Fuxing Kang

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 471.30xa0μgxa0kg-1 and 341.40xa0μgxa0kg-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 352.12xa0μgxa0kg-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 2.19xa0×xa010-4, 2.53xa0×xa010-4, and 9.17xa0×xa010-4, and for females were 2.21xa0×xa010-4, 2.50xa0×xa010-4, and 9.68xa0×xa010-4 for childhood, adolescence, and adulthood, respectively. Soils contaminated with PAHs posed a lower risk than crops, but the ILCR values, 4.40xa0×xa010-5 and 3.82xa0×xa010-5 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.

Sequestration of nanoparticles by an EPS matrix reduces the particle-specific bactericidal activity.

Most artificial nanomaterials are known to exhibit broad-spectrum bactericidal activity; however, the defence mechanisms that bacteria use based on extracellular polymeric substances (EPS) to detoxify nanoparticles (NPs) are not well known. We ruled out the possibility of ion-specific bactericidal activity by showing the lack of equivalent dissolved zinc and silicon toxicity and determined the particle-specific toxicity of ZnO and SiO2 nanoparticles (ZnONPs/SiO2NPs) through dialysis isolation experiments. Surprisingly, the manipulation of the E. coli EPS (i.e., no EPS manipulation or EPS removal by sonication/centrifugation) showed that their particle-specific bactericidal activity could be antagonized by NP-EPS sequestration. The survival rates of pristine E. coli (no EPS manipulation) reached 65% (ZnONPs, 500u2009mg L−1) and 79% (SiO2NPs, 500u2009mg L−1), whereas survival rates following EPS removal by sonication/centrifugation were 11% and 63%, respectively. Transmission electron microscopy (TEM) combined with fluorescence micro-titration analysis and Fourier-transform infrared spectroscopy (FTIR) showed that protein-like substances (N-H and C-N in amide II) and secondary carbonyl groups (C=O) in the carboxylic acids of EPS acted as important binding sites that were involved in NP sequestration. Accordingly, the amount and composition of EPS produced by bacteria have important implications for the bactericidal efficacy and potential environmental effects of NPs.

Inhibition of free DNA degradation by the deformation of DNA exposed to trace polycyclic aromatic hydrocarbon contaminants.

A rapid inhibitory effect of polycyclic aromatic hydrocarbons (PAHs) on DNA degradation was examined by conventional spectral analysis and microtitration. The purpose was to determine whether PAHs inhibited free DNA degradation by the enzyme DNase I. The results showed that model PAHs phenanthrene and pyrene combined with free DNA to decelerate DNA degradation by DNase I. Phenanthrene-induced inhibition was stronger than that of pyrene. Trace level of PAHs did not induce DNase I deactivation. The DNase I enzyme exhibited only slight shifts in IR absorption bands related to amide II and III upon PAH exposure, and no change was observed with other bands. The decelerating degradation of DNA is attributed to the changes in structure, backbone composition, and guanine constituents of DNA induced by PAHs inserted into double strands, and to the imidazole-like derivates from the combination of imidazole rings with pyrene.

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.

Inoculating plants with the endophytic bacterium Pseudomonas sp. Ph6-gfp to reduce phenanthrene contamination

Plant organic contamination poses a serious threat to the safety of agricultural products and human health worldwide, and the association of endophytic bacteria with host plants may decrease organic pollutants in planta. In this study, we firstly determined the growth response and biofilm formation of endophytic Pseudomonas sp. Ph6-gfp, and then systematically evaluated the performance of different plant colonization methods (seed soaking (SS), root soaking (RS), leaf painting (LP)) for circumventing the risk of plant phenanthrene (PHE) contamination. After inoculation for 48xa0h, strain Ph6-gfp grew efficiently with PHE, oxalic acid, or malic acid as the sole sources of carbon and energy. Moreover, strain Ph6-gfp could form robust biofilms in LB medium. In greenhouse hydroponic experiments, strain Ph6-gfp could actively colonize inoculated plants internally, and plants colonized with Ph6-gfp showed a higher capacity for PHE removal. Compared with the Ph6-gfp-free treatment, the accumulations of PHE in Ph6-gfp-colonized plants via SS, RS, and LP were 20.1, 33.1, and 7.1xa0%, respectively, lower. Our results indicate that inoculating plants with Ph6-gfp could lower the risk of plant PHE contamination. RS was most efficient for improving PHE removal in whole plant bodies by increasing the cell numbers of Ph6-gfp in plant roots. The findings in this study provide an optimized method to strain Ph6-gfp reduce plant PAH residues, which may be applied to agricultural production in PAH-contaminated soil.

Noncovalent Binding of Polycyclic Aromatic Hydrocarbons with Genetic Bases Reducing the in Vitro Lateral Transfer of Antibiotic Resistant Genes.

In current studies of noncovalent interactions of polycyclic aromatic hydrocarbons (PAHs) with genetic units, the impact of such interactions on gene transfer has not been explored. In this study, we examined the association of some widely occurring PAHs (phenanthrene, pyrene, benzo[g,h,i]perylene, and other congeners) with antibiotic resistant plasmids (pUC19). Small molecular PAHs (e.g., phenanthrene) bind effectively with plasmids to form a loosely clew-like plasmid-PAH complex (16.5-49.5 nm), resulting in reduced transformation of ampicillin resistance gene (Ampr). The in vitro transcription analysis demonstrated that reduced transformation of Ampr in plasmids results from the PAH-inhibited Ampr transcription to RNA. Fluorescence microtitration coupled with Fourier transform infrared spectroscopy (FTIR) and theoretical interaction models showed that adenine in plasmid has a stronger capacity to sequester small Phen and Pyre molecules via a π-π attraction. Changes in Gibbs free energy (ΔG) suggest that the CT-PAH model reliably depicts the plasmid-PAH interaction through a noncovalently physical sorption mechanism. Considering the wide occurrence of PAHs and antibiotic resistant genes (ARGs) in the environment, our findings suggest that small-sized PAHs can well affect the behavior of ARGs via above-described noncovalent interactions.

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+ (0-3.5xa0mmol/L, CIP: 1.25xa0μmol/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.

Transformation of 17β-estradiol in humic acid solution by ε-MnO2 nanorods as probed by high-resolution mass spectrometry combined with 13C labeling

Steroidal estrogens (SEs), widespread in aquatic systems, have a potential to disrupt the endocrine system of wildlife species and humans. In our experiments, the performance of ε-MnO2 nanorods in transforming 17β-estradiol (E2) was investigated, and the effect of humic acid (HA) on the reaction behaviors was systematically characterized. Reconfiguration of humic molecules was also investigated by high-performance size exclusion chromatography (HPSEC). Results indicated that ε-MnO2 nanomaterials ensured efficient removal of E2 from the aqueous solution. The presence of HA hindered the transformation of E2, while enhanced the cross-coupling between E2 and humic molecules. In particular, we used a mixture of un-labeled E2 and (13)C3-labeled E2 at a 1: 1 set ratio (w/w) to probe the reaction products via high-resolution mass spectrometry (HRMS). The combination of HRMS and (13)C3-labeling revealed the intermediate products including estrone (E1), and hydroxylated, quinone-like, and ring-opened species, as well as E2 dimer and trimer. More importantly, possible cross-coupling products between E2 and HA were also identified. A reaction mechanism including two-electron oxidation and single-electron oxidation was proposed. The applied analytical approach using HRMS along with (13)C3-labeling for reaction-product identification is crucial to understanding the role of HA in the transformation of SEs.

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 0.05xa0mmol/L Al(III) or 0.075xa0mmol/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.