Formation Of DBPs Research Articles

Identification of Toxicity Forcing Agents from Individual Aliphatic and Aromatic Disinfection Byproducts Formed in Drinking Water: Implications and Limitations.

Recently, a study found that aromatic DBP fractions dominate the overall toxicity of chlorinated drinking water. However, key toxicity drivers have not been reported via comprehensive evaluation based on the formation of aliphatic and aromatic DBPs in drinking water. In this study, the occurrence of 37 aliphatic and 19 aromatic DBPs in drinking samples with different water characteristics collected in a Chinese megacity was explored. According to the individual DBP concentrations and cytotoxicity potencies as well as the "TIC-Tox" method, haloacetonitriles and halonitrophenols were found to be the toxicity drivers among the measured aliphatic and aromatic DBPs, respectively. However, when aromatic and aliphatic DBPs are taken into consideration together, aliphatic DBPs were calculated to present higher toxicity contribution than aromatic DBPs, which is inconsistent with the previous study. TOX showed significant positive correlations with most aliphatic DBPs but no aromatic DBPs, and the overall toxicity of the water sample concentrates is significantly related to the total calculated cytotoxicity and aliphatic DBPs, suggesting that current selected aromatic DBPs are insufficient to represent the overall aromatic DBPs. UV254 and DOC rather than SUVA are better surrogates for predicting DBP formation potential for DOM with a lower humification degree as indicated by fluorescence results.

Probing into the mechanisms of disinfection by-product formation from natural organic matter and model compounds after UV/chlorine treatment

Compared to regulated DBPs such as TCM and TCAA, the significant formation of chloral hydrate and nitrogenous DBPs associated with UV/chlorine treatment needs close scrutiny when considering this process being applied in practice.

Molecular characteristics of unknown chlorinated disinfection byproducts during chlorination in sedimentation sludge water

Recycling sedimentation sludge water (SSW) supernatant to the head of drinking water treatment plants also recycles a large fraction of dissolved organic matter (DOM), which can react with chlorine to generate abundant DBPs. Among them, the majority of Cl-DBPs are not well understood. We characterized the DOM and chlorinated DBPs (Cl-DBPs) during the chlorination of SSW using Fourier transform ion cyclotron resonance mass spectrometry. Aromatic compounds and oxidized molecules preferentially reacted with chlorine to form aromatic DBPs. The unknown non-nitrogenous Cl-DBPs (i.e., CHOCl and CHOSCl) contained a large amount of aromatic ring structure, easily reacting with chlorine to form aromatic DBPs. During chlorination reaction, one precursor could be associated with 1–4 products, and one product can be associated with 1–7 precursors. The primary reaction was +Cl–H, +ClO–H, and +HClO, possessing the largest number of possible precursor-product pairs. Vascular plant-derived polyphenols, which are regarded as highly unsaturated and phenolic compounds were the primary precursors participated in the chlorination reaction. The products mainly distributed in the area with highly unsaturated and phenolic compounds illustrated that unknown Cl-DBPs had a large number of highly unsaturated bonds and aromatic rings showing the high toxicity. Understanding the transformation of DOM and characteristics of unknown Cl-DBPs may not only lead to development of more effective treatment strategies to minimize the formation of DBPs in recycled SSW but also can be extended to understanding unknown DBPs and their precursors in drinking water sources.

Chlorination of L-tyrosine and metal complex: degradation kinetics and disinfection by-products generation

The presence of metal ions in drinking water treatment and distribution systems may affect the disinfection process of organic matter, which had aroused people's concern. L-tyrosine can complex with metal ions through carboxyl, carbonyl and amino groups and affected its chemical reactions. In this paper, the complexation of L-tyrosine with common metal ions was studied and the influence of complexation in chlorination with different experimental factors were investigated. It was inferred that L-tyrosine complexed with metal ions by single dentate ligand or double dentate chelation in a ratio of 2:1. The degradation of L-tyrosine-metal complex followed the pseudo-first-order reaction kinetic. TCM, DCAA and TCAA were the main species DBPs in chlorination of L-tyrosine. Compared with L-tyrosine, the reaction rate constants of complex increased by 5.6%, the formation of trihalomethane production decreased by 21.5% and the formation of haloacetic acids production increased by 26.9% at the state of metal complexation. The effect of metal complexation on chlorination was more obvious than that of metal coexistence. For different metal complexation, the order of inhibition on trihalomethane production was Ca2+> Fe3+> Mn2+ and the order of promotion on haloacetic acids production was Mn2+> Fe3+> Ca2+. Moreover, it was found that alkaline conditions were favorable to the formation of DBPs due to the hydroxyl radical. The combination of ultraviolet (UV) and chlorine disinfection promoted L-Tyr degradation and DBPs generation, and the promotion efficiency follow the order: UV/Cl2> UV-Cl2> Cl2.

Acute toxicity of disinfection by-products from chlorination of algal organic matter to the cladocerans Ceriodaphnia silvestrii and Daphnia similis: influence of bromide and quenching agent.

Algal organic matter (AOM) in water reservoirs is a worldwide concern for drinking water treatment; once it is one of the main precursors for disinfection by-products formation (DBPs). In this context, this study investigated the ecotoxicity of DBPs from chlorination of AOM to Ceriodaphnia silvestrii and Daphnia similis (Crustacea, Cladocera). The bioassays evaluated three scenarios, including the AOM extracted from Chlorella sorokiniana, the quenching condition used in the tests, and the DBPs formed after the chlorination of the two test waters with AOM (with and without bromide presence). The results showed that AOM has no toxic effects for the tested species under typical environmental concentration (5mg∙L-1). However, since AOM is a potential precursor of DBPs, the toxicity of two test waters (TW-1 and TW-2) after the chlorination process (25mg Cl2·L-1, for 7days, at 20°C) was tested. The sample with higher toxicity to the tested species was TW-1, in which chloroform and chloral hydrate were quantified (615 and 267µg∙L-1, respectively). However, TW-2 showed lower concentration of chloroform and chloral hydrate (260 and 157µg∙L-1, respectively), although bromodichloromethane, dibromochloromethane, and bromoform were also detected (464, 366, and 141µg∙L-1, respectively). Although free chlorine is highly toxic to the tested species, the quenching conditions also affected the organisms' survival due to the use of ascorbic acid and the presence of reaction intermediates. Nonetheless, both species were more affected by TW-1 and TW-2 than the quenching condition. These results endorse the importance of removing the AOM before the disinfection process to avoid the formation of DBPs. In addition, ecotoxicological analyses could provide a more comprehensive assessment of water quality, especially considering the challenges of quantifying DBPs and other emerging contaminants.

Degradation of Organics and Formation of Dbps in the Combined Led-Uv and Chlorine Processes: Effects of Water Matrix and Fluorescence Analysis

Degradation of Organics and Formation of Dbps in the Combined Led-Uv and Chlorine Processes: Effects of Water Matrix and Fluorescence Analysis

New iodine-based electrochemical advanced oxidation system for water disinfection: Are disinfection by-products a concern?

A novel electrochemical Advanced Oxidation System (AOS) has been recently developed for water disinfection where iodide is used to generate active iodine species in-situ. However, the presence of iodide during water disinfection can lead to the formation of iodinated disinfection byproducts (I-DBPs), which have been shown to be more cyto- and genotoxic than their chlorinated and brominated analogs. In this study, the formation of DBPs was assessed in ultrapure water, river water and secondary wastewater effluents treated by the AOS. A comprehensive total organic halogen and target DBP analysis was used that included 25 unregulated DBPs, and the total organic halogen (TOX) quantified as total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI). Ultrapure water disinfection only quantified iodoform (TIM) at a maximum concentration of 0.90 ± 0.05 µg/L. River water results show that TOI increase from 1.3 ± 0.3 µg/L before disinfection (t = 0) to a maximum of 3.5 ± 1.1 µg/L. TIM and bromodiiodomethane (BDIM) were the only targeted iodo-trihalomethanes (I-THMs) that were quantified with a maximum total I-THM concentration of 0.44 µg/L. Secondary wastewater effluent disinfection results show that TOI increased from 1.8 ± 0.3 µg/L (t = 0) to a maximum concentration of 35.3 ± 0.3 µg/L. Iodide and iodate were the main iodinated species exiting the AOS system with a iodine recovery of 94–101%. The results from this study show that the AOS formed low levels of iodinated DBPs in treated water sources that are comparable to the levels found in disinfected drinking water and wastewater.

Degradation of tetrabromobisphenol A by ferrate(VI)-CaSO3 process: Kinetics, products, and impacts on following disinfection by-products formation

Tetrabromobisphenol A (TBBPA) is one of the most widely applied brominated flame retardants and has been widely detected in water environment, which might pose risks of brominated disinfection by-products formation in water treatment system. Ferrate(VI)-CaSO3 (Fe(VI)-CaSO3) system could effectively degrade TBBPA at pH 7.0–9.0 but the decomposition rate of TBBPA dropped with increasing pH. The presence of 0.5 mg C/L humic acid (HA) had negligible impact on TBBPA removal, but the removal of TBBPA decreased to ~87% and 80% at pH 7.0 and 8.0, respectively, in the presence of 5.0 mg C/L HA. The transformation products of TBBPA detected in Fe(VI)-CaSO3 process revealed that TBBPA degradation mainly proceeded via electron abstraction, debromination, and ring-opening pathways and Br− was released. In the presence of TBBPA, Fe(VI)-CaSO3 pre-oxidation decreased the generation of all determined DBPs during chlorination at pH 8.0 but it lessened the generation of some DBPs and slightly increased the formation of the other DBPs at pH 7.0. The toxic risk analysis showed that Fe(VI)-CaSO3 pre-oxidation of TBBPA could reduce the toxic risk of DBPs in both synthetic water and natural water at pH 8.0, indicating that Fe(VI)-CaSO3 process has the potential to be applied in practical water treatment.

Iodinated trihalomethanes formation in iopamidol-contained water during ferrate/chlor(am)ination treatment

Iopamidol is a commonly used iodinated X-ray contrast media in medical field, and its residue in water can react with disinfectants to form highly toxic iodinated disinfection by-products (I-DBPs). This study investigated the degradation of iopamidol and formation of DBPs, especially iodinated trihalomethanes (I-THMs), during ferrate (Fe(VI)) pre-oxidation and subsequent chlor(am)ination under raw water background. It was found that iopamidol degradation efficiency in raw water by Fe(VI) at pH 9 could reach about 80%, which was much higher than that at pH 5 and pH 7 (both about 25%). With Fe(VI) dose increasing, iopamidol removal efficiency increased obviously. During the iopamidol degradation by Fe(VI), IO3− was the dominant product among all the iodine species. After pre-treated by Fe(VI), yields of THM4 and I-THMs can be reduced in subsequent chlor(am)ination. Besides, pH was a crucial factor for Fe(VI) pre-oxidition controlling DBPs. With the pH increasing from 5 to 9, the yield of THM4 kept increasing in subsequent chlorination but showed the highest amount at pH 6 in subsequent chloramination. The yield of I-THMs increased first and then decreased with the increase of pH in both subsequent chlorination and chloramination. I-THM concentrations in chlorinated samples were lower than chloraminated ones under acidic conditions but became higher under neutral and alkaline conditions. The total CTI of THMs during Fe(VI)-chloramination was higher than that during Fe(VI)-chlorination under neutral condition, but sharply decreased under alkaline conditions. In summary, Fe(VI)-chloramination subsequent treatment under alkaline conditions should be an effective method for iopamidol removal and DBP control.

Source identification and characteristics of dissolved organic matter and disinfection by-product formation potential using EEM-PARAFAC in the Manas River, China.

Dissolved organic matter (DOM) is ubiquitous in natural water and reacts with disinfectants to form disinfection by-products (DBPs). The analysis of DOM in raw water is helpful in evaluating the formation potential of DBPs. However, there is relatively little research on the DOM identification of raw water in northern China. In this study, the sources and characteristics of DOM were investigated in the samples collected from the Manas River. Dissolved organic carbon (DOC), UV254, specific ultraviolet absorbance, and fluorescence indices (fluorescence index, humification index, and biological index) were measured to characterize the DOM, and trihalomethanes (THMs) were quantified following formation potential tests with free chlorine. The maximum amount of total trihalomethane formation potential (THMsFP) was 225.57 μg L−1. The DOM of the Manas River consisted of microorganisms and soil resources. The excitation–emission matrix combined with parallel factor analysis (EEM-PARAFAC) identified microbial humus (C1, 54%) and tryptophan-like protein (C2, 46%). PARAFAC components were evaluated as the precursor surrogate parameters of THMsFP. Additionally, the linear THMsFP correlation was stronger with C1 + C2 (r = 0.529, p < 0.01) than with C1 (r = 0.485, p < 0.01). Thus, C1 + C2 is an accurate THMsFP precursor surrogate parameter for the Manas River, and the use of fluorescence spectroscopy may be a robust alternative for predicting DOC removal.

Highly efficient chloramphenicol degradation by UV and UV/H2 O2 processes based on LED light source.

In this study, UV-LED was employed as a novel light source to investigate the degradation of a representative antibiotic compound, chloramphenicol (CAP), in the absence or presence of H2 O2 . The UV-LED irradiation showed a higher capability for degradation of CAP than conventional UV-Hg vapor lamps. Effects of the initial CAP concentration, UV wavelength, and light intensity on the degradation of CAP by UV-LED were evaluated. Introduction of H2 O2 evidently enhanced the degradation efficiency of CAP due to the production of reactive hydroxyl radicals. Results showed that the UV-LED/H2 O2 removed CAP by up to 95% within 60min at pH 5.0, which was twice as that achieved by the UV-LED alone. The degradation products were identified to propose plausible degradation pathways. Moreover, the formation potentials of typical carbonaceous disinfection by-products (C-DBPs) and nitrogenous disinfection by-products (N-DBPs) were assessed for the CAP polluted water treated by the UV-LED alone and UV-LED/H2 O2 processes. Results indicate unintended formation of certain DBPs, thereby highlighting the importance of health risk assessments before practical application. This study opens a new avenue for developing environment-friendly and high-performance UV-LED photocatalytic reactors for abatement of CAP pollution in water. PRACTITIONER POINTS: UV-LED bore higher capability to degrade CAP than low-pressure Hg lamp. The optimal performance to degrade CAP can be achieved at the UV wavelength of 280nm. The degradation efficiency under UV-LED/H2 O2 process was double of that under UV-LED process. TCM, DCAN, and TCNM formation were higher under the existence of UV-LED radiation. The addition of H2 O2 had greater influence on the formation of DCAcAm than the introduction of UV-LED.

Decreased formation of disinfection by-products during electrochemical leachate oxidation and their post-removal by electro-adsorption

Membrane electrochemical reactor (MER) is an effective treatment system to remove recalcitrant compounds in landfill leachate but harmful byproducts can be formed during the treatment. Herein, we have investigated the formation of total halogenated organics and the associated toxicity as a side effect of leachate treatment by the MER. Those byproducts are represented by the term “disinfection byproducts, or DBPs”, because of the similar formation mechanisms. Several DBP groups were detected during the leachate treatment; however, the amount of DBP generated in the MER only accounted for 19.1 ± 4.5% of that in a membrane-less electrooxidation system (control). Likewise, the total toxicity value in the MER effluent was 26.6 × 10−3, only 15.1% of that in the control system. While trihalomethanes dominated mass concentration by 84.1% in the MER, haloacetonitriles contributed to majority of the additive toxicity due to their higher toxicity index. Increasing the initial leachate pH from 9.5 to 13 could increase the DBP concentration by 2.18 times because of less removal of humic acids. A high initial ammonia concentration of 6000 mg L−1 resulted in the increased DBP formation by 146.8%, compared to that with 2500 mg L−1, due to the increased formation of nitrogenous DBPs. A higher current density of 30 mA cm−2 doubled the DBP formation because of a faster reaction rate and a higher solution temperature. The extended treatment time caused trihalomethanes to continue forming DBP and degradation of most DBPs to some extent. With removing 67.5% of DBP mass concentration and 74.4% of the additive toxicity, the GAC-electrode system was shown more effective than GAC adsorption alone in remediating DBP from the MER effluent.

Formation of Disinfection Byproducts from Algal Organic Matter Exposed to Monochloramine: Effects of Monochloramine Dosages, pH, and Bromide Concentrations

The formation of volatile DBPs and haloacetic acids (HAAs) from algal organic matter (AOM) in different chloramination conditions (i.e., different monochloramine (NH2Cl) dosages, pH values, and bromide concentrations) was studied. In chloramination of AOM, HAAs were the major DBP species, followed by trihalomethanes (THMs), haloacetonitriles (HANs), and haloketones (HKs). The levels of THMs, HAAs, HKs, and HANs generated in chloramination were 75%, 69%, 68%, and 122% of those in chlorination, respectively. The concentrations of THMs and HAAs both doubled as the NH2Cl dosage doubled. The proportions of bromodichloromethane and dibromochloromethane in THMs and the proportions of dichloroacetic acid and trichloroacetic acid in HAAs increased with the NH2Cl dosage. Accelerating the pH value enhanced the formation of THMs, HAAs, and HANs, respectively, and favored the formation of brominated THMs. The HAN species distribution was unaffected by the NH2Cl dosage and pH. Increasing bromide levels slightly increased the yield of THMs and slightly decreased the yields of HAAs and HKs. The species shift from the chlorinated to the brominated was more significant for THMs and HANs than for HAAs. The THM-BSF and dichloroacetonitrile-BSF values were lower in chloramination than in chlorination. The high pH value and bromide level significantly accelerated the THM-BSFs. The maximum values of THM-BSFs and dichloroacetonitrile-BSF were 0.6 and 0.5.

Factors affecting the formation of DBPs by chlorine disinfection in water distribution system

Factors affecting the formation of DBPs by chlorine disinfection in water distribution system

Formation potential of emerging disinfection by-products during ozonation and chlorination of sewage effluents

This study investigates the formation potential of emerging DBPs (haloacetonitriles, halonitromethanes and halopropanones) during ozonation and ozonation/hydrogen peroxide treatment and subsequent chlorination of sewage effluent under various experimental conditions. Estimation of possible risk due to DBPs by calculation of cytotoxicity and genotoxicity was attempted.The studied DBPs showed different formation behavior during chlorination, with maximum yields within 0.5–48 h. Maximum cytotoxicity and genotoxicity was observed after 4 h of chlorination with dibromoacetonitrile being the major contributor. Ozonation and O3/H2O2 treatment resulted in increase of trichloronitromethane followed by a decline at higher doses, and reduction of haloacetonitriles. High ozone doses reduced cytotoxicity and genotoxicity of treated effluents. The presence of bromide shifted to bromo-DBPs formation and enhanced both cytotoxicity and genotoxicity. Particulate fraction in effluents significantly contributed to the formation of DBPs and consequently to the their toxicity.

Chloramination of iodide-containing waters: Formation of iodinated disinfection byproducts and toxicity correlation with total organic halides of treated waters

The formation of iodinated disinfection byproducts (I-DBPs) in drinking waters is of a concern due to their higher cyto- and genotoxicity than their chlorinated and brominated analogues. This study investigated the formation of I-DBPs under chloramination conditions using preformed chloramine and associated cyto- and geno-toxicities obtained with Chinese Hamster Ovary (CHO) cell assay. Cyto- and geno-toxicity of the samples were also calculated using DBP toxicity index values and correlated with total organic halide (TOX) formation. In low iodide (I-) (0.32 μM, 40 μg L−1) water, increasing dissolved organic carbon (DOC) concentration of selected waters from 0.1 to 0.25 mg L−1 increased the formation of iodinated trihalomethanes (I-THMs), while further increases from 0.25 to 4 mg L−1 produced an opposite trend. In high iodide water (3.2 μM, 400 μg L−1), increasing DOC from 0.5 to 4 mg L−1 gradually increased the I-THM formation, while a decrease was observed at 5.4 mg L−1 DOC. Iodoform was the most influenced species from the changes in DOC concentration. While increasing the initial iodide concentration from 0 to 5 μM increased the formation of iodoform, it did not make any considerable impact on the formation of other I-THMs. The measured cytotoxicity of samples was significantly correlated with increasing DOC concentration. Unknown TOCl and TOI showed a high correlation with measured cytotoxicity, while calculated total organic chlorine (TOCl) and total organic iodine (TOI) did not correlate. The comparison of measured and calculated cytotoxicity values showed that the calculated values do not always represent the overall cytotoxicity, since the formation of unknown DBPs are not taken into consideration during the toxicity calculations.

Full-scale comparison of UV/H2O2 and UV/Cl2 advanced oxidation: The degradation of micropollutant surrogates and the formation of disinfection byproducts

The photolysis of chlorine by UV light leads to the formation of the hydroxyl radicals (OH) as well as reactive chlorine species (RCS) that can be effective as advanced oxidation processes (AOPs) for water treatment. Much of the research to date has been done at laboratory- or bench-scale. This study reports results from a model that demonstrates that the relative effectiveness of the UV/Cl2 AOP compared to the more traditional UV/H2O2 AOP is a function of optical path length. As such, the relative effectiveness of the two treatment options evaluated at small scale may not reflect the relative performance at full-scale, making results previously obtained at small-scale potentially less scalable. This study therefore compares the performance of UV/Cl2 to UV/H2O2 at a full-scale water treatment plant, using sucralose and caffeine as spiked surrogates for contaminants that are reactive solely to OH radicals, and to both OH and RCS, respectively. pH was varied between 6.5 and 8.0. The results demonstrated that when using a medium pressure UV lamp, UV/Cl2 might lead to approximately twice the production of OH radicals as UV/H2O2 at pH 6.5 when using the same molar oxidant concentration, but adding chlorine to the UV reactor at pH 8.0 had a negligible impact on OH radical concentration in comparison to UV alone. The study also confirmed previous small-scale results that RCS can be a major contributor to UV/Cl2 treatment for compounds such as caffeine that are susceptible to RCS, with UV/Cl2 effective at both pH 6.5 and 8.0 for such compounds. Disinfection byproducts were monitored, with adsorbable organohalide (AOX) formation increasing by approximately 10 μg-Cl/L due to chlorine photolysis, but only at pH 6.5 and not at pH 8.0. This implies that UV/Cl2 might increase AOX mostly due to reaction between OH and organic precursors to make them more reactive with chlorine, and not due to RCS. The formation of specific DBPs of current or emerging regulatory interest was minimal under all conditions, except for chlorate. Chlorate yields were in the order of 6–18% of the photolysed chlorine.

Integrated control of CX3R-type DBP formation by coupling thermally activated persulfate pre-oxidation and chloramination

The alternative disinfectant chloramine can lower the formation of carbonaceous DBPs (C-DBPs) but promote the formation of nitrogenous DBPs (N-DBPs), which are more cytotoxic and genotoxic. In this study, the combination of thermally activated persulfate pre-oxidation and post-chloramination (TA/PS-NH2Cl) was proposed to control the formation and reduce the toxicity of both C-DBPs and N-DBPs. The formation, speciation and toxicity of trihalomethanes, haloacetic acids, haloaldehydes, haloacetonitriles, halonitromethanes and haloacetamides, collectively defined as CX3R-type DBPs, under TA/PS-NH2Cl process were compared with processes of chlorination alone (Cl2), chloramination alone (NH2Cl) and coupled thermally activated persulfate pre-oxidation with post-chlorination (TA/PS-Cl2). Results showed that chloramination could reduce formation of C-DBPs and total organic halogen (TOX) while increase N-DBP formation, and the introduction of TA/PS pretreatment process slightly increased the formation of C-DBPs and TOX but sharply reduced the formation of N-DBPs with higher toxicity as well as brominated CX3R-type DBPs that are more toxic than their chlorinated analogues. By comprehensive toxicity calculation, an outright decline of both cytotoxicity and genotoxicity risk of CX3R-type DBPs was observed during TA/PS-NH2Cl process compared with Cl2, NH2Cl, and TA/PS-Cl2 processes. In summary, TA/PS-NH2Cl process was a potential effective method for integrally controlling the formation of CX3R-type DBPs and their toxicity and is suggested to be used to treat raw waters containing no bromide or low levels of bromide considering bromate caused by TA/PS pre-oxidation. The study may provide a feasible and economical method for DBP control on the background of global warming.

The influence of bromide on the degradation of sulfonamides in UV/free chlorine treatment: Degradation mechanism, DBPs formation and toxicity assessment

The degradation of sulfonamides (SAs) in the presence of bromide during the UV/free chlorine process was investigated in this study. The reactions followed pseudo first-order kinetics. With increasing bromide concentrations of 1, 5, 10–20 µM, the degradation rate was gradually raised. The contribution of different reactive species has been calculated. The degradation products and DBPs formed by SAs were determined. The mechanisms of the degradation of SAs in the presence of bromide included hydroxylation, cleavage of the pyrimidinyl group, and bromine and chlorine electrophilic addition. The concentration of brominated disinfection by-products, including DBCM, TBM and DBAN, increased with increasing bromide dosage and degradation time, while 1, 1, 1-TCP and 1, 1-DCP decreased. In an acute toxicity test, the inhibition rate decreased in the first 5–10 min then increased after 10 min degradation when 10 µM Br− was added to the system. The initial decrease may due to the formation of low toxicity substances after the cleavage of the pyrimidinyl group, while the subsequent increase may be attributable to the increased formation of DBPs.

Formation of DBPs and halogen-specific TOX in the presence of iopamidol and chlorinated oxidants

Iopamidol is a known direct precursor to iodinated and chlorinated DBP formation; however, the influence of iopamidol on both iodo/chloro-DBP formation has yet to be fully investigated. This study investigated the effect of iopamidol on the formation and speciation of halogen-specific total organic halogen (TOX), as well as iodo/chloro-DBPs, in the presence of 3 source waters (SWs) from Northeast Ohio and chlorinated oxidants. Chlorination and chloramination of SWs were carried out at pH 6.5–9.0 and, different iopamidol and dissolved organic carbon (DOC) concentrations. Total organic iodine (TOI) loss was approximately equal (22–35%) regardless of SW. Total organic chlorine (TOCl) increased in all SWs and was substantially higher in the higher SUVA254 SWs. Iopamidol was a direct precursor to chloroform (CHCl3), trichloroacetic acid (TCAA), and dichloroiodomethane (CHCl2I) formation. While CHCl3 and TCAA exhibited different formation trends with varying iopamidol concentrations, CHCl2I increased with increasing iopamidol and DOC concentrations. Low concentrations of iodo-acids were detected without discernible trends. Total trihalomethanes (THMs), total haloacetic acids (HAAs), TOCl, and unknown TOCl (UTOCl) were correlated with fluorescence regional volumes and SUVA254. The yields of all these species showed a strong positive correlation with fulvic, humic, and combined humic and fulvic regions, as well as SUVA254. Iopamidol was then compared to the 3 SWs with respect to DBP yield. Although the SUVA254 of iopamidol was relatively high, it did not produce high yields of THMs and HAAs compared to the 3 SWs. However, chlorination of iopamidol did result in high yields of TOCl and UTOCl.