Correlation between the Limiting pH of Metal Ion Solubility and Total Metal Concentration

Quantification of Free Radicals from Vaping Electronic Cigarettes Containing Nicotine Salt Solutions with Different Organic Acid Types and Concentrations

Electronic (e-) cigarette formulations containing nicotine salts from a range of organic acid conjugates and pH values have dominated the commercial market. The acids in the nicotine salt formulations may alter the redox environment in e-cigarettes, impacting free radical formation in e-cigarette aerosol. Here, the generation of aerosol mass and free radicals from a fourth-generation e-cigarette device was evaluated at 2 wt % nicotine salts (pH 7, 30:70 mixture propylene glycol to vegetable glycerin) across eight organic acids used in e-liquids: benzoic acid (BA), salicylic acid (SLA), lactic acid (LA), levulinic acid (LVA), succinic acid (SA), malic acid (MA), tartaric acid (TA), and citric acid (CA). Furthermore, 2 wt % BA nicotine salts were studied at the following nicotine to acid ratios: 1:2 (pH 4), 1:1 (pH 7), and 2:1 (pH 8), in comparison with freebase nicotine (pH 10). Radical yields were quantified by spin-trapping and electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of free radicals in the nicotine salt aerosol matched those generated from the Fenton reaction, which are primarily hydroxyl (OH) radicals and other reactive oxygen species (ROS). Although the aerosol mass formation was not significantly different for most of the tested nicotine salts and acid concentrations, notable ROS yields were observed only from BA, CA, and TA under the study conditions. The e-liquids with SLA, LA, LVA, SA, and MA produced less ROS than the 2 wt % freebase nicotine e-liquid, suggesting that organic acids may play dual roles in the production and scavenging of ROS. For BA nicotine salts, it was found that the ROS yield increased with a higher acid concentration (or a lower nicotine to acid ratio). The observation that BA nicotine salts produce the highest ROS yield in aerosol generated from a fourth-generation vape device, which increases with acid concentration, has important implications for ROS-mediated health outcomes that may be relevant to consumers, manufacturers, and regulatory agencies.

Evaluation of a pH- and time-dependent model for the sorption of heavy metal cations by poultry litter-derived biochar

Common isotherm and kinetic models cannot describe the pH-dependent sorption of heavy metal cations by biochar. In this paper, we evaluated a pH-dependent, equilibrium/kinetic model for describing the sorption of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) by poultry litter-derived biochar (PLB). We performed sorption experiments across a range of solution pH, initial metal concentration, and reaction time. The sorption of all five metals increased with increasing pH. For Cd, Cu, and Pb, kinetics experiments demonstrated that sorption rates were greater at pH 6.5 than at pH 4.5. For each metal, all sorption data were described using single set of four adjustable parameters. Sorption edge and isotherm data were well described with R2 > 0.93 in all cases. Time-dependent sorption was well described (R2 ≥ 0.90) for all metals except Pb (R2 = 0.77). We then used the best-fit model parameters to calculate linear distribution coefficients (KD) and equilibration times as a function of pH and initial solution concentration. These calculations provide a more robust way of characterizing biochar affinity for metal cations than Freundlich distribution coefficients or Langmuir sorption capacity. Because this model can characterize metal cation sorption by biochar across a wider range of reaction conditions than traditional isotherm or kinetic models, it is better suited for estimating metal cation/biochar interactions in engineered or natural systems.

Expression and function of an S1-type nuclease in the digestive fluid of a sundew, Drosera adelae

BACKGROUND AND AIMS

Carnivorous plants trap and digest insects and similar-sized animals. Many studies have examined enzymes in the digestive fluids of these plants and have gradually unveiled the origins and gene expression of these enzymes. However, only a few attempts have been made at characterization of nucleases. This study aimed to reveal gene expression and the structural, functional and evolutionary characteristics of an S1-type nuclease (DAN1) in the digestive fluid of an Australian sundew, Drosera adelae, whose trap organ shows unique gene expression and related epigenetic regulation.

METHODS

Organ-specificity in Dan1 expression was examined using glandular tentacles, laminas, roots and inflorescences, and real-time PCR. The methylation status of the Dan1 promoter in each organ was clarified by bisulphite sequencing. The structural characteristics of DAN1 were studied by a comparison of primary structures of S1-type nucleases of three carnivorous and seven non-carnivorous plants. DAN1 was prepared using a cell-free protein synthesis system. Requirements for metal ions, optimum pH and temperature, and substrate preference were examined using conventional methods.

KEY RESULTS

Dan1 is exclusively expressed in the glandular tentacles and its promoter is almost completely unmethylated in all organs. This is in contrast to the S-like RNase gene da-I of Dr. adelae, which shows similar organ-specific expression, but is controlled by a promoter that is specifically unmethylated in the glandular tentacles. Comparison of amino acid sequences of S1-type nucleases identifies seven and three positions where amino acid residues are conserved only among the carnivorous plants and only among the non-carnivorous plants, respectively. DAN1 prefers a substrate RNA over DNA in the presence of Zn2+, Mn2+ or Ca2+ at an optimum pH of 4.0.

CONCLUSIONS

Uptake of phosphates from prey is suggested to be the main function of DAN1, which is very different from the known functions of S1-type nucleases. Evolution has modified the structure and expression of Dan1 to specifically function in the digestive fluid.

Development of Cd (II) Ion Probe Based on Novel Polyaniline-Multiwalled Carbon Nanotube-3-aminopropyltriethoxylsilane Composite

Cadmium belongs to the group of potentially toxic metals that have high health and environmental significance. Due to its adverse effects on the environment, this study develops an effective electrochemical sensor for detecting a polyaniline-multiwalled carbon nanotube-3-aminopropyltriethoxysilane (PANI-MWCNT-APTES) substrate cast on the GCE. The as-prepared PANI-MWCNT-APTES was prepared by a wet chemical method, and its formation was investigated using several techniques. As a result, the prepared material exhibited a limit of detection of 0.015 µM for cadmium ions (Cd²⁺) in the linear dynamic range of 0.05 µM to 50 µM. Furthermore, the PANI-MWCNT-APTES-modified GCE current response was stable, repeatable, reproducible, and short. In addition, PANI-MWCNT-APTES/GCE was harnessed for the first time for cadmium detection in real water samples, and the result was satisfactory. Therefore, the recorded results suggest that the newly designed PANI-MWCNT-APTES is a promising material for detecting Cd in the near future for human health and environmental protection.

Spatial variation of heavy metals and uptake potential by Typha domingensis in a tropical reservoir in the midlands region, Zimbabwe

Pollution of aquatic ecosystems with heavy metals is now of global concern due to their dangers to human health and persistence in the environment. An investigation on the spatial distribution of heavy metals in water and sediments and the bioaccumulation potential of heavy metals by plant parts (i.e. roots, stems and leaves) of aquatic macrophyte Typha domingensis (Pers.) Steud in a tropical reservoir was carried out. The results showed no difference in spatial distribution of heavy metals (Fe, Cu, Cd, Cr, Pb, Zn, Mn) in water and sediments from the riverine to the dam wall. The concentration of heavy metals Fe, Cu, Cr and Zn in T. domingensis was of the order root > stem > leaves, but for Pb, Cd and Mn, it followed the order root > leaf > stem. The metal transfer between roots and shoots of T. domingensis followed the order Zn > Pb > Fe > Cu > Cd > Cr. The bio-concentration factor (BCF) was low (BCF < 1) for all the selected metals while the transfer factor (TF) varied among metals suggesting that T. domingensis is not an accumulator of the studied metals. The high concentration of heavy metals found in the water (0.7-16.14 mg L^-1) and sediments (43.6-569.18 mg kg^-1) present a potential risk to both ecological health and human health for the population living in the area. The results of metal concentration in water and sediments from this study are important as a baseline for future monitoring studies. Further studies on bioavailability of metals to other macrophytes and aquatic organisms are recommended.

Impact of repeated topical-loaded manganese-enhanced MRI on the mouse visual system

PURPOSE

Optic nerve degeneration in diseases such as glaucoma and multiple sclerosis evolves in months to years. The use of Mn(2+)-Enhanced Magnetic Resonance Imaging (MEMRI) in a time-course study may provide new insights into the disease progression. Previously, we demonstrated the feasibility of using a topical administration for Mn(2+) delivery to the visual system. This study is to evaluate the impact of biweekly or monthly repeated Mn(2+) topical administration and the pH levels of the Mn(2+) solutions for MEMRI on the mouse visual pathway.

METHODS

Using groups of mice, the MEMRI with an acidic or pH neutralized 1 M MnCl(2) solution was performed. To evaluate the feasibility of repeated MEMRIs, topical-loaded MEMRI was conducted biweekly seven times or monthly three times. The enhancement of MEMRI in the visual system was quantified. After repeated MEMRIs, the corneas were examined by optical coherence tomography. The retinal ganglion cells (RGCs) and optic nerves were examined by histology.

RESULTS

All mice exhibited consistent enhancements along the visual system following repeated MEMRIs. The acidic Mn(2+) solution induced a greater MEMRI enhancement as compared with a neutral pH Mn(2+) solution. Significant 20% RGC loss was found after three biweekly Mn(2+) inductions, but no RGC loss was found after three monthly Mn(2+) treatments. The corneal thickness was found increased after seven biweekly topical-loaded MEMRI.

CONCLUSIONS

Acidic Mn(2+) solutions enhanced the uptake of Mn(2+) observed on the MEMRI. Increasing the time intervals of repeated Mn(2+) topical administration reduced the adverse effects caused by MEMRI.

Industrial wastewater pre-treatment for heavy metal reduction by employing a sorbent-assisted ultrafiltration system

This work examined the adoption of a sorbent-assisted ultrafiltration (UF) system for the reduction of Pb(II), Cu(II), Zn(II) and Ni(II) from industrial wastewater. In such a system metals were removed via several processes which included precipitation through the formation of hydroxides, formation of precipitates/complexes among the metal ions and the wastewater compounds, adsorption of metals onto minerals (bentonite, zeolite, vermiculite) and retention of insoluble metal species by the UF membranes. At pH=6 the metal removal sequence obtained by the UF system was Pb(II)>Cu(II)>Zn(II)>Ni(II) in mg g⁻¹ with significant amount of lead and copper being removed due to chemical precipitation and formation of precipitates/complexes with wastewater compounds. At this pH, zinc and nickel adsorption onto minerals was significant, particularly when bentonite and vermiculite were employed as adsorbents. Metal adsorption onto zeolite and bentonite followed the sequence Zn(II)>Ni(II)>Cu(II)>Pb(II), while for vermiculite the sequence was Ni(II)>Zn(II)>Cu(II)>Pb(II) in mg g⁻¹. The low amount of Pb(II) and Cu(II) adsorbed by minerals was attributed to the low available lead and copper concentration. At pH=9 the adoption of UF could effectively reduce heavy metals to very low levels. The same was observed at pH=8, provided that minerals were added. The prevailing metal removal process was the formation of precipitates/complexes with wastewater compounds.

Adsorption of uranium on halloysite

Adsorption of uranium (U(VI)) from aqueous solutions on halloysite type clay was studied as a function of amount of adsorbent, initial concentration and pH. The values of adsorption data were fitted to Freundlich, Langmuir and Dubinin–Radushkevich (D–R) adsorption isotherms. The mean energy of adsorption was calculated as 5.91 kJ/mol from D–R adsorption isotherm. Lagergren and Bangham equation has been used for dynamic modelling of process and the rate constants of adsorption of uranium on halloysite type clay were calculated at 293, 313 and 333 K. In order to explain the mechanism of adsorption reaction, the rate constants were calculated at high and low uranium concentrations. Adsorption reaction was studied at 293, 303, 313, 323 and 333 K for halloysite type clay and also thermodynamic constants have been calculated. The results show that the adsorption reaction was endothermic and more spontaneous at high temperature.

Surface complexation modelling of uranyl adsorption onto kaolinite based clay minerals using FITEQL 3.2

The aim of this study is to explain how the kaolinite-based clay minerals adsorb hexavalent uranium (uranyl ion), and to model uranyl adsorption based on inner-sphere surface complexation with the kaolinite edge hydroxyl sites and outer-sphere complexation with the permanent charge sites. The adsorption of UO2 2+ on kaolinite-based clay was modeled with the aid of FITEQL 3.2 code using the single-site binding model of the Langmuir approach. Potentiometric titrations and adsorption capacity experiments were carried out in solutions containing different concentrations of the inert electrolyte NaClO4, however adsorption modeling was deliberately done at low ionic strength (0.01 M electrolyte) for enabling adsorption onto the permanent negatively charged sites of kaolinite. When a ‘two-site’ binding model was adopted, i.e., ≡S1OH sites representing silanol and ≡S2OH sites aluminol, a good fit was not obtained, and therefore the involvement of merely aluminol sites in surface complexation was assumed along with the ion exchange-held X2 2-–UO2 2+ species by the NaX permanent charge sites. The uranyl cation was assumed to bind to the clay surface as the sole (unhydrolyzed) UO2 2+ ion and form monodentate surface complexes. The modeling system comprised of surface complexation and ion exchange was resolved with respect to species distributions and relevant stability constants. Electrostatic effects were accounted for using a diffuse layer model (DLM) requiring the minimum number of adjustable parameters. Metal adsorption onto clay showed a steady increase with increasing pH up to pH 5.5, i.e., the edge pH for bulk precipitation at the studied concentration range.

Solubility of heavy metals added to MSW

This paper aims to investigate the six heavy metal levels (Cd, Cr, Cu, Pb, Ni and Zn) in municipal solid waste (MSW) at different pHs. It intends to provide the baseline information of metals solubility in MSW co-disposed or co-digested with MSW incinerator ashes in landfill or anaerobic bioreactors or heavy metals contaminated in anaerobic digesters. One milliliter (equal to 1mg) of each metal was added to the 100ml MSW and the batch reactor test was carried out. The results showed that higher HNO3 and NaOH were consumed at extreme pH of 1 and 13 compared to those from pH 2 to 11 due to the comparably higher buffer capacity. Pb was found to have the least soluble level, highest metal adsorption (%) and highest partitioning Kd (lg(-1)) between pH 3 and 12. In contrast, Ni showed the highest soluble level, lowest metal adsorption (%) and lowest Kd (lg(-1)) between pH 4 and 12. Except Ni and Cr, other four metals seemed to show the amphibious properties as comparative higher solubility was found in the acidic and basic conditions.

Modeling of Copper(II), Cadmium(II), and Lead(II) Adsorption on Red Mud from Metal-EDTA Mixture Solutions

The adsorption of toxic heavy metal cations, i.e., Cu(II), Cd(II), and Pb(II), from metal-EDTA mixture solutions on a composite adsorbent having a heterogeneous surface, i.e., bauxite waste red mud, has been investigated and modeled with the aid of a modified surface complexation approach in respect to pH and complexant dependency of heavy metal adsorption. EDTA was selected as the modeling ligand in view of its wide usage as an anthropogenic chelating agent and abundance in natural waters. The adsorption experiments were conducted for metal salts (nitrates), metal-EDTA complexes alone, or in mixtures containing (metal+metal-EDTA). The adsorption equilibrium constants for the metal ions and metal-EDTA complexes were calculated. For all studied cases, the solid adsorbent phase concentrations of the adsorbed metal and metal-EDTA complexes were found by using the derived model equations with excellent compatibility of experimental and theoretically generated adsorption isotherms. The model was useful for metal and metal-EDTA mixture solutions either at their natural pH of equilibration with the sorbent, or after pH elevation with NaOH titration up to a certain pH. Thus adsorption of every single species (M(2+) or MY(2-)) or of possible mixtures (M(2+)+MY(2-)) at natural pH or after NaOH titration could be calculated by the use of simple quadratic model equations, once the initial concentrations of the corresponding species, i.e., [M(2+)](0) or [MY(2-)](0), were known. The compatibility of theoretical and experimental data pairs of adsorbed species concentrations was verified by means of nonlinear regression analysis. The findings of this study can be further developed so as to serve environmental risk assessment concerning the expansion of a heavy metal contaminant plume with groundwater move ment in soil consisting of hydrated-oxide type minerals. Copyright 2000 Academic Press.