Novel chlorinated disinfection byproducts from tannic acid: nontargeted identification, formation pathways, and computationally predicted toxicity

Aromatic Structures Govern the Formation of Chlorinated Byproducts in Dichlorine Radical Reactions

Radical-induced disinfection byproduct (DBP) formation is drawing attention with increasing applications of advanced oxidation processes (AOPs). Cl2•- represents one of the extensively generated radicals in AOPs, whose behavior in DBP formation remains unknown. In this study, we found that aromatic structures serve as the main DBP precursors in Cl2•- reactions by employing diverse groups of model compounds. At a typical Cl2•- exposure of 1.2 × 10-9 M·s, the sum concentrations of 7 regulated aliphatic DBPs (e.g., trichloromethane, chloroacetic acids) are ∼0.10 to 0.48 μM for aromatic precursors and <0.05 μM for aliphatic ones. The DBP formation mechanisms from Cl2•- reactions involved the formation of chlorinated aromatics, radical-induced oxygen incorporation followed by ring cleavage, and the interactions of Cl2•- with ring-cleavage intermediates. In reacting with DOM, Cl2•- reactions produced much fewer aliphatic DBPs (5% of the total organochlorine vs 40% for chlorination) and chloroacetic acids dominated the aliphatic DBPs (usually trihalomethane for chlorination), which can be well interpreted by the precursors and mechanisms proposed. This work comprehensively reveals the precursors, formation patterns, and mechanisms of DBPs during the less-studied Cl2•- reactions, highlighting the importance of eliminating the aromatic structures of DOM before the AOPs.

Cell Type-Specific Anti- and Pro-Oxidative Effects of Punica granatum L. Ellagitannins

Pomegranate and its by-products contain a broad spectrum of phytochemicals, such as flavonoids, phenolic acids and tannins, having pleiotropic preventive and prophylactic properties in health disorders related to oxidative stress and microbial contamination. Here, we examined the biological effects of a pomegranate peel ellagitannins-enriched (>90%) extract, PETE. In vitro studies revealed that PETE has a strong antiradical action towards synthetic radicals and biologically relevant ROS surpassing or comparable to that of Trolox. In cellular models, it showed concentration-dependent (25-100 µg/mL) yet opposing effects depending on the cell membrane type and exposure conditions. In erythrocytes, PETE protected membrane integrity in the presence of the strong oxidant HClO and restored reduced glutathione levels to up to 85% of the control value while having much weaker acute and long-term intrinsic effects. Such protection persisted even after the removal of the extract from cells, indicating strong membrane interaction. In HeLa cancer cells, and at concentrations lower than those used for red blood cells, PETE induced robust potentiation of ROS production and mitochondrial potential dissipation, leading to autophagy-like membrane morphology changes and cell death. In S. aureus, the growth arrest and bacterial death in the presence of PETE (with MIC = 31.25 µg/mL and MBC = 125 µg/mL, respectively) can be linked to the tripled ROS induction by the extract in the same concentration range. This study indicates a specificity of ROS production by the pomegranate extract depending on the type of cell, the concentration of the extract and the time of incubation. This specificity witnesses a strong potential of the extract components as candidates in antioxidant and pro-oxidant therapy.

Formation of the emerging disinfection byproducts halocyclopentadienes from phenolic compounds after chlorination

Halocyclopentadienes (HCPDs) are an emerging class of alicyclic disinfection by-products (DBPs) with high toxicity in disinfected drinking water. However, their potential precursors remain unclear, which hinders the understanding of their formation and further development of control strategies. In this study, two HCPDs, 1,2,3,4-tetrachloro-1,3-cyclopentadiene (TCC) and 1,2,3,4,5,5-hexachloro-1,3-cyclopentadiene (HCC), were identified in chlorinated lignin and tannic acid samples for the first time. The chlorination of four lignin-like and two tannic-like phenolic model compounds confirmed that guaiacol and digallic acid can produce HCPDs. According to their structures, ortho-substituents of phenolic compounds were speculated to be crucial for HCPDs formation. The simulated disinfection of catechol, 2-ethoxyphenol (2-EOP), 2-propoxyphenol (2-POP) and 3,4-dihydroxy-5-methoxybenzoic acid (DH-5-MBA) with different ortho-substituents demonstrated that three of these compounds can generate HCPDs, except catechol, which further indicates that ortho-substituents, such as the methoxy, ethoxy and propoxy groups, contribute to HCPDs generation. Guaiacol was the simplest compound for generating HCPDs, and possible formation pathways during chlorination were proposed. Seven hydroxy-chlorocyclopentadienes were tentatively identified and are likely important intermediates of HCPDs formation. Additionally, TCC and HCC were confirmed in tap water and chlorinated SRNOM samples with total concentrations up to 11.07 ng/L and 65.66 ng/L, respectively, further demonstrating the wide existence of HCPDs and their precursors. This study reports the clear precursors of HCPDs and provides a theoretical foundation for controlling HCPDs formation in disinfected drinking water.

Estrogenic disruption effects and formation mechanisms of transformation products during photolysis of preservative parabens

The ubiquitous presence of emerging contaminants (ECs) in the environment and their associated adverse effects has raised concerns about their potential risks. The increased toxicity observed during the environmental transformation of ECs is often linked to the formation of their transformation products (TPs). However, comprehension of their formation mechanisms and contribution to the increased toxicity remains an unresolved challenge. To address this gap, by combining quantum chemical and molecular simulations with photochemical experiments in water, this study investigated the formation of TPs and their molecular interactions related to estrogenic effect using the photochemical degradation of benzylparaben (BZP) preservative as a representative example. A non-targeted analysis was carried out and three previously unknown TPs were identified during the transformation of BZP. Noteworthy, two of these novel TPs, namely oligomers BZP-o-phenol and BZP-m-phenol, exhibited higher estrogenic activities compared to the parent BZP. Their IC50 values of 0.26 and 0.50 μM, respectively, were found to be lower than that of the parent BZP (6.42 μM). The binding free energies (ΔGbind) of BZP-o-phenol and BZP-m-phenol (-29.71 to -23.28 kcal·mol-1) were lower than that of the parent BZP (-20.86 kcal·mol-1), confirming their stronger binding affinities toward the estrogen receptor (ER) α-ligand binding domain. Subsequent analysis unveiled that these hydrophobic residues contributed most favorably to ER binding, with van der Waals interactions playing a significant role. In-depth examination of the formation mechanisms indicated that these toxic TPs primarily originated from the successive cleavage of ester bonds (OCH2C6H5 and COO group), followed by their combination with BZP*. This study provides valuable insight into the mechanisms underlying the formation of toxic TPs and their binding interactions causing the endocrine-disrupting effects. It offers a crucial framework for elucidating the toxicological patterns of ECs with similar structures.

Multifunctional tannic acid-based nanocomposite methacrylated silk fibroin hydrogel with the ability to scavenge reactive oxygen species and reduce inflammation for bone regeneration

The microenvironment of bone defect site is vital for bone regeneration. Severe bone defect is often accompanied with severe inflammation and elevated generation of reactive oxygen species (ROS) during bone repair. In recent years, the unfriendly local microenvironment has been paid more and more attention. Some bioactive materials with the ability to regulate the microenvironment to promote bone regeneration urgently need to be developed. Here, we develop a multifunctional composite hydrogel composed of photo-responsive methacrylate silk fibroin (SFMA), laponite (LAP) nanocomposite and tannic acid (TA), aiming to endow hydrogel with antioxidant, anti-inflammatory and osteogenic induction ability. Characterization results confirmed that the SFMA-LAP@TA hydrogel could significantly improve the mechanical properties of hydrogel. The ROS-Scavenging ability of the hydrogel enabled bone marrow mesenchymal stem cells (BMSCs) to survive against H2O2-induced oxidative stress. In addition, the SFMA-LAP@TA hydrogel effectively decreased the expression of pro-inflammatory factors in RAW264.7. More importantly, the SFMA-LAP@TA hydrogel could enhance the expression of osteogenic markers of BMSCs under inflammatory condition and greatly promote new bone formation in a critical-sized cranial defect model. Above all, the multifunctional hydrogel could effectively promote bone regeneration in vitro and in vivo by scavenging ROS and reducing inflammation, providing a prospective strategy for bone regeneration.

Effects of ozone dose on brominated DBPs in subsequent chlor(am)ination: A comprehensive study of aliphatic, alicyclic and aromatic DBPs

Ozone‒chlor(am)ine is a commonly used combination of disinfectants in drinking water treatment. Although there are quite a few studies on the formation of some individual DBPs in the ozone‒chlor(am)ine disinfection, an overall picture of the DBP formation in the combined disinfection is largely unavailable. In this study, the effects of ozone dose on the formation and speciation of organic brominated disinfection byproducts (DBPs) in subsequent chlorination, chloramination, or chlorination‒chloramination of simulated drinking water were investigated. High-molecular-weight, aliphatic, alicyclic and aromatic brominated DBPs were selectively detected and studied using a powerful precursor ion scan method with ultra performance liquid chromatography/electrospray ionization triple quadrupole mass spectrometry (UPLC/ESI-tqMS). Two groups of unregulated yet relatively toxic DBPs, dihalonitromethanes and dihaloacetaldehydes, were detected by the UPLC/ESI-tqMS for the first time. With increasing ozone dose, the levels of high-molecular-weight (m/z 300-500) and alicyclic and aromatic brominated DBPs generally decreased, the levels of brominated aliphatic acids were slightly affected, and the levels of dihalonitromethanes and dihaloacetaldehydes generally increased in the subsequent disinfection processes. Despite different molecular compositions of the detected DBPs, increasing ozone dose generally shifted the formation of DBPs from chlorinated ones to brominated analogues in the subsequent disinfection processes. This study provided a comprehensive analysis of the impact of ozone dose on the DBP formation and speciation in subsequent chlor(am)ine disinfection.

Recent progress in identification of water disinfection byproducts and opportunities for future research

Numerous disinfection by-products (DBPs) are formed from reactions between disinfectants and organic/inorganic matter during water disinfection. More than seven hundred DBPs that have been identified in disinfected water, only a fraction of which are regulated by drinking water guidelines, including trihalomethanes, haloacetic acids, bromate, and chlorite. Toxicity assessments have demonstrated that the identified DBPs cannot fully explain the overall toxicity of disinfected water; therefore, the identification of unknown DBPs is an important prerequisite to obtain insights for understanding the adverse effects of drinking water disinfection. Herein, we review the progress in identification of unknown DBPs in the recent five years with classifications of halogenated or nonhalogenated, aliphatic or aromatic, followed by specific halogen groups. The concentration and toxicity data of newly identified DBPs are also included. According to the current advances and existing shortcomings, we envisioned future perspectives in this field.

Formation and speciation of hazardous trihalomethanes and haloacetic acids during chlorinated washing of brined kimchi cabbage in the presence of bromide

Brominated disinfection byproducts (Br-DBPs) may be generated in high concentrations during the chlorinated washing of brined kimchi cabbage (BKC) in kimchi manufacturing. However, the generation of these DBPs is not sufficiently understood. Therefore, in this study, we investigated the formation and speciation of the DBPs trihalomethanes (THMs) and haloacetic acids (HAAs) during the chlorinated washing process. The average bromide content in 22 salt products sourced from various regions of Korea was 1600 ± 468 mg/kg. Increasing bromide content shifted the speciation of DBPs from chlorinated to mixed bromochloro to brominated species, which would be more harmful than their chlorinated analogs. DBP formation during the washing of BKC at average bromide levels changed based on the brine salinity, salting temperature, and disinfectant type. Based on our findings, we recommend that low salinity and low temperature should be maintained during the salting of KC and that NaOCl should be used as the disinfectant rather than slightly acidic electrolyzed water during the chlorinated washing of KC to alleviate the formation of Br-DBPs. Moreover, we recommend the use of salts with low bromide levels for the salting of KC and the addition of a rinse step after chlorinated washing.

Chemiluminescence of doped carbon dots with H2O2-KMnO4 system for the detection of Cu2+ and tannin

The carbon dots doped with chlorine and phosphorus (CDs-Cl,P) were used as chemiluminescence (CL) reagent for the sensitive detection of copper ions (Cu²⁺) and tannin (TA). The CDs-Cl,P was found to strongly enhance the reaction of H₂O₂ and KMnO₄ in alkaline medium. The enhanced CL behavior of CDs-Cl,P was investigated and it was found that some radicals such as ^•OH, ^•O₂^- and ¹O₂ appeared in the CL reaction process. The participation of Cu²⁺ could result in an enhanced CL intensity of the CDs-Cl,P-H₂O₂-KMnO₄ system due to the Cu²⁺-catalyzed decomposition of H₂O₂ resulting in more ^•OH generation. Therefore, the CDs-Cl,P-H₂O₂-KMnO₄ system was used to selectively quantify Cu²⁺ in solution by CL emission. A linear increase was observed between CL intensity and Cu²⁺ concentration. The CDs-Cl,P-H₂O₂-KMnO₄ system allowed the detection of Cu²⁺ down to lower concentration of 0.1 μM with a linear range of 0.2-60.0 μM. Moreover, TA as a common polyphenolic compound, could selectively decrease the CL signal of the CDs-Cl,P-H₂O₂-KMnO₄-Cu²⁺ system due to its complexation with Cu²⁺. On this basis, the CL assay for TA was also developed. The detection limit was 0.14 μM and the linear range was from 5.0 μM to 100.0 μM. The proposed method was successfully applied to the determination of Cu²⁺ and TA in water, rice dumplings leaves, sodium copper chlorophyllin and wine samples with satisfactory results.

Formation pathway of disinfection by-products of lignin monomers in raw water during disinfection

In this study, the dissolved organic matter (DOM) profiles of water samples from a water source in northeastern China were analyzed by high-resolution mass spectrometry (HRMS), and its changes after chlorination were investigated. The results showed that lignin substances accounted for a significant proportion in DOM and chlorinated products and were the main precursors of disinfection by-products (DBPs). During disinfection, macromolecular DOM was transformed into small molecules, and lignin substances have the most obvious and complex changes in reaction. Two lignin monomers 4-propylphenol (4PP) and 4-propylguaiacol (4PG) were used as model compounds to study their reaction kinetics and degradation pathways during disinfection. The degradation of both lignin monomers conformed to pseudo-first-order reaction kinetics, and the reaction rate constant of 4PG was higher than that of 4PP. The effects of chlorine dosage, pH and temperature on the degradation reaction kinetics of two lignin monomers were investigated. The degradation rates of 4PP and 4PG increased with increasing chlorine dosage, pH and temperature. The two monomers showed similar properties in the chlorination degradation process, and generated multiple intermediates, which were mainly transformed into small molecules by chlorine electrophilic substitution and nucleophilic substitution, and further generated DBPs.