Comparative analysis of chlorine-resistant bacteria after chlorination and chloramination in drinking water treatment plants.

Chlorine-resistant bacteria (CRB) in drinking water treatment plants (DWTPs) jeopardize water quality and pose a potential risk to human health. However, the specific response of CRB to chlorination and chloramination remains uncharacterized. Therefore, we analyzed 16 S rRNA sequencing data from water samples before and after chlorination and chloramination taken between January and December 2020. Proteobacteria and Firmicutes dominated all finished water samples. After chloramination, Acinetobacter, Pseudomonas, Methylobacterium, Ralstonia, and Sphingomonas were the dominant CRB, whereas Ralstonia, Bacillus, Acinetobacter, Pseudomonas, and Enterococcus were prevalent after chlorination. Over 75% of the CRB e.g. Acinetobacter, Pseudomonas, Bacillus, and Enterococcus were shared between the chlorination and chloramination, involving potentially pathogens, such as Acinetobacter baumannii and Pseudomonas aeruginosa. Notably, certain genera such as Faecalibacterium, Geobacter, and Megasphaera were enriched as strong CRB after chloramination, whereas Vogesella, Flavobacterium, Thalassolituus, Pseudoalteromonas, and others were enriched after chlorination according to LEfSe analysis. The shared CRB correlated with temperature, pH, and turbidity, displaying a seasonal pattern with varying sensitivity to chlorination and chloramination in cold and warm seasons. These findings enhance our knowledge of the drinking water microbiome and microbial health risks, thus enabling better infectious disease control through enhanced disinfection strategies in DWTPs.

Synergistic catalysis of TiO2/WO3 photoanode and Sb-SnO2 electrode with highly efficient ClO• generation for urine treatment.

Urine is the major source of nitrogen pollutants in domestic sewage and is a neglected source of H2. Although ClO• is used to overcome the poor selectivity and slow kinetics of urea decomposition, the generation of ClO• suffers from the inefficient formation reaction of HO• and reactive chlorine species (RCS). In this study, a synergistic catalytic method based on TiO2/WO3 photoanode and Sb-SnO2 electrode efficiently producing ClO• is proposed for urine treatment. The critical design is that TiO2/WO3 photoanode and Sb-SnO2 electrode that generate HO• and RCS, respectively, are assembled in a confined space through face-to-face (TiO2/WO3//Sb-SnO2), which effectively strengthens the direct reaction of HO• and RCS. Furthermore, a Si solar panel as rear photovoltaic cell (Si PVC) is placed behind TiO2/WO3//Sb-SnO2 to fully use sunlight and provide the driving force of charge separation. The composite photoanode (TiO2/WO3//Sb-SnO2 @Si PVC) has a ClO• generation rate of 260% compared with the back-to-bake assembly way. In addition, the electrons transfer to the NiFe LDH@Cu NWs/CF cathode for rapid H2 production by the constructed photoelectric catalytic (PEC) cell without applied external biasing potential, in which the H2 production yield reaches 84.55 µmol h-1 with 25% improvement of the urine denitrification rate. The superior performance and long-term stability of PEC cell provide an effective and promising method for denitrification and H2 generation.

Nonlinear differential equations and their application to evaluating the integrated impacts of multiple parameters on the biochemical safety of drinking water.

The present study aimed to narrow such gaps by applying nonlinear differential equations to biostability in drinking water. Biostability results from the integrated dynamics of nutrients and disinfectants. The linear dynamics of biostability have been well studied, while there remain knowledge gaps concerning nonlinear effects. The nonlinear effects are explained by phase plots for specific scenarios in a drinking water system, including continuous nutrient release, flush exchange with the adjacent environment, periodic pulse disinfection, and periodic biofilm development. The main conclusions are, (1) The correlations between the microbial community and nutrients go through phases of linear, nonlinear, and chaotic dynamics. Disinfection breaks the chaotic phase and returns the system to the linear phase, increasing the microbial growth potential. (2) Post-disinfection after multiple microbial peaks produced via metabolism can increase disinfection efficiency and decrease the risks associated with disinfectant byproduct risks. This can provide guidelines for optimizing the disinfection strategy, according to the long-term water safety target or a short management. Limited disinfection and ultimate disinfection may be more effective and have low chemical risk, facing longer stagnant conditions. (3) Periodic biofilm formation and biofilm detachment increase the possibility of uncertainty in the chaotic phase. For future study, nonlinear differential equation models can accordingly be applied at the molecular and ecological levels to further explore more nonlinear regulation mechanisms.

Identification of reaction sites and chlorinated products of purine bases and nucleosides during chlorination: a computational study.

Hypochlorous acid (HOCl) released from activated leukocytes plays a significant role in the human immune system, but is also implicated in numerous diseases due to its inappropriate production. Chlorinated nucleobases induce genetic changes that potentially enable and stimulate carcinogenesis, and thus have attracted considerable attention. However, their multiple halogenation sites pose challenges to identify them. As a good complement to experiments, quantum chemical computation was used to uncover chlorination sites and chlorinated products in this study. The results indicate that anion salt forms of all purine compounds play significant roles in chlorination except for adenosine. The kinetic reactivity order of all reaction sites in terms of the estimated apparent rate constant kobs-est (in M-1 s-1) is heterocyclic NH/N (102-107) > exocyclic NH2 (10-2-10) > heterocyclic C8 (10-5-10-1), but the order is reversed for thermodynamics. Combining kinetics and thermodynamics, the numerical simulation results show that N9 is the most reactive site for purine bases to form the main initial chlorinated product, while for purine nucleosides N1 and exocyclic N2/N6 are the most reactive sites to produce the main products controlled by kinetics and thermodynamics, respectively, and C8 is a possible site to generate the minor product. The formation mechanisms of biomarker 8-Cl- and 8-oxo-purine derivatives were also investigated. Additionally, the structure-kinetic reactivity relationship study reveals a good correlation between lg kobs-est and APT charge in all purine compounds compared to FED2 (HOMO), which proves again that the electrostatic interaction plays a key role. The results are helpful to further understand the reactivity of various reaction sites in aromatic compounds during chlorination.

Impact of changes in biofilm composition response following chlorine and chloramine disinfection on nitrogenous disinfection byproduct formation and toxicity risk in drinking water distribution systems.

In practical drinking water treatment, chlorine and chloramine disinfection exhibit different mechanisms that affect biofilm growth. This study focused on the influence of biofilm composition changes, especially extracellular polymeric substance (EPS) fractions, on the potential formation and toxicity of nitrogenous disinfection by-products (N-DBP). Significant differences in microbial diversity and community structure were observed between the chlorine and chloramine treatments. Notably, the biofilms from the chloramine-treated group had higher microbial dominance and greater accumulation of organic precursors, as evidenced by the semi-quantitative confocal laser-scanning microscopy assay of more concentrated microbial aggregates and polysaccharide proteins in the samples. Additionally, the chloramine-treated group compared with chlorine had a higher EPS matrix content, with a 13.5 % increase in protein. Furthermore, the protein distribution within the biofilm differed; in the chlorine group, proteins were concentrated in the central region, whereas in the chloramine group, proteins were primarily located at the water-biofilm interface. Notably, functional prediction analyses of protein fractions in biofilms revealed specific functional regulation patterns and increased metabolism-related abundance of proteins in the chlorine-treated group. This increase was particularly pronounced for proteins such as dehydrogenases, reductases, transcription factors, and acyl-CoA dehydrogenases. By combining the Fukui function and density functional calculations to further analyse the effect of biofilm component changes on N-DBP production under chlorine/chloramine and by assessing the toxicity risk potential of N-DBP, it was determined that chloramine disinfection is detrimental to biofilm control and the accumulation of protein precursors has a higher formation potential of N-DBPs and toxicity risk, increasing the health risk of drinking water.

Transformation pathways of enrofloxacin chlorination disinfection by-products in constructed wetlands.

Antibiotic residues and their chlorinated disinfection by-products (Cl-DBPs) have adverse effects on organisms in aquaculture water. Taking enrofloxacin (ENR) as target antibiotic, this study investigated the degradation and transformation of ENR Cl-DBPs in constructed wetlands (CWs). Results showed that, ENR and its Cl-DBPs affected the biodegradation of CWs at the preliminary stage, but did not affect the adsorption by plant roots, substrates, and biofilms. The piperazine group of ENR had great electronegativity, and was prone to electrophilic reactions. The carboxyl on quinolone group of ENR had strong nucleophilicity, and was prone to nucleophilic reactions. C atoms with significant negative charges on the aromatic structure of quinolone group were prone to halogenation. During the chlorination of ENR, one pathway was the reaction of quinolone group, in which nucleophilic substitution reaction by chlorine occurred at C26 atom on carboxyl group, then halogenation occurred under the action of Cl+ at C17 site on the aromatic ring; the other pathway was the reaction of piperazine group, in which N7 atom was firstly attacked by HOCl, resulting in piperazine ring cleavage, then followed by deacylation, dealkylation, and halogenation. During the biodegradation of ENR Cl-DBPs, the reactivity of piperazine structure was strong, especially at N6, N7, C13, and C14 sites, while the ring structure of quinolone group was quite stable, and only occurred decyclopropyl at N5 site. Overall, the biodegradation of ENR Cl-DBPs in CWs went through processes including piperazine ring cleavage, tertiary amine splitting, dealkylation, and aldehyde oxidation under the action of coenzymes, in which metabolites such as ketones, aldehydes, carboxylic acids, amides, primary amines, secondary amines, tertiary amines and acetaldehyde esters were produced. Most ENR Cl-DBPs had greater bioaccumulation potential and stronger toxicity than their parent compound, fortunately, CWs effectively reduced the environmental risk of ENR Cl-DBPs through the cooperation of adsorption and biodegradation.

Degradation and transformation of carbamazepine in aqueous medium under non-thermal plasma oxidation process.

Carbamazepine (CBZ) is a pharmaceutical compound detected in various water resources. With a view to removing this contaminant, the applicability of non-thermal plasma (NTP) oxidation process has been widely tested in recent years. This study utilized NTP from a dielectric barrier discharge reactor in the treatment of CBZ. NTP on the surface of a water sample containing 25 mg.L-1 of CBZ resulted in a removal efficiency of over 90% with an energy yield of 0.19 g. (kWh)-1. On the other hand, a rapid reduction in pH and an increase of conductivity and nitrate/nitrite ions concentration were observed during the degradation. The applied voltage amplitude significantly affected the removal efficiency and the energy yield as the degradation efficiency was 55%, 70%, and 72% respectively with an applied voltage of 8, 10, and 12 kV. The water matrices containing inorganic anions such as chloride and carbonate ions reduced the removal efficiency by scavenging the reactive species. Accordingly, a reduction in the removal efficiency was observed in tap water. The high-resolution mass spectrometry (HRMS) results revealed that both reactive oxygen and nitrogen species take part in the reaction process which yields many intermediate products including aromatic nitro-products. This study concluded that NTP can effectively degrade CBZ in both pure and tap water, but special attention must be paid to changes in the water quality parameters (pH, conductivity, and nitrate/nitrite ions) and the fate of nitro products.

Verification of chlorine exposure via LC-MS/MS analysis of base hydrolyzed chlorophenols from chlorotyrosine-protein adducts.

Inhalation of chlorine gas, with subsequent hydrolysis in the airway and lungs to form hydrochloric acid (HCl) and hypochlorous acid (HOCl), can cause pulmonary edema (i.e., fluid build-up in the lungs), pulmonary inflammation (with or without infection), respiratory failure, and death. The HOCl produced from chlorine is known to react with tyrosine to form adducts via electrophilic aromatic substitution, resulting in 3-chlorotyrosine and 3,5-dichlorotyrosine adducts. While several analysis methods are available for determining these adducts, each method has significant disadvantages. Hence, a simple and sensitive ultra-high performance liquid chromatography-tandem mass spectroscopy (UHPLC-MS/MS) method was developed for the determination of chlorotyrosine adducts. The sample preparation involves base hydrolysis of isolated plasma proteins to form 2-chlorophenol (CP) from monochlorotyrosine adducts and 2,6-dichlorophenol (2,6-DCP), from dichlorotyrosine adducts, as markers of chlorine exposure. The chlorophenols are extracted with cyclohexane prior to UHPLC-MS/MS analysis. The method produced excellent sensitivity for 2,6-DCP with a limit of detection of 2.2 µg/kg, calibration curve linearity extending from 0.054-54 mg/kg (R2 ≥ 0.9997 and %RA > 94), and accuracy and precision of 100 ± 14 %, and <15 % relative standard deviation, respectively. The sensitivity of the method for 2-CP was relatively poor, so it was used only as a secondary marker for severe chlorine exposure. The method successfully detected elevated levels of 2,6-DCP from hypochlorite-spiked plasma protein and plasma protein isolated from chlorine-exposed rats.

Natural Disinfection-like Process Unveiled in Soil Microenvironments by Enzyme-Catalyzed Chlorination.

Substantial natural chlorination processes are a growing concern in diverse terrestrial ecosystems, occurring through abiotic redox reactions or biological enzymatic reactions. Among these, exoenzymatically mediated chlorination is suggested to be an important pathway for producing organochlorines and converting chloride ions (Cl-) to reactive chlorine species (RCS) in the presence of reactive oxygen species like hydrogen peroxide (H2O2). However, the role of natural enzymatic chlorination in antibacterial activity occurring in soil microenvironments remains unexplored. Here, we conceptualized that heme-containing chloroperoxidase (CPO)-catalyzed chlorination functions as a naturally occurring disinfection process in soils. Combining antimicrobial experiments and microfluidic chip-based fluorescence imaging, we showed that the enzymatic chlorination process exhibited significantly enhanced antibacterial activity against Escherichia coli and Bacillus subtilis compared to H2O2. This enhancement was primarily attributed to in situ-formed RCS. Based on semiquantitative imaging of RCS distribution using a fluorescence probe, the effective distance of this antibacterial effect was estimated to be approximately 2 mm. Ultrahigh-resolution mass spectrometry analysis showed over 97% similarity between chlorine-containing formulas from CPO-catalyzed chlorination and abiotic chlorination (by sodium hypochlorite) of model dissolved organic matter, indicating a natural source of disinfection byproduct analogues. Our findings unveil a novel natural disinfection process in soils mediated by indigenous enzymes, which effectively links chlorine-carbon interactions and reactive species dynamics.

Migration and transformation of Pb, Cu, and Zn during co-combustion of high-chlorine-alkaline coal and Si/Al dominated coal.

Shaerhu (SEH) coal is abundant in Xinjiang, China. The utilization of SEH suffers from severe ash deposition, slagging, and fouling problems due to its high-chlorine-alkaline characteristics. The co-combustion of high-alkaline coal and other type coals containing high Si/Al oxides has been proven to be a simple and effective method that will alleviate ash-related problems, but the risk of heavy metals (HMs) contamination in this process is nonnegligible. Hence, the volatilization rates and chemical speciation of Pb, Cu, and Zn in co-combusting SEH and a high Si/Al oxides coal, i.e., Yuanbaoshan (YBS) coal were investigated in this study. The results showed that the addition of SEH increased the volatilization rates of Pb, Cu, and Zn during the co-combustion at 800°C from 23.70%, 23.97%, and 34.98% to 82.31%, 30.01%, and 44.03%, respectively, and promoted the extractable state of Cu and Zn. In addition, the interaction between SEH and YBS inhibited the formation of the Pb residue state. SEM-EDS mapping results showed that compared to Zn and Cu, the signal intensity of Pb was extremely weak in regions where some of the Si and Al signal distributions overlap. The DFT results indicated that the O atoms of the metakaolin (Al2O3⋅2SiO2) (001) surface were better bound to the Zn and Cu than Pb atoms after adsorption of the chlorinated HMs. These results contribute to a better understanding of the effects of high-alkaline coal blending combustion on Pb, Cu, and Zn migration and transformation.

Formation of halonitromethanes from benzylamine during UV/chlorination: Impact factors, toxicity alteration, and pathways.

Halonitromethanes (HNMs), a representative nitrogen-containing disinfection byproduct, have gained significant concerns due to their higher cytotoxicity and genotoxicity. UV/chlorination is considered a promising alternative disinfection technology for chlorination. This study aimed to investigate the HNMs formation from benzylamine (BZA) during UV/chlorination. The experimental results revealed that the yields of HNMs initially raised to a peak then dropped over time. Higher chlorine dosage and BZA concentration promoted the formation of HNMs, whereas alkaline pH inhibited their formation. The presence of bromine ion (Br-) not only converted chlorinated-HNMs (Cl-HNMs) to brominated (chlorinated)-HNMs Br (Cl)-HNMs) and brominated-HNMs (Br-HNMs) but also enhanced the total concentration of HNMs. Besides, the calculated cytotoxicity index (CTI) and genotoxicity index (GTI) of HNMs were elevated by 68.97% and 60.66% as Br- concentration raised from 2 to 6 µM. The possible formation pathways of HNMs from BZA were proposed based on the intermediates identified by a gas chromatography/mass spectrometry (GC/MS). In addition, the formation rules of HNMs in actual water verified the results in deionized water during UV/chlorination. The results of this study provide basic data and a theoretical basis for the formation and control of HNMs, which is conducive to applying UV/chlorination.

Copper ion affects oxidant decay and combined aspartic acid transformation during chlorination in water pipes: Differentiated action on the yield of trihalomethanes and haloacetonitriles.

The chlorination of extracellular polymeric substances (EPS) secreted by biofilm often induces the formation of high-toxic disinfection byproducts (DBPs) in drinking water distribution systems. The protein components in EPS are the main precursors of DBPs, which mostly exist in the form of combined amino acids. The paper aimed to study the action of a pipe corrosion product (Cu2+) on the formation of DBPs (trihalomethanes, THMs; haloacetonitriles, HANs) with aspartic acid tetrapeptide (TAsp) as a precursor. Cu2+ mainly promoted the reaction of oxidants with TAsp (i.e., TAsp-induced decay) to produce DBPs, rather than self-decay of oxidants to generate BrO3‒ and ClO3‒. Cu2+ increased THMs yield, but decreased HANs yield due to the catalytic hydrolysis. Cu2+ was more prone to promote the reaction of TAsp with HOCl than with HOBr, leading to a DBPs shift from brominated to chlorinated species. The chemical characterizations of Cu2+-TAsp complexations demonstrate that Cu2+ combined with TAsp at the N and O sites in both amine and amide groups, and the intermediate identification suggests that Cu2+ enhanced the stepwise chlorination process by promoting the substitution of chlorine and the breakage of CC bonds. The effect of Cu2+ on THMs yield changed from promoting to inhibiting with the increase of pH, while that on HANs yield was inhibiting regardless of pH variation. Additionally, the impact of Cu2+ on the formation of DBPs was also affected by Cu2+ dose, Cl2/C ratio and Br- concentration. This study helps to understand the formation of EPS-derived DBPs in water pipes, and provides reference for formulating control strategies during biofilm outbreaks.

Impact of non-aged and UV-aged microplastics on the formation of halogenated disinfection byproducts during chlorination of drinking water and its mechanism.

Microplastics (MPs) are ubiquitously present in source water and undergo ultraviolet (UV) aging in aquatic environments before entering drinking water treatment plants. The presence of MPs in drinking water can impact the formation of halogenated disinfection byproducts (DBPs) during chlorine disinfection, yet the exact effect of MPs on DBP formation remain unclear. In this study, we conducted an investigation into the influence of non-aged and UV-aged MPs on halogenated DBP formation in drinking water and unveiled the underlying mechanisms. In comparison to source water samples devoid of MPs, the total organic halogen concentration was reduced by 19%-43% and 4%-13% in the drinking water samples containing non-aged and aged MPs, respectively. The differing effects on halogenated DBP formation can be attributed to the alternation in physical and chemical characteristics of MPs following UV aging. Aged MPs exhibited larger surface area with signs of wear and tear, heightened hydrophilicity, surface oxidation, increased oxygen-containing functional groups and dechlorination during the UV aging process. Both non-aged and aged MPs possess the capability to adsorb natural organic matter, leading to a reduction in the concentration of DBP precursors in the source water. However, the release of organic compounds from aged MPs outweighed the adsorption of organics. Furthermore, as a result of the surface activation of MPs through the UV aging process, the aged MPs themselves can also serve as DBP precursors. Consequently, the presence of halogenated DBP precursors in source water increased, contributing to a higher level of DBP formation compared to source water containing non-aged MPs. Overall, this study illuminates the intricate relationship among MPs, UV aging, and DBP formation in drinking water. It highlights the potential risks posed by aged MPs in influencing DBP formation and offers valuable insights for optimizing water treatment processes.

N-dealkylation of amines during water disinfection - Revealing a new direction in the formation of disinfection by-products.

Among numerous disinfection by-products (DBP) forming during aqueous chlorination nitrogen containing species are of special concern due to their toxicological properties. Nevertheless, corresponding reaction products of these natural and anthropogenic compounds are not sufficiently studied so far. An interesting reaction involves dealkylation of the substituted amine moiety. Here we present the results of the comparative study of one-electron oxidation and aqueous chlorination of several aliphatic and aromatic amines. The reaction products were reliably identified with gas chromatography - high resolution mass spectrometry (GC-HRMS), high pressure liquid chromatography - electrospray ionization high resolution mass spectrometry HPLC-ESI/HRMS), and electrochemistry - electrospray ionization high resolution mass spectrometry (EC-ESI/HRMS). Certain similarities dealing with the formation of the corresponding aldehydes and substitution of alkyl groups at the nitrogen atom for hydrogen were shown for the studied processes. The mechanism of the substituted amines' aqueous chlorination involving one-electron oxidation is proposed and confirmed by the array of the observed reaction products. Alternative reactions taking place in conditions of aqueous chlorination, i.e. aromatic electrophilic substitution, may successfully compete with dealkylation and produce major products.

Sulfadiazine chlorination disinfection by-products in constructed wetlands: Identification of biodegradation products and inference of transformation pathways.

Disinfection by-products (DBPs) formed from chlorination of antibiotics have greater toxicity than their parent compounds. Herein, this study investigated the biotransformation process of sulfadiazine Cl-DBPs in constructed wetlands (CWs). Results showed that, S atom on sulfonyl group, and N atoms on primary and secondary amine groups were the most reactive sites of sulfadiazine molecule. S1-N4 and S1-C8 of sulfadiazine are the most vulnerable bonds to cleave, followed by C14-N4 and C11-N5 bonds. In the chlorination process, sulfadiazine went through C-N bond cleavage, N-reductive alkylation, halogenation, and desulfonation to produce two aromatic Cl-DBPs. In the biodegradation process in CWs, sulfadiazine Cl-DBPs went through processes mainly including dechlorination, S-N bond cleavage, aniline-NH2 oxidation, desulfonation, phenol-OH oxidation, benzene ring cleavage, C-N bond cleavage, and ß-oxidation of fatty acids under the action of a variety of oxidoreductases and hydrolases, during which a total of ten biodegradation products was identified. Moreover, sulfadiazine affected the biodegradation rather than the adsorption process in CWs. The two aromatic sulfadiazine Cl-DBPs had much higher bioaccumulation potentials than their parent sulfadiazine, but for the ten biodegradation products of sulfadiazine Cl-DBPs in CWs, 70% and almost 100% of them had lower bioaccumulation potentials than sulfadiazine and their parent sulfadiazine Cl-DBPs, respectively. The CWs were effective in reducing the environmental risk of sulfadiazine Cl-DBPs.

Far-UV-C irradiation promotes synergistic bactericidal action against adhered cells of Escherichia coli and Staphylococcus epidermidis.

The contamination of indoor areas is a global health problem that can cause the dispersion of infectious diseases. In that sense, it is urgent to find new strategies applying a lower concentration of the traditional chemicals used for cleaning and disinfection. Ultraviolet radiation (UV), in particular far-UV-C (200-225 nm), has emerged as a successful, powerful, easy-to-apply, and inexpensive approach for bacterial eradication that still requires scientific assessment. This study investigated new strategies for disinfection based on far-UV-C (222 nm) combined with chlorine and mechanical cleaning, providing an innovative solution using low doses. The bactericidal activity of far-UV-C (222 nm) was tested at an intensity of irradiation from 78.4 µW/cm2 to 597.7 µW/cm2 (for 1 min) against Escherichia coli and Staphylococcus epidermidis adhered on polystyrene microtiter plates. It was further tested in combination with mechanical cleaning (ultrasounds for 1 min) and free chlorine (0.1, 0.5, and 1 mg/L for 5 min). The triple combination consisting of mechanical cleaning + free chlorine (0.5 mg/L) + far-UV-C (54 mJ/cm2) was tested against cells adhered to materials found in hospital settings and other public spaces: polyvinyl chloride (PVC), stainless steel (SS), and polyetheretherketone (PEEK). Disinfection with far-UV-C (54 mJ/cm2) and free chlorine at 0.5 mg/L for 5 min allowed a total reduction of culturable E. coli cells and a logarithmic reduction of 2.98 ± 0.03 for S. epidermidis. The triple combination of far-UV-C, free chlorine, and mechanical cleaning resulted in a total reduction of culturable cells for both adhered bacteria. Bacterial adhesion to PVC, SS, and PEEK occurred at distinct extents and influenced the bactericidal activity of the triple combination, with logarithmic reductions of up to three. The overall results highlight that, based on culturability assessment, far-UV-C (54 mJ/cm2) with chlorine (0.5 mg/L; 5 min) and mechanical cleaning (1 min) as an efficient disinfection strategy using mild conditions. The combination of culturability and viability assessment of disinfection is recommended to detect regrowth events and increase the effectiveness in microbial growth control.

Epidermal and dermal cells from adult rat eccrine sweat gland-containing skin can reconstruct the three-dimensional structure of eccrine sweat glands.

BACKGROUND: Previously, we have demonstrated that eccrine sweat gland cells (ESGCs) can reconstruct the three-dimensional (3D) structure of eccrine sweat glands (ESGs). However, there is still a need to explore source cells capable of regenerating ESG to address the issue of ESG regeneration in ESGC-deficient conditions, such as severe burns. METHODS: The epidermal cells and dermal cells in adult rat ventral foot skin (ESG-bearing) were isolated. The isolated single epidermal cells and dermal cells were mixed with Matrigel, and then the mixture was implanted into the axillary/inguinal fat pads of nude mice. Five weeks after implantation, the Matrigel plugs were harvested and the morphology and differentiation of the cells were examined by H&E staining and fluorescent immunohistochemical staining for ESG markers, such as Na+ -K+ -2Cl- cotransporter 1 (NKCC1), Na+ -K+ -ATPase (NKA), Foxa1 and K14. RESULTS: The epidermal cells and dermal cells of adult rat ventral foot skin can reconstruct 3D structure and express specific markers of ESGs in skin, such as NKCC1, NKA and Foxa1, indicating the ESG-phenotypic differentiation of the 3D structures. Double immunofluorescence staining showed that some 3D structures expressed both the myoepithelial cell marker alpha-SMA and the common marker K14 of duct cells and myoepithelial cells, while some 3D structures expressed only K14, indicating that ESG-like 3D structures differentiated into duct-like and secretory coiled cells. CONCLUSION: Epidermal and dermal cells from adult ESG-bearing skin can be used as a cell source for ESG regeneration.

Cocamidopropyl betaine - a potential source of nitrogen-containing disinfection by-products in pool water.

Water treatment for most public pools involves disinfection with active chlorine leading to the formation of disinfection by-products (DBPs). Among them, nitrogen-containing compounds (N-DBPs) having increased toxicity and adverse effects on human health are of the greatest concern. Being the major component of various body washers for swimmers, cocamidopropyl betaine (CAPB) represents a potential and still underestimated anthropogenic precursor of N-DBPs in pool water. The purpose of this study was to investigate CAPB transformation pathways and mechanisms under the aqueous chlorination conditions. High-performance liquid and two-dimensional gas chromatography hyphenated with high-resolution mass spectrometry were used for the search and tentative identification of the primary and final CAPB transformation products. A wide range of DBPs containing up to five chlorine atoms including these in combination with hydroxyl and additional carbonyl groups has been revealed in model chlorination experiments for the first time. The proposed mechanism of their formation involves nucleophilic substitution of the secondary amide hydrogen atom at the first stage with subsequent free radical and electrophilic addition reactions resulting in non-selective introduction of halogen atoms and hydroxyl groups in the alkyl chain. The deep transformation products include short-chain chlorinated hydrocarbons and their oxidation products as well as dimethylcarbamoyl chloride possessing high toxicity and carcinogenic properties. Targeted analysis of real swimming pool water samples confirmed the results of model experiments enabling semi-quantitative determination of CAPB (0.8 µg L-1) and 18 primary DBPs, including 10 chlorine-containing compounds with the total concentration of 0.1 µg L-1. Among them, monochloro (50%) and hydroxydichloro (25%) derivatives predominate. The toxicity and health of the main DBPs has been estimated using QSAR/QSTR approach. Thus, the possibility of formation of new classes of potentially toxic chlorine-containing DBPs associated with the widespread use of detergents and cosmetics was shown.

Insight into the chemical transformation and organic release of polyurethane microplastics during chlorination.

The ubiquitous occurrence of microplastics in water and wastewater is a growing concern. In this study, the chemical transformation and organic release of virgin and UV-aged thermoplastic polyurethane (TPU) polymers during chlorination were investigated. As compared to virgin TPU polymer, the UV-aged TPU polymer exhibited high chlorine reactivity with noticeable destruction on its surface functional groups after chlorination, which could be ascribed to the UV-induced activation of hard segment of TPU backbone and increased contact area. The concentrations of leached organics increased by 1.6-fold with obviously high abundances of low-molecular-weight components. Additives, monomers, compounds relating to TPU chain extension, and their chlorination byproducts contributed to the increased organic release. Meanwhile, the formation of chloroform, haloacetic acids, trichloroacetaldehyde, and dichloroacetonitrile increased by 3.8-, 1.7-, 4.9-, and 2.4-fold, respectively. Two additives and six chlorination byproducts in leachate from chlorinated UV-aged TPU were predicted as highly toxic, e.g., butyl octyl phthalate, palmitic acid, 2,6-di-tert-butyl-1,4-benzoquinone, and chlorinated aniline. Evaluated by human hepatocarcinoma cells, the 50% lethal concentration factor of organics released from chlorinated UV-aged TPU was approximately 10% of that from its virgin counterpart, indicating a substantially increased level of cytotoxicity. This study highlights that the release of additives and chlorination byproducts from the chemical transformation of UV-aged microplastics during chlorination may be of potentially toxic concern.

Effect of UV/peroxymonosulfate pretreatment on disinfection byproduct (DBP) formation during post-chlorination of humic acid.

UV/peroxymonosulfate (UV/PMS) is a promising advanced oxidation technology in water treatment. This study aimed to investigate the impact of UV/PMS on humic acid (HA) and the influence of PMS dosage, pretreatment time, pH pretreatment, nitrate, nitrite, ammonium, and bicarbonate influencing factors on disinfection byproduct (DBP) formation during post-chlorination. With increased PMS dosage or pretreatment time, the UV/PMS treatment significantly reduced ultraviolet absorbance and increased mineralization. It altered the fractional constituent as humic substances were gradually transformed into building blocks and low-molecular-weight acids. However, most DBP formation increased initially and then decreased after subsequent chlorination. Rising nitrate or nitrite concentrations markedly promoted halonitromethane (HNM) formation. The presence of ammonia had a more significant impact on dichloroacetonitrile (DCAN) formation. Bicarbonate in UV/PMS pretreatment increased carbonated disinfection byproduct (C-DBP) formation, whereas it had a negligible impact on nitrogenous disinfection byproduct (N-DBP) formation. The present study revealed the impact of a series of influencing factors on DBP formation in UV/PMS reaction systems, providing comprehensive insights on applying UV/PMS in actual practice.