlorinated pes-ticides (OCPs) and some industrial by-products from manufacture processes, most of which are lipophilic or…     

A surface-imprinted polymer for removing dibenzothiophene from gasoline

A surface-imprinted polymer for the adsorption of dibenzothiophene (DBT) was obtained from DBT (the template), titanium dioxide (the support), methacrylic acid (the functional monomer), ethylene glycol dimethacrylate (the cross-linker), 2,2´-azobisisobutyronitrile (the initiator) and toluene (the porogen). The material was characterized by Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller model and Scanning electron microscopy. Batch adsorption experiments were performed to study the adsorption of the material in terms of adsorption kinetics, isotherms, and thermodynamic parameters. The adsorption follows pseudo-second-order kinetics, the Freundlich adsorption equation fits the experimental data well, and there is strong evidence for multiple layer adsorption. The negative values of the Gibbs free energy (ΔG₀) range from -6.04 kJ?mol^-1 to -7.69 kJ?mol^-1 between 298 and 318 K, which reveals that the adsorption is endothermic. The material can selectively recognize DBT over similar compounds present in gasoline (such as benzothiophene and 4-methyldibenzothiphene).