Chlorinated Transformation Products Research Articles

Degradation of benzophenone-8 in UV/oxidation processes: Comparison of UV/H2O2, UV/persulfate, UV/chlorine processes

Benzopenone-8 (BP8) is an ultraviolet (UV) filter commonly used in sunscreen and plastic products. BP8 can cause acute and chronic toxicity in living organisms because it is biologically toxic and bioaccumulates. Advanced oxidation processes (AOPs) are widely used to treat contaminated water using powerful radical species. In this study, we compared the degradation kinetics and mechanisms of BP8 under UV/H2O2, UV/persulfate (PS), and UV/chlorine processes. BP8 reacts quickly with reactive oxidants following pseudo-first-order kinetics. At an oxidant concentration of 12.5 μM within the pH range of 6–10, the degradation rate constant (kobs) was the highest for the UV/chlorine ((5.29–14.2) ×10−3 s−1), followed by UV/PS ((1.38–2.90) ×10−3 s−1) and UV/H2O2 ((0.79–2.41) ×10−3 s−1). kobs increased linearly with increasing oxidant dosage, with the highest value at pH 6 in the UV/H2O2 and UV/PS and pH 8 in the UV/chlorine process. At the pH with the highest kobs, hydroxyl radicals (∙OH), sulfate radicals (∙SO4–), and reactive chlorine species played significant roles in removing 99.7 %, 82.3 %, and 56.2 % of BP8 in the UV/H2O2, UV/PS, and UV/chlorine processes, respectively. Humic acids significantly inhibited BP8 degradation, whereas NO3– ions promoted BP8 degradation in UV/H2O2 process, NO3– and Cl– ions promoted BP8 degradation in UV/PS process and Br– ions promoted BP8 degradation in UV/chlorine process. The electricity consumption (EE/O) in various water matrices was in the order of UV/H2O2 > UV/PS >> UV/chlorine process; however, the chlorinated transformation products (TPs) produced in the UV/chlorine process were more toxic than the hydroxylated TPs from the UV/H2O2 and UV/PS processes, implying that the UV/PS process was most suitable for removing BP8 while controlling the formation of toxic products.

Heat-activated peroxydisulfate and peroxymonosulfate-mediated degradation of benzotriazole: Effects of chloride on kinetics, pathways and transformation product toxicity

The impact of chloride (Cl⁻) in heat-activated peroxydisulfate (PDS) and peroxymonosulfate (PMS) processes for benzotriazole (BTA) degradation was investigated. Results showed that 0.42 mM BTA could be degraded by PDS and PMS under 70 °C in presence and absence of Cl⁻. The PMS-mediated BTA degradation rate increased with increasing Cl⁻ concentration up to 1000 mg/L, while a further increase of Cl⁻ concentration decreased the BTA degradation rate. In contrast, Cl⁻ inhibited PDS-mediated BTA degradation at concentrations tested between 100 and 10,000 mg/L. Radical scavenging experiments indicated that BTA degradation was mainly driven by hydroxyl and sulfate radicals in PDS and PMS systems without Cl⁻. However, reactive chlorine species (RCS) significantly boosted the PMS system for BTA degradation in presence of Cl⁻. Variation in pH substantially influenced the PMS system, but not the PDS system, whether in presence and absence of Cl⁻. By LC-MS/MS analysis, forty-two transformation products (TPs) were identified resulting from BTA degradation. Based on the TPs, polymerization, hydroxylation, benzene ring-opening, and carboxylic acid formation were hypothesized to be the main degradation mechanisms in absence of Cl⁻, whereas chlorination, triazole ring-opening, and nitration were the additional degradation steps in presence of Cl⁻. These findings help understand the influence of Cl⁻ on BTA removal rate and degradation pathway in saline wastewater. Moreover, more chlorinated TPs were found in PMS/Cl⁻ system than in PDS/Cl⁻ system, which was also reflected in absorbable organic halides (AOX) and end-product toxicity analyses. The PMS/Cl⁻ process also produced other undesirable by-products, such as chlorates which were not detected in the PDS/Cl⁻ process. This shows that PDS and PMS-based advanced oxidation processes can notably differ in terms of toxic by-product formation. Thus, they need to be critically evaluated before applying for organic pollutant degradation under saline conditions.

Aspartame-Sweetened Tap Water: Transformation Products and 2,6-Dichloro-1,4-Benzoquinone Formation.

Aspartame (APM), a dipeptide of aspartic acid (ASP) and phenylalanine (PHE), is a widely used artificial sweetener in beverages. It is unclear whether residual chlorine in tap water can react with APM to form disinfection byproducts (DBPs). Therefore, we investigated the formation of DBPs from the reaction of APM with residual chlorine in authentic tap water. APM and a commercial sweetener (CS) packet containing APM were studied under authentic and simulated tap water conditions. Eight chlorinated products of APM were detected using solid-phase extraction (SPE) and high performance liquid chromatography quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS). These new chloro-products were tentatively identified based on accurate masses, isotopic patterns of 35,37Cl, and MS/MS spectra. Furthermore, we identified APM as a precursor to 2,6-dichloro-1,4-benzoquinone (DCBQ). DCBQ significantly increased to 2.3-12 ng/L with the addition of APM or CS in tap waters collected from different locations compared to 1.4-1.8 ng/L in the same tap water samples without sweetener. DCBQ and two of the chlorinated transformation products were identified in cold prepared tea containing APM. DCBQ formation was eliminated when the residual chlorine in tap water was reduced by ascorbic acid or boiling prior to the addition of APM or CS. This study found that eight new DBPs and DCBQ were produced by the reactions of residual chlorine with APM and CS. These findings show an unintended exposure source of emerging DBPs via APM sweetened beverages.

Transformation of macrolide antibiotics during chlorination process: Kinetics, degradation products, and comprehensive toxicity evaluation

Antibiotics are ubiquitous in wastewater and surface water and their presence is of grave concern. Chlorination, an important disinfection process used in wastewater treatment plants and waterworks, causes antibiotics to be degraded. However, interactions of antibiotics with chlorine result in the generation of multiple transformation products (TPs). TPs may be more toxic than the parent compounds, but their structures, yields and ecotoxicity remain to be ascertained in most cases. This study examined the degradation by chlorine of two typical macrolide (MLs) antibiotics, erythromycin (ERY) and roxithromycin (ROX), and identified the TPs formed as a result of ERY and ROX chlorination. The ecotoxicity of ERY, ROX and their TPs was evaluated using a combination of bioassay and ECOSAR prediction. The degradation of ERY and ROX followed pseudo-first-order kinetic at the molar ratio of FAC to MLs of 10:1, and the degradation kinetic rate depends on pH values. Six TPs of ERY including three chlorinated TPs, and six TPs of ROX including two chlorinated TPs were identified. The tertiary N of the desosamine moiety of ERY and ROX was determined to be the main reactive site. Demethylation and chlorine substitution at the reactive site are the main degradation pathways of ERY and ROX. ECOSAR results showed that the chlorinated byproducts of ERY TP578, TP542 and TP528, and the reduced hydroxylation products of ROX TP851 exhibited higher ecotoxicity than their parent compounds. However, algae growth inhibition assays indicated that the overall ecotoxicity of the chlorinated ERY or ROX mixture was lower than that of ERY or ROX prior to chlorination. This may be attributed to the removal of the parent compound and lower yields of toxic substances. While the yields of the toxic TPs may be low, their accumulation and combined effects of the TPs and other co-occurring pollutants should be examined further.

Comparative endocrine disrupting compound removal from real wastewater by UV/Cl and UV/H2O2: Effect of pH, estrogenic activity, transformation products and toxicity

Extensive use of endocrine disruptor compounds (EDCs) and their release through various pathways into the environment are emerging environmental concerns. In this context, H2O2 and chlorine UV-based treatments were carried out to evaluate their efficiency in the removal of the bisphenol A (BPA), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) at 100 μg L−1 from ultrapure water and from wastewater treatment plants (WWTP). Photolysis was performed under different irradiation sources, i.e. UVC and UVA. The effect of H2O2 (3 and 30 mg·L−1), free chlorine concentrations (1 and 2 mg·L−1) and pH (5, 7 and 9) were also investigated. Toxicity (Raphidocelis subcapitata) and estrogenic activity (yeast estrogen screen - YES assay) were assessed during the processes. Compound removal at optimal operating parameters reached 100% after 15 and 2 min for UVC/H2O2 (pH 9 and 3 mg L−1 of H2O2), and UVC/Cl (pH 9 and 2 mg L−1 of chlorine), respectively. Total organic carbon (TOC) removal achieved 37% and 45% for the H2O2 and Cl-UV based process, respectively. The in vitro YES assay indicated that the formed by-products were non-estrogenic compounds, while the toxicity evaluation revealed high cell growth inhibition due to UVC/Cl byproducts. During the UV-based processes, 30 transformation products (TPs) were identified, in which three new chlorinated TPs from E2 and EE2 may be responsible for toxicity effects. EDC degradation by UV/Cl is faster than by UV/H2O2, although chlorinated toxic byproducts were also formed during the UV/Cl process.

Core-Shell Fe/FeS Nanoparticles with Controlled Shell Thickness for Enhanced Trichloroethylene Removal.

Zero-valent iron nanoparticles (nZVI) treated by reduced sulfur compounds (i.e., sulfidated nZVI, S-nZVI) have attracted increased attention as promising materials for environmental remediation. While the preparation of S-nZVI and its reactions with various groundwater contaminants such as trichloroethylene (TCE) were already a subject of several studies, nanoparticle synthesis procedures investigated so far were suited mainly for laboratory-scale preparation with only a limited possibility of easy and cost-effective large-scale production and FeS shell property control. This study presents a novel approach for synthesizing S-nZVI using commercially available nZVI particles that are treated with sodium sulfide in a concentrated slurry. This leads to S-nZVI particles that do not contain hazardous boron residues and can be easily prepared off-site. The resulting S-nZVI exhibits a core–shell structure where zero-valent iron is the dominant phase in the core, while the shell contains mostly amorphous iron sulfides. The average FeS shell thickness can be controlled by the applied sulfide concentration. Up to a 12-fold increase in the TCE removal and a 7-fold increase in the electron efficiency were observed upon amending nZVI with sulfide. Although the FeS shell thickness correlated with surface-area-normalized TCE removal rates, sulfidation negatively impacted the particle surface area, resulting in an optimal FeS shell thickness of approximately 7.3 nm. This corresponded to a particle S/Fe mass ratio of 0.0195. At all sulfide doses, the TCE degradation products were only fully dechlorinated hydrocarbons. Moreover, a nearly 100% chlorine balance was found at the end of the experiments, further confirming complete TCE degradation and the absence of chlorinated transformation products. The newly synthesized S-nZVI particles thus represent a promising remedial agent applicable at sites contaminated with TCE.

Targeted profiling of chlorinated transformation products and the parent micropollutants in the aquatic environment: A comparison between two coastal cities.

This study investigated chlorinated transformation products (TPs) and their parent micropollutants, aromatic pharmaceuticals and personal care products (PPCPs) in the urban water bodies of two metropolitan cities. Nine PPCPs and 16 TPs were quantitatively or semi-quantitatively determined using isotope dilution techniques and liquid chromatography-tandem mass spectrometry. TPs and most PPCPs were effectively removed by conventional wastewater treatments in a wastewater treatment plant (WWTP). Chlorinated parabens and all PPCPs (at concentrations below 1000 ng/L) were present in the waters receiving treated wastewater. By contrast, the waters receiving untreated wastewater contained higher levels of PPCPs (up to 9400 ng/L) and more species of chlorinated TPs including chlorinated parabens, triclosan, diclofenac, and bisphenol A. The very different chemical profiles between the water bodies of the two cities of similar geographical and climatic properties may be attributed to their respective uses of chemicals and policies of wastewater management. No apparent increase in the number of species or abundances of TPs was observed in either the chlorinated wastewater or the seawater rich in halogens. This is the first study to elucidate and compare the profiles of multiple TPs and their parent PPCPs in the water bodies of coastal cities from tropical islands. Our findings suggest that chlorinated derivatives of bisphenol A, diclofenac, triclosan, and parabens in the surface water originate from sources other than wastewater disinfection or marine chlorination. Although further studies are needed to identify the origins, conventional wastewater treatments may protect natural water bodies against contamination by those chlorinated substances.

Systematic screening and identification of the chlorinated transformation products of aromatic pharmaceuticals and personal care products using high-resolution mass spectrometry

Pharmaceuticals and personal care products (PPCPs) are an emerging concern because of the large amount of PPCPs that is discharged and its potential ecological effects on the aquatic environment. Chlorination has proven efficient for removing some aromatic PPCPs from wastewater, but the formation of by-products has not been thoroughly investigated partly because of analytical difficulties. This study developed a method for systematically screening and identifying the transformation products (TPs) of multiple aromatic PPCPs through high-resolution mass spectrometry (HRMS). We spiked an environmentally relevant concentration (5000 ng/L) of three anti-inflammatory drugs, four parabens, bisphenol A, oxybenzone, and triclosan in the Milli-Q water and water containing natural organic matter (NOM). Low-dose chlorination (0.2–0.7 mg/L) was performed. We compared the chemical profiles of the chlorinated and untreated water and selected the ions to be identified based on the results of t-test and the ratio of signal intensities. Compound matching and isotopic pattern comparison were applied to characterising the molecular formulae of TPs. The fragmentation of the PPCPs and TPs was used in elucidating the structures of the TPs. The confirmation of TPs was achieved by comparing the retention time and fragment patterns of TPs with the isomer standards. In the chlorinated water, the aromatic PPCPs were substantially removed, except for the anti-inflammatory drugs (removal rates −5.2%–26%). Even with moderate chlorine dosages, all of the aromatic PPCPs, except for acetylsalicylic acid, were transformed into chlorinated derivatives in the Milli-Q water, and so were some PPCPs in the NOM-added water. The results of structure elucidation and compound confirmation as well as the increases in log Kow suggested that chlorination could transform aromatic PPCPs into more persistent, bioaccumulative, and toxic TPs. The presence of these TPs in the effluents where the PPCPs are removed through chlorination may pose increased risks to aquatic organisms.

Mechanistic Insight into the Reactivity of Chlorine-Derived Radicals in the Aqueous-Phase UV-Chlorine Advanced Oxidation Process: Quantum Mechanical Calculations.

The combined ultraviolet (UV) and free chlorine (UV-chlorine) advanced oxidation process that produces highly reactive hydroxyl radicals (HO•) and chlorine radicals (Cl•) is an attractive alternative to UV alone or chlorination for disinfection because of the destruction of a wide variety of organic compounds. However, concerns about the potential formation of chlorinated transformation products require an understanding of the radical-induced elementary reaction mechanisms and their reaction-rate constants. While many studies have revealed the reactivity of oxygenated radicals, the reaction mechanisms of chlorine-derived radicals have not been elucidated due to the data scarcity and discrepancies among experimental observations. We found a linear free-energy relationship quantum mechanically calculated free energies of reaction and the literature-reported experimentally measured reaction rate constants, kexp, for 22 chlorine-derived inorganic radical reactions in the UV-chlorine process. This relationship highlights the discrepancy among literature-reported rate constants and aids in the determination of the rate constant using quantum mechanical calculations. We also found linear correlations between the theoretically calculated free energies of activation and kexp for 31 reactions of Cl• with organic compounds. The correlation suggests that H-abstraction and Cl-adduct formation are the major reaction mechanisms. This is the first comprehensive study on chlorine-derived radical reactions, and it provides mechanistic insight into the reaction mechanisms for the development of an elementary reaction-based kinetic model.

Degradation of the anticancer drug erlotinib during water chlorination: Non-targeted approach for the identification of transformation products

Erlotinib is a highly potent tyrosine kinase inhibitor used in the treatment of the most common type of lung cancer. Due to its recent introduction, very scarce information is available on its occurrence, environmental fate and toxicological effects on aquatic organisms. During chlorination processes normally carried out in wastewater treatment plants and in the pretreatment of hospital effluents, chlorinated transformation products can be formed with an enhanced toxicity relative to the parent compound.Thus, the reactivity of the cytostatic drug erlotinib in free chlorine-containing water was investigated for the first time in the present work. A non-targeted screening approach based on the use of differential profiling tools was applied in order to reveal its potential transformation products. Structural elucidation of the detected transformation products was performed by ultra-performance liquid chromatography coupled to high-resolution hybrid quadrupole-Orbitrap tandem mass spectrometry. The proposed approach allowed detecting a total of nineteen transformation products, being eighteen of them described for the first time in this work, which demonstrates its potential in environmental analysis. Among them, six compounds presented chlorine atoms in their structures, which may be of major concern. Other transformation products involved hydroxylation and oxidation reactions. Time-course profiles of erlotinib and its transformation products were followed in real wastewater samples under conditions that simulate wastewater disinfection. Although the structures of these transformation products could not be positively confirmed due to lack of standards, their chemical formulas and product ions can be added to databases, which will allow their screening in future monitoring studies.

Assessment of potential positive effects of nZVI surface modification and concentration levels on TCE dechlorination in the presence of competing strong oxidants, using an experimental design

Nanoscale zero-valent iron (nZVI) particles are efficient for the remediation of aquifers polluted by trichloroethylene (TCE). But for on-site applications, their reactivity can be affected by the presence of common inorganic co-pollutants, which are equally reduced by nZVI particles. The aim of this study was to assess the potential positive effects of nZVI surface modification and concentration level on TCE removal in the concomitant presence of two strong oxidants, i.e., Cr(VI) and NO3−. A design of experiments, testing four factors (i.e. nZVI concentration, nZVI surface modification, Cr(VI) concentration and NO3− concentration), was used to select the best trials for the identification of the main effects of the factors and of the factors interactions. The effects of these factors were studied by measuring the following responses: TCE removal rates at different times, degradation kinetic rates, and the transformation products formed. As expected, TCE degradation was delayed or inhibited in most of the experiments, due to the presence of inorganics. The negative effects of co-pollutants can be palliated by combining surface modification with a slight increase in nZVI concentration. Encouragingly, complete TCE removal was achieved for some given experimental conditions. Noteworthily, nZVI surface modification was found to promote the efficient degradation of TCE. When degradation occurred, TCE was mainly transformed into innocuous non-chlorinated transformation products, while hazardous chlorinated transformation products accounted for a small percentage of the mass-balance.

LC/MS study of the UV filter hexyl 2‐[4‐(diethylamino)‐2‐hydroxybenzoyl]‐benzoate (DHHB) aquatic chlorination with sodium hypochlorite

The fate of modern personal care products in the environment is becoming a matter of increasing concern because of the growing production and assortment of these compounds. More and more chemicals of this class are treated as emerging contaminants. Transformation of commercially available products in the environment may result in the formation of a wide array of their metabolites. Personal care products in swimming pools and in drinking water reservoirs may undergo oxidation or chlorination. There is much data on the formation of more toxic metabolites from original low toxicity commercial products. Therefore, reliable identification of all possible transformation products and a thorough study of their physicochemical and biological properties are of high priority. The present study deals with the identification of the products of the aquatic chlorination of the hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]-benzoate ultraviolet filter. High-performance liquid chromatography/mass spectrometry (HPLC/MS) and HPLC/MS/MS with accurate mass measurements were used for this purpose. As a result, three chlorinated transformation products were identified.

Formation of chlorinated by-products during photo-Fenton degradation of pyrimethanil under saline conditions. Influence on toxicity and biodegradability

This study evaluated the formation of chlorinated transformation products during photo-Fenton treatment of pyrimethanil (PYR-20mgL−1) in two water matrices, demineralised water (DW) and water containing 5gL−1 of NaCl (DWNaCl). All experiments were carried out in compound parabolic collectors (CPC) at an initial Fe2+ concentration of 5mgL−1 and H2O2 concentration of 150–350mgL−1. Dissolved Organic Carbon (DOC), High-Performance Liquid Chromatography with Diode-Array Detection (HPLC–DAD), Liquid Chromatography–Time-Of-Flight Mass Spectrometry (LC–TOF-MS), toxicity and biodegradability tests were conducted to control the photocatalytic treatment. In DW, PYR was completely eliminated after 11.8min of illumination and initial DOC was reduced 50% after 79min of illumination with 33mM of H2O2 consumed. On the other hand, in DWNaCl water matrix, the same reduction in DOC took 110min of illumination and H2O2 consumption of 39mM, and total degradation of PYR was observed at 12min of illumination. PYR transformation products (TPs) were identified by LC–TOF-MS. It was demonstrated that photo-Fenton in a DWNaCl produces some chlorinated TPs in addition to the non-chlorinated TPs identified during degradation in the DW. All TPs formed were eliminated during photo-Fenton. Additionally, the presence of chlorinated TPs does not increase the toxicity of the water, and TPs formed are more biodegradable than PYR.

Trichlorofluoroethene: A reactive tracer for evaluating reductive dechlorination in large‐diameter permeable columns

AbstractTrichlorofluoroethene (TCFE) was used as a reactive tracer to determine the in situ rate of reductive dechlorination in treatment zones impacted by three large‐diameter permeable columns (LDPCs) that were installed at a trichloroethene (TCE)–contaminated site. The LDPCs were part of a pilot study to evaluate the effectiveness of hydrogen, lactate, and zero‐valent iron for remediating TCE‐contaminated ground water. The rate of TCFE reductive dechlorination was determined for each LDPC by means of push‐pull tests conducted in each treatment layer. In addition, the distribution of TCFE's lesser chlorinated transformation products was determined. The rates of TCFE reductive dechlorination ranged from 0.05/d to 0.20/d and corresponded to half‐lives ranging from 3.5 to 13.9 d. cis‐Dichlorofluoroethene was the dominant transformation product detected in all the tests, which is consistent with the findings from pilot tests conducted in the LDPCs prior to the TCFE push‐pull tests. cis‐Chlorofluoroethene (CFE) and 1,1‐CFE also were detected and indicate the potential for vinyl chloride to form under all treatment regimes. Significant production of fluoroethene (FE), the analog of ethene, was observed for only one of the hydrogen treatments. Unambiguous and sensitive detection of the lesser chlorinated products, such as CFE and FE, is possible because TCFE and its transformation products are not found in the background ground water at contaminated sites. Good agreement between the rates and transformation product profiles for TCFE and TCE in both field and laboratory experiments indicates the suitability of TCFE as a surrogate for predicting the rates of TCE reductive dechlorination.