Treatment of iodine-containing water by the UV/NH2Cl process: Dissolved organic matters transformation, iodinated trihalomethane formation and toxicity variation

UV/NH₂Cl process is becoming increasingly important for water treatment, while its impact on iodine-containing water remains unknown. In this study, the structure transformation of dissolved organic matters (DOMs), generation of iodinated trihalomethanes (I-THMs), and variation of acute toxicity were evaulated during the UV/NH₂Cl treatment of iodine-containing water. The combination of exciation emission matrix-parallel factor analysis and two-dimensional correlation spectroscopy integrated with synchronous fluorescence and infrared absorption spectroscopy showed that fulvic-like fraction of DOM was more susceptible to UV/NH₂Cl process and particularly iodo and polysaccharide groups gave the fastest resopnses. Consequently, UV fluence lower than 60 mJ/cm² promoted the production of I-THMs, while excessive UV exhausted NH₂Cl and reactive iodine species and subsequently reduced I-THM generation. Moreover, DOM concentration and source, NH₂Cl dosage, and I^- concentration had significant impacts on I-THM formation in the UV/NH₂Cl process. Additionally, a positive correlation was found between acute toxicity variation and I-THM formation when treating iodine-containing waters with UV/NH₂Cl. These results together provide a comprehensive understanding on UV/NH₂Cl treatment of iodine-containing water.

Association of Blood Trihalomethane Concentrations with Risk of All-Cause and Cause-Specific Mortality in U.S. Adults: A Prospective Cohort Study

Water chlorination can lead to the formation of disinfection byproducts, including trihalomethanes (THMs). However, few epidemiologic studies have explored associations between THM exposure and mortality. This study included 6720 adults aged ≥40 years from the National Health and Nutrition Examination Survey 1999-2012 who had blood THM concentrations quantified. A higher risk of all-cause mortality was found across increasing quartile concentrations of blood chloroform (TCM) and total THMs (TTHMs; sum of all four THMs) (both p for trend = 0.02). Adults in the highest quartile of TCM and TTHM concentrations had hazard ratios (HRs) of 1.35 (95% confidence intervals: 1.05-1.74) and 1.37 (1.05-1.79), respectively, for all-cause mortality, compared with adults in the lowest quartile. When cause-specific mortality was evaluated, a positive relationship was found between blood bromodichloromethane (BDCM), dibromochloromethane (DBCM), bromoform (TBM), total brominated THMs (Br-THMs; sum of BDCM, DBCM, and TBM), and TTHM concentrations and risk of cancer death and between blood TCM and TTHMs and risk of other cause (noncancer/nonheart disease) mortality. Our findings suggest that higher exposure to Br-THMs was associated with increased cancer mortality risk, whereas TCM was associated with a greater risk of noncancer/nonheart disease mortality.

Derivates variation of phenylalanine as a model disinfection by-product precursor during long term chlorination and chloramination

Dissolved nitrogenous organic matter in water can contain precursors of disinfection by-products (DBPs), especially nitrogenous DBPs (N-DBPs). Amino acids are ubiquitous as dissolved nitrogenous organic matter in source water and can pass through drinking water treatment processes to react with disinfectants in finished water and in the distribution system. Phenylalanine (Phe) was selected as a model amino acid precursor to investigate its derived DBPs and their variations during a chlorination regime that simulated water distribution with residue chlorine. The 7-day DBPs formation potential (DBPsFP) test with chlorine revealed chlorination by-products of phenylalanine including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and halonitromethanes (HNMs), but not trichloronitromethane (TCNM) which was a significant N-DBP detected during the first 48 h of chlorine contact. The formation of most carbonaceous DBPs (C-DBPs) increased with chlorination time; however N-DBPs and non-chlorinated byproducts of phenylacetonitrile and phenylacetaldehyde reached their highest concentration after 2 h of reaction, and then gradually decreased until below detection after 7 days. The chlorination influencing factors indicated that light enhanced the peak yield of DBPs; the pH value showed different influences associated with corresponding DBPs; and the presence of bromide ions (Br^-) generated a variety of bromine-containing DBPs. The DBPsFP test with chloramine reduced C-DBPs generation to about 1/3 of the level observed for chlorine disinfection and caused an increase in dichloroacetonitrile. Surveillance of DBPs during drinking water distribution to consumers should consider the varying contact times with disinfectants to accurately profile the types and concentrations of C-DBPs and N-DBPs present in drinking water.

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.

Reaction of DMS and HOBr as a Sink for Marine DMS and an Inhibitor of Bromoform Formation

Recently, we suggested that hypobromous acid (HOBr) is a sink for the marine volatile organic sulfur compound dimethyl sulfide (DMS). However, HOBr is also known to react with reactive moieties of dissolved organic matter (DOM) such as phenolic compounds to form bromoform (CHBr₃) and other brominated compounds. The reaction between HOBr and DMS may thus compete with the reaction between HOBr and DOM. To study this potential competition, kinetic batch and diffusion-reactor experiments with DMS, HOBr, and DOM were performed. Based on the reaction kinetics, we modeled concentrations of DMS, HOBr, and CHBr₃ during typical algal bloom fluxes of DMS and HOBr (10^-13 to 10^-9 M s^-1). For an intermediate to high HOBr flux (≥10^-11 M s^-1) and a DMS flux ≤10^-11 M s^-1, the model shows that the DMS degradation by HOBr was higher than for photochemical oxidation, biological consumption, and sea-air gas exchange combined. For HOBr fluxes ≤10^-11 M s^-1 and a DMS flux of 10^-11 M s^-1, our model shows that CHBr₃ decreases by 86% compared to a lower DMS flux of 10^-12 M s^-1. Therefore, the reaction between HOBr and DMS likely not only presents a sink for DMS but also may lead to suppressed CHBr₃ formation.

Formation and control of C- and N-DBPs during disinfection of filter backwash and sedimentation sludge water in drinking water treatment

Drinking water treatment plants (DWTPs) produce filter backwash water (FBW) and sedimentation sludge water (SSW) that may be partially recycled to the head of DWTPs. The impacts of key disinfection conditions, water quality parameters (e.g., disinfection times, disinfectant types and doses, and pH values), and bromide concentration on controlling the formation of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and haloacetamides (HAMs) during disinfection of FBW and SSW were investigated. Concentrations of most disinfection byproducts (DBPs) and associated calculated toxicity increased with extended chlorination for both FBW and SSW. During chlorination of both FBW and SSW, elevated chlorine doses significantly increased THM yields per unit dissolved organic carbon (DOC), but decreased HAN and HAM yields, with minimum effect on HAA yields. Chloramine disinfection effectively inhibited C-DBP formation but promoted N-DBPs yields, which increased with chloramine dose. Calculated toxicities after chloramination increased with chloramine dose, which was opposite to the trend found after free chlorine addition. An examination of pH effects demonstrated that C-DBPs were more readily generated at alkaline pH (pH=8), while acidic conditions (pH=6) favored N-DBP formation. Total DBP concentrations increased at higher pH levels, but calculated DBP toxicity deceased due to lower HAN and HAM concentrations. Addition of bromide markedly increased bromo-THM and bromo-HAN formation, which are more cytotoxic than chlorinated analogues, but had little impact on the formation of HAAs and HAMs. Bromide incorporation factors (BIFs) for THMs and HANs from both water samples all significantly increased as bromide concentrations increased. Overall, high bromide concentrations increased the calculated toxicity values in FBW and SSW after chlorination. Therefore, while currently challenging, technologies capable of removing bromide should be explored as part of a strategy towards controlling cumulative toxicity burden (i.e., hazard) while simultaneously lowering individual DBP concentrations (i.e., exposure) to manage DBP risks in drinking water.

Reduction of bromate by zero valent iron (ZVI) enhances formation of brominated disinfection by-products during chlorination

Bromate (BrO₃^-) is a predominant undesired toxic disinfection by-product (DBP) during ozonation of bromide-containing waters. The reduction of BrO₃^- by zero valent iron (ZVI) and its effect on formation of organic halogenated DBPs during chlorination were investigated in this study. The presence of ZVI could reduce BrO₃^- to bromide (Br^-), and Br^- formed could be transformed to free bromine (HOBr/OBr^-) during chlorination, further leading to organic brominated (Br-) DBPs formation. Formation of DBPs during chlorination, including trihalomethanes (THMs) and haloacetonitriles (HANs) was detected under different conditions. The results showed that when ZVI dosage increased from 0 to 1 g L^-1, the formation of Br-DBPs (e.g., TBM and DBCM) was significantly improved, while the formation of Cl-DBPs (e.g., TCM, TCAN and DCAN) reduced. Higher ZVI dosage exhibited inhibitory effect on Br-DBPs formation due to the competition between ZVI and free chlorine (HOCl/OCl^-). The bromine substitution factor (BSF) of THMs significantly decreased from 0.61 ± 0.06 to 0.22 ± 0.02, as the pH was raised from 5.0 to 9.0. Besides, the increase of initial BrO₃^- concentration significantly improved the formation of Br-DBPs and decreased the formation of Cl-DBPs, leading to an obvious rise on the BSF of THMs. As the initial concentration of HOCl increased, all THMs and HANs gradually increased. Moreover, the analysis based on the cytotoxicity index (CTI) of the determined DBPs showed that reduction of BrO₃^- by ZVI during chlorination had certain risks in real water sources, which should be paid attention to in the application.

Halogen Radicals Contribute to the Halogenation and Degradation of Chemical Additives Used in Hydraulic Fracturing

In hydraulic fracturing fluids, the oxidant persulfate is used to generate sulfate radical to break down polymer-based gels. However, sulfate radical may be scavenged by high concentrations of halides in hydraulic fracturing fluids, producing halogen radicals (e.g., Cl^•, Cl₂^•-, Br^•, Br₂^•-, and BrCl^•-). In this study, we investigated how halogen radicals alter the mechanisms and kinetics of the degradation of organic chemicals in hydraulic fracturing fluids. Using a radical scavenger (i.e., isopropanol), we determined that halogenated products of additives such as cinnamaldehyde (i.e., α-chlorocinnamaldehyde and α-bromocinnamaldehyde) and citrate (i.e., trihalomethanes) were generated via a pathway involving halogen radicals. We next investigated the impact of halogen radicals on cinnamaldehyde degradation rates. The conversion of sulfate radicals to halogen radicals may result in selective degradation of organic compounds. Surprisingly, we found that the addition of halides to convert sulfate radicals to halogen radicals did not result in selective degradation of cinnamaldehyde over other compounds (i.e., benzoate and guar), which may challenge the application of radical selectivity experiments to more complex molecules. Overall, we find that halogen radicals, known to react in advanced oxidative treatment and sunlight photochemistry, also contribute to the unintended degradation and halogenation of additives in hydraulic fracturing fluids.

Evaluation of Histidine Reactivity and Byproduct Formation during Peptide Chlorination

The covalent modifications resulting from chlorine reactions with peptide-bound amino acids contribute to pathogen inactivation and disinfection byproduct (DBP) formation. Previous research suggested that histidine is the third most reactive of the seven chlorine-reactive amino acids, leading to the formation of 2-chlorohistidine, 2-oxohistidine, or low-molecular-weight byproducts such as trihalomethanes. This study demonstrates that histidine is less reactive toward formation of chlorine transformation products (transformation time scale of hours to days) than five of the seven chlorine-reactive amino acids, including tyrosine (transformation time scale of minutes). Chlorine targeted tyrosine in preference to histidine within peptides, indicating that chlorine reactions with tyrosine and other more reactive amino acids could contribute more to the structural modifications to proteins over the short time scales relevant to pathogen inactivation. Over the longer time scales relevant to disinfection byproduct formation in treatment plants or distribution systems, this study identified β-cyanoalanine as the dominant transformation product of chlorine reactions with peptide-bound histidine, with molar yields of ∼50% after 1 day. While a chlorinated histidine intermediate was observed at lower yields (maximum ∼5%), the cumulative concentration of the conventional low-molecular-weight DBPs (e.g., trihalomethanes) was ≤7%. These findings support the need to identify the high-yield initial transformation products of chlorine reactions with important precursor structures to facilitate the identification of unknown DBPs.

Simultaneous determination of stable chlorine and bromine isotopic ratios for bromochlorinated trihalomethanes using GC-qMS

Bromochlorinated compounds are organic contaminants originating from different natural and anthropic sources and increasingly found in different environmental compartments. This work presents an online approach for compound specific stable isotope analysis of chlorine and bromine isotope ratios for bromochlorinated trihalomethanes using gas chromatography coupled to quadrupole mass spectrometry (GC-qMS). An evaluation scheme was developed to simultaneously determine stable chlorine and bromine isotope ratios based on the mass spectral data of two target compounds: dibromochloromethane and dichlorobromomethane. The analytical technique was optimized by assessing the impact of different instrumental parameters, including dwell time, split ratios, and ionization energy. Successively, static headspace samples containing the two target compounds at aqueous concentrations ranging from 0.1 mg/L to 5 mg/L were analyzed in order to test the precision and reproducibility of the proposed approach. The results showed a good precision under the optimized instrumental conditions, with relative standard deviations ranging between 0.05% and 0.5% for chlorine and bromine isotope analysis. Finally, the method was tested in a source identification problem in which the simultaneous determination of chlorine and bromine stable isotope ratios allowed the clear distinction of dibromochloromethane from three different manufacturers.

Effects of feed solution characteristics and membrane fouling on the removal of THMs by UF/NF/RO membranes

Ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) are widely used in drinking water treatment and wastewater recycling. However, limited information was available regarding their performance in removing trihalomethanes (THMs). The present study investigated the effect of feed solution characteristics and membrane fouling on THM removal by UF/NF/RO membranes. The results indicated that THMs were poorly removed by UF membrane, and the removal was dominated by hydrophobic adsorption. In contrast, high removal of THMs was observed for NF/RO membranes, which was contributed by both size exclusion and hydrophobic adsorption. By comparing the adsorption of THMs on NF/RO membranes at different feed concentration, it was found that the role of hydrophobic adsorption was more important at lower feed concentration. The removal of THMs by UF/NF/RO membranes increased with increasing feed concentration, which can be ascribed to the enhanced diffusion at higher concentration gradient. With increasing ionic strength, THM removal was decreased significantly for UF membrane, but the removal by NF/RO membranes remained largely unchanged. By comparing THM removal by clean and fouled membranes, the effect of membrane fouling was examined. The removal of most THMs (except trichloromethane) decreased after fouling for UF membrane, whereas decreased removal was only observed for iodinated THMs for fouled NF/RO membranes.

Toxicological assessment of seven unregulated drinking water Disinfection By-products (DBPs) using the zebrafish embryo bioassay

Disinfection By-products (DBPs) are formed during the chemical treatment of water for human consumption, by the reaction of raw water with chemical agents used in the different steps of the process. Disinfection is one of the most important steps, inactivating pathogens and preventing their regrowth during water distribution. However, it is also involved in DBPs formation due to the use of disinfectant agents, such as chlorine, which reacts with dissolved precursors, such as pharmaceuticals, toxins, pesticides, among others. Given their widespread occurrence, potential human health and (eco) toxicological impacts are of particular interest due to their potential carcinogenicity and various non-carcinogenic effects, such as endocrine disruption. In this study, the developmental toxicity of chemically- different unregulated DBPs was evaluated using zebrafish embryo bioassay. Embryos were exposed to different concentrations of the target DBPs and multiple endpoints, including, mortality, morphological abnormalities and locomotor behavior were assessed at specific developmental stages (24, 48, 72 and 96 hpf). The different families of DBPs tested included nitrosamines, aldehydes, alcohols and ketones. The results show that the effects were compound dependent, with EC10 values varying between 0.04 mg/L (2-ethyl-1-hexanal) to 9.2 mg/L (hexachloroacetone). Globally, several of the tested unregulated DBPs displayed higher toxicity when compared with the available data for some already regulated, such as trihalomethanes (THMs), which highlights the importance of screening the toxicity of still untested and poorly characterized DBPs.

Removal of CX3R-type disinfection by-product precursors from rainwater with conventional drinking water treatment processes

In addition to surface water and groundwater, rainwater is used as an important drinking water source in many parts of the world, especially in areas with serious water pollution or insufficient water resources. Conventional drinking water treatment technologies can remove dissolved organic matter and therefore reduce the formation of disinfection by-products (DBPs) during subsequent disinfection using surface water or groundwater as drinking water sources. However, little information has been known about the effect of conventional water treatment processes on DBP formation when rainwater is used as drinking water source. This study evaluated CX₃R-type DBP precursors removal from rainwater by conventional drinking water treatments and the corresponding decrease of CX₃R-type DBP (trihalomethanes (THMs), haloaldehydes (HALs), haloacetonitriles (HANs) and haloacetamides (HAMs)) formation and toxicity during the subsequent chlor(am)ination. The result showed that both sand filtration (SF) and activated carbon filtration (GAC) were able to remove DBP precursors and GAC outperformed SF, but no DBP precursors removal was observed during coagulation-sedimentation treatment. Among all treatments, SF + GAC was the most effective for DBP precursors removal, with removal efficiencies of 64.2% DOC, 98% DON and 76.6% UV₂₅₄. Correspondingly, both SF and GAC decreased the formation of THMs, HALs, HANs and HAMs, and GAC performed better than SF. The combination of SF and GAC, especially SF + GAC, greatly decreased DBP formation, with average reduction of 79.2% and 85% during chlorination and chloramination respectively. After different treatments, the comprehensive toxicity risk of CX₃R-type DBPs was all reduced, among which GAC + SF exhibited superior performance. Generally, the main contribution of integrated toxicity was HANs during chlor(am)ination. The formation potential of THMs, HALs, HANs and HAMs and the corresponding integrated toxicity were greater during chlorination than that during chloramination. Therefore, the combination of GAC and chloramination was promising in mitigating the comprehensive toxicity risk of THMs, HALs, HANs and HAMs for rainwater.

Removal of trihalomethanes and haloacetamides from drinking water during tea brewing: Removal mechanism and kinetic analysis

Disinfection by-products (DBPs) are associated with various adverse health effects. Diversiform advanced treatment processes have been applied for the control of DBPs, but DBPs can still be frequently detected in tap water. Tea-leaves can be made into popular beverage and is itself a porous bio-adsorbent. By simulating tea brewing process, this study evaluated the removal of DBPs from drinking water during the tea brewing process. Removal of four trihalomethanes (THMs) and four haloacetamides (HAMs) by different fermentation degree tea-leaves was investigated. Little DBPs were removed by unfermented and semi-fermented tea-leaves (i.e., Meitan turquoise bud and Dahongpao tea) with less than 5% removal of HAMs, whereas 40% HAMs can be removed by fermented tea (i.e., Jinjunmei tea and Shuixian tea). Tea soup is neutral and slightly acidic, so little DBP hydrolysis was observed under typical tea-leaf brewing process. DBPs were mainly removed by volatilization and adsorption during tea brewing. Removal difference caused by DBP volatilization is very small. The DBP removal difference of four kinds of tea-leaves may be caused by fermentation degree. The surface of unfermented Meitan turquoise bud had a smooth and regular morphology, whereas a rough, irregular, hollow and spongy surface of fermented tea (i.e., Jinjunmei and Shuixian tea) was observed. Generally, the higher the degree of tea fermentation, the more adsorption sites, and the more removal of DBPs. Finally, the model, which takes the DBP initial concentration, tea-leaf dose and brewing time into account, was established under the experimental conditions to predict the variation of DBP concentration during tea brewing, and suggestions for DBP removal were provided to reduce DBP exposure risk. The integrated toxic risk during tea brewing was also investigated, and about 30% integrated cytotoxicity and 26% genotoxicity was reduced during Jinjunmei and Shuixian tea-leaf brewing.

Effective enzyme activity: A proposed monitoring methodology for biofiltration systems with or without ozone

"Effective Enzyme Activity", or simply "Effective Activity", is proposed as a biofiltration monitoring tool which combines enzyme activity with empty bed contact time (EBCT) to quantify biodegradation potential. The primary objective of this study was to evaluate the applicability of the Effective Activity concept for predicting water quality in biofiltration systems. This pilot-scale study evaluated eight different biofilter configurations in order to quantify impacts associated with filter media (anthracite/sand or granular activated carbon), pre-treatment (settled water with or without ozonation) and operating conditions (15- and 30-min EBCT, and backwash with or without chlorine). Microbial characterization included biomass concentration, as measured by adenosine triphosphate (ATP), in addition to esterase and phosphatase activity. Water quality parameters included dissolved organic carbon (DOC), trihalomethane (THM) formation potential (FP), haloacetic acid (HAA) FP, haloacetonitrile (HAN) FP, iodinated DBP FP (THMs and HAAs) and inorganic nutrients (phosphorus and nitrogen). Results confirmed the benefits to treated water quality associated with the application of an ozone residual of 0.5 mg/L, utilization of GAC filter media, eliminating chlorinated backwash, and extending EBCT. This study demonstrated a good relationship between effective esterase activity and reductions in DOC and THM FP, including those systems which incorporate pre-ozonation. As such, this study showed that Effective Activity may be appropriate for relating biomass characterization to treated water quality and highlights the importance of quantifying biomass activity in addition to quantity.

Non-volatile disinfection byproducts are far more toxic to mammalian cells than volatile byproducts

Water is often chlorinated to protect public health, but chlorination causes harmful disinfection byproducts to form. Currently available in vitro assays generally determine non-volatile disinfection byproduct (NVDBP) toxicities because of the limitation of pretreatments used, but chemical analyses and regulations are focused on volatile disinfection byproducts (VDBPs) such as trihalomethanes. The gap of VDBP toxicities have been of concern for some time. In this study, we extracted VDBPs from two chlorinated effluent organic matters and one chlorinated natural organic matter, using a helium aeration-liquid nitrogen condensation system, and systematically assessed the VDBP and NVDBP toxicities to mammalian cells. VDBPs accounted for 10%-20% of the total organic halogen concentrations in three chlorinated water samples. VDBPs were much less cytotoxic, caused fewer DNA double-strand breaks, induced less reactive oxygen species and DNA/RNA oxidative damage marker of 8-hydroxyl(deoxy)guanosine in cells than did NVDBPs. Moreover, by collecting the VDBPs, toxicity measurement of the full range of DBPs was achieved. Cytotoxicity, reactive oxygen species and 8-hydroxyl(deoxy)guanosine levels were significantly higher for cells exposed to the mixture of VDBPs and NVDBPs than only NVDBPs, but not by large percentages (20%-30% for cytotoxicity), suggesting NVDBPs mainly contributed to the toxicity of chlorinated water. Our study suggested that future research should focus more on NVDBP toxicity and identifying toxicity drivers from NVDBPs.

Impacts of permanganate/bisulfite pre-oxidation on DBP formation during the post chlorine disinfection of ciprofloxacin-contaminated waters

Bisulfite-activated permanganate (PM/BS) oxidation process can oxidize ciprofloxacin in complex water matrices rapidly. However, effects of PM/BS pre-oxidation on the formation of disinfection byproducts (DBPs) during post-chlorination of ciprofloxacin-contaminated waters need to be addressed. This study investigated the formation of trihalomethanes (THMs), haloacetonitriles (HANs), haloketones and trichloronitromethane during chlorination of ciprofloxacin-contaminated humic acid (HA), bovine serum albumin (BSA) and alginate solutions, and revealed the effects of PM/BS pre-oxidation on ciprofloxacin degradation and DBP formation during post-chlorination, considering the presence of Br^-. Only THMs and HANs were quantifiable. THMs were the most abundant. Ciprofloxacin-contaminated HA exhibited the highest formation potential of DBPs and integrated toxic risk value (ITRV). In the absence of Br^-, PM/BS pre-oxidation reduced or hardly affected the toxicity risks derived from DBPs formed from the post-chlorination. However, the presence of Br^- greatly reduced the degradation of ciprofloxacin (30-50%) in various waters. In the ciprofloxacin-contaminated waters containing Br^-, the total ITRVs of DBPs formed from post-chlorination increased by 60%-800% with PM/BS pre-oxidation, attributing to the enhanced formation of DBPs especially bromochloroacetonitrile and dibromoacetonitrile. Overall, PM/BS is a potential pre-oxidation technology for the treatment of ciprofloxacin-contaminated waters without bromide.

Two years of post-wildfire impacts on dissolved organic matter, nitrogen, and precursors of disinfection by-products in California stream waters

We investigated the effects of two California wildfires (Rocky and Wragg Fires, 2015) compared to an unburned reference watershed on water quality, dissolved organic matter (DOM), and precursors of disinfection by-products (DBPs) for two years' post-fire. The two burned watersheds both experienced wildfires but differed in the proportion of burned watershed areas. Burned watersheds showed rapid water quality degradation from elevated levels of turbidity, color, and suspended solids, with greater degradation in the more extensively burned watershed. During the first year's initial flushes, concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium (NH₄⁺/NH₃), and specific ultraviolet absorbance (SUVA₂₅₄) were significantly higher (67 ± 40%, 418 ± 125%, 192 ± 120%, and 31 ± 17%, respectively) in the more extensively burned watershed compared to the reference watershed. These elevated values gradually declined and finally returned to levels like the reference watershed in the second year. Nitrate concentrations were near detection limits (0.01 mg-N/L) in the first year but showed a large increase in fire-impacted streams during the second rainy season, possibly due to delayed nitrification. Changes in DOM composition, especially during the initial storm events, indicated that fires can attenuate humic-like and soluble microbial by-product-like (SMP) DOM while increasing the proportion of fulvic-like, tryptophan-like, and tyrosine-like compounds. Elevated bromide (Br^-) concentrations (up to 8.7 μM]) caused a shift in speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) to brominated species for extended periods (up to 2 years). Wildfire also resulted in elevated concentrations of N-nitrosodimethylamine (NDMA) precursors. Such changes in THM, HAA, and NDMA precursors following wildfires pose a potential treatability challenge for drinking water treatment, but the effects are relatively short-term (≤1 year).

Dynamics of dissolved organic matter and disinfection byproduct precursors along a low elevation gradient in woody wetlands - an implication of hydrologic impacts of climate change on source water quality

Foliar litter is an important terrestrial source of dissolved organic matter (DOM) and disinfection byproducts (DBPs) in the source water supply. Climate changes could alter precipitation patterns and hydroperiods in woody wetlands, resulting in a hydrologic shift along the low elevation gradient and change the productions of DOC and DBP precursors and their exports to source water. Here, we conducted an 80-week field decomposition study using fresh-fallen leaves along an elevation gradient, representing well-drained, relatively moist, and inundated environments, in Congaree National Park, South Carolina. The dissolved organic carbon (DOC) yield and formation potential (FP) of trihalomethanes (THMs; a dominant category of studied DBPs) were 48.9-79.7 mg-DOC/g-litter and 2.23-6.57 mg/g-litter in the freshly fallen leaf litter, respectively. The level of leachable DOM and its DBP FP decreased with time, and during the first 16 weeks of decomposition, the decomposing litter served as an important source of leachable DOM and DBP precursors. Week 28 was a turning point for DOM optical properties, with fewer tyrosine/tryptophan/soluble microbial byproduct-like compounds and more aromatic, humified, and fulvic/humic acid-like compounds. Litterfall primarily occurred from September to January, while less precipitation occurred from October to January, indicating that large amounts of DOC and DBP precursors could be leached from litterfall in February. In the first 16 weeks of field exposure study, we observed higher residual mass and lower water-extractable DOC and DTN in more inundated environments, demonstrating that the shifts of DOM composition and DBP precursors if climate reduces rainfall in the southeastern US.

Assessment of exposure of children swimmers to trihalomethanes in an indoor swimming pool

This study aimed to understand the exposure levels of trihalomethanes (THMs) in an indoor swimming pool and calculate the risks of exposure to THMs, based on the presence of each THM species, of children swimmers aged 6-17, in Beijing, China. We obtained exposure factors for the children through questionnaires and measured THM concentrations through laboratory tests, and we combined the results with an exposure model to calculate the risks, with consideration of different exposure routes (oral ingestion, inhalation and dermal absorption). In terms of exposure factors for the swimmers aged 6-17, the average body weight, exposure duration, exposure frequency, swimming time, shower time, changing time, warm-up exercise and rest time, skin surface area and ingestion rate of pool water were 40.46 kg, 2.70 years, 96 events/year, 64.03 min/event, 17.04 min/event, 15.31 min/event, 12.71 min/event, 1.37 m² and 48.93 ml/event, respectively. The THM concentrations in swimming pool water, shower water, swimming pool air and locker room air were 67.17 μg/L, 12.64 μg/L, 358.66 μg/m³ and 40.98 μg/m³, respectively. The average cancer risk of THMs was 5.44 × 10^-6, which is an unacceptable risk according to the United State Environmental Protection Agency (USEPA) Guidelines. The average hazard index was 0.007, i.e., less than 1, indicating that the noncancer risk was acceptable. Chloroform (TCM) was the main substance in four species of THMs and inhalation exposure was the main exposure pathway. The risk of cancer and noncancer from inhalation exposure to THMs accounts for 97-99% of the total risk. As a result, the disease control authorities and administrative department should pay attention to the health and safety of swimming facilities and, at the same time, establish standards for THMs in the air through further research.

Characterization of organic matter by HRMS in surface waters: Effects of chlorination on molecular fingerprints and correlation with DBP formation potential

In order to understand and minimize the formation of halogenated disinfection by-products (DBPs), it is important to investigate how dissolved organic matter (DOM) contributes to their generation. In the present study, we analysed the DOM profile of water samples from the Barcelona catchment area by high resolution mass spectrometry (HRMS) and we studied the changes after chlorination. Chlorination produced significant changes in the DOM, decreased the average m/z and Kendrick mass defect (KMD) of their spectra and decreased the number and abundance of lignin-like features. The Van Krevelen (VK) fingerprint exhibited several noticeable changes, including the appearance of highly oxidized peaks in the tannin-like region (average O/C, 0.78 ± 0.08), the appearance of features with low H/C and the disappearance of more than half of the lipids-like features. Up to 657 halogenated peaks were generated during sample chlorination, most of which in the condensed hydrocarbons-like and the lignin-like region of the VK diagram. Around 200 features were found to be strongly correlated (ρ ≥ 0.795) to the formation potential of trihalomethanes (THMs) and 5 were correlated with the formation potential of haloacetonitrile (HANs). They all were plotted in the lignin fraction of the VK diagram, but both groups of features exhibited different nitrogen content: those features related to HANs FP had at least one nitrogen atoms in their structures, whilst those related to THMs did not.

Characteristics of microplastic polymer-derived dissolved organic matter and its potential as a disinfection byproduct precursor

Although there are numerous studies concerning the occurrence of microplastics (MP) in the environment and its impact on the ecosystem, dissolved organic matter (DOM) leached from MP (MP-DOM) has received little attention, and its characteristics have been rarely examined. It is presumed that the DOM leaching from plastics could be accelerated when plastics lost their protective additives during their transport and weathering processes in aquatic systems. In this study, two additive-free MPs (or micro-sized plastic polymers) were leached in artificial freshwater under UV irradiation and dark conditions. The leached DOM was characterized by typical analyses for naturally occurring DOM (N-DOM) such as dissolved organic carbon (DOC), size exclusion chromatography (SEC), and Fourier-transform infrared spectroscopy (FTIR). The potential to generate trihalomethanes (THMs), a well-known environmental impact of N-DOM, was also explored for the DOM with plastic origins for the first time. The leaching results demonstrated that UV irradiation promoted the leaching of DOM from the plastic polymers with an amount corresponding to ∼3% of the total mass of the polymers. The leached amounts were much greater than those previously reported using commercial plastics which presumably contained protective additives. The SEC results revealed that, different from typical aquatic N-DOM, MP-DOM is mostly composed of low molecular weight fractions <350 Da. For the two polymer types (polyethylene and polypropylene), the MP-DOM exhibited a high potential to form THMs upon chlorination, which was comparable to those of typical aquatic N-DOM. This study highlighted an overlooked contribution of UV irradiation to the DOM leaching from additive-free plastics and the potential risk of MP-DOM to produce toxic disinfection byproducts (DBPs) upon chlorination.

Influence of granular activated carbon media properties on natural organic matter and disinfection by-product precursor removal from drinking water

Operational and financial constraints challenge effective removal of natural organic matter (NOM), and specifically disinfection by-product (DBP) precursors, at remote and/or small sites. Granular activated carbon (GAC) is a widely used treatment option for such locations, due to its relatively low maintenance and process operational simplicity. However, its efficacy is highly dependent on the media capacity for the organic matter, which in turn depends on the media characteristics. The influence of GAC media properties on NOM/DBP precursor removal has been studied using a range of established and emerging media using both batch adsorption tests and rapid small-scale column tests. DBP formation propensity (DBPFP) was measured with reference to trihalomethanes (THMs) and haloacetic acids (HAAs). All GAC media showed no selectivity for specific removal of precursors of regulated DBPs; DBP formation was a simple function of residual dissolved organic carbon (DOC) levels. UV₂₅₄ was found to be a good surrogate measurement of DBPFP for an untreated water source having a high DOC. Due to the much-reduced concentration of DBP precursors, the correlation was significantly poorer for the coagulation/flocculation-pretreateed water source. Breakthrough curves generated from the microcolumn trials revealed DOC removal and consequent DBP reduction to correlate reasonably well with the prevalence pores in the 5-10 nm range. A 3-6 fold increase in capacity was recorded for a 0.005-0.045 cm³/g change in 5-10 nm-sized pore volume density. No corresponding correlation was evident with other media pore size ranges.

Removal of disinfection by-products and their precursors during drinking water treatment processes

In this study, we investigated the control efficiency of a wide variety of disinfection by-products (DBPs) (including trihalomethanes [THMs], haloacetic acids [HAAs], haloacetonitiles [HANs], haloketones [HKs], haloaldehydes [Has], and trihalonitromethanes [THNMs]) with different drinking water treatment processes including pre-ozonation, coagulation-sedimentation, sand filtration, and ozone combined with biological activated carbon (O₃ -BAC) advanced treatment processes. The assessment of the treatment efficiency regarding the removal of organic matter was measured by the excitation emission matrix (EEM) spectra. There was a superior efficiency in reducing the formation of DBPs and their precursors by different drinking water treatment processes. Though some DBPs such as THMs could be promoted by ozonation, these by-products from ozonation could be degraded by the following BAC filtration process. In addition, the organic matter from the aromaticity, fulvic acid-like, protein, and soluble microbial by-products-like regions could be further degraded by the O₃ -BAC treatment. PRACTITIONER POINTS: A wide variety of DBPs in different drinking water treatment processes was investigated. The treatment efficiency regarding the removal of organic matter was measured. Some DBPs such as THMs and HAAs could be increased by ozonation. The removal percentage of nitrogen precursors and organic carbon would be increased by BAC filtration.

Organic Amines Enhance the Formation of Iodinated Trihalomethanes during Chlorination of Iodide-Containing Waters

The effects of organic amines (OAs) including glycine (Gly), sarcosine (Sar), and triethanolamine (Tea), representing primary, secondary, and tertiary amines, respectively, on iodinated trihalomethanes (I-THMs) formation during chlorination of iodide (I^-)-containing waters were investigated. The total concentration of I-THMs formed in the co-presence of an OA and natural organic matter (NOM) was more than 3 times the sum of those formed in the presence of an OA alone and NOM alone, as OAs competed for free chlorine (FC) to form organic chloramines. Taking Gly as an example, the transformation of I^- was determined. In the absence of NOM, the yields of iodate (IO₃^-) were 89%, 60%, and nearly 0 at [Gly]_o/[FC]_o = 0:1, 3:4, and 1:1, but 0, 2%, and 43% for hypoiodous acid (HOI), respectively. In the presence of NOM, as [Gly]_o/[FC]_o increased from 0:1 to 1:1, the yield of IO₃^- decreased from 66% to 0, while that of I-THMs increased from 2.9% to 16.1%. The competition of FC by OAs inhibited the oxidation of HOI to IO₃^-, and the formed organic chloramines can oxidize I^- to HOI, thus promoting I-DBPs formation. Finally, the enhanced I-THMs formation was verified in real waters.

GAC to BAC: Does it make chloraminated drinking water safer?

Biological activated carbon (BAC) is widely used as a polishing step at full-scale drinking water plants to remove taste and odor compounds and assimilable organic carbon. BAC, especially with pre-ozonation, has been previously studied to control regulated disinfection by-products (DBPs) and DBP precursors. However, most previous studies only include regulated or a limited number of unregulated DBPs. This study explored two full-scale drinking water plants that use pre-chloramination followed by BAC and chloramine as the final disinfectant. While chloramine generally produces lower concentrations of regulated DBPs, it may form increased levels of unregulated nitrogenous and iodinated DBPs. We evaluated 71 DBPs from ten DBP classes including haloacetonitriles, haloacetamides, halonitromethanes, haloacetaldehydes, haloketones, iodinated acetic acids, iodinated trihalomethanes, nitrosamines, trihalomethanes, and haloacetic acids, along with speciated total organic halogen (total organic chlorine, bromine and iodine) across six different BAC filters of increasing age. Most preformed DBPs were well removed by BAC with different ages (i.e., operation times). However, some preformed DBPs were poorly removed or increased following treatment with BAC, including chloroacetaldehyde, dichloronitromethane, bromodichloronitromethane, N-nitrosodimethylamine, dibromochloromethane, tribromomethane, dibromochloroacetic acid, and tribromoacetic acid. Some compounds, including dibromoacetaldehyde, bromochloroacetamide, and dibromoacetamide, were formed only after treatment with BAC. Total organic halogen removal was variable in both plants and increases in TOCl or TOI were observable on one occasion at each plant. While calculated genotoxicity decreased in all filters, decreases in overall DBP formation did not correlate with decreases in calculated cytotoxicity. In three of the six filters, calculated toxicity increased by 4-27%. These results highlight that DBP concentration alone may not always provide an adequate basis for risk assessment.

Analysis of Cumulative Cancer Risk Associated with Disinfection Byproducts in United States Drinking Water

Hundreds of different disinfection byproducts form in drinking water following necessary treatment with chlorine and other disinfectants, and many of those byproducts can damage DNA and increase the risk of cancer. This study offers the first side-by-side comparison of cancer risk assessments based on toxicological and epidemiological studies of disinfection byproducts using a comprehensive contaminant occurrence dataset for haloacetic acids and trihalomethanes, two groups of disinfection byproducts that are regulated in drinking water. We also provide the first analysis of a new occurrence dataset for unregulated haloacetic acids that became available from the latest, fourth round of the U.S. EPA-mandated unregulated contaminant monitoring program (UCMR4). A toxicological assessment indicated that haloacetic acids, and in particular brominated haloacetic acids, are more carcinogenic and are associated with a greater number of attributable cancer cases than trihalomethanes. Based on the toxicological analysis, cumulative lifetime cancer risk due to exposure to trihalomethanes and haloacetic acids for community water systems monitored under UCMR4, estimated with standard default parameters for body weight and water intake, corresponds to 7.0 × 10-5 (3.5 × 10-5-1.3 × 10-4). The same analysis conducted with age sensitivity factors to account for elevated risk in infants and children yielded a cumulative risk estimate of 2.9 × 10-4 (1.7 × 10-4-6.2 × 10-4). Epidemiological data suggest that lifetime cancer risk from disinfection byproducts for the U.S. population served by community water systems is approximately 3.0 × 10-3 (2.1 × 10-4-5.7 × 10-3), or a lifetime cancer risk of three cases per thousand people. Overall, this analysis highlights the value of using human data in health risk assessments to the greatest extent possible.

Low toxicological impact of wastewaters on drinking water sources

Surface waters may contain varying levels of wastewater effluent associated with de facto reuse, which may influence their toxicological properties both prior to and following treatment. This study examined the genotoxic response of three surface waters containing a range of wastewater effluent (5%, 10%, and 25% by volume). The SOS Chromotest™ was used to assay the genotoxicity of both chlorinated and unchlorinated mixtures. Chlorinated mixtures were also analyzed for trihalomethanes (THMs), haloacetonitriles (HANs), and halonitromethanes (HNMs); their concentrations were used to calculate a relative toxicity index for each sample, based on published potencies in the comet assay and subsequently referred to as predicted genotoxicity. Wastewater effluents were observed to be reactive in the genotoxicity assay, whereas raw and chlorinated surface waters were not. Upon chlorination, surface waters containing 5% or 10% wastewater did not elicit a response and only modest effects were observed for higher wastewater ratios (25%). The measured SOS responses correlated well with predicted genotoxicity (R = 0.92) and THM concentrations (R = 0.92). This is important since THMs themselves are non-reactive in either the SOS or comet genotoxic assays, but their formation may serve as surrogates for non-regulated DBPs which drive toxic effects.

Characterization of dissolved organic matter derived from atmospheric dry deposition and its DBP formation

Disinfection by-products (DBPs) precursors can be regarded mainly from the drinking water sources and the water treatment processes. A recent study showed that dissolved organic matter (DOM) in atmosphere is an important precursor source of DBPs through atmospheric wet deposition. However, little information is available on the characteristics of DOM derived from dry deposition particulate matter (PM) and the impact of dry deposition on CX₃R-type DBP formation. This study determined whether dry deposition directly contributed the production of DBPs during chlor (am)ination and investigated the mechanism behind the contribution based on the combination of the resin and membrane for fractionating DOM fractions. The results showed that the hydrophilic fraction (HPI) contributed the most DOM and low molecular weight DOM (<10 kDa) was the main component of HPI. In addition, aromatic proteins and soluble microbial products-like compounds were the dominant fluorescent species in DOM derived from PM, and <10 kDa transphilic was the most abundant. The concentrations of C-DBPs and N-DBPs in disinfected PM solution were trihalomethanes (THMs) > haloacetic acids (HAAs) > haloaldehydes and haloacetamides > haloacetonitriles > halonitromethanes for both chlorination and chloramination. The main contributors of calculated toxicity are transphilic and hydrophobic in chlorination and chloramination respectively. Dry deposition PM was deduced to contribute DOM and DBP formation after chlorination in surface water, especially THMs and HAAs. These results presented herein provide key information for controlling DBPs from the perspectives of atmospheric dry deposition, especially in the case of heavy air pollution.

Disinfection byproducts and halogen-specific total organic halogen speciation in chlorinated source waters - The impact of iopamidol and bromide

This study investigated the speciation of halogen-specific total organic halogen and disinfection byproducts (DBPs) upon chlorination of natural organic matter (NOM) in the presence of iopamidol and bromide (Br^-). Experiments were conducted with low bromide source waters with different NOM characteristics from Northeast Ohio, USA and varied spiked levels of bromide (2-30 μmol/L) and iopamidol (1-5 μmol/L). Iopamidol was found to be a direct precursor to trihalomethane (THM) and haloacetic acid formation, and in the presence of Br^- favored brominated analogs. The concentration and speciation of DBPs formed were impacted by iopamidol and bromide concentrations, as well as the presence of NOM. As iopamidol increased the concentration of iodinated DBPs (iodo-DBPs) and THMs increased. However, as Br^- concentrations increased, the concentrations of non-brominated iodo- and chloro-DBPs decreased while brominated-DBPs increased. Regardless of the concentration of either iopamidol or bromide, bromochloroiodomethane (CHBrClI) was the most predominant iodo-DBP formed except at the lowest bromide concentration studied. At relevant concentrations of iopamidol (1 μmol/L) and bromide (2 μmol/L), significant quantities of highly toxic iodinated and brominated DBPs were formed. However, the rapid oxidation and incorporation of bromide appear to inhibit iodo-DBP formation under conditions relevant to drinking water treatment.

Assessing the potential effect of extreme weather on water quality and disinfection by-product formation using laboratory simulation

Increased frequency and severity of extreme weather events (i.e., floods and droughts) combined with higher temperatures can threaten surface water quality and downstream drinking water production. This study characterized the effects of extreme weather events on dissolved organic matter (DOM) washout from watershed soils and the corresponding contribution to disinfection by-product (DBP) precursors under simulated weather conditions. A laboratory simulation was performed to assess the effects of temperature, drought, rainfall intensity, sea level rise, and acid deposition on the amount of DOM released from soil samples. DBP formation potentials (DBPFPs) were obtained to assess the effect of extreme weather events on DBP formation and drinking water quality. The results demonstrated that the dissolved organic carbon (DOC) and carbonaceous DBP levels increased with increasing temperature in a dry (drought) scenario. Regardless of the watershed from which a soil sample was obtained and the incubation temperature during rewetting or chlorination processes, the DOC and carbonaceous DBP levels also increased with increasing temperature. Brominated DBP formation was increased when bromide was present during the rewetting of soil, indicating the effect of sea level rise. When bromide was present during the chlorination of water for DBPFP tests, only the level of brominated DBPs increased. Acid deposition had various effects under different weather conditions. The results of heavy rainfall simulations suggested that water quality deteriorates at the beginning of an extreme rainfall event. Abundant DOM was washed out of soil, leading to a peak in the DBPFP level. The level of DOM in seepage water was less than that of the surface runoff water during rainfall. The situation was more severe when the rainfall came after a long drought and the drought-rewetting cycle effect occurred.

Comprehensive assessment of the indoor air quality in a chlorinated Olympic-size swimming pool

Elite swimmers and swimming pool employees are likely to be at greater health risk due to their regular and intense exposure to air stressors in the indoor swimming pool environment. Since data on the real long-term exposure is limited, a long-term monitoring and sampling plan (22 non-consecutive days, from March to July 2017) was carried out in an indoor Olympic-size pool with a chlorine-based disinfection method to characterize indoor environments to which people involved in elite swimming and maintenance staff may be exposed to. A comprehensive set of parameters related with comfort and environmental conditions (temperature, relative humidity (RH), carbon dioxide (CO₂) and monoxide and ultrafine particles (UFP)) were monitored both indoors and outdoors in order to determine indoor-to-outdoor (I/O) ratios. Additionally, an analysis of volatile organic compounds (VOC) concentration and its dynamics was implemented in three 1-hr periods: early morning, evening elite swimmers training session and late evening. Samplings were simultaneously carried out in the air layer above the water surface and in the air surrounding the pool, selected to be representative of swimmers and coaches/employees' breathing zones, respectively. The results of this work showed that the indoor climate was very stable in terms of air temperature, RH and CO₂. In terms of the other measured parameters, mean indoor UFP number concentrations (5158 pt/cm³) were about 50% of those measured outdoors whereas chloroform was the predominant substance detected in all samples collected indoors (13.0-369.3 µg/m³), among a varied list of chemical compounds. An I/O non-trihalomethanes (THM) VOC concentration ratio of 2.7 was also found, suggesting that, beyond THM, other potentially hazardous VOC have also their source(s) indoors. THM and non-THM VOC concentration were found to increase consistently during the evening training session and exhibited a significant seasonal pattern. Compared to their coaches, elite swimmers seemed to be exposed via inhalation to significantly higher total THM levels, but to similar concentrations of non-THM VOC, during routine training activities. Regarding swimming employees, the exposure to THM and other VOC appeared to be significantly minimized during the early morning period. The air/water temperature ratio and RH were identified as important parameters that are likely to trigger the transfer processes of volatile substances from water to air and of their accumulation in the indoor environment of the swimming pool, respectively.

Natural and anthropogenic sources of bromoform and dibromomethane in the oceanographic and biogeochemical regime of the subtropical North East Atlantic

The organic bromine compounds bromoform (CHBr₃) and dibromomethane (CH₂Br₂) influence tropospheric chemistry and stratospheric ozone depletion. Their atmospheric abundance is generally related to a common marine source, which is not well characterized. A cruise between the three Macaroenesian Archipelagos of Cape Verde, the Canaries and Madeira revealed that anthropogenic sources increased oceanic CHBr₃ emissions significantly close to some islands, especially at the Canaries, while heterotrophic processes in the ocean increased the flux of CH₂Br₂ from the sea to the atmosphere in the Cape Verde region. As anthropogenic disinfection processes, which release CHBr₃ in coastal areas increase, and as more CH₂Br₂ may be produced from increased heterotrophy in a warming, deoxygenated ocean, both sources could supply higher fractions of stratospheric bromine in the future, with yet unknown consequences for stratospheric ozone.

Dominant formation of unregulated disinfection by-products during electrocoagulation treatment of landfill leachate

During the electrocoagulation (EC) treatment of landfill leachate, the production of chlorine species may result in the formation of harmful disinfection by-products (DBPs). This formation was investigated in the present study by monitoring five classes of DBPs (haloacetic acids-HAA, trihalomethanes-THM, haloacetonitriles-HAN, haloketones-HK, and halonitromethanes-HNM) in two leachate samples treated by EC. It was shown that the applied current has stimulated the formation of DBPs, which were dominated by unregulated DBPs. With a current density of 100 mA cm^-2, the unregulated HK dominated the weight-based DBP concentration (96% in Leachate A and 44.3% in Leachate B), while the unregulated HAN contributed to >80% of the DBP additive toxicity in both leachates. The concentrations of regulated THM and HAA species were below US EPA regulations. The in situ generation of active chlorine has resulted in the DBP formation, as demonstrated in the scavenging test. Applying granular activated carbon as a post-treatment step could successfully reduce the total DBP concentration from 295.33 μg L^-1 to 82.04 μg L^-1 in Leachate A, leading to a total DBP removal of 72.2% and a toxicity removal of 50%. Given the dominant concentration and lack of toxicity information, the unregulated DBPs should receive more attention.

Formation and removal of disinfection by-products in a full scale drinking water treatment plant

In this case study, high sensitivity simple methods for the analysis of trihalomethanes (THM4), iodinated-trihalomethanes (I-THMs), haloacetic acids (HAAs), bromide, iodide and iodate have been developed. A one-step procedure for the analysis of haloacetic acids by head-space GC-MS provides good reproducibility and low limits of quantification (≤50 ng L^-1). These methods were applied to characterize the formation of disinfection by-products (DBPs) in a full scale drinking water treatment plant. In this treatment plant, the incorporation of bromine into THMs increases throughout the water treatment line, due to the formation of bromine reactive species favored by the decrease of competition between dissolved organic carbon (DOC) and bromide towards chlorine. A linear correlation has been observed between the bromine incorporation factor and the Br^-/DOC mass ratio. The conversion of iodine to iodate by chlorination occurs in this water due to the relatively high bromide concentration. Moreover, a higher formation of iodate compared to iodide levels in the raw water is observed indicating a degradation of organic iodinated compounds. The formation of I-THMs was constant in terms of quantity and speciation between campaigns despite fluctuating concentrations of DOC and total iodine in the raw water. A preferential removal of DBPs formed by the intermediate chlorination in the order I-DBPs > Br-DBPs > Cl-DBPs occurs during the subsequent activated carbon filtration. The removal rates range from 25 to 36% for the regulated THM4, from 82 to 93% for the ∑I-THMs and 95% for haloacetic acids. The assessment of the relative toxicity shows that despite a much lower concentration of HAAs (<10% of the total mass of measured DBPs) compared to THMs, these compounds are responsible for 75% of the relative cytotoxicity of the treated water. Bromoacetic acid on its own accounts for more than 60% of the overall toxicity of the 17 compounds included in this study.

Advanced treatment of urban wastewater by UV-C/free chlorine process: Micro-pollutants removal and effect of UV-C radiation on trihalomethanes formation

The effect of the UV-C/free chlorine (FC) process on the removal of contaminants of emerging concern (CECs) from real urban wastewater as well as the effect of UV-C radiation on the formation of trihalomethanes (THMs) compared to FC process alone was investigated. Unlike of FC process, UV-C/FC was really effective in the degradation of the target CECs (carbamazepine (CBZ), diclofenac, sulfamethoxazole and imidacloprid) in real wastewater (87% degradation of total CECs within 60 min, Q_UVC = 1.33 kJ L^-1), being CBZ the most refractory one (49.5%, after 60 min). The UV-C radiation significantly affected the formation of THMs. THMs concentration (mainly chloroform) was lower in UV-C/FC process after 30 min treatment (<1 μgL^-1 = limit of quantification (LOQ)) than in FC process in dark (2.3 μgL^-1). Noteworthy, while in FC treated wastewater chloroform concentration increased after treatment, UV-C/FC process resulted in a significant decrease (residual concentrations below the LOQ), even after 24 h and 48 h post-treatment incubation. The formation of radicals due to UV-C/FC process can reduce THMs compared to chlorination process, because part of FC reacts with UV-C radiation to form radicals and it is no longer available to form THMs. These results are encouraging in terms of possible use of UV-C/FC process as advanced treatment of urban wastewater even for possible effluent reuse.

Comparison of the yields of mono-, Di- and tri-chlorinated HAAs and THMs in chlorination and chloramination based on experimental and quantum-chemical data

Thermodynamic and kinetic aspects of the formation of trihalomethanes and haloacetic acids determined based on the quantum chemical (QC) simulations were compared in this study with the experimental data generated using the differential spectroscopy approach in chlorination and chloramination. The ratios of the slopes of the correlations between -DlnA₃₅₀ values and individual DBPs concentrations (S_NH2Cl/S_HOCl) were observed to be linearly correlated with the ratios of the Gibbs free energies (ΔG_NH2Cl/ΔG_HOCl) of the corresponding reactions of chloramine and chlorine with acetaldehyde which was used as a model DBP precursor in QC simulations. Further QC examination of the kinetics of chlorination and chloramination of the model compound acetoacetic acid showed that the activation energy of reactions between monochloramine that directly participates in substitution reactions to form mono-, di and tri-halogenated intermediates are 2-3 times higher than those of HOCl formed via the hydrolysis monochloramine. This result confirms that the interactions of chloramine with NOM and ensuing DBP formation are primarily mediated by the free chlorine released as a result of the hydrolysis of monochloramine while direct halogenation of NOM by monochloramine is likely to provide a small contribution to DBP formation.

Application of stabilized hypobromite for controlling membrane fouling and N-nitrosodimethylamine formation

Chloramination is a conventional and successful pre-disinfection approach to control biological fouling for reverse osmosis (RO) treatment in water reuse. This study aimed to evaluate the possibility of using a new disinfectant-stabilized hypobromite-in controlling membrane fouling and the formation of a particular carcinogenic disinfection byproduct (DBP)-N-nitrosodimethylamine (NDMA). Our accelerated chemical exposure tests showed that the new disinfectant reduced the permeability of a polyamide RO membrane permeability from 6.7 to 4.1 L/m²hbar; however, its treatment impact was equivalent to that of chloramine. The disinfection efficacy of stabilized hypobromite was greater than that of chloramine when evaluated with intact bacterial counts, which suggests its potential for mitigating membrane biofouling. Additional pilot-scale tests using synthetic wastewater demonstrated that pre-disinfection with the use of stabilized hypobromite inhibits membrane fouling. Among 13 halogenated DBPs evaluated, the formation of bromoform by stabilized hypobromite was higher than that by chloramine at a high dose of 10 mg/L, thus suggesting the need for optimizing chemical doses for achieving sufficient biofouling mitigation. NDMA formation upon stabilized hypobromite treatment in two different types of actual treated wastewaters was found to be negligible and considerably lower than that by chloramine treatment. In addition, NDMA formation potential by stabilized hypobromite was 2-5 orders of magnitude lower than that by chloramine. Our findings suggest the potential of using stabilized hypobromite for controlling NDMA formation and biofouling, which are the keys to successful potable water reuse.

Synergistic effects of quenching agents and pH on the stability of regulated and unregulated disinfection by-products for drinking water quality monitoring

Quenching agents (QAs) are widely used in order to prevent the additional formation of disinfection by-products (DBPs) during the sample holding time. In addition, DBP levels are usually stabilized by adjusting the pH of water samples. Previous studies have mostly focused on the individual effects of QAs or of pH on the stability of DBPs in water samples. Considering that disinfectant quenching and pH adjustments are applied simultaneously during routine analyses, it is more appropriate to evaluate the stability of DBPs with all the chemicals (e.g., disinfectants, QAs, buffers) present in the water. This study investigated the synergistic effects of different QAs (ascorbic acid, ammonium chloride, or no quenching) and pH adjustment (3-9) strategies on the stability of different classes of DBPs (i.e., trihalomethanes (THMs), halogenated acetaldehydes (HALs), haloacetonitriles (HANs), haloketones (HKs), and halonitromethane (HNM)). Sample preservation conditions that did not include a QA were shown to be inadequate for GC-ECD analysis, due to interference problems. Ammonium chloride was found to be effective for most DBPs. However, some HALs continued to form in the presence of chloramine, which is a by-product of dechlorination using ammonium chloride. Conversely, using ascorbic acid efficiently inactivated residual chlorine, providing a clean chromatographic baseline. Based on the results of this study, we recommend the use of ascorbic acid for quenching and sulfuric acid for acidifying (pH 3.5) samples. Considering the instability of some DBPs in water matrices over long periods (i.e., 14 days), samples should be processed as soon as possible after collection.

Modeling Trihalomethane Increases Associated with Source Water Bromide Contributed by Coal-Fired Power Plants in the Monongahela River Basin

Increases in source water bromide concentrations are challenging for drinking water utilities since bromide contributes to the formation of disinfection byproducts (DBPs) that have negative human-health effects. The present work evaluates the role of coal-fired power plant wet flue gas desulfurization (FGD)-associated bromide loads on in-stream bromide concentrations in the Monongahela River Basin in the water year (WY) 1998 (during a nationwide study) and over a five-year period from WYs 2013 through 2017. Under mean flow conditions in the lower Monongahela River for the WYs of interest, the median-estimated wet FGD bromide discharges are modeled to represent a significant fraction (27-57%) of observed bromide concentrations with the range representing the change in load conditions across WYs. Seasonal effects are predicted due to changes in the dilution capacity of the river with elevated concentrations under lower flows in the third and fourth quarters (July through December). The effect of these bromide concentration contributions, which range from 6.8 to 23 μg/L under median load estimates and median flow conditions, on trihalomethane (THM) formation and associated risk were assessed. A simple model was applied to demonstrate an analytical approach for evaluating the power plant total THM (TTHM) and risk contributions. Utilizing this model, the power plant TTHM contribution was estimated to range from 7.6 to 27 μg/L with a median risk contribution of 0.0014.

Factors Associated with Exposure to Trihalomethanes, NHANES 2001-2012

Disinfection is critical for maintaining a safe water supply, but the use of chlorine or chloramine leads to exposure to disinfection byproducts (DBPs), including trihalomethanes (THMs), which have been associated with adverse reproductive outcomes and bladder cancer. The U.S. Environmental Protection Agency revised the DBP regulations starting in 1998 to further limit levels of THMs in household water. We analyzed data from the National Health and Nutrition Examination Survey (NHANES) collected between 2001 and 2012 (with 2 years per cycle) using models with and without water-related predictors to examine the utility of including these measures. Median blood chloroform levels (25th-75th percentiles) were 16.2 (9.13-31.2) ng/L in 2001-2002 and 5.97 (2.92-12.3) ng/L in 2011-2012. Median blood bromodichloromethane (BDCM) levels (25th-75th percentiles) were 2.22 (1.06-4.61) ng/L in 2001-2002 and 1.18 (<limit of detection-2.92) ng/L in 2011-2012. THM water concentrations and measures of the recency since time spent in water use activities were associated with blood THM levels. Being in a pool/hot tub/sauna within 24 h or taking a shower/bath within 6 h of blood collection was associated with elevated blood levels of chloroform and BDCM. When possible, it is important to include recency and external dose when assessing associations to internal dose levels for nonpersistent compounds.

The use of peracetic acid for estrogen removal from urban wastewaters: E2 as a case study

17β-Estradiol (E2) is a natural estrogen produced by the feminine endocrine system. It is excreted mainly through urine and feces. Exposure to E2 may affect the reproductive system of both animals and humans, especially since the removal of E2 in conventional processes and technologies present in the wastewater treatment plants is not sufficient. Chlorine is one of the most studied and used oxidant worldwide. Although there are studies that demonstrate the endocrine disrupting compounds removal like E2, its reaction with organic matter can originate by-products, namely, trihalomethanes, which are known to have high toxic potential. The main aim of the present study was to evaluate the removal of E2 (50 μg E2 L^-1-maximum concentration) using peracetic acid (PAA), a seeming cleaner and innocuous alternative to chlorine. To this end, a series of jar tests were performed, using different peracetic acid concentrations (1, 5, 10, and 15 mg L^-1) and contact times (10, 15, and 20 min). The results obtained showed that a peracetic acid concentration of 15 mg L^-1 with a contact time of 20 min had a removal efficacy of approximately 100%. The second main goal of this study was to evaluate the ecotoxicological potential of the tested treatments on the zebrafish Danio rerio. Several oxidative stress biomarkers were evaluated, namely glutathione S-transferase, lipid peroxidation, and catalase, besides vitellogenin. Both peracetic acid and E2 caused significant increases in the oxidative stress biomarkers, although this did not lead to increased lipid peroxidation levels. In addition, peracetic acid significantly decreased the estrogenic activity of E2, as indicated by decreased vitellogenin levels. Peracetic acid demonstrated to have great potential as an alternative disinfectant for chlorine treatments, and indications for future research are discussed.

Trihalomethanes in Drinking Water and Bladder Cancer Burden in the European Union

BACKGROUND

Trihalomethanes (THMs) are widespread disinfection by-products (DBPs) in drinking water, and long-term exposure has been consistently associated with increased bladder cancer risk.

OBJECTIVE

We assessed THM levels in drinking water in the European Union as a marker of DBP exposure and estimated the attributable burden of bladder cancer.

METHODS

We collected recent annual mean THM levels in municipal drinking water in 28 European countries (EU28) from routine monitoring records. We estimated a linear exposure-response function for average residential THM levels and bladder cancer by pooling data from studies included in the largest international pooled analysis published to date in order to estimate odds ratios (ORs) for bladder cancer associated with the mean THM level in each country (relative to no exposure), population-attributable fraction (PAF), and number of attributable bladder cancer cases in different scenarios using incidence rates and population from the Global Burden of Disease study of 2016.

RESULTS

We obtained 2005-2018 THM data from EU26, covering 75% of the population. Data coverage and accuracy were heterogeneous among countries. The estimated population-weighted mean THM level was 11.7μg/L [standard deviation (SD) of 11.2]. The estimated bladder cancer PAF was 4.9% [95% confidence interval (CI): 2.5, 7.1] overall (range: 0-23%), accounting for 6,561 (95% CI: 3,389, 9,537) bladder cancer cases per year. Denmark and the Netherlands had the lowest PAF (0.0% each), while Cyprus (23.2%), Malta (17.9%), and Ireland (17.2%) had the highest among EU26. In the scenario where no country would exceed the current EU mean, 2,868 (95% CI: 1,522, 4,060; 43%) annual attributable bladder cancer cases could potentially be avoided.

DISCUSSION

Efforts have been made to reduce THM levels in the European Union. However, assuming a causal association, current levels in certain countries still could lead to a considerable burden of bladder cancer that could potentially be avoided by optimizing water treatment, disinfection, and distribution practices, among other possible measures. https://doi.org/10.1289/EHP4495.

Using UV/H2O2 pre-oxidation combined with an optimised disinfection scenario to control CX3R-type disinfection by-product formation

The effects of UV/H₂O₂ pre-oxidation or disinfection methods on the formation of partial disinfection by-products (DBPs) have been studied previously. This study assessed the effect of UV/H₂O₂ pre-oxidation combined with optimisation of the disinfection method on the formation of six classes of CX₃R-type DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetaldehydes (HALs), haloacetonitriles (HANs), halonitromethanes (HNMs), and haloacetamides (HAMs). Experimental results showed that a simulated distribution system (SDS) in-situ chloramination or pre-chlorination followed by chloramination effectively decreased total CX₃R-type DBP formation by 51.1-63.5% compared to SDS chlorination, but little reduction in DBP-associated toxicity was observed. The dominant contributors to the calculated toxicity were HANs and HALs. UV/H₂O₂ pre-oxidation was able to destroy the aromatic and dissolved organic nitrogen components of natural organic matter. As a consequence, THM, HAA, and HAL formations increased by 49.5-55.0%, 47.8-61.9%, and 42.0-67.1%, respectively, whereas HAN, HNM, and HAM formations significantly decreased by 52.1-83.6%, 42.9-87.3%, and 74.1-100.0%. UV/H₂O₂ pre-oxidation increased total CX₃R-type DBP formation, during SDS chlorination, whereas SDS in-situ chloramination or pre-chlorination followed by chloramination of UV/H₂O₂-treated water produced lower total CX₃R-type DBPs than water without UV/H₂O₂ pre-oxidation. Nevertheless, the DBP-associated toxicity of water with UV/H₂O₂ pre-oxidation was substantially lower than the toxicity for water without UV/H₂O₂ pre-oxidation, decreased by 24.1-82.7%. HALs followed by HANs contribute to major toxic potencies in UV/H₂O₂ treated water. The best DBP concentration and DBP-associated toxicity abatement results were achieved for water treated by UV/H₂O₂ coupled with in-situ chloramination treatment.

Evidence-based analysis on the toxicity of disinfection byproducts in vivo and in vitro for disinfection selection

Disinfection is a key step in drinking water treatment process to prevent water-borne infections. However, reactions between chlorine, one of the most common disinfectants, and natural organic matter (NOM) often lead to the formation of hazardous disinfection byproducts (DBPs). However, the cytotoxicity of some DBPs is still poorly understood. Such knowledge is critical for proper selection of disinfection processes. We investigated the effects of DBPs on mouse acute liver injury. The exacerbation of liver damage increased with the DBPs concentrations, likely due to the increased hepatic macrophages. Haloacetonitriles (HANs) and haloketones (HKs) are more toxic to Human Hepatocellular (Hep3B) cells than trihalomethanes (THMs). Cytotoxicity of DBPs were governed by the halogen type (brominated DBPs > chlorinated DBPs) and the numbers of halogen atoms per molecule. Then, we used the pilot-scale WDS to study the best conditions for reducing the formation of DBPs. The result showed that the formation of DBPs followed the order: stainless-steel (SS) > ductile iron (DI) > polyethylene (PE) pipe. Higher flowrate promoted the formation of DBPs in all three pipes. The results suggest that the formation of DBPs in chlorine disinfection can be reduced by using PE pipes and low flow rate in water distribution systems (WDS).

Assessment of the chlorine demand and disinfection byproduct formation potential of surface waters via satellite remote sensing

The ability of satellites to assess surface water quality indicators such as colored dissolved organic matter (CDOM) suggests that remote sensing could be a useful tool for evaluating water treatability metrics in considering potential drinking water supplies. To explore this possibility, 24 surface water samples were collected throughout Minnesota, USA with wide ranging values of CDOM (a₄₄₀; 0.41-27.9 m^-1), dissolved organic carbon (DOC; 5.5-47.6 mg/L) and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄; 1.3-5.1 L/mg-M). Laboratory experiments were performed to quantify chlorine demand and the formation of two classes of halogenated disinfection byproducts (DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), using the uniform formation conditions (UFC) test. Chlorine demand and THM_UFC were linearly correlated with CDOM (R² = 0.97 and 0.91, respectively), indicating that CDOM is a useful predictor of these parameters. On the other hand, data comparing di- and tri-HAA_UFC with CDOM were better fit by a logarithmic relationship (R² = 0.73 and 0.87, respectively), while mono-HAA_UFC was linearly correlated with CDOM (R² = 0.46) but only for low-to moderately-colored waters (a₄₄₀ ≤ 11 m^-1). The correlations relating chlorine demand and DBP_UFC values with CDOM were coupled with satellite CDOM assessments to estimate chlorine demand and DBP_UFC values for all surface waters larger than 0.05 km² in the state of Minnesota, USA. The resulting maps suggest that only 21.8% of Minnesota lakes would meet both the THM and HAA maximum contaminant levels, but only when pre-disinfection treatment removes 75% of DBP precursors. There are limitations to determining CDOM using satellites for high color surface waters (a₄₄₀ > 11 m^-1), however, leading to underpredicted values for CDOM, chlorine demand, and DBP_UFC. Overall, the results demonstrate the potential benefits of satellite remote sensing for assessing potential drinking water sources and water treatability metrics.

Disinfection Byproducts in Rajasthan, India: Are Trihalomethanes a Sufficient Indicator of Disinfection Byproduct Exposure in Low-Income Countries?

The implementation of chlorine disinfection in low-income countries reduces the risk of waterborne illness but initiates exposure to disinfection byproducts (DBPs). Like high-income countries, low-income countries typically are adopting regulations focusing on trihalomethanes (THM4) as an indicator of overall DBP exposure. However, the use of impaired water sources can decouple the formation of THM4 from other DBP classes that are more potent toxins. The documentation of DBP species other than THM4 is rare in low-income countries, where water sources may be degraded by inadequate sanitation infrastructure and other uncontrolled wastewater discharges. We measured THM4 and 21 unregulated DBPs in tap waters and laboratory-treated source waters from two cities in northwestern India. The contribution of each DBP class to the cumulative toxicity was estimated by weighting each species by metrics of toxic potency; haloacetonitriles typically were the dominant contributor, while the contribution of THM4 was negligible. THM4 concentrations did not correlate with the total toxic potency-weighted DBP concentrations. Although THM4 rarely exceeded international guidelines, DBPs of greater toxicological concern were observed in high concentrations. The total toxic potency-weighted DBP concentrations in some waters were elevated compared to conventional drinking waters in high-income countries and more closely resembled chlorine-disinfected wastewater effluents. Artificial sweeteners confirmed widespread contamination of both surface and groundwaters by domestic sewage. The results suggest that THM4 may not be an adequate indicator of overall DBP exposure in impaired water supplies prevalent in some low-income nations.

Urinary Biomarker of Prenatal Exposure to Disinfection Byproducts, Maternal Genetic Polymorphisms in CYP2E1 and GSTZ1, and Birth Outcomes

The effects of disinfection byproducts (DBPs) on adverse birth outcomes remain unsettled. Maternal genetic variants in relation to DBP metabolism may modify this effect. Pregnant women during late pregnancy (n = 1306) were included from a Chinese cohort. Maternal urinary trichloroacetic acid (TCAA) was measured as a biomarker of DBP exposure. Maternal genotyping was conducted in cytochrome P450 2E1 (CYP2E1; rs2031920, rs3813867, and rs915906) and glutathione S-transferase zeta-1 (GSTZ1; rs7975). The associations between maternal urinary TCAA and birth outcomes and statistical interactions between maternal exposure and genetic polymorphisms were estimated. We found that maternal urinary TCAA levels were associated with decreased birth weight (P for trend = 0.003) and ponderal index (P for trend = 0.004). Interaction analyses showed that maternal urinary TCAA in association with decreased birth weight was observed only among subjects with CYP2E1 rs3813867 GC/CC versus GG (P_int = 0.07) and associations with decreased birth length, ponderal index, and gestational age were observed only among subjects with GSTZ1 rs7975 GA/AA versus GG (P_int = 0.07, 0.02, and 0.02, respectively). Our results suggested that prenatal DBP exposure was negatively associated with birth weight and ponderal index, and maternal genetic polymorphisms in CYP2E1 and GSTZ1 might modify these associations.

Formation of iodinated trihalomethanes and noniodinated disinfection byproducts during chloramination of algal organic matter extracted from Microcystis aeruginosa

The increasing occurrence of harmful algal blooms in surface waters may increase the input of algal organic matter (AOM) to the dissolved organic matter pool. The formation of iodinated trihalomethanes (I-THMs) and noniodinated disinfection byproducts (DBPs) in synthetic waters containing AOM extracted from Microcystis aeruginosa was investigated in chloramination (preformed and in-situ formed chloramine, NH₂Cl and Cl₂-NH₂Cl, respectively) and chlorination (Cl₂) processes. AOM is much more favorable for iodine incorporation than natural organic matter (NOM). For example, the formation of I-THM from AOM is much higher than NOM isolate extracted from treated water (e.g., 3.5 times higher in the NH₂Cl process), and thus higher iodine utilization and substitution factors from AOM were observed. Short contact time (2 min) chlorination in Cl₂-NH₂Cl process leading to the formation of halogenated intermediates favored I-THM formation, compared with NH₂Cl process. However, further increasing chlorine contact time from 5 min to 24 h facilitated the conversion from iodide to iodate and thus I-THM formation decreased. Meanwhile, the formation of noniodinated THM4, haloacetonitriles (HANs), and haloacetaldehydes (HALs) increased. Factors including concentrations of AOM and bromide, pH, and chlorine/nitrogen ratios influenced the formation of I-THMs and noniodinated DBPs. To evaluate the benefit of mitigating I-THM formation over the risk of noniodinated DBP formation, measured DBPs were weighed against their mammalian cell toxicity indexes. Increasing the chlorine exposure increased the calculated cytotoxicity based on concentrations of measured I-THMs and noniodinated DBPs since unregulated HANs and HALs were the controlling agents.

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.