Lake Water Samples Research Articles

A fluorescent probe based on carbon quantum dots with spectral selectivity for sensitive detection of Cr(VI) and Hg(II) in environmental waters

In this paper, fluorescent carbon dots were prepared by hydrothermal method using 3,5-dihydroxybenzoic acid and l-Arginine as precursors. The synthesized CDs have excitation-dependent emission with emission peaks at 354 nm and 460 nm, corresponding to the optimal excitation wavelengths of 295 nm and 330 nm, respectively. CDs have good dispersion and resistance to photobleaching in aqueous solution, and can maintain stable fluorescence in highly concentrated salt environment. Based on the inner filter effect, Cr(VI) with strong absorption can shield the excitation light of CDs at 295 nm and absorb the emission fluorescence at 354 nm simultaneously. Due to the intermolecular electrostatic interaction, Hg(II) can coordinate with CDs surface groups and cause static quenching, which significantly reduces the fluorescence intensity of CDs emitted at 460 nm. The linear ranges were 0.1–2 μM and 0.4–5 μM for Cr(VI) and Hg(II) detection, respectively, and limits of detection were 0.024 μM and 0.084 μM. Additionally, the probe was successfully applied to tap water and lake water samples. With high sensitivity and spectral selectivity, this sensing strategy realized the detection of two heavy metal ions by a single fluorescent probe, demonstrating its great potential in the field of environmental metal analysis.

Analysis of total thiol concentrations in environmental samples using ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS)

In this study, we developed an ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) approach to measure the concentration of total reactive thiol binding sites in a range of types of environmental samples by monitoring the decrease of monobromo-(trimethylammonio)-bimane (qBBr) caused by thiol-qBBr binding reactions. We first examined the stability of qBBr and potential side reactions that could reduce the accuracy of the UHPLC-MS approach. We found that significant loss of qBBr occurs in the absence of thiols in aqueous solutions after 2–4 h due to qBBr degradation and other side reactions, such as a chloride-for-bromide substitution reaction. To address these issues, in our approach we conduct the thiol-qBBr binding reaction in the presence of excessive qBBr for only 1 h, and we compare the MS signal of unbound qBBr in a thiol-free qBBr standard with that in a thiol-bearing qBBr standard in order to calculate the decrease in the concentration of free qBBr in solution that is caused by thiol-qBBr binding. Using 100–600 nM of N-Acetyl-L-cysteine (ACYS) as a model thiol in a 2 μM qBBr standard, we found that the measured decrease in the MS signal of unbound qBBr linearly correlates to the concentration of added ACYS, with a R2 of 0.988, demonstrating that monitoring the decrease in unbound qBBr can be used to calculate the concentration of total thiol sites in a sample. We demonstrate that the new UHPLC-MS approach yields accurate results when measuring a series of single and mixed thiol standards in the 200–500 nM range, with measured values ranging from 86% to 109% of the known concentration of thiols. In addition to the above control tests, we also used the UHPLC-MS approach to measure dissolved thiol concentrations in several lake water samples. These measurements revealed that each lake contained low μM levels of total thiols, not only demonstrating the ability of the analytical approach to determine thiol site concentrations in natural waters, but also suggesting the widespread importance of these sites in controlling chalcophile element behavior in these systems. The UHPLC-MS approach not only can be used to determine the concentration of dissolved thiol sites at nM levels, but can also be adapted to measure the concentration of thiol binding sites on other environmental samples such as soil, sediment, and solid-phase organic matter surfaces.

Size–controllable synthesis of large–size spherical 3D covalent organic frameworks as efficient on–line solid-phase extraction sorbents coupled to HPLC

BackgroundCovalent organic frameworks (COFs) have found promising applications in separation fields due to their large surface area and high adsorption capacity, but the exiting COFs can not be directly used as the packing materials of on–line solid-phase extraction (SPE) coupled to HPLC and HPLC because their nano/submicron size or irregular shapes might cause ultrahigh column back pressure and low column efficiency. To synthesize the large-size spherical COFs larger than 3 μm as sorbents might be able to address these problems, however it is still a great challenge till now. ResultsIn this work, two large-size spherical 3D COFs (COF–320 and COF–300) were size–controllably synthesized within 10–90 μm via a two–step strategy. These two spherical COFs showed large surface area, fine crystallinity, good chemical/mechanical stability, and good reproducibility. As an application case, when used as the on–line SPE sorbents coupled to HPLC, the large–size spherical COF–320 displayed high binding capacity for bisphenol F (Qmax of 452.49 mg/g), low column back pressure (6–8 psi at flow rate of 1 mL/min), and good reusability (at least 30 cycles). The developed on–line–SPE–HPLC–UV method presented good analytical performance with enrichment factor of 667 folds, linear range of 1.0–400 ng/mL, limit of detection (LOD, S/N = 3) of 0.3 ng/mL, limit of quantification (LOQ, S/N = 10) of 1.0 ng/mL, and recoveries of 100.3–103.2 % (RSDs of 2.0–3.5 %) and 95.2–97.0 % (RSDs of 4.3–5.6 %) for tap water and lake water samples, respectively. SignificanceThis is the first case to synthesize the large–size spherical COFs within 10–90 μm, and this work made it possible to directly use COFs as the filling materials of on–line SPE coupled to HPLC and HPLC. The developed analytical method can be potentially applied to the rapid and sensitive detection of trace bisphenol F in environmental water samples.

Improvements in the determination of attogram-sized 231Pa in dissolved and particulate fractions of seawater via multi-collector inductively coupled plasma mass spectrometry

A technique is developed to quantify the ultra-trace 231Pa (35–3904 ag) concentration in seawater using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The method is a modification of the process developed by Shen et al. (Anal Chem 75(5):1075–1079, 2003. https://doi.org/10.1021/ac026247r) and extends it to the application of very low levels of actinides, and the 35 ag 231Pa can be measured with a precision of 15%. The total process blank for the water column was 0.02 ag/g, while the values of the large and small particles were ~ 30 ag/g. The ionization efficiency (ions generated/atom loaded) varies from 0.7 to 2.4%. The measurement time is 2–5 min. The amount of 231Pa needed to produce 231Pa data with an uncertainty of ± 0.8–15% is 35–3904 ag (~ 0.9 × 105 to 10 × 106 atoms). Replicate measurements of known standards and seawater samples demonstrate that the analytical precision approximates that expected from counting statistics, and that based on detection limits of 52 ag, 55 ag, and 28 ag, protactinium can be detected in a minimum seawater sample size of ~ 2.6 L for small suspended particulate matter (> 0.8 μm and < 51 μm), ~ 3.0 L for large suspended particulate matter (> 51 μm), and ~ 56 mL for filtered (< 0.45 μm) seawater. The concentration of 231Pa (several attograms per liter) can be determined with an uncertainty of ± 2–8% (2σ) for suspended particulate matter filtered from ~ 60 L of seawater. For the dissolved fraction, ~ 1 L of seawater yields 231Pa measurements with a precision of 0.8–10%. The sample size requirements are several orders of magnitude less than traditional decay-counting techniques, and the precision is better than that previously reported for ICP-MS techniques. Our technique can also be applied to other environmental samples, including river, lake, and cave water samples.

A label-free 5CB-based aptasensor for highly selective optical detection of amoxicillin residue in freshwater samples

ABSTRACT A novel application of thermotropic liquid crystal (LC) 5CB in an optical aptasensor for the sensitive detection of amoxycillin (AMOX) antibiotic has been reported. In the studied system, the glass substrates were treated with dimethyloctadecyl [3–(trimethoxysilyl) propyl] ammonium chloride (DMOAP) and an aqueous solution of cationic surfactant cetyltrimethylammonium bromide (CTAB) was used to obtain a homeotropically aligned 5CB monolayer at the LC-aqueous interface resulting in a uniformly dark appearance. A highly specific amoxycillin aptamer (AMXA) was immobilised on the glass substrate as a target recognition probe for AMOX molecules. The specific binding of AMXA and AMOX molecules induces orientational changes in LC ordering resulting in a change in LC optical textures observed under a Polarized Optical Microscope (POM). A low limit of detection (LOD) of 10 nM for AMOX was obtained using this sensing system. Additionally, a high specificity for AMOX was also observed during comparative analysis. Finally, the developed biosensor was used to successfully detect AMOX in environments of potential application like tap water and lake water samples. Thus, the developed LC-based aptasensor can be a simple, sensitive and label‐free platform for monitoring real‐time levels of AMOX in freshwater environments.

An electrochemical aptamer sensor for rapid quantification sulfadoxine based on synergistic signal amplification of indole and MWCNTs and its electrooxidation mechanism

Unreasonable disposal of sulfadoxine (SDX) causing food safety and eventually result water pollution, and shows great significance of detection. A sensitive unit Aptamer (Apt) was adopted to construct an electrochemical sensor BSA/Apt/indole/MWCNTs/GCE with the synergistic amplification of multi-walled carbon nanotubes (MWCNTs) and indole for the detection of SDX. Optimization of the conditions allowed the detection of SDX shows a wide linear range from 0.10 to 1000.00 µmol/L by differential pulse voltammetry (DPV). The LOD and sensitivity were determined to be 0.033 µmol/L and 0.29 µA/(µmol/L·cm²), respectively. The recovery rate of SDX in pork and lake water samples range 98.57 %−104.93 %, 93.6 %−106.2 %, respectively. Both the relative standard deviation (RSD) was lower than 7.40 %, which proved that the sensor has good practicability. In addition, DFT calculation was established that a restricted of B3LYP and a basis set of 6–31 G, the electrooxidation of SDX involves two-electron and one-proton transfer.

Thiol-Functionalized MIL-100(Fe)/Device for the Removal of Heavy Metals in Water.

The preparation of a functional device based on a functionalized MIL-100(Fe) metal-organic framework for the solid-phase extraction of heavy metals is reported. By a simple and easy straightforward grafting procedure, a thiol-functionalized MIL-100(Fe) material (MIL-100(Fe)-SH) with a S/Fe ratio of 0.80 and a surface area of 840 m2 g-1 was obtained. MIL-100(Fe)-SH exhibited a higher Hg(II) extraction (96 ± 5%) than that of MIL-100(Fe) (78 ± 4%) due to the interaction between thiol groups and Hg(II) ions. For practical applications, the obtained MIL-100(Fe)-SH was integrated by a simple method to a 3D printed support based on a matrix of interconnected cubes using poly(vinylidene fluoride) as binder, obtaining a functional device that simultaneously acts as stirrer and sorbent. The developed device showed high efficiency for the removal of Hg(II), good reusability, and excellent performance for the simultaneous preconcentration and further detection and quantification of Hg(II), Pb(II), and As(V) in tap, well, and lake water samples.

Water Physico-Chemical Indicators and Metal Assessment of Teceu Lake and the Adjacent Groundwater Located in a Natura 2000 Protected Area, NW of Romania

This study closely analyzes the water quality dynamics of Teceu Lake, situated in a Natura 2000 protected area in Romania. The research investigates seasonal variations and interconnections with groundwater, assessing various ecological impacts. The main physico-chemical indicators of water, such as electrical conductivity (EC), dissolved oxygen (DO), oxygen saturation (OS), temperature, pH, turbidity, ammonium concentration (NH4+), nitrates (NO3−), nitrites (NO2−), orthophosphates (PO43−), water hardness, alkalinity (A), and chlorides (Cl−), were measured over the January–December 2022 period. Metal concentrations for both major metals (Na, K, Ca, Mg, Al) and trace metals (Li, Ga, Fe, Mn, Pb, Cu, Zn, Ni, Ti, Mo, Sr, Ba) were assessed. The evolution of the physico-chemical indicators revealed an increase in nutrient compounds (ammonium and phosphates) during the spring and autumn months. The EC values ranged from 180–444 μS/cm for the lake and 1575–2480 μS/cm for groundwater. The pH values (7.12–7.96) indicated a slightly alkaline environment. DO levels (6.79–11.21 mg/L) indicated good water quality. Chlorides exceeded levels in drinking water in some instances. Water hardness varied due to pH, temperature, and atmospheric pressure. Metal composition revealed diverse levels of aluminum, barium, nickel, copper, zinc, and manganese, which carries implications for environmental and human health. The water quality index (WQI) score, which is based on major ions, indicated that 93% of the groundwater samples were classified as excellent and good for drinking. WQI, based on the main physico-chemical indicators, revealed that 79.17% of the Teceu Lake-water samples and 41.66% of the groundwater samples gathered were classified as good quality; the difference indicated poor quality, especially in autumn. Q- and R-mode cluster analyses revealed distinct clusters for seasonal months and sampling points, suggesting shared sources and geological influences. Notable connections between physico-chemical indicators and metal content were identified, emphasizing the need for a tailored conservation strategy. Correlation analyses highlighted both positive and negative relationships between metal pairs. Understanding these parameters is vital for water resource management and preserving biodiversity in the region. The results of this study are important for monitoring pollution in Lake Teceu and might prompt local communities and authorities to take measures to reduce and prevent pollution.

2D Fluorinated Graphene Oxide (FGO)-Polyethyleneimine (PEI) Based 3D Porous Nanoplatform for Effective Removal of Forever Toxic Chemicals, Pharmaceutical Toxins, and Waterborne Pathogens from Environmental Water Samples.

Although water is essential for life, as per the United Nations, around 2 billion people in this world lack access to safely managed drinking water services at home. Herein we report the development of a two-dimensional (2D) fluorinated graphene oxide (FGO) and polyethylenimine (PEI) based three-dimensional (3D) porous nanoplatform for the effective removal of polyfluoroalkyl substances (PFAS), pharmaceutical toxins, and waterborne pathogens from contaminated water. Experimental data show that the FGO-PEI based nanoplatform has an estimated adsorption capacity (qm) of ∼219 mg g-1 for perfluorononanoic acid (PFNA) and can be used for 99% removal of several short- and long-chain PFAS. A comparative PFNA capturing study using different types of nanoplatforms indicates that the qm value is in the order FGO-PEI > FGO > GO-PEI, which indicates that fluorophilic, electrostatic, and hydrophobic interactions play important roles for the removal of PFAS. Reported data show that the FGO-PEI based nanoplatform has a capability for 100% removal of moxifloxacin antibiotics with an estimated qm of ∼299 mg g-1. Furthermore, because the pore size of the nanoplatform is much smaller than the size of pathogens, it has a capability for 100% removal of Salmonella and Escherichia coli from water. Moreover, reported data show around 96% removal of PFAS, pharmaceutical toxins, and pathogens simultaneously from spiked river, lake, and tap water samples using the nanoplatform.

Synthesis of novel oxytetracycline-molecularly imprinted polymer using a semi-covalent chemical imprinting approach for magnetic dispersive solid phase extraction of tetracyclines in water and milk samples

In the present study, a highly efficient analytical method based on preconcentration of tetracyclines (TCs) in water and milk samples using a magnetic molecularly imprinted polymer (Fe3O4/SiO2/MIP) synthesized by means of a novel semi-covalent synthesis for TCs and determination by HPLC-DAD was proposed. Fe3O4/SiO2/MIP showed specific superficial area of 216.0 m2/g, superior to Fe3O4/SiO2/NIP (non-imprinted material) (103.6 m2/g). Using the Fe3O4/SiO2/MIP, the magnetic dispersive solid phase extraction (MDSPE) for four TCs (chlortetracycline, doxycycline, oxytetracycline, and tetracycline) was based on the preconcentration of 40.0 mL of sample (pH 4.0) vortex-assisted with 10 mg of Fe3O4/SiO2/MIP during 60 s. The method presented a limit of detection (LOD) in the range 0.26–0.60 µg/L, and preconcentration factor in the range 52.3–87.4-fold for the TCs. The method was applied to determine TCs in samples of lake water and cow milk with recovery results ranging from 96.0 to 102.0 %.

Deep eutectic solvent-based ferrofluid for vortex-assisted liquid-liquid microextraction of nonsteroidal anti-inflammatory drugs from environmental waters

A novel ferrofluid of Fe3O4 nanoparticles and a deep eutectic solvent (DES) composed of menthol and pentanoic acid was introduced as a green microextraction medium. The ferrofluid was successfully used as an extractant for vortex-assisted liquid-liquid microextraction (VALLME) of nonsteroidal anti-inflammatory drugs (NSAIDs) in environmental waters prior to their determination by HPLC-DAD. Once the ferrofluid was dispersed in the sample by vortex agitation, phase separation could be easily achieved by placing a neodymium magnet next to the tube, which eliminated the centrifugation step and simplified the operational procedure. As a result, the sample pretreatment took only ≈2 min. The experimental parameters, including pH, nanoparticle amount, ferrofluid volume, vortex time, salt amount, and disruptive solvent type and its volume, were optimized stepwise. The method showed linear behavior for all NSAIDs from 5 to 100 μg/L, with limit of detection values and enrichment factors in the ranges of 1.68–2.05 μg/L and 38.9–50.6, respectively. Intra- and Inter-day accuracies obtained from the analysis of spiked river, lake, and tap water samples at low and high-quality control levels (20 and 80 μg/L) ranged from 90.3% to 108.0%, with relative standard deviations less than <12.3%. The results of this study demonstrate that the use of DES-based ferrofluid in VALLME can be considered a simple, environmentally friendly, and reliable alternative for the determination of NSAIDs in environmental waters.

Tumebacillus lacus sp. nov., isolated from lake water.

A Gram-stain-positive, aerobic, rod-shaped, endospore-forming and motile, by means of peritrichous flagella, bacterium, designated DT12T, was isolated from a lake water sample from Datun Lake of Yunnan Province, PR China. The results of phylogenetic analysis based on 16S rRNA gene sequence and the concatenated alignment of 120 ubiquitous single-copy proteins indicated that the novel strain represented a member of the genus Tumebacillus. The sole quinone was menaquinone-7 and the cell-wall peptidoglycan was type-A1γ. The major fatty acids (>10 %) of the novel strain were iso-C15 : 0 and anteiso-C15 : 0, while the major polar lipids were phosphatidylmonomethylethanolamine, phosphatidylethanolamine and phosphatidylglycerol. The results of phylogenetic analyses combined with phylogenetic, phenotypic and chemotaxonomic features, strongly supported the hypothesis that the strain should be classified as representing a novel species of the genus Tumebacillus, for which the name Tumebacillus lacus sp. nov. is proposed. The type strain is DT12T (=KCTC 33958T= MCCC 1H00320T). The genomic analysis revealed that DT12T has various biosynthetic gene clusters for secondary metabolites, and members of the genus Tumebacillus may represent a promising source of new natural products. Our study also showed that members of the genus Tumebacillus are widely distributed in a variety of habitats throughout the globe, particularly in soils, human-, animal- and plant-associated environments. Members of the genus Tumebacillus may have an important role in the growth and health of humans, plants and animals.

Research of Physical-Chemical and Ecological Characteristics of Ukkadam Lake Water Coimbatore District, Tamil Nadu, India

Degradation of lake water quality has been seen for many years, particularly in lakes close to urban areas with human activity. The goal of the current inquiry was to identify the various physical, chemical, and biological aspects of the surface water quality of several lakes in Coimbatore, India. The significance of the sampling points was considered when choosing them. Water samples were mostly taken from open wells in and around the Coimbatore district from the following sampling locations: Ukkadam Lake. The physical-chemical characteristics, such as total dissolved solids, pH, electrical conductivity, biochemical oxygen requirement, faeces coliforms, dissolved oxygen, and turbidity, Alkalinity, Sulphate, Nitrate, Phosphate, Chlorides. The findings indicated that lake water samples taken at several locations in and around Coimbatore city were above WHO criteria.

Evaluation of water from Lake Coatetelco in central-south Mexico and surrounding groundwater wells for drinking and irrigation, and the possible health risks

Due to an increasing reduction of hydrological resources across Mexico and their growing contamination from global warming and anthropogenic activities, this study evaluated water from the perennial Lake Coatetelco (Ca–Mg–HCO3) in tropical central-southern Mexico and groundwater (Ca–Mg–HCO3 and Na–HCO3–Cl) from the surrounding wells for drinking as well as irrigation qualities. Comparison with the WHO guidelines and the estimated water quality indices (DWQI and IWQI) grouped almost all the samples collected after the warm season rainfall in excellent and good categories (DWQI < 100) for drinking, even though fluoride remained > 1.5 mg/L in 50% samples. Except for one groundwater sample, all showed > 25% permeability (classes I and II) in Donnen classification indicating their suitability for irrigation. USSL and Wilcox classifications, however, catalogued some in the high-salinity hazard group and some as doubtful for irrigating regular plants. Samples from about 53% wells were also in high and severe restriction categories of IWQI for the irrigation. Total Hazard Quotient Index (THQI) for estimating the non-carcinogenic risk (HQfluoride > 1) showed that at least one lake water sample and 53% of groundwater might expose the adult and child population to dental and skeletal fluorosis. This water quality assessment data posterior to the rainfall season could be useful as a baseline for both the short- and long-term monitoring in attention to the United Nation’s Sustainable Development Goal 6.

Multiplexed SELEX for Sulfonamide Antibiotics Yielding a Group-Specific DNA Aptamer for Biosensors.

The widespread use of sulfonamide (SA) antibiotics in animal husbandry has led to residues of SAs in the environment, causing adverse effects to the ecosystem and a risk of bacterial resistance, which is a potential threat to public health. Therefore, it is highly desirable to develop simple, high-throughput methods that can detect multiple SAs simultaneously. In this study, we isolated aptamers with different specificities based on a multi-SA systematic evolution of ligands by the exponential enrichment (SELEX) strategy using a mixture of sulfadimethoxine (SDM), sulfaquinoxaline (SQX), and sulfamethoxazole (SMZ). Three aptamers were obtained, and one of them showed a similar binding to all tested SAs, with dissociation constant (Kd) ranging from 0.22 to 0.63 μM. For the other two aptamers, one is specific for SQX, and the other is specific for SDM and sulfaclozine. A label-free detection method based on the broad-specificity aptamer was developed for the simultaneous detection of six SAs, with detection of limits ranging from 0.14 to 0.71 μM in a lake water sample. The aptasensor has no binding for other broad-spectrum antibiotics such as β-lactam antibiotics, quinolones, tetracyclines, and chloramphenicol. This work provides a promising biosensor for rapid, multiresidue, and high-throughput detection of SAs, as well as a shortcut for the preparation of different specific recognition elements required for the detection of broad-spectrum antibiotics.

Appraisal of heavy metal contents, spatial-temporal variation, toxic metal pollution, and health risk in water and sediment of Uluabat Lake (Ramsar Site, Turkey).

Uluabat Lake holds a significant status as one of our country's essential Ramsar areas. Nevertheless, the lake faces considerable pressure from environmental pollutants. This study employed GIS-based index methods to examine the heavy metal pollution and water quality in Uluabat Lake. To achieve this, sediment and water samples were collected from 19 different locations during various seasons. The concentrations of As, Ni, Cr, Zn, Cu, Cd, Pb, Hg, Al, Fe, and Mn in these samples were analyzed. The average contents of the investigated heavy metals in the lake waters were found to be in the following order: Al > Fe > Mn > As > Zn > Ni > Pb > Cu > Cr > Hg > Cd. The As content in the lake waters exceeded the limit value of 10 μg/L, as defined by TS-266 (2005) and WHO (2017) guidelines. Consequently, the lake waters were deemed unsuitable for drinking. The health risk assessments revealed that consuming the lake waters could lead to both carcinogenic and non-carcinogenic health problems. However, all other metal concentrations were measured below the specified limit values. Based on index calculations, the heavy metal pollution index value indicated that the lake water samples were suitable for drinking water use. Additionally, all samples fell into the "low pollution" category according to the heavy metal evaluation index, and degree of contamination values. However, geoaccumulation index values indicated that As was moderately contaminated. Moreover, enrichment factors of As, Cr, Ni, Pb, and Cd exhibited significant enrichment in lake sediments, with pollution load index values of all sediment samples indicating the impact of anthropogenic pollutants and a decline in sediment quality. Considering all the obtained results together, it can be concluded that environmental pollutants, especially heavy metal pollution, primarily enter the lake water through stream transports, leading to pollution in Uluabat Lake.

A colorimetric sensor array based on nanoceria crosslinked and heteroatom-doped graphene oxide nanoribbons for the detection and discrimination of multiple pesticides

Nanozymes have demonstrated high potential in constructing colorimetric sensor array for pesticides. However, rarely array for pesticides constructed without bio-enzyme were reported. Herein, nanoceria crosslinked graphene oxide nanoribbons (Ce-GONRs) and heteroatom-doped graphene oxide nanoribbons (Ce-BGONRs and Ce-NGONRs) were prepared, demonstrating excellent peroxidase-like activities. A colorimetric sensor array was developed based on directly inhibiting the peroxidase-like activities of the above three nanozymes, which realized the discrimination and quantitative analysis of six pesticides. In the presence of pesticides including carbaryl (Car), fluroxypyr-mepthyl (Flu), thiophanate-methyl (Thio), thiram (Thir), diafenthiuron (Dia) and fomesafen (Fom), the peroxidase-like activities of three nanozymes were inhibited to different degrees, resulting in different fingerprint responses. The six pesticides in the concentration range of 0.1–50 μg/mL and two pesticides mixtures at varied ratios could be detected and discriminated, and minimum detection limit for pesticides was 0.022 μg/mL. In addition, this sensor array has been successfully applied for pesticides discrimination in lake water and apple samples. This work provided a new strategy of constructing simple and sensitive colorimetric sensor array for pesticides based on directly inhibiting the catalytic activities of nanozymes.

Self-assembled Fe3O4-NH2 @g-C3N4 composite for magnetic solid-phase extraction of benzophenones in sea water and lake water coupled with LC-MS/MS determination

Magnetic solid-phase extraction (MSPE) was developed based on a well-designed Fe3O4-NH2 @g-C3N4 nanocomposite as sorbent for a mixture of six benzophenones (BPs) in environmental water samples. The composite fabricated via in-situ self-assembled g-C3N4 shell with homogeneous polymerization of cyanuric chloride and cyanuric acid on Fe3O4-NH2 core. While high adsorption capacity was derived from g-C3N4 via hydrophobic, π-π and hydrogen bonding interactions to the targets, the fast magnetic separation was realized with Fe3O4 core for less solvent consumption. In combination with LC-MS/MS, the Fe3O4-NH2 @g-C3N4 sorbent minimized the interfering components, reduced the matrix effects, and provided the enrichment factors of 121–150 for six BPs with relative standard deviations ≤ 9.7% even after 20 times extraction-desorption cycles. The present method gave the detection limits of 0.3–2.5 ng/L for six BPs with the linear ranges of 1.0–2000 ng/L, and the recoveries of 84.6%−104% in sea water and 86.2%−107% in lake water samples. Thus, the Fe3O4-NH2 @g-C3N4-based MSPE coupled with LC-MS/MS method provided a convenient, efficient, and reliable alternative to monitor trace BPs in environmental water samples.

A Nanocomposite Paste Electrode Sensor for Simultaneous Detection of Uric Acid and Bisphenol A Using Zinc Hydroxide Nitrate-Sodium Dodecylsulfate Bispyribac.

The fabrication of a zinc hydroxide nitrate-sodium dodecylsulfate bispyribac modified with multi-walled carbon nanotube (ZHN-SDS-BP/MWCNT) paste electrode for uric acid and bisphenol A detection was presented in this study. Electrochemical impedance spectroscopy, chronocoulometry, square-wave voltammetry, and cyclic voltammetry were all used to examine the electrocatalytic activities of modified paste electrodes. The modified electrode's sensitivity and selectivity have been considered in terms of the composition of the modifier in percentages, the types of supporting electrolytes used, the pH of the electrolyte, and square-wave voltammetry parameters like frequency, pulse size, and step increment. Square-wave voltammetry is performed by applying a small amplitude square-wave voltage to a scanning potential from -0.3 V to +1.0 V, demonstrating a quick response time and high sensitivity. The ZHN-SDS-BP/MWCNT sensor demonstrated a linear range for uric acid and bisphenol A from 5.0 µM to 0.7 mM, with a limit of detection of 0.4 µM and 0.8 µM, respectively, with good reproducibility, repeatability, and stability as well. The modified paste electrode was successfully used in the determination of uric acid and bisphenol A in samples of human urine and lake water.

Fluid-mineral dynamics at the Rincón de la Vieja volcano—hydrothermal system (Costa Rica) inferred by the study of major, minor and rare earth elements in the hyperacid crater lake

Volcanic lakes are complex natural systems and their chemical composition is related to a myriad of processes. The chemical composition of major, minor, Rare Earth Elements (REE) and physico-chemical parameters at the hyperacid crater lake of Rincón de la Vieja volcano (Costa Rica) are here investigated during February 2013–August 2014. The study of the lake chemical composition allows to identify the main geochemical processes occurring in the lake and to track the changes in the volcanic activity, both important for active volcanoes monitoring. The total REE concentration (∑REE) dissolved in the crater lake varies from 2.7 to 3.6 mg kg−1 during the period of observation. REE in the water lake samples normalized to the average volcanic local rock (REEN-local rock) are depleted in light REE (LREE). On the contrary REEN-local rock in the solids precipitated (mainly gypsum/anhydrite), from lake water samples in laboratory at 22°C, are enriched in LREE. The low variability of (La/Pr)N-local rock and (LREE/HREE)N-local rock ratios (0.92–1.07 and 0.66–0.81, respectively) in crater lake waters is consistent with the low phreatic activity (less than 10 phreatic eruptions in 2 years) observed during the period of observation. This period of low activity precedes the unrest started in 2015, thus, it could be considered as a pre-unrest, characterized by infrequent phreatic eruptions. No clear changes in the REE chemistry are associated with the phreatic eruption occurred at mid-2013. The results obtained investigating water-rock interaction processes at the Rincón de la Vieja crater lake show that rock dissolution and mineral precipitation/dissolution are the main processes that control the variability of cations composition over time. In particular, precipitation and dissolution of gypsum and alunite are responsible for the variations of REE in the waters. Despite the low variations of (La/Pr)N-local rock and (LREE/HREE)N-local rock ratios, this study allows to suggest that REE can be used, together with major elements, as practical tracers of water-rock interaction processes and mineral precipitation/dissolution at active hyperacid crater lakes over time, also during periods of quiescence and low phreatic activity.