Human exposure to methyl and butyl parabens and their transformation products in settled dust collected from urban, semi-urban, rural, and tribal settlements in a tropical environment.

The present study involved monitoring the distribution of two widely consumed parabens (methyl paraben (MeP) and butyl paraben (BuP)) and their transformation products in indoor dust from different categories of settlement (urban, semi-urban, rural, and tribal homes). The results revealed a prevalent occurrence of parabens in all the settlement categories. A non-normal distribution pattern for MeP and BuP levels across the sampling sites was noted. While comparing the residence time of parabens in dust samples, it was found that the half-lives of the analytes were greater in the dust from urban (MeP t1/2: 47.510 h; BuP t1/2: 22.354 h) and rural (MeP t1/2: 27.725 h and BuP t1/2: 31.500 h) areas. The presence of paraben metabolites, such as hydroxy methylparaben (OH-MeP), para hydroxy benzoic acid (p-HBA), and benzoic acid (BA) in dust samples supports their transformation within indoor spaces. The average daily intake of parabens through dust ingestion and dermal absorption by children was higher than adults. BuP was the prime contributor (>85%) to the total estradiol equivalency quotient (tEEQ) in all the settlement categories.

Screening and quantification of emerging contaminants in Periyar River, Kerala (India) by using high-resolution mass spectrometry (LC-Q-ToF-MS).

The presence of emerging contaminants (ECs) in different aquatic systems may contribute to hazardous effects on aquatic organisms and subsequently on human health. In the present work, liquid chromatography coupled to a quadrupole time of flight mass spectrometer (LC-Q-ToF-MS) was used to identify and quantify a series of ECs in Periyar River in Aluva region, Kerala, India. The water samples were pre concentrated using solid-phase extraction (SPE) prior to analysis. The compounds were probed in both positive and negative ionization mode using electro spray ionization (ESI). Method validations were performed for linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy, and precision (intraday and inter day). The ECs were quantified using standard calibration curve. The identified nine ECs include pharmaceuticals, personal care products, steroids, surfactants, and phthalate. A relatively high concentration was observed in the case of 2-dodecyl benzene sulfonic acid (1012 ng/l) and low concentration was observed for lignocaine (4.3 ng/l; since this is below LOQ, the value is only approximate). In addition, we have identified another 28 organic compounds using the technique of non-target analysis out of which seven compounds fall in the category of surfactants. Being the first report on ECs in Periyar River, the data is very important as this river is one of the biggest and important rivers of Kerala having several purification units for drinking water in the province.

Photo-transformation of ofloxacin in natural aquatic conditions: Impact of indirect photolysis on the product profile and transformation mechanism.

The natural phototransformation of organic pollutants in the environment depends on several water constituents, including inorganic ions, humic substances, and pH. However, the literature information concerning the influence of various water components on the amount of phototransformation and their impact on the development of various transformation products (TPs) is minimal. This study investigated the phototransformation of ofloxacin (OFL), a fluoroquinolone antibiotic, in the presence of various water components such as cations (K+, Na+, Ca2+, NH4+, Mg2+), anions (NO3-, SO42-, HCO3-, CO32-, PO43-), pH, and humic substances when exposed to natural sunlight. The study reveals that neutral pH levels (0.39374 min⁻1) enhance the phototransformation of OFL in aquatic environments. Carbonate, among anions, shows the highest rate constant (2.89966 min⁻1), significantly influencing OFL phototransformation, while all anions exhibit a notable impact. In aquatic environments, indirect phototransformation of OFL, driven by increased reactive oxygen species, expedites light-induced reactions, potentially enhancing OFL phototransformation. A clear difference was visible in the type of transformation products (TPs) formed during direct and indirect photolysis. The impact of indirect photolysis in the product profile was evaluated by examining the unique properties of TPs in direct and indirect photolysis. The primary transformation products were generated by oxidation and cleavage processes directed towards the ofloxacin piperazinyl, oxazine, and carboxyl groups. The toxicity assessment of TPs derived from OFL revealed that among the 26 identified TPs, TP3 (demethylated product), TP7 and TP8 (decarboxylated products), and TP15 (piperazine ring cleaved product) could potentially have some toxicological effects. These findings suggest that the phototransformation of OFL in the presence of various water components is necessary when assessing this antibiotic's environmental fate.

Organic micropollutant removal and phosphate recovery by polyelectrolyte multilayer membranes: Impact of buildup interactions.

Polyelectrolyte multilayer (PEM) deposition conditions can favorably or adversely affect the membrane filtration performance of various pollutants. Although pH and ionic strength have been proven to alter the characteristics of PEM, their role in determining the buildup interactions that control filtration efficacy has not yet been conclusively proved. A PEM constructed using electrostatic or non-electrostatic interactions from controlled deposition of a weak polyelectrolyte could retain both charged and uncharged pollutants from water. The fundamental relationship between polyelectrolyte charge density, PEM buildup interaction, and filtration performance was explored using a weak-strong electrolyte pair consisting of branching poly (ethyleneimine) and poly (styrene sulfonate) (PSS) across pH ranges of 4-10 and NaCl concentrations of 0 M-0.5 M. PEI/PSS multilayers at acidic pH were dominated by electrostatic interactions, which favored the selective removal of a charged solute, phosphate over chloride, while at alkaline pH, non-electrostatic interactions dominated, which favored the removal of oxybenzone (OXY), a neutral hydrophobic solute. The key factor determining these interactions was the charge density of PEI, which is controlled by pH and ionic strength of the deposition solutions. These findings indicate that the control of buildup interactions can largely influence the physico-chemical and transport characteristics of PEM membranes.

Identifying the Transients and Transformation Products in Hydroxyl Radical-Methimazole Reactions Using DFT and UPLC-Q-TOF MS/MS Approaches.

Oxidative reactions of the hydroxyl radical (·OH) with methimazole (MMI), an antithyroid drug, are crucial for understanding its fate in oxidizing environments. By synergistically integrating density functional theory and ultraperformance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UPLC-Q-TOF MS/MS) techniques, we elucidated the transients and transformation products (TPs) arising from the ·OH-MMI reactions. We probed two hydrogen-atom abstraction (HA) reactions, three radical adduct formation reactions, and single electron transfer (SET) at the M06-2X/6-311++G(d,p)/SMD(water) level. All proposed reaction channels, except for HA from the methyl group and SET, were found to be barrier-free. SET is the dominant oxidation pathway, accounting for 44% of oxidations, as determined by branching ratio analysis. The selenium analogue, MSeI, exhibited minor reactivity differences compared to MMI, yet its overall patterns resembled those of ·OH-MMI reactions. TPs were generated experimentally by reacting MMI with ·OH produced by UV-photolysis of H2O2. Eight TPs were identified from an approximately 24% degradation of MMI using UPLC-Q-TOF MS/MS analysis, and an additional two TPs were identified from the approximately 52% degraded MMI sample. The exact identities of all of the TPs were established through their corresponding fragmentation patterns. This study elucidates the drug's susceptibility to free radical species under physiologically relevant conditions.

Occurrence and distribution of steroid hormones (estrogen) and other contaminants of emerging concern in a south indian water body.

Steroid hormones (SHs) are among the important classes of Contaminants of Emerging Concern (CECs) whose detection in aquatic environments is vital due to their potential adverse health impacts. Their detection is challenging because of their lower stability in natural conditions and low concentrations. This study reports the presence of steroid hormones in a major river system, the Periyar River, in Kerala (India). Water samples were collected from thirty different river locations in the case of SHs and five locations within these in the case of other CECs. These were subjected to LC-MS/MS and LC-Q-ToF/MS analyses. Five SHs, estriol, estrone, 17 ß estradiol, progesterone, and hydroxy progesterone, were separated and targeted using MS techniques. The studies of the water samples confirmed the presence of the first three estrogens in different sampling sites, with estrone present in all the sampling sites. The concentration of estrone was detected in the range from 2 to 15 ng/L. Estriol and estradiol concentrations ranged from 1.0 to 5 ng/L and 1-6 ng/L, respectively. The hormones at some selected sites were continuously monitored for seven months. The chosen areas include the feed water sites for the drinking water treatment plants across the river. The monthly data revealed that estrone is the only SHs detected in all the samples in the selected months. The highest concentration of SH was found in August. Twelve CECs belonging to pharmaceuticals and personal care products were identified and quantified. In addition, 31 other CECs were also identified using non-target analysis. A detailed study of the hormone mapping reported here is the first from any South Indian River.

Delineating the cascade of molecular events in protein aggregation triggered by Glyphosate, aminomethylphosphonic acid, and Roundup in serum albumins.

The molecular basis of protein unfolding on exposure to the widely used herbicide, Glyphosate (GLY), its metabolite aminomethylphosphonic acid (AMPA), and the commercial formulation Roundup have been probed using human and bovine serum albumins (HSA and BSA). Protein solutions were exposed to chemical stress at set experimental conditions. The study proceeds with spectroscopic and imaging tools. Steady-state and time-resolved fluorescence (TRF) measurements indicated polarity changes with the possibility of forming a ground-state complex. Atomic force microscopy imaging results revealed the formation of fibrils from BSA and dimer, trimer, and tetramer forms of oligomers from HSA under the chemical stress of GLY. In the presence of AMPA, serum albumins (SAs) form a compact network of oligomers. The compact network of oligomers was transformed into fibrils for HSA with increasing concentrations of AMPA. In contrast, Roundup triggered the formation of amorphous aggregates from SAs. Analysis of the Raman amide I band of all aggregates showed a significant increase in antiparallel ß-sheet fractions at the expense of α-helix. The highest percentage, 24.6%, of antiparallel ß-sheet fractions was present in amorphous aggregate formed from HSA under the influence of Roundup. These results demonstrated protein unfolding, which led to the formation of oligomers and fibrils.

Singlet oxygen in the removal of organic pollutants: An updated review on the degradation pathways based on mass spectrometry and DFT calculations.

The degradation of pollutants by a non-radical pathway involving singlet oxygen (1O2) is highly relevant in advanced oxidation processes. Photosensitizers, modified photocatalysts, and activated persulfates can generate highly selective 1O2 in the medium. The selective reaction of 1O2 with organic pollutants results in the evolution of different intermediate products. While these products can be identified using mass spectrometry (MS) techniques, predicting a proper degradation mechanism in a 1O2-based process is still challenging. Earlier studies utilized MS techniques in the identification of intermediate products and the mechanism was proposed with the support of theoretical calculations. Although some reviews have been reported on the generation of 1O2 and its environmental applications, a proper review of the degradation mechanism by 1O2 is not yet available. Hence, we reviewed the possible degradation pathways of organic contaminants in 1O2-mediated oxidation with the support of density functional theory (DFT). The Fukui function (FF, f-, f+, and f0), HOMO-LUMO energies, and Gibbs free energies obtained using DFT were used to identify the active site in the molecule and the degradation mechanism, respectively. Electrophilic addition, outer sphere type single electron transfer (SET), and addition to the hetero atoms are the key mechanisms involved in the degradation of organic contaminants by 1O2. Since environmental matrices contain several contaminants, it is difficult to experiment with all contaminants to identify their intermediate products. Therefore, the DFT studies are useful for predicting the intermediate compounds during the oxidative removal of the contaminants, especially for complex composition wastewater.

Bioactive Metabolites of Serratia sp. NhPB1 Isolated from Pitcher of Nepenthes and its Application to Control Pythium aphanidermatum.

Plant-associated bacteria have already been considered as the store house of bioactive compounds that confer the plant growth promotion and disease protection. Hence, the unique plant parts have already been expected to harbor diverse microbial communities with multi-beneficial properties. Based on this, the current study has been designed to identify the potential of Serratia sp. NhPB1 isolated from the pitcher of Nepenthes plant for its activity against the infamous pathogen Pythium aphanidermatum. The in vitro antifungal, plant growth promoting and enzymatic activities of the isolate indicated its promises for agricultural application. The isolate NhPB1 was also demonstrated to have positive effect on Solanum lycopersicum and Capsicum annuum, due to its plant beneficial metabolites. From the results of LC-MS/MS analysis, the isolate has also been revealed to have the ability to synthesize bioactive compounds including salicylic acid, cyclodipeptides, acyl homoserine lactone, indole-3-acetic acid, and serrawettin W1. These identified compounds and their known biological properties make the isolate characterized in the study to have significant promises as an eco-friendly solution for the improvement of agricultural productivity.

Spectro-kinetic investigations on the release mechanism of lysozyme from layer-by-layer reservoirs.

The investigations of protein adsorption and release on interfaces aid in the elucidation of the protein-surface interaction mechanism, which has several applications in the biomedical area. The spectro-kinetic and morphological analysis of the release of lysozyme (Lyz) from chitosan/polystyrene sulphonate (CHI/PSS) multilayer immobilized at pHs 10.6, 8.8 and 5.0 shows that the extent of release strongly depends on the pH of Lyz loading and the ionic strength of the desorbing solution. When compared to pH 8.8, the release for pH 10.6 achieves equilibrium more rapidly. At loading pH 10.6, the release is surface-mediated, at pH 8.8, it is both surface- and bulk-mediated, while at pH 5.0 it is bulk mediated with minimal release. Lyz released for loading pH 10.6 retains its native secondary structure. Kinetic fitting suggests that high loading pH 8.8-10.6 and high release ionic strength (0.5-1.0 M NaCl) lead to burst release of Lyz from CHI/PSS multilayer. Surface morphology changes of multilayer interface upon Lyz loading and release are highlighted by SEM topography and AFM height distribution analysis. The present work indicates that CHI/PSS multilayer system can function as a reservoir for burst as well as controlled release of lysozyme by selecting the loading pH and ionic strength.

Identification of micropollutants from graywater of different complexity and remediation using multilayered membranes.

Graywater reuse is one of the important concepts in attaining water sustainability. A major challenge in this area is to realize various components present in graywater. The present study involves the identification of the chemical components of graywater collected from three different environments and to investigate the efficiency of removal of some of these chemical components using ultrafiltration membranes (polyelectrolyte multilayer (PEM) membranes). The chemical components were analyzed using liquid chromatography connected with quadrupole time-of-flight (UPLC-Q-ToF-MS). A number of micropollutants including surfactants and certain contaminants of emerging concern (CECs) were identified from these samples. Out of 16 compounds identified, 13 were surfactants and the remaining were caffeine, oxybenzone, and benzophenone. These surfactants are mostly the ingredients of various detergents. Low-pressure filtration studies of the collected samples were carried out utilizing chitosan/polyacrylic acid (CHI/PAA) multilayer membranes. A 5.5 bilayer membrane showed more than 95% rejection of the identified compounds in the selected samples and significant improvement in the water quality parameters. This demonstrates that the membrane used in this work is effective in the removal of various chemicals from graywater as well as enhancing the water quality.

Bio-physical and computational studies on serum albumin / target protein binding of a potential anti-cancer agent.

The successful evolution of an effective drug depends on its pharmacokinetics, efficiency and safety and these in turn depend on the drug-target/drug-carrier protein binding. This work, deals with the interaction of a pyridine derivative, 2-hydroxy-5-(4-methoxyphenyl)-6-phenylpyridine 3-carbonitrile (HDN) with serum albumins at physiological conditions utilizing the steady state and time-resolved fluorescence techniques by probing the emission behavior of Trp in BSA and HSA. In-silico studies revealed a combined static and dynamic quenching mechanism for the interactions. The binding studies suggests a spontaneous binding between HDN and the albumins with a moderate binding affinity (Kb ∼ 10-5 M-1) with a single class of binding site. The FRET mediated emission from HDN indicates preferential binding of HDN in subdomain IIA of the albumins with Trp residue in close proximity. Circular dichroism results indicate HDN induced conformational changes for BSA and HSA, but the α-helical secondary structure was well preserved even up to a concentration of 10 µM HDN. Moderate binding affinity of HDN with BSA and HSA and the unaltered secondary structure of proteins on binding propose the potential application of HDN as an efficient drug. The application of docking method on the affinity of HDN towards the proposed target/receptor is discussed.

Alcohol ethoxysulfates (AES) in environmental matrices.

Extensive use of surfactants in numerous fields resulted in their discharge into various environmental compartments including soil, sediment, and water. Alcohol ethoxysulfates (AES) together with alcohol ethoxylates (AE), alkyl sulfates (AS), and linear alkyl benzene sulfonates (LAS) find wide variety of applications in consumer products including both domestic and industrial applications. Consequently, all these surfactants pose several concerns to both aquatic and human health. In the context of environmental impacts, AES has almost equal importance as that of LAS though the literature on this topic is only emerging. This review provides a detailed overview on the various aspects of the anionic surfactant, AES, such as toxicity of AES, its fate in the ecosystem, technical advancements in the area of identification and quantification, its occurrence and distribution in different environmental compartments spanning across the world, and finally a remark of its potential removal strategy from the environment.

Potential involvement of environmental triggers in protein aggregation with mercuric chloride as a model.

Heavy metal based toxicity has a direct relation with the perturbation of protein structure. We have investigated the progressive unfolding of ovalbumin, in the presence of increasing concentration mercury (0-6.25 µM) using different spectroscopic techniques. Formation of amorphous aggregate has been observed at the physiological pH. Initial addition of HgCl2 resulted in the association of monomers to oligomers that proceeded to non-fibrillar aggregates on further addition. The sigmoidal curve obtained from the Stern-Volmer plot clearly divided into three stage transition. A strong lag phase is observed indicating the time dependence for the association of competent monomers. The second stage was resolved into non-cooperative binding. These results match very well with the data from atomic force microscopy and the free energy change observed in the regions. Raman spectroscopic studies indicated toxic antiparallel ß-sheets structure. Time dependent atomic force microscopy study revealed the off-pathway nature of amorphous aggregates. At molten globular state, similar quenching behaviour is observed. The atomic force microscopy images clearly indicate at pH 2.2 the initiation of fibril formation occurs at lower concentration of HgCl2 itself. Our results revealed the conformation switch of ovalbumin upon the contact of an environmental toxin and its possible way of toxicity.

Probing the Role of Cu(II) Ions on Protein Aggregation Using Two Model Proteins.

Copper is an essential trace element for human biology where its metal dyshomeostasis accounts for an increased level of serum copper, which accelerates protein aggregation. Protein aggregation is a notable feature for many neurodegenerative disorders. Herein, we report an experimental study using two model proteins, bovine serum albumin (BSA) and human serum albumin (HSA), to elucidate the mechanistic pathway by which serum albumins get converted from a fully folded globular protein to a fibril and an amorphous aggregate upon interaction with copper. Steady-state fluorescence, time-resolved fluorescence studies, and Raman spectroscopy were used to monitor the unfolding of serum albumin with increasing copper concentrations. Steady-state fluorescence studies have revealed that the fluorescence quenching of BSA/HSA by Cu(II) has occurred through a static quenching mechanism, and we have evaluated both the quenching constants individually. The binding constants of BSA-Cu(II) and HSA-Cu(II) were found to be 2.42 × 104 and 0.05 × 104 M-1, respectively. Further nanoscale morphological changes of BSA mediated by oligomers to fibril and HSA to amorphous aggregate formation were studied using atomic force microscopy. This aggregation process correlates with the Stern-Volmer plots in the absence of discernible lag phase. Raman spectroscopy results obtained are in good agreement with the increase in antiparallel ß-sheet structures formed during the aggregation of BSA in the presence of Cu(II) ions. However, an increase in α-helical fractions is observed for the amorphous aggregate formed from HSA.

Effect of zinc oxide nanoparticle supplementation on the enhanced production of surfactin and iturin lipopeptides of endophytic Bacillus sp. Fcl1 and its ameliorated antifungal activity.

BACKGROUND: Lipopeptides from the Bacillus spp. possess an excellent spectrum of antimicrobial properties which make them suitable candidates to be explored for the food, agricultural, pharmaceutical and biotechnological applications. As the low yield of the lipopeptides limits their applications, methods to enhance their production are highly significant. RESULTS: In this study, extracts prepared from endophytic Bacillus sp. Fcl1 cultured in the presence of various supplements were screened for antifungal activity against Pythium aphanidermatum. From the results, the supplementation of carbon sources and zinc oxide nanoparticles (ZnONPs) was found to have an enhancement effect on the antifungal activity of Bacillus sp. Fcl1. Among these, the highest antifungal activity (73.2%) could be observed for the Fcl1 sample cultured with 5 mg L-1 of ZnONP supplementation. The growth of Fcl1 in the presence of ZnONPs also indicated its compatibility with the nano-supplement in the concentration range used. By liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS) analysis, the synthesis of increased numbers of lipopeptide surfactin derivatives could be identified from the extracts of Fcl1 prepared from the carbon sources and ZnONP-supplemented cultures. In addition to the surfactin derivatives, the presence of another lipopeptide iturin was also detected from the extracts of Fcl1 cultured with ZnONPs. CONCLUSION: ZnONP supplementation was found to enhance antifungal activity and lipopeptide production in the Bacillus sp. Fcl1. The use of nanoparticles to enhance the antifungal mechanisms of Fcl1 as observed in the study provides novel insights to explore its applications for sustainable agricultural productivity.

Impact of Supplements on Enhanced Activity of Bacillus amyloliquefaciens BmB1 Against Pythium aphanidermatum Through Lipopeptide Modulation.

The present study has been designed to improve the activity of endophytic Bacillus amyloliquefaciens BmB1 against Pythium aphanidermatum through the culture supplementation with carbon sources, nitrogen sources and zinc oxide nanoparticles (ZnONPs). From the results of the study, supplementation with glucose (45 g/L), yeast extract (7.5 g/L) and ZnONPs (5 mg/L) were found to enhance the antifungal activity of B. amyloliquefaciens BmB1. This was also confirmed by comparative statistical analysis with experimental control. Further LC-Q-TOF-MS analysis of extracts of B. amyloliquefaciens BmB1 cultured with supplements showed a remarkable modulation of its lipopeptide profile. The blend of lipopeptides enhanced during the culture supplementation of B. amyloliquefaciens BmB1 as evidenced by the mass spectrometric analysis can consider to be the basis of its increased activity against P. aphanidermatum. As Bacillus spp. are well known for their biocontrol activities, the results of the study offer ways to improve its agricultural applications.

Unravelling the fibrillation mechanism of ovalbumin in the presence of mercury at its isoelectric pH.

The intriguing resemblances of amyloid fibrils and spider silk in protein aggregation diseases have instigated the exploration of identical structural features if any in their oligomeric pathways. The serpin group protein, ovalbumin, on defolding in HgCl2 shares commonness to the micellar pathway of spidroins for their aggregation in response to a pH trigger. The structural feature changes from monomer to worm like fibril with a shift in the primary protein pH to slightly acidic pH (4.5), and then proceeds through a secondary nucleation pathway to 'hillock' and 'hydra' like protofibrils rich in ß-sheet and random coil conformers upon exposure to mercury. The findings are backed by atomic force microscopy, confocal Raman spectroscopy and fluorescence measurements. Unlocking such structural features can favorably assist in the design of therapeutics.

Occurrence, distribution and removal of organic micro-pollutants in a low saline water body.

A low saline backwater canal, mainly utilized for domestic and agricultural purposes, has been analyzed for the possible presence of organic micropollutants (OMP) and their potential removal was explored by multilayered microfiltration membranes. The qualitative as well as quantitative analysis were carried out for a span of one year using the technique of liquid chromatography connected with high resolution mass spectrometry (LC-Q-TOF-MS). The identification of the formally unknown compounds was initially done using non-target analysis based on the mass accuracy, isotopic pattern and MS/MS spectral interpretation. Results of the non target screening revealed the presence of 11 OMPs. Five of these OMPs were confirmed using standards; these include chlorophene (CHP), oxybenzone (OXY), N, N-diethyl-meta-toluamide (DEET), N, N-diethyl-benzamide (DEB) and dibutyl phthalate (DBP). Among the confirmed OMPs, the highest concentration was observed for DBP (244.61 ng l-1). The most frequently observed OMP in the study area was DBP while the least was DEB which is an insect repellent as well as a degradation product of DEET. The ecological risk associated with the target compounds has also been analyzed by calculating the risk quotient (RQ) and the results revealed that at the detected levels, these compounds are capable of causing low to medium risk. Low pressure (<0.3 bar) filtrations of the compounds were attempted using microfiltration (MF) and, poly(ethyleneimine)/poly(styrene sulfonate) (PEI/PSS) multi-layered MF membrane for spiked ultrapure water and also for natural water from the back-water canal. The batch mode illustrates nearly complete removal of CHP and OXY in spiked solutions and a good removal efficiency from natural water. The effect of coexisting ions and surfactants in feed is also illustrated. The high efficiency of the removal of both CHP and OXY, in such a complex medium highlights the potential application of the present method for the removal of similar OMPs in natural waters.

Halide-induced dissolution of lead(IV) oxide in frozen solution.

The dark dissolution behavior of plattnerite (ß-PbO2) was investigated in frozen solutions containing halide ions and compared with those in aqueous solution. The amount of dissolved lead in the frozen solutions varied depending on the solution pH and the kind and concentration of halide ions. The presence of bromide and iodide ions enhanced the dissolution of lead in the aqueous phase, whereas the effect of chloride was insignificant. Compared with the aqueous phase dissolution, ß-PbO2 dissolution in the frozen solution was slightly enhanced in the presence of bromide but suppressed in the presence of iodide. Iodide ions seemed to be relatively more trapped in the bulk ice (ice-crystal lattice) than bromide ions, which might be related to the suppressed dissolution of lead oxide in the presence of iodide. The co-existence of bromide (or iodide) and chloride ions in the frozen solution enhanced the dissolution of lead, which seems to be enabled by an additional reaction pathway involving the formation of mixed halide radicals, whereas such kind of synergistic enhancements were not observed in aqueous solution. The halide-induced lead oxide dissolution in frozen solutions can be related to the behavior of lead ions found in various media of frozen environments.