Copper Catalysis-Based Amperometric Microsensors for Carbon Dioxide Monitoring.

A fast response microsensor that can detect the distribution of CO2 at the microscale level is essential for the observation of biophysiological activity, carbon flux, and carbon burial. Inspired by the previous success of Cu catalysis, we attempted to use this metal Cu material to develop an amperometric microsensor that can meet the requirements. Specifically, the ambient gases diffuse through a silicone membrane into a trap casing filled with an acidic CrCl2 solution, where the otherwise interfering O2 interferent is removed by a redox with Cr2+. The gases then diffuse through a second silicone membrane into an electrolyte, where CO2 is selectively reduced to methanol (CH3OH) at a Cu cathode through a carbon monoxide (CO) pathway. Due to the use of Cu catalysis at the WE tip, CO2 can be reduced at a less negative polarization (-470 mV) instead of the previously reported -1200 mV, thus avoiding hydrogen-evolution interference due to water from the byproduct or from water diffusion through the silicone membrane. This moderate polarization results in a stable baseline, making the microsensor suitable for long-term monitoring. Interferences from other gases, such as N2O, which may be of much concern in environmental monitoring, can be ignored. Applications and limitations are also discussed with a view to further improvement in the future.

Highly Selective Microsensor for Monitoring Trace Phosphine in the Environment.

Monitoring P flux at the Earth's surface-atmosphere interface has many challenges. Therefore, the development of a technology with high selectivity and high sensitivity to in situ trace PH3 in aquatic or sedimentary environments has become a priority. Herein, an amperometric PH3 microsensor meeting the above conditions is developed. The sensor is equipped with a Au-coated Pt working electrode (WE) and a Pt guard electrode (GE) positioned in an outer glass casing. The WE and GE are polarized at a fixed value of +150 mV with respect to a pseudo-reference electrode. The outer casing is filled with an acid electrolyte solution, and the tip is sealed using a thin silicone membrane. Mixed gases from the environment diffuse through the first layer of the silicone membrane, and the major H2S disruptor is eliminated by a ZnCl2-propylene carbonate trap positioned in the front of the microsensor. Later, the gases diffuse into an electrolytic solution through the second layer of the silicone membrane, and PH3 is selectively oxidized into H3PO4 on the Au-coated Pt WE. This electrochemical oxidation thereby creates a current that is proportional to the concentration of PH3 (>2 nmol·L-1). With the aid of the H2S trap casing and selective catalysis, the effects of other gases on the microsensor can be ignored in terms of environmental monitoring. An example from the sedimentary profile shows that high PH3 accumulations are found 13 mm below the sediment surface.

Weak interaction-alleviated toxicity of aromatic compounds in EPS matrices: Quantifying the noncovalent bonding-to-EPS ecoservice chain.

Extracellular polymeric substances (EPSs) constitute a largely global carbon pool that could participate in geochemical process of organic chemicals. Besides the chemical hydrolysis and redox of chemicals exerted by the EPS, weakly noncovalent interactions with dispersive EPS control the toxicity of numerous organic compounds. Nevertheless, there has been a lack of in-depth research on this issue. This work quantified a chain of links from bonding to detoxification using natural biofilms to explore the control behavior of fragile noncovalent bonding to the ecotoxicity of aromatic compounds. Such bonding decreases cell absorbability of m-phenylenediamine, 2-naphthol, and phenanthrene by 5.3-53.6%, resultantly increasing the indices of microbial diversity by 122.2-279.5%. Herein, the 60 kDa chaperonin in EPS acts as the most important contributor (16.4% of the top 20 proteins) to noncovalent interactions. Hydrophilic carboxyl groups in EPS bind with hydroxyl and amino groups of m-phenylenediamine and 2-naphthol via H-bonds, respectively. Methylene and carboxyl groups combine with hydrophobic phenanthrene via CH···π and H-bonding, respectively. A quantified chain was consequently established that weak interaction linearly controls ecotoxicity of aromatic compounds via the above suppressive cell absorbability of aromatic compounds (R2 =0.82). Considering ubiquitous EPS and prevailing aromatic compounds, our findings revealed a previously unnoticed phenomenon in which seemingly fragile noncovalent bonding profoundly alleviates the ecotoxicity of aromatic compounds in Earth's surface system.

Spontaneous assembly of microbial extracellular polymeric substances into microcapsules involved in trapping and immobilizing degradation-resistant oxoanions.

Despite the ubiquity of microbial extracellular polymeric substances (EPS) in soils and aquatic environments, the roles played by EPS in the nonreductive transformation of toxic and degradation-resistant oxoanions are poorly understood. Here, we used perchlorate, which is ubiquitous in surface environments, as an initiator to study the spontaneous assembly of EPS into microcapsules involved in trapping and immobilizing oxoanions. The results confirmed that ClO4- oxoanions could be rapidly trapped in 20 min by EPS extracted from a common Bacillus subtilis, whereas no chemical reduction of ClO4- occurred in 48 h. Integrated spectroscopic analyses with florescence quenching microtitration and theoretical models showed that amino functionalities of EPS are responsible for sequestering ClO4-, with lower pH values being more favorable to formation of EPS-ClO4- micelles. Combined molecular dynamics scheme with wave function analyses showed that besides amino residues, the protonated side-chain amino groups in the basic proteins have a greater capacity for sequestering ClO4- through a noncovalent H-bonding mechanism in which dissociable protons serve as the nodes to bridge ClO4-. A quantitative association between the number of hydrogen bonds and bioavailability revealed that immobilization by EPS mitigates the uptake of toxic oxoanions by forage ryegrass, reducing their risk exposure to edible produce. MAIN FINDING OF THE WORK: Micelles formed by freely dissolved EPS mitigate the uptake of toxic oxoanions by forage ryegrass.

Synergistic Adsorption and Oxidation of Ciprofloxacin by Biochar Derived from Metal-Enriched Phytoremediation Plants: Experimental and Computational Insights.

Biochar is a promising candidate for the adsorptive removal of organic/inorganic pollutants, yet its role in metal-free catalyzed advanced oxidation processes still remains ambiguous. In this work, five biochar samples (PPBKx, where x represents the pyrolysis temperature) were prepared by using metal-enriched phytoremediation plant residue as the feedstock. Notably, PPBK exhibited a high specific surface area (as high as 1090.7 m2 g-1) and outstanding adsorption capacity toward ciprofloxacin (CIP, as much as 1.51 ± 0.19 mmol g-1). By introducing peroxymonosulfate (PMS, 5 mM) as the chemical oxidant, over 2 mmol g-1 CIP was synergistically adsorbed and oxidized within 30 min although PMS itself could not oxidize CIP efficiently, suggesting the formation of reactive oxidative species. Theoretical calculations revealed that PMS anions preferentially adsorbed on the activated C atoms adjacent to the graphitic N dopant, where the carbon matrix served as the electron donor, instead of as an electron mediator. The adsorbed PMS possessed a smaller molecular orbital energy gap, indicating that it was much easier to be activated than free PMS anions. Surface-bound reactive species were elucidated to be the dominant contributor through chemical quenching experiments and electrochemical characterizations. The catalytic activity of PPBK700 could be greatly retained in repeated oxidations because of the stable N species, which serve as the active catalytic sites, while the CIP adsorption was greatly deteriorated because of the diminishing active adsorption sites (carbon matrix edge) caused by the partial oxidation of PMS. This work not only provides a facile and low-cost approach for the synthesis of functional biochar toward environmental remediation but also deepens the understanding of biochar-catalyzed PMS activation and nonradical oxidation.

Regional-scale investigation for microbial competition-through-environment interactions modulating antibiotic resistance.

Originating from a long history of competition between microbes, antibiotic resistance is a serious global health concern. To avoid the risk of antibiotic resistance, tremendous efforts have been directed towards restricting antibiotic consumption worldwide, but to date with limited success. Resistance is governed by multiple pressures from natural and anthropogenic origins which further create problems with control. This study identifies a chain of links from antibiotic resistant genes (ARGs) to microbial communities to environmental pressures in the surface sediments of forty-two lake clusters across the 1000-km Yangtze Basin of China, and attempts to expound on a control pathway for this resistance risk. Results show that eleven of the 670 bacterial families can be classified as antibiotic-resistant or nonresistant communities which antagonize each other. In natural systems, antagonistic competition controls the increase and decrease in ARGs. Superiority of antibiotic-resistant strains initiates a loss in microbial diversity associated with the prevalence of resistance risk. This study shows that, antibiotics shape the evolution of ARGs in resistant communities through a nonlinear role of orientor; other selected pressures serve as a facilitator to enhance the antibiotic resistance through an investigated chain of links. Furthermore, according to tolerances of the classified communities, abiogenetic development through temperature, salinity and Mg were identified and selected for study from seventy lake parameters. Linear feedbacks to selected pressures make the nonresistant communities outcompete the resistant communities, theoretically modulating the risk of antibiotic resistance.

Probing extracellular reduction mechanisms of Bacillus subtilis and Escherichia coli with nitroaromatic compounds.

Redox transformations of organic contaminants by bacterial extracellular polymeric substances (EPS) and the associated electron transfer mechanisms are rarely reported. Here we show that a nitroaromatic compound (1,3-dinitrobenzene) can be readily reduced to 3-hydroxylaminonitrobenzene and 3-nitroaniline in aqueous suspension of common bacteria (E. coli or B. subtilis) or in aqueous dissolved EPS extracted from the bacteria. The loss ratio of 1,3-dinitrobenzene by E. coli was unaffected after knocking out the nfsA gene encoding nitroreductase, but was suppressed by removing EPS attached to cells. In contrast, the loss ratio was enhanced by adding aqueous dissolved EPS to E. coli or B. subtilis suspension. The residual 1,3-dinitrobenzene and products formed after reduction were only presented outside the bacterial cells. Thus, bacterial reduction of 1,3-dinitrobenzene was mediated by nonenzymatic extracellular reduction. This was further corroborated by the observation that the stoichiometric demand of electrons in 1,3-dinitrobenzene reduction was nearly equal to the quantity of electrons donated by bacterial cells in the electrochemical cell experiment. Inhibition on the reduction of 1,3-dinitrobenzene by chemical probes combined with fluorescence detection demonstrated that reducing sugars in EPS might act as electron donors, while cytochromes and some low-molecular weight molecules (flavins and quinones) were involved as electron transfer mediators. Linear relationships were observed between the reduction kinetics and the one-electron reduction potentials for a series of substituted dinitrobenzenes in the presence of bacterial cells or dissolved EPS. Their close linear regression slope values suggest that the extracellular matrix and the exfoliated EPS utilized the same reducing agents (likely hydroquinones and reduced flavins) as terminal electron donors to reduce NACs. These results reveal a previously unrecognized mechanism for nonenzymatic extracellular reduction of NACs by common bacteria. CAPSULE: The extracellular matrix of E. coli or B. subtilis supplies both electron donors and electron transfer mediators to efficiently reduce nitroaromatic compounds.

Role of Extracellular Polymeric Substances in Microbial Reduction of Arsenate to Arsenite by Escherichia coli and Bacillus subtilis.

We show that arsenate can be readily reduced to arsenite on cell surfaces of common bacteria (E. coli or B. subtilis) or in aqueous dissolved extracellular polymeric substances (EPS) extracted from different microorganisms (E. coli, B. subtilis, P. chrysosporium, D. gigas, and a natural biofilm) in the absence of exogenous electron donors. The efficiency of arsenate reduction by E. coli after a 7-h incubation was only moderately reduced from 51.3% to 32.7% after knocking out the arsenic resistance genes (arsB and arsC). Most (>97%) of the reduced arsenite was present outside the bacterial cells, including for the E. coli blocked mutant lacking arsB and arsC. Thus, extracellular processes dominated arsenate reduction. Arsenate reduction was facilitated by removing EPS attached to E. coli or B. subtilis, which was attributed to enhanced access to reduced extracellular cytochromes. This highlights the role of EPS as a permeability barrier to arsenate reduction. Fourier-transform infrared (FTIR) combined with other chemical analyses implicated some low-molecular weight (<3 kDa) molecules as electron donors (reducing saccharides) and electron transfer mediators (quinones) in arsenate reduction by dissolved EPS alone. These results indicate that EPS act as both reducing agent and permeability barrier for access to reduced biomolecules in bacterial reduction of arsenate.

Spectroscopic and molecular modeling investigation on inhibition effect of nitroaromatic compounds on acetylcholinesterase activity.

Nitroaromatic compounds (NACs) are widely distributed in the environment and are considered toxic or carcinogenic. However, little attention has been paid to the binding interactions between NACs and biomacromolecules (e.g., proteins). Here we investigated the effects of three model NACs, nitrobenzene (NB), 1,3-dinitrobenzene (DNB), and 1,3,5-trinitrobenzene (TNB), on the activity of acetylcholinesterase (AChE). The presence of NACs (up to 0.5 mM) effectively suppressed the AChE-catalyzed hydrolysis of acetylthiocholine iodide, with the suppression effect increasing with the nitro-group substitution (TNB > DNB > NB). Consistently, the UV absorption of AChE at 206 nm arising from the skeleton structure decreased by the addition NACs, and the decrease exhibited the same compound sequence, reflecting the perturbing interactions with the skeleton enzyme structure. However, no changes were made on the secondary structure of AChE, as evidenced by the circular dichroism analysis. The fluorescence quenching analysis of AChE demonstrated that NB and DNB interacted with both tryptophan (Trp) and tyrosine (Tyr) residues, whereas TNB interacted only with Trp. The UV absorption and fluorescence quenching analyses both reflected that the interactions with the non-skeleton aromatic amino acids were weak. 1H NMR analysis confirmed the strong π-π coupling interactions between TNB and model Trp. Molecular simulation indicated that the DNB or TNB molecule was sandwiched between Trp84 and Phe330 at the catalytic site via π-π coupling interactions. The findings highlight the importance of specific interactions of NACs with proteins to cause them to malfunction.

Extracellular Polymeric Substances Acting as a Permeable Barrier Hinder the Lateral Transfer of Antibiotic Resistance Genes.

Antibiotic resistance genes (ARGs) in bacteria are emerging contaminants as their proliferation in the environment poses significant threats to human health. It is well recognized that extracellular polymeric substances (EPS) can protect microorganisms against stress or damage from exogenous contaminants. However, it is not clear whether EPS could affect the lateral transfer of ARGs into bacteria, which is one of the major processes for the dissemination of ARGs. This study investigated the lateral transfer of ARGs carried by plasmids (pUC19, pHSG298, and pHSG396) into competent Escherichia coli cells with and without EPS. Transformant numbers and transformation efficiency for E. coli without EPS were up to 29 times of those with EPS at pH 7.0 in an aqueous system. The EPS removal further increased cell permeability in addition to the enhanced cell permeability by Ca2+, which could be responsible for the enhanced lateral transfer of ARGs. The fluorescence quenching experiments showed that EPS could strongly bind to plasmid DNA in the presence of Ca2+ and the binding strength (LogK A = 10.65-15.80 L mol-1) between EPS and plasmids was positively correlated with the enhancement percentage of transformation efficiency resulting from the EPS removal. X-ray photoelectron spectroscopy (XPS) analyses and model computation further showed that Ca2+ could electrostatically bind with EPS mainly through the carboxyl group, hydroxyl group, and RC-O-CR in glucoside, thus bridging the plasmid and EPS. As a result, the binding of plasmids with EPS hindered the lateral transfer of plasmid-borne ARGs. This study improved our understanding on the function of EPS in controlling the fate and transport of ARGs on the molecular and cellular scales.

Degradation of antibiotics in multi-component systems with novel ternary AgBr/Ag3PO4@natural hematite heterojunction photocatalyst under simulated solar light.

Abatement of antibiotics from aquatic systems is of great importance but remains a challenge. Herein, we prepared ternary AgBr/Ag3PO4@natural hematite (AgBr/Ag3PO4@NH) heterojunction composite via a simple route for the photocatalytic degradation of antibiotic pollutants. By adjusting the dose of Ag species, four products with different Ag content (denoted as Ag0.5BrPFe, Ag1BrPFe, Ag1.5BrPFe, and Ag2BrPFe) were developed. Among them, Ag1.5BrPFe exhibited the best photocatalytic activity. Four antibiotics (i.e. ciprofloxacin (CIP), norfloxacin (NOR), sulfadiazine (SDZ), and tetracycline (TTC)) could be degraded with synthesized Ag1.5BrPFe in multi-component systems. Water matrix indexes including solution pH, coexisting anions, humic acids exhibited distinct effects on the degradation process. The results revealed that the degradation process was accelerated at acidic conditions while depressed at basic conditions. Superoxide radical and hole were detected by in situ electron spin resonance technique and played the dominant roles. The degradation pathway TTC was tentatively established followed with the identification of the degradation intermediates and computational analysis. This work would shed light on the photocatalytic degradation mechanism of organic pollutants by the AgBr/Ag3PO4@NH composite.

Substituted Aromatic-Facilitated Dissemination of Mobile Antibiotic Resistance Genes via an Antihydrolysis Mechanism Across an Extracellular Polymeric Substance Permeable Barrier.

Mobile antibiotic resistance genes (ARGs) in environmental systems may pose a threat to public health. The coexisting substituted aromatic pollutants may help the ARGs cross the extracellular polymeric substance (EPS) permeable barrier into the interior of cells, facilitating ARG dissemination, but the mechanism is still unknown. Here, we demonstrated that a specific antihydrolysis mechanism of mobile plasmid in the extracellular matrix makes a greater contribution to this facilitated dissemination. Specifically, fluorescence microtitration with a Tb3+-labeled pUC19 plasmid was used to study the formation of substituted aromatic-plasmid complexes associated with ARG dissemination. Manipulations of the endA gene and an EPS confirmed that these forming complexes antagonize the EPS-mediated hydrolysis of the plasmid. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and computational chemistry demonstrated that substituents alter the polarity of aromatic molecules, making the carbon at the 6-position of 1,3-dichlorobenzene as well as the labile protons (-NH2/-OH) of m-phenylenediamine, aniline, and 2-naphthol interact with the deprotonated hydroxy group of the phosphate (P-O···H-C/N/O), mainly via hydrogen bonds. Linear correlations among ARG disseminations, association constants, and bonding energies highlight the quantitative dependency of ARG proliferation on a combination of functionalities templated by d-ribose-phosphate.

Nature and Value of Freely Dissolved EPS Ecosystem Services: Insight into Molecular Coupling Mechanisms for Regulating Metal Toxicity.

Extracellular polymeric substances (EPSs) dispersed in natural waters play a significant role in relieving impacts to microbial survival associated with heavy metal release, yet little is known about the association of freely dissolved EPS ecosystem services with metal transformation in natural waters. Here, we demonstrate that dispersive EPSs mitigate the metal toxicity to microbial cells through an associative coordination reaction. Microtitrimetry coupled with fluorescence spectroscopy ascribes the combination of freely dissolved EPSs from Escherichia coli (E. coli) with Cu2+/Cd2+ to a coordination reaction associated with chemical static quenching. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and computational chemistry confirm that carboxyl residues in protein-like substances of the EPSs are responsible for the coordination. Frontier molecular orbitals (MOs) of a deprotonated carboxyl integrate with the occupied d orbitals of Cu2+ and/or d, s orbitals of Cd2+ to form metal-EPS complexes. Microcosmic systems show that because the metal-EPS complexes decrease cellular absorbability of metals, E. coli survivals increase by 4.3 times for Cu2+ and 1.6 times for Cd2+, respectively. Based on bonding energies for six metals-EPS coordination, an associative toxic effect further confirms that increased bonding energies facilitate retardation of metals in the EPS matrix, protecting against E. coli apoptosis.

Environmentally-relevant concentrations of Al(III) and Fe(III) cations induce aggregation of free DNA by complexation with phosphate group.

Environmental persistence of free DNA is influenced by its complexation with other chemical species and its aggregation mechanisms. However, it is not well-known how naturally-abundant metal ions, e.g., Al(III) and Fe(III), influence DNA aggregation. This study investigated aggregation behaviors of model DNA from salmon testes as influenced by metal cations, and elucidated the predominant mechanism responsible for DNA aggregation. Compared to monovalent (K+ and Na+) and divalent (Ca2+ and Mg2+) cations, Al(III) and Fe(III) species in aqueous solution caused rapid DNA aggregations. The maximal DNA aggregation occurred at 0.05 mmol/L Al(III) or 0.075 mmol/L Fe(III), respectively. A combination of atomic force microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy revealed that Al(III) and Fe(III) complexed with negatively charged phosphate groups to neutralize DNA charges, resulting in decreased electrostatic repulsion and subsequent DNA aggregation. Zeta potential measurements and molecular computation further support this mechanism. Furthermore, DNA aggregation was enhanced at higher temperature and near neutral pH. Therefore, DNA aggregation is collectively determined by many environmental factors such as ion species, temperature, and solution pH.

Extracellular Saccharide-Mediated Reduction of Au3+ to Gold Nanoparticles: New Insights for Heavy Metals Biomineralization on Microbial Surfaces.

Biomineralization is a critical process controlling the biogeochemical cycling, fate, and potential environmental impacts of heavy metals. Despite the indispensability of extracellular polymeric substances (EPS) to microbial life and their ubiquity in soil and aquatic environments, the role played by EPS in the transformation and biomineralization of heavy metals is not well understood. Here, we used gold ion (Au3+) as a model heavy metal ion to quantitatively assess the role of EPS in biomineralization and discern the responsible functional groups. Integrated spectroscopic analyses showed that Au3+was readily reduced to zerovalent gold nanoparticles (AuNPs, 2-15 nm in size) in aqueous suspension of Escherichia coli or dissolved EPS extracted from microbes. The majority of AuNPs (95.2%) was formed outside Escherichia coli cells, and the removal of EPS attached to cells pronouncedly suppressed Au3+ reduction, reflecting the predominance of the extracellular matrix in Au3+ reduction. XPS, UV-vis, and FTIR analyses corroborated that Au3+ reduction was mediated by the hemiacetal groups (aldehyde equivalents) of reducing saccharides of EPS. Consistently, the kinetics of AuNP formation obeyed pseudo-second-order reaction kinetics with respect to the concentrations of Au3+ and the hemiacetal groups in EPS, with minimal dependency on the source of microbial EPS. Our findings indicate a previously overlooked, universally significant contribution of EPS to the reduction, mineralization, and potential detoxification of metal species with high oxidation state.

Sources and health risks of polycyclic aromatic hydrocarbons during haze days in eastern China: A 1-year case study in Nanjing City.

The concentrations of 16 priority polycyclic aromatic hydrocarbons (PAHs) in ambient air were investigated for a 1-year period to assess their sources and health risks during haze days in Nanjing City, eastern China. The highest level of total PAHs (∑16 PAHs) in the gaseous phase during the haze days was 18.0±13.3µg/m3. Their sources may be attributable to pyrogenic products (55.2%), petrochemical refining industry (8.7%), and petrol volatilization (36.1%). The incremental lifetime cancer risk during the haze days exceeded or was close to the priority level of risk (10-4), indicating that PAH pollution during the haze days has caused public health problems associated with the respiratory system. The priority PAHs in the particle phase are mainly composed of low-ring components (<4 rings), accounting for 65.2-96.8% of the ∑16 PAHs during haze days. These particles are derived from petroleum hydrocarbons (16.5%), incomplete combustion of gasoline (62.2%), and burning of coal and biomass (21.4%). The priority level of risk fell within an acceptable range (10-7-10-6). The PAHs in suspended particles can be transported to the surfaces of vegetables by gravitational deposition, causing an increase in PAH concentrations in vegetable leaves. The increased carcinogenic risk associated with human dietary intake was 6.9×10-5 for S. oleracea, 1.7×10-5 for B. pekinensis, and 6.2×10-6 for B. chinensis. These levels were close to the critical value (10-4), and the potential health risks from dietary intake of PAHs should be prioritized.

Laccase-mediated transformation of triclosan in aqueous solution with metal cations and humic acid.

Triclosan (TCS) is a broad-spectrum antimicrobial agent that is found extensively in natural aquatic environments. Enzyme-catalyzed oxidative coupling reactions (ECOCRs) can be used to remove TCS in aqueous solution, but there is limited information available to indicate how metal cations (MCs) and natural organic matter (NOM) influence the environmental fate of TCS during laccase-mediated ECOCRs. In this study, we demonstrated that the naturally occurring laccase from Pleurotus ostreatus was effective in removing TCS during ECOCRs, and the oligomerization of TCS was identified as the dominant reaction pathway by high-resolution mass spectrometry (HRMS). The growth inhibition studies of green algae (Chlamydomonas reinhardtii and Scenedesmus obliquus) proved that laccase-mediated ECOCRs could effectively reduce the toxicity of TCS. The presence of dissolved MCs (Mn2+, Al3+, Ca2+, Cu2+, and Fe2+ ions) influenced the removal and transformation of TCS via different mechanisms. Additionally, the transformation of TCS in systems with NOM derived from humic acid (HA) was hindered, and the apparent pseudo first-order kinetics rate constants (k) for TCS decreased as the HA concentration increased, which likely corresponded to the combined effect of both noncovalent (sorption) and covalent binding between TCS and humic molecules. Our results provide a novel insight into the fate and transformation of TCS by laccase-mediated ECOCRs in natural aquatic environments in the presence of MCs and NOM.

Alkali-earth metal bridges formed in biofilm matrices regulate the uptake of fluoroquinolone antibiotics and protect against bacterial apoptosis.

Bacterially extracellular biofilms play a critical role in relieving toxicity of fluoroquinolone antibiotic (FQA) pollutants, yet it is unclear whether antibiotic attack may be defused by a bacterial one-two punch strategy associated with metal-reinforced detoxification efficiency. Our findings help to assign functions to specific structural features of biofilms, as they strongly imply a molecularly regulated mechanism by which freely accessed alkali-earth metals in natural waters affect the cellular uptake of FQAs at the water-biofilm interface. Specifically, formation of alkali-earth-metal (Ca2+ or Mg2+) bridge between modeling ciprofloxacin and biofilms of Escherichia coli regulates the trans-biofilm transport rate of FQAs towards cells (135-nm-thick biofilm). As the addition of Ca2+ and Mg2+ (0-3.5 mmol/L, CIP: 1.25 µmol/L), the transport rates were reduced to 52.4% and 63.0%, respectively. Computational chemistry analysis further demonstrated a deprotonated carboxyl in the tryptophan residues of biofilms acted as a major bridge site, of which one side is a metal and the other is a metal girder jointly connected to the carboxyl and carbonyl of a FQA. The bacterial growth rate depends on the bridging energy at anchoring site, which underlines the environmental importance of metal bridge formed in biofilm matrices in bacterially antibiotic resistance.

Contamination and health risk assessment of PAHs in soils and crops in industrial areas of the Yangtze River Delta region, China.

This is the first investigation into both soil and crop contamination and associated health risks by polycyclic aromatic hydrocarbons (PAHs) in industrial areas of the Yangtze River Delta region (YRDR). Soil and crop samples were collected from farmland surrounded by three typical industries (a steelworks [SW], a petrochemical facility [PF] and a power plant [PP]), and the concentrations and health risks of PAHs in soils and crops were evaluated. The average concentrations of 16 USEPA priority PAHs in surface soil and subsoil were 471.30 µg kg-1 and 341.40 µg kg-1, respectively. The respective average concentrations of 16 PAHs in amaranth, spinach, Chinese chive, and rice tissues were 1710.49, 1176.96, 1218.36 and 352.12 µg kg-1. Based on both the results of a principal component analysis (PCA) and the PAH ratios, the main sources of the PAHs in soils were determined to be the combustion of coal and petroleum. The total values of incremental lifetime cancer risk (ILCR) for males induced by both soils and crops were 2.19 × 10-4, 2.53 × 10-4, and 9.17 × 10-4, and for females were 2.21 × 10-4, 2.50 × 10-4, and 9.68 × 10-4 for childhood, adolescence, and adulthood, respectively. Soils contaminated with PAHs posed a lower risk than crops, but the ILCR values, 4.40 × 10-5 and 3.82 × 10-5 for males and females, was still much higher than the baseline value. The results of this investigation provide novel information for contamination evaluation and human health risk assessment in PAH-contaminated sites.

Understanding the sorption mechanisms of aflatoxin B1 to kaolinite, illite, and smectite clays via a comparative computational study.

In current adsorption studies of biotoxins to phyllosilicate clays, multiply weak bonding types regarding these adsorptions are not well known; the major attractive forces, especially for kaolinite and illite, are difficult to be identified as compared to smectite with exchangeable cations. Here, we discriminated the bonding types of aflatoxin B1 (AFB1) contaminant to these clays by combined batch experiment with model computation, expounded their bonding mechanisms which have been not quantitatively described by researchers. The observed adsorbent-to-solution distribution coefficients (Kd) of AFB1 presented in increasing order of 18.5-37.1, 141.6-158.3, and 354.6-484.7L/kg for kaolinite, illite, and smectite, respectively. Normalization of adsorbent-specific surface areas showed that adsorption affinity of AFB1 is mainly dependent on the outside surfaces of clay aggregates. The model computation and test of ionic effect further suggested that weakly electrostatic attractions ((Si/Al-OH)2⋯(OC)2) are responsible for AFB1-kaolinite adsorption (Kd, 18.5-37.1L/kg); a moderate electron-donor-acceptor attraction ((CO)2⋯K+⋯(O-Al)3) is related to AFB1-illite adsorption (Kd, 141.6-158.3L/kg); a strong calcium-bridging linkage ((CO)2⋯Ca2+⋯(O-Si)4) is involved in AFB1-smectite adsorption (Kd, 354.6-484.7L/kg). Changes in Gibbs free energy (ΔG°) suggested that the computed result is reliable, providing a good reproduction of AFB1-clay interaction.