Natural Lake Water Research Articles

Mesoporous g-C3N4/β-CD nanocomposites modified glassy carbon electrode for electrochemical determination of 2,4,6-trinitrotoluene

A novel method using mesoporous g-C3N4 and β-cyclodextrin nanocomposite (mpg-C3N4/β-CD) for the electrochemical detection of 2,4,6-trinitrotoluene (TNT) is presented. The unique structure of the mesoporous g-C3N4/β-CD nanocomposite facilitates both mpg-C3N4 electrocatalysis and β-CD inclusion-complexation of the analytes. When compared to GCE or mpg-C3N4 modified GCE, the mpg-C3N4/β-CD modified glassy carbon electrode exhibits superior performance in the detection of TNT. Hence, we used mpg-C3N4/β-CD modified GCE for the development of TNT detection method using linear sweep voltammetry at −0.45 V reduction potential with 100 s accumulation time. The TNT calibration curve is linear within the 1–100 μM concentration range and the corresponding sensitivity and LOD values are 0.2 μA/μM and 68 ppb respectively. When p-nitrophenol and o-nitrophenol introduced into the matrix, the mpg-C3N4/β-CD modified GCE sensor showed high selectivity and sensitivity to the nitroaromatic compounds. Optimized mpg-C3N4/β-CD modified GCE sensor was used for the detection of TNT in a natural lake water sample with an 96.8% peak recovery. The results shown in work illustrate the potential of using g-C3N4/β-CD modified GCE sensors in monitoring TNT and other nitroaromatic compounds in environmental analysis.

Low invasion success of an invasive cyanobacterium in a chlorophyte dominated lake

Biological invasions are a major threat to biodiversity and ecosystem functioning. Successful invasions depend on the interplay of multiple abiotic and biotic factors, however, the process of the invasion itself is often overlooked. The temporal variation of environmental factors suggests that a ‘window of opportunity’ for successful invasions exists. Especially aquatic habitats, like temperate lakes, undergo pronounced seasonal fluctuations and show temporally varying environmental conditions in e.g. nutrient availability, temperature and the composition of the resident community including competitors and consumers. We experimentally tested if an invasion window for the globally invasive cyanobacterium Cylindrospermopsis raciborskii exists. From May to September, we determined the invasion success of C. raciborskii in laboratory mesocosms with natural lake water. Although the invasion success was generally low, the invasiveness varied among months and differed in total invasive biomass, net development and final share of C. raciborskii in the community. During the first days, C. raciborskii strongly declined and this initial, short-term decline was independent of the ambient consumptive pressure. These results are in contrast to laboratory studies in which C. raciborskii successfully invaded, suggesting that a complex natural system develops a resistance to invasions.

Nanoparticle stability in lake water shaped by natural organic matter properties and presence of particulate matter

Predicting nanoparticle (NP) fate in the environment continues to remain a challenge, especially for natural surface water systems, where NPs can hetero-aggregate with natural organic and mineral suspended matter. Here we present the interactions and aggregation behavior of TiO2 NPs with natural organic matter (NOM) in a natural lake water. NP fate in a synthetic water of the same pH and ionic composition was also tested in the presence and absence of NOM analogs to gain insight into the different stabilizing effects of each NOM type. Several complementary analytical techniques were utilized to assess lake NOM composition, including pyrolysis−gas chromatography–mass spectrometry, gel permeation chromatography, the polarity rapid-assessment method, and Nanoparticle Tracking Analysis. In the natural lake water, the TiO2 NPs preferentially interacted with mostly anionic NOM of high and medium molecular weight (~1200–1450 and 400–520 Da). Specifically, strong interactions with proteins and polyhydroxy aromatics were observed. NP fate and stability were determined in both raw lake water containing mineral particulate matter and total NOM (NOMtot) and filtered lake water containing only NOM <0.8 μm (NOM<0.8), with different aggregation profiles observed over time. Additionally, three times the number of TiO2 NPs remained in suspension when only NOM<0.8 was present compared to the unfiltered water containing mineral particulate matter and NOMtot. These results demonstrate the contrasting NP fates in the aquatic environment according to the presence of NOMtot vs. NOM<0.8 and further suggest that the use of pure NOM analogs may not accurately represent NP interactions and fate in the natural system.

Enhancing solar disinfection of water in PET bottles by optimized in-situ formation of iron oxide films. From heterogeneous to homogeneous action modes with H2O2 vs. O2 – Part 2: Direct use of (natural) iron oxides

Solar disinfection (SODIS) is a well-accepted intervention method, leading to an improvement in contaminated water sources. In this work, we attempted to further enhance the bacterial inactivation process during light exposure. By means of iron oxide addition, we generated a film on the inner surface of PET bottles used in SODIS, in order to induce further pathways of solar-mediated inactivation. More specifically, in this 2nd part, the deposition process has been systematically assessed, using iron oxides (Fe-Ox). The deposition parameters, namely, the precursor concentration (50 mg/L to 1 g/L), deposition time (1–4 h), oxide type (semiconductor, Fe species), size (μm vs. nm), and specific surface area (∼5–150 m2/g), were assessed. The use of H2O2 as the electron acceptor (and heterogeneous photo-Fenton induction) enhanced the efficacy without decreasing the reuse potential. More than 60% and 75% reduction in the treatment time was observed, compared with that for SODIS in a normal bottle, with O2 and H2O2 (in situ photo-Fenton) as the electron acceptors, respectively. The semiconductor mode of action and controlled iron leaching in the system both demonstrated bactericidal capacity; particularly, it was found that the factors affecting the process partially correlated with the oxide characteristics (size, band gap, and isoelectric point), rather than the capacity to photo-dissolve iron. Consequently, the use of a natural Fe source yielded results (deposition parameters and efficacy) resembling those for iron salts, indicating the dominant inactivation pathways governing the process in the presence or absence of H2O2. Finally, the disinfection of natural lake water with natural Fe–deposed bottles showed similar results to those of Fe-salt–deposed bottles, indicating that in a suitable matrix, the process can work equally well.

An Innovative Portable Biosensor System for the Rapid Detection of Freshwater Cyanobacterial Algal Bloom Toxins.

Harmful algal blooms in freshwater systems are increasingly common and present threats to drinking water systems, recreational waters, and ecosystems. A highly innovative simple to use, portable biosensor system (MBio) for the rapid and simultaneous detection of multiple cyanobacterial toxins in freshwater is demonstrated. The system utilizes a novel planar waveguide optical sensor that delivers quantitative fluorescent competitive immunoassay results in a disposable cartridge. Data are presented for the world's first duplex microcystin (MC)/cylindrospermopsin (CYN) assay cartridge using a combination of fluorophore-conjugated monoclonal antibodies as detector molecules. The on-cartridge detection limits of 20% inhibitory concentration (IC20) was 0.4 μg/L for MC and 0.7 μg/L for CYN. MC assay coverage of eight important MC congeners was demonstrated. Validation using 45 natural lake water samples from Colorado and Lake Erie showed quantitative correlation with commercially available laboratory-based enzyme linked immunosorbent assays. A novel cell lysis module was demonstrated using cyanobacteria cultures. Results show equivalent or better performance than the gold-standard but more tedious 3× freeze-thaw method, with >90% cell lysis for laboratory cultures. The MBio system holds promise as a versatile tool for multiplexed field-based cyanotoxin detection, with future analyte expansion including saxitoxin, anatoxin-a, and marine biotoxins.

Reactions of Rana arvalis Nilss. Tadpoles at Early Developmental Stages to Some Natural Chemical Stimuli

We have investigated behavioral responses of Rana arvalis Nilss. tadpoles to water carrying various water-soluble chemical stimuli: natural lake water; dechlorinated tap water; water in which tadpoles were kept; water with chemical characteristics of the jellylike remains of their own or other clutches after tadpole hatching; boiled nettle, which was used as food for laboratory animals; and water containing toxins of the skin glands of the common toad Bufo bufo L. The preference for natural water over the tap water was revealed, as well as the fact that naive tadpoles were attracted by the “smell” of nettles and tried to avoid toxins.

Degradation of phenol via ortho-pathway by Kocuria sp. strain TIBETAN4 isolated from the soils around Qinghai Lake in China.

Based on the feature of high-altitude permafrost topography and the diverse microbial ecological communities of the Qinghai-Tibetan Plateau, soil samples from thirteen different collection points around Qinghai lake were collected to screen for extremophilic strains with the ability to degrade phenol, and one bacterial strain recorded as TIBETAN4 that showed effective biodegradation of phenol was isolated and identified. TIBETAN4 was closely related to Kocuria based on its observed morphological, molecular and biochemical characteristics. TIBETAN4 grew well in the LB medium at pH 7–9 and 0–4% NaCl showing alkalophilicity and halophilism. The isolate could also tolerate up to 12.5 mM phenol and could degrade 5 mM phenol within 3 days. It maintained a high phenol degradation rate at pH 7–9 and 0–3% NaCl in MSM with 5 mM phenol added as the sole carbon source. Moreover, TIBETAN4 could maintain efficient phenol degradation activity in MSM supplemented with both phenol and glucose and complex water environments, including co-culture Penicillium strains or selection of non-sterilized natural lake water as a culture. It was found that TIBETAN4 showed enzymatic activity of phenol hydroxylase and catechol 1,2-dioxygenase after induction by phenol and the corresponding genes of the two enzymes were detected in the genome of the isolate, while catechol 2,3-dioxygenase or its gene was not, which means there could be a degradation pathway of phenol through the ortho-pathway. The Q-PCR results showed that the transcripts of both the phenol hydroxylase gene and catechol 1,2-dioxygenase gene were up-regulated under the stimulation of phenol, demonstrating again that the strain degraded phenol via ortho-degradation pathway.

Predators and nutrient availability favor protozoa-resisting bacteria in aquatic systems

The long co-existence of bacteria and protozoa has led to the development of bacterial protozoa resistance strategies, which are suggested to serve as drivers for the evolution of pathogenic bacteria. However, the ecological mechanisms underpinning selection for protozoa-resistance in aquatic bacteria are poorly known. To assess the role of nutrient availability and predation-pressure on selection for protozoa-resisting bacteria (PRB), an enrichment-dilution experiment was designed using laboratory microcosms containing natural lake water. PRB was monitored by screening 16S rRNA amplicon sequence data for reads assigned to bacteria that previously has been shown to resist degradation by amoebae. To estimate the effects of the microbial food web dynamics (microscopy of; heterotrophic bacteria, phytoplankton, protozoa and rotifers) and physicochemical variables on the PRB abundance in the study system, a joint species distribution modelling approach was used. The predation-pressure (ratio between predator and bacterial biomass) had a positive effect on the abundance of the PRB genus Mycobacterium, while perturbation (enrichment and dilution) favored the PRB genus Pseudomonas that dominated the bacterial community in the disturbed systems. Our results show that PRB with different ecological strategies can be expected in water of high and intermediate nutrient levels and after major disturbances of an aquatic system.

Determining major factors controlling phosphorus removal by promising adsorbents used for lake restoration: A linear mixed model approach

Phosphorus (P) removal from lake/drainage waters by novel adsorbents may be affected by competitive substances naturally present in the aqueous media. Up to date, the effect of interfering substances has been studied basically on simple matrices (single-factor effects) or by applying basic statistical approaches when using natural lake water. In this study, we determined major factors controlling P removal efficiency in 20 aquatic ecosystems in the southeast Spain by using linear mixed models (LMMs). Two non-magnetic -CFH-12® and Phoslock®- and two magnetic materials -hydrous lanthanum oxide loaded silica-coated magnetite (Fe-Si-La) and commercial zero-valent iron particles (FeHQ)- were tested to remove P at two adsorbent dosages. Results showed that the type of adsorbent, the adsorbent dosage and color of water (indicative of humic substances) are major factors controlling P removal efficiency. Differences in physico-chemical properties (i.e. surface charge or specific surface), composition and structure explain differences in maximum P adsorption capacity and performance of the adsorbents when competitive ions are present. The highest P removal efficiency, independently on whether the adsorbent dosage was low or high, were 85–100% for Phoslock and CFH-12®, 70–100% for Fe-Si-La and 0–15% for FeHQ. The low dosage of FeHQ, compared to previous studies, explained its low P removal efficiency. Although non-magnetic materials were the most efficient, magnetic adsorbents (especially Fe-Si-La) could be proposed for P removal as they can be recovered along with P and be reused, potentially making them more profitable in a long-term period.

Bioaccumulation of microcystin congeners in soil-plant system and human health risk assessment: A field study from Lake Taihu region of China

A 120-day field study was carried out near Lake Taihu to evaluate the bioaccumulation of microcystin (MC) congeners in a soil-plant system, as well as to assess human health risk when consuming edible plants irrigated with MCs-contaminated water. Natural cyanobacteria bloom-containing lake water (lake water) and half-diluted natural cyanobacteria bloom-containing lake water with tap water (half-lake water) were used to irrigate lettuce and rice. An additional treatment involving fertilization with a cyanobacteria bloom was applied just to the lettuce experiment. MCs in soils, roots, leaves and grains (rice) were detected. In the soil-lettuce system, the three MC congeners in soils fertilized with a cyanobacteria bloom were not detected. The highest concentrations of MCs detected in soils, lettuce roots and leaves were 24.8 (MC-LR 10.1, MC-RR 10.5, MC-YR 4.2) μg kg−1, 424 (MC-LR 168, MC-RR 194, MC-YR 61.5) μg kg−1 and 183 (MC-LR 78.0, MC-RR 76.8, MC-YR 28.1) μg kg−1, respectively, in the lake water treatment. In the soil-rice system, the highest concentration of MCs was accumulated in roots 1504 (MC-LR 634, MC-RR 573, MC-YR 297) μg kg−1, in the lake water treatment. However, the concentration of MCs that accumulated in grains was extremely low with a total MCs concentration of 5.2 (MC-LR 2.1, MC-RR 2.0, MC-YR 1.1) μg kg−1 in the lake water treatment. According to the estimated daily intake (EDI) value, fertilizing with an appropriate amount (0.2% or less, w/w, dry weight (DW)) of a cyanobacteria bloom, as well as consuming rice irrigated with lake water would not pose a threat to human health. However, the EDI values for both adults and children reached tolerable daily intake (TDI) value, assuming they consumed lettuce irrigated with lake water. Results obtained from the growth and yield indicators suggest that MCs bioaccumulation in edible plants is not necessarily coupled with phytotoxic effects.

Host and Aquatic Environment Shape the Amphibian Skin Microbiome but Effects on Downstream Resistance to the Pathogen Batrachochytrium dendrobatidis Are Variable.

Symbiotic microbial communities play key roles in the health and development of their multicellular hosts. Understanding why microbial communities vary among different host species or individuals is an important step toward understanding the diversity and function of the microbiome. The amphibian skin microbiome may affect resistance to the fungal pathogen Batrachochytrium dendrobatidis (Bd). Still, the factors that determine the diversity and composition of the amphibian skin microbiome, and therefore may ultimately contribute to disease resistance, are not well understood. We conducted a two-phase experiment to first test how host and environment shape the amphibian skin microbiome, and then test if the microbiome affects or is affected by Bd infection. Most lab experiments testing assembly of the amphibian skin microbiome so far have compared sterile to non-sterile environments or heavily augmented to non-augmented frogs. A goal of this study was to evaluate, in an experimental setting, realistic potential drivers of microbiome assembly that would be relevant to patterns observed in nature. We tested effects of frog genetic background (2 source populations) and 6 natural lake water sources in shaping the microbiome of the frog Rana sierrae. Water in which frogs were housed affected the microbiome in a manner that partially mimicked patterns observed in natural populations. In particular, frogs housed in water from disease-resistant populations had greater bacterial richness than frogs housed in water from populations that died out due to Bd. However, in the experiment this difference in microbiomes did not lead to differences in host mortality or rates of pathogen load increase. Frog source population also affected the microbiome and, although none of the frogs in this study showed true resistance to infection, host source population had a small effect on the rate of pathogen load increase. This difference in infection trajectories could be due to the observed differences in the microbiome, but could also be due to other traits that differ between frogs from the two populations. In addition to examining effects of the microbiome on Bd, we tested the effect of Bd infection severity on the microbiome. Specifically, we studied a time series of the microbiome over the course of infection to test if the effects of Bd on the microbiome are dependent on Bd infection severity. Although limited to a small subset of frogs, time series analysis suggested that relative abundances of several bacterial phylotypes changed as Bd loads increased through time, indicating that Bd-induced disturbance of the R. sierrae microbiome is not a binary effect but instead is dependent on infection severity. We conclude that both host and aquatic environment help shape the R. sierrae skin microbiome, with links to small changes in disease resistance in some cases, but in this study the effect of Bd on the microbiome was greater than the effect of the microbiome on Bd. Assessment of the microbiome differences between more distantly related populations than those studied here is needed to fully understand the role of the microbiome in resistance to Bd.

Bench-scale Study on the Removal of TiO2Nanoparticles in Natural Lake Water by Coagulation

Titanium dioxide nanoparticles (TiO2 NPs) are an emerging environmental concern, considering their proven toxicity and wide commercial application nowadays. Once entering natural water bodies, they...

Carbon black supported Au–Pd core-shell nanoparticles within a dihexadecylphosphate film for the development of hydrazine electrochemical sensor

An amperometric method for the determination of hydrazine (HDZ) using a glassy carbon (GC) electrode modified with carbon black supported Au–Pd core–shell structured nanoparticles (Au@Pd/CB) within dihexadecylphosphate (DHP) film (Au@Pd/CB-DHP/GCE) is proposed. Au@Pd nanoparticles were synthesized by chemical reduction of AuCl3 and PdCl2 using ethylene glycol as a reducing agent, and the nanoparticles supported on CB were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The proposed Au@Pd/CB-DHP/GCE and CB-DHP/GCE (without Au@Pd) electrodes were used to investigate the electrochemical behavior of HDZ using cyclic voltammetry. When the Au@Pd/CB-DHP/GCE was used, an electrocatalytic effect was observed, the analytical signal was substantially increased (87%) and the oxidation potential decreased, i.e. in 728mV. Additionally, the apparently heterogeneous electron-transfer rate constant (k0) obtained for the Au@Pd/CB-DHP/GCE (0.15cms−1) was about two orders of magnitude greater than that obtained using the CB-DHP/GCE (0.068cms−1). Under the optimized conditions for the amperometric technique, a linear analytical curve for HDZ was obtained in the range of 2.50–88.0μmolL−1, with a limit of detection of 0.23μmolL−1 (0.0074ppm). The proposed method was satisfactorily applied to determine the concentration of HDZ in natural lake and tap water samples.

Seasonal variability of natural water chemistry affects the fate and behaviour of silver nanoparticles

Understanding the environmental behaviour of nanoparticles (NPs) after release into aquatic systems is essential to predict the environmental implications of nanotechnology. Silver nanoparticles (AgNPs) represent a major class of engineered NPs with a significant potential for environmental impact. Therefore, investigating their transformations in natural waters will help predict their long term environmental fate and behaviour. AgNPs were characterized in natural lake water collected seasonally from the same freshwater source, using column microcosms to assess their behaviour and transport at different depths. Building on our previous work using similar systems with synthetic waters, the influence of water chemistry and NP surface modifications on colloidal stability and dissolution in natural lake water over time was investigated. A simple sedimentation-diffusion model parameterized by the particle properties and total Ag concentration was successfully used to understand AgNPs transport behaviour. PVP coated AgNPs remained colloidally stable, with their transport in the water column dominated by diffusion, and exhibited no significant or substantial changes in data or model parameters for different seasons. Citrate coated AgNPs were susceptible to rapid aggregation, sedimentation, dissolution and reprecipitation; their transport in the water column was determined by both diffusion and sedimentation.

Efficient Bacterial Inactivation by Transition Metal Catalyzed Auto-Oxidation of Sulfite.

Disinfection is an indispensable process in wastewater treatment plants. New bacterial inactivation technologies are of increasing interest and persistent demand. A category of simple and efficient bactericidal systems have been established in this study, that is,the combination of divalent transition metal (Mn(II), Co(II), Fe(II), or Cu(II)) and sulfite. In these systems, metal catalyzed auto-oxidation of sulfite was manifested to generate reactive intermediary SO4•- that played the major role in Escherichia coli inactivation at pH 5-8.5. Increasing concentrations of metal ion or sulfite, and lower pH, led to higher bacterial deaths. Bacterial inactivation by Me(II)/sulfite systems was demonstrated to be a surface-bound oxidative damage process through destructing vital cellular components, such as NADH and proteins. Additionally, the developed Me(II)/sulfite systems also potently killed other microbial pathogens, that is, Pseudomonas aeruginosa, Bacillus subtilis, and Cu(II)-antibiotic-resistant E. coli. The efficacy of Me(II)/sulfite in treating real water samples was further tested with two sewages from a wastewater treatment plant and a natural lake water body, and Cu(II)/sulfite and Co(II)/sulfite rapidly inactivated viable bacteria regardless of bacteria species and cell density, therefore holding great promises for wastewater disinfection.

Gold nanoparticles based colorimetric probe for Cr(III) and Cr(VI) detection

A simple and highly practical colorimetric method has been proposed for detection of chromium ions (Cr3+ and Cr6+) synchronously by sodium hyaluronate functionalized gold nanoparticles (SH-AuNPs). The SH-AuNPs were synthesized and characterized by UV–vis spectra and transmission electron microscopy (TEM). The colorimetric response of Cr3+ and Cr6+ can be performed simultaneously by the same probe SH-AuNPs, based on the property of special localized surface plasmon resonance (LSPR). The interaction between chromium ions and sodium hyaluronate causes rapid aggregation of the SH–AuNPs conjugates and a concurrent color conversion from wine red to blue gray which is clearly detectable by the naked eye. By using SH-AuNPs as colorimetric probe, the color change with 3μM Cr3+, 1μM Cr6+, or 10μM mixed chromium ions can be recognized easily by naked eye with highly selectivity. The detection limit calculated by the linear relationship of LSPR were at 0.78nM (for Cr3+), 2.90nM (Cr6+) and 0.69nM (mixed chromium ions) respectively, which were all below the guideline value set by World Health Organization (0.962μM). The practical applicability of the SH-AuNPs was also verified by the detection of chromium ions in natural lake water samples.

Evaluation of the pH buffer capacity of natural lake waters in western Siberia: Criteria of resistance to acidification

A new technique is suggested for evaluating the pH buffer capacity of natural aquatic systems (as exemplified by small lakes in western Siberia) with regard for the pH values of the lake waters and the concentrations of the hydrocarbonate ion and anions of humic acids,. The acid-neutralizing capacity evaluated for small lakes in western Siberia by conventionally used techniques (which was suggested by Norwegian researchers) is compared with evaluations by the technique suggested by the authors. Criteria are suggested for quantifying the immunity of natural waters to acidification in various natural climatic zones in western Siberia.

A Method for Preparing Silver Nanoparticle Suspensions in Bulk for Ecotoxicity Testing and Ecological Risk Assessment.

Methods are needed to prepare stable suspensions of engineered nanoparticles in aqueous matrixes for ecotoxicity testing and ecological risk assessments. We developed a novel method of preparing large volumes of silver nanoparticles (AgNP) in suspension using a commercially available rotor-stator dispersion mill. AgNP in powder form (PVP capped, 30-50nm) was suspended in deionized water and natural lake water at 1g/L and the addition of 0.025% (w/v) gum arabic (GA) increased stability over 2 weeks after preparation. The concentrations of total and dissolved Ag in the suspensions did not change significantly over this period. Analysis of hydrodynamic diameters of the major peaks in suspension using dynamic light scattering showed that suspensions prepared with GA were stable, and this was confirmed by single-particle ICP-MS analysis. This method for dispersing AgNPs provides an inexpensive, yet reliable method for preparing suspensions for toxicity testing and ecosystem level studies of the fate and biological effects of AgNPs in aquatic ecosystems.

The use of modified electrode with carbon black as sensor to the electrochemical studies and voltammetric determination of pesticide mesotrione

A new, simple, sensitive and fast analytical method has been developed for the quantification of the pesticide mesotrione (MST) using square-wave voltammetry (SWV) and a modified glassy carbon electrode with carbon black (CB/GCE) in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB). MST exhibited three well-defined irreversible reduction peaks, at −242, −710 and −1105mV (vs. Ag/AgCl (3.0molL−1 KCl)), by cyclic voltammetry in phosphate buffer solution (pH2.0) containing 30.0μmolL−1 CTAB. An electrocatalytic effect was observed for the first peak; the apparent heterogeneous electron-transfer rate constant (k0) obtained using electrochemical impedance spectroscopy for a 5.0mmolL−1 K3[Fe(CN)6]/5.0mmolL−1 K4[Fe(CN)6] (1:1) solution was 9.77×10−3cms−1, almost two orders of magnitude greater than the rate constant obtained for the GCE electrode (2.15×10−4cms−1). The analytical curve for MST was linear in the MST concentration range from 0.040 to 7.2μmolL−1 with a limit of detection of 0.026μmolL−1. This method was used to determine MST concentration in natural lake and tap water samples and in a sugarcane juice sample, with satisfactory results.

Photo-induced Phosphate Release from Organic Phosphorus Decomposition Driven by Fe(Ⅲ)-oxalate Complex in Lake Water

The phosphate released from organic phosphorus photo-decomposition has a significantly influence on the phosphorus levels in the water column in lakes. In order to reveal the effect of organic phosphorus photo-decomposition on phosphate level in lake water, the phosphate released from organic phosphorus photo-decomposition driven by Fe(Ⅲ)-oxalate complex under UV-Vis and sunlight irradiation was investigated in natural lake water using glyphosate as the model organic phosphorus. The effects of pH and initial concentration of Fe(Ⅲ), oxalate and glyphosate on the phosphate released from glyphosate photolysis were studied. The results showed that phosphate could be released from glyphosate degradation by Fe(Ⅲ)-oxalate complex under UV-Vis and sunlight irradiation. The concentration of phosphate reached 0.25 mg·L-1 and 0.18 mg·L-1 under UV-Vis and sunlight irradiation for 60 and 720 min, respectively. The amount of phosphate released increased with the increase of the initial concentration of Fe(Ⅲ), as well as the increasing oxalate and glyphosate concentration in lake water. However, the increase of pH could significantly inhibit this process in the reaction system. The concentration of phosphorus decreased with the addition of isopropanol, which indicated that the hydroxyl radical (·OH) was one of the main active oxygen species of Fe(Ⅲ)-oxalate complex. The rates of·OH production for Fe(Ⅲ)-oxalate/UV-Vis and Fe(Ⅲ)-oxalate/sunlight systems were 0.52×10-2 μmol·(L·min)-1 and 0.03×10-2 μmol·(L·min)-1, respectively. The steady-state concentrations of hydroxyl radical (·OH) for the Fe(Ⅲ)-oxalate/UV-Vis conditions were 4.74×10-16 mol·L-1 and 0.27×10-16 mol·L-1 for the Fe(Ⅲ)-oxalate/sunlight system.