Natural Water Matrices Research Articles

QSAR models for the removal of organic micropollutants in four different river water matrices

Ozonation is an advanced water treatment process used to remove organic micropollutants (OMPs) such as pharmaceuticals and personal care products (PPCPs). In this study, Quantitative Structure Activity Relationship (QSAR) models, for ozonation and advanced oxidation process (AOP), were developed with percent-removal of OMPs by ozonation as the criterion variable. The models focused on PPCPs and pesticides elimination in bench-scale studies done within natural water matrices: Colorado River, Passaic River, Ohio River and Suwannee synthetic water. The OMPs removal for the different water matrices varied depending on the water quality conditions such as pH, DOC, alkalinity. The molecular descriptors used to define the OMPs physico-chemical properties range from one-dimensional (atom counts) to three-dimensional (quantum-chemical). Based on a statistical modeling approach using more than 40 molecular descriptors as predictors, descriptors influencing ozonation/AOP were chosen for inclusion in the QSAR models. The modeling approach was based on multiple linear regression (MLR). Also, a global model based on neural networks was created, compiling OMPs from all the four river water matrices. The chemically relevant molecular descriptors involved in the QSAR models were: energy difference between lowest unoccupied and highest occupied molecular orbital (ELUMO–EHOMO), electron-affinity (EA), number of halogen atoms (#X), number of ring atoms (#ring atoms), weakly polar component of the solvent accessible surface area (WPSA) and oxygen to carbon ratio (O/C). All the QSAR models resulted in a goodness-of-fit, R2, greater than 0.8. Internal and external validations were performed on the models.

Determination of Cd, Pb, Cu, Ni and Mn in effluents and natural waters by a novel salt induced mixed-micelle cloud point extraction using ETAAS

A novel salt induced low temperature mixed-micelle cloud point extraction procedure is developed for simultaneous separation and pre-concentration of Cd, Pb, Cu, Mn and Ni from industrial effluents and natural water matrices. Electrothermal atomic absorption spectrometry has been used for their determination. The mixed-micelles are formed by micelle–micelle interaction of Triton X-114 and sodium dodecyl sulfate (SDS) micelles. These mixed aggregates have a strong hydrophobic core, due to strong packing of both hydrophobic cores of Triton X-114 and SDS micelles, which is further enhanced by the addition of an electrolyte. These enhanced hydrophobic solubilising sites are used for efficient extraction of ammonium pyrrolidine dithiocarbamate (APDC) metal chelates at temperatures of 25–5 °C. This low temperature extraction avoids the thermal decomposition of these thermally labile complexes. The parameters affecting the extraction procedures are optimized. Under the optimized conditions, a pre-concentration factor of 10 was obtained with limits of detection of 5, 80, 30, 50 and 10 pg mL−1, respectively for Cd, Pb, Cu, Ni and Mn. The recoveries are in the range of 95–102% with 2–5% relative standard deviation. The accuracy of the procedure is evaluated by analyzing various certified reference materials such as BCR-713 final effluent, BCR-715 industrial effluent, BCR-609 ground water and NIST-1640a natural water matrices and also applied to real samples.

Non-catalytic and catalytic wet air oxidation of pharmaceuticals in ultra-pure and natural waters

A wet air oxidation (WAO) process was applied to four selected pharmaceuticals (metoprolol, naproxen, amoxicillin, and phenacetin) individually dissolved in ultra-pure water, varying the temperature and oxygen pressure. Due to the moderate (amoxicillin) or low (metoprolol, naproxen, and phenacetin) efficiency found in the oxidation of these pollutants, a catalytic wet air oxidation (CWAO) process was then tested using a platinum catalyst supported on multi-walled carbon nanotubes (CNT). In this CWAO process, the pharmaceuticals were dissolved together in ultra-pure water and in four natural water matrices—a reservoir water, a groundwater, and two waters from different municipal wastewater treatment plants. On the basis of the measurements of their removals, a discussion is given of the influence of the main operating variables: the presence or absence of catalyst, type of catalyst (the synthesized Pt/CNT or a commercial Pt/AC), catalyst dosage (0.005–0.050 g), temperature (120–140 °C), and oxygen pressure (20–40 bar). In most experiments, the removals were in the sequence: amoxicillin > naproxen > phenacetin. In addition, total organic carbon (TOC) removal measurements were made of some of the natural waters tested.

Two‐dimensional fluorescence as a fingerprinting tool for monitoring wastewater treatment systems

AbstractBACKGROUND: The use of two‐dimensional (2D) fluorescence for monitoring complex biological systems requires careful assessment of the effect of chemical species present, which may be fluorescent and/or may interfere with the fluorescence response of target fluorophores. Given the complexity of fluorescence data (excitation emission matrices—EEMs), the challenge is how to recover the information embedded into those EEMs that can be related quantitatively with the observed performance of the biological processes under study.RESULTS: This work shows clearly that interference effects (such as quenching and inner filter effects) occur due to the presence of multiple species in complex biological media, such as natural water matrices, wastewaters and activated sludge. A statistical multivariate analysis is proposed to recover quantitative information from 2D fluorescence data, correlating EEMs with the observed performance. A selected case study is discussed, where 2D fluorescence spectra obtained from the effluent of a membrane bioreactor were compressed using PARAFAC and successfully correlated with the effluent chemical oxygen demand, using projection to latent structures modelling.CONCLUSION: This study demonstrates the potential of using 2D fluorescence spectroscopy as a status fingerprint. Additionally, it is shown how statistical multivariate data analysis can be used to correlate EEMs with selected performance parameters for monitoring of biological systems. Copyright © 2011 Society of Chemical Industry

Removal of pesticides and polycyclic aromatic hydrocarbons from different drinking water sources by nanofiltration

This study evaluates the efficiency of nanofiltration to remove pesticides and polycyclic aromatic hydrocarbons (PAHs) from drinking water sources with different compositions (groundwater, spring water, surface water, and surface water after sedimentation) as well as the main mechanisms governing the rejection of these compounds. All the polycyclic aromatic hydrocarbons compounds were highly removed from the different water matrices due to strong hydrophobic interactions between these compounds and the membrane. Lower and variable rejections were obtained for pesticides in different natural water matrices. Atrazine rejection was found to be independent from the water matrix composition and appears to be influenced by a combined effect of hydrophobic and coulombic interactions with the membrane as well as size exclusion. The rejection of alachlor may be related to the composition of the water in terms of ionic content. The ions present in the water may have a “shielding” effect on the solute and membrane surface charge, reducing the repulsive electrostatic interactions and therefore, decreasing the rejection of alachlor in the matrices with higher alkalinity. The main mechanism of pentachlorophenol rejection is the hydrophobic interaction with the membrane, although electrostatic interactions cannot be excluded because pentachlorophenol is deprotonated at the pH of the water matrices. This work clearly shows that the composition of the water matrices may highly influence the efficiency of the nanofiltration process in terms of the removal of the micropollutants.

Photodegradation of the brevetoxin PbTx‐2 in coastal seawater

The photodegradation rate of the brevetoxin analog PbTx‐2 was investigated in a variety of natural water matrices. The observed first‐order photodegradation rate coefficient of the logarithmic‐transformed dissolved PbTx‐2 concentrations vs. irradiation time was 0.20 ± 0.04 h−1 in coastal seawater, corresponding to a half‐life of approximately 3 h based on 10 separate photolysis experiments. No loss of PbTx‐2 occurred in dark controls, indicating that this was primarily a photo‐mediated process. Photodegradation rate coefficients in samples in which dissolved organic matter was removed by ultraviolet oxidation prior to photolysis resulted in significantly slower rates of PbTx‐2 photodegradation (0.08 ± 0.03 h−1). When trace metals were also removed prior to photolysis, no loss of PbTx‐2 occurred, indicating that direct photolytic loss of PbTx‐2 is insignificant in coastal seawater. The proposed mechanism of PbTx‐2 decay is a photosensitized pathway involving organic matter and trace metals that is significantly accelerated by decreasing oxygen concentrations. The influence of molecular oxygen on the rate of toxin loss has important ramifications for the fate of PbTx‐2 during Karenia brevis blooms, as in situ dissolved O2 concentrations fluctuate widely during bloom development and decay. Sunlight‐mediated reactions are therefore a significant, yet previously unrecognized, sink of dissolved PbTx‐2 in seawater under environmentally relevant conditions.

Rapid Metal-Catalyzed Hydrodehalogenation of Iodinated X-Ray Contrast Media

Iodinated X-ray contrast media (ICM) are detected in natural waters at high concentrations relative to other pharmaceuticals due to extensive use in medical diagnostics and high recalcitrance during conventional wastewater treatment. This study examines, for the first time, reductive treatment of ICM in water with hydrogen gas in combination with supported palladium and porous nickel catalysts. Kinetic experiments demonstrate rapid and complete hydrodehalogenation of both ionic (diatrizoate) and neutral (iopromide) ICM. Reaction rates in batch systems (continuous mixing, P(H2) = 0.1 MPa, 25 degrees C) appear to be surface-reaction controlled and are dependent upon catalyst identity (e.g., 5 wt % versus 1 wt % Pd/ Al2O3) as well as the concentration of ICM and catalyst. Reaction rates are not markedly affected by ICM structure, pH, or by the presence of many common ions (Na+, Ca2+, Mg2+, F-, Cl-, Br-, ClO4-, SO4(2-), HCO3-, and NO3-). In contrast, elevated concentrations of iodide, (bi)sulfide, and dissolved organic matter inhibit hydrodehalogenation of ICM. However, catalyst activity can be regained by washing the catalyst (e.g., with water, NaOCl, or alkaline solution). Catalytic reduction of ICM present in treated wastewater effluent is slower than in deionized water, but similar reaction rates are observed when the effluent is pretreated to reduce the level of dissolved organic matter. The high selectivity of reductive catalytic treatment processes suggest that this is a promising strategy for targeted treatment of ICM present in mixed waste streams and natural water matrices containing much higher concentrations of nontarget constituents.

The role of particles on the biogeochemical cycling of domoic acid and its isomers in natural water matrices

The adsorption of dissolved domoic acid (DA) and its geometrical isomers was assessed in aqueous solutions containing various types of particles. In one series of experiments carried out in coastal seawater, detectable net adsorption of 100 nM DA occurred only onto natural seawater particles (unfiltered seawater) and 0.5 g L −1 chromatographic silica (18%) in 0.2 μm-filtered seawater. Some net adsorption (<5%) also occurred in the 0.5 g L −1 suspension of estuarine sediment and 0.5 g L −1 solution of humic acid in filtered seawater. No losses were seen in 0.5 g L −1 suspensions of illite, kaolinite, montmorillonite, and silica sand. Biological degradation accounted for small losses (8–10%) in filtered seawater without particles. A second series of experiments using organic-free, <5 μm fractions of kaolinite and montmorillonite in deionized water (DIW) demonstrated that ∼70% of DA adsorbed onto kaolinite, but only 5% onto montmorillonite. Geometrical isomers of DA ( iso-DA D, E, and F) showed negligible adsorption (0–8%) onto a variety of particles in filtered seawater, suggesting that major ions in seawater neutralize electrostatic attractions between particles and DA isomers. These results suggest that DA and its isomers are relatively hydrophilic and not particle reactive. Our data suggest that photochemical and biological degradation of dissolved DA and its isomers appears to occur in bulk surface seawater and its transport to bottom sediments must be mainly biologically driven.

Photodegradation of the algal toxin domoic acid in natural water matrices

We investigated the photodegradation rate of the powerful marine toxin domoic acid in a variety of natural water matrices. The observed first-order photodegradation rate coefficient (obs), obtained by linear regression of the logarithmic-transformed domoic acid concentrations versus irradiation time in simulated sunlight, was 0.15 6 0.01 h 21 in coastal seawater. Photodegradation rate coefficients in deionized water were not significantly different than those in coastal seawater, indicating that domoic acid is mainly photodegraded through a direct photochemical pathway. Addition of 100 nmol L 21 spikes of iron III [Fe(III)] and copper II [Cu(II)] had no significant effect on domoic acid photodegradation, indicating that the formation of trace-metal chelates did not enhance photodegradation of the toxin in seawater. We observed an increase of domoic acid photodegradation rates with temperature with a corresponding energy of activation of 13 kJ mol 21 . The effect on photodegradation of pH, added humic material, and dissolved oxygen removal was also investigated. The quantum yield of domoic acid photodegradation in seawater decreased with increasing wavelength and decreasing energy of incoming radiation, with the average value ranging from 0.03 to 0.20 in the ultraviolet wavelength range (280‐400 nm). Using these quantum yields together with modeled solar spectral irradiance and seawater optical properties, we estimated turnover rate coefficients for the photochemical degradation of domoic acid ranging from 0.017 to 0.035 d 21 . These observations indicate that sunlight-mediated reactions are an important, yet previously unrecognized, sink of dissolved domoic acid in seawater.

Effects of iron on arsenic speciation and redox chemistry in acid mine water

Concern about arsenic is increasing throughout the world, including areas of the United States. Elevated levels of arsenic above current drinking-water regulations in ground and surface water can be the result of purely natural phenomena, but often are due to anthropogenic activities, such as mining and agriculture. The current study correlates arsenic speciation in acid mine drainage and mining-influenced water with the important water-chemistry properties Eh, pH, and iron(III) concentration. The results show that arsenic speciation is generally in equilibrium with iron chemistry in low pH AMD, which is often not the case in other natural-water matrices. High pH mine waters and groundwater do not always hold to the redox predictions as well as low pH AMD samples. The oxidation and precipitation of oxyhydroxides deplete iron from some systems, and also affect arsenite and arsenate concentrations through sorption processes.

Solid-phase extraction–high-performance liquid chromatography–ion trap mass spectrometry for analysis of trace concentrations of macrolide antibiotics in natural and waste water matrices

A method using solid-phase extraction (SPE) combined with high-performance liquid chromatography–ion trap tandem mass spectrometry (LC–MS–MS) has been developed for determination of trace concentrations of erythromycin-H 2O (ETM-H 2O), roxithromycin (RTM) and tylosin (TLS) in natural and waste water matrices. These macrolides (MLs) were extracted from water samples using Oasis HLB cartridges, and the average recovery was 93.6±8.6, 92.1±10.0, and 94.3±8.9% for ETM-H 2O, RTM and TLS in surface water, respectively. For water from the influent of a wastewater treatment plant (WWTP), the average recovery was 84.8±14.0, 83.2±13.1, and 86.1±13.4% for ETM-H 2O, RTM and TLS, respectively. Method detection limits in a natural water matrices were 0.07, 0.03, and 0.05 μg/l for ETM-H 2O, RTM, and TLS, respectively. Fragment or product ions from MS spectra using in-source collision-induced dissociation and MS–MS spectra have been identified. The accuracy and day-to-day variation of the method fell within acceptable ranges. The method was evaluated by studying the occurrence of the three macrolides on a river and a WWTP in northern Colorado. None of the antibiotics were detected in the stream except immediately downstream of a WWTP, a result consistent with their presence in the influent and effluent of the treatment facility.

Simultaneous determination of endocrine disrupting phenolic compounds and steroids in water by solid-phase extraction–gas chromatography–mass spectrometry

A solid-phase extraction (SPE)–gas chromatography (GC)–mass spectrometry (MS) analytical method for the simultaneous separation and determination of endocrine disrupting chemicals (EDCs) from water samples is described in detail. Important and contrasting EDCs including estrone, 17β-estradiol, 17α-ethynylestradiol, 16α-hydroxyestrone, 4-nonylphenol, bisphenol A and 4- tert-octylphenol were selected as the target compounds. The SPE technique, followed by the derivatisation with bis (trimethylsilyl) trifluoroacetamide was used for the extraction recoveries of target compounds from water samples. A number of parameters that may affect the recovery of EDCs, such as the type of SPE cartridges, eluents, as well as water properties including pH value, and concentration of salts and humic substances were investigated. It is shown that the Oasis cartridges produced the best recoveries of target EDCs while ethyl acetate was efficient in eluting EDCs from SPE cartridges. The recovery of some EDCs was enhanced by the addition of salt, but reduced by the increase in pH value and humic acid concentration. The optimised method was further verified by performing spiking experiments in natural river water and seawater matrices, with good recovery and reproducibility for all the selected compounds. The established method was successfully applied to environmental water samples from East and West Sussex, UK, for the determination of the target EDCs.

Comparison of sample storage protocols for the determination of nutrients in natural waters

There have been several reports on storage protocols for the determination of nutrients in natural waters but each one has been limited to a particular sample matrix and they have reached different, matrix specific conclusions. The aim of this study was therefore to systematically apply the various recommended storage protocols to a range of natural water matrices. Samples from four contrasting sites in the UK, collected in late winter (February, 1999), were filtered and stored under different conditions (−80°C, −20°C, 4°C and at 4°C and −20°C with 0.1% (v/v) chloroform) for up to 247 days prior to analysis. The sites were the River Frome in Dorset (a chalk stream catchment) and three sites from the Tamar Estuary (draining a non-chalk catchment) with salinities of 0.5‰, 10‰ and 34‰. Samples and controls were analysed for total oxidised nitrogen (TON) and filterable reactive phosphorus (FRP) using a segmented flow analyser with spectrophotometric detection. To investigate possible seasonal effects (particularly changes in biological and chemical matrix composition), a second sampling campaign was undertaken in early autumn (October, 1999). The results showed that the optimum storage conditions for the determination of TON and FRP were highly matrix dependent, with significant differences in FRP stability between the Frome and Tamar catchments (due to different calcium concentrations) and between samples of different salinities (due to different bacterial populations and/or dissolved organic matter). General guidelines for sample handling and storage are listed and matrix specific recommendations presented for samples rich in calcium and dissolved organic matter.

Measurement of Petroleum Fuel Contamination in Water by Solid-Phase Microextraction with Direct Raman Spectroscopic Detection

A method is described for determining petroleum fuel contamination in water based on solid-phase microextraction and Raman spectroscopy (SPME/Raman). In this method, contaminants are extracted from aqueous solutions into a solid phase and then detected directly by using spontaneous Raman spectroscopy. The solid phase consists of a small volume (∼ 20 μL) of poly(dimethylsiloxane) that has an optical window in the 830–1600 cm−1 Raman shift region. This region is suitable for determining both aromatic and aliphatic fuel components. Four “real world” fuels—aviation gasoline, unleaded gasoline, jet fuel A, and #1 fuel oil—were used to test this new method. As shown, the SPME/Raman determinations performed in the visible spectral region were not adversely affected from the fluorescence of the marker dyes in these fuels. The linear dynamic ranges for the determinations exceeded the water solubility limits and spanned 1–3 orders of magnitude. The limits of detection with the use of the most sensitive Raman bands in each fuel were in the 8–12 ppm range with the exception of #1 fuel oil (25 ppm), and relative standard deviations typically were 2–10%. Finally, the SPME/Raman method was applied to the determination of total petroleum hydrocarbons in natural water matrices. With the use of hexane and undecane as standards, the results of the determinations compared favorably to the standard methods of purge-and-trap gas chromatography and liquid-liquid extraction followed by infrared detection.

A chemiluminescence method for the analysis of H2O2 in natural waters

Abstract Hydrogen peroxide (H 2 O 2 ) was determined at nanomolar levels in natural waters by a chemiluminescent method involving reaction of hydrogen peroxide with an acridinium ester 10-methyl-9-( p -formylphenyl)-acridinium carboxylate trifluoromethanesulfonate. The method is simple, rapid, requires no catalyst or metal ion complexes, and has an analytical precision of 4% RSD at typical natural water concentrations. The analysis also produces a linear response over the concentration range, 5×10 −9 to 60×10 −6 M, simply by changing the pH of the solution prior to addition of the acridinium compound or by varying the concentration of the acridinium ester at constant pH. The detection limit is 5 nM and is limited primarily by the capability to obtain H 2 O 2 -free blank water. Analytical results were verified in distilled and a variety of natural water matrices by intercomparison with a completely independent fluorescence decay technique involving the hydrogen peroxide oxidation of the fluorophore scopoletin. The two methods produced results with no statistical differences in the data at the 99.9% confidence level. In addition, the method does not suffer from background fluorescence matrix effects in organic-rich environments, which hinders the applicability of commonly used natural water hydrogen peroxide analyses. Application of the method to these highly fluorescent waters is also presented.

Quantitation of hydroxyl radical during Fenton oxidation following a single addition of iron and peroxide

Chemical probes were used to study the formation of hydroxyl radical in aqueous iron–hydrogen peroxide reaction. Hydroxyl radical formation rate and time dependent concentration were determined in pure water, in aqueous fulvic acid (FA) and humic acid (HA) solutions, and in natural surface waters. Indirect determinations of hydroxyl radical were made by quantitating hydroxyl radical reactions with probe compounds under controlled conditions. High probe concentrations were used to determine radical formation rates and low probe concentrations were used to determine time dependent radical concentration. Two independent probes were used for intercomparison: benzoic acid and 1-propanol. Good agreement between the two probes was observed. Natural water matrices resulted in lower radical formation rates and lower hydroxyl radical concentrations, with observed formation rate and yield in natural waters up to four times lower than in pure water. HA and FA also reduced hydroxyl radical formation under most conditions, although increased radical formation was observed with FA at certain pH values. Hydroxyl radical formation increased linearly with hydrogen peroxide concentration.

Fiber-Optic Sensor for Aromatic Compounds in Water Based on Solid-Phase Microextraction and Ultraviolet Evanescent Wave Absorption Spectroscopy

A method is described for the determination of aromatic contaminants in water samples that combines solid-phase microextraction and ultraviolet evanescent wave absorption (UV-EWA) spectroscopy. In this method, the aromatic compounds are partitioned from a 10 mL sample of water into the polymer cladding of a 10 cm length of UV-transmitting fiber. The aromatics are then detected directly in the cladding by EWA spectroscopy. The time required for four BTEX compounds to reach concentration equilibrium between the aqueous phase and the cladding ranges from 12 to 80 min, although we show that quantitative determinations can be accomplished in 30 min. Detection limits for these compounds range from 1 to 18 ppm, with relative standard deviations from 3 to 17%. Finally, preliminary work demonstrates that natural water matrices pose no significant matrix effects and that this method shows promise in determining the total aromatic concentrations of water samples contaminated with gasoline.

Remote electrochemical monitoring of trace silver

A novel electrochemical sensor for remote monitoring of trace silver is described. The probe relies on linear scan stripping voltammetry at a newly-designed carbon-fiber working electrode assembly, connected to a 50-ft. long shielded cable. High sensitivity and selectivity are achieved while the probe is fully submersed in unaltered river-, lake- or groundwater samples. The optimization of various parameters has resulted in low detection limits (e.g., 0.3 μg/1 with 10 min accumulation) and good precision (relative standard deviation (R.S.D.) = 8% for n = 18 at 3 μg/1 silver). The new probe can operate over a broad pH and ionic-strength ranges relevant to natural water matrices.

Two-method verification of hydrogen peroxide determinations in natural waters

An iodometric titration method is investigated for verifying H/sub 2/O/sub 2/ determinations in natural water matrices. Hydrogen peroxide oxidizes iodide to iodine at pH 4 in the presence of (NH/sub 4/)/sub 6/Mo/sub 7/O/sub 24/ x 4H/sub 2/O. The I/sub 2/ that is generated reacts with an added spike of phenylarsine oxide, the excess of which is titrated with a standardized iodine titrant to an amperometrically determined end point. The difference between titrations with and without the enzyme catalase is proportional to the H/sub 2/O/sub 2/ concentration. The detection limit is estimated to be 0.02 ..mu..M. A previously described independent fluorometric method is in excellent agreement with this method when applied to fresh and saline natural waters containing 0.05-5.00 ..mu..M H/sub 2/O/sub 2/. Demonstration of such agreement can be used for verification purposes in the absence of certified standards.

Reduction of matrix interferences in furnace atomic absorption with the L'vov Platform

Use of a modified L'vov Platform and ammonium phosphate as a matrix modifier greatly reduced matrix interferences in a commercial Massmann-type atomic absorption furnace. Platforms were readily fabricated from furnace tubes and, once positioned in the furnace, caused no inconvenience in operation. Two volatile elements (Pb, Cd), two of intermediate volatility (Co, Cr) and two which form stable oxides (Al, Sn) were tested in natural water and selected synthetic matrices. In every case for which there was a significant matrix effect during atomization from the tube wall, the platform and platform plus modifier gave improved performance. With lead, for example, an average ratio of 0.48 ± 0.11 was found when the slope of the standard additions plot for six different natural water samples was compared to the slope of the standard working curve in dilute acid. The average slope ratio between the natural water matrices and the dilute acid matrix was 0.94 ± 0.03 with the L'vov Platform and 0.96 ± 0.03 with the platform and matrix modifier. In none of the cases studied did the use of the platform or platform plus modifier cause an interference problem where none existed while atomizing from the tube wall. An additional benefit of the platform was a factor of about two improvement in peak height precision.